Rapid Activation of Ras by Fluid Flow Is Mediated by Gα q and Gβγ Subunits of Heterotrimeric G Proteins in Human Endothelial Cells

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Abstract
Objective— Temporal gradients in fluid shear stress have been shown to induce a proatherogenic phenotype in endothelial cells. The biomechanical mechanism(s) that enables the endothelium to respond to fluid shear stress requires rapid activation and signal transduction. The small G protein Ras has been identified as an early link between rapid mechanotransduction events and the effects of shear stress on downstream signal-transduction cascades. The aim of this study was to elucidate the upstream mechanotransduction signaling events mediating the rapid activation of Ras by fluid shear stress in human endothelial cells. Methods and Results— Direct measurement of Ras-bound GTP and GDP showed that fluid-flow activation of Ras was rapid (10-fold within 5 seconds) and dose dependent on shear stress magnitude. Treatment with protein tyrosine kinase inhibitors or pertussis toxin did not significantly affect flow-induced Ras activation. However, activation was inhibited by transient transfection with antisense to Gαq or the Gβγ scavenger β-adrenergic receptor kinase carboxy terminus. Transfection with several Gβγ subunit isoforms revealed flow-induced Ras activation was most effectively enhanced by Gβ1γ2. Conclusions— These results suggest that the rapid, shear-induced activation of Ras is mediated by Gαq through the activity of Gβγ subunits in human vascular endothelial cells.