Nontranscriptional actions of the glucocorticoid receptor

Association of glucocorticoid receptor expression with key members of the insulin signaling pathway and heat shock proteins in the bovine ovary

Glucocorticoids (GCs) act through their receptor (GR) as regulators in different biological processes such as reproduction. In the absence of GCs, the GR remains inactive in the cytoplasm by associating with heat shock proteins (HSPs), which act as molecular chaperones, among which the most relevant are HSP90 and HSP70. Cytoplasmic GC-activated GR mediates non-genomic effects, interacting with members of signaling pathways such as PI3K/Akt, which participates in several metabolic processes, including the insulin signaling pathway. The aim of the present study was to evaluate possible associations between the cytoplasmic GR and the main intermediates of the insulin signaling pathway and HSP90 and HSP70 in ovaries of dairy cows. To this end, the protein expression of cytoplasmic GR, key members of the insulin signaling pathway, and HSPs was evaluated in ovarian preovulatory follicles of non-lactating Holstein cows in proestrus. Positive associations were observed between protein expression of GR and HSP90, IRS1, pIRS1, PI3K and pAkt (p < 0.05; β > 0) in granulosa cells of dominant follicles of dairy cows. Instead, in theca cells, no associations were observed between protein expression of GR and members of the insulin signaling pathway or HSPs. These data provide evidence of the possible association between the non-genomic mechanisms of action of the GR and the insulin signaling pathway in the bovine ovary.

Physiologic effects of stress dose corticosteroids in in-hospital cardiac arrest (CORTICA): A randomized clinical trial

Aim

Postresuscitation hemodynamics are associated with hospital mortality/functional outcome. We sought to determine whether low-dose steroids started during and continued after cardiopulmonary resuscitation (CPR) affect postresuscitation hemodynamics and other physiological variables in vasopressor-requiring, in-hospital cardiac arrest.

Methods

We conducted a two-center, randomized, double-blind trial of patients with adrenaline (epinephrine)-requiring cardiac arrest. Patients were randomized to receive either methylprednisolone 40 mg (steroids group) or normal saline-placebo (control group) during the first CPR cycle post-enrollment. Postresuscitation shock was treated with hydrocortisone 240 mg daily for 7 days maximum and gradual taper (steroids group), or saline-placebo (control group). Primary outcomes were arterial pressure and central-venous oxygen saturation (ScvO₂) within 72 hours post-ROSC.

Results

Eighty nine of 98 controls and 80 of 86 steroids group patients with ROSC were treated as randomized. Primary outcome data were collected from 100 patients with ROSC (control, n = 54; steroids, n = 46). In intention-to-treat mixed-model analyses, there was no significant effect of group on arterial pressure, marginal mean (95% confidence interval) for mean arterial pressure, steroids vs. control: 74 (68–80) vs. 72 (66–79) mmHg] and ScvO₂ [71 (68–75)% vs. 69 (65–73)%], cardiac index [2.8 (2.5–3.1) vs. 2.9 (2.5–3.2) L/min/m²], and serum cytokine concentrations [e.g. interleukin-6, 89.1 (42.8–133.9) vs. 75.7 (52.1–152.3) pg/mL] determined within 72 hours post-ROSC (P = 0.12–0.86). There was no between-group difference in body temperature, echocardiographic variables, prefrontal blood flow index/cerebral autoregulation, organ failure-free days, and hazard for poor in-hospital/functional outcome, and adverse events (P = 0.08–>0.99).

Conclusions

Our results do not support the use of low-dose corticosteroids in in-hospital cardiac arrest.

Trial Registration:ClinicalTrials.gov number: NCT02790788 (https://www.clinicaltrials.gov).

The osteocyte as a signaling cell

Osteocytes, former osteoblasts encapsulated by mineralized bone matrix, are far from being passive and metabolically inactive bone cells. Instead, osteocytes are multifunctional and dynamic cells capable of integrating hormonal and mechanical signals and transmitting them to effector cells in bone and in distant tissues. Osteocytes are a major source of molecules that regulate bone homeostasis by integrating both mechanical cues and hormonal signals that coordinate the differentiation and function of osteoclasts and osteoblasts. Osteocyte function is altered in both rare and common bone diseases, suggesting that osteocyte dysfunction is directly involved in the pathophysiology of several disorders affecting the skeleton. Advances in osteocyte biology initiated the development of novel therapeutics interfering with osteocyte-secreted molecules. Moreover, osteocytes are targets and key distributors of biological signals mediating the beneficial effects of several bone therapeutics used in the clinic. Here we review the most recent discoveries in osteocyte biology demonstrating that osteocytes regulate bone homeostasis and bone marrow fat via paracrine signaling, influence body composition and energy metabolism via endocrine signaling, and contribute to the damaging effects of diabetes mellitus and hematologic and metastatic cancers in the skeleton.

Homeostatic Regulation of Glucocorticoid Receptor Activity by Hypoxia-Inducible Factor 1: From Physiology to Clinic

Glucocorticoids (GCs) represent a well-known class of lipophilic steroid hormones biosynthesised, with a circadian rhythm, by the adrenal glands in humans and by the inter-renal tissue in teleost fish (e.g., zebrafish). GCs play a key role in the regulation of numerous physiological processes, including inflammation, glucose, lipid, protein metabolism and stress response. This is achieved through binding to their cognate receptor, GR, which functions as a ligand-activated transcription factor. Due to their potent anti-inflammatory and immune-suppressive action, synthetic GCs are broadly used for treating pathological disorders that are very often linked to hypoxia (e.g., rheumatoid arthritis, inflammatory, allergic, infectious, and autoimmune diseases, among others) as well as to prevent graft rejections and against immune system malignancies. However, due to the presence of adverse effects and GC resistance their therapeutic benefits are limited in patients chronically treated with steroids. For this reason, understanding how to fine-tune GR activity is crucial in the search for novel therapeutic strategies aimed at reducing GC-related side effects and effectively restoring homeostasis. Recent research has uncovered novel mechanisms that inhibit GR function, thereby causing glucocorticoid resistance, and has produced some surprising new findings. In this review we analyse these mechanisms and focus on the crosstalk between GR and HIF signalling. Indeed, its comprehension may provide new routes to develop novel therapeutic targets for effectively treating immune and inflammatory response and to simultaneously facilitate the development of innovative GCs with a better benefits-risk ratio.

Dexamethasone Induces the Expression and Function of Tryptophan-2-3-Dioxygenase in SK-MEL-28 Melanoma Cells

Tryptophan-2,3-dioxygenase (TDO) is one of the key tryptophan-catabolizing enzymes with immunoregulatory properties in cancer. Contrary to expectation, clinical trials showed that inhibitors of the ubiquitously expressed enzyme, indoleamine-2,3-dioxygenase-1 (IDO1), do not provide benefits in melanoma patients. This prompted the hypothesis that TDO may be a more attractive target. Because the promoter of TDO harbors glucocorticoid response elements (GREs), we aimed to assess whether dexamethasone (dex), a commonly used glucocorticoid, modulates TDO expression by means of RT-PCR and immunofluorescence and function by assessing cell proliferation and migration as well as metalloproteinase activity. Our results show that, in SK-Mel-28 melanoma cells, dex up-regulated TDO and its downstream effector aryl hydrocarbon receptor (AHR) but not IDO1. Furthermore, dex stimulated cellular proliferation and migration and potentiated MMP2 activity. These effects were inhibited by the selective TDO inhibitor 680C91 and enhanced by IDO1 inhibitors. Taken together, our results demonstrate that the metastatic melanoma cell line SK-Mel-28 possesses a functional TDO which can also modulate cancer cell phenotype directly rather than through immune suppression. Thus, TDO appears to be a promising, tractable target in the management or the treatment of melanoma progression.

