Stimulatory Effect Of Dexamethasone Research Articles

Glucocorticoids stimulate endolymphatic water reabsorption in inner ear through aquaporin 3 regulation.

Menière's disease, clinically characterized by fluctuating, recurrent, and invalidating vertigo, hearing loss, and tinnitus, is linked to an increase in endolymph volume, the so-called endolymphatic hydrops. Since dysregulation of water transport could account for the generation of this hydrops, we investigated the role of aquaporin 3 (AQP3) in water transport into endolymph, the K-rich, hyperosmotic fluid that bathes the apical ciliated membrane of sensory cells, and we studied the regulatory effect of dexamethasone upon AQP3 expression and water fluxes. The different AQP subtypes were identified in inner ear by RT-PCR. AQP3 was localized in human utricle and mouse inner ear by immunohistochemistry and confocal microscopy. Unidirectional transepithelial water fluxes were studied by means of (3)H2O transport in murine EC5v vestibular cells cultured on filters, treated or not with dexamethasone (10(-7)M). The stimulatory effect of dexamethasone upon AQP3 expression was assessed in EC5v cells and in vivo in mice. AQP3 was unambiguously detected in human utricle and was highly expressed in both endolymph secretory structures of the mouse inner ear, and EC5v cells. We demonstrated that water reabsorption, from the apical (endolymphatic) to the basolateral (perilymphatic) compartments, was stimulated by dexamethasone in EC5v cells. This was accompanied by a glucocorticoid-dependent increase in AQP3 expression at both messenger RNA (mRNA) and protein level, presumably through glucocorticoid receptor-mediated AQP3 transcriptional activation. We show that glucocorticoids enhance AQP3 expression in human inner ear and stimulate endolymphatic water reabsorption. These findings should encourage further clinical trials evaluating glucocorticoids efficacy in Menière's disease.

The Paradoxical Increase in Cortisol Secretion Induced by Dexamethasone in Primary Pigmented Nodular Adrenocortical Disease Involves a Glucocorticoid Receptor-Mediated Effect of Dexamethasone on Protein Kinase A Catalytic Subunits

Context: Primary pigmented nodular adrenocortical disease (PPNAD) results in most cases from mutations of the protein kinase A (PKA) regulatory subunit 1A (PRKAR1A) gene. Patients with PPNAD exhibit a paradoxical increase in cortisol secretion in response to dexamethasone. Objective: The aim was to investigate the mechanism of the action of dexamethasone on adrenocortical cells removed from patients with PPNAD and a transgenic model of PPNAD [Tg(tTA/X2AS) mice]. Design and Setting: We performed an in vitro study in an academic research laboratory. Patients: Eleven patients with histologically proven PPNAD were included in the study. Intervention: Cultured PPNAD cells were incubated with dexamethasone in the presence of various modulators of the cAMP/PKA pathway and the glucocorticoid receptor antagonist RU486. Main Outcome Measure: Cortisol and corticosterone were measured by radioimmunological assays in cell culture supernatants. Results: Dexamethasone stimulated in vitro cortisol secretion from PPNAD tissues in six patients. The stimulatory effect of dexamethasone on cortisol release was not reduced by the adenylyl cyclase inhibitor SQ22536 or potentiated by the phosphodiesterase inhibitor IMBX and the cAMP analog 8Br-cAMP. Conversely, the PKA inhibitor H89 and RU486 inhibited the cortisol response to dexamethasone. Dexamethasone had no effect on cortisol production from normal human adrenocortical cells but stimulated corticosteroidogenesis in the presence of RU486. Similarly, dexamethasone failed to influence corticosterone release by adrenocortical cells removed from Tg(tTA/X2AS) mice but stimulated corticosteroidogenesis in the presence of RU 486. Conclusions: These results indicate that, in human PPNAD tissues, dexamethasone paradoxically stimulates cortisol release through a glucocorticoid receptor-mediated effect on PKA catalytic subunits. Mol Endocrinol, June 2009, 23(6):943–945 mend.endojournals.org 945

