Triamcinolone acetonide regulates glucocorticoid-receptor levels by decreasing the half-life of the activated nuclear-receptor form

Therapeutic targeting of the androgen receptor (AR) and AR variants in prostate cancer

Prostate cancer (PCa) accounted for over 300 000 deaths world-wide in 2018. Most of the PCa deaths occurred due to the aggressive castration-resistant PCa (CRPC). Since the androgen receptor (AR) and its ligands contribute to the continued growth of androgen-dependent PCa (ADPCa) and CRPC, AR has become a well-characterized and pivotal therapeutic-target. Although AR signaling was identified as therapeutic-target in PCa over five-decades ago, there remains several practical issues such as lack of antagonist-bound AR crystal structure, stabilization of the AR in the presence of agonists due to N-terminus and C-terminus interaction, unfavorable large-molecule accommodation of the ligand-binding domain (LBD), and generation of AR splice variants that lack the LBD that impede the discovery of highly potent fail-safe drugs. This review summarizes the AR-signaling pathway targeted therapeutics currently used in PCa and the approaches that could be used in future AR-targeted drug development of potent next-generation molecules. The review also outlines the discovery of molecules that bind to domains other than the LBD and those that inhibit both the full length and splice variant of ARs.

Evidence for a Partially Stalled γ Rotor in F1-ATPase from Hydrogen-Deuterium Exchange Experiments and Molecular Dynamics Simulations

F₁-ATPase uses ATP hydrolysis to drive rotation of the γ subunit. The γ C-terminal helix constitutes the rotor tip that is seated in an apical bearing formed by α₃β₃. It remains uncertain to what extent the γ conformation during rotation differs from that seen in rigid crystal structures. Existing models assume that the entire γ subunit participates in every rotation. Here we interrogated E. coli F₁-ATPase by hydrogen-deuterium exchange (HDX) mass spectrometry. Rotation of γ caused greatly enhanced deuteration in the γ C-terminal helix. The HDX kinetics implied that most F₁ complexes operate with an intact rotor at any given time, but that the rotor tip is prone to occasional unfolding. A molecular dynamics (MD) strategy was developed to model the off-axis forces acting on γ. MD runs showed stalling of the rotor tip and unfolding of the γ C-terminal helix. MD-predicted H-bond opening events coincided with experimental HDX patterns. Our data suggest that in vitro operation of F₁-ATPase is associated with significant rotational resistance in the apical bearing. These conditions cause the γ C-terminal helix to get "stuck" (and unfold) sporadically while the remainder of γ continues to rotate. This scenario contrasts the traditional "greasy bearing" model that envisions smooth rotation of the γ C-terminal helix. The fragility of the apical rotor tip in F₁-ATPase is attributed to the absence of a c₁₀ ring that stabilizes the rotation axis in intact F_oF₁. Overall, the MD/HDX strategy introduced here appears well suited for interrogating the inner workings of molecular motors.

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-induced changes in glucocorticoid receptor mRNA and protein expression in the human placenta as a potential factor for altering fetal growth and development

Glucocorticoids (GCs) control essential metabolic processes in virtually every cell in the body and play a vital role in the development of fetal tissues and organ systems. The biological actions of GCs are mediated via glucocorticoid receptors (GRs), the cytoplasmic transcription factors that regulate the transcription of genes involved in placental and fetal growth and development. Several experimental studies have demonstrated that fetal exposure to high maternal GC levels early in gestation is associated with adverse fetal outcomes, including low birthweight, intrauterine growth restriction and anatomical and structural abnormalities that may increase the risk of cardiovascular, metabolic and neuroendocrine disorders in adulthood. The response of the fetus to GCs is dependent on gender, with female fetuses becoming hypersensitive to changes in GC levels whereas male fetuses develop GC resistance in the environment of high maternal GCs. In this paper we review GR function and the physiological and pathological effects of GCs on fetal development. We propose that GC-induced changes in the placental structure and function, including alterations in the expression of GR mRNA and protein levels, may play role in inhibiting in utero fetal growth.

Inhibition of proteasome-mediated glucocorticoid receptor degradation restores nitric oxide bioavailability in myocardial endothelial cells in vitro

BACKGROUND INFORMATION

Glucocorticoids (GCs), including the synthetic GC derivate dexamethasone, are widely used as immunomodulators. One of the numerous side effects of dexamethasone therapy is hypertension arising from reduced release of the endothelium-derived vasodilator nitric oxide (NO).

RESULTS

Herein, we described the role of dexamethasone and its glucocorticoid receptor (GR) in the regulation of NO synthesis in vitro using the mouse myocardial microvascular endothelial cell line, MyEND. GC treatment caused a firm decrease of extracellular NO levels, whereas the expression of endothelial NO synthase (eNOS) was not affected. However, GC application induced an impairment of tetrahydrobiopterin (BH4 ) concentrations as well as GTP cyclohydrolase-1 (GTPCH-1) expression, both essential factors for NO production upstream of eNOS. Moreover, dexamethasone stimulation resulted in a substantially decreased GR gene and protein expression in MyEND cells. Importantly, inhibition of proteasome-mediated proteolysis of the GR or overexpression of an ubiquitination-defective GR construct improved the bioavailability of BH4 and strengthened GTPCH-1 expression and eNOS activity.

CONCLUSIONS

Summarising our results, we propose a new mechanism involved in the regulation of NO signalling by GCs in myocardial endothelial cells. We suggest that a sufficient GR protein expression plays a crucial role for the management of GC-induced harmful adverse effects, including deregulations of vasorelaxation arising from disturbed NO biosynthesis.

Dietary fructose-related adiposity and glucocorticoid receptor function in visceral adipose tissue of female rats

PURPOSE

Excessive fructose intake coincides with the growing rate of obesity and metabolic syndrome, with women being more prone to these disorders than men. Findings that detrimental effects of fructose might be mediated by glucocorticoid regeneration in adipose tissue only indirectly implicated glucocorticoid receptor (GR) in the phenomenon. The aim of the present study was to elucidate whether fructose overconsumption induces derangements in GR expression and function that might be associated with fructose-induced adiposity in females.

METHODS

We examined effects of fructose-enriched diet on GR expression and function in visceral adipose tissue of female rats. Additionally, we analyzed the expression of genes involved in glucocorticoid prereceptor metabolism [11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and hexose-6-phosphate dehydrogenase], lipolysis (hormone-sensitive lipase) and lipogenesis (sterol regulatory element binding protein 1 and peroxisomal proliferator-activated receptor γ).

RESULTS

Fructose-fed rats had elevated energy intake that resulted in visceral adiposity, as indicated by increased visceral adipose tissue mass and its share in the whole-body weight. GR hormone binding capacity and affinity, as well as the expression of GR gene at both mRNA and protein levels were reduced in visceral adipose tissue of the rats on fructose diet. The glucocorticoid prereceptor metabolism was stimulated, as evidenced by elevated tissue corticosterone, while the key regulators of lipolysis and lipogenesis remained unaffected by fructose diet.

CONCLUSIONS

The results suggest that the 11βHSD1-mediated elevation of intracellular corticosterone may induce GR downregulation, which may be associated with failure of GR to stimulate lipolysis in fructose-fed female rats.

Corticosterone targets distinct steps of synaptic transmission via concentration specific activation of mineralocorticoid and glucocorticoid receptors

Hippocampal neurons are affected by chronic stress and have a high density of cytoplasmic mineralocorticoid and glucocorticoid receptors (MR and GR). Detailed studies on the genomic effects of the stress hormone corticosterone at physiologically relevant concentrations on different steps in synaptic transmission are limited. In this study, we tried to delineate how activation of MR and GR by different concentrations of corticosterone affects synaptic transmission at various levels. The effect of 3-h corticosterone (25, 50, and 100 nM) treatment on depolarization-mediated calcium influx, vesicular release and properties of miniature excitatory post-synaptic currents (mEPSCs) were studied in cultured hippocampal neurons. Activation of MR with 25 nM corticosterone treatment resulted in enhanced depolarization-mediated calcium influx via a transcription-dependent process and increased frequency of mEPSCs with larger amplitude. On the other hand, activation of GR upon 100 nM corticosterone treatment resulted in increase in the rate of vesicular release via the genomic actions of GR. Furthermore, GR activation led to significant increase in the frequency of mEPSCs with larger amplitude and faster decay. Our studies indicate that differential activation of the dual receptor system of MR and GR by corticosterone targets the steps in synaptic transmission differently.

