The brain corticotropin-releasing factor (CRF) receptor is of lower apparent molecular weight than the CRF receptor in anterior pituitary. Evidence from chemical cross-linking studies

Corticotropin-releasing factor decreases IL-18 in the monocyte-derived dendritic cell

Recent evidence suggests that crosstalk between mast cells, nerves and keratinocytes might be involved in the exacerbation of inflammatory conditions by stress, but the mechanism by which this occurs remains unclear. Corticotropin-releasing factor (CRF), which activates the hypothalamo-pituitary-adrenal (HPA) axis under stress, also has pro-inflammatory peripheral effects. However, there have been no reports about CRF receptor expression and the functional role of CRF in the dendritic cell (DC), which is considered to be the link between allergen uptake and the clinical manifestations of allergic diseases, such as atopic dermatitis. The purpose of this study was to investigate the expression of CRF receptors and the functional role of CRF in the monocyte-derived DC (MoDC) of atopic dermatitis patients and non-atopic healthy controls. In this study, mRNAs for CRF-R1alpha and 1beta, as well as the CRF-R1 protein, were detected in MoDCs. CRF-R2alpha (but not R2beta or R2gamma) mRNA and the CRF-R2 protein were present in MoDCs. Exposure of DCs to CRF resulted in a decrease of IL-18 in both atopic dermatitis patients and non-atopic healthy controls. However, CRF did not alter the expression of IL-6, CCL17, CCL18, and CCL22. Therefore, our results demonstrate that CRF could modulate immune responses by acting directly upon DCs.

Characterization and regulation of corticotropin-releasing factor receptors in the central nervous, endocrine and immune systems

Corticotropin-releasing factor (CRF) plays a major role in coordinating the endocrine, autonomic, behavioural and immune responses to stress through actions in the brain and in the periphery. CRF receptors identified in brain, pituitary and spleen have comparable kinetic and pharmacological characteristics, guanine nucleotide sensitivity and adenylate cyclase-stimulating activity. Differences were observed in the molecular mass of the CRF receptor complex between brain (58,000 Da) and pituitary and spleen (75,000 Da), which appeared to be due to differential glycosylation of the receptor proteins. In autoradiographic studies, CRF receptors were localized in highest densities in anterior and intermediate lobes of the pituitary, olfactory bulb, cerebral cortex, amygdala, cerebellum and the macrophage-rich marginal zones and red pulp regions of the spleen. CRF can modulate the number of CRF receptors in both the brain and pituitary in a reciprocal manner. The demonstration of functional CRF receptors in brain, pituitary and spleen suggests the importance of this neuropeptide in integrating the responses of the CNS, endocrine and immune systems to physiological, psychological and immunological stimuli.

Dimerization between vasopressin V1b and corticotropin releasing hormone type 1 receptors

1. Increasing evidence indicates that guanyl protein coupled receptors (GPCRs), including members of the vasopressin (VP) receptor family can act as homo- and heterodimers. Regulated expression and interaction of pituitary VP V1b receptor (V1bR) and corticotropin releasing hormone receptor type 1 (CRHR1) are critical for hypothalamic pituitary adrenal (HPA) axis adaptation, but it is unknown whether this involves physical interaction between these receptors.2. Bioluminescence resonance energy transfer (BRET) experiments using V1bR and CRHR1 fused to either Renilla luciferase (Rluc) or yellow fluorescent protein (YFP) at the N-terminus, but not the carboxyl-terminus, revealed specific interaction (BRET(50) = 0.39 +/- 0.08, V1bR) that was inhibited by untagged V1b or CRHR1 receptors, suggesting homo- and heterodimerization. The BRET data were confirmed by coimmunoprecipitation experiments using fully bioactive receptors tagged at the aminoterminus with c-myc and Flag epitopes, demonstrating specific homodimerization of the V1b receptor and heterodimerization of the V1b receptor with CRHR1 receptors.3. Heterodimerization between V1bR and CRHR1 is not ligand dependent since stimulation with CRH and AVP had no effect on coimmunoprecipitation. In membranes obtained from cells cotransfected with CRHR1 and V1bR, incubation with the heterologous nonpeptide antagonist did not alter the binding affinity or capacity of the receptor.4. The data demonstrate that V1bR and CRHR1 can form constitutive homo- and heterodimers and suggests that the heterodimerization does not influence the binding properties of these receptors.

Evidence for the presence of the type 2 corticotropin releasing factor receptor in the rodent cerebellum

