Glucocorticoid receptor control of transcription: precision and plasticity via allostery

Glucocorticoid-driven transcriptomes in human airway epithelial cells: commonalities, differences and functional insight from cell lines and primary cells

Background

Glucocorticoids act on the glucocorticoid receptor (GR; NR3C1) to resolve inflammation and, as inhaled corticosteroids (ICS), are the cornerstone of treatment for asthma. However, reduced efficacy in severe disease or exacerbations indicates a need to improve ICS actions.

Methods

Glucocorticoid-driven transcriptomes were compared using PrimeView microarrays between primary human bronchial epithelial (HBE) cells and the model cell lines, pulmonary type II A549 and bronchial epithelial BEAS-2B cells.

Results

In BEAS-2B cells, budesonide induced (≥2-fold, P ≤ 0.05) or, in a more delayed fashion, repressed (≤0.5-fold, P ≤ 0.05) the expression of 63, 133, 240, and 257 or 15, 56, 236, and 344 mRNAs at 1, 2, 6, and 18 h, respectively. Within the early-induced mRNAs were multiple transcriptional activators and repressors, thereby providing mechanisms for the subsequent modulation of gene expression. Using the above criteria, 17 (BCL6, BIRC3, CEBPD, ERRFI1, FBXL16, FKBP5, GADD45B, IRS2, KLF9, PDK4, PER1, RGCC, RGS2, SEC14L2, SLC16A12, TFCP2L1, TSC22D3) induced and 8 (ARL4C, FLRT2, IER3, IL11, PLAUR, SEMA3A, SLC4A7, SOX9) repressed mRNAs were common between A549, BEAS-2B and HBE cells at 6 h. As absolute gene expression change showed greater commonality, lowering the cut-off (≥1.25 or ≤ 0.8-fold) within these groups produced 93 induced and 82 repressed genes in common. Since large changes in few mRNAs and/or small changes in many mRNAs may drive function, gene ontology (GO)/pathway analyses were performed using both stringency criteria. Budesonide-induced genes showed GO term enrichment for positive and negative regulation of transcription, signaling, proliferation, apoptosis, and movement, as well as FOXO and PI3K-Akt signaling pathways. Repressed genes were enriched for inflammatory signaling pathways (TNF, NF-κB) and GO terms for cytokine activity, chemotaxis and cell signaling. Reduced growth factor expression and effects on proliferation and apoptosis were highlighted.

Conclusions

While glucocorticoids repress mRNAs associated with inflammation, prior induction of transcriptional activators and repressors may explain longer-term responses to these agents. Furthermore, positive and negative effects on signaling, proliferation, migration and apoptosis were revealed. Since many such gene expression changes occurred in human airways post-ICS inhalation, the effects observed in cell lines and primary HBE cells in vitro may be relevant to ICS in vivo.

Electronic supplementary material

The online version of this article (10.1186/s12920-018-0467-2) contains supplementary material, which is available to authorized users.

Regulation of Fgf15 expression in the intestine by glucocorticoid receptor

Fibroblast growth factor 15 (FGF15) was previously identified to be highly expressed in the ileum and functions as an endocrine factor to regulate bile acid synthesis in the liver. FGF15 targets its receptor fibroblast growth factor receptor 4 in the liver and serves important roles in energy metabolism, including bile acid homeostasis, glucose metabolism and protein synthesis. The expression of FGF15 is known to be regulated by the transcription factor farnesoid X receptor (FXR). In the present study, reverse transcription-quantitative polymerase chain reaction was used for measuring Fgf15 expression from the animal and tissue culture experiments, and it was identified that dexamethasone, a drug widely used in anti-inflammation therapy, and a classical inducer of glucocorticoid receptor (GR)- and pregnane X receptor (PXR)-target genes, may downregulate Fgf15 expression in the ileum. GR was identified to be highly expressed in the ileum by western blot analysis. Furthermore, it was demonstrated that the downregulation of Fgf15 by dexamethasone is due to the repression of ileal FXR activity via GR; however, not PXR, in the ileum. The present results provide insight for a better understanding of the adverse effects associated with dexamethasone therapy.

Glucocorticoid signaling and osteoarthritis

Glucocorticoids are steroid hormones synthesized and released by the adrenal cortex. Their main function is to maintain cell homeostasis through a variety of signaling pathways, responding to changes in an organism's environment or developmental status. Mimicking the actions of natural glucocorticoids, synthetic glucocorticoids have been recruited to treat many diseases that implicate glucocorticoid receptor signaling such as osteoarthritis. In osteoarthritis, synthetic glucocorticoids aim to alleviate inflammation and pain. The variation of patients' response and the possibility of complications associated with their long-term use have led to a need for a better understanding of glucocorticoid receptor signaling in osteoarthritis. In this review, we performed a literature search in the molecular pathways that link the osteoarthritic joint to the glucocorticoid receptor signaling. We hope that this information will advance research in the field and propose new molecular targets for the development of more optimized therapies for osteoarthritis.

Corticosteroid Action in the Brain: The Potential of Selective Receptor Modulation

Glucocorticoid hormones have important effects on brain function in the context of acute and chronic stress. Many of these are mediated by the glucocorticoid receptor (GR). GR has transcriptional activity which is highly context-specific and differs between tissues and even between cell types. The outcome of GR-mediated transcription depends on the interactome of associated coregulators. Selective GR modulators (SGRMs) are a class of GR ligands that can be used to activate only a subset of GR-coregulator interactions, thereby giving the possibility to induce a unique combination of agonistic and antagonistic GR properties. We describe SGRM action in animal models of brain function and pathology, and argue for their utility as molecular filters, to characterize context-specific GR interactome and transcriptional activity that are responsible for particular glucocorticoid-driven effects in cognitive processes such as memory consolidation. The ultimate objective of this approach is to identify molecular processes that are responsible for adaptive and maladaptive effects of glucocorticoids in the brain.

Identification of Transcription Factor-Binding Sites in the Mouse FOXO1 Promoter

One critical determinant of levels of gene expression is binding of transcription factors to cognate DNA sequences in promoter and enhancer regions of target genes. Transcription factors are DNA-binding proteins to which transcriptional co-regulators are bound, ultimately resulting in histone modifications that change chromatin structure to regulate transcription. Examples of transcription factors include hormone-activated transcription factors such as the glucocorticoid receptor, transcription factors regulated by cell surface receptors such as FOXO1 and Smad2/Smad3, and many others. Promoter regions typically contain multiple, diverse transcription factor-binding sites. Binding sites for cell-type-specific transcription factors involved in cell fate determination such as Runx2, MyoD, or myogenin are frequently observed. Promoter regions are located within ~2 kb upstream of the transcriptional start site, whereas enhancers may be located at some distance from promoter sequences and exert long-range effects. Here, we will discuss classical and emerging technologies by which one can understand the role of binding of specific transcription factors in regulation of transcription of FOXO genes.