Glucocorticoid resistance in a multiple myeloma cell line is regulated by a transcription elongation block in the glucocorticoid receptor gene (NR3C1)

Glucocorticoid (GC) effects are mediated by the glucocorticoid receptor (GR). Several studies have demonstrated that a lower number of receptors per cell were associated with poor GC response. The regulation of GR expression is complex; the levels of GR can be autologously regulated by its ligand and also by transcriptional, post-transcriptional and post-translational mechanisms. Using three human myeloma cell lines that parallel the development of GC resistance, this work describes the mechanism involved in the downregulation of GR expression. The decreased expression was neither due to mutations in the gene encoding GR, NR3C1, nor due to methylation of the promoters. A gradual decrease in NR3C1 transcripts was seen during the development of resistance, the level of expression of exon 1 to 2 RNA fragments remained the same in sensitive and resistant cell lines but a chromatin immunoprecipitation assay demonstrated that RNA polymerase II, detectable throughout exon 2 to 3 in the sensitive cells, was undetectable on exon 3 in the resistant variant, suggesting lower or no transcription at this site. These studies demonstrated that downregulation of NR3C1 mRNA in a resistant cell line involves a block to transcriptional elongation within intron B of NR3C1. This block may represent an important element in the regulation of GR expression.

Is there tachyphylaxis to intravitreal anti-vascular endothelial growth factor pharmacotherapy in age-related macular degeneration?

PURPOSE

To determine whether repetitive injections of intravitreal bevacizumab and/or triamcinolone acetate in patients with exudative age-related macular degeneration (AMD) results in a decrease in biological response.

DESIGN

Retrospective comparative case series.

PARTICIPANTS

Forty-three eyes of 43 patients with exudative AMD.

METHODS

Pre- and postinjection optical coherence tomography (OCT) sections of 43 patients with AMD were analyzed to determine the change in the biologic response after each subsequent injection of intravitreal bevacizumab (2.5 mg/100 microL), preservative-free triamcinolone acetonide (pfTA) (4.0 mg/100 microL), or a combination of bevacizumab (1.25 mg/50 microL) and pfTA (2.0 mg/50 microL). The retinal thickness of each OCT sector was determined and expressed as volume. Standardized volumetric change index (SVCI) was determined to identify a statistically significant change. Pre- and postinjection (6 weeks) SVCI differences were plotted as a function of time to determine the biological response after each intravitreal treatment.

MAIN OUTCOME MEASURES

Change in SVCI after intravitreal injections and the number of injections required to decrease the biological response by 50% (INJ(50)).

RESULTS

There was no difference in the age, gender, and preinjection thickness of the retina in each of the 3 groups. The SVCI after intravitreal bevacizumab injections decreased, indicating a possible tachyphylactic response to bevacizumab. This decrease in biological response was partially alleviated with the addition of pfTA. Combination of pfTA and bevacizumab increased the INJ(50) from 2.9 with bevacizumab alone to 5.1 injections. A biphasic biologic response was observed with pfTA characterized by a rapid increase in efficacy with the second injection, peaking at the third injection and gradually decreasing afterward.

CONCLUSIONS

Repeated intravitreal injections of bevacizumab in exudative AMD seemed to be associated with decreased bioefficacy. However, combined pharmacotherapy with triamcinolone acetate lessened this effect. Thus, multitargeted pharmacotherapy in exudative AMD may have a therapeutic benefit.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

TNF-alpha and glucocorticoid receptor interaction in L6 muscle cells: a cooperative downregulation of myosin heavy chain

Sepsis is associated with increased expression of TNF-alpha with subsequent activation of nuclear factor-kappa B (NF-kappaB). The glucocorticoid receptor (GR) and NF-kappaB function as mutual antagonists and induction of the latter is believed to play a major role in the acquired glucocorticoid resistance that occurs in some septic patients. GR expression and function has been reported to be elevated in septic muscle suggesting a limited effect of the activated NF-kappaB on GR function in this context. In this study, the L6 myocyte cell line was used as an in vitro model for a sepsis-like condition in skeletal muscle. While short or long term treatment with TNF-alpha had no effect on GR expression, glucocorticoid-dependent downregulation of GR occurred with a kinetic profile that is accelerated relative to that observed in most cells. This downregulation was not affected by co-treatment or prior priming of L6 cells with TNF-alpha. The synthetic glucocorticoid, dexamethasone (DEX) blunted TNF-alpha-stimulated NF-kappaB activation in L6 cells. However, although effective at activating an NF-kappaB transcriptional response, TNF-alpha treatment exerted a minimal effect in myoblasts and no effect in myotubes on GR transcriptional activity. This limited impact of TNF-alpha on GR activity was not universal as TNF-alpha and DEX exerted an additive effect on the reduction in myosin heavy chain (MHC) protein expression caused by either agent alone. Thus, the selective perseverance of GR function in the presence of increased levels of glucocorticoids and TNF-alpha during sepsis or other inflammatory states may exacerbate muscle protein breakdown.

Modeling receptor/gene-mediated effects of corticosteroids on hepatic tyrosine aminotransferase dynamics in rats: dual regulation by endogenous and exogenous corticosteroids

Receptor/gene-mediated effects of corticosteroids on hepatic tyrosine aminotransferase (TAT) were evaluated in normal rats. A group of normal male Wistar rats were injected with 50 mg/kg methylprednisolone (MPL) intramuscularly at the nadir of their plasma corticosterone (CST) rhythm (early light cycle) and sacrificed at various time points up to 96 h post-treatment. Blood and livers were collected to measure plasma MPL, CST, hepatic glucocorticoid receptor (GR) mRNA, cytosolic GR density, TAT mRNA, and TAT activity. The pharmacokinetics of MPL showed bi-exponential disposition with two first-order absorption components from the injection site and bioavailability was 21%. Plasma CST was reduced after MPL dosing, but resumed its daily circadian pattern within 36 h. Cytosolic receptor density was significantly suppressed (90%) and returned to baseline by 72 h resuming its biphasic pattern. Hepatic GR mRNA follows a circadian pattern which was disrupted by MPL and did not return during the study. MPL caused significant down-regulation (50%) in GR mRNA which was followed by a delayed rebound phase (60-70 h). Hepatic TAT mRNA and activity showed up-regulation as a consequence of MPL, and returned to their circadian baseline within 72 and 24 h of treatment. A mechanistic receptor/gene-mediated pharmacokinetic/pharmacodynamic model was able to satisfactorily describe the complex interplay of exogenous and endogenous corticosteroid effects on hepatic GR mRNA, cytosolic free GR, TAT mRNA, and TAT activity in normal rats.

Opercular epithelial cells: a simple approach for in vitro studies of cellular responses in fish

This study evaluated the efficacy of fish opercular external (skin) and inner (opercular membrane) epithelium as an in vitro model for toxic and other substances studies. The rainbow trout (Oncorhynchus mykiss) operculum was cultured in 12-well dishes containing sterile Leibovitz 15 (L-15) supplemented with glutamine medium during 24h at 9 degrees C, and the effect of copper, a toxic agent, and/or cortisol, an endogenous agent, on the epithelial cells was analyzed using light microscopy techniques. The opercula were submitted to four treatments: (i) control (Cont), L-15 medium only, (ii) 0.28 microM cortisol (Cort), (iii) 100 microM CuSO(4) (Cu), and (iv) 0.28 microM cortisol+100 microM CuSO(4) (Cort-Cu). The tissue condition after 24h incubation was analyzed by staining the mucous cells for neutral and acid mucosubstances. Cellular necrosis was evaluated by measuring the lactate dehydrogenase (LDH) leakage at 12 and 24h incubation. Cellular proliferation, apoptosis, metallothionein (MT) and glucocorticoid receptor (GR) expression were evaluated by immunohistochemistry. The LDH leakage was higher and the proliferating cell nuclear antigen (PCNA) positive-stained cells were lower in Cu treatment in both, epidermis and opercular membrane. Apoptotic cells in the opercular membrane were higher in the Cort and Cort-Cu treatments while, in the epidermis, they were higher in Cu and Cort-Cu treatments. GR-positive stained cells decreased significantly in all treatments in both epithelia and the MT-positive cells increased in the Cu and Cort-Cu treated groups. Copper showed to be a potent toxic stressor killing the cells via necrosis, decreasing the number of PCNA-positive cells and inducing MT synthesis while cortisol did not affect the MT synthesis, although it might stimulate apoptosis. The results are evidence that the opercular epithelia serve as a suitable model for studying in vitro effects of toxic agents, as well as endogenous factors on the cellular responses without interference of the physiological state of fish being useful to predict in vivo toxicity.