The Paradoxical Increase in Cortisol Secretion Induced by Dexamethasone in Primary Pigmented Nodular Adrenocortical Disease Involves a Glucocorticoid Receptor-Mediated Effect of Dexamethasone on Protein Kinase A Catalytic Subunits

Primary pigmented nodular adrenocortical disease (PPNAD) results in most cases from mutations of the protein kinase A (PKA) regulatory subunit 1A (PRKAR1A) gene. Patients with PPNAD exhibit a paradoxical increase in cortisol secretion in response to dexamethasone. The aim was to investigate the mechanism of the action of dexamethasone on adrenocortical cells removed from patients with PPNAD and a transgenic model of PPNAD [Tg(tTA/X2AS) mice]. We performed an in vitro study in an academic research laboratory. Eleven patients with histologically proven PPNAD were included in the study. Cultured PPNAD cells were incubated with dexamethasone in the presence of various modulators of the cAMP/PKA pathway and the glucocorticoid receptor antagonist RU486. Cortisol and corticosterone were measured by radioimmunological assays in cell culture supernatants. Dexamethasone stimulated in vitro cortisol secretion from PPNAD tissues in six patients. The stimulatory effect of dexamethasone on cortisol release was not reduced by the adenylyl cyclase inhibitor SQ22536 or potentiated by the phosphodiesterase inhibitor IMBX and the cAMP analog 8Br-cAMP. Conversely, the PKA inhibitor H89 and RU486 inhibited the cortisol response to dexamethasone. Dexamethasone had no effect on cortisol production from normal human adrenocortical cells but stimulated corticosteroidogenesis in the presence of RU486. Similarly, dexamethasone failed to influence corticosterone release by adrenocortical cells removed from Tg(tTA/X2AS) mice but stimulated corticosteroidogenesis in the presence of RU 486. These results indicate that, in human PPNAD tissues, dexamethasone paradoxically stimulates cortisol release through a glucocorticoid receptor-mediated effect on PKA catalytic subunits.

The Paradoxical Increase in Cortisol Secretion Induced by Dexamethasone in Primary Pigmented Nodular Adrenocortical Disease Involves a Glucocorticoid Receptor-Mediated Effect of Dexamethasone on Protein Kinase A Catalytic Subunits

Primary pigmented nodular adrenocortical disease (PPNAD) results in most cases from mutations of the protein kinase A (PKA) regulatory subunit 1A (PRKAR1A) gene. Patients with PPNAD exhibit a paradoxical increase in cortisol secretion in response to dexamethasone. The aim was to investigate the mechanism of the action of dexamethasone on adrenocortical cells removed from patients with PPNAD and a transgenic model of PPNAD [Tg(tTA/X2AS) mice]. We performed an in vitro study in an academic research laboratory. Eleven patients with histologically proven PPNAD were included in the study. Cultured PPNAD cells were incubated with dexamethasone in the presence of various modulators of the cAMP/PKA pathway and the glucocorticoid receptor antagonist RU486. Cortisol and corticosterone were measured by radioimmunological assays in cell culture supernatants. Dexamethasone stimulated in vitro cortisol secretion from PPNAD tissues in six patients. The stimulatory effect of dexamethasone on cortisol release was not reduced by the adenylyl cyclase inhibitor SQ22536 or potentiated by the phosphodiesterase inhibitor IMBX and the cAMP analog 8Br-cAMP. Conversely, the PKA inhibitor H89 and RU486 inhibited the cortisol response to dexamethasone. Dexamethasone had no effect on cortisol production from normal human adrenocortical cells but stimulated corticosteroidogenesis in the presence of RU486. Similarly, dexamethasone failed to influence corticosterone release by adrenocortical cells removed from Tg(tTA/X2AS) mice but stimulated corticosteroidogenesis in the presence of RU 486. These results indicate that, in human PPNAD tissues, dexamethasone paradoxically stimulates cortisol release through a glucocorticoid receptor-mediated effect on PKA catalytic subunits.

