Glucocorticoids inhibit MAP kinase via increased expression and decreased degradation of MKP-1

Glucocorticoids suppress inflammation via the upregulation of negative regulator IRAK-M

Glucocorticoids are among the most commonly used anti-inflammatory agents. Despite the enormous efforts in elucidating the glucocorticoid-mediated anti-inflammatory actions, how glucocorticoids tightly control overactive inflammatory response is not fully understood. Here we show that glucocorticoids suppress bacteria-induced inflammation by enhancing IRAK-M, a central negative regulator of Toll-like receptor signalling. The ability of glucocorticoids to suppress pulmonary inflammation induced by non-typeable Haemophilus influenzae is significantly attenuated in IRAK-M-deficient mice. Glucocorticoids improve the survival rate after a lethal non-typeable Haemophilus influenzae infection in wild-type mice, but not in IRAK-M-deficient mice. Moreover, we show that glucocorticoids and non-typeable Haemophilus influenzae synergistically upregulate IRAK-M expression via mutually and synergistically enhancing p65 and glucocorticoid receptor binding to the IRAK-M promoter. Together, our studies unveil a mechanism by which glucocorticoids tightly control the inflammatory response and host defense via the induction of IRAK-M and may lead to further development of anti-inflammatory therapeutic strategies.

Melatonin ameliorates dexamethasone-induced inhibitory effects on the proliferation of cultured progenitor cells obtained from adult rat hippocampus

Glucocorticoids, hormones that are released in response to stress, induce neuronal cell damage. The hippocampus is a primary target of glucocorticoids in the brain, the effects of which include the suppression of cell proliferation and diminished neurogenesis in the dentate gyrus. Our previous study found that melatonin, synthesized primarily in the pineal, pretreatment prevented the negative effects of dexamethasone, the glucocorticoid receptor agonist, on behavior and neurogenesis in rat hippocampus. In the present study, we attempted to investigate the interrelationship between melatonin and dexamethasone on the underlying mechanism of neural stem cell proliferation. Addition of dexamethasone to hippocampal progenitor cells from eight-week old rats resulted in a decrease in the number of neurospheres; pretreatment with melatonin precluded these effects. The immunocytochemical analyses indicated a reduction of Ki67 and nestin-positive cells in the dexamethasone-treated group, which was minimized by melatonin pretreatment. A reduction of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation and G1-S phase cell cycle regulators cyclin E and CDK2 in dexamethasone-treated progenitor cells were prevented by pretreatment of melatonin. Moreover, luzindole, a melatonin receptor antagonist blocked the positive effect of melatonin whereas RU48, the glucocorticoid receptor antagonist blocked the negative effect of dexamethasone on the number of neurospheres. Moreover, we also found that dexamethasone increased the glucocorticoid receptor protein but decreased the level of MT1 melatonin receptor, whereas melatonin increased the level of MT1 melatonin receptor but decreased the glucocorticoid receptor protein. These suggest the crosstalk and cross regulation between the melatonin receptor and the glucocorticoid receptor on hippocampal progenitor cell proliferation.

Effects of Glucocorticoids in the Immune System

Glucocorticoids (GCs) are steroid hormones with widespread effects. They control intermediate metabolism by stimulating gluconeogenesis in the liver, mobilize amino acids from extra hepatic tissues, inhibit glucose uptake in muscle and adipose tissue, and stimulate fat breakdown in adipose tissue. They also mediate stress response. They exert potent immune-suppressive and anti-inflammatory effects particularly when administered pharmacologically. Understanding these diverse effects of glucocorticoids requires a detailed knowledge of their mode of action. Research over the years has uncovered several details on the molecular action of this hormone, especially in immune cells. In this chapter, we have summarized the latest findings on the action of glucocorticoids in immune cells with a view of identifying important control points that may be relevant in glucocorticoid therapy.

Protein tyrosine phosphatases in mast cell signaling

For a time, mast cells were viewed as simple granulocytic effector cells that mediate allergic symptoms. More recent discoveries show that mast cells can also function as potent pro- and anti-inflammatory immune regulators in a plethora of human diseases. Much of the current knowledge about mast cell functions comes from studies on rodent models. The membrane receptors for antigen/IgE and growth factors are the core initiators of signaling cascades that trigger various mast cell responses. Yet, the regulation and multifunctionality of key receptor-proximal protein tyrosine phosphorylation events are still not well understood. The roles of the members of the protein tyrosine phosphatase superfamily of enzymes in regulating mast cell development, survival, and immune activation will be reviewed in this chapter.

Attenuation of TNF production and experimentally induced inflammation by PDE4 inhibitor rolipram is mediated by MAPK phosphatase-1

BACKGROUND AND PURPOSE

3',5'-Cyclic nucleotide PDE4 is expressed in several inflammatory and immune cells, and PDE4 catalyses the hydrolysis of cAMP to 5'AMP, down-regulating cAMP signalling in cells. MAPK phosphatase-1 (MKP-1) is an endogenous p38 MAPK signalling suppressor and limits inflammatory gene expression and inflammation. In the present study, we investigated the effect of a PDE4 inhibitor rolipram on MKP-1 expression and whether MKP-1 is involved in the anti-inflammatory effects of rolipram.

EXPERIMENTAL APPROACH

The effect of rolipram on TNF production was investigated in J774 mouse macrophage cell line and in primary mouse peritoneal macrophages (PM) from wild-type (WT) and MKP-1(-/-) mice. We also investigated the effect of rolipram on carrageenan-induced paw inflammation in WT and MKP-1(-/-) mice.

KEY RESULTS

MKP-1 expression was enhanced by rolipram, by a non-selective PDE inhibitor IBMX and by a cAMP analogue 8-Br-cAMP in J774 cells and in PM. Enhanced MKP-1 mRNA expression by rolipram was reversed by a PKA inhibitor. Rolipram, IBMX and 8-Br-cAMP also inhibited TNF production in activated macrophages. Accordingly, rolipram inhibited TNF production in PMs from WT mice but, interestingly, not in PMs from MKP-1(-/-) mice. Furthermore, rolipram attenuated carrageenan-induced paw inflammation in WT but not in MKP-1(-/-) mice.

CONCLUSIONS AND IMPLICATIONS

PDE4 inhibitor rolipram was found to enhance the expression of MKP-1, and MKP-1 mediated, at least partly, the anti-inflammatory effects of PDE4 inhibition. The results suggest that compounds that enhance MKP-1 expression and/or MKP-1 activity hold potential as novel anti-inflammatory drugs.

MKP-1 is a target of miR-210 and mediate the negative regulation of miR-210 inhibitor on hypoxic hPASMC proliferation

Chonic hypoxia, smooth muscle cell (SMC) proliferation and vascular remodeling are hallmark features of pathogenic pulmonary artery hypertension. MicroRNAs (miRNAs), endogenously expressed small noncoding RNAs, regulate gene expression at the post-transcriptional level. MiR-210 is considered a "master miRNA" in the control of diverse functions in hypoxic cells and tissues and has a cytoprotective function in pulmonary artery SMCs during hypoxic stress. MiR-210 is also upregulated in lung tissue of chonically hypoxic mice suffering from pulmonary hypertension. Jin et al. () showed that mice deficient in mitogen-activated protein kinase phosphatase 1 (MKP-1) had severe hypoxia-induced pulmonary hypertension, so MKP-1 may be important in the progression of hypoxic pulmonary artery hypertension. We investigated the possible interactions between miR-210 and MKP-1 and the effect on cell proliferation in hypoxic human pulmonary artery SMCs (hPASMCs). miR-210 was significantly increased in cultured hPASMCs exposed to 1% O2 hypoxia for 48 h, as was MKP-1 mRNA and protein expression. Furthermore, inhibiting miR-210 expression increased MKP-1 mRNA and protein expression in hPASMCs and decreased cell proliferation under hypoxia. Conversely, overexpressing miR-210 prevented hypoxia-induced MKP-1 expression with no effect on cell proliferation. siRNA knockdown of MKP-1 abolished the miR-210-inhibition prevention of cell proliferation under hypoxia. MKP-1 is a target of miR-210 and could mediate the negative regulation of miR-210 inhibition on hypoxic hPASMCs.

Increased frequency of dual-positive TH2/TH17 cells in bronchoalveolar lavage fluid characterizes a population of patients with severe asthma

BACKGROUND

TH2 cells can further differentiate into dual-positive TH2/TH17 cells. The presence of dual-positive TH2/TH17 cells in the airways and their effect on asthma severity are unknown.

OBJECTIVE

We sought to study dual-positive TH2/TH17 cells in bronchoalveolar lavage (BAL) fluid from asthmatic patients, examine their response to glucocorticoids, and define their relevance for disease severity.

