Negative Glucocorticoid Response Element Research Articles

Ghrelin Represses Thymic Stromal Lymphopoietin Gene Expression through Activation of Glucocorticoid Receptor and Protein Kinase C Delta in Inflamed Skin Keratinocytes.

Ghrelin, a peptide hormone secreted from enteroendocrine cells of the gastrointestinal tract, has anti-inflammatory activity in skin diseases, including dermatitis and psoriasis. However, the molecular mechanism underlying the beneficial effect of ghrelin on skin inflammation is not clear. In this study, we found that ghrelin alleviates atopic dermatitis (AD)-phenotypes through suppression of thymic stromal lymphopoietin (TSLP) gene activation. Knockdown or antagonist treatment of growth hormone secretagogue receptor 1a (GHSR1a), the receptor for ghrelin, suppressed ghrelin-induced alleviation of AD-like phenotypes and suppression of TSLP gene activation. We further found that ghrelin induces activation of the glucocorticoid receptor (GR), leading to the binding of GR with histone deacetylase 3 (HDAC3) and nuclear receptor corepressor (NCoR) NCoR corepressor to negative glucocorticoid response element (nGRE) on the TSLP gene promoter. In addition, ghrelin-induced protein kinase C δ (PKCδ)-mediated phosphorylation of p300 at serine 89 (S89), which decreased the acetylation and DNA binding activity of nuclear factor- κB (NF-κB) p65 to the TSLP gene promoter. Knockdown of PKCδ abolished ghrelin-induced suppression of TSLP gene activation. Our study suggests that ghrelin may help to reduce skin inflammation through GR and PKCδ-p300-NF-κB-mediated suppression of TSLP gene activation.

Hypothalamic Regulation of Corticotropin-Releasing Factor under Stress and Stress Resilience.

This review addresses the molecular mechanisms of corticotropin-releasing factor (CRF) regulation in the hypothalamus under stress and stress resilience. CRF in the hypothalamus plays a central role in regulating the stress response. CRF stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary. ACTH stimulates glucocorticoid secretion from the adrenal glands. Glucocorticoids are essential for stress coping, stress resilience, and homeostasis. The activated hypothalamic-pituitary-adrenal axis is suppressed by the negative feedback from glucocorticoids. Glucocorticoid-dependent repression of cAMP-stimulated Crf promoter activity is mediated by both the negative glucocorticoid response element and the serum response element. Conversely, the inducible cAMP-early repressor can suppress the stress response via inhibition of the cAMP-dependent Crf gene, as can the suppressor of cytokine signaling-3 in the hypothalamus. CRF receptor type 1 is mainly involved in a stress response, depression, anorexia, and seizure, while CRF receptor type 2 mediates “stress coping” mechanisms such as anxiolysis in the brain. Differential effects of FK506-binding immunophilins, FKBP4 and FKBP5, contribute to the efficiency of glucocorticoids under stress resilience. Together, a variety of factors contribute to stress resilience. All these factors would have the differential roles under stress resilience.

Glucocorticoid and Mineralocorticoid Receptors in the Brain: A Transcriptional Perspective.

Adrenal glucocorticoid hormones are crucial for maintenance of homeostasis and adaptation to stress. They act via the mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs)—members of the family of nuclear receptors. MRs and GRs can mediate distinct, sometimes opposite, effects of glucocorticoids. Both receptor types can mediate nongenomic steroid effects, but they are best understood as ligand-activated transcription factors. MR and GR protein structure is similar; the receptors can form heterodimers on the DNA at glucocorticoid response elements (GREs), and they share a number of target genes. The transcriptional basis for opposite effects on cellular physiology remains largely unknown, in particular with respect to MR-selective gene transcription. In this review, we discuss proven and potential mechanisms of transcriptional specificity for MRs and GRs. These include unique GR binding to “negative GREs,” direct binding to other transcription factors, and binding to specific DNA sequences in conjunction with other transcription factors, as is the case for MRs and NeuroD proteins in the brain. MR- and GR-specific effects may also depend on specific interactions with transcriptional coregulators, downstream mediators of transcriptional receptor activity. Current data suggest that the relative importance of these mechanisms depends on the tissue and physiological context. Insight into these processes may not only allow a better understanding of homeostatic regulation but also the development of drugs that target specific aspects of disease.

