Glucocorticoid receptor alpha isoform-selective regulation of antiapoptotic genes in osteosarcoma cells: a new mechanism for glucocorticoid resistance

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Delta-9 tetrahydrocannabinol (THC) effects on the cortisol stress response in bovine granulosa cells

Maternal stress can result in changes in the hypothalamic-pituitary-adrenal (HPA) axis and lead to stress-related behaviours in offspring. Under physiological conditions, delta-9 tetrahydrocannabinol (THC) appears to be detrimental for fertility. However, cannabis is also commonly used for stress-relief. THC acts on the endocannabinoid receptors in granulosa cells (GCs), which affect oocyte competency. The objective of this study was to evaluate the effects of THC on in vitro bovine granulosa cell viability, apoptosis, and stress response pathway. GCs were cultured in vitro in the presence of clinically relevant therapeutic and recreational plasma doses of THC. Cortisol doses reflecting normal and elevated plasma levels were used to evaluate the effects of THC under induced stress in vitro. No effect of THC was observed on cell viability or apoptosis. High and low cortisol concentrations caused significant increases in 11β-HSD1 mRNA expression (n = 6, p < 0.0001). Interestingly, when combined with high [THC], there was a significant decrease in 11β-HSD1 expression compared to high and low cortisol treatments alone (p < 0.001, p < 0.05). GR expression was unaffected by cortisol treatments, and low [THC] treatment maintained increased expression in the presence of high and low cortisol treatments (n = 6, p < 0.01, p < 0.0001). Our findings represent a foundation to obtain useful data for evaluating THC potential therapeutic benefit.

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.

Advantages and drawbacks of dexamethasone in glioblastoma multiforme

The most widespread, malignant, and deadliest type of glial tumor is glioblastoma multiforme (GBM). Despite radiation, chemotherapy, and radical surgery, the median survival of afflicted individuals is about 12 months. Unfortunately, existing therapeutic interventions are abysmal. Dexamethasone (Dex), a synthetic glucocorticoid, has been used for many years to treat brain edema and inflammation caused by GBM. Several investigations have recently shown that Dex also exerts antitumoral effects against GBM. On the other hand, more recent disputed findings have questioned the long-held dogma of Dex treatment for GBM. Unfortunately, steroids are associated with various undesirable side effects, including severe immunosuppression and metabolic changes like hyperglycemia, which may impair the survival of GBM patients. Current ideas and concerns about Dex's effects on GBM cerebral edema, cell proliferation, migration, and its clinical outcomes were investigated in this study.

Corticosterone and Glucocorticoid Receptor in the Cortex of Rats during Aging-The Effects of Long-Term Food Restriction

Numerous beneficial effects of food restriction on aging and age-related pathologies are well documented. It is also well-established that both short- and long-term food restriction regimens induce elevated circulating levels of glucocorticoids, stress-induced hormones produced by adrenal glands that can also exert deleterious effects on the brain. In the present study, we examined the effect of long-term food restriction on the glucocorticoid hormone/glucocorticoid receptor (GR) system in the cortex during aging, in 18- and 24-month-old rats. Corticosterone level was increased in the cortex of aged ad libitum-fed rats. Food restriction induced its further increase, accompanied with an increase in the level of 11β-hydroxysteroid dehydrogenase type 1. However, alterations in the level of GR phosphorylated at Ser²³² were not detected in animals on food restriction, in line with unaltered CDK5 level, the decrease of Hsp90, and an increase in a negative regulator of GR function, FKBP51. Moreover, our data revealed that reduced food intake prevented age-related increase in the levels of NFκB, gfap, and bax, confirming its anti-inflammatory and anti-apoptotic effects. Along with an increase in the levels of c-fos, our study provides additional evidences that food restriction affects cortical responsiveness to glucocorticoids during aging.

Glucocorticoid therapy in assisted reproduction

As glucocorticoids are well-known as important regulators of stress and the immune system, their function and clinical use have elicited substantial interest in the field of reproduction. In particular, the effect of glucocorticoid therapy on endometrial receptivity during assisted reproduction, including in vitro fertilization (IVF) cycles, has led to a great deal of interest and controversy. However, previous studies have not been able to provide consistent and reliable evidence due to their small, non-controlled designs and use of different criteria. Considering the potential risk of exposure to glucocorticoids for mothers and fetuses in early pregnancy, the use of glucocorticoids in IVF cycles should be carefully evaluated, including the balance between risk and benefit. To date, there is no conclusive evidence that the use of glucocorticoids improves the pregnancy rate in IVF cycles with unselected subjects, and a further investigation should be considered with a proper study design.

Conserved allosteric ensembles in disordered proteins using TROSY/anti-TROSY R2-filtered spectroscopy

Defining the role of intrinsic disorder in proteins in the myriad of biological processes with which it is involved represents a significant goal in modern biophysics. Toward this end, NMR is uniquely suited for molecular studies of dynamic and disordered regions, but studying these regions in concert with their more structured domains and binding partners presents spectroscopic challenges. Here, we investigate the interactions between the structured and disordered regions of the human glucocorticoid receptor (GR). To do this, we developed an NMR strategy that relies on a novel relaxation filter for the simultaneous study of structured and unstructured regions. Using this approach, we conducted a comparative analysis of three translational isoforms of GR containing a folded DNA-binding domain (DBD) and two disordered regions that flank the DBD, one of which varies in size in the different isoforms. Notably, we were able to assign resonances that had previously been inaccessible because of the spectral complexity of the translational isoforms, which in turn allowed us to 1) identify a region of the structured DBD that undergoes significant changes in the local chemical environment in the presence of the disordered region and 2) determine differences in the conformational ensembles of the disordered regions of the translational isoforms. Furthermore, an ensemble-based thermodynamic analysis of the isoforms reveals conserved patterns of stability within the N-terminal domain of GR that persist despite low sequence conservation. These studies provide an avenue for further investigations of the mechanistic underpinnings of the functional relevance of the translational isoforms of GR while also providing a general NMR strategy for studying systems containing both structured and disordered regions.

