中文摘要：

目的观察5-氮杂-2′-脱氧胞苷（5-Aza—dC）对体外培养的胃癌细胞MGC-803中p16和MGMT基因启动子区DNA甲基化状态及表达的影响，探讨胃癌细胞p16和MGMT基因失活的机制及去甲基化制剂对p16和MGMT基因表达的调控。方法5-Aza-dC处理体外培养的胃癌细胞MGC-803后，甲基化特异性PCR（MSP）法检测用药前后细胞中p16和MGMT基因的甲基化状态，RT—PCR法检测用药前后细胞中p16和MGMT mRNA表达的变化。结果胃癌细胞系MGC-803中p16和MGMT mRNA表达缺失，其启动子区域表现为DNA甲基化。5-Aza—dC不但能使MGC-803细胞中p16和MGMT基因发生DNA去甲基化，而且能使表达缺失的p16和MGMT mRNA重新表达。结论启动子区高甲基化是胃癌细胞p16和MGMT基因失活的主要原因之一，去甲基化制剂-5-Aza—dC能逆转p16和MGMT基因甲基化状态，从而调控p16和MGMT基因表达。

英文摘要：

Objective To investigate the effects of 5-Aza-2′-deoxycytidine （5-Aza-dC） on DNA methylation and expression of p16 and MGMT gene in the human gastric cancer cell line MGC-803,and to explore the mechanism of p16 and MGMT gene silencing in human gastric cancer cells and the regulating effect of the demethylating agent on p16 and MGMT gene expression. Methods MGC-803 cells were cultured in RPMI-1640 medium and were treated with 5 μ mol/L of DNA methyltransferase inhibitor 5-Aza-dC. Methylation-specific polymerase chain reaction （MSP） was used to detect the promoter methylation state of the p16 and MGMT gene. RT-PCR was used to detect the mRNA expression of p16 and MGMT before and after treatment with 5-Aza-dC, respectively. Results Promoter hypermethylation of the p16 and MGMT gene were detected in MGC-803 cells, and p16 and MGMT expressions were absent before treatment. After treatment with 5-Aza-dC,the promoter region of the p16 and MGMT gene exhibited a demethylation state,and their mRNA expressions were increased. Conclusion Promoter hypermethylation is a major mechanism of p16 and MGMT gene silencing in human gastric cancer cells,and can be reversed by the demethylating agent 5-Aza-dC, which can regulate the expressions of the p16 and MGMT gene.