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

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-q uantitative 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, DN MT3b, and MBD2 mRNA expression were not associated with either tumor stage or histologic type. Promoter hypermethylation of hMLH1, p16(INK4a), and CDH 1 was detected in 5/20 (25%), 8/20 (40%) and 8/20 (40%) of gastric carcinom as, respectively. There was no clear relation between DNA methylation statu s of hMLH1, p16(INK4a), and CDH1 and the mRNA expression levels of DNMT1, D NMT3a, DNMT3b or MBD2. We divided the examined cases into two groups accord ing to the number of hypermethylated genes. Cases with more than two hyperm ethylated genes comprised a hypermethylation group, and cases with no hyper methylation comprised a non-hypermethylation group. We found no group assoc iation for levels of DNMT1, DNMT3a, DNMT3b, and MBD2 mRNA expression. Our r esults suggest that the mRNA expression levels for pro-methylating (DNMT1, DNMT3a, DNMT3b) and anti-methylating (MBD2) enzymes is not a critical deter minate of tumor-specific promoter hypermethylation of hMLH1, p16(INK4a), or CDH1 in gastric carcinoma.