Target-specific utilization of transcriptional regulatory surfaces by the glucocorticoid receptor

GPAT3 deficiency attenuates corticosterone-caused hepatic steatosis and oxidative stress through GSK3β/Nrf2 signals

The development of nonalcoholic fatty liver disease (NAFLD) may worsen due to chronic stress or prolonged use of glucocorticoids. Glycerol-3-phosphate acyltransferase 3 (GPAT3), has a function in obesity and serves as a key rate-limiting enzyme that regulates triglyceride synthesis. However, the precise impact of GPAT3 on corticosterone (CORT)-induced NAFLD and its underlying molecular mechanism remain unclear. For our in vivo experiments, we utilized male and female mice that were GPAT3-/- and wild type (WT) and treated them with CORT for a duration of 4 weeks. In our in vitro experiments, we transfected AML12 cells with GPAT3 siRNA and subsequently treated them with CORT. Under CORT-treated conditions, the absence of GPAT3 greatly improved obesity and hepatic steatosis while enhancing the expression of genes involved in fatty acid oxidation, as evidenced by our findings. In addition, the deletion of GPAT3 significantly inhibited the production of reactive oxygen species (ROS), increased the expression of antioxidant genes, and recovered the mitochondrial membrane potential in AML12 cells treated with CORT. In terms of mechanism, the absence of GPAT3 encouraged the activation of the glycogen synthase kinase 3β (GSK3β)/nuclear factor-erythroid 2 related factor 2 (Nrf2) pathway, which served as a defense mechanism against liver fat accumulation and oxidative stress. Furthermore, GPAT3 expression was directly controlled at the transcriptional level by the glucocorticoid receptor (GR). Collectively, our findings suggest that GPAT3 deletion significantly alleviated hepatic steatosis and oxidative stress through promoting GSK3β/Nrf2 signaling pathways.

Acetylation-induced proteasomal degradation of the activated glucocorticoid receptor limits hormonal signaling

Glucocorticoid (GC) signaling is essential for mounting a stress response, however, chronic stress or prolonged GC therapy downregulates the GC receptor (GR), leading to GC resistance. Regulatory mechanisms that refine this equilibrium are not well understood. Here, we identify seven lysine acetylation sites in the amino terminal domain of GR, with lysine 154 (Lys154) in the AF-1 region being the dominant acetyl-acceptor. GR-Lys154 acetylation is mediated by p300/CBP in the nucleus in an agonist-dependent manner and correlates with transcriptional activity. Deacetylation by NAD+-dependent SIRT1 facilitates dynamic regulation of this mark. Notably, agonist-binding to both wild-type GR and an acetylation-deficient mutant elicits similar short-term target gene expression. In contrast, upon extended treatment, the polyubiquitination of the acetylation-deficient GR mutant is impaired resulting in higher protein stability, increased chromatin association and prolonged transactivation. Taken together, reversible acetylation fine-tunes duration of the GC response by regulating proteasomal degradation of activated GR.

The Biologist's Guide to the Glucocorticoid Receptor's Structure

The glucocorticoid receptor α (GRα) is a member of the nuclear receptor superfamily and functions as a glucocorticoid (GC)-responsive transcription factor. GR can halt inflammation and kill off cancer cells, thus explaining the widespread use of glucocorticoids in the clinic. However, side effects and therapy resistance limit GR's therapeutic potential, emphasizing the importance of resolving all of GR's context-specific action mechanisms. Fortunately, the understanding of GR structure, conformation, and stoichiometry in the different GR-controlled biological pathways is now gradually increasing. This information will be crucial to close knowledge gaps on GR function. In this review, we focus on the various domains and mechanisms of action of GR, all from a structural perspective.

RNA binding by the glucocorticoid receptor attenuates dexamethasone-induced gene activation

The glucocorticoid receptor (GR) is a ligand-activated transcription factor that regulates a suite of genes through direct binding of GR to specific DNA promoter elements. GR also interacts with RNA, but the function of this RNA-binding activity remains elusive. Current models speculate that RNA could repress the transcriptional activity of GR. To investigate the function of the GR-RNA interaction on GR's transcriptional activity, we generated cells that stably express a mutant of GR with reduced RNA binding affinity and treated the cells with the GR agonist dexamethasone. Changes in the dexamethasone-driven transcriptome were quantified using 4-thiouridine labeling of RNAs followed by high-throughput sequencing. We find that while many genes are unaffected, GR-RNA binding is repressive for specific subsets of genes in both dexamethasone-dependent and independent contexts. Genes that are dexamethasone-dependent are activated directly by chromatin-bound GR, suggesting a competition-based repression mechanism in which increasing local concentrations of RNA may compete with DNA for binding to GR at sites of transcription. Unexpectedly, genes that are dexamethasone-independent instead display a localization to specific chromosomal regions, which points to changes in chromatin accessibility or architecture. These results show that RNA binding plays a fundamental role in regulating GR function and highlights potential functions for transcription factor-RNA interactions.

Intense inhibitory avoidance training increases nuclear-phosphorylated glucocorticoid receptors in neurons of CA1 of hippocampus and ventral caudate putamen

Corticosterone (CORT), the principal glucocorticoid in rodents, is released after stressful experiences such as training with high foot-shock intensities in the inhibitory avoidance task (IA). CORT reaches the glucocorticoid receptor (GR) located in almost all brain cells; the GR is subsequently phosphorylated at serine 232 (pGRser232). This has been reported as an indicator of ligand-dependent activation of the GR, as well as a requirement for its translocation into the nucleus for its transcription factor activity. The GR is present in the hippocampus with a high concentration in CA1 and dentate gyrus (DG), and a smaller proportion in CA3, and sparsely present in the caudate putamen (CPu); both structures are involved in memory consolidation of IA. To study the participation of CORT in IA, we quantified the ratio of pGR-positive neurons in both dorsal hippocampus (CA1, CA3 and DG) and dorsal and ventral regions of CPu of rats trained in IA, using different foot-shock intensities. Brains were dissected 60 min after training for immunodetection of pGRser232 positive cells. The results show that the groups trained with 1.0 and 2.0 mA had higher retention latencies than the 0.0 mA or 0.5 mA groups. An increase in the ratio of pGR-positive neurons was found in CA1 and ventral region of CPu only for the 2.0 mA trained group. These findings suggest that activation of GRs in CA1 and ventral CPu is involved in the consolidation of a stronger memory of IA, possibly through the modulation of gene expression.

The multivalency of the glucocorticoid receptor ligand-binding domain explains its manifold physiological activities

The glucocorticoid receptor (GR) is a ubiquitously expressed transcription factor that controls metabolic and homeostatic processes essential for life. Although numerous crystal structures of the GR ligand-binding domain (GR-LBD) have been reported, the functional oligomeric state of the full-length receptor, which is essential for its transcriptional activity, remains disputed. Here we present five new crystal structures of agonist-bound GR-LBD, along with a thorough analysis of previous structural work. We identify four distinct homodimerization interfaces on the GR-LBD surface, which can associate into 20 topologically different homodimers. Biologically relevant homodimers were identified by studying a battery of GR point mutants including crosslinking assays in solution, quantitative fluorescence microscopy in living cells, and transcriptomic analyses. Our results highlight the relevance of non-canonical dimerization modes for GR, especially of contacts made by loop L1-3 residues such as Tyr545. Our work illustrates the unique flexibility of GR's LBD and suggests different dimeric conformations within cells. In addition, we unveil pathophysiologically relevant quaternary assemblies of the receptor with important implications for glucocorticoid action and drug design.