NADPH oxidases and HIF1 promote cardiac dysfunction and pulmonary hypertension in response to glucocorticoid excess

Cardiovascular side effects are frequent problems accompanying systemic glucocorticoid therapy, although the underlying mechanisms are not fully resolved. Reactive oxygen species (ROS) have been shown to promote various cardiovascular diseases although the link between glucocorticoid and ROS signaling has been controversial. As the family of NADPH oxidases has been identified as important source of ROS in the cardiovascular system we investigated the role of NADPH oxidases in response to the synthetic glucocorticoid dexamethasone in the cardiovascular system in vitro and in vivo in mice lacking functional NADPH oxidases due to a mutation in the gene coding for the essential NADPH oxidase subunit p22phox. We show that dexamethasone induced NADPH oxidase-dependent ROS generation, leading to vascular proliferation and angiogenesis due to activation of the transcription factor hypoxia-inducible factor-1 (HIF1). Chronic treatment of mice with low doses of dexamethasone resulted in the development of systemic hypertension, cardiac hypertrophy and left ventricular dysfunction, as well as in pulmonary hypertension and pulmonary vascular remodeling. In contrast, mice deficient in p22phox-dependent NADPH oxidases were protected against these cardiovascular side effects. Mechanistically, dexamethasone failed to upregulate HIF1α levels in these mice, while vascular HIF1α deficiency prevented pulmonary vascular remodeling. Thus, p22phox-dependent NADPH oxidases and activation of the HIF pathway are critical elements in dexamethasone-induced cardiovascular pathologies and might provide interesting targets to limit cardiovascular side effects in patients on chronic glucocorticoid therapy.

Investigating the effects of dexamethasone on blood-brain barrier permeability and inflammatory response following focused ultrasound and microbubble exposure

Rationale: Clinical trials are currently underway to test the safety and efficacy of delivering therapeutic agents across the blood-brain barrier (BBB) using focused ultrasound and microbubbles (FUS+MBs). While acoustic feedback control strategies have largely minimized the risk of overt tissue damage, transient induction of inflammatory processes have been observed following sonication in preclinical studies. The goal of this work was to explore the potential of post-sonication dexamethasone (DEX) administration as a means to mitigate treatment risk. Vascular permeability, inflammatory protein expression, blood vessel growth, and astrocyte activation were assessed. Methods: A single-element focused transducer (transmit frequency = 580 kHz) and Definity^TM microbubbles were used to increase BBB permeability unilaterally in the dorsal hippocampi of adult male rats. Sonicating pressure was calibrated based on ultraharmonic emissions. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to quantitatively assess BBB permeability at 15 min (baseline) and 2 hrs following sonication. DEX was administered following baseline imaging and at 24 hrs post-FUS+MB exposure. Expression of key inflammatory proteins were assessed at 2 days, and astrocyte activation and blood vessel growth were assessed at 10 days post-FUS+MB exposure. Results: Compared to saline-treated control animals, DEX administration expedited the restoration of BBB integrity at 2 hrs, and significantly limited the production of key inflammation-related proteins at 2 days, following sonication. Indications of FUS+MB-induced astrocyte activation and vascular growth were diminished at 10 days in DEX-treated animals, compared to controls. Conclusions: These results suggest that DEX provides a means of modulating the duration of BBB permeability enhancement and may reduce the risk of inflammation-induced tissue damage, increasing the safety profile of this drug-delivery strategy. This effect may be especially relevant in scenarios for which the goal of treatment is to restore or preserve neural function and multiple sonications are required.

Glucocorticoids regulate pentraxin-3 expression in human airway smooth muscle cells

Pentraxin-3 (PTX3) is a multifunctional protein involved in both innate and adaptive immunity. Glucocorticoid (GC) is the first-line therapy to mitigate airway inflammation in asthma. Previous pieces of evidence showed that GC has divergent effects on PTX3 production in various cell types. The molecular mechanisms controlling PTX3 expression in HASMC are, however, not yet characterized. In this study, we demonstrate that the synthetic GC, dexamethasone (DEX) increases the expression of PTX3 both at the protein and mRNA levels. We also found that such an effect of DEX was dependent on de novo protein synthesis and the GC receptor (GR). While DEX increases PTX3 mRNA stability, it did not affect its promoter activity. Interestingly, HASMC pre-treated with p42/p44 ERK inhibitor, but not with p38 or JNK-MAPK inhibitors, significantly interfered with DEX-induced PTX3 secretion. Taken together, our data suggest that GC regulates PTX3 expression in HASMC through transcriptional and post-transcriptional mechanisms in a GR and ERK-dependent manner.

Non-genomic Effects of Glucocorticoids: An Updated View

Glucocorticoid (GC) anti-inflammatory effects generally require a prolonged onset of action and involve genomic processes. Because of the rapidity of some of the GC effects, however, the concept that non-genomic actions may contribute to GC mechanisms of action has arisen. While the mechanisms have not been completely elucidated, the non-genomic effects may play a role in the management of inflammatory diseases. For instance, we recently reported that GCs 'rapidly' enhanced the effects of bronchodilators, agents used in the treatment of allergic asthma. In this review article, we discuss (i) the non-genomic effects of GCs on pathways relevant to the pathogenesis of inflammatory diseases and (ii) the putative role of the membrane GC receptor. Since GC side effects are often considered to be generated through its genomic actions, understanding GC non-genomic effects will help design GCs with a better therapeutic index.

Cell-Type Specific Changes in Glial Morphology and Glucocorticoid Expression During Stress and Aging in the Medial Prefrontal Cortex

Repeated exposure to stressors is known to produce large-scale remodeling of neurons within the prefrontal cortex (PFC). Recent work suggests stress-related forms of structural plasticity can interact with aging to drive distinct patterns of pyramidal cell morphological changes. However, little is known about how other cellular components within PFC might be affected by these challenges. Here, we examined the effects of stress exposure and aging on medial prefrontal cortical glial subpopulations. Interestingly, we found no changes in glial morphology with stress exposure but a profound morphological change with aging. Furthermore, we found an upregulation of non-nuclear glucocorticoid receptors (GR) with aging, while nuclear levels remained largely unaffected. Both changes are selective for microglia, with no stress or aging effect found in astrocytes. Lastly, we show that the changes found within microglia inversely correlated with the density of dendritic spines on layer III pyramidal cells. These findings suggest microglia play a selective role in synaptic health within the aging brain.

GLUCOCORTICOID EXCESS IN BONE AND MUSCLE

Glucocorticoids (GC), produced and released by the adrenal glands, regulate numerous physiological processes in a wide range of tissues. Because of their profound immunosuppressive and anti-inflammatory actions, GC are extensively used for the treatment of immune and inflammatory conditions, the management of organ transplantation, and as a component of chemotherapy regimens for cancers. However, both pathologic endogenous elevation and long-term use of exogenous GC are associated with severe adverse effects. In particular, excess GC has devastating effects on the musculoskeletal system. GC increase bone resorption and decrease formation leading to bone loss, microarchitectural deterioration and fracture. GC also induce loss of muscle mass and strength leading to an increased incidence of falls. The combined effects on bone and muscle account for the increased fracture risk with GC. This review summarizes the advance in knowledge in the last two decades about the mechanisms of action of GC in bone and muscle and the attempts to interfere with the damaging actions of GC in these tissues with the goal of developing more effective therapeutic strategies.

