Molecular basis of cell membrane estrogen receptor interaction with phosphatidylinositol 3-kinase in endothelial cells

Objective-Nontranscriptional signaling mechanisms mediate some of the biological effects of estrogen, such as the rapid actions on the blood vessels. By interacting with phosphatidylinositol 3-kinase (PI3K), estrogen receptor (ER) alpha leads to activation of protein kinase Akt and to subsequent increase in endothelial nitric oxide synthase activity. Because PI3K is mainly a cytoplasmic complex, we studied the cellular site of interaction between this enzyme and ERalpha, and we dissected the molecular mechanisms that mediate this interaction. Methods and Results-By using cultured human saphenous vain endothelial cells, we found that cell membrane-bound ERalpha colocalizes with PI3K and may be responsible for PI3K activation. Furthermore, we characterized the subsequent steps in the activation of the PI3K/Akt signaling cascade, comparing the molecular events that follow insulin or estradiol activation of PI3K. Conclusions-We provide novel evidence for an important role of nonnuclear estrogen receptor in rapid, nontranscriptional responses of human endothelial cells to estrogen.