Aberrant Promoter Methylation Profiles of Tumor Suppressor Genes in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most fatal human malignancies, but the molecular mechanisms of hepatocarcinogenesis remain unclear. Although p53 mutations are frequently observed in Asian HCC, it is not a common event in Western HCC. Recent studies suggest that tumor suppressor genes (TSGs) can also be silenced through epigenetic disruption, such as promoter CpG island methylation, during carcinogenesis. To further understand the molecular mechanism of hepatocarcinogenesis, we have investigated the promoter methylation status of nine TSGs (SOCS-1, GSTP, APC, E-cadherin, RAR-β, p14, p15, p16, and p73) in 51 cases of HCC using methylation-specific polymerase chain reaction. We found that 82% of HCCs had methylation of at least one TSG promoter. The most frequently methylated TSGs in HCC were: SOCS-1 (65%), GSTP (54%), APC (53%), E-cadherin (49%), and p15 (49%). Methylation of SOCS-1, GSTP, APC, E-cadherin, and p15 was more frequent in HCC than in nontumor liver (P < 0.05). Methylation of SOCS-1, GSTP, and p15 was also significantly more frequent in HCC than cirrhotic liver (P < 0.05). Although methylation of one or two genes could be seen in both nontumor and cirrhotic livers, 53% of the HCC cases had three or more TSG promoters methylated, in comparison to 0% in nontumor liver and 13% in cirrhosis (P = 0.001). Methylation of SOCS-1, APC, and p15 was more frequently seen in hepatitis C virus-positive HCC than hepatitis C virus/hepatitis B virus-negative HCC. Our data suggest that promoter hypermethylation of TSGs is a common event in HCC and may play an important role in hepatocarcinogenesis. Hepatocellular carcinoma (HCC) is one of the most fatal human malignancies, but the molecular mechanisms of hepatocarcinogenesis remain unclear. Although p53 mutations are frequently observed in Asian HCC, it is not a common event in Western HCC. Recent studies suggest that tumor suppressor genes (TSGs) can also be silenced through epigenetic disruption, such as promoter CpG island methylation, during carcinogenesis. To further understand the molecular mechanism of hepatocarcinogenesis, we have investigated the promoter methylation status of nine TSGs (SOCS-1, GSTP, APC, E-cadherin, RAR-β, p14, p15, p16, and p73) in 51 cases of HCC using methylation-specific polymerase chain reaction. We found that 82% of HCCs had methylation of at least one TSG promoter. The most frequently methylated TSGs in HCC were: SOCS-1 (65%), GSTP (54%), APC (53%), E-cadherin (49%), and p15 (49%). Methylation of SOCS-1, GSTP, APC, E-cadherin, and p15 was more frequent in HCC than in nontumor liver (P < 0.05). Methylation of SOCS-1, GSTP, and p15 was also significantly more frequent in HCC than cirrhotic liver (P < 0.05). Although methylation of one or two genes could be seen in both nontumor and cirrhotic livers, 53% of the HCC cases had three or more TSG promoters methylated, in comparison to 0% in nontumor liver and 13% in cirrhosis (P = 0.001). Methylation of SOCS-1, APC, and p15 was more frequently seen in hepatitis C virus-positive HCC than hepatitis C virus/hepatitis B virus-negative HCC. Our data suggest that promoter hypermethylation of TSGs is a common event in HCC and may play an important role in hepatocarcinogenesis. Hepatocellular carcinoma (HCC) is one of the most common malignancies in the world and among the most fatal of human neoplasms, but the molecular mechanisms of hepatocarcinogenesis are primarily unknown. Recent genetic studies have indicated that both the p53 and pRb pathways may be involved in hepatocarcinogenesis. It has been shown that point mutations of the p53 tumor suppressor gene (TSG) were frequently seen in HCCs in Chinese and African populations.1Bressac B Kew M Wands J Ozturk M Selective G to T mutations of p53 gene in hepatocellular carcinoma from southern Africa.Nature. 1991; 350: 429-431Crossref PubMed Scopus (1293) Google Scholar, 2Hollstein MC Wild CP Bleicher F Chutimataewin S Harris CC Srivatanakul P Montesano R p53 mutations and aflatoxin B1 exposure in hepatocellular carcinoma patients from Thailand.Int J Cancer. 1993; 53: 51-55Crossref PubMed Scopus (105) Google Scholar, 3Hsu IC Metcalf RA Sun T Welsh JA Wang NJ Harris CC Mutational hotspot in the p53 gene in human hepatocellular carcinomas.Nature. 1991; 350: 427-428Crossref PubMed Scopus (1474) Google Scholar However, p53 mutation is not a frequent event in American and European HCCs.4Boix-Ferrero J Pellin A Blesa R Adrados M Llombart-Bosch A Absence of p53 gene mutations in hepatocarcinomas from a Mediterranean area of Spain. A study of 129 archival tumour samples.Virchows Arch. 1999; 434: 497-501Crossref PubMed Scopus (30) Google Scholar, 5Challen C Lunec J Warren W Collier J Bassendine MF Analysis of the p53 tumor-suppressor gene in hepatocellular carcinomas from Britain.Hepatology. 1992; 16: 1362-1366Crossref PubMed Scopus (103) Google Scholar, 6Kazachkov Y Khaoustov V Yoffe B Solomon H Klintmalm GB Tabor E p53 abnormalities in hepatocellular carcinoma from United States patients: analysis of all 11 exons.Carcinogenesis. 1996; 17: 2207-2212Crossref PubMed Scopus (27) Google Scholar This discrepancy may result from different ethic backgrounds and/or different etiologies, such as hepatitis B virus (HBV) and hepatitis C virus (HCV) infections or toxin exposure. Both HBV and HCV infections are thought to be involved in hepatocarcinogenesis because chronic hepatitis and cirrhosis associated with either HBV or HCV infection precede most HCCs. It has been shown that HBV encodes a X-gene product, HBx, that not only can activate the JAK/STAT signaling pathway,7Lee YH Yun Y HBx protein of hepatitis B virus activates Jak1-STAT signaling.J Biol Chem. 1998; 273: 25510-25515Crossref PubMed Scopus (214) Google Scholar but can also interact with p53 and impair the function of wild-type p53.8Kew MC Increasing evidence that hepatitis B virus X gene protein and p53 protein may interact in the pathogenesis of hepatocellular carcinoma