Epigenetic analysis of hepatocellular carcinoma development : involvement of HBV-modulated DNA methylation

Abstract

Hepatocellular carcinoma (HCC) is one of the most aggressive human malignancies. Epidemiological studies have shown that HCC is closely associated with chronic hepatitis B virus (HBV). However, the underlying mechanisms of the HBV-associated HCC development remain unclear. DNA methylation, one of the mechanisms in epigenetics, affects gene expression at the transcriptional level. Evidence has revealed the association between HCC and HBV-mediated DNA methylation. Within the four proteins encoded by HBV genome, the HBV X protein (HBx) has been found to epigenetically inhibit some tumor suppressor genes (TSGs), which may lead to development of HCC. To investigate comprehensively the role of HBV/HBx in DNA methylation, a protein profile affected by HBV in HBV-producing HepG2.2.15 cells compared with HepG2, was analyzed by our iTRAQ-coupled 2-D LC/MS-MS analysis. Fifteen proteins including S100A6 and ANXA2 were identified. A role of these proteins as target of HBV-mediated DNA methylation was supported by validation assays, including their re-activation in cells treated with 5-Aza-dC (a DNA methyltransferase inhibitor). DNA methylation analysis suggested that, the proteins were down-regulated by HBV via DNA hypermethylation.