Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hypothalamic regulatory peptides bind to specific receptors on target cells in the pituitary and control secretion. They in turn can be regulated at the pituitary level by steroid and peptide modulators. Affinity cytochemical techniques are important tools for the identification of specific target binding sites for these regulatory peptides. This presentation reviews the work in which potent, biotinylated ligands of gonadotropin releasing hormone (bio-GnRH), corticotropin releasing hormone (bio-CRH), and arginine vasopressin (bio-AVP) were applied to study the target cell responses. Bio-GnRH, bio-CRH, and bio-AVP bind to membrane receptors on specific anterior pituitary cells. Dual labeling for either gonadotropin or adrenocorticotropin (ACTH) antigens further identified the target cells. After 1-3 minutes, the label was in patches or capped on the surface. After 3 minutes, it was internalized in small vesicles and sent to receptosomes and vacuoles in the Golgi complex. Eventually the biotinylated peptides, or a metabolite, was found in the lysosomes (multivesicular bodies) and a subpopulation of secretory granules. The route and rate of uptake was similar to that described for the classical receptor-mediated endocytosis process. In contrast, intermediate lobe corticotropes internalized the bio-CRH in less than 1 minute. The route through the Golgi complex appeared to be bypassed. Instead the labeled peptide was in vesicles, on the membranes of scattered vacuoles, and in multivesicular bodies. Modulation of ligand binding by steroids showed that changes in receptor numbers correlated with changes in the number of cells that bound the ligand. In male rats, dihydrotestosterone reduced the percentage of GnRH-bound cells by 50%. Most of the reduction appeared in cells that stored luteinizing hormone (LH) antigens. In diestrous female rats, estradiol increased the percentage of bio-GnRH-bound cells. However, the steroid decreased the percentage of GnRH-bound cells in cells from proestrous rats. Glucocorticoids decreased the percentage of CRH-bound corticotropes in as little as 10 minutes. Potentiation of secretion by these ligands was correlated with increases in the percentage of ligand-bound cells. AVP pretreatment of corticotropes increased the percentage of cells that bound bio-CRH. It also increased the rate of receptor-mediated endocytosis of CRH and changed the route so that the Golgi complex was bypassed. This effect could be mimicked by activation of its second messengers (calcium and protein kinase C). Similarly, CRH pretreatment increased the percentage of corticotropes that bound AVP. Thyrotropin releasing hormone (TRH) pretreatment also increased the percentage of thyrotropes that bound AVP.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Hypothalamic regulatory peptides and their receptors: cytochemical studies of their role in regulation at the adenohypophyseal level. 166 66

1. Coexisting with oxytocin or vasopressin in the cell bodies and nerve terminals of the hypothalamic-neurohypophysial system are smaller amounts of other peptides. For a number of these "copeptides" there is strong evidence of corelease with the major magnocellular hormones. Guided by the location of their specific receptors we have studied the effects of three copeptides, dynorphin, cholecystokinin (CCK), and corticotropin releasing hormone (CRH), on the secretion of oxytocin and vasopressin from isolated rat neural lobe or neurointermediate lobe preparations in vitro. 2. Dynorphin is coreleased with vasopressin from neural lobe nerve terminals and acts on neural lobe kappa-opiate receptors to inhibit the electrically stimulated secretion of oxytocin. Naloxone augments oxytocin release from the neural lobe in a manner directly proportional to the amount of vasopressin (and presumably dynorphin) released. 3. Cholecystokinin, coreleased with oxytocin by neural lobe terminals, has been shown to have high-affinity receptors located in the NL and to stimulate secretion of both oxytocin and vasopressin. CCK's secretagogue effect was independent of electrical stimulation and extracellular Ca2+ and was blocked by an inhibitor of protein kinase C. 4. CRH, coreleased with OT from the neural lobe, has receptors in the intermediate lobe of the pituitary, but not in the neural lobe itself. CRH stimulates the secretion of oxytocin and vasopressin from combined neurointermediate lobes but not from isolated neural lobes. Intermediate lobe peptides, alpha and gamma melanocyte stimulating hormone, induced secretion of oxytocin and vasopressin from isolated neural lobes. Their effect was, like that of CCK, independent of electrical stimulation and extracellular Ca2+ and blocked by an inhibitor of protein kinase C. 5. Among the CRH-producing parvocellular neurons of the paraventricular nucleus, in the normal rat, approximately half also produce and store vasopressin. After removal of glucocorticoid influence by adrenalectomy, virtually all of the CRH neurons contain vasopressin. 6. The two subtypes of CRH neurosecretory cells found in the normal rat possess different topographical distributions in the paraventricular nucleus, suggesting the possibility of differential innervation. Stress selectively activates the vasopressin containing subpopulation of CRH neurons, indicating that there are separate channels of regulatory input controlling the two components of the parvocellular CRH neurosecretory system.
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PMID:Coexisting peptides in hypothalamic neuroendocrine systems: some functional implications. 257 30