Corticotropin releasing factor (CRF), localized in afferent inputs to the cerebellum, binds to two receptors defined as the Type 1 (CRF-R1) and the Type 2 (CRF-R2alpha). CRF-R1 has been localized to the cerebellum, as has a truncated isoform of CRF-R2alpha. Evidence for the presence of the full length isoform of CRF-R2alpha in the cerebellum is conflicting. We used RT-PCR, immunohistochemical, and physiologic techniques to resolve this conflict. RT-PCR data show low levels of CRF-R2alpha in the vermis and hemisphere of the cerebellum. These observations were confirmed by the Gene Expression Nervous System Atlas (GENSAT) database. A CRF-R2alpha antibody was used to determine the cellular distribution of the receptor in the cerebellum. The vast majority of the receptors are localized to Bergmann glial cells located throughout the cerebellum, as well as astrocytes in the granule cell layer. Neuronal labeling is present in sub-populations of Purkinje cells, Golgi cells, basket cells, and cerebellar nuclear neurons. Physiologic data show that urocortin II, which binds selectively to CRF-R2alpha, increases the firing rate of both Purkinje cells and nuclear neurons; this response can be blocked by the CRF-R2alpha-specific antagonist, antisauvagine-30. The present results confirm that CRF-R2alpha is present in the cerebellum and functions in circuits that modulate the firing rate of Purkinje cells and cerebellar nuclear neurons. A comparative analysis showed that the patterns of distribution of CRF-R1, CRF-R2alpha and CRF-R2alpha-tr are distinct. These data indicate that the CRF family of peptides modulates cerebellar output by binding to multiple CRF receptors.

Molecular cloning and initial characterization of African green monkey (Cercopithecus aethiops) corticotropin releasing factor receptor type 1 (CRF1) from COS-7 cells

We report the expression of endogenous CRF1 in COS-7 cells (African green monkey origin). Cloning of the coding region of CRF1 gene identified three alternatively spliced isoforms with nucleotide and predicted amino acid sequences corresponding to the membrane bound alpha and c and soluble e isoforms. DNA sequencing of the main isoform CRF1alpha showed homologies of 99%, 97% and 91% with the rhesus monkey, human and rodent genes, respectively; the deduced protein sequence differed in only one amino acid with rhesus monkey and human. Western blot analysis with antibodies against human CRF1 demonstrated immunoreactive proteins with MW of 37, 52, 70 and 80-85 in crude membrane or cytoplasm preparation; two additional species of 40 and 60 kDa were detected only in the cytoplasmic fraction. On immunocytochemistry CRF1 was localized to both the cell surface and intracellularly. The receptor was functional, e.g., addition of CRF to COS-7 cells inhibited cell proliferation and stimulated release of arachidonic acid; nevertheless, it was poorly coupled to cAMP production (its stimulation was minimal in native cells). In conclusion, COS cells that are routinely used for the study of transfected CRF receptors do express endogenous CRF1 mRNA with splicing behavior similar to that reported in human and rodent cells, and translated into functional CRF1 receptors.

CRH functions as a growth factor/cytokine in the skin

We tested the effect of CRH and related peptides in a large panel of human skin cells for growth factor/cytokine activities. In skin cells CRH action is mediated by CRH-R1, a subject to posttranslational modification with expression of alternatively spliced isoforms. Activation of CRH-R1 induced generation of both cAMP and IP3 in the majority of epidermal and dermal cells (except for normal keratinocytes and one melanoma line), indicating cell type-dependent coupling to signal transduction pathways. Phenotypic effects on cell proliferation were however dependent on both cell type and nutrition conditions. Specifically, CRH stimulated dermal fibroblasts proliferation, by increasing transition from G1/0 to the S phase, while in keratinocytes CRH inhibited cell proliferation. In normal and immortalized melanocytes CRH effect showed dichotomy and thus, it inhibited melanocyte proliferation in serum-containing medium CRH through G2 arrest, while serum free media led instead to CRH enhanced DNA synthesis (through increased transition from G1/G0 to S phase and decreased subG1 signal, indicating DNA degradation). CRH also induced inhibition of early and late apoptosis in the same cells, demonstrated by analysis with the annexin V stains. Thus, CRH acts on epidermal melanocytes as a survival factor under the stress of starvation (anti-apoptotic) as well as inhibitor of growth factors induced cell proliferation. In conclusion, CRH and related peptides can couple CRH-R1 to any of diverse signal transduction pathways; they also regulate cell viability and proliferation in cell type and growth condition-dependent manners.

Presynaptic localization of a truncated isoform of the type 2 corticotropin releasing factor receptor in the cerebellum

It is now well established that corticotropin releasing factor is present in two major excitatory afferent systems to the cerebellum, namely climbing fibers and mossy fibers. Two major classes of corticotropin releasing factor receptors, each with unique binding characteristics, have been identified as type 1 and type 2. In this study we used an antibody made to the n-terminus of the type 2 corticotropin releasing factor receptor. Characterization of this antibody showed that it strongly labeled a protein with a molecular weight of 16-32 kDa and only faintly labels a 62-83 kDa protein. The lower molecular weight protein corresponds to the weight of a recently described truncated isoform of this receptor that is designated corticotropin releasing factor-type 2alpha-truncated isoform. We carried out transfection paradigms using corticotropin releasing factor-type 2alpha-truncated isoform constructs and confirmed that the antibody recognized the truncated isoform of the type 2 corticotropin releasing factor receptor. Further, light and electron microscopic studies were carried out in mice and rats to define the distribution of the truncated receptor. Immunoreactivity is evident in the basal region of many, but not all Purkinje cell bodies and their initial axonal segments, as well as the initial axonal segments of isolated Golgi cells, and cerebellar nuclear neurons. In addition, punctate elements in the molecular layer were immunolabeled. The localization of the receptor to the initial segment of Purkinje cells was confirmed with electron microscopy. Further, the punctate labeling in the molecular layer was localized to parallel fibers and their terminals. In conclusion, evidence has been presented to show that distinct isoforms of the corticotropin releasing factor receptor are present in the cerebellum. The complex interactions between corticotropin releasing factor and other members of the corticotropin releasing factor family of peptides with both pre- and postsynaptic receptors support a growing concept that corticotropin releasing factor plays an important role in modulating activity in cerebellar circuits and ultimately in controlling motor behavior.