METHODS

Bronchoscopy and lavage were performed in 52 asthmatic patients and 25 disease control subjects. TH2 and TH2/TH17 cells were analyzed by using multicolor flow cytometry and confocal immunofluorescence microscopy. Cytokines were assayed by means of ELISA.

RESULTS

Dual-positive TH2/TH17 cells were present at a higher frequency in BAL fluid from asthmatic patients compared with numbers seen in disease control subjects. High-level IL-4 production was typically accompanied by high-level IL-17 production and coexpression of GATA3 and retinoic acid receptor-related orphan receptor γt. Increased presence of TH2/TH17 cells was associated with increased IL-17 production in lavage fluid. TH2/TH17 cell counts and IL-17 production correlated with PC20 for methacholine, eosinophil counts, and FEV1. TH2/TH17 cells, unlike TH2 cells, were resistant to dexamethasone-induced cell death. They expressed higher levels of mitogen-activated protein-extracellular signal-regulated kinase kinase 1, a molecule that induces glucocorticoid resistance. On the basis of the dominance of BAL fluid TH2 or TH2/TH17 cells, we identified 3 subgroups of asthma: TH2(predominant), TH2/TH17(predominant), and TH2/TH17(low). The TH2/TH17(predominant) subgroup manifested the most severe form of asthma, whereas the TH2/TH17(low) subgroup had the mildest asthma.

CONCLUSION

Asthma is associated with a higher frequency of dual-positive TH2/TH17 cells in BAL fluid. The TH2/TH17(predominant) subgroup of asthmatic patients manifested glucocorticoid resistance in vitro. They also had the greatest airway obstruction and hyperreactivity compared with the TH2(predominant) and TH2/TH17(low) subgroups.

Anti-inflammatory and corticosteroid-enhancing actions of vitamin D in monocytes of patients with steroid-resistant and those with steroid-sensitive asthma

BACKGROUND

Vitamin D is known for its anti-inflammatory effects.

OBJECTIVE

Vitamin D regulation of responses in patients with steroid-resistant (SR) versus steroid-sensitive (SS) asthma has not been studied.

METHODS

Peripheral blood cells from 11 patients with SR asthma and 8 patients with SS asthma were preincubated with 1,25-dihydroxyvitamin D (1,25[OH]2D [VitD]), followed by dexamethasone (DEX) treatment and LPS stimulation. LPS-induced phosphorylated p38 mitogen-activated protein kinase (p-p38) in monocytes was examined by means of flow cytometry. Mitogen-activated protein kinase phosphatase-1 (MKP-1) mRNA expression, which inhibits p-p38, was analyzed by means of real-time PCR. Glucocorticoid receptor (GR) binding and histone H4 acetylation in the glucocorticoid response element of the MKP-1 promoter in monocytes were analyzed by means of chromatin immunoprecipitation.

RESULTS

DEX significantly inhibited LPS-induced p-p38 in monocytes from patients with SS asthma but not those from patients with SR asthma (P < .01). VitD inhibited LPS-induced p-p38 in monocytes from both patient groups (P < .01) but enhanced DEX suppression of LPS-induced p-p38 only in monocytes from patients with SS asthma (P < .01). VitD induced MKP-1 expression and enhanced DEX induction of MKP-1 in both patients with SS asthma and patients with SR asthma. VitD/DEX-induced MKP-1 mRNA levels remained significantly lower in monocytes from patients with SR asthma (P < .05). DEX-stimulated recruitment of GR and histone H4 acetylation at the glucocorticoid response element 4.6 kbp upstream of the MKP-1 gene were significantly lower in monocytes from patients with SR asthma compared with those from patients with SS asthma. VitD pretreatment enhanced DEX-induced GR binding and histone acetylation in monocytes from both patient groups. However, GR binding and histone H4 acetylation remained significantly lower in monocytes from patients with SR asthma.

CONCLUSION

VitD demonstrated anti-inflammatory and corticosteroid-enhancing effects in monocytes of patients with SR asthma and patients with SS asthma. However, the responses to corticosteroids in patients with SR asthma remained significantly lower than those in patients with SS asthma.

Role of glucocorticoid-induced leucine zipper (GILZ) in bone acquisition

Glucocorticoids (GCs) have both anabolic and catabolic effects on bone. However, no GC anabolic effect mediator has been identified to date. Here we show that targeted expression of glucocorticoid-induced leucine zipper (GILZ), a GC anti-inflammatory effect mediator, enhances bone acquisition in mice. Transgenic mice, in which the expression of GILZ is under the control of a 3.6-kb rat type I collagen promoter, exhibited a high bone mass phenotype with significantly increased bone formation rate and osteoblast numbers. The increased osteoblast activity correlates with enhanced osteogenic differentiation and decreased adipogenic differentiation of bone marrow stromal cell cultures in vitro. In line with these changes, the mRNA levels of key osteogenic regulators (Runx2 and Osx) increased, and the level of adipogenic regulator peroxisome proliferator-activated receptor (PPAR) γ2 decreased significantly. We also found that GILZ physically interacts with C/EBPs and disrupts C/EBP-mediated PPARγ gene transcription. In conclusion, our results showed that GILZ is capable of increasing bone acquisition in vivo, and this action is mediated via a mechanism involving the inhibition of PPARγ gene transcription and shifting of bone marrow MSC/progenitor cell lineage commitment in favor of the osteoblast pathway.

Roles for the mitogen-activated protein kinase (MAPK) phosphatase, DUSP1, in feedback control of inflammatory gene expression and repression by dexamethasone

Glucocorticoids act on the glucocorticoid receptor (NR3C1) to repress inflammatory gene expression. This is central to their anti-inflammatory effectiveness and rational improvements in therapeutic index depend on understanding the mechanism. Human pulmonary epithelial A549 cells were used to study the role of the mitogen-activated protein kinase (MAPK) phosphatase, dual-specificity phosphatase 1 (DUSP1), in the dexamethasone repression of 11 inflammatory genes induced, in a MAPK-dependent manner, by interleukin-1β (IL1B). Adenoviral over-expression of DUSP1 inactivated MAPK pathways and reduced expression of all 11 inflammatory genes. IL1B rapidly induced DUSP1 expression and RNA silencing revealed a transient role in feedback inhibition of MAPKs and inflammatory gene expression. With dexamethasone, which induced DUSP1 expression, plus IL1B (co-treatment), DUSP1 expression was further enhanced. At 1 h, this was responsible for the dexamethasone inhibition of IL1B-induced MAPK activation and CXCL1 and CXCL2 mRNA expression, with a similar trend for CSF2. Whereas, CCL20 mRNA was not repressed by dexamethasone at 1 h, repression of CCL2, CXCL3, IL6, and IL8 was unaffected, and PTGS2 repression was partially affected by DUSP1 knockdown. At later times, dexamethasone repression of MAPKs was unaffected by DUSP1 silencing. Likewise, 6 h post-IL1B, dexamethasone repression of all 11 mRNAs was essentially unaffected by DUSP1 knockdown. Qualitatively similar data were obtained for CSF2, CXCL1, IL6, and IL8 release. Thus, despite general roles in feedback inhibition, DUSP1 plays a transient, often partial, role in the dexamethasone-dependent repression of certain inflammatory genes. Therefore this also illustrates key roles for DUSP1-independent effectors in mediating glucocorticoid-dependent repression.

A steroid-mimicking nanomaterial that mediates inhibition of human lung mast cell responses

Water-soluble fullerenes can be engineered to regulate activation of mast cells (MC) and control MC-driven diseases in vivo. To further understand their anti-inflammatory mechanisms a C70-based fullerene conjugated to four myo-inositol molecules (C70-I) was examined in vitro for its effects on the signaling pathways leading to mediator release from human lung MC. The C70-I fullerene stabilizes MC and acts synergistically with long-acting β2-adrenergic receptor agonists (LABA) to enhance inhibition of MC mediator release through FcεRI-simulation. The inhibition was paralleled by the upregulation of dual-specificity phosphatase one (DUSP1) gene and protein levels. Concomitantly, increases in MAPK were blunted in C70-I treated cells. The increase in DUSP1 expression was due to the ability of C70-I to prevent the ubiquitination and degradation of DUSP1. These findings identify a mechanism of how fullerenes inhibit inflammatory mediator release from MC and suggest they could potentially be an alternative therapy for steroid resistant asthmatics.

FROM THE CLINICAL EDITOR

This study investigates the role and mechanism of action of fullerenes in deactivating mast cell-based inflammation, paving the way to the development of a novel, non-steroid therapy in reactive airway disease.

