Heterotrimeric Gα_q/Gα₁₁ proteins function upstream of vascular endothelial growth factor (VEGF) receptor-2 (KDR) phosphorylation in vascular permeability factor/VEGF signaling

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) functions by activating two receptor-tyrosine kinases, Flt-1 (VEGF receptor (VEGFR)-1) and KDR (VEGFR-2), both of which are selectively expressed on primary vascular endothelium. KDR is responsible for VPF/VEGF-stimulated endothelial cell proliferation and migration, whereas Flt-1 down-modulates KDR-mediated endothelial cell proliferation. Our most recent works show that pertussis toxin-sensitive G proteins and Gβγ subunits are required for Flt-1-mediated down-regulation of human umbilical vein endothelial cell (HUVEC) proliferation and that G_q/11 proteins are required for KDR-mediated RhoA activation and HUVEC migration. In this study, we demonstrate that G_q/11 proteins are also required for VPF/ VEGF-stimulated HUVEC proliferation. Our results further indicate that G_q/11 proteins specifically mediate KDR signaling such as intracellular Ca²⁺ mobilization rather than Flt-1-induced CDC42 activation and that a G_q/11 antisense oligonucleotide completely inhibits MAPK phosphorylation induced by KDR but has no effect on Flt-1-induced MAPK activation. More importantly, we demonstrate that G_q/11 proteins interact with KDR in vivo, and the interaction of G_q/11 proteins with KDR does not require KDR tyrosine phosphorylation. Surprisingly, the G_q/11 antisense oligonucleotide completely inhibits VPF/VEGF-stimulated KDR phosphorylation. Expression of a constitutively active mutant of G₁₁ but not G_q can cause phosphorylation of KDR and MAPK. In addition, a Gβγ minigene, hβARK1(495), inhibits VPF/VEGF-stimulated HUVEC proliferation, MAPK phosphorylation, and intracellular Ca²⁺ mobilization but has no effect on KDR phosphorylation. Taken together, this study demonstrates that G_q/11 proteins mediate KDR tyrosine phosphorylation and KDR-mediated HUVEC proliferation through interaction with KDR.