Endothelial cell mineralocorticoid receptors oppose VEGF-induced gene expression and angiogenesis

Aldosterone is a key factor in adverse cardiovascular remodeling by acting on the mineralocorticoid receptor (MR) in different cell types. Endothelial MR activation mediates hypertrophy, inflammation and fibrosis. Cardiovascular remodeling is often accompanied by impaired angiogenesis, which is a risk factor for the development of heart failure. In this study, we evaluated the impact of MR in endothelial cells on angiogenesis. Deoxycorticosterone acetate (DOCA)-induced hypertension was associated with capillary rarefaction in the heart of WT mice but not of mice with cell type-specific MR deletion in endothelial cells. Consistently, endothelial MR deletion prevented the inhibitory effect of aldosterone on the capillarization of subcutaneously implanted silicon tubes and on capillary sprouting from aortic ring segments. We examined MR-dependent gene expression in cultured endothelial cells by RNA-seq and identified a cluster of differentially regulated genes related to angiogenesis. We found opposing effects on gene expression when comparing activation of the mineralocorticoid receptor in ECs to treatment with vascular endothelial growth factor (VEGF), a potent activator of angiogenesis. In conclusion, we demonstrate here that activation of endothelial cell MR impaired angiogenic capacity and lead to capillary rarefaction in a mouse model of MR-driven hypertension. MR activation opposed VEGF-induced gene expression leading to the dysregulation of angiogenesis-related gene networks in endothelial cells. Our findings underscore the pivotal role of endothelial cell MR in the pathophysiology of hypertension and related heart disease.

Glucocorticoid Receptor Binding Inhibits an Intronic IL33 Enhancer and is Disrupted by rs4742170 (T) Allele Associated with Specific Wheezing Phenotype in Early Childhood

Interleukin 33 (IL-33) is a cytokine constitutively expressed by various cells of barrier tissues that contribute to the development of inflammatory immune responses. According to its function as an alarmin secreted by lung and airway epithelium, IL-33 plays a significant role in pathogenesis of allergic disorders. IL-33 is strongly involved in the pathogenesis of asthma, anaphylaxis, allergy and dermatitis, and genetic variations in IL33 locus are associated with increased susceptibility to asthma. Genome-wide association studies have identified risk "T" allele of the single-nucleotide polymorphism rs4742170 located in putative IL33 enhancer area as susceptible variant for development of specific wheezing phenotype in early childhood. Here, we demonstrate that risk "T" rs4742170 allele disrupts binding of glucocorticoid receptor (GR) transcription factor to IL33 putative enhancer. The IL33 promoter/enhancer constructs containing either 4742170 (T) allele or point mutations in the GR-binding site, were significantly more active and did not respond to cortisol in a pulmonary epithelial cell line. At the same time, the constructs containing rs4742170 (C) allele with a functional GR-binding site were less active and further inhibitable by cortisol. The latter effect was GR-dependent as it was completely abolished by GR-specific siRNA. This mechanism may explain the negative effect of the rs4742170 (T) risk allele on the development of wheezing phenotype that strongly correlates with allergic sensitization in childhood.

Adrenocortical incidentalomas and bone: from molecular insights to clinical perspectives

Adrenal incidentalomas constitute a common clinical problem with an overall prevalence of around 2-3%, but are more common with advancing age being present in 10% of those aged 70 years. The majority of these lesions are benign adrenocortical adenomas (80%), characterized in 10-40% of the cases by autonomous cortisol hypersecretion, and in 1-10% by aldosterone hypersecretion. Several observational studies have shown that autonomous cortisol and aldosterone hypersecretion are more prevalent than expected in patients with osteopenia and osteoporosis: these patients have accelerated bone loss and an increased incidence of vertebral fractures. In contrast to glucocorticoid action, the effects of aldosterone on bone are less well understood. Recent data, demonstrating a concomitant co-secretion of glucocorticoid metabolites in patients with primary aldosteronism, could explain some of the metabolic abnormalities seen in patients with aldosterone hypersecretion. In clinical practice, patients with unexplained osteoporosis, particularly when associated with other features such as impaired glucose tolerance or hypertension, should be investigated for the possible presence of autonomous cortisol or aldosterone secretion due to an adrenal adenoma. Randomized intervention studies are needed, however, to investigate the optimum interventions for osteoporosis and other co-morbidities in these patients.

Targeting the turnover of oncoproteins as a new avenue for therapeutics development in castration-resistant prostate cancer

The current therapeutic armamentarium for castration-resistant prostate cancer (CRPC) includes second-generation agents such as the Androgen Receptor (AR) inhibitor enzalutamide and the androgen synthesis inhibitor abiraterone acetate, immunotherapies like sipuleucel-T, chemotherapies including docetaxel and cabazitaxel and the radiopharmaceutical radium 223 dichloride. However, relapse of CRPC resistant to these therapeutic modalities occur rapidly. The mechanisms of resistance to these treatments are complex, including specific mutations or alternative splicing of oncogenic proteins. An alternative approach to treating CRPC may be to target the turnover of these molecular drivers of CRPC. In this review, the mechanisms by which protein stability of several oncoproteins such as AR, ERG, GR, CYP17A1 and MYC, will be discussed, as well as how these findings could be translated into novel therapeutic agents.

Disease- and treatment-associated acquired glucocorticoid resistance

The development of resistance to glucocorticoids (GCs) in therapeutic regimens poses a major threat. Generally, GC resistance is congenital or acquired over time as a result of disease progression, prolonged GC treatment or, in some cases, both. Essentially, disruptions in the function and/or pool of the glucocorticoid receptor α (GRα) underlie this resistance. Many studies have detailed how alterations in GRα function lead to diminished GC sensitivity; however, the current review highlights the wealth of data concerning reductions in the GRα pool, mediated by disease-associated and treatment-associated effects, which contribute to a significant decrease in GC sensitivity. Additionally, the current understanding of the molecular mechanisms involved in driving reductions in the GRα pool is discussed. After highlighting the importance of maintaining the level of the GRα pool to combat GC resistance, we present current strategies and argue that future strategies to prevent GC resistance should involve biased ligands with a predisposition for reduced GR dimerization, a strategy originally proposed as the SEMOGRAM-SEDIGRAM concept to reduce the side-effect profile of GCs.

Osteoblast autophagy in glucocorticoid-induced osteoporosis

Administration of glucocorticoids is an effective strategy for treating many inflammatory and autoimmune diseases. However, glucocorticoid treatment can have adverse effects on bone, leading to glucocorticoid-induced osteoporosis (GIO), the most common form of secondary osteoporosis. Although the pathogenesis of GIO has been studied for decades, over the past ten years the autophagy machinery has been implicated as a novel mechanism. Autophagy in osteoblasts, osteocytes, and osteoclasts plays a critical role in the maintenance of bone homeostasis. Herein, we specifically discuss how osteoblast autophagy responds to glucocorticoids and its role in the development of GIO.

