Human mismatch repair gene, MLH1, is transcriptionally repressed by the hypoxia-inducible transcription factors, DEC1 and DEC2
Human mismatch repair gene, MLH1, is transcriptionally repressed by the hypoxia-inducible transcription factors, DEC1 and DEC2
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DOI：
10.1038/onc.2008.58
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发表时间：
2008-07-01
期刊：
影响因子：
8
通讯作者：
Nishiyama, M.
中科院分区：
文献类型：
--
作者：
Nakamura, H.;Tanimoto, K.;Nishiyama, M.
肿瘤缺氧可导致DNA错配修复（MMR）基因表达下调，导致MMR系统功能丧失，但其确切的分子机制尚不清楚。在本研究中，我们专注于一个关键的MMR基因，MLH 1的下调，并证明缺氧诱导的转录抑制因子，分化的胚胎软骨细胞（DEC 1和2），参与其转录调控通过其结合到MLH 1启动子区的E-box样模体（S）。在所有检测的癌细胞系中，缺氧增加了DEC 1和2（称为缺氧诱导基因）的表达，但在mRNA和蛋白质水平上以暴露时间依赖性方式降低了MLH 1的表达。共转染报告基因分析显示，DEC 1，并在更大程度上，DEC 2以及缺氧抑制MLH 1启动子活性。我们进一步发现，该行动显着抑制了阿司他丁A，并确定了一个可能的DEC响应元件MLH 1启动子。体外电泳凝胶迁移率变化和染色质免疫沉淀试验表明，DEC 1或2直接绑定到建议的元素，和瞬时转染试验表明，DEC 2的过表达抑制内源性MLH 1在细胞中的表达。缺氧诱导的DEC可能通过抑制MLH 1表达而损害MMR功能，这可能是通过癌细胞中组蛋白脱乙酰酶介导的机制实现的。
Tumor hypoxia has been reported to cause a functional loss in DNA mismatch repair (MMR) system as a result of downregulation of MMR genes, although the precise molecular mechanisms remain unclear. In this study, we focused on the downregulation of a key MMR gene, MLH1, and demonstrated that hypoxia-inducible transcription repressors, differentiated embryo chondrocytes (DEC1 and 2), participated in its transcriptional regulation via their bindings to E-box-like motif(s) in MLH1 promoter region. In all cancer cell lines examined, hypoxia increased expression of DEC1 and 2, known as hypoxia-inducible genes, but decreased MLH1 expression in an exposure time-dependent manner at both the mRNA and protein levels. Co-transfection reporter assay revealed that DEC1 and, to greater extent, DEC2 as well as hypoxia-repressed MLH1 promoter activity. We further found that the action was remarkably inhibited by trichostatin A, and identified a possible DEC-response element in the MLH1 promoter. In vitro electrophoretic gel mobility shift and chromatin immunoprecipitation assays demonstrated that DEC1 or 2 directly bounds to the suggested element, and transient transfection assay revealed that overexpression of DEC2 repressed endogenous MLH1 expression in the cells. Hypoxia-induced DEC may impair MMR function through repression of MLH1 expression, possibly via the histone deacethylase-mediated mechanism in cancer cells.