Therapeutic targeting of pancreatic cancer stem cells by dexamethasone modulation of the MKP-1-JNK axis

Postoperative recurrence from microscopic residual disease must be prevented to cure intractable cancers, including pancreatic cancer. Key to this goal is the elimination of cancer stem cells (CSCs) endowed with tumor-initiating capacity and drug resistance. However, current therapeutic strategies capable of accomplishing this are insufficient. Using in vitro models of CSCs and in vivo models of tumor initiation in which CSCs give rise to xenograft tumors, we show that dexamethasone induces expression of MKP-1, a MAPK phosphatase, via glucocorticoid receptor activation, thereby inactivating JNK, which is required for self-renewal and tumor initiation by pancreatic CSCs as well as for their expression of survivin, an anti-apoptotic protein implicated in multidrug resistance. We also demonstrate that systemic administration of clinically relevant doses of dexamethasone together with gemcitabine prevents tumor formation by CSCs in a pancreatic cancer xenograft model. Our study thus provides preclinical evidence for the efficacy of dexamethasone as an adjuvant therapy to prevent postoperative recurrence in patients with pancreatic cancer.

Latest perspectives on glucocorticoid-induced apoptosis and resistance in lymphoid malignancies

Glucocorticoids are essential drugs in the treatment protocols of lymphoid malignancies. These steroidal hormones trigger apoptosis of the malignant cells by binding to the glucocorticoid receptor (GR), which is a member of the nuclear receptor superfamily. Long term glucocorticoid treatment is limited by two major problems: the development of glucocorticoid-related side effects, which hampers patient quality of life, and the emergence of glucocorticoid resistance, which is a gradual process that is inevitable in many patients. This emphasizes the need to reevaluate and optimize the widespread use of glucocorticoids in lymphoid malignancies. To achieve this goal, a deep understanding of the mechanisms governing glucocorticoid responsiveness is required, yet, a recent comprehensive overview is currently lacking. In this review, we examine how glucocorticoids mediate apoptosis by detailing GR's genomic and non-genomic action mechanisms in lymphoid malignancies. We continue with a discussion of the glucocorticoid-related problems and how these are intertwined with one another. We further zoom in on glucocorticoid resistance by critically analyzing the plethora of proposed mechanisms and highlighting therapeutic opportunities that emerge from these studies. In conclusion, early detection of glucocorticoid resistance in patients remains an important challenge as this would result in a timelier treatment reorientation and reduced glucocorticoid-instigated side effects.

Glucocorticoid receptor isoforms and effects of glucocorticoids in ovulated mouse oocytes and preimplantation embryos†

To investigate possible involvement of glucocorticoid receptor (GR) in mediating effects of maternal stress or therapeutically administered glucocorticoids on early embryo, we analyzed the expression of GR subtypes in ovulated mouse oocytes and preimplantation embryos. RT-PCR analysis results showed that GRα and GRγ transcripts are relatively highly expressed in mouse oocytes, and both transcripts are present at lower amounts in preimplantation embryos. We also detected low expression of two other splice variants, GRβ and a transcript orthologous to the human GR-P subtype, mainly at the blastocyst stage. Using western blot analysis, we detected several GR protein bands that differed in size between oocytes and preimplantation embryos. To compare the effects of corticosterone (a major endogenous glucocorticoid in rodents) and dexamethasone (a synthetic glucocorticoid) on early embryos, we cultured mouse preimplantation embryos in the presence of these glucocorticoids. Corticosterone showed a strong inhibitory effect on embryo development (starting from a 50 μM concentration), without a significant influence on apoptosis incidence. On the other hand, dexamethasone induced apoptosis in early embryo cells (starting from a 1.5 μM concentration), and its effect on embryo development was less detrimental than that found with the same dose of corticosterone. In summary, our results showed that different GR subtypes are expressed in ovulated mouse oocytes and preimplantation embryos and that the composition of GR subtypes changes during early embryo development. Moreover, we found significant differences in the effects of the two glucocorticoids on early embryo development, which might be associated with activation of different GR subtypes.

A multifunctional dexamethasone-delivery implant fabricated using atmospheric plasma and its effects on apoptosis, osteogenesis and inflammation

Implant-based local drug delivery is a unique surgical therapy with many clinical advantages. Atmospheric pressure plasma is a novel non-thermal surface biotechnology that has only recently been applied in enhancing a surgical implant. We are the first to use this technology to successfully create a dexamethasone-delivery metallic implant. Irrespective of the loaded medication, the surface of this novel implant possesses advantageous material features including homogeneity, hydrophilicity, and optimal roughness. UV-vis spectroscopy revealed much more sustainable drug release compared to the implants produced using simple drug attachment. In addition, our drug-releasing implant was found to have multiple biological benefits. As proven by the ELISA data, this multi-layer drug complex provides differential regulation on the cell apoptosis, as well as pro-osteogenic and anti-inflammatory effects on the peri-implant tissue. Furthermore, using the pathway-specific PCR array, our study discovered 28 and 26 upregulated and downregulated genes during osteogenesis and inflammation on our newly fabricated drug-delivery implant, respectively. The medication-induced change in molecular profile serves as a promising clue for designing future implant-based therapy. Collectively, we present atmospheric pressure plasma as a potent tool for creating a surgical implant-based drug-delivery system, which renders multiple therapeutic potentials. Graphical abstract Schematic of the APP-facilitated Dex-delivery implant. This layer-by-layer drug-releasing complex consisted of bottom plasma activation layer, middle medication layer, and top absorbable polymer layer.

Glucocorticoid Receptor Mutations and Hypersensitivity to Endogenous and Exogenous Glucocorticoids

BACKGROUND

The glucocorticoid receptor (GR) consists of two alternatively spliced isoforms: GRα, which activates gene transcription, and GRβ, a dominant-negative receptor. Theoretically, inactivating variants of GRβ could result in glucocorticoid hypersensitivity.

DESIGN

A 46-year-old woman presented for evaluation of adrenal insufficiency prompted by low plasma cortisol levels and multiple unexplained symptoms but without clinical evidence of glucocorticoid insufficiency. To explain these findings, extensive clinical, genetic, and molecular studies were performed.

METHODS

Standard clinical methods assessed the patient's hypothalamic-pituitary-adrenal axis. Validated molecular techniques were used for receptor sequencing, stable transfections, stimulation of candidate genes, cDNA arrays, Ingenuity Pathway Analysis, volcano analysis, and isolation and analysis of the patient's mononuclear cells.

