Abstract 5846: Extranuclear Estrogen Receptor α Signaling Promotes Endothelial Monolayer Integrity but Not Breast Cancer or Uterine Growth in Mice
Although estrogen receptors (ER) function classically as transcription factors, a membrane-associated ER subpopulation initiates extranuclear responses in various cell types including endothelial cells (EC) and breast cancer cells. We investigated the basis and relevance of extranuclear ER function in endothelium using an estrogen-dendrimer conjugate (EDC) with 21 estrogen molecules stably conjugated to a large inert dendrimer that is excluded from the cell nucleus. Estradiol (E2) and EDC stimulated comparable EC growth and migration that was dependent on ER α, Src, G αi and endothelial NO synthase (eNOS) stimulation. The utility of EDC for in vivo studies was then examined. Ovariectomized female mice were given vehicle, E2, dendrimer, or EDC to yield estrogen-equivalent plasma concentrations for E2 and EDC of 10 −8M. In whole body imaging of estrogen-response-element-luciferase (ERE-Luc) reporter mice, E2 caused luciferase activation and EDC did not. Similarly, ER-regulated genes in mouse uterus were modified by E2 but not EDC. In addition, serum from EDC-treated mice did not activate ERE-Luc in HEK293 cells expressing ER α, but it stimulated nongenomic eNOS activation in EC. As such, EDC remains intact to specifically target extranuclear processes in vivo. Following perivascular electric injury of the carotid artery, E2 and EDC caused comparable 70 – 80% reendothelialization that was negated by the ER antagonist ICI 182,780 and was also absent in ER α −/− mice. In contrast, E2 elicited a uterotrophic response that was prevented by ICI 182,780, but EDC did not. Reendothelialization with E2 or EDC was prevented by pertussis toxin but not by B-oligomer. To study extranuclear ER signaling and breast cancer growth in vivo, MCF-7 cell tumor xenografts were established with E2 for 28d in SCID mice that were then treated with vehicle, E2, dendrimer or EDC for 21d. Whereas E2 caused further tumor growth, EDC did not, mimicking prior findings in cultured MCF-7 cells. Thus, EDC is a novel extranuclear selective ER modulator (SERM) in vivo, extranuclear ER α signaling is operative in vivo and promotes endothelial monolayer integrity, and these processes can potentially be harnessed to provide cardiovascular protection without increasing uterine or breast cancer risk.