The nuclear receptor superfamily: A structural perspective

Nuclear receptors (NRs) are a family of transcription factors that regulate numerous physiological processes such as metabolism, reproduction, inflammation, as well as the circadian rhythm. NRs sense changes in lipid metabolite levels to drive differential gene expression, producing distinct physiologic effects. This is an allosteric process whereby binding a cognate ligand and specific DNA sequences drives the recruitment of diverse transcriptional co-regulators at chromatin and ultimately transactivation or transrepression of target genes. Dysregulation of NR signaling leads to various malignances, metabolic disorders, and inflammatory disease. Given their important role in physiology and ability to respond to small lipophilic ligands, NRs have emerged as valuable therapeutic targets. Here, we summarize and discuss the recent progress on understanding the complex mechanism of action of NRs, primarily from a structural perspective. Finally, we suggest future studies to improve our understanding of NR signaling and better design drugs by integrating multiple structural and biophysical approaches.

Single-molecule force spectroscopy reveals folding steps associated with hormone binding and activation of the glucocorticoid receptor

The glucocorticoid receptor (GR) is a prominent nuclear receptor linked to a variety of diseases and an important drug target. Binding of hormone to its ligand binding domain (GR-LBD) is the key activation step to induce signaling. This process is tightly regulated by the molecular chaperones Hsp70 and Hsp90 in vivo. Despite its importance, little is known about GR-LBD folding, the ligand binding pathway, or the requirement for chaperone regulation. In this study, we have used single-molecule force spectroscopy by optical tweezers to unravel the dynamics of the complete pathway of folding and hormone binding of GR-LBD. We identified a "lid" structure whose opening and closing is tightly coupled to hormone binding. This lid is located at the N terminus without direct contacts to the hormone. Under mechanical load, apo-GR-LBD folds stably and readily without the need of chaperones with a folding free energy of [Formula: see text] The folding pathway is largely independent of the presence of hormone. Hormone binds only in the last step and lid closure adds an additional [Formula: see text] of free energy, drastically increasing the affinity. However, mechanical double-jump experiments reveal that, at zero force, GR-LBD folding is severely hampered by misfolding, slowing it to less than 1·s^-1 From the force dependence of the folding rates, we conclude that the misfolding occurs late in the folding pathway. These features are important cornerstones for understanding GR activation and its tight regulation by chaperones.

Corticosteroid Receptors in the Brain: Transcriptional Mechanisms for Specificity and Context-Dependent Effects

Corticosteroid hormones act in the brain to support adaptation to stress via binding to mineralocorticoid and glucocorticoid receptors (MR and GR). These receptors act in large measure as transcription factors. Corticosteroid effects can be highly divergent, depending on the receptor type, but also on brain region, cell type, and physiological context. These differences ultimately depend on differential interactions of MR and GR with other proteins, which determine ligand binding, nuclear translocation, and transcriptional activities. In this review, we discuss established and potential mechanisms that confer receptor and cell type-specific effects of the MR and GR-mediated transcriptional effects in the brain.

The first crystal structure of a DNA-free nuclear receptor DNA binding domain sheds light on DNA-driven allostery in the glucocorticoid receptor

The glucocorticoid receptor (GR) is a steroid hormone receptor of the nuclear receptor family that regulates gene expression in response to glucocorticoid hormone signaling. Interaction with specific GR DNA binding sequences causes conformational changes in the GR DNA binding domain (DBD) that result in recruitment of specific sets of co-regulators that determine transcriptional outcomes. We have solved the crystal structure of GR DBD in its DNA-free state, the first such crystal structure from any nuclear receptor. In contrast to previous NMR structures, this crystal structure reveals that free GR DBD adopts a conformation very similar to DNA-bound states. The lever arm region is the most variable element in the free GR DBD. Molecular dynamics of the free GR DBD as well as GR DBD bound to activating and repressive DNA elements confirm lever arm flexibility in all functional states. Cluster analysis of lever arm conformations during simulations shows that DNA binding and dimerization cause a reduction in the number of conformations sampled by the lever arm. These results reveal that DNA binding and dimerization drive conformational selection in the GR DBD lever arm region and show how DNA allosterically controls GR structure and dynamics.

Endogenous glucocorticoids control host resistance to viral infection through the tissue-specific regulation of PD-1 expression on NK cells

Controlling the balance between immunity and immunopathology is crucial for host resistance to pathogens. After infection, activation of the hypothalamic-pituitary-adrenal (HPA) axis leads to the production of glucocorticoids. However, the pleiotropic effects of these steroid hormones make it difficult to delineate their precise role(s) in vivo. Here we found that the regulation of natural killer (NK) cell function by the glucocorticoid receptor (GR) was required for host survival after infection with mouse cytomegalovirus (MCMV). Mechanistically, endogenous glucocorticoids produced shortly after infection induced selective and tissue-specific expression of the checkpoint receptor PD-1 on NK cells. This glucocorticoid-PD-1 pathway limited production of the cytokine IFN-γ by spleen NK cells, which prevented immunopathology. Notably, this regulation did not compromise viral clearance. Thus, the fine tuning of NK cell functions by the HPA axis preserved tissue integrity without impairing pathogen elimination, which reveals a novel aspect of neuroimmune regulation.

Recent advances in understanding corticotroph pituitary tumor initiation and progression

Cushing’s disease is the most frequent form of hypercortisolism and is caused by hypophyseal corticotroph adenomas secreting excessive amounts of adrenocorticotropic hormone. Most of the tumors develop sporadically and only a limited number of corticotroph adenomas have been found to be associated with different neuroendocrine syndromes or with familial isolated pituitary adenomas. The pathogenic mechanisms of corticotroph adenomas are largely unknown, but the discovered aberrant chaperoning activity of heat shock protein 90 on the one hand and the presence of ubiquitin-specific protease 8 mutations on the other hand partially explained the causes of their development. Corticotroph tumors arise initially as benign microadenomas but with time form invasively growing aggressive macroadenomas which can switch to corticotroph carcinomas in extremely rare cases. The mechanisms through which corticotroph tumors escape from glucocorticoid negative feedback are still poorly understood, as are the processes that trigger the progression of benign corticotroph adenomas toward aggressive and malignant phenotypes. This review summarizes recent findings regarding initiation and progression of corticotroph pituitary tumors.

Differentially Tolerized Mouse Antigen Presenting Cells Share a Common miRNA Signature Including Enhanced mmu-miR-223-3p Expression Which Is Sufficient to Imprint a Protolerogenic State

Dendritic cells (DCs) are pivotal for the induction and maintenance of antigen-specific tolerance and immunity. miRNAs mediate post-transcriptional gene regulation and control in part the differentiation and stimulation-induced immunogenic function of DCs. However, the relevance of miRNAs for the induction and maintenance of a tolerogenic state of DCs has scarcely been highlighted yet. We differentiated mouse bone marrow cells to conventional/myeloid DCs or to tolerogenic antigen presenting cells (APCs) by using a glucocorticoid (dexamethasone) or interleukin-10, and assessed the miRNA expression patterns of unstimulated and LPS-stimulated cell populations by array analysis and QPCR. Differentially tolerized mouse APCs convergingly down-regulated a set of miRNA species at either state of activation as compared with the corresponding control DC population (mmu-miR-9-5p, mmu-miR-9-3p, mmu-miR-155-5p). These miRNAs were also upregulated in control DCs in response to stimulation. In contrast, miRNAs that were convergingly upregulated in both tolerized APC groups at stimulated state (mmu-miR-223-3p, mmu-miR-1224-5p) were downregulated in control DCs in response to stimulation. Overexpression of mmu-miR-223-3p in DCs was sufficient to prevent stimulation-associated acquisition of potent T cell stimulatory capacity. Overexpression of mmu-miR-223-3p in a DC line resulted in attenuated expression of known (Cflar, Rasa1, Ras) mRNA targets of this miRNA species shown to affect pathways that control DC activation. Taken together, we identified sets of miRNAs convergingly regulated in differentially tolerized APCs, which may contribute to imprint stimulation-resistant tolerogenic function as demonstrated for mmu-miR-223-3p. Knowledge of miRNAs with protolerogenic function enables immunotherapeutic approaches aimed to modulate immune responses by regulating miRNA expression.

