Alterations of RB1, p53 and Wnt pathways in hepatocellular carcinomas associated with hepatitis C, hepatitis B and alcoholic liver cirrhosis

Major etiologic factors associated with human hepatocellular carcinomas (HCCs) include infection with hepatitis C (HCV) and hepatitis B virus (HBV), excess alcohol intake and aflatoxin B-1 exposure. While the G-->T p53 mutation at codon 249 has been identified as a genetic hallmark of HCC caused by aflatoxin B-1 the genetic profile associated with other etiologic factors appears to be less distinctive. In our study, we screened HCCs resulting from HCV infection (5 1 cases), HBV infection (26 cases) or excess alcohol intake (23 cases) for alterations in genes involved in the RB I pathway (p16(INK4a), p15(INK4b) RBI CDK4 and cyclin DI), the p53 pathway (p53, p14(ARF) and MDM2) and the Writ pathway (beta-catenin, APC). Alterations of the RBI pathway, mainly p16(INK4a) methylation, loss of 11131 expression and cyclin D1 amplification, were most common (69-100% of cases). There was a significant correlation between loss of RB I expression and RB I methylation. All 24 HCCs with RB I promoter methylation lacked RBI expression, while none of the 67 cases with RBI expression exhibited RBI methylation(p < 0.0001), suggesting that promoter methylation is a major mechanism of loss of RBI expression in HCCs. Alterations of the p53 pathway consisted mostly of p53 mutations or p14ARF promoter methylation (20-48%). Mutations of the p53 gene were found at a similar frequency (13-15%) in all etiologic groups, without any consistent base change or hot spot. Mutations of beta-catenin were found in 13-31% of cases, while no APC mutations were detected in any of the HCCs analyzed. With the exception of only 3 of 39 cases (8%), cyclin D I amplification and beta-catenin mutations were mutually exclusive, supporting the view that cyclin D I is a target of the Wnt signaling pathway. Overall, the RB I, p53 and Writ pathways were commonly affected in HCCs of different etiology, probably reflecting common pathogenetic mechanisms, i.e., chronic liver injury and cirrhosis, but tumors associated with alcoholism had more frequent alterations in the RB I and p53 pathways than those caused by HCV infection. (C) 2003 Wiley-Liss, Inc.