Differential profile of CRF receptor distribution in the rat stomach and duodenum assessed by newly developed CRF receptor antibodies

Peripheral corticotropin-releasing factor (CRF) receptor ligands inhibit gastric acid secretion and emptying while stimulating gastric mucosal blood flow in rats. Endogenous CRF ligands are expressed in the upper gastrointestinal (GI) tissues pointing to local expression of CRF receptors. We mapped the distribution of CRF receptor type 1 (CRF1) and 2 (CRF2) in the rat upper GI. Polyclonal antisera directed against the C-terminus of the CRF receptor protein were generated in rabbits and characterized by western blotting and immunofluorescence using CRF1- and CRF2-transfected cell lines and in primary cultured neurons from rat brain cortex. A selective anti-CRF1 antiserum (4467a-CRF1) was identified and used in parallel with another antiserum recognizing both CRF1 and CRF2 (4392a-CRF1&2) to immunostain gastric tissue sections. Antiserum 4467a-CRF1 demonstrated specific immunostaining in a narrow zone in the upper oxyntic gland within the stomach corpus. Conversely, 4392a-CRF1&2 labeled cells throughout the oxyntic gland and submucosal blood vessels. Pre-absorption with the specific antigen peptide blocked immunostaining in all experiments. Doublestaining showed co-localization of 4392a-CRF1&2 but not 4467a-CRF1 immunoreactivity with H/K-ATPase and somatostatin immunostaining in parietal and endocrine cells of the oxyntic gland. No specific staining was observed in the antrum with either antisera, whereas only antiserum 4392a-CRF1&2 showed modest immunoreactivity in the duodenal mucosa. Finally, co-localization of CRF2 and urocortin immunoreactivity was found in the gastric glands. These results indicate that both CRF receptor subtypes are expressed in the rat upper GI tissues with a distinct pattern and regional differences suggesting differential function.

Pharmacological characterization of a novel nonpeptide antagonist radioligand, (+/-)-N-[2-methyl-4-methoxyphenyl]-1-(1-(methoxymethyl) propyl)-6-methyl-1H-1,2,3-triazolo[4,5-c]pyridin-4-amine ([3H]SN003) for corticotropin-releasing factor1 receptors

The in vitro pharmacological profile of a novel small molecule corticotropin-releasing factor 1 (CRF(1)) receptor antagonist, (+/-)-N-[2-methyl-4-methoxyphenyl]-1-(1-(methoxymethyl)propyl)-6-methyl-1H-1,2,3-triazolo[4,5-c]pyridin-4-amine (SN003), and the characteristics of its radioligand ([(3)H]SN003) are described. SN003 has high affinity and selectivity for CRF(1) receptors expressed in rat cortex, pituitary, and recombinant HEK293EBNA (HEK293e) cells with respective radiolabeled ovine CRF ([(125)I]oCRF) binding K(i) values of 2.5, 7.9, and 6.8 nM. SN003 was shown to be a CRF(1) receptor antagonist inasmuch as it inhibited CRF-induced cAMP accumulation in human CRF(1)HEK293e cells and CRF-stimulated adrenocorticotropin hormone release from rat pituitary cells without agonist activities. Significant decreases in the B(max) of [(125)I]oCRF binding by SN003 suggest that this antagonist is not simply competitive. To further explore the interaction of SN003 with the CRF(1) receptors, [(3)H]SN003 binding to rat cortex and human CRF(1)HEK293e cell membranes was characterized and shown to be reversible and saturable, with K(D) values of 4.8 and 4.6 nM, and B(max) values of 0.142 and 7.42 pmol/mg protein, respectively. The association and dissociation rate constants of [(3)H]SN003 (k(+1) 0.292 nM(-1) min(-1) and k(-1) 0.992 x 10(-2) min(-1)) were also assessed using human CRF(1)HEK293e cell membranes, giving an equilibrium dissociation constant of 3.4 nM. Moreover, [(3)H]SN003 binding displayed a single affinity state and insensitivity to 5'-guanylylimidodiphosphate, consistent with characteristics of antagonist binding. Incomplete inhibition of [(3)H]SN003 binding by CRF peptides also suggests that SN003 is not simply competitive with CRF at CRF(1) receptors. The distribution of [(3)H]SN003 binding sites was consistent with the expression pattern of CRF(1) receptors in rat brain regions. Small molecule CRF(1) antagonist radioligands like [(3)H]SN003 should enable a better understanding of small molecule interactions with the CRF(1) receptor.