Glucocorticoid receptor single nucleotide polymorphisms are associated with acute crisis pain in sickle cell disease

AIM

Pain in sickle cell disease patients is heterogeneous and genetic polymorphisms may predispose an individual to varied vulnerability to painful events. We studied the association of SNPs in the glucocorticoid receptor gene (NR3C1) with pain in sickle cell disease.

METHOD

Acute pain was scored as the number of utilizations due to crisis pain in a 12-month period. Chronic pain was calculated as the Composite Pain Index score.

RESULTS & CONCLUSION

rs33389 T allele (IRR = 1.53, p = 0.014 additive; IRR = 1.64, p = 0.011 recessive), rs2963155 G allele (IRR = 1.80, p < 0.001 additive; IRR = 2.25, p = 0.021 dominant; IRR = 2.07, p < 0.001 recessive) and rs9324918 C allele (IRR = 1.43, p = 0.021 additive) were associated with higher utilization rates, indicating the potential contribution of NR3C1 polymorphisms to acute pain heterogeneity in sickle cell disease.

Immune Effects of Corticosteroids in Sepsis

Sepsis, a life-threatening organ dysfunction, results from a dysregulated host response to invading pathogens that may be characterized by overwhelming systemic inflammation or some sort of immune paralysis. Sepsis remains a major cause of morbidity and mortality. Treatment is nonspecific and relies on source control and organ support. Septic shock, the most severe form of sepsis is associated with the highest rate of mortality. Two large multicentre trials, undertaken 15 years apart, found that the combination of hydrocortisone and fludrocortisone significantly reduces mortality in septic shock. The corticosteroids family is composed of several molecules that are usually characterized according to their glucocorticoid and mineralocorticoid power, relative to hydrocortisone. While the immune effects of glucocorticoids whether mediated or not by the intracellular glucocorticoid receptor have been investigated for several decades, it is only very recently that potential immune effects of mineralocorticoids via non-renal mineralocorticoid receptors have gained popularity. We reviewed the respective role of glucocorticoids and mineralocorticoids in counteracting sepsis-associated dysregulated immune systems.

Development of a Molecular Signature to Monitor Pharmacodynamic Responses Mediated by In Vivo Administration of Glucocorticoids

OBJECTIVE

To develop an objective, readily measurable pharmacodynamic biomarker of glucocorticoid (GC) activity.

METHODS

Genes modulated by prednisolone were identified from in vitro studies using peripheral blood mononuclear cells from normal healthy volunteers. Using the criteria of a >2-fold change relative to vehicle controls and an adjusted P value cutoff of less than 0.05, 64 up-regulated and 18 down-regulated genes were identified. A composite score of the up-regulated genes was generated using a single-sample gene set enrichment analysis algorithm.

RESULTS

GC gene signature expression was significantly elevated in peripheral blood leukocytes from normal healthy volunteers following oral administration of prednisolone. Expression of the signature increased in a dose-dependent manner, peaked at 4 hours postadministration, and returned to baseline levels by 48 hours after dosing. Lower expression was detected in normal healthy volunteers who received a partial GC receptor agonist, which is consistent with the reduced transactivation potential of this compound. In cohorts of patients with systemic lupus erythematosus and patients with rheumatoid arthritis, expression of the GC signature was negatively correlated with the percentages of peripheral blood lymphocytes and positively correlated with peripheral blood neutrophil counts, which is consistent with the known biology of the GC receptor. Expression of the signature largely agreed with reported GC use in these populations, although there was significant interpatient variability within the dose cohorts.

CONCLUSION

The GC gene signature identified in this study represents a pharmacodynamic marker of GC exposure.

A Comprehensive Overview on Stress Neurobiology: Basic Concepts and Clinical Implications

Stress is recognized as an important issue in basic and clinical neuroscience research, based upon the founding historical studies by Walter Canon and Hans Selye in the past century, when the concept of stress emerged in a biological and adaptive perspective. A lot of research after that period has expanded the knowledge in the stress field. Since then, it was discovered that the response to stressful stimuli is elaborated and triggered by the, now known, stress system, which integrates a wide diversity of brain structures that, collectively, are able to detect events and interpret them as real or potential threats. However, different types of stressors engage different brain networks, requiring a fine-tuned functional neuroanatomical processing. This integration of information from the stressor itself may result in a rapid activation of the Sympathetic-Adreno-Medullar (SAM) axis and the Hypothalamus-Pituitary-Adrenal (HPA) axis, the two major components involved in the stress response. The complexity of the stress response is not restricted to neuroanatomy or to SAM and HPA axes mediators, but also diverge according to timing and duration of stressor exposure, as well as its short- and/or long-term consequences. The identification of neuronal circuits of stress, as well as their interaction with mediator molecules over time is critical, not only for understanding the physiological stress responses, but also to understand their implications on mental health.

Molecular mechanisms of glucocorticoids on skeleton and bone regeneration after fracture

Glucocorticoid hormones (GCs) have profound effects on bone metabolism. Via their nuclear hormone receptor - the GR - they act locally within bone cells and modulate their proliferation, differentiation, and cell death. Consequently, high glucocorticoid levels - as present during steroid therapy or stress - impair bone growth and integrity, leading to retarded growth and glucocorticoid-induced osteoporosis, respectively. Because of their profound impact on the immune system and bone cell differentiation, GCs also affect bone regeneration and fracture healing. The use of conditional-mutant mouse strains in recent research provided insights into the cell-type-specific actions of the GR. However, despite recent advances in system biology approaches addressing GR genomics in general, little is still known about the molecular mechanisms of GCs and GR in bone cells. Here, we review the most recent findings on the molecular mechanisms of the GR in general and the known cell-type-specific actions of the GR in mesenchymal cells and their derivatives as well as in osteoclasts during bone homeostasis, GC excess, bone regeneration and fracture healing.

