中文摘要：

目的：探讨叶酸在N-甲基-N-硝基-N-亚硝基胍（MNNG）影响哈萨克族食管上皮细胞DNA甲基转移酶1（DNMT1）活性及表达中的作用,为食管癌的防治提供理论依据。方法：采用3因素3水平（3×3）析因设计将体外培养的哈萨克族食管上皮细胞分别暴露于不同浓度叶酸（0.000、0.400、0.800μg/m L）和MNNG（0.000、0.750、1.500μg/m L）的培养液中作用48、72和96 h后,采用ELISA法检测DNMT1酶活性;采用RT-PCR的方法检测DNMT1 mRNA表达水平;采用Western blot法检测DNMT1蛋白的表达水平。结果：不同浓度叶酸、MNNG作用细胞不同时间后,在固定MNNG浓度和时间因素下,随着叶酸浓度的增加DNMT1酶活性、DNMT1 mRNA和蛋白表达水平均逐渐降低（P均〈0.01）;固定叶酸浓度和时间,随着MNNG浓度的增加DNMT1酶活性、DNMT1 mRNA和蛋白表达水平均逐渐升高（P均〈0.01）;固定MNNG和叶酸浓度,随着干预时间的延长DNMT1酶活性、DNMT1 mRNA和蛋白表达水平均逐渐升高（P均〈0.01）;叶酸浓度与MNNG浓度之间、MNNG浓度与作用时间之间均存在交互作用（P〈0.01）。不同叶酸浓度与不同MNNG浓度之间、不同叶酸浓度与不同作用时间之间、不同MNNG浓度与不同作用时间之间差异均有统计学意义（P〈0.05）。结论：叶酸浓度降低对MNNG影响哈萨克族食管上皮细胞DNMT1酶活性及表达有一定的激发作用,对食管癌的发生有一定的促进作用,而保持充足的叶酸则对MNNG的损害起到一定的保护作用。

英文摘要：

OBJECTIVE：To investigate the effects of folic acid on N-methyl-N-nitro-N＇-nitrosoguanidine（MNNG）-treated esophageal epithelial cells,in expression of DNMT1 activity and to provide a theoretical basis for the prevention and treatment of esophageal cancer.METHODS：Using a 3 factors and 3 levels（3 × 3） factorial design,esophageal epithelial cells in culture were exposed to different concentrations of folic acid（0.000,0.400,0.800 μg/mL） and MNNG（0,0.750,1.500 μg/mL） for 48,72 and 96 h.DNA methyltransferase activity was detected by ELISA;DNMT1 mRNA expression by RT-PCR;DNMT1 protein expression by Western blot method.RESULTS：Treatment of cells with different concentrations of folic acid and MNNG and in different times,at a fixed MNNG concentration and time factors,and with increasing concentrations of folic acid,the DNMT1 activity,DNMT1 mRNA and protein expression levels all gradually decreased（P〈0.01）.By fixing folic acid concentrations and time,and with increasing concentrations of MNNG,DNMT1 enzyme activity,DNMT1 mRNA and protein expression levels all increased（P〈0.01）.By fixing the MNNG and folic acid concentrations with intervention,the extension of time of DNMT1 activity,DNMT1 mRNA and protein expression levels all gradually increased（P〈0.01）.There were interactions between MNNG concentrations and action time,and folic acid and MNNG concentrations（P〈0.01）.There were significant differences between different concentrations of folic acid and different action time,between different MNNG concentrations and different time of action（P〈0.05）.CONCLUSION：Lower folate concentrations had a negative impact on the expression and effect of MNNG on DNMT1 activity in esophageal epithelial cells.The results suggest that folic acid played a role in promoting the occurrence of esophageal carcinoma,and had a protective effect against MNNG toxicity.