Abstract
Hepatitis B virus (HBV) infection is closely associated with the development of hepatocellular carcinoma (HCC), but definite mechanisms by which it could play an etiologic role have not yet been identified. Modifications of the function of the RB tumor suppressor gene, which regulates the cell cycle, could provide such a mechanism. In the present study, the expression of the protein product of RB, pRB, was evaluated by immunohistochemical staining in HCC tissues from 25 patients from China and the United States, adjacent nontumorous liver from 19 of those patients, five human HCC cell lines, three human hepatoblastoma cell lines, and five specimens of normal human liver. Representative samples were also evaluated by western blot. Altered expression of RB was detected in eight HCC tissues (pRB undetectable in five HCCs and detected in <1% of nuclei of HCC cells in three others); all eight had detectable hepatitis B surface or core antigen in the adjacent nontumorous liver, indicating active HBV infection. pRB was detected in 10ββ95% of nuclei (normal expression) in the remaining 17 HCCs, and in many nuclei in all 19 nontumorous livers, and in the 5 normal livers. No pRB staining 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 lines. The relationship of pRB expression to mutations of the p53 tumor suppressor gene was also examined. The absence of detectable nuclear pRB 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 detectable pRB also had a p53 mutation or a p53 deletion. HCCs with altered 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), suggesting that abnormal pRB expression may be associated with more advanced histologic grades of HCC. These data indicate that interference with the normal function of the tumor suppressor gene RB or its product pRB, often with concomitant p53 mutation, may be one of several mechanisms that contribute to the development or progression of HCC in humans infected with HBV. Β© 1994WileyβLiss, Inc.