Interference between pathway-specific transcription factors: glucocorticoids antagonize phorbol ester-induced AP-1 activity without altering AP-1 site occupation in vivo

How to tame your genes: mechanisms of inflammatory gene repression by glucocorticoids

Glucocorticoids (GCs) are widely used therapeutic agents to treat a broad range of inflammatory conditions. Their functional effects are elicited by binding to the glucocorticoid receptor (GR), which regulates transcription of distinct gene networks in response to ligand. However, the mechanisms governing various aspects of undesired side effects versus beneficial immunomodulation upon GR activation remain complex and incompletely understood. In this review, we discuss emerging models of inflammatory gene regulation by GR, highlighting GR's regulatory specificity conferred by context-dependent changes in chromatin architecture and transcription factor or co-regulator dynamics. GR controls both gene activation and repression, with the repression mechanism being central to favorable clinical outcomes. We describe current knowledge about 3D genome organization and its role in spatiotemporal transcriptional control by GR. Looking beyond, we summarize the evidence for dynamics in gene regulation by GR through cooperative convergence of epigenetic modifications, transcription factor crosstalk, molecular condensate formation and chromatin looping. Further characterizing these genomic events will reframe our understanding of mechanisms of transcriptional repression by GR.

Molecular Signaling and Transcriptional Regulation of Histamine H1 Receptor Gene

Histamine-activated histamine H₁ receptor (H1R) signaling regulates many gene expressions, mainly through the protein kinase C (PKC)/extracellular signal-regulated kinases (ERK) signaling. Involvement of other signaling, including NF-κB, Wnt, RUNX-2, and Rho A signaling was also demonstrated. In addition, cAMP production through the activation of H1R signaling was reported. H1R gene itself is also up-regulated by the activation of H1R signaling with histamine. Here, we review our recent findings in the molecular signaling and transcriptional regulation of the H1R gene. Stimulation with histamine up-regulates H1R gene expression through the activation of H1R in HeLa cells. The PKCδ/ERK/poly(ADP)ribosyl transferase-1 (PARP-1) signaling was involved in this up-regulation. Heat shock protein 90 also plays an important role in regulating PKCδ translocation. Promoter analyses revealed the existence of two promoters in the human H1R gene in HeLa cells. H1R-activated H1R gene up-regulation in response to histamine was also observed in U373 astroglioma cells. However, this up-regulation was mediated not through the PKCδ signaling but possibly through the PKCα signaling. In addition, the promoter region responsible for histamine-induced H1R gene transcription in U373 cells was different from that of HeLa cells. These findings suggest that the molecular signaling and transcriptional regulation of the H1R gene are different between neuronal cells and non-neuronal cells.

Nuclear hormone receptors inhibit matrix metalloproteinase (MMP) gene expression through diverse mechanisms

Agents like retinoids, thyroid hormone, glucocorticoids, progesterone, androgens, which bind to members of the nuclear receptor superfamily, inhibit the synthesis of matrix metalloproteinases (MMPs) in many cell types. These Zn2(+)- and Ca2(+)-dependent MMPs degrade components of the extracellular matrix (ECM), and precise regulation of their expression is crucial in many normal processes. However, inappropriate expression of MMPs contributes to a variety of invasive and erosive diseases, and inhibition of MMP synthesis provides an important mechanism for controlling such aberrant or dysregulated responses. Nuclear receptors control MMPs through a variety of seemingly redundant mechanisms. First, nuclear receptors act on the promoters of MMP genes to enhance or suppress trans-activation. Ironically, in a family of genes that exhibits substantial regulation by nuclear receptors, few consensus hormone responsive elements (HREs) have been deomonstrated in MMP promoters. Rather, inhibition of MMPs occurs primarily, but not exclusively, at AP-1 sites. Here, nuclear receptors form complexes on the DNA through interactions with AP-1 proteins, sequester Fos/Jun and/or decrease the mRNAs for these transcription factors. Second, nuclear receptors and their ligands can indirectly inhibit MMPs. For instance, both retinoids and glucocorticoids induce the transcription of TIMPs (tissue inhibitor of metalloproteinases), which complex with MMPs and inhibit enzymatic activity, and progesterone stimulates production of transforming growth factor-beta (TGF-beta), which in turn suppresses MMP-7 (matrilysin). Finally, nuclear receptors bind to coactivators, corepressors, and components of the general transcriptional apparatus, but the potential role of these interactions in MMP regulation remains to be determined. We conclude that nuclear receptors utilize multiple, apparently redundant, mechanisms to inhibit MMP gene expression, assuring precise control of ECM degradation under a variety of physiologic and pathologic conditions.

Mineralocorticoid Receptor (MR) trans-Activation of Inflammatory AP-1 Signaling: DEPENDENCE ON DNA SEQUENCE, MR CONFORMATION, AND AP-1 FAMILY MEMBER EXPRESSION

Glucocorticoids are commonly used to treat inflammatory disorders. The glucocorticoid receptor (GR) can tether to inflammatory transcription factor complexes, such as NFκB and AP-1, and trans-repress the transcription of cytokines, chemokines, and adhesion molecules. In contrast, aldosterone and the mineralocorticoid receptor (MR) primarily promote cardiovascular inflammation by incompletely understood mechanisms. Although MR has been shown to weakly repress NFκB, its role in modulating AP-1 has not been established. Here, the effects of GR and MR on NFκB and AP-1 signaling were directly compared using a variety of ligands, two different AP-1 consensus sequences, GR and MR DNA-binding domain mutants, and siRNA knockdown or overexpression of core AP-1 family members. Both GR and MR repressed an NFκB reporter without influencing p65 or p50 binding to DNA. Likewise, neither GR nor MR affected AP-1 binding, but repression or activation of AP-1 reporters occurred in a ligand-, AP-1 consensus sequence-, and AP-1 family member-specific manner. Notably, aldosterone interactions with both GR and MR demonstrated a potential to activate AP-1. DNA-binding domain mutations that eliminated the ability of GR and MR to cis-activate a hormone response element-driven reporter variably affected the strength and polarity of these responses. Importantly, MR modulation of NFκB and AP-1 signaling was consistent with a trans-mechanism, and AP-1 effects were confirmed for specific gene targets in primary human cells. Steroid nuclear receptor trans-effects on inflammatory signaling are context-dependent and influenced by nuclear receptor conformation, DNA sequence, and the expression of heterologous binding partners. Aldosterone activation of AP-1 may contribute to its proinflammatory effects in the vasculature.

