Promoter hypomethylation regulates CD133 expression in human gliomas
Promoter hypomethylation regulates CD133 expression in human gliomas
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DOI：
10.1038/cr.2008.270
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发表时间：
2008-10-01
期刊：
影响因子：
44.1
通讯作者：
Tanaka, Shinya
中科院分区：
文献类型：
--
作者：
Tabu, Kouichi;Sasai, Ken;Tanaka, Shinya
针对细胞表面蛋白CD133的抗体已经使脑肿瘤起始细胞(BTICs)变得丰富，然而，CD133在人脑胶质瘤中表达的生物学相关性和调控机制尚不清楚。在这项研究中，我们最初证明了CD133在高级别的人胶质母细胞瘤中过表达，其中CD133阳性的细胞被局部观察为微簇。此外，带有外显子1A、1B或1C的CD133转录本主要在胶质母细胞瘤中表达。为了阐明这种CD133异常表达的调控机制，我们分离了含有CpG岛的三个近端启动子(P1、P2和P3)。在U251 MG和T98G胶质母细胞瘤细胞中，外显子1A两侧的P1区显示出最高的活性，该活性被体外甲基化显著失活。经去甲基化药物5-氮杂胞苷和/或组蛋白去乙酰酶抑制剂丙戊酸处理后，胶质瘤细胞CD133基因的表达水平明显恢复。重要的是，通过亚硫酸氢盐测序发现，在CD133基因丰富的人胶质母细胞瘤组织中，P1、P2和P3区域的CpG位点发生了低甲基化。综上所述，我们的结果表明，DNA低甲基化是CD133在胶质母细胞瘤中表达的一个重要决定因素，这一表观遗传学事件可能与表达CD133的BTICs的发展有关。
Brain tumor-initiating cells (BTICs) have been enriched using antibodies against the cell surface protein CD133; however, the biological relevance and the regulatory mechanism of CD133 expression in human gliomas are not yet understood. In this study, we initially demonstrated that CD133 was overexpressed in high-grade human glioblastomas where CD133-positive cells were focally observed as a micro-cluster. In addition, CD133 transcripts with exon 1A, 1B, or 1C were predominantly expressed in glioblastomas. To elucidate the mechanism regulating this aberrant expression of CD133, three proximal promoters (P1, P2, and P3) containing a CpG island were isolated. In U251MG and T98G glioblastoma cells, the P1 region flanking exon 1A exhibited the highest activity among the three promoters, and this activity was significantly inactivated by in vitro methylation. After treatment with the demethylating agent 5-azacytidine and/or the histone deacetylase inhibitor valproic acid, the expression level of CD133 mRNA was significantly restored in glioma cells. Importantly, hypomethylation of CpG sites within the P1, P2, and P3 regions was observed by bisulfite sequencing in human glioblastoma tissues with abundant CD133 mRNA. Taken together, our results indicate that DNA hypomethylation is an important determinant of CD133 expression in glioblastomas, and this epigenetic event may be associated with the development of BTICs expressing CD133.