Mutation and methylation of hMLH1 in gastric carcinomas with microsatellite instability

AIM: To appraise the correlation of mutation and methylation of hMSH1 with microsatellite instability (MSI) in gastric cancers.METHODS: Mutation of hMLH1 was detected by Twodimensional electrophoresis (Two-D) and DNA sequencing;Methylation of hMLH1 promoter was measured with methylation-specific PCR; MST was analyzed by PCR-basecl methods.RESULTS: Sixty-eight cases of sporadic gastric carcinoma were studied for mutation and methylation of hMLH1 promoter and MSI. Three mutations were found, two of them were caused by a single bp substitution and one was caused by a 2 bp substitution, which displayed similar Two-D band pattern.Methylation of hMLH1 promoter was detected in 11(16.2%)gastric cancer. By using five MSI markers, MSI in at least one locus was detected in 17/68(25 %) of the tumors analyzed.Three hMLH1 mutations were all detected in MSI-H (≥2 loci,n=8), but no mutation was found in MSI-L (only one locus,n=9) or MSS (tumor lacking MSI or stable, n=51). Methylation frequency of hMLH1 in MSI-H (87.5 %, 7/8) was significantly higher than that in MSI-L (11.1%, 1/9) or MSS (5.9%, 3/51)(P＜0.01-0.001), but no difference was found between MSI-L and MSS (P＞0.05).CONCLUSION: Both mutation and methylation of hMLH1are involved in the MSI pathway but not related to the LOH pathway in gastric carcinogenesis.