Estrogen Increases Expression of the Human Prostacyclin Receptor within the Vasculature through an ERα-Dependent Mechanism

Prostacyclin and the prostacyclin receptor (IP) are implicated in mediating many of the atheroprotective effects of estrogen in both humans and in animal models but through unknown mechanisms. Hence, herein the influence of estrogen on IP gene expression in endothelial EA.hy926, human erythroleukemia 92.1.7 and primary human aortic smooth muscle cells was investigated. Estrogen increased hIP mRNA levels, promoter (PrmIP)-directed reporter gene expression and cicaprost-dependent cAMP generation in all cell types, effects that were abrogated by actinomycin D and the general estrogen receptor (ER)-α/ERβ antagonist ICI 182,780. Furthermore, the ERα-selective agonist 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), but not the ERβ-agonist 2,3-bis(4-hydroxyphenyl)-propionitrile, significantly increased hIP mRNA and PrmIP-directed gene expression. Deletional and mutational analysis of PrmIP uncovered an evolutionary conserved estrogen-response element, while electrophoretic mobility shift, antibody-supershift and chromatin immunoprecipitations assays confirmed the direct binding of ERα, but not ERβ, to PrmIP both in vitro and in vivo. Moreover, immunofluorescence microscopy corroborated that estrogen and PPT increased hIP expression in primary human aortic smooth muscle cells. In conclusion, the hIP gene is directly regulated by estrogen that largely occurs through an ERα-dependent transcriptional mechanism and thereby provides critical insights into the role of prostacyclin/hIP in mediating the atheroprotective effects of estrogen within the human vasculature.