颅内原始神经外胚叶肿瘤中TIG1启动子的高甲基化

Hypermethylation of TIG1 promoter in intracranial primitive neuroectodermal tumors

目的检测颅内原始神经外胚叶肿瘤(primitive neuroectodermal tumor,PNET)中TIG1(tazarotene induced gene-1)基因启动子的甲基化状态。方法使用甲基化特异PCR(MSP)法检测25例原发髓母细胞瘤(medulloblastoma,MB)、9例原发幕上原始神经外胚叶肿瘤(supratentorial primitive neuroectodermal tumor,SPNET)和7株PNET细胞系中TIG1的甲基化水平。用RT-PCR方法检测PNET细胞中TIG1的转录水平。并用去甲基化试剂处理PNET细胞,观察基因转录水平与甲基化状态间的关系。结果原发MB及SPNET中TIG1启动子的异常甲基化率分别为40%(10/25)和44%(4/9)。该基因在PNET中的甲基化异常是肿瘤特异性的。PNET细胞系中均有TIG1高甲基化,并伴有转录水平的表达减少或丢失(7/7)。TIG1的表达水平与启动子甲基化状态呈明显负相关。并且,这种相关性得到去甲基化试剂处理实验的支持。经去甲基化试剂5-aza-2′-deoxycyti-dine处理的全部细胞系中TIG1的表达都得到了恢复。结论大部分PNET细胞系中都有TIG1表达的减少和缺失,且该基因缺失与启动子高甲基化密切相关。同时,TIG1的高甲基化率在原发PNET中也能检测到,提示TIG1可能在颅内PNET的肿瘤发生中起重要作用。

Purpose To detect the methylation status of TIG1 promoter in intracranial primitive neuroectodermal tumor （PNET）. Methods 25 cases of primary medulloblastomas （MBs）, 9 primary supratentorial intracranial primitive neuroectodermal tumor （SPNETs） and 7 PNET cell lines were examined by methylation specific PCR （MSP）method. Expression of TIG1 was identified in PNET cells by RT-PCR. Six cell lines were treated by the demethylation reagent, 5-aza-2＇-deoxycytidine. The correlation between TIG1 promoter hypermethylation and its transcriptional status was explored. Results Aberrant promoter methylation of TIG1 in MBs and SPNET was 40% （10/25） and 44% （4/9）, respectively. Aberrant methylation of TIG1 in PNET is tumor specific. Loss of or reduced transcript of TIG1 was identified in the majority of PNET cell lines （7/7）, which is highly correlated with promoter hypermethylation of the gene. The inverse correlation is supported by the reversed expression of TIG1 in all six cell lines tested after treatment by 5-aza-2＇-deoxycytidine. Conclusions TIG1 expression is lost or reduced in the majority of PNET cell lines and the TIG1 gene silencing has close relationship with promoter hypermethylation. Moreover, the frequent aberrant methylation of TIG1 is also observed in primary PNETs, suggesting that TIG1 may play an important role in tumorigenesis of intracranial PNET.