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Li X, Tang X, Xiang Y, Zhao Z, Li Y, Ding Q, Zhang L, Xu J, Zhao L, Chen Y. N-glycosylation of SCAP exacerbates hepatocellular inflammation and lipid accumulation via ACSS2-mediated histone H3K27 acetylation. Am J Physiol Gastrointest Liver Physiol 2024; 326:G697-G711. [PMID: 38591127 DOI: 10.1152/ajpgi.00273.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 03/11/2024] [Accepted: 03/25/2024] [Indexed: 04/10/2024]
Abstract
Sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP) is a widely expressed membrane glycoprotein that acts as an important modulator of lipid metabolism and inflammatory stress. N-glycosylation of SCAP has been suggested to modulate cancer development, but its role in nonalcoholic steatohepatitis (NASH) is poorly understood. In this study, the N-glycosylation of SCAP was analyzed by using sequential trypsin proteolysis and glycosidase treatment. The liver cell lines expressing wild-type and N-glycosylation sites mutated SCAP were constructed to investigate the N-glycosylation role of SCAP in regulating inflammation and lipid accumulation as well as the underlying mechanisms. The hepatic SCAP protein levels were significantly increased in C57BL/6J mice fed with Western diet and sugar water (WD + SW) and diabetic db/db mice, which exhibited typical liver steatosis and inflammation accompanied with hyperglycemia. In vitro, the enhanced N-glycosylation by high glucose increased the protein stability of SCAP and hence increased its total protein levels, whereas the ablation of N-glycosylation significantly decreased SCAP protein stability and alleviated lipid accumulation and inflammation in hepatic cell lines. Mechanistically, SCAP N-glycosylation increased not only the SREBP-1-mediated acetyl-CoA synthetase 2 (ACSS2) transcription but also the AMPK-mediated S659 phosphorylation of ACCS2 protein, causing the enhanced ACSS2 levels in nucleus and hence increasing the histone H3K27 acetylation (H3K27ac), which is a key epigenetic modification associated with NASH. Modulating ACSS2 expression or its location in the nuclear abolished the effects of SCAP N-glycosylation on H3K27ac and lipid accumulation and inflammation. In conclusion, SCAP N-glycosylation aggravates inflammation and lipid accumulation through enhancing ACSS2-mediated H3K27ac in hepatocytes.NEW & NOTEWORTHY N-glycosylation of SCAP exacerbates inflammation and lipid accumulation in hepatocytes through ACSS2-mediated H3K27ac. Our data suggest that SCAP N-glycosylation plays a key role in regulating histone H3K27 acetylation and targeting SCAP N-glycosylation may be a new strategy for treating nonalcoholic steatohepatitis (NASH).
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Affiliation(s)
- Xuemei Li
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Xiaoqin Tang
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Yue Xiang
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Zhibo Zhao
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Yanping Li
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Qiuying Ding
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Linkun Zhang
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Jingyuan Xu
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Lei Zhao
- Centre for Lipid Research and Chongqing Key Laboratory of Metabolism on Lipid and Glucose, Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
| | - Yao Chen
- Centre for Health Medicine, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, People's Republic of China
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Chandrasekaran P, Weiskirchen R. The Role of SCAP/SREBP as Central Regulators of Lipid Metabolism in Hepatic Steatosis. Int J Mol Sci 2024; 25:1109. [PMID: 38256181 PMCID: PMC10815951 DOI: 10.3390/ijms25021109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 01/09/2024] [Accepted: 01/14/2024] [Indexed: 01/24/2024] Open
Abstract
The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is rapidly increasing worldwide at an alarming pace, due to an increase in obesity, sedentary and unhealthy lifestyles, and unbalanced dietary habits. MASLD is a unique, multi-factorial condition with several phases of progression including steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Sterol element binding protein 1c (SREBP1c) is the main transcription factor involved in regulating hepatic de novo lipogenesis. This transcription factor is synthesized as an inactive precursor, and its proteolytic maturation is initiated in the membrane of the endoplasmic reticulum upon stimulation by insulin. SREBP cleavage activating protein (SCAP) is required as a chaperon protein to escort SREBP from the endoplasmic reticulum and to facilitate the proteolytic release of the N-terminal domain of SREBP into the Golgi. SCAP inhibition prevents activation of SREBP and inhibits the expression of genes involved in triglyceride and fatty acid synthesis, resulting in the inhibition of de novo lipogenesis. In line, previous studies have shown that SCAP inhibition can resolve hepatic steatosis in animal models and intensive research is going on to understand the effects of SCAP in the pathogenesis of human disease. This review focuses on the versatile roles of SCAP/SREBP regulation in de novo lipogenesis and the structure and molecular features of SCAP/SREBP in the progression of hepatic steatosis. In addition, recent studies that attempt to target the SCAP/SREBP axis as a therapeutic option to interfere with MASLD are discussed.
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Affiliation(s)
| | - Ralf Weiskirchen
- Institute of Molecular Pathobiochemistry, Experimental Gene Therapy and Clinical Chemistry (IFMPEGKC), Rheinisch-Westfälische Technische Hochschule (RWTH) University Hospital Aachen, D-52074 Aachen, Germany
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Peng Z, Chen L, Wang M, Yue X, Wei H, Xu F, Hou W, Li Y. SREBP inhibitors: an updated patent review for 2008-present. Expert Opin Ther Pat 2023; 33:669-680. [PMID: 38054657 DOI: 10.1080/13543776.2023.2291393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 11/22/2023] [Indexed: 12/07/2023]
Abstract
INTRODUCTION Sterol regulatory element-binding proteins (SREBPs) are a family of membrane-binding transcription factors that activate genes encoding enzymes required for cholesterol and unsaturated fatty acid synthesis. Overactivation of SREBP is related to the occurrence and development of diabetes, nonalcoholic fatty liver, tumor, and other diseases. In the past period, many SREBP inhibitors have been found. AREAS COVERED This manuscript is a patent review of SREBP inhibitors. We searched 2008 to date for all data from the US patent database (https://www.uspto.gov/) and the European patent database (https://www.epo.org/) with 'SREBP' and 'inhibitor' as keywords and analyzed the search results. EXPERT OPINION Both synthetic and natural SREBP inhibitors have been reported. Despite the lack of cocrystal structure of SREBP inhibitor, the mechanisms of several compounds have been clarified. Importantly, some SREBP inhibitors have been proved to have good activity in preclinical studies. As the characteristics of lipid metabolism reprogramming in cardio-cerebrovascular diseases and tumors are gradually revealed, more and more attention will be focused on SREBP.
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Affiliation(s)
- Zhenyu Peng
- Institute of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - Leyuan Chen
- Institute of Radiation Medicine, Peking Union Medical College & Chinese Academy of Medical Sciences, Tianjin, China
| | - Manjiang Wang
- Institute of Radiation Medicine, Peking Union Medical College & Chinese Academy of Medical Sciences, Tianjin, China
| | - Xufan Yue
- Institute of Traditional Chinese Medicine, Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - Huiqiang Wei
- Institute of Radiation Medicine, Peking Union Medical College & Chinese Academy of Medical Sciences, Tianjin, China
| | - Feifei Xu
- Institute of Radiation Medicine, Peking Union Medical College & Chinese Academy of Medical Sciences, Tianjin, China
| | - Wenbin Hou
- Institute of Radiation Medicine, Peking Union Medical College & Chinese Academy of Medical Sciences, Tianjin, China
| | - Yiliang Li
- Institute of Radiation Medicine, Peking Union Medical College & Chinese Academy of Medical Sciences, Tianjin, China
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Uehara K, Santoleri D, Whitlock AEG, Titchenell PM. Insulin Regulation of Hepatic Lipid Homeostasis. Compr Physiol 2023; 13:4785-4809. [PMID: 37358513 PMCID: PMC10760932 DOI: 10.1002/cphy.c220015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
Abstract
The incidence of obesity, insulin resistance, and type II diabetes (T2DM) continues to rise worldwide. The liver is a central insulin-responsive metabolic organ that governs whole-body metabolic homeostasis. Therefore, defining the mechanisms underlying insulin action in the liver is essential to our understanding of the pathogenesis of insulin resistance. During periods of fasting, the liver catabolizes fatty acids and stored glycogen to meet the metabolic demands of the body. In postprandial conditions, insulin signals to the liver to store excess nutrients into triglycerides, cholesterol, and glycogen. In insulin-resistant states, such as T2DM, hepatic insulin signaling continues to promote lipid synthesis but fails to suppress glucose production, leading to hypertriglyceridemia and hyperglycemia. Insulin resistance is associated with the development of metabolic disorders such as cardiovascular and kidney disease, atherosclerosis, stroke, and cancer. Of note, nonalcoholic fatty liver disease (NAFLD), a spectrum of diseases encompassing fatty liver, inflammation, fibrosis, and cirrhosis, is linked to abnormalities in insulin-mediated lipid metabolism. Therefore, understanding the role of insulin signaling under normal and pathologic states may provide insights into preventative and therapeutic opportunities for the treatment of metabolic diseases. Here, we provide a review of the field of hepatic insulin signaling and lipid regulation, including providing historical context, detailed molecular mechanisms, and address gaps in our understanding of hepatic lipid regulation and the derangements under insulin-resistant conditions. © 2023 American Physiological Society. Compr Physiol 13:4785-4809, 2023.
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Affiliation(s)
- Kahealani Uehara
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Dominic Santoleri
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Anna E. Garcia Whitlock
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Paul M. Titchenell
- Institute of Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Li D, Yao Y, Rao Y, Huang X, Wei L, You Z, Zheng G, Hou X, Su Y, Varghese Z, Moorhead JF, Chen Y, Ruan XZ. Cholesterol sensor SCAP contributes to sorafenib resistance by regulating autophagy in hepatocellular carcinoma. JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH : CR 2022; 41:116. [PMID: 35354475 PMCID: PMC8966370 DOI: 10.1186/s13046-022-02306-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 02/28/2022] [Indexed: 01/08/2023]
Abstract
Background Hepatocellular carcinoma (HCC) is one of the most malignant tumors and the fourth leading cause of cancer-related death worldwide. Sorafenib is currently acknowledged as a standard therapy for advanced HCC. However, acquired resistance substantially limits the clinical efficacy of sorafenib. Therefore, further investigations of the associated risk factors are highly warranted. Methods We analysed a group of 78 HCC patients who received sorafenib treatment after liver resection surgery. The expression of SCAP and its correlation with sorafenib resistance in HCC clinical samples were determined by immunohistochemical analyses. Overexpression and knockdown approaches in vitro were used to characterize the functional roles of SCAP in regulating sorafenib resistance. The effects of SCAP inhibition in HCC cell lines were analysed in proliferation, apoptosis, and colony formation assays. Autophagic regulation by SCAP was assessed by immunoblotting, immunofluorescence and immunoprecipitation assays. The combinatorial effect of a SCAP inhibitor and sorafenib was tested using nude mice. Results Hypercholesterolemia was associated with sorafenib resistance in HCC treatment. The degree of sorafenib resistance was correlated with the expression of the cholesterol sensor SCAP and consequent deposition of cholesterol. SCAP is overexpressed in HCC tissues and hepatocellular carcinoma cell lines with sorafenib resistance, while SCAP inhibition could improve sorafenib sensitivity in sorafenib-resistant HCC cells. Furthermore, we found that SCAP-mediated sorafenib resistance was related to decreased autophagy, which was connected to decreased AMPK activity. A clinically significant finding was that lycorine, a specific SCAP inhibitor, could reverse acquired resistance to sorafenib in vitro and in vivo. Conclusions SCAP contributes to sorafenib resistance through AMPK-mediated autophagic regulation. The combination of sorafenib and SCAP targeted therapy provides a novel personalized treatment to enhance sensitivity in sorafenib-resistant HCC. Supplementary Information The online version contains supplementary material available at 10.1186/s13046-022-02306-4.
