Regulation of glucocorticoid receptor expression

Hormone-controlled cooperative binding of transcription factors drives synergistic induction of fasting-regulated genes

During fasting, hepatocytes produce glucose in response to hormonal signals. Glucagon and glucocorticoids are principal fasting hormones that cooperate in regulating glucose production via gluconeogenesis. However, how these hormone signals are integrated and interpreted to a biological output is unknown. Here, we use genome-wide profiling of gene expression, enhancer dynamics and transcription factor (TF) binding in primary mouse hepatocytes to uncover the mode of cooperation between glucagon and glucocorticoids. We found that compared to a single treatment with each hormone, a dual treatment directs hepatocytes to a pro-gluconeogenic gene program by synergistically inducing gluconeogenic genes. The cooperative mechanism driving synergistic gene expression is based on ‘assisted loading’ whereby a glucagon-activated TF (cAMP responsive element binding protein; CREB) leads to enhancer activation which facilitates binding of the glucocorticoid receptor (GR) upon glucocorticoid stimulation. Glucagon does not only activate single enhancers but also activates enhancer clusters, thereby assisting the loading of GR also across enhancer units within the cluster. In summary, we show that cells integrate extracellular signals by an enhancer-specific mechanism: one hormone-activated TF activates enhancers, thereby assisting the loading of a TF stimulated by a second hormone, leading to synergistic gene induction and a tailored transcriptional response to fasting.

Chronic cortisol differentially impacts stem cell-derived astrocytes from major depressive disorder patients

Major depressive disorder (MDD) is a prevalent psychiatric disorder, and exposure to stress is a robust risk factor for MDD. Clinical data and rodent models have indicated the negative impact of chronic exposure to stress-induced hormones like cortisol on brain volume, memory, and cell metabolism. However, the cellular and transcriptomic changes that occur in the brain after prolonged exposure to cortisol are less understood. Furthermore, the astrocyte-specific contribution to cortisol-induced neuropathology remains understudied. Here, we have developed an in vitro model of "chronic stress" using human induced pluripotent stem cell (iPSC)-derived astrocytes treated with cortisol for 7 days. Whole transcriptome sequencing reveals differentially expressed genes (DEGs) uniquely regulated in chronic cortisol compared to acute cortisol treatment. Utilizing this paradigm, we examined the stress response transcriptome of astrocytes generated from MDD patient iPSCs. The MDD-specific DEGs are related to GPCR ligand binding, synaptic signaling, and ion homeostasis. Together, these data highlight the unique role astrocytes play in the central nervous system and present interesting genes for future study into the relationship between chronic stress and MDD.

Regulation of Melanophilin (Mlph) gene expression by the glucocorticoid receptor (GR)

Mlph plays a crucial role in regulating skin pigmentation through the melanosome transport process. Although Mlph is a major component involved in melanosome transport, the mechanism that regulates the expression of the Mlph gene has not been identified. In this study, we demonstrate that Mlph expression is regulated by the glucocorticoid receptor (GR). Alteration of GR activity using a specific GR agonist or antagonist only regulated the expression of Mlph among the 3 key melanosome transport proteins. Translocation of GR from the cytosol into the nucleus following Dex treatment was confirmed by separating the cytosol and nuclear fractions and by immunofluorescence staining. In ChIP assays, Dex induced GR binding to the Mlph promoter and we determined that Dex induced the GR binding motif on the Mlph promoter. Our findings contribute to understanding the regulation of Mlph expression and to the novel role of GR in Mlph gene expression.

Increased serum levels of advanced glycation end products due to induced molting in hen layers trigger a proinflammatory response by peripheral blood leukocytes

Induced molting (IM), a severe detriment to animal welfare, is still used in the poultry industry in some countries to increase or rejuvenate egg production and is responsible for several physiological perturbations, possibly including reactive oxidative stress, a form of metabolic stress. Because metabolic stress has been shown to induce a proinflammatory response involved in attempts to restore homeostasis, we hypothesized that similar responses followed IM. To confirm this hypothesis, we initially confirmed the establishment of oxidative stress during IM in 75-wk-old layers by demonstrating increased production of advanced glycation end products (AGE). Concomitant with increased oxidative metabolites, cellular stress was demonstrated in peripheral blood leukocytes (PBL) by increased levels of stress gene products (the glucocorticoid receptor, sirtuin-1, and heat shock protein 70 mRNA). Increased expression of stress proteins in PBL was followed by a proinflammatory response as demonstrated by increased levels of proinflammatory gene products (IL-6 and IL-1β mRNA); increased expression of these gene products was also demonstrated in direct response to AGE in vitro, thus establishing a direct link between oxidative and cellular stress. To establish a possible pathway for inducing a proinflammatory response by PBL, we showed that AGE increased a time dependent expression of galactin-3, Toll-like receptor-4, and nuclear factor - κB, all involved in the proinflammatory activation pathway. In vivo, AGE formed complexes with increased levels of circulating acute phase proteins (lysozyme and transferrin), products of a proinflammatory immune response, thereby demonstrating an effector response to cope with the consequences of oxidative stress. Thus, the harmful consequences of IM for animal welfare are extended here by demonstrating the activation of a resource-demanding proinflammatory response.

Adrenal insufficiency: Physiology, clinical presentation and diagnostic challenges

Adrenal insufficiency (AI) is a serious condition, which can arise from pathology affecting the adrenal gland itself (primary adrenal insufficiency, PAI), hypothalamic or pituitary pathology (secondary adrenal insufficiency, SAI), or as a result of suppression of the hypothalamic-pituitaryadrenal (HPA) axis by exogenous glucocorticoid therapy (tertiary adrenal insufficiency, TAI). AI is associated with an increase in morbidity and mortality and a reduction in quality of life. In addition, the most common cause of PAI, autoimmune adrenalitis, may be associated with a variety of other autoimmune disorders. Untreated AI can present with chronic fatigue, weight loss and vulnerability to infection. The inability to cope with acute illness or infection can precipitate life-threatening adrenal crisis. It is therefore a critical diagnosis to make in a timely fashion, in order to institute appropriate management, aimed at reversing chronic ill health, preventing acute crises, and restoring quality of life. In this review, we will describe the normal physiology of the HPA axis and explain how knowledge of the physiology of this axis helps us understand the clinical presentation of AI, and forms the basis for the biochemical investigations which lead to the diagnosis of AI.

β-Arrestin-1 inhibits glucocorticoid receptor turnover and alters glucocorticoid signaling

Glucocorticoids are among the most widely used drugs to treat many autoimmune and inflammatory diseases. Although much research has been focused on investigating glucocorticoid activity, it remains unclear how glucocorticoids regulate distinct processes in different cells. Glucocorticoids exert their effects through the glucocorticoid receptor (GR), which, upon glucocorticoid binding, interacts with regulatory proteins, affecting its activity and function. These protein-protein interactions are necessary for the resolution of glucocorticoid-dependent physiological and pharmacological processes. In this study, we discovered a novel protein interaction between the glucocorticoid receptor and β-arrestin-1, a scaffold protein with a well-established role in G protein-coupled receptor signaling. Using co-immunoprecipitation and in situ proximity ligation assays in A549 cells, we observed that β-arrestin-1 and unliganded GR interact in the cytoplasm and that, following glucocorticoid binding, the protein complex is found in the nucleus. We show that siRNA-mediated β-arrestin-1 knockdown alters GR protein turnover by up-regulating the E3 ubiquitin ligase Pellino-1, which catalyzes GR ubiquitination and thereby marks the receptor for proteasomal degradation. The enhanced GR turnover observed in β-arrestin-1-deficient cells limits the duration of the glucocorticoid response on GR target genes. These results demonstrate that β-arrestin-1 is a crucial player for the stability of the glucocorticoid receptor. The GR/β-arrestin-1 interaction uncovered here may help unravel mechanisms that contribute to the cell type-specific activities of glucocorticoids.

Characterization of the Glucocorticoid Receptor in Children Undergoing Cardiac Surgery

OBJECTIVES

Postoperative administration of corticosteroids is common practice for managing catecholamine refractory low cardiac output syndrome. Since corticosteroid activity is dependent on the glucocorticoid receptor, we sought to characterize glucocorticoid receptor levels in children undergoing cardiac surgery and examined the association between glucocorticoid receptor levels and cardiovascular dysfunction.

