Selected phytoestrogens distinguish roles of ERa transactivation and ligand binding for anti-inflammatory activity

Abstract

Estrogen receptor a (ERa) is a ligand-activated transcriptional activator that is also involved vascular inflammation and atherosclerosis. Whether different ligands may affect this activity has not been explored. We screened a panel of phytoestrogens for their role in ERa binding and transcriptional transcription, and correlated the findings to anti-inflammatory activities in vascular endothelial cells stably expressing either a wild-type or mutant form of ERa deficient in its membrane association. Taxifolin and silymarin were “high binders” for ERa ligand binding; quercetin and curcumin were “high activators” for ERa transactivation. Using these phytoestrogens as functional probes, we found, in endothelial cells expressing wild-type ERa, the ERa high activator, but not the ERa high binder, promoted ERa nuclear translocation, estrogen response element (ERE) reporter activity, and the downstream gene expression. In endothelial cells expressing membrane association–deficient mutant ERa, the ERa nuclear translocation was significantly enhanced by taxifolin and silymarin, which still failed to activate ERa. Inflammation response was examined using the systemic or vascular inflammation inducers lipopolysaccharide or oxidized low-density lipoprotein. In both cases, only the ERa high activator inhibited nuclear translocation of nuclear factor kB, JNK, and p38, and the production of inflammatory cytokines IL-1b and TNFa. We confirm a threshold nuclear accumulation of ERa is necessary for its transactivation. The anti-inflammatory activity of phytoestrogens is highly dependent on ERa transactivation, less so on the ligand binding, and independent of its membrane association. A pre-examination of phytoestrogens for their mode of ERa interaction could facilitate their development as better targeted receptor modifiers.