ABCA1, ABCG1 and SR-BI: hormonal regulation in primary rat hepatocytes and human cell lines

BackgroundScavenger receptor type B class I (SR-BI), ABC transporter A1 (ABCA1) -and G1 (ABCG1) all play important roles in the reverse cholesterol transport. Reverse cholesterol transport is a mechanism whereby the body can eliminate excess cholesterol. Here, the regulation of SR-BI, ABCA1, and ABCG1 by dexamethasone (a synthetic glucocorticoid) and insulin were studied in order to gain more insight into the role of these two hormones in the cholesterol metabolism.ResultsBy use of real time RT-PCR and Western blotting we examined the expression of our target genes. The results show that SR-BI, ABCA1 and ABCG1 mRNA expression increased in response to dexamethasone while insulin treatment reduced the expression in primary rat hepatocytes. The stimulatory effect of dexamethasone was reduced by the addition of the anti-glucocorticoid mifepristone. In HepG2 cells and THP-1 macrophages, however, the effect of dexamethasone was absent or inhibitory with no significant change in the presence of mifepristone. The latter observation may be a result of the low protein expression of glucocorticoid receptor (GR) in these cell lines.ConclusionOur results illustrates that insulin and glucocorticoids, two hormones crucial in the carbohydrate metabolism, also play an important role in the regulation of genes central in reverse cholesterol transport. We found a marked difference in mRNA expression between the primary cells and the two established cell lines when studying the effect of dexamethasone which may result from the varying expression levels of GR.

Isoform-specific modulation of coronary artery PKC by glucocorticoids

Glucocorticoids (GC) exert diverse cellular effects in response to both acute and chronic stress, the functional consequences of which have been implicated in the development of cardiovascular pathology such as hypertension and atherosclerosis. However, the mechanisms by which GCs activate divergent signaling pathways are poorly understood. The present study examined the direct effects of natural (cortisol) and synthetic (dexamethasone) GCs on protein kinase C (PKC) isoform expression in coronary arteries. Porcine right coronary arteries were treated in vitro for 18 h in the presence and absence of either dexamethasone (10, 100, or 500 nM) or cortisol (50, 125, 250, or 500 nM). PKC isoform levels and subcellular distribution were determined by immmunoblotting of whole cell homogenates and immunocytofluorescence using PKC-α, -β II, -ε, -δ, and -ζ specific antibodies. Dexamethasone caused a ∼4-fold increase in PKC-α, a ∼2.5-fold increase in PKC-β II, and a 2-fold increase in PKC-ε ( p < 0.05). In contrast, dexamethasone had no effect on PKC-δ or PKC- ζ levels. Dexamethasone also caused an increase in the activity of PKC-α (285%), -β II (170%), and -ε (210%). Cortisol produced similar effects on PKC isoform expression. Confocal microscopy revealed that while dexamethasone altered localization patterns for PKC-α, -β II, and -ε, no such effect was observed for PKC-δ or PKC-ζ. The stimulatory effects of dexamethasone and cortisol on coronary PKC levels and translocation were prevented by the GC receptor (GR) blocker, RU486. These results demonstrate, for the first time, that GCs modulate coronary PKC expression and subcellular distribution in an isoform-specific manner through a GR-dependent mechanism.

