Abstract
Aberrant DNA methylation is deeply involved in human cancers, but its inducers and targets are still mostly unclear. Helicobacter pylori infection was recently shown to induce aberrant methylation in gastric mucosae, and produce a predisposed field for cancerization. Here, we analyzed the presence of target genes in methylation induction by H. pylori and the mechanism for the gene specificity. Noncancerous gastric mucosae were collected from 4 groups of individuals (with and without a gastric cancer, and with and without current H. pylori infection; N = 11 for each group), and methylation of promoter CpG islands of 48 genes that can be methylated in gastric cancer cell lines was analyzed by methylation‐specific PCR. In total, 26 genes were consistently methylated in individuals with current or past infection by H. pylori, whereas 7 genes were not methylated at all. In addition, 14 genes were randomly or intermediately methylated in individuals with gastric cancers and the remaining 1 gene was methylated in all the cases. The methylation‐susceptible genes had significantly lower mRNA expression levels than the methylation‐resistant genes. H. pylori infection did not induce mRNA and protein expression of DNA methyltransferases; DNMT1, DNMT3A or DNMT3B. Gene specificity was present in the induction of aberrant DNA methylation by H. pylori infection, and low mRNA expression, which could precede methylation, was one of the mechanisms for the gene specificity. These findings open up the possibility that a methylation fingerprint can be used as a novel marker for past exposure to a specific carcinogenic factor. © 2008 Wiley‐Liss, Inc.