肺癌细胞株APC基因启动子甲基化对其转录的影响

Effect of Adenomatous Polyposis Coli(APC) Promoter Methylation on Gene Transcription in Lung Cancer Cell Lines

背景与目的:抑癌基因家族性腺瘤样结肠息肉病易感基因(adenomatous polyposis coli,APC)启动子区的高甲基化在很多肿瘤中被发现,与这些肿瘤的发生发展相关。本实验室在肺癌患者肿瘤组织中检测到APC甲基化率达47%,为了研究其在肺癌细胞株中的甲基化情况,并进一步了解甲基化对其转录的影响,本研究检测了3株肺癌细胞的抑癌基因APC启动子甲基化状态及其对该基因转录水平的影响。方法:提取3株肺癌细胞株(肺腺癌细胞株SPC-A1、小细胞肺癌细胞株NCI-H446、大细胞肺癌细胞株NCI-H460)的DNA,以经转甲基处理和未做处理的脐带血DNA为阳性、阴性对照,亚硫酸氢盐化学修饰后,用甲基化特异性基因扩增(methylation specific-polymerase chain reaction,MSP)和甲基化基因芯片对APC基因启动子1ACpG岛甲基化进行研究,并用实时荧光定量PCR(real time-polymerase chain reaction)技术,以Sybr-GreenⅠ为荧光染料,β-actin基因为内参照,检测mRNA转录;对甲基化阳性的NCI-H460细胞,分别用1、5、10、15μmol/L的5′-杂氮-2'-脱氧胞嘧啶(5-aza-2-deoxycytidine,5-aza-dC)试剂进行脱甲基化,提取RNA,荧光定量检测其转录变化。结果:SPC-A1和NCI-H446细胞APC甲基化阴性,NCI-H460细胞APC甲基化阳性;甲基化芯片检测NCI-H460细胞在APC启动子1A5个CpG位点均存在甲基化(687、707、714、719、726),SPC-A1和NCI-H446甲基化阴性,荧光定量结果NCI-H460的APC转录较SPC-A1和NCI-H446有明显的下降,仅为二者平均的30.04%;经5-aza-dC脱甲基化作用后,NCI-H460细胞的APC表达增加了约5～10倍,其中10μmol/L浓度作用下,APC表达增加最多。结论:肺癌细胞株NCI-H460中存在APC基因高甲基化,5-aza-dC脱甲基化试剂可以激活其转录。

BACKGROUND ＆ OBJECTIVE： Hypermethylation of CpG islands in adenomatous polyposis coil （APC） gene has been detected in a variety of human tumors, which is involved in the pathogenesis of these tumors. In previous research, we detected APC promoter methylation in 47% lung tumor tissues. This study was to analyze the effect of APC promoter methylation on the gene transcription in 3 lung cancer cell lines. METHODS, The methylation status of APC promoter 1A in lung adenocarcinoma cell line SPCA1, small cell lung cancer cell line NCI-H446, and big cell lung cancer cell line NCI-H460 was detected by methylation-specific polymerase chain reaction （MSP） and microarray; methylated cord blood DNA served as positive control, and unmethylated cord blood DNA served as negative control. The expression of APC was examined by real-time quantitative polymerase chain reaction （PCR） with Sybr-Green I staining. After treatment of 1, 5, 10, 15 μmol/L DNA methyltransferase inhibitor 5-aza-2-deoxycytidine （5-aza-dC）, the expression of APC in NCI-H460 cells was detected by realtime PCR. RESULTS： APC promoter 1A was methylated in NCI-H460 cells, and unmethylated in NCI-H446 and SPC-A1 cells. Hypermethylation was detected in all 5 CpG islands （687, 707, 714, 719, 726） of APC promoter 1A in NCI-H460 cells. The expression of APC in NCI-H460 cells was decreased by 26.04% of that in NCI-H446 ceils and by 32.36% of that in SPCA1 cells. After treatment of 1, 5, 10, 15 iJmol/L 5-aza-dC, the expression of APC promoter 1A in NCI-H460 cells was enhanced by 4.59, 5.78, 9.58, 5.98 folds, respectively. CONCLUSION： APC gene is hypermethylated in HCI-H460 cells, and its transcription coud be activated by 5-aza-dC.