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Papadaki T, Tsilimbaris M, Pallikaris I, Thermos K. Somatostatin receptor activation (sst(1) -sst(5) ) differentially influences human retinal pigment epithelium cell viability. Acta Ophthalmol 2010; 88:e228-33. [PMID: 20632998 DOI: 10.1111/j.1755-3768.2010.01945.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
PURPOSE To investigate the differential effects of somatostatin and its receptors (sst(1-5) ) on the viability of cultured human retinal pigment epithelium (hRPE) cells. METHODS MTT [3 (4, 5-dimethylthiazol-2yl)-2, 5 diphenyltetrazolium bromide], APO Percentage(TM) and trypan blue assays were performed to assess the mechanisms via which somatostatin (10(-10) -10(-4) m) and selective receptor (sst(1-5) ) ligands (10(-12) -10(-4) m) affect cell viability. The effect of orthovanadate (phosphatase inhibitor, 10(-7) -10(-5) m) on somatostatin's (10(-5) m) actions was examined, and western blot analysis was employed to determine the presence of ssts and phosphotyrosine phosphatase SHP-1 in human RPE cells. RESULTS Somatostatin and selective ligands for the five somatostatin receptor subtypes (sst(1-5) ) decreased cell viability in a concentration-dependent manner. The observed decrease in cell number was partly because of apoptosis via the activation of sst(1) and sst(5) receptors. Activation of sst(2) , sst(3) and sst(4) receptors led to inhibition of cell growth that did not involve apoptosis, but rather antiproliferative actions. SHP-1 was found in the human RPE cells and sodium orthovanadate reversed somatostatin's actions. CONCLUSIONS This study provides new information regarding the involvement of ssts in human RPE cell viability and suggests that a pathway involving the phosphotyrosine phosphatase may mediate somatostatin's actions.
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Affiliation(s)
- Thekla Papadaki
- Department of Pharmacology, Faculty of Medicine, University of Crete, Crete, Greece
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Stengel A, Coskun T, Goebel M, Wang L, Craft L, Alsina-Fernandez J, Rivier J, Taché Y. Central injection of the stable somatostatin analog ODT8-SST induces a somatostatin2 receptor-mediated orexigenic effect: role of neuropeptide Y and opioid signaling pathways in rats. Endocrinology 2010; 151:4224-35. [PMID: 20610566 PMCID: PMC2940496 DOI: 10.1210/en.2010-0195] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Somatostatin and octreotide injected into the brain have been reported to modulate food intake. However, little is known regarding the underlying mechanisms. The stable oligosomatostatin analog, des-AA(1,2,4,5,12,13)-[DTrp(8)]-somatostatin (ODT8-SST), like somatostatin, binds to all five somatostatin receptors (sst(1-5)). We characterized the effects of ODT8-SST injected intracerebroventricularly (i.c.v.) on food consumption and related mechanisms of action in freely fed rats. ODT8-SST (0.3 and 1 microg per rat, i.c.v.) injected during the light or dark phase induced an early onset (within 1 h) and long-lasting (4 h) increase in food intake in nonfasted rats. By contrast, i.p. injection (0.3-3 mg/kg) or i.c.v. injection of selective sst(1) or sst(4) agonists (1 microg per rat) had no effect. The 2 h food intake response during the light phase was blocked by i.c.v. injection of a sst(2) antagonist, the neuropeptide Y (NPY) Y(1) receptor antagonist, BIBP-3226, and ip injection of the mu-opioid receptor antagonist, naloxone, and not associated with changes in plasma ghrelin levels. ODT8-SST (1 microg per rat, i.c.v.) stimulated gastric emptying of a solid meal which was also blocked by naloxone. The increased food intake was accompanied by a sustained increase in respiratory quotient, energy expenditure, and drinking as well as mu-opioid receptor-independent grooming behavior and hyperthermia, while ambulatory movements were not altered after ODT8-SST (1 microg per rat, i.c.v.). These data show that ODT8-SST acts primarily through brain sst(2) receptors to induce a long-lasting orexigenic effect that involves the activation of Y(1) and opiate-receptors, accompanied by enhanced gastric transit and energy expenditure suggesting a modulation of NPYergic and opioidergic orexigenic systems by brain sst(2) receptors.
