Shear stress induces Gα_q/11 activation independently of G protein-coupled receptor activation in endothelial cells

Mechanochemical signal transduction occurs when mechanical forces, such as fluid shear stress, are converted into biochemical responses within the cell. The molecular mechanisms by which endothelial cells (ECs) sense/transduce shear stress into biological signals, including the nature of the mechanosensor, are still unclear. G proteins and G protein-coupled receptors (GPCRs) have been postulated independently to mediate mechanotransduction. In this study, we used in situ proximity ligation assay (PLA) to investigate the role of a specific GPCR/Gα_q/11 pair in EC shear stress-induced mechanotransduction. We demonstrated that sphingosine 1-phosphate (S1P) stimulation causes a rapid dissociation at 0.5 min of Gα_q/11 from its receptor S1P₃, followed by an increased association within 2 min of GPCR kinase-2 (GRK2) and β-arrestin-1/2 with S1P₃ in human coronary artery ECs, which are consistent with GPCR/Gα_q/11 activation and receptor desensitization/internalization. The G protein activator AlF₄ resulted in increased dissociation of Gα_q/11 from S1P₃, but no increase in association between S1P₃ and either GRK2 or β-arrestin-1/2. The G protein inhibitor guanosine 5'-(β-thio) diphosphate (GDP-β-S) and the S1P₃ antagonist VPC23019 both prevented S1P-induced activation. Shear stress also caused the rapid activation within 7 s of S1P₃/Gα_q/11 There were no increased associations between S1P₃ and GRK2 or S1P₃ and β-arrestin-1/2 until 5 min. GDP-β-S, but not VPC23019, prevented dissociation of Gα_q/11 from S1P₃ in response to shear stress. Shear stress did not induce rapid dephosphorylation of β-arrestin-1 or rapid internalization of S1P₃, indicating no GPCR activation. These findings suggest that Gα_q/11 participates in the sensing/transducing of shear stress independently of GPCR activation in ECs.