Hypothalamic-Pituitary-Adrenal Axis Modulation of Glucocorticoids in the Cardiovascular System

The collective of endocrine organs acting in homeostatic regulation—known as the hypothalamic-pituitary-adrenal (HPA) axis—comprises an integration of the central nervous system as well as peripheral tissues. These organs respond to imminent or perceived threats that elicit a stress response, primarily culminating in the release of glucocorticoids into the systemic circulation by the adrenal glands. Although the secretion of glucocorticoids serves to protect and maintain homeostasis in the typical operation at baseline levels, inadequate regulation can lead to physiologic and psychologic pathologies. The cardiovascular system is especially susceptible to prolonged dysregulation of the HPA axis and glucocorticoid production. There is debate about whether cardiovascular health risks arise from the direct detrimental effects of stress axis activation or whether pathologies develop secondary to the accompanying metabolic strain of excess glucocorticoids. In this review, we will explore the emerging research that indicates stress does have direct effects on the cardiovascular system via the HPA axis activation, with emphasis on the latest research on the impact of glucocorticoids signaling in the vasculature and the heart.

Genome-Wide Identification of Basic Helix-Loop-Helix and NF-1 Motifs Underlying GR Binding Sites in Male Rat Hippocampus

Glucocorticoids regulate hippocampal function in part by modulating gene expression through the glucocorticoid receptor (GR). GR binding is highly cell type specific, directed to accessible chromatin regions established during tissue differentiation. Distinct classes of GR binding sites are dependent on the activity of additional signal-activated transcription factors that prime chromatin toward context-specific organization. We hypothesized a stress context dependency for GR binding in hippocampus as a consequence of rapidly induced stress mediators priming chromatin accessibility. Using chromatin immunoprecipitation sequencing to interrogate GR binding, we found no effect of restraint stress context on GR binding, although analysis of sequences underlying GR binding sites revealed mechanistic detail for hippocampal GR function. We note enrichment of GR binding sites proximal to genes linked to structural and organizational roles, an absence of major tethering partners for GRs, and little or no evidence for binding at negative glucocorticoid response elements. A basic helix-loop-helix motif closely resembling a NeuroD1 or Olig2 binding site was found underlying a subset of GR binding sites and is proposed as a candidate lineage-determining transcription factor directing hippocampal chromatin access for GRs. Of our GR binding sites, 54% additionally contained half-sites for nuclear factor (NF)-1 that we propose as a collaborative or general transcription factor involved in hippocampal GR function. Our findings imply a dose-dependent and context-independent action of GRs in the hippocampus. Alterations in the expression or activity of NF-1/basic helix-loop-helix factors may play an as yet undetermined role in glucocorticoid-related disease susceptibility and outcome by altering GR access to hippocampal binding sites.

New Insights in Glucocorticoid Receptor Signaling-More Than Just a Ligand-Binding Receptor

The clinical use of classical glucocorticoids (GC) is narrowed by the many side effects it causes and the resistance to GC observed in some diseases. Since the great majority of GC effects depend on the activation of a glucocorticoid receptor (GR), many research groups had focused to better understand the signaling pathways involving those receptors. Transgenic animal models and genetic modifications of the receptor brought a huge insight into GR mechanisms of action. This in turn opened a new window for the search of selective GR modulators that ideally may have agonistic and antagonistic combined effects and activate one specific signaling pathway, inducing mostly transrepression or transactivation mechanisms. Another important research field concerns to posttranslational modifications that affect the GR and consequently also affect its signaling and function. In this mini review, we discuss many of those aspects of GR signaling, as well as findings like the ligand-independent activation of GR, which add another layer of complexity in GR signaling pathways. Although several recent data have been added to the GR field, much work has yet to be done, especially to find out the biological relevance of those alternative GR signaling pathways. Improving the knowledge about alternative GR signaling pathways and understanding how these pathways intercommunicate and in which situations they are relevant might help to develop new strategies to take benefit of it and to improve GC or other compounds efficacy causing minimal side effects.

Glucocorticoid receptor function in health and disease

Glucocorticoid hormones are essential for life in vertebrates. They act through the glucocorticoid receptor (GR), which is expressed in virtually all cells of the human body. Yet the actions of glucocorticoids (GCs) are specific to particular cell types. Broadly GCs regulate carbohydrate metabolism, inflammation, stress and cell fate. Synthetic GCs are widely used in medicine and are by far the most frequent cause of Cushing's syndrome in routine practice. The advent of novel drugs targeting the GR offers new opportunities to treat patients with immune, or malignant disease, and may also offer new opportunities to manage patients with adrenal insufficiency also. This review covers the latest understanding of how GCs work, how their actions are affected by disease, and where the new drugs may take us.

Novel glucocorticoid receptor agonists in the treatment of asthma

INTRODUCTION

Inhaled corticosteroids are the only drugs that effectively suppress the airway inflammation, but they can induce considerable systemic and adverse effects when they are administered chronically at high doses. Consequently, the pharmaceutical industry is still searching for newer entities with an improved therapeutic index.

AREAS COVERED

Herein, the authors review the research in the glucocorticoid field to identify ligands of the glucocorticoid receptor (GR). These ligands preferentially induce transrepression with little or no transactivating activity, in order to have a potent anti-inflammatory action and a low side-effects profile.

EXPERT OPINION

Several agents have been synthesized, but few have been tested in experimental models of asthma. Furthermore, only three (BI-54903, GW870086X and AZD5423) have entered clinical development, although the development of at least one of them (BI-54903) was discontinued. The reason for the limited success so far obtained is that the model of transactivation versus transrepression is a too simplistic representation of GR activity. It is difficult to uncouple the therapeutic and harmful effects mediated by GR, but some useful information that might change the current perspective is appearing in the literature. The generation of gene expression 'fingerprints' produced by different GR agonists in target and off-target human tissues could be useful in identifying drug candidates with an improved therapeutic ratio.

Ambiguous role of glucocorticoids on survival of retinal neurons

Glucocorticoids (GCs) have a wide range of functions on several mammalian cell types, most of which are aimed at boosting survival, which is the raison d'être of the acute stress response. The role GCs play in the survival and viability of neurons is incongruous, as studies have revealed neuroprotective as well as neurodegenerative effects. These effects seem to depend on multiple factors amongst which are; the cell type involved, the mode of injury or underlying cause of cell death, likewise the concentration and or duration of GC exposure.In this mini review, we discuss mechanisms of GC action and their effect on neurodegeneration in general, and specifically review the effect of GCs on retinal neurons, in animal models of retinal degeneration or acute neuronal damage. Finally, we summarize potential protective and harmful GC-mediated mechanisms, which might be involved in the determination of neuronal fate in the retina following injury or during degeneration.

Activation of GRs-Akt-nNOs-NR2B signaling pathway by second dose GR agonist contributes to exacerbated hyperalgesia in a rat model of radicular pain

Central Akt, neuronal nitric oxide synthase (nNOS) and N-methyl-D-aspartate receptor subunit 2B (NR2B) play key roles in the development of neuropathic pain. Here we investigate the effects of glucocorticoid receptors (GRs) on the expression and activation of spinal Akt, nNOS and NR2B after chronic compression of dorsal root ganglia (CCD). Thermal hyperalgesia test and mechanical allodynia test were used to measure rats after intrathecal injection of GR antagonist mifepristone or GR agonist dexamethasone for 21 days postoperatively. Expression of spinal Akt, nNOS, NR2B and their phosphorylation state after CCD was examined by western blot. The effects of intrathecal treatment with dexamethasone or mifepristone on nociceptive behaviors and the corresponding expression of Akt, nNOS and NR2B in spinal cord were also investigated. Intrathecal injection of mifepristone or dexamethasone inhibited PWMT and PWTL in CCD rats. However, hyperalgesia was induced by intrathecal injection of dexamethasone on days 12 to 14 after surgery. Treatment of dexamethasone increased the expression and phosphorylation levels of spinal Akt, nNOS, GR and NR2B time dependently, whereas administration of mifepristone downregulated the expression of these proteins significantly. GRs activated spinal Akt-nNOS/NR2B pathway play important roles in the development of neuropathic pain in a time-dependent manner.

