DNA甲基化对大肠癌相关基因表达的调控意义

目的:探讨大肠癌发生与演进中p16,Rb,cyclin D1甲基化状态与蛋白表达的关系及意义．方法:提取正常黏膜、腺瘤、癌旁组织及癌组织基因组DNA,应用MSP法检测不同病变阶段组织中各基因的甲基化状态,并对其与蛋白表达及临床病理参数的关系进行分析．结果:在大肠癌发生与演进过程中,p16,Rb 基因甲基化率呈增高趋势,cyclin D1基因甲基化率呈下降趋势,p16(切缘:r=-0．185,P =0．173;腺瘤:r=-0．381,P=0．013:癌旁:r= -0．419,P=0．001;癌:r=-0．516,P=0．000)、 cyclin D1(切缘:r=-0．282,P=0．035;腺瘤:r= -0．329,P=0．033;癌旁:r=-0．298,P=0．026; 癌:r=-0．618,P=0．000)基因甲基化程度分别与其蛋白表达呈明显负相关,且在癌组织分化程度(p16:X2=11.232,P=0．002,cyclin D1:X2 =9．144,P=0．015)、浸润深度(p16:X2=6．229, P=0．013;cyclin D1:X2=8．023,P=0．006)和淋巴结转移(p16:X2=5．707,P=0．016;cyclin D1: X2=7．794,P=0．005)上有显著性差异．Rb基因的甲基化状态在Rb表达抑制上不起主要作用．结论:大肠癌p16高甲基化和cyclin D1低甲基化可能是p16失活和cyclin D1过表达的主要机制,在大肠癌的发生、发展中发挥重要作用, 对于大肠癌的早期诊断、恶性程度及预后判断有重要意义．

Role of DNA methylation in control of tumor suppressor gene and oncogene expression in colorectal carcinoma

AIM: To investigate the relationship between DNA methylation and expression of p16, Rb, and cyclin D1 in the carcinogenesis of colorectal carcinoma. METHODS: Methylation-specific polymerase chain reaction (MS-PCR) was used to detect the methylation status of p16, Rb, and cyclin D1 in the specimens from colorectal carcinoma, cancer-adjacent tissues of carcinoma and adenoma, and normal colorectal mucosa, respectively. The correlations of methylation with protein expression and the clinicopathological indexes were analyzed. RESULTS: For the levels of p16 and Rb methylation, there were increased tendencies in the carcinogenesis of colorectal cancer, while for the level of cyclin D1 methylation, there was a decreased tendency. The expression of p16 and cyclin D1 protein were inversely correlated with the methylation status of p16 (normal mucosa: r = -0.185, P = 0.173; adenoma: r = -0.381, P = 0.013; cancer-adjacent tissues: r = -0.419, P = 0.001; cancer tissues: r = -0.516, P = 0.000) and cyclin D1 gene (normal mucosa: r = -0.282, P = 0.035; adenoma: r = -0.329, P = 0.033; cancer-adjacent tissues: r = -0.298, P = 0.026; cancer tissues: r = -0.618, P = 0.000). The levels of p16 and cyclin D1 methylation were significantly correlated with the degrees of differentiation (p16:X2 = 11.232, P = 0.002, cyclin D1:X2 = 9.144, P = 0.015), the depth of invasion (p16: X2 =6.229, P = 0.013; cyclin D1: X2 = 8.023, P = 0.006) and the metastasis of lymph node (p16:X2 = 5.707, P = 0.016; cyclin D1: X2 = 7.794, P = 0.005). The methylation of Rb gene didn't play a main role in the inhibition of Rb protein expression during colorectal carcino genesis. CONCLUSION: Aberrant methylations of p16 and cyclin D1 are the main mechanisms of p16 inactivation and cyclin D1 over-expression, which play important roles in colorectal carcino genesis. They are valuble in the early diagnosis and prognosis of colorectal carcinoma.