食管鳞状细胞癌中MGMT基因异常甲基化与MTHFR C677T基因多态的关系

Correlation of Aberrant Methylation of MGMT Gene to MTHFR C677T Genetic Polymorphisms in Esophageal Squamous Cell Carcinoma

背景与目的:作为基因失活的主要原因之一,肿瘤相关基因启动子区异常甲基化正日益受到关注,但是在食管癌方面研究尚十分有限。本研究的目的在于探讨DNA损伤修复基因MGMT异常甲基化与食管鳞状细胞癌临床特征和叶酸代谢酶基因MTHFR C677T多态之间的联系。方法:选择2005年1月至2006年3月间新发的、经病理学检查确诊并在江苏省扬中市人民医院进行手术治疗的食管鳞癌患者开展流行病学问卷调查,并采集其外周静脉血标本、癌组织和癌旁正常组织标本。应用甲基化特异性PCR法检测MGMT基因启动子区CpG岛甲基化状态,应用限制性片断长度多态(restriction fragment length polymorphism,RFLP)技术检测叶酸代谢酶基因MTHFR C677T多态,并分析和探讨食管粘膜组织中MGMT基因甲基化分布规律及其与MTHFR C677T基因多态间的联系。结果:125例食管鳞状细胞癌组织中MGMT基因甲基化频率达27.2%,癌旁组织甲基化频率11.2%,10例正常成人健康对照的食管粘膜均呈去甲基化状态。患者淋巴结转移与否与DNA甲基化频率有关,存在淋巴结转移的患者癌组织中MGMT基因甲基化频率(37.3%)高于无淋巴结转移的患者(18.2%)。患者性别、年龄、吸烟、饮酒、饮茶等因素与DNA异常甲基化之间的相关性无统计学意义(P>0.05)。在调整了相关潜在混杂因素后,携带MTHFR变异基因型CT和TT者食管癌组织中MGMT基因甲基化频率增高,与野生基因型CC比较,比值比OR分别为3.34(95%CI:1.07～10.39)和3.83(95%CI:1.13～12.94)。结论:食管鳞状细胞癌中MGMT基因启动子区异常甲基化与MTHFR基因多态有关,携带MTHFR C677基因变异基因型CT与TT的癌组织中MGMT基因异常甲基化频率更高。

BACKGROUND ＆ OBJECTIVE= As one of the principal causes of gene inactivation, aberrant hypermethylation in the promoter of cancer-related genes has attracted more and more attention. However, such studies on esophageal cancer are still limited. This study was to investigate the association between aberrant hypermethylation of MGMT gene and clinical characteristics as well as MTHFR C677T genetic polymorphisms in esophageal squamous ceil carcinoma in a Chinese epidemiologic study was conducted at of China, on histologically confirmed population. METHODS. A molecular Yangzhong County, Jiangsu Province esophageal squamous cell carcinoma patients who were operated in the People＇s Hospital of Yangzhong County between January 2005 and March 2006. Peripheral blood samples, esophageal cancer tissues and paracanoerous normal tissues were collected. Methylation-specific polymerase chain reaction（MSP） was used to detect the CpG island methylation status of MGMT gene. Restrictive fragment length polymorphism （RFLP） technique was used to test polymorphisms of folate metabolism enzyme gene MTHFR. The assocoation between methylation status of MGMT gene and clinical characteristics as well as MTHFR C677T polymorphisms were analyzed. RESULTS： Among 125 esophageal squamous cell carcinoma patients, the aberrant hypermethylation rate of MGMT gene was 27.2% in cancer tissues and 11.2% in paracancerous normal tissues. No hypermethylation was found in normal esophageal tissues from 10 healthy adult subjects. Methyiation rate of MGMT gene in cancer tissues was significantly higher in the patients with lymph node metastasis than in those without lymph node metastasis （37.3% vs. 18.2%, P=0.017）. No association was found between aberrant DNA methylation and selected factors including sex, age, tobacco smoking, alcohol drinking and green tea drinking. After adjusting by potential confounders, variant allele of MTHFR C677T was found to be associated with hypermethylation of MGMT gene. Compared with wild type CC, the odds ratio was 3.34 （95% CI. 1.07-10.39） for CT and 3.83 （95% CI： 1.13-12.94） for TT. CONCLUSION= Aberrant CpG island hypermethylation of MGMT gene is closely related with the genesis and progression of esophageal squmaous cell carcinoma.