A novel Rho GTPase-activating-protein interacts with Gem, a member of the Ras superfamily of GTPases

Abstract

Gem is a Ras-related protein whose expression is induced in several cell types upon activation by extracellular stimuli. With the aim of isolating the cellular partners of Gem that mediate its biological activity we performed a yeast two-hybrid screen and identified a novel protein of 970 amino acids, Gmip, that interacts with Gem through its N-terminal half, and presents a cysteine-rich domain followed by a Rho GTPase-activating protein (RhoGAP) domain in its C-terminal half. The RhoGAP domain of Gmip stimulates in vitro the GTPase activity of RhoA, but is inactive towards other Rho family proteins such as Rac1 and Cdc42; it is also specific for RhoA in vivo. The same is true for the full-length protein, which is furthermore able to down-regulate RhoA-dependent stress fibres in Ref-52 rat fibroblasts. These findings suggest that the signalling pathways controlled by two proteins of the Ras superfamily, RhoA and Gem, are linked via the action of the RhoGAP protein Gmip (Gem-interacting protein).

Speed control for neuronal migration in the postnatal brain by Gmip-mediated local inactivation of RhoA

“…Next, we studied the role of a downstream component of Gmip signalling. Gmip has a Rho-GAP activity 28 and regulates cell morphology in cultured fibroblasts by deactivating RhoA. Although several studies suggested that RhoA is crucial for neuronal migration in the embryonic cerebral cortex [31][32][33][34][35] , neither the spatio-temporal activation pattern of RhoA signalling in the migrating OB neurons nor its regulatory mechanisms has been demonstrated.…”

“…In this study, we focused on one of the signal-transduction proteins, Gmip (Gem-interacting protein; Supplementary Fig. 1a), a Rho-GAP 28,29 .…”

“…We identified Gem-interacting protein (Gmip), a RhoA-specific GAP (Rho-GAP) 28,29 , in a proteomics screen for proteins interacting with Girdin (Girders of actin), an actin-binding protein essential for neuronal migration to the OB 30 . We demonstrate that RhoA is activated at the proximal leading process, where Gmip is also localized and negatively controls RhoA.…”

The RGK family of GTP-binding proteins: Regulators of voltage-dependent calcium channels and cytoskeleton remodeling

“…In addition to directly inhibiting ROK activity, recent yeast-two hybrid studies have identified a second Gem-mediated cytoskeletal regulatory cascade [60] which involves both the novel Gem-interacting protein Gmip [66] and the membrane cytoskeletal linker protein Ezrin [60] (Fig. 2).…”

“…2). GTP-bound Gem binds to active Ezrin at the plasma membrane-cytoskeleton interface, and this complex appears to be required for both the recruitment and activation of Gmip, which functions as a RhoGAP [66]. The recruitment of Gmip to the cell surface leads to the localized inactivation of Rho signaling [60].…”