In vitroquantification of dexamethasone-induced surfactant protein B expression in human lung cells

Objective: To determine whether the effect of a single 48-h exposure to dexamethasone in human lung cells is limited to 7–8 days.Study design: We used the NCI-H441 cell line, in which stability can be maintained beyond 7 days. The outcome was the stimulatory effect of dexamethasone on surfactant protein B (SP-B) gene transcription as expressed by SP-B mRNA accumulation. The experiment was conducted five times, in parallel with control. SP-B mRNA was determined at baseline, 48 h after dexamethasone exposure, and at 48-h intervals thereafter, up to 14 days, by quantitative reverse transcription polymerase chain reaction. Comparisons were made by the Mann-Whitney test.Results: In conditions of our experiment, the inductive profile of SP-B mRNA after exposure to dexamethasone demonstrated maximal stimulation at 48 h (13-fold over control). Subsequently, there was a decline in mRNA, with return to near control levels by day 8, suggesting reversibility of dexamethasone action.Conclusion: Our data support the view that the surfactant-inducing properties of corticosteroids are limited to 7–8 days.

Stimulatory effect of dexamethasone on angiotensin-converting enzyme in neonatal rat cardiac myocytes.

Angiotensin-converting enzyme (ACE) plays a central role in cardiac remodeling associated with pathological conditions such as myocardial infarction. The existence of different cell types in the heart expressing components of the renin-angiotensin system makes it difficult to evaluate their relative role under physiological and pathological conditions. Since myocytes are the predominant cellular constituent of the heart by mass, in the present study we studied the effects of glucocorticoids on ACE activity using well-defined cultures of neonatal rat cardiac myocytes. Under steady-state conditions, ACE activity was present at very low levels, but after dexamethasone treatment ACE activity increased significantly (100 nmol/l after 24 h) in a time-dependent fashion. These results demonstrate the influence of dexamethasone on ACE activity in rat cardiac myocytes. This is consistent with the idea that ACE activation occurs under stress conditions, such as myocardial infarction, in which glucocorticoid levels may increase approximately 50-fold.

Differential Regulation in Human Amnion Epithelial and Fibroblast Cells of Prostaglandin E2Production and Prostaglandin H Synthase-2 mRNA Expression by Dexamethasone but not Tumour Necrosis Factor-α

Previous studies have identified both pro-inflammatory cytokines and glucocorticoids as positive regulators of amnion prostaglandin (PG) biosynthesis. The stimulatory effects of dexamethasone (Dex), a glucocorticoid agonist, on prostaglandin endoperoxide H synthase (PGHS)-2 mRNA expression and PG biosynthesis in amnion have been attributed to an atypical response by the mesenchymal cells of the amnion. The objective of this study was to confirm previous findings concerning cell type-dependant Dex-induced upregulation of PGHS-2 mRNA expression and PG production using separated amnion cell populations, in comparison with the effects of the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-α). Amnion cells from placentae delivered at term by caesarian section were isolated by tryptic digestion and epithelial cells were then separated from mesenchymal cells by differential absorption onto plastic. After 24–72h, the two cell populations were passaged and sub-cultured. Cells were treated with Dex (10−9–10−6m) or TNF-α (0.1–50ng/ml) or media alone. Thereafter, PGE2production was determined and PGHS-2 mRNA content analysed by a competitive quantitative RT-PCR method established and validated for this study. PGE2production in fibroblast-enriched cultures was increased to 310±41 per cent (mean±sem, n=4 wells per treatment point) of control in the presence of 10−8m Dex. Conversely, PGE2production in Dex-treated amnion epithelial cells was decreased to 67±24 per cent of control. Altered PGE2biosynthesis was accompanied by the upregulation of PGHS-2 mRNA in amnion fibroblasts but not in epithelial cells. TNF-α increased PG output and PGHS-2 expression independent of cell type. Glucocorticoids therefore appear to have opposing effects on PG biosynthesis in the two major cellular components of the human amnion.