DESIGN

Prospective observational cohort study.

SETTING

Large, tertiary pediatric cardiac center.

SUBJECTS

Children undergoing corrective or palliative cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A prospective observational cohort study was conducted in 83 children with congenital heart disease. Total glucocorticoid receptor levels were measured in the peripheral WBCs using flow cytometry. In addition, blood samples were collected for total cortisol levels. The primary outcome studied was the time to being inotrope free. An increase in glucocorticoid receptor level from postoperative day 1 to postoperative day 3 was associated with a longer time to being inotrope free (hazard ratio, 0.49 [0.29-0.81]; p = 0.01) in the univariate analysis. This association remained significant after adjusting for age, weight, cardiopulmonary bypass time, cross clamp time, Risk Adjustment for Congenital Heart Surgery-1 score, and postoperative steroid use (hazard ratio, 0.53 [0.29-0.99]; p = 0.05). Postoperative day 3 glucocorticoid receptor level showed a trend to have longer time to being inotrope free (hazard ratio, 0.66 [0.42-1.02]; p = 0.0.06). The cortisol levels minimally increased during the study duration and did not correlate with glucocorticoid receptor levels.

CONCLUSIONS

Increasing glucocorticoid receptor levels in peripheral WBCs of children undergoing cardiac surgery are associated with a longer time to being inotrope free. Cortisol levels minimally increased during the study duration. These results suggest that exposure to high-dose perioperative corticosteroids may suppress the hypothalamic-pituitary-adrenal axis leading to increase in glucocorticoid receptor levels in response to a low cortisol environment. Further studies are required to better delineate the interplay between glucocorticoid receptor levels, cortisol levels, corticosteroid exposure, and postoperative inotropic requirements.

Glucocorticoid receptor isoform expression in peripheral blood mononuclear leukocytes of patients with chronic rhinosinusitis

BACKGROUND

In several inflammatory disorders, altered peripheral blood mononuclear leukocyte (PBML) glucocorticoid (GC) receptor isoform expression has been associated with GC resistance and disease severity. However, it is unclear if PBML GC receptor isoforms are expressed differentially and are associated with worsened disease severity in chronic rhinosinusitis (CRS).

METHODS

PBMLs were isolated from control (n = 8), CRS without nasal polyps (CRSsNP) (n = 8), atopic CRS with nasal polyps (CRSwNP) (n = 8), non-atopic CRSwNP (n = 8), and allergic fungal rhinosinusitis (AFRS) (n = 8) patients. Demographics, atopic status, asthmatic status, 22-item Sino-Nasal Outcome Test (SNOT-22) scores, Lund-Kennedy nasal endoscopy scores, Lund-Mackay sinus computed tomography (CT) scores, Kennedy Osteitis scores, and GC utilization 6 months postoperatively were collected. Intracellular immunostaining was then performed for functional GC receptor α (GCRα) and nonfunctional GC receptor β (GCRβ), followed by flow cytometry analysis of geometric mean fluorescent intensity (MFI) and the percentage of cells expressing each GC receptor isoform.

RESULTS

Compared to controls, each CRS subtype had decreased PBML GCRα and GCRα:GCRβ MFI expression, but no difference in GCRβ expression. Decreasing PBML GCRα in AFRS was associated with increasing Lund-Mackay sinus CT scores (r = -0.880, p =0.004). No significant associations were found between GC receptor isoform expression and other clinical measures.

CONCLUSION

CRS patients have reduced functional PBML GCRα expression and decreased GCRα:GCRβ compared to controls. Reductions in GCRα in AFRS are associated with worsening Lund-Mackay sinus CT scores. The clinical implications of decreased functional GC receptor expression merits further investigation.

Increased glucocorticoid receptor expression in sepsis is related to heat shock proteins, cytokines, and cortisol and is associated with increased mortality

Background

The purposes of this study are to examine if the human glucocorticoid receptor (hGR) isoform-α mRNA and hGR protein expressions are deficient in the acute phase of sepsis (S) compared to systemic inflammatory response syndrome (SIRS) and healthy subjects (H) and to evaluate if the hGRα and hGR alterations are associated with cortisol changes and if they are related to (1) extracellular and intracellular heat shock proteins (HSP) 72 and 90α; (2) ACTH, prolactin, and interleukins (ILs); and (3) outcome.

Methods

Patients consecutively admitted to a university hospital intensive care unit (ICU) with S (n = 48) or SIRS (n = 40) were enrolled in the study. Thirty-five H were also included. Total mRNA was isolated from peripheral blood samples and cDNA was prepared. RT-PCR was performed. Intracellular hGR and HSP expression in monocytes and/or neutrophils was evaluated using four-colour flow cytometry. Serum prolactin, ACTH, and cortisol concentrations were also measured. ELISA was used to evaluate serum ILs and extracellular (e) HSPs (eHSP72, eHSP90α).

Results

hGR protein was higher in S compared to H and SIRS; hGRα mRNA was higher in S compared to H (p < 0.05). In sepsis, hGR protein and eHSP72 were higher among non-survivors compared to survivors (p < 0.05). The hGR MFI and hGRα mRNA fold changes were significantly related to each other (r_s = 0.64, p < 0.001). Monocyte hGR protein expression was positively correlated with extracellular and intracellular HSPs, cortisol, and ILs and negatively to organ dysfunction (p < 0.05). HSPs, hGR, and cortisol were able to discriminate sepsis from SIRS (AUROC > 0.85, p < 0.05). In sepsis, monocyte-hGR protein and eHSP72 were strong predictors of mortality (AUROC > 0.95, p < 0.04).

Conclusions

Acute-phase sepsis is associated with increased hGR expression and cortisol concentrations, possibly implying no need for exogenous steroids. At this stage, hGR is able to predict sepsis and outcome and is related to stress-activated bio-molecules and organ dysfunction.

The role of glucocorticoid receptors in metabolic syndrome and psychiatric illness

Glucocorticoids (GCs) are involved in a large number of the physiological changes associated with metabolic syndrome and certain psychiatric illness. Although significance is often given to the concentration of GC, its biological action is determined by the activation of intracellular GC receptors (GR). Genetic polymorphisms of the GR and the large array of GR related cofactors can directly or indirectly affect the pathophysiology and evolution of these conditions. This review will discuss the effects of GR mutations on metabolic syndrome and psychotic depression.

Effect of cAMP signaling on expression of glucocorticoid receptor, Bim and Bad in glucocorticoid-sensitive and resistant leukemic and multiple myeloma cells

Stimulation of cAMP signaling induces apoptosis in glucocorticoid-sensitive and resistant CEM leukemic and MM.1 multiple myeloma cell lines, and this effect is enhanced by dexamethasone in both glucocorticoid-sensitive cell types and in glucocorticoid-resistant CEM cells. Expression of the mRNA for the glucocorticoid receptor alpha (GR) promoters 1A3, 1B and 1C, expression of mRNA and protein for GR, and the BH3-only proapoptotic proteins, Bim and Bad, and the phosphorylation state of Bad were examined following stimulation of the cAMP and glucocorticoid signaling pathways. Expression levels of GR promoters were increased by cAMP and glucocorticoid signaling, but GR protein expression was little changed in CEM and decreased in MM.1 cells. Stimulation of these two signaling pathways induced Bim in CEM cells, induced Bad in MM.1 cells, and activated Bad, as indicated by its dephosphorylation on ser112, in both cell types. This study shows that leukemic and multiple myeloma cells, including those resistant to glucocorticoids, can be induced to undergo apoptosis by stimulating the cAMP signaling pathway, with enhancement by glucocorticoids, and the mechanism by which this occurs may be related to changes in Bim and Bad expression, and in all cases, to activation of Bad.

Effects of Budesonide on the Expression of the Glucocorticoid Receptor-α in Nasal Polyp Epithelial Cells

Background

This study explores effects of budesonide on the proliferation of nasal polyp epithelial cells and expression of the glucocorticoid receptor (GR) alpha in nasal polyp epithelial cells.