RESULTS

Clinical studies excluded primary or secondary adrenal insufficiency, established consistently low basal cortisol levels, and demonstrated hypersensitivity to ultra-low-dose dexamethasone. Receptor sequencing identified two variants of GR9β (A3669G and G3134T) as well as the known Bcl1 polymorphism. Reductionist studies using stable osteosarcoma cell lines transfected with the GRβ variants demonstrated glucocorticoid hypersensitivity of transcribed genes on cDNA array analysis. The patient's monocytes responded to hydrocortisone with exaggerated stimulation of the candidate genes GILZ and FKBP5.

CONCLUSION

Two variants of the dominant-negative GRβ, in conjunction with a common Bcl1 intron variant, resulted in hypersensitivity to endogenous and exogenous glucocorticoids and, as a reflection of severity, low circulating cortisol levels without clinical evidence of glucocorticoid insufficiency. This prismatic case exemplifies the unique effects of variants of a dominant-negative receptor.

Glucocorticoids and Reproduction: Traffic Control on the Road to Reproduction

Glucocorticoids are steroid hormones that regulate diverse cellular functions and are essential to facilitate normal physiology. However, stress-induced levels of glucocorticoids result in several pathologies including profound reproductive dysfunction. Compelling new evidence indicates that glucocorticoids are crucial to the establishment and maintenance of reproductive function. The fertility-promoting or -inhibiting activity of glucocorticoids depends on timing, dose, and glucocorticoid responsiveness within a given tissue, which is mediated by the glucocorticoid receptor (GR). The GR gene and protein are subject to cellular processing, contributing to signaling diversity and providing a mechanism by which both physiological and stress-induced levels of glucocorticoids function in a cell-specific manner. Understanding how glucocorticoids regulate fertility and infertility may lead to novel approaches to the regulation of reproductive function.

Gene expression profiling of tumor-initiating stem cells from mouse Krebs-2 carcinoma using a novel marker of poorly differentiated cells

Using the ability of poorly differentiated cells to natively internalize fragments of extracellular double-stranded DNA as a marker, we isolated a tumorigenic subpopulation present in Krebs-2 ascites that demonstrated the features of tumor-inducing cancer stem cells. Having combined TAMRA-labeled DNA probe and the power of RNA-seq technology, we identified a set of 168 genes specifically expressed in TAMRA-positive cells (tumor-initiating stem cells), these genes remaining silent in TAMRA-negative cancer cells. TAMRA+ cells displayed gene expression signatures characteristic of both stem cells and cancer cells. The observed expression differences between TAMRA+ and TAMRA- cells were validated by Real Time PCR. The results obtained corroborated the biological data that TAMRA+ murine Krebs-2 tumor cells are tumor-initiating stem cells. The approach developed can be applied to profile any poorly differentiated cell types that are capable of immanent internalization of double-stranded DNA.

Corticosteroids: Mechanisms of Action in Health and Disease

Glucocorticoids are primary stress hormones that regulate a variety of physiologic processes and are essential for life. The actions of glucocorticoids are predominantly mediated through the classic glucocorticoid receptor (GR). GRs are expressed throughout the body, but there is considerable heterogeneity in glucocorticoid sensitivity and biologic responses across tissues. The conventional belief that glucocorticoids act through a single GR protein has changed dramatically with the discovery of a diverse collection of receptor isoforms. This article provides an overview of the molecular mechanisms that regulate glucocorticoid actions, highlights the dynamic nature of hormone signaling, and discusses the molecular properties of the GR isoforms.

GR SUMOylation and formation of an SUMO-SMRT/NCoR1-HDAC3 repressing complex is mandatory for GC-induced IR nGRE-mediated transrepression

Unique among the nuclear receptor superfamily, the glucocorticoid (GC) receptor (GR) can exert three distinct transcriptional regulatory functions on binding of a single natural (cortisol in human and corticosterone in mice) and synthetic [e.g., dexamethasone (Dex)] hormone. The molecular mechanisms underlying GC-induced positive GC response element [(+)GRE]-mediated activation of transcription are partially understood. In contrast, these mechanisms remain elusive for GC-induced evolutionary conserved inverted repeated negative GC response element (IR nGRE)-mediated direct transrepression and for tethered indirect transrepression that is mediated by DNA-bound NF-κB/activator protein 1 (AP1)/STAT3 activators and instrumental in GC-induced anti-inflammatory activity. We demonstrate here that SUMOylation of lysine K293 (mouse K310) located within an evolutionary conserved sequence in the human GR N-terminal domain allows the formation of a GR-small ubiquitin-related modifiers (SUMOs)-NCoR1/SMRT-HDAC3 repressing complex mandatory for GC-induced IR nGRE-mediated direct repression in vitro, but does not affect transactivation. Importantly, these results were validated in vivo: in K310R mutant mice and in mice ablated selectively for nuclear receptor corepressor 1 (NCoR1)/silencing mediator for retinoid or thyroid-hormone receptors (SMRT) corepressors in skin keratinocytes, Dex-induced direct repression and the formation of repressing complexes on IR nGREs were impaired, whereas transactivation was unaffected. In mice selectively ablated for histone deacetylase 3 (HDAC3) in skin keratinocytes, GC-induced direct repression, but not bindings of GR and of corepressors NCoR1/SMRT, was abolished, indicating that HDAC3 is instrumental in IR nGRE-mediated repression. Moreover, we demonstrate that the binding of HDAC3 to IR nGREs in vivo is mediated through interaction with SMRT/NCoR1. We also show that the GR ligand binding domain (LBD) is not required for SMRT-mediated repression, which can be mediated by a LBD-truncated GR, whereas it is mandatory for NCoR1-mediated repression through an interaction with K579 in the LBD.

