RAS相关家族1A基因在胃癌中的表达和启动子甲基化

The expression and methylation of RAS association domain family 1A gene (RASSF1A) in human gastric cancer

目的分析散发性胃癌中RAS相关家族1A基因(RASSF1A基因)的表达、突变和启动子甲基化状况,探讨RASSF1A基因在胃癌发生、发展中的意义。方法采用定量PCR、RT-PCR和SSCP检测90例胃癌组织和30例相应癌旁正常组织中RASSF1A基因表达水平以及基因突变的情况；采用甲基化特异性PCR(MSP)方法检测RASSF1A基因启动子甲基化情况。结果 90例胃癌中有52例(57．8％)RASSF1A无表达或表达低下。RASSF1A无表达或表达低下和肿瘤细胞的分化(P＜0．05)以及分期(P＜0．001)相关,但是和肿瘤的浸润深度以及淋巴结转移不相关(P＞0．05)。90例胃癌中52例启动子发生甲基化(57．8％),其中90．3％(47／52)的RASSF1A无表达或表达低下组织中检测到RASSF1A基因启动子的甲基化,然而癌旁正常组织未发现有RASSF1A基因启动子的甲基化,SSCP没有发现任何突变。结论胃癌中存在较多的启动子异常甲基化造成RASSF1A基因失活,这可能是胃癌发生发展的因素之一。

Objective In this study, analyses of transcriptional expression,mutation and methylation status of the CpG island locating in the promoter region of RASSF1A gene were performed in 90 sporadic gastric specimens and the significance of RASSF1A gene was explored in tumorigenesis of gastric cancer. Methods The genomic expression level and mutation of RASSF1A gene were detected by quantitive PCR, RT-PCR and single-strand conformation polymorphism（SSCP） in 90 cases of gastric cancer tissues and adjacent normal tissues. The methylation status of RASSF1A gene in promoter region was detected by methylationspecific PCR technique. Results Among 90 primary gastric cancers examined, 52 （57. 8%） expressed no or low levels of RASSF1A. Loss or low expression of RASSF1A correlated with tumor stage （ P 〈0. 001） and differentiation （ P 〈0.05） but not with depth of invasion and lymph node metastasis of tumors（ P 〉0.05）. Fifty-two in 90 cases of cancers （57.8%） were methylated in the promoter region of RASSF1A. Methylation-specific PCR analysis demonstraled that 90.3% （47 of 52） of RASSF1A of no-or-low-expressing primary tumors are methylated at the CpG sites in the promoter, whereas none of the adjacent normal tissues are methylated. No mutations were detected in RASSF1A transcripts expressed in tumors by SSCP analysis. Conclusion Our data suggest that the epigenetic inactivation of RASSF1A by methylation is a very common event in gastric cancer and might be involved in the progression of the disease.