Molecular Mechanisms Of The Inhibition Of CD82 Gene Expression By Hepatitis B Virus At HCC

Human hepatitis B virus (HBV) is a partially non-cytopathic double-stranded DNA virus which could cause acute or chronic hepatic diseases. HBV infection is an vital health threat to human health in public, and about a million people worldwide died of hepatic failure, cirrhosis and liver cancer which were caused by HBV infection every year. About 75% hepatocelluar carcinomas (HCC) were caused by HBV infection. In 1970, the relationship between HBV and HCC was first reported in Lacent, which was confirmed by abundant researchers in the following years. Although it is clear that HBV is carcinogenic, researchers also found that a variety of cytokines may be involved in the process of pathogenesis and carcinogenesis. However, the mechanism how HBV caused hepatocellular carcinoma has not been determined yet.CD82, a tumor suppressor gene, is a member of transmembrane 4 superfamily (TM4SF). In recent years, researches showed that the decreased or absent expression of CD82 gene was related to numerous kinds of tumors of human being. This study was conducted to explore the potential mechanisms of this issue.Firstly, we examined the expression of CD82 in the liver tissues of patients with HCC (HBV carrier) and normal volunteers, as well as in HepG2 cell lines and HepG2.215 cell lines. The expression of CD82 in hepatocellular carcinoma tissues(carrying HBV) was significantly lower than that in normal liver tissues, we also found the expression of CD82 in Hep2.215 was significantly lower than that in HepG2. Then, We demonstrated that HBV could inhibit the expression of CD82 at the levels of mRNA and protein. Among the seven proteins encoded by HBV, we found that HBx could inhibit the expression of CD82 significantly, suggesting that HBV may inhibit the expression of CD82 mainly by HBx. In order to explore the mechanism of HBx inhibiting the expression of CD82, we started from transcriptional regulation. Through the experiments of the truncated promoter, EMSA and CHIP, the results showed that the sites of EGR1 in the promoter of CD82 gene played a major role in its expression. Meanwhile, we found that HBx could interact with the transcription factor of EGR1, which could inhibit the expression of CD82 by suppressing EGR1 binding to the site of its promoter.After that, we tested the potential mechanism of epigenetics by DNA methylation sequencing and MSP test, and found that HBV might suppress the expression of CD82 by enhancing the methylation of its promoter region.In conclusion, the combination of epigenetic modification and transcription regulation in our research showed that HBV inhibited the expression of CD82 through the interaction between HBx and EGR1 and high methylation level of its promoter region. The results provided a new idea and method for us to understand the molecular mechanisms of gene regulated by HBV and the clinical treatment of hepatocellular carcinoma deeply.