EXTENSIVE ANALYSIS OF DUPLICATED-INVERTED HEPATITIS-B VIRUS INTEGRATIONS IN HUMAN HEPATOCELLULAR-CARCINOMA

Hepatitis B virus (HBV) DNA is found chromosomally integrated into the genome of the majority of hepatocellular carcinomas (HCC) arising in chronic HBV carriers suggesting that, in some instances, viral sequenc es may be directly responsible for oncogenic conversion. In an attempt to clarify the oncogenic potential of integrated HBV sequences, we pe rformed an extensive analysis of two single integrations present in HC C which developed in non-cirrhotic livers from HBsAg-positive Korean p atients, In both cases, integrated viral sequences were characterized by a duplicated-inverted configuration involving the Ranking cellular sequences, a pattern consistently found in many amplicons isolated fro m mammalian cells. Integration sites are characterized by an AT-rich c ontent and the presence of topoisomerase I and II cleavage target sequ ences as well as other recombination-prone motifs. The chromosomal loc ations of the integration sites were determined as 8q13 and 10q22 in t he human genome, two regions known to harbour genes involved in tumori genesis. The cis-activating potential of the integrations in their ori ginal configuration was also investigated in a transient transfection assay in HepG2 cells, Integrated sequences, rather than activating het erologous promoters, show either no activity or a weak tendency to inh ibit activation of neighbouring reporter genes, The implications of ou r findings for the understanding of primary liver cancer development a re discussed.