Cao Ru, Wang Hengbin, He Jin, Erdjument-Bromage Hediye, Tempst Paul, Zhang Yi
Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295, USA.
Mol Cell Biol. 2008 Mar;28(5):1862-72. doi: 10.1128/MCB.01589-07. Epub 2007 Dec 17.
Polycomb group (PcG) proteins are required for maintaining the silent state of the homeotic genes and other important developmental regulators. The silencing function of the PcG proteins has been linked to their intrinsic histone modifying enzymatic activities. The EED-EZH2 complex, containing the core subunits EZH2, EED, SUZ12, and RbAp48, functions as a histone H3K27-specific methyltransferase. Here we describe the identification and characterization of a related EED-EZH2 protein complex which is distinguished from the previous complex by the presence of another PcG protein, hPHF1. Consistent with the ability of hPHF1 to stimulate the enzymatic activity of the core EED-EZH2 complex in vitro, manipulation of mPcl1, the mouse counterpart of hPHF1, in NIH 3T3 cells and cells of the mouse male germ cell line GC1spg results in global alteration of H3K27me2 and H3K27me3 levels and Hox gene expression. Small interfering RNA-mediated knockdown of mPcl1 affects association of the Eed-Ezh2 complex with certain Hox genes, such as HoxA10, as well as Hox gene expression concomitant with an alteration on the H3K27me2 levels of the corresponding promoters. Therefore, our results reveal hPHF1 as a component of a novel EED-EZH2 complex and demonstrate its important role in H3K27 methylation and Hox gene silencing.
多梳蛋白家族（PcG）蛋白对于维持同源异型基因和其他重要发育调节因子的沉默状态是必需的。PcG蛋白的沉默功能与其内在的组蛋白修饰酶活性有关。包含核心亚基EZH2、EED、SUZ12和RbAp48的EED-EZH2复合物作为一种组蛋白H3K27特异性甲基转移酶发挥作用。在此，我们描述了一种相关的EED-EZH2蛋白复合物的鉴定和特征，该复合物与先前的复合物不同之处在于存在另一种PcG蛋白hPHF1。与hPHF1在体外刺激核心EED-EZH2复合物酶活性的能力一致，在NIH 3T3细胞和小鼠雄性生殖细胞系GC1spg的细胞中对hPHF1的小鼠对应物mPcl1进行操作，会导致H3K27me2和H3K27me3水平以及Hox基因表达的全局改变。小干扰RNA介导的mPcl1敲低会影响Eed-Ezh2复合物与某些Hox基因（如HoxA10）的结合，以及Hox基因表达，同时相应启动子的H3K27me2水平也会发生改变。因此，我们的结果揭示hPHF1是一种新型EED-EZH2复合物的组成部分，并证明了其在H3K27甲基化和Hox基因沉默中的重要作用。
