Overlapping roles of the methylated DNA-binding protein MBD1 and polycomb group proteins in transcriptional repression of HOXA genes and heterochromatin foci formation
Overlapping roles of the methylated DNA-binding protein MBD1 and polycomb group proteins in transcriptional repression of HOXA genes and heterochromatin foci formation
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DOI：
10.1074/jbc.m700011200
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发表时间：
2007-06-01
影响因子：
4.8
通讯作者：
Nakao, Mitsuyoshi
中科院分区：
文献类型：
--
作者：
Sakamoto, Yasuo;Watanabe, Sugiko;Nakao, Mitsuyoshi
甲基化的DNA结合域（MBD）蛋白和Polycomb group （PcG）蛋白维持转录活性的表观遗传沉默。我们报道DNA甲基化介导的抑制因子MBD1与Polycomb抑制复合体1的主要成分Ring1b和hPc2相互作用。MBD1的富含半胱氨酸的CXXC结构域与Ring1b和hPc2的色域结合。染色质免疫沉淀分析显示，MBD1和hPc2存在于沉默的Homeobox A （HOXA）基因中，敲低MBD1或hPc2均可使HOXA基因重新激活，表明MBD1和hPc2协同抑制HOXA基因的转录。在HeLa细胞的细胞核中，MBD1与这些PcG蛋白在一些异染色质病灶中密切相关，而缺乏CXXC结构域的MBD1突变体或缺乏色域的hPc2突变体在病灶中失去了这种共定位。使用DNA去甲基化剂5-氮杂脱氧胞苷可以消除MBD1病灶的形成，但不能消除PcG病灶的形成。小干扰rna敲低MBD1不影响含有hPc2和Ring1b的病灶，而敲低hPc2不影响MBD1病灶。这些结果表明，显示MBD1和hPc2共定位的异染色质灶是通过MBD1和hPc2的相互作用产生的，并且MBD1的灶与PcG蛋白本身是可分离的。我们目前的研究结果表明MBD1和PcG蛋白通过相互作用在表观遗传基因沉默和异染色质病灶形成中具有重叠作用。
Methylated DNA binding domain (MBD) proteins and Polycomb group ( PcG) proteins maintain epigenetic silencing of transcriptional activity. We report that the DNA methylation-mediated repressor MBD1 interacts with Ring1b and hPc2, the major components of Polycomb repressive complex 1. The cysteine-rich CXXC domains of MBD1 bound to Ring1b and the chromodomain of hPc2. Chromatin immunoprecipitation analysis revealed that MBD1 and hPc2 were present in silenced Homeobox A (HOXA) genes which could be reactivated by knockdown of either MBD1 or hPc2, suggesting that MBD1 and hPc2 cooperate for transcriptional repression of HOXA genes. In the nuclei of HeLa cells, MBD1 existed in close association with these PcG proteins in some heterochromatin foci, whereas an MBD1 mutant lacking the CXXC domains or an hPc2 mutant lacking the chromodomain lost this colocalization in foci. Use of the DNA demethylating agent 5-azadeoxycytidine abolished the formation of MBD1 foci but not PcG foci. Knockdown of MBD1 by small interfering RNAs did not affect the foci containing hPc2 and Ring1b, whereas the MBD1 foci were not influenced by knockdown of hPc2. These indicate that the heterochromatin foci showing MBD1 and hPc2 colocalization arise through the interaction of MBD1 and hPc2 and that the foci of MBD1 are separable from those of the PcG proteins per se. Our present findings suggest that MBD1 and PcG proteins have overlapping roles in epigenetic gene silencing and heterochromatin foci formation through their interactions.