Dexamethasone-induced Up-regulation of Adrenomedullin and Atrial Natriuretic Peptide Genes in Cultured Rat Ventricular Myocytes

To determine whether adrenomedullin (AM), a novel 51-residue vasodilator peptide originally isolated from human pheochromocytoma, is expressed by the heart, and whether the expression of cardiac AM gene is regulated by glucocorticoids, the effect of dexamethasone (DEX) on the expression of protein and mRNA of AM and atrial natriuretic peptide (ANP) was tested in cultured ventricular myocytes prepared from the neonatal rats. Northern blot analysis of rat ventricular myocytes with cDNAs for rat AM and ANP as probes revealed distinct bands corresponding to the sizes of rat AM mRNA (1.6 kb) and rat ANP mRNA (1 kb), respectively. Dexamethasone increased steady-state levels of both AM and ANP mRNA as well as secretion of both AM and ANP immunoreactivity in a time- and dose-dependent manner. The stimulatory effects of dexamethasone were completely abolished by a glucocorticoid antagonist (RU38486) and a RNA synthesis inhibitor (actinomycin D). The approximate half-lives of basal and dexamethasone-induced AM mRNA were about 4 h, suggesting that dexamethasone-induced up-regulation of AM mRNA was unlikely due to its decreased degradation. These data suggest that glucocorticoids directly stimulate gene expression of AM as well as ANP in rat ventricular myocytes.

A new fluorometric assay for determination of osteoblastic proliferation: effects of glucocorticoids and insulin-like growth factor-I.

A novel fluorometric proliferation assay, AlamarBlue (AB), was used to study the proliferative capacity of isolated human osteoblasts (hOBs). AB is an oxidation-reduction indicator that yields a fluorescent signal in response to metabolic activity. The assay was performed by replacing the experiment media in a microtiter plate with a 10% AB solution and measuring fluorescence after a 3-8-hour incubation. The assay was optimized with respect to incubation time, cell density, and AB concentration. When the results of the AB assay were compared with cell counting in a Bürker chamber there were consistently good correlations (r > 0.9), regardless of the agonist with which the cells were treated. The mean intraassay coefficient of variance (CV) values were 9.9-11.8% in experiments where osteoblasts were treated for 12 days with insulin-like growth factor-I (IGF-I; 100 nM), or dexamethasone (1 micro;M). IGF-I dose dependently, at and above 1 nM, stimulated proliferation of hOBs. This effect was detectable after 3 days and reached 130-140% of untreated controls after 12 days in culture. The effects of dexamethasone (DEX) on the proliferation rate of hOBs were more complex. In short-term cultures, 3 days, DEX dose dependently stimulated proliferation. However, at and above 6 days, DEX exerted a biphasic effect, with stimulation seen at 1-10 nM and a marked inhibition of cell proliferation at and above 100 nM. dexamethasone, hydrocortisone, prednisolone, and deflazacort had almost identical biphasic effects on osteoblastic proliferation in 12 day cultures with a stimulation seen at 1-10 nM, and a marked inhibition down to 50-60% of untreated controls at and above 100 nM. When IGF-I (0. 1-100 nM; 12 day culture) was combined with different doses of DEX, IGF-I still dose dependently stimulated the proliferation rate in hOBs regardless of the amount of DEX added. The stimulatory effect of DEX (10 nM, 12 days culture) was additive to the effect of 100 nM IGF-I. We conclude that AB is an easy and reliable assay for osteoblastic cell proliferation, well suited for large scale studies of cell growth using small amounts of cells, and that IGF-I partly reverses the glucocorticoid-induced inhibition of osteoblastic proliferation.

Plasmid Insertional Mutation May Confer Glucocorticoid Responsiveness of Cell Growth