Methods

Primary cultured, purified, and identified the epithelial cells collected from nasal polyps. The proliferation of nasal polyp epithelial cells was examined by a cell counting kit, and expression of GR-alpha mRNA in nasal polyp epithelial cells was examined by reverse transcription polymerase chain reaction, after training nasal polyp epithelial cells in budesonide solution.

Results

The average survival rate of nasal polyp epithelial cells was the lowest in 1 × 10−6 M budesonide solution (29.284 ± 0.311%), compared with other concentrations. Budesonide at 1 × 10−8 M caused down-regulation of GR-alpha mRNA expression levels at 6 and 12 ours, compared with the 0-hour group (p < 0.001); compared with the 0-hour group, there were significantly lower expression levels of GR-alpha mRNA at both 24 and 48 hours (p < 0.001); Expression of GR-alpha mRNA at either 48 or 12 hours was not significantly different from that at 24 hours.

Conclusion

Budesonide can significantly inhibit the proliferation of nasal polyp epithelial cells, down-regulate the expression of GR-alpha mRNA in nasal polyp epithelial cells with time dependence.

Maternal corticosterone exposure in the mouse has sex-specific effects on placental growth and mRNA expression

Maternal exposure to increased synthetic glucocorticoids (GC) during pregnancy is known to disturb fetal development and increase the risk of long-term disease. Maternal exposure to elevated levels of natural GC is likely to be common yet is relatively understudied. The placenta plays an important role in regulating fetal exposure to maternal GC but is itself vulnerable to maternal insults. This study uses a mouse model of maternal corticosterone (Cort) exposure to investigate its effects on the developing placenta. Mice were treated with Cort (33 μg/kg·h) for 60 h starting at embryonic d 12.5 (E12.5) before collection of placentas at E14.5 and E17.5. Although Cort exposure did not affect fetal size, placentas of male fetuses were larger at E17.5 in association with changes in placental Igf2. This increase in size was associated with an increase in placental thickness and an increase in placental junctional zone volume. Placentas from female fetuses were of normal size and had no changes in growth factor mRNA levels. The expression of the protective enzyme 11β-hydroxysteroid dehydrogenase type 2 was increased at E14.5 but was decreased in males at E17.5. In contrast, the expression of Nr3c1 (which encodes the GC receptor) was increased during the Cort exposure and remained elevated at E17.5 in the placentas of male fetuses. Our study has shown that maternal Cort exposure infers a sex-specific alteration to normal placental growth and growth factor expression, thus further adding to our understanding of the mechanisms of male dominance of programmed disease.

Mechanisms and significance of nuclear receptor auto- and cross-regulation

The number of functional hormone receptors expressed by a cell in large part determines its responsiveness to the hormonal signal. The regulation of hormone receptor gene expression is therefore a central component of hormone action. Vertebrate steroid and thyroid hormones act by binding to nuclear receptors (NR) that function as ligand-activated transcription factors. Nuclear receptor genes are regulated by diverse and interacting intracellular signaling pathways. Nuclear receptor ligands can regulate the expression of the gene for the NR that mediates the hormone's action (autoregulation), thus influencing how a cell responds to the hormone. Autoregulation can be either positive or negative, the hormone increasing or decreasing, respectively, the expression of its own NR. Positive autoregulation (autoinduction) is often observed during postembryonic development, and during the ovarian cycle, where it enhances cellular sensitivity to the hormonal signal to drive the developmental process. By contrast, negative autoregulation (autorepression) may become important in the juvenile and adult for homeostatic negative feedback responses. In addition to autoregulation, a NR can influence the expression other types of NRs (cross-regulation), thus modifying how a cell responds to a different hormone. Cross-regulation by NRs is an important means to temporally coordinate cell responses to a subsequent (different) hormonal signal, or to allow for crosstalk between hormone signaling pathways.

Use of recombinant cell-permeable small peptides to modulate glucocorticoid sensitivity of acute lymphoblastic leukemia cells

Glucocorticoid (GC) hormones induce apoptosis in T-cell and pre-B-cell acute lymphoblastic leukemia (ALL) cells. Steroid-mediated apoptosis requires a threshold level of the glucocorticoid receptor (GR) protein, and increasing the intracellular GR levels in ALL cells would augment their hormone sensitivity. A protein transduction domain (PTD) approach was used to accomplish this. We produced an HIV Tat PTD domain fusion protein (Tat-GR(554-777)) that potentially competes for the degradation of GR protein by the ubiquitin-proteasome system and should thus increase its intracellular levels by "stabilizing" the GR. We also designed a fusion peptide for the c-Myb DNA binding domain, Tat-c-Myb DBD, since the biological function of this peptide as a dominant negative inhibitor of the c-Myb protein was already known. Purified, bacterially expressed Tat-c-Myb DBD and Tat-GR(554-777) exhibited highly efficient transduction into cultured ALL cell lines including 697 (pre-B-ALL) and CEM-C7 (T-ALL) cells. As expected, the transduced Tat-c-Myb DBD peptide inhibited steroid-mediated stimulation of a GR promoter-luciferase reporter gene. Significantly, transduced Tat-GR(554-777) effectively increased intracellular GR levels in the GC-resistant T-ALL cell line, CEM-C1, and in the pre-B-ALL 697 cell line. Furthermore, transduction of Tat-GR(554-777) rendered GC-resistant CEM-C1 cells sensitive to steroid killing and further sensitized 697 cells to steroid. The use of Tat-fusion peptide transduction may eventually lead to innovative therapeutic modalities to improve the clinical response of patients suffering from T-cell and pre-B-cell acute lymphoblastic leukemia by increasing steroid responsiveness and perhaps converting steroid-resistant leukemia to a hormone-responsive phenotype.

Simultaneous evaluation of in vivo glucocorticoid sensitivity and expression of glucocorticoid receptor alpha-isoform in rheumatoid arthritis patients

OBJECTIVES: To analyze glucocorticoid (GC) sensitivity using intravenous very low dose dexamethasone suppression test (IV-VLD-DST) in patients with rheumatoid arthritis (RA) and its correlation with glucocorticoid receptor alpha-isoform (GRα) gene expression. METHODS: We evaluated 20 healthy controls and 32 RA patients with Health Assessment Questionnaire (HAQ) and Disease Activity Score 28 joints (DAS) scores and IV-VLD-DST and GRα expression in mononuclear cells. RESULTS: Basal cortisol and the percentage of cortisol reduction after IV-VLD-DST were lower in RA patients than in controls, whereas GRα expression was similar among groups. In the RA group there was an inverse correlation between GRα expression and the percentage of cortisol suppression that was not observed in controls. There was a direct relationship between DAS and GRα expression. CONCLUSIONS: Mechanisms involved in GC resistance observed in patients with RA are possibly not at the level of GRα gene expression, since it was similar among groups and GRα increased with disease activity.

Early timing of low-dose dexamethasone decreases inflammation in a murine model of eosinophilic airway disease

CONCLUSION

A very low dose of dexamethasone (DEX) was as equally as sufficient as a pharmacological dose to decrease eosinophil inflammation in airways and bone marrow. The timing of DEX treatment in relation to allergen challenge was strongly decisive for the outcome of the inflammatory response.

OBJECTIVES

We aimed to study compartmental allergic airway inflammatory responses to classic pharmacological and also extremely low physiological DEX dosage, given at different time points close to allergen challenge in a murine model.

MATERIALS AND METHODS

Ovalbumin-sensitized BALB/c-mice were exposed to intra-nasal ovalbumin. DEX was given i.p. as 1 microg/kg low-dose or 500 microg/kg pharmacological single-dose 2 h before, immediately before or 7 h after each of three challenges. Inflammatory cells were evaluated in bronchoalveolar lavage (BAL), lungs, nasal mucosa, and bone marrow.

RESULTS

Groups treated with low-dose DEX decreased eosinophilia in BAL to the same extent as the pharmacological dose, but only when administered before challenge. The most prominent decrease of eosinophils in BAL was seen in mice treated with the low dose 2 h before challenge. A similar response pattern as in BAL eosinophilia was detected in lung histopathology. DEX treatments had no obvious effects on inflammation in nasal mucosa.