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MESH Headings
- Animals
- Anti-Anxiety Agents/administration & dosage
- Anti-Anxiety Agents/pharmacology
- Arginine/administration & dosage
- Arginine/analogs & derivatives
- Arginine/pharmacology
- Body Temperature/drug effects
- Eating/drug effects
- Eating/physiology
- Energy Metabolism/drug effects
- Gastric Emptying/drug effects
- Grooming/drug effects
- Injections, Intraperitoneal
- Injections, Intraventricular
- Male
- Mice
- Mice, Inbred C57BL
- Naloxone/administration & dosage
- Naloxone/pharmacology
- Peptide Fragments/administration & dosage
- Peptide Fragments/pharmacology
- Rats
- Rats, Sprague-Dawley
- Receptors, Neuropeptide Y/antagonists & inhibitors
- Receptors, Neuropeptide Y/physiology
- Receptors, Opioid, mu/antagonists & inhibitors
- Receptors, Opioid, mu/physiology
- Receptors, Somatostatin/agonists
- Receptors, Somatostatin/antagonists & inhibitors
- Receptors, Somatostatin/physiology
- Somatostatin/administration & dosage
- Somatostatin/analogs & derivatives
- Somatostatin/pharmacology
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Affiliation(s)
- Andreas Stengel
- Department of Medicine, Center for Ulcer Research and Education, Digestive Diseases Division, University of California Los Angeles, and Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California 90073, USA
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3
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Le Verche V, Kaindl AM, Verney C, Csaba Z, Peineau S, Olivier P, Adle-Biassette H, Leterrier C, Vitalis T, Renaud J, Dargent B, Gressens P, Dournaud P. The somatostatin 2A receptor is enriched in migrating neurons during rat and human brain development and stimulates migration and axonal outgrowth. PLoS One 2009; 4:e5509. [PMID: 19434240 PMCID: PMC2677669 DOI: 10.1371/journal.pone.0005509] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2008] [Accepted: 04/16/2009] [Indexed: 01/06/2023] Open
Abstract
The neuropeptide somatostatin has been suggested to play an important role during neuronal development in addition to its established modulatory impact on neuroendocrine, motor and cognitive functions in adults. Although six somatostatin G protein-coupled receptors have been discovered, little is known about their distribution and function in the developing mammalian brain. In this study, we have first characterized the developmental expression of the somatostatin receptor sst2A, the subtype found most prominently in the adult rat and human nervous system. In the rat, the sst2A receptor expression appears as early as E12 and is restricted to post-mitotic neuronal populations leaving the ventricular zone. From E12 on, migrating neuronal populations immunopositive for the receptor were observed in numerous developing regions including the cerebral cortex, hippocampus and ganglionic eminences. Intense but transient immunoreactive signals were detected in the deep part of the external granular layer of the cerebellum, the rostral migratory stream and in tyrosine hydroxylase- and serotonin- positive neurons and axons. Activation of the sst2A receptor in vitro in rat cerebellar microexplants and primary hippocampal neurons revealed stimulatory effects on neuronal migration and axonal growth, respectively. In the human cortex, receptor immunoreactivity was located in the preplate at early development stages (8 gestational weeks) and was enriched to the outer part of the germinal zone at later stages. In the cerebellum, the deep part of the external granular layer was strongly immunoreactive at 19 gestational weeks, similar to the finding in rodents. In addition, migrating granule cells in the internal granular layer were also receptor-positive. Together, theses results strongly suggest that the somatostatin sst2A receptor participates in the development and maturation of specific neuronal populations during rat and human brain ontogenesis.
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Affiliation(s)
- Virginia Le Verche
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Angela M. Kaindl
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Catherine Verney
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Zsolt Csaba
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Stéphane Peineau
- MRC centre for Synaptic Plasticity, Department of Anatomy, Bristol, United Kingdom
| | - Paul Olivier
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Homa Adle-Biassette
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Christophe Leterrier
- Inserm, Unité Mixte de Recherche 641, Marseille, France
- Université de la Méditerranée, Faculté de Médecine Secteur-Nord, Institut Fédératif de Recherche 11, Marseille, France
| | - Tania Vitalis
- Ecole Supérieure de Physique et de Chimie Industrielles–CNRS 7537, Paris, France
| | - Julie Renaud
- Inserm, Unité Mixte de Recherche S968, Institut de la Vision, Department of Development, Paris, France
- Université Pierre et Marie Curie-Paris 6, Institut de la Vision, Paris, France
| | - Bénédicte Dargent
- Inserm, Unité Mixte de Recherche 641, Marseille, France
- Université de la Méditerranée, Faculté de Médecine Secteur-Nord, Institut Fédératif de Recherche 11, Marseille, France
| | - Pierre Gressens
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
| | - Pascal Dournaud
- Inserm, Unité Mixte de Recherche U676, Paris, France
- Université de Médecine Denis Diderot-Paris 7, Paris, France
- * E-mail:
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Abstract
This study investigated how the administration (acute and chronic) of the antidepressants citalopram and desmethylimipramine (DMI) influences somatostatin (somatotropin release inhibitory factor, SRIF) levels and SRIF receptor density (sst(1-5)) in rat brain. Animals received either of the following treatments: (1) saline for 21 days (control group), (2) saline for 20 days and citalopram or DMI for 1 day (citalopram or DMI acute groups), (3) citalopram or DMI for 21 days (citalopram or DMI chronic groups). Somatostatin levels were determined by radioimmunoassay. [(125)I]LTT SRIF-28 binding in the absence (labeling of sst(1-5)) or presence of 3 nM MK678 (labeling of sst(1/4)) and [(125)I]Tyr(3) octreotide (labeling of sst(2/5)) binding with subsequent autoradiography was performed in brains of rats treated with both antidepressants. Somatostatin levels were increased after citalopram, but not DMI administration, in the caudate-putamen, hippocampus, nucleus accumbens, and prefrontal cortex. Autoradiography studies illustrated a significant decrease in receptor density in the superficial and deep layers of frontal cortex (sst(2)), as well as a significant increase in the CA1 (sst(1/4)) hippocampal field in brains of chronically citalopram-treated animals. DMI administration increased sst(1/4) receptors levels in the CA1 hippocampal region. These results suggest that citalopram and to a lesser extent DMI influence the function of the somatostatin system in brain regions involved in the emotional, motivational, and cognitive aspects of behavior.
