Institut de Recherches Cliniques de Montréal, 110 Avenue des Pins Ouest, Montréal, PQ H2W 1R7, Canada.
Curr Biol. 2010 Nov 23;20(22):2021-7. doi: 10.1016/j.cub.2010.10.028. Epub 2010 Oct 28.
Dedicator of cytokinesis (DOCK) proteins are guanine nucleotide exchange factors (GEFs) controlling the activity of Rac1/Cdc42 during migration, phagocytosis, and myoblast fusion [1-4]. Engulfment and cell motility (ELMO) proteins bind a subset of DOCK members and are emerging as critical regulators of Rac signaling [5-10]. Although formation of a DOCK180/ELMO complex is not essential for Rac1 activation, ELMO mutants deficient in binding to DOCK180 are unable to promote cytoskeleton remodeling [11]. How ELMO regulates signaling through DOCK GEFs is poorly understood. Here, we identify an autoinhibitory switch in ELMO presenting homology to a regulatory unit described for Dia formins. One part of the switch, composed of a Ras-binding domain (RBD) and Armadillo repeats, is positioned N-terminally while the other is housed in the C terminus. We demonstrate interaction between these fragments, suggesting autoinhibition of ELMO. Using a bioluminescence resonance energy transfer biosensor, we establish that ELMO undergoes conformational changes upon disruption of autoinhibition. We found that engagement of ELMO to RhoG, or with DOCK180, promotes the relief of autoinhibition in ELMO. Functionally, we found that ELMO mutants with impaired autoregulatory activity promote cell elongation. These results demonstrate an unsuspected level of regulation for Rac1 signaling via autoinhibition of ELMO.
细胞分裂蛋白（DOCK）是鸟嘌呤核苷酸交换因子（GEF），在迁移、吞噬和肌母细胞融合过程中控制 Rac1/Cdc42 的活性[1-4]。吞噬和细胞运动（ELMO）蛋白结合了一组 DOCK 成员，并且作为 Rac 信号的关键调节剂而出现[5-10]。尽管 DOCK180/ELMO 复合物的形成对于 Rac1 的激活不是必需的，但不能与 DOCK180 结合的 ELMO 突变体不能促进细胞骨架重塑[11]。ELMO 如何通过 DOCK GEF 调节信号尚不清楚。在这里，我们鉴定出 ELMO 中的一个自动抑制开关，与 Dia formin 描述的调控单元具有同源性。开关的一部分由 Ras 结合域（RBD）和 Armadillo 重复组成，位于 N 端，而另一部分位于 C 端。我们证明了这些片段之间的相互作用，表明 ELMO 存在自动抑制。使用生物发光共振能量转移生物传感器，我们确定 ELMO 在自动抑制被破坏时会发生构象变化。我们发现，ELMO 与 RhoG 的结合，或与 DOCK180 的结合，促进了 ELMO 自动抑制的解除。在功能上，我们发现具有受损自身调节活性的 ELMO 突变体促进细胞伸长。这些结果表明 Rac1 信号通过 ELMO 的自动抑制存在未被察觉的调节水平。