Mice fed rapamycin have an increase in lifespan associated with major changes in the liver transcriptome

Rapamycin was found to increase (11% to 16%) the lifespan of male and female C57BL/6J mice most likely by reducing the increase in the hazard for mortality (i.e., the rate of aging) term in the Gompertz mortality analysis. To identify the pathways that could be responsible for rapamycin's longevity effect, we analyzed the transcriptome of liver from 25-month-old male and female mice fed rapamycin starting at 4 months of age. Few changes (<300 transcripts) were observed in transcriptome of rapamycin-fed males; however, a large number of transcripts (>4,500) changed significantly in females. Using multidimensional scaling and heatmap analyses, the male mice fed rapamycin were found to segregate into two groups: one group that is almost identical to control males (Rapa-1) and a second group (Rapa-2) that shows a change in gene expression (>4,000 transcripts) with more than 60% of the genes shared with female mice fed Rapa. Using ingenuity pathway analysis, 13 pathways were significantly altered in both Rapa-2 males and rapamycin-fed females with mitochondrial function as the most significantly changed pathway. Our findings show that rapamycin has a major effect on the transcriptome and point to several pathways that would likely impact the longevity.

Absence of glucocorticoids augments stress-induced Mkp1 mRNA expression within the hypothalamic-pituitary-adrenal axis

Stress-induced activation of hypothalamic paraventricular nucleus (PVN) corticotropin-releasing hormone (CRH) neurons trigger CRH release and synthesis. Recent findings have suggested that this process depends on the intracellular activation (phosphorylation) of ERK1/2 within CRH neurons. We have recently shown that the presence of glucocorticoids constrains stress-stimulated phosphorylation of PVN ERK1/2. In some peripheral cell types, dephosphorylation of ERK has been shown to be promoted by direct glucocorticoid upregulation of the MAP kinase phosphatase 1 (Mkp1) gene. In this study, we tested the hypothesis that glucocorticoids regulate Mkp1 mRNA expression in the neural forebrain (medial prefrontal cortex, mPFC, and PVN) and endocrine tissue (anterior pituitary) by subjecting young adult male Sprague-Dawley rats to various glucocorticoid manipulations with or without acute psychological stress (restraint). Restraint led to a rapid increase in Mkp1 mRNA within the mPFC, PVN, and anterior pituitary, and this increase did not require glucocorticoid activity. In contrast to glucocorticoid upregulation of Mkp1 gene expression in the peripheral tissues, we found that the absence of glucocorticoids (as a result of adrenalectomy) augmented basal mPFC and stress-induced PVN and anterior pituitary Mkp1 gene expression. Taken together, this study indicates that the presence of glucocorticoids may constrain Mkp1 gene expression in the neural forebrain and endocrine tissues. This possible constraint may be an indirect consequence of the inhibitory influence of glucocorticoids on stress-induced activation of ERK1/2, a known upstream positive regulator of Mkp1 gene transcription.

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

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

Mitogen-activated protein kinase phosphatase 1 as an inflammatory factor and drug target

Mitogen-activated protein kinases (MAPKs) are signaling proteins that are activated through phosphorylation, and they regulate many physiological and pathophysiological processes in cells. Mitogen-activated protein kinase phosphatase 1 (MKP-1) is an inducible nuclear phosphatase that dephosphorylates MAPKs, and thus, it is a negative feedback regulator of MAPK activity. MKP-1 has been found as a key endogenous suppressor of innate immune responses, as well as a regulator of the onset and course of adaptive immune responses. Altered MKP-1 signaling is implicated in chronic inflammatory diseases in man. Interestingly, MKP-1 expression and protein function have been found to be regulated by certain anti-inflammatory drugs, namely by glucocorticoids, antirheumatic gold compounds and PDE4 inhibitors, and MKP-1 has been shown to mediate many of their anti-inflammatory effects. In this Mini Review, we summarize the effect of MKP-1 in the regulation of innate and adaptive immune responses and its role as a potential anti-inflammatory drug target and review recent findings concerning the role of MKP-1 in certain anti-inflammatory drug effects.

Molecular determinants of glucocorticoid actions in inflammatory joint diseases

Since their discovery in 1948, glucocorticoids have been widely used clinically to treat inflammatory disorders like rheumatoid arthritis. However, their usefulness, especially in rheumatoid arthritis therapy, is hampered by severe side effects on bone leading to glucocorticoid-induced osteoporosis. The molecular and cellular mechanisms mediating the beneficial and adverse effects remain poorly understood. Nevertheless, advanced molecular biological analyses and in vivo approaches using conditional mutant mice have helped to unravel in part the underlying mechanisms of immunosuppression and side effects of glucocorticoid therapy in arthritis, thereby contributing to an improved understanding of these therapeutically important hormones.

Molecular mechanisms of glucocorticoid action in mast cells

Glucocorticoids are compounds that have successfully been used over the years in the treatment of inflammatory disorders. They are known to exhibit their effects through the glucocorticoid receptor (GR) that acts to downregulate the action of proinflammatory transcription factors such as AP-1 and NF-κB. The GR also exerts anti-inflammatory effects through activation of distinct genes. In addition to their anti-inflammatory actions, glucocorticoids are also potent antiallergic compounds that are widely used in conditions such as asthma and anaphylaxis. Nevertheless the mechanism of action of this hormone in these disorders is not known. In this article, we have reviewed reports on the effects of glucocorticoids in mast cells, one of the important immune cells in allergy. Building on the knowledge of the molecular action of glucocorticoids and the GR in the treatment of inflammation in other cell types, we have made suggestions as to the likely mechanisms of action of glucocorticoids in mast cells. We have further identified some important questions and research directions that need to be addressed in future studies to improve the treatment of allergic disorders.

Rhinovirus infection causes steroid resistance in airway epithelium through nuclear factor κB and c-Jun N-terminal kinase activation

BACKGROUND

Although inhaled glucocorticoids are the mainstays of asthma treatment, they are poorly effective at treating and preventing virus-induced asthma exacerbations. The major viruses precipitating asthma exacerbations are rhinoviruses.

OBJECTIVE

We sought to evaluate whether rhinovirus infection interferes with the mechanisms of action of glucocorticoids.

METHODS

Cultured primary human bronchial or transformed (A549) respiratory epithelial cells were infected with rhinovirus 16 (RV-16) before dexamethasone exposure. Glucocorticoid receptor (GR) α nuclear translocation, glucocorticoid response element (GRE) binding, and transactivation/transrepression functional readouts were evaluated by using immunocytochemistry, Western blotting, DNA binding assays, real-time quantitative PCR, coimmunoprecipitation, and ELISA techniques. Specific inhibitors of c-Jun N-terminal kinase (JNK) and of IκB kinase (IKK) were used to investigate the involvement of intracellular signaling pathways.

RESULTS

RV-16 infection impaired dexamethasone-dependent (1) inhibition of IL-1β-induced CXCL8 release, (2) induction of mitogen-activated protein kinase phosphatase 1 gene expression, and (3) binding of GR to GREs in airway epithelial cells. This was associated with impaired GRα nuclear translocation, as assessed by means of both immunochemistry (54.0% ± 6.8% vs 24.7% ± 3.8% GR-positive nuclei after 10 nmol/L dexamethasone treatment in sham- or RV-16-infected cells, respectively; P < .01) and Western blotting. RV-16 infection induced nuclear factor κB activation and GRα phosphorylation, which were prevented by inhibitors of IKK2 and JNK, respectively. In rhinovirus-infected cells the combination of JNK and IKK2 inhibitors totally restored dexamethasone suppression of CXCL8 release, induction of mitogen-activated protein kinase phosphatase 1 gene expression, and GRα nuclear translocation.

CONCLUSION

RV-16 infection of human airway epithelium induces glucocorticoid resistance. Inhibition of RV-16-induced JNK and nuclear factor κB activation fully reversed rhinovirus impairment of both GRα nuclear translocation and the transactivation/transrepression activities of glucocorticoids.

A potent and selective small-molecule inhibitor for the lymphoid-specific tyrosine phosphatase (LYP), a target associated with autoimmune diseases

Lymphoid-specific tyrosine phosphatase (LYP), a member of the protein tyrosine phosphatase (PTP) family of signaling enzymes, is associated with a broad spectrum of autoimmune diseases. Herein we describe our structure-based lead optimization efforts within a 6-hydroxy-benzofuran-5-carboxylic acid series culminating in the identification of compound 8b, a potent and selective inhibitor of LYP with a K(i) value of 110 nM and more than 9-fold selectivity over a large panel of PTPs. The structure of LYP in complex with 8b was obtained by X-ray crystallography, providing detailed information about the molecular recognition of small-molecule ligands binding LYP. Importantly, compound 8b possesses highly efficacious cellular activity in both T- and mast cells and is capable of blocking anaphylaxis in mice. Discovery of 8b establishes a starting point for the development of clinically useful LYP inhibitors for treating a wide range of autoimmune disorders.