Activation of calcium-activated, phospholipid-dependent protein kinase C by phorbol esters such as 12-O-tetradecanoyl-phorbol-13-acetate (TPA) has been shown to mediate release of hormones in many systems. To investigate the role of protein kinase C in the mechanism of pituitary ACTH release, we studied the effect of the following conditions on TPA mediated ACTH release in primary rat pituitary cultures; corticotropin releasing hormone (CRH), different concentrations of extracellular calcium (Ca+2), nifedipine (a calcium channel blocker), PGE2 and cortisol (regulators of ACTH secretions). TPA induced ACTH release in a dose dependent fashion with an ED50 of 4.2 x 10(-10) M. The maximal amount of ACTH release individually induced by TPA (10(-8) M) and CRH (10(-8)) were identical. TPA (10(-8)) potentiated the amount of ACTH release from cells already maximally stimulated with CRH (4 x 10(-8) M). TPA mediated ACTH release was dependent on extracellular calcium and inhibited by nifedipine, to a maximum of 35%. Cortisol decreased the amount of ACTH individually released by TPA and CRH in a similar and dose dependent fashion with maximal inhibition of 47% occurring at 10(-7) M. PGE2 caused a dose dependent reduction of TPA mediated ACTH release. In conclusion, the pathways of ACTH release induced by CRH and TPA are not entirely the same but may share a common regulatory pathway. Extracellular calcium and calcium cell influx may be important for maximal ACTH release induced by TPA. Protein kinase C activation may play an important role in CRH stimulated ACTH release.
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PMID:Characterization of 12-O-tetradecanoyl-phorbol-13 acetate mediated ACTH release. 284 20

Over the past twenty years, each of the five major hypothalamic releasing or release-inhibiting hormones has been sequenced and its gene structure determined. With the use of molecular biological techniques, such as in situ hybridization, Northern blot analysis or gene constructs for in vitro or in vivo transfection studies--together with 'traditional' neuroendocrinological techniques, such as immunocytochemistry, radio-immunoassay and portal vessel cannulation--investigators have been able to address major issues in neuroendocrine regulation. Several common themes have emerged: messenger RNA expression is uniformly present in neurons that are immunopositive for the specific hypothalamic hormone. Steady state RNA levels within the hypophysiotropic neuron groups are either increased or reduced by changes in specific target hormones that conform to predictions based on previous physiological data. Regulation by the requisite peripheral hormone is exquisitely anatomically specific and is not evident in extrahypophysiotropic regions. Determining the receptor or genetic basis of this specificity is a major focus of current research. Clarifying the apparently lesser role of afferent neural pathways to the hypothalamus in regulating releasing hormone mRNA levels is also an important challenge. Clinically, the measurement of levels of releasing hormones in the peripheral circulation appears to be of limited usefulness, except in rare cases of ectopic GRH or CRH secretion. For diagnostic purposes, each of the releasing hormones has specific utility in amplifying the release and measurement of pituitary hormones, both to clarify the overall physiological activity of the hypothalamic-pituitary-target hormone axis and to further define the anatomic locus of any underlying disturbance. The usefulness of somatostatin as a diagnostic tool is presently limited, but the development of SS receptor antagonists might have significant impact in future clinical investigation. The molecular mechanisms of action of the hypothalamic hormones have been separated into those whose receptor-effector function is mediated by the cAMP-adenylate cyclase pathway(s), GRH and CRH, and those working through the phosphoinositide-protein kinase C cascade, GnRH and TRH. Each of the hormone receptors is coupled to intermediary G proteins, somatostatin uniquely to the inhibitory subclass. The mechanisms responsible for sensitization (priming) or desensitization are not fully understood but are presumably related to receptor down regulation and protein phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Molecular biology and regulation of the hypothalamic hormones. 290 17

