DNA methylation of multiple genes in gastric carcinoma: association with histological type and CpG island methylator phenotype

Hypermethylation of CpG islands is associated with silencing of various tumor suppressor genes. Recent studies on colorectal and gastric cancer have identified a CpG island methylator phenotype (CIMP), which involves the targeting of multiple genes by promoter hypermethylation. For determination of association between DNA methylation pattern or histological type and CIMP status in gastric carcinoma, CpG islands in the promoters of hMLH1 and CDH1 genes, CpG islands overlapping exon 1 of MGMT and p16^INK4a genes, and a non-CpG island in exon 1 of the RAR-β gene were studied. The presence of the CIMP was determined by monitoring five methylated in tumor (MINT) loci in 103 gastric carcinomas. Among the 103 gastric carcinomas, DNA hypermethylation was detected in the following frequencies: 14 (14%) for hMLH1 , 26 (25%) for MGMT , 26 (25%) for p16^INK4a , 54 (52%) for CDH1 , and 53 (52%) for RAR-β. Forty-two (41%) of 103 gastric carcinomas were positive for the CIMP. CIMP and hypermethylation of p16^INK4a gene were found more frequently in intestinal and diffuse-adherent types than in diffuse-scattered type ( P =0.013 and 0.017, respectively). In contrast, hypermethylation of the CDH1 and RAR-β genes was more common in the diffuse-scattered type than in the other types ( P =0.008 and 0.007, respectively). In intestinal- and diffuse-adherent-type gastric carcinomas, we found significant associations between the presence of the CIMP and hypermethylation of several genes: hMLH1 ( P =0.006), p16^INK4a ( P =0.018), CDH1 ( P =0.024), and RAR-β ( P =0.044). Our overall results suggest that in some intestinal- and diffuse-adherent-type gastric carcinomas, DNA hypermethylation affects non-specific gene promoters concordantly, at least in part, whereas in diffuse-scattered-type gastric carcinoma, DNA hyper-methylation affects specific genes such as CDH1 and RAR-β.