rho family GTPase activating proteins p190, bcr and rhoGAP show distinct specificities in vitro and in vivo.

Abstract

to rac-dependent actin polymerization at the plasma membrane, and membrane ruffling. The product of the breakpoint cluster region gene bcr, rho GTPase accelerating protein (rhoGAP) and rasGAP-associated p190 share structurally related rho GAP domains, and possess GAP activity for rho family members in vitro. We have directly compared the activities of the isolated GAP domains of these three proteins in regulating different rho family GTPases, both by in vitro assays and by microinjection, to address their possible physiologic functions. We show that bcr accelerates the GTPase activity of rac, but not rho in vitro, and inhibits rac-mediated membrane ruffling, but not rho-mediated stress fibre formation, after microinjection into Swiss 3T3 fibroblasts. In vitro, rhoGAP has a striking preference for G25K as a substrate, whilst p190GAP has marked preferential activity for rho. Furthernore, p190 preferentially inhibits rho-mediated stress fibre formation in vivo. Our data suggest that p190, rhoGAP and bcr play distinct roles in signalling pathways mediated through different rho family GTPases.

Mechanism of activation of Pak1 kinase by membrane localization

“…We utilized three GAP proteins in this study: Bcr, RhoGAP, and 3BP-1. Bcr contains a domain with strong GAP activity towards Cdc42 and Rac1, but not RhoA (Diekmann et al, 1991;Ridley et al, 1993). 3BP-1, a GAP protein that binds the SH3 domain of Abl, has the same speci®city as Bcr except that the GAP activity is relatively less potent (Cicchetti et al, 1995).…”

Effect of Bcr sequences on the cellular function of the Bcr-Abl oncoprotein

“…DBL: region of homology to the DBL proto-oncogene which encodes a guanine nucleotide exchange factor for the Rho GTPase (Cerione and Zheng, 1996). RAC-GAP: domain with GTPase-activating activity for the p21 rac GTPase (Ridley et al, 1993). The c-Abl domains are: V: variable ®rst exon domain.…”

“…This Dblhomology domain of Bcr is present in p210 Bcr-Abl , but not in p190 Bcr-Abl (Daley and Ben-Neriah, 1991). Second, the C-terminal region of Bcr contains an GTPase-activating protein function for the small GTPase Rac (Ridley et al, 1993). Activation of Rac stimulates membrane ru ing and pinocytosis , thus, the Rac-GAP function of Bcr may play a role in the downregulation of membrane ru ing and pinocytosis.…”

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: A perspective

“…It is presently not clear how MAPK regulates Rho and ROCK activities downstream of FAK, although logical targets would include the GEFs and GAPs that set GTP loading of Rho. Integrin engagement activates p190RhoGAP, a negative regulator of Rho [105], through the tyrosine kinases Src [106][107][108][109][110], FAK [111] and Arg [112,113]. p190RhoGAP localizes to structures relatively poor in stress fibers [108] and arc-like structures in EGF stimulated cells with concomitant reduction in actin stress fibers [114], suggesting a functional link between the RhoGAP and actin dynamics during cell spreading and growth factor signaling [114,115].…”