Estradiol Suppresses NF-κB Activation through Coordinated Regulation of let-7a and miR-125b in Primary Human Macrophages

Abstract

Previous findings suggest that 17β-estradiol (estradiol) has a suppressive effect on TNF-α, but the mechanism by which estradiol regulates TNF-α expression in primary human macrophages is unknown. In this article, we demonstrate that pretreatment of human macrophages with estradiol attenuates LPS-induced TNF-α expression through the suppression of NF-κB activation. Furthermore, we show that activation of macrophages with LPS decreases the expression of κB-Ras2, an inhibitor of NF-κB signaling. Estradiol pretreatment abrogates this decrease, leading to the enhanced expression of κB-Ras2 with LPS stimulation. Additionally, we identified two microRNAs, let-7a and miR-125b, which target the κB-Ras2 3′ untranslated region (UTR). LPS induces let-7a and inhibits miR-125b expression in human macrophages, and pretreatment with estradiol abrogates these effects. 3′UTR reporter assays demonstrate that let-7a destabilizes the κB-Ras2 3′UTR, whereas miR-125b enhances its stability, resulting in decreased κB-Ras2 in response to LPS. Our data suggest that pretreatment with estradiol reverses this effect. We propose a novel mechanism for estradiol inhibition of LPS-induced NF-κB signaling in which κB-Ras2 expression is induced by estradiol via regulation of let-7a and miR-125b. These findings are significant in that they are the first to demonstrate that estradiol represses NF-κB activation through the induction of κB-Ras2, a key inhibitor of NF-κB signaling.