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Affiliation(s)
- Danyang Li
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Yingcheng Yao
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Yuhan Rao
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Xinyu Huang
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Li Wei
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Zhimei You
- Department of General Medicine, Affiliated Cancer Hospital of Chongqing University, Chongqing, 400016, China
| | - Guo Zheng
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Xiaoli Hou
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Yu Su
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China
| | - Zac Varghese
- John Moorhead Research Laboratory, Centre for Nephrology, University College London Medical School, Royal Free Campus, University College London, London, NW3 2PF, UK
| | - John F Moorhead
- John Moorhead Research Laboratory, Centre for Nephrology, University College London Medical School, Royal Free Campus, University College London, London, NW3 2PF, UK
| | - Yaxi Chen
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China.
| | - Xiong Z Ruan
- Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, 400016, Chongqing, China. .,John Moorhead Research Laboratory, Centre for Nephrology, University College London Medical School, Royal Free Campus, University College London, London, NW3 2PF, UK.
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Huang D, Xu B, Liu L, Wu L, Zhu Y, Ghanbarpour A, Wang Y, Chen FJ, Lyu J, Hu Y, Kang Y, Zhou W, Wang X, Ding W, Li X, Jiang Z, Chen J, Zhang X, Zhou H, Li JZ, Guo C, Zheng W, Zhang X, Li P, Melia T, Reinisch K, Chen XW. TMEM41B acts as an ER scramblase required for lipoprotein biogenesis and lipid homeostasis. Cell Metab 2021; 33:1655-1670.e8. [PMID: 34015269 DOI: 10.1016/j.cmet.2021.05.006] [Citation(s) in RCA: 77] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Revised: 04/06/2021] [Accepted: 05/05/2021] [Indexed: 02/06/2023]
Abstract
How amphipathic phospholipids are shuttled between the membrane bilayer remains an essential but elusive process, particularly at the endoplasmic reticulum (ER). One prominent phospholipid shuttling process concerns the biogenesis of APOB-containing lipoproteins within the ER lumen, which may require bulk trans-bilayer movement of phospholipids from the cytoplasmic leaflet of the ER bilayer. Here, we show that TMEM41B, present in the lipoprotein export machinery, encodes a previously conceptualized ER lipid scramblase mediating trans-bilayer shuttling of bulk phospholipids. Loss of hepatic TMEM41B eliminates plasma lipids, due to complete absence of mature lipoproteins within the ER, but paradoxically also activates lipid production. Mechanistically, scramblase deficiency triggers unique ER morphological changes and unsuppressed activation of SREBPs, which potently promotes lipid synthesis despite stalled secretion. Together, this response induces full-blown nonalcoholic hepatosteatosis in the TMEM41B-deficient mice within weeks. Collectively, our data uncovered a fundamental mechanism safe-guarding ER function and integrity, dysfunction of which disrupts lipid homeostasis.
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Affiliation(s)
- Dong Huang
- State Key Laboratory of Membrane Biology, Peking University, Beijing 100871, China; Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Bolin Xu
- State Key Laboratory of Membrane Biology, Peking University, Beijing 100871, China; Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Lu Liu
- State Key Laboratory of Membrane Biology, Peking University, Beijing 100871, China; Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Lingzhi Wu
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Yuangang Zhu
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Alireza Ghanbarpour
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Yawei Wang
- Center for Life Sciences, Peking University, Beijing 100871, China
| | - Feng-Jung Chen
- Institute of Metabolism and Integrative Biology, Fudan University, Shanghai 200438, China
| | - Jia Lyu
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Yating Hu
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Yunlu Kang
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Wenjing Zhou
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Xiao Wang
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Wanqiu Ding
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Xin Li
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Zhaodi Jiang
- National Institute of Biological Sciences, Tsinghua University, Beijing 100086, China
| | - Jizheng Chen
- Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510503, China
| | - Xu Zhang
- The Key Laboratory of Rare Metabolic Disease, Department of Biochemistry and Molecular Biology, The Key Laboratory of Human Functional Genomics of Jiangsu Province, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Hongwen Zhou
- Department of Endocrinology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
| | - John Zhong Li
- The Key Laboratory of Rare Metabolic Disease, Department of Biochemistry and Molecular Biology, The Key Laboratory of Human Functional Genomics of Jiangsu Province, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Chunguang Guo
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Wen Zheng
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Xiuqin Zhang
- Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China
| | - Peng Li
- Institute of Metabolism and Integrative Biology, Fudan University, Shanghai 200438, China; School of Life Sciences, Tsinghua University, Beijing 100086, China
| | - Thomas Melia
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Karin Reinisch
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Xiao-Wei Chen
- State Key Laboratory of Membrane Biology, Peking University, Beijing 100871, China; Institute of Molecular Medicine, College of Future Technology, Peking University, Beijing 100871, China; Center for Life Sciences, Peking University, Beijing 100871, China.
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Li D, Liu M, Li Z, Zheng G, Chen A, Zhao L, Yang P, Wei L, Chen Y, Ruan XZ. Sterol-resistant SCAP Overexpression in Vascular Smooth Muscle Cells Accelerates Atherosclerosis by Increasing Local Vascular Inflammation through Activation of the NLRP3 Inflammasome in Mice. Aging Dis 2021; 12:747-763. [PMID: 34094640 PMCID: PMC8139202 DOI: 10.14336/ad.2020.1120] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Accepted: 11/20/2020] [Indexed: 12/01/2022] Open
Abstract
Atherosclerosis is a serious age-related pathology, and one of its hallmarks is the presence of chronic inflammation. Sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP) is a cholesterol sensor that plays an essential role in regulating intracellular cholesterol homeostasis. Accordingly, dysregulation of the SCAP-SREBP pathway has been reported to be closely associated with an increased risk of obesity, hypercholesterolemia, and cardiovascular disease. In this study, we explored whether sterol-resistant SCAP (D443N mutation) in vascular smooth muscle cells (VSMCs) of mice promotes vascular inflammation and accelerates the occurrence and progression of atherosclerosis. We established a transgenic knock-in mouse model of atherosclerosis with an activating D443N mutation at the sterol-sensing domain of SCAP (SCAPD443N) by microinjection. Next, SCAPD443N/ApoE-/- mice were generated by crossing SCAPD443N mice with apolipoprotein E-/- (ApoE-/-) background mice. We found that sterol-resistant SCAP markedly amplified and accelerated the progression of atherosclerotic plaques in SCAPD443N/ApoE-/- mice compared with that in control ApoE-/- mice. Similarly, in SCAPD443N mice, aortic atherosclerotic plaques both appeared earlier and were greater in number than that in control SCAP+/+ mice, both of which were fed a Western diet for 12 or 24 weeks. Moreover, we observed that sterol-resistant SCAP significantly increased local inflammation and induced endothelial dysfunction in the aortas of SCAPD443N mice and SCAPD443N/ApoE-/- mice. In vitro, we also found that sterol-resistant SCAP overexpression in VSMCs increased the release of inflammatory cytokines and induced endothelial cell injury when both cell types were cocultured. Furthermore, we demonstrated that sterol-resistant SCAP overexpression in VSMCs promoted SCAP and NLRP3 inflammasome cotranslocation to the Golgi and increased the activation of the NLRP3 inflammasome pathway. These findings suggested that sterol-resistant SCAP in VSMCs of mice induced vascular inflammation and endothelial dysfunction, consequently accelerating atherosclerosis by activating the NLRP3 inflammasome pathway.
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Affiliation(s)
- Danyang Li
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Mihua Liu
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Zhe Li
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Guo Zheng
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Amei Chen
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Lei Zhao
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Ping Yang
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Li Wei
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Yaxi Chen
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Xiong Z Ruan
- 1Centre for Lipid Research & Key Laboratory of Molecular Biology for Infectious Diseases (Ministry of Education), Institute for Viral Hepatitis, Department of Infectious Diseases, the Second Affiliated Hospital, Chongqing Medical University, Chongqing, China.,2National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China.,3John Moorhead Research Laboratory, Centre for Nephrology, University College London Medical School, Royal Free Campus, University College London, London, United Kingdom
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Azzu V, Vacca M, Kamzolas I, Hall Z, Leslie J, Carobbio S, Virtue S, Davies SE, Lukasik A, Dale M, Bohlooly-Y M, Acharjee A, Lindén D, Bidault G, Petsalaki E, Griffin JL, Oakley F, Allison MED, Vidal-Puig A. Suppression of insulin-induced gene 1 (INSIG1) function promotes hepatic lipid remodelling and restrains NASH progression. Mol Metab 2021; 48:101210. [PMID: 33722690 PMCID: PMC8094910 DOI: 10.1016/j.molmet.2021.101210] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 02/19/2021] [Accepted: 03/06/2021] [Indexed: 01/22/2023] Open
Abstract
Objective Non-alcoholic fatty liver disease (NAFLD) is a silent pandemic associated with obesity and the metabolic syndrome, and also increases cardiovascular- and cirrhosis-related morbidity and mortality. A complete understanding of adaptive compensatory metabolic programmes that modulate non-alcoholic steatohepatitis (NASH) progression is lacking. Methods and results Transcriptomic analysis of liver biopsies in patients with NASH revealed that NASH progression is associated with rewiring of metabolic pathways, including upregulation of de novo lipid/cholesterol synthesis and fatty acid remodelling. The modulation of these metabolic programmes was achieved by activating sterol regulatory element-binding protein (SREBP) transcriptional networks; however, it is still debated whether, in the context of NASH, activation of SREBPs acts as a pathogenic driver of lipotoxicity, or rather promotes the biosynthesis of protective lipids that buffer excessive lipid accumulation, preventing inflammation and fibrosis. To elucidate the pathophysiological role of SCAP/SREBP in NASH and wound-healing response, we used an Insig1 deficient (with hyper-efficient SREBPs) murine model challenged with a NASH-inducing diet. Despite enhanced lipid and cholesterol biosynthesis, Insig1 KO mice had similar systemic metabolism and insulin sensitivity to Het/WT littermates. Moreover, activating SREBPs resulted in remodelling the lipidome, decreased hepatocellular damage, and improved wound-healing responses. Conclusions Our study provides actionable knowledge about the pathways and mechanisms involved in NAFLD pathogenesis, which may prove useful for developing new therapeutic strategies. Our results also suggest that the SCAP/SREBP/INSIG1 trio governs transcriptional programmes aimed at protecting the liver from lipotoxic insults in NASH.
