RB TUMOR-SUPPRESSOR GENE-EXPRESSION IN HEPATOCELLULAR CARCINOMAS FROMPATIENTS INFECTED WITH THE HEPATITIS-B VIRUS

Hepatitis B virus (HBV) infection is closely associated with the devel opment of hepatocellular carcinoma (HCC), but definite mechanisms by w hich it could play an etiologic role have not yet been identified. Mod ifications of the function of the RB tumor suppressor gene, which regu lates the cell cycle, could provide such a mechanism. In the present s tudy, the expression of the protein product of RB, pRB, was evaluated by immunohistochemical staining in HCC tissues from 25 patients from C hina and the United States, adjacent nontumorous liver from 19 of thos e patients, five human HCC cell lines, three human hepatoblastoma cell lines, and five specimens of normal human liver. Representative sampl es were also evaluated by western blot. Altered expression of RB was d etected in eight HCC tissues (pRB undetectable in five HCCs and detect ed in <1% of nuclei of HCC cells in three others); all eight had detec table hepatitis B surface or core antigen in the adjacent nontumorous liver, indicating active HBV infection. pRB was detected in 10-95% of nuclei (normal expression) in the remaining 17 HCCs, and in many nucle i in all 19 nontumorous livers, and in the 5 normal livers. No pRB sta ining was detected in the nuclei of three HCC cell lines, but pRB was detected in >90% of nuclei of the other HCC and hepatoblastoma cell li nes. The relationship of pRB expression to mutations of the p53 tumor suppressor gene was also examined. The absence of detectable nuclear p RB by immunohistochemical staining was associated with the presence of presumed mutant p53 detected by immunohistochemical staining in four out of five HCC cases. In addition, all three HCC cell lines lacking d etectable pRB also had a p53 mutation or a p53 deletion. HCCs with alt ered pRB expression included more grade III and IV tumors (8/8, 100%) than did HCCs with normal pRB expression (7/17, 41%) (P < 0.02), sugge sting that abnormal pRB expression may be associated with more advance d histologic grades of HCC. These data indicate that interference with the normal function of the tumor suppressor gene RB or its product pR B, often with concomitant p53 mutation, may be one of several mechanis ms that contribute to the development or progression of HCC in humans infected with HBV. (C) 1994 Wiley-Liss, Inc.