Stimulation of osteoclast formation and bone resorption by glucocorticoids: Synergistic interactions with the calcium regulating hormones parathyroid hormone and 1,25(OH)2-vitamin D3

Osteoporosis is a significant health problem, with skeletal fractures increasing morbidity and mortality. Excess glucocorticoids (GC) represents the leading cause of secondary osteoporosis. The first phase of glucocorticoid-induced osteoporosis is increased bone resorption. In this Chapter, in vitro studies of the direct glucocorticoid receptor (GR) mediated cellular effects of GC on osteoclasts to affect bone resorption and indirect effects on osteoblast lineage cells to increase the RANKL/OPG ratio and stimulate osteoclastogenesis and bone resorption are reviewed in detail, together with detailed descriptions of in vivo effects of GC in different portions of the skeleton in research animals and humans. Brief sections are devoted to contrasting functions of GC in osteonecrosis, vitamin D formation, in vitro and in vivo bone resorptive actions dependent on vitamin D receptor and vitamin D toxicity, as well as the molecular basis of GR action. Included are also more detailed assessments of the interactions of GC with the major calcium regulating hormones, 1,25(OH)₂-vitamin D3 and parathyroid hormone, describing the in vitro increases in RANKL/OPG ratios, osteoclastogenesis and synergistic bone resorption that occurs when GC is combined with either 1,25(OH)₂-vitamin D3 or parathyroid hormone. Additionally, a molecular basic for the synergistic interaction of GC with 1,25(OH)₂-vitamin D3 is provided along with a suggested molecular basic for the interaction between GC and parathyroid hormone.

How to tame your genes: mechanisms of inflammatory gene repression by glucocorticoids

Glucocorticoids (GCs) are widely used therapeutic agents to treat a broad range of inflammatory conditions. Their functional effects are elicited by binding to the glucocorticoid receptor (GR), which regulates transcription of distinct gene networks in response to ligand. However, the mechanisms governing various aspects of undesired side effects versus beneficial immunomodulation upon GR activation remain complex and incompletely understood. In this review, we discuss emerging models of inflammatory gene regulation by GR, highlighting GR's regulatory specificity conferred by context-dependent changes in chromatin architecture and transcription factor or co-regulator dynamics. GR controls both gene activation and repression, with the repression mechanism being central to favorable clinical outcomes. We describe current knowledge about 3D genome organization and its role in spatiotemporal transcriptional control by GR. Looking beyond, we summarize the evidence for dynamics in gene regulation by GR through cooperative convergence of epigenetic modifications, transcription factor crosstalk, molecular condensate formation and chromatin looping. Further characterizing these genomic events will reframe our understanding of mechanisms of transcriptional repression by GR.

Antihistamines Potentiate Dexamethasone Anti-Inflammatory Effects. Impact on Glucocorticoid Receptor-Mediated Expression of Inflammation-Related Genes

Antihistamines and glucocorticoids (GCs) are often used together in the clinic to treat several inflammation-related situations. Although there is no rationale for this association, clinical practice has assumed that, due to their concomitant anti-inflammatory effects, there should be an intrinsic benefit to their co-administration. In this work, we evaluated the effects of the co-treatment of several antihistamines on dexamethasone-induced glucocorticoid receptor transcriptional activity on the expression of various inflammation-related genes in A549 and U937 cell lines. Our results show that all antihistamines potentiate GCs' anti-inflammatory effects, presenting ligand-, cell- and gene-dependent effects. Given that treatment with GCs has strong adverse effects, particularly on bone metabolism, we also examined the impact of antihistamine co-treatment on the expression of bone metabolism markers. Using MC3T3-E1 pre-osteoblastic cells, we observed that, though the antihistamine azelastine reduces the expression of dexamethasone-induced bone loss molecular markers, it potentiates osteoblast apoptosis. Our results suggest that the synergistic effect could contribute to reducing GC clinical doses, ineffective by itself but effective in combination with an antihistamine. This could result in a therapeutic advantage, as the addition of an antihistamine may reinforce the wanted effects of GCs, while related adverse effects could be diminished or at least mitigated. By modulating the patterns of gene activation/repression mediated by GR, antihistamines could enhance only the desired effects of GCs, allowing their effective dose to be reduced. Further research is needed to correctly determine the clinical scope, benefits, and potential risks of this therapeutic strategy.

Repression of transcription by the glucocorticoid receptor: A parsimonious model for the genomics era

Glucocorticoids are potent anti-inflammatory drugs that are used to treat an extraordinary range of human disease, including COVID-19, underscoring the ongoing importance of understanding their molecular mechanisms. Early studies of GR signaling led to broad acceptance of models in which glucocorticoid receptor (GR) monomers tether repressively to inflammatory transcription factors, thus abrogating inflammatory gene expression. However, newer data challenge this core concept and present an exciting opportunity to reframe our understanding of GR signaling. Here, we present an alternate, two-part model for transcriptional repression by glucocorticoids. First, widespread GR-mediated induction of transcription results in rapid, primary repression of inflammatory gene transcription and associated enhancers through competition-based mechanisms. Second, a subset of GR-induced genes, including targets that are regulated in coordination with inflammatory transcription factors such as NF-κB, exerts secondary repressive effects on inflammatory gene expression. Within this framework, emerging data indicate that the gene set regulated through the cooperative convergence of GR and NF-κB signaling is central to the broad clinical effectiveness of glucocorticoids in terminating inflammation and promoting tissue repair.

An intrinsically disordered region-mediated confinement state contributes to the dynamics and function of transcription factors

Transcription factors (TFs) regulate gene expression by binding to specific consensus motifs within the local chromatin context. The mechanisms by which TFs navigate the nuclear environment as they search for binding sites remain unclear. Here, we used single-molecule tracking and machine-learning-based classification to directly measure the nuclear mobility of the glucocorticoid receptor (GR) in live cells. We revealed two distinct and dynamic low-mobility populations. One accounts for specific binding to chromatin, while the other represents a confinement state that requires an intrinsically disordered region (IDR), implicated in liquid-liquid condensate subdomains. Further analysis showed that the dwell times of both subpopulations follow a power-law distribution, consistent with a broad distribution of affinities on the GR cistrome and interactome. Together, our data link IDRs with a confinement state that is functionally distinct from specific chromatin binding and modulates the transcriptional output by increasing the local concentration of TFs at specific sites.