Expression and regulation of glucocorticoid receptor in human placental villous fibroblasts

The human placenta is a glucocorticoid (GC)-responsive organ consisting of multiple cell types including smooth muscle cells, fibroblasts, and trophoblast that demonstrate changes in gene expression after hormone treatment. However, little is known about the relative expression or activity of the GC receptor (GR) among the various placental cell types. Normal term human placentas were examined by immunohistochemistry using either GR phosphorylation site-specific antibodies that are markers for various activation states of the GR or a GR antibody that recognizes the receptor independent of its phosphorylation state (total GR). We found strong total GR and phospho-GR immunoreactivity in stromal fibroblasts of terminal villi, as well as perivascular fibroblasts and vascular smooth muscle cells of the stem villi. Lower levels of both total GR and phospho-GR were found within cytotrophoblast cells relative to fibroblasts, whereas syncytiotrophoblast showed very little total GR or phospho-GR immunoreactivity. This pattern holds true for immunoblot analysis of extracts from cell fractions cultured ex vivo. In cultured placental fibroblasts, phosphorylation of GR increased upon short-term GC treatment, consistent with a role for GR phosphorylation in receptor transactivation. Total GR levels were reduced by nearly 90% after long-term hormone treatment; however, this down-regulation was independent of changes in GR mRNA levels. These findings demonstrate that GR levels in fibroblasts can be modulated by changes in hormone exposure. Such cell type-specific differences in GR protein expression and phosphorylation may provide the means of differentially regulating the GC response among the cells of the human placenta.

Leukemia inhibitory factor regulates glucocorticoid receptor expression in the hypothalamic-pituitary-adrenal axis

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine belonging to the gp130 family. LIF is induced peripherally and within the brain during inflammatory or chronic autoimmune diseases and is a potent stimulator of the hypothalamic-pituitary-adrenal (HPA) axis. Here we investigated the role of LIF in mediating glucocorticoid receptor (GR) expression in the HPA axis. LIF treatment (3 microg/mouse, i.p.) markedly decreased GR mRNA levels in murine hypothalamus (5-fold, P < 0.01) and pituitary (1.7-fold, P < 0.01) and downregulated GR protein levels. LIF decreased GR expression in murine corticotroph cell line AtT20 within 2 h, and this effect was sustained for 8 h after treatment. LIF-induced GR mRNA reduction was abrogated in AtT20 cells overexpressing dominant-negative mutants of STAT3, indicating that intact JAK-STAT signaling is required to mediate LIF effects on GR expression. Conversely, mice with LIF deficiency exhibited increased GR mRNA levels in the hypothalamus and pituitary (3.5- and 3.5-fold, respectively; P < 0.01 for both) and increased GR protein expression when compared with wild-type littermates. The suppressive effects of dexamethasone on GR were more pronounced in LIF-null animals. These data suggest that LIF maintains the HPA axis activation by decreasing GR expression and raise the possibility that LIF might contribute to the development of central glucocorticoid resistance during inflammation.

Three mechanisms are involved in glucocorticoid receptor autoregulation in a human T-lymphoblast cell line

Glucocorticoids up-regulate the glucocorticoid receptor (GR) in the human T-lymphoblast cell line CEM-C7. One mechanism for the up-regulation of the GR protein is the well-known up-regulation of GR transcripts. We have investigated the effect of other factors on the up-regulation. At least three promoters (1A, 1B, and 1C) exist, which give rise to GR transcripts with different exon 1 sequences. Transcripts with different exon 1 sequences have similar stabilities. Glucocorticoids have little, if any, effect on mRNA stability. In transfection experiments of the GR-deficient mouse fibroblast cell line E8.2, different exon 1 sequences furthermore caused no significant differences in the translational efficiencies of GR transcripts. However, the ratio between the concentrations of the glucocorticoid receptor B (GR-B) isoform and the glucocorticoid receptor A (GR-A) isoform was higher for transcripts containing the exon 1A3 sequence arising from promoter 1A than in transcripts containing exon 1 sequences from promoters 1B and 1C. Because the GR-B isoform is more active in transactivation then GR-A, this would tend to fine-tune glucocorticoid responsiveness of CEM-C7 cells, which express exon 1A3-containing transcripts. We also found that glucocorticoids do not decrease the stability of the GR protein in CEM-C7 cells. In contrast to other cell lines that downregulate GR expression in response to glucocorticoids, CEM-C7 lymphoblasts possess three mechanisms ensuring high glucocorticoid responsiveness: an up-regulation of GR mRNA by glucocorticoids, no destabilization of GR protein by glucocorticoids, and a high activity of promoter 1A with concomitant high expression of the GR-B isoform.

The origin and functions of multiple human glucocorticoid receptor isoforms

Glucocorticoid hormones are necessary for life and are essential in all aspects of human health and disease. The actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), which binds glucocorticoid hormones and regulates gene expression, cell signaling, and homeostasis. Decades of research have focused on the mechanisms of action of one isoform of GR, GRa. However, in recent years, increasing numbers of human GR (hGR) isoforms have been reported. Evidence obtained from this and other laboratories indicates that multiple hGR isoforms are generated from one single hGR gene via mutations and/or polymorphisms, transcript alternative splicing, and alternative translation initiation. Each hGR protein, in turn, is subject to a variety of posttranslational modifications, and the nature and degree of posttranslational modification affect receptor function. We summarize here the processes that generate and modify various hGR isoforms with a focus on those that impact the ability of hGR to regulate target genes. We speculate that unique receptor compositions and relative receptor proportions within a cell determine the specific response to glucocorticoids. Unchecked expression of some isoforms, for example hGRbeta, has been implicated in various diseases.

Effects of chronic and acute training on glucocorticoid receptors concentrations in rats

The effects of chronic endurance training and acute exercise on glucocorticoid receptors were investigated in rats. For chronic endurance training, rats were exposed to progressive running training on a motor-driven treadmill for 3, 5 and 7 weeks, twice a day and 6 days a week. The samples were taken, 34-36 hours after the last exercise bout. Some of the 7-week training rats were killed by decapitation 7 days following the last exercise bout. The glucocorticoid receptors in hepatic cytosol in 5-week and 7-week rats decreased as compared to the sedentary control. There was no significant difference between the glucocorticoid receptors in hepatic cytosol in some of the 7-week rats those who had stopped training for 7 days and those in the controls. The chronic endurance training did not lead to change of the apparent dissociation constant (Kd). The changes of glucocorticoid receptors after acute exercise have also been investigated and it showed profound decreases of glucocorticoid receptors in renal and myocardial cytosol in low intensity (swimming without an extra weight for 60 minutes) and high intensity (swimming with a weight equal to 6% of body mass for 60 minutes) training groups. The decreases in glucocorticoid receptors in renal and myocardial cytosol were less prominent after low intensity training. These results demonstrated that both acute exercise training and chronic endurance training could lead to a decrease in glucocorticoid receptors, which was in a training intensity- and training load volume-dependent manner, and the changes in glucocorticoid receptors during exercise training were reversible.

15-Deoxy-Δ12,14-Prostaglandin J2 Inhibits Glucocorticoid Binding and Signaling in Macrophages through a Peroxisome Proliferator-Activated Receptor γ-Independent Process

15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is involved in the control of inflammatory reaction. We tested the hypothesis that 15d-PGJ(2) would exert this control in part by modulating the sensitivity of inflammatory cells to glucocorticoids. Human U937cells and mouse RAW 264.7 cells were exposed to 15d-PGJ(2), and binding experiments were performed with [(3)H]dexamethasone as a glucocorticoid receptor (GR) ligand. 15d-PGJ(2) caused a transient and concentration-dependent decrease in [(3)H]dexamethasone-specific binding to either cells through a decrease in the number of GR per cell without significant modification of the K(d) value. These changes were related to functional alteration of the GR rather than to a decrease in GR protein. They did not require the engagement of peroxisome proliferator-activated receptor gamma (PPARgamma), because the response to 15d-PGJ(2) was neither mimicked by the PPARgamma agonist ciglitazone nor prevented by the PPARgamma antagonist bisphenol A diglycidyl ether. 15d-PGJ(2) altered GR possibly through the interaction of its cyclopentenone ring with GR cysteine residues because the cyclopentenone ring per se could mimic the effect of 15d-PGJ(2), and modification of GR cysteine residues with methyl methanethiosulfonate suppressed the response to 15d-PGJ(2). Finally, 15d-PGJ(2)-induced decreases in glucocorticoid binding to GR resulted in parallel decreases in the ability of GR to activate the transcription of a glucocorticoid-inducible reporter gene and to reduce the expression of monocyte chemoattractant protein-1. Together these data suggest that 15d-PGJ(2) limits glucocorticoid binding and signaling in monocytes/macrophages through a PPARgamma-independent and cyclopentenone-dependent mechanism. It provides a way in which 15d-PGJ(2) would exert proinflammatory activities in addition to its known anti-inflammatory activities.