Distribution and corticosteroid regulation of glucocorticoid receptor in the brain of Xenopus laevis

Glucocorticoids (GCs) play essential roles in physiology, development, and behavior that are mediated largely by the glucocorticoid receptor (GR). Although the GR has been intensively studied in mammals, very little is known about the GR in nonmammalian tetrapods. We analyzed the distribution and GC regulation of GR in the brain of the frog Xenopus laevis by immunohistochemistry. GR-immunoreactive (GR-ir) cells were widely distributed, with the highest densities in the medial pallium (mp; homolog of the mammalian hippocampus), accumbens, anterior preoptic area (POA; homolog of the mammalian paraventricular nucleus), Purkinje cell layer of the cerebellum, and rostral anterior pituitary gland (location of corticotropes). Lower but distinct GR-ir was observed in the internal granule cell layer of the olfactory bulbs, dorsal and lateral pallium, striatum, various subfields of the amygdala, bed nucleus of the stria terminalis (BNST), optic tectum, various tegmental nuclei, locus coeruleus, raphe nuclei, reticular nuclei, and the nuclei of the trigeminal motor nerves. Treatment with corticosterone (CORT) for 4 days significantly decreased GR-ir in the POA, mp, medial amygdala (MeA), BNST, and rostral pars distalis. Treatment with the corticosteroid synthesis inhibitor metyrapone (MTP) also significantly reduced GR-ir in the POA, mp, MeA and BNST, but not in the rostral pars distalis. Replacement with a low dose of CORT in MTP-treated animals reversed these effects in brain. Thus, chronic increase or decrease in circulating corticosteroids reduces GR-ir in regions of the frog brain. Our results show that the central distribution of GR-ir and regulation by corticosteroids are highly conserved among vertebrates.

Patients with ulcerative colitis responding to steroid treatment up-regulate glucocorticoid receptor levels in colorectal mucosa

BACKGROUND AND AIMS

Glucocorticosteroid treatment (GCS) is effective for attacks of ulcerative colitis (UC). However, 25-30% of patients fails to respond and may be considered steroid resistant. Glucocorticoid receptors (GR) mediate the effects of GCS. Colorectal mucosa levels of GR and NF-κB were analysed before, during and after treatment with GCS-compounds.

METHODS

Patients with moderate-severe attacks of ulcerative colitis were included. Patients undergoing colonoscopy with normal finding served as controls. GR and NF-κB levels in colorectal mucosa were analysed by Western Blotting and the DNA-binding activity of NF-κB by EMSA.

RESULTS

Twenty-eight patients and seven controls were included. Ten patients were judged clinically steroid resistant. Responders had significantly higher levels of GR in colorectal mucosa after one week of treatment than non-responders (P=0.039) and significantly higher levels of GR were found in responders in remission as compared to before treatment (P=0.013). NF-κB levels did not differ between the groups at first visit. Increasing levels were found only in responders as remission was obtained (P=0.031). EMSA detected 20% lower DNA-binding of NF-κB in responders in remission as compared to first visit (P=0.021).

CONCLUSION

GR levels increase in UC-patients responding to GCS-therapy but not in steroid resistant patients and may be the reason for the lack of steroid-efficacy. Increasing NF-κB levels were found in responders attaining remission, possibly reflecting a lower turnover. A decrease in DNA-binding of NF-κB was found in these patients, perhaps because of the increased GR levels counteracting NF-κB activity.

Uteroplacental insufficiency alters nephrogenesis and downregulates cyclooxygenase-2 expression in a model of IUGR with adult-onset hypertension

Clinical and animal studies indicate that intrauterine growth restriction (IUGR) following uteroplacental insufficiency (UPI) reduces nephron number and predisposes toward renal insufficiency early in life and increased risk of adult-onset hypertension. In this study, we hypothesized that the inducible enzyme cyclooxygenase-2 (COX-2), a pivotal protein in nephrogenesis, constitutes a mechanism through which UPI and subsequent glucocorticoid overexposure can decrease nephron number. We further hypothesized that UPI downregulates the key enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), which converts corticosterone to inert 11-dehydrocorticosterone, thereby protecting both the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR) from the actions of corticosterone. Following bilateral uterine ligation on the pregnant rat, UPI significantly decreased renal COX-2, 11beta-HSD2, and GR mRNA and protein levels, but upregulated expression of MR at birth. At day 21 of life, 11beta-HSD2, GR, and also MR mRNA and protein levels were downregulated. UPI did not affect blood pressures (BP) at day 21 of life but significantly increased systolic BP in both genders at day 140. We conclude that in our animal model, UPI decreases fetal COX-2 expression during a period of active nephrogenesis in the IUGR rat, which is also characterized by decreased nephron number and adult-onset hypertension.

Sound conditioning protects hearing by activating the hypothalamic-pituitary-adrenal axis

Sound conditioning primes the auditory system to low levels of acoustic stimuli and reduces damage caused by a subsequent acoustic trauma. This priming activates the HPA axis resulting in the elevation of plasma corticosterone with a consequent upregulation of glucocorticoid receptors (GR) in the cochlea and the paraventricular nucleus (PVN) of the hypothalamus in the mouse. This protective effect is blocked by adrenalectomy or pharmacological treatment with RU486 + metyrapone. Sound conditioning prevents GR down-regulation induced by acoustic trauma and subsequently enhances GR activity in spiral ganglion neurons. Increased SRC-1 expression, triggered by sound conditioning, positively correlates with the upregulation of GR in the cochlea. These findings will help to define the cellular mechanisms responsible for protecting the auditory system from hearing loss by sound conditioning.

Glucocorticoid receptor and nuclear factor-kappa B interactions in restraint stress-mediated protection against acoustic trauma

The role of glucocorticoid receptors (GRs) in the protective effect of restraint stress (RS) before acoustic trauma was studied in spiral ganglion neurons of CBA mice. RS increased corticosterone and protected against elevated auditory brain stem thresholds caused by acoustic trauma. This protection was inhibited by the pretreatment with a corticosterone synthesis inhibitor, metyrapone (MET), and a GR antagonist (RU486). RS followed by acoustic trauma caused an immediate increase in corticosterone that triggered nuclear translocation of GR, without a change in the expression of GR protein. RU486 + MET before RS and acoustic trauma caused an immediate increase in GR mRNA followed by increased GR protein expression (24 h after trauma). GR signaling was further characterized by analyzing nuclear factor-kappaB (NF kappaB) nuclear translocation and protein expression. NF kappaB nuclear translocation was reduced after acoustic trauma or pretreatment with RU486 + MET before RS and acoustic trauma. On the contrary, RS protected against the trauma-induced NF kappaB reduction of its nuclear translocation in inhibitory-kappaB (I kappaB)-dependent manner. RU486 + MET caused a simultaneous decreased I kappaB expression and NF kappaB nuclear translocation, demonstrating an interference with the I kappaB-mediated activation of NF kappaB. In summary, RS protects the cochlea from acoustic trauma by increasing corticosterone and activating GRs. These results emphasis how GR activity modulates hearing sensitivity and its importance for the rationale use of glucocorticoids in inner ear diseases.

Restraint stress modulates glucocorticoid receptors and nuclear factor kappa B in the cochlea

The regulation of glucocorticoid receptors and nuclear factor kappaB was evaluated in the spiral ganglion neurons after 4 h of restraint stress in the mouse cochlea. Immediately after restraint stress, glucocorticoid receptor protein expression was not altered in spiral ganglion neurons even though both the plasma corticosterone levels and glucocorticoid receptor nuclear translocation increased. By 24 h after restraint stress, the protein expression of glucocorticoid receptors was decreased in spiral ganglion neurons. Pre-treatment with RU486 and metyrapone prevented nuclear translocation of glucocorticoid receptors and nuclear factor kappaB. Moreover, the synthesis of nuclear factor kappaB protein (p65) and inhibitory factor kappaBalpha decreased when RU486 and metyrapone treatment was given before restraint stress. These findings suggest that restraint stress modulates glucocorticoid receptor and nuclear factor kappaB activity in the spiral ganglion neurons, resulting in an altered response to stress.