Expression of glucocorticoid-induced leucine zipper (GILZ) in cardiomyocytes

Glucocorticoids (GCs) are frequently prescribed pharmacological agents most notably for their immunosuppressive effects. Endogenous GCs mediate biological processes such as energy metabolism and tissue development. At the cellular level, GCs bind to the glucocorticoid receptor (GR), a cytosolic protein that translocates to the nuclei and functions to alter transcription upon ligand binding. Among a long list of genes activated by GCs is the glucocorticoid-induced leucine zipper (GILZ). GC-induced GILZ expression has been well established in lymphocytes and mediates GC-induced apoptosis. Unlike lymphocytes, cardiomyocytes respond to GCs by gaining resistance against apoptosis. We determined GILZ expression in cardiomyocytes in vivo and in vitro. Expression of GILZ in mouse hearts as a result of GC administration was confirmed by Western blot analyses. GCs induced dose- and time-dependent elevation of GILZ expression in primary cultured rat cardiomyocytes, with dexamethasone (Dex) as low as 0.1 μM being effective. Time course analysis indicated that GILZ protein levels increased at 8 h and peaked at 48 h after exposure to 1 μM Dex. H9c2(2-1) cell line showed a similar response of GILZ induction by Dex as primary cultured rat cardiomyocytes, providing a convenient model for studying the biological significance of GILZ expression. With corticosterone (CT), an endogenous form of corticosteroids in rodents, 0.1-2.5 μM was found to induce GILZ in H9c2(2-1) cells. Time course analysis with 1 μM CT indicated induction of GILZ at 6 h with peak expression at 18 h. Inhibition of the GR by mifepristone led to blunting of GILZ induction by GCs. Our data demonstrate GILZ induction in cardiomyocytes both in vivo and in vitro by GCs, pointing to H9c2(2-1) cells as a valid model for studying the biological function of GILZ in cardiomyocytes.

Glucocorticoid sensitivity in health and disease

Glucocorticoids regulate many physiological processes and have an essential role in the systemic response to stress. For example, gene transcription is modulated by the glucocorticoid-glucocorticoid receptor complex via several mechanisms. The ultimate biologic responses to glucocorticoids are determined by not only the concentration of glucocorticoids but also the differences between individuals in glucocorticoid sensitivity, which is influenced by multiple factors. Differences in sensitivity to glucocorticoids in healthy individuals are partly genetically determined by functional polymorphisms of the gene that encodes the glucocorticoid receptor. Hereditary syndromes have also been identified that are associated with increased and decreased sensitivity to glucocorticoids. As a result of their anti-inflammatory properties, glucocorticoids are widely used in the treatment of allergic, inflammatory and haematological disorders. The variety in clinical responses to treatment with glucocorticoids reflects the considerable variation in glucocorticoid sensitivity between individuals. In immune-mediated disorders, proinflammatory cytokines can induce localized resistance to glucocorticoids via several mechanisms. Individual differences in how tissues respond to glucocorticoids might also be involved in the predisposition for and pathogenesis of the metabolic syndrome and mood disorders. In this Review, we summarize the mechanisms that influence glucocorticoid sensitivity in health and disease and discuss possible strategies to modulate glucocorticoid responsiveness.

Low doses of fludrocortisone and hydrocortisone, alone or in combination, on vascular responsiveness to phenylephrine in healthy volunteers

AIMS

A single administration of hydrocortisone has been shown to enhance the pressor response to phenylephrine in healthy volunteers and to norepinephrine in septic shock patients. Similar data do not exist for fludrocortisone. Since there continues to be disagreement about the utility of fludrocortisone in septic shock, we assessed the effects of a single administration of low doses of hydrocortisone (50 mg intravenously) and fludrocortisone (50 μg orally), given either alone or in combination, on phenylephrine mean arterial pressure and cardiac systolic and diastolic function dose-response relationships in 12 healthy male volunteers with hypo-aldosteronism induced by intravenous sodium loading.

METHODS

This was a placebo-controlled, randomized, double-blind, crossover study performed according to a 2 × 2 factorial design. Subjects received first a 2000 ml infusion of NaCl 0.9% during 2 h. Then fludrocortisone 50 μg (or its placebo) was administered orally and hydrocortisone 50 mg (or its placebo) was injected intravenously. At 1.5 h after treatment administration, incremental doses of phenylephrine were infused (from 0.01 to 3 μg kg(-1) min(-1)), each dose being infused during 5 min.

RESULTS

Both fludrocortisone (P < 0.001) and hydrocortisone (P = 0.002) induced a significant decrease in pressor response to phenylephrine, their effects being additive (fludrocortisone × hydrocortisone interaction, P = 0.792). The two drugs did not induce any detectable cardiac effect.

CONCLUSIONS

Single administrations of fludrocortisone and hydrocortisone decreased the pressor response to phenylephrine in healthy volunteers with hypo-aldosteronism. These similar effects of hydrocortisone and fludrocortisone probably express a rapid non-genomic vasodilating effect of the two steroids in the context of acute volume loading.

Mining functional subgraphs from cancer protein-protein interaction networks

Background

Protein-protein interaction (PPI) networks carry vital information about proteins' functions. Analysis of PPI networks associated with specific disease systems including cancer helps us in the understanding of the complex biology of diseases. Specifically, identification of similar and frequently occurring patterns (network motifs) across PPI networks will provide useful clues to better understand the biology of the diseases.

Results

In this study, we developed a novel pattern-mining algorithm that detects cancer associated functional subgraphs occurring in multiple cancer PPI networks. We constructed nine cancer PPI networks using differentially expressed genes from the Oncomine dataset. From these networks we discovered frequent patterns that occur in all networks and at different size levels. Patterns are abstracted subgraphs with their nodes replaced by node cluster IDs. By using effective canonical labeling and adopting weighted adjacency matrices, we are able to perform graph isomorphism test in polynomial running time. We use a bottom-up pattern growth approach to search for patterns, which allows us to effectively reduce the search space as pattern sizes grow. Validation of the frequent common patterns using GO semantic similarity showed that the discovered subgraphs scored consistently higher than the randomly generated subgraphs at each size level. We further investigated the cancer relevance of a select set of subgraphs using literature-based evidences.

Conclusion

Frequent common patterns exist in cancer PPI networks, which can be found through effective pattern mining algorithms. We believe that this work would allow us to identify functionally relevant and coherent subgraphs in cancer networks, which can be advanced to experimental validation to further our understanding of the complex biology of cancer.

Single prolonged stress enhances hippocampal glucocorticoid receptor and phosphorylated protein kinase B levels

Animal models of posttraumatic stress disorder (PTSD) can explore neurobiological mechanisms by which trauma enhances fear and anxiety reactivity. Single prolonged stress (SPS) shows good validity in producing PTSD-like behavior. While SPS-induced behaviors have been linked to enhanced glucocorticoid receptor (GR) expression, the molecular ramifications of enhanced GR expression have yet to be identified. Phosphorylated protein kinase B (pAkt) is critical for stress-mediated enhancement in general anxiety and memory, and may be regulated by GRs. However, it is currently unknown if pAkt levels are modulated by SPS, as well as if the specificity of GR and pAkt related changes contribute to anxiety-like behavior after SPS. The current study set out to examine the effects of SPS on GR and pAkt protein levels in the amygdala and hippocampus and to examine the specificity of these changes to unconditioned anxiety-like behavior. Levels of GR and pAkt were increased in the hippocampus, but not amygdala. Furthermore, SPS had no effect on unconditioned anxiety-like behavior suggesting that generalized anxiety is not consistently observed following SPS. The results suggest that SPS-enhanced GR expression is associated with phosphorylation of Akt, and also suggest that these changes are not related to an anxiogenic phenotype.