Glucocorticoid-induced tethered transrepression requires SUMOylation of GR and formation of a SUMO-SMRT/NCoR1-HDAC3 repressing complex

Upon binding of a glucocorticoid (GC), the GC receptor (GR) can exert one of three transcriptional regulatory functions. We recently reported that SUMOylation of the GR at position K293 in humans (K310 in mice) within the N-terminal domain is indispensable for GC-induced evolutionary conserved inverted repeated negative GC response element (IR nGRE)-mediated direct transrepression. We now demonstrate that the integrity of this GR SUMOylation site is mandatory for the formation of a GR-small ubiquitin-related modifiers (SUMOs)-SMRT/NCoR1-HDAC3 repressing complex, which is indispensable for NF-κB/AP1-mediated GC-induced tethered indirect transrepression in vitro. Using GR K310R mutant mice or mice containing the N-terminal truncated GR isoform GRα-D3 lacking the K310 SUMOylation site, revealed a more severe skin inflammation than in WT mice. Importantly, cotreatment with dexamethasone (Dex) could not efficiently suppress a 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced skin inflammation in these mutant mice, whereas it was clearly decreased in WT mice. In addition, in mice selectively ablated in skin keratinocytes for either nuclear receptor corepressor 1 (NCoR1)/silencing mediator for retinoid or thyroid-hormone receptors (SMRT) corepressors or histone deacetylase 3 (HDAC3), Dex-induced tethered transrepression and the formation of a repressing complex on DNA-bound NF-κB/AP1 were impaired. We previously suggested that GR ligands that would lack both (+)GRE-mediated transactivation and IR nGRE-mediated direct transrepression activities of GCs may preferentially exert the therapeutically beneficial GC antiinflammatory properties. Interestingly, we now identified a nonsteroidal antiinflammatory selective GR agonist (SEGRA) that selectively lacks both Dex-induced (+)GRE-mediated transactivation and IR nGRE-mediated direct transrepression functions, while still exerting a tethered indirect transrepression activity and could therefore be clinically lesser debilitating on long-term GC therapy.

Specificity and sensitivity of glucocorticoid signaling in health and disease

Endogenous glucocorticoids regulate a variety of physiologic processes and are crucial to the systemic stress response. Glucocorticoid receptors are expressed throughout the body, but there is considerable heterogeneity in glucocorticoid sensitivity and induced biological responses across tissues. The immunoregulatory properties of glucocorticoids are exploited in the clinic for the treatment of inflammatory and autoimmune disorders as well as certain hematological malignancies, but adverse side effects hamper prolonged use. Fully understanding the molecular events that shape the physiologic effects of glucocorticoid treatment will provide insight into optimal glucocorticoid therapies, reliable assessment of glucocorticoid sensitivity in patients, and may advance the development of novel GR agonists that exert immunosuppressive effects while avoiding harmful side effects. In this review, we provide an overview of mechanisms that affect glucocorticoid specificity and sensitivity in health and disease, focusing on the distinct isoforms of the glucocorticoid receptor and their unique regulatory and functional properties.

Ectopic microRNA-150-5p transcription sensitizes glucocorticoid therapy response in MM1S multiple myeloma cells but fails to overcome hormone therapy resistance in MM1R cells

Glucocorticoids (GCs) selectively trigger cell death in the multiple myeloma cell line MM1S which express NR3C1/Glucocorticoid Receptor (GR) protein, but fail to kill MM1R cells which lack GR protein. Given recent demonstrations of altered microRNA profiles in a diverse range of haematological malignancies and drug resistance, we characterized GC inducible mRNA and microRNA transcription profiles in GC sensitive MM1S as compared to GC resistant MM1R cells. Transcriptome analysis revealed that GCs regulate expression of multiple genes involved in cell cycle control, cell organization, cell death and immunological disease in MM1S cells, which remain unaffected in MM1R cells. With respect to microRNAs, mir-150-5p was identified as the most time persistent GC regulated microRNA, out of 5 QPCR validated microRNAs (mir-26b, mir-125a-5p, mir-146-5p, mir-150-5p, and mir-184), which are GC inducible in MM1S but not in MM1R cells. Functional studies further revealed that ectopic transfection of a synthetic mir-150-5p mimics GR dependent gene expression changes involved in cell death and cell proliferation pathways. Remarkably, despite the gene expression changes observed, overexpression of mir-150-5p in absence of GCs did not trigger significant cytotoxicity in MM1S or MM1R cells. This suggests the requirement of additional steps in GC induced cell death, which can not be mimicked by mir-150-5p overexpression alone. Interestingly, a combination of mir-150-5p transfection with low doses GC in MM1S cells was found to sensitize therapy response, whereas opposite effects could be observed with a mir-150-5p specific antagomir. Although mir-150-5p overexpression did not substantially change GR expression levels, it was found that mir-150-5p evokes GR specific effects through indirect mRNA regulation of GR interacting transcription factors and hormone receptors, GR chaperones, as well as various effectors of unfolded protein stress and chemokine signalling. Altogether GC-inducible mir-150-5p adds another level of regulation to GC specific therapeutic responses in multiple myeloma.

Cortisol biosynthesis in the human ocular surface innate immune response

Innate immune responses have a critical role in regulating sight-threatening ocular surface (OcS) inflammation. While glucocorticoids (GCs) are frequently used to limit tissue damage, the role of intracrine GC (cortisol) bioavailability via 11-beta-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in OcS defense, remains unresolved. We found that primary human corneal epithelial cells (PHCEC), fibroblasts (PHKF) and allogeneic macrophages (M1, GM-CSF; M2, M-CSF) were capable of generating cortisol (M1>PHKF>M2>PHCEC) but in corneal cells, this was independent of Toll-like receptor (TLR) activation. While PolyI∶C induced maximal cytokine and chemokine production from both PHCEC (IFNγ, CCL2, CCL3, and (CCL4), IL6, CXCL10, CCL5, TNFα) and PHKF (CCL2, IL-6, CXCL10, CCL5), only PHKF cytokines were inhibited by GCs. Both Poly I∶C and LPS challenged-corneal cells induced M1 chemotaxis (greatest LPS-PHKF (250%), but down-regulated M1 11β-HSD1 activity (30 and 40% respectively). These data were supported by clinical studies demonstrating reduced human tear film cortisol∶cortisone ratios (a biomarker of local 11β-HSD1 activity) in pseudomonas keratitis (1∶2.9) versus healthy controls (1∶1.3; p<0.05). This contrasted with putative TLR3-mediated OcS disease (Stevens-Johnson Syndrome, Mucous membrane pemphigoid) where an increase in cortisol∶cortisone ratio was observed (113.8∶1; p<0.05). In summary, cortisol biosynthesis in human corneal cells is independent of TLR activation and is likely to afford immunoprotection under physiological conditions. Contribution to ocular mucosal innate responses is dependent on the aetiology of immunological challenge.

