Effect of siRNA-mediated depletion of Gα12, Gα13, and Gαq on constitutive vs thrombin-induced vWF release from HUVECs. (A) Western blot analysis shows specific and complete downregulation of Gα12, Gα13, and Gαq. (B) In Gα12-deficient HUVECs, both constitutive and thrombin-induced vWF release was inhibited. Gα13 depletion had no effect on basal or thrombin-induced vWF release. In Gαq-deficient HUVECs, thrombin-induced vWF secretion was reduced by 40%, whereas basal vWF secretion was not affected. (C) Western blots show siRNA-mediated downregulation of α-SNAP, p115 RhoGEF, and RhoA. (D) α-SNAP siRNA completely blocked constitutive and thrombin-induced vWF release by HUVECs. Depletion of p115 RhoGEF and RhoA had no effect on constitutive vWF secretion, although both reduced thrombin-induced vWF secretion. Data are mean ± SEM; n = 3. *P < .05 vs respective (basal or thrombin-treated) control siRNA values.