Comprehensive Analysis of DNA Hypermethylation and Mismatch Repair Genes in Primary Gastric Adenocarcinoma
Abstracts
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Introduction: Microsatellite instability (MSI) is characterized by length mutations in tandem oligonucleotide repeats and is a hallmark of altered DNA mismatch repair (MMR). Hypermethylation of promoter CpG islands is associated with transcriptional silencing. In sporadic gastric cancers, hypermethylation of the hMLH1 gene accounts for many, but not all, cases of microsatellite instability. Hypermethylation in other MMR genes has not yet been described. We sought to investigate the prevalence of hypermethylation in a panel of MMR genes in primary gastric adenocarcinomas. Methods: A total of 31 primary sporadic gastric cancers were categorized according to MSI status (High(H), Low(L) or Stable(S)) by analysis of 5 standard microsatellite loci. Locus-specific hypermethylation was evaluated using real-time methylation-specific polymerase chain reaction for 5 DNA MMR genes (hMLH1, hMLH3, hMSH2, hMSH3 and hMSH6) that were selected based on the presence of CpG islands in their respective promoter regions. Results: By MSI analysis, we noted 5 MSI-H, 4 MSI-L and 22 MSS tumors. Five out of 5 MSI-H, 1/4 MSI-L and 1/22 MSS cancers demonstrated hypermethylation of hMLH1. There was no evidence of hypermethylation in the hMLH3, hMSH2, hMSH3 and hMSH6 genes. Conclusions: MSI in the setting of sporadic gastric cancers is predominantly a result of hMLH1 methylation. Our data suggest that the remaining cases of microsatellite unstable tumors are not associated with MMR gene promoter methylation and may, instead, be due to sporadic mutations in other known or unknown MMR genes. |