Human NASH biopsies’ transcriptomics analysis features metabolic pathway rewiring. SCAP/SREBP/INSIG1 modulation promotes lipid/cholesterol synthesis/remodelling in NASH. Loss of Insig1 promotes lipid remodelling, preventing hepatic lipotoxicity in NASH. Loss of Insig1 improves liver damage and wound healing and restrains NASH progression.
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Affiliation(s)
- Vian Azzu
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK; Liver Unit, Cambridge NIHR Biomedical Research Centre, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK; Department of Gastroenterology and Hepatology, Norfolk and Norwich University Hospitals, Norwich, UK
| | - Michele Vacca
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK; Department of Biochemistry and Cambridge Systems Biology Centre, University of Cambridge, Cambridge, UK; Clinica Medica Cesare Frugoni, Department of Interdisciplinary Medicine, University of Bari Aldo Moro, Bari, Italy
| | - Ioannis Kamzolas
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK; European Molecular Biology Laboratory, European Bioinformatics Institute (EMBL-EBI), Wellcome Genome Campus, Hinxton, UK
| | - Zoe Hall
- Department of Biochemistry and Cambridge Systems Biology Centre, University of Cambridge, Cambridge, UK; Biomolecular Medicine, Systems Medicine, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Jack Leslie
- Newcastle Fibrosis Research Group, Biosciences Institute, Faculty of Medical Sciences, 5 Newcastle University, Newcastle upon Tyne, UK
| | - Stefania Carobbio
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK
| | - Samuel Virtue
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK
| | - Susan E Davies
- Department of Pathology, Cambridge University Hospitals, Cambridge, UK
| | - Agnes Lukasik
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK
| | - Martin Dale
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK
| | - Mohammad Bohlooly-Y
- Translational Genomics, Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
| | - Animesh Acharjee
- Department of Biochemistry and Cambridge Systems Biology Centre, University of Cambridge, Cambridge, UK; College of Medical and Dental Sciences, Institute of Cancer and Genomic Sciences, Centre for Computational Biology, University of Birmingham, UK
| | - Daniel Lindén
- Bioscience Metabolism, Research and Early Development Cardiovascular, Renal and Metabolism (CVRM), BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden; Division of Endocrinology, Department of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, Sweden
| | - Guillaume Bidault
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK
| | - Evangelia Petsalaki
- European Molecular Biology Laboratory, European Bioinformatics Institute (EMBL-EBI), Wellcome Genome Campus, Hinxton, UK
| | - Julian L Griffin
- Department of Biochemistry and Cambridge Systems Biology Centre, University of Cambridge, Cambridge, UK; Biomolecular Medicine, Systems Medicine, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Fiona Oakley
- Newcastle Fibrosis Research Group, Biosciences Institute, Faculty of Medical Sciences, 5 Newcastle University, Newcastle upon Tyne, UK
| | - Michael E D Allison
- Liver Unit, Cambridge NIHR Biomedical Research Centre, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK.
| | - Antonio Vidal-Puig
- Wellcome Trust/MRC Institute of Metabolic Science, Metabolic Research Laboratories, University of Cambridge, Cambridge, UK; Wellcome Trust Sanger Institute, Hinxton, UK; Cambridge University Nanjing Centre of Technology and Innovation, Jiangbei, Nanjing, China.
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9
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Abstract
Individuals with elevated lipid levels are at risk for developing cardiovascular disease as well as cancer. Sterol regulatory element-binding protein transcription factors (SREBPs) are inducers of lipid synthesis. Elevated SREBPs levels are linked to cell proliferation and metastasis. Using biochemical and mouse models of cancer, Zhao et al. have discovered that nuclear SREBP-1a-dependent transcription is activated by pyruvate kinase M2 in cancer cells, which promotes tumor growth. Targeting the lipogenesis pathway may therefore be a promising avenue for cancer treatment.
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Affiliation(s)
- Joseph T Nickels
- From the Institute of Metabolic Disorders, Genesis Biotechnology Group, Hamilton, New Jersey 08691 and .,the Rutgers Center for Lipid Research, New Jersey Institute for Food, Nutrition, and Health, Rutgers University, New Brunswick, New Jersey 08901
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10
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Engelking LJ, Cantoria MJ, Xu Y, Liang G. Developmental and extrahepatic physiological functions of SREBP pathway genes in mice. Semin Cell Dev Biol 2017; 81:98-109. [PMID: 28736205 DOI: 10.1016/j.semcdb.2017.07.011] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 07/07/2017] [Indexed: 12/17/2022]
Abstract
Sterol regulatory element-binding proteins (SREBPs), master transcriptional regulators of cholesterol and fatty acid synthesis, have been found to contribute to a diverse array of cellular processes. In this review, we focus on genetically engineered mice in which the activities of six components of the SREBP gene pathway, namely SREBP-1, SREBP-2, Scap, Insig-1, Insig-2, or Site-1 protease have been altered through gene knockout or transgenic approaches. In addition to the expected impacts on lipid metabolism, manipulation of these genes in mice is found to affect a wide array of developmental and physiologic processes ranging from interferon signaling in macrophages to synaptic transmission in the brain. The findings reviewed herein provide a blueprint to guide future studies defining the complex interactions between lipid biology and the physiologic processes of many distinct organ systems.
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Affiliation(s)
- Luke J Engelking
- Departments of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA; Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Mary Jo Cantoria
- Departments of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yanchao Xu
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Guosheng Liang
- Departments of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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11
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Li N, Zhou ZS, Shen Y, Xu J, Miao HH, Xiong Y, Xu F, Li BL, Luo J, Song BL. Inhibition of the sterol regulatory element-binding protein pathway suppresses hepatocellular carcinoma by repressing inflammation in mice. Hepatology 2017; 65:1936-1947. [PMID: 28027595 DOI: 10.1002/hep.29018] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 12/20/2016] [Indexed: 12/25/2022]
Abstract
UNLABELLED Obesity is a critical risk factor for hepatocellular carcinoma (HCC). However, it remains unknown whether inhibition of de novo lipid biosynthesis can suppress HCC. In this study, we blocked the sterol regulatory element-binding protein (SREBP) pathway, one of the key determinants of lipid homeostasis, by ablating 78-kDa cell-surface glycoprotein or SREBP cleavage-activating protein in hepatocytes, as well as by administering a chemical compound called betulin. We found that either genetically or pharmacologically inhibiting the SREBP pathway dramatically reduced diethylnitrosamine-induced HCC progression by down-regulating tumor-promoting cytokines, including interleukin (IL)-6, tumor necrosis factor alpha, and IL-1β. CONCLUSION Inhibition of de novo lipid biosynthesis by suppressing the SREBP pathway prevents HCC. This study identifies a previously underappreciated role of the SREBP pathway in HCC and suggests a novel metabolic strategy to control liver cancer. (Hepatology 2017;65:1936-1947).
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Affiliation(s)
- Na Li
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Zhang-Sen Zhou
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, the Institute for Advanced Studies, Wuhan University, Wuhan, China
| | - Yang Shen
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Jie Xu
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Hong-Hua Miao
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Ying Xiong
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Feng Xu
- Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore, Republic of Singapore
| | - Bo-Liang Li
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Jie Luo
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, the Institute for Advanced Studies, Wuhan University, Wuhan, China
| | - Bao-Liang Song
- Hubei Key Laboratory of Cell Homeostasis, College of Life Sciences, the Institute for Advanced Studies, Wuhan University, Wuhan, China
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12
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Zhang ZH, Liu XQ, Zhang C, He W, Wang H, Chen YH, Liu XJ, Chen X, Xu DX. Tlr4-mutant mice are resistant to acute alcohol-induced sterol-regulatory element binding protein activation and hepatic lipid accumulation. Sci Rep 2016; 6:33513. [PMID: 27627966 PMCID: PMC5024165 DOI: 10.1038/srep33513] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2015] [Accepted: 08/30/2016] [Indexed: 12/20/2022] Open
Abstract
Previous studies demonstrated that acute alcohol intoxication caused hepatic lipid accumulation. The present study showed that acute alcohol intoxication caused hepatic lipid accumulation in Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic sterol-regulatory element binding protein (SREBP)-1, a transcription factor regulating fatty acid and triglyceride (TG) synthesis, was activated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic Fas, Acc, Scd-1 and Dgat-2, the key genes for fatty acid and TG synthesis, were up-regulated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Additional experiment showed that hepatic MyD88 was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic NF-κB was activated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Moreover, hepatic GSH content was reduced and hepatic MDA level was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic CYP2E1 was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic p67phox and gp91phox, two NADPH oxidase subunits, were up-regulated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Alpha-phenyl-N-t-butylnitrone (PBN), a free radical spin-trapping agent, protected against alcohol-induced hepatic SREBP-1 activation and hepatic lipid accumulation. In conclusion, Tlr4-mutant mice are resistant to acute alcohol-induced hepatic SREBP-1 activation and hepatic lipid accumulation.
