Center for Vascular and Tumor Biology, The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel.
Biochem Biophys Res Commun. 2011 May 13;408(3):393-8. doi: 10.1016/j.bbrc.2011.04.025. Epub 2011 Apr 12.
Methylation of lysine 27 on histone H3 by the polycomb repressive complex 2 (PRC2) leads to transcriptional repression of genes which are critical to development. PRC2 core complex is composed of the histone methyltransferase EZH2, EED, and SUZ12. Knockdown of any of the PRC2 core subunits results in a concomitant loss of the other subunits which is mediated by the ubiquitin (Ub)-proteasome system (UPS). Inhibition of cellular methyltransferases by 3-deazaneplanocin A (DZNep) also leads to dissociation of the PRC2 complex and rapid degradation of its subunits. Interestingly, the expression of several Ub ligases was induced following DZNep treatment, suggesting that PRC2 might repress the Ub ligase(s) that target its subunits for degradation. Here we confirm that individual PRC2 subunits are ubiquitinated and rapidly degraded by the proteasome. One of the DZNep-induced Ub ligases, PRAJA1, can target PRC2 subunits for proteasomal degradation. PRAJA1 directly ubiquitinates individual PRC2 subunits in a cell free system, which leads to their proteasomal degradation. Expression of PRAJA1 but not of an inactive RING finger mutant of the protein, enhanced the degradation of individual PRC2 subunits in cells. Taken together, our results suggest a role for PRAJA1 in regulating the level of PRC2 by targeting its free subunits for Ub-mediated proteasomal degradation.
组蛋白 H3 赖氨酸 27 上的甲基化由多梳抑制复合物 2（PRC2）介导，导致对发育至关重要的基因的转录抑制。PRC2 核心复合物由组蛋白甲基转移酶 EZH2、EED 和 SUZ12 组成。敲降任何一个 PRC2 核心亚基都会导致其他亚基的伴随丢失，这是由泛素（Ub）-蛋白酶体系统（UPS）介导的。3-去氮杂胞苷（DZNep）抑制细胞甲基转移酶也会导致 PRC2 复合物的解离和其亚基的快速降解。有趣的是，DZNep 处理后，几种 Ub 连接酶的表达被诱导，这表明 PRC2 可能抑制其亚基降解的 Ub 连接酶。在这里，我们证实了单个 PRC2 亚基被泛素化并被蛋白酶体迅速降解。DZNep 诱导的 Ub 连接酶之一，PRAJA1，可以将 PRC2 亚基靶向蛋白酶体降解。PRAJA1 在无细胞系统中直接泛素化单个 PRC2 亚基，导致它们被蛋白酶体降解。PRAJA1 的表达而非该蛋白的无活性 RING 指突变体的表达增强了细胞中单个 PRC2 亚基的降解。总之，我们的结果表明 PRAJA1 通过将其游离亚基靶向 Ub 介导的蛋白酶体降解来调节 PRC2 的水平。