Phasing the intranuclear organization of steroid hormone receptors

Steroid receptors (SRs) encompass a family of transcription factors that regulate the expression of thousands of genes upon binding to steroid hormones and include the glucocorticoid, androgen, progesterone, estrogen and mineralocorticoid receptors. SRs control key physiological and pathological processes, thus becoming relevant drug targets. As with many other nuclear proteins, hormone-activated SRs concentrate in multiple discrete foci within the cell nucleus. Even though these foci were first observed ∼25 years ago, their exact structure and function remained elusive. In the last years, new imaging methodologies and theoretical frameworks improved our understanding of the intranuclear organization. These studies led to a new paradigm stating that many membraneless nuclear compartments, including transcription-related foci, form through a liquid–liquid phase separation process. These exciting ideas impacted the SR field by raising the hypothesis of SR foci as liquid condensates involved in transcriptional regulation. In this work, we review the current knowledge about SR foci formation under the light of the condensate model, analyzing how these structures may impact SR function. These new ideas, combined with state-of-the-art techniques, may shed light on the biophysical mechanisms governing the formation of SR foci and the biological function of these structures in normal physiology and disease.

Genomic determinants implicated in the glucocorticoid-mediated induction of KLF9 in pulmonary epithelial cells

Ligand-activated glucocorticoid receptor (GR) elicits variable glucocorticoid-modulated transcriptomes in different cell types. However, some genes, including Krüppel-like factor 9 (KLF9), a putative transcriptional repressor, demonstrate conserved responses. We show that glucocorticoids induce KLF9 expression in the human airways in vivo and in differentiated human bronchial epithelial (HBE) cells grown at air-liquid interface (ALI). In A549 and BEAS-2B pulmonary epithelial cells, glucocorticoids induce KLF9 expression with similar kinetics to primary HBE cells in submersion culture. A549 and BEAS-2B ChIP-seq data reveal four common glucocorticoid-induced GR binding sites (GBSs). Two GBSs mapped to the 5'-proximal region relative to KLF9 transcription start site (TSS) and two occurred at distal sites. These were all confirmed in primary HBE cells. Global run-on (GRO) sequencing indicated robust enhancer RNA (eRNA) production from three of these GBSs in BEAS-2B cells. This was confirmed in A549 cells, plus submersion, and ALI culture of HBE cells. Cloning each GBS into luciferase reporters revealed glucocorticoid-induced activity requiring a glucocorticoid response element (GRE) within each distal GBS. While the proximal GBSs drove modest reporter induction by glucocorticoids, this region exhibited basal eRNA production, RNA polymerase II enrichment, and looping to the TSS, plausibly underlying constitutive KLF9 expression. Post glucocorticoid treatment, interactions between distal and proximal GBSs and the TSS correlated with KLF9 induction. CBP/P300 silencing reduced proximal GBS activity, but negligibly affected KLF9 expression. Overall, a model for glucocorticoid-mediated regulation of KLF9 involving multiple GBSs is depicted. This work unequivocally demonstrates that mechanistic insights gained from cell lines can translate to physiologically relevant systems.

Hypoxia regulates GR function through multiple mechanisms involving microRNAs 103 and 107

Glucocorticoids (Gcs) potently inhibit inflammation, and regulate liver energy metabolism, often acting in a hypoxic environment. We now show hypoxic conditions open a specific GR cistrome, and prevent access of GR to part of the normoxic GR cistrome. Motif analysis identified enrichment of KLF4 binding sites beneath those peaks of GR binding exclusive to normoxia, implicating KLF4 as a pioneer, or co-factor under these conditions. Hypoxia reduced KLF4 expression, however, knockdown of KLF4 did not impair GR recruitment. KLF4 is a known target of microRNAs 103 and 107, both of which are induced by hypoxia. Expression of mimics to either microRNA103, or microRNA107 inhibited GR transactivation of normoxic target genes, thereby replicating the hypoxic effect. Therefore, studies in hypoxia reveal that microRNAs 103 and 107 are potent regulators of GR function. We have now identified a new pathway linking hypoxia through microRNAs 103 and 107 to regulation of GR function.

ETS Proteins Bind with Glucocorticoid Receptors: Relevance for Treatment of Ewing Sarcoma

The glucocorticoid receptor (GR) acts as a ubiquitous cortisol-dependent transcription factor (TF). To identify co-factors, we used protein-fragment complementation assays and found that GR recognizes FLI1 and additional ETS family proteins, TFs relaying proliferation and/or migration signals. Following steroid-dependent translocation of FLI1 and GR to the nucleus, the FLI1-specific domain (FLS) binds with GR and strongly enhances GR's transcriptional activity. This interaction has functional consequences in Ewing sarcoma (ES), childhood and adolescence bone malignancies driven by fusions between EWSR1 and FLI1. In vitro, GR knockdown inhibited the migration and proliferation of ES cells, and in animal models, antagonizing GR (or lowering cortisol) retarded both tumor growth and metastasis from bone to lung. Taken together, our findings offer mechanistic rationale for repurposing GR-targeting drugs for the treatment of patients with ES.

GR-mediated FTO transactivation induces lipid accumulation in hepatocytes via demethylation of m6A on lipogenic mRNAs

Chronic stress or excessive exposure to glucocorticoids (GC) contributes to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Glucocorticoid receptor (GR) mediates the action of GC, but its downstream signalling is not fully understood. Fat mass and obesity associated (FTO) protein and its demethylation substrate N6-methyladenosine (m⁶A) are both reported to participate in the regulation of lipid metabolism, yet it remains unknown whether they are involved in GC-induced hepatic lipid accumulation as new components of GR signalling. In this study, we use both in vivo and in vitro models of GC-induced hepatic lipid accumulation and demonstrate that the activation of lipogenic genes and accumulation of lipid in liver cells are mediated by GR-dependent FTO transactivation and m⁶A demethylation on mRNA of lipogenic genes. Targeted mutation of m⁶A methylation sites and FTO knockdown further validated the role of m⁶A on 3'UTR of sterol regulatory element-binding transcription factor 1 and stearoyl-CoA desaturase mRNAs. Finally, FTO knockdown significantly alleviated dexamethasone-induced fatty liver in mice. These results demonstrate a role of GR-mediated FTO transactivation and m⁶A demethylation in the pathogenesis of NAFLD and provide new insight into GR signalling in the regulation of fat metablism in the liver.

Beyond the heterodimer model for mineralocorticoid and glucocorticoid receptor interactions in nuclei and at DNA

Glucocorticoid (GR) and mineralocorticoid receptors (MR) are believed to classically bind DNA as homodimers or MR-GR heterodimers to influence gene regulation in response to pulsatile basal or stress-evoked glucocorticoid secretion. Pulsed corticosterone presentation reveals MR and GR co-occupy DNA only at the peaks of glucocorticoid oscillations, allowing interaction. GR DNA occupancy was pulsatile, while MR DNA occupancy was prolonged through the inter-pulse interval. In mouse mammary 3617 cells MR-GR interacted in the nucleus and at a chromatin-associated DNA binding site. Interactions occurred irrespective of ligand type and receptors formed complexes of higher order than heterodimers. We also detected MR-GR interactions ex-vivo in rat hippocampus. An expanded range of MR-GR interactions predicts structural allostery allowing a variety of transcriptional outcomes and is applicable to the multiple tissue types that co-express both receptors in the same cells whether activated by the same or different hormones.