Molecular mechanisms of glucocorticoid action and resistance

The actions of glucocorticoid hormones are mediated by an intracellular receptor, the glucocorticoid receptor (GR). The mechanism of action of this ligand-inducible transcription factor is discussed, focusing on mechanisms of glucocorticoid resistance. Three mechanisms are highlighted: ligand-induced down-regulation of the receptor, the dominant-negative inhibition by the beta-isoform of the receptor, and repression by the transcription factor NF-kappa B. It has been shown that these mechanisms can significantly inhibit glucocorticoid signaling, and could therefore seriously decrease the efficacy of glucocorticoids used clinically.

Glucocorticoid receptors in hippocampal neurons that do not engage proteasomes escape from hormone-dependent down-regulation but maintain transactivation activity

The glucocorticoid receptor (GR) protein is subjected to hormone-dependent down-regulation in most cells and tissues. This reduction in receptor levels that accompanies chronic hormone exposure serves to limit hormone responsiveness and operates at transcriptional, posttranscriptional, and posttranslational levels. The ability of glucocorticoid hormones to trigger GR down-regulation may be not universal, particularly in mature and developing neurons in which conflicting results regarding hormone control of GR protein have been reported. We find that endogenous GR is not down-regulated in the HT22 mouse hippocampal cell line and in primary hippocampal neurons derived from embryonic rats. Because GR has the capacity to be ubiquitylated in HT22 cells, receptor down-regulation must be limited by defects in either targeting of polyubiquitylated receptor to the proteasome or processing of the targeted receptor by the proteasome. Despite the lack of GR down-regulation in the HT22 cells, glucocorticoid-induced transcription from transiently transfected templates is attenuated upon prolonged hormone treatment. This termination of GR transactivation is not due to inefficient nuclear import or nuclear retention of the receptor. Furthermore, GR efficiently exports from HT22 cell nuclei in hormone-withdrawn cells, indicating that the receptor has access to both nuclear and cytoplasmic degradation pathways. Our results suggest that appropriate maturation of proteasomal degradative or targeting activities may be required, particularly in hippocampal neurons, for hormone-dependent down-regulation of GR.

Proteasome-mediated glucocorticoid receptor degradation restricts transcriptional signaling by glucocorticoids

Ligand-dependent down-regulation of the glucocorticoid receptor (GR) has been shown to limit hormone responsiveness, but the mechanisms involved in this process are poorly understood. The glucocorticoid receptor is a phosphoprotein that upon ligand binding becomes hyperphosphorylated, and recent evidence indicates that phosphorylation status of the glucocorticoid receptor plays a prominent role in receptor protein turnover. Because phosphorylation is a key signal for ubiquitination and proteasomal catabolism of many proteins, we evaluated whether the ubiquitin-proteasomal pathway had a role in glucocorticoid receptor down-regulation and the subsequent transcriptional response to glucocorticoids. Pretreatment of COS-1 cells expressing mouse glucocorticoid receptor with the proteasome inhibitor MG-132 effectively blocks glucocorticoid receptor protein down-regulation by the glucocorticoid dexamethasone. Interestingly, both MG-132 and a second proteasome inhibitor beta-lactone significantly enhanced hormone response of transfected mouse glucocorticoid receptor toward transcriptional activation of glucocorticoid receptor-mediated reporter gene expression. The transcriptional activity of the endogenous human glucocorticoid receptor in HeLa cells was also enhanced by MG-132. Direct evidence for ubiquitination of the glucocorticoid receptor was obtained by immunoprecipitation of cellular extracts from proteasome-impaired cells. Examination of the primary sequence of mouse, human, and rat glucocorticoid receptor has identified a candidate PEST degradation motif. Mutation of Lys-426 within this PEST element both abrogated ligand-dependent down-regulation of glucocorticoid receptor protein and simultaneously enhanced glucocorticoid receptor-induced transcriptional activation of gene expression. Unlike wild type GR, proteasomal inhibition failed to enhance significantly transcriptional activity of K426A mutant GR. Together these findings suggest a major role of the ubiquitin-proteasome pathway in regulating glucocorticoid receptor protein turnover, thereby providing a mechanism to terminate glucocorticoid responses.

Effect of glucocorticoid therapy on glucocorticoid receptors in children with autoimmune diseases

Low-dose glucocorticoids (GC) achieve their action completely by classical genomic effects, mediated by the glucocorticoid receptor (GCR). In high doses of GC, nongenomic effects have also been found, but it is still unclear to what extent they contribute to a beneficial outcome. In this study, we present a determination of the number of lymphocyte GCR sites and the binding affinity in healthy children and children with autoimmune diseases. We further assess the effect of GC administration, especially of high-dose pulse therapy on the number of binding sites. The number of GCR sites per cell was analyzed with [(3)H]-dexamethasone radioligand binding assay and binding affinity (Kd given in nM) in peripheral blood mononuclear cells isolated from 48 healthy children and 35 patients. The patients were divided into three groups based on GC treatment: 0 mg/kg (group 1), 0.01-0.3 mg/kg orally (group 2), and 10-15 mg/kg i.v. pulse therapy (group 3) of prednisolone equivalent per day. Gender- and age-independent normal values of 4338 +/- 1687 sites/lymphocytes and Kd 6.7 +/- 2.2 nM were found. At 3463 +/- 1574, the number of receptor sites in patients without GC (group 1) was significantly lower than that of healthy volunteers (p < 0.05). In patients receiving GC treatment, this value was reduced to 2952 +/- 512 (group 2). Significant down-regulation to a minimum of 479 +/- 168 (group 3) was found after pulse therapy compared with untreated patients (p < 0.01). In pulse therapy, GC lead to a fast and dramatic receptor down-regulation. We suppose that the increase in therapeutic success of pulse-therapy may partly be mediated through additional nongenomic effects.

Effects of copper on cortisol receptor and metallothionein expression in gills of Oncorhynchus mykiss

Effects of waterborne Cu (2.4 microM) on the expression of glucocorticoid receptor (GR) and metallothionein (MT) in the branchial epithelium of freshwater rainbow trout (Oncorhynchus mykiss) was studied by immunocytochemistry. After 5 days of Cu exposure, the number of GR-immunoreactive (GR-ir) cells in the gill epithelium had decreased, whereas the number of MT-ir cells had increased. Localization of GR in chloride cells was achieved by double staining for Na(+)/K(+)-ATPase; other cell types were identified on the basis of their topology. GRs were present in the chloride cells in both the filaments and lamellae, in respiratory cells in the lamellae, in pavement cells, basal layer cells and undifferentiated cells in the filaments. Co-localization of Na(+)/K(+)-ATPase and MT revealed chat MT was expressed in chloride cells, both in filaments and lamellae. Occasionally, MT immunoreactivity was found in pavement cells and in undifferentiated cells. By double staining for Na(+)/K(+)-ATPase and GR, for Na(+)/K(+)-ATPase and MT and for GR and MT, we can conclude that after 5 days of Cu stress there are chloride cells that express GR and MT, GR or MT alone or neither of the two proteins. This apparent functional heterogeneity of branchial chloride cells may reflect a limited window when chloride cell subpopulations show an adaptive response to Cu.

