The MOE Key Laboratory of Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China.
School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
J Cell Sci. 2019 Sep 23;132(18):jcs232314. doi: 10.1242/jcs.232314.
Importin-α serves as an adaptor linking importin-β to proteins carrying a nuclear localization sequence (NLS). During interphase, this interaction enables nuclear protein import, while in mitosis it regulates spindle assembly factors (SAFs) and controls microtubule nucleation, stabilization and spindle function. Here, we show that human importin-α1 is regulated during the cell cycle and is phosphorylated at two sites (threonine 9 and serine 62) during mitosis by the major mitotic protein kinase CDK1-cyclin B. Mutational analysis indicates that the mitotic phosphorylation of importin-α1 inhibits its binding to importin-β and promotes the release of TPX2 and KIFC1, which are then targeted like importin-β to the spindle. Loss of importin-α1 or expression of a non-phosphorylated mutant of importin-α1 results in the formation of shortened spindles with reduced microtubule density and induces a prolonged metaphase, whereas phosphorylation-mimicking mutants are functional in mitosis. We propose that phosphorylation of importin-α1 is a general mechanism for the spatial and temporal control of mitotic spindle assembly by CDK1-cyclin B1 that acts through the release of SAFs such as TPX2 and KIFC1 from inhibitory complexes that restrict spindle assembly.
输入蛋白-α作为衔接蛋白，将输入蛋白-β与携带核定位序列（NLS）的蛋白质连接起来。在有丝分裂间期，这种相互作用使核蛋白能够进入细胞核，而在有丝分裂过程中，它调节纺锤体组装因子（SAFs）并控制微管的成核、稳定和纺锤体功能。在这里，我们表明，人输入蛋白-α 1 在细胞周期中受到调节，并在有丝分裂过程中被主要的有丝分裂蛋白激酶 CDK1-细胞周期蛋白 B 磷酸化两个位点（苏氨酸 9 和丝氨酸 62）。突变分析表明，输入蛋白-α 1 的有丝分裂磷酸化抑制其与输入蛋白-β的结合，并促进 TPX2 和 KIFC1 的释放，然后像输入蛋白-β一样被靶向到纺锤体。输入蛋白-α 1 的缺失或表达非磷酸化突变的输入蛋白-α 1 导致形成缩短的纺锤体，微管密度降低，并诱导中期延长，而磷酸化模拟突变体在有丝分裂中是有功能的。我们提出，输入蛋白-α 1 的磷酸化是 CDK1-细胞周期蛋白 B1 通过释放抑制纺锤体组装的 SAFs（如 TPX2 和 KIFC1）来控制有丝分裂纺锤体组装的时空调节的一种普遍机制。
