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

Previous findings suggest that 17 beta-estradiol (estradiol) has a suppressive effect on TNF-alpha, but the mechanism by which estradiol regulates TNF-alpha expression in primary human macrophages is unknown. In this article, we demonstrate that pretreatment of human macrophages with estradiol attenuates LPS-induced TNF-alpha expression through the suppression of NF-kappa B activation. Furthermore, we show that activation of macrophages with LPS decreases the expression of kappa B-Ras2, an inhibitor of NF-kappa B signaling. Estradiol pretreatment abrogates this decrease, leading to the enhanced expression of kappa B-Ras2 with LPS stimulation. Additionally, we identified two microRNAs, let-7a and miR-125b, which target the kappa B-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 kappa B-Ras2 3'UTR, whereas miR-125b enhances its stability, resulting in decreased kappa B-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-kappa B signaling in which KB-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 NE-kappa B activation through the induction of kappa B-Ras2, a key inhibitor of NE-kappa B signaling. The Journal of Immunology, 2010, 184: 5029-5037.