Different regulation of cardiac and renal corticosteroid receptors in aldosterone-salt treated rats: effect of hypertension and glucocorticoids

This study analysed the regulation of cardiac mineraloreceptor (MR) and glucoreceptor (GR) in aldosterone-salt treatment (AST). AST causes hypertension, left ventricle (LV) hypertrophy and decreases plasma corticosterone level. Ribonuclease protection assay and Western blot analysis showed a rise of MR mRNA (1.5- and 1.4-fold at day 15 and 30, respectively) and protein levels (1.8- and 4.1-fold at day 30 and 60, respectively) in the LV, but not in either the right ventricle (RV) or in kidney of treated rats. Addition of MR antagonist spironolactone (20 mg/kg/day) for 30 days failed to prevent these changes but was able to reduce AST-induced cardiac fibrosis. Similar hypertension-induced MR upregulations were observed in the LV of AngII-hypertensive rats and of 12-week-old SHR when compared to 4-week-old prehypertensive SHR. AST also enhanced left ventricular GR mRNA (2.0- and 3.0-fold at day 7 and 15, respectively) and protein contents (2.0- and 1.7-fold at day 30 and 60, respectively). In contrast to MR, GR levels were also upregulated in both RV and kidney. Such an upregulation was equally observed at mRNA and protein levels in LV, RV and kidney after adrenalectomy (15 days) and was prevented in both tissues after glucocorticoid replacement (adrenalectomy + dexamethasone at 100 micro g/kg/day for 15 days). Therefore, MR level may be controlled by hemodynamical factors whereas that of GR depends upon glucocorticoids level.

Discrimination between changes in glucocorticoid receptor expression and activation in rat brain using western blot analysis

These studies investigated autoregulation of glucocorticoid receptor (GR) protein expression and activation in rat brain using western blot methodology. By comparing GR immunoblot reactivity present in various tissue subcellular preparations we were able to discriminate between corticosterone-induced changes in GR activation or GR protein expression. Our cytosolic tissue preparation yielded a similar pattern of treatment effects on relative GR as measured by receptor binding assay or western blot. In both cases, short-term adrenalectomy (18 h) produced no change in cytosolic GR. On the other hand, long-term adrenalectomy (3-14 days) resulted in a large increase in cytosolic GR, whereas acute (1-2 h) treatment with high dose corticosterone produced a large decrease in cytosolic GR. Western blot measurement of GR levels in a nuclear extract or whole-cell extract from the same brains indicated that acute corticosterone treatment produced a large increase in nuclear GR and no change in whole-cell GR. Thus, all of the decrease in cytosolic GR observed after acute corticosterone treatment could be accounted for by receptor redistribution to the nuclear tissue fraction as opposed to rapid receptor protein downregulation. Long-term treatment of rats with adrenalectomy or high dose corticosterone produced a large increase and decrease, respectively, in whole-cell GR, indicating genuine changes in receptor protein expression. These studies indicate that in vivo regulation of GR protein expression in the rat brain can be studied using western blot analysis of a whole-cell tissue preparation. This procedure has an important advantage over receptor binding studies in that GR protein expression can be measured in adrenal-intact rats. These studies also support the validity of using cytosolic receptor binding assays to estimate relative changes in GR occupation/activation when appropriate comparison groups are included.

Responsiveness of gill Na+/K+-ATPase to cortisol is related to gill corticosteroid receptor concentration in juvenile rainbow trout

A positive relationship between receptor concentration and tissue responsiveness is an often-assumed and rarely tested principle in endocrinology. In salmonids, seasonal changes in levels of plasma cortisol and gill corticosteroid receptors (CRs) during the spring indicate a potential role for this hormone in the parr-smolt transformation. It is not known whether these seasonal changes result in alterations in gill responsiveness to cortisol. The relationship between CR concentration and tissue responsiveness was, therefore, examined in the gills of juvenile rainbow trout (Oncorhynchus mykiss). Gill CR concentration (Bmax) and affinity (Kd) were assessed using a radioligand binding assay with the synthetic glucocorticoid triamcinolone acetonide. Gill responsiveness to cortisol was quantified by measuring in vitro Na+/K+-ATPase activity. Gill CR concentration was manipulated by stress or hormonal treatments. Repeated handling stresses resulted in a significant reduction in CR numbers. The decrease in CR Bmax corresponded to a reduction in gill responsiveness to cortisol. Triiodothyronine, but not growth hormone, treatment was found to increase CR Bmax significantly. The increase in CR numbers was correlated with a marked increase in gill responsiveness to cortisol. A significant positive linear relationship exists between the in vitro gill Na+/K+-ATPase activity response to cortisol and CR Bmax (r2=0.614, P&lt;0.001). We have demonstrated that binding sites for cortisol in the gills of rainbow trout have high affinity, high specificity and saturable binding and that the number of binding sites is correlated with the tissue response to cortisol.

Specific deactivation of the mouse mammary tumor virus long terminal repeat promoter upon continuous hormone treatment

We have studied the transcriptional behavior of the mouse mammary tumor virus long repeat (MMTV-LTR) promoter during a prolonged exposure to glucocorticoids. When integrated into XC-derived cells, MMTV-LTR expression reached its maximum during the first day of dexamethasone treatment, but longer exposure to the hormone resulted in the deactivation of the promoter. In contrast, glucocorticoid-responsive resident genes or MMTV-based transiently transfected plasmids maintained or even increased their mRNA levels during the same period of hormone treatment. An integrated chimeric construct containing the hormone-responsive elements from MMTV-LTR but in different sequence context became also deactivated after a prolonged hormone treatment but with a deactivation kinetics significantly slower than constructs containing the entire, chromatin-positioning MMTV-LTR sequence. The decrease on MMTV-LTR-driven transcription was concomitant with a parallel closure of the MMTV-LTR chromatin and with a decrease in glucocorticoid receptor (GR) concentration in the cell. We concluded that the chromatin-organized MMTV-LTR promoter is particularly sensitive to any decrease on GR levels. We propose that chromatin structure may contribute decisively to the differential expression of MMTV-LTR by two mechanisms: limiting MMTV-LTR accessibility to activating transcription factors and accelerating its shutting down upon a decrease on GR levels.

Differential effects of agonist and antagonists on autoregulation of glucocorticoid receptors in a rat colonic adenocarcinoma cell line

The relative abilities of a potent glucocorticoid receptor (GR) agonist (RU 28362), a weak GR agonist (aldosterone) and a potent GR antagonist (RU 38486) to promote in vivo activation/transformation and subsequent down-regulation of GR mRNA and protein levels were compared using the PROb rat colonic adenocarcinoma cell line. In vivo activation, which is followed immediately by nuclear translocation, by these ligands (1 microM) was evaluated in terms of their abilities to deplete cytoplasmic GR protein levels after a 30 min incubation period. Western blotting experiments with the anti-GR monoclonal antibody BuGR2 demonstrated that a brief incubation with RU 28362 resulted in nearly complete depletion of cytoplasmic GR, whereas incubation with aldosterone resulted in a 50% depletion of the cytoplasmic GR protein. Incubation with RU 38486 was even more effective than aldosterone in promoting this key step in the GR pathway. Prolonged treatment (18 h) with RU 28362 resulted in significant down-regulation of GR mRNA and total cellular GR protein levels. Similar incubation with aldosterone resulted in a transient decrease in the GR mRNA level and also down-regulated the total GR protein level. Although prolonged incubation with RU 38486 did not result in detectable down-regulation of the GR mRNA level, this antagonist very effectively down-regulated total cellular GR protein levels. Taken collectively, these data demonstrate that agonists capable of promoting in vivo activation (and subsequent nuclear translocation) of GR are also effective at down-regulating GR at both the mRNA and protein levels. Although the antagonist RU 38486 is also capable of down-regulating GR protein levels by shortening the half-life of the receptor, it appears to be incapable of altering the rate of transcription of the GR gene. Glucocorticoid target tissue sensitivity may thus be decreased via two independent mechanisms: agonist-induced repression of GR gene transcription; and/or ligand-induced degradation of total cellular GR protein levels.

Mouse glucocorticoid receptor phosphorylation status influences multiple functions of the receptor protein

Although studies have shown that the mouse glucocorticoid receptor (mGR) contains eight phosphorylation sites (Bodwell, J. E., Ortí, E. , Coull, J. M., Pappin, D. J. C., Smith, L. I., and Swift, F. (1991) J. Biol. Chem. 266, 7549-7555), the effect of phosphorylation on receptor function is unclear. We have examined the consequences of single or multiple phosphorylation site mutations on several properties of mGR including receptor expression, ligand-dependent nuclear translocation, hormone-mediated transactivation, ligand-dependent down-regulation of mGR, and receptor protein half-life. Mutations had little effect on receptor expression, subcellular distribution, ligand-dependent nuclear translocation, or on the ability to activate hormone-mediated transcription from a complex (murine mammary tumor virus) promoter. In contrast, the phosphorylation status of the mGR had a profound effect on the ability to transactivate a minimal promoter containing simple glucocorticoid response elements after hormone administration. Similarly, ligand-dependent down-regulation by glucocorticoids of both receptor mRNA and protein was abrogated in mutants containing three or more phosphorylation site alterations. Finally, we show that the phosphorylation status of mGR has a profound effect on the stability of the glucocorticoid receptor protein. Receptors containing seven or eight mutated sites have a markedly extended half-life and do not show the ligand-dependent destabilization seen with wild type receptor. These data show that receptor phosphorylation may play a crucial role in regulating receptor levels and hence control receptor functions.