Fighting the Fire: Mechanisms of Inflammatory Gene Regulation by the Glucocorticoid Receptor

For many decades, glucocorticoids have been widely used as the gold standard treatment for inflammatory conditions. Unfortunately, their clinical use is limited by severe adverse effects such as insulin resistance, cardiometabolic diseases, muscle and skin atrophies, osteoporosis, and depression. Glucocorticoids exert their effects by binding to the Glucocorticoid Receptor (GR), a ligand-activated transcription factor which both positively, and negatively regulates gene expression. Extensive research during the past several years has uncovered novel mechanisms by which the GR activates and represses its target genes. Genome-wide studies and mouse models have provided valuable insight into the molecular mechanisms of inflammatory gene regulation by GR. This review focusses on newly identified target genes and GR co-regulators that are important for its anti-inflammatory effects in innate immune cells, as well as mutations within the GR itself that shed light on its transcriptional activity. This research progress will hopefully serve as the basis for the development of safer immune suppressants with reduced side effect profiles.

GR Dimerization and the Impact of GR Dimerization on GR Protein Stability and Half-Life

Pharmacologically, glucocorticoids, which mediate their effects via the glucocorticoid receptor (GR), are a most effective therapy for inflammatory diseases despite the fact that chronic use causes side-effects and acquired GC resistance. The design of drugs with fewer side-effects and less potential for the development of resistance is therefore considered crucial for improved therapy. Dimerization of the GR is an integral step in glucocorticoid signaling and has been identified as a possible molecular site to target for drug development of anti-inflammatory drugs with an improved therapeutic index. Most of the current understanding regarding the role of GR dimerization in GC signaling derives for dimerization deficient mutants, although the role of ligands biased toward monomerization has also been described. Even though designing for loss of dimerization has mostly been applied for reduction of side-effect profile, designing for loss of dimerization may also be a fruitful strategy for the development of GC drugs with less potential to develop GC resistance. GC-induced resistance affects up to 30% of users and is due to a reduction in the GR functional pool. Several molecular mechanisms of GC-mediated reductions in GR pool have been described, one of which is the autologous down-regulation of GR density by the ubiquitin-proteasome-system (UPS). Loss of GR dimerization prevents autologous down-regulation of the receptor through modulation of interactions with components of the UPS and post-translational modifications (PTMs), such as phosphorylation, which prime the GR for degradation. Rational design of conformationally biased ligands that select for a monomeric GR conformation, which increases GC sensitivity through improving GR protein stability and increasing half-life, may be a productive avenue to explore. However, potential drawbacks to this approach should be considered as well as the advantages and disadvantages in chronic vs. acute treatment regimes.

Airway smooth muscle cells are insensitive to the anti-proliferative effects of corticosteroids: The novel role of insulin growth factor binding Protein-1 in asthma

Airway remodeling in asthma manifests, in part, as enhanced airway smooth muscle (ASM) mass, due to myocyte proliferation. While the anti-proliferative effects of glucocorticoid (GC) were investigated in normal ASM cells (NASMC), little is known about such effects in ASM cells derived from asthma subjects (AASMC). We posit that GC differentially modulates mitogen-induced proliferation of AASMC and NASMC. Cells were cultured, starved, then treated with Epidermal growth factor (EGF) (10 ng/ml) and Platelet-derived growth factor (PDGF) (10 ng/ml) for 24 h and/or fluticasone propionate (FP) (100 nM) added 2 h before. Cell counts and flow cytometry analyses showed that FP failed to decrease the cell number of and DNA synthesis in AASMC irrespective of mitogens used. We also examine the ability of Insulin Growth Factor Binding Protein-1 (IGFBP-1), a steroid-inducible gene that deters cell growth in other cell types, to inhibit proliferation of AASMC where FP failed. We found that FP increased IGFBP1 mRNA and protein levels. Interestingly, the addition of IGFBP1 (1 μg/ml) to FP completely inhibited the proliferation of AASMC irrespective to the mitogens used. Further investigation of different signaling molecules involved in ASM growth and GC receptor functions (Protein kinase B (PKB/AKT), Mitogen-activated protein kinases (MAPKs), Focal Adhesion Kinase (FAK)) showed that IGFBP-1 selectively decreased mitogen-induced p38 phosphorylation in AASMC. Collectively, our results show the insensitivity of AASMC to the anti-proliferative effects of GC, and demonstrate the ability of IGFBP1 to modulate AASMC growth representing, hence, a promising strategy to control ASM growth in subjects with GC insensitive asthma.

Temporal dynamics of cortisol-associated changes in mRNA expression of glucocorticoid responsive genes FKBP5, GILZ, SDPR, PER1, PER2 and PER3 in healthy humans

Secretion of the stress hormone cortisol follows a circadian rhythm and is stimulated following stress exposure. Cortisol regulates the transcription of several genes, primarily through activation of the glucocorticoid receptor (GR). Previously, we showed an upregulation of PERIOD genes PER1 and PER3 after pharmacological/glucocorticoid challenge in vivo and in vitro. The current study aims to investigate the temporal association between unstimulated, diurnal cortisol secretion and the expression of selected GR-target genes (PER1, PER2, PER3, FKBP5, GILZ and SDPR) in vivo to determine the timing of the most pronounced coupling between cortisol and mRNA expression. Unstimulated plasma and saliva cortisol concentrations and gene expression levels in whole blood were measured every 15 min from early morning until 16:00 h in 18 healthy men. Time-lagged correlations of cortisol concentrations with mRNA expression levels were assessed allowing lags between -240 and + 240 min. Strong positive correlations at non-zero lags between cortisol levels and the expression of FKBP5 (plasma: r = 0.74 (CI = 0.65-0.81), p <  0.001, lag + 90 min; saliva: r = 0.71 (CI = 0.61-0.78), p <  0.001, lag + 75 min), and GILZ (plasma: r = 0.59 (CI = 0.46-0.69), p <  0.001, lag + 30 min; saliva r = 0.53 (CI = 0.41-0.63), p <  0.001, lag +15 min) were observed. Expressions of PERIOD genes and SDPR correlated only weakly with cortisol (all |r| < 0.25). Our findings demonstrate strong correlations between cortisol secretion and gene expression in humans under unstimulated conditions. The observed time-lags can guide future research aiming to characterize glucocorticoid-dependent gene expression in clinical samples with stress-related disorders.

A Model of Glucocorticoid Receptor Interaction With Coregulators Predicts Transcriptional Regulation of Target Genes

Regulatory factors that control gene transcription in multicellular organisms are assembled in multicomponent complexes by combinatorial interactions. In this context, nuclear receptors provide well-characterized and physiologically relevant systems to study ligand-induced transcription resulting from the integration of cellular and genomic information in a cell- and gene-specific manner. Here, we developed a mathematical model describing the interactions between the glucocorticoid receptor (GR) and other components of a multifactorial regulatory complex controlling the transcription of GR-target genes, such as coregulator peptides. We support the validity of the model in relation to gene-specific GR transactivation with gene transcription data from A549 cells and in vitro real time quantification of coregulator-GR interactions. The model accurately describes and helps to interpret ligand-specific and gene-specific transcriptional regulation by the GR. The comprehensive character of the model allows future insight into the function and relative contribution of the molecular species proposed in ligand- and gene-specific transcriptional regulation.

