Mineralocorticoid Receptor (MR) trans-Activation of Inflammatory AP-1 Signaling

Abstract

Glucocorticoids are commonly used to treat inflammatory disorders. The glucocorticoid receptor (GR) can tether to inflammatory transcription factor complexes, such as NFB and AP-1, and trans-repress the transcription of cytokines, chemokines, and adhesion molecules. In contrast, aldosterone and the mineralocorticoid receptor (MR) primarily promote cardiovascular inflammation by incompletely understood mechanisms. Although MR has been shown to weakly repress NFB, its role in modulating AP-1 has not been established. Here, the effects of GR and MR on NFB and AP-1 signaling were directly compared using a variety of ligands, two different AP-1 consensus sequences, GR and MR DNA-binding domain mutants, and siRNA knockdown or overexpression of core AP-1 family members. Both GR and MR repressed an NFB reporter without influencing p65 or p50 binding to DNA. Likewise, neither GR nor MR affected AP-1 binding, but repression or activation of AP-1 reporters occurred in a ligand-, AP-1 consensus sequence-, and AP-1 family member-specific manner. Notably, aldosterone interactions with both GR and MR demonstrated a potential to activate AP-1. DNA-binding domain mutations that eliminated the ability of GR and MR to cis-activate a hormone response element-driven reporter variably affected the strength and polarity of these responses. Importantly, MR modulation of NFB and AP-1 signaling was consistent with a trans-mechanism, and AP-1 effects were confirmed for specific gene targets in primary human cells. Steroid nuclear receptor trans-effects on inflammatory signaling are context-dependent and influenced by nuclear receptor conformation, DNA sequence, and the expression of heterologous binding partners. Aldosterone activation of AP-1 may contribute to its proinflammatory effects in the vasculature.

Spironolactone-induced degradation of the TFIIH core complex XPB subunit suppresses NF-κB and AP-1 signalling

“…Selective expression in HEK293 cells allowed for the separate assessment of relevant nuclear receptors. As expected and previously reported, 16,20 HEK293 cells expressed only low levels of endogenous GR, but not MR or AR ( Figure 1A). Likewise, PR and PXR were not detected in HEK293 cells, but low levels of RXRc were found by Western blotting (see see Supplementary material online, Figure S1A and S1B).…”

“…decreased basal AP-1 activity, but at concentrations of SPL < _5 lM, dosedependently increased AP-1 activity, which was then decreased at 10 lM of SPL (see Supplementary material online, Figure S1A). Although this pattern suggests PR-SPL trans-activation of AP-1 signalling, 16 this possibility was not further investigated. As with MR, AR and GR, SPL dosedependently suppressed NF-jB and AP-1 in the absence and presence of PXR, RXRc and PXR þ RXRc (see Supplementary material online, Figure S1B).…”

“…Here, SPL and EPL were compared for effects on canonical NF-jB and AP-1 inflammatory signalling. Selective overexpression 16 of MR, GR, AR, PR, PXR and RXRc was used to examine the role of all relevant nuclear receptors. Although not previously shown to affect basal transcription, 17 SPL-induced XPB loss potently suppressed NF-jB and AP-1 reporters, as well as corresponding target genes in primary human pulmonary artery endothelial cells (PAECs).…”

Epidermal glucocorticoid and mineralocorticoid receptors act cooperatively to regulate epidermal development and counteract skin inflammation

“…The increased AP-1 activity in DKO cells even in the absence of active ERK may reflect transcriptional repression mediated by tethering of GR/MR to AP-1 or the lack of induction of other negative repressors of this pathway. Moreover, these mechanisms could account for the differences in AP-1 activity observed between single KO and DKO cells, despite having similar levels of ERK and p38 activation 28 .…”

Contribuciones relativas de los receptores de glucocorticoides y mineralocorticoides en la biología cutánea

“…Los resultados del bloqueo farmacológico de ERK en las células DKO sugieren un papel importante para esta MAPK, ya que su inhibición reducía un 30% la actividad del reporter AP-1-luc. Estos datos sugieren la existencia de mecanismos adicionales que bloquean la vía AP-1, mediante tethering o debido a una falta de inducción de complejos represores(Dougherty et al 2016).…”