Development of a selective photoactivatable antagonist for corticotropin-releasing factor receptor, type 2 (CRF2)

A novel photoactivatable analog of antisauvagine-30 (aSvg-30), a specific antagonist for corticotropin-releasing factor (CRF) receptor, type 2 (CRF2), has been synthesized and characterized. The N-terminal amino-acid d-Phe in aSvg-30 [d-Phe11,His12]Svg(11-40) was replaced by a phenyldiazirine, the 4-(1-azi-2,2,2-trifluoroethyl)benzoyl (ATB) residue. The photoactivatable aSvg-30 analog ATB-[His12]Svg was tested for its ability to displace [125I-Tyr0]oCRF or [125I-Tyr0]Svg from membrane homogenates of human embryonic kidney (HEK) 293 cells stably transfected with cDNA coding for rat CRF receptor, type 1 (rCRF1) or mouse CRF receptor, type 2beta (mCRF2beta). Furthermore, the ability of ATB-[His12]Svg(12-40) to inhibit oCRF- or Svg-stimulated cAMP production of transfected HEK 293 cells expressing either rCRF1 (HEK-rCRF1 cells) or mCRF2beta (HEK-mCRF2beta cells) was determined. Unlike astressin and photo astressin, ATB-[His12]Svg(12-40) showed high selective binding to mCRF2beta (Ki = 3.1 +/- 0.2 nm) but not the rCRF1 receptor (Ki = 142.5 +/- 22.3 nm) and decreased Svg-stimulated cAMP activity in mCRF2beta-expressing cells in a similar fashion as aSvg-30. A 66-kDa protein was identified by SDS/PAGE, when the radioactively iodinated analog of ATB-[His12]Svg(12-40) was covalently linked to mCRF2beta receptor. The specificity of the photoactivatable 125I-labeled CRF2beta antagonist was demonstrated with SDS/PAGE by the finding that this analog could be displaced from the receptor by antisauvagine-30, but not other unrelated peptides such as vasoactive intestinal peptide (VIP).

Novel high-affinity photoactivatable antagonists of corticotropin-releasing factor (CRF) photoaffinity labeling studies on CRF receptor, type 1 (CRFR1)

Novel photoactivatable antagonists of human/rat corticotropin-releasing factor (h/rCRF) have been synthesized and characterized. The N-terminal amino acid D-phenylalanine in astressin ¿cyclo(30-33) [D-Phe12, Nle21,38, Glu30, Lys33]h/rCRF-(12-41)¿, a potent CRF peptide antagonist, was replaced by a phenyldiazirine, the 4-(1-azi-2,2,2-trifluoroethyl)benzoyl (ATB) residue. Additionally, His32 of astressin was substituted by either alanine or tyrosine for specific radioactive labeling with 125I at either His13 or Tyr32, respectively. The photoactivatable CRF antagonists were tested for their ability to displace 125I-labeled Tyr0 ovine CRF ([125I-labeled Tyr0]oCRF) in binding experiments and to inhibit oCRF-stimulated adenylate cyclase activity in human embryonic kidney (HEK) 293 cells, permanently transfected with cDNA coding for rat CRF receptor, type 1 (rCRFR1) or human Y-79 retinoblastoma cells known to carry endogenous functional human CRFR1 (hCRFR1). ATB-cyclo(30-33)[Nle21,38, Glu30, Ala32, Lys33]h/rCRF-(13-41) (compound 1) was found to bind with higher affinity to rat or human CRFR1 when compared with ATB-cyclo(30-33)[Nle21,38, Glu30, Tyr32, Lys33]h/rCRF-(13-41) (compound 2) and exhibited higher inhibition of oCRF-stimulated cAMP accumulation in HEK 293 cells stably transfected with cDNA coding for rCRFR1 (HEK-rCRFR1 cells) or Y-79 cells. A highly glycosylated, 66-kDa protein was identified with SDS/PAGE, when the radioactively iodinated compounds 1 or 2 were covalently linked to rCRFR1. The specificity of the photoactivatable 125I-labeled CRF antagonists was demonstrated with SDS/PAGE by the finding that these analogs could be displaced from the receptor by their corresponding nonlabeled form, but not other unrelated peptides such as vasoactive intestinal peptide. The observed molecular size of the receptor was in agreement with the size of CRFR1 found in rat pituitary (66 kDa), but was significantly larger than the size of CRFR1 found in rat cerebellum and olfactory bulb (53 kDa).

The role of the fourth extracellular domain of the rat corticotropin-releasing factor receptor type 1 in ligand binding

The role of the fourth extracellular loop (e4) of rat corticotropin-releasing factor (CRF) receptor, type 1, in ligand binding was investigated using chimeric receptor molecules. e4 of CRF receptor, type 1, was replaced by the corresponding domains of two other G protein-coupled receptors, the rat glucagon receptor or the human pituitary adenylate cyclase activating polypeptide (PACAP) receptor. Both chimeras were transported properly to the cell membranes of transfected chinese hamster ovary cells as indicated by immunocytochemical analysis. Ovine CRF (oCRF) was bound specifically, but with low affinity (Kd = 2-5 microm). Cyclic AMP was not accumulated intracellularly in response to increasing concentrations of oCRF. Based on these data, it is concluded that e4 of rat CRF receptor, type 1, is involved in ligand binding. To confirm the importance of e4 in binding CRF, three negatively charged amino acids of e4, Glu336, Asp337 and Glu338, were replaced by Gln, Asn and Gln, respectively. No effect on ligand binding and cyclic AMP accumulation was observed (Kd = 5 nm; EC50 = 1.5 nm). However, when Tyr346, Phe347 and Asn348 of e4 were changed to three alanine residues, ligand binding affinity as well as efficacy in cyclic AMP accumulation were significantly decreased (Kd = 64 nm; EC50 = 32 nm).

