Clinical and Translational Research
Copyright ©The Author(s) 2020. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Clin Cases. Jul 26, 2020; 8(14): 2917-2929
Published online Jul 26, 2020. doi: 10.12998/wjcc.v8.i14.2917
Identification of APEX2 as an oncogene in liver cancer
Ru Zheng, Heng-Liang Zhu, Bing-Ren Hu, Xiao-Jiao Ruan, Hua-Jie Cai
Ru Zheng, Bing-Ren Hu, Xiao-Jiao Ruan, Hua-Jie Cai, Department of General Surgery, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, Zhejiang Province, China
Heng-Liang Zhu, Department of General Surgery, Shenzhen University General Hospital, Shenzhen 518107, Guangdong Province, China
Author contributions: Cai HJ conceived and designed the study; Zheng R conducted the experiments and data analysis; Zhu HL performed the statistical analysis; Hu BR and Ruan XJ wrote the manuscript; all authors reviewed and approved the final manuscript.
Supported by Wenzhou Science and Technology Bureau, No. Y20180147.
Institutional review board statement: This study was reviewed and approved by the Ethics Committee of the First Affiliated Hospital of Wenzhou Medical University.
Informed consent statement: Patients were not required to give informed consent to this study because the analysis used anonymous clinical data and the confidentiality of the patients was preserved.
Conflict-of-interest statement: All authors have no conflict of interests to declare.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (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/
Corresponding author: Hua-Jie Cai, MD, Associate Chief Physician, Department of General Surgery, The First Affiliated Hospital of Wenzhou Medical University, Nanbaixiang Street, Ouhai District, Wenzhou 325000, Zhejiang Province, China. huajie.cai@outlook.com
Received: April 17, 2020
Peer-review started: April 17, 2020
First decision: May 26, 2020
Revised: May 27, 2020
Accepted: June 12, 2020
Article in press: June 12, 2020
Published online: July 26, 2020
Processing time: 98 Days and 9.7 Hours
Abstract
BACKGROUND

DNA damage is one of the critical contributors to the occurrence and development of some cancers. APEX1 and APEX2 are the most important molecules in the DNA damage, and APEX1 has been identified as a diagnostic and prognostic biomarker in liver hepatocellular carcinoma (LIHC). However, the expression of APEX2 and its functional mechanisms in LIHC are still unclear.

AIM

To examine the expression of APEX2 and the potential mechanism network in LIHC.

METHODS

We conducted a pan-cancer analysis of the expression of APEX1 and APEX2 using the interactive TIMER tool. GEO datasets, including GSE14520, GSE22058, and GSE64041, were used to compare the APEX2 expression level in tumor tissues and adjacent non-tumor tissues. Then, we calculated the 5-year survival rate according to the web-based Kaplan-Meier analysis. We included the TCGA liver cancer database in GSEA analysis based on the high and low APEX2 expression, showing the potential mechanisms of APEX2 in LIHC. After that, we conducted Pearson correlation analysis using GEPIA2. Next, we performed quantitative polymerase chain reaction (qPCR) assay to examine the APEX2 levels in normal liver cell line LO2 and several liver cancer cell lines, including HepG2, Huh7, SMMC7721, and HCCLM3. APEX2 in HCCLM3 cells was knocked down using small interfering RNA. The role of APEX2 in cell viability was confirmed using CCK-8. Dual-luciferase reporter assay was performed to examine the promoter activity of CCNB1 and MYC.

RESULTS

APEX1 and APEX2 are both highly expressed in the tumor tissues of BLCA, BRCA, CHOL, COAD, ESCA, HNSC, LIHC, LUAD, LUSC, READ, and STAD. APEX2 overexpression in LIHC was validated using GSE14520, GSE22058, and GSE64041 datasets. The survival analysis showed that LIHC patients with high expression of APEX2 had a lower overall survival rate, even in the AJCC T1 patients. High level of APEX2 could indicate a lower overall survival rate in patients with or without viral hepatitis. The GSEA analysis identified that kinetochore and spindle microtubules are the two main cellular components of APEX2 in GO Ontology. APEX2 was also positively associated with molecular function regulation of chromosome segregation and DNA replication. The results of KEGG analysis indicated that APEX2 expression was positively correlated with cell cycle pathway and pro-oncogenic MYC signaling. Pearson correlation analysis showed that APEX2 had a significant positive correlation with CCNB1 and MYC. APEX2 level was higher in liver cancer cell lines than in normal liver LO2 cells. Small interfering RNA could knock down the APEX2 expression in HCCLM3 cells. Knockdown of APEX2 resulted in a decrease in the viability of HCCLM3 cells as well as the expression and promoter activity of CCNB1 and MYC.

CONCLUSION

APEX2 is overexpressed in LIHC, and the higher APEX2 level is associated with a worse prognosis in overall survival. APEX2 is closely involved in the biological processes of chromosome segregation and DNA replication. APEX2 expression is positively correlated with the pro-oncogenic pathways. Knockdown of APEX2 could inhibit the cell viability and CCNB1 and MYC pathways, suggesting that APEX2 is an oncogene in LIHC, which could be a potential pharmaceutic target in the anti-tumor therapy.

Keywords: APEX2; High expression; Worse prognosis; Pro-oncogenic pathway; Oncogene; Liver cancer

Core tip: In this study, we identified that APEX2 is highly expressed in liver hepatocellular carcinoma (LIHC), and overexpression of APEX2 could act as a poor prognostic factor. The GO Ontology-based GSEA analysis suggested that APEX2 is an important regulator in the kinetochore and spindle microtubule. Besides, APEX2 is closely associated with the biological processes of chromosome segregation and DNA replication. The molecular mechanism analysis indicated that APEX2 is positively associated with cell cycle and MYC pathways. Knockdown of APEX2 can impede the viability of liver cancer cells, and inhibit CCNB1 and MYC pathways, suggesting that APEX2 is an oncogene in LIHC.