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Affiliation(s)
- Zhi-Hui Zhang
- Department of Toxicology, Anhui Medical University, Hefei, 230032, China
| | - Xiao-Qian Liu
- Department of Toxicology, Anhui Medical University, Hefei, 230032, China
| | - Cheng Zhang
- Department of Toxicology, Anhui Medical University, Hefei, 230032, China
| | - Wei He
- First Affiliated Hospital, Anhui Medical University, Hefei, 230032, China
| | - Hua Wang
- Department of Toxicology, Anhui Medical University, Hefei, 230032, China
| | - Yuan-Hua Chen
- Department of Toxicology, Anhui Medical University, Hefei, 230032, China
| | - Xiao-Jing Liu
- First Affiliated Hospital, Anhui Medical University, Hefei, 230032, China
| | - Xi Chen
- First Affiliated Hospital, Anhui Medical University, Hefei, 230032, China
| | - De-Xiang Xu
- Department of Toxicology, Anhui Medical University, Hefei, 230032, China
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13
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Klipsic D, Landrock D, Martin GG, McIntosh AL, Landrock KK, Mackie JT, Schroeder F, Kier AB. Impact of SCP-2/SCP-x gene ablation and dietary cholesterol on hepatic lipid accumulation. Am J Physiol Gastrointest Liver Physiol 2015; 309:G387-99. [PMID: 26113298 PMCID: PMC4556946 DOI: 10.1152/ajpgi.00460.2014] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 06/22/2015] [Indexed: 01/31/2023]
Abstract
While a high-cholesterol diet induces hepatic steatosis, the role of intracellular sterol carrier protein-2/sterol carrier protein-x (SCP-2/SCP-x) proteins is unknown. We hypothesized that ablating SCP-2/SCP-x [double knockout (DKO)] would impact hepatic lipids (cholesterol and cholesteryl ester), especially in high-cholesterol-fed mice. DKO did not alter food consumption, and body weight (BW) gain decreased especially in females, concomitant with hepatic steatosis in females and less so in males. DKO-induced steatosis in control-fed wild-type (WT) mice was associated with 1) loss of SCP-2; 2) upregulation of liver fatty acid binding protein (L-FABP); 3) increased mRNA and/or protein levels of sterol regulatory element binding proteins (SREBP1 and SREBP2) as well as increased expression of target genes of cholesterol synthesis (Hmgcs1 and Hmgcr) and fatty acid synthesis (Acc1 and Fas); and 4) cholesteryl ester accumulation was also associated with increased acyl-CoA cholesterol acyltransferase-2 (ACAT2) in males. DKO exacerbated the high-cholesterol diet-induced hepatic cholesterol and glyceride accumulation, without further increasing SREBP1, SREBP2, or target genes. This exacerbation was associated both with loss of SCP-2 and concomitant downregulation of Ceh/Hsl, apolipoprotein B (ApoB), MTP, and/or L-FABP protein expression. DKO diminished the ability to secrete excess cholesterol into bile and oxidize cholesterol to bile acid for biliary excretion, especially in females. This suggested that SCP-2/SCP-x affects cholesterol transport to particular intracellular compartments, with ablation resulting in less to the endoplasmic reticulum for SREBP regulation, making more available for cholesteryl ester synthesis, for cholesteryl-ester storage in lipid droplets, and for bile salt synthesis and/or secretion. These alterations are significant findings, since they affect key processes in regulation of sterol metabolism.
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Affiliation(s)
- Devon Klipsic
- Department of Pathobiology, Texas A&M University, College Station, Texas; and
| | - Danilo Landrock
- Department of Pathobiology, Texas A&M University, College Station, Texas; and
| | - Gregory G Martin
- Department of Physiology and Pharmacology, Texas A&M University, College Station, Texas
| | - Avery L McIntosh
- Department of Physiology and Pharmacology, Texas A&M University, College Station, Texas
| | - Kerstin K Landrock
- Department of Physiology and Pharmacology, Texas A&M University, College Station, Texas
| | - John T Mackie
- Department of Pathobiology, Texas A&M University, College Station, Texas; and
| | - Friedhelm Schroeder
- Department of Physiology and Pharmacology, Texas A&M University, College Station, Texas
| | - Ann B Kier
- Department of Pathobiology, Texas A&M University, College Station, Texas; and
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14
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Sun S, Wang M, Song H, Wu T, Wei H, He S, Ding Z, Ji G. SCAP gene polymorphisms decrease the risk of nonalcoholic fatty liver disease in females with metabolic syndrome. J Genet 2014; 92:565-70. [PMID: 24371177 DOI: 10.1007/s12041-013-0280-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Shanshan Sun
- Institute of Digestive Diseases, Longhua Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200032, People's Republic of China.
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15
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Singh AB, Kan CFK, Shende V, Dong B, Liu J. A novel posttranscriptional mechanism for dietary cholesterol-mediated suppression of liver LDL receptor expression. J Lipid Res 2014; 55:1397-407. [PMID: 24792925 DOI: 10.1194/jlr.m049429] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Indexed: 12/21/2022] Open
Abstract
It is well-established that over-accumulation of dietary cholesterol in the liver inhibits sterol-regulatory element binding protein (SREBP)-mediated LDL receptor (LDLR) gene transcription leading to a reduced hepatic LDLR mRNA level in hypercholesterolemic animals. However, it is unknown whether elevated cholesterol levels can elicit a cellular response to increase LDLR mRNA turnover to further repress LDLR expression in liver tissue. In the current study, we examined the effect of a high cholesterol diet on the hepatic expression of LDLR mRNA binding proteins in three different animal models and in cultured hepatic cells. Our results demonstrate that high cholesterol feeding specifically elevates the hepatic expression of LDLR mRNA decay promoting factor heterogeneous nuclear ribonucleoprotein (HNRNP)D without affecting expressions of other LDLR mRNA binding proteins in vivo and in vitro. Employing the approach of adenovirus-mediated gene knockdown, we further show that depletion of HNRNPD in the liver results in a marked reduction of serum LDL-cholesterol and a substantial increase in liver LDLR expression in hyperlipidemic mice. Additional studies of gene knockdown in albumin-luciferase-untranslated region (UTR) transgenic mice provide strong evidence supporting the essential role of 3'UTR in HNRNPD-mediated LDLR mRNA degradation in liver tissue. Altogether, this work identifies a novel posttranscriptional regulatory mechanism by which dietary cholesterol inhibits liver LDLR expression via inducing HNRNPD to accelerate LDLR mRNA degradation.
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Affiliation(s)
- Amar Bahadur Singh
- Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304 Department of Medicine, Stanford University, Stanford, CA 94305
| | | | - Vikram Shende
- Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304 Department of Medicine, Stanford University, Stanford, CA 94305
| | - Bin Dong
- Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304
| | - Jingwen Liu
- Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304
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16
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The association between TCM syndromes and SCAP polymorphisms in subjects with non-alcoholic fatty liver disease. Eur J Integr Med 2013. [DOI: 10.1016/j.eujim.2013.06.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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17
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Pro-apoptotic miRNA-128-2 modulates ABCA1, ABCG1 and RXRα expression and cholesterol homeostasis. Cell Death Dis 2013; 4:e780. [PMID: 23990020 PMCID: PMC3763462 DOI: 10.1038/cddis.2013.301] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 06/25/2013] [Accepted: 07/10/2013] [Indexed: 12/14/2022]
Abstract
Aberrant regulation of cholesterol homeostasis is associated with obesity as well as multiple types of cancer. However, the mechanism behind these is largely missing. Here, we show that microRNA (miRNA)-128-2 is not only a pro-apoptotic microRNA but it also alters the expression of genes involved in cellular cholesterol homeostasis. Cholesterol efflux via ATP-binding cassette transporters (ABCA1 and ABCG1) is a mechanism for cells to eliminate excess cholesterol and prevent cellular cholesterol accumulation. The regulation of these pathways is complex with transcriptional regulation by sterol-regulatory element-binding protein (SREBP) and liver X receptor/retinoid X receptor (RXR) transcription factors but poorly understood at the post-transcriptional levels. MiR-128-2 increases the expression of SREBP2 and decreases the expression of SREBP1 in HepG2, MCF7 and HEK293T cells independent of sirtuin 1 (SIRT1) status. MiR-128-2 inhibits the expression of ABCA1, ABCG1 and RXRα directly through a miR-128-2-binding site within their respective 3'untranslated regions. The administration of miR-128-2 leads to decline in the protein and mRNA levels of ABCA1, ABCG1 and RXRα. Conversely, anti-miRNA treatment leads to increased ABCA1, ABCG1 and RXRα expression. The inverse correlation between miR-128-2 and its targets viz. ABCA1 and ABCG1 was also established during high-fat diet in different mice tissues. Our data show that cholesterol efflux is attenuated by miR-128-2 overexpression and, conversely, stimulated by miR-128-2 silencing. Further, we also observed the induction of ER stress response by miR-128-2. In this study, we provide the first evidence of miR-128-2 to be a new regulator of cholesterol homeostasis. Our study shows dual role of miR-128-2, as a pro-apoptotic molecule as well as a regulator of cholesterol homeostasis.
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18
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Sen S, Jumaa H, Webster NJG. Splicing factor SRSF3 is crucial for hepatocyte differentiation and metabolic function. Nat Commun 2013; 4:1336. [PMID: 23299886 PMCID: PMC4314219 DOI: 10.1038/ncomms2342] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Accepted: 11/28/2012] [Indexed: 12/23/2022] Open
Abstract
SR family RNA binding proteins regulate splicing of nascent RNAs in vitro but their physiological role in vivo is largely unexplored, as genetic deletion of many SR protein genes results in embryonic lethality. Here we show that SRSF3HKO mice carrying a hepatocyte-specific deletion of Srsf3 (homologous to human SRSF3/SRp20) have a disrupted hepatic architecture and show pre- and postnatal growth retardation. SRSF3HKO mice exhibit impaired hepatocyte maturation with alterations in glucose and lipid homeostasis characterized by reduced glycogen storage, fasting hypoglycemia, increased insulin sensitivity and reduced cholesterol synthesis. We identify various splicing alterations in the SRSF3HKO liver that explain the in vivo phenotype. In particular, loss of SRSF3 causes aberrant splicing of Hnf1α, Ern1, Hmgcs1, Dhcr7 and Scap genes, which are critical regulators of glucose and lipid metabolism. Our study provides the first evidence for a SRSF3-driven genetic programme required for morphological and functional differentiation of hepatocytes that may have relevance for human liver disease and metabolic dysregulation.
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Affiliation(s)
- Supriya Sen
- Medical Research Service, VA San Diego Healthcare System, 3350 La Jolla Village Drive, San Diego, California 92161, USA
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19
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Dong XY, Tang SQ, Chen JD. Dual functions of Insig proteins in cholesterol homeostasis. Lipids Health Dis 2012; 11:173. [PMID: 23249523 PMCID: PMC3564778 DOI: 10.1186/1476-511x-11-173] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Accepted: 12/05/2012] [Indexed: 01/29/2023] Open
Abstract
The molecular mechanism of how cells maintain cholesterol homeostasis has become clearer for the understanding of complicated association between sterol regulatory element-binding proteins (SREBPs), SREBP cleavage-activating protein (SCAP), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) and Insuin induced-genes (Insigs). The pioneering researches suggested that SREBP activated the transcription of genes encoding HMG-CoA reductase and all of the other enzymes involved in the synthesis of cholesterol and lipids. However, SREBPs can not exert their activities alone, they must form a complex with another protein, SCAP in the endoplasmic reticulum (ER) and translocate to Golgi. Insigs are sensors and mediators that regulate cholesterol homeostasis through binding to SCAP and HMG-CoA reductase in diverse tissues such as adipose tissue and liver, as well as the cultured cells. In this article, we aim to review on the dual functions of Insig protein family in cholesterol homeostasis.
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Affiliation(s)
- Xiao-Ying Dong
- College of Veterinary Medicine, South China Agricultural University, No,483 Wu Shan Road, Tian He District, Guangzhou, 510642, China.
