Estrogen receptor alpha mediates the nongenomic activation of endothelial nitric oxide synthase by estrogen

Estrogen is an important vasoprotective molecule that causes the rapid dila tion of blood vessels by activating endothelial nitric oxide synthase (eNOS ) through an unknown mechanism. In studies of intact ovine endothelial cell s, 17 beta-estradiol (E-2) caused acute (five-minute) activation of eNOS th at was unaffected by actinomycin D but was fully inhibited by concomitant a cute treatment with specific estrogen receptor (ER) antagonists. Overexpres sion of the known transcription factor ER alpha led to marked enhancement o f the acute response to E-2, and this was blocked by ER antagonists, was sp ecific to E-2, and required the ER alpha hormone-binding domain. In additio n, the acute response of eNOS to E-2 was reconstituted in COS-7 cells cotra nsfected with wild-type ER alpha and eNOS, but not by transfection with eNO S alone. Furthermore, the inhibition of tyrosine kinases or mitogen-activat ed protein (MAP) kinase kinase prevented the activation of eNOS by E-2, and E-2 caused rapid ER-dependent activation of MAP kinase. These findings dem onstrate that the short-term effects of estrogen central to cardiovascular physiology are mediated by ER alpha functioning in a novel, nongenomic mann er to activate eNOS via MAP kinase-dependent mechanisms.