title: Inactivation of the DNA repair gene O6-methylguanine-DNA methyltransferase by promoter hypermethylation and its relationship to aflatoxin B1-DNA adducts and p53 mutation in hepatocellular carcinoma.
abstract: O(6)-methylguanine-DNA methyltransferase (MGMT) is a repair protein that specifically removes promutagenic alkyl groups from the O(6) position of guanine in DNA. MGMT is transcriptionally silenced by promoter hypermethylation in several human cancers. Methylation-specific PCR (MSP) was used to analyze the MGMT promoter methylation status of 83 hepatocellular carcinomas (HCC) and 2 HCC cell lines (HepG2 and Hep3B). Hypermethylation was detected in 32 of 83 (39%) HCC tissues, but it was not found in either HCC cell line. We also analyzed MGMT expression by immunohistochemical analysis of HCC tissue samples. The presence of aberrant hypermethylation was associated with loss of MGMT protein. The relationship between methylation status and risk factors and tumor markers including environmental exposure to aflatoxin B(1) (AFB(1)), measured as DNA adducts, and status of tumor suppressor gene p53 was also investigated. A statistically significant association was found between MGMT promoter hypermethylation and high level of AFB(1)-DNA adducts in tumor tissues (OR = 5.05, 95% CI = 1.29-19.73). A significant association was also found between methylation and p53 mutation status (OR = 2.97, 95% CI = 1.09-8.11). These results suggest that epigenetic inactivation of MGMT plays an important role in the development of HCC and exposure to environmental carcinogens may be related to altered methylation of genes involved in cancer development. The role of chemical carcinogens in hypermethylation needs further investigation.
authors.affiliation: Departments of Environmental Health Sciences and Epidemiology, Mailman School of Public Health, Columbia University, 700 West 168th Street, New York, NY 10032, USA.
authors.forename: Yu-Jing
authors.initials: YJ
authors.lastname: Zhang
authors.forename: Yu
authors.initials: Y
authors.lastname: Chen
authors.forename: Habibul
authors.initials: H
authors.lastname: Ahsan
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Lunn
authors.forename: Po-Huang
authors.initials: PH
authors.lastname: Lee
authors.forename: Chien-Jen
authors.initials: CJ
authors.lastname: Chen
authors.forename: Regina M
authors.initials: RM
authors.lastname: Santella
mesh_terms: D016604:Aflatoxin B1 / Q000494:pharmacology*; D002273:Carcinogens; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000473:pathology; D018899:CpG Islands; D004247:DNA / Q000378:metabolism; D018736:DNA Adducts; D019175:DNA Methylation; D020868:Gene Silencing; D016158:Genes, p53; D006801:Humans; D007150:Immunohistochemistry; D008113:Liver Neoplasms / Q000235:genetics*; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics* / Q000378:metabolism*; D016017:Odds Ratio; D011401:Promoter Regions, Genetic; D012307:Risk Factors; D014407:Tumor Cells, Cultured
chemical_list: D002273:Carcinogens; D018736:DNA Adducts; D004247:DNA; D016604:Aflatoxin B1; D019853:O(6)-Methylguanine-DNA Methyltransferase