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.

Review of the interaction between TCDD and glucocorticoids in embryonic palate

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant that produces adverse biological effects including developmental toxicity and teratogenesis. In the mouse embryo, TCDD induces cleft palate and hydronephrosis. The synthetic glucocorticoid, hydrocortisone (HC), induces cleft palate and a potent, synergistic interaction has been observed between TCDD and HC in C57BL/6N embryonic mice. The morphology and etiology of TCDD- and HC-induced clefts are distinctly different with formation of small palatal shelves following HC exposure and failure of normally-sized shelves to fuse after TCDD treatment. Each exposure also alters expression of several growth factors. When EGF, TGF alpha, EGF receptor, and the TGF beta's are considered as a combinatorial, interacting set of regulators, TCDD and HC each produce a unique pattern of increased and/or decreased expression across the set. The interaction of HC and TCDD results in a cleft palate whose etiology most closely resembles that observed after HC exposure, i.e. small palatal shelves. HC+TCDD-exposure also produces a pattern of growth factor expression which closely resembles that seen after HC. Both TCDD and HC act through receptor-mediated mechanisms and each compound has its own receptor. The Ah receptor (AhR) binds TCDD and the glucocorticoid receptor (GR) binds HC. On gestation day (GD) 14, in the embryonic palate exposed to TCDD, the AhR was downregulated and the GR expression increased. Conversely, following HC exposure, the GR was downregulated and AhR levels were elevated. HC+TCDD produced increased expression of both receptors and this pattern would be predicted to produce HC-like clefts as the GR-mediated responses would result in small palatal shelves. The observed cross-regulation of the receptors is believed to be important in the synergistic interaction between TCDD and HC for the induction of cleft palate.

Potential mechanisms underlying autoregulation of glucocorticoid receptor mRNA levels in the DHD/K12/PROb rat colonic adenocarcinoma cell line

The DHD/K12/PROb rat colonic epithelial cell line, which was originally derived from a chemically induced adenocarcinoma, expresses functional glucocorticoid receptors (GR) and has been reported to be growth inhibited by glucocorticoid agonists. In the present study the potential mechanisms underlying corticosteroid-mediated autoregulation of GR mRNA levels in this colonic cell line were investigated. The GR mRNA levels in the various treatment groups were quantitated via the ribonuclease protection assay using a specific 32P-cRNA probe. Time-course experiments demonstrated that in contrast to several other cell lines that are also growth inhibited by glucocorticoids, treatment of confluent monolayers of PROb cells with the pure GR agonist RU 28362 (1 microM) elicits a rapid and significant (65%) down-regulation of GR mRNA levels that is sustained for at least 36 h. This down-regulation, which is also elicited to a lesser extent by weaker GR agonists including corticosterone and aldosterone, is blocked by the GR antagonist RU 38486. The protein synthesis inhibitor cycloheximide was utilized to demonstrate that the initial phase (6 h) of agonist-mediated down-regulation occurs independently of ongoing protein synthesis, although new protein synthesis, perhaps of the GR protein itself, is required to maintain this down-regulation. Although agonist-mediated down-regulation in these cells probably occurs primarily at the level of GR gene transcription, inhibition of ongoing RNA synthesis with actinomycin D or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) demonstrated that during the initial phase (1 h) of this down-regulation, but not following maximal (18 h) down-regulation, RU 28362 treatment also significantly reduces the stability of the GR mRNA.

Gamma interferon down-regulates glucocorticoid receptor expression and attenuates hormone action in a human osteosarcoma cell line

The effect of gamma interferon (IFN) on glucocorticoid receptor (GR) expression was studied in HOS-8603 cells, a human osteogenic sarcoma cell line. Treatment of HOS-8603 cells with IFN resulted in down-regulation of GR number, with no change in the binding affinity for glucocorticoids. The maximum decrease in receptor binding was evident at 10 IU/ml IFN concentration. Time-course studies revealed that the effect reached a maximum at 36 h treatments. To clarify the molecular basis for the down-regulation of GR by IFN, change in GR mRNA levels was further investigated by RNA blot hybridization analysis. It was found that there also existed a time-dependent decrease in GR mRNA levels in HOS-8603 cells after treatment with IFN. In the presence of IFN, the inhibitory effect of glucorticoids on HOS-8603 cell proliferation was blunted. Moreover, the induction of alkaline phosphatase (AKP) activity by glucocorticoids was attenuated in response to IFN treatment. These data suggest that IFN may influence GR activity which at least partially occurs at mRNA levels, and that the decrease in receptor activity in HOS-8603 cells parallels with the decrease in glucocorticoid-mediated functional responses.

Subcellular distribution of the glucocorticoid receptor and evidence for its association with microtubules

The cellular distribution of the glucocorticoid receptor (GR) has not yet been firmly established. The extensive literature indicates that GR is present both in the cytoplasm and the cell nucleus, however, some studies have failed to detect cytoplasmic GR. It is still controversial as to whether GR is randomly diffusing in the cytoplasm and nucleus, or if the GR-distribution is organized or controlled in some way, which may be of importance for the transduction of glucocorticoid effects to cells. There is evidence that both non-activated and activated GR is associated with the plasma membrane, a number of cytoplasmic organelles and the nucleus. Both morphological and biochemical evidence show that GR is associated with microtubules during different stages of the cell cycle, i.e. GR co-localizes, co-purifies and co-polymerizes with tubulin. This indicates that GR is structurally linked to the intracellular MT-network which may be of importance in the mechanism of action of glucocorticoid hormones. The literature in this field is reviewed including the reported data on subcellular GR-localization.

Calcium and protein kinase C regulation of the glucocorticoid receptor in mouse corticotrope tumor cells

The effect of increasing intracellular free calcium and activating protein kinase C on glucocorticoid receptor (GR) expression was investigated in AtT-20 cells, a mouse corticotrope tumor cell line. Treatment of AtT-20 cells with the calcium ionophore A23187 induced a rapid time- and dose-dependent decrease in [3H]dexamethasone ([3H]DEX) binding when measured in intact cells. Binding fell to 16% of control following 3 h of treatment with 10 microM A23187. In contrast, A23187 did not acutely effect steady state levels of GR mRNA, although levels fell to 76 +/- 1% of control after 8-15 h of treatment. Scatchard analysis of A23187 treated cultures demonstrated a decrease in GR binding capacity but no change in affinity for [3H]DEX. Acute inhibition of protein synthesis with cycloheximide had no effect on [3H]DEX binding, suggesting that the calcium-dependent decrease was not simply due to inhibition of GR protein synthesis. In contrast to the A23187 induced decrease in [3H]DEX binding in intact cells, when binding was measured in cytosol extract from A23187 treated cultures there was no decrease. These data suggest that the A23187 induced decrease in GR binding in whole cells is not due to a decrease in GR protein but reversible conversion of the receptor to a non-binding form. Inducing calcium influx only through L-type voltage-dependent calcium channels with BAY K8644 also decreased [3H]DEX binding at AtT-20 cells, though the effect was less than that induced by A23187. Although activation of protein kinase C with phorbol ester transiently increases intracellular free calcium in AtT-20 cells, when cells were treated for 0.5 to 22 h with phorbol 12-myristate 13-acetate, there was no acute fall in [3H]DEX binding, and only a small decrease following 16 h of treatment. These data demonstrate that sustained increases in intracellular calcium in corticotropes can induce a rapid and marked decrease in GR binding. The mechanism is post-translational and involves the reversible conversion of the receptor to a non-binding form. In addition, the cellular milieu is clearly important in conferring non-binding status on GR since once the cell is disrupted GR binding is restored.

