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.

MiR-125 in normal and malignant hematopoiesis

“…MiR-125b acts as a negative regulator of this pathway by reducing the levels of its target tumor necrosis factora 15,34 and, unusual for miRNAs, by enhancing the stability of the NF-kb inhibitor NKIRAS2 (KBRAS2) 35 ( Figure 3). Enhancement of the stability of a target gene transcript was described in several recent publications.…”

“…37 Interestingly, NF-kb can either repress or activate pri-miR-125b transcription depending on the cell type and on the amount of time after encountering the pathogen, thereby either further enhancing or suppressing the inflammatory response. [15][16][17]35 Hence, miR-125b has been suggested to have a remarkably diverse role in the hematopoietic system. It enhances survival and proliferation of some early hematopoietic progenitors and blocks their terminal differentiation.…”

“…30 Although not much is known about the added function of the whole cluster, beyond the activity of miR-125b, in hematopoietic malignancies and in normal hematopoiesis, coordinated regulation of miR-125b and let-7a (a let-7 family member) in inflammation was demonstrated. 16,17,35,60,62 For example, activation of macrophage cells with LPS mediated the repression of miR-125b levels and the induction of let-7a expression. This coordinated regulation resulted in the activation of NF-kb and induction of the inflammatory response.…”

Estrogens and atherosclerosis: insights from animal models and cell systems

“…In addition, E 2 was reported to inhibit MHC-II expression in macrophages exposed to INFg (Adamski et al 2004). While no single mechanism underlying these effects could be identified, estrogens were found to interfere with several intracellular pro-inflammatory signaling pathways including phosphorylation, nuclear translocation, and DNA binding of the transcription factor NFkB as well as phosphorylation and activation of signal In particular, inhibitory effects of E 2 on NF-kB activation were uniformly found in several macrophage cell systems and were attributed to both genomic (regulation of let-7a and miR-125b micro-RNAs) and nongenomic (regulation of protein kinases MAPK and AKT) action (Ghisletti et al 2005, Murphy et al 2010. Moreover, the reduced iNOS expression, TNFa production, and NF-kB activation seen in the presence of E 2 were partially abolished in macrophages lacking peroxisome proliferation-activating receptor a (PPARa; Crisafulli et al 2009).…”

Estrogen Receptors in Leukocytes - Possible Impact on Inflammatory Processes in the Female Reproductive System

“…Further, plasma membrane associated ER and cytosolic ER oppose the function of each other thereby promoting cell survival suggesting the importance of both receptors (Kramer & Wray, 2002;Subramanian & Shaha, 2009). A recent study showed that estradiol suppresses LPS induced NFkB activation in primary human macrophages (Murphy et al, 2010). These reports indicate that estrogen dependent ER signaling is necessary to perform various important activities in monocytes and macrophages.…”