Induction of apoptosis by the transactivating domains of the hepatitis B virus X gene leads to suppression of oncogenic transformation of primary ratembryo fibroblasts

Epidemiology shows a clear correlation between chronic infection with the h epatitis B virus (HBV) and development of hepatocellular carcinoma (HCC). T he potential role of the transactivating hepatitis B virus X protein (HBx) in transformation by HBV is controversial, Here we report that HBx suppress es transformation of primary rat embryo fibroblasts (REFs), Cooperating onc ogenes like c-Ha-ras and c-myc transform REF very efficiently but cotransfe ction with HBx suppressed transformation of REFs down to 5%, Similarly, tra nsfection of HBx together with the cooperating oncogenes Ha-ras and SV40 LT Ag or c-Ha-ras and mutant p53 reduced the number of foci to 13%. Comparable results were obtained with HBx in the context of the whole HBV, Suppressio n of focus formation in REF could be partly relieved by cotransfection of a poptosis inhibitors Bcl-2 or E1B, However, cotransfection of apoptosis inhi bitors crmA and p35 did not influence the proapoptotic functions of HBx, Th us, HBx may specifically activate the Bcl-2 sensitive pathway leading to ap optosis. Experiments with 13 HBx linker scanning mutants revealed that the domains necessary for HBx dependent transactivation overlap with the domain s needed for the apoptotic/growth arrest functions of HBx.