CYK-4 regulates Rac, but not Rho, during cytokinesis.
CYK-4 regulates Rac, but not Rho, during cytokinesis.
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DOI：
10.1091/mbc.e17-01-0020
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发表时间：
2017-05-01
影响因子：
3.3
通讯作者：
Canman JC
中科院分区：
文献类型：
--
作者：
Zhuravlev Y;Hirsch SM;Jordan SN;Dumont J;Shirasu-Hiza M;Canman JC
在秀丽隐杆线虫胚胎中研究了 Rho 家族 GAP CYK-4 和小 GTPase Rac 在胞质分裂过程中的作用。 CYK-4 在胞质分裂过程中对抗 Rac（以及潜在的 Cdc42）活性。没有证据表明 CYK-4 是 Rho 活性的上游，也没有证据表明 Rac 破坏是胞质分裂失败的一般抑制因子。细胞分裂是由 Rho 家族小 GTP 酶控制的肌动球蛋白收缩环的收缩驱动的。 Rho 由鸟嘌呤核苷酸交换因子 ECT-2 激活，位于肌球蛋白-II 激活和透明福明介导的丝状肌动蛋白 (f-肌动蛋白) 组装的上游，后者驱动环收缩。 Rac 及其调节剂的作用更具争议性，但是，基于当 GTP 酶激活蛋白 (GAP) CYK-4 被破坏时，Rac 失活可以挽救胞质分裂失败的发现，Rac 活性被认为可以抑制收缩环收缩，因此在分裂平面被 CYK-4 特异性失活。另一种模型提出，Rac 失活通常通过降低皮质张力来挽救胞质分裂失败，从而在环收缩受到损害时使细胞更容易分裂。在这个替代模型中，CYK-4 被提议通过结合 ECT-2 来激活 Rho。结合体内延时单细胞分析和秀丽隐杆线虫遗传学，我们的证据不支持这种替代模型。首先，我们发现 Rac 破坏通常不会挽救胞质分裂失败：抑制 Rac 可以特异性挽救由于 CYK-4 或 ECT-2 破坏而导致的胞质分裂失败，但不能挽救由于其他两个收缩环成分（Rho 效应器透明福明和肌球蛋白-II）破坏而导致的胞质分裂失败。其次，如果 CYK-4 通过 Rho 而不是 Rac 调节胞质分裂，那么 CYK-4 抑制应该会降低 Rho 下游靶标的水平。与此不一致的是，当 CYK-4 GAP 活性降低时，我们发现分割平面的 f-肌动蛋白或肌球蛋白-II 水平没有变化，这表明 CYK-4 不是 ECT-2/Rho 激活的上游。相反，我们发现通过 Rac 失活来拯救 CYK-4 突变体中的胞质分裂是 Cdc42 依赖性的。我们的数据表明，CYK-4 GAP 活性在胞质分裂过程中对抗 Rac（或许还有 Cdc42）。
The roles of the Rho-family GAP CYK-4 and small GTPase Rac during cytokinesis are examined in Caenorhabditis elegans embryos. CYK-4 opposes Rac (and potentially Cdc42) activity during cytokinesis. There is no evidence that CYK-4 is upstream of Rho activity or that Rac disruption is a general suppressor of cytokinesis failure. Cytokinesis is driven by constriction of an actomyosin contractile ring that is controlled by Rho-family small GTPases. Rho, activated by the guanine-nucleotide exchange factor ECT-2, is upstream of both myosin-II activation and diaphanous formin-mediated filamentous actin (f-actin) assembly, which drive ring constriction. The role for Rac and its regulators is more controversial, but, based on the finding that Rac inactivation can rescue cytokinesis failure when the GTPase-activating protein (GAP) CYK-4 is disrupted, Rac activity was proposed to be inhibitory to contractile ring constriction and thus specifically inactivated by CYK-4 at the division plane. An alternative model proposes that Rac inactivation generally rescues cytokinesis failure by reducing cortical tension, thus making it easier for the cell to divide when ring constriction is compromised. In this alternative model, CYK-4 was instead proposed to activate Rho by binding ECT-2. Using a combination of time-lapse in vivo single-cell analysis and Caenorhabditis elegans genetics, our evidence does not support this alternative model. First, we found that Rac disruption does not generally rescue cytokinesis failure: inhibition of Rac specifically rescues cytokinesis failure due to disruption of CYK-4 or ECT-2 but does not rescue cytokinesis failure due to disruption of two other contractile ring components, the Rho effectors diaphanous formin and myosin-II. Second, if CYK-4 regulates cytokinesis through Rho rather than Rac, then CYK-4 inhibition should decrease levels of downstream targets of Rho. Inconsistent with this, we found no change in the levels of f-actin or myosin-II at the division plane when CYK-4 GAP activity was reduced, suggesting that CYK-4 is not upstream of ECT-2/Rho activation. Instead, we found that the rescue of cytokinesis in CYK-4 mutants by Rac inactivation was Cdc42 dependent. Together our data suggest that CYK-4 GAP activity opposes Rac (and perhaps Cdc42) during cytokinesis.