HES1 is a master regulator of glucocorticoid receptor-dependent gene expression

Hairy and enhancer of split-1 (HES1) is a basic helix-loop-helix transcription factor that is a key regulator of development and organogenesis. However, little is known about the role of HES1 after birth. Glucocorticoids, primary stress hormones that are essential for life, regulate numerous homeostatic processes that permit vertebrates to cope with physiological challenges. The molecular actions of glucocorticoids are mediated by glucocorticoid receptor-dependent regulation of nearly 25% of the genome. Here, we established a genome-wide molecular link between HES1 and glucocorticoid receptors that controls the ability of cells and animals to respond to stress. Glucocorticoid signaling rapidly and robustly silenced HES1 expression. This glucocorticoid-dependent repression of HES1 was necessary for the glucocorticoid receptor to regulate many of its target genes. Mice with conditional knockout of HES1 in the liver exhibited an expanded glucocorticoid receptor signaling profile and aberrant metabolic phenotype. Our results indicate that HES1 acts as a master repressor, the silencing of which is required for proper glucocorticoid signaling.

Multiple structurally distinct ERα mRNA variants in zebrafish are differentially expressed by tissue type, stage of development and estrogen exposure

It is well established that estrogen-like environmental chemicals interact with the ligand-binding site of estrogen receptors (ERs) to disrupt transcriptional control of estrogen responsive targets. Here we investigate the possibility that estrogens also impact splicing decisions on estrogen responsive genes, such as that encoding ERα itself. Targeted PCR cloning was applied to identify six ERα mRNA variants in zebrafish. Sequencing revealed alternate use of transcription and translation start sites, multiple exon deletions, intron retention and alternate polyadenylation. As determined by quantitative (q)PCR, N-terminal mRNA variants predicting long (ERαA(L)) and short (ERα(S)) isoforms were differentially expressed by tissue-type, sex, stage of development and estrogen exposure. Whereas ERα(L) mRNA was diffusely distributed in liver, brain, heart, eye, and gonads, ERα(S) mRNA was preferentially expressed in liver (female>male) and ovary. Neither ERα(L) nor ERα(S) transcripts varied significantly during development, but 17β-estradiol selectively increased accumulation of ERα(S) mRNA (∼170-fold by 120 hpf), an effect mimicked by bisphenol-A and diethylstilbestrol. Significantly, a C-truncated variant (ERα(S)-Cx) lacking most of the ligand binding and AF-2 domains was transcribed exclusively from the short isoform promoter and was similar to ERα(S) in its tissue-, stage- and estrogen inducible expression. These results support the idea that promoter choice and alternative splicing of the esr1 gene of zebrafish are part of the autoregulatory mechanism by which estrogen modulates subsequent ERα expression, and further suggest that environmental estrogens could exert some of their toxic effects by altering the relative abundance of structurally and functionally distinct ERα isoforms.

Glucocorticoid receptor antagonism as a novel therapy for triple-negative breast cancer

PURPOSE

Triple-negative breast cancer (TNBC) accounts for 10% to 20% of newly diagnosed invasive breast cancer. Finding effective targets for chemotherapy-resistant TNBC has proven difficult in part because of TNBC's molecular heterogeneity. We have previously reported that likely because of the antiapoptotic activity of glucocorticoid receptor (GR) in estrogen receptor (ER)-negative breast epithelial and cancer cells, high GR expression/activity in early-stage TNBC significantly correlates with chemotherapy resistance and increased recurrence. We hypothesized that pretreatment with mifepristone, a GR antagonist, would potentiate the efficacy of chemotherapy in GR+ TNBCs by inhibiting the antiapoptotic signaling pathways of GR and increasing the cytotoxic efficiency of chemotherapy.

EXPERIMENTAL DESIGN

TNBC cell apoptosis was examined in the context of physiologic glucocorticoid concentrations, chemotherapy, and/or pharmacologic concentrations of mifepristone. We used high-throughput live microscopy with continuous recording to measure apoptotic cells stained with a fluorescent dye and Western blot analysis to detect caspase-3 and PARP cleavage. The effect of mifepristone on GR-mediated gene expression was also measured. TNBC xenograft studies were performed in female severe combined immunodeficient (SCID) mice and tumors were measured following treatment with vehicle, paclitaxel, or mifepristone/paclitaxel.

RESULTS

We found that although mifepristone treatment alone had no significant effect on TNBC cell viability or clonogenicity in the absence of chemotherapy, the addition of mifepristone to dexamethasone/paclitaxel treatment significantly increased cytotoxicity and caspase-3/PARP cleavage. Mifepristone also antagonized GR-induced SGK1 and MKP1/DUSP1 gene expression while significantly augmenting paclitaxel-induced GR+ MDA-MB-231 xenograft tumor shrinkage in vivo.

CONCLUSIONS

These results suggest that mifepristone pretreatment could be a useful strategy for increasing tumor cell apoptosis in chemotherapy-resistant GR+ TNBC.

How glucocorticoid receptors modulate the activity of other transcription factors: a scope beyond tethering

The activity of the glucocorticoid receptor (GR), a nuclear receptor transcription factor belonging to subclass 3C of the steroid/thyroid hormone receptor superfamily, is typically triggered by glucocorticoid hormones. Apart from driving gene transcription via binding onto glucocorticoid response elements in regulatory regions of particular target genes, GR can also inhibit gene expression via transrepression, a mechanism largely based on protein:protein interactions. Hereby GR can influence the activity of other transcription factors, without contacting DNA itself. GR is known to inhibit the activity of a growing list of immune-regulating transcription factors. Hence, GCs still rule the clinic for treatments of inflammatory disorders, notwithstanding concomitant deleterious side effects. Although patience is a virtue when it comes to deciphering the many mechanisms GR uses to influence various signaling pathways, the current review is testimony of the fact that groundbreaking mechanistic work has been accumulating over the past years and steadily continues to grow.