Corticosteroids: the mainstay in asthma therapy

Inflammation is now marked as a central feature of asthma pathophysiology and aims of current asthma management are not only to treat acute symptoms of wheezing, breathlessness, chest tightness, cough but also to suppress the underlying inflammatory component. Despite the availability of a number of drugs, corticosteroids remain the mainstay in the management of all types of asthma as these are the most potent and effective antiinflammatory agents available so far. Corticosteroids suppress virtually every step in inflammation. However therapeutic doses of oral glucocorticoids are associated with a range of adverse reactions. To overcome these side effects, inhalations have been developed to deliver glucocorticoids directly to the lungs and in the process a number of aerosol preparations have become available, which have advantage of significantly lower toxicity due to low systemic absorption from the respiratory tract and rapid inactivation. Despite considerable efforts by pharmaceutical industry, it has been difficult to develop novel therapeutic agents for asthma management, which could surpass inhaled corticosteroids. Currently the data favours using inhaled corticosteroids as monotherapy in the majority of patients in all kinds of asthma. If combination therapy is recommended to achieve additional control in severe asthma cases, other drugs such as beta-agonists, antileukotrienes, theophylline, etc. are considered as adjunct therapies to corticosteroids. This review discusses the importance of corticosteroids as first line therapy for asthma treatment with the availability of inhaled corticosteroids for chronic treatment and oral formulations for treating acute exacerbations of moderate to severe asthma.

Glucocorticoid receptors in human airways

Inhaled and intranasal glucocorticoids are the most common and effective drugs for controlling symptoms and airway inflammation in respiratory diseases such as asthma, allergic rhinitis, and nasal polyposis. The last few years have seen a growing understanding of the mechanisms of glucocorticoid action and, in particular, the receptor that mediates glucocorticoid actions, the glucocorticoid receptor (GR). In this revision we present an update on the GR gene, the expression and regulation of its gene products, namely GRalpha and GRbeta, as well as their alterations in pathological states. GRalpha is responsible for the induction and repression of target genes, it is expressed in virtually all human cells and tissues, and its expression is known to be downregulated by glucocorticoids. GRbeta has been found to act as a dominant negative inhibitor of GRalpha-mediated transactivation in in vitro studies with transfected cells, but it does not appear to have a significant inhibitory effect on GRalpha-mediated transrepression. In addition, for most tissues the expression of GRbeta, at least at the mRNA level, is extremely low compared with that of GRalpha. Some pro-inflammatory cytokines appear to upregulate the expression of GRbeta, and increased GRbeta expression has been reported in diseases associated with glucocorticoid resistance or insensitivity, such as bronchial asthma, nasal polyposis, and ulcerative colitis. However, the possible role of GRbeta in modulating glucocorticoid sensitivity and/or resistance in vivo has been highly debated and it is not yet clear.

Pituitary expression of type I and type II glucocorticoid receptors during chicken embryonic development and their involvement in growth hormone cell differentiation

Glucocorticoids can induce somatotroph differentiation in vitro and in vivo during chick embryonic and rat fetal development. In the present study, we identified the nuclear receptors involved in somatotroph differentiation and examined their ontogeny and cellular distribution during pituitary development in the chicken embryo. Several steroids were tested for their ability to induce GH cell differentiation. Only glucocorticoids and aldosterone were effective at low nanomolar concentrations, suggesting involvement of both type I (mineralocorticoid) and type II (glucocorticoid) receptors (MR and GR, respectively). ZK98299 and spironolactone (GR and MR antagonists, respectively) when used alone were unable to block corticosterone or aldosterone (2 nm)-induced somatotroph differentiation. However, ZK98299 and spironolactone in combination abolished corticosterone or aldosterone (2 nm)-induced somatotroph differentiation. When used separately, both antagonists attenuated induction of GH mRNA by corticosterone. Spironolactone alone blocked somatotroph differentiation induced by 0.2 nm corticosterone or aldosterone, indicating that corticosteroids at subnanomolar concentrations act only through the MR. GR protein was detected in pituitary extracts as early as embryonic d 8, whereas MR protein was readily detectable only around d 12. GR were expressed in greater than 95% of all pituitary cells, whereas MR were expressed in about 40% of all pituitary cells. Dual-label immunofluorescence revealed that the majority of somatotrophs on d 12 expressed MR. Given the high affinity of corticosteroids for MR and that corticosteroid concentrations during embryonic development are in the subnanomolar range, expression of MR may constitute a significant developmental event during somatotroph differentiation.

Glucocorticoid receptor expression in inflammatory bowel disease: evidence for a mucosal down-regulation in steroid-unresponsive ulcerative colitis

BACKGROUND

Glucocorticoids (GC) play a major role in the attenuation of inflammation. Glucocorticoid receptor (GR) expression is an important determinant of steroid sensitivity.

AIMS

To investigate whether GR mRNA expression is altered in inflammatory bowel disease, and whether GR mRNA expression correlates with disease activity and may predict response to GC therapy.

METHODS

Mucosal biopsies were taken from 33 patients with ulcerative colitis, 21 with Crohn's disease and 11 controls. Peripheral blood mononuclear cells were isolated from 24 ulcerative colitis and 18 Crohn's disease patients and 11 controls. GR mRNA was measured by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), and correlated to endoscopic findings, clinical activity and outcome of GC therapy. In a subset of subjects GR localisation was shown by immunohistochemistry.

RESULTS

In patients with inflammatory bowel disease GR expression was not different from controls. However, GR was decreased in biopsies from ulcerative colitis patients with impaired GC response. The inhibitory subtype GRbeta was expressed 100-1000 times lower than GRalpha. GR immunoreactivity was identified in immune and epithelial cells except for colonic crypts.

CONCLUSION

In inflammatory bowel disease systemic and mucosal GR mRNA expression is not altered. However, in ulcerative colitis patients, low mucosal GR expression may predict the outcome of GC therapy. The low expression of GRbeta challenges its role in steroid refractoriness in inflammatory bowel disease.

Primary pigmented nodular adrenocortical disease: paradoxical responses of cortisol secretion to dexamethasone occur in vitro and are associated with increased expression of the glucocorticoid receptor

Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of ACTH-independent adrenal Cushing's syndrome (CS), which is often associated with Carney complex (CNC). We have recently described a paradoxical increase in cortisol excretion after dexamethasone administration in most patients with PPNAD. In the present study we investigated the hypothesis that this phenomenon is due to a primary abnormality of the tissues affected by PPNAD, rather than a defect of the patients' hypothalamic-pituitary-adrenal axis; as such it should be replicated in vitro by adrenal slices exposed directly to dexamethasone. We were able to study adrenal tissues from eight patients with CS caused by PPNAD; two patients were also studied in vivo according to a protocol first described in ACTH-independent macronodular adrenal hyperplasia (AIMAH) for the clinical detection of aberrant hormone receptor expression. Their DNA has been previously screened for inactivating mutations of the PRKAR1A gene, the most frequent molecular defect leading to PPNAD and/or CNC. We also investigated whether glucocorticoid receptor (GR) expression underlies paradoxical dexamethasone responses in PPNAD by immunohistochemistry and semiquantitative PCR, and we correlated GR expression with that of other markers for PPNAD (e.g. synaptophysin). Indeed, we demonstrated that dexamethasone induced cortisol secretion in vitro in five of these tumors; no such increase was seen in adenomatous or AIMAH tissues that were treated in the same manner. GR mRNA was expressed, and GR immunoreactivity was detected in PPNAD nodular cells. Staining for GR was not seen in surrounding cortical cells, and hence, it correlated with synaptophysin, which also stains PPNAD in a similar manner. In normal adrenal tissue, GR was detected mostly in medullary areas, whereas GR immunoreactivity was weak in adenomatous and AIMAH tissues. We conclude that 1) dexamethasone produces an increase in glucocorticoid synthesis by PPNAD adrenal slices in vitro, suggesting a direct effect on adrenocortical tissue, and 2) this phenomenon is accompanied by increased expression of the GR in PPNAD nodules. PPNAD and/or CNC patients with and without mutations leading to protein kinase A activation demonstrated in vitro and/or in vivo paradoxical dexamethasone responses and GR expression, indicating that PRKAR1A alterations are not necessary for these phenomena.

