Analysis of six distinct integrated hepatitis B virus sequences cloned from the cellular DNA of a human hepatocellular carcinoma.

Six distinct hepatitis B virus (HBV) integrations and the flanking cellular sequences were cloned from a hepatoma DNA preparation. None of the cloned fragments retains the entire HBV sequences but the surface antigen (HBsAg) gene and the HBV enhancer are retained in three of the six clones. The other three clones carry only short and possibly highly rearranged HBV genomic sequences and seem to contain some GC-rich clusters. Members of the repetitive Alu family are also found in the vicinity of five of the six integration regions which may have contributed to genome instability. In these six clones, the preferred integration sites are shown to lie within the single-strand region of the HBV genome. None of the clones carries in the flanking cellular sequences any of the 17 oncogenes tested, although the possibility still exists that an oncogene may be found on the side of the genome which has not been cloned. This work thus paves the way for detailed sequence analysis of virus-host junctions, for transfection studies of the HBV integration events, and for a search of genes in the flanking cellular sequences which may have been activated by the retained HBV enhancer using the clones described.