Abstract 884: The Rho Protein Exchange Factor Vav3 Regulates Arterial Smooth Muscle Cell Proliferation
Rho exchange factors (Rho-GEFs) are signaling molecules responsible for Rho protein activation by catalyzing the exchange of GDP for GTP. Although over-activation of RhoA is recognized as a common component for the pathogenesis of hypertension and vascular proliferative disorders, the molecular mechanisms and the Rho-GEFs regulating RhoA activity in vascular smooth muscle cells are still unknown. By developing a functional screening using siRNA-mediated RhoA-GEFs silencing, our aim was to identify RhoA-GEFs responsible for RhoA-mediated functions in vascular smooth muscle cells from rat aorta. We have identified 29 rat RhoA-GEFs in databases and designed specific siRNA for each of them. Efficiency of siRNA-mediated RhoA GEFs silencing has been assessed by real-time RT-PCR. All but one of the 29 RhoA-GEFs mRNA were expressed in vascular smooth muscle cells, and mRNA level of each RhoA-GEFs was selectively reduced by more than 50% by transfection of siRNA duplex (48 h). However, only siRNA targeting the Vav3 Rho-GEF inhibited serum (10%)-induced vascular smooth muscle cell proliferation. Three independent Vav3-siRNA duplexes reduced serum-induced proliferation by 71±1%, 72±3% and 67±3%, respectively (n=3; p<0.01 vs scrambled siRNA). siRNA-mediated Vav3 gene silencing also inhibited, in a similar extent, the proliferation induced by angiotensin II (100 nM) or insulin growth factor 1 (100 ng/ml). To further analyze the role of Vav3, we have next transfected vascular smooth muscle cells with wild-type Vav3 or inactive Vav3 mutant (Y173F-Vav3). Over-expression of wild-type Vav3 but not Y173F-Vav3 potentiated serum-induced proliferation (154±5%, n=3; p<0.01 vs control). Similar effects were observed on angiotensin II- and insulin growth factor 1-induced proliferation. Our study thus demonstrates for the first time that the Rho-GEF Vav3 is a common point in intracellular signaling responsible for vascular smooth muscle cell proliferation and suggests possible role of Vav3 in the development of vascular wall remodeling associated with arterial diseases.