Polycomb-group complex 1 acts as an E3 ubiquitin ligase for Geminin to sustain hematopoietic stem cell activity
Polycomb-group complex 1 acts as an E3 ubiquitin ligase for Geminin to sustain hematopoietic stem cell activity
复制标题
DOI：
10.1073/pnas.0800672105
复制
发表时间：
2008-07-29
影响因子：
11.1
通讯作者：
Takihara, Yoshihiro
中科院分区：
文献类型：
--
作者：
Ohtsubo, Motoaki;Yasunaga, Shin'ichiro;Takihara, Yoshihiro
多梳组（PcG）基因编码多聚核蛋白复合物，PcG复合物1和2。PcG复合物2被证明诱导转录抑制，并进一步甲基化组蛋白H3的赖氨酸-27（H3 K27）。随后，PcG复合物1通过识别甲基化的H3 K27被募集，并通过介导组蛋白H2 A在赖氨酸119处的单泛素化来维持转录沉默。遗传学证据表明PcG复合物1在干细胞中起着至关重要的作用，而PcG复合物1的成员Bmi 1被证明通过直接抑制编码细胞周期蛋白依赖性激酶抑制剂、p16 CKI和p19 ARF的INK 4a位点来维持成体干细胞。然而，PcG复合物1的分子功能仍然没有得到充分的理解。在我们的研究中，发现PcG复合物1的成员Rae 28的缺乏损害了泛素-蛋白酶体介导的DNA复制许可因子Cdt 1的抑制剂Geminin的降解，并增加了蛋白质的稳定性。根据逆转录病毒转导实验的证据，由此产生的Geminin积累可能消除了Rae 28缺陷小鼠的造血干细胞活性。Rae 28介导Scmh 1的募集，Scmh 1为Geminin提供PcG复合物1的相互作用域。此外，PcG复合物1作为Geminin的E3泛素连接酶，正如我们通过使用在昆虫细胞中重构的纯化的重组PcG复合物1在体内和体外证明的。我们的研究结果表明，PcG复合物1支持造血干细胞的活性，其中高水平的Geminin表达诱导静止，通过直接调节Geminin增强循环能力和造血活性，从而确保基因组稳定性。
Polycomb-group (PcG) genes encode multimeric nuclear protein complexes, PcG complex 1 and 2. PcG complex 2 was proved to induce transcription repression and to further methylate histone H3 at lysine-27 (H3K27). Subsequently PcG complex 1 is recruited through recognition of methylated H3K27 and maintains the transcription silencing by mediating monoubiquitination of histone H2A at lysine119. Genetic evidence demonstrated a crucial role for PcG complex 1 in stem cells, and Bmi1, a member of PcG complex 1, was shown to sustain adult stem cells through direct repression of the INK4a locus encoding cyclin-dependent kinase inhibitor, p16CKI, and p19ARF. The molecular functions of PcG complex 1, however, remain insufficiently understood. In our study, deficiency of Rae28, a member of PcG complex 1, was found to impair ubiquitin-proteasome-mediated degradation of Geminin, an inhibitor of DNA replication licensing factor Cdt1, and to increase protein stability. The resultant accumulation of Geminin, based on evidence from retroviral transduction experiments, presumably eliminated hematopoietic stem cell activity in Rae28-deficient mice. Rae28 mediates recruiting Scmh1, which provides PcG complex 1 an interaction domain for Geminin. Moreover, PcG complex 1 acts as the E3 ubiquitin ligase for Geminin, as we demonstrated in vivo as well as in vitro by using purified recombinant PcG complex 1 reconstituted in insect cells. Our findings suggest that PcG complex 1 supports the activity of hematopoietic stem cells, in which high-level Geminin expression induces quiescence securing genome stability, by enhancing cycling capability and hematopoietic activity through direct regulation of Geminin.