Dexamethasone inhibits the maturation of newly formed neurons and glia supplemented with polyunsaturated fatty acids

Stress bears a negative impact on adult neurogenesis. High levels of corticoids have been shown to inhibit neural stem cell proliferation, and are considered responsible for the loss of neural precursors. Their effects on the differentiation of the glial and neuronal lineages have been less studied. We examined the effect of dexamethasone (Dex), a synthetic glucocorticoid, on the differentiation of rat neural stem cells in vitro. Dex had no effect on the differentiation of cells cultured under standard conditions. Since we previously determined that NSC, when cultured under classical conditions, were deprived of polyunsaturated fatty acids (PUFA), and displayed phospholipid compositions very different from the in vivo figures [1], we examined the effect of Dex under PUFA supplementation. Dex impaired neuron and oligodendrocyte maturation in PUFA-supplemented cells, demonstrated by the reduction of neurite lengths and oligodendrocyte sizes. This effect was mediated by the glucocorticoid receptor (GR), since it was eliminated by mifepristone, a GR antagonist, and could be relayed by a reduction of ERK phosphorylation. We determined that GR was associated with PPAR β and α under basal conditions, and that this association was disrupted when PUFA were added in combination with Dex. We assumed that this effect on the receptor status enabled the effect of Dex on PUFA supplemented cells, since we determined that the binding to the glucocorticoid response element was higher in cells incubated with PUFA and Dex. In conclusion, corticoids can impair NSC differentiation, and consequently impact the entire process of neurogenesis.

The biology of the glucocorticoid receptor: new signaling mechanisms in health and disease

Glucocorticoids are primary stress hormones necessary for life that regulate numerous physiologic processes in an effort to maintain homeostasis. Synthetic derivatives of these hormones have been mainstays in the clinic for treating inflammatory diseases, autoimmune disorders, and hematologic cancers. The physiologic and pharmacologic actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), a member of the nuclear receptor superfamily of ligand-dependent transcription factors. Ligand-occupied GR induces or represses the transcription of thousands of genes through direct binding to DNA response elements, physically associating with other transcription factors, or both. The traditional view that glucocorticoids act through a single GR protein has changed dramatically with the discovery of a large cohort of receptor isoforms with unique expression, gene-regulatory, and functional profiles. These GR subtypes are derived from a single gene by means of alternative splicing and alternative translation initiation mechanisms. Posttranslational modification of these GR isoforms further expands the diversity of glucocorticoid responses. Here we discuss the origin and molecular properties of the GR isoforms and their contribution to the specificity and sensitivity of glucocorticoid signaling in healthy and diseased tissues.

Glucocorticoid receptor β regulates injury-mediated astrocyte activation and contributes to glioma pathogenesis via modulation of β-catenin/TCF transcriptional activity

Astrocytes react to central nervous system (CNS) injury and participate in gliotic responses, imparting negative, as well as positive effects on axonal regeneration. Despite the considerable biochemical and morphological changes astrocytes undergo following insult, and the known influence of steroids on glial activation, details surrounding glucocorticoid receptor expression and activity are lacking. Such mechanistic information is essential for advancing and enhancing therapies in the treatment of CNS injuries. Using an in vitro wound-healing assay, we found glucocorticoid receptor β (GRβ), not GRα, is upregulated and acts as a regulator of gliosis after injury. In addition, our results suggest that GRβ interacts with β-catenin and is a necessary component for proliferation and migration in both injured astrocytes and glioma cells. Further analysis indicated GRβ/β-catenin interaction as a key modulator of astrocyte reactivity through sustained Wnt/β-catenin/TCF signaling in its dominant-negative effect on GRα mediated trans-repression by a GSK-3β-independent manner. These findings expand our knowledge of the mechanism of GRβ action in promoting astrocyte proliferation and migration following injury and in glioma. This information furthers our understanding the function of glucocorticoid receptor in CNS injury and disease, as well as in the basic biochemical responses astrocytes undergo in response to injury and glioma pathogenesis.

Determinants of the heightened activity of glucocorticoid receptor translational isoforms

Translational isoforms of the glucocorticoid receptor α (GR-A, -B, -C1, -C2, -C3, -D1, -D2, and -D3) have distinct tissue distribution patterns and unique gene targets. The GR-C3 isoform-expressing cells are more sensitive to glucocorticoid killing than cells expressing other GRα isoforms and the GR-D isoform-expressing cells are resistant to glucocorticoid killing. Whereas a lack of activation function 1 (AF1) may underlie the reduced activity of the GR-D isoforms, it is not clear how the GR-C3 isoform has heightened activity. Mutation analyses and N-terminal tagging demonstrated that steric hindrance is probably the mechanism for the GR-A, -B, -C1, and -C2 isoforms to have lower activity than the GR-C3 isoform. In addition, truncation scanning analyses revealed that residues 98 to 115 are critical in the hyperactivity of the human GR-C3 isoform. Chimera constructs linking this critical fragment with the GAL4 DNA-binding domain showed that GR residues 98 to 115 do not contain any independent transactivation activity. Mutations at residues Asp101 or Gln106 and Gln107 all reduced the activity of the GR-C3 isoform. In addition, functional studies indicated that Asp101 is crucial for the GR-C3 isoform to recruit coregulators and to mediate glucocorticoid-induced apoptosis. Thus, charged and polar residues are essential components of an N-terminal motif that enhances the activity of AF1 and the GR-C3 isoform. These studies, together with the observations that GR isoforms have cell-specific expression patterns, provide a molecular basis for the tissue-specific functions of GR translational isoforms.

Tissue-specific actions of glucocorticoids on apoptosis: a double-edged sword

First described for their metabolic and immunosuppressive effects, glucocorticoids are widely prescribed in clinical settings of inflammation. However, glucocorticoids are also potent inducers of apoptosis in many cell types and tissues. This review will focus on the established mechanisms of glucocorticoid-induced apoptosis and outline what is known about the apoptotic response in cells and tissues of the body after exposure to glucocorticoids. Glucocorticoid-induced apoptosis affects the skeletal system, muscular system, circulatory system, nervous system, endocrine system, reproductive system, and the immune system. Interestingly, several cell types have an anti-apoptotic response to glucocorticoids that is cytoprotective. Lastly, we will discuss the pro- and anti-apoptotic effects of glucocorticoids in cancers and their clinical implications.

