Department of Experimental Oncology, European Institute of Oncology, Milan, Italy.
Curr Biol. 2011 Mar 8;21(5):391-8. doi: 10.1016/j.cub.2010.12.039. Epub 2011 Feb 25.
Kinetochores are proteinaceous scaffolds implicated in the formation of load-bearing attachments of chromosomes to microtubules during mitosis. Kinetochores contain distinct chromatin- and microtubule-binding interfaces, generally defined as the inner and outer kinetochore, respectively (reviewed in). The constitutive centromere-associated network (CCAN) and the Knl1-Mis12-Ndc80 complexes (KMN) network are the main multisubunit protein assemblies in the inner and outer kinetochore, respectively. The point of contact between the CCAN and the KMN network is unknown. Cenp-C is a conserved CCAN component whose central and C-terminal regions have been implicated in chromatin binding and dimerization. Here, we show that a conserved motif in the N-terminal region of Cenp-C binds directly and with high affinity to the Mis12 complex. Expression in HeLa cells of the isolated N-terminal motif of Cenp-C prevents outer kinetochore assembly, causing chromosome missegregation. The KMN network is also responsible for kinetochore recruitment of the components of the spindle assembly checkpoint, and we observe checkpoint impairment in cells expressing the Cenp-C N-terminal segment. Our studies unveil a crucial and likely universal link between the inner and outer kinetochore.
着丝粒是一种蛋白支架，在有丝分裂过程中，它参与了染色体与微管之间的负载附着的形成。着丝粒包含不同的染色质和微管结合界面，通常分别定义为内着丝粒和外着丝粒（综述于）。着丝粒核心复合物（CCAN）和 Knl1-Mis12-Ndc80 复合物（KMN）网络分别是内着丝粒和外着丝粒的主要多亚基蛋白组装体。CCAN 和 KMN 网络之间的接触点尚不清楚。Cenp-C 是一个保守的 CCAN 组成部分，其中心和 C 末端区域被认为与染色质结合和二聚化有关。在这里，我们表明 Cenp-C 的 N 端区域中的一个保守基序可以直接与 Mis12 复合物结合，并具有高亲和力。在 HeLa 细胞中表达 Cenp-C 的分离 N 端基序会阻止外着丝粒的组装，导致染色体错误分离。KMN 网络还负责纺锤体组装检查点的着丝粒募集，我们观察到表达 Cenp-C N 端片段的细胞中的检查点受损。我们的研究揭示了内着丝粒和外着丝粒之间的一个关键的、可能普遍存在的联系。