Fluticasone furoate is more effective than mometasone furoate in restoring tobacco smoke inhibited SOCS-3 expression in airway epithelial cells

Fluticasone furoate (FF) and mometasone furoate (MF) are potent glucocorticoids recommended for the treatment of allergic rhinitis and other inflammatory diseases. However, whether these drugs render any anti-inflammatory effects in Chronic Obstructive Pulmonary Disease (COPD) is unclear. Emerging data on suppressors of cytokine signaling-3 (SOCS-3) activation in the lungs during inflammation suggests that SOCS3 can be potential targets for regulating pulmonary inflammatory responses in COPD. In this study, we compared the effect of FF with MF on SOCS-3 expression in tobacco smoke (TS) exposed BAEpCs in vitro and in a mouse model of COPD in vivo. BAEpCs were exposed to TS or room air and later were treated with either FF (1nmol-100nmol) or MF (10-500nmol) inhibitors in the presence and absence of Jak1 and Stat-3 inhibitors. C57BL/6 mice were exposed to TS for 6 months, and treated with either FF, MF for 2 and 4 weeks. FF induced 7 fold increases in SOCS-3 expression in BAEpCs whereas MF induced a three fold increase when compared to control. Jak1 and Stat-3 inhibitors significantly inhibited the FF and MF induced SOCS-3 expression in BAEpCs. In addition, FF and MF restored TS inhibited SOCS-3 expression in the airway epithelium of COPD mice. FF and MF treatments significantly reduced leukocyte infiltration in airways and inhibited lung inflammation. Our study elucidates a novel mechanism for the anti-inflammatory action of FF in COPD. The superior efficacy of FF may be in part due to the increased expression of SOCS-3 in BAEpCs.

Nuclear receptors in inflammation control: repression by GR and beyond

Inflammation is a protective response of organisms to pathogens, irritation or injury. Primary inflammatory sensors activate an array of signaling pathways that ultimately converge upon a few transcription factors such as AP1, NFκB and STATs that in turn stimulate expression of inflammatory genes to ultimately eradicate infection and repair the damage. A disturbed balance between activation and inhibition of inflammatory pathways can set the stage for chronic inflammation which is increasingly recognized as a key pathogenic component of autoimmune, metabolic, cardiovascular and neurodegenerative disorders. Nuclear receptors (NRs) are a large family of transcription factors many of which are known for their potent anti-inflammatory actions. Activated by small lipophilic ligands, NRs interact with a wide range of transcription factors, cofactors and chromatin-modifying enzymes, assembling numerous cell- and tissue-specific DNA-protein transcriptional regulatory complexes with diverse activities. Here we discuss established and emerging roles and mechanisms by which NRs and, in particular, the glucocorticoid receptor (GR) repress genes encoding cytokines, chemokines and other pro-inflammatory mediators.

Glucocorticoid receptor represses proinflammatory genes at distinct steps of the transcription cycle

Widespread anti-inflammatory actions of glucocorticoid hormones are mediated by the glucocorticoid receptor (GR), a ligand-dependent transcription factor of the nuclear receptor superfamily. In conjunction with its corepressor GR-interacting protein-1 (GRIP1), GR tethers to the DNA-bound activator protein-1 and NF-κB and represses transcription of their target proinflammatory cytokine genes. However, these target genes fall into distinct classes depending on the step of the transcription cycle that is rate-limiting for their activation: Some are controlled through RNA polymerase II (PolII) recruitment and initiation, whereas others undergo signal-induced release of paused elongation complexes into productive RNA synthesis. Whether these genes are differentially regulated by GR is unknown. Here we report that, at the initiation-controlled inflammatory genes in primary macrophages, GR inhibited LPS-induced PolII occupancy. In contrast, at the elongation-controlled genes, GR did not affect PolII recruitment or transcription initiation but promoted, in a GRIP1-dependent manner, the accumulation of the pause-inducing negative elongation factor. Consistently, GR-dependent repression of elongation-controlled genes was abolished specifically in negative elongation factor-deficient macrophages. Thus, GR:GRIP1 use distinct mechanisms to repress inflammatory genes at different stages of the transcription cycle.

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.

Small-molecule hormones: molecular mechanisms of action

Small-molecule hormones play crucial roles in the development and in the maintenance of an adult mammalian organism. On the molecular level, they regulate a plethora of biological pathways. Part of their actions depends on their transcription-regulating properties, exerted by highly specific nuclear receptors which are hormone-dependent transcription factors. Nuclear hormone receptors interact with coactivators, corepressors, basal transcription factors, and other transcription factors in order to modulate the activity of target genes in a manner that is dependent on tissue, age and developmental and pathophysiological states. The biological effect of this mechanism becomes apparent not earlier than 30-60 minutes after hormonal stimulus. In addition, small-molecule hormones modify the function of the cell by a number of nongenomic mechanisms, involving interaction with proteins localized in the plasma membrane, in the cytoplasm, as well as with proteins localized in other cellular membranes and in nonnuclear cellular compartments. The identity of such proteins is still under investigation; however, it seems that extranuclear fractions of nuclear hormone receptors commonly serve this function. A direct interaction of small-molecule hormones with membrane phospholipids and with mRNA is also postulated. In these mechanisms, the reaction to hormonal stimulus appears within seconds or minutes.

Glucocorticoid receptor-mediated transcriptional activation of S100P gene coding for cancer-related calcium-binding protein

S100P is a member of the S100 family of calcium-binding proteins involved in calcium sensing and signal transduction. Its abnormal expression and biological activities are linked to tumor phenotype, namely to increased survival, proliferation, invasion and metastatic propensity of tumor cells. Association of S100P with outcome of tumor treatment and preliminary data from S100P promoter analysis prompted us to study regulation of S100P expression by glucocorticoids, which are implicated in tumor response to chemotherapy. We showed that dexamethasone (DX), a representative glucocorticoid, was capable to induce activity of S100P promoter by means of increased expression, nuclear translocation, and transactivation properties of the glucocorticoid receptor (GR). Moreover, DX treatment led to decreased phosphorylation of ERK1/2, reduced transcriptional activity of AP1, and modulated activity of some additional transcription factors. We identified a promoter region responsible for DX-mediated transactivation and proved GR binding to S100P promoter. We found that the effect of DX was enhanced by partial but not complete inhibition of the MAPK/ERK pathway, supporting an active crosstalk between GR and MAPK/ERK signal transduction in control of S100P expression. On the other hand, suppression of GR mRNA level by transient siRNA expression resulted in reduced S100P transcription. The role of GR activation in S100P regulation was supported by co-expression of GR with S100P in cells treated with DX. These data suggest that S100P is a direct transcriptional target of glucocorticoid-mediated signaling in tumor cells that is activated through the interplay of GR and MAPK pathways.

The role of nasal corticosteroids in the treatment of rhinitis

Intranasal corticosteroids (INSs) are the first choice for rhinitis pharmacotherapy. This preference is because of their broad range of actions that result in reductions of proinflammatory mediators, cytokines, and cells. Over the past 30 years, INSs have been modified to improve their pharmacodynamic, pharmacokinetic, and delivery system properties, with attention to improving characteristics such as receptor binding affinity, lipophilicity, low systemic bioavailability, and patient preference. Clinically, they have been shown to be the most effective class of nasal medications for treating allergic rhinitis and nonallergic rhinopathy, with no clear evidence that any specific INS is superior to others.