Non-genomic effect of glucocorticoids on cardiovascular system

Glucocorticoids (GCs) are essential steroid hormones for homeostasis, development, metabolism, and cognition and possess anti-inflammatory and immunosuppressive actions. Since glucocorticoid receptor II (GR) is nearly ubiquitous, chronic activation or depletion of GCs leads to dysfunction of diverse organs, including the heart and blood vessels, resulting predominantly from changes in gene expression. Most studies, therefore, have focused on the genomic effects of GC to understand its related pathophysiological manifestations. The nongenomic effects of GCs clearly differ from well-known genomic effects, with the former responding within several minutes without the need for protein synthesis. There is increasing evidence that the nongenomic actions of GCs influence various physiological functions. To develop a GC-mediated therapeutic target for the treatment of cardiovascular disease, understanding the genomic and nongenomic effects of GC on the cardiovascular system is needed. This article reviews our current understanding of the underlying mechanisms of GCs on cardiovascular diseases and stress, as well as how nongenomic GC signaling contributes to these conditions. We suggest that manipulation of GC action based on both GC and GR metabolism, mitochondrial impact, and the action of serum- and glucocorticoid-dependent kinase 1 may provide new information with which to treat cardiovascular diseases.

In vitro glucocorticoid sensitivity is associated with clinical glucocorticoid therapy outcome in rheumatoid arthritis

Introduction

Genetic and disease-related factors give rise to a wide spectrum of glucocorticoid (GC) sensitivity in rheumatoid arthritis (RA). In clinical practice, GC treatment is not adapted to these differences in GC sensitivity. In vitro assessment of GC sensitivity before the start of therapy could allow more individualized GC therapy. The aim of the study was to investigate the association between in vitro and in vivo GC sensitivity in RA.

Methods

Thirty-eight early and 37 established RA patients were prospectively studied. In vitro GC sensitivity was assessed with dexamethasone-induced effects on interleukin-2 (IL-2) and glucocorticoid-induced leucine zipper (GILZ) messenger RNA expression in peripheral blood mononuclear cells (PBMCs). A whole-cell dexamethasone-binding assay was used to measure number and affinity (1/K_D) of glucocorticoid receptors (GRs).

In vivo GC sensitivity was determined by measuring the disease activity score (DAS) and health assessment questionnaire disability index (HAQ-DI) score before and after 2 weeks of standardized GC treatment.

Results

GR number was positively correlated with improvement in DAS. IL-2-EC₅₀ and GILZ-EC₅₀ values both had weak near-significant correlations with clinical improvement in DAS in intramuscularly treated patients only. HAQ responders had lower GILZ-EC₅₀ values and higher GR number and K_D.

Conclusions

Baseline cellular in vitro glucocorticoid sensitivity is modestly associated with in vivo improvement in DAS and HAQ-DI score after GC bridging therapy in RA. Further studies are needed to evaluate whether in vitro GC sensitivity may support the development of tailor-made GC therapy in RA.

Glucocorticoid receptor mediated suppression of natural killer cell activity: identification of associated deacetylase and corepressor molecules

Physical and psychological stressors reduce natural killer cell function. This reduction in cellular function results from stress-induced release of glucocorticoids. Glucocorticoids act upon natural killer cells to deacetylate and transrepress immune response genes through epigenetic processes. However, other than the glucocorticoid receptor, the proteins that participate in this process are not well described in natural killer cells. The purpose of this study was to identify the proteins associated with the glucocorticoid receptor that are likely epigenetic participants in this process. Treatment of natural killer cells with the synthetic glucocorticoid, dexamethasone, produced a significant time dependent reduction in natural killer cell activity as early as 8h post treatment. This reduction in natural killer cell activity was preceded by nuclear localization of the glucocorticoid receptor with histone deacetylase 1 and the corepressor, SMRT. Other class I histone deacetylases were not associated with the glucocorticoid receptor nor was the corepressor NCoR. These results demonstrate histone deacetylase 1 and SMRT to associate with the ligand activated glucocorticoid receptor within the nuclei of natural killer cells and to be the likely participants in the histone deacetylation and transrepression that accompanies glucocorticoid mediated reductions in natural killer cell function.

Glucocorticoid receptor-mediated apoptosis: mechanisms of resistance in cancer cells

Glucocorticoids (Gcs) are commonly used to treat patients suffering from a wide range of cancers. Their main therapeutic role is based on Gc receptor (GR)-mediated mechanisms that trigger cell death but this varies depending on the cancer type. This review aims to provide an overview of the mechanisms of Gc-induced cell death and more importantly the changes in GR that lead to resistance to Gc treatment in cancer. The three main cancer types, which are susceptible to Gc resistance and therefore loss of Gc-induced apoptotic effects, are acute lymphoblastic leukaemia, osteosarcoma and small-cell lung carcinoma. A common theme is the loss of GR function and/or a downregulation of GR expression which leads to failure of the cell death-inducing effects of Gcs. Loss of GR function is attributed to mutations in the GR gene, and in some cases a dominant-negative effect on any functional GR still present. The downregulation of GR expression can be due to decreased GR promoter activation, increased GR promoter methylation or increased expression of alternative splice isoforms of GR that have decreased transcriptional activity. Understanding the mechanisms behind Gc-triggered apoptosis and the resistance to it in these cancer types will help in further refining treatment regimens for patients and will decrease the chance of relapse caused by Gc-resistant cancer phenotypes.

The molecular mechanisms of glucocorticoids-mediated neutrophil survival

Neutrophil-dominated inflammation plays an important role in many airway diseases including asthma, chronic obstructive pulmonary disease (COPD), bronchiolitis and cystic fibrosis. In cases of asthma where neutrophil-dominated inflammation is a major contributing factor to the disease, treatment with corticosteroids can be problematic as corticosteroids have been shown to promote neutrophil survival which, in turn, accentuates neutrophilic inflammation. In light of such cases, novel targeted medications must be developed that could control neutrophilic inflammation while still maintaining their antibacterial/anti-fungal properties, thus allowing individuals to maintain effective innate immune responses to invading pathogens. The aim of this review is to describe the molecular mechanisms of neutrophil apoptosis and how these pathways are modulated by glucocorticoids. These new findings are of potential clinical value and provide further insight into treatment of neutrophilic inflammation in lung disease.

Ginsenoside Rg3 increases nitric oxide production via increases in phosphorylation and expression of endothelial nitric oxide synthase: essential roles of estrogen receptor-dependent PI3-kinase and AMP-activated protein kinase

We previously showed that ginsenosides increase nitric oxide (NO) production in vascular endothelium and that ginsenoside Rg3 (Rg3) is the most active one among ginseng saponins. However, the mechanism for Rg3-mediated nitric oxide production is still uncertain. In this study, we determined whether Rg3 affects phosphorylation and expression of endothelial nitric oxide synthase (eNOS) in ECV 304 human endothelial cells. Rg3 increased both the phosphorylation and the expression of eNOS in a concentration-dependent manner and a maximal effect was found at 10μg/ml of Rg3. The enzyme activities of phosphatidylinositol 3-kinase (PI3-kinase), c-Jun N-terminal kinase (JNK), and p38 kinase were enhanced as were estrogen receptor (ER)- and glucocorticoid receptor (GR)-dependent reporter gene transcriptions in Rg3-treated endothelial cells. Rg3-induced eNOS phosphorylation required the ER-mediated PI3-kinase/Akt pathway. Moreover, Rg3 activates AMP-activated protein kinase (AMPK) through up-regulation of CaM kinase II and Rg3-stimulated eNOS phosphorylation was reversed by AMPK inhibition. The present results provide a mechanism for Rg3-stimulated endothelial NO production.