Anti-inflammatory glucocorticoids: changing concepts

Despite being the most effective anti-inflammatory treatment for chronic inflammatory diseases, the mechanisms by which glucocorticoids (corticosteroids) effect repression of inflammatory gene expression remain incompletely understood. Direct interaction of the glucocorticoid receptor (NR3C1) with inflammatory transcription factors to repress transcriptional activity, i.e. transrepression, represents one mechanism of action. However, transcriptional activation, or transactivation, by NR3C1 also represents an important mechanism of glucocorticoid action. Glucocorticoids rapidly and profoundly increase expression of multiple genes, many with properties consistent with the repression of inflammatory gene expression. For example: the dual specificity phosphatase, DUSP1, reduces activation of mitogen-activated protein kinases; glucocorticoid-induced leucine zipper (TSC22D3) represses nuclear factor-κB (NF-κB) and activator protein 1 (AP-1) transcriptional responses; inhibitor of κBα (NFKBIA) inhibits NF-κB; tristraprolin (ZFP36) destabilises and translationally represses inflammatory mRNAs; CDKN1C, a cell cycle regulator, may attenuate JUN N-terminal kinase signalling; and regulator of G-protein signalling 2 (RGS2), by reducing signalling from Gαq-linked G protein-coupled receptors (GPCRs), is bronchoprotective. While glucocorticoid-dependent transrepression can co-exist with transactivation, transactivation may account for the greatest level and most potent repression of inflammatory genes. Equally, NR3C1 transactivation is enhanced by β2-adrenoceptor agonists and may explain the enhanced clinical efficacy of β2-adrenoceptor/glucocorticoid combination therapies in asthma and chronic obstructive pulmonary disease. Finally, NR3C1 transactivation is reduced by inflammatory stimuli, including respiratory syncytial virus and human rhinovirus. This provides an explanation for glucocorticoid resistance. Continuing efforts to understand roles for glucocorticoid-dependent transactivation will provide opportunities to improve glucocorticoid therapies.

Crude extract of Ceriporia lacerata has a protective effect on dexamethasone-induced cytotoxicity in INS-1 cells via the modulation of PI3K/PKB activity

Excessive and/or long-term glucocorticoid therapy reduces β-cell mass and induces hyperglycemia, which contribute to the development of steroid‑induced diabetes. Ceriporia (C.) lacerata is one of the white‑rot fungi and has been used in bioremediations, such as lignocellulose degradation, in nature. The pharmacologic effect of C. lacerata on steroid-induced β-cell toxicity is not known. In this study, we evaluated the effect of a crude extract from a submerged cultivation of C. lacerata on the survival and apoptosis of INS-1 rat insulin-secreting cells exposed to dexamethasone (Dex), a synthetic diabetogenic glucocorticoid. Treatment with the C. lacerata crude extract (CLCE) largely blocked the Dex-induced reduction in survival and apoptosis of INS-1 cells. Moreover, CLCE treatment inhibited Dex-induced protein kinase B (PKB) dephosphorylation without affecting Dex-induced extracellular signal-regulated protein kinase-1/2 dephosphorylation and MKP-1 upregulation. Importantly, the protective effect of CLCE on Dex-induced cytotoxicity in INS-1 cells was attenuated by LY294002, an inhibitor of PI3K/PKB. CLCE treatment, however, did not protect the INS-1 cells from the cytotoxic effects triggered by other insults, such as interleukin-1β (an inflammatory cytokine), streptozotocin (a diabetogenic drug), thapsigargin (a calcium mobilizing agent), and tunicamycin (an ER stress inducer). Collectively, these findings demonstrate for the first time the ability of CLCE to specifically protect INS-1 cells from Dex-induced cytotoxicity through the modulation of the PI3K/PKB pathway. It is suggested that CLCE may be applied for the prevention and/or treatment of steroid diabetes in which reduction of β-cell survival and induction of β-cell apoptosis play pathogenic roles.

Vitamin D enhances glucocorticoid action in human monocytes: involvement of granulocyte-macrophage colony-stimulating factor and mediator complex subunit 14

Vitamin D (VitD) is now recognized for its pleiotrophic roles in regulating immune function. VitD interaction with other steroid receptor superfamily receptors in peripheral blood mononuclear cells is poorly understood. In the current study, we demonstrate that VitD enhanced glucocorticoid (GC) responses in human peripheral blood mononuclear cells because it stimulated GC induction of mitogen-activated protein kinase phosphatase-1 (MKP-1) and enhanced GC inhibition of LPS-induced IL-6. These VitD effects were abolished in purified CD14(+) and CD14(-) cells but were recovered in CD14(+) cells co-cultured with CD14(-) cells separated by tissue culture inserts. GM-CSF, found in culture supernatants from CD14(-) cells, was shown to mediate VitD enhancement of GC-induced MKP-1 production in monocytes via increased production of mediator complex subunit 14 (MED14). Recruitment of VitD receptor and MED14, 4.7 kbp upstream of the human MKP-1 gene transcription start site, enhanced binding of glucocorticoid receptor and histone H4 acetylation at the 4.6-kbp glucocorticoid response element of the MKP-1 promoter in the presence of GM-CSF in U937 cells. Knockdown of MED14 abolished VitD-mediated enhancement of GC-induced MKP-1 production. These data demonstrate VitD-mediated stimulation of GC anti-inflammatory effects in human monocytes and identify a role for GM-CSF and MED14 as mediators of this process.

mTOR is frequently active in GH-secreting pituitary adenomas without influencing their morphopathological features

Initiating factors and mechanisms of tumor formation are poorly understood in nonfamilial pituitary adenomas. Alteration of intracellular pathways is an underlying event in numerous neoplasms. Among them, excessive activation of mammalian target of rapamycin (mTOR) pathway and its two main regulators, Akt and Erk, has been detected frequently in solid tumors. This study tests the activation of mTOR pathway in pituitary adenomas and its influence on their morphopathological features. Fifty-three pituitary adenomas were fresh frozen after surgery and analyzed by western blotting using phospho-specific antibodies. The impact of Akt and Erk activation on mTOR pathway was assessed in five primary cultures derived from the excised adenomas using selective kinase inhibitors. Statistical correlations of size, volume, Ki-67 %, Knosp's grading, and somatostatin receptor (SSTR) expression with the activation of mentioned kinases was performed. GHomas showed the highest frequency (71 %) and level of mTOR pathway activity comparing to other adenomas (33 %). No significant correlation was found between mTOR activation and any of the morphopathological features in the studied samples. mTOR kinase phosphorylation was independent of Erk and Akt in primary cultures. Erk activity was significant in all types of adenomas but was the highest in control samples. Its phosphorylation correlated inversely with the Knosp's grading in nonfunctional pituitary adenomas and directly with somatostatin receptor subtype 2 A expression in GHomas. Presented data point to the noteworthy mTOR activity in GHomas. However, the lack of correlation with morphopathological features, its independence of Erk and Akt phosphorylation, and high level of Erk activity in control pituitary necessitate further research for clarifying the role of these pathways in pituitary adenomas.

Effects of dexamethasone on the TGF-β1-induced epithelial-to-mesenchymal transition in human peritoneal mesothelial cells

The epithelial-to-mesenchymal transition (EMT) is known to have a role in appropriate embryonic development, the physiological response to injury and pathological events such as organ fibrosis and cancer progression. Glucocorticoid (GC), one of the most commonly used anti-inflammatory drugs, inhibits the deposition of extracellular matrix independent of its anti-inflammatory effect. The EMT of human peritoneal mesothelial cells (HPMCs) is a key mechanism of peritoneal fibrosis; however, it has not yet been investigated whether GC imposes any effect on the EMT of HPMCs. To investigate the therapeutic potential of GC on preserving peritoneal membrane function, we studied the effect of dexamethasone (DEXA), a synthetic GC, on the transforming growth factor-β1 (TGF-β1)-induced EMT in HPMCs. As assessed by changes in cell morphology, the expression of epithelial and mesenchymal cell markers (such as E-cadherin, ZO-1 and α-SMA, α-smooth muscle actin) and cell migration, DEXA inhibited the TGF-β1-induced EMT. RU486, a glucocorticoid receptor (GR) antagonist, blocked the effect of DEXA on the TGF-β1-induced EMT. Importantly, DEXA also induced the mesenchymal-to-epithelial transition of TGF-β1-stimulated HPMCs. The beneficial effect of DEXA on the TGF-β1-induced EMT was mediated through the amelioration of ERK and p38 mitogen-activated protein kinase (MAPK) phosphorylation; however, this effect was not related to the TGF-β1-induced activation of Smad2/3 signaling. DEXA inhibited glycogen synthase kinase-3β (GSK-3β) phosphorylation and the Snail upregulation induced by TGF-β1, which were also ameliorated by inhibitors of MAPK. In conclusion, this is the first study demonstrating the protective effect of DEXA on the EMT in TGF-β1-stimulated HPMCs by inhibiting MAPK activation, GSK-3β phosphorylation and Snail upregulation.