Single Nucleotide Variations of the Human GR Gene Manifested as Pathologic Mutations or Polymorphisms

The human genome contains numerous single nucleotide variations, and the human glucocorticoid receptor (GR) gene harbors ∼450 of these genetic changes. Among them, extremely rare, nonsynonymous variants, known as pathologic GR gene mutations, develop a characteristic pathologic condition, familial/sporadic generalized glucocorticoid resistance syndrome, by replacing the amino acids critical for GR protein structure and functions, whereas others, known as pathologic polymorphisms, develop mild manifestations recognized mainly at population bases by changing the GR activities slightly. Recent progress on the structural analysis to the GR protein and subsequent computer-based structural simulation revealed details of the molecular defects caused by such pathologic GR gene mutations, including their impact on the receptor interaction to ligands, nuclear receptor coactivators (NCoAs) or DNA glucocorticoid response elements (GREs). Indeed, those found in the GR ligand-binding domain significantly damage protein structure of the ligand-binding pocket and/or the activation function-2 transactivation domain and change their molecular interaction to glucocorticoids or the LxxLL signature motif of NCoAs. Two mutations found in GR DNA-binding domain also affect interaction of the mutant receptors to GRE DNA by affecting the critical amino acid for the interaction or changing local hydrophobic circumstance. In this review, I discuss recent findings on the structural simulation of the pathologic GR mutants in connection to their functional and clinical impacts, along with a brief explanation to recent research achievement on the GR polymorphisms.

Roles of the Glucocorticoid and Mineralocorticoid Receptors in Skin Pathophysiology

The nuclear hormone receptor (NR) superfamily comprises approximately 50 evolutionarily conserved proteins that play major roles in gene regulation by prototypically acting as ligand-dependent transcription factors. Besides their central role in physiology, NRs have been largely used as therapeutic drug targets in many chronic inflammatory conditions and derivatives of their specific ligands, alone or in combination, are frequently prescribed for the treatment of skin diseases. In particular, glucocorticoids (GCs) are the most commonly used compounds for treating prevalent skin diseases such as psoriasis due to their anti-proliferative and anti-inflammatory actions. However, and despite their therapeutic efficacy, the long-term use of GCs is limited because of the cutaneous adverse effects including atrophy, delayed wound healing, and increased susceptibility to stress and infections. The GC receptor (GR/NR3C1) and the mineralocorticoid receptor (MR/NR3C2) are members of the NR subclass NR3C that are highly related, both structurally and functionally. While the GR is ubiquitously expressed and is almost exclusively activated by GCs; an MR has a more restricted tissue expression pattern and can bind GCs and the mineralocorticoid aldosterone with similar high affinity. As these receptors share 95% identity in their DNA binding domains; both can recognize the same hormone response elements; theoretically resulting in transcriptional regulation of the same target genes. However, a major mechanism for specific activation of GRs and/or MRs is at the pre-receptor level by modulating the local availability of active GCs. Furthermore, the selective interactions of each receptor with spatio-temporally regulated transcription factors and co-regulators are crucial for the final transcriptional outcome. While there are abundant genome wide studies identifying GR transcriptional targets in a variety of tissue and cell types; including keratinocytes; the data for MR is more limited thus far. Our group and others have studied the role of GRs and MRs in skin development and disease by generating and characterizing mouse and cellular models with gain- and loss-of-function for each receptor. Both NRs are required for skin barrier competence during mouse development and also play a role in adult skin homeostasis. Moreover, the combined loss of epidermal GRs and MRs caused a more severe skin phenotype relative to single knock-outs (KOs) in developing skin and in acute inflammation and psoriasis, indicating that these corticosteroid receptors play cooperative roles. Understanding GR- and MR-mediated signaling in skin should contribute to deciphering their tissue-specific relative roles and ultimately help to improve GC-based therapies.

A noncanonical PPARγ/RXRα-binding sequence regulates leptin expression in response to changes in adipose tissue mass

Leptin gene expression is highly correlated with the lipid content of individual fat cells, suggesting that it is regulated by a “fat-sensing” signal transduction pathway. This possibility is thus analogous to the identification of a cholesterol-sensing pathway by studying the regulation of the LDL receptor gene by intracellular cholesterol. Several lines of investigation have suggested that, in addition to adipocytes, liver, neurons, and other cell types can sense changes in lipid content, although the molecular mechanisms are unknown. The data here provide a critical step toward elucidating the components of this putative system, which would be of great importance. These studies also identify a previously underappreciated role of the PPARγ/RXRα complex to regulate leptin expression.

Leptin expression decreases after fat loss and is increased when obesity develops, and its proper quantitative regulation is essential for the homeostatic control of fat mass. We previously reported that a distant leptin enhancer 1 (LE1), 16 kb upstream from the transcription start site (TSS), confers fat-specific expression in a bacterial artificial chromosome transgenic (BACTG) reporter mouse. However, this and the other elements that we identified do not account for the quantitative changes in leptin expression that accompany alterations of adipose mass. In this report, we used an assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) to identify a 17-bp noncanonical peroxisome proliferator-activated receptor gamma (PPARγ)/retinoid X receptor alpha (RXRα)-binding site, leptin regulatory element 1 (LepRE1), within LE1, and show that it is necessary for the fat-regulated quantitative control of reporter (luciferase) expression. While BACTG reporter mice with mutations in this sequence still show fat-specific expression, luciferase is no longer decreased after food restriction and weight loss. Similarly, the increased expression of leptin reporter associated with obesity in ob/ob mice is impaired. A functionally analogous LepRE1 site is also found in a second, redundant DNA regulatory element 13 kb downstream of the TSS. These data uncouple the mechanisms conferring qualitative and quantitative expression of the leptin gene and further suggest that factor(s) that bind to LepRE1 quantitatively control leptin expression and might be components of a lipid-sensing system in adipocytes.

Selinexor synergizes with dexamethasone to repress mTORC1 signaling and induce multiple myeloma cell death

Multiple myeloma (MM) is a plasma cell neoplasm that results in over 11,000 deaths in the United States annually. The backbone therapy for the treatment of MM patients almost always includes combinations with corticosteroids such as dexamethasone (DEX). We found that DEX in combination with selinexor, an inhibitor of exportin-1 (XPO1) activity, synergistically inhibits the mTOR pathway and subsequently promotes cell death in MM cells. Specifically, we show that selinexor induces the expression of the glucocorticoid receptor (GR) and when combined with dexamethasone increases GR transcriptional activity. Moreover, we found that key downstream targets of the mTOR pathway are deregulated by the combination and identified a mechanism in which GR enhances the expression of REDD1 in GR positive cells while suppressing mTOR activity and cell viability. While the single agent activity of selinexor in MM cells appears to be GR-independent, synergy with DEX depends on GR expression. These data suggest that patients with tumor cells that are GR positive will benefit substantially from the combination. The current findings are consistent with the beneficial therapeutic outcome in patients with MM when treated with the combination of selinexor and DEX. In addition, they provide a rationale for testing GR and REDD1 as predictive and prognostic markers of response, respectively, for patients treated with this beneficial combination.

