USP7 is a deubiquitinase that regulates many diverse cellular processes, including tumor suppression, epigenetics, and genome stability. Several substrates, including GMPS, UHRF1, and ICP0, were shown to bear a specific KxxxK motif that interacts within the C-terminal region of USP7. We identified a similar motif in Enhancer of Zeste 2 (EZH2), the histone methyltransferase found within Polycomb Repressive Complex 2 (PRC2). PRC2 is responsible for the methylation of Histone 3 Lys27 (H3K27) leading to gene silencing. GST pull-down and coimmunoprecipitation experiments showed that USP7 interacts with EZH2. We determined the structural basis of interaction between USP7 and EZH2 and identified residues mediating the interaction. Mutations in these critical residues disrupted the interaction between USP7 and EZH2. Furthermore, USP7 silencing and knockout experiments showed decreased EZH2 levels in HCT116 carcinoma cells. Finally, we demonstrated decreased H3K27Me3 levels in HCT116 USP7 knockout cells. These results indicate that USP7 interacts with EZH2 and regulates both its stability and function.

中文翻译：

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泛素特异性蛋白酶7与Zeste同源2增强子相互作用的结构基础。

USP7是一种去泛素化酶，可调节许多不同的细胞过程，包括肿瘤抑制，表观遗传学和基因组稳定性。已显示包括GMPS，UHRF1和ICP0在内的几种底物带有在USP7的C端区域内相互作用的特定KxxxK基序。我们在Zeste 2（EZH2）增强子（在Polycomb Repressive Complex 2（PRC2）中发现的组蛋白甲基转移酶）中鉴定了类似的基序。PRC2负责组蛋白3 Lys27（H3K27）的甲基化，从而导致基因沉默。GST下拉和免疫共沉淀实验表明，USP7与EZH2相互作用。我们确定了USP7和EZH2之间相互作用的结构基础，并确定了介导相互作用的残基。这些关键残基中的突变破坏了USP7和EZH2之间的相互作用。此外，USP7沉默和敲除实验表明，HCT116癌细胞中EZH2水平降低。最后，我们证明了HCT116 USP7基因敲除细胞中H3K27Me3水平降低。这些结果表明，USP7与EZH2相互作用并调节其稳定性和功能。