Dexamethasone suppresses JMJD3 gene activation via a putative negative glucocorticoid response element and maintains integrity of tight junctions in brain microvascular endothelial cells

The blood–brain barrier (BBB) exhibits a highly selective permeability to support the homeostasis of the central nervous system (CNS). The tight junctions in the BBB microvascular endothelial cells seal the paracellular space to prevent diffusion. Thus, disruption of tight junctions results in harmful effects in CNS diseases and injuries. It has recently been demonstrated that glucocorticoids have beneficial effects on maintaining tight junctions in both in vitro cell and in vivo animal models. In the present study, we found that dexamethasone suppresses the expression of JMJD3, a histone H3K27 demethylase, via the recruitment of glucocorticoid receptor α (GRα) and nuclear receptor co-repressor (N-CoR) to the negative glucocorticoid response element (nGRE) in the upstream region of JMJD3 gene in brain microvascular endothelial cells subjected to TNFα treatment. The decreased JMJD3 gene expression resulted in the suppression of MMP-2, MMP-3, and MMP-9 gene activation. Dexamethasone also activated the expression of the claudin 5 and occludin genes. Collectively, dexamethasone attenuated the disruption of the tight junctions in the brain microvascular endothelial cells subjected to TNFα treatment. Therefore, glucocorticoids may help to preserve the integrity of the tight junctions in the BBB via transcriptional and post-translational regulation following CNS diseases and injuries.

Genome-Wide Identification of Basic Helix-Loop-Helix and NF-1 Motifs Underlying GR Binding Sites in Male Rat Hippocampus.

Glucocorticoids regulate hippocampal function in part by modulating gene expression through the glucocorticoid receptor (GR). GR binding is highly cell type specific, directed to accessible chromatin regions established during tissue differentiation. Distinct classes of GR binding sites are dependent on the activity of additional signal-activated transcription factors that prime chromatin toward context-specific organization. We hypothesized a stress context dependency for GR binding in hippocampus as a consequence of rapidly induced stress mediators priming chromatin accessibility. Using chromatin immunoprecipitation sequencing to interrogate GR binding, we found no effect of restraint stress context on GR binding, although analysis of sequences underlying GR binding sites revealed mechanistic detail for hippocampal GR function. We note enrichment of GR binding sites proximal to genes linked to structural and organizational roles, an absence of major tethering partners for GRs, and little or no evidence for binding at negative glucocorticoid response elements. A basic helix–loop–helix motif closely resembling a NeuroD1 or Olig2 binding site was found underlying a subset of GR binding sites and is proposed as a candidate lineage-determining transcription factor directing hippocampal chromatin access for GRs. Of our GR binding sites, 54% additionally contained half-sites for nuclear factor (NF)-1 that we propose as a collaborative or general transcription factor involved in hippocampal GR function. Our findings imply a dose-dependent and context-independent action of GRs in the hippocampus. Alterations in the expression or activity of NF-1/basic helix–loop–helix factors may play an as yet undetermined role in glucocorticoid-related disease susceptibility and outcome by altering GR access to hippocampal binding sites.

Inhibition of Lysyl Oxidase by Cortisol Regeneration in Human Amnion: Implications for Rupture of Fetal Membranes.