Culture of CHO.K1, a Chinese hamster ovary cell line, requires no particular care about the glucocorticoid level in media. Cell growth of CHO.K1 is little affected by dexamethasone at concentrations up to 3 microM. A clone of CHO.K1 stably transfected with an expression vector displayed a favored growth in dexamethasone-containing media. Ironically, dexamethasone was used to trigger the expression of antisense PCNA from the expression vector to impede the cell growth. Proliferating cell nuclear antigen (PCNA), an auxiliary factor of DNA polymerase delta, is required for cell proliferation. The stable cell clone, designated as B11 had a retarded growth rate as compared to its parental cell. However, the B11 cell growth rate and the cell cycle progression were increased by dexamethasone. The glucocorticoid produced no similar effect on the parental cell or other stable transfectants of the same plasmid. Thus, the stimulatory effect of dexamethasone on B11 has little connection with the expression of antisense PCNA and possibly involves a relevant gene in the B11 genome that was mutated due to the random plasmid insertion. A preliminary effort in identifying the targeted gene was made by using plasmid rescue method, and two plasmids were obtained. The rescued DNA of both plasmids specifically hybridized genomic DNA of the parental cells, and one of these plasmids detected a cellular transcript that was absent in B11 cells, suggesting its potential for further investigation.

Glucocorticoid stimulation of fatty-acid synthase gene transcription in fetal lung: antagonism by retinoic acid.

Glucocorticoid hormones are known to stimulate the rate of fatty acid biosynthesis and to increase the activity and mRNA level of fatty-acid synthase (FAS) in late gestation fetal lung. We have now examined the effect of dexamethasone on FAS transcription in fetal rat lung. Explants of 19-day fetal rat lung cultured for 48 h in serum-free medium were exposed to dexamethasone (10(-7) M) for various time periods. Nuclei were isolated, and the rate of [32P]UTP incorporation into FAS and gamma-actin RNA transcripts was measured by transcription-elongation assay. Dexamethasone increased FAS transcription but had no effect on that of actin. The maximum effect of the hormone, approximately threefold increase, was observed 1-2 h after addition of the hormone but was still apparent up to 48 h. FAS transcription but not that of actin was inhibited by cycloheximide and puromycin in both control and dexamethasone-treated cultures. However, the stimulatory effect of the hormone was not significantly reduced by the inhibitors. Retinoic acid antagonized the stimulatory effects of dexamethasone on FAS activity, mRNA content as measured by Northern analysis, mass as measured by Western blotting, and rate of transcription. The effect of retinoic acid was dependent on concentration in the relatively narrow range of 5 x 10(-6) to 5 x 10(-4) M. These data show that glucocorticoids stimulate transcription of the FAS gene in late gestation fetal rat lung, that normal transcription of the FAS gene is dependent on ongoing protein synthesis, and that glucocorticoid stimulation of FAS gene expression is antagonized by retinoic acid.

Beta-adrenergic receptors and angiotensinogen gene expression in mouse hepatoma cells in vitro.

We have previously reported that addition of 8-bromocyclic AMP enhances the stimulatory effect of dexamethasone on the expression of the angiotensinogen gene in mouse hepatoma cells in vitro. Isoproterenol is known to stimulate the synthesis of hepatic intracellular cyclic AMP via beta-adrenergic receptors. To study the possible effect of beta-adrenergic receptors on the expression of the angiotensinogen gene in mouse hepatoma cells, we transiently transfected them with a fusion gene with the 5'-flanking region of the angiotensinogen gene linked to a bacterial chloramphenicol acetyltransferase coding sequence as a reporter, pOCAT (ANG N-1498/+18). The addition of isoproterenol (10(-9) to 10(-5) mol/L) alone had no stimulatory effect on the expression of pOCAT (ANG N-1498/+18). In the presence of dexamethasone (10(-6) mol/L), however, isoproterenol enhanced the stimulatory effect on the dexamethasone on the expression of pOCAT (ANG N-1498/+18). The enhancing effect of isoproterenol was inhibited by the presence of propranolol (beta 1- and beta 2-adrenergic receptor antagonist) and ICI 118,551 (beta 2-adrenergic receptor antagonist) but not by the presence of atenolol (beta 1-adrenergic receptor antagonist). Furthermore, the addition of Rp-cAMP (an inhibitor of protein kinase A I and II) blocked the enhancing effect of isoproterenol. These studies demonstrated that isoproterenol enhances the stimulatory effect of dexamethasone on the expression of the angiotensinogen gene in mouse hepatoma cells via beta 2-adrenergic receptor and cyclic AMP-dependent protein kinase pathways. Our data may be important in understanding the molecular mechanism(s) of the stimulatory effect of catecholamines/glucocorticoid-induced expression of the angiotensinogen gene in the liver.