Glucocorticoid receptor over-expression promotes human small cell lung cancer apoptosis in vivo and thereby slows tumor growth

Small cell lung cancer (SCLC) is an aggressive tumor, associated with ectopic ACTH syndrome. We have shown that SCLC cells are glucocorticoid receptor (GR) deficient, and that restoration of GR expression confers glucocorticoid sensitivity and induces apoptosis in vitro. To determine the effects of GR expression in vivo, we characterized a mouse SCLC xenograft model that secretes ACTH precursor peptides, and so drives high circulating corticosterone concentrations (analogous to the ectopic ACTH syndrome). Infection of SCLC xenografts with GR-expressing adenovirus significantly slowed tumor growth compared with control virus infection. Time to fourfold initial tumor volume increased from a median of 9 days to 16 days (P=0.05; n=7 per group). Post-mortem analysis of GR-expressing tumors revealed a threefold increase in apoptotic (TUNEL positive) cells (P<0.01). Infection with the GR-expressing adenovirus caused a significant reduction in Bcl-2 and Bcl-xL transcripts. Furthermore, in both the GR-expressing adenovirus-infected cells and tumors, a significant number of uninfected cells underwent apoptosis, supporting a bystander cell killing effect. Therefore, GR expression is pro-apoptotic for human SCLCs in vivo, as well as in vitro, suggesting that loss of GR confers a survival advantage to SCLCs.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Central actions of glucocorticoids in the control of body fluid homeostasis: review

The involvement of the hypothalamic-pituitary-adrenal axis in the control of body fluid homeostasis has been extensively investigated in the past few years. In the present study, we reviewed the recent results obtained using different approaches to investigate the effects of glucocorticoids on the mechanisms of oxytocin and vasopressin synthesis and secretion in response to acute and chronic plasma volume and osmolality changes. The data presented here suggest that glucocorticoids are not only involved in the mechanisms underlying the fast release but also in the transcriptional events that lead to decreased synthesis and secretion of these neuropeptides, particularly oxytocin, under diverse experimental conditions of altered fluid volume and tonicity. The endocannabinoid system, through its effects on glutamatergic neurotransmission within the hypothalamus and the nuclear factor kappaB-mediated transcriptional activity, seems to be also involved in the specific mechanisms by which glucocorticoids exert their central effects on neurohypophyseal hormone synthesis and secretion.

Mechanisms regulating the susceptibility of hematopoietic malignancies to glucocorticoid-induced apoptosis

Glucocorticoids (GCs) are commonly used in the treatment of hematopoietic malignancies owing to their ability to induce apoptosis of these cancerous cells. Whereas some types of lymphoma and leukemia respond well to this drug, others are resistant. Also, GC-resistance gradually develops upon repeated treatments ultimately leading to refractory relapsed disease. Understanding the mechanisms regulating GC-induced apoptosis is therefore uttermost important for designing novel treatment strategies that overcome GC-resistance. This review discusses updated data describing the complex regulation of the cell's susceptibility to apoptosis triggered by GCs. We address both the genomic and nongenomic effects involved in promoting the apoptotic signals as well as the resistance mechanisms opposing these signals. Eventually we address potential strategies of clinical relevance that sensitize GC-resistant lymphoma and leukemia cells to this drug. The major target is the nongenomic signal transduction machinery where the interplay between protein kinases determines the cell fate. Shifting the balance of the kinome towards a state where Glycogen synthase kinase 3alpha (GSK3alpha) is kept active, favors an apoptotic response. Accumulating data show that it is possible to therapeutically modulate GC-resistance in patients, thereby improving the response to GC therapy.

Glucocorticoid-mediated apoptosis resistance of solid tumors

More than a quarter of a century ago, the phenomenon of glucocorticoid-induced apoptosis in the majority of hematological cells was first recognized. More recently, glucocorticoid-induced antiapoptotic signaling associated with apoptosis resistance towards cytotoxic therapy has been identified in cells of epithelial origin, most of malignant solid tumors and some other tissues. Despite these huge amounts of data demonstrating differential pro- and anti-apoptotic effects of glucocorticoids, the underlying mechanisms of cell type-specific glucocorticoid signaling are just beginning to be described. This review summarizes our present understanding of cell type-specific pro- and anti-apoptotic signaling induced by glucocorticoids. We shortly introduce mechanisms of glucocorticoid resistance of hematological cells. We highlight and discuss the emerging molecular evidence of a general induction of survival signaling in epithelial cells and carcinoma cells by glucocorticoids. We give a summary of our current knowledge of decreased proliferation rates in response to glucocorticoid pre- and combination treatment, which are suspicious to be involved not only in protection of normal tissues, but also in protection of solid tumors from cytotoxic effects of anticancer agents.

Glucocorticoid regulation of CD38 expression in human airway smooth muscle cells: role of dual specificity phosphatase 1

The enzymatic activity of CD38, ADP-ribosyl cyclase, synthesizes the calcium mobilizing molecule cyclic ADP-ribose from beta-NAD. In human airway smooth muscle (HASM) cells, CD38 expression is augmented by the inflammatory cytokine, TNF-alpha, causing increased intracellular calcium response to agonists. The transcriptional and posttranscriptional regulation of CD38 expression involves signaling through MAPKs and requires activation of NF-kappaB and activator protein-1 (AP-1). The cytokine-augmented CD38 expression is decreased by anti-inflammatory glucocorticoids due to inhibition of NF-kappaB activation and other mechanisms. In this study, we investigated glucocorticoid regulation of CD38 expression in HASM cells through the MKP-1. In HASM cells, dexamethasone and TNF-alpha induced MKP-1 expression (both mRNA and protein) rapidly. Dexamethasone decreased TNF-alpha-induced phosphorylation of the major MAPKs, i.e., ERK, p38, and JNK, and decreased the activation of NF-kappaB and AP-1. Dexamethasone also decreased CD38 expression induced by TNF-alpha, and part of this effect was attributable to decreased transcript stability. In cells transfected with MKP-1-specific small interfering RNAs (siRNAs), there was significant attenuation of MKP-1 expression and partial, but nonsignificant, reversal of dexamethasone inhibition of CD38 expression. These results indicate that regulation of CD38 expression in HASM cells by glucocorticoids involves decreased signaling through MAPKs and activation of transcription factors. The glucocorticoid effects on decreased CD38 expression and function result from regulation through transcription and transcript stability.

Inhibition of Akt pathway phosphorylation as a mechanism in the pathogenesis of functional intestinal obstruction in carcinomatosis peritonei

BACKGROUND AND OBJECTIVES

The purpose of this study was to confirm our hypothesis that the development of functional intestinal obstruction in carcinomatosis peritonei (CP) is related to cytokine-mediated inhibition of the Akt pathway and to investigate the phenomenon of relative adrenal insufficiency in CP.

METHODS

Human adrenocortical cells (NCI-H295R) were treated with serum derived from eight cancer patients who had intestinal obstruction and functional adrenal insufficiency. Serum from three normal healthy subjects and three who had CP but without intestinal obstruction or adrenal insufficiency were used as controls. The differential effects of serum on the treated cells were studied using Western blot analysis. Cortisol production of these treated cells was assayed with cortisol ELISA kits.

RESULTS

Phosphorylation of Akt at Ser473 and Ser308 in cells was significantly reduced when treated with serum from patients with intestinal obstruction but not controls. Phosphorylation of PDK1 at Ser241, mTOR downstream targets like p70S6 at Thr421/Ser424 and Thr389, and lastly 4EBP-1 at Ser70 a downstream target of p70S6 was reduced by approximately 50%, 40%, and 70%, respectively. There was enhanced phosphorylation of elF4E an initiating factor in protein translation in cells treated with patient serum compared to controls. Cortisol synthesis was stimulated upon treatment with patient serum but not with control serum.

CONCLUSION

Inhibition of Akt phosphorylation is a mechanism that could play a major role in the development of intestinal obstruction in carcinomatosis peritonei. The identification of the mediating cytokines will lead to the development of cogent targeted therapeutic strategies.

