title: Epigenetic modulation of insulin-like growth factor-II overexpression by hepatitis B virus X protein in hepatocellular carcinoma.
abstract: Hepatitis B virus X protein (HBx) is involved in the pathogenesis of hepatocellular carcinoma (HCC). Overexpression of the transcripts from the P3 and P4 promoters of the insulin-like growth factor-II (IGF-II) gene is observed in HCC. The present study investigated the involvement of HBx in IGF-II overexpression and its epigenetic regulation. Firstly, the effects of HBx on P3 and P4 mRNA expression, the methylation status of the P3 and P4 promoters, and MBD2 expression were analyzed in human HCC cells and HCC samples. Next, interaction between HBx and MBD2 or CBP/p300 was assessed by co-immunoprecipitation, and HBx-mediated binding of MBD2 and CBP/p300 to the P3 and P4 promoters and the acetylation of the corresponding histones H3 and H4 were evaluated by quantitative chromatin immunoprecipitation. Finally, using siRNA knockdown, we investigated the roles of MBD2 and CBP/p300 in IGF-II overexpression and its epigenetic regulation. Our results showed that HBx promotes IGF-II expression via inducing the hypomethylation of the P3 and P4 promoters, and that HBx increases MBD2 expression, directly interacts with MBD2 and CBP/p300, and elevates their recruitment to the hypomethylated P3 and P4 promoters with increased acetylation levels of the corresponding histones H3 and H4. Further results showed that endogenous MBD2 and CBP/p300 are necessary for HBx-induced IGF-II overexpression and that CBP/p300 presence and CBP/p300-mediated acetylation of histones H3 and H4 are partially required for MBD2 binding and its demethylase activity. These data suggest that HBx induces MBD2-HBx-CBP/p300 complex formation via interaction with MBD2 and CBP/p300, which contributes to the hypomethylation and transcriptional activation of the IGF-II-P3 and P4 promoters and that CBP/p300-mediated acetylation of histones H3 and H4 may be a rate-limiting step for the hypomethylation and activation of these two promoters. This study provides an alternative mechanism for understanding the pathogenesis of HBx-mediated HCC.
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Xu You
authors.initials: XY
authors.lastname: Liu
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Shao Hui
authors.initials: SH
authors.lastname: Tang
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Sheng Lan
authors.initials: SL
authors.lastname: Wu
authors.affiliation: Department of General Surgery, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Yu Hong
authors.initials: YH
authors.lastname: Luo
authors.affiliation: Department of General Surgery, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Ming Rong
authors.initials: MR
authors.lastname: Cao
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Hong Ke
authors.initials: HK
authors.lastname: Zhou
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Xiang Wu
authors.initials: XW
authors.lastname: Jiang
authors.affiliation: Department of Gastroenterology, Guangzhou Red Cross Hospital Affiliated to Medical College of Jinan University Guangzhou, 510220, China.
authors.forename: Jian Chang
authors.initials: JC
authors.lastname: Shu
authors.affiliation: Department of Gastroenterology, The Affiliated Shenzhen Shajing Hospital, Guangzhou Medical University Shenzhen, 518104, China.
authors.forename: Cai Qun
authors.initials: CQ
authors.lastname: Bie
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Si Min
authors.initials: SM
authors.lastname: Huang
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Zhan Hong
authors.initials: ZH
authors.lastname: Zheng
authors.affiliation: Department of Gastroenterology, The First Affiliated Hospital, Jinan University Guangzhou, 510632, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
keywords: Hepatitis B virus X protein; MBD2-HBx-CBP/p300 complex; hepatocellular carcinoma; hypomethylation; insulin-like growth factor II