Department of Biochemistry, University of Oxford, Oxford OX1 3QU, England, UK.
J Cell Biol. 2012 Sep 3;198(5):865-80. doi: 10.1083/jcb.201204107.
In mitosis, animal cells lose their adhesion to the surrounding surfaces and become rounded. During mitotic exit, they reestablish these adhesions and at the same time physically contract and divide. How these competing processes are spatially segregated at the cell cortex remains mysterious. To address this question, we define the specific effector pathways used by RhoA and Rac1 in mitotic cells. We demonstrate that the MKlp1-CYK4 centralspindlin complex is a guanosine triphosphatase-activating protein (GAP) for Rac1 and not RhoA and that CYK4 negatively regulated Rac1 activity at the cell equator in anaphase. Cells expressing a CYK4 GAP mutant had defects in cytokinesis and showed elevated staining for the cell adhesion marker vinculin. These defects could be rescued by depletion of ARHGEF7 and p21-activated kinase, Rac1-specific effector proteins required for cell adhesion. Based on these findings, we propose that CYK4 GAP activity is required during anaphase to inhibit Rac1-dependent effector pathways associated with control of cell spreading and adhesion.
在有丝分裂过程中，动物细胞会失去与周围表面的黏附力，变成圆形。在有丝分裂后期，它们重新建立这些黏附力，同时物理性地收缩和分裂。这些相互竞争的过程如何在细胞皮层上进行空间分隔仍然是个谜。为了解决这个问题，我们定义了 RhoA 和 Rac1 在有丝分裂细胞中使用的特定效应途径。我们证明，MKlp1-CYK4 中心体纺锤体复合物是 Rac1 的鸟嘌呤三磷酸酶激活蛋白 (GAP)，而不是 RhoA，并且在后期细胞赤道处，CYK4 负调控 Rac1 的活性。表达 CYK4 GAP 突变体的细胞在胞质分裂过程中出现缺陷，并显示出细胞黏附标记物 vinculin 的染色升高。这些缺陷可以通过 ARHGEF7 和 p21 激活激酶的耗竭得到挽救，这两种蛋白是细胞黏附所必需的 Rac1 特异性效应蛋白。基于这些发现，我们提出 CYK4 GAP 活性在后期需要抑制 Rac1 依赖性效应途径，这些途径与控制细胞铺展和黏附有关。
