胰腺癌微卫星不稳定性、hMLH1启动子甲基化及其蛋白表达研究

目的探讨胰腺癌中微卫星不稳定性（MSI）与hMLH1启动子甲基化及蛋白表达之间的联系，揭示胰腺癌发生的分子机制。方法从35例胰腺癌患者的正常胰腺组织、癌组织中提取DNA；SSCP法检测标本中微卫星不稳定性发生情况；免疫组织化学法检测错配修复基因hMLH1在胰腺癌中的表达情况；MSP法检测hMLH1基因启动子甲基化状态。结果35例胰腺癌中微卫星高度不稳定7例，低度不稳定14例，稳定11例，正常组织中没有出现微卫星不稳定，两者之间差异有统计学意义（P〈0．05）。hMLH1在微卫星不稳定胰腺癌组织中常为缺失表达。在微卫星稳定胰腺癌组织中呈正常表达。35例胰腺癌中hMLH1启动子CpG岛甲基化发生率为60％（21/35）。正常组织中未发现甲基化，两者之间差异有统计学意义（P〈0．05）。结论与胰腺癌有关的错配修复基因hMLH1启动子CpG岛甲基化是hMLH1基因失活的重要机制，而hMLH1的表达失活则可能导致MSI的产生，促进胰腺癌的发生。

Protein expression and methylation of hMLH1 gene in pancreatic cancer

Objective To investigate the relationship between the DNA microsatellite instability (MSI) and the expression of DNA mismatch repair gene (hMLH1) in pancreatic carcinoma. Methods DNA was extracted from 35 cases of pancreatic carcinoma and adjacent normal tissue. SSCP was used to detect MSI. Immunohistochemistry was performed to measure the expression of hMLH1 protein in pancreatic carcinoma. Methylation of hMLH1 gene promoter was verified by MSP analysis. Results Of the 35 cases of pancreatic carcinoma, 7 had hige MSI, 14 had low MSI, and 11 had microsatellite stability, and 0 in normal group (P< 0.05). The methylation status of hMLH1 promoter was accordant with loss of hMLH1 protein expression. The incidence of hMLH1 promoter methylation of CpG island was 60% (21/ 35) in 35 cases of pancreatic carcinoma, but none was found in normal group (P<0.05). Conclusion Methylation of CpG island induces inactivity of DNA mismatch repair gene hMLH1, and loss expression of hMLH1 protein, which might cause the generation of MSI and oncogenesis in pancreatic carcinoma.