Suppression of store-operated Ca2+ entry by activation of GPER: contribution to a clamping effect on endothelial Ca2+ signaling

Abstract

The G Protein-coupled Estrogen Receptor 1 (GPER, formerly a.k.a. GPR30) modulates many Ca²⁺-dependent activities in endothelial cells. However, the underlying mechanisms are poorly understood. We recently reported that GPER acts to prolong cytoplasmic Ca²⁺ signals by interacting with and promoting inhibitory phosphorylation of the plasma membrane Ca²⁺-ATPase. In this study, we examined the role of GPER activation in modulating store-operated Ca²⁺ entry (SOCE) via effects on the Stromal Interaction Molecule 1 (STIM1). GPER activation by agonist G-1 reduces the peak but prolongs the plateau of bradykinin-induced Ca²⁺ signals in primary endothelial cells. G-1 dose-dependently inhibits thapsigargin-induced SOCE measured by the Mn²⁺ quenching method. GPER heterologous expression reduces SOCE, which is further pronounced by G-1 treatment. Consistently, GPER gene silencing in endothelial cells is associated with an increase in SOCE. Treatment with G-1 reduces puncta formation by STIM1 triggered by activation of SOCE. The effect of GPER activation to inhibit SOCE is not affected by combined non-phosphorylatable substitutions at serines 486 and 668 on STIM1, but is substantially reduced by similar substitutions at serines 575, 608 and 621. Taken together with our recently reported inhibitory actions of GPER on Ca²⁺ efflux, the current data contribute to a model in which GPER acts to clamp agonist-induced cytoplasmic Ca²⁺ signals. Kinetic modeling based on current and reported data is used to estimate the overall effect of GPER activation on point activity of endothelial nitric oxide synthase during the time course of agonist-induced total Ca²⁺ signals.