Characterization of native corticotropin-releasing factor receptor type 1 (CRFR1) in the rat and mouse central nervous system

Corticotropin releasing factor (CRF), the most important regulator of various responses to stress, acts through CRF receptors (CRFR). For their characterization in brain tissue of Sprague-Dawley rats and C57BL/6J mice, a recently described polyclonal antibody directed against the N-terminus of rat CRFR1 (rCRFR1) was used. The molecular weights of rat and mouse brain receptors were determined by Western blot analysis to be 80,000-76,000 and 83,000-79,000, respectively, whereas molecular weights of 72,000-59,000 were observed for CRFR1 from rat and mouse pituitary. Immunohistochemical analysis was performed with brain sections of naive rats and mice. Strong CRFR1 staining was detected in the cortex, cerebellum, mesencephalon and pons of both species, whereas weak staining was observed in amygdala and hippocampus. The striatum did not show immunoreactivity. The density of immunostaining was significantly lower in murine than in rat cortex. In contrast, in the pons and mesencephalon of mice, higher density of immunostaining was observed than in the same brain structures of rats. On the basis of the observed differences, it is suggested that CRFR1 is differentially processed in rats and mice. In addition, the density of CRFR1 staining differed between both species.

Molecular Properties of the CRF Receptor

Research into the biology of corticotropin-releasing factor (CRF) has been intensified significantly by the structural characterization of the CRF receptor (CRF-R). Two receptor subtypes, CRF-R1 and CRF-R2, and three functional splice variants of CRF-R2 have been discovered. It appears that ligand binding requires interaction of the N-terminal domain with one or two other extracellular domains of the CRF-R. In contrast to the mammalian CRF-R1, the frog CRF-R1 discriminates between naturally occurring CRF-like peptides.

Corticotropin-releasing factor and defensive withdrawal: inhibition of monoamine oxidase prevents habituation to chronic stress

There is growing evidence for a role of extrahypothalamic corticotropin-releasing factor (CRF) in the pathogenesis of anxiety. A modified form of the defensive withdrawal test was used to test the anxiogenic effects of acute administration of intracerebroventricular (1 microg, i.c.v.) CRF in adult male rats. Habituation to the mild stress of daily handling and subcutaneous (s.c.) saline injection over 2-6 weeks abolished the anxiogenic effects of exogenous CRF. At 6 weeks this habituation also resulted in attenuation of baseline withdrawal behavior. CRF receptor binding was significantly decreased in the amygdala of chronically handled animals and may have been responsible for this habituation phenomenon. Comparison of rats treated with the monoamine oxidase (MAO) inhibitor, phenelzine [3 mg/kg, s.c., daily for 2-6 weeks] to the saline-treated groups revealed a failure to habituate to the chronic handling, as the baseline withdrawal (after injection of artificial CSF) by the phenelzine-treated animals was not different from the baseline withdrawal by unhandled rats. In comparison to rats treated chronically with saline, phenelzine treatment enhanced the anxiogenic effect of CRF. In summary, habituation to a mild chronic stress decreased baseline defensive withdrawal. Intraventricular administration of CRF produced an anxiogenic response as measured in the defensive withdrawal test, which was lost through exposure to mild chronic stress. Two or 6 weeks of daily handling and SC saline injection caused a downregulation of CRF receptors in the amygdala, which could account for the behavioral habituation and the loss of CRF-induced defensive withdrawal. Phenelzine treatment concurrent with mild chronic stress prevented habituation and maintained the anxiogenic effect of CRF in spite of the downregulation of CRF receptors in the amygdala.

Solubilization and biochemical characterization of the human myometrial corticotrophin-releasing hormone receptor

We have solubilized an active form of the myometrial corticotrophin-releasing hormone (CRH) receptor using 1% w/v digitonin. The solubilized receptor retains its capacity for high-affinity binding as demonstrated by Scatchard analysis, although there was a shift in dissociation constant (Kd) from 83.6 +/- 15-195 +/- 35 pM for the membrane-bound and soluble receptor respectively. There was no difference in the maximum binding site concentrations (Bmax) of 13 +/- 5 and 21.5 +/- 6 fmol/mg protein for the membrane-bound and soluble receptor respectively. Sauvagine unlike CRH had no effect on radiolabeled CRH binding which suggests that the CRH-R2 receptor is not present in the myometrium. The solubilized receptor did not retain guanine-nucleotide sensitivity. The isoelectric focusing (IEF) profile of the human myometrial CRH receptors was significantly different from that of the rat cerebral cortex. Furthermore, solubilization of human myometrial membrane proteins followed by gel filtration and SDS-PAGE revealed a specifically labeled protein with an apparent molecular weight of 42000-47000 kDa. Our results suggest that during solubilization the human myometrial CRH receptor is dissociated from the guanine nucleotide-binding protein (Gs) and that high affinity binding for soluble CRH receptors is not dependent on the coupling of a guanine nucleotide-binding protein.