Caveolin mediates rapid glucocorticoid effects and couples glucocorticoid action to the antiproliferative program

Many glucocorticoid (Gc) actions are of rapid onset and therefore require acute regulation of intracellular signaling cascades. Integration of diverse extracellular signals requires cross-talk between intracellular pathways, suggesting the existence of nodes for signal interaction, such as the specialized membrane microdomains caveolae. We have identified rapid Gc-dependent phosphorylation of caveolin, and protein kinase B (PKB)/Akt, in the lung epithelial cell line A549 and found this was dependent on src kinases. There was also activation of PKB downstream molecules glycogen synthase kinase-3beta, and mammalian target of rapamycin. Subcellular fractionation colocalized glucocorticoid receptor (GR) and c-src to caveolin-containing membrane fractions. Coimmunoprecipitation studies also identified interactions between GR and caveolin and suggested that the activation function 1 domain within the GR may serve to support an interaction between GR and caveolin. Disruption of lipid raft formation, impairment of caveolin function using dominant-negative caveolin, down-regulation of caveolin-1 using short hairpin RNA or complete ablation of caveolin-1 prevented Gc-induced activation of PKB. Loss of caveolin-1 also prevents Gc activation of glycogen synthase kinase-3beta and mammalian target of rapamycin. In contrast, caveolin interference/down-regulation had no effect on Gc transactivation. Functional analysis of caveolin-1 knockdown and knockout cells identified profound loss of Gc-mediated growth inhibition compared with controls, with a requirement for caveolin in order for Gc to regulate cell cycle progression. Therefore, disruption of caveolae leads to dissociation of Gc action, with impaired induction of PKB activation, and cell growth inhibition, but with negligible effects on Gc transactivation. These observations have implications for understanding the diverse physiological actions of Gc.

Extranuclear steroid receptors: nature and actions

Rapid effects of steroid hormones result from the actions of specific receptors localized most often to the plasma membrane. Fast-acting membrane-initiated steroid signaling (MISS) leads to the modification of existing proteins and cell behaviors. Rapid steroid-triggered signaling through calcium, amine release, and kinase activation also impacts the regulation of gene expression by steroids, sometimes requiring integration with nuclear steroid receptor function. In this and other ways, the integration of all steroid actions in the cell coordinates outcomes such as cell fate, proliferation, differentiation, and migration. The nature of the receptors is of intense interest, and significant data suggest that extranuclear and nuclear steroid receptor pools are the same proteins. Insights regarding the structural determinants for membrane localization and function, as well as the nature of interactions with G proteins and other signaling molecules in confined areas of the membrane, have led to a fuller understanding of how steroid receptors effect rapid actions. Increasingly, the relevance of rapid signaling for the in vivo functions of steroid hormones has been established. Examples include steroid effects on reproductive organ development and function, cardiovascular responsiveness, and cancer biology. However, although great strides have been made, much remains to be understood concerning the integration of extranuclear and nuclear receptor functions to organ biology. In this review, we highlight the significant progress that has been made in these areas.

The hypothalamic-pituitary-adrenal axis in critical illness

Hypothalamic-pituitary-adrenal (HPA) axis function is crucial to maintain and restore homeostasis. The HPA axis does not function in isolation. Rather, the HPA axis modulates and reacts to signals from endocrine, neural, and immune systems. Cortisol is the major glucocorticoid secreted by the human adrenal cortex. Its actions are largely mediated by the glucocorticoid receptor. The potent anti-inflammatory actions of glucocorticoids led to their use in critically ill patients. Metaanalyses of these early studies (before 1985) concluded that large glucocorticoid doses had no effect and were potentially detrimental. More recently, the pendulum has swung in the opposite direction based on the concept that critically ill patients may have relative adrenal insufficiency and/or acquired glucocorticoid resistance. However, inconsistent diagnostic criteria, heterogeneity of subjects, variable nutritional status, and pre-existing conditions preclude formulating definitive conclusions regarding glucocorticoid use among critically patients. Diagnosing adrenal insufficiency in the critically ill patient remains challenging. To resolve the issue, our challenge is to develop physiologically relevant tools to assess glucocorticoid action and GR function at the cellular level.

Glucocorticoid receptor action in beneficial and side effects of steroid therapy: lessons from conditional knockout mice

Glucocorticoids (GCs) are potent immune suppressive drugs with unfortunately severe side effects. Different molecular modes of actions of the GC receptor (GR) have been identified. Transcriptional transactivation by binding of a dimerized GR protein complex to the promoter of GC regulated genes or interference with activity of pro-inflammatory transcription factors by GR monomers are considered as the two major mechanisms. It has been hypothesized that selective GR agonists (SEGRAs) addressing dimer-independent function would reveal potent steroid therapeutic activity with reduced side effects. Recent studies of a mouse knock-in strain with a dimerization-deficient GR demonstrate that some inflammatory processes can be suppressed by GCs, while others cannot. Also side effects of GCs occur in these mice. Thus, depending on the process that is treated, SEGRA could be therapeutically more or less effective and not all side effects of steroid therapy may be reduced.

Dexamethasone decreases contraction to electrical field stimulation in mesenteric arteries from spontaneously hypertensive rats through decreases in thromboxane A2 release

Glucocorticoids play a role in the control of vascular smooth muscle tone through the alteration of vasoconstrictor and vasodilator factor production. We studied the effect of dexamethasone on vasoconstriction induced by electrical field stimulation (EFS) in rat mesenteric arteries (MAs) and the role of hypertension in this effect. Endothelium-denuded MAs were obtained from Wistar-Kyoto rats and spontaneously hypertensive rats (SHRs). EFS response was analyzed by isometric tension recordings and cyclooxygenase (COX-1 and COX-2) expression by Western blot. Noradrenaline (NA) release was evaluated in segments incubated with [(3)H]NA. Dexamethasone (0.1 and 1 microM; 2-8 h) reduced vasoconstriction to EFS (200 mA, 0.3 ms, 1-16 Hz), in a dose- and time-dependent manner only in SHRs. However, the EFS-induced release of [(3)H]NA was increased in SHR arteries preincubated with dexamethasone (1 microM; 6 h). The thromboxane A(2) (TxA(2)) synthase inhibitor furegrelate (10 microM), the selective COX-2 inhibitor NS-398 (N-[2-cyclohexyloxy-4-nitrophenyl] methanesulfonamide; 10 microM), or the TxA(2) receptor antagonist SQ 29548 (1 microM), reduced EFS and NA induced vasoconstrictor responses. However, the effect of these drugs was abolished in arteries preincubated with dexamethasone. Both dexamethasone and phentolamine (1 microM) inhibited the increased thromboxane B(2) levels observed after EFS. COX-2 protein expression was reduced by dexamethasone in SHR arteries. Results suggest that dexamethasone reduces vasoconstriction to EFS in MAs from SHRs by decreasing COX-2 expression, thereby decreasing the smooth muscle TXA(2) release induced by alpha-adrenoceptor activation. The undetectable COX-2 expression in MAs from normotensive animals explains the noneffect of dexamethasone in their arteries.