Clinical Use and Molecular Action of Corticosteroids in the Pediatric Age

Corticosteroids are the mainstay of therapy for many pediatric disorders and sometimes are life-saving. Both endogenous and synthetic derivatives diffuse across the cell membrane and, by binding to their cognate glucocorticoid receptor, modulate a variety of physiological functions, such as glucose metabolism, immune homeostasis, organ development, and the endocrine system. However, despite their proved and known efficacy, corticosteroids show a lot of side effects, among which growth retardation is of particular concern and specific for pediatric age. The aim of this review is to discuss the mechanism of action of corticosteroids, and how their genomic effects have both beneficial and adverse consequences. We will focus on the use of corticosteroids in different pediatric subspecialties and most common diseases, analyzing the most recent evidence.

Molecular dynamics simulations of the glucocorticoid receptor DNA-binding domain suggest a role of the lever-arm mobility in transcriptional output

One of the first and essential steps in gene expression regulation involves the recruitment of transcription factors (TFs) to specific response elements located at enhancers and/or promoters of targeted genes. These DNA elements have a certain variability in both sequence and length, which may affect the final transcriptional output. The molecular mechanisms in which TFs integrate the subtle differences within specific recognition sequences to offer different transcriptional responses is still largely unknown. Here we used molecular dynamics simulations to study the DNA binding behavior of the glucocorticoid receptor (GR), a ligand-regulated TF with pleiotropic effects in almost all cells. By comparing the behavior of the wild type receptor and a well characterized Ala477Thr substitution within the rat GR DNA binding domain, we found that the region that connects the two-zinc fingers (i.e. the lever arm) would likely play a key role in GR transcriptional output.

Site-specific phosphorylation regulates the structure and function of an intrinsically disordered domain of the glucocorticoid receptor

Intrinsically disordered (ID) regions of the transcription factor proteins have much larger frequency of phosphorylation sites than ordered regions, suggesting an important role in their regulatory capacity. Consistent with this phenomenon, most of the functionally known phosphorylation sites in the steroid receptor family of transcription factors are located in the ID N-terminal domain that contains a powerful activation function (AF1) region. In this study, we determined the structural and functional consequences of functionally known phosphorylation residues (Ser203, 211, and 226) located in the human glucocorticoid receptor’s (GR’s) ID AF1 domain. We report the relative importance of each phosphorylation site in inducing a functionally active ordered conformation in GR’s ID AF1 domain. Our data demonstrate a mechanism through which ID domain of the steroid receptors and other similar transcription factors may adopt a functionally active conformation under physiological conditions.

Glucocorticoid Receptor:MegaTrans Switching Mediates the Repression of an ERα-Regulated Transcriptional Program

The molecular mechanisms underlying the opposing functions of glucocorticoid receptors (GRs) and estrogen receptor α (ERα) in breast cancer development remain poorly understood. Here we report that, in breast cancer cells, liganded GR represses a large ERα-activated transcriptional program by binding, in trans, to ERα-occupied enhancers. This abolishes effective activation of these enhancers and their cognate target genes, and it leads to the inhibition of ERα-dependent binding of components of the MegaTrans complex. Consistent with the effects of SUMOylation on other classes of nuclear receptors, dexamethasone (Dex)-induced trans-repression of the estrogen E₂ program appears to depend on GR SUMOylation, which leads to stable trans-recruitment of the GR-N-CoR/SMRT-HDAC3 corepressor complex on these enhancers. Together, these results uncover a mechanism by which competitive recruitment of DNA-binding nuclear receptors/transcription factors in trans to hot spot enhancers serves as an effective biological strategy for trans-repression, with clear implications for breast cancer and other diseases.

Identification and characterization of BATF3 as a context-specific coactivator of the glucocorticoid receptor

The ability of the glucocorticoid receptor (GR) to regulate the transcriptional output of genes relies on its interactions with transcriptional coregulators. However, which coregulators are required for GR-dependent activation is context-dependent and can be influenced by the sequence of the DNA bound by GR and by the nature of the GR isoform responsible for the regulation of a gene. Here, we screened for GR-interacting proteins for which the interaction signal differed between two GR isoforms GRα and GRγ. These isoforms diverge by a single amino acid insertion in a domain, the lever arm, which adopts DNA sequence-specific conformations. We identify Basic Leucine Zipper ATF-Like Transcription Factor 3 (BATF3), an AP-1 family transcription factor, as a GR coregulator whose interaction with GR is modulated by the lever arm. Further, a combination of experiments uncovered that BATF3 acts as a gene-specific coactivator of GR whose coactivator potency is influenced by the sequence of the GR binding site. Together, our findings suggest that GR isoform and the sequence of GR binding site influence the interaction of GR with BATF3, which might direct the assembly of gene-specific regulatory complexes to fine-tune the expression of individual GR target genes.

The nature of the GRE influences the screening for GR-activity enhancing modulators

Glucocorticoid resistance (GCR), i.e. unresponsiveness to the beneficial anti-inflammatory activities of the glucocorticoid receptor (GR), poses a serious problem in the treatment of inflammatory diseases. One possible solution to try and overcome GCR, is to identify molecules that prevent or revert GCR by hyper-stimulating the biological activity of the GR. To this purpose, we screened for compounds that potentiate the dexamethasone (Dex)-induced transcriptional activity of GR. To monitor GR transcriptional activity, the screen was performed using the lung epithelial cell line A549 in which a glucocorticoid responsive element (GRE) coupled to a luciferase reporter gene construct was stably integrated. Histone deacetylase inhibitors (HDACi) such as Vorinostat and Belinostat are two broad-spectrum HDACi that strongly increased the Dex-induced luciferase expression in our screening system. In sharp contrast herewith, results from a genome-wide transcriptome analysis of Dex-induced transcripts using RNAseq, revealed that Belinostat impairs the ability of GR to transactivate target genes. The stimulatory effect of Belinostat in the luciferase screen further depends on the nature of the reporter construct. In conclusion, a profound discrepancy was observed between HDACi effects on two different synthetic promoter-luciferase reporter systems. The favorable effect of HDACi on gene expression should be evaluated with care, when considering them as potential therapeutic agents. GEO accession number GSE96649.

Glucocorticoid receptor control of transcription: precision and plasticity via allostery

The glucocorticoid receptor (GR) is a constitutively expressed transcriptional regulatory factor (TRF) that controls many distinct gene networks, each uniquely determined by particular cellular and physiological contexts. The precision of GR-mediated responses seems to depend on combinatorial, context-specific assembly of GR-nucleated transcription regulatory complexes at genomic response elements. In turn, evidence suggests that context-driven plasticity is conferred by the integration of multiple signals, each serving as an allosteric effector of GR conformation, a key determinant of regulatory complex composition and activity. This structural and mechanistic perspective on GR regulatory specificity is likely to extend to other eukaryotic TRFs.

