The RhoGAP Domain of CYK-4 Has an Essential Role in RhoA Activation

Abstract

Cytokinesis in animal cells is mediated by a cortical actomyosinbased contractile ring. The GTPase RhoA is a critical regulator of this process as it activates both non-muscle 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.

Progressive loss of RacGAP1/ ogre activity has sequential effects on cytokinesis and zebrafish development

“…2B and C) that occurs within the predicted atypical C1 domain and before the catalytic GAP domain (Fig. 2D), domains that are highly critical for cytokinesis (Basant et al, 2015;Bastos et al, 2012;Canman et al, 2008;Lekomtsev et al, 2012;Loria et al, 2012). In situ analysis showed that zebrafish racgap1 mRNA is expressed maternally (Fig.…”

“…If translated, mutant mRNAs would produce a shorter protein having a truncated atypical C1 domain and no catalytic GAP domain-each highly critical for cytokinesis (Basant et al, 2015;Bastos et al, 2012;Canman et al, 2008;Lekomtsev et al, 2012;Loria et al, 2012). However, in situ analysis shows that racgap1 transcripts are present in lesser amounts in mutant embryos and eventually lost in keeping with these mRNAs being targeted for degradation through the process of nonsense-mediated mRNA decay (reviewed in: Chang et al, 2007).…”

Molecular control of animal cell cytokinesis

“…Alternatively, CYK-4 GAP may activate RhoA by positive regulation of ECT-2 (ref. 59). It is controversial whether the GAP domain of CYK-4 also regulates another small GTPase, Rac (refs 59,60).…”

MgcRacGAP inhibition stimulates JAK‐dependent STAT3 activity

“…During the contractile ring constriction, centralspindlin inactivates Rac1 and in parallel, RhoA is activated in the equatorial region to initiate and progress through furrow formation [6,7]. Without the components of centralspindlin (MgcRacGAP/MKLP1) or Ect2, cleavage furrow ingression will not complete [2,4,5,[8][9][10]. Thus, the centralspindlin complex is crucial for initiation and completion of cytokinesis.…”