To elucidate critical genetic elements in the development of hepatocellular carcinoma associated with hepatitis B virus DNA integration, a single integrant in hepatocellular carcinoma cells and one species of multiple integrants in hepatocytes, both obtained from the same patient, were compared structurally using molecular cloning techniques. Both hepatitis B virus integrants showed similar inverted repeat sequences consisting of two defective virus genomes. The recombination of viral DNAs seemed to be mediated by short regions of base homology near the direct repeat 1 and at other regions of the virus genomes in both integrants. The virus component in the junction with host DNAs was the cohesive end region in each identical end of the viral integrant in hepatocellular carcinoma cells and in one end of the viral integrant in hepatocytes. The structure of the integrant in hepatocellular carcinoma cells was characterized by an inverted, duplicated conformation composed not only of integrated virus genomes but also of flanking cellular sequences. It was shown to be the so-called “alpha dimer” of satellite DNA. In contrast, the flanking, nonreiterated cellular DNA in the hepatocyte-derived clone did not show discernible rearrangement.
These findings suggest that a common mechanism underlies the integeration of hepatitis B virus DNA so that a similar organization of inverted repeat genomes is found in hepatocellular carcinoma cells and in hepatocytes. The unstable nature of cellular DNA where DNA integration occurs may be important in generating chromosome alterations found in hepatocellular carcinoma (HEPATOLOGY 1990;11:1017-1023.).