白血病细胞系中抑癌基因PTEN启动子区甲基化状态检测及其去甲基化研究

Promoter methylation status of PTEN gene and the effect of induced demethylation in leukemia cell lines

目的探讨抑癌基因PTEN表达沉默的机制及诱导PTEN表达对白血病细胞的作用。方法应用甲基化特异性聚合酶链反应（Methylation specific PCR，MSP）检测白血病细胞系HL-60、Nalm-6、Raji、KG-1a、U937、NB4、K562中PTEN基因启动子区域甲基化状态；用甲基化转移酶抑制剂5-氮-2’-脱氧胞苷（5-Aza-CdR）处理白血病细胞，MSP检测甲基化状态的改变、RT-PCR检测PTEN mRNA水平的改变、瑞特染色观察细胞形态学改变、膜联蛋白V／碘化丙锭（Annexin V／PI）标记染色检测细胞凋亡。结果检测的白血病细胞系中HL-60、Nalm-6、Raji、KG-1a、U937细胞PTEN基因显示超甲基化状态，而NB4和K562细胞显示低甲基化状态；5-Aza-CdR处理HL-60和Nalm-6细胞后，PTEN基因甲基化降低、mRNA表达水平则逐渐增高，并呈剂量依赖性，细胞出现凋亡现象。结论PTEN基因启动子区异常甲基化可能导致该基因转录表达失活或沉默，甲基化抑制剂可以诱导PTEN表达，并引起白血病细胞凋亡。

Objective To explore the mechanism of PTEN gene expression silence in leukemia cells, and the effect of induced PTEN gene expression in leukemia cells. Methods Methylation status of PTEN in leukemic cell lines, including HL-60, Nalm-6, NB4, U937, Raji, K562 and KG-1a was assessed by methyl- ation specific PCR （MSP）. The cell lines were then treated with different concentrations of methyltransferase inhibitor 5-Aza-2＇-deoxycytidine（5-Aza-CdR）. After that the changes in PTEN methylation status were detected by MSP, and PTEN mRNA expression level by reverse transcription PCR （RT-PCR）. Growth inhibition and apoptosis of HL-60 and Nalm-6 cells induced by 5-Aza-CdR were observed by MTT assay, and Wright and Annexin V staining, respectively. Results Hypermethylation of PTEN promoter was detected in HL-60, U937, Nalm-6, Raji and KG-1a, while hypomethylation was found in NB4 and K562 by MSP. After 5-Aza- CdR treatment, the hypermethylation status of PTEN promoter in HL-60 and Nalm-6 cells was reversed and their PTEN mRNA expression levels were up regulated in dose dependent manner with the 5-Aza-CdR concentrations, and the cell apoptosis was induced. Conclusion Hypermethylation in the promoter region is one of major mechanisms responsible for transcriptional suppression of PTEN. Methyhransferase inhibitor could induce the expression of PTEN gene and lead to the leukemia cells apoptosis.