Glucocorticoid repression of inflammatory gene expression shows differential responsiveness by transactivation- and transrepression-dependent mechanisms

Binding of glucocorticoid to the glucocorticoid receptor (GR/NR3C1) may repress inflammatory gene transcription via direct, protein synthesis-independent processes (transrepression), or by activating transcription (transactivation) of multiple anti-inflammatory/repressive factors. Using human pulmonary A549 cells, we showed that 34 out of 39 IL-1β-inducible mRNAs were repressed to varying degrees by the synthetic glucocorticoid, dexamethasone. Whilst these repressive effects were GR-dependent, they did not correlate with either the magnitude of IL-1β-inducibility or the NF-κB-dependence of the inflammatory genes. This suggests that induction by IL-1β and repression by dexamethasone are independent events. Roles for transactivation were investigated using the protein synthesis inhibitor, cycloheximide. However, cycloheximide reduced the IL-1β-dependent expression of 13 mRNAs, which, along with the 5 not showing repression by dexamethasone, were not analysed further. Of the remaining 21 inflammatory mRNAs, cycloheximide significantly attenuated the dexamethasone-dependent repression of 11 mRNAs that also showed a marked time-dependence to their repression. Such effects are consistent with repression occurring via the de novo synthesis of a new product, or products, which subsequently cause repression (i.e., repression via a transactivation mechanism). Conversely, 10 mRNAs showed completely cycloheximide-independent, and time-independent, repression by dexamethasone. This is consistent with direct GR transrepression. Importantly, the inflammatory mRNAs showing attenuated repression by dexamethasone in the presence of cycloheximide also showed a significantly greater extent of repression and a higher potency to dexamethasone compared to those mRNAs showing cycloheximide-independent repression. This suggests that the repression of inflammatory mRNAs by GR transactivation-dependent mechanisms accounts for the greatest levels of repression and the most potent repression by dexamethasone. In conclusion, our data indicate roles for both transrepression and transactivation in the glucocorticoid-dependent repression of inflammatory gene expression. However, transactivation appears to account for the more potent and efficacious mechanism of repression by glucocorticoids on these IL-1β-induced genes.

Dexamethasone Induces FcγRIIb Expression in RBL-2H3 Cells

Mast cells are involved in allergic responses, protection against pathogens and autoimmune diseases. Dexamethasone (Dex) and other glucocorticoids suppress FcεRI-mediated release of inflammatory mediators from mast cells. The inhibition mechanisms were mainly investigated on the downstream signaling of Fc receptor activations. Here, we addressed the effects of Dex on Fc receptor expressions in rat mast cell line RBL-2H3. We measured mRNA levels of Fc receptors by real-time PCR. As expected, Dex decreased the mRNA levels of activating Fc receptor for IgE (FcεR) I and increased the mRNA levels of the inhibitory Fc receptor for IgG FcγRIIb. Interestingly, Dex stimulated transcriptions of other activating receptors such as Fc receptors for IgG (FcγR) I and FcγRIII. To investigate the mechanisms underlying transcriptional regulation, we employed a transcription inhibitor actinomycin D and a translation inhibitor cycloheximide. The inhibition of protein synthesis without Dex treatment enhanced FcγRI and FcγRIII mRNA levels potently, while FcεRI and FcγRIIb were minimally affected. Next, we examined expressions of the Fc receptors on cell surfaces by the flow cytometric method. Only FcγRIIb protein expression was significantly enhanced by Dex treatment, while FcγRI, FcγRIII and FcεRI expression levels were marginally changed. Our data showed, for the first time, that Dex regulates Fc receptor expressions resulting in augmentation of the inhibitory receptor FcγRIIb.

Corticosteroids and β₂-agonists upregulate mitogen-activated protein kinase phosphatase 1: in vitro mechanisms

BACKGROUND AND PURPOSE

Airway remodelling is a consequence of long-term inflammation and MAPKs are key signalling molecules that drive pro-inflammatory pathways. The endogenous MAPK deactivator--MAPK phosphatase 1 (MKP-1)--is a critical negative regulator of the myriad pro-inflammatory pathways activated by MAPKs in the airway.

EXPERIMENTAL APPROACH

Herein we investigated the molecular mechanisms responsible for the upregulation of MKP-1 in airway smooth muscle (ASM) by the corticosteroid dexamethasone and the β₂-agonist formoterol, added alone and in combination.

KEY RESULTS

MKP-1 is a corticosteroid-inducible gene whose expression is enhanced by long-acting β₂-agonists in an additive manner. Formoterol induced MKP-1 expression via the β₂-adrenoceptor and we provide the first direct evidence (utilizing overexpression of PKIα, a highly selective PKA inhibitor) to show that PKA mediates β₂-agonist-induced MKP-1 upregulation. Dexamethasone activated MKP-1 transcription in ASM cells via a cis-acting corticosteroid-responsive region located between -1380 and -1266 bp of the MKP-1 promoter. While the 3'-untranslated region of MKP-1 contains adenylate + uridylate elements responsible for regulation at the post-transcriptional level, actinomycin D chase experiments revealed that there was no increase in MKP-1 mRNA stability in the presence of dexamethasone, formoterol, alone or in combination. Rather, there was an additive effect of the asthma therapeutics on MKP-1 transcription.

CONCLUSIONS AND IMPLICATIONS

Taken together, these studies allow us a greater understanding of the molecular basis of MKP-1 regulation by corticosteroids and β₂-agonists and this new knowledge may lead to elucidation of optimized corticosteroid-sparing therapies in the future.

The plant-derived glucocorticoid receptor agonist Endiandrin A acts as co-stimulator of colonic epithelial sodium channels (ENaC) via SGK-1 and MAPKs

In a search for secondary plant compounds that bind to the glucocorticoid receptor (GR), the cyclobutane lignan endiandrin A was discovered from the rainforest tree Endiandra anthropophagorum Domin. Our present study aims to characterize the effect of endiandrin A on GR-dependent induction of colonic sodium transport. The effect of endiandrin A was analyzed in GR-expressing colonic HT-29/B6 cells (HT-29/B6-GR). GR transactivation and subcellular localization were investigated by reporter gene assay and immunofluorescence. Epithelial sodium channel (ENaC) was analyzed by qRT-PCR and by measuring amiloride-sensitive short-circuit current (I_sc) in Ussing chambers. Endiandrin A (End A) has been identified as GR receptor binder. However, it did not cause significant GR transactivation as pGRE-luciferase activity was only 7% of that of the maximum effect of dexamethasone. Interestingly, endiandrin A had a significant impact on dexamethasone-dependent sodium absorption in cells co-exposed to tumor necrosis factor (TNF)-α. This was in part due to up-regulation of β- and γ-ENaC subunit expression. Endiandrin A potentiated GR-mediated transcription by increasing GR protein expression and phosphorylation. It inhibited c-Jun N-terminal kinase (JNK) activation induced by dexamethasone and/or TNF-α and increased levels of GR localized to the nucleus. Additionally, endiandrin A increased the serum- and glucocorticoid-induced kinase (sgk)-1 via activation of p38. Finally, the regulation of ENaC function by endiandrin A was confirmed in rat native colon. In conclusion, endiandrin A potentiates glucocorticoid-driven activation of colonic epithelial sodium channels via JNK inhibition and p38 activation due to transcriptional up-regulation of β- and γ-ENaC-subunits along with induction of sgk-1.

Kaposi's sarcoma-associated herpesvirus suppression of DUSP1 facilitates cellular pathogenesis following de novo infection

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma (KS), and KSHV activation of mitogen-activated protein kinases (MAPKs) initiates a number of key pathogenic determinants of KS. Direct inhibition of signal transduction as a therapeutic approach presents several challenges, and a better understanding of KSHV-induced mechanisms regulating MAPK activation may facilitate the development of new treatment or prevention strategies for KS. MAPK phosphatases, including dual-specificity phosphatase-1 (DUSP1), negatively regulate signal transduction and cytokine activation through MAPK dephosphorylation or interference with effector molecule binding to MAPKs, including the extracellular signal-regulated kinase (ERK). We found that ERK-dependent latent viral gene expression, the induction of promigratory factors, and cell invasiveness following de novo infection of primary human endothelial cells are in part dependent on KSHV suppression of DUSP1 expression during de novo infection. KSHV-encoded miR-K12-11 upregulates the expression of xCT (an amino acid transporter and KSHV fusion/entry receptor), and existing data indicate a role for xCT in the regulation of 14-3-3β, a transcriptional repressor of DUSP1. We found that miR-K12-11 induces endothelial cell secretion of promigratory factors and cell invasiveness through upregulation of xCT-dependent, 14-3-3β-mediated suppression of DUSP1. Finally, proof-of-principle experiments revealed that pharmacologic upregulation of DUSP1 inhibits the induction of promigratory factors and cell invasiveness during de novo KSHV infection. These data reveal an indirect role for miR-K12-11 in the regulation of DUSP1 and downstream pathogenesis.

