Integration of woodchuck hepatitis virus (WHY) DNA at two chromosomal sites ( Vk and gag-like) in a hepatocellular carcinoma

Abstract

Integration of woodchuck hepatitis virus (WHY) DNA into the liver DNA of a woodchuck infected by the virus was investigated. Clonal viral integration was not detected three months before the appearance of four hepatocellular carcinomas (HCC). Integration of the viral DNA was detected in all four HCCs, of which one was chosen to determine the structure of the viral integration completely in a single tumor. The integration occurred in two sites. One part contains the viral DNA from the middle of the gene encoding surface antigen to two-thirds of the way through the gene encoding X protein ( X) with no structural changes. The coding frame of the truncated X gene continues into the chromosomal sequence to make a possible fusion protein. The integration seems to have occurred by recombination within two direct repeats of the viral genome in one junction and by homologous recombination between viral DNA and chromosomal DNA in the other junction. The viral DNA is integrated into a spacer of the immunoglobulin L-chain V k (Ig V k ) region without any chromosomal rearrangement accompanying the integration. The viral DNA at the second site has a complex structural rearrangement: part of the preS gene is duplicated and attached to the terminus of the gene encoding core antigen in a head-to-tail fashion, followed by three small fragments derived from other parts of the viral DNA. The integrated preS gene has its own 5′ regulatory element and a coding frame consisting of the truncated preS gene, the other parts of viral DNA and the chromosomal sequence. At both virus-chromosome junctions 28 nucleotides of the chromosomal DNA are duplicated as often seen in retrovirus integration. At the virus-virus junctions, viral DNA may have been rearranged by possible intramolecular homologous recombination using hexamers within the viral genome. The viral DNA is integrated in the vicinity of a retroviral gag-like open reading frame associated with highly repetitive sequences.