Structure-function relationship of different domains of the rat corticotropin-releasing factor receptor

The significance of different domains of corticotropin-releasing factor receptor, type 1, (CRFR1) for ligand binding and cAMP accumulation was investigated with C-terminally truncated forms of rat CRFR1 (rCRFR1) tagged by a sequence of six histidine residues (His-tag) to facilitate protein purification and identification. These different forms of the receptor were N-glycosylated and transported properly to the membranes of transfected mammalian cells as indicated by Western blot analysis and immunocytochemical staining with two polyclonal antibodies developed against the N- and C-terminus of rCRFR1. The N-terminal fragment, rCRFR1(23-121), expressed in Escherichia coli bound oCRF specifically, but with low affinity. Several mutants lacking transmembrane domain (TM) 7 and the C-terminus exhibited similarly low affinities to oCRF after expression in transfected mammalian cells. None of these cells produced significant amounts of cAMP after exposure to oCRF. Only mutants containing the N-terminus, all loops and TMs bound oCRF and produced cAMP with high affinity (Kd = 62 nM) and efficacy (EC50 = 0.8 nM). The additional presence of the C-terminus provided similar characteristics (Kd = 5 nM, EC50 = 0.3 nM) as known for the native receptor. It is suggested on the basis of these data that the last extracellular loop is involved in ligand binding.

Characterization of corticotropin-releasing hormone binding sites in the human placenta

The human placenta synthesizes and secretes large amounts of corticotropin-releasing hormone (CRH) which has been implicated in the triggering of parturition. The placental CRH was found to act in a paracrine manner to stimulate secretion of ACTH and beta-endorphin. In view of this we sought to characterize CRH binding sites in the human placenta. The specific binding of 125I-tyrosyl-ovine CRH (125I-oCRH) to placental membranes was dependent on time, temperature, pH, divalent cations and was reversible on addition of excess oCRH. Scatchard analysis revealed a high afinity binding site with a dissociation constant of approximately 0.7 nmol/L and maximum number of binding sites approximately 44 fmol/mg protein. Disuccinimidyl suberate, a chemical cross-linker, was used to covalently attach 125I-oCRH to placental membranes. The labelled placental membranes were analyzed by SDS-PAGE and autoradiography. A major radioactively labelled band with a molecular weight of 55,000 Da was identified. In this study we have identified placental binding sites for CRH with properties similar to CRH receptors described in a number of human and animal tissues and with a molecular weight similar to that of the brain CRH receptor. These binding sites may be involved in the regulation of the placental CRH/ACTH-beta-endorphin axis during pregnancy and parturition.

Corticotropin-releasing factor receptors: physiology, pharmacology, biochemistry and role in central nervous system and immune disorders

Corticotropin-releasing factor (CRF) plays a major role in coordinating the endocrine, autonomic, behavioral and immune responses to stress through actions in the brain and the periphery. CRF receptors identified in brain, pituitary and spleen have comparable kinetic and pharmacological characteristics, guanine nucleotide sensitivity and adenylate cyclase-stimulating activity. Differences were observed in the molecular mass of the CRF receptor complex between the brain (58,000 Da) and the pituitary and spleen (75,000 Da), which appeared to be due to differential glycosylation of the receptor proteins. The recently cloned CRF receptor in the pituitary and the brain (designated as CRF1) encodes a 415 amino acid protein comprising seven putative membrane-spanning domains and is structurally related to the calcitonin/vasoactive intestinal peptide/growth hormone-releasing hormone subfamily of G-protein-coupled receptors. A second member of the CRF receptor family encoding a 411 amino acid rat brain protein with approximately 70% homology to CRF1 has recently been identified (designated as CRF2); there exists an additional splice variant of the CRF2 receptor with a different N-terminal domain encoding a protein of 431 amino acids. In autoradiographic studies, CRF receptors were localized in highest densities in the anterior and intermediate lobes of the pituitary gland, olfactory bulb, cerebral cortex, amygdala, cerebellum and the macrophage-enriched zones and red pulp regions of the spleen. CRF can modulate the number of CRF receptors in a reciprocal manner. For example, stress and adrenalectomy increase hypothalamic CRF secretion which, in turn, down-regulates CRF receptors in the anterior pituitary. CRF receptors in the brain and pituitary are also altered as a consequence of the development and aging processes. In addition to a physiological role for CRF in integrating the responses of the brain, endocrine and immune systems to physiological, psychological and immunological stimuli, recent clinical data implicate CRF in the etiology and pathophysiology of various endocrine, psychiatric, neurologic and inflammatory illnesses. Hypersecretion of CRF in the brain may contribute to the symptomatology seen in neuropsychiatric disorders, such as depression, anxiety-related disorders and anorexia nervosa. Furthermore, overproduction of CRF at peripheral inflammatory sites, such as synovial joints may contribute to autoimmune diseases such as rheumatoid arthritis. In contrast, deficits in brain CRF are apparent in neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease and Huntington's disease, as they relate to dysfunction of CRF neurons in the brain areas affected in the particular disorder. Strategies directed at developing CRF-related agents may hold promise for novel therapies for the treatment of these various disorders.