Relationship Between Homodimeric Glucocorticoid Receptor and Transcriptional Regulation Assessed via an In Vitro Fluorescence Correlation Spectroscopy-Microwell System

Glucocorticoid receptor (GR) is a hormone-activated transcription regulatory protein involved in metabolism as well as adrenocortical responses to psychosocial stress. Ligand-activated GR localizes to the nucleus, where GR homodimers regulate gene transcription via direct binding to glucocorticoid response elements (GREs). The role of GR homodimers in transcriptional activation has not yet been elucidated. In this study, we determined the concentration of GR homodimer, and its dissociation constant (K_d), at the single-cell level, by using fluorescence correlation spectroscopy (FCS) combined with a microwell system. Results from dissociation constant analysis and diffusion analysis suggested that GR forms complexes with other proteins as well as homodimers. We determined the relationship between the concentration of GR homodimer and transcriptional activity using a triple-color FCS-microwell system-based fluorescent reporter assay. The binding affinity of GR to GREs was analyzed via fluorescence cross-correlation spectroscopy (FCCS). Our findings indicate that the GR homodimer is essential for activating target gene transcription.

Corticosteroid receptors adopt distinct cyclical transcriptional signatures

Mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) are two closely related hormone-activated transcription factors that regulate major pathophysiologic functions. High homology between these receptors accounts for the crossbinding of their corresponding ligands, MR being activated by both aldosterone and cortisol and GR essentially activated by cortisol. Their coexpression and ability to bind similar DNA motifs highlight the need to investigate their respective contributions to overall corticosteroid signaling. Here, we decipher the transcriptional regulatory mechanisms that underlie selective effects of MRs and GRs on shared genomic targets in a human renal cellular model. Kinetic, serial, and sequential chromatin immunoprecipitation approaches were performed on the period circadian protein 1 ( PER1) target gene, providing evidence that both receptors dynamically and cyclically interact at the same target promoter in a specific and distinct transcriptional signature. During this process, both receptors regulate PER1 gene by binding as homo- or heterodimers to the same promoter region. Our results suggest a novel level of MR-GR target gene regulation, which should be considered for a better and integrated understanding of corticosteroid-related pathophysiology.-Le Billan, F., Amazit, L., Bleakley, K., Xue, Q.-Y., Pussard, E., Lhadj, C., Kolkhof, P., Viengchareun, S., Fagart, J., Lombès, M. Corticosteroid receptors adopt distinct cyclical transcriptional signatures.

Possible roles for glucocorticoid signalling in breast cancer

Our understanding of breast cancer biology, and our ability to manipulate breast cancers have grown exponentially in the last 20 years. Much of that expansion has focused on the roles of steroids in driving these neoplasms. Initially this research focused on estrogens and progesterone receptors, and more recently on androgen actions in breast cancers. This review aims to make the case for glucocorticoids as the next essential steroid subclass that contributes significantly to our understanding of steroidogenic regulation of these neoplasms. Glucocorticoids have the potential to play multiple roles in the regulation of breast cancers including their control of cellular differentiation, apoptosis and proliferation. Beyond this they also act as a master integrator of organ homeostats in relation to such as circadian rhythms and stress responses. Therefore a better understanding of glucocorticoids and breast cancer could help to explain some of the epidemiological links between circadian disruption and/or stress and breast cancer development. Finally glucocorticoids are currently used during chemotherapeutic treatment in breast cancer therapy and yet results of various studies suggest that this may have an adverse impact on treatment success. This review aims to summarise the current evidence for glucocorticoids as actors in breast cancer and then suggest future essential approaches in order to determine the roles of glucocorticoids in this disease.

Alternative dimerization interfaces in the glucocorticoid receptor-α ligand binding domain

BACKGROUND

Nuclear hormone receptors (NRs) constitute a large family of multi-domain ligand-activated transcription factors. Dimerization is essential for their regulation, and both DNA binding domain (DBD) and ligand binding domain (LBD) are implicated in dimerization. Intriguingly, the glucocorticoid receptor-α (GRα) presents a DBD dimeric architecture similar to that of the homologous estrogen receptor-α (ERα), but an atypical dimeric architecture for the LBD. The physiological relevance of the proposed GRα LBD dimer is a subject of debate.

METHODS

We analyzed all GRα LBD homodimers observed in crystals using an energetic analysis based on the PISA and on the MM/PBSA methods and a sequence conservation analysis, using the ERα LBD dimer as a reference point.

RESULTS

Several dimeric assemblies were observed for GRα LBD. The assembly generally taken to be physiologically relevant showed weak binding free energy and no significant residue conservation at the contact interface, while an alternative homodimer mediated by both helix 9 and C-terminal residues showed significant binding free energy and residue conservation. However, none of the GRα LBD assemblies found in crystals are as stable or conserved as the canonical ERα LBD dimer. GRα C-terminal sequence (F-domain) forms a steric obstacle to the canonical dimer assembly in all available structures.

CONCLUSIONS

Our analysis calls for a re-examination of the currently accepted GRα homodimer structure and experimental investigations of the alternative architectures.

GENERAL SIGNIFICANCE

This work questions the validity of the currently accepted architecture. This has implications for interpreting physiological data and for therapeutic design pertaining to glucocorticoid research.

Cryptic glucocorticoid receptor-binding sites pervade genomic NF-κB response elements

Glucocorticoids (GCs) are potent repressors of NF-κB activity, making them a preferred choice for treatment of inflammation-driven conditions. Despite the widespread use of GCs in the clinic, current models are inadequate to explain the role of the glucocorticoid receptor (GR) within this critical signaling pathway. GR binding directly to NF-κB itself-tethering in a DNA binding-independent manner-represents the standing model of how GCs inhibit NF-κB-driven transcription. We demonstrate that direct binding of GR to genomic NF-κB response elements (κBREs) mediates GR-driven repression of inflammatory gene expression. We report five crystal structures and solution NMR data of GR DBD-κBRE complexes, which reveal that GR recognizes a cryptic response element between the binding footprints of NF-κB subunits within κBREs. These cryptic sequences exhibit high sequence and functional conservation, suggesting that GR binding to κBREs is an evolutionarily conserved mechanism of controlling the inflammatory response.

Discovery of a Novel Oral Glucocorticoid Receptor Modulator (AZD9567) with Improved Side Effect Profile

Synthetic glucocorticoids (GC) are essential for the treatment of a broad range of inflammatory diseases. However, their use is limited by target related adverse effects on, e.g., glucose homeostasis and bone metabolism. Starting from a nonsteroidal GR ligand (4) that is a full agonist in reporter gene assays, we exploited key functional triggers within the receptor, generating a range of structurally diverse partial agonists. Of these, only a narrow subset exhibited full anti-inflammatory efficacy and a significantly reduced impact on adverse effect markers in human cell assays compared to prednisolone. This led to the discovery of AZD9567 (15) with excellent in vivo efficacy when dosed orally in a rat model of joint inflammation. Compound 15 is currently being evaluated in clinical trials comparing the efficacy and side effect markers with those of prednisolone.

