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Viruses 2013, 5(3), 858-872; doi:10.3390/v5030858
Review

Deregulation of Epigenetic Mechanisms by the Hepatitis B Virus X Protein in Hepatocarcinogenesis

Department of Basic Medical Science and Center for Cancer Research, Purdue University West Lafayette, IN 47907, USA
Received: 4 February 2013 / Revised: 12 March 2013 / Accepted: 13 March 2013 / Published: 18 March 2013
(This article belongs to the Special Issue Chromatin Control of Viral Infection)
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Abstract

This review focuses on the significance of deregulation of epigenetic mechanisms by the hepatitis B virus (HBV) X protein in hepatocarcinogenesis and HBV replication. Epigenetic mechanisms, DNA methylation, and specific histone modifications, e.g., trimethylation of H3 on lysine-27 or lysine-4, maintain ‘cellular memory’ by silencing expression of lineage-inducing factors in stem cells and conversely, of pluripotency factors in differentiated cells. The X protein has been reported to induce expression of DNA methyltransferases (DNMTs), likely promoting epigenetic changes during hepatocarcinogenesis. Furthermore, in cellular and animal models of X-mediated oncogenic transformation, protein levels of chromatin modifying proteins Suz12 and Znf198 are down-regulated. Suz12 is essential for the Polycomb Repressive Complex 2 (PRC2) mediating the repressive trimethylation of H3 on lysine-27 (H3K27me3). Znf198, stabilizes the LSD1-CoREST-HDAC complex that removes, via lysine demethylase1 (LSD1), the activating trimethylation of H3 on lysine-4 (H3K4me3). Down-regulation of Suz12 also occurs in liver tumors of woodchucks chronically infected by woodchuck hepatitis virus, an animal model recapitulating HBV-mediated hepatocarcinogenesis in humans. Significantly, subgroups of HBV-induced liver cancer re-express hepatoblast and fetal markers, and imprinted genes, suggesting hepatocyte reprogramming during oncogenic transformation. Lastly, down-regulation of Suz12 and Znf198 enhances HBV replication. Collectively, these observations suggest deregulation of epigenetic mechanisms by HBV X protein influences both the viral cycle and the host cell.
Keywords: Hepatitis B virus (HBV); HBV X protein; Hepatocellular Carcinoma (HCC); HBV replication; epigenetic regulation; DNA methylation; DNA methyl transferases (DNMTs); Polycomb Repressive complex 2 (PRC2); Suz12; suppressor of zeste 12 homolog (Drosophila); Znf198; zinc finger; MYM-type 2; LSD1-Co-REST-HDAC1 Hepatitis B virus (HBV); HBV X protein; Hepatocellular Carcinoma (HCC); HBV replication; epigenetic regulation; DNA methylation; DNA methyl transferases (DNMTs); Polycomb Repressive complex 2 (PRC2); Suz12; suppressor of zeste 12 homolog (Drosophila); Znf198; zinc finger; MYM-type 2; LSD1-Co-REST-HDAC1
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Andrisani, O.M. Deregulation of Epigenetic Mechanisms by the Hepatitis B Virus X Protein in Hepatocarcinogenesis. Viruses 2013, 5, 858-872.

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