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Wells MY, Voute H, Lonchampt MO, Fisch C, Boulifard V, Picaut P. Intimal Hyperplasia in Rats after Subcutaneous Injection of a Somatostatin Analog. Toxicol Pathol 2009; 37:235-43. [DOI: 10.1177/0192623308329284] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The somatostatin analog octreotide was administered to male and female Sprague-Dawley rats by subcutaneous injection for thirteen weeks at 0 (saline control), 0 (placebo control [mannitol and lactic acid; pH 4.2]), 1.25 mg/kg/day and 2.5 mg/kg/day to explore its potential effect on cutaneous vascular morphology. The placebo caused an increase in the incidence of intimal hyperplasia compared to saline controls in female rats; octreotide increased the incidence and severity of intimal hyperplasia in males and females. Intimal hyperplasia consisted of increased numbers of cells located between the endothelial cell layer and the internal elastic lamina. Severity was based on the degree of compromise of the vascular lumen (regardless of vessel size and number), with severely affected vessels having no visible lumen. Intimal hyperplasia in rats treated with octreotide was considered to be an unexpected and adverse finding, given that this compound and other somatostatin analogs have been investigated as reducers of intimal proliferation or restenosis after angioplasty in humans and that no such lesion has been reported in the literature for this class of compound to date. The induction of intimal hyperplasia by the placebo is also a notable finding; this may be because of the low pH of the formulation.
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Affiliation(s)
- Monique Y. Wells
- Toxicology/Pathology Services Inc., Houston, Texas, USA and Paris, France
| | - Hélène Voute
- MDS Pharma, Saint Germain sur l’Arbresle, France
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6
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Biondi C, Ferretti ME, Lunghi L, Medici S, Cervellati F, Abelli L, Bertoni F, Adinolfi E, Vesce F, Bartolini G, Papi A, D'Andrea S, Berton S, Baldassarre G. Somatostatin as a regulator of first-trimester human trophoblast functions. Placenta 2008; 29:660-70. [PMID: 18617261 DOI: 10.1016/j.placenta.2008.05.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 05/09/2008] [Accepted: 05/31/2008] [Indexed: 12/19/2022]
Abstract
We have tested the hypothesis that human early trophoblast is a target for somatostatin (SRIF) regulatory actions. We report for the first time that SSTR2A and 2B transcripts and proteins are present in first-trimester human chorionic villi and the trophoblast-derived HTR-8/SVneo and JAR cells. In both cell lines, SSTR are functional since SRIF inhibits cyclic AMP pathway, stimulates arachidonic acid release and enhances cell proliferation. Moreover, in HTR-8/SVneo cells, considered a good model of first-trimester EVT, SRIF also enhances migration. An involvement of the cyclic AMP pathway in mediating SRIF effects on proliferation and migration is suggested. Our data support the idea that SRIF regulates early trophoblast functions mainly through an interaction with SSTR2.
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Affiliation(s)
- C Biondi
- Department of Biology and Evolution, Sections of General Physiology, University of Ferrara, 44100 Ferrara, Italy
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7
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Holliday ND, Tough IR, Cox HM. A functional comparison of recombinant and native somatostatin sst2 receptor variants in epithelia. Br J Pharmacol 2007; 152:132-40. [PMID: 17603546 PMCID: PMC1978267 DOI: 10.1038/sj.bjp.0707365] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND AND PURPOSE Somatostatin (SRIF-14) exerts broad spectrum antisecretory effects by activating the somatostatin 2 (sst(2)) receptor. The rat (r) sst(2) receptor exists in 'long' (sst(2a)) and 'short' (sst(2b)) forms that differ in their C termini, while a single human (h) sst(2a) exists. This study compares the characteristics of recombinant rsst(2a), rsst(2b) and hsst(2a) activation in human epithelia, and with native sst(2) responses in rat colon. EXPERIMENTAL APPROACH Epithelial layers of each clone or rat colon were placed in Ussing chambers and short-circuit current (I (SC)) measured in response to SRIF-14 and chosen analogues. The relative potencies and ability to cause desensitization to SRIF-14 were assessed, and the affinities of the sst(2) antagonist, D-Tyr(8) CYN154806 for hsst(2a), rsst(2a) and native rat colon sst(2) receptors were established. KEY RESULTS Basolateral SRIF-14 responses were transient in hsst(2a) and rsst(2a) epithelia, but prolonged in rsst(2b)-expressing cells. Activation of rsst(2a) resulted in significant desensitization to SRIF-14 and receptor phosphorylation, whereas the rsst(2b) receptor did neither. Sst(2)-preferred agonists (BIM23190C and BIM23027) reduced I (sc) with similar potency and both caused complete desensitization to SRIF-14. CYN154806 antagonized hsst(2a) and rsst(2a) receptors with pK (B) values of 7.9 and 7.8, respectively. In rat colon mucosa, CYN154806 blocked SRIF-14 responses with a pA (2) value of 8.2, and BIM23190C responses with a pK (B) of 8.4. CONCLUSIONS AND IMPLICATIONS SRIF-14 caused rapid rsst(2a) receptor phosphorylation and desensitization of epithelial antisecretory responses, neither of which occurred with the rsst(2b) receptor. These mechanisms are most likely to be a prerequisite for sensitivity to sst(2)-analogues with radiotherapeutic potential.