Glucocorticoids induce osteocyte apoptosis by blocking focal adhesion kinase-mediated survival. Evidence for inside-out signaling leading to anoikis

Bone fragility induced by chronic glucocorticoid excess is due, at least in part, to induction of osteocyte apoptosis through direct actions on these cells. However, the molecular mechanism by which glucocorticoids shorten osteocyte life span has remained heretofore unknown. We report that apoptosis of osteocytic MLO-Y4 cells induced by the synthetic glucocorticoid dexamethasone is abolished by the glucocorticoid receptor antagonist RU486, but not by inhibition of protein or RNA synthesis. Dexamethasone-induced apoptosis is preceded by a decrease in the number of cytoplasmic processes, an indicator of cell detachment. In addition, the focal adhesion kinase FAK prevents dexamethasone-induced apoptosis, whereas the FAK-related kinase Pyk2 increases the basal levels of apoptosis. Dexamethasone-induced apoptosis is also prevented in cells expressing kinase-deficient or phosphorylation-defective (Y402F) dominant negative mutants of Pyk2. Consistent with the requirement of tyrosine 402, dexamethasone induces rapid Pyk2 phosphorylation in this residue. Moreover, knocking down Pyk2 expression abolishes apoptosis and cell detachment induced by dexamethasone, and transfection with human Pyk2 rescues both responses. Furthermore, induction of apoptosis as well as cell detachment by dexamethasone is abolished by inhibiting the activity of JNK, a recognized downstream target of Pyk2 activation. These results demonstrate that glucocorticoids promote osteocyte apoptosis via a receptor-mediated mechanism that does not require gene transcription and that is mediated by rapid activation of Pyk2 and JNK, followed by inside-out signaling that leads to cell detachment-induced apoptosis or anoikis.

Regulation of differential pro- and anti-apoptotic signaling by glucocorticoids

More than a quarter of a century ago, the phenomenon of glucocorticoid-induced apoptosis in the majority of hematological cells was first recognized. More recently, glucocorticoid-induced antiapoptotic signaling associated with apoptosis resistance has been identified in cells of epithelial origin, most of malignant solid tumors and some other tissues. Despite these huge amount of data demonstrating differential pro- and anti-apoptotic effects of glucocorticoids, the underlying mechanisms of cell type specific glucocorticoid signaling are just beginning to be described. This review summarizes our present understanding of cell type-specific pro- and anti-apoptotic signaling induced by glucocorticoids. In the first section we give a summary and update of known glucocorticoid-induced pathways mediating apoptosis in hematological cells. We shortly introduce mechanisms of glucocorticoid resistance of hematological cells. We highlight and discuss the emerging molecular evidence of a general induction of survival signaling in epithelial cells and carcinoma cells by glucocorticoids. We provide a model for glucocorticoid-induced resistance in cells growing in a tissue formation. Thus, attachment to the extracellular matrix and cell-cell contacts typical for e.g. epithelial and tumor cells may be crucially involved in switching the balance of several interacting pathways to survival upon treatment with glucocorticoids.

Non-genomic effects of ginsenoside-Re in endothelial cells via glucocorticoid receptor

We demonstrated that ginsenoside-Re (Re), a pharmacological active component of ginseng, is a functional ligand of glucocorticoid receptor (GR) using competitive ligand-binding assay (IC(50)=156.6 nM; K(d)=49.7 nM) and reporter gene assay. Treatment with Re (1 microM) raises intracellular Ca(2+) ([Ca(2+)](i)) and nitric oxide (NO) levels in human umbilical vein endothelial cells as measured using fura-2 and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, respectively. Western blot analysis shows that Re increased phosphorylation of endothelial nitric oxide synthase. These effects were abolished by GR antagonist RU486, siRNA targeting GR, non-selective cation channel blocker 2-aminoethyldiphenylborate, or in the absence of extracellular Ca(2+), indicating Re is indeed an agonistic ligand for the GR and the activated GR induces rapid Ca(2+) influx and NO production in endothelial cells.

MAPK phosphatase-1 represents a novel anti-inflammatory target of glucocorticoids in the human endothelium

Glucocorticoids are well-established anti-inflammatory drugs thought to mainly act by inhibition of proinflammatory transcription factors like NF-kappaB. In recent years, however, transcription factor-independent mechanisms of glucocorticoid action have been proposed, namely the influence on MAPK pathways. Here we identify MAPK phosphatase-1 (MKP-1) as a pivotal mediator of the anti-inflammatory action of glucocorticoids in the human endothelium. We applied dexamethasone (Dex) to TNF-alpha-activated human endothelial cells and used the adhesion molecule E-selectin as inflammatory read-out parameter. Dex is known to reduce the expression of E-selectin, which is largely regulated by NF-kappaB. Here, we communicate that Dex at low concentrations (1-100 nM) markedly attenuates E-selectin expression without affecting NF-kappaB. Importantly, Dex is able to increase the expression of MKP-1, which causes an inactivation of TNF-alpha-induced p38 MAPK and mediates inhibition of E-selectin expression. In endothelial MKP-1(-/-) cells differentiated from MKP-1(-/-) embryonic stem cells and in MKP-1-silenced human endothelial cells, Dex did not inhibit TNF-alpha-evoked E-selectin expression. Thus, our findings introduce MKP-1 as a novel and crucial mediator of the anti-inflammatory action of glucocorticoids at low concentrations in the human endothelium and highlight MKP-1 as an important and promising anti-inflammatory drug target.

Down-modulation of granulocyte macrophage-colony stimulating factor receptor on monocytes during human septic shock

OBJECTIVE

Loss of surface human leukocyte antigen-DR (HLA-DR) on monocytes is a major factor of immunosuppression in sepsis. Granulocyte macrophage-colony stimulating factor (GM-CSF) up-regulates HLA-DR expression on monocytes via the GM-CSF receptor (GM-CSFr) through a transcriptional mechanism involving the class II transactivator factor (CIITA). We investigated monocyte GM-CSFr expression and its relationship with HLA-DR in septic patients.

DESIGN

Prospective clinical experimental study.

SETTING

University hospital intensive care unit and research facility.

PATIENTS

Septic patients with and without septic shock, control patients.

INTERVENTIONS

Flow cytometry and real-time quantitative reverse polymerase chain reaction were used to characterize GM-CSFr expression and transcription in septic patients and in ex vivo stimulated healthy monocytes.

MEASUREMENTS AND MAIN RESULTS

We showed an early GM-CSFr down-modulation in patients with septic shock compared with those without septic shock and controls. A persistent low GM-CSFr expression was observed in patients who acquired secondary infections or in those who died, and this persistent defect correlated with severity scores. We demonstrated that GM-CSFr down-modulation occurs at a posttranscriptional level since we observed no alteration in GM-CSFr transcription in monocytes isolated from septic patients. Furthermore, we demonstrated that GM-CSFr expression levels on monocytes correlated not only with HLA-DR expression and transcription levels but also with RNA levels of its main transcriptional factor CIITA. Because we previously showed in septic patients a relationship between high cortisol plasma level and low monocyte HLA-DR expression, we investigated the effects of glucocorticoids on monocyte GM-CSFr expression and observed a similar posttranscriptional down-modulation of GM-CSFr by steroids. However, the in vivo putative role of steroids in HLA-DR down-regulation via GM-CSFr down-modulation needs further investigation.

CONCLUSION

Monocyte GM-CSFr down-modulation occurred in septic shock, was associated with severity, and might be either another manifestation of monocyte deactivation linked to sepsis or an additional mechanism participating in immunosuppression.

Signaling pathway of ginsenoside-Rg1 leading to nitric oxide production in endothelial cells

We here provide definitive evidence that ginsenoside-Rg1, the pharmacologically active component of ginseng, is a functional ligand of the glucocorticoid receptor (GR) as determined by fluorescence polarization assay. Rg1 increased the phosphorylation of GR, phosphatidylinositol-3 kinase (PI3K), Akt/PKB and endothelial nitric oxide synthase (eNOS) leading to increase nitric oxide (NO) production in human umbilical vein endothelial cell. Rg1-induced eNOS phosphorylation and NO production were significantly reduced by RU486, LY294,002, or SH-6. Also, knockdown of GR completely eliminated the Rg1-induced NO production. This study revealed that Rg1 can indeed serve as an agonist ligand for GR and the activated GR can induce rapid NO production from eNOS via the non-transcriptional PI3K/Akt pathway.