Regulation of the CCL2 gene in pancreatic β-cells by IL-1β and glucocorticoids: role of MKP-1

Release of pro-inflammatory cytokines from both resident and invading leukocytes within the pancreatic islets impacts the development of Type 1 diabetes mellitus. Synthesis and secretion of the chemokine CCL2 from pancreatic β-cells in response to pro-inflammatory signaling pathways influences immune cell recruitment into the pancreatic islets. Therefore, we investigated the positive and negative regulatory components controlling expression of the CCL2 gene using isolated rat islets and INS-1-derived β-cell lines. We discovered that activation of the CCL2 gene by IL-1β required the p65 subunit of NF-κB and was dependent on genomic response elements located in the -3.6 kb region of the proximal gene promoter. CCL2 gene transcription in response to IL-1β was blocked by pharmacological inhibition of the IKKβ and p38 MAPK pathways. The IL-1β-mediated increase in CCL2 secretion was also impaired by p38 MAPK inhibition and by glucocorticoids. Moreover, multiple synthetic glucocorticoids inhibited the IL-1β-stimulated induction of the CCL2 gene. Induction of the MAP Kinase Phosphatase-1 (MKP-1) gene by glucocorticoids or by adenoviral-mediated overexpression decreased p38 MAPK phosphorylation, which diminished CCL2 gene expression, promoter activity, and release of CCL2 protein. We conclude that glucocorticoid-mediated repression of IL-1β-induced CCL2 gene transcription and protein secretion occurs in part through the upregulation of the MKP-1 gene and subsequent deactivation of the p38 MAPK. Furthermore, the anti-inflammatory actions observed with MKP-1 overexpression were obtained without suppressing glucose-stimulated insulin secretion. Thus, MKP-1 is a possible target for anti-inflammatory therapeutic intervention with preservation of β-cell function.

The multiple facets of glucocorticoid action in rheumatoid arthritis

Glucocorticoids have potent anti-inflammatory effects and have been used to treat patients with rheumatoid arthritis for more than 60 years. However, severe adverse effects of glucocorticoid treatment, including loss of bone mass and increased risk of fractures, are common. Data from studies of glucocorticoid-mediated gene regulation, which utilized conditional knockout mice in animal models of arthritis or glucocorticoid-induced osteoporosis, have substantially increased our understanding of the mechanisms by which glucocorticoids act via the glucocorticoid receptor. Following glucocorticoid binding, the receptor regulates gene expression either by interacting with DNA-bound transcription factors as a monomer or by binding directly to DNA as a dimer. In contrast to the old hypothesis that transrepression mechanisms involving monomeric glucocorticoid receptor actions were responsible for the anti-inflammatory effects of glucocorticoids, whereas dimeric glucocorticoid receptor binding resulted in adverse effects, data from animal models have shown that the anti-inflammatory and adverse effects of glucocorticoids are mediated by both monomeric and dimeric glucocorticoid receptor binding. This improved knowledge of the molecular mechanisms that underlie the beneficial and adverse effects of glucocorticoid therapy might lead to the development of rationales for novel glucocorticoid receptor ligands that could potentially have anti-inflammatory efficacy without adverse effects on bone.

The absence of somatotroph proliferation during continuous stress is a result of the lack of extracellular signal-regulated kinase 1/2 activation

The integrity of homeostasis can be affected by chronic stress, and hyposomatotropism is evident in chronic stress-associated illnesses. In the present study, we demonstrated that a continuous stress (CS) severely affected somatotrophs among hormone-secreting cells in the anterior lobe (AL) of the pituitary by using a rat CS model. Among AL cells, the proliferation of somatotrophs was almost entirely suppressed in rats that had 3-5 days of CS (5dCS), although other hormone-secreting cells continued to proliferate. The cell size of somatotrophs was reduced at 5dCS (P<0.01), the number of secretory granules was increased at 3dCS (P<0.01) and serum growth hormone (GH) was on declining trend during 1 to 5dCS, suggesting that GH release was inhibited. GH-releasing hormone (GHRH) mRNA level in the arcuate nucleus was transiently decreased, whereas its receptor expression in the AL was significantly increased in CS rats. When 5dCS rats were injected with GHRH, transient GH secretion was observed, whereas proliferation of somatotrophs did not occur. The GHRH administration failed to stimulate extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and the nuclear translocation of ERK in somatotrophs. These results suggest that somatotrophs of 5dCS rats expressed sufficient GHRH receptor, which could transfer a signal for GH release. However, the GHRH-induced proliferation signal was blocked somewhere between the receptor and ERK1/2. Because significant increase of corticosterone in the initial stage (the 1-3dCS) was observed in this model, the corticosterone may affect the signalling. Although the mechanism underlying the blockage of the proliferation signal in somatotrophs under CS remains unclear, these somatotrophic disorder, suggesting that the present animal model may be useful for understanding the molecular mechanisms of chronic stress-associated illnesses.

Glucocorticoid regulation of brain-derived neurotrophic factor: relevance to hippocampal structural and functional plasticity

Glucocorticoids serve as key stress response hormones that facilitate stress coping. However, sustained glucocorticoid exposure is associated with adverse consequences on the brain, in particular within the hippocampus. Chronic glucocorticoid exposure evokes neuronal cell damage and dendritic atrophy, reduces hippocampal neurogenesis and impairs synaptic plasticity. Glucocorticoids also alter expression and signaling of the neurotrophin, brain-derived neurotrophic factor (BDNF). Since BDNF is known to promote neuroplasticity, enhance cell survival, increase hippocampal neurogenesis and cellular excitability, it has been hypothesized that specific adverse effects of glucocorticoids may be mediated by attenuating BDNF expression and signaling. The purpose of this review is to summarize the current state of literature examining the influence of glucocorticoids on BDNF, and to address whether specific effects of glucocorticoids arise through perturbation of BDNF signaling. We integrate evidence of glucocorticoid regulation of BDNF at multiple levels, spanning from the well-documented glucocorticoid-induced changes in BDNF mRNA to studies examining alterations in BDNF receptor-mediated signaling. Further, we delineate potential lines of future investigation to address hitherto unexplored aspects of the influence of glucocorticoids on BDNF. Finally, we discuss the current understanding of the contribution of BDNF to the modulation of structural and functional plasticity by glucocorticoids, in particular in the context of the hippocampus. Understanding the mechanistic crosstalk between glucocorticoids and BDNF holds promise for the identification of potential therapeutic targets for disorders associated with the dysfunction of stress hormone pathways.

Mechanisms of the anti-inflammatory effects of glucocorticoids: genomic and nongenomic interference with MAPK signaling pathways

Glucocorticoids (GCs) are steroid hormones produced by the adrenal gland and regulated by the hypothalamus-pituitary-adrenal axis. GCs mediate effects that mostly result in transcriptional regulation of glucocorticoid receptor target genes. Mitogen-activated protein kinases (MAPKs) comprise a family of signaling proteins that convert extracellular stimuli into the activation of intracellular transduction pathways via phosphorylation of a cascade of substrates. They modulate a variety of physiological cell processes, such as proliferation, apoptosis, and development. However, when MAPKs are improperly activated by proinflammatory and/or extracellular stress stimuli, they contribute to the regulation of proinflammatory transcription factors, thus perpetuating activation of the inflammatory cascade. One of the mechanisms by which GCs exert their anti-inflammatory effects is negative interference with MAPK signaling pathways. Several functional interactions between GCs and MAPK signaling have been discovered and studied. Some of these interactions involve the GC-mediated up-regulation of proteins that in turn interfere with the activation of MAPK, such as glucocorticoid-induced-leucine zipper, MAPK phosphatase-1, and annexin-1. Other mechanisms include activated GR directly interacting with components of the MAPK pathway and negatively regulating their activation. The multiple interactions between GCs and MAPK pathways and their potential biological relevance in mediating the anti-inflammatory effects of GCs are reviewed.

Obesity and pulmonary disease: unanswered questions

Obesity is associated with risk of pulmonary disease, and adversely affects lung function. The parallel increase in obesity and asthma suggests the two conditions are linked; indeed, they can worsen each other. Obesity and inadequate asthma control are associated with poor quality of life, and place a high economic burden on public health. Although the obesity-lung interaction is a major issue for basic research and clinical studies, various questions remain unanswered. Do intrauterine and early life factors impact on the development of obesity and lung disease? If so, can this be prevented? Asthma is generally more severe in obese subjects, but is adiposity a driver of a new asthma phenotype that features greater morbidity and mortality, worse control and decreased response to medications? Obese individuals have small lung volumes, hence their airway calibre is reduced and airway resistance is increased. What puzzles physicians is whether peripheral airways undergo remodelling, which would increase bronchoconstriction. Obese asthmatics respond suboptimally to anti-inflammatory treatment, which raises the question: 'what drug for what patient?' Life expectancy is decreased in obesity and in chronic pulmonary disorders, but does obesity protect against or trigger chronic obstructive pulmonary disease? The time has come to find answers to these questions.

