Programme in Molecular and Cellular Biology, Faculty of Medicine, Université Laval, 1050 Avenue de la Médecine, Bureau 4633, Université Laval, Québec, QC G1V0A6, Canada; Axe of Reproduction, Mother and Youth Health, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Québec, QC G1V 4G2, Canada.
Wellcome Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, UK.
Curr Biol. 2018 Mar 19;28(6):872-883.e5. doi: 10.1016/j.cub.2018.02.002. Epub 2018 Mar 1.
Monopolar spindle 1 (Mps1) is a conserved apical kinase in the spindle assembly checkpoint (SAC) that ensures accurate segregation of chromosomes during mitosis. Mps1 undergoes extensive auto- and transphosphorylation, but the regulatory and functional consequences of these modifications remain unclear. Recent findings highlight the importance of intermolecular interactions between the N-terminal extension (NTE) of Mps1 and the Hec1 subunit of the NDC80 complex, which control Mps1 localization at kinetochores and activation of the SAC. Whether the NTE regulates other mitotic functions of Mps1 remains unknown. Here, we report that phosphorylation within the NTE contributes to Mps1 activation through relief of catalytic autoinhibition that is mediated by the NTE itself. Moreover, we find that this regulatory NTE function is independent of its role in Mps1 kinetochore recruitment. We demonstrate that the NTE autoinhibitory mechanism impinges most strongly on Mps1-dependent SAC functions and propose that Mps1 activation likely occurs sequentially through dimerization of a "prone-to-autophosphorylate" Mps1 conformer followed by autophosphorylation of the NTE prior to maximal kinase activation segment trans-autophosphorylation. Our observations underline the importance of autoregulated Mps1 activity in generation and maintenance of a robust SAC in human cells.
单体纺锤体 1（Mps1）是纺锤体组装检查点（SAC）中保守的顶端激酶，可确保有丝分裂过程中染色体的准确分离。Mps1 经历广泛的自身和转磷酸化，但这些修饰的调节和功能后果仍不清楚。最近的发现强调了 Mps1 的 N 端延伸（NTE）与 NDC80 复合物的 Hec1 亚基之间的分子间相互作用的重要性，这种相互作用控制着 Mps1 在着丝粒处的定位和 SAC 的激活。NTE 是否调节 Mps1 的其他有丝分裂功能尚不清楚。在这里，我们报告说，NTE 内的磷酸化有助于 Mps1 的激活，其通过自身的 NTE 介导的催化自身抑制的缓解来实现。此外，我们发现这种调节性 NTE 功能与其在 Mps1 着丝粒招募中的作用无关。我们证明了 NTE 自身抑制机制对 Mps1 依赖性 SAC 功能的影响最大，并提出 Mps1 激活可能通过“易于自动磷酸化”的 Mps1 构象的二聚化，然后在最大激酶激活片段的转自磷酸化之前进行自动磷酸化，从而依次发生。我们的观察结果强调了在人类细胞中产生和维持强大的 SAC 时，自动调节的 Mps1 活性的重要性。
