Caretti Giuseppina, Di Padova Monica, Micales Bruce, Lyons Gary E, Sartorelli Vittorio
Muscle Gene Expression Group, Laboratory of Muscle Biology, NIAMS, National Institutes of Health, Bethesda, Maryland 20892, USA.
Genes Dev. 2004 Nov 1;18(21):2627-38. doi: 10.1101/gad.1241904.
The Ezh2 protein endows the Polycomb PRC2 and PRC3 complexes with histone lysine methyltransferase (HKMT) activity that is associated with transcriptional repression. We report that Ezh2 expression was developmentally regulated in the myotome compartment of mouse somites and that its down-regulation coincided with activation of muscle gene expression and differentiation of satellite-cell-derived myoblasts. Increased Ezh2 expression inhibited muscle differentiation, and this property was conferred by its SET domain, required for the HKMT activity. In undifferentiated myoblasts, endogenous Ezh2 was associated with the transcriptional regulator YY1. Both Ezh2 and YY1 were detected, with the deacetylase HDAC1, at genomic regions of silent muscle-specific genes. Their presence correlated with methylation of K27 of histone H3. YY1 was required for Ezh2 binding because RNA interference of YY1 abrogated chromatin recruitment of Ezh2 and prevented H3-K27 methylation. Upon gene activation, Ezh2, HDAC1, and YY1 dissociated from muscle loci, H3-K27 became hypomethylated and MyoD and SRF were recruited to the chromatin. These findings suggest the existence of a two-step activation mechanism whereby removal of H3-K27 methylation, conferred by an active Ezh2-containing protein complex, followed by recruitment of positive transcriptional regulators at discrete genomic loci are required to promote muscle gene expression and cell differentiation.
Ezh2蛋白赋予多梳PRC2和PRC3复合物组蛋白赖氨酸甲基转移酶（HKMT）活性，该活性与转录抑制相关。我们报告称，Ezh2在小鼠体节的肌节部分受到发育调控，其下调与肌肉基因表达的激活以及卫星细胞来源的成肌细胞分化同时发生。Ezh2表达的增加抑制了肌肉分化，这种特性由其HKMT活性所需的SET结构域赋予。在未分化的成肌细胞中，内源性Ezh2与转录调节因子YY1相关。在沉默的肌肉特异性基因的基因组区域检测到Ezh2和YY1以及去乙酰化酶HDAC1。它们的存在与组蛋白H3的K27甲基化相关。YY1是Ezh2结合所必需的，因为YY1的RNA干扰消除了Ezh2的染色质募集并阻止了H3-K27甲基化。基因激活后，Ezh2、HDAC1和YY1从肌肉基因座解离，H3-K27去甲基化，MyoD和SRF被募集到染色质上。这些发现表明存在一种两步激活机制，即由含有活性Ezh2的蛋白质复合物赋予的H3-K27甲基化的去除，随后在离散的基因组位点募集正转录调节因子，是促进肌肉基因表达和细胞分化所必需的。
