Expression of mutated hepatitis B virus X genes in human hepatocellular carcinomas

To explore the role of hepatitis B virus (HBV) X protein in liver carcinoge nesis, independently from its role in viral replication, we have analyzed X gene structure and expression in tumorous and non-tumorous tissues obtaine d from 9 hepatitis B surface antigen (HBsAg)-negative, HBV DNA-positive pat ients. HBV replication was undetectable in tumorous tissues, HBV X gene was truncated at its 3' end in 5 of 9 tumorous tissues and I of 8 non-tumorous livers. Sequence analysis performed on uninterrupted X genes from 3 tumors and 3 surrounding non-tumorous tissues showed a high rate of mutations, se lectively in the tumorous livers, In I of the 3 tumors, a frameshift mutati on induced a new stop at codon 129, HBV RNAs were tested by reverse transcr iptase-polymerase chain reaction (RT-PCR) with surface (S), core (C) and X specific primers, X, but not S and C, RNA expression was found in 6 of 8 tu mors and in 6 of 7 nontumorous tissues. This finding was consistent with im munohistochemical detection of X, but not S and C, antigens in all tumors a lso expressing X RNA. Our results provide evidence for selective expression of HBV X, but not S and C, RNA and protein in the tumorous and non-tumorou s tissue of HBsAg-negative, HBV DNA-positive patients. It also shows that t he structure of the X gene is modified (interrupted or highly mutated) in t he majority of tumorous livers, Taken together, our findings are consistent with a potential role of mutated X proteins in HBV-related liver oncogenes is. (C) 1999 Wiley-Liss, Inc.