Glucocorticoids increase insulin-like growth factor-II mRNA accumulation in cultured human phaeochromocytoma cells

Human phaeochromocytomas abundantly express insulin-like growth factor-II (IGF-II), but its regulation and biological role in these neoplasms is not known at present. To clarify the regulation of IGF-II gene expression in phaeochromocytomas, we studied the effects of glucocorticoids, nerve growth factor (NGF), and protein kinase A and C regulators in primary cultures of human phaeochromocytoma cells. Cytoplasmic RNA was extracted and analysed by Northern and dot blotting with a 32P-labelled cDNA probe for IGF-II. Dexamethasone treatment (500 ng/ml) for 3 and 7 days resulted in a 260% and 515% increase in the accumulation of IGF-II mRNA respectively. The stimulatory effect of dexamethasone was time- and dose-dependent. The increases in the 6.0 and 2.2 kb species of IGF-II mRNAs were the most apparent. Cortisol (1 microgram/ml) increased the amount of IGF-II mRNA by threefold compared with the control. NGF (200 ng/ml), dibutyryl cyclic AMP (1 mM) and 12-O-tetradecanoyl phorbol-13-acetate (a protein kinase C activator; 100 ng/ml) had no significant effect on IGF-II mRNA levels. These data suggest that IGF-II gene expression in human phaeochromocytomas may be regulated by microenvironmental glucocorticoids.

Dexamethasone stimulates osteoclast-like cell formation by inhibiting granulocyte-macrophage colony-stimulating factor production in mouse bone marrow cultures.

We investigated the effect of glucocorticoid on the generation of osteoclasts. In mouse bone marrow culture systems, dexamethasone, a synthetic glucocorticoid analog, enhanced osteoclast-like cell formation induced by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in a dose-dependent manner. Conversely, dexamethasone inhibited the endogenous production of granulocyte-macrophage colony-stimulating factor (GM-CSF) in bone marrow cultures. GM-CSF, when added exogenously, suppressed not only the osteoclast-like cell formation induced by 1,25-(OH)2D3, but also the stimulatory effect of dexamethasone, and addition of anti-GM-CSF neutralizing antibody to the cultures significantly increased the osteoclast-like cell formation induced by 1,25-(OH)2D3. These observations suggest that dexamethasone directly affects bone marrow cells and enhances osteoclast generation by inhibiting the endogenous production of GM-CSF, which may function as a negative regulator of osteoclast formation.

Dexamethasone increases and serum decreases growth hormone receptor binding to UMR-106.01 rat osteosarcoma cells.

Dexamethasone (DEX) is known to exert major effects on functions of osteoblast-like cells. We investigated its action on the regulation of GH receptors in the osteoblast-like osteosarcoma cells UMR-106.01. DEX stimulated [125I]human GH (hGH) binding to UMR-106.01 cells. This effect was dose dependent and significant in a concentration range of 10(-8)-10(-6) M. The maximum effect was an increase of 42 +/- 1.4% (n = 3; mean +/- SE) above control, P < 0.01, at 10(-7) M DEX. Time dependence of this stimulation was observed, with a peak between the 12th and the 16th h of incubation, an effect being still detectable at 48 h. Cycloheximide decreased [125I]hGH binding and completely abolished the stimulating effect of DEX, suggesting that modulation of [125I]hGH binding by DEX is fully dependent on protein synthesis. Addition of fetal calf serum (FCS) resulted in a dose-dependent decrease of [125I]hGH binding to 24 +/- 2% of control (n = 3; mean +/- SE), P < 0.001, without interfering with the stimulatory effect of DEX, the ratio of DEX vs. control being higher with increasing FCS doses. Taken together, these results suggest the existence of different pathways for the regulation of GH receptor binding to UMR-106.01 cells, including a stimulatory one at the pretranslational level for DEX and an inhibitory one for (growth) factors present in FCS.