Aldosterone modulates glucocorticoid receptor binding in hippocampal cell cultures via the mineralocorticoid receptor

The regulation of corticosteroid receptor expression in the rat brain by adrenal steroids remains controversial. The results of in vivo studies [Brinton and McEwen, 1988; Luttge et al., 1989] suggest that activation of type I receptors can modulate both mineralocorticoid (MR; type I) and glucocorticoid (GR; type II) receptor binding in selected brain regions. The present study utilized primary hippocampal cell cultures from rats sacrificed at E19-20 days of gestation to examine the effects of RU 28362, corticosterone (CORT) and aldosterone (ALDO) on GR binding ([3H]dexamethasone +/- RU 28362). Four days of exposure to 10 nM RU 28362, a highly selective GR agonist, resulted in a robust (approximately 70%) decrease in GR binding. Similar exposure to 10 nM of either CORT or ALDO also produced a significant (50-55%) decrease in GR binding capacity. Scatchard analyses confirmed that the diminished GR binding capacity in response to ALDO was due to a decrease in total number of binding sites (Bmax for Control = 112 +/- 25 fmol/mg vs. ALDO = 48 +/- 12 fmol/mg) with no significant change in the affinity constant. The calculated EC50 from the ALDO concentration response curve was 3.5 nM. Competition studies demonstrated that such low nM concentrations of ALDO were unable to displace specific [3H]dexamethasone +/- RU 28362 binding. Spironolactone, a highly specific MR antagonist, inhibited the ALDO-induced down-regulation of GR binding. These findings support the hypothesis that MR activation can modulate GR binding in hippocampal cells.

Regulation of glucocorticoid receptor (GR) mRNA and protein levels by phorbol ester in MCF-7 cells. Mechanism of GR mRNA induction and decay

Treatment of MCF-7 cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (10(-7) M) was associated with a time-dependent increase in specific binding of [3H]dexamethasone (34.8 +/- 4.6 fmol/mg protein after 9 h of TPA treatment compared with 16.0 +/- 2.3 fmol/mg protein in control cells) as well as a transient induction in the level of glucocorticoid receptor (GR) mRNA (4- to 8-fold stimulation after 2-3 h, followed by a decline towards the control value after 6 h). In the presence of the transcription inhibitor actinomycin D (AMD) (5.0 micrograms/ml) the TPA-dependent induction of GR mRNA was completely abolished, and GR mRNA showed a gradual decline with a half-life of 2-3 h. In contrast, treatment with TPA and the protein synthesis inhibitor cycloheximide (50 microM) resulted in a superinduction of GR mRNA (> 50-fold after 6 h). Inhibition of a half-life of 2-3 h, which is identical to that observed in non-treated cells. We conclude that the increase in GR mRNA in the presence of TPA is dependent on ongoing transcription, whereas the rate by which GR transcripts are degraded, is not altered by TPA.

An analysis of autologous glucocorticoid receptor protein regulation in AtT-20 cells also reveals differential specificity of the BuGR2 monoclonal antibody

When the anti-glucocorticoid receptor monoclonal antibody (BuGR2) was initially incorporated either into a new immunoassay strategy or into a traditional sedimentation analysis technique, both methods failed to reveal any change in the cellular content or distribution of BuGR2-reactive antigen following glucocorticoid treatment of AtT-20 cells. Furthermore, the immunoassay also generated strong positive signals with cytosol and nuclear extracts from a receptor-negative cell line (E8.2) derived from L929 cells. However, when the BuGR2 antibody was incorporated into a combined immunoprecipitation/Western blot analysis of AtT-20 cell extracts, only the glucocorticoid receptor protein produced a signal on the Western blot, even though other proteins had been specifically immunoprecipitated by BuGR2 antibody and were clearly present on the Western blot membrane. Applying the latter approach to AtT-20 cells chronically treated with glucocorticoid, we observed not only that the receptor protein rapidly and persistently (1-96 h) accumulated in the nucleus, but also that its total cellular content was first depleted (24 h) and then was progressively replenished (48-96 h). From these studies in AtT-20 cells we conclude: (i), the BuGR2 antibody can exhibit differential immunospecificity dependent upon whether antigen mixtures are denatured or not; (ii), glucocorticoid receptor protein resided almost exclusively in the nucleus during four days of glucocorticoid treatment and (iii), the same treatment regimen resulted in total receptor protein levels being regulated in a biphasic pattern. Together, these results suggest that receptor regulation in AtT-20 cells is a complex event, and that, since steroid was constantly present during our experiments, other factors are involved in regulation of receptor levels.

Ontogeny of corticosteroid receptors in the brain

1. In the brain, glucocorticoids bind to both the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). These receptors show clearly distinct developmental patterns in the infant rat. 2. Low levels of GRs are present around the time of birth throughout the brain. Concentrations rise slowly, and do not achieve adult levels until the third week of life, approximately. GR affinity for corticosterone is higher perinatally than at later ages. Receptor microdistribution changes dramatically during ontogeny. In particular, certain regions, such as the suprachiasmatic nucleus of the hypothalamus, express high levels of receptor only during the first week of life. GRs may show impaired capacity to undergo transformation and/or nuclear translocation during the second postnatal week. Environmental manipulations during early ontogeny (e.g., early handling) may have permanent effects on GR capacity. 3. MRs are present at very low concentrations in the first days of life. Binding capacity rises rapidly thereafter and resembles that found in the adult by the end of 1 week. Neither binding affinity in vitro nor overall distribution changes with age. As in the adult, low doses of corticosterone, in vivo, bind mainly to the MRs. Levels of corticosterone are low and relatively unperturbable in the intact infant rat. It is likely, therefore, that most of the physiological actions of this hormone during this period are mediated by the MR.

Subcellular compartmentalization of MCF-7 estrogen receptor synthesis and degradation

Turnover of the estrogen receptor protein was studied by using enucleation of human breast cancer-derived MCF-7 cells, to examine receptor synthesis and receptor degradation in the separated cytoplasmic compartment (cytoplasts) and nuclear compartment (nucleoplasts). Cytoplasts synthesized estrogen receptors as measured by both hormone-binding and immunoassay, while estrogen receptors (but not progesterone or glucocorticoid receptors) were rapidly degraded in nucleoplasts with a half-life of 3-4 h. Little or no degradation of estrogen receptors in cytoplasts was observed under several conditions. Interestingly, MCF-7 cytoplasts contained approximately 15% of the cell's estrogen receptors, which were not 'translocated' by treatment with 17 beta-estradiol before enucleation. We conclude that the estrogen receptor can be synthesized at least to a hormone binding form in the cytoplasm alone without requiring processing in the nucleus, while the nucleus (or perinuclear cytoplasm) is the primary site of degradation of the estrogen receptor protein. In addition, the presence of a population of estrogen receptors that is cytoplasmic but nontranslocatable may need to be considered in the subcellular localization and actions of steroid receptors.

Characterization of selective glucocorticoid-dependent responses in a glucocorticoid-resistant smooth muscle tumor cell line

The DDT1 MF2 smooth muscle cell line was derived from an estrogen/androgen-induced leiomyosarcoma arising in the hamster ductus deferens. Growth of this cell line is arrested in G0/G1 by treatment with glucocorticoids. To facilitate the study of the mechanism of glucocorticoid-induced cell growth arrest, a glucocorticoid-resistant variant cell line, DDT1 MF2 GR1 (GR1), was developed by genetic selection. Growth of this mutant cell line is completely resistant to the inhibitory action of glucocorticoids. However, we now demonstrate that both primary and secondary glucocorticoid-induced events still exist in the GR1 cell line. By analyzing the expression and genetic pattern of glucocorticoid receptor, no detectable rearrangement of the glucocorticoid receptor gene was found although the expression of both mRNA and protein levels of the receptor were lower in the variant compared to wild-type cells. In addition, we found that the expression of two growth-associated genes, Ha-ras and transforming growth factor beta 1 (TGF-beta 1) are down-regulated by glucocorticoids in wild-type DDT1 MF2 cells but not in GR1 cells. These results indicated that the function or activity of glucocorticoid receptor in the GR1 cells is not qualitatively altered. Our data suggest that a lower glucocorticoid receptor level is not the real cause or at least not the single cause for the GR1 cell's loss of sensitivity to the inhibitory action of glucocorticoid. Instead, we postulate the existence of a defect downstream of the primary site of action of glucocorticoid receptor complexes in GR1 cells.