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20
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McKeegan PJ, Sturmey RG. The role of fatty acids in oocyte and early embryo development. Reprod Fertil Dev 2012; 24:59-67. [PMID: 22394718 DOI: 10.1071/rd11907] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Growing evidence suggests that endogenous and exogenous fatty acids play diverse roles in developing mammalian oocytes and early embryos. In this review, we describe some of the regulatory roles of fatty acids in early development, in addition to their metabolic functions. We focus initially on the provision of individual fatty acids, and then discuss how these might affect metabolism, oxidative stress, membrane composition, cell signalling events and gene expression. We propose that ongoing research should focus on physiologically relevant ratios and combinations of fatty acids, rather than isolated individual fatty acids, as their combined roles are both subtle and complex. Changing the ratio of specific fatty acids in the diet of animal models, and in vitro culture medium can cause significant dysregulation of cellular processes and development, an issue that extends to human fertility.
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Affiliation(s)
- Paul J McKeegan
- Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, HU6 7RX, UK
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21
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Jeon TI, Osborne TF. SREBPs: metabolic integrators in physiology and metabolism. Trends Endocrinol Metab 2012; 23:65-72. [PMID: 22154484 PMCID: PMC3273665 DOI: 10.1016/j.tem.2011.10.004] [Citation(s) in RCA: 391] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2011] [Revised: 10/26/2011] [Accepted: 10/31/2011] [Indexed: 12/16/2022]
Abstract
Recent advances have significantly increased our understanding of how sterol regulatory element binding proteins (SREBPs) are regulated at the transcriptional and post-transcriptional levels in response to cellular signaling. The phosphatidyl inositol-3-kinase (PI3K) and SREBP pathways intersect at multiple points, and recent insights demonstrate the importance of tight regulation of the PI3K pathway for regulating SREBPs in the adaptation to fluctuating dietary calorie load in the mammalian liver. In addition, genetic and genome-wide approaches highlight new functions for SREBPs in connecting lipid metabolism with other cellular processes where lipid pathway flux affects physiologic or pathophysiologic adaptation, such as cancer, steatosis, and innate immunity. This review focuses on recent advances and new roles for mammalian SREBPs in physiology and metabolism.
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Affiliation(s)
- Tae-Il Jeon
- Korea Food Research Institute, Seongnam, Republic of Korea 463–746
| | - Timothy F. Osborne
- Metabolic Signaling and Disease Program, Diabetes and Obesity Center, Sanford-Burnham Medical Research Institute, Orlando, Florida 32827
- Corresponding author : Osborne, T. F. ()
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Ye J, DeBose-Boyd RA. Regulation of cholesterol and fatty acid synthesis. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a004754. [PMID: 21504873 DOI: 10.1101/cshperspect.a004754] [Citation(s) in RCA: 177] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In mammals, intracellular levels of cholesterol and fatty acids are controlled through a feedback regulatory system mediated by a family of transcription factors called sterol regulatory element-binding proteins (SREBPs). SREBPs are synthesized as inactive precursors bound to membranes of the endoplasmic reticulum. When cells are deprived of cholesterol and fatty acids, NH(2)-terminal fragments of SREBPs become proteolytically released from membranes and migrate to the nucleus to activate transcription of genes required for lipid synthesis and uptake. Conversely, lipid repletion inhibits proteolytic processing of SREBPs and thereby suppresses lipid accumulation. We review here studies in cultured cells that reveal the mechanism for regulation of SREBP proteolytic activation, and those in animal models in which SREBP proteolysis has been either activated or inhibited to show the essential role of SREBPs in regulating hepatic lipid homeostasis.
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Affiliation(s)
- Jin Ye
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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Gokey NG, Lopez-Anido C, Gillian-Daniel AL, Svaren J. Early growth response 1 (Egr1) regulates cholesterol biosynthetic gene expression. J Biol Chem 2011; 286:29501-10. [PMID: 21712389 DOI: 10.1074/jbc.m111.263509] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The early growth response (EGR) family of transcription factors has been implicated in control of lipid biosynthetic genes. Egr1 is induced by insulin both in vitro and in vivo and is the most highly expressed family member in liver. In this study, we investigated whether Egr1 regulates cholesterol biosynthetic genes in liver. Using an insulin-sensitive liver cell line, we show that localization of Egr1 to cholesterol biosynthetic genes is induced by insulin treatment and that this localization precedes the induction of the genes. Reduction in Egr1 expression using targeted siRNA blunted the insulin-dependent induction of cholesterol genes. A similar reduction in squalene epoxidase expression was also observed in Egr1 null mice. In addition, application of chromatin immunoprecipitation (ChIP) samples to tiled gene microarrays revealed localization of Egr1 in promoter regions of many cholesterol gene loci. In vivo ChIP assays using liver tissue show that Egr1 localization to several cholesterol biosynthetic gene promoters is induced by feeding. Finally, analysis of plasma cholesterol in Egr1(-/-) mice indicated a significant decrease in serum cholesterol when compared with wild-type mice. Together these data point to Egr1 as a modulator of the cholesterol biosynthetic gene family in liver.
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Affiliation(s)
- Nolan G Gokey
- Comparative Biomedical Sciences Graduate Program, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin 53705, USA
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Yamamoto T, Watanabe K, Inoue N, Nakagawa Y, Ishigaki N, Matsuzaka T, Takeuchi Y, Kobayashi K, Yatoh S, Takahashi A, Suzuki H, Yahagi N, Gotoda T, Yamada N, Shimano H. Protein kinase Cbeta mediates hepatic induction of sterol-regulatory element binding protein-1c by insulin. J Lipid Res 2010; 51:1859-70. [PMID: 20179320 DOI: 10.1194/jlr.m004234] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Sterol-regulatory element binding protein-1c (SREBP-1c) is a transcription factor that controls lipogenesis in the liver. Hepatic SREBP-1c is nutritionally regulated, and its sustained activation causes hepatic steatosis and insulin resistance. Although regulation of SREBP-1c is known to occur at the transcriptional level, the precise mechanism by which insulin signaling activates SREBP-1c promoter remains to be elucidated. Here we show that protein kinase C beta (PKCbeta) is a key mediator of insulin-mediated activation of hepatic SREBP-1c and its target lipogenic genes. Activation of SREBP-1c in the liver of refed mice was suppressed by either adenoviral RNAi-mediated knockdown or dietary administration of a specific inhibitor of protein kinase C beta. The effect of PKCbeta inhibition was cancelled in insulin depletion by streptozotocin (STZ) treatment of mice. Promoter analysis indicated that PKCbeta activates SREBP-1c promoter through replacement of Sp3 by Sp1 for binding to the GC box in the sterol regulatory element (SRE) complex, a key cis-element of SREBP-1c promoter. Knockdown of Sp proteins demonstrated that Sp3 and Sp1 play reciprocally negative and positive roles in nutritional regulation of SREBP-1c, respectively. This new understanding of PKCbeta involvement in nutritional regulation of SREBP-1c activation provides a new aspect of PKCbeta inhibition as a potential therapeutic target for diabetic complications.
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Affiliation(s)
- Takashi Yamamoto
- Department of Internal Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
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Wouters K, van Bilsen M, van Gorp PJ, Bieghs V, Lütjohann D, Kerksiek A, Staels B, Hofker MH, Shiri-Sverdlov R. Intrahepatic cholesterol influences progression, inhibition and reversal of non-alcoholic steatohepatitis in hyperlipidemic mice. FEBS Lett 2010; 584:1001-5. [PMID: 20114046 DOI: 10.1016/j.febslet.2010.01.046] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Accepted: 01/21/2010] [Indexed: 02/07/2023]
Abstract
Hepatic inflammation is the key factor in non-alcoholic steatohepatitis (NASH) and promotes progression to liver damage. We recently identified dietary cholesterol as the cause of hepatic inflammation in hyperlipidemic mice. We now show that hepatic transcriptome responses are strongly dependent on cholesterol metabolism during diet-induced NASH and its inhibition by fenofibrate. Furthermore, we show that, despite doubling hepatic steatosis, pharmacological LXR activation reverses hepatic inflammation, in parallel with reversing hepatic cholesterol levels. Together, the results indicate a prominent role of cholesterol during the development, inhibition and reversal of hepatic inflammation in NASH and reveal potential new therapeutic strategies against NASH.
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Affiliation(s)
- Kristiaan Wouters
- Department of Molecular Genetics, Institutes of Maastricht University Maastricht, Maastricht, The Netherlands.
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Korade Z, Kenworthy AK, Mirnics K. Molecular consequences of altered neuronal cholesterol biosynthesis. J Neurosci Res 2009; 87:866-75. [PMID: 18951487 DOI: 10.1002/jnr.21917] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The first dedicated step in de novo cholesterol biosynthesis begins with formation of squalene and ends with the reduction of 7-dehydrocholesterol by 7-dehydrocholesterol reductase (Dhcr7) into cholesterol, which is an essential structural and signaling molecule. Mutations in the Dhcr7 gene lead to Smith-Lemli-Opitz syndrome (SLOS), which is characterized by developmental deformities, incomplete myelination, and mental retardation. To understand better the molecular consequences of Dhcr7 deficiency in neuronal tissue, we analyzed the effect of cholesterol deficiency on the transcriptome in Neuro2a cells. Transient down-regulation of Dhcr7 by siRNA led to altered expression of multiple molecules that play critical roles in intracellular signaling or vesicular transport or are inserted into membrane rafts (e.g. Egr1, Snx, and Adam19). A similar down-regulation was also observed in stable Dhrc7-shRNA-transfected cell lines, and the findings were verified by qPCR. Furthermore, we investigated the Dhcr7-deficient and control cells for the expression of several critical genes involved in lipid biosynthesis. Among these, fatty acid synthase, sterol-regulatory element binding protein 2, SREBF chaperone, site-1 protease, and squalene synthase showed a significant down-regulation, suggesting that, in a neuronal cell line, Dhcr7 is a potent regulator of lipid biosynthesis. Importantly, the gene expression changes were present in both lipid-containing and cholesterol-deficient media, suggesting that intrinsic cholesterol biosynthesis is necessary for normal neuronal function and cannot be supplemented from extrinsic sources.
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Affiliation(s)
- Zeljka Korade
- Department of Biochemistry, Vanderbilt University, Nashville, Tennessee 37232, USA.