Gene-specific mechanisms direct glucocorticoid-receptor-driven repression of inflammatory response genes in macrophages

The glucocorticoid receptor (GR) potently represses macrophage-elicited inflammation, however, the underlying mechanisms remain obscure. Our genome-wide analysis in mouse macrophages reveals that pro-inflammatory paused genes, activated via global negative elongation factor (NELF) dissociation and RNA Polymerase (Pol)2 release from early elongation arrest, and non-paused genes, induced by de novo Pol2 recruitment, are equally susceptible to acute glucocorticoid repression. Moreover, in both cases the dominant mechanism involves rapid GR tethering to p65 at NF-kB-binding sites. Yet, specifically at paused genes, GR activation triggers widespread promoter accumulation of NELF, with myeloid cell-specific NELF deletion conferring glucocorticoid resistance. Conversely, at non-paused genes, GR attenuates the recruitment of p300 and histone acetylation, leading to a failure to assemble BRD4 and Mediator at promoters and enhancers, ultimately blocking Pol2 initiation. Thus, GR displays no preference for a specific pro-inflammatory gene class; however, it effects repression by targeting distinct temporal events and components of transcriptional machinery.

PXR: More Than Just a Master Xenobiotic Receptor

Pregnane X receptor (PXR) is a nuclear receptor considered to be a master xenobiotic receptor that coordinately regulates the expression of genes encoding drug-metabolizing enzymes and drug transporters to essentially detoxify and eliminate xenobiotics and endotoxins from the body. In the past several years, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied, and the role of PXR as a xenobiotic sensor has been well established. It is now clear, however, that PXR plays many other roles in addition to its xenobiotic-sensing function. For instance, recent studies have discovered previously unidentified roles of PXR in inflammatory response, cell proliferation, and cell migration. PXR also contributes to the dysregulation of these processes in diseases states. These recent discoveries of the role of PXR in the physiologic and pathophysiologic conditions of other cellular processes provides the possibility of novel targets for drug discovery. This review highlights areas of PXR regulation that require further clarification and summarizes the recent progress in our understanding of the nonxenobiotic functions of PXR that can be explored for relevant therapeutic applications.

Epigenetic mechanisms underlie the crosstalk between growth factors and a steroid hormone

Crosstalk between growth factors (GFs) and steroid hormones recurs in embryogenesis and is co-opted in pathology, but underlying mechanisms remain elusive. Our data from mammary cells imply that the crosstalk between the epidermal GF and glucocorticoids (GCs) involves transcription factors like p53 and NF-κB, along with reduced pausing and traveling of RNA polymerase II (RNAPII) at both promoters and bodies of GF-inducible genes. Essentially, GCs inhibit positive feedback loops activated by GFs and stimulate the reciprocal inhibitory loops. As expected, no alterations in DNA methylation accompany the transcriptional events instigated by either stimulus, but forced demethylation of regulatory regions broadened the repertoire of GF-inducible genes. We report that enhancers, like some promoters, are poised for activation by GFs and GCs. In addition, within the cooperative interface of the crosstalk, GFs enhance binding of the GC receptor to DNA and, in synergy with GCs, promote productive RNAPII elongation. Reciprocally, within the antagonistic interface GFs hyper-acetylate chromatin at unmethylated promoters and enhancers of genes involved in motility, but GCs hypoacetylate the corresponding regions. In conclusion, unmethylated genomic regions that encode feedback regulatory modules and differentially recruit RNAPII and acetylases/deacetylases underlie the crosstalk between GFs and a steroid hormone.

Mechanisms of erythrocyte development and regeneration: implications for regenerative medicine and beyond

Hemoglobin-expressing erythrocytes (red blood cells) act as fundamental metabolic regulators by providing oxygen to cells and tissues throughout the body. Whereas the vital requirement for oxygen to support metabolically active cells and tissues is well established, almost nothing is known regarding how erythrocyte development and function impact regeneration. Furthermore, many questions remain unanswered relating to how insults to hematopoietic stem/progenitor cells and erythrocytes can trigger a massive regenerative process termed 'stress erythropoiesis' to produce billions of erythrocytes. Here, we review the cellular and molecular mechanisms governing erythrocyte development and regeneration, and discuss the potential links between these events and other regenerative processes.

The Two Faces of Adjuvant Glucocorticoid Treatment in Ovarian Cancer

Adjuvant glucocorticoid treatment is routinely used in the treatment of ovarian cancer to mitigate the undesirable side effects of chemotherapy, thereby enhancing tolerability to higher cytotoxic drug doses and frequency of treatment cycles. However, in vitro and preclinical in vivo and ex vivo studies indicate that glucocorticoids may spare tumor cells from undergoing cell death through enhanced cell adhesion, promotion of anti-inflammatory signaling, and/or inhibition of apoptotic pathways. The implications of laboratory studies showing potential negative impact on the efficacy of chemotherapy have been long overlooked since clinical investigations have found no apparent survival detriment attributable to adjuvant glucocorticoid use. Importantly, these clinical studies were not randomized and most did not consider glucocorticoid receptor status, a vital determinant of tumor response to glucocorticoid administration. Additionally, the clinically beneficial elements of increased chemotherapy treatment adherence and dosing afforded by adjuvant glucocorticoids may offset and therefore mask their anti-chemotherapy activities. This review summarizes the current evidence on the impact of glucocorticoids in ovarian cancer and discusses the need for further research and development of alternative strategies to ameliorate untoward side effects of chemotherapy.

The role of microRNAs in glucocorticoid action

Glucocorticoids (GCs) are steroids with profound anti-inflammatory and immunomodulatory activities. Synthetic GCs are widely used for managing chronic inflammatory and autoimmune conditions, as immunosuppressants in transplantation, and as anti-tumor agents in certain hematological cancers. However, prolonged GC exposure can cause adverse effects. A detailed understanding of GCs' mechanisms of action may enable harnessing of their desirable actions while minimizing harmful effects. Here, we review the impact on the GC biology of microRNAs, small non-coding RNAs that post-transcriptionally regulate gene expression. Emerging evidence indicates that microRNAs modulate GC production by the adrenal glands and the cells' responses to GCs. Furthermore, GCs influence cell proliferation, survival, and function at least in part by regulating microRNA expression. We propose that the beneficial effects of GCs may be enhanced through combination with reagents targeting specific microRNAs.

Glucocorticoid Signaling in Health and Disease: Insights From Tissue-Specific GR Knockout Mice

Glucocorticoids are adrenally produced hormones critically involved in development, general physiology, and control of inflammation. Since their discovery, glucocorticoids have been widely used to treat a variety of inflammatory conditions. However, high doses or prolonged use leads to a number of side effects throughout the body, which preclude their clinical utility. The primary actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), a transcription factor that regulates many complex signaling pathways. Although GR is nearly ubiquitous throughout the body, glucocorticoids exhibit cell- and tissue-specific effects. For example, glucocorticoids stimulate glucose production in the liver, reduce glucose uptake in the skeletal muscle, and decrease insulin secretion from the pancreatic β-cells. Mouse models represent an important approach to understanding the dynamic functions of GR signaling in normal physiology, disease, and resistance. In the absence of a viable GR null model, gene-targeting techniques utilizing promoter-driven recombination have provided an opportunity to characterize the tissue-specific actions of GR. The aim of the present review is to describe the organ systems in which GR has been conditionally deleted and summarize the functions ascribed to glucocorticoid action in those tissues.