Expression of the glucocorticoid receptor alpha and beta isoforms in human nasal mucosa and polyp epithelial cells

The lower sensitivity of the inflamed nasal mucosa to glucocorticoids might be related to an increased expression of the glucocorticoid receptor (GR) beta isoform. We investigated GRalpha and GRbeta mRNA expression in epithelial cells from nasal mucosa and nasal polyps. GRalpha mRNA was at least 1000 times more expressed than GRbeta mRNA in both tissues. GRbeta expression (mean+/-SEM of 10(3) cDNA copies/microg of total RNA) was higher in nasal polyps (1.15+/-0.19; n=27; P<0.01) than in nasal mucosa (0.62+/-0.10; n=32). Nasal polyps with > 3% of inflammatory cells had higher GRbeta levels (1.40+/-0.29; n=16) than both nasal mucosa (P<0.01) and polyps with < or = 3% of inflammatory cells (0.80+/-0.18; n=11; P<0.05). No difference in GRbeta expression was found between nasal mucosa and polyps with < or = 3% of inflammatory cells. GRbeta expression correlated with the inflammatory cell number, especially with mast cells (r=0.50, P<0.0001). There was no difference in GRalpha mRNA expression between nasal mucosa and nasal polyps. In summary, GRalpha is far more expressed than GRbeta in both tissues. The increased expression of GRbeta may be related to the presence of inflammatory cells.

Expression of glucocorticoid receptor alpha- and beta-isoforms in human cells and tissues

Alternative splicing of the human glucocorticoid receptor (GR) primary transcript generates two protein isoforms: GR-alpha and GR-beta. We investigated the expression of both GR isoforms in healthy human cells and tissues. GR-alpha mRNA abundance (x10(6) cDNA copies/microg total RNA) was as follows: brain (3.83 +/- 0.80) > skeletal muscle > macrophages > lung > kidney > liver > heart > eosinophils > peripheral blood mononuclear cells (PBMCs) > nasal mucosa > neutrophils > colon (0.33 +/- 0.04). GR-beta mRNA was much less expressed than GR-alpha mRNA. Its abundance (x10(3) cDNA copies/microg total RNA) was as follows: eosinophils (1.55 +/- 0.58) > PBMCs > liver > or = skeletal muscle > kidney > macrophages > lung > neutrophils > brain > or = nasal mucosa > heart (0.15 +/- 0.08). GR-beta mRNA was not found in colon. While GR-alpha protein was detected in all cells and tissues, GR-beta was not detected in any specimen. Our results suggest that, in physiological conditions, the default splicing pathway is the one leading to GR-alpha. The alternative splicing event leading to GR-beta is minimally activated.

Expression and binding activity of the glucocorticoid receptor are upregulated in septic muscle

We examined the influence of sepsis, induced by cecal ligation and puncture in rats, on the protein and gene expression and hormone binding activity of the glucocorticoid receptor (GR) in skeletal muscle. Sepsis resulted in increased GR mRNA and protein levels and upregulated hormone binding activity in extensor digitorum longus and soleus muscles. Scatchard analysis suggested that the increased GR hormone binding activity reflected an increased number of hormone binding sites, whereas receptor affinity for glucocorticoids was unchanged. The GR antagonist RU-38486 blocked the sepsis-induced increase in GR expression and hormone binding activity, implicating a positive regulatory effect of glucocorticoids on GR expression and binding activity under the present experimental conditions. The results suggest that glucocorticoid-dependent metabolic changes in skeletal muscle during sepsis may reflect not only high circulating glucocorticoid levels but increased amounts and hormone binding activity of the GR as well.

Relationship between glucocorticoid-mediated early decrease of protein synthesis and the steady state decreases of glucocorticoid receptor and TGF-beta activator protein

The present studies were undertaken to better elucidate the mechanism(s) by which glucocorticoids inhibit the process of tissue repair. The aim was to determine the importance of the effect of glucocorticoids on decreasing the nuclear TGF-beta activator protein. The relationship amongst inhibition of noncollagen protein synthesis and the steady state levels of glucocorticoid receptor and the TGF-beta activator protein was examined. Both collagen and noncollagen synthesis were determined in skin fibroblast cell culture and in dermis. Fetal rat skin fibroblasts were treated for 24 h with dexamethsone. Noncollagen protein synthesis was decreased to approximately one-half that of collagen synthesis. Similar results were obtained in dermis in vivo. At 48 h, dexamethasone treatment resulted in practically no nuclear glucocorticoid receptor being noted and a 40-45% steady state decrease of the TGF-beta activator protein. We have recently reported that the TGF-beta activator protein exists as a protein complex with SP1 and NFKB (p 49). The present data indicate that although the marked decrease of the nuclear glucocorticoid receptor DNA binding following dexamethasone treatment is not comparable to the early 24 h decrease of noncollagen protein synthesis, the decrease of the TGF-beta activator protein complex binding to DNA is. The present studies indicate the importance of the effect of dexamethasone on the steady state level of the TGF-beta activator protein complex in the glucocorticoid-mediated process inhibition of tissue repair and the relationship of this decrease to the earlier inhibition of protein synthesis.

Glucocorticoid-regulated transcription factors

Glucocorticoids are the most effective antiinflammatory drugs used in the treatment of asthma. They act by binding to a specific receptor (GR) that, upon activation, translocates to the nucleus and either increases (transactivates) or decreases (transrepresses) gene expression. Inhibition of pro-inflammatory transcription factors such as activator protein (AP)-1, signal transducers and activators of transcription (STATs), nuclear factor of activated T cells (NFAT) and nuclear factor (NF)-kappa B is thought to be a major action of glucocorticoids. Acetylation of histones allows unwinding of the local DNA structure and enables RNA polymerase II to enhance gene transcription. Histone acetylation is regulated by a balance between the activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs). GR acts as a direct inhibitor of NF-kappa B-induced HAT activity and also by recruiting HDAC2 to the NF-kappa B/HAT complex. A sub-group of patients with glucocorticoid-insensitive asthma have an inability to induce histone acetylation in response to dexamethasone suggesting reduced expression of a GR-specific HAT. This suggests that pharmacological manipulation of specific histone acetylation status is a potentially useful approach for the treatment of inflammatory diseases. Identification of the precise mechanism by which activated GR recruits HDAC2 may reveal new targets for the development of drugs that may dissociate the antiinflammatory actions of glucocorticoids from their side effects that are largely due to gene induction.

Glucocorticoid receptor mRNA in patients with ulcerative colitis: a study of responders and nonresponders to glucocorticosteroid therapy

BACKGROUND AND AIMS

Up to 30% of patients with severe-to-moderate attacks of ulcerative colitis (UC) respond poorly to glucocorticosteroid (GCS) treatment. The reason for this unresponsiveness is unknown.

AIM

Our aim was to evaluate possible differences in glucocorticoid receptor (GR) density in peripheral leukocytes and effects of low-dose GCS treatment on GR density and on the hypothalamic-pituitary-adrenal axis in UC patients who had received high-dose GCS treatment due to a moderate or severe attack. Eleven UC patients in remission who were responders (Rs) to previous GCS treatment were compared with 10 patients who failed GCS therapy and had a colectomy (nonresponders. NRs). Ten healthy individuals served as controls.

METHODS

Quantitation of GR mRNA by a solution hybridization assay in peripheral leukocytes and a low-dose adrenocorticotropin hormone stimulation test was performed before and after low-dose dexamethasone (DEX) treatment for 14 days. The glucocorticoid-responsive gene for metallothionein IIa (MTIIa) was also analyzed by a solution hybridization assay in peripheral leukocytes.

RESULTS

Overall, basal GR mRNA levels were higher in patients than in controls (p < 0.0001). There were no significant differences between NRs and Rs. None of the groups down-regulated their GR mRNA levels in response to DEX treatment. Basal and stimulated cortisol levels decreased significantly only among NRs after DEX (p = 0.012 and 0.0093). MTIIa levels were lower in NRs as compared with Rs, both in mononuclear (p = 0.0059) and in polynuclear leukocytes (p = 0.030).

CONCLUSION

Patients with UC in remission exhibit higher levels of GR mRNA in peripheral leukocytes. We speculate that this may be secondary to an underlying up-regulation of proinflammatory factors also present in patients in clinical remission. Differences in GR mRNA levels per se thus may not be important for the ability of patients with UC to respond to GCS treatment. The hypothalamic pituitary adrenal axis was suppressed by low-dose DEX treatment only in NRs, possibly indicating that steroid-resistance is not a generalized phenomenon. Lower levels of MTIIa in NRs may indicate a diminished efficiency of GR regulation in steroid-refractory patients.

