Estrogen causes dynamic alterations in endothelial estrogen receptor expression

Estrogen receptor (ER)α mediates many of the effects of estrogen on the vascular endothelium. The purpose of the present study was to determine whether estrogen modifies endothelial ERα expression. In experiments in cultured ovine endothelial cells, physiological concentrations of 17β-estradiol (E₂, 10^-10 to 10^-8 mol/L) caused an increase in ERα protein abundance that was evident after 6 hours of hormone exposure. Shorter (2-hour) E₂ treatment caused ERα downregulation. In contrast to the upregulation in ERα after long-term E₂, the expression of the other ER isoform, ERβ, was downregulated. Both nonselective ER antagonism with ICI 182,780 and the inhibition of gene transcription with actinomycin D blocked the increase in ERα with E₂. In studies using the human ERα gene promoter P-1 coupled to luciferase, an increase in ERα gene transcription was evident in endothelial cells within 4 hours of E₂ exposure. The transcriptional activation was fully blocked by ICI 182,780, whereas the specific ERβ antagonist RR-tetrahydrochrysene yielded partial blockade. Overexpression of ERα or ERβ caused comparable 10- and 8-fold increases, respectively, in ERα promoter activation by E₂. Thus, long-term exposure to E₂ upregulates ERα expression in endothelial cells through the actions of either ERα or ERβ on ERα gene transcription; in contrast, E₂ causes ERβ downregulation in the endothelium. We postulate that E₂-induced changes in ERα and ERβ expression modify the effects of the hormone on vascular endothelium.