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Affiliation(s)
- N D Holliday
- Wolfson Centre for Age-Related Diseases, King's College London, Hodgkin Building, Guy's Campus London, UK
| | - I R Tough
- Wolfson Centre for Age-Related Diseases, King's College London, Hodgkin Building, Guy's Campus London, UK
| | - H M Cox
- Wolfson Centre for Age-Related Diseases, King's College London, Hodgkin Building, Guy's Campus London, UK
- Author for correspondence:
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8
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Mastrodimou N, Kiagiadaki F, Hodjarova M, Karagianni E, Thermos K. Somatostatin receptors (sst2) regulate cGMP production in rat retina. ACTA ACUST UNITED AC 2005; 133:41-6. [PMID: 16280179 DOI: 10.1016/j.regpep.2005.09.034] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Accepted: 09/08/2005] [Indexed: 10/25/2022]
Abstract
The present study investigated the effect of somatostatin in the regulation of cGMP levels in rat retina and the mechanisms involved in this process. Isolated rat retinas were treated alone or in the presence of somatostatin (0.01-10 microM), BIM23014 (sst2 agonist, 0.01-10 microM), L-796,778 (sst3 agonist, 10 microM), somatostatin (0.1 microM) in combination with CYN154806 (sst2 antagonist, 1 microM), N(G)-methyl-L-arginine acetate salt (NMMA, inhibitor of the nitric oxide synthase (NOS), 250 microM), orthovanadate (inhibitor of tyrosine phosphatase, SHP-1, 1 microM), and arginine alone (250 microM). cGMP levels were quantified by ELISA. Immunohistochemistry studies were performed for the detection of cGMP and nNOS, while Western blot analysis was employed for the detection of SHP-1. Somatostatin increased cGMP levels in a concentration-dependent manner. This increase was inhibited by CYN154806. BIM23014 increased cGMP levels only at the concentration of 10 microM, while L-796,778 had no effect. NMMA blocked completely the somatostatin stimulated increase of cGMP levels and nNOS was detected in rat retina. cGMP immunoreactivity was observed primarily in bipolar cells only of nitroprusside-treated retinas. SHP-1 inhibition by orthovanadate reduced the somatostatin effect in a statistically significant manner. These results suggest that a SRIF/SHP-1/NO/cGMP mechanism underlies the actions of somatostatin in the retina and in its influence of retinal circuitry.
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Affiliation(s)
- Niki Mastrodimou
- Laboratory of Pharmacology, Department Basic Sciences, University of Crete, Faculty of Medicine, Heraklion, Crete, Greece
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Meis S, Sosulina L, Schulz S, Höllt V, Pape HC. Mechanisms of somatostatin-evoked responses in neurons of the rat lateral amygdala. Eur J Neurosci 2005; 21:755-62. [PMID: 15733093 DOI: 10.1111/j.1460-9568.2005.03922.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effects of somatostatin in the rat lateral amygdala (LA) in vitro were investigated through whole cell recording techniques. Somatostatin induced an inwardly rectifying K+ current in approximately 98% of LA projection neurons. Half-maximal effects were obtained by 189 nM somatostatin. The effects of somatostatin were insensitive to tetrodotoxin, reduced by Ba2+, occluded or abolished by the presence of nonhydrolysable GTP or GDP analogues, respectively, and blocked or mimicked by a somatostatin receptor type 2 antagonist (BIM-23627) or somatostatin receptor type 2 agonist (L-779,976), respectively, while somatostatin receptor type 1, 3 and 4 agonists were ineffective (L-797,591, L-796,778, L-803,087). Responses to somatostatin were associated with membrane hyperpolarization and decrease in input resistance, resulting in a dampening of cell excitability. It is suggested that these cellular mechanisms contribute to the role of somatostatin in decreasing anxiety behaviour as well as to anticonvulsant and antiepileptogenic actions of somatostatin or somatostatin agonists in the amygdala.
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Affiliation(s)
- Susanne Meis
- Institut für Physiologie, Medizinische Fakultät, Otto-von-Guericke-Universität, Leipziger Str. 44, D-39120 Magdeburg, Germany.
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11
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Eberle AN, Mild G, Froidevaux S. Receptor-Mediated Tumor Targeting with Radiopeptides. Part 1. General Concepts and Methods: Applications to Somatostatin Receptor-Expressing Tumors. J Recept Signal Transduct Res 2004; 24:319-455. [PMID: 15648449 DOI: 10.1081/rrs-200040939] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Radiolabeled peptides have become important tools in nuclear oncology, both as diagnostics and more recently also as therapeutics. They represent a distinct sector of the molecular targeting approach, which in many areas of therapy will implement the old "magic bullet" concept by specifically directing the therapeutic agent to the site of action. In this three-part review, we present a comprehensive overview of the literature on receptor-mediated tumor targeting with the different radiopeptides currently studied. Part I summarizes the general concepts and methods of targeting, the selection of radioisotopes, chelators, and the criteria of peptide ligand development. Then, the >400 studies on the application to somatostatin/somatostatin-release inhibiting factor receptor-mediated tumor localization and treatment will be reviewed, demonstrating that peptide radiopharmaceuticals have gained an important position in clinical medicine.
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Affiliation(s)
- Alex N Eberle
- Laboratory of Endocrinology, Department of Research, University Hospital and University Children's Hospital, Basel, Switzerland.