Hormone release in culture in response to pituitary adenylate cyclase-activating polypeptide (PACAP) was examined in 28 human pituitary adenomas: 10 null cell adenomas, 4 gonadotropin-, 6 GH-, 6 ACTH-, and 2 PRL-producing adenomas. The effects of PACAP38 were compared with those of the classical hypothalamic releasing hormones and other activators of intracellular signaling pathways. PACAP38 significantly stimulated GH release from 1 somatotrope tumor (125 +/- 3% of control; P < 0.05) and ACTH release from 3 corticotrope tumors (134 +/- 6%, 136 +/- 7%, and 137 +/- 9% of control; P < 0.05). The effects of PACAP38 were less potent than either GHRH on GH release in the somatotrope tumor or CRH on ACTH release in the corticotrope tumors but similar to the responses seen with the cAMP analog 8-bromo-cAMP (8-Br-cAMP). No detectable effects of PACAP38 on hormone release from null cell, gonadotropin-, or PRL-producing adenomas were observed. Of the 5 somatotrope tumors that failed to respond to PACAP38, all also failed to respond to either 8-Br-cAMP, TRH, or GHRH. Of the corticotrope tumors that failed to respond, 2 of the 3 also failed to respond to CRH. In addition to eliciting hormone release appropriate to the tumor type, PACAP38 also stimulated glycoprotein hormone alpha-subunit (alpha SU) release from one somatotrope tumor (229 +/- 35% of control, P < 0.01) and one corticotrope tumor (149 +/- 4% of control; P < 0.01). This response was not mimicked by 8-Br-cAMP in the somatotrope tumor, but in the corticotrope tumor a significant alpha SU release was also seen after stimulation with the protein kinase C activator 12-O-tetradecanoyl-phorbol-13-acetate and 8-Br-cAMP. These results suggest that the novel hypothalamic peptide PACAP38 has a modest role in the regulation of GH, ACTH, and alpha SU secretion from some human tumourous pituitary corticotropes and somatotropes. Further studies are needed to elucidate the intracellular signaling pathways that mediate the effects of PACAP on hormone secretion by these tumor types.
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PMID:Effects of pituitary adenylate cyclase-activating polypeptide on hormone secretion by human pituitary adenomas in vitro. 752 12

We have investigated the effects of the novel phospholipid drug glyceryl-phosphoryl-O-serine (GPS) on pituitary ACTH and hypothalamic corticotropin releasing hormone secretion in vitro in cultures from both 2- and 24 month-old Sprague-Dawley rats. Basal levels of ACTH in primary cultures of pituitary cells from 24 month-old rats were lower than (100 +/- 12 pg/10(5) cells) in 2 month-old rats (207 +/- 18 pg/10(5) cells). Basal medium corticotropin releasing hormone levels in hypothalamic cultures were higher in 24 month-old rats (45 +/- 7 pg/well/20 min.), than in 2 month-old rats (29 +/- 5.5 pg/well/20 min). Treatment of both pituitary cells with corticotropin releasing hormone and hypothalami with serotonin resulted respectively in a significant, concentration-dependent, increase of medium ACTH and corticotropin releasing hormone. However, concentration-response curves for ACTH and corticotropin releasing hormone were shifted to the right in cultures from 24 month-old rats. Incubation with graded concentrations of GPS produced significant increase in medium ACTH and corticotropin releasing hormone in cultures from 24 month-old rats, whereas the drug was ineffective in stimulating secretion of both hormones from 2 month-old rat cells. In addition, the adenylate cyclase stimulator forskolin and the protein kinase C activator oleyl-acyl-glycerol stimulated ACTH secretion in pituicytes from rats of both ages. However, response to oleyl-acyl-glycerol was blunted in pituicytes from 24 month-old rats. Combination of either forskolin or oleyl-acyl-glycerol with GPS resulted in a potentiation of the effect. Our data confirm an impairment of both pituitary ACTH and hypothalamic corticotropin releasing hormone secretion in the aging rat.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The phospholipid drug glyceryl-phosphoryl-O-serine modulates pituitary adrenocorticotropin and hypothalamic corticotropin releasing hormone in vitro secretion in the aging rat. 775 60

The most potent, physiologic activator of proopiomelanocortin (POMC) gene transcription is corticotropin releasing hormone (CRH) and increased intracellular cAMP is critical for this effect. The 5'-flanking region of the murine POMC gene has several potential binding sites for regulatory proteins. To characterize the region between nucleotides -141 and -106, which includes a TRE-like site and an adjacent AP-2 consensus sequence, and to study its role in signal-transcription coupling, gel mobility shift assays and transient expression of CAT chimeras were performed. In transient transfections of AtT-20 cells with pCATp-141/-106, CRH treatment led to significant increases in CAT expression compared with CRH treatment of cells transfected with the enhancerless vector. However, no response to direct activation of cAMP dependent protein kinase or protein kinase C was detected. Despite the high homology of the sequence -137/-131 to the consensus AP-1 binding site (TRE), the nuclear factor(s) in AtT-20 cells binding to this region appears to be different than authentic AP-1 since neither a competitor oligonucleotide having the authentic TRE sequence nor antibodies against Jun or Fos affected the gel shift pattern of a probe having the -137/-131 sequence. We conclude that the -141 to -106 region of the murine POMC gene contains a functional CRH responsive element and that second messenger systems that transduce the CRH signal to this element do not exert their actions solely through activation of PKA or PKC.
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PMID:Characterization of a corticotropin releasing hormone responsive region in the murine proopiomelanocortin gene. 814

