Promoter hypermethylation of MGMT is associated with protein loss in gastric carcinoma

Aberrant methylation of CpG islands within promoter regions is associated w ith transcriptional inactivation of various tumor suppressor genes in neopl asms. Recently, O-6-methylguanine-DNA methyltransferase, MGMT, was shown to be hypermethylated in certain carcinomas, resulting in loss of MGMT protei n. We studied DNA methylation of CpG islands of the MGMT gene by methylatio n specific PCR in 26 gastric carcinoma tissues and 8 gastric carcinoma cell lines for comparison with levels of MGMT protein expression. In addition, we examined p53 mutation status in the same tissues by PCR-SSCP analysis fo r comparison with MGMT protein expression levels. In total, promoter hyperm ethylation of the MGMT gene was found in 8 (31%) of the 26 gastric carcinom as with reduced expression of MGMT protein, whereas the hypermethylation wa s not detected in the 18 carcinomas with non-reduced MGMT expression. MGMT protein expression levels were associated with promoter hypermethylation of MGMT (p = 0.0001; Mann-Whitney test); however, MGMT expression was not ass ociated with p53 mutation status (P = 0.461; Mann-Whitney test). Among in g astric carcinoma cell lines, the TMK-I cell line showed loss of the MG MT p rotein association with promoter hypermethylation and this loss was rectifi ed by treatment with a demethylating agent, 5-Aza-2'-deoxycytidine. Our res ults suggest that transcriptional inactivation of MGMT by aberrant methylat ion of the promoter region may participate in carcinogenesis in the stomach . (C) 2001 Wiley-Liss, Inc.