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12
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Vasilaki A, Papasava D, Hoyer D, Thermos K. The somatostatin receptor (sst1) modulates the release of somatostatin in the nucleus accumbens of the rat. Neuropharmacology 2004; 47:612-8. [PMID: 15380378 DOI: 10.1016/j.neuropharm.2004.06.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2004] [Revised: 05/28/2004] [Accepted: 06/11/2004] [Indexed: 10/26/2022]
Abstract
The aim of the present study was to examine the function of the somatostatin receptor (sst(1)) in the nucleus accumbens (NAc) of the basal ganglia. Radioligand binding studies were performed in rats to assess the presence of the receptor, while in vivo microdialysis studies were performed to examine its role in somatostatin release. CH-275, which is selective for sst(1), MK-678, selective for sst(2) and L-803,087, selective for sst(4) receptors displaced [(125)I]-Tyr(11)-somatostatin specific binding in a concentration-dependent manner with IC(50) values of 75, 0.21 and 11 nM, respectively. Infusion of CH-275 (10(-5), 10(-6) or 10(-7) M) in the NAc of freely moving rats resulted in a decrease in somatostatin levels only at the concentration of 10(-5) M. This effect was reversed by 10(-5) M of the selective sst(1) antagonist SRA-880. The sst(1) agonist L-797,591 (10(-5) M) mimicked the effect of CH-275, while MK-678 and L-803,087 at the same concentration were unable to influence somatostatin levels. These results provide functional evidence to demonstrate that the sst(1) receptor modulates somatostatin release in the basal ganglia.
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Affiliation(s)
- Anna Vasilaki
- Laboratory of Pharmacology, Department of Basic Sciences, Faculty of Medicine, University of Crete, Heraklion, 71110 Crete, Greece
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13
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Valatas V, Kolios G, Manousou P, Notas G, Xidakis C, Diamantis I, Kouroumalis E. Octreotide regulates CC but not CXC LPS-induced chemokine secretion in rat Kupffer cells. Br J Pharmacol 2004; 141:477-87. [PMID: 14718256 PMCID: PMC1574216 DOI: 10.1038/sj.bjp.0705633] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Kupffer cells (KC) and lipopolysaccharide (LPS) interaction is the initial event leading to hepatic inflammation and fibrosis in many types of liver injury. We studied chemokine secretion by KC activated with LPS and the possible effect of the somatostatin analogue octreotide, in the regulation of this process. KC isolated from Sprague-Dawley rats were cultured in the presence of LPS added alone or with different concentrations of octreotide for 24 and 48 h, and chemokine production was assessed in culture supernatants by ELISA. CC chemokine mRNA expression was assessed by semiquantitative RT-PCR. Vehicle-stimulated KC produced a basal amount of CC and CXC chemokines. LPS-stimulated KC secreted significantly increased amounts of IL-8 (GRO/CINC-1) (P<0.001), MIP-2 (P<0.001), MCP-1 (P<0.001), and RANTES (P<0.01). Octreotide inhibited LPS-induced secretion of the CC chemokines MCP-1 (P<0.05) and RANTES (P<0.05), but not the CXC chemokines IL-8 (GRO/CINC-1) and MIP-2, in a concentration-dependent manner. Downregulation of basal and LPS-induced mRNA expression of the CC chemokines was also observed in the presence of octreotide. Pretreatment with phosphatidylinositol 3 (PI3)-kinase inhibitors reduced chemokine production by LPS-treated KC in both the mRNA and protein level. Furthermore, it prevented the octreotide inhibitory effect on LPS-induced chemokine secretion, indicating a possible involvement of the PI3-kinase pathway. In conclusion, these data demonstrate that chemokine secretion by KC can be differentially regulated by octreotide, and suggest that this somatostatin analogue may have immunoregulatory effects on resident liver macrophages. British Journal of Pharmacology (2004) 141, 477-487. doi:10.1038/sj.bjp.0705633
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Affiliation(s)
- Vassilis Valatas
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
| | - George Kolios
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
- Author for correspondence:
| | - Pinelopi Manousou
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
| | - George Notas
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
| | - Costas Xidakis
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
| | - Ioannis Diamantis
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
| | - Elias Kouroumalis
- Gastroenterology Department, Faculty of Medicine, University of Crete, Heraklion GR-71003, Greece
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14
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Møller LN, Stidsen CE, Hartmann B, Holst JJ. Somatostatin receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2003; 1616:1-84. [PMID: 14507421 DOI: 10.1016/s0005-2736(03)00235-9] [Citation(s) in RCA: 255] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In 1972, Brazeau et al. isolated somatostatin (somatotropin release-inhibiting factor, SRIF), a cyclic polypeptide with two biologically active isoforms (SRIF-14 and SRIF-28). This event prompted the successful quest for SRIF receptors. Then, nearly a quarter of a century later, it was announced that a neuropeptide, to be named cortistatin (CST), had been cloned, bearing strong resemblance to SRIF. Evidence of special CST receptors never emerged, however. CST rather competed with both SRIF isoforms for specific receptor binding. And binding to the known subtypes with affinities in the nanomolar range, it has therefore been acknowledged to be a third endogenous ligand at SRIF receptors. This review goes through mechanisms of signal transduction, pharmacology, and anatomical distribution of SRIF receptors. Structurally, SRIF receptors belong to the superfamily of G protein-coupled (GPC) receptors, sharing the