科研之友
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摘要
Promoter hypermethylation is an alternative mechanism of gene silencing in human cancers including gastric cancer. To date, several reports on methylation of various genes in gastric cancer have been published. However, most of these studies have focused on cancer tissues or only a single gene. In this study, we determined the methylation frequency of 5 genes, including p 16, Runx3, MGMT, DAPK, and RASSF1A, by methylation-specific polymerase chain reaction, in a series of formalin-fixed paraffin-embedded tissues including normal gastric mucosa (n = 20), intestinal metaplasia (n = 14), gastric epithelial dysplasia (n = 27), and early gastric adenocarcinoma (n = 16). Immunohistochemistry was used to determine expression of MGMT and RASSF1A protein. All 20 histologically normal gastric biopsy specimens were methylation-free for all 5 genes. Aberrant hypermethylation of RASSF1A was not detected in any case from intestinal metaplasia to early gastric adenocarcinoma. The methylation rate of the other 4 genes increased with the histological progression from intestinal metaplasia to gastric epithelial dysplasia, to early gastric adenocarcinoma. Methylation was detected in 28.6% of intestinal metaplasia (4/14), in 77.8% of gastric epithelial dysplasia (21/27), and in 87.5% of early gastric adenocarcinoma (14/16). The average number of methylated genes in intestinal metaplasia, gastric epithelial dysplasia, and early gastric adenocarcinoma was 0.43, 1.3, and 1.8, respectively. Concurrent methylation in 3 or more genes was found in 7.1% of intestinal metaplasia, 11.1% of gastric epithelial dysplasia, and 31.3% of early gastric adenocarcinoma. No correlation was found between hypermethylation and other clinicopathologic parameters such as age, sex, Helicobacter pylori infection, and location of lesions. However, we observed a significant association between hypermethylation of p 16 and MGMT and elevated serum carcinoembryonic antigen level. No reduction or loss of RASSF1A expression was observed in our study. Weak or loss of MGMT expression was found in 20 lesions and was significantly associated with promoter hypermethylation (P < .01). Our results suggest that promoter hypermethylation of the p 16, Runx3, MGMT, and DAPK genes may play an important role in the pathogenesis of gastric precancerous lesions and early gastric adenocarcinoma. Hypermethylation and inactivation of RASSF1A, however, could be a later event in malignant transformation. Further studies are warranted to determine whether the presence of promoter hypermethylation in gastric precancerous lesions is associated with higher risk of subsequent cancer development and how to interrupt the malignant transition from intestinal metaplasia and gastric epithelial dysplasia to early gastric adenocarcinoma by developing some gene-targeting therapies that may reverse aberrant methylation.
