Binding of genistein with membrane estrogen receptor and the potentiating effect of genistein in rapid, non-genomic vascular action

Abstract

BACKGROUND: Genistein is a phytoestrogen which enhances endothelial functions in a receptor-mediated manner. The present study was designed to characterize the mechanism involved in the rapid vascular actions of genistein and to determine whether genistein share the same receptor with estrogen in its non-genomic action. METHODS: Using tissue bath studies, isometric tension was measured in aortic rings isolated from 32-week-old male spontaneously hypertensive rats. The nuclear and membranous isoforms of estrogen receptor (ER)-α, ER-α66 and ER-α46, were cloned and expressed using a cell-free expression system. Binding study was performed subsequently. RESULTS: Genistein acutely potentiated acetylcholine-induced relaxation. This effect was insensitive to the transcription and translation inhibitors, actinomycin D and cycloheximide, respectively. The potentiation of acetylcholine and A23187-induced relaxation by genistein was inhibited by NF023 and GP antagonist-2A, the selective Gi and Gq α-subunit antagonists, respectively, but not by NF449, a selective Gs α-subunit antagonist. ER-α66 and ER-α46 were successfully cloned and expressed in vitro, with molecular sizes confirmed by Western blotting. 17β-estradiol bound to the ER-α66 and ER-α46 with similar affinity and genistein competed with 17β-estradiol for binding to both receptors. CONCLUSION: The tissue bath studies demonstrate that rapid potentiating effect of genistein in acetylcholine-induced relaxation is non-genomic and G protein-coupled. In addition, our data also suggests that genistein may bind to nuclear and membranous estrogen receptors. Further studies are required to reveal whether the non-genomic vascular effect of genistein is mediated through the membranous estrogen receptors.