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©The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Feb 14, 2017; 23(6): 986-998
Published online Feb 14, 2017. doi: 10.3748/wjg.v23.i6.986
Melatonin, a novel selective ATF-6 inhibitor, induces human hepatoma cell apoptosis through COX-2 downregulation
Li-Jia Bu, Han-Qing Yu, Lu-Lu Fan, Xiao-Qiu Li, Fang Wang, Jia-Tao Liu, Fei Zhong, Cong-Jun Zhang, Wei Wei, Hua Wang, Guo-Ping Sun
Li-Jia Bu, Han-Qing Yu, Lu-Lu Fan, Xiao-Qiu Li, Fang Wang, Jia-Tao Liu, Fei Zhong, Cong-Jun Zhang, Hua Wang, Guo-Ping Sun, Department of Oncology, the First Affiliated Hospital of Anhui Medical University, Hefei 230022, Anhui Province, China
Jia-Tao Liu, Department of Pharmacy, the First Affiliated Hospital of Anhui Medical University, Hefei 230022, Anhui Province, China
Wei Wei, Institute of Clinical Pharmacology, Anhui Medical University, Hefei 230032, Anhui Province, China
Hua Wang, Institute for Liver Diseases of Anhui Medical University, Hefei 230032, Anhui Province, China
Author contributions: Bu LJ, Yu HQ and Fan LL contributed equally to this work; Bu LJ, Yu HQ and Fan LL performed select experiments and analyzed data; Li XQ and Wang F performed select experiments; Liu JT and Zhong F performed select histopathological experiments; Zhang CJ and Wei W read the manuscript and gave important intellectual suggestions; Wang H and Sun GP prepared the manuscript, and designed and supervised the project.
Supported by grants from the National Natural Science Foundation of China, No. 81572430 and No. 81272739.
Institutional review board statement: The study was carried out in accordance with a protocol approved by the Ethics Committee of Anhui Medical University (Anhui, China).
Conflict-of-interest statement: No conflicts of interest exist for any of the authors.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Dr. Guo-Ping Sun, Department of Oncology, the First Affiliated Hospital of Anhui Medical University, No. 218 Jixi Road, Hefei 230022, Anhui Province, China. sunguoping@ahmu.edu.cn
Telephone: +86-551-62923509 Fax: +86-551-62923509
Received: August 31, 2016
Peer-review started: August 31, 2016
First decision: September 28, 2016
Revised: October 11, 2016
Accepted: October 27, 2016
Article in press: October 27, 2016
Published online: February 14, 2017
AIM
To clarify the mechanisms involved in the critical endoplasmic reticulum (ER) stress initiating unfolded protein response pathway modified by melatonin.
METHODS
Hepatoma cells, HepG2, were cultured in vitro. Flow cytometry and TUNEL assay were used to measure HepG2 cell apoptosis. Western blotting and quantitative reverse transcription-polymerase chain reaction methods were used to determine the protein and messenger RNA levels of ER stress and apoptosis related genes’ expression, respectively. Tissue microarray construction from patients was verified by immunohistochemical analysis.
RESULTS
In the present study, we first identified that melatonin selectively blocked activating transcription factor 6 (ATF-6) and then inhibited cyclooxygenase-2 (COX-2) expression, leading to enhanced liver cancer cell apoptosis under ER stress condition. Dramatically increased CCAAT-enhancer-binding protein homologous protein level, suppressed COX-2 and decreased Bcl-2/Bax ratio by melatonin or ATF-6 siRNA contributed the enhanced HepG2 cell apoptosis under tunicamycin (an ER stress inducer) stimulation. In clinical hepatocellular carcinoma patients, the close relationship between ATF-6 and COX-2 was further confirmed.
CONCLUSION
These findings indicate that melatonin as a novel selective ATF-6 inhibitor can sensitize human hepatoma cells to ER stress inducing apoptosis.
Core tip: Endoplasmic reticulum (ER) stress plays an important role in tumor growth and resistance to treatment. Our previous studies have already shown that melatonin sensitizes the human hepatocellular carcinoma cell to ER stress-induced apoptosis and attenuates ER stress-induced doxorubicin resistance. In this study, we first identified that melatonin selectively blocked ER stress downstream activating transcription factor 6 (ATF-6) and then inhibited cyclooxygenase-2 expression, leading to enhanced liver cancer cell apoptosis under ER stress condition. Our findings indicate that melatonin as a novel selective ATF-6 inhibitor can sensitize human hepatoma cells to ER stress inducing apoptosis.