The mechanisms underlying human parturition are still not understood, yet we need this knowledge to combat preterm birth. Fetal membranes express abundant 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), which converts inert cortisone to active cortisol. We examined whether cortisol regeneration in the amnion might play a role in human parturition through regulation of lysyl oxidase (LOX), a collagen cross-linking enzyme, thereby contributing to the rupture of fetal membranes. By using cultured human primary amnion fibroblasts, we demonstrated that, in addition to the induction of the key enzymes involved in prostaglandin E2 (PGE2) synthesis, cortisol stimulated 11β-HSD1 and inhibited LOX reciprocally. These results were reproduced in human amnion tissue explants after cortisol treatment. Cortisone also inhibited LOX expression, which was abolished by the inhibition of 11β-HSD1. Despite the inhibition of LOX by PGE2, inhibition of the PGE2 pathway failed to block the inhibition of LOX by cortisol. However, inhibition of glucocorticoid receptor and mutation of a negative glucocorticoid response element in LOX promoter abolished the inhibition of LOX by cortisol. Chromatin immunoprecipitation assay revealed that cortisol increased GR binding to the LOX promoter. Moreover, increased cortisol and 11β-HSD1 abundance and decreased LOX abundance were observed in human amnion tissue after the labor-initiated spontaneous rupture of membranes. These data highlight a crucial role for local cortisol regeneration by 11β-HSD1 in the down-regulation of LOX expression via glucocorticoid receptor binding to a negative glucocorticoid response element to its promoter in the amnion, which may contribute to rupture of fetal membranes at parturition.

Role of oxidative stress in disrupting the function of negative glucocorticoid response element in daily amphetamine-treated rats

Amphetamine (AMPH)-induced appetite suppression is associated with changes in hypothalamic reactive oxygen species (ROS), antioxidants, neuropeptides, and plasma glucocorticoid. This study explored whether ROS and glucocorticoid response element (GRE), which is the promoter site of corticotropin-releasing hormone (CRH) gene, participated in neuropeptides-mediated appetite control. Rats were treated daily with AMPH for four days, and changes in food intake, plasma glucocorticoid and expression levels of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), superoxide dismutase (SOD), CRH, and glucocorticoid receptor (GR) were examined and compared. Results showed that food intake decreased and NPY gene down-regulated, while POMC, SOD, and CRH gene up-regulated during AMPH treatment. GR and GRE-DNA bindings were disrupted on Day 1 and Day 2 when glucocorticoid levels were still high. Pretreatment with GR inhibitor or ROS scavenger modulated mRNA levels in NPY, POMC, SOD and CRH in AMPH-treated rats. We suggest that disruptions of negative GRE (nGRE) on Day 1 and Day 2 are associated with an increase in oxidative stress during the regulation of NPY/POMC-mediated appetite control in AMPH-treated rats. These results advance the understanding of molecular mechanism in regulating AMPH-mediated appetite suppression.

Rapid Down-Regulation of Glucocorticoid Receptor Gene Expression in the Dentate Gyrus after Acute Stress in vivo: Role of DNA Methylation and MicroRNA Activity

Background: Although glucocorticoid receptors (GRs) in the hippocampus play a vital role in the regulation of physiological and behavioural responses to stress, the regulation of receptor expression remains unclear. This work investigates the molecular mechanisms underpinning stress-induced changes in hippocampal GR mRNA levels in vivo. Methods: Male Wistar rats were killed either under baseline conditions or after forced swim stress (FSS; 15 min in 25°C water). Rat hippocampi were micro-dissected (for mRNA, microRNA, and DNA methylation analysis) or frozen whole (for chromatin immunoprecipitation). In an additional experiment, rats were pre-treated with RU486 (a GR antagonist) or vehicle. Results: FSS evoked a dentate gyrus-specific reduction in GR mRNA levels. This was related to an increased DNMT3a protein association with a discreet region of the Nr3c1 (GR gene) promoter, shown here to undergo increased DNA methylation after FSS. FSS also caused a time-dependent increase in the expression of miR-124a, a microRNA known to reduce GR mRNA expression, which was inversely correlated with a reduction in GR mRNA levels 30 min after FSS. FSS did not affect GR binding to a putative negative glucocorticoid response element within the Nr3c1 gene. Conclusions: Acute stress results in decreased GR mRNA expression specifically in the dentate gyrus. Our results indicate that a complex interplay of multiple molecular mechanisms - including increased DNA methylation of discrete CpG residues within the Nr3c1 gene, most likely facilitated by DNMT3a, and increased expression of miR-124a - could be responsible for these changes.

Distal substitutions drive divergent DNA specificity among paralogous transcription factors through subdivision of conformational space

Many genomes contain families of paralogs--proteins with divergent function that evolved from a common ancestral gene after a duplication event. To understand how paralogous transcription factors evolve divergent DNA specificities, we examined how the glucocorticoid receptor and its paralogs evolved to bind activating response elements [(+)GREs] and negative glucocorticoid response elements (nGREs). We show that binding to nGREs is a property of the glucocorticoid receptor (GR) DNA-binding domain (DBD) not shared by other members of the steroid receptor family. Using phylogenetic, structural, biochemical, and molecular dynamics techniques, we show that the ancestral DBD from which GR and its paralogs evolved was capable of binding both nGRE and (+)GRE sequences because of the ancestral DBD's ability to assume multiple DNA-bound conformations. Subsequent amino acid substitutions in duplicated daughter genes selectively restricted protein conformational space, causing this dual DNA-binding specificity to be selectively enhanced in the GR lineage and lost in all others. Key substitutions that determined the receptors' response element-binding specificity were far from the proteins' DNA-binding interface and interacted epistatically to change the DBD's function through DNA-induced allosteric mechanisms. These amino acid substitutions subdivided both the conformational and functional space of the ancestral DBD among the present-day receptors, allowing a paralogous family of transcription factors to control disparate transcriptional programs despite high sequence identity.

Evolution of Novel Response Element Specificity in the Glucocorticoid Receptor

Specific recognition of DNA response elements by transcription factors is a key step in the regulation of gene expression. Some transcription factors recognize multiple, distinct response elements to mediate transrepression of transactivation of target genes. However, the mechanism by which a single transcription factor can evolve to recognize multiple response elements is unclear. Here, we study the evolution of the glucocorticoid receptor, which recognizes distinct response elements to mediate activation or repression its target genes. The glucocorticoid receptor binds to activating glucocorticoid response elements, or (+)GREs, as a dimer to activate transcription. Alternatively, GR binds to negative glucocorticoid response elements (nGREs) in a monomeric fashion to repress transcription. We demonstrate that, of the extant 3-keto steroid receptors, only the glucocorticoid receptor can bind to and repress transcription in a nGRE-dependent manner, despite the ability of all 3-keto steroid receptors to bind to and activate gene transcription from (+)GREs. Surprisingly, using ancestral gene reconstruction, we find that nGRE binding and gene repression was a feature of the ancestor of all extant 3-keto steroid receptors. nGRE binding and repression originated as a subfunction of the ancestral 3-keto steroid receptor coincident with (+)GRE binding, and this subfunction was optimized in the evolutionary lineage of the glucocorticoid receptor but lost in the ancestors of the mineralocorticoid, progesterone, and androgen receptors. Further, using x-ray crystallography and other structural biology approaches, we define the structural mechanisms by which the modern-day DNA binding specificity evolved in the glucocorticoid receptor.

Untethering Glucocorticoid Receptor‐Mediated Transcriptional Repression of Inflammatory Genes

The glucocorticoid receptor (GR), a ligand regulated transcription factor, that controls the expression of thousands of genes driving both up‐ and down‐regulation at equal frequencies. To activate transcription, GR cooperatively dimerizes on DNA at glucocorticoid response elements (GREs). However, the mechanism of gene repression by GR is more debated but it thought to occur through DNA‐dependent and DNA‐independent mechanisms. The DNA‐dependent mechanism involves direct binding of GR to the newly discovered negative glucocorticoid response elements (nGREs). The DNA‐independent mechanism involves GRs interaction with activator protein‐1 (AP‐1), which is a central transcription factor in immune systems that drives expression of inflammatory response genes. This mechanism, known as “tethering”, is the prevailing model for GR‐mediated repression at inflammatory genes. However, recent discoveries regarding DNA‐dependent transrepression at nGREs reveal that the mutations used to develop the tethering hypothesis are inadequate. We show using x‐ray crystallography, in vitro, and in cell assays that GR binds directly to nGRE‐like sites, leading us to hypothesize that GR‐mediated repression on inflammatory genes occurs through an alternative mechanism involving direct DNA binding.

Dexamethasone downregulates caveolin-1 causing muscle atrophy via inhibited insulin signaling.

Glucocorticoids play a major role in the development of muscle atrophy in various medical conditions, such as cancer, burn injury, and sepsis, by inhibiting insulin signaling. In this study, we report a new pathway in which glucocorticoids reduce the levels of upstream insulin signaling components by downregulating the transcription of the gene encoding caveolin-1 (CAV1), a scaffolding protein present in the caveolar membrane. Treatment with the glucocorticoid dexamethasone (DEX) decreased CAV1 protein and Cav1 mRNA expression, with a concomitant reduction in insulin receptor alpha (IRα) and IR substrate 1 (IRS1) levels in C2C12 myotubes. On the basis of the results of promoter analysis using deletion mutants and site-directed mutagenesis a negative glucocorticoid-response element in the regulatory region of the Cav1 gene was identified, confirming that Cav1 is a glucocorticoid-target gene. Cav1 knockdown using siRNA decreased the protein levels of IRα and IRS1, and overexpression of Cav1 prevented the DEX-induced decrease in IRα and IRS1 proteins, demonstrating a causal role of Cav1 in the inhibition of insulin signaling. Moreover, injection of adenovirus expressing Cav1 into the gastrocnemius muscle of mice prevented DEX-induced atrophy. These results indicate that CAV1 is a critical regulator of muscle homeostasis, linking glucocorticoid signaling to the insulin signaling pathway, thereby providing a novel target for the prevention of glucocorticoid-induced muscle atrophy.

Dexamethasone Induces a Putative Repressor Complex and Chromatin Modifications in the CRH Promoter

Glucocorticoids down-regulate expression of hypothalamic CRH; however, mechanisms by which they do so are not fully understood. The proximal promoter cAMP response element, negative glucocorticoid response element (nGRE), and methylated CpG islands all play a role in crh down-regulation. Dexamethasone (Dex)-repressed crh expression is associated with glucocorticoid receptor (GR) and histone deacetylase 1 (HDAC1) recruitment to the region of the crh promoter. Given that HDAC1 may be present in methylated CpG binding protein 2 (MeCP2) complexes, and that MeCP2 is known to play a role in regulating crh expression, we sought to determine whether or not HDAC1 and/or MeCP2 could interact with the GR. Dex enhanced GR interactions with both proteins. Glucocorticoid regulation of crh has also been associated with CpG methylation; thus we assessed whether GR could interact with a DNA methyltransferase (DnMT). Indeed, the GR interacted with DnMT3b, but not DnMT3a. In addition, Dex-induced occupancy of the crh promoter by HDAC1, MeCP2, and DnMT3b was associated with an increased level of promoter methylation, which appeared to be CpG site specific. Lastly, to extend previous assessment of chromatin modifications in this promoter region, the degree of histone methylation was measured. Dex increased trimethylation of histone 3-lysine 9, a marker of gene suppression; however, levels of di- and trimethylated histone 3-lysine 4, markers of gene activation, were not significantly changed. Taken together, the data suggest that Dex-mediated crh suppression involves formation of a repressor complex consisting of GR, MeCP2, and HDAC1, recruitment of DnMT3b, and associated changes in proximal promoter CpG methylation.

Ligand-Induced Repression of the Glucocorticoid Receptor Gene Is Mediated by an NCoR1 Repression Complex Formed by Long-Range Chromatin Interactions with Intragenic Glucocorticoid Response Elements

Glucocorticoids are among the most potent and effective agents for treating inflammatory diseases and hematological cancers. However, subpopulations of patients are often resistant to steroid therapy, and determining the molecular mechanisms that contribute to glucocorticoid resistance is thus critical to addressing this clinical problem affecting patients with chronic inflammatory disorders. Since the cellular level of the glucocorticoid receptor (GR) is a critical determinant of glucocorticoid sensitivity and resistance, we investigated the molecular mechanisms mediating repression of glucocorticoid receptor gene expression. We show here that glucocorticoid-induced repression of GR gene expression is mediated by inhibition of transcription initiation. This process is orchestrated by the recruitment of agonist-bound GR to exon 6, followed by the assembly of a GR-NCoR1-histone deacetylase 3-containing repression complex at the transcriptional start site of the GR gene. A functional negative glucocorticoid response element (nGRE) in exon 6 of the GR gene and a long-range interaction occurring between this intragenic response element and the transcription start site appear to be instrumental in this repression. This autoregulatory mechanism of repression implies that the GR concentration can coordinate repression with excess ligand, regardless of the combinatorial associations of tissue-specific transcription factors. Consequently, the chronic nature of inflammatory conditions involving long-term glucocorticoid administration may lead to constitutive repression of GR gene transcription and thus to glucocorticoid resistance.

The structural basis of direct glucocorticoid-mediated transrepression

A newly discovered negative glucocorticoid response element (nGRE) mediates DNA-dependent transrepression by the glucocorticoid receptor (GR) across the genome and plays a major role in immunosuppressive therapy. The nGRE differs dramatically from activating response elements and the mechanism driving GR binding and transrepression is unknown. To unravel the mechanism of nGRE-mediated transrepression by the glucocorticoid receptor, we characterize the interaction between GR and a nGRE in the thymic stromal lymphopoetin (TSLP) promoter. We show using structural and mechanistic approaches that nGRE binding represents a new mode of sequence recognition by human GR and that nGREs prevent receptor dimerization through a unique GR-binding orientation and strong negative cooperativity, ensuring the presence of monomeric GR at repressive elements.

Transcriptional suppression of the neuronal PAS domain 4 (Npas4) gene by stress via the binding of agonist‐bound glucocorticoid receptor to its promoter

Neuronal PAS domain 4 (NPAS4), a brain-specific helix-loop-helix transcription factor, has recently been shown to regulate the development of GABAergic inhibitory neurons. We previously reported that Npas4 mRNA expression levels were reduced in the hippocampus of mice exposed to social isolation or restraint stress, which was accompanied by impairment of memory, emotional behavior, and hippocampal neurogenesis. Therefore, the reduction of NPAS4 expression may play a role in stress-induced brain dysfunction. In this study, to investigate the transcriptional regulation of Npas4 by stress, we focused on the effect of glucocorticoids (GCs) upon Npas4 transcription. Corticosterone treatment reduced Npas4 expression in the frontal cortex and hippocampus, whereas adrenalectomy caused an increase in expression. GC receptor (GR) antagonist, mifepristone, inhibited the stress-induced reduction of Npas4 expression. Putative negative glucocorticoid response elements (GREs) were found -2000 to -1000 upstream of the Npas4 transcription initiation site. Npas4 promoter activity was increased by mifepristone or by mutation of the negative GRE sequences. A chromatin immunoprecipitation assay revealed that restraint stress increased the binding of GR to Npas4 promoter region in the hippocampus. These results suggest that transcription of Npas4 is down-regulated by stress via the binding of agonist-bound GR to its promoter.

Glucorticoid receptor in human cutaneous melanoma: immunohistochemical and immunofluorescence study

GR is a nuclear receptor which, when activated by its specific ligand, can act as a transcription factor that binds to glucocorticoid response elements (GRE) or negative GRE. It affects inflammatory responses, differentiation and cell proliferation. The ligand activated glucocorticoid receptor induces a G1 cell cycle arrest or apoptosis in immature thymocytes and impairs proliferation of fibroblasts of undifferentiated mammary epithelial cells. It impairs proliferation and differentiation of neural progenitor cells in vivo and in vitro. Glucocorticoids are widely used in cancer therapy and have cell type-specific pro- or antiapoptotic effects. In melanoma, however, the antitumor activity of glucocorticoids remains an open question. A recent report demonstrated that in mouse embryo tissue and in human undifferentiated cells, cytoplasmic accumulation of GR is determined by nestin in conjunction with vimentin, copolymerised into an intermediate filament system, and that this anchoring of GR to the nestin/vimentin etheromeric complex is related to the maintenance of a high proliferation rate. The aim of this study was to analyse the expression of subcellular GR in cutaneous melanoma by immunofluorescence, immunohistochemistry and laser scanning confocal microscopy and to evaluate any effect in melanoma progression. The results will be discussed.

Alcohol Dysregulates Corticotropin-Releasing-Hormone (CRH) Promoter Activity by Interfering with the Negative Glucocorticoid Response Element (nGRE)

EtOH exposure in male rats increases corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus of the hypothalamus (PVN), a brain region responsible for coordinating stress and anxiety responses. In this study we identified the molecular mechanisms involved in mediating these effects by examining the direct effects of EtOH on CRH promoter activity in a neuronal cell line derived from the PVN (IVB). In addition, we investigated the potential interactions of EtOH and glucocorticoids on the CRH promoter by concomitantly treating cells with EtOH and the glucocorticoid receptor (GR) antagonist RU486, and by sequentially deleting GR binding sites within glucocorticoid response element (GRE) on the CRH promoter. Cells were transiently transfected with a firefly luciferase reporter construct containing 2.5 kb of the rat wild type (WT) or mutated CRH promoter. Our results showed that EtOH treatment induced a biphasic response in CRH promoter activity. EtOH exposure for 0.5 h significantly decreased promoter activity compared to vehicle treated controls, whereas promoter activity was significantly increased after 2.0 h of EtOH exposure. Treatment with RU486, or deletion of the GR binding sites 1 and 2 within the GRE, abolished the EtOH-induced increase in the promoter activity, however did not affect EtOH-induced decrease in CRH promoter activity at an earlier time point. Overall, our data suggest that alcohol exposure directly regulates CRH promoter activity by interfering with the normal feedback mechanisms of glucocorticoids mediated by GR signaling at the GRE site of the CRH promoter.

Epigenetic modulation of the renal β-adrenergic–WNK4 pathway in salt-sensitive hypertension

How high salt intake increases blood pressure is a key question in the study of hypertension. Salt intake induces increased renal sympathetic activity resulting in sodium retention. However, the mechanisms underlying the sympathetic control of renal sodium excretion remain unclear. In this study, we found that β(2)-adrenergic receptor (β(2)AR) stimulation led to decreased transcription of the gene encoding WNK4, a regulator of sodium reabsorption. β(2)AR stimulation resulted in cyclic AMP-dependent inhibition of histone deacetylase-8 (HDAC8) activity and increased histone acetylation, leading to binding of the glucocorticoid receptor to a negative glucocorticoid-responsive element in the promoter region. In rat models of salt-sensitive hypertension and sympathetic overactivity, salt loading suppressed renal WNK4 expression, activated the Na(+)-Cl(-) cotransporter and induced salt-dependent hypertension. These findings implicate the epigenetic modulation of WNK4 transcription in the development of salt-sensitive hypertension. The renal β(2)AR-WNK4 pathway may be a therapeutic target for salt-sensitive hypertension.

Signal transduction in the hypothalamic corticotropin-releasing factor system and its clinical implications

Corticotropin-releasing factor (CRF) is a major regulatory peptide in the hypothalamic–pituitary–adrenal (HPA) axis under stress conditions. In response to stress, CRF is produced in the hypothalamic paraventricular nucleus. Forskolin- or pituitary adenylate cyclase-activating polypeptide-stimulated CRF gene transcription is mediated by the cyclic AMP (cAMP) response element on the CRF 5′-promoter region. Estrogens enhance activation of the CRF gene in stress, while inducible cAMP-early repressor suppresses the stress response via inhibition of the cAMP-dependent CRF gene. Glucocorticoid-dependent repression of cAMP-stimulated CRF promoter activity is mediated by both the negative glucocorticoid-response element and the serum-response element, while interleukin-6 (IL-6) stimulates the CRF gene. Suppressor of cytokine signaling-3, stimulated by IL-6 and cAMP, is involved in the negative regulation of CRF gene expression. Such complex mechanisms contribute to stress responses and homeostasis in the hypothalamus. Moreover, disruption of the HPA axis may cause a number of diseases related to stress. For example, CRF-induced p21-activated kinase 3 mRNA expression may be related to the proliferation of corticotrophs in Nelson's syndrome. A higher molecular weight form of immunoreactive β-endorphin, putative proopiomelanocortin (POMC), is increased in CRF-knockout mice, suggesting the important role of CRF in the processing of POMC through changes in prohormone convertase type-1 expression levels.