Corticotropin-releasing factor stimulates cyclic AMP, arachidonic acid release, and growth of lung cancer cells

The effects of corticotropin-releasing factor (CRF) on human lung cancer cell lines was investigated. Corticotropin-releasing factor increased the cAMP levels in a dose-dependent manner; CRF (100 nM) elevated the cAMP levels approximately eleven-fold using NCI-H345 cells and increased the gastrin-releasing peptide (GRP) secretion rate by approximately 70%. Similarly, sauvagine, a structural analogue of CRF, elevated the cAMP levels with a half-maximal effective dose (ED50) of 20 nM. The increase in cAMP caused by CRF and sauvagine was reversed by alpha-helical CRF(9-41). Corticotropin-releasing factor had no effect on cytosolic calcium but stimulated [3H]arachidonic acid release from NCI-H1299 cells with an ED50 of 30 nM. The increase in [3H]arachidonic acid release caused by 100 nM CRF was significantly reversed by 1 or 10 microM alpha-helical CRF(9-41). Also, CRF stimulated the clonal growth of NCI-H345 and H720 cells and the growth increase caused by CRF was reversed by alpha-helical CRF(9-41). These data suggest that CRF may be a regulatory peptide in lung cancer.

Corticotropin-releasing factor and interleukin-1 receptors in the brain-endocrine-immune axis. Role in stress response and infection

CRF and IL-1 receptors were identified, characterized, and localized in brain, endocrine, and immune tissues. CRF receptors with comparable kinetic and pharmacological characteristics were localized in the anterior and intermediate lobes of the pituitary, in brain areas involved in mediating stress responses, and in the macrophage-enriched marginal zones of the spleen. The discrete localization of IL-1 receptors in neurons of the hippocampus provides further support for the role of IL-1 as a neurotransmitter/neuromodulator/growth factor in the CNS. The neuroendocrine effects of IL-1 may be mediated through actions of the cytokine in brain. However, given the high densities of IL-1 receptors in the anterior pituitary and testis, direct effects of the cytokine at the pituitary or gonadal levels seem highly likely. Overall, these data support a role for IL-1 and CRF in coordinating and integrating the brain-endocrine-immune responses to physiological, pharmacological, and pathological stimuli.

Microheterogeneity of dopamine transporters in rat striatum and nucleus accumbens

Previously we have shown that the [125I]DEEP-labeled dopamine transporter from the rat nucleus accumbens has a higher apparent molecular weight than that from striatum. The present study confirms and extends these observations. Experiments with nucleus accumbens showed [125I]-DEEP to specifically bind to a protein with an apparent molecular weight of 76 kDa and with the pharmacological properties of the dopamine transporter. In exoglycosidase studies, treatment with neuraminidase, but not alpha-mannosidase, reduced the apparent molecular weight of the dopamine transporter from both the striatum and nucleus accumbens; however, a difference in the apparent molecular weight was still observed. N-Glycanase treatment, on the other hand, did reduce the apparent molecular weight of the dopamine transporters from the two regions to a similar value, approximately 56 kDa. In radioligand binding studies examining the effect of partial deglycosylation on striatal dopamine transporters, neuraminidase did not affect specific [3H]WIN 35,428 binding at 4 and 40 nM concentrations. In conclusion, the present study demonstrates that the difference in the apparent molecular weight of the dopamine transporter from these two regions is due to a difference in glycosylation and that the dopamine transporter from both regions contains similar amounts of sialic acid in their carbohydrate structure. Furthermore, the present data also indicate that the polypeptide portion of the dopamine transporter from both regions could be the same gene product.

The effects of rat corticotrophin-releasing factor-41 Peptide fragments on bioassay and immunoassay determination of corticotrophin-releasing factor-41 levels

Abstract Peptide fragments of rat corticotrophin-releasing factor-41 (CRF-41) containing amino-acid residues 21-33 antagonized the 5 nmol/l CRF-41-stimulated adrenocorticotrophin secretion from the adult rat pituitary gland in vitro. The CRF 6-33 sequence had antagonistic effects at equimolar (5 nmol/l) concentrations which were not observed at high (50 nmol/l) concentrations whilst the CRF 21-41 sequence had effects only at high (50 nmol/l) concentrations. Similar effects were observed with CRF 6-33 on basal release of adrenocorticotrophin. Peptide fragments elevated radioimmunoassay measurement of CRF-41 whilst inhibiting measurement of CRF-41 in a two-site enzyme amplified immunometric assay. The inhibitory effects of peptide fragments in the enzyme amplified immunometric assay could be removed by dilution to within the lower end of the standard curve or by increasing the concentration of antibody bound to the solid phase. These inhibitory effects mimic those of peptide fragments on basal adrenocorticotrophin release seen in a rat pituitary gland in vitro bioassay indicating that such two-site immunoassay determinations bear closer relation to bioactivity than those obtained using radioimmunoassay.

