DNA methylation status of hMLH1, p16(INK4a), and CDH1 is not associated with mRNA expression levels of DNA methyltransferase and DNA demethylase in gastric carcinomas

Abstract

DNA methyltransferase and DNA demethylase are enzymes potentially affecting promoter methylation status. We examined levels of DNA methyltransferase (DNMT1, DNMT3a, DNMT3b) and DNA demethylase (MBD2) mRNA expression by semi-quantitative RT-PCR. In addition, we examined promoter methylation status of hMLH1, p16(INK4a), and CDH1 by methylation-specific PCR since all three of these genes are reported to be hypermethylated in gastric carcinoma. MBD2 appeared to be down-regulated in neoplasms. The levels of DNMT1, DNMT3a, DNMT3b, and MBD2 mRNA expression were not associated with either tumor stage or histologic type. Promoter hypermethylation of hMLH1, p16(INK4a), and CDH1 was detected in 5/20 (25%), 8/20 (40%) and 8/20 (40%) of gastric carcinomas, respectively. There was no clear relation between DNA methylation status of hMLH1, p16(INK4a), and CDH1 and the mRNA expression levels of DNMT1, DNMT3a, DNMT3b or MBD2. We divided the examined cases into two groups according to the number of hypermethylated genes. Cases with more than two hypermethylated genes comprised a hypermethylation group, and cases with no hypermethylation comprised a non-hypermethylation group. We found no group association for levels of DNMT1, DNMT3a, DNMT3b, and MBD2 mRNA expression. Our results suggest that the mRNA expression levels for pro-methylating (DNMT1, DNMT3a, DNMT3b) and anti-methylating (MBD2) enzymes is not a critical determinate of tumor-specific promoter hypermethylation of hMLH1, p(16INK4a), or CDH1 in gastric carcinoma.