Rnd proteins function as RhoA antagonists by activating p190 RhoGAP.
BACKGROUND
The Rnd proteins Rnd1, Rnd2, and Rnd3 (RhoE) comprise a unique branch of Rho-family G-proteins that lack intrinsic GTPase activity and consequently remain constitutively "active." Prior studies have suggested that Rnd proteins play pivotal roles in cell regulation by counteracting the biological functions of the RhoA GTPase, but the molecular basis for this antagonism is unknown. Possible mechanisms by which Rnd proteins could function as RhoA antagonists include sequestration of RhoA effector molecules, inhibition of guanine nucleotide exchange factors, and activation of GTPase-activating proteins (GAPs) for RhoA. However, effector molecules of Rnd proteins with such properties have not been identified.


RESULTS
Here we identify p190 RhoGAP (p190), the most abundant GAP for RhoA in cells, as an interactor with Rnd proteins and show that this interaction is mediated by a p190 region that is distinct from the GAP domain. Using Rnd3-RhoA chimeras and Rnd3 mutants defective in p190 binding, as well as p190-deficient cells, we demonstrate that the cellular effects of Rnd expression are mediated by p190. We moreover show that Rnd proteins increase the GAP activity of p190 toward GTP bound RhoA and, finally, demonstrate that expression of Rnd3 leads to reduced cellular levels of RhoA-GTP by a p190-dependent mechanism.


CONCLUSIONS
Our results identify p190 RhoGAPs as effectors of Rnd proteins and demonstrate a novel mechanism by which Rnd proteins function as antagonists of RhoA.
Wennerberg
Krister
K
Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Forget
Marie-Annick
MA
Ellerbroek
Shawn M
SM
Arthur
William T
WT
Burridge
Keith
K
Settleman
Jeffrey
J
Der
Channing J
CJ
Hansen
Steen H
SH
D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D015870:Gene Expression; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000378:metabolism*; D011233:Precipitin Tests; D012097:Repressor Proteins; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism
C513041:Arhgap35 protein, mouse; C513042:Arhgap5 protein, mouse; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; D012097:Repressor Proteins; C085379:rho GTPase-activating protein; C513341:Rnd3 protein, mouse; C508705:RND3 protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein