Regulated activity of the distal promoter-like element of the human corticotropin-releasing hormone gene and secondary structural features of its corresponding transcripts

Sex-specific effects of relaxin-3 on food intake and brain expression of corticotropin-releasing factor in rats

This study compared the effects of relaxin-3 (RLN3) on food intake, plasma corticosterone, and the expression of corticotropin-releasing factor (CRF) in male and female rats. RLN3 was injected into the lateral ventricle at 25, 200, and 800 pmol concentrations. RLN3 at 25 pmol increased food intake (grams) at 30 and 60 minutes after injection in female but not male rats. Female rats also showed higher increase in relative to body weight (BW) food intake (mg/g BW) for all RLN3 concentrations at 30 minutes and for 800 pmol of RLN3 at 60 minutes. Moreover, RLN3 at 800 pmol significantly increased 24-hour BW gain in female but not male rats. At 60 minutes after administration, 800 pmol of RLN3 produced a significant increase in plasma corticosterone and in the expression of CRF and c-fos mRNAs in the parvocellular paraventricular hypothalamic nucleus (PVN) in male but not female rats. The levels of c-fos mRNA in the magnocellular PVN were increased by RLN3 but did not differ between the sexes. Conversely, expression of CRF mRNA in the medial preoptic area was increased in female rats but was not sensitive to 800 pmol of RLN3. In the bed nucleus of the stria terminalis, 800 pmol of RLN3 significantly increased CRF mRNA expression in female but not male rats. Therefore, female rats showed more sensitivity and stronger food intake increase in response to RLN3. The differential effects of RLN3 on CRF expression in the PVN and bed nucleus of the stria terminalis may contribute to the sex-specific difference in the behavioral response.

Methylation of the Corticotropin Releasing Hormone Gene Promoter in BeWo Cells: Relationship to Gene Activity

Corticotropin releasing hormone (CRH) production by the human placenta increases exponentially as pregnancy advances, and the rate of increase predicts gestational length. CRH gene expression is regulated by cAMP in trophoblasts through a cyclic AMP-response element (CRE), which changes its transcription factor binding properties upon methylation. Here we determined whether methylation of the CRH proximal promoter controls basal and cAMP-stimulated CRH expression in BeWo cells, a well-characterized trophoblastic cell line. We treated the cells with 8-Br-cAMP and the DNA methyltransferase inhibitor 5-aza-2' deoxycytidine (5-AZA-dC) and determined the effects on CRH mRNA level and promoter methylation. Clonal bisulfite sequencing showed partial and allele independent methylation of CpGs in the CRH promoter. CRH mRNA expression and the methylation of a subset of CpGs (including CpG2 in the CRE) increased spontaneously during culture. 8-Br-cAMP stimulated CRH expression without affecting the increase in methylation. 5-AZA-dC decreased methylation and augmented 8-Br-cAMP-stimulated CRH expression, but it blocked the spontaneous increase of CRH mRNA level. We conclude that the CRH promoter is a dynamically and intermediately methylated genomic region in BeWo cells. Promoter methylation did not inhibit CRH gene expression under the conditions employed; rather it determined the contribution of alternative cAMP-independent pathways and cAMP-independent mechanisms to CRH expression control.

Regulation of corticotropin releasing hormone receptor type 1 messenger RNA level in Y-79 retinoblastoma cells: potential implications for human stress response and immune/inflammatory reaction

We report the regulation of type 1 receptor mRNA in Y-79 human retinoblastoma cells, grown in the absence or presence of pharmacological levels of phorbol esters, forskolin, glucocorticoids and their combinations. To control for inducibility and for assessing the sensitivity of the Y-79 system to glucocorticoids, corticotropin releasing hormone mRNA levels were measured in parallel. All treatments stimulated corticotropin releasing hormone receptor type 1 gene expression relative to baseline. A weak suppression of corticotropin releasing hormone mRNA level was observed during dexamethasone treatment. The cell line expressed ten-fold excess of receptor to ligand mRNA under basal conditions. The findings predict the presence of functional phorbol ester, cyclic AMP and glucocorticoid response elements in the promoter region of corticotropin releasing hormone receptor type 1 gene and support a potential role for its product during chronic stress and immune/inflammatory reaction.

Direct inhibitory effect of glucocorticoids on corticotrophin-releasing hormone gene expression in neurones of the paraventricular nucleus in rat hypothalamic organotypic cultures

Corticotrophin-releasing hormone (CRH) in the parvocellular neurosecretory neurones of hypothalamic paraventricular nucleus governs neuroendocrine stress cascade and is the major target of the negative feedback effect of corticosteroids. To assess whether glucocorticoids exert their inhibitory effect on CRH expression directly on parvocellular neurones or indirectly through a complex neuronal circuit, we examined the effect of corticosterone (CORT) and dexamethasone (DEX) on CRH mRNA levels in slice explant cultures of the rat hypothalamus. Organotypic slice cultures were prepared from 6 days old rat pups and maintained in vitro for 14 days. CRH mRNA expression was measured by in situ hybridisation histochemistry. Under basal conditions, CRH mRNA expressing cells were exclusively revealed in the paraventricular region along the third ventricle. Inhibition of action potential spike activity by tetrodotoxin (TTX, 1 microm) reduced CRH mRNA signal in the organotypic cultures. CORT (500 nm) or DEX (50 nm) treatment for 24 h significantly inhibited CRH expression in the parvocellular neurones and this effect of corticosteroids was not affected following blockade of voltage dependent sodium channels by TTX. Forskolin-stimulated CRH mRNA levels in the paraventricular nucleus were also inhibited by CORT or DEX in the presence and in the absence of TTX. These studies identify paraventricular CRH neurones as direct target of corticosteroid feedback. Type II corticosteroid receptor agonists act directly on paraventricular neurones to inhibit basal and forskolin-induced CRH mRNA expression in explant cultures of the rat hypothalamus.

Evolutionarily conserved glucocorticoid regulation of corticotropin-releasing factor expression

Glucocorticoids (GCs) exert feedback regulation on corticotropin-releasing factor (CRF) neurons in mammals. The nature of GC actions is cell-type specific, being either inhibitory (e.g. paraventricular nucleus) or stimulatory (e.g. amygdala and bed nucleus of the stria terminalis). Nothing is known about differential regulation of CRF gene expression by GCs in nonmammalian vertebrates. We studied the actions of GCs on CRF expression in discrete brain regions of the frog Xenopus laevis. Treatment with corticosterone (CORT) decreased, whereas the corticosteroid synthesis inhibitor metyrapone increased CRF expression in the anterior preoptic area (homolog of the mammalian paraventricular nucleus), as measured by CRF primary transcript, mRNA, and CRF immunoreactivity (ir) (by immunocytochemistry). By contrast to the preoptic area, CORT increased CRF-ir in the medial amygdala and bed nucleus of the stria terminalis, whereas metyrapone decreased CRF-ir in the medial amygdala. CRF-ir and glucocorticoid receptor-ir were colocalized in cells in the frog brain. In transient transfection assays in PC-12 cells, GCs decreased forskolin-induced activation of the frog CRF promoters. Treatment with CORT also reduced CRF promoter activity in transfected tadpole brain in vivo. Frog glucocorticoid receptor bound with high-affinity in vitro to regions in the proximal promoters of frog CRF genes that are homologous with the human CRF gene. Our findings suggest that the neural cell-type specificity and molecular mechanisms of GC-dependent regulation of CRF are phylogenetically ancient, and that the limbic pathways mediating behavioral and physiological responses to stressors were likely present in the earliest land-dwelling vertebrates.

Amygdala protein kinase C epsilon regulates corticotropin-releasing factor and anxiety-like behavior

Corticotropin-releasing factor (CRF), its receptors, and signaling pathways that regulate CRF expression and responses are areas of intense investigation for new drugs to treat affective disorders. Here, we report that protein kinase C epsilon (PKCepsilon) null mutant mice, which show reduced anxiety-like behavior, have reduced levels of CRF messenger RNA and peptide in the amygdala. In primary amygdala neurons, a selective PKCepsilon activator, psiepsilonRACK, increased levels of pro-CRF, whereas reducing PKCepsilon levels through RNA interference blocked phorbol ester-stimulated increases in CRF. Local knockdown of amygdala PKCepsilon by RNA interference reduced anxiety-like behavior in wild-type mice. Furthermore, local infusion of CRF into the amygdala of PKCepsilon(-/-) mice increased their anxiety-like behavior. These results are consistent with a novel mechanism of PKCepsilon control over anxiety-like behavior through regulation of CRF in the amygdala.

Regulation of vertebrate corticotropin-releasing factor genes

Developmental, physiological, and behavioral adjustments in response to environmental change are crucial for animal survival. In vertebrates, the neuroendocrine stress system, comprised of the hypothalamus, pituitary, and adrenal/interrenal glands (HPA/HPI axis) plays a central role in adaptive stress responses. Corticotropin-releasing factor (CRF) is the primary hypothalamic neurohormone regulating the HPA/HPI axis. CRF also functions as a neurotransmitter/neuromodulator in the limbic system and brain stem to coordinate endocrine, behavioral, and autonomic responses to stressors. Glucocorticoids, the end products of the HPA/HPI axis, cause feedback regulation at multiple levels of the stress axis, exerting direct and indirect actions on CRF neurons. The spatial expression patterns of CRF, and stressor-dependent CRF gene activation in the central nervous system (CNS) are evolutionarily conserved. This suggests conservation of the gene regulatory mechanisms that underlie tissue-specific and stressor-dependent CRF expression. Comparative genomic analysis showed that the proximal promoter regions of vertebrate CRF genes are highly conserved. Several cis regulatory elements and trans acting factors have been implicated in stressor-dependent CRF gene activation, including cyclic AMP response element binding protein (CREB), activator protein 1 (AP-1/Fos/Jun), and nerve growth factor induced gene B (NGFI-B). Glucocorticoids, acting through the glucocorticoid and mineralocorticoid receptors, either repress or promote CRF expression depending on physiological state and CNS region. In this review, we take a comparative/evolutionary approach to understand the physiological regulation of CRF gene expression. We also discuss evolutionarily conserved molecular mechanisms that operate at the level of CRF gene transcription.

Sequence variants of the CRH 5'-flanking region: effects on DNA-protein interactions studied by EMSA in PC12 cells

Recently, studies in adult rheumatoid arthritis patients have shown an association with four single-nucleotide polymorphisms (SNPs) in the 3.7-kb regulatory region of human corticotropin-releasing hormone (hCRH) gene located at positions -3531, -3371, -2353, and -684 bp. Three of these novel polymorphisms are in absolute linkage disequilibrium, resulting in three combined alleles, named A1B1, A2B1, and A2B2. To study whether the described polymorphic nucleotide sequences in the 5' region of the hCRH gene interfere with binding of nuclear proteins, an electric mobility shift assay (EMSA) was performed. At position -2353 bp, a specific DNA protein complex was detected for the wild-type sequence only, possibly interfering with a binding site for the activating transcription factor 6 (ATF6). In contrast, no difference could be detected for the other SNPs. However, at position -684, a quantitative difference in protein binding due to cAMP incubation could be observed. To further investigate whether these SNPs in the CRH promoter are associated with an altered regulation of the CRH gene, we performed a luciferase reporter gene assay with transiently transfected rat pheochromocytoma cells PC12. Incubation with 8-Br-cAMP alone or in combination with cytokines enhanced significantly the promoter activity in PC12 cells. The promoter haplotypes studied exhibited a differential capacity to modulate CRH gene expression. In all our experiments, haplotype A1B1 showed the most pronounced influence on promoter activity. Taken together, our results demonstrate a differential binding capacity of nuclear proteins of the promoter polymorphisms resulting in a different gene regulation. Most probably the SNP at position -2,353 plays a major role in mediating these differences.

Regulation of gene promoters of hypothalamic peptides

In order to fulfill their roles in neuroendocrine regulation, specific hypothalamic neurons are devoted to produce and deliver biologically active peptides to the pituitary gland. The biosynthesis and release of peptides are strictly controlled by afferents to these hypothalamic neurons. Cell-specific expression and biosynthetic regulation largely relies on transcription from the gene promoter for which the 5(')-flanking regions of the peptidergic genes contain essential elements. Cell-specific transcription factors employ these regulatory elements to exert their control over the expression of the peptidergic gene. This article explores the properties of regulatory elements of the major hypothalamic peptides, somatostatin, growth hormone-releasing hormone, gonadotropin-releasing hormone, thyrotropin-releasing hormone, corticotropin-releasing hormone, vasopressin and oxytocin, and the transcription factors acting on them. These transcription factors are often endpoints of signal transduction pathways that can be activated by neurotransmitters or steroid hormones. Others are essential to provide cell-specific expression of the peptidergic gene during development and mature regulation.

C/EBP activates the human corticotropin-releasing hormone gene promoter

The purpose of these studies was to identify whether transcription factors, associated with cytokine signalling, affected promoter activity of the corticotropin releasing hormone (CRH) gene. Fragments of a 3.6 kb sequence of the human CRH gene promoter were amplified by PCR and ligated upstream of a CAT reporter. These constructs were transfected into a variety of cell lines, either alone or together, with transcription factor expression vectors. Basal activity of a 3070 bp CRH promoter fragment was only seen in neuronal and lymphoblastoid cell lines. Promoter activity was increased by the transcription factors C/EBPbeta (NF-IL6) and more strongly, by C/EBPdelta (NF-IL6beta). Increased CRH promoter activity following phorbol ester treatment was inhibited by a dominant negative NF-IL6 mutant, showing that the effects of phorbol ester were principally mediated by C/EBP. Moreover, the inverse changes in the expression of CRH in the hypothalamus and spleens of arthritic rats were paralleled by similar inverse changes in NF-IL6beta expression in these organs. These data show that some transcription factors associated with cytokine signalling can also activate the CRH promoter.

Structure of the distal human gonadotropin releasing hormone (hGnrh) gene promoter and functional analysis in Gt1-7 neuronal cells

To assess potential species-specific expression of gonadotropin releasing hormone (GnRH), the distal human (h) GnRH promoter was cloned, characterized and tested in gene transfer studies. The nucleotide sequence of approximately 3.8 kb of 5'-flanking region was determined. Homology to the rat (r) GnRH sequence was observed in the proximal promoter region between -551 h (-424 r) and the transcriptional start site and within multiple distal promoter regions. In contrast, there was little similarity in the sequences between -1131/-551 h and -1031/-424 r. A deletion panel of 5'-flanking hGnRH promoter constructs was made and tested in transient transfection assays in GnRH-producing mouse GT1-7 neuronal cells. The largest hGnRH promoter construct (-3832/+5 h) exhibited high levels of reporter activity, similar to that observed with the largest rGnRH construct (-3026/+116 r). However, in contrast to the rat gene, deletion of distal promoter sequences of the hGnRH promoter to -1971, -1131 or -551 did not result in a decrease in luciferase reporter activity. Further truncation to -350 resulted in a 3-fold decrease in luciferase activity. There was no preferential use of the putative upstream hGnRH start site in neuronal cells. DNase I protection assays showed unique protection patterns with nuclear extracts from GT1-7 and Gn10 neuronal cells and the hGnRH and rGnRH promoter fragments. These data suggest the presence of different cis-acting elements and transacting factors that mediate species-specific neuronal GnRH expression.

Stress-induced activation of neuronal activity and corticotropin-releasing factor gene expression in the paraventricular nucleus is modulated by glucocorticoids in rats

Intronic in situ hybridization methodology provides a means of determining the rate of gene transcription under basal and stimulated conditions. In the present study, we have used intronic in situ hybridization to the corticotropin-releasing factor (CRF) gene to measure hypothalamic CRF gene transcription after stress as well as its modulation by glucocorticoids. Using this and conventional exonic in situ hybridization we examined the time course of changes in c-fos mRNA, and CRF heteronuclear RNA (hnRNA) and mRNA concentrations in the paraventricular nucleus (PVN) of male Wistar rats after restraint stress. In addition, we determined the effects of adrenalectomy and dexamethasone administration on c-fos and CRF gene expression in the PVN. Restraint stress induced a rapid induction (within 5 min) of c-fos mRNA and CRF hnRNA expression in the PVN. Both RNA concentrations peaked at 30 min then decreased and were undetectable 2 h after stress onset. In contrast, the concentration of CRF mRNA increased gradually and a significant elevation was first detected 60 min after the beginning of stress. Adrenalectomy augmented and dexamethasone pretreatment inhibited c-fos mRNA, CRF hnRNA, and mRNA induction after stress. The data suggest that stress-induced activation of neurons, CRF gene transcription, and CRF synthesis in the PVN are modulated by glucocorticoids.

Tissue-specific expression of heat shock proteins 70 and 90: potential implication for differential sensitivity of tissues to glucocorticoids

Heat shock proteins (hsps) and glucocorticoids are key elements of the organism's adaptive response to adverse physiological conditions. Glucocorticoids are pleiotropic hormones acting through receptor-mediated processes and eliciting tissue-specific biologic effects. The inactive form of the glucocorticoid receptor (GR) in the cytoplasm appears to be bound to hsps of the 90K family (hsp90 alpha and hsp90 beta). This interaction facilitates binding of glucocorticoid to its receptor, and depends on the relative amounts of the interacting components, GR and hsp90. To gain insight into the mechanisms of glucocorticoid regulation in a physiological context, the level of the hsp70/90 system in a panel of tissues, including testis, spleen, liver, thymus, pituitary, hypothalamus, hippocampus, brain cortex, pineal and adrenal, was examined by Western blotting. The hsp90 component showed greater variation (up to about forty-fold) relative to the less variable (up to about three-fold) hsp70 component of the system. The relative distribution of the hsp90 alpha and beta forms in the various tissues was also examined by a combination of Western and Northern blotting techniques. It was found that the alpha form predominated in the brain and the testis and the beta form predominated in the other peripheral organs. There was no relation between tissue hsp90 content and differential expression of either form. These findings suggest that tissue hsp90 content, an important physiological parameter of cellular homeostasis, may confer tissue specificity and sensitivity to glucocorticoids.

Corticotropin-releasing hormone, proopiomelanocortin, and glucocorticoid receptor gene expression in adrenocorticotropin-producing tumors in vitro

To differentiate between ectopic ACTH syndrome and Cushing's disease, gene expression of corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), and glucocorticoid receptor was examined in 10 pituitary adenomas (Cushing's disease) and in 10 ectopic ACTH-producing tumors. CRH increased plasma ACTH levels in all patients with Cushing's disease and in five patients with ectopic ACTH syndrome whose tumors contained CRH and CRH mRNA. In five CRH nonresponders, CRH was not detected in tumors that contained no CRH mRNA or that contained only long-size CRH mRNA. Dexamethasone (Dex) decreased plasma ACTH levels in all patients with Cushing's disease and in three patients with ectopic ACTH-producing bronchial carcinoid. These tumors contained glucocorticoid receptor mRNA. CRH increased and Dex decreased ACTH release and POMC mRNA levels in pituitary adenoma and bronchial carcinoid cells. PMA increased POMC mRNA levels only in carcinoid cells. These results reveal characteristics of ectopic ACTH-producing tumors: long-size CRH mRNA and PMA-induced POMC gene expression. In addition, there are two ectopic ACTH syndrome subtypes: tumors containing ACTH with CRH (CRH responder) and tumors without CRH. Dex decreases ACTH release and POMC mRNA levels in some bronchial carcinoids. Therefore, CRH and Dex tests have limited usefulness in differentiating between Cushing's disease and ectopic ACTH syndrome.

Evidence of direct estrogenic regulation of human corticotropin-releasing hormone gene expression. Potential implications for the sexual dimophism of the stress response and immune/inflammatory reaction

Corticotropin-releasing hormone (CRH) plays major roles in coordination of the stress response and regulation of the immune/inflammatory reaction, two important functions associated with sexual dimorphism. Two overlapping segments of the 5' flanking region of the human (h) CRH gene, the proximal 0.9 kb (containing two perfect half-palindromic estrogen-responsive elements [EREs]) and the 2.4 kb (including the former and containing two additional perfect half-palindromic EREs), were examined for their ability to confer estrogen-mediated transcriptional enhancement to a homologous or heterologous promoter. The level of estrogen-induced transactivation by the 0.9- and 2.4-kb segments was determined by chloramphenicol acetyltransferase analysis in CV-1 cells cotransfected with estrogen receptor (ER) cDNA expression plasmids, and found to be respectively approximately 10% and 20% of that of the strongly estrogen-responsive Xenopus vitellogenin A2 enhancer. Gel retardation and immunoprecipitation demonstrated specific association between the perfect half-palindromic EREs of hCRH gene and the DNA binding domain of hER in vitro. These findings may constitute the basis of sexual dimorphism in the expression of the CRH gene in the central nervous system and periphery, and might shed light in existing gender differences in stress response and immune regulation.

Structural organization of the 5' flanking region of the human corticotropin releasing hormone gene

We have determined the nucleotide sequence of the proximal 3625 nucleotides 5' flanking the major mRNA start site of the human corticotropin releasing hormone gene (hCRH) and identified several putative regulatory elements. Interestingly, we did not detect any glucocorticoid responsive elements; we did however find five interspersed perfect half palindromic estrogen responsive elements, which might confer estrogen regulatability to the hCRH gene. We have identified a segment spanning from -2835 to -2972, which has about 72% homology to the 3' terminal half of the human Alu I family of highly repetitive elements, and another one, which spans from -2213 to -2580 and has greater than 80% homology to members of human type O family of repetitive elements. These elements may confer DNA fragility, since the loci for hCRH and the human fragile site FRA8F colocalize in human chromosome 8. The structural information reported represents a first step in the study of regulation of the hCRH gene at the molecular level.