VEGF-induced Rac1 activation in endothelial cells is regulated by the guanine nucleotide exchange factor Vav2

Abstract

Vascular endothelial growth factor (VEGF) signaling is critical for both normal and diseaseassociated vascular development. Dysregulated VEGF signaling has been implicated in ischemic stroke, tumor angiogenesis, and many other vascular diseases. VEGF signals through several effectors, including the Rho family of small GTPases. As a member of this family, Rac1 promotes VEGF-induced endothelial cell migration by stimulating the formation of lamellipodia and membrane ruffles. To form these membrane protrusions, Rac1 is activated by guanine nucleotide exchange factors (GEFs) that catalyze the exchange of GDP for GTP. The goal of this study was to identify the GEF responsible for activating Rac1 in response to VEGF stimulation. We have found that VEGF stimulates biphasic activation of Rac1 and for these studies we focused on the peak of activation that occurs at 30 min. Inhibition of VEGFR-2 signaling blocks VEGF-induced Rac1 activation. Using a Rac1 nucleotide-free mutant (G15ARac1), which has a high affinity for binding activated GEFs, we show that the Rac GEF Vav2 associates with G15ARac1 after VEGF stimulation. Additionally, we show that depleting endothelial cells of endogenous Vav2 with siRNA prevents VEGF-induced Rac1 activation. Moreover, Vav2 is tyrosine phosphorylated upon VEGF treatment, which temporally correlates with Rac1 activation and requires VEGFR-2 signaling and Src kinase activity. Finally, we show that depressing Vav2 expression by siRNA impairs VEGF-induced endothelial cell migration. Taken together, our results provide evidence that Vav2 acts downstream of VEGF to activate Rac1.

Robo4 stabilizes the vascular network by inhibiting pathologic angiogenesis and endothelial hyperpermeability

“…2f). Recently, several reports have shown that Src-dependent activation of the Rho family small GTPase Rac1 is essential for VEGF-165-induced endothelial cell migration and permeability 18,19 . Treatment of endothelial cell mono-layers with Slit2 prevented VEGF-165-dependent Rac1 activation (Fig.…”

Filamin B Plays a Key Role in Vascular Endothelial Growth Factor-induced Endothelial Cell Motility through Its Interaction with Rac-1 and Vav-2

“…Thus, filamin B plays a key role in the control of Rac-1-PAK signaling necessary for the cycles of attachment and detachment that take place during cell migration. Our results suggest that filamin B exerts this role by acting as a scaffolding protein, facilitating the interaction of Rac-1 and the guanine nucleotide exchange factor Vav-2, which controls Rac-1 stimulation in endothelial cells (39). Filamin B is bound to Vav-2 and Rac-1 in basal conditions, ensuring the proper interaction of these proteins with VEGFR2 and proangiogenic integrins after VEGF stimulation and their subsequent activation.…”

The Bipartite Rac1 Guanine Nucleotide Exchange Factor Engulfment and Cell Motility 1/Dedicator of Cytokinesis 180 (Elmo1/Dock180) Protects Endothelial Cells from Apoptosis in Blood Vessel Development

“…Activation of Rac1 is also known to be required for endothelial migration in response to VEGF. This activation is mediated by the VEFG receptor type 2 and the GEF Vav2 (65). Elmo1/ Dock180 is apparently not contributing to VEGF-induced Rac1 activation as gain-of-function and loss-of-function for Elmo1 and Dock180 in ECs did not alter the VEGF-dependent sprouting response.…”