A Retrospective on Nuclear Receptor Regulation of Inflammation: Lessons from GR and PPARs

Members of the nuclear receptor superfamily have vital roles in regulating immunity and inflammation. The founding member, glucocorticoid receptor (GR), is the prototype to demonstrate immunomodulation via transrepression of the AP-1 and NF-κB signaling pathways. Peroxisome proliferator-activated receptors (PPARs) have emerged as key regulators of inflammation. This review examines the history and current advances in nuclear receptor regulation of inflammation by the crosstalk with AP-1 and NF-κB signaling, focusing on the roles of GR and PPARs. A better understanding of the molecular mechanism by which nuclear receptors inhibit proinflammatory signaling pathways will enable novel therapies to treat chronic inflammation.

Coactivation of GR and NFKB alters the repertoire of their binding sites and target genes

Glucocorticoid receptor (GR) exerts anti-inflammatory action in part by antagonizing proinflammatory transcription factors such as the nuclear factor kappa-b (NFKB). Here, we assess the crosstalk of activated GR and RELA (p65, major NFKB component) by global identification of their binding sites and target genes. We show that coactivation of GR and p65 alters the repertoire of regulated genes and results in their association with novel sites in a mutually dependent manner. These novel sites predominantly cluster with p65 target genes that are antagonized by activated GR and vice versa. Our data show that coactivation of GR and NFKB alters signaling pathways that are regulated by each factor separately and provide insight into the networks underlying the GR and NFKB crosstalk.

Minireview: Glucocorticoids in autoimmunity: unexpected targets and mechanisms

For decades, natural and synthetic glucocorticoids (GC) have been among the most commonly prescribed classes of immunomodulatory drugs. Their unsurpassed immunosuppressive and antiinflammatory activity along with cost-effectiveness makes these compounds a treatment of choice for the majority of autoimmune and inflammatory diseases, despite serious side effects that frequently accompany GC therapy. The activated GC receptor (GR) that conveys the signaling information of these steroid ligands to the transcriptional machinery engages a number of pathways to ultimately suppress autoimmune responses. Of those, GR-mediated apoptosis of numerous cell types of hematopoietic origin and suppression of proinflammatory cytokine gene expression have been described as the primary mechanisms responsible for the antiinflammatory actions of GC. However, along with the ever-increasing appreciation of the complex functions of the immune system in health and disease, we are beginning to recognize new facets of GR actions in immune cells. Here, we give a brief overview of the extensive literature on the antiinflammatory activities of GC and discuss in greater detail the unexpected pathways, factors, and mechanisms that have recently begun to emerge as novel targets for GC-mediated immunosuppression.

Androgen receptor signaling and mutations in prostate cancer

Normal and neoplastic growth of the prostate gland are dependent on androgen receptor (AR) expression and function. Androgenic activation of the AR, in association with its coregulatory factors, is the classical pathway that leads to transcriptional activity of AR target genes. Alternatively, cytoplasmic signaling crosstalk of AR by growth factors, neurotrophic peptides, cytokines or nonandrogenic hormones may have important roles in prostate carcinogenesis and in metastatic or androgen-independent (AI) progression of the disease. In addition, cross-modulation by various nuclear transcription factors acting through basal transcriptional machinery could positively or negatively affect the AR or AR target genes expression and activity. Androgen ablation leads to an initial favorable response in a significant number of patients; however, almost invariably patients relapse with an aggressive form of the disease known as castration-resistant or hormone-refractory prostate cancer (PCa). Understanding critical molecular events that lead PCa cells to resist androgen-deprivation therapy is essential in developing successful treatments for hormone-refractory disease. In a significant number of hormone-refractory patients, the AR is overexpressed, mutated or genomically amplified. These genetic alterations maintain an active presence for a highly sensitive AR, which is responsive to androgens, antiandrogens or nonandrogenic hormones and collectively confer a selective growth advantage to PCa cells. This review provides a brief synopsis of the AR structure, AR coregulators, posttranslational modifications of AR, duality of AR function in prostate epithelial and stromal cells, AR-dependent signaling, genetic changes in the form of somatic and germline mutations and their known functional significance in PCa cells and tissues.

Corticosteroid treatment in chronic rhinosinusitis: the possibilities and the limits

Chronic rhinosinusitis, including nasal polyps, is an inflammatory disease of the nose and sinuses. The medical treatment, mainly topical intranasal and oral corticosteroids, constitutes its first line of therapy. Long-term treatment with corticosteroid nasal spray reduces inflammation and nasal polyp size, and improves nasal symptoms such as nasal blockage, rhinorrea, and the loss of smell. Corticosteroid intranasal drops may be used when intranasal spray fails to demonstrate efficacy. Short courses of oral steroids are recommended in severe chronic rhinosinusitis with nasal polyps or when a rapid symptomatic improvement is needed. Endoscopic sinus surgery is only recommended when the medical treatment fails. Intranasal corticosteroids should be continued postoperatively. When using intranasal corticosteroids, care should be taken in selected populations such as children, pregnant women, and elderly patients; especially in those patients with comorbid conditions such as asthma, in which the overall steroid intake can be high due to the administration of both intranasal and inhaled corticosteroids.

Regulation of high-density lipoprotein by inflammatory cytokines: establishing links between immune dysfunction and cardiovascular disease

Coronary artery disease is a primary co-morbidity in metabolic diseases such as metabolic syndrome, diabetes and obesity. One contributing risk factor for coronary artery disease is low high-density lipoprotein-cholesterol (HDLc). Several factors influence steady-state HDLc levels, including diet, genetics and environment. Perhaps more important to coronary artery disease is factors that attribute to the dynamics of reverse cholesterol transport, storage, and excretion of excess cholesterol. HDLc biogenesis, clearance and innate ability to serve as a cholesterol acceptor and transporter all contribute to HDLc's function as a negative regulator of cardiovascular disease. With the recent failure of torcetrapid, focus is being placed on HDLc biology and its role in various metabolic diseases. Low HDLc levels are often associated with an increased state of background inflammation. Recently, several syndromes with clear pro-inflammatory components have been shown to be inversely correlated with low HDLc levels in the absence of obesity, diabetes and metabolic syndrome. Early studies with HDLc during the acute-phase response suggest that HDLc is substantially physically modified during acute infection and sepsis, and recent studies show that HDLc is physically modified by chronic pro-inflammatory disease. In this review, several of these connections are described and cytokine signalling related to HDLc is examined.

The human glucocorticoid receptor: molecular basis of biologic function

The characterization of the subfamily of steroid hormone receptors has enhanced our understanding of how a set of hormonally derived lipophilic ligands controls cellular and molecular functions to influence development and help achieve homeostasis. The glucocorticoid receptor (GR), the first member of this subfamily, is a ubiquitously expressed intracellular protein, which functions as a ligand-dependent transcription factor that regulates the expression of glucocorticoid-responsive genes. The effector domains of the GR mediate transcriptional activation by recruiting coregulatory multi-subunit complexes that remodel chromatin, target initiation sites, and stabilize the RNA-polymerase II machinery for repeated rounds of transcription of target genes. This review summarizes the basic aspects of the structure and actions of the human (h) GR, and the molecular basis of its biologic functions.