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Brown MS, Goldstein JL. Cholesterol feedback: from Schoenheimer's bottle to Scap's MELADL. J Lipid Res 2009; 50 Suppl:S15-27. [PMID: 18974038 PMCID: PMC2674699 DOI: 10.1194/jlr.r800054-jlr200] [Citation(s) in RCA: 367] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2008] [Revised: 10/29/2008] [Indexed: 01/12/2023] Open
Abstract
Cholesterol biosynthesis is among the most intensely regulated processes in biology. Synthetic rates vary over hundreds of fold depending on the availability of an external source of cholesterol. Studies of this feedback regulatory process have a rich history. The field began 75 years ago when Rudolf Schoenheimer measured cholesterol balance in mice in a bottle. He found that cholesterol feeding led to decreased cholesterol synthesis, thereby introducing the general phenomenon by which end products of biosynthetic pathways inhibit their own synthesis. Recently, cholesterol feedback has been explained at a molecular level with the discovery of membrane-bound transcription factors called sterol regulatory element-binding proteins (SREBPs), and an appreciation of the sterol-sensing role of their partner, an escort protein called Scap. The key element in Scap is a hexapeptide sequence designated MELADL (rhymes with bottle). Thus, over 75 years, Schoenheimer's bottle led to Scap's MELADL. In addition to their basic importance in membrane biology, these studies have implications for the regulation of plasma cholesterol levels and consequently for the development of atherosclerotic plaques, myocardial infarctions, and strokes. In this article we review the major milestones in the cholesterol feedback story.
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Affiliation(s)
- Michael S. Brown
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Joseph L. Goldstein
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
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Abstract
Cholesterol is an essential component of mammalian cell membranes and is required for proper membrane permeability, fluidity, organelle identity, and protein function. Cells maintain sterol homeostasis by multiple feedback controls that act through transcriptional and posttranscriptional mechanisms. The membrane-bound transcription factor sterol regulatory element binding protein (SREBP) is the principal regulator of both sterol synthesis and uptake. In mammalian cells, the ER membrane protein Insig has emerged as a key component of homeostatic regulation by controlling both the activity of SREBP and the sterol-dependent degradation of the biosynthetic enzyme HMG-CoA reductase. In this review, we focus on recent advances in our understanding of the molecular mechanisms of the regulation of sterol synthesis. A comparative analysis of SREBP and HMG-CoA reductase regulation in mammals, yeast, and flies points toward an equilibrium model for how lipid signals regulate the activity of sterol-sensing proteins and their downstream effectors.
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Affiliation(s)
- Peter J Espenshade
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Sterol regulatory element binding protein 1 interacts with pregnane X receptor and constitutive androstane receptor and represses their target genes. Pharmacogenet Genomics 2008; 18:325-37. [PMID: 18334917 DOI: 10.1097/fpc.0b013e3282f706e0] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Sterol regulatory element binding protein 1 (SREBP-1) is a lipogenic transcription factor of the basic helix-loop-helix family. SREBP-1 binds to sterol regulatory elements (SREs) in the promoter of lipogenic genes and induces fatty acid and triglyceride synthesis. Decreased drug clearance has been observed in obese and other dyslipidemic rodents as well as in diabetic, obese or overfed rodents. A hallmark of these conditions is increased expression of SREBP-1 in the liver. We therefore searched for a possible link between regulation of cytochromes P450 (CYPs) and SREBP-1. METHODS We combined gene expression analysis, lipid analysis, effects of high levels of SREBP-1 in hepatocyte cultures to characterize the effects and protein interaction and chromatin immunoprecipitation assays to define the underlying mechanism. Finally, mice were fed a diet enriched in cholesterol to demonstrate the relevance of our data in vivo. By analyzing gene expression and lipids in cholesterol-fed mice or transfection of recombinant SREBP-1 in hepatocyte cultures the effect on CYPs was characterized. By use of protein interaction assays and chromatin immunoprecipitation the underlying mechanism was defined. RESULTS We observed that SREBP-1 represses drug-mediated induction of hepatic CYPs, mainly members of the 2B and the 3A subfamilies. These drugs induce transcription of CYPs and other drug metabolizing enzymes via activation of the nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR). Here we report that the activation of SREBP-1 by insulin or cholesterol in mouse liver and primary human hepatocytes inhibits the transcriptional effects in PXR and CAR. Our results suggest that SREBP-1 functions as a non-DNA binding inhibitor and blocks the interaction of PXR and CAR with cofactors such as steroid receptor coactivator 1. Consequently, mRNA induction of CYPs by drugs and other xenochemicals is impaired. CONCLUSION We conclude that PXR and CAR respond to lipid accumulation by direct interaction with SREBP-1 and show that drug metabolism and lipid metabolism are interconnected within a complex network of transcriptional regulators.
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Torres-Gonzalez M, Shrestha S, Sharman M, Freake HC, Volek JS, Fernandez ML. Carbohydrate restriction alters hepatic cholesterol metabolism in guinea pigs fed a hypercholesterolemic diet. J Nutr 2007; 137:2219-23. [PMID: 17885001 DOI: 10.1093/jn/137.10.2219] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The current study was undertaken to evaluate the effect of carbohydrate restriction on hepatic cholesterol metabolism in guinea pigs fed a hypercholesterolemic diet. Hartley male guinea pigs (n = 10 per group) were fed 1 of 3 diets: a diet with a percent energy distribution of 42:23:35 carbohydrate:protein:fat and 0.04% cholesterol (control), a diet with the same macronutrient distribution but with 0.25% cholesterol (HChol), or a carbohydrate-restricted (CR) diet with a percent energy distribution of 11:30:59 carbohydrate:protein:fat and 0.25% cholesterol for 12 wk. There was more accumulation of hepatic cholesterol and triglycerides as well as lower 3-hydroxy-3-methyl glutaryl-CoA reductase messenger RNA abundance in guinea pigs fed the high-cholesterol diets (HChol and CR) (P < 0.01). Guinea pigs fed the CR diet had lower concentrations of hepatic total cholesterol and cholesteryl ester than those fed the HChol diet (P < 0.05). There was no diet effect on hepatic LDL receptor expression. Hepatic acyl CoA cholesteryl acyltransferase (ACAT) activity was lowest in guinea pigs fed the low-cholesterol diet (9.7 +/- 4.8 pmol.min(-1).mg(-1)), intermediate in those fed the CR diet (37.3 +/- 12.4 pmol.min(-1).mg protein(-1)), and highest in guinea pigs fed the HChol diet (55.9 +/- 11.2 pmol.min(-1).mg(-1)). ACAT activity was significantly correlated with hepatic cholesterol (r = 0.715; P < 0.01) and LDL cholesterol (r = 0.59; P < 0.01) for all dietary groups, suggesting a major role of this enzyme in hepatic cholesterol homeostasis and in lipoprotein concentrations. These results indicate that dietary cholesterol increases hepatic lipid accumulation and affects hepatic cholesterol homeostasis. Carbohydrate restriction in the presence of high cholesterol is associated with lower hepatic ACAT activity and an attenuation of hepatic cholesterol accumulation.
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Kotzka J, Müller-Wieland D. Sterol regulatory element-binding protein (SREBP)-1: gene regulatory target for insulin resistance? Expert Opin Ther Targets 2006; 8:141-9. [PMID: 15102555 DOI: 10.1517/14728222.8.2.141] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The combined appearance of different cardiovascular risk factors seems to be more prevalent in individuals with decreased insulin sensitivity and increased visceral obesity, thereby being components of the so-called metabolic syndrome. Alterations in transcription factors result in complex dysregulation of gene expression, which might be the key to understanding insulin resistance-associated clinical clustering of coronary risk factors at the cellular or gene regulatory level. Recent examples are peroxisome proliferator-activated receptors and sterol regulatory element-binding proteins (SREBPs), which also appear to be novel drug targets. The authors have recently shown that SREBPs are substrates of mitogen-activated protein kinases, and propose that SREBP-1 might play a role in the development of cellular features belonging to lipotoxicity and, possibly, syndrome X.
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Affiliation(s)
- Jorg Kotzka
- Klinische Biochemie und Pathobiochemie, Deutsches Diabetes-Forschungsinstitut, Leibniz-Institut an der Heinrich-Heine-Universität Düsseldorf, Germany
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Engelking LJ, Liang G, Hammer RE, Takaishi K, Kuriyama H, Evers BM, Li WP, Horton JD, Goldstein JL, Brown MS. Schoenheimer effect explained--feedback regulation of cholesterol synthesis in mice mediated by Insig proteins. J Clin Invest 2005; 115:2489-98. [PMID: 16100574 PMCID: PMC1184040 DOI: 10.1172/jci25614] [Citation(s) in RCA: 173] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Accepted: 05/31/2005] [Indexed: 11/17/2022] Open
Abstract
End-product feedback inhibition of cholesterol synthesis was first demonstrated in living animals by Schoenheimer 72 years ago. Current studies define Insig proteins as essential elements of this feedback system in mouse liver. In cultured cells, Insig proteins are required for sterol-mediated inhibition of the processing of sterol regulatory element-binding proteins (SREBPs) to their nuclear forms. We produced mice with germline disruption of the Insig2 gene and Cre-mediated disruption of the Insig1 gene in liver. On a chow diet, these double-knockout mice overaccumulated cholesterol and triglycerides in liver. Despite this accumulation, levels of nuclear SREBPs and mRNAs for SREBP target genes in lipogenic pathways were not reduced. Whereas cholesterol feeding reduced nuclear SREBPs and lipogenic mRNAs in wild-type mice, this feedback response was severely blunted in the double-knockout mice, and synthesis of cholesterol and fatty acids was not repressed. The amount of HMG-CoA reductase protein was elevated out of proportion to the mRNA in the double-knockout mice, apparently owing to the failure of cholesterol to accelerate degradation of the enzyme. These studies indicate that the essential elements of the regulatory pathway for lipid synthesis function in liver as they do in cultured cells.
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Affiliation(s)
- Luke J Engelking
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046, USA
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Smith LH, Petrie MS, Morrow JD, Oates JA, Vaughan DE. The sterol response element binding protein regulates cyclooxygenase-2 gene expression in endothelial cells. J Lipid Res 2005; 46:862-71. [PMID: 15716578 DOI: 10.1194/jlr.m500021-jlr200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We previously demonstrated that cholesterol deprivation increases endothelial cyclooxygenase-2 (COX-2)-dependent prostacyclin [prostaglandin I2 (PGI2)] production in vitro. Cholesterol directly regulates gene transcription through the sterol response element binding protein (SREBP). In this work, we demonstrate that SREBP directly regulates COX-2 expression. Cholesterol reduces human COX-2 promoter-luciferase reporter construct activity in transiently transfected endothelial cells. Conversely, cotransfection with a constitutively active mutant SREBP increases COX-2 promoter activity. SREBP-1a and -2 specifically bind a putative sterol response element (SRE) sequence in the COX-2 promoter. This sequence competes for SREBP binding to a low density lipoprotein receptor consensus sequence in an electromobility-shift assay. These data indicate that endothelial COX-2 is regulated by cholesterol via the SREBP pathway. The present study identifies COX-2 as the first vascular gene without a clear role in lipid metabolism transactivated by SREBP, and suggests that enhanced production of PGI2 through this pathway may be an additional benefit of cholesterol-lowering therapies.