Glucocorticoids stimulate Na+/H+ antiporter in OKP cells.

Previous studies have demonstrated that systemic administration of glucocorticoids stimulates proximal tubule acidification in part by increasing Na+/H+ antiporter activity; however, these studies could not exclude the possibility that changes in Na+/H+ antiporter activity were secondary to glucocorticoid-induced hemodynamic changes. The present study examined the effect of dexamethasone on Na+/H+ antiporter activity in quiescent OKP cells. Na+/H+ antiporter activity was assayed as the initial rate of Na(+)-dependent pH recovery from an acid load. Intracellular pH was measured using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Dexamethasone produced a dose- and time-dependent stimulation of Na+/H+ antiporter activity in OKP cells. Dexamethasone produced a 24% stimulation in Na+/H+ antiporter activity at 10(-9) M and an approximately 40% stimulation of Na+/H+ antiporter activity at both 10(-8) and 10(-6) M. The effect of 10(-6) M dexamethasone was seen within 4 h of incubation and was due to an increase in maximal velocity (Vmax, 3.03 vs. 1.79 pH units/min) with no change in the affinity constant for sodium (KNa, 47.2 vs. 42.0 mM). The stimulatory effect of dexamethasone on Na+/H+ antiporter activity was blocked by cycloheximide and was not observed with 10(-8) M aldosterone. These data demonstrate a direct effect of glucocorticoids to stimulate Na+/H+ antiporter activity in OKP cells.

Glucocorticoid stimulates hepatitis B viral gene expression in cultured human hepatoma cells.

Glucocorticoids have been shown to influence the severity of hepatitis B virus-related chronic hepatitis in human. However, very little is known about the effects of glucocorticoids on hepatitis B virus replication in vitro. In this report, we used a well-differentiated human hepatoma cell line, Hep3B, transfected with hepatitis B virus complementary DNA as a model to show that a glucocorticoid analog, dexamethasone, can directly stimulate the production of HBsAg and HBeAg. Elevation of 3.5-kb pregenomic RNA and all other viral RNAs in the transfected Hep3B cells after dexamethasone treatment supports the hypothesis that glucocorticoids directly stimulate hepatitis B virus gene expression in vitro. The concentration of dexamethasone for its half-maximal stimulatory activity toward HBsAg, HBeAg and all viral transcripts was approximately 10(-8) mol/L, close to the affinity of glucocorticoid receptors to [3H]-triamcinolone acetonide in Hep3B cells (approximately 10(-8) mol/L). Specific glucocorticoid antagonist RU38486 completely blocked dexamethasone-induced HBV gene expression, suggesting that the stimulatory effect of dexamethasone was mediated through specific glucocorticoid receptors.

Implication of glucocorticoid receptors in the stimulation of human glioma cell proliferation by dexamethasone.

Dexamethasone is frequently used in the therapy of brain tumor patients. We investigated the effect of dexamethasone on the proliferation of three short-term and four established human glioma cell lines in vitro, using a microculture tetrazolium assay to determine growth rates. In one short-term culture and in one established cell line dexamethasone consistently stimulated the proliferation in a concentration-dependent way. The proliferation was maximally enhanced at a concentration of approximately 0.1 microM. In these two cell lines a relatively high level of glucocorticoid receptors was present, whereas low levels of glucocorticoid receptors were found in the other cell lines. In addition, we demonstrated that the stimulatory effects of dexamethasone on the proliferation of the glioma cell lines can be antagonized by the antiglucocorticoid RU38486. The results demonstrate unequivocally that the glucocorticoid receptor plays a role in the growth stimulating effect of dexamethasone.