Glucocorticoid Insensitivity in Virally Infected Airway Epithelial Cells Is Dependent on Transforming Growth Factor-β Activity

Asthma and chronic obstructive pulmonary disease (COPD) exacerbations are commonly associated with respiratory syncytial virus (RSV), rhinovirus (RV) and influenza A virus (IAV) infection. The ensuing airway inflammation is resistant to the anti-inflammatory actions of glucocorticoids (GCs). Viral infection elicits transforming growth factor-β (TGF-β) activity, a growth factor we have previously shown to impair GC action in human airway epithelial cells through the activation of activin-like kinase 5 (ALK5), the type 1 receptor of TGF-β. In the current study, we examine the contribution of TGF-β activity to the GC-resistance caused by viral infection. We demonstrate that viral infection of human bronchial epithelial cells with RSV, RV or IAV impairs GC anti-inflammatory action. Poly(I:C), a synthetic analog of double-stranded RNA, also impairs GC activity. Both viral infection and poly(I:C) increase TGF-β expression and activity. Importantly, the GC impairment was attenuated by the selective ALK5 (TGFβRI) inhibitor, SB431542 and prevented by the therapeutic agent, tranilast, which reduced TGF-β activity associated with viral infection. This study shows for the first time that viral-induced glucocorticoid-insensitivity is partially mediated by activation of endogenous TGF-β.

In this study, we investigate how respiratory viral infection interferes with the anti-inflammatory actions of glucocorticoid (GC) drugs, which are a highly effective group of anti-inflammatory agents widely used in the treatment of chronic inflammatory airway diseases, including asthma and chronic obstructive pulmonary disease (COPD). Exacerbations of both asthma (“asthma attacks”) and COPD are often caused by viral infection, which does not respond well to GC therapy. Patients are often hospitalized placing a large burden on healthcare systems around the world, with the young, elderly, and those with a poor immune system particularly at risk. We show that viral infection of airway epithelial cells causes increased expression and activity of transforming growth factor-beta (TGF-β), which interferes with GC drug action. Importantly, we have shown for the first time that inhibiting TGF-β activity in the airways could serve as a new strategy to prevent and/or treat viral exacerbations of chronic airway diseases.

Glucocorticoid Signaling: An Update from a Genomic Perspective

Glucocorticoid hormones (GC) regulate essential physiological functions including energy homeostasis, embryonic and postembryonic development, and the stress response. From the biomedical perspective, GC have garnered a tremendous amount of attention as highly potent anti-inflammatory and immunosuppressive medications indispensable in the clinic. GC signal through the GC receptor (GR), a ligand-dependent transcription factor whose structure, DNA binding, and the molecular partners that it employs to regulate transcription have been under intense investigation for decades. In particular, next-generation sequencing-based approaches have revolutionized the field by introducing a unified platform for a simultaneous genome-wide analysis of cellular activities at the level of RNA production, binding of transcription factors to DNA and RNA, and chromatin landscape and topology. Here we describe fundamental concepts of GC/GR function as established through traditional molecular and in vivo approaches and focus on the novel insights of GC biology that have emerged over the last 10 years from the rapidly expanding arsenal of system-wide genomic methodologies.

Crosstalk between C/EBP homologous protein (CHOP) and glucocorticoid receptor in lung cancer

Loss of homeostasis triggers the endoplasmic reticulum (ER) stress response and activates the unfolded protein response (UPR) resulting in the induction of the CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP). Glucocorticoids (GCs), via the glucocorticoid receptor (GR), regulate numerous physiological processes in an effort to maintain homeostasis. Previous studies demonstrated that glucocorticoids suppress ER stress by enhancing correct folding of secreted proteins and degradation of misfolded proteins. Here, we describe a novel crosstalk between ER-stress and the glucocorticoid receptor signaling. We showed that treatment of wild type mice with Tunicamycin (inducer of ER-stress) increased GR protein levels in the lungs. Treatment of A549 cells (human lung cancer cells) with ER stress inducers modulated the Dexamethasone-induced subcellular localization of GR and the phosphorylated forms of GR (pGRSer211 and pGRSer203) with concomitant changes in the expression of primary GR-target genes. We demonstrated a significant protein-protein interaction between GR and CHOP, (GR-CHOP heterocomplex formation) under ER stress conditions. The functional consequences of ER stress- GR signaling crosstalk were assessed and demonstrated that long time exposure (24-48 h) of A549 cells to dexamethasone (10(-6) M) reversed the Tunicamycin-induced cell death, a phenomenon associated with parallel increases in GR protein content, increases in cell survival parameters and decreases in cell apoptosis-related parameters. Our study provides evidence that there is a cross talk between ER-stress and GR signaling, this being associated with mutual functional antagonism between CHOP and GR-mediated pathways in lung cells with important implications in lung cell function.

Sequences flanking the core-binding site modulate glucocorticoid receptor structure and activity

The glucocorticoid receptor (GR) binds as a homodimer to genomic response elements, which have particular sequence and shape characteristics. Here we show that the nucleotides directly flanking the core-binding site, differ depending on the strength of GR-dependent activation of nearby genes. Our study indicates that these flanking nucleotides change the three-dimensional structure of the DNA-binding site, the DNA-binding domain of GR and the quaternary structure of the dimeric complex. Functional studies in a defined genomic context show that sequence-induced changes in GR activity cannot be explained by differences in GR occupancy. Rather, mutating the dimerization interface mitigates DNA-induced changes in both activity and structure, arguing for a role of DNA-induced structural changes in modulating GR activity. Together, our study shows that DNA sequence identity of genomic binding sites modulates GR activity downstream of binding, which may play a role in achieving regulatory specificity towards individual target genes.

Glucocorticoid and TNF signaling converge at A20 (TNFAIP3) to repress airway smooth muscle cytokine expression

Airway smooth muscle is a major target tissue for glucocorticoid (GC)-based asthma therapies, however, molecular mechanisms through which the GC receptor (GR) exerts therapeutic effects in this key airway cell type have not been fully elucidated. We previously identified the nuclear factor-κB (NF-κB) inhibitor, A20 (TNFAIP3), as a mediator of cytokine repression by glucocorticoids (GCs) in airway epithelial cells and defined cooperative regulation of anti-inflammatory genes by GR and NF-κB as a key mechanistic underpinning of airway epithelial GR function. Here, we expand on these findings to determine whether a similar mechanism is operational in human airway smooth muscle (HASM). Using HASM cells derived from normal and fatal asthma samples as an in vitro model, we demonstrate that GCs spare or augment TNF-mediated induction of A20 (TNFAIP3), TNIP1, and NFKBIA, all implicated in negative feedback control of NF-κB-driven inflammatory processes. We applied chromatin immunoprecipitation and reporter analysis to show that GR and NF-κB directly regulate A20 expression in HASM through cooperative induction of an intronic enhancer. Using overexpression, we show for the first time that A20 and its interacting partner, TNIP1, repress TNF signaling in HASM cells. Moreover, we applied small interfering RNA-based gene knockdown to demonstrate that A20 is required for maximal cytokine repression by GCs in HASM. Taken together, our data suggest that inductive regulation of A20 by GR and NF-κB contributes to cytokine repression in HASM.