Modulation of interferon-γ-induced glial cell activation by transforming growth factor β1: a role for STAT1 and MAPK pathways

Overactivated glial cells can produce neurotoxic oxidant molecules such as nitric oxide (NO·) and superoxide anion (O(2)·(-)). We have previously reported that transforming growth factor β1 (TGFβ1) released by hippocampal cells modulates interferon-γ (IFNγ)-induced production of O(2)·(-) and NO· by glial cells. However, underlying molecular mechanisms are not completely understood, thereby, the aim of this work was to study the effect of TGFβ1 on IFNγ-induced signaling pathways. We found that costimulation with TGFβ1 decreased IFNγ-induced phosphorylation of signal transducer and activator of transcription-type-1 (STAT1) and extracellular signal-regulated kinase (ERK), which correlated with a reduced O(2)·(-) and NO· production in mixed and purified glial cultures. Moreover, IFNγ caused a decrease in TGFβ1-mediated phosphorylation of P38, whereas pre-treatment with ERK and P38 inhibitors decreased IFNγ-induced phosphorylation of STAT1 on serine727 and production of radical species. These results suggested that modulation of glial activation by TGFβ1 is mediated by deactivation of MAPKs. Notably, TGFβ1 increased the levels of MAPK phosphatase-1 (MKP-1), whose participation in TGFβ1-mediated modulation was confirmed by MKP-1 siRNA transfection in mixed and purified glial cultures. Our results indicate that the cross-talk between IFNγ and TGFβ1 might regulate the activation of glial cells and that TGFβ1 modulated IFNγ-induced production of neurotoxic oxidant molecules through STAT1, ERK, and P38 pathways.

Anti-inflammatory effects of mapracorat, a novel selective glucocorticoid receptor agonist, is partially mediated by MAP kinase phosphatase-1 (MKP-1)

Mapracorat is a novel selective glucocorticoid receptor agonist (SEGRA), structurally distinct from corticosteroids. In preclinical studies, mapracorat potently inhibits the production of a variety of inflammatory mediators including cytokines and prostaglandin E2 (PGE(2)), with limited side effects associated with traditional corticosteroids. The objective of this study was to delineate the mechanisms underlying the anti-inflammatory properties of mapracorat. We found that mapracorat potently inhibited the production of GM-CSF and TNF-α in LPS-stimulated Raw 264.7 macrophages. Mapracorat also substantially attenuated the expression of COX-2 and the production of PGE(2). The inhibition of mapracorat on the inflammatory response was dose-dependent, and substantially inhibitory effects were observed at concentrations in the 10-100 nm range. Examination of the activation kinetics of p38 and its downstream target MAPK-activated protein kinase-2 (MK-2) revealed a shortened activation course after LPS stimulation in cells pretreated with mapracorat. Supporting the notion that mapracorat augments a feedback control mechanism restraining the p38 pathway, we found that mapracorat enhanced the expression of MAPK phosphatase-1 (MKP-1), a critical negative regulator of MAPKs that drive the production of cytokines and other inflammatory mediators. While mapracorat alone did not stimulate MKP-1 expression, it markedly enhanced the expression of MKP-1 in cells stimulated by LPS, in a similar manner and potency to the augmenting effect of dexamethasone. Blocking MKP-1 expression by triptolide also abolished the accelerating effects of mapracorat on p38 and MK-2 deactivation, further supporting a role of MKP-1 in the anti-inflammatory mechanism of mapracorat. Taken together, these results indicate that mapracorat exerts its anti-inflammatory effects, at least in part, by augmenting MKP-1 expression.

Endogenous inhibitor proteins that connect Ser/Thr kinases and phosphatases in cell signaling

Protein phosphatase activity acts as a primary determinant of the extent and duration of phosphorylation of cellular proteins in response to physiological stimuli. Ser/Thr protein phosphatase-1 (PP1) belongs to the PPP superfamily, and is associated with regulatory subunits that confer substrate specificity, allosteric regulation, and subcellular compartmentalization. In addition, all eukaryotic cells contain multiple heat-stable proteins that originally were thought to inhibit phosphatase catalytic subunits released from the regulatory subunits, as a fail-safe mechanism. However, discovery of C-kinase-activated PP1 inhibitor, Mr of 17 kDa (CPI-17) required fresh thinking about the endogenous inhibitors as specific regulators of particular phosphatase complexes, acting in addition to, not instead of, regulatory subunits. The cellular actions of the endogenous inhibitors are controlled by phosphorylation, connecting them to kinase pathways. More recent progress has unveiled additional functions of PP1 inhibitor-2 (I-2), including regulation of protein kinases. Transcriptional mechanisms govern the expression levels of CPI-17 in response to stimuli. If true for other inhibitor proteins, they have the potential of being diagnostic markers for pathological conditions. We discuss specific examples of PP1 inhibitor proteins regulating particular cellular functions and the rationale for incorporating phosphatase inhibitor proteins in development of new therapeutic strategies.

Corticosteroid-induced gene expression in allergen-challenged asthmatic subjects taking inhaled budesonide

BACKGROUND AND PURPOSE

Inhaled corticosteroids (ICS) are the cornerstone of asthma pharmacotherapy and, acting via the glucocorticoid receptor (GR), reduce inflammatory gene expression. While this is often attributed to a direct inhibitory effect of the GR on inflammatory gene transcription, corticosteroids also induce the expression of anti-inflammatory genes in vitro. As there are no data to support this effect in asthmatic subjects taking ICS, we have assessed whether ICS induce anti-inflammatory gene expression in subjects with atopic asthma.

EXPERIMENTAL APPROACH

Bronchial biopsies from allergen-challenged atopic asthmatic subjects taking inhaled budesonide or placebo were subjected to gene expression analysis using real-time reverse transcriptase-PCR for the corticosteroid-inducible genes (official gene symbols with aliases in parentheses): TSC22D3 [glucocorticoid-induced leucine zipper (GILZ)], dual-specificity phosphatase-1 (MAPK phosphatase-1), both anti-inflammatory effectors, and FKBP5 [FK506-binding protein 51 (FKBP51)], a regulator of GR function. Cultured pulmonary epithelial and smooth muscle cells were also treated with corticosteroids before gene expression analysis.

KEY RESULTS

Compared with placebo, GILZ and FKBP51 mRNA expression was significantly elevated in budesonide-treated subjects. Budesonide also increased GILZ expression in human epithelial and smooth muscle cells in culture. Immunostaining of bronchial biopsies revealed GILZ expression in the airways epithelium and smooth muscle of asthmatic subjects.

CONCLUSIONS AND IMPLICATIONS

Expression of the corticosteroid-induced genes, GILZ and FKBP51, is up-regulated in the airways of allergen-challenged asthmatic subjects taking inhaled budesonide. Consequently, the biological effects of corticosteroid-induced genes should be considered when assessing the actions of ICS. Treatment modalities that increase or decrease GR-dependent transcription may correspondingly affect corticosteroid efficacy.

Diversity and specificity of the mitogen-activated protein kinase phosphatase-1 functions

The balance of protein phosphorylation is achieved through the actions of a family of protein serine/threonine kinases called the mitogen-activated protein kinases (MAPKs). The propagation of MAPK signals is attenuated through the actions of the MAPK phosphatases (MKPs). The MKPs specifically inactivate the MAPKs by direct dephosphorylation. The archetypal MKP family member, MKP-1 has garnered much of the attention amongst its ten other MKP family members. Initially viewed to play a redundant role in the control of MAPK signaling, it is now clear that MKP-1 exerts profound regulatory functions on the immune, metabolic, musculoskeletal and nervous systems. This review focuses on the physiological functions of MKP-1 that have been revealed using mouse genetic approaches. The implications from studies using MKP-1-deficient mice to uncover the role of MKP-1 in disease will be discussed.