Pharmacological strategies for improving the efficacy and therapeutic ratio of glucocorticoids in inflammatory lung diseases

Glucocorticoids are widely used to treat various inflammatory lung diseases. Acting via the glucocorticoid receptor (GR), they exert clinical effects predominantly by modulating gene transcription. This may be to either induce (transactivate) or repress (transrepress) gene transcription. However, certain individuals, including those who smoke, have certain asthma phenotypes, chronic obstructive pulmonary disease (COPD) or some interstitial diseases may respond poorly to the beneficial effects of glucocorticoids. In these cases, high dose, often oral or parental, glucocorticoids are typically prescribed. This generally leads to adverse effects that compromise clinical utility. There is, therefore, a need to enhance the clinical efficacy of glucocorticoids while minimizing adverse effects. In this context, a long-acting beta(2)-adrenoceptor agonist (LABA) can enhance the clinical efficacy of an inhaled corticosteroid (ICS) in asthma and COPD. Furthermore, LABAs can augment glucocorticoid-dependent gene expression and this action may account for some of the benefits of LABA/ICS combination therapies when compared to ICS given as a monotherapy. In addition to metabolic genes and other adverse effects that are induced by glucocorticoids, there are many other glucocorticoid-inducible genes that have significant anti-inflammatory potential. We therefore advocate a move away from the search for ligands of GR that dissociate transactivation from transrepression. Instead, we submit that ligands should be functionally screened by virtue of their ability to induce or repress biologically-relevant genes in target tissues. In this review, we discuss pharmacological methods by which selective GR modulators and "add-on" therapies may be exploited to improve the clinical efficacy of glucocorticoids while reducing potential adverse effects.

Characterization of conserved tandem donor sites and intronic motifs required for alternative splicing in corticosteroid receptor genes

Alternative splicing events from tandem donor sites result in mRNA variants coding for additional amino acids in the DNA binding domain of both the glucocorticoid (GR) and mineralocorticoid (MR) receptors. We now show that expression of both splice variants is extensively conserved in mammalian species, providing strong evidence for their functional significance. An exception to the conservation of the MR tandem splice site (an A at position +5 of the MR+12 donor site in the mouse) was predicted to decrease U1 small nuclear RNA binding. In accord with this prediction, we were unable to detect the MR+12 variant in this species. The one exception to the conservation of the GR tandem splice site, an A at position +3 of the platypus GRgamma donor site that was predicted to enhance binding of U1 snRNA, was unexpectedly associated with decreased expression of the variant from the endogenous gene as well as a minigene. An intronic pyrimidine motif present in both GR and MR genes was found to be critical for usage of the downstream donor site, and overexpression of TIA1/TIAL1 RNA binding proteins, which are known to bind such motifs, led to a marked increase in the proportion of GRgamma and MR+12. These results provide striking evidence for conservation of a complex splicing mechanism that involves processes other than stochastic spliceosome binding and identify a mechanism that would allow regulation of variant expression.

The treatment of vasomotor rhinitis with intranasal corticosteroids

Objective

Intranasal steroids (INS) are firmly established as the therapy for choice for allergic rhinitis, but their role in vasomotor rhinitis (VMR) is not fully characterized. This review examines the potential mechanisms of action and reported efficacy of INS in patients with VMR.

Results

INS, through intracellular activation of the glucocorticoid receptor, down-regulate the recruitment and activation of inflammatory cells (T-lymphocytes, eosinophils, mast cells, basophils, neutrophils, macrophages), increase degradation of neuropeptides, and reduce epithelial cell activity, vascular permeability, and chemokine secretion. It is likely that more than vasoconstriction is responsible for the clinical effects of INS.

Eight INS can be prescribed for rhinitis in the US; only 4 have been studied for VMR. Seventy-four percent of patients treated with beclomethasone dipropionate considered themselves symptom-free or greatly improved versus 31% with placebo. Budesonide significantly reduced rhinitis symptoms and methacholine-induced nasal secretions compared with placebo. Fluticasone propionate compared with placebo provided significantly greater relief from nasal obstruction; computed tomographic scans showed significant reductions in the mucosal area of the lower turbinates. Mometasone furoate produced numerically better rhinitis symptom scores and, when discontinued, lower relapse rates than placebo.

Conclusion

Data supports INS as beneficial pharmacotherapy for VMR.

Glucocorticoids and the emerging importance of T cell subsets in steroid refractory diseases

Glucocorticoids remain the first-line treatment for a range of autoimmune and allergic diseases. However, 30% of patients fail to achieve disease control at tolerable systemic doses and continue to have an increased immune response with poor clinical outcome. This steroid refractory (SR) phenotype has previously been attributed to enhanced expression of inactive glucocorticoid receptor isoforms and cytokine-mediated suppression of glucocorticoid (GC) signaling, in particular by interleukin-2. These mechanisms are discussed, with emphasis on recent evidence for the role of the CD4(+)CD25(int) and GC-induced T regulatory cell subsets in perpetrating SR disease.

Characterization of ZK 245186, a novel, selective glucocorticoid receptor agonist for the topical treatment of inflammatory skin diseases

BACKGROUND AND PURPOSE

Glucocorticoids are highly effective in the therapy of inflammatory diseases. Their value, however, is limited by side effects. The discovery of the molecular mechanisms of the glucocorticoid receptor and the recognition that activation and repression of gene expression could be addressed separately opened the possibility of achieving improved safety profiles by the identification of ligands that predominantly induce repression. Here we report on ZK 245186, a novel, non-steroidal, low-molecular-weight, glucocorticoid receptor-selective agonist for the topical treatment of inflammatory dermatoses.

EXPERIMENTAL APPROACH

Pharmacological properties of ZK 245186 and reference compounds were studied in terms of their potential anti-inflammatory and side effects in functional bioassays in vitro and in rodent models in vivo.

KEY RESULTS

Anti-inflammatory activity of ZK 245186 was demonstrated in in vitro assays for inhibition of cytokine secretion and T cell proliferation. In vivo, using irritant contact dermatitis and T cell-mediated contact allergy models in mice and rats, ZK 245186 showed anti-inflammatory efficacy after topical application similar to the classical glucocorticoids, mometasone furoate and methylprednisolone aceponate. ZK 245186, however, exhibits a better safety profile with regard to growth inhibition and induction of skin atrophy after long-term topical application, thymocyte apoptosis, hyperglycaemia and hepatic tyrosine aminotransferase activity.

CONCLUSIONS AND IMPLICATIONS

ZK 245186 is a potent anti-inflammatory compound with a lower potential for side effects, compared with classical glucocorticoids. It represents a promising drug candidate and is currently in clinical trials.