Effects of topical budesonide treatment on glucocorticoid receptor mRNA down-regulation and cytokine patterns in nasal polyps

The effects of a topically applied corticosteroid, budesonide, on the expression of glucocorticoid receptor (GR) mRNA and regulation of pro-inflammatory cytokine patterns in patients with nasal polyps were evaluated. All patients were eligible for surgical polypectomy, and a majority of them had been treated with nasal steroids. Patients were given 400 microg b.i.d. (group A, n = 11), 200 microg b.i.d. (group B, n = 10), or no treatment (group C, n = 15) during two months before polypectomy. Morning serum cortisol was analyzed on the day of surgery. Surgically removed polyps were taken for analysis of GR mRNA expression by solution hybridization. Remaining tissue was cryostat-sectioned, whereafter quantification of the cytokines interleukin 1beta, interleukin 2, interleukin 4, interleukin 5, interleukin 6, interleukin 10, tumor necrosis factor alpha, and interferon gamma was made by immunohistochemistry and digitized image analysis. No significant differences among the three groups were found for any of the parameters investigated.

CONCLUSION

nasal polyps do not respond with down-regulation of GR mRNA or cytokines following topical corticosteroid treatment. The proposed corticosteroid resistance may be inherent, or induced by a change of local tissue bioavailability.

Expression of the human glucocorticoid receptor alpha and beta isoforms in human respiratory epithelial cells and their regulation by dexamethasone

Two isoforms of the human glucocorticoid receptor (hGR) have been described, hGRalpha and hGRbeta. We analyzed the expression and regulation of both hGR isoforms in human respiratory epithelial cells (BEAS-2B, A549, and primary nasal epithelial cells). In BEAS-2B cells, the expression of hGRalpha messenger RNA (mRNA) was much higher than that of hGRbeta mRNA. Dexamethasone (DEX) (10(-6) M) downregulated hGRalpha mRNA at 6 and 24 h (55 +/- 8 and 58 +/- 5% of control, respectively; P < 0.01), whereas it decreased hGRbeta mRNA only at 6 h (55 +/- 7% of control; P < 0.01). Downregulation of hGRalpha and hGRbeta mRNAs occurred even in the presence of cycloheximide. Actinomycin-D studies revealed that DEX enhanced the stabilization of hGRalpha and hGRbeta messages. hGRalpha but not hGRbeta protein was detected in BEAS-2B, A549, and nasal epithelial cells. After 24 h of incubation, 10(-6) M DEX decreased the expression of hGRalpha protein in BEAS-2B, A549, and nasal epithelial cells (16 +/- 4, 14 +/- 4, and 28 +/- 7% of control, respectively; P < 0.01). These results suggest that in respiratory epithelial cells: (1) hGRalpha is much more expressed than hGRbeta at both the mRNA and protein levels; (2) hGRalpha is downregulated by corticosteroids both in cell lines (BEAS-2B, A549) and in nasal primary cells; and (3) transcriptional, post-transcriptional, and post-translational mechanisms appear to be involved in the regulation of hGR expression by corticosteroids.

Glucocorticoid resistance in thymocytes from mice expressing a T cell receptor transgene

A majority of thymocytes undergo apoptosis during differentiation due to lack of survival signals provided by T cell receptor (TCR) activation. As glucocorticoids (GC) have been suggested to be involved in this process, we have investigated the GC sensitivity in thymocytes from mice expressing a transgenic selecting TCR. We now report that immature CD4(+)CD8(+) double-positive thymocytes from these mice are comparatively more resistant to corticosterone-induced apoptosis. This is associated with reduced glucocorticoid receptor (GR) expression, increased levels of membrane CD28, increased NF-kappaB DNA binding activity, and increased binding to the CD28 response element in the interleukin-2 gene promoter. Analysis of NF-kappaB/Rel proteins from nuclear extracts demonstrated altered levels of some of these proteins. Our results suggest that TCR recognition of self major histocompatibility antigens generates intracellular signals which alter the thymocyte GC sensitivity and thereby protect them against apoptosis induced by endogenous GC.

Pharmacological characterization of glucocorticoid receptors in primary human bronchial epithelial cells

Bronchial epithelial cells play an important role in amplifying and perpetuating airway inflammation and may be a target for inhaled steroids. We have characterized glucocorticoid receptors in primary human bronchial epithelial cells. Northern and western blot analyses demonstrated the expression of glucocorticoid receptor mRNA and protein, respectively, in primary bronchial epithelial cells. The activity of these receptors was shown using a radioligand binding assay. High-affinity binding with pharmacological specificity was demonstrated for [3H]dexamethasone. The equilibrium dissociation constant (Kd) and density of binding sites (Bmax) for [3H]dexamethasone determined from saturation isotherms were 4.4 nM x/divided by 0.95 (SEM) and 30.1 fmol/mg protein +/-6.4 (SEM). Glucocorticoid receptors were activated by dexamethasone as assessed using a glucocorticoid-responsive reporter plasmid, pTAT3-CAT. Transfection of primary human bronchial epithelial cells with this reporter plasmid resulted in 35-fold activation of transcription following dexamethasone stimulation (10(-6) M). The glucocorticoid receptor antagonist RU-486 (mifepristone) significantly counteracted the effect of dexamethasone on glucocorticoid receptor activation, indicating that the dexamethasone effect is specific and is mediated through the glucocorticoid receptor. In summary, our study demonstrated that primary cultures of human bronchial epithelial cells possess glucocorticoid receptors that function as a ligand-activated transcriptional regulator. The presence of glucocorticoid receptors confers their responsiveness to glucocorticoids and indicates that the airway epithelium may be a target for the anti-inflammatory effects of inhaled steroids.

Alpha and beta glucocorticoid receptor mRNA expression in skeletal muscle

The aim of the present study was to investigate the occurrence and autoregulation of both glucocorticoid receptor mRNAs in rat gastrocnemius muscle. The expression of both receptor forms was studied 1, 4 or 12 hours after intra-tracheal instillation of a high dose (100 micrograms) of budesonide; muscular expression was compared with glucocorticoid receptor expression in lung tissue. After Northern blot analysis, hybridization was performed with glucocorticoid receptor, glyceraldehyde-3-phosphate dehydrogenase and glutamine synthetase probes. In the gastrocnemius muscle, both the alpha and beta glucocorticoid receptor mRNA forms were detected and found to be downregulated four hours after the budesonide instillation. alpha/beta glucocorticoid receptor ratios were lower in the gastrocnemius (1.1 +/- 0.2) than in the lungs (2.6 +/- 0.6). In the lungs, at all time points, the average alpha glucocorticoid receptor mRNA levels did not differ from controls, although glutamine synthetase mRNA levels were upregulated. The beta glucocorticoid receptor mRNA was slightly reduced at 1 and 4 hours. In conclusion, after intra-tracheal instillation of budesonide, both alpha and beta glucocorticoid receptor forms were downregulated in muscle tissue. The difference in alpha/beta glucocorticoid receptor mRNA ratios and concentrations between lung and gastrocnemius muscle supports the hypothesis of differential gene regulation by glucocorticoids in different cell types.

Glucocorticoid receptor mRNA and protein in fetal rat lung in vivo: modulation by glucocorticoid and androgen

Pulmonary glucocorticoid receptor (GR) is essential to timely preparation for the onset of breathing air at birth. We have previously used primary culture of late-gestation fetal rat lung cells to demonstrate differential regulation of GR by glucocorticoid depending on cell type. In this study, we hypothesized that the action of glucocorticoid on GR mRNA expression and protein elaboration in lung cells might be modulated by interactions present in vivo but not in primary culture. Given that male sex hormone (androgen) has an inhibitory effect on antenatal lung development, we also postulated that androgen would decrease antenatal lung GR. We report that antenatal maternal injection of the glucocorticoid dexamethasone (1 mg/kg) enhanced fetal lung cellular levels of GR mRNA and protein as assessed by in situ hybridization and immunocytochemistry (ICC), respectively. ICC was performed using polyclonal rabbit anti-human antibody that reacts with rat GR whether bound to ligand or not and does not interfere with GR binding to DNA. Levels of GR mRNA and protein were enhanced in cells throughout all areas of the lung tissue, suggesting that interactions occurring in intact tissue may override the previously reported direct inhibition by glucocorticoid of GR protein elaboration in isolated fetal rat lung epithelial cells. Furthermore, antenatal administration of the androgen 5alpha-dihydrotestosterone (0.2 mg/kg) reduced tissue levels of GR mRNA and protein, consistent with androgenic inhibition of antenatal lung development by decreasing GR. We conclude that glucocorticoids and androgens exert opposite effects on fetal lung GR.

