Abstract 4811: Analysis of epigenetic alterations in mice with humanized liver after hepatitis virus infection
Authors: Okamoto Yasuyuki , Shinjo Keiko , Tanaka Yasuhito , Fujii Makiko , Murakami Hideki , Osada Hirotaka , Kataoka Hiromi , Joh Takashi , Sekido Yoshitaka , Kondo Yutaka 
Published: June 2012

Background and aims: While the connection between chronic inflammation and tumorigenesis was suspected in hepatocellular carcinomas (HCCs), key factors linking these two processes were not completely understood. Ample evidence shows that accumulation of genetic and epigenetic abnormalities may be fundamental mechanisms underlying tumor formation. The aim of this study is to examine whether viral infection affects epigenetic profile in chronic hepatitis/liver cirrhosis (CH/LC) and HCC tissues.

Methods: To evaluate the direct effects of viral infection, we examined DNA methyaltion changes in hepatitis C virus (HCV) infected cells in vitro. Genome-wide DNA methylation status was examined in liver tissues repopulated with human hepatocytes (humanized liver) in uPA/SCID mice, which were infected with hepatitis B virus (HBV-mice, 13 mice) or HCV-mice (14 mice), using methylated CpG island amplification-microarrays (MCAM, 6,157 CpG islands). Genome-wide DNA methylation status was also examined in 37 HCCs: 19 and 18 were associated with HCV and HBV infection, respectively (HCC-HBV and HCC-HCV). Further, quantitative pyrosequencing analysis was performed to examine the methylation status of selected genes.

Result: MCAM analysis in humanized mouse liver revealed that larger number of genes were methylated in HCV-mice than HBV-mice (287 genes versus 157 genes, P=0.034, respectively). DNA methylation target genes in HBV-mice were also methylated in HCV-mice, while both HBV-mice and HCV-mice had own specific targets. Association between aberrant DNA methylation and infection period was more strongly observed in HBV-mice (r=0.769) than HCV-mice (r=0.175). Interestingly, both HBV and HCV affected DNA methylation not only in infected humanized liver (hepatocytes) but also surrounding mouse tissues (non-infected cells). In vitro analysis of HCV infection did not affect DNA methylaion in cultured cells for more than a month. Thses data suggest that HCV infection may affect DNA methylaiton via inflammatory responses. Consistently, various cytokines from mouse tissues were upregulated after HBV and HCV infections. In clinical samples, most of the DNA methylation target genes in HCC-HBV were also methylated in HCC-HCV, as was found in mouse model. In addition, many DNA methylation target genes in human HCCs were also identified in mouse model with MCAM analysis.

Conclusion: We developed mouse model to assess DNA methylaton profiling after hepatitis viral infection. Although HBV protein has been known to induce aberrant DNA methylation, our data sugget that viral infection is a strong inducer of aberrant DNA methylation via inflammatory responses.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4811. doi:10.1158/1538-7445.AM2011-4811