Detection of Clonally Expanded Hepatocytes in Chimpanzees with Chronic Hepatitis B Virus Infection

Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
Journal of Virology (Impact Factor: 4.44). 06/2009; 83(17):8396-408. DOI: 10.1128/JVI.00700-09
Source: PubMed


During a hepadnavirus infection, viral DNA integrates at a low rate into random sites in the host DNA, producing unique virus-cell junctions detectable by inverse nested PCR (invPCR). These junctions serve as genetic markers of individual hepatocytes, providing a means to detect their subsequent proliferation into clones of two or more hepatocytes. A previous study suggested that the livers of 2.4-year-old woodchucks (Marmota monax) chronically infected with woodchuck hepatitis virus contained at least 100,000 clones of >1,000 hepatocytes (W. S. Mason, A. R. Jilbert, and J. Summers, Proc. Natl. Acad. Sci. USA 102:1139-1144, 2005). However, possible correlations between sites of viral-DNA integration and clonal expansion could not be explored because the woodchuck genome has not yet been sequenced. In order to further investigate this issue, we looked for similar clonal expansion of hepatocytes in the livers of chimpanzees chronically infected with hepatitis B virus (HBV). Liver samples for invPCR were collected from eight chimpanzees chronically infected with HBV for at least 20 years. Fifty clones ranging in size from approximately 35 to 10,000 hepatocytes were detected using invPCR in 32 liver biopsy fragments (approximately 1 mg) containing, in total, approximately 3 x 10(7) liver cells. Based on searching the analogous human genome, integration sites were found on all chromosomes except Y, approximately 30% in known or predicted genes. However, no obvious association between the extent of clonal expansion and the integration site was apparent. This suggests that the integration site per se is not responsible for the outgrowth of large clones of hepatocytes.

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    • "It is believed that the activation of cellular oncogenes, particularly c-myc and N-myc, through the integration of viral promoter sequences near these genes or through rearrangements of the genes, is responsible for the higher rates of HCC in woodchucks than in humans. However, WHV DNA can also integrate randomly into the hepatocyte genome, similarly to HBV DNA in human and chimpanzee hepatocytes (Feitelson & Lee, 2007; Mason et al., 2009). Another difference is that CH type B in humans frequently advances to cirrhosis, while this is not the case during CH in woodchucks. "

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