高甲基化导致EphA7基因在结直肠癌中低表达

Down-regulation of EphA7 by aberrant methylation in colorectal cancer

目的:Eph基因和配体在多种肿瘤中呈高表达,并可能在肿瘤的发生、发展及预后中发挥重要作用。作者探讨EphA7基因在大肠癌细胞系和结直肠癌组织及其正常黏膜中的表达情况,以及EphA7基因在大肠癌发生、发展中的作用。方法:定量RT-PCR检测大肠癌细胞系和原发性结直肠癌标本中EphA7的表达。经甲基化特异性PCR(MSP)和亚硫酸氢钠处理后,用DNA测序等方法分析EphA7基因启动子区CpG岛甲基化状况。构建pEGFP-N3-EphA7质粒,并转染至EphA7表达丢失的大肠癌细胞系中,对转染子进行mRNA基因表达芯片分析。结果:大肠癌细胞系DLD1、HT29、HCT116、SW 480和SW 620中EphA7基因低表达。59例进行定量RT-PCR测定的原发性结直肠癌患者中,29例患者癌组织中EphA7基因的表达水平低于来源相同患者的正常黏膜(P=0.008)。经MSP、亚硫酸氢钠处理后DNA测序等发现,EphA7基因启动子区CpG岛高甲基化。EphA7的高甲基化与肿瘤分化、性别以及肿瘤发生部位等有关。对EphA7质粒转染子mRNA基因芯片分析,观察到多种基因表达改变。结论:EphA7基因启动子区CpG岛甲基化是EphA7在大肠癌中低表达的机制。EphA7基因可能在结直肠癌的肿瘤发生、发展中起重要作用。

Objective：Ephs have been found to be over-expressed in numerous human tumors, and relate to the development and prognosis of cancers. The expression of EphA7 in colon cancer cell lines and primary colorectal cancers was detected. The role of EphA7 in the development of colorectal cancer was investigated. Methods：Quantitative reverse transcription-polymerase chain reaction was used to detect the expression of EphA7. Methylation specific PCR and bisulfite sequencing were used to examine the methylation status of EphA7. pEGFP-EphA7 plasmid was constructed and was transfected into HCT116 which lost the expression of EphAT. Gene chip was analyzed for the expression of genes between transfectant and mock cell. Results： Down-regulation of EphA7 was observed in cell lines of primary colorectal cancers, and the evidence of aberrant methylation was found in CpG island of EphA7 promoter. The methylation status of EphA7 gene was related to sex, differentiation and location of colorectal cancers. Some genes were up or down regulated in pEGFP-EphA7 transfectant. Conclusion： EphA7 gene may be involved in the carcinogenesis of colorectal cancer. The hypermethylation of CpG island is an important mechanism leading to the down regulation of EphA7 in colorectal cancer.