Glucocorticoid receptor signaling represses the antioxidant response by inhibiting histone acetylation mediated by the transcriptional activator NRF2

Abstract

NRF2 (nuclear factor erythroid 2-related factor 2) is a key transcriptional activator that mediates the inducible expression of antioxidant genes. NRF2 is normally ubiquitinated by KEAP1 (Kelch-like ECH-associated protein 1) and subsequently degraded by proteasomes. Inactivation of KEAP1 by oxidative stress or electrophilic chemicals allows NRF2 to activate transcription through binding to antioxidant response elements (AREs) and recruiting histone acetyltransferase CBP (CREB-binding protein). Whereas KEAP1-dependent regulation is a major determinant of NRF2 activity, NRF2-mediated transcriptional activation varies from context to context, suggesting that other intracellular signaling cascades may impact NRF2 function. To identify a signaling pathway that modifies NRF2 activity, we immunoprecipitated endogenous NRF2 and its interacting proteins from mouse liver and identified glucocorticoid receptor (GR) as a novel NRF2-binding partner. We found that glucocorticoids, dexamethasone and betamethasone, antagonize diethyl maleate-induced activation of NRF2 target genes in a GR-dependent manner. Dexamethasone treatment enhanced GR recruitment to AREs without affecting chromatin binding of NRF2, resulting in the inhibition of CBP recruitment and histone acetylation at AREs. This repressive effect was canceled by the addition of histone deacetylase inhibitors. Thus, GR signaling decreases NRF2 transcriptional activation through reducing the NRF2-dependent histone acetylation. Consistent with these observations, GR signaling blocked NRF2-mediated cytoprotection from oxidative stress. This study suggests that an impaired antioxidant response by NRF2 and a resulting decrease in cellular antioxidant capacity account for the side effects of glucocorticoids, providing a novel viewpoint for the pathogenesis of hypercorticosteroidism.

Therapeutic targeting of the NRF2 and KEAP1 partnership in chronic diseases

“…Increasing evidence indicates that NRF2 exhibits multiple layers of regulation in addition to that exerted by KEAP1, such as transcriptional 196 , epigenetic 254,255 , covalent protein modification 256,257 , proteasome degradation in KEAP1-independent manner [258][259][260][261] , and regulation of NRF2-dimerizing partners that target binding to ARE sequences 262,263 . At the level of pharmacological development, a KEAP1-independent mechanism of AREmediated gene regulation involves modulation of the transcriptional repressor BACH1 (i.e., broad complex, tramtrack and bric à brac and cap'n'collar homology 1), which inhibits the transactivation of a subset of NRF2-regulated genes and more specifically HMOX1 28 .…”

A distinct class of antioxidant response elements is consistently activated in tumors with NRF2 mutations

“…For example, in certain tumors the KEAP1 locus is hypermethylated, leading to low KEAP1 expression and high NRF2 activity [40] , [41] , [42] , [43] , [44] , and NRF2 is also indirectly activated via oncogenic KRAS or BRAF signaling [45] . Multiple other proteins that bind KEAP1/NRF2 and/or modulate NRF2 activity have also been identified [46] , [47] , [48] , [49] , [50] , [51] . Considering the diverse molecular changes that can result in hyperactivation of NRF2, it is quite plausible that a number of as-yet unidentified mechanisms exist.…”

Enhancer Remodeling Promotes Tumor-Initiating Activity in NRF2-Activated Non-Small Cell Lung Cancers

“…NRF2 binding at this site was clearly observed in all three NRF2-activated NSCLC cell lines ( Figure 3b). Because NRF2 is known to recruit histone acetyltransferases CBP/p300 together with the SWI/SNF complex and Mediator complex (Katoh et al, 2001;Zhang et al, 2007;Sekine et al, 2015;Alam et al, 2017), NRF2-dependent deposition of acetylated histone H3K27 (H3K27ac), an enhancer mark, was also examined at this site. NRF2-dependent H3K27ac deposition was commonly observed in NRF2-activated NSCLC cell lines (Figure 3c), suggesting that this intergenic NRF2-dependent enhancer is a common feature of NRF2-activated NSCLCs.…”

“…The samples were sonicated to shear the DNA. Sonication was conducted according to previously described procedures (Zhang et al, 2007;Alam et al, 2017). The solubilized chromatin fraction was incubated with the primary antibodies overnight, which were prebound to anti-mouse IgG-conjugated Dynabeads (anti-H3K27ac antibody) or anti-rabbit IgG-conjugated Dynabeads (the rest of the antibodies) (Thermo Fisher Scientific).…”