Cell Cycle Control and Carcinogenesis, F045, German Cancer Research Center, DKFZ, 69120 Heidelberg, Germany.
Faculty of Biosciences, Heidelberg University, 69120 Heidelberg, Germany.
J Cell Sci. 2018 May 21;131(10):jcs214544. doi: 10.1242/jcs.214544.
Correct spindle orientation is achieved through signaling pathways that provide a molecular link between the cell cortex and spindle microtubules in an F-actin-dependent manner. A conserved cortical protein complex, composed of LGN (also known as GPSM2), NuMA (also known as NUMA1) and dynein-dynactin, plays a key role in establishing proper spindle orientation. It has also been shown that the actin-binding protein MISP and the ERM family, which are activated by lymphocyte-oriented kinase (LOK, also known as STK10) and Ste20-like kinase (SLK) (hereafter, SLK/LOK) in mitosis, regulate spindle orientation. Here, we report that MISP functions downstream of the ERM family member ezrin and upstream of NuMA to allow optimal spindle positioning. We show that MISP directly interacts with ezrin and that SLK/LOK-activated ezrin ensures appropriate cortical MISP levels in mitosis by competing with MISP for actin-binding sites at the cell cortex. Furthermore, we found that regulation of the correct cortical MISP levels, by preventing its excessive accumulation, is essential for crescent-like polarized NuMA localization at the cortex and, as a consequence, leads to highly dynamic astral microtubules. Our results uncover how appropriate MISP levels at the cortex are required for proper NuMA polarization and, therefore, an optimal placement of the mitotic spindle within the cell.This article has an associated First Person interview with the first author of the paper.
正确的纺锤体取向是通过信号通路实现的，该通路以依赖于 F-肌动蛋白的方式在细胞皮层和纺锤体微管之间提供分子连接。一个保守的皮层蛋白复合物，由 LGN（也称为 GPSM2）、NuMA（也称为 NUMA1）和动力蛋白-动力蛋白复合物组成，在建立适当的纺锤体取向方面发挥着关键作用。已经表明，肌动蛋白结合蛋白 MISP 和 ERM 家族在有丝分裂中被淋巴细胞定向激酶（LOK，也称为 STK10）和 Ste20 样激酶（SLK）（以下简称 SLK/LOK）激活，调节纺锤体取向。在这里，我们报告 MISP 作为 ERM 家族成员 ezrin 的下游和 NuMA 的上游发挥作用，以允许最佳的纺锤体定位。我们表明 MISP 直接与 ezrin 相互作用，并且 SLK/LOK 激活的 ezrin 通过与肌动蛋白结合位点竞争确保有丝分裂中适当的皮层 MISP 水平，这些结合位点位于细胞皮层上。此外，我们发现通过防止其过度积累来调节正确的皮层 MISP 水平对于皮质新月形极化的 NuMA 定位至关重要，并且因此导致高度动态的星体微管。我们的研究结果揭示了皮层中适当的 MISP 水平对于正确的 NuMA 极化以及因此在细胞内最佳放置有丝分裂纺锤体的重要性。本文附有对该论文第一作者的第一人称采访。