Therapeutic Mechanisms of Glucocorticoids

Glucocorticoids (GCs) have been used clinically for decades as potent anti-inflammatory and immunosuppressive agents. Nevertheless, their use is severely hampered by the risk of developing side effects and the occurrence of glucocorticoid resistance (GCR). Therefore, efforts to understand the complex mechanisms underlying GC function and GCR are ongoing. The goal is to generate new glucocorticoid receptor (GR) ligands that can dissociate anti-inflammatory from metabolic side effects and/or overcome GCR. In this review paper we discuss recent insights into GR-mediated actions in GCR and novel therapeutic strategies for acute and chronic inflammatory diseases.

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.

The FKBP51 Glucocorticoid Receptor Co-Chaperone: Regulation, Function, and Implications in Health and Disease

Among the chaperones and co-chaperones regulating the glucocorticoid receptor (GR), FK506 binding protein (FKBP) 51 is the most intensely investigated across different disciplines. This review provides an update on the role of the different co-chaperones of Hsp70 and Hsp90 in the regulation of GR function. The development leading to the focus on FKBP51 is outlined. Further, a survey of the vast literature on the mechanism and function of FKBP51 is provided. This includes its structure and biochemical function, its regulation on different levels—transcription, post-transcription, and post-translation—and its function in signaling pathways. The evidence portraying FKBP51 as a scaffolding protein organizing protein complexes rather than a chaperone contributing to the folding of individual proteins is collated. Finally, FKBP51’s involvement in physiology and disease is outlined, and the promising efforts in developing drugs targeting FKBP51 are discussed.

Coregulator profiling of the glucocorticoid receptor in lymphoid malignancies

Coregulators cooperate with nuclear receptors, such as the glucocorticoid receptor (GR), to enhance or repress transcription. These regulatory proteins are implicated in cancer, yet, their role in lymphoid malignancies, including multiple myeloma (MM) and acute lymphoblastic leukemia (ALL), is largely unknown. Here, we report the use and extension of the microarray assay for real-time nuclear receptor coregulator interactions (MARCoNI) technology to detect coregulator associations with endogenous GR in cell lysates. We use MARCoNI to determine the GR coregulator profile of glucocorticoid-sensitive (MM and ALL) and glucocorticoid-resistant (ALL) cells, and identify common and unique coregulators for different cell line comparisons. Overall, we identify SRC-1/2/3, PGC-1α, RIP140 and DAX-1 as the strongest interacting coregulators of GR in MM and ALL cells and show that the interaction strength does not correlate with GR protein levels. Lastly, as a step towards patient samples, we determine the GR coregulator profile of peripheral blood mononuclear cells. We profile the interactions between GR and coregulators in MM and ALL cells and suggest to further explore the GR coregulator profile in hematological patient samples.

Organizing combinatorial transcription factor recruitment at cis-regulatory modules

Gene transcriptional regulation relies on cis-regulatory DNA modules (CRMs), which serve as nexus sites for integration of multiple transcription factor (TF) activities. Here, we provide evidence and discuss recent literature indicating that TF recruitment to CRMs is organized into combinations of trans-regulatory protein modules (TRMs). We propose that TRMs are functional entities composed of TFs displaying the most highly interdependent chromatin binding which are, in addition, able to modulate their recruitment to CRMs through inter-TRM effects. These findings shed light on the architectural organization of TF recruitment encoded by their recognition motifs within CRMs.

Glucocorticoid-induced phosphorylation by CDK9 modulates the coactivator functions of transcriptional cofactor GRIP1 in macrophages

The glucocorticoid (GC) receptor (GR) suppresses inflammation by activating anti-inflammatory and repressing pro-inflammatory genes. GR-interacting protein-1 (GRIP1) is a GR corepressor in macrophages, however, whether GRIP1 mediates GR-activated transcription, and what dictates its coactivator versus corepressor properties is unknown. Here we report that GRIP1 loss in macrophages attenuates glucocorticoid induction of several anti-inflammatory targets, and that GC treatment of quiescent macrophages globally directs GRIP1 toward GR binding sites dominated by palindromic GC response elements (GRE), suggesting a non-redundant GRIP1 function as a GR coactivator. Interestingly, GRIP1 is phosphorylated at an N-terminal serine cluster by cyclin-dependent kinase-9 (CDK9), which is recruited into GC-induced GR:GRIP1:CDK9 hetero-complexes, producing distinct GRE-specific GRIP1 phospho-isoforms. Phosphorylation potentiates GRIP1 coactivator but, remarkably, not its corepressor properties. Consistently, phospho-GRIP1 and CDK9 are not detected at GR transrepression sites near pro-inflammatory genes. Thus, GR restricts actions of its own coregulator via CDK9-mediated phosphorylation to a subset of anti-inflammatory genes.

Glucocorticoid reduces inflammation by both inducing anti-inflammatory genes and suppressing pro-inflammatory genes, but how these two functions are dictated is unclear. Here the authors show that phosphorylated glucocorticoid receptor-interacting protein 1 (GRIP1) serves as a coactivator for this response in macrophage.

Host resistance to endotoxic shock requires the neuroendocrine regulation of group 1 innate lymphoid cells

Quatrini et al. demonstrate that neuroendocrine regulation of IFN-γ production by group 1 innate lymphoid cells (ILCs) is required to develop an IL-10–dependent resistance to endotoxin-induced septic shock, revealing a novel strategy of host protection from immunopathology.

Upon infection, the immune system produces inflammatory mediators important for pathogen clearance. However, inflammation can also have deleterious effect on the host and is tightly regulated. Immune system–derived cytokines stimulate the hypothalamic–pituitary–adrenal (HPA) axis, triggering endogenous glucocorticoid production. Through interaction with ubiquitously expressed glucocorticoid receptors (GRs), this steroid hormone has pleiotropic effects on many cell types. Using a genetic mouse model in which the gene encoding the GR is selectively deleted in NKp46⁺ innate lymphoid cells (ILCs), we demonstrated a major role for the HPA pathway in host resistance to endotoxin-induced septic shock. GR expression in group 1 ILCs is required to limit their IFN-γ production, thereby allowing the development of IL-10–dependent tolerance to endotoxin. These findings suggest that neuroendocrine axes are crucial for tolerization of the innate immune system to microbial endotoxin exposure through direct corticosterone-mediated effects on NKp46-expressing innate cells, revealing a novel strategy of host protection from immunopathology.

Stress and the HPA Axis: Balancing Homeostasis and Fertility

An organism’s reproductive fitness is sensitive to the environment, integrating cues of resource availability, ecological factors, and hazards within its habitat. Events that challenge the environment of an organism activate the central stress response system, which is primarily mediated by the hypothalamic–pituitary–adrenal (HPA) axis. The regulatory functions of the HPA axis govern the cardiovascular and metabolic system, immune functions, behavior, and reproduction. Activation of the HPA axis by various stressors primarily inhibits reproductive function and is able to alter fetal development, imparting a biological record of stress experienced in utero. Clinical studies and experimental data indicate that stress signaling can mediate these effects through direct actions in the brain, gonads, and embryonic tissues. This review focuses on the mechanisms by which stress activation of the HPA axis impacts fertility and fetal development.