Glucocorticoid receptor and molecular chaperones in the pathogenesis of adrenal incidentalomas: potential role of reduced sensitivity to glucocorticoids

Glucocorticoid (GC) sensitivity depends on glucocorticoid receptor (GR) and heat shock proteins (Hsps). We investigated whether common GR genes (ER22/23EK, N363S, Bcl I, and 9β) and adrenocorticotropin receptor promoter polymorphisms influence susceptibility for unilateral adrenal incidentaloma (AI), plus GR and Hsp expression in tumorous (n = 19), peritumorous (n = 13) and normal adrenocortical (n = 11) tissues. Patients (n = 112), population-matched controls (n = 100) and tumor tissues (n = 32) were genotyped for these polymorphisms. Postdexamethasone serum cortisol was higher in patients (p < 0.001). GR gene variants, larger allele of Bcl I (odds ratio [OR] 2.9; 95% confidence interval [CI] 1.7-5.1; p < 0.001] and minor allele of 9β (OR 3.0; 95% CI 1.6-5.7; p < 0.001) were independent predictors of AI. In patients, the first allele is linked with larger tumors (p = 0.002) and the latter with higher postdexamethasone cortisol levels (p = 0.025). Both allele carriers had lesser waist circumference (p = 0.02), similar adrenocorticotropin and higher basal (p = 0.024) and postdexamethasone cortisol concentrations (p < 0.001). Tumorous and constitutional genotypes were similar. GR-D is the major receptor isoform in normal adrenal cortex by Western blotting. Loss of other receptor isoforms, decrease in immunostaining for GR (p < 0.0001), underexpression of chaperones (p ≤ 0.01) and the presence of inducible Hsp70 were found in adenomas. In conclusion, GR gene variants, C allele of Bcl I and minor allele of 9β, are associated with AIs. Their concurrent presence in patients reduces GC sensitivity. Normal adrenal cortex preferentially expresses GR-D. In adenomas, the lack of other GR isoforms and underexpression of heat shock proteins perhaps permanently impair GC signaling, which could promote dysregulated cortisol production and tumor growth. The innate GC sensitivity probably modifies these effects.

Selective glucocorticoid receptor translational isoforms reveal glucocorticoid-induced apoptotic transcriptomes

Induction of T-cell apoptosis contributes to the anti-inflammatory and antineoplastic benefits of glucocorticoids. The glucocorticoid receptor (GR) translational isoforms have distinct proapoptotic activities in osteosarcoma cells. Here we determined whether GR isoforms selectively induce apoptosis in Jurkat T lymphoblastic leukemia cells. Jurkat cells stably expressing individual GR isoforms were generated and treated with vehicle or dexamethasone (DEX). DEX induced apoptosis in cells expressing the GR-A, -B, or -C, but not the GR-D, isoform. cDNA microarray analyses of cells sensitive (GR-C3) and insensitive (GR-D3) to DEX revealed glucocorticoid-induced proapoptotic transcriptomes. Genes that were regulated by the proapoptotic GR-C3, but not by the GR-D3, isoform likely contributed to glucocorticoid-induced apoptosis. The identified genes include those that are directly involved in apoptosis and those that facilitate cell killing. Chromatin immunoprecipitation assays demonstrated that distinct chromatin modification abilities may underlie the distinct functions of GR isoforms. Interestingly, all GR isoforms, including the GR-D3 isoform, suppressed mitogen-stimulated cytokines. Furthermore, the GR-C isoforms were selectively upregulated in mitogen-activated primary T cells and DEX treatment induced GR-C target genes in activated T cells. Cell-specific expressions and functions of GR isoforms may help to explain the tissue- and individual-selective actions of glucocorticoids and may provide a basis for developing improved glucocorticoids.

Glucocorticoid receptor translational isoforms underlie maturational stage-specific glucocorticoid sensitivities of dendritic cells in mice and humans

Although glucocorticoids are a profoundly important class of anti-inflammatory and immunosuppressive agents, their actions in dendritic cells (DCs) are not well understood. We found that dexamethasone, a potent glucocorticoid, selectively induced apoptosis in mature, but not in immature, DCs in healthy mice, in mice with experimental airway inflammation, and in vitro in bone marrow–derived DCs. Distinct glucocorticoid receptor (GR) translational isoforms expressed in immature and mature DCs probably contribute to the DC maturational stage-specific glucocorticoid sensitivity. The GR-D isoforms were the predominant isoforms in immature DCs, whereas the proapoptotic GR-A isoform was the main isoform in mature DCs. Ectopic expression of the GR-A isoform in immature DCs increased glucocorticoid sensitivity and RU486, a selective GR antagonist, inhibited the glucocorticoid sensitivity of mature DCs. Furthermore, the distinct expression pattern of GR isoforms in immature and mature murine DCs was also observed in human monocyte–derived DCs. These studies suggest that glucocorticoids may spare immature DCs and suppress mature DCs and inflammation via differential expression of GR translational isoforms.

Exploring the molecular mechanisms of glucocorticoid receptor action from sensitivity to resistance

Glucocorticoids regulate a variety of physiological processes, and are commonly used to treat disorders of inflammation, autoimmune diseases, and cancer. Glucocorticoid action is predominantly mediated through the classic glucocorticoid receptor (GR), but sensitivity to glucocorticoids varies among individuals, and even within different tissues from the same individual. The molecular basis of this phenomenon can be partially explained through understanding the process of generating bioavailable ligand and the molecular heterogeneity of the GR. The molecular mechanisms that regulate glucocorticoid action highlight the dynamic nature of hormone signaling and provide novel insights into genomic glucocorticoid actions and glucocorticoid sensitivity. Although glucocorticoids are highly effective for therapeutic purposes, long-term and/or high-dose glucocorticoid administration often leads to reduced glucocorticoid sensitivity or resistance. Here, we summarize our current understanding of the mechanisms that modulate glucocorticoid sensitivity and resistance with a focus on GR-mediated signaling.