Glucocorticoid receptors in bovine adrenal medullary cells in culture: regulation by cyclic nucleotides

Glucocorticoid receptor levels within a given cell determine the glucocorticoid effect in the target tissue. Glucocorticoid receptors are present in adrenal medullary cells in culture where they are involved in the regulation of catecholamine biosynthesis. Modulation of glucocorticoid receptor protein and/or messenger RNA levels in response to cyclic nucleotides has been found in various cell types. In this study, we have investigated the effects of cyclic AMP and cyclic GMP on glucocorticoid receptor binding and glucocorticoid receptor-mediated function in Percoll-isolated bovine adrenal medullary cells in culture. Four-day treatment of cells with 8-bromo-cyclic AMP (10(-3) M) an analogue of cAMP, or forskolin (10(-5) M), an activator of adenylate cyclase, decreased soluble [3H]dexamethasone binding by 55 and 54%, respectively. 8-Bromo-cyclic GMP treatment decreased [3H]dexamethasone binding by 31 and 34% at 10(-5) and 10(-4) M, respectively. Treatment with 8-bromo-cyclic AMP or forskolin, but not 8-bromo-cyclic GMP, elevated cortisol levels in the medium of treated cells, presumably by elevating steroidogenesis in contaminating cortical cells. Cultures further purified to produce chromaffin-enriched cell cultures, also showed a loss (41%) in soluble [3H]dexamethasone binding when treated with 8-bromo-cyclic AMP (10(-3) M). Four-day treatment of standard Percoll-isolated cells with low concentrations of cortisol (10(-9) to 2 x 10(-7) M) similar to that found in the medium of 8-bromo-cyclic AMP-treated cells, did not decrease soluble [3H]dexamethasone binding, whereas higher cortisol concentrations (10(-6) M) produced a 62% loss in soluble binding. Adsorption of cortisol with bovine serum albumin (5 mg/ml) prevented a cortisol (10(-6) M)-induced loss in soluble [3H]dexamethasone binding with no effect on the 8-bromo-cyclic AMP-induced loss in binding, suggesting that the decrease in binding observed following 8-bromo-cyclic AMP treatment is not due to the release of cortisol from contaminating cortical cells. Finally, we report a loss in the ability of 8-bromo-cyclic AMP- or 8-bromo-cyclic GMP-treated cells to fully induce the activity of phenylethanolamine N-methyltransferase in response to cortisol, indicating that decreases in soluble [3H]dexamethasone binding translate into a decrease in the functional consequence of glucocorticoid receptor binding in adrenal medullary cells. In conclusion, these results indicate that long-term increases in cyclic nucleotide second messengers are able to decrease glucocorticoid receptor binding in bovine adrenal medullary cells, via a mechanism independent of released cortisol.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated immobilization stress alters tyrosine hydroxylase, corticotropin-releasing hormone and corticosteroid receptor messenger ribonucleic Acid levels in rat brain

In situ hybridization histochemistry was used to localize and quantify the effects of acute and repeated immobilization stress on mRNA levels of tyrosine hydroxylase (TH) in catecholaminergic neurons in the locus ceruleus and substantia nigra and on mRNA levels of relevant markers of the hypothalamic-pituitary-adrenal axis, namely corticotropin-releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN), proopiomelanocortin in the pituitary, and mineralocorticoid receptors (MR, type I) and glucocorticoid receptors (GR, type II) in the hippocampus, PVN and pituitary. Control, acutely stressed (1 × lMO, sacrificed immediately after 2 h of immobilization), and repeatedly stressed (6 × IMO plus delay, sacrificed 24 h after 6 daily 2-h immobilizations and 6 × lMO plus challenge, sacrificed immediately after the seventh daily 2-h immobilization) male Sprague-Dawley rats were examined. TH mRNA expression was increased in the locus ceruleus in the acutely stressed and repeatedly stressed animals. The increase in TH mRNA levels was greatest in the repeatedly stressed (6 × IMO plus challenge) group. TH mRNA levels were not altered in the substantia nigra. CRH mRNA levels in the PVN were significantly increased in the three stressed groups and the increase was greatest in the 6 × IMO plus challenge group. CRH mRNA levels were increased in the central nucleus of the amygdala only after acute stress. Proopiomelanocortin mRNA levels were elevated in the anterior pituitary during acute and repeated stress, but the magnitude of the effect was largest after acute stress. The changes in the hypothalamic-pituitary-adrenal axis were accompanied by an acute stress-induced increase in MR mRNA levels in the hippocampus, MR and GR mRNA levels in the PVN and GR mRNA levels in the pituitary. MR mRNA levels continued to be elevated in the PVN in the 6 × IMO plus challenge animals. Plasma corticosterone levels were elevated in the acute and repeated stress conditions. The results show that repeated immobilization stress produces a rapid and persistent increase in mRNA expression of TH in the locus ceruleus, CRH in the PVN, and proopiomelanocortin in the anterior pituitary. The TH-containing neurons in the locus ceruleus and the CRH-containing neurons in the PVN appear to preserve the capability to respond to repeated stimulation (6 × IMO plus challenge) indicating altered feedback mechanisms under repeated stress conditions. GR and MR mRNA levels are differentially regulated in the hippocampus, PVN and pituitary by acute and repeated stress. It is of interest that the central nervous system systems which are activated during repeated stress, namely the locus ceruleus-norepinephrine system and hypothalamic-pituitary-adrenal axis, are dysregulated in melancholic depression. Further studies of the central nervous system effects of prolonged exposure to stress may help elucidate the mechanisms underlying dysregulation of the locus ceruleus-norepinephrine system and hypothalamic-pituitary-adrenal axis in depression and other stress-related psychiatric diseases.

Liver and brain glucocorticoid receptor in rainbow trout, Oncorhynchus mykiss: down-regulation by dexamethasone

Total glucocorticoid binding sites were identified and quantitated in liver and brain of rainbow trout using an exchange method and [3H]dexamethasone as the ligand. Both tissues contained a predominantly cytosolic moiety that bound dexamethasone with high specificity. Binding was saturable, time dependent, and completely reversible. Scatchard analysis showed a linear relationship suggesting that receptors belong to a single class. Dexamethasone down-regulated both liver and brain receptors. Down-regulation was rapid (within hours) and dose dependent (ED50 = 1.5 mg/kg body weight). Dexamethasone-induced down-regulation was not a result of cytoplasm to nuclei translocation or due to increases in tissue concentrations of steroid. Dexamethasone administration resulted in a lowering of Bmax (82.3 +/- 2.5 to 20.6 +/- 10.5 fmol/mg protein) and an increase in Kd (15.6 +/- 0.2 to 44.3 +/- 5.0 nM) suggesting a conformational change in the receptor molecule as part of the mechanism. The brain and liver of the rainbow trout thus have glucocorticoid receptors similar to those described in the mammalian system. Further, these receptors are subjected to autologous regulation similar to their counterparts in other systems.

Receptor-mediated methylprednisolone pharmacodynamics in rats: Steroid-induced receptor down-regulation

Several approaches to receptor down-regulation were examined to extend previous receptor/gene-mediated pharmacokinetic/dynamic models of corticosteroids. Down-regulation of the glucocorticoid receptor was considered as an instantaneous event or as a gradual steroid-receptor-mediated process. Concentrations of plasma methylprednisolone, free hepatic cytosolic receptors, and the activity of hepatic tyrosine aminotransferase (TAT) enzyme were measured for 16 hr following administration of 0, 10, and 50 mg/kg methylprednisolone sodium succinate to 93 adrenalectomized rats. Receptor down-regulation was best described by a fractional decrement in the rate of return of free cytosolic glucocorticoid receptor. Predicted values for free receptor, bound receptor, nuclear bound receptor, and transfer compartments were in accord with the expected rank order values based on the high and low steroid doses. Model parameter estimates were independent of dose and described the rapid depletion of free cytosolic receptor, late-phase return of cytosolic receptor to a new baseline level that was 20-40% lower than control, and the TAT induction/dissipation pattern following steroid dosing. The microscopic association and dissociation constants describing the steroid-receptor interaction were 0.23 L/nmole per hr (k(on)) and 4.74 hr-1 (k(off)) for methylprednisolone compared to previously obtained values of 0.20 L/nmole per hr and 15.7 hr-1 for the related steroid prednisolone. The time course of TAT induction was similar to that observed previously for prednisolone. Efficiency of TAT induction was more closely related to steroid receptor occupancy than plasma methylprednisolone concentrations due to receptor saturability and receptor recycling.