亚硝胺诱导食管癌变早期基因差异表达与表观遗传修饰的关系

Relationship between differentially expressed genes and epigenetic modification during the early stage of esophageal carcinoma induced by nitrosamine

目的:通过基因芯片技术检测亚硝胺诱导食管癌变过程中,食管组织基因表达的差异,分析不同阶段基因表达的特点以及基因差异表达与DNA甲基化的相关性.方法:小鼠随机分为2组,A组(对照组)40只,灌喂蒸馏水;B组(实验组)70只,灌喂诱导混合物(20g/L亚硝酸钠+200g/LN,N-二甲基苄胺).在诱导时间4、8、20wk时,提取食管组织RNA,反转录合成cDNA,并与芯片杂交,对芯片结果进行分析,比较诱导进程中不同组别的表达差异.结果:亚硝胺诱导早期病变进程中原癌基因表达的变化呈现整体逐步上升的趋势,且阶段表达特性显著,但多数抑癌基因未表现出明显变化.甲基化酶基因在4wk无明显改变,但在8、20wk稍有升高,去甲基化酶基因中Mbd2b从8wk开始上调,但Gadd45a从4wk就已诱导上调,8、20wk依然明显上调.未发现明显改变的组蛋白乙酰化酶基因.结论:在亚硝胺诱导食管癌变过程中,大量基因的上调表达可能与早期基因组的低甲基化密切相关,Gadd45a可能参与了诱导早期的脱甲基作用.

AIM： To detect the differentially expressed genes in the process of esophageal carcinoma induced by nitrosamine, and analyze the property of gene expression at different stages, especially the relationship between differentially expressed genes and DNA methylation. METHODS： One hundred and ten mice were randomly divided into group A （n = 40） and B （n = 70）. The mice in group A were fed with distilled water, while those in group B were fed with carcinoma-inducing mixture containing 20 g/L sodium nitrite and 200 g/L N, N-dimethyl benzyl amine. At the 4, 8, and 20 wk of induction stages, the total RNA from esophageal tissues was isolated and reversely transcripted, and then hybridization with gene-chip was performed. The differentially expressed genes of the two groups were analyzed. RESULTS： During the process of induction, the number of up-regulated oncogenes increased in a step-by-step fashion in group B as compared with that in group A, and the phase-specificity of oncogenes was observed. But most antioncogenes did not change remarkably. Most genes of DNA methylation did not change at 4 wk, but were up-regulated at 8 and 20 wk. The DNA demethylation gene Mdb2b was up-regulated from the 8 wk, but Gadd45a was up-regulated from the 4 wk and maintained a high level at 8 and 20 wk. Genes of histone acetylation, which were changed obviously, were not found. CONCLUSION： During the process of nitrosamine-induced esophageal carcinoma, up-regulation of numerous genes may associate with the demethylation of genomic DNA at the early stage. Gadd45a may be involved in the demethylation during the early weeks.