Molecular and clinical pharmacology of intranasal corticosteroids: clinical and therapeutic implications

Intranasal corticosteroids (INSs) are effective treatments for allergic rhinitis, rhinosinusitis, and nasal polyposis. In recent years, increased understanding of corticosteroid and glucocorticoid receptor pharmacology has enabled the development of molecules designed specifically to achieve potent, localized activity with minimal risk of systemic exposure. Pharmacologic potency studies using affinity and other assessments have produced similar rank orders of potency, with the most potent being mometasone furoate, fluticasone propionate, and its modification, fluticasone furoate. The furoate and propionate ester side chains render these agents highly lipophilic, which may facilitate their absorption through nasal mucosa and uptake across phospholipid cell membranes. These compounds demonstrate negligible systemic absorption. Systemic absorption rates are higher among the older corticosteroids (flunisolide, beclomethasone dipropionate, triamcinolone acetonide, and budesonide), which have bioavailabilities in the range of 34-49%. Studies, including 1-year studies with mometasone furoate, fluticasone propionate, and budesonide that evaluated potential systemic effects of INSs in children have generally found no adverse effects on hypothalamic-pituitary-adrenal axis function or growth. Clinical data suggest no significant differences in efficacy between the INSs. Theoretically, newer agents with lower systemic availability may be preferable, and may come closer to the pharmacokinetic/pharmacologic criteria for the ideal therapeutic choice.

Inhibition of apoptosis in prostate cancer cells by androgens is mediated through downregulation of c-Jun N-terminal kinase activation

Androgen deprivation induces the regression of prostate tumors mainly due to an increase in the apoptosis rate; however, the molecular mechanisms underlying the antiapoptotic actions of androgens are not completely understood. We have studied the antiapoptotic effects of androgens in prostate cancer cells exposed to different proapoptotic stimuli. Terminal deoxynucleotidyl transferase-mediated nick-end labeling and nuclear fragmentation analyses demonstrated that androgens protect LNCaP prostate cancer cells from apoptosis induced by thapsigargin, the phorbol ester 12-O-tetradecanoyl-13-phorbol-acetate, or UV irradiation. These three stimuli require the activation of the c-Jun N-terminal kinase (JNK) pathway to induce apoptosis and in all three cases, androgen treatment blocks JNK activation. Interestingly, okadaic acid, a phosphatase inhibitor that causes apoptosis in LNCaP cells, induces JNK activation that is also inhibited by androgens. Actinomycin D, the antiandrogen bicalutamide or specific androgen receptor (AR) knockdown by small interfering RNA all blocked the inhibition of JNK activation mediated by androgens indicating that this activity requires AR-dependent transcriptional activation. These data suggest that the crosstalk between AR and JNK pathways may have important implications in prostate cancer progression and may provide targets for the development of new therapies.

Time-course of immediate early gene expression in hippocampal subregions of adrenalectomized rats after acute corticosterone challenge

Corticosterone hormones mediate the stress response and function in the survival of hippocampal neurons via activation of gluco-(GR) and mineralocorticoid (MR) receptors. Activated GR and MR couple the corticosterone signal through immediate early genes (IEGs) to the late expression of downstream genes, such as neurotrophic factors. The potential importance of IEGs in GR/MR-dependent plasticity in the brain is largely unknown. We examined the region- and time-dependent transcriptional profiles of six IEGs (c-fos, fosB, fra-1, junB, c-jun and egr-1) by in situ hybridization after acute corticosterone challenge in the hippocampus and the primary somatosensory cortex (S1). Adrenalectomized rats and subsequent hormone injections were used as a model system to eliminate interference of endogenous corticosterone on IEG expression. In the hippocampus, a single corticosterone dose (10 mg/kg, s.c.) caused a widespread and transient reduction of fosB mRNA after 0.8 h, whereas changes in both c-fos and fra-1 mRNA levels were restricted to the dentate gyrus region. Corticosterone treatment gave rise to a delayed and significant reduction of junB mRNA signals after 2 h in all hippocampal regions, which reversed to increase at 4 h. c-jun and egr-1 mRNA levels were unaffected by corticosterone treatment. On the contrary, in the S1, IEG expression seems to be unaffected by corticosterone treatment, with the exception of a transient increase of junB transcripts at 0.8 h. The early reduction in c-fos family and junB transcripts may contribute to the GR/MR-dependent changes on hippocampal plasticity and may be dependent on rapid corticosteroid signaling.

Separating transrepression and transactivation: a distressing divorce for the glucocorticoid receptor?

Glucocorticoids (corticosteroids) are highly effective in combating inflammation in the context of a variety of diseases. However, clinical utility can be compromised by the development of side effects, many of which are attributed to the ability of the glucocorticoid receptor (GR) to induce the transcription of, or transactivate, certain genes. By contrast, the anti-inflammatory effects of glucocorticoids are due largely to their ability to reduce the expression of pro-inflammatory genes. This effect has been predominantly attributed to the repression of key inflammatory transcription factors, including AP-1 and NF-kappaB, and is termed transrepression. The ability to functionally separate these transcriptional functions of GR has prompted a search for dissociated GR ligands that can differentially induce transrepression but not transactivation. In this review, we present evidence that post-transcriptional mechanisms of action are highly important to the anti-inflammatory actions of glucocorticoids. Furthermore, we present the case that mechanistically distinct forms of glucocorticoid-inducible gene expression are critical to the development of anti-inflammatory effects by repressing inflammatory signaling pathways and inflammatory gene expression at multiple levels. Considerable care is therefore required to avoid loss of anti-inflammatory effectiveness in the development of novel transactivation-defective ligands of GR.

Crosstalk between the glucocorticoid receptor and other transcription factors: molecular aspects

Glucocorticoids (GCs) regulate cell fate by altering gene expression via the glucocorticoid receptor (GR). Ligand-bound GR can activate the transcription of genes carrying the specific GR binding sequence, the glucocorticoid response element (GRE). In addition, GR can modulate, positively or negatively, directly or indirectly, the activity of other transcription factors (TFs), a process referred to as "crosstalk". In the indirect crosstalk, GR interferes with transduction pathways upstream of other TFs. In the direct crosstalk, GR and other TFs modulate each other's activity when bound to the promoters of their target genes. The multiplicity of molecular actions exerted by TFs, particularly the GR, is not only fascinating in terms of molecular structure, it also implies that the TFs participate in a wide range of regulatory processes, broader than anticipated. This review focuses on the molecular mechanisms involved in the crosstalk, on both current ideas and unresolved questions, and discusses the possible significance of the crosstalk for the physiologic and therapeutic actions of GCs.