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Affiliation(s)
- Layton Harris Smith
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, USA
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McPherson R, Gauthier A. Molecular regulation of SREBP function: the Insig-SCAP connection and isoform-specific modulation of lipid synthesis. Biochem Cell Biol 2004; 82:201-11. [PMID: 15052338 DOI: 10.1139/o03-090] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sterol regulatory element binding proteins (SREBPs) are a family of membrane-bound transcription factors that play a unique and fundamental role in both cholesterol and fatty acid metabolism, relevant to human disease. There are three SREBPs that regulate the expression of over 30 genes. SREBPs are subject to regulation at three levels: proteolytic cleavage, rapid degradation by the ubiquitin-proteasome pathway, and sumoylation. Recently, there have been exciting advances in our understanding of the molecular mechanism of SREBP trafficking and processing with new information on the role of insulin-induced genes and the differential role and regulation of SREBP-1c and -2, which may ultimately lead to novel strategies for the treatment of dyslipidemia and insulin resistance.
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Affiliation(s)
- Ruth McPherson
- Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, ON, Canada.
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Abstract
The molecular mechanism of how hepatocytes maintain cholesterol homeostasis has become much more transparent with the discovery of sterol regulatory element binding proteins (SREBPs) in recent years. These membrane proteins are members of the basic helix-loop-helix-leucine zipper (bHLH-Zip) family of transcription factors. They activate the expression of at least 30 genes involved in the synthesis of cholesterol and lipids. SREBPs are synthesized as precursor proteins in the endoplasmic reticulum (ER), where they form a complex with another protein, SREBP cleavage activating protein (SCAP). The SCAP molecule contains a sterol sensory domain. In the presence of high cellular sterol concentrations SCAP confines SREBP to the ER. With low cellular concentrations, SCAP escorts SREBP to activation in the Golgi. There, SREBP undergoes two proteolytic cleavage steps to release the mature, biologically active transcription factor, nuclear SREBP (nSREBP). nSREBP translocates to the nucleus and binds to sterol response elements (SRE) in the promoter/enhancer regions of target genes. Additional transcription factors are required to activate transcription of these genes. Three different SREBPs are known, SREBPs-1a, -1c and -2. SREBP-1a and -1c are isoforms produced from a single gene by alternate splicing. SREBP-2 is encoded by a different gene and does not display any isoforms. It appears that SREBPs alone, in the sequence described above, can exert complete control over cholesterol synthesis, whereas many additional factors (hormones, cytokines, etc.) are required for complete control of lipid metabolism. Medicinal manipulation of the SREBP/SCAP system is expected to prove highly beneficial in the management of cholesterol-related disease.
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Affiliation(s)
- Lutz-W Weber
- Institute of Toxicology, GSF-National Research Center for Environment and Health, Munich, D-85758 Neuherberg, Germany.
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Maxwell KN, Soccio RE, Duncan EM, Sehayek E, Breslow JL. Novel putative SREBP and LXR target genes identified by microarray analysis in liver of cholesterol-fed mice. J Lipid Res 2003; 44:2109-19. [PMID: 12897189 DOI: 10.1194/jlr.m300203-jlr200] [Citation(s) in RCA: 291] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
High-cholesterol diets elicit changes in gene expression via such transcription factors as sterol-regulatory element binding proteins (SREBPs) and liver X receptors (LXRs). We used Affymetrix microarrays to identify genes in mouse liver regulated by dietary cholesterol (0.0% vs. 0.5% cholesterol wt/wt). Three independent experiments were performed, and data were analyzed with Affymetrix Microarray Suite and ANOVA statistical software. There were 69 unique Unigene clusters consistently regulated by dietary cholesterol (37 downregulated and 32 upregulated). The array results were confirmed by quantitative RT-PCR (Q-PCR) for seven of nine downregulated genes and five of six upregulated genes. A time course of dietary cholesterol feeding over 1 week revealed different temporal patterns of gene regulation for these confirmed genes. Six downregulated genes were examined in transgenic mice overexpressing truncated nuclear forms of SREBP-1a and SREBP-2, and all were induced in these mice. A second microarray analysis of mice treated with the LXR agonist TO901317 confirmed that 13 of the 32 cholesterol upregulated genes were also LXR-activated. This array result was confirmed by Q-PCR for three of three genes. In summary, these studies identified and confirmed six novel dietary cholesterol-regulated genes, three putative SREBP target genes (calcium/calmodulin-dependent protein kinase 1D, fatty acid binding protein 5, and proprotein convertase subtilisin/kexin 9), and three putative LXR target genes (a disintegrin and metalloprotease domain 11, apoptosis-inhibitory 6, and F-box-only protein 3).
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Affiliation(s)
- Kara N Maxwell
- Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, 1230 York Avenue, Box 179, New York, NY 10021, USA
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Shimano H. Sterol regulatory element-binding protein family as global regulators of lipid synthetic genes in energy metabolism. VITAMINS AND HORMONES 2003; 65:167-94. [PMID: 12481547 DOI: 10.1016/s0083-6729(02)65064-2] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Sterol regulatory element-binding proteins (SREBPs) have been established as lipid synthetic transcription factors for cholesterol and fatty acid synthesis. SREBPs are synthesized as membrane-bound precursors with their N-terminal active portions entering the nucleus to activate target genes after proteolytic cleavage in a sterol-regulated manner. This cleavage step is regulated by a putative sterol-sensing molecule, SREBP-activating protein (SCAP), that forms a complex with SREBPs and traffics between the rough endoplasmic reticulum and Golgi. DNA cis-elements that SREBPs bind, originally identified as sterol-regulatory elements (SREs), now expands to a variety of SRE-like sequences and some of E-boxes, which makes SREBPs eligible to regulate a wide range of lipid genes. Animal experiments including transgenic and knockout mice suggest that three isoforms, SREBP-1a, -1c, and -2, have different roles in lipid synthesis. In differentiated tissues and organs, SREBP-1c is involved in fatty acid, whereas SREBP-2 plays a major role in regulation of cholesterol synthesis. SREBP-1a is expressed in growing cells, providing both cholesterol and fatty acids that are required for membrane synthesis. SREBP-1c seems to be a mediator for insulin/glucose signaling to lipogenesis, and could be involved in insulin resistance, remnant lipoproteins, and fatty livers. Future studies in this field will certainly focus on understanding the molecular mechanisms sensing cellular sterol and energy states leading to the activation of SREBP-mediated gene transcription.
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Affiliation(s)
- Hitoshi Shimano
- Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
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Schwartz CC, VandenBroek JM, Cooper PS. Modeling Cholesterol in Humans: Update and Dealing with the Problem of Exchange in Vivo Using the Blood Cell-Lipoprotein Paradigm. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 537:207-19. [PMID: 14995038 DOI: 10.1007/978-1-4419-9019-8_14] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
Affiliation(s)
- Charles C Schwartz
- Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA.
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39
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Wang H, Liu F, Millette CF, Kilpatrick DL. Expression of a novel, sterol-insensitive form of sterol regulatory element binding protein 2 (SREBP2) in male germ cells suggests important cell- and stage-specific functions for SREBP targets during spermatogenesis. Mol Cell Biol 2002; 22:8478-90. [PMID: 12446768 PMCID: PMC139869 DOI: 10.1128/mcb.22.24.8478-8490.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Cholesterol biosynthesis in somatic cells is controlled at the transcriptional level by a homeostatic feedback pathway involving sterol regulatory element binding proteins (SREBPs). These basic helix-loop-helix (bHLH)-Zip proteins are synthesized as membrane-bound precursors, which are cleaved to form a soluble, transcriptionally active mature SREBP that regulates the promoters for genes involved in lipid synthesis. Homeostasis is conferred by sterol feedback inhibition of this maturation process. Previous work has demonstrated the expression of SREBP target genes in the male germ line, several of which are highly up-regulated during specific developmental stages. However, the role of SREBPs in the control of sterol regulatory element-containing promoters during spermatogenesis has been unclear. In particular, expression of several of these genes in male germ cells appears to be insensitive to sterols, contrary to SREBP-dependent gene regulation in somatic cells. Here, we have characterized a novel isoform of the transcription factor SREBP2, which is highly enriched in rat and mouse spermatogenic cells. This protein, SREBP2gc, is expressed in a stage-dependent fashion as a soluble, constitutively active transcription factor that is not subject to feedback control by sterols. These findings likely explain the apparent sterol-insensitive expression of lipid synthesis genes during spermatogenesis. Expression of a sterol-independent, constitutively active SREBP2gc in the male germ line may have arisen as a means to regulate SREBP target genes in specific developmental stages. This may reflect unique roles for cholesterol synthesis and other functional targets of SREBPs during spermatogenesis.
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Affiliation(s)
- Hang Wang
- Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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40
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Horton JD, Goldstein JL, Brown MS. SREBPs: activators of the complete program of cholesterol and fatty acid synthesis in the liver. J Clin Invest 2002. [PMID: 11994399 DOI: 10.1172/jci200215593] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Jay D Horton
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046, USA.
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41
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Horton JD, Goldstein JL, Brown MS. SREBPs: activators of the complete program of cholesterol and fatty acid synthesis in the liver. J Clin Invest 2002. [DOI: 10.1172/jci0215593] [Citation(s) in RCA: 3192] [Impact Index Per Article: 138.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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Horton JD, Goldstein JL, Brown MS. SREBPs: activators of the complete program of cholesterol and fatty acid synthesis in the liver. J Clin Invest 2002; 109:1125-31. [PMID: 11994399 PMCID: PMC150968 DOI: 10.1172/jci15593] [Citation(s) in RCA: 1694] [Impact Index Per Article: 73.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Affiliation(s)
- Jay D Horton
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046, USA.
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43
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44
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Shimano H. Sterol regulatory element-binding proteins (SREBPs): transcriptional regulators of lipid synthetic genes. Prog Lipid Res 2001; 40:439-52. [PMID: 11591434 DOI: 10.1016/s0163-7827(01)00010-8] [Citation(s) in RCA: 556] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Roles of sterol regulatory element-binding proteins (SREBPs) have been established as lipid synthetic transcription factors especially for cholesterol and fatty acid synthesis. SREBPs have unique characteristics. Firstly, they are membrane-bound proteins and the N-terminal active portions enter nucleus to activate their target genes after proteolytic cleavage, which requires sterol-sensing molecule, SREBP-activating protein (SCAP) and is crucial for sterol-regulation. Secondly, they bind and activate sterol-regulatory (SREs) containing promoters as well as some E-boxes, which makes SREBPs eligible to regulate a wide range of lipid genes. Finally, three isoforms, SREBP-1a-1c, and have different roles in lipid synthesis. In vivo studies using transgenic and knockout mice suggest that SREBP-1 seems to be involved in energy metabolism including fatty acid and glucose/insulin metabolism, whereas SREBP-2 is specific to cholesterol synthesis. Future studies will be focused on understanding molecular mechanisms sensing cellular sterol and energy states where SREBPs are deeply involved.