Glucocorticoid receptors in cord blood lymphocytes of healthy neonates and of preterms suffering from respiratory distress syndrome

We measured the number of glucocorticoid receptors (GR) in cord blood lymphocytes and the binding affinity (Kd) in 15 term and in 20 preterm babies. Thirteen preterms of the latter group received prenatal steroid treatment. Seven preterms developed neonatal respiratory distress syndrome (NRDS). The number of GR and the Kd were similar in the term and preterm (with and without NRDS) babies. The maximum (3H)-thymidine incorporation into DNA of cord blood lymphocytes from all preterms, with or without NRDS was suppressed when compared to that from term babies or adults. This could partly be explained by the antenatal steroid treatment. Sensitivity (ID50) of the lymphocytes for the inhibitory effect of dexamethasone was the same in all groups. In this study on the number and function of GR in lymphocytes, we were unable to find a relation between the functionality of the GR and the development of NRDS.

Regulation of glucocorticoid receptor by the tyrosine kinase inhibitor herbimycin A in the cytosolic fraction of primary cultured rat hepatocytes

The participation of tyrosine kinase in the regulation of the glucocorticoid receptor (GR) was studied in primary cultured rat hepatocytes using the tyrosine kinase inhibitor herbimycin A. Herbimycin A decreased the number of high-affinity binding sites of glucocorticoids in the cytosolic fraction and increased the equilibrium dissociation constant (Kd). Western blot analysis revealed that it also decreased the amount of GR protein. On the other hand, cycloheximide did not affect the GR protein level. Although herbimycin A slightly increased the amount of GR protein in the nuclear fraction, the increase was much lower than that of its decrease in the cytosolic fraction. Therefore, the decrease of GR protein in the cytosolic fraction was not caused by the inhibition of GR protein synthesis nor the translocation of GR from cytosol to nuclei. As herbimycin A also suppressed the dexamethasone (Dex)-dependent induction of tyrosine aminotransferase (TAT) activity, the decrease of GR protein was followed by the suppression of the GR-mediated biological response. These findings indicate that tyrosine kinase is necessary for the maintenance of the level of GR protein and its affinity of binding sites in the cytosolic fraction. Our results also suggested that the increase of GR protein stability is the most probable explanation for the maintenance of its level.

Coordinate regulation of glucocorticoid receptor and c-jun gene expression is cell type-specific and exhibits differential hormonal sensitivity for down- and up-regulation

We have previously proposed a novel mechanism for the coupled regulation of glucocorticoid receptor (GR) and c-jun transcription in triamcinolone acetonide (TA)-treated AtT-20 cells. This involved transcriptional interference of AP-1 (Fos/Jun)-driven gene transcription by the formation of inactive GR/Jun heterodimers. To further elucidate the molecular mechanism for GR autoregulation, the expression of GR and c-jun mRNA and protein levels were examined in both mouse L929 fibroblast cells and human CEM-C7 acute lymphoblastic leukemia cells. A rapid down-regulation of both GR and c-jun mRNA and protein levels occurs in TA-treated L929 cells. All-trans-retinoic acid (RA) treatment of Jun-deficient, mouse F9, teratocarcinoma cells causes the induction of c-jun expression. The increased expression of both c-jun mRNA and protein is accompanied by the induction of GR expression. These data further suggest that functional cJun is needed for the expression of the GR and c-jun genes in F9 cells. CEM-C7 cells undergo apoptosis after exposure to glucocorticoids. There is a parallel up-regulation of GR and c-jun mRNA levels in TA-treated CEM-C7 cells. This is accompanied by a concomitant increase in GR and cJun protein levels. Dose-response analyses reveal the expected coordinate regulation of both GR and c-jun mRNA and protein in L929 cells (decreasing) and in CEM-C7 cells (increasing). However, approximately 20-fold less TA is required for the inhibition of GR and c-jun expression as compared to that required for the stimulation of these two genes. These data demonstrate that the coordinate regulation of GR and c-jun gene expression is dose-dependent and cell type-specific. These results, along with previously reported data, suggest that GR complex formation with itself or with another transcription factor is important for the coordinate up- and down-regulation, respectively, of the GR and c-jun genes.

Glucocorticoids coordinately regulate type I collagen pro alpha 1 promoter activity through both the glucocorticoid and transforming growth factor beta response elements: a novel mechanism of glucocorticoid regulation of eukaryotic genes

Glucocorticoids have previously have shown to decrease Type I collagen synthesis in vivo and in fibroblast cell culture. Several studies have demonstrated that glucocorticoids decrease Type I procollagen gene expression. These latter studies have included uridine incorporation into pro alpha 1 (I) and pro alpha 2 (I) mRNAs and nuclear run-off experiments. Using the ColCat 3.6 plasmid, which contains part of the 5' flanking region of the pro alpha 1 (I) collagen gene and the reporter gene, chloramphenicol acetyltransferase, the present studies demonstrate by stable transfection of fetal rat skin fibroblasts that dexamethasone down regulates the promoter activity of the pro alpha 1 (I) collagen gene. The glucocorticoid-mediated down-regulation of procollagen gene expression was demonstrated using the ColCat 3.6, 2.4, 1.7, or 0.9 plasmid. In addition, competitive oligonucleotide transfection experiments and site specific mutation of the glucocorticoid response element (GRE) in the whole ColCat 3.6 plasmid did not eliminate the effect. The possibility existed that another cis-element in the 5' flanking region of the pro alpha 1 (I) collagen gene was also required for the collagen glucocorticoid-mediated down-regulation of procollagen gene expression, since TGF-beta has been shown to stimulate in a decrease of transforming growth factor-beta (TGF-beta) secretion into the media. Gel mobility studies demonstrated that glucocorticoid treatment of rat skin fibroblasts decreased glucocorticoid receptor binding to the GRE and TGF-beta activator protein to the TGF-beta element which were brought back to control values by coordinate exogenous TGF-beta treatment. Thus the interaction of these TGF-beta molecules with cellular membrane receptors and subsequent transduction is dramatically decreased resulting in less signals to regulate collagen gene expression. These data indicate that glucocorticoids coordinately regulate procollagen gene expression through both the GRE and TGF-beta elements. Depression of procollagen gene expression by glucocorticoids through the TGF-beta element is mediated by decreased TGF-beta secretion, possibly involving a secondary effect on regulatory protein(s) encoded by noncollagenous protein gene(s). The present studies provide the basis for a novel mechanism of glucocorticoid-mediator regulation of eukaryotic genes containing the TGF-beta element.

Retinoids modulate the binding capacity of the glucocorticoid receptor and its translocation from cytosol to nucleus in liver cells

The binding capacity (Cmax) of the glucocorticoid hormone receptor (GR) was affected by vitamin A status in rat liver. In rats fed on a vitamin A-overloaded diet as well as in rats administered with retinoic acid (RA) there was an increased ratio Cmax of nuclear GR (expressed as fmol/mg liver): Cmax of cytosolic GR (expressed as fmol/mg liver) while in rats fed on a vitamin A-deficient diet this ratio was decreased. These results suggested that an increased amount of RA, resulting from either metabolization of an increased amount of dietary retinol or RA administration, enhanced the translocation of GR from the cytosolic compartment to the nuclear compartment. Moreover such an increased amount of RA could also induce the observed decreased Cmax of the total GR that we observed. These observations were similar to the well known effects of dexamethasone administration on the properties of GR. It is probable that RA, similarly to dexamethasone treatment, induces a dissociation of the tetrameric form of the cytosolic GR and thus enhances translocation of the monomeric form from cytosol to nucleus and also resulting in an increased proteolytic degradation of the receptor.