In vitro tumorigenicity of hepatitis B virus DNA and HBx protein

Persistent infection by hepatitis B virus (HBV) is strongly associated with the development of hepatocellular carcinoma. This linkage may be caused by oncogenic HBV gene products. Our initial in vitro studies have revealed that a non-tumorigenic, fetal mouse hepatocyte line (FMH202-1), harboring simian virus 40 large tumor antigen (SV40TAg) as transgene, can be converted into a full-malignant phenotype by transfection with dimeric HBV-DNA Höhne, M., Schaefer, S., Seifer, M., Feitelson, M.A., Paul, D. and Gerlich, W.H. (1990) EMBO J 9, 1137-1145. The oncogenic effect was neither dependent on simultaneous expression of SV40TAg nor on the cell type, since HBV-transfected permanent mouse fibroblasts (LTK-) also displayed enhanced colony formation in soft agar. Transfection of FMH202-1 with the X region of HBV generated clones that also formed colonies in soft agar and were tumorigenic in nude mice. Growth in soft agar and induction of nude mice tumors both depended on high expression of HBx protein. Although HBx expression was stronger in X-transfected than HBV-transfected clones, the former did not grow well in soft agar, and the X-derived tumors developed more slowly. In the tumors, expression of HBx was almost shut off, but again high in the tumor-derived cell lines. Constitutive expression of c-fos was strongly enhanced in the X-transfected cell lines and tumors. Transfection of FMH202-1 with an isogenic HBx-deficient mutant fragment generated several clones, which expressed normal levels of HBx transcripts, but did not grow in soft agar.(ABSTRACT TRUNCATED AT 250 WORDS)