The Interactome of the Glucocorticoid Receptor and Its Influence on the Actions of Glucocorticoids in Combatting Inflammatory and Infectious Diseases

Glucocorticoids (GCs) have been widely used for decades as a first-line treatment for inflammatory and autoimmune diseases. However, their use is often hampered by the onset of adverse effects or resistance. GCs mediate their effects via binding to glucocorticoid receptor (GR), a transcription factor belonging to the family of nuclear receptors. An important aspect of GR's actions, including its anti-inflammatory capacity, involves its interactions with various proteins, such as transcription factors, cofactors, and modifying enzymes, which codetermine receptor functionality. In this review, we provide a state-of-the-art overview of the protein-protein interactions (PPIs) of GR that positively or negatively affect its anti-inflammatory properties, along with mechanistic insights, if known. Emphasis is placed on the interactions that affect its anti-inflammatory effects in the presence of inflammatory and microbial diseases.

Bisphenol S Induces Adipogenesis in Primary Human Preadipocytes From Female Donors

Human exposure to bisphenol A has been associated with negative health outcomes in humans and its use is now regulated in a number of countries. Bisphenol S (BPS) is increasingly used as a replacement for bisphenol A; however, its effects on cellular metabolism and potential role as an endocrine disruptor have not been fully characterized. In the current study, we evaluated the effect of BPS on adipogenesis in primary human preadipocytes. The effect of BPS on the differentiation of human preadipocytes was determined after treatment with BPS at concentrations ranging from 0.1 nM to 25 μM by quantifying lipid accumulation and mRNA and protein levels of key adipogenic markers. Treatment of preadipocytes with 25 μM BPS induced lipid accumulation and increased the mRNA and protein levels of several adipogenic markers including lipoprotein lipase and adipocyte protein 2 (aP2). Cotreatment of cells with the estrogen receptor antagonist ICI-182,780 significantly inhibited BPS-induced lipid accumulation and affected aP2 but not lipoprotein lipase protein levels. Cotreatment of cells with the glucocorticoid receptor antagonist RU486 had no effect on BPS-induced lipid accumulation or protein levels. Furthermore, reporter gene assays using a synthetic promoter containing peroxisome proliferator-activated receptor-γ (PPARG)-response elements and a PPARG-responsive human aP2 promoter region showed that BPS was able to activate PPARG. To our knowledge, this study is the first to show that BPS induces lipid accumulation and differentiation of primary human preadipocytes, and this effect may be mediated through a PPARG pathway.

Transcriptional and metabolic effects of glucocorticoid receptor α and β signaling in zebrafish

In humans and zebrafish, 2 glucocorticoid (GC) receptor (GR) splice variants exist: the canonical GR α-isoform (GRα), and the GRβ. In the present study, we have used the zebrafish model system in order to reveal genes affected by each of these 2 receptor isoforms. By injecting zebrafish embryos with different splice-blocking morpholinos, we could knock down both GR isoforms or could target the alternative splicing of the GR pre-mRNA in favor of the GRβ. In addition, specific GRβ overexpression was achieved by injecting mRNA. Embryos were treated with the synthetic GC dexamethasone, and transcriptome analysis was performed. Two distinct gene clusters were found that were regulated by GRα: one that was regulated by GRα under basal conditions (presence of endogenous cortisol only), and one that was regulated upon increased activation of GRα (using a pharmacological dose of dexamathasone). GRβ may act as a dominant-negative inhibitor of GRα when GRβ is overexpressed and the GRα expression level is knocked down simultaneously. However, without GRα knockdown, no evidence for this activity was found. In addition, the data indicate regulation of gene transcription through other mechanisms of action by GRβ. We also investigated the concentrations of several metabolites using nuclear magnetic resonance spectroscopy. We found that dexamethasone treatment and knockdown of GRα together with overexpression of GRβ had opposite effects on glucose, amino acid, and fatty acid levels. Thus, we have shed new light on the molecular mechanisms of GC-induced effects on metabolism, which are known to increase the risk of obesity, hyperglycemia, and diabetes.

Sustained interleukin-1β exposure modulates multiple steps in glucocorticoid receptor signaling, promoting split-resistance to the transactivation of prominent anti-inflammatory genes by glucocorticoids

Clinical treatment with glucocorticoids (GC) can be complicated by cytokine-induced glucocorticoid low-responsiveness (GC-resistance, GCR), a condition associated with a homogeneous reduction in the expression of GC-receptor- (GR-) driven anti-inflammatory genes. However, GR level and phosphorylation changes modify the expression of individual GR-responsive genes differently. As sustained IL-1β exposure is key in the pathogenesis of several major diseases with prevalent GCR, we examined GR signaling and the mRNA expression of six GR-driven genes in cells cultured in IL-1β and afterwards challenged with GC. After a GC challenge, sustained IL-1β exposure reduced the cytoplasmic GR level, GR(Ser203) and GR(Ser211) phosphorylation, and GR nuclear translocation and led to selective GCR in the expression of the studied genes. Compared to GC alone, in a broad range of GC doses plus sustained IL-1β, FKBP51 mRNA expression was reduced by 1/3, TTP by 2/3, and IRF8 was completely knocked down. In contrast, high GC doses did not change the expression of GILZ and DUSP1, while IGFBP1 was increased by 5-fold. These effects were cytokine-selective, IL-1β dose- and IL-1R1-dependent. The integrated gain and loss of gene functions in the "split GCR" model may provide target cells with a survival advantage by conferring resistance to apoptosis, chemotherapy, and GC.

EPHB4 Protein Expression in Vascular Smooth Muscle Cells Regulates Their Contractility, and EPHB4 Deletion Leads to Hypotension in Mice

EPH kinases are the largest family of receptor tyrosine kinases, and their ligands, ephrins (EFNs), are also cell surface molecules. This work presents evidence that EPHB4 on vascular smooth muscle cells (VSMCs) is involved in blood pressure regulation. We generated gene KO mice with smooth muscle cell-specific deletion of EPHB4. Male KO mice, but not female KO mice, were hypotensive. VSMCs from male KO mice showed reduced contractility when compared with their WT counterparts. Signaling both from EFNBs to EPHB4 (forward signaling) and from EPHB4 to EFNB2 (reverse signaling) modulated VSMC contractility. At the molecular level, the absence of EPHB4 in VSMCs resulted in compromised signaling from Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) to myosin light chain kinase (MLCK) to myosin light chain, the last of which controls the contraction force of motor molecule myosin. Near the cell membrane, an adaptor protein GRIP1, which can associate with EFNB2, was found to be essential in mediating EPHB4-to-EFNB reverse signaling, which regulated VSMC contractility, based on siRNA gene knockdown studies. Our research indicates that EPHB4 plays an essential role in regulating small artery contractility and blood pressure.