Glucocorticoid and growth factor synergism requirement for Notch4 chromatin domain activation

The Notch signaling pathway modulates cell fate in diverse contexts, including vascular development. Notch4 is selectively expressed in vascular endothelium and regulates vascular remodeling. The signal-dependent transcription factor activator protein 1 (AP-1) activates Notch4 transcription in endothelial cells, but other factors/signals that regulate Notch4 are largely unknown. We demonstrate that, unlike the established transrepression mechanism in which the glucocorticoid receptor (GR) antagonizes AP-1, AP-1 and GR synergistically activated Notch4 transcription in endothelial cells. Fibroblast growth factor 2 (FGF-2) and cortisol induced AP-1 and GR occupancy, respectively, at a Notch4 promoter composite response element consisting of an imperfect half-glucocorticoid response element and an AP-1 motif, which mediated signal-dependent activation. Analysis of Notch4 promoter complex assembly provided evidence that GR and AP-1 independently occupy the composite response element, but AP-1 stabilizes GR occupancy. In multipotent 10T1/2 cells, FGF-2 and cortisol induced a histone modification pattern at the Notch4 locus mimicking that present in endothelial cells and reprogrammed Notch4 from a repressed to an active state. These results establish the molecular basis for a novel AP-1/GR-Notch4 axis in vascular endothelium.

Role of Brg1 and HDAC2 in GR trans-repression of the pituitary POMC gene and misexpression in Cushing disease

Negative feedback regulation of the proopiomelanocortin (POMC) gene by the glucocorticoid (Gc) receptor (GR) is a critical feature of the hypothalamo-pituitary-adrenal axis, and it is in part exerted by trans-repression between GR and the orphan nuclear receptors related to NGFI-B. We now show that Brg1, the ATPase subunit of the Swi/Snf complex, is essential for this trans-repression and that Brg1 is required in vivo to stabilize interactions between GR and NGFI-B as well as between GR and HDAC2. Whereas Brg1 is constitutively present at the POMC promoter, recruitment of GR and HDAC2 is ligand-dependent and results in histone H4 deacetylation of the POMC locus. In addition, GR-dependent repression inhibits promoter clearance by RNA polymerase II. Thus, corecruitment of repressor and activator at the promoter and chromatin modification jointly contribute to trans-repression initiated by direct interactions between GR and NGFI-B. Loss of Brg1 or HDAC2 should therefore produce Gc resistance, and we show that approximately 50% of Gc-resistant human and dog corticotroph adenomas, which are the hallmark of Cushing disease, are deficient in nuclear expression of either protein. In addition to providing a molecular basis for Gc resistance, these deficiencies may also contribute to the tumorigenic process.

Substance P-induced cyclooxygenase-2 expression in human umbilical vein endothelial cells

Substance P (SP) is a neuropeptide involved in neurogenic inflammation and an agonist for NK(1), NK(2), and NK(3) receptors. SP induces prostaglandin (PG) production in various cell types, and these eicosanoids are responsible for numerous inflammatory and vascular effects. Cyclooxygenase (COX) are needed to convert arachidonic acid to PGs. The study evaluated the effect of SP on COX expression in human umbilical vein endothelial cells (HUVEC). COX-2 protein expression was upregulated by SP with a peak at 100 nM and at 20 h; in the same experimental conditions COX-1 protein expression was unchanged. A correlation between COX-2 expression and PGI(2) and PGE(2) release was detected. Dexamethasone (DEX) inhibited SP-mediated COX-2 expression. Mitogen-activated protein kinases (MAPK) p38 and p42/44 were activated by SP, whereas SB202190 and PD98059, inhibitors of these kinases, blocked COX-2 expression. 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furanone (DFU), an experimental selective COX-2 inhibitor, blocked SP-induced PG release. By RT-PCR and Western blot analysis, we demonstrated that NK(1) and NK(2) but not NK(3) receptors are present on HUVEC. Selective NK(1) and NK(2) agonists, namely [Sar(9), Met(O(2))(11)]SP and [beta-Ala(8)] NKA(4-10), upregulated COX-2 protein expression and PG production, whereas senktide (Suc-Asp-Phe-MePhe-Gly-Leu-Met-NH(2)), a selective NK(3) agonist, was ineffective in this respect. The NK(1) selective antagonist L703,606 ((cis)-2-(diphenylmethyl)-N-((2-iodophenyl)-methyl)-1-azabicyclo(2.2.2)octan-3-amine) and the NK(2) selective antagonist SR 48,968 ((S)-N-methyl-N-(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4 dichlorophenyl)butyl) benzamide) competitively antagonised SP-induced effects. The study shows HUVEC to possess functional NK(1) and NK(2) receptors, which mediate the ability of SP to induce expression of COX-2 in HUVEC, thus showing a previously-undetected effect of SP on endothelial cells.

Role of 11-beta-hydroxysteroid dehydrogenase type 1 in differentiation of 3T3-L1 cells and in rats with diet-induced obesity

AIM

To observe the roles of 11-beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in in vitro preadipocyte differentiation and in rats with diet-induced obesity (DIO).

METHODS

Protein expression of 11beta-HSD1 in the process of 3T3-L1 cell differentiation and in various tissues of the rats were detected by Western blot analysis; expression of 11beta-HSD1 mRNA and glucocorticoid receptor (GR) and other marker genes of preadipocyte differentiation were detected by using real-time PCR.

RESULTS

Lipid droplets in 3T3-L1 cells accumulated and increased after stimulation. A dramatically elevated protein level of 11beta-HSD1, especially in the late stages of 3T3-L1 cell differentiation, was detected. The relative mRNA levels of 11beta-HSD1, GR and cell differentiation markers LPL, aP2, and FAS were upregulated, and Pref-1 was downregulated during the differentiation. In DIO rats, bodyweight, visceral adipose mass index and the protein expression of 11beta-HSD1 increased, especially in adipose tissue, brain and muscles. Serum insulin, triglyceride, total cholesterol and low-density lipoprotein cholesterol were found to be increased in DIO rats, but without any obvious changes in blood glucose or tumor necrosis factor-alpha levels.

CONCLUSION

11beta-HSD1 may promote preadipocyte differentiation, and may be involved in the development of obesity.

Dexamethasone suppresses human interleukin-5 gene promoter

Synthetic glucocorticoid dexamethasone suppressed interleukin-5 gene expression in PER-117 human T cells at the level of transcription. The conserved lymphokine element 0 in the interleukin-5 gene promoter context served as a target for dexamethasone.

ERα-AHR-ARNT Protein-Protein Interactions Mediate Estradiol-dependent Transrepression of Dioxin-inducible Gene Transcription

The aryl hydrocarbon receptor (AHR) and the aryl hydrocarbon receptor nuclear translocator (ARNT) form a heterodimeric transcription factor upon binding a wide variety of environmental pollutants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AHR target gene activation can be repressed by estrogen and estrogen-like compounds. In this study, we demonstrate that a significant component of TCDD-inducible Cyp1a1 transcription is the result of recruitment of estrogen receptor (ER)-alpha by AHR/ARNT as a transcriptional co-repressor. Both AHR and ARNT were capable of interacting directly with ER alpha, as ascertained by glutathione S-transferase pull-down. 17Beta-estradiol repressed TCDD-activated Cyp1a1 and Cyp1b1 gene transcription in MCF-7 cells in the presence of cycloheximide, as determined by reverse transcription/real-time PCR. Furthermore, chromatin immunoprecipitation (ChIP) assays have shown that ER alpha is present at the Cyp1a1 enhancer only after co-treatment with E2 and TCDD, in MCF-7 cells. Sequential two-step ChIP assays were performed which demonstrate that AHR and ER alpha are present together at the same time on the Cyp1a1 enhancer during transrepression. Taken together these data support a role for ER-mediated transrepression of AHR-dependent gene regulation.

