Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Curr Biol. 2012 Feb 7;22(3):213-9. doi: 10.1016/j.cub.2011.12.019. Epub 2012 Jan 5.
Cytokinesis in animal cells is mediated by a cortical actomyosin-based contractile ring. The GTPase RhoA is a critical regulator of this process as it activates both nonmuscle myosin and a nucleator of actin filaments [1]. The site at which active RhoA and its effectors accumulate is controlled by the microtubule-based spindle during anaphase [2]. ECT-2, the guanine nucleotide exchange factor (GEF) that activates RhoA during cytokinesis, is regulated by phosphorylation and subcellular localization [3-5]. ECT2 localization depends on interactions with CYK-4/MgcRacGAP, a Rho GTPase-activating protein (GAP) domain containing protein [5, 6]. Here we show that, contrary to expectations, the Rho GTPase-activating protein (GAP) domain of CYK-4 promotes activation of RhoA during cytokinesis. Furthermore, we show that the primary phenotype caused by mutations in the GAP domain of CYK-4 is not caused by ectopic activation of CED-10/Rac1 and ARX-2/Arp2. However, inhibition of CED-10/Rac1 and ARX-2/Arp2 facilitates ingression of weak cleavage furrows. These results demonstrate that a GAP domain can contribute to activation of a small GTPase. Furthermore, cleavage furrow ingression is sensitive to the balance of contractile forces and cortical tension.
动物细胞的胞质分裂是由皮质肌动球蛋白收缩环介导的。GTP 酶 RhoA 是该过程的关键调节因子，因为它激活非肌肉肌球蛋白和肌动蛋白丝的核化因子 [1]。有活性的 RhoA 和其效应物积累的部位受纺锤体的微管控制，纺锤体在后期 [2] 起作用。ECT-2 是胞质分裂过程中激活 RhoA 的鸟嘌呤核苷酸交换因子 (GEF)，受磷酸化和亚细胞定位调控 [3-5]。ECT2 的定位取决于与 CYK-4/MgcRacGAP 的相互作用，后者是一种含有 Rho GTPase 激活蛋白 (GAP) 结构域的蛋白 [5,6]。在这里，我们表明，与预期相反，CYK-4 的 Rho GTPase 激活蛋白 (GAP) 结构域促进了胞质分裂过程中 RhoA 的激活。此外，我们还表明，CYK-4 的 GAP 结构域突变引起的主要表型不是由 CED-10/Rac1 和 ARX-2/Arp2 的异位激活引起的。然而，抑制 CED-10/Rac1 和 ARX-2/Arp2 促进了弱分裂沟的入侵。这些结果表明，GAP 结构域可以促进小 GTPase 的激活。此外，分裂沟的入侵对收缩力和皮质张力的平衡敏感。
