Stable integration of woodchuck hepatitis virus DNA in transplanted tumors and established tissue culture cells derived from a woodchuck primary hepatocellular carcinoma.

The fate of integrated woodchuck hepatitis viral (WHV) DNA was systematically investigated in DNA samples from primary hepatocellular carcinoma (HCC) of woodchucks, solid tumors transplanted in athymic mice derived from a primary HCC of woodchuck, and an established cell line of tissue culture originating from the transplanted tumor. In four of five woodchuck primary HCCs, WHV DNA integration was demonstrated in addition to various amounts of extrachromosomal replicative intermediate WHV DNA. The integration pattern of the primary HCCs does not indicate a common integration site on the host chromosome. The integration pattern in the established cells is identical to that in the transplanted tumor and similar but slightly different from that of the primary HCC. No extrachromosomal or replicative intermediates of WHV DNA were detected in the transplanted tumors or in the established cells of tissue culture. There are three integration sites on the chromosomes of the established cells. Results of Southern hybridization and restriction maps of cloned fragments suggest that all of these integrated WHV DNA sequences are not a complete genome but a part of the genome. A small portion corresponding to the cohesive region of the genome was not detected in all of these integrated WHV DNA. A positive role of WHV DNA integration on the generation of HCC is strongly suggested by the high incidence of WHV DNA integration in woodchuck primary HCCs and the stable maintenance of a certain mode of WHV DNA integration in the hepatoma-derived cell populations during passages of transplantation or serial growth of tissue culture.