FoxO3 mediates antagonistic effects of glucocorticoids and interleukin-2 on glucocorticoid-induced leucine zipper expression

We have analyzed the promoter of human gilz (glucocorticoid-induced leucine zipper), a dexamethasone-inducible gene that is involved in regulating apoptosis, and identified six glucocorticoid (GC)-responsive elements and three Forkhead responsive elements (FHREs). Promoter deletion analysis and point mutations showed that individual mutation of the GC-responsive elements does not affect GC-induced transcription and that FHRE-1 and FHRE-3 elements contribute to the effects of GCs. Furthermore, overexpression of the Forkhead transcription factor FoxO3 enhances GC-induced gilz mRNA expression. The functional significance of the interaction between FoxO3 and GC receptor was established in T lymphocytes. Indeed, we show that GCs failed to induce GILZ expression in the presence of IL-2, a cytokine known to antagonize GC effects in T cells. Using a constitutive active mutant of protein kinase B that inactivates FoxO3 or a FoxO3 mutant that cannot be inactivated by protein kinase B, we demonstrate that IL-2 inhibitory effects on GILZ expression are mediated through inhibition of FoxO3 transcriptional activity. Therefore, FoxO3 appears to be a key factor mediating GC and IL-2 antagonism for gilz regulation in T lymphocytes. This regulation of GILZ expression was placed in a meaningful context in evaluating the effects of GILZ on GC-induced apoptosis in T lymphocytes.

A nuclear isoform of the focal adhesion LIM-domain protein Trip6 integrates activating and repressing signals at AP-1- and NF-kappaB-regulated promoters

Glucocorticoid receptor (GR)-mediated transrepression of the transcription factors AP-1 and NF-kappaB, responsible for most of the anti-inflammatory effects of glucocorticoids, is initiated by the tethering of GR to the promoters of target genes. We report that this tethering is mediated by a nuclear isoform of the focal adhesion LIM domain protein Trip6. Trip6 functions as a coactivator for both AP-1 and NF-kappaB. As shown by chromatin immunoprecipitation, Trip6 is recruited to the promoters of target genes together with AP-1 or NF-kappaB. In the presence of glucocorticoids, GR joins the Trip6 complex. Reducing the level of Trip6 by RNA interference or abolishing its interaction with GR by dominant-negative mutation eliminates transrepression. We propose that GR tethering to the target promoter through Trip6 forms the basis of transrepression, and that Trip6 exerts its nuclear functions by acting as a molecular platform, enabling target promoters to integrate activating or repressing signals.

Protein-protein interactions and transcriptional antagonism between the subfamily of NGFI-B/Nur77 orphan nuclear receptors and glucocorticoid receptor

Glucocorticoids (Gc) act through the glucocorticoid receptor (GR) to enhance or repress transcription of glucocorticoid-responsive genes depending on the promoter and cellular context. Repression of proopiomelanocortin (POMC) gene expression by Gc was proposed to use different mechanisms. We described the POMC promoter Nur response element (NurRE) as a target for Gc repression. NGFI-B (Nur77), an orphan nuclear receptor, and two related factors, Nurr1 and NOR1, bind the NurRE as homo- or heterodimers to enhance POMC gene expression in response to CRH. Gc antagonize CRH-stimulated as well as NGFI-B-dependent transcription. We now show that GR antagonizes NurRE-dependent transcription induced by all members of the Nur77 subfamily and that these nuclear receptors can all interact directly with GR. Transcriptional antagonism as well as direct protein-protein interaction between NGFI-B and GR take place primarily via their respective DNA binding domains, although DNA binding itself and the GR homodimerization interface are not involved. In vivo, GR and Nur factors can be coimmunoprecipitated whereas GR is recruited to the POMC promoter upon glucocorticoid action. Thus, our data suggest a mechanism for transrepression between two nuclear receptors, GR and NGFI-B, that is unique, although quite similar to that proposed for transrepression between GR and activator protein 1 (AP-1) or nuclear factor-kappaB (NFkappaB).

Les glucocorticoïdes et leur récepteur : mécanismes d'action et conséquences cliniques

BACKGROUND

Glucocorticoids are used as anti-inflammatory, immuno-modulatory, anti-proliferative and cytotoxic drugs, but they also trigger important side-effects. These hormones bind to glucocorticoid receptor alpha (GRalpha), an intracellular protein, which acts essentially in the nucleus.

MAIN POINTS

GRalpha is a ligand-activated transcription factor that positively or negatively regulates gene expression by distinct mechanisms. Stimulation of gene transcription occurs after direct binding of the receptor to specific responsive DNA elements. Gene activation by glucocorticoids is mainly responsible for certain adverse effects. In contrast, the therapeutic effects of glucocorticoids are predominantly mediated through repression of genes encoding inflammatory mediators. Inhibitory protein-protein interaction between the hormone-activated receptor and the transcription factors NF-kappaB and AP-1 was found to be the underlying mechanism. However, inhibition of other transcription factors may account for deleterious effects of glucocorticoids, such as adrenal suppression and osteoporosis. GRalpha also mediates rapid non-genomic effects of glucocorticoids. Side-effects are reduced by using topical glucocorticoids which have a low systemic bioavailability. Moreover, it is important to determine the lowest effective maintenance dose of systemic and topical glucocorticoids to further decrease the risk of adverse effects. This is particularly justified because inhibition of AP-1 and NF-kappaB activities, that is the anti-inflammatory effect, occurs at much lower hormone concentrations than transactivation.

PERSPECTIVES

Clinical use of glucocorticoids is limited by occurrence of severe adverse effects. Therefore, the current aim is to design GRalpha ligands that retain only the anti-inflammatory activities of GC.

Inhibition by dexamethasone of interleukin 13 production via glucocorticoid receptor-mediated inhibition of c-Jun phosphorylation

The antigen stimulation of RBL-2H3 cells induced interleukin 13 (IL-13) production, which was inhibited by the steroidal anti-inflammatory drug dexamethasone and by the c-Jun N-terminal kinase (JNK) inhibitor SP600125. Dexamethasone did not inhibit the antigen-induced phosphorylation of JNK but inhibited that of c-Jun. In a cell-free system, the phosphorylation of glutathione S-transferase-fused c-Jun by recombinant JNK was not inhibited by dexamethasone but was inhibited by the addition of recombinant glucocorticoid receptor (GR). These findings suggest that the inhibition of antigen-induced IL-13 production by dexamethasone is due to the GR-mediated inhibition of c-Jun phosphorylation induced by JNK.

