Cell Cycle Control and Carcinogenesis, F045, German Cancer Research Center, DKFZ, 69120, Heidelberg, Germany.
Heidelberg University, Heidelberg, Germany.
Sci Rep. 2018 Apr 20;8(1):6330. doi: 10.1038/s41598-018-24682-8.
Precise mitotic spindle orientation is essential for both cell fate and tissue organization while defects in this process are associated with tumorigenesis and other diseases. In most animal cell types, the dynein motor complex is anchored at the cell cortex and exerts pulling forces on astral microtubules to position the spindle. The actin-binding protein MISP controls spindle orientation and mitotic progression in human cells. However, the exact underlying mechanism remains to be elucidated. Here we report that MISP interacts with the multidomain scaffolding protein IQGAP1. We further show that MISP binds to the active form of Cdc42 through IQGAP1. Depletion of MISP promotes increased accumulation of IQGAP1 at the cell cortex and a decrease in its Cdc42-binding capacity leading to reduced active Cdc42 levels. Interestingly, overexpression of IQGAP1 can rescue mitotic defects caused by MISP downregulation including spindle misorientation, loss of astral microtubules and prolonged mitosis and also restores active Cdc42 levels. Importantly, we find that IQGAP1 acts downsteam of MISP in regulating astral microtubule dynamics and the localization of the dynactin subunit p150 that is crucial for proper spindle positioning. We propose that MISP regulates IQGAP1 and Cdc42 to ensure proper mitotic progression and correct spindle orientation.
精确的有丝分裂纺锤体定向对于细胞命运和组织组织至关重要，而该过程的缺陷与肿瘤发生和其他疾病有关。在大多数动物细胞类型中，动力蛋白复合物锚定在细胞皮层上，并对星体微管施加拉力，以定位纺锤体。肌动蛋白结合蛋白 MISP 控制人类细胞的纺锤体定向和有丝分裂进程。然而，确切的潜在机制仍有待阐明。在这里，我们报告 MISP 与多域支架蛋白 IQGAP1 相互作用。我们进一步表明，MISP 通过 IQGAP1 与 Cdc42 的活性形式结合。MISP 的耗竭会促进 IQGAP1 在细胞皮层上的积累增加，并且其与 Cdc42 的结合能力降低，导致活性 Cdc42 水平降低。有趣的是，IQGAP1 的过表达可以挽救由 MISP 下调引起的有丝分裂缺陷，包括纺锤体定向错误、星体微管丢失和有丝分裂延长，并且还可以恢复活性 Cdc42 水平。重要的是，我们发现 IQGAP1 在调节星体微管动力学和动力蛋白亚单位 p150 的定位方面，p150 对于正确的纺锤体定位至关重要，它是 MISP 下游调节的。我们提出 MISP 调节 IQGAP1 和 Cdc42 以确保有丝分裂进程的正常进行和纺锤体定向的正确性。
