Sex steroids control cell movement and tissue organization; however, little is known of the involved mechanisms. This report describes the ongoing dynamic regulation by estrogen of the actin cytoskeleton and cell movement in human vascular endothelial cells that depends on rapid activation of the actin-regulatory protein moesin. Moesin activation is triggered by the interaction of the C-terminal portion of cell membrane estrogen receptor alpha with the G protein Galpha(13), leading to activation of the small GTPase RhoA and of the downstream effector Rho-associated kinase. The resulting phosphorylation of moesin on Thr(558) is the means of moesin's binding to actin and the remodeling of the actin cytoskeleton. This cascade of events ensues within minutes of estradiol administration and results in changes in cell morphology and to the development of specialized cell membrane structures such as ruffles and pseudopodia that are necessary for cell movement. These findings expand our knowledge of the basis of estrogen's effects on human cells, including the regulation of actin assembly, cell movement and migration. They highlight novel pathways of signal transduction of estrogen receptor alpha through nontranscriptional mechanisms. Furthermore, exposure of this estrogen receptor-dependent, nongenomic action of estrogen on human vascular endothelial cells is especially relevant to the present interest in the role of estrogen in cardiovascular protection.

Dehydroepiandrosterone (DHEA) and its sulfate ester (DHEAS) are the major circulating steroid hormones in humans, and their levels progressively decline with age. Epidemiological studies suggest that DHEA/DHEAS concentrations may be inversely related to cardiovascular risk, but disagreement exists on this issue. Preliminary studies show that DHEA regulates vascular function, but few data have been published on the mechanisms. We show that DHEA administration to human endothelial cells triggers nitric oxide synthesis, due to enhanced expression and stabilization of endothelial nitric oxide synthase (eNOS). Additionally, DHEA rapidly activates eNOS, through a nontranscriptional mechanism that depends on ERK1/2 MAPK, but not on phosphatidylinositol 3-kinase/Akt. DHEA is not converted to estrogens or androgens by endothelial cells, and its genomic and nongenomic effects are not blocked by antagonists of the estrogen, progesterone, glucocorticoid, or androgen receptors, suggesting that DHEA acts through a specific receptor. Oral DHEA administration to ovariectomized Wistar rats dose-dependently restores aortic eNOS levels and eNOS activity, confirming the effects of DHEA in vivo. Our present data suggest that DHEA may have direct genomic and nongenomic effects on the vascular wall that are not mediated by other steroid hormone receptors, leading to eNOS activation and induction.

The conjugated equine estrogens-only arm of the Women's Health Initiative trial, showing a trend toward protection from heart disease as opposed to women receiving also medroxyprogesterone acetate (MPA), strengthens the debate on the cardiovascular effects of progestins. We compared the effects of progesterone (P) or MPA on the synthesis of nitric oxide and on the expression of leukocyte adhesion molecules, characterizing the signaling events recruited by these compounds. Although P significantly increases nitric oxide synthesis via transcriptional and nontranscriptional mechanisms, MPA is devoid of such effects. Moreover, when used together with physiological estradiol (E2) concentrations, P potentiates E2 effects, whereas MPA impairs E2 signaling. These findings are observed both in isolated human endothelial cells as well as in vivo, in ovariectomized rat aortas. A marked difference in the recruitment of MAPK and phosphatidylinositol-3 kinase explains the divergent effects of the two gestagens. In addition, both P and MPA decrease the adhesiveness of endothelial cells for leukocytes when given alone or with estrogen. MPA is more potent than P in inhibiting the expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1. However, when administered together with physiological amounts of glucocorticoids, MPA (which also binds glucocorticoid receptor) markedly interferes with the hydrocortisone-dependent stabilization of the transcription factor nuclear factor kappaB and with the expression of adhesion molecules, acting as a partial glucocorticoid receptor antagonist. Our findings show significant differences in the signal transduction pathways recruited by P and MPA in endothelial cells, which may have relevant clinical implications.

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