Identification of glucocorticoid receptor domains involved in transrepression of transforming growth factor-beta action

The transforming growth factor-beta (TGF-beta) and glucocorticoid signaling pathways interact both positively and negatively in regulating a variety of physiological and pathologic processes. We previously reported that liganded glucocorticoid receptor (GR) repressed TGF-beta induction of human plasminogen activator inhibitor-1 gene transcription by directly targeting the transcriptional activation function of Smad3. To identify the domain(s) in the glucocorticoid receptor involved in this repression, we have examined the ability of various GR truncation, deletion, and substitution mutants to repress TGF-beta transactivation in Hep3B human hepatoma cells that lack functional endogenous GR. Partial deletions in the ligand-binding domain (LBD), including the tau2 and tauc regions, greatly reduced or eliminated GR repression, whereas deletion of the N-terminal AF1 (tau1) domain and substitution mutations in the DNA-binding domain had little or no effect. Liganded androgen receptor repressed TGF-beta transactivation, whereas mineralocorticoid receptor did not, and studies with rat GR-mineralocorticoid receptor chimeras confirmed that the GR C-terminal domains were required for repression. RU486, a strong antagonist of transactivation by GR, partially reversed repression by wild type GR. Co-immunoprecipitation experiments in Hep3B cells indicated that physical interaction between GR and Smad3 is necessary but not sufficient for repression. Physical interaction required activation of Smad3 by TGF-beta but not dexamethasone binding to GR. Glutathione S-transferase pull-down assays demonstrated that several regions of the LBD could mediate GR-Smad3 physical interaction. We conclude that the LBD of GR, but not the DNA-binding domain or the N-terminal activation domain, is required for GR-mediated transrepression of TGF-beta transactivation.

Hematopoietic Protection by Dexamethasone or Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) in Patients Treated With Carboplatin and Ifosfamide

Based on preclinical studies, the authors undertook a pilot study to determine the hematologic and biologic effects of pretreatment with dexamethasone (Dex) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in patients receiving carboplatin and ifosfamide. Patients (n = 28) with metastatic solid tumors were randomized to receive pretreatment with Dex or GM-CSF or no pretreatment prior to courses 1 or 2 of carboplatin and ifosfamide. No alteration in dose of chemotherapy was allowed between course 1 and 2. Alterations of hematologic and nonhematologic toxicity and selected biologic parameters were compared between courses 1 and 2. Patients without any pretreatment demonstrated worsening hematologic toxicity in course 2 compared to course 1. In contrast, Dex pretreatment reduced hematopoietic toxicity and improved the absolute granulocyte count (AGC) and platelet count recovery times. For example, course 1 versus course 2 (with Dex pretreatment): AGC nadir (mm3) 153 versus 549 (p = 0.07), days AGC <500/mm3 7.8 versus 4.0 (p = 0.10), days to AGC recovery >1,500/mm3, 26 versus 22 (p = 0.034). Overall comparison between all five cohorts by analyses of variance demonstrated that intervention with Dex improved multiple hematopoietic toxicities, including AGC nadir (p = 0.015), and recovery times to AGC >1,500/mm3 (p = 0.07) and platelet count to >100,000/mm3 (p = 0.05). GM-CSF pretreatment did not worsen hematopoietic parameters after course 2 compared to course 1. Expected biologic effects of Dex and GM-CSF treatment were observed. Patients demonstrated an overall response rate of 32%, 1 complete response, and 8 partial responses. In patients with cancer, pretreatment with Dex or GM-CSF may significantly decrease the hematopoietic toxicity of chemotherapeutic agents.

c-fos reduces corticosterone-mediated effects on neurotrophic factor expression in the rat hippocampal CA1 region

The transcription of neurotrophic factors, i.e., basic fibroblast growth factor (bFGF) and brain-derived neurotrophic factor (BDNF) is regulated by glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation despite the lack of a classical glucocorticoid response element in their promoter region. A time course for corticosterone (10 mg/kg, s.c.) in adrenalectomized rats revealed a peak hormone effect at the 4 hr time interval for bFGF (110-204% increase), BDNF (53-67% decrease), GR (53-64% decrease), and MR (34-56% decrease) mRNA levels in all hippocampal subregions using in situ hybridization. c-fos mRNA levels were affected exclusively in the dentate gyrus after 50 min to 2 hr (38-46% decrease). Furthermore, it was evaluated whether corticosterone regulation of these genes depends on interactions with the transcription factor complex activator protein-1. c-fos antisense oligodeoxynucleotides were injected into the dorsal hippocampus of adrenalectomized rats. Corticosterone was given 2 hr later, and the effects on gene expression were measured 4 hr later. In CA1, antisense treatment significantly and selectively enhanced the hormone action on the expression of bFGF (44% enhanced increase) and BDNF (38% enhanced decrease) versus control oligodeoxynucleotide treatment. In addition, an upregulation of c-fos expression (89% increase) was found. There were no effects of c-fos antisense on hippocampal GR and MR expression. Thus it seems that a tonic c-fos mechanism exists within CA1, which reduces GR- and MR-mediated effects on expression of bFGF and BDNF.

Modulation of the folate receptor type beta gene by coordinate actions of retinoic acid receptors at activator Sp1/ets and repressor AP-1 sites

Folate receptor (FR) type beta is a promising target for therapeutic intervention in acute myelogenous leukemia (AML) owing particularly to its specific up-regulation in AML cells by all-trans retinoic acid (ATRA). Here we identify functional elements in the FR-beta gene and examine the molecular mechanism of transcriptional induction of FR-beta by ATRA. The basal promoter activity of FR-beta resulted from synergistic interaction between Sp1 and ets binding sites (EBSs) and repression by upstream AP-1-like elements, whose action required EBSs. A minimal promoter containing the Sp1 and ets elements was ATRA-responsive. The repressor elements bound Fos family proteins; association of the proteins with the repressor elements correlated negatively with FR-beta expression in peripheral blood neutrophils and monocytes and also in KG-1 (AML) cells grown in the absence or in the presence of ATRA. Furthermore, down-regulation of FR-beta in KG-1 cells treated with O-tetradecanoylphorbol 13-acetate (TPA) was accompanied by increased AP-1 binding to the repressor elements. From chromatin immunoprecipitation (ChIP) assays, the nuclear retinoic acid receptor alpha (RARalpha) associated with the Sp1 region, and RARs beta and gamma associated with the AP-1 and Sp1 regions; treatment of KG-1 cells with ATRA did not alter Sp1 binding but increased the association of RARalpha and decreased the association of RARs beta and gamma. ATRA also decreased RAR expression levels. The results suggest that the FR-beta gene is a target for multiple coordinate actions of nuclear receptors for ATRA directly and indirectly acting on a transcriptional complex containing activating Sp1/ets and inhibitory AP-1 proteins. The multiple mechanisms favor the prediction that ATRA will induce FR-beta expression in a broad spectrum of AML cells. Further, optimal FR-beta induction may be expected when all 3 RAR subtypes bind agonist.