The effect of the antidiarrheal drug loperamide, a mu-opiate agonist, on ACTH secretion and biosynthesis, cAMP generation and phosphoinositide turnover was studied in rat anterior pituitary cell cultures. The cAMP-dependent protein kinase A pathway was stimulated with both corticotropin-releasing hormone (CRH; 2-5 nM) and the membrane-permeable Bu(2)cAMP (0.5-2.5 mM). The protein kinase C pathway was stimulated with 1 microM arginine vasopressin (AVP) and 1-10 nM phorbol 12-myristate 13-acetate (PMA). After 3.5 h, loperamide (10 microM) had no effect on basal ACTH levels but significantly suppressed CRH-induced ACTH release, in a dose-dependent manner, to 60 +/- 4% of control (100%) (p < 0.0001). After 24 h, basal proopiomelanocortin mRNA was significantly decreased to 50% of control by loperamide (p < 0.05). The suppressive effect of loperamide on CRH-induced ACTH secretion was not reversible by naloxone (0.1-1,000 microM). Morphine (0.01-10 microM) had no effect on basal and CRH-induced ACTH secretion. Loperamide did not influence basal and CRH-induced adenylate cyclase activity in anterior pituitary cell membrane preparations, but it significantly blunted Bu(2)cAMP-induced ACTH secretion in cell culture from 100 +/- 4 to 77 +/- 4% (p < 0.05). In Ca(2+)-depleted medium (Ca2+ < 0.1 mM), loperamide had no suppressive effect on CRH-induced ACTH secretion. AVP-induced ACTH secretion was significantly suppressed by loperamide from 100 +/- 5 to 74 +/- 3% (p < 0.0001), while basal and AVP-induced inositol 1-phosphate generation and PMA-induced ACTH secretion were not affected by loperamide.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Loperamide inhibits corticotrophic cell function by a naloxone-insensitive mechanism in the rat in vitro. 823 60

We previously characterized the transcriptional activity of the human CRH (hCRH) gene promoter in the mouse anterior pituitary cell line AtT20. Here, we show that phorbolester stimulated through the cAMP response element (CRE), located between -227 and -220 relative to the putative cap site, about 2.6-fold the expression of a chimeric hCRH-chloramphenicol-acetyl-transferase gene which was transiently transfected into chicken macrophages (HD11 cell line). The induction was dependent on the cell types, and was not observed when AtT20 were used as target cells. Elevated mouse c-fos protein expressed from a cotransfecting plasmid pRSVfos or human c-jun protein expressed from RSVjun led to 2.1-fold and 3.1-fold stimulation of the activity of the hCRH promoter. Tetradecanoyl-phorbol-13-acetate stimulated the c-fos and c-jun transactivation by a factor of 10 and 2.6, indicating a modification of c-fos and c-jun is required for the transactivation induced by protein kinase C activation. Mutation within the cAMP response element abolished this transcriptional activation. This result suggests an involvement of the protein kinase C pathway in the regulation of the CRH gene expression.
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PMID:Phorbolester stimulates the activity of human corticotropin-releasing hormone gene promoter via 3',5'-cyclic adenosine monophosphate response element in transiently transfected chicken macrophages. 838 Mar 80

Arginine-vasopressin (AVP) is a hypothalamic hormone that, like CRH, stimulates the pituitary release of ACTH, thereby activating adrenal glucocorticoid secretion. Evidence indicates that rat adrenal medulla contains a CRH-ACTH system duplicating that existing at the hypothalamo-pituitary level and involved in the paracrine stimulation of the cortex secretion. Therefore, we investigated by RIA the effect of AVP on the release of CRH and ACTH immunoreactivities (IR) by rat adrenal medulla in vitro. AVP concentration-dependently enhanced the release of both CRH-IR and ACTH-IR, and the effect was blocked by a selective antagonist of the V1 subtype of AVP receptors. The CRH receptor antagonist alpha-helical-CRH partially reversed AVP-evoked rise in ACTH-IR release, without altering either CRH response or basal secretions of CRH and ACTH. The specific inhibitors of protein kinase C Ro31-8220 and calphostin C abolished both CRH and ACTH responses to AVP. In conclusion, our present findings suggest that AVP stimulates intramedullary the CRH-ACTH system, acting via V1 receptors and activating protein kinase C.
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PMID:Arginine-vasopressin stimulates CRH and ACTH release by rat adrenal medulla, acting via the V1 receptor subtype and a protein kinase C-dependent pathway. 914 90


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