结直肠癌MTAP基因的表达及启动子去甲基化的研究

背景与目的：研究报道甲硫腺苷磷酸化酶（5’-methylthioadenosine phosphorylase，MTAP）在多种肿瘤组织中出现异常表达。本研究检测MTAP基因在结直肠腺癌、结直肠腺瘤和正常结直肠粘膜组织中的表达以及MTAP启动子甲基化的改变，探讨结直肠癌MTAP基因表达的变化与启动子去甲基化的关系。方法：定量PCR检测50例结直肠癌及癌周正常组织中MTAP mRNA的表达量；免疫组织化学的方法检测MTAP在结直肠癌中的表达；甲基化特异多聚酶链反应（Methylation—specified PCR，MSP）检测正常肠粘膜和结直肠癌组织中MTAP基因启动子发生甲基化的情况。结果：定量PCR结果显示：正常结直肠组织中MTAP mRNA的相对水平显著低于结直肠癌组织（P〈0．01）：免疫组织化学结果显示MTAP在结直肠腺癌中的表达高于结直肠腺瘤及正常结直肠粘膜（98．00％vs．85．00％和12．50％，P〈0．05），结直肠腺瘤与正常结直肠粘膜差异亦具有统计学意义（P〈0．01）；MSP检测16例正常结直肠组织，20例结直肠腺瘤，50例结直肠癌组织启动子甲基化频率分别是93．75％，75．00％，32．00％。结直肠癌中甲基化率较腺瘤和正常组织均显著降低（P〈0．01）。结论：MTAP在结直肠腺癌组织中的表达高于腺瘤和正常组织，MTAP在结直肠腺癌组织中高表达可能与MTAP启动子去甲基化有关。

Expression of methylthioadenosine phosphorylase(MTAP)gene and demethylation of its promoter in human colorectal cancer

Background and Objective. Abnormal expression of 5＇- methylthioadenosine phosphorylase （MTAP） is found in various tumor tissues. This study was to explore the correlation of MTAP expression to demethylation of MTAP promoter in colorectal cancer tissues. Methods： The contents of MTAP mRNA in 50 colorectal cancer tissue samples and the adjacent normal tissues were detected by real-time PCR; expression of MTAP protein was detected by immunohistochemistry; methylation of MTAP promoter in colorectal cancer tissues and its adjacent normal tissues were detected by methylationspecified PCR （MSP）. Results： Compared with the adjacent normal tissues, the expression of MTAP mRNA was dramatically increased in colorectal cancer tissues （P〈0.01）. The positive rate of MTAP protein in colorectal cancer was significantly higher than that in colorectal adenoma and in adjacent normal tissues （98.0% vs. 85.0% and 12.5%, P〈0.05）, and the difference of the latter two groups was also significantly different （P〈0.01）. The methylation frequency of MTAP promoter was significantly lower in colorectal cancer group （32.0%） than in normal tissue （93.8%） and colorectal adenoma （75.0%） groups （P〈0.01）. Conclusions： Expression of MTAP is significantly higher in human colorectal cancer than in normal colorectal tissues. Demethylation of MTAP promoter may play an important role in upregulating MTAP expression.