Combination of a selective activator of the glucocorticoid receptor Compound A with a proteasome inhibitor as a novel strategy for chemotherapy of hematologic malignancies

Glucocorticoids are widely used for the treatment of hematological malignancies; however, their chronic use results in numerous metabolic side effects. Thus, the development of selective glucocorticoid receptor (GR) activators (SEGRA) with improved therapeutic index is important. GR regulates gene expression via (1) transactivation that requires GR homodimer binding to gene promoters and is linked to side effects and (2) transrepression-mediated via negative GR interaction with other transcription factors. Novel GR modulator Compound A (CpdA) prevents GR dimerization, retains glucocorticoid anti-inflammatory activity and has fewer side effects compared with glucocorticoids in vivo. Here we tested CpdA anticancer activity in human T- and B-lymphoma and multiple myeloma cells expressing GR and their counterparts with silenced GR. We found that CpdA in GR-dependent manner strongly inhibited growth and viability of human T-, B-lymphoma and multiple myeloma cells. Furthermore, primary leukemia cell cultures from T-ALL patients appeared to be equally sensitive to glucocorticoid dexamethasone and CpdA. It is known that GR expression is controlled by proteasome. We showed that pretreatment of lymphoma CEM and NCEB cells with proteasome-inhibitor Bortezomib resulted in GR accumulation and enhanced ligand properties of CpdA, shifting GR activity toward transrepression evaluated by inhibition of NFкB and AP-1 transcription factors. We also revealed remarkable GR-dependent cooperation between CpdA and Bortezomib in suppressing growth and survival of T- and B-lymphoma and multiple myeloma MM.1S cells. Overall, our data provide the rationale for novel GR-based therapy for hematological malignancies based on combination of SEGRA with proteasome inhibitors.

Possible link between the synthesis of GR alpha isoforms and eIF2 alpha phosphorylation state

Glucocorticoid hormones regulate numerous physiological processes and are widely used in the treatment of inflammation, autoimmune disease and cancer. Glucocorticoid receptor (GR) - a transcription factor, derived from a single gene, is responsible for the diverse actions of glucocorticoids. It was shown that GR gene gives rise a variety of mRNA species that produces several protein isoforms, among them GRα is the most abundant. In addition, GRα N-end-truncated protein isoforms (A, B, C, D) are generated by translational mechanisms. As it was found that the ratio between the translational isoforms amounts varied in different tissues and cell lines and distinct isoforms could control transcription of different sets of genes, molecular mechanisms underlining the synthesis of translational GRα isoforms are of great interest. It was considered that GRα isoform A is translated by a conventional linear scanning, isoform B is translated by leaky scanning, isoform C is translated by leaky scanning and ribosomal shunt whereas translation of isoform D occurs through ribosomal shunt only. Since the sequence organization of GRα mRNA strongly resembles the cases of ATF4 or ATF5, the well-known examples of reinitiation-dependent synthesis of functional isoforms, we hypothesize that translation of isoform C could be controlled by reinitiation mechanism also. If this assumption is correct, the ratio between GRα N-end isoforms could depend on the eIF2α phosphorylation state that could provide an additional connection between the GR and cellular stresses. We believe that this hypothesis could be of interest to plan more robust experiments or for better interpretation of available data.

Current concepts in glucocorticoid resistance

Glucocorticoids (GCs) are the most potent anti-inflammatory agents known. A major factor limiting their clinical use is the wide variation in responsiveness to therapy. The high doses of GC required for less responsive patients means a high risk of developing very serious side effects. Variation in sensitivity between individuals can be due to a number of factors. Congenital, generalized GC resistance is very rare, and is due to mutations in the glucocorticoid receptor (GR) gene, the receptor that mediates the cellular effects of GC. A more common problem is acquired GC resistance. This localized, disease-associated GC resistance is a serious therapeutic concern and limits therapeutic response in patients with chronic inflammatory disease. It is now believed that localized resistance can be attributed to changes in the cellular microenvironment, as a consequence of chronic inflammation. Multiple factors have been identified, including alterations in both GR-dependent and -independent signaling downstream of cytokine action, oxidative stress, hypoxia and serum derived factors. The underlying mechanisms are now being elucidated, and are discussed here. Attempts to augment tissue GC sensitivity are predicted to permit safe and effective use of low-dose GC therapy in inflammatory disease.

Proinflammatory actions of glucocorticoids: glucocorticoids and TNFα coregulate gene expression in vitro and in vivo

Synthetic glucocorticoids are widely used for treatment of many inflammatory diseases. However, long-term glucocorticoid treatment can cause a variety of negative side effects. A genome-wide microarray analysis was performed in human lung A549 cells to identify genes regulated by both the antiinflammatory steroid dexamethasone (Dex) and the proinflammatory cytokine TNFα. Unexpectedly, we discovered that numerous genes were coregulated by treatment with both Dex and TNFα. We evaluated the mechanism of coregulation of one of these genes, serpinA3 (α-1 antichymotrypsin), a secreted, acute phase protein strongly associated with numerous inflammatory diseases. Up-regulation of serpinA3 requires the presence of both the glucocorticoid receptor and TNFα soluble receptor 1. Treatment with Dex or TNFα resulted in a 10- to 25-fold increase of serpinA3 mRNA, whereas coadministration of Dex and TNFα led to a synergistic increase in serpinA3 mRNA. The naturally occurring glucocorticoid, cortisol, also resulted in a synergistic increase in serpinA3 mRNA levels in A549 cells. Furthermore, in vivo treatment of C57BL/6 mice with Dex and TNFα resulted in coregulation of serpinA3 mRNA levels in both lung and liver tissues. Finally, chromatin immunoprecipitation analyses suggest that glucocorticoid receptor binding to the serpinA3 transcriptional start site can be enhanced by the combination of Dex plus TNFα treatment of A549 cells. These studies demonstrate that glucocorticoids and proinflammatory compounds can coregulate genes associated with human disease. This discovery may underlie the basis of some of the adverse effects associated with long-term glucocorticoid therapy.

Glucocorticoid receptor signaling in bone cells

Glucocorticoids are used for treating a wide range of diseases including inflammation and autoimmune disorders. However, there are drawbacks, primarily due to adverse effects on bone cells resulting in osteoporosis. Evidence indicates that the ratio of benefits to adverse effects depends greatly on glucocorticoid receptor (GR)-mediated mechanisms. Delineating GR-mediated signaling in bone cells will allow development of selective GR ligands/agonists (SEGRAs), which would dissociate the positive therapeutic (anti-inflammatory) effects from the negative effects on the skeleton. The present review provides an in-depth account of the current knowledge of GR-mediated transcriptional regulation of specific genes and proteins engaged in the proliferation, differentiation, and apoptosis of bone cells (osteoblasts, osteocytes, osteoclasts). We hope this knowledge will advance research in the development of SEGRAs with improved benefit/risk ratios.