ER Has Nongenomic Action in Caveolae

ER and ER serve classically as transcription factors, and ER also mediates nongenomic responses to E2 such as the activation of endothelial nitric oxide synthase (eNOS). In contrast, the nongenomic capacities of endogenous ER are poorly understood. We evaluated eNOS activation by E2 in cultured endothelial cells that express endogenous ER to determine whether the ER isoform has nongenomic action and to reveal the subcellular locale of that function. A subpopulation of ER was localized to the endothelial cell plasma membrane, overexpression of ER enhanced rapid eNOS stimulation by E2, and the response to endogenous ER activation was inhibited by the ER -selective antagonist RR-tetrahydrochrysene (THC). eNOS activation through ER was reconstituted and shown to occur independent of ER in COS-7 cells, and ER protein in COS-7 was directed to the plasma membrane. THC also blunted E2 activation of eNOS in isolated endothelial cell plasma membranes. Furthermore, ER protein was detected and THC attenuated E2 stimulation of eNOS in isolated endothelial cell caveolae, and functional ER -eNOS coupling was recapitulated in caveolae from transfected COS-7 cells. These findings in the ER-eNOS signaling paradigm indicate that endogenous ER has nongenomic action in caveolae. (Molecular Endocrinology 16: 938–946, 2002)