characteristic seven-transmembrane-segment (STMS) topography. Years of intensive research have resulted in cloning of five receptor subtypes (sst(1)-sst(5)), one of which is represented by two splice variants (sst(2A) and sst(2B)). The individual subtypes, functionally coupled to the effectors of signal transduction, are differentially expressed throughout the mammalian organism, with corresponding differences in physiological impact. It is evident that receptor function, from a physiological point of view, cannot simply be reduced to the accumulated operations of individual receptors. Far from being isolated functional units, receptors co-operate. The total receptor apparatus of individual cell types is composed of different-ligand receptors (e.g. SRIF and non-SRIF receptors) and co-expressed receptor subtypes (e.g. sst(2) and sst(5) receptors) in characteristic proportions. In other words, levels of individual receptor subtypes are highly cell-specific and vary with the co-expression of different-ligand receptors. However, the question is how to quantify the relative contributions of individual receptor subtypes to the integration of transduced signals, ultimately the result of collective receptor activity. The generation of knock-out (KO) mice, intended as a means to define the contributions made by individual receptor subtypes, necessarily marks but an approximation. Furthermore, we must now take into account the stunning complexity of receptor co-operation indicated by the observation of receptor homo- and heterodimerisation, let alone oligomerisation. Theoretically, this phenomenon adds a novel series of functional megareceptors/super-receptors, with varied pharmacological profiles, to the catalogue of monomeric receptor subtypes isolated and cloned in the past. SRIF analogues include both peptides and non-peptides, receptor agonists and antagonists. Relatively long half lives, as compared to those of the endogenous ligands, have been paramount from the outset. Motivated by theoretical puzzles or the shortcomings of present-day diagnostics and therapy, investigators have also aimed to produce subtype-selective analogues. Several have become available.
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Affiliation(s)
- Lars Neisig Møller
- Department of Medical Physiology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark
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15
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Abstract
The peptide somatostatin is one of many neuroactive agents that influence retinal physiology. It is synthesized primarily in a subclass of amacrine cells and believed to function as a neurotransmitter, neuromodulator or trophic factor. The cloning of the somatostatin receptors (sst1-5) in the early nineties provided the appropriate tools for the study of ssts in many tissues, including the retina. In this review, emphasis is given to recent studies that have provided significant information on the functional role of somatostatin in retinal circuitry and the retinal pigment epithelium. The important role of somatostatin in retinal disease therapeutics is also discussed.
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Affiliation(s)
- Kyriaki Thermos
- Department of Basic Sciences, Faculty of Medicine, University of Crete, Laboratory of Pharmacology, Heraclion, Crete 71 110, Greece.
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16
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Nunn C, Langenegger D, Hurth K, Schmidt K, Fehlmann D, Hoyer D. Agonist properties of putative small-molecule somatostatin sst2 receptor-selective antagonists. Eur J Pharmacol 2003; 465:211-8. [PMID: 12681432 DOI: 10.1016/s0014-2999(03)01482-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The availability of antagonist ligands for somatostatin receptors is very limited, with those that are available often displaying agonist properties or limited receptor subtype selectivity. Hay et al. [Bioorg. Med. Chem. Lett. 11 (2001) 2731] recently described the development of small-molecule somatostatin receptor subtype 2 (sst(2)) selective compounds. This study investigates the binding affinity and functional characteristics of two of those antagonists (2 and 3) and the agonist compound, from which they were derived (1). In radioligand binding studies using the agonist radioligands [125I][Tyr(11)]SRIF-14 (Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-(125I-Tyr)-Thr-Ser-Cys]-OH), [125I]LTT-SRIF-28 ([Leu(8),DTrp(22),125I-Tyr(25)]SRIF-28; Ser-Ala-Asn-Ser-Asn-Pro-Ala-Leu-Ala-Pro-Arg-Glu-Arg-Lys-Ala-Gly-c[Cys-Lys-Asn-Phe-Phe-DTrp-Lys-Thr-(125I-Tyr)-Thr-Ser-Cys]-OH), [125I]CGP 23996 (c[Lys-Asu-Phe-Phe-Trp-Lys-Thr-(125I-Tyr)-Thr-Ser]), [125I][Tyr(3)]octreotide (DPhe-c[Cys-(125I-Tyr)-DTrp-Lys-Thr-Cys]-Thr-OH) and [125I][Tyr(10)]cortistatin-14 (Pro-c[Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-(125I-Tyr)-Ser-Ser-Cys]-Lys) at human recombinant somatostatin receptors expressed in Chinese hamster lung fibroblast (CCL39) cells and native rat cortex, the compounds bound with high affinity (pK(d) 6.8-9.7) and selectivity to human sst(2) receptors. Some affinity was also observed for sst(5) labelled by [125I][Tyr(3)]octreotide and [125I]CGP 23996. In functional studies at human sst(2) receptors expressed in Chinese hamster ovary (CHO) cells, both the agonist 1 and the two putative antagonists 2 and 3 concentration dependently inhibited forskolin-stimulated adenylate cyclase and stimulated luciferase reporter gene expression, with similar efficacy to the natural ligand somatotropin release inhibiting factor (SRIF)-14. Compound 1 had similar potency to SRIF-14, which was in the nanomolar range, whereas 2 and 3 were 10-100-fold less potent. The intrinsic activity of 2 and 3 was too high to allow antagonist studies to be carried out. In conclusion, in contrast to previous findings, all three compounds are potent agonists at recombinant human sst(2) receptors.
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Affiliation(s)
- Caroline Nunn
- Nervous System Research, Novartis Pharma AG, CH-4002, Basel, Switzerland
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17
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Csaba Z, Simon A, Helboe L, Epelbaum J, Dournaud P. Targeting sst2A receptor-expressing cells in the rat hypothalamus through in vivo agonist stimulation: neuroanatomical evidence for a major role of this subtype in mediating somatostatin functions. Endocrinology 2003; 144:1564-73. [PMID: 12639941 DOI: 10.1210/en.2002-221090] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Numerous physiological studies as well as in situ hybridization and PCR experiments concur in reporting a role for the sst2A receptor in transducing somatostatin (SRIF) actions in the rat hypothalamus. However, the distribution of this receptor protein is not known within this structure. Regional and cellular localization of the sst2A receptor was therefore examined in the rat hypothalamus using highly sensitive immunohistochemical techniques. In close correspondence with the distribution of SRIF-immunoreactive fibers, numerous hypothalamic areas displayed sst2A receptor immunoreactivity. Receptor labeling was, however, diffusely distributed over the tissue, and few immunopositive cells were apparent. Unraveling the distribution of receptor-expressing cells was achieved through acute in vivo agonist stimulation and subsequent receptor internalization. At the cellular level, double-immunolabeling experiments with synaptophysin and microtubule-associated protein 2 demonstrated that sst2A receptors were predominantly internalized in perikarya and dendrites. Double-labeling experiments with SRIF revealed that 93% of arcuate, but only 18% of periventricular, SRIF-positive neurons expressed internalized receptors. Taken together, these results demonstrate for the first time that the sst2A receptor protein is widely, but selectively, distributed in the hypothalamus, and that postsynaptic sst2A auto- and heteroreceptors are well poised to play an important role in the somatostatinergic regulation of hypothalamic endocrine and metabolic processes.
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Affiliation(s)
- Zsolt Csaba
- Institut National de la Santé et de la Recherche Médicale, Unité-549, IFR Broca-Sainte Anne, Centre Paul Broca, 75014 Paris, France
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18
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Vasilaki A, Georgoussi Z, Thermos K. Somatostatin receptors (sst2) are coupled to Go and modulate GTPase activity in the rabbit retina. J Neurochem 2003; 84:625-32. [PMID: 12562507 DOI: 10.1046/j.1471-4159.2003.01570.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The role of somatostatin and its mechanism of action in the retina remains an important target for investigation. Biochemical and pharmacological studies were engaged to characterize the somatostatin receptors in the rabbit retina, and their coupling to G-proteins. The ability of selective ligands to inhibit [125I]Tyr11-somatostatin-14 binding to rabbit retinal membranes was examined. The sst2 analogues SMS201-995, MK678, and BIM23014, displayed IC50 values of 0.28 +/- 0.12, 0.04 +/- 0.01 and 1.57 +/- 0.39 nm, respectively. The sst1 analogue CH275 moderately displaced the [125I]Tyr11-somatostatin-14 binding, while selective analogues for sst3, sst4 and sst5 had minimal effect. Immunoblotting and/or immunohistochemistry studies revealed the presence of the pertussis toxin sensitive Gi1/2, and Go proteins, as well as Gs. Somatostatin-14 and MK678 stimulated GTPase activity in a concentration-dependent manner with EC50 values of 42.8 +/- 16.8 and 70.0 +/- 16.5 nm, respectively, thus supporting the functional coupling between the receptor and the G-proteins. CH275 stimulated the GTPase activity moderately, in agreement with its binding profile. The antisera raised against Goalpha and Gi1/2alpha inhibited the somatostatin-induced high-affinity GTPase activity, but only anti-Goalpha inhibited the MK678 stimulation of the enzyme. These results suggest that somatostatin mediates its actions in the rabbit retina by interacting mainly with sst2 receptors that couple to Goalpha.
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Affiliation(s)
- Anna Vasilaki
- Laboratory of Pharmacology, Department of Basic Science, Faculty of Medicine, University of Crete, Heraklion, Crete 71110, Greece
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19
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Nunn C, Rueping M, Langenegger D, Schuepbach E, Kimmerlin T, Micuch P, Hurth K, Seebach D, Hoyer D. Beta(2)/beta(3)-di- and alpha/beta(3)-tetrapeptide derivatives as potent agonists at somatostatin sst(4) receptors. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2003; 367:95-103. [PMID: 12595949 DOI: 10.1007/s00210-002-0673-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2002] [Accepted: 11/21/2002] [Indexed: 10/25/2022]
Abstract
Four linear beta(2)/beta(3)-di- and alpha/beta(3)-tetrapeptides (1-4) were investigated as somatostatin sst(4) receptor agonists on recombinant human and mouse somatostatin receptors. Human somatostatin receptor subtypes 1-5 (sst(1-5)), and mouse somatostatin receptor subtypes 1,3,4 and 5, were characterised using the agonist radioligands [(125)I]LTT-SRIF-28, [(125)I][Tyr(10)]CST(14) and [(125)I]CGP 23996 in stably transfected Chinese hamster lung fibroblast (CCL39) cells. The peptides bound selectively to sst(4) receptors with nanomolar affinity (pK(d)=5.4-7.8). The peptides were investigated on second messenger systems both as agonists, and as antagonists to SRIF-14-mediated effects in CCL39 cells expressing mouse sst(4 )receptors, via measurement of inhibition of forskolin-stimulated adenylate cyclase activity, and stimulation of luciferase expression. The peptides showed full agonism or pronounced partial agonism (40 to 100% relative intrinsic activity) in both inhibition of forskolin-stimulated adenylate cyclase activity (pEC(50)=5.5-6.8), and luciferase expression (pEC(50)=5.5-6.5). The agonist potential was confirmed since antagonism was very difficult to establish. The data show that beta(2)/beta(3)-di- and alpha/beta(3)-tetrapeptide derivatives have agonist potential at recombinant somatostatin sst(4) receptors. Therefore, they may be used to elucidate physiological and biochemical effects mediated by sst(4), and may also have potential as therapeutic agents.
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Affiliation(s)
- Caroline Nunn
- Nervous System Research, WSJ 386/745, Novartis Pharma AG, 4002, Basel, Switzerland
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20
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Abstract
Since the discovery of somatostatin (sst) in 1973, numerous chemical and biological studies have been carried out to develop sst analogs with enhanced resistance to proteases and prolonged activity. Three highly potent sst analogs-octreotide, lanreotide, and vapreotide-are now available in the clinic, and demonstrate efficacy in the treatment of tumors of the pituitary and the gastroenteropancreatic tract. The most striking effect is the control of hormone hypersecretion associated with these tumors. Available data on growth suppression in patients indicate a limited antiproliferative action, tumor shrinkage is observed in 10-20% patients, and tumor stabilization in about half of the patients for duration of 8-16 months. Eventually, however, all patients escape from sst analog therapy with regard to both hormone hypersecretion and tumor growth, the only exception being observed in acromegalic patients who do not experience tachyphylaxis even after more than 10 years of daily octreotide injection. The mechanism underlying the escape phenomenon is not yet clarified. Regarding the molecular mechanisms involved in sst antineoplastic activity, both indirect and direct effects via specific somatostatin receptors (SSTRs) expressed in the target cells have be described. Direct action may result from blockade of mitogenic growth signal or induction of apoptosis following interaction with SSTRs. Indirect effects may be the result of reduced or inhibited secretion of growth-promoting hormones and growth factors that stimulate the growth of various types of cancer; also, inhibition of angiogenesis or influence on the immune system are important factors. Five SSTR subtypes have been identified so far, which are variably expressed in a variety of tumors such as gastroenteropancreatic (GEP) tumors, pituitary tumors, and carcinoid tumors. Although all five SSTR subtypes are linked to adenylate cyclase, they are now known to affect multiple other cellular signaling systems and hence they differentially participate in the regulation of the various cellular processes. The finding of several laboratories that SSTR-expressing tumors frequently contain two or more SSTR subtypes, and the recent discovery that SSTR subtypes might form homo/heterodimers to create a novel receptor with different functional characteristics, expand the array of selective SSTR activation pathways and subsequent intracellular signaling cascades. This may lead to improved clinical protocols that take into account possible synergistic interactions between the SSTR subtypes present on the same cancer cell. Radiolabeled sst analogs, such as [(111)In]-[diethylenetriamine pentaacetic acid (DTPA)-D-Phe(1)]-octreotide (OcreoScan), have proved to be very useful for tumor scintigraphy and internal radiotherapy of SSTR overexpressing tumors. The recent introduction of the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) considerably improved the stability of the radioconjugates, making possible the incorporation of a variety of radionuclides, such as (90)Y for receptor-mediated radionuclide therapy or (68)Ga for positron emission tomography (PET). Another promising area is the development of sst conjugates incorporating cytotoxic anticancer drugs.
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Affiliation(s)
- Sylvie Froidevaux
- Laboratory of Endocrinology, Department of Research, University Hospital and University Children's Hospital, CH-4031 Basel, Switzerland.
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21
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Allen JP, Canty AJ, Schulz S, Humphrey PPA, Emson PC, Young HM. Identification of cells expressing somatostatin receptor 2 in the gastrointestinal tract of Sstr2 knockout/lacZ knockin mice. J Comp Neurol 2002; 454:329-40. [PMID: 12442323 DOI: 10.1002/cne.10466] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Somatostatin is found in neurons and endocrine cells in the gastrointestinal tract. The actions of somatostatin are mediated by a family of G-protein-coupled receptors that compose five subtypes (SSTR1-5), each of which is encoded by a separate gene. lacZ "knockin" mice, in which the reporter gene lacZ was engineered into the genomic locus of Sstr2 by gene targeting, were used to examine the expression pattern of Sstr2 and identify potential targets for neurally released and hormonal somatostatin in the gastrointestinal tract. In the body of the stomach, a large proportion of epithelial cells and subpopulations of myenteric neurons expressed Sstr2. Double- or triple-labeling with antisera to H(+)K(+)ATPase (to identify parietal cells) and/or histidine decarboxylase (to identify enterochromaffin-like [ECL] cells) combined with beta-galactosidase staining revealed that both parietal