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Affiliation(s)
- H Shimano
- Department of Internal Medicine, Institute of Clinical Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan.
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45
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Riddle TM, Kuhel DG, Woollett LA, Fichtenbaum CJ, Hui DY. HIV protease inhibitor induces fatty acid and sterol biosynthesis in liver and adipose tissues due to the accumulation of activated sterol regulatory element-binding proteins in the nucleus. J Biol Chem 2001; 276:37514-9. [PMID: 11546771 DOI: 10.1074/jbc.m104557200] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism by which human immunodeficiency virus (HIV) protease inhibitor therapy adversely induces lipodystrophy and hyperlipidemia has not been defined. This study explored the mechanism associated with the adverse effects of the prototype protease inhibitor ritonavir in mice. Ritonavir treatment increased plasma triglyceride and cholesterol levels through increased fatty acid and cholesterol biosynthesis in adipose and liver. Ritonavir treatment also resulted in hepatic steatosis and hepatomegaly. These abnormalities, which were especially pronounced after feeding a Western type high fat diet, were due to ritonavir-induced accumulation of the activated forms of sterol regulatory binding protein (SREBP)-1 and -2 in the nucleus of liver and adipose, resulting in elevated expression of lipid metabolism genes. Interestingly, protease inhibitor treatment did not alter SREBP mRNA levels in these tissues. Thus, the adverse lipid abnormalities associated with protease inhibitor therapy are caused by the constitutive induction of lipid biosynthesis in liver and adipose tissues due to the accumulation of activated SREBP in the nucleus.
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Affiliation(s)
- T M Riddle
- Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0529, USA
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46
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Matsuda M, Korn BS, Hammer RE, Moon YA, Komuro R, Horton JD, Goldstein JL, Brown MS, Shimomura I. SREBP cleavage-activating protein (SCAP) is required for increased lipid synthesis in liver induced by cholesterol deprivation and insulin elevation. Genes Dev 2001; 15:1206-16. [PMID: 11358865 PMCID: PMC313801 DOI: 10.1101/gad.891301] [Citation(s) in RCA: 274] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
In liver, the synthesis of cholesterol and fatty acids increases in response to cholesterol deprivation and insulin elevation, respectively. This regulatory mechanism underlies the adaptation to cholesterol synthesis inhibitors (statins) and high calorie diets (insulin). In nonhepatic cells, lipid synthesis is controlled by sterol regulatory element-binding proteins (SREBPs), membrane-bound transcription factors whose active domains are released proteolytically to enter the nucleus and activate genes involved in the synthesis and uptake of cholesterol and fatty acids. SCAP (SREBP cleavage-activating protein) is a sterol-regulated escort protein that transports SREBPs from their site of synthesis in the endoplasmic reticulum to their site of cleavage in the Golgi. Here, we produced a conditional deficiency of SCAP in mouse liver by genomic recombination mediated by inducible Cre recombinase. SCAP-deficient mice showed an 80% reduction in basal rates of cholesterol and fatty acid synthesis in liver, owing to decreases in mRNAs encoding multiple biosynthetic enzymes. Moreover, these mRNAs failed to increase normally in response to cholesterol deprivation produced by a cholesterol synthesis inhibitor and to insulin elevation produced by a fasting-refeeding protocol. These data provide in vivo evidence that SCAP and the SREBPs are required for hepatic lipid synthesis under basal and adaptive conditions.
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Affiliation(s)
- M Matsuda
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046, USA
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47
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Bené H, Lasky D, Ntambi JM. Cloning and characterization of the human stearoyl-CoA desaturase gene promoter: transcriptional activation by sterol regulatory element binding protein and repression by polyunsaturated fatty acids and cholesterol. Biochem Biophys Res Commun 2001; 284:1194-8. [PMID: 11414710 DOI: 10.1006/bbrc.2001.5102] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Stearoyl-CoA desaturase (SCD) is a microsomal enzyme required for the biosynthesis of oleate (C18:1) and palmitoleate (C16:1) which are the major monounsaturated fatty acids of membrane phospholipids, triglycerides and cholesterol esters. Previously the full-length human skin cDNA was sequenced and the exon and intron structure of the single functional SCD gene determined. Here we report on the cloning and characterization of the promoter region of the human SCD gene. The human promoter structure is very similar to that of the mouse SCD1 isoform and contains conserved regulatory sequences for the binding of several transcription factors including the sterol regulatory element binding protein (SREBP), CCAAT enhancer binding protein-alpha (C/EBPalpha) and nuclear factor-1 (NF-1) that have been shown to transactivate the transcription of the mouse SCD1 gene. Polyunsaturated fatty acids and cholesterol decreased the SCD promoter-luciferase activity when transiently transfected into HepG2 cells. The decrease in promoter activity correlated with decreases in endogenous SCD mRNA and protein levels. Cotransfection experiment in HepG2 cells showed transactivation of the SCD promoter-luciferase activity by an expression vector containing SREBP-1a and 1c. Our studies indicate that the transcription of the human SCD gene is repressed by polyunsaturated fatty acids and cholesterol and that SREBP plays a role in the transcriptional activation of this gene.
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Affiliation(s)
- H Bené
- Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA
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48
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Ntambi JM, Bené H. Polyunsaturated fatty acid regulation of gene expression. J Mol Neurosci 2001; 16:273-8; discussion 279-84. [PMID: 11478382 DOI: 10.1385/jmn:16:2-3:273] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2000] [Accepted: 11/01/2000] [Indexed: 11/11/2022]
Abstract
Polyunsaturated fatty acids (PUFAs), specifically the n-3 and n-6 series, play a key role in the progression or prevention of human diseases such as obesity, diabetes, cancer, neurological and heart disease, mainly by affecting cellular membrane lipid composition, metabolism, signal-transduction pathways, and by direct control of gene expression. PUFAs show regulation of gene expression in several tissues, including brain, liver, heart, and adipose. Most recently, research has focused on identifying the mechanisms by which PUFAs regulate lipogenic gene expression. Research to date indicates that PUFA-mediated regulation of the genetic expression and proteolytic maturation of a group of transcription factors termed sterol regulatory element binding proteins (SREBPs) accounts for the suppression of hepatic lipogenic gene expression. However, our recent studies on the transcriptional regulation of the stearoyl-coenzyme A (CoA) desaturase gene, encoding a key enzyme in the cellular synthesis of monounsaturated fatty acids from saturated fatty acids indicates that PUFA can suppress gene transcription by a mechanism independent of SREBP maturation.
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Affiliation(s)
- J M Ntambi
- Department of Biochemistry, University of Wisconsin-Madison, 53706-1544, USA.
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49
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Repa JJ, Liang G, Ou J, Bashmakov Y, Lobaccaro JM, Shimomura I, Shan B, Brown MS, Goldstein JL, Mangelsdorf DJ. Regulation of mouse sterol regulatory element-binding protein-1c gene (SREBP-1c) by oxysterol receptors, LXRalpha and LXRbeta. Genes Dev 2000; 14:2819-30. [PMID: 11090130 PMCID: PMC317055 DOI: 10.1101/gad.844900] [Citation(s) in RCA: 1328] [Impact Index Per Article: 53.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The liver X receptors (LXRs) are members of the nuclear hormone receptor superfamily that are bound and activated by oxysterols. These receptors serve as sterol sensors to regulate the transcription of gene products that control intracellular cholesterol homeostasis through catabolism and transport. In this report, we describe a novel LXR target, the sterol regulatory element-binding protein-1c gene (SREBP-1c), which encodes a membrane-bound transcription factor of the basic helix-loop-helix-leucine zipper family. SREBP-1c expression was markedly increased in mouse tissues in an LXR-dependent manner by dietary cholesterol and synthetic agonists for both LXR and its heterodimer partner, the retinoid X receptor (RXR). Expression of the related gene products, SREBP-1a and SREBP-2, were not increased. Analysis of the mouse SREBP-1c gene promoter revealed an RXR/LXR DNA-binding site that is essential for this regulation. The transcriptional increase in SREBP-1c mRNA by RXR/LXR was accompanied by a similar increase in the level of the nuclear, active form of the SREBP-1c protein and an increase in fatty acid synthesis. Because this active form of SREBP-1c controls the transcription of genes involved in fatty acid biosynthesis, our results reveal a unique regulatory interplay between cholesterol and fatty acid metabolism.
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MESH Headings
- Animals
- Base Sequence
- CCAAT-Enhancer-Binding Proteins/genetics
- Cholesterol/metabolism
- Cholesterol, Dietary/metabolism
- DNA-Binding Proteins/genetics
- Dimerization
- Fatty Acids/metabolism
- Lipid Metabolism
- Liver X Receptors
- Male
- Mice
- Mice, Knockout
- Molecular Sequence Data
- Orphan Nuclear Receptors
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Retinoic Acid/agonists
- Receptors, Retinoic Acid/metabolism
- Receptors, Steroid/agonists
- Receptors, Steroid/metabolism
- Receptors, Thyroid Hormone/agonists
- Receptors, Thyroid Hormone/metabolism
- Response Elements
- Retinoid X Receptors
- Sterol Regulatory Element Binding Protein 1
- Sterols/metabolism
- Transcription Factors/agonists
- Transcription Factors/genetics
- Up-Regulation
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Affiliation(s)
- J J Repa
- Howard Hughes Medical Institute and Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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50
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Luong A, Hannah VC, Brown MS, Goldstein JL. Molecular characterization of human acetyl-CoA synthetase, an enzyme regulated by sterol regulatory element-binding proteins. J Biol Chem 2000; 275:26458-66. [PMID: 10843999 DOI: 10.1074/jbc.m004160200] [Citation(s) in RCA: 219] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Through suppressive subtractive hybridization, we identified a new gene whose transcription is induced by sterol regulatory element-binding proteins (SREBPs). The gene encodes acetyl-CoA synthetase (ACS), the cytosolic enzyme that activates acetate so that it can be used for lipid synthesis or for energy generation. ACS genes were isolated previously from yeast, but not from animal cells. Recombinant human ACS was produced by expressing the cloned cDNA transiently in human cells. After purification by nickel chromatography, the 701-amino acid cytosolic enzyme was shown to function as a monomer. The recombinant enzyme produced acetyl-CoA from acetate in a reaction that required ATP. As expected for a gene controlled by SREBPs, ACS mRNA was induced when cultured cells were deprived of sterols and repressed by sterol addition. The pattern of regulation resembled the regulation of enzymes of fatty acid synthesis. ACS mRNA was also elevated in livers of transgenic mice that express dominant-positive versions of all three isoforms of SREBP. We conclude that ACS mRNA, and hence the ability of cells to activate acetate, is regulated by SREBPs in parallel with fatty acid synthesis in animal cells.
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Affiliation(s)
- A Luong
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046, USA
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