Selective coregulator function and restriction of steroid receptor chromatin occupancy by Hic-5

Steroid receptors (SRs) bind specific DNA regulatory sequences, thereby activating and repressing gene expression. We previously showed that transcriptional coregulator Hic-5 facilitates glucocorticoid regulation of some genes but blocks glucocorticoid regulation of others. Here, in a genome-wide analysis, Hic-5 depletion dramatically increased the global number of sites occupied by glucocorticoid receptor (GR) α (the major GR isoform), and many binding sites blocked by Hic-5 were associated with genes for which Hic-5 also blocked glucocorticoid-regulated expression. Hic-5 had similar effects on GRγ (a splice variant of GRα) and estrogen receptor α (ERα), facilitating hormonal regulation of some genes and blocking hormonal regulation of others. As with GRα, Hic-5 blocking of hormonal gene regulation mediated by GRγ and ERα was associated with blocking of GRγ and ERα occupancy at nearby sites. Hic-5 supported hormonal regulation of many more genes for GRα than for GRγ or ERα and thus exhibited selective coregulator functions for different SRs. In contrast, the number of Hic-5-blocked genes was similar for all 3 SRs. In addition to classic coregulator activity, Hic-5 influences the genomic occupancy of multiple SRs and thereby blocks some aspects of hormonal regulation. Thus, Hic-5, because of its tissue-specific expression, could contribute to tissue-specific genomic occupancy and gene regulation by SRs.

An analysis of glucocorticoid receptor-mediated gene expression in BEAS-2B human airway epithelial cells identifies distinct, ligand-directed, transcription profiles with implications for asthma therapeutics

BACKGROUND AND PURPOSE

International asthma guidelines recommend that inhaled glucocorticoids be used as a monotherapy in all patients with mild to moderate disease because of their ability to suppress airways inflammation. Current evidence suggests that the therapeutic benefit of glucocorticoids is due to the transactivation and transrepression of anti-inflammatory and pro-inflammatory genes respectively. However, the extent to which clinically relevant glucocorticoids are equivalent in their ability to modulate gene expression is unclear.

EXPERIMENTAL APPROACH

A pharmacodynamics investigation of glucocorticoid receptor (GR)-mediated gene transactivation in BEAS-2B human airway epithelial cells was performed using a glucocorticoid response element luciferase reporter coupled with an analysis of glucocorticoid-inducible genes encoding proteins with anti-inflammatory and adverse-effect potential.

KEY RESULTS

Using transactivation as a functionally relevant output, a given glucocorticoid displayed a unique, gene expression 'fingerprint' where intrinsic efficacy and GR density were essential determinants. We showed that depending on the gene selected for analysis, a given glucocorticoid can behave as an antagonist, partial agonist, full agonist or even 'super agonist'. In the likely event that different, tissue-dependent gene expression profiles are reproduced in vivo, then the anti-inflammatory and adverse-effect potential of many glucocorticoids currently available as asthma therapeutics may not be equivalent.

CONCLUSIONS AND IMPLICATIONS

The generation of gene expression 'fingerprints' in target and off-target human tissues could assist the rational design of GR agonists with improved therapeutic ratios. This approach could identify compounds that are useful in the management of severe asthma and other inflammatory disorders where systemic exposure is desirable.

Heterogeneity in mechanisms influencing glucocorticoid sensitivity: the need for a systems biology approach to treatment of glucocorticoid-resistant inflammation

Glucocorticoids (GCs) have impressive anti-inflammatory and immunosuppressive effects and show a diversity of actions across a variety of cell phenotypes. Implicit in efforts to optimize GCs as anti-inflammatory agents for any or all indications is the notion that the relevant mechanism(s) of action of GCs are fully elucidated. However, recent advances in understanding GC signalling mechanisms have revealed remarkable complexity and contextual dependence, calling into question whether the mechanisms of action are sufficiently well-described to embark on optimization. In the current review, we address evidence for differences in the mechanism of action in different cell types and contexts, and discuss contrasts in mechanisms of glucocorticoid insensitivity, with a focus on asthma and Chronic Obstructive Pulmonary Disease (COPD). Given this complexity, we consider the potential breadth of impact and selectivity of strategies directed to reversing the glucocorticoid insensitivity.

Mechanisms of Glucocorticoid-Regulated Gene Transcription

One fascinating aspect of glucocorticoid signaling is their broad range of physiological and pharmacological effects. These effects are at least in part a consequence of transcriptional regulation by the glucocorticoid receptor (GR). Activation of GR by glucocorticoids results in tissue-specific changes in gene expression levels with some genes being activated whereas others are repressed. This raises two questions: First, how does GR regulate different subsets of target genes in different tissues? And second, how can GR both activate and repress the expression of genes?To answer these questions, this chapter will describe the function of the various "components" and how they cooperate to mediate the transcriptional responses to glucocorticoids. The first "component" is GR itself. The second "component" is the chromatin and its role in specifying where in the genome GR binds. Binding to the genome however is just the first step in regulating the expression of genes and transcriptional regulation by GR depends on the recruitment of coregulator proteins that either directly or indirectly influence the recruitment and or activity of RNA polymerase II. Ultimately, the integration of inputs including GR isoform, DNA sequence, chromatin and cooperation with coregulators determines which genes are regulated and the direction of their regulation.

Identification of gene signatures for prednisolone-induced metabolic dysfunction in collagen-induced arthritic mice

BACKGROUND

Prednisolone is a potent anti-inflammatory glucocorticoid (GC) but chronic use is hampered by metabolic side effects. Little is known about the long-term effects of GCs on gene-expression in vivo during inflammation.

AIM

Identify gene signatures underlying prednisolone-induced metabolic side effects in a complex in vivo inflammatory setting after long-term treatment.

MATERIALS & METHODS

We performed whole-genome expression profiling in liver and muscle from arthritic and nonarthritic mice treated with several doses of prednisolone for 3 weeks and used text-mining to link gene signatures to metabolic pathways.

RESULTS

Prednisolone-induced gene signatures were highly tissue specific. We identified a short-list of genes significantly affected by both prednisolone and inflammation in liver and involved in glucose and fatty acid metabolism. For several of these genes the association with GCs is novel.

CONCLUSION

The identified gene signatures may provide useful starting points for the development of GCs with a better safety profile.

Glucocorticoid receptor binds half sites as a monomer and regulates specific target genes

Background

Glucocorticoid receptor (GR) is a hormone-activated, DNA-binding transcriptional regulatory factor that controls inflammation, metabolism, stress responses, and other physiological processes. In vitro, GR binds as an inverted dimer to a motif consisting of two imperfectly palindromic 6 bp half sites separated by 3 bp spacers. In vivo, GR employs different patterns of functional surfaces of GR to regulate different target genes. The relationships between GR genomic binding and functional surface utilization have not been defined.

Results

We find that A477T, a GR mutant that disrupts the dimerization interface, differs from wild-type GRα in binding and regulation of target genes. Genomic regions strongly occupied by A477T are enriched for a novel half site motif. In vitro, GRα binds half sites as a monomer. Through the overlap between GRα- and A477T-bound regions, we identify GRα-bound regions containing only half sites. We further identify GR target genes linked with half sites and not with the full motif.

Conclusions

Genomic regions bound by GR differ in underlying DNA sequence motifs and in the GR functional surfaces employed for regulation. Identification of GR binding regions that selectively utilize particular GR surfaces may discriminate sub-motifs, including the half site motif, that favor those surfaces. This approach may contribute to predictive models for GR activity and therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0418-y) contains supplementary material, which is available to authorized users.