Central effects of CRF on metabolism and energy balance

CRF is recognised for its actions on pituitary ACTH release, but also has direct effects within the brain which are important in mediating physiological responses to stress. Behavioral effects of CRF include increased locomotor activity and inhibition of food intake and its actions on metabolism are mediated mainly by activation of the sympathetic nervous system. CRF appears to be important in the regulation of energy balance and body weight, influencing both food intake and sympathetically-mediated thermogenesis. A defect in the synthesis or release of CRF has been implicated in the development of obesity in laboratory animals, since the condition is alleviated by adrenalectomy, hypophysectomy or exogenous CRF treatment. Recent data have revealed an additional role for CRF as a mediator of the neuroendocrine and metabolic responses to immune signals, particularly cytokines. The central actions of CRF are independent of the pituitary but may involve release of proopiomelanocortin products within the brain. CRF is thus emerging as an important integrator of the physiological responses to stress, infection and immunity, a finding which may have important implications for future therapies.

Physicochemical characterization of corticotrophin releasing factor receptor in rat pituitary and brain

The physicochemical characteristics of solubilized crosslinked CRF receptor-ligand complexes were studied in the anterior and intermediate pituitary lobes and brain of the rat. In all tissues studied, there was a major labeled band with a molecular weight of 72 +2- 3.5 kDa, (n = 15), 71 +/- 1.3 (n = 6), 73 +2- 2.5 (n = 7) and 75 +2- 3.5 (n = 7) kDa in the anterior and intermediate lobes of the pituitary, amygdala and cerebral cortex, respectively. The density of this band was inhibited by CRF analogs, but not by unrelated peptides. This is consistent with the comparable binding properties of CRF in membrane preparations of these tissues. These results suggest that differences in receptor regulation and the reported ability of CRF to stimulate cAMP is due to differences in ligand receptor processing and coupling to membrane transduction systems, rather than to major differences in the binding protein.

Beta-endorphin secretion by human peripheral blood mononuclear cells: regulation by glucocorticoids

Corticotropin-releasing factor (CRF), a 41-aminoacid neuropeptide, can induce lymphocytes to production of beta-endorphin (beta E). Furthermore, the neuropeptide Arginine-Vasopressin (AVP) can enhance CRF-induced production of beta E. We have demonstrated that CRF acts by stimulating monocytes to production of the cytokine interleukin-1 (IL-1). IL-1 can in its turn activate the lymphocytes to secretion of beta E. Here we demonstrate that the glucocorticoid analogue dexamethasone is capable of modulating CRF-induced beta E secretion by lymphocytes. It appeared that dexamethasone can inhibit secretion of lymphocyte-derived beta E. The mechanism by which dexamethasone exerts its inhibitory activity is by blocking CRF-induced production of IL-1, thereby preventing induction of beta E secretion by B cells. These results support the concept that peptide hormones and glucocorticoids are mediating a reciprocal modulation of neuroendocrine and immunological activities.

Normal pattern of labeling of cerebral cortical corticotropin-releasing factor (CRF) receptors in Alzheimer's disease: evidence from chemical cross-linking studies

Recent data have demonstrated that in Alzheimer's disease, the concentrations of corticotropin-releasing factor (CRF) were reduced and that there were reciprocal increases in CRF receptors in affected cerebrocortical areas. In order to determine whether the increases in CRF receptors in Alzheimer's disease were due to altered molecular composition of the binding protein, we compared the labeling pattern of 125I-Tyr0-ovine CRF in temporal neocortex of Alzheimer's patients and age-matched controls using chemical cross-linking techniques. A similar pattern of 125I-Tyr0-ovine CRF labeling was seen in Alzheimer's and control brains, with the major CRF binding protein corresponding to an apparent molecular weight of 58,000 Da. These data indicate that the increased CRF receptor population in cerebral cortex in Alzheimer's disease comprises bona fide CRF receptor binding subunits with no apparent change in the molecular structure.

Corticotropin-releasing factor (CRF) receptors in intermediate lobe of the pituitary: biochemical characterization and autoradiographic localization

CRF receptors were characterized using radioligand binding and chemical affinity cross-linking techniques and localized using autoradiographic techniques in porcine, bovine and rat pituitaries. The binding of 125I-[Tyr0]-ovine CRF (125I-oCRF) to porcine anterior and neurointermediate lobe membranes was saturable and of high affinity with comparable KD values (200-600 pM) and receptor densities (100-200 fmoles/mg protein). The pharmacological rank order of potencies for various analogs and fragments of CRF in inhibiting 125I-oCRF binding in neurointermediate lobe was characteristic of the well-established CRF receptor in anterior pituitary. Furthermore, the binding of 125I-oCRF to both anterior and neurointermediate lobes of the pituitary was guanine nucleotide-sensitive. Affinity cross-linking studies revealed that the molecular weight of the CRF binding protein in rat intermediate lobe was identical to that in rat anterior lobe (Mr = 75,000). While the CRF binding protein in the anterior lobes of porcine and bovine pituitaries had identical molecular weights to CRF receptors in rat pituitary (Mr = 75,000), the molecular weight of the CRF binding protein in porcine and bovine intermediate lobe was slightly higher (Mr = 78,000). Pituitary autoradiograms from the three species showed specific binding sites for 125I-oCRF in anterior and intermediate lobes, with none being apparent in the posterior pituitary. The identification of CRF receptors in the intermediate lobe with comparable characteristics to those previously identified in the anterior pituitary substantiate further the physiological role of CRF in regulating intermediate lobe hormone secretion.