Differential expression and functional analysis of the tristetraprolin family during early differentiation of 3T3-L1 preadipocytes

The tristetraprolin (TTP) family comprises zinc finger-containing AU-rich element (ARE)-binding proteins consisting of three major members: TTP, ZFP36L1, and ZFP36L2. The present study generated specific antibodies against each TTP member to evaluate its expression during differentiation of 3T3-L1 preadipocytes. In contrast to the inducible expression of TTP, results indicated constitutive expression of ZFP36L1 and ZFP36L2 in 3T3-L1 preadipocytes and their phosphorylation in response to differentiation signals. Physical RNA pull-down and functional luciferase assays revealed that ZFP36L1 and ZFP36L2 bound to the 3' untranslated region (UTR) of MAPK phosphatase-1 (MKP-1) mRNA and downregulated Mkp-1 3'UTR-mediated luciferase activity. Mkp-1 is an immediate early gene for which the mRNA is transiently expressed in response to differentiation signals. The half-life of Mkp-1 mRNA was longer at 30 min of induction than at 1 h and 2 h of induction. Knockdown of TTP or ZFP36L2 increased the Mkp-1 mRNA half-life at 1 h of induction. Knockdown of ZFP36L1, but not ZFP36L2, increased Mkp-1 mRNA basal levels via mRNA stabilization and downregulated ERK activation. Differentiation induced phosphorylation of ZFP36L1 through ERK and AKT signals. Phosphorylated ZFP36L1 then interacted with 14-3-3, which might decrease its mRNA destabilizing activity. Inhibition of adipogenesis also occurred in ZFP36L1 and TTP knockdown cells. The findings indicate that the differential expression of TTP family members regulates immediate early gene expression and modulates adipogenesis.

Glucocorticoid receptor dimerization induces MKP1 to protect against TNF-induced inflammation

Glucocorticoids acting through the glucocorticoid receptor (GR) inhibit TNF-induced lethal inflammation. Here, we demonstrate that GR dimerization plays a role in reducing TNF sensitivity. In mutant mice unable to dimerize GR, we found that TNF failed to induce MAPK phosphatase 1 (MKP1). We assessed TNF sensitivity in Mkp1(-/-) mice and found increased inflammatory gene induction in livers, increased circulating cytokines, cell death in intestinal epithelium, severe intestinal inflammation, hypothermia, and death. Mkp1(-/-) mice had increased levels of phosphorylated JNK, which promotes apoptosis, in liver tissue. We further examined JNK-deficient mice for their response to TNF. Although Jnk1(-/-) mice showed no change in sensitivity to TNF, Jnk2(-/-) mice were significantly protected against TNF, identifying JNK2 as an essential player in inflammation induced by TNF. Furthermore, we found that loss of Jnk2 partially rescued the increased sensitivity of Mkp1(-/-) and mutant GR mice to TNF. Our data show that GR dimerization inhibits JNK2 through MKP1 and protects from TNF-induced apoptosis and lethal inflammation.

Depression and treatment response: dynamic interplay of signaling pathways and altered neural processes

Since the 1960s, when the first tricyclic and monoamine oxidase inhibitor antidepressant drugs were introduced, most of the ensuing agents were designed to target similar brain pathways that elevate serotonin and/or norepinephrine signaling. Fifty years later, the main goal of the current depression research is to develop faster-acting, more effective therapeutic agents with fewer side effects, as currently available antidepressants are plagued by delayed therapeutic onset and low response rates. Clinical and basic science research studies have made significant progress towards deciphering the pathophysiological events within the brain involved in development, maintenance, and treatment of major depressive disorder. Imaging and postmortem brain studies in depressed human subjects, in combination with animal behavioral models of depression, have identified a number of different cellular events, intracellular signaling pathways, proteins, and target genes that are modulated by stress and are potentially vital mediators of antidepressant action. In this review, we focus on several neural mechanisms, primarily within the hippocampus and prefrontal cortex, which have recently been implicated in depression and treatment response.

Cluster analysis of obesity and asthma phenotypes

Background

Asthma is a heterogeneous disease with variability among patients in characteristics such as lung function, symptoms and control, body weight, markers of inflammation, and responsiveness to glucocorticoids (GC). Cluster analysis of well-characterized cohorts can advance understanding of disease subgroups in asthma and point to unsuspected disease mechanisms. We utilized an hypothesis-free cluster analytical approach to define the contribution of obesity and related variables to asthma phenotype.

Methodology and Principal Findings

In a cohort of clinical trial participants (n = 250), minimum-variance hierarchical clustering was used to identify clinical and inflammatory biomarkers important in determining disease cluster membership in mild and moderate persistent asthmatics. In a subset of participants, GC sensitivity was assessed via expression of GC receptor alpha (GCRα) and induction of MAP kinase phosphatase-1 (MKP-1) expression by dexamethasone. Four asthma clusters were identified, with body mass index (BMI, kg/m²) and severity of asthma symptoms (AEQ score) the most significant determinants of cluster membership (F = 57.1, p<0.0001 and F = 44.8, p<0.0001, respectively). Two clusters were composed of predominantly obese individuals; these two obese asthma clusters differed from one another with regard to age of asthma onset, measures of asthma symptoms (AEQ) and control (ACQ), exhaled nitric oxide concentration (F_ENO) and airway hyperresponsiveness (methacholine PC₂₀) but were similar with regard to measures of lung function (FEV₁ (%) and FEV₁/FVC), airway eosinophilia, IgE, leptin, adiponectin and C-reactive protein (hsCRP). Members of obese clusters demonstrated evidence of reduced expression of GCRα, a finding which was correlated with a reduced induction of MKP-1 expression by dexamethasone

Conclusions and Significance

Obesity is an important determinant of asthma phenotype in adults. There is heterogeneity in expression of clinical and inflammatory biomarkers of asthma across obese individuals. Reduced expression of the dominant functional isoform of the GCR may mediate GC insensitivity in obese asthmatics.

Time-course analysis of injured skeletal muscle suggests a critical involvement of ERK1/2 signaling in the acute inflammatory response

INTRODUCTION

The coupling and timing of pro- and anti-inflammatory processes in skeletal muscle injury is poorly understood. We investigated the temporal response and regulated processes of extracellular signal-regulated kinases 1 and 2 (ERK1/2), p38, and IkappaB kinase (IKK) α/β signaling pathways after traumatic injury.

METHODS

Traumatic freeze injury was delivered to the tibialis anterior (TA) muscle in C57BL/6J mice, and injured and uninjured TA muscles were analyzed 3-72 h into the recovery period.

RESULTS

Significant increases in pro-inflammatory cytokine transcription accompanied IKKβ phosphorylation, robust ERK pathway activation, and reduced heat shock protein (Hsp) protein expression at 3-24 h. At 24 h, ERK activation was abolished concomitantly with a significant increase in mitogen-activated protein kinase phosphatase-1 (MKP-1). After 24 h, cytokine transcription along with ERK1/2 and IKKβ phosphorylation remained suppressed, whereas Hsp protein expression rose to significant levels by 72 h and associated with IKKβ.

CONCLUSIONS

Results indicate a bimodal regulation of ERK1/2 in acute inflammation in which it is supportive from 3 to 24 h, and suppressive from 24 to 72 h.

Ginsenoside Rg1 protection against β-amyloid peptide-induced neuronal apoptosis via estrogen receptor α and glucocorticoid receptor-dependent anti-protein nitration pathway

Ginsenoside Rg1 (Rg1) acts as a neuroprotective agent against various insults, however, the underlying mechanism has not been fully elucidated yet. Here, we report that Rg1 protects primary rat cerebrocortical neurons against β-amyloid peptide₂₅₋₃₅ (Aβ₂₅₋₃₅) injury via estrogen receptor α (ERα) and glucocorticoid receptor (GR)-dependent anti-protein nitration pathway. In primary rat cerebrocortical neuron cultures under basal conditions, Rg1 leads to nuclear translocation of ERα and GR, induces related responsive gene PR, pS₂ and MKP-1, SGK transcription. Meantime, Rg1 also increases the basal level of ERK1/2 phosphorylation. In the presence of toxic level of Aβ₂₅₋₃₅, Rg1 maintains ERK1/2 phosphorylation, attenuates iNOS expression, NO production, and inhibits NF-κB nuclear translocation, protein nitration and cell death. The antiapoptotic effects of Rg1 via both ERα and GR were abolished by small interfering RNAs (siRNA). ERK1/2 phosphorylation inhibitor U0126 can block downstream iNOS expression and NO generation. Interestingly, the anti-protein nitration effect of Rg1 is well matched with ERα and GR activation, although its anti-ROS production effect is in an ERα- and GR-independent manner. These results suggest that Rg1 ameliorates Aβ₂₅₋₃₅-induced neuronal apoptosis at least in part by two complementary ERα- and GR-dependent downstream pathways: (1) upregulation of ERK1/2 phosphorylation followed by inhibiting iNOS expression, NO generation and protein tyrosine nitration. (2) reduction NF-κB nuclear translocation. These data provide new understanding into the mechanisms of Rg1 anti-apoptotic functions after Aβ₂₅₋₃₅ exposure, suggesting that ERα and GR-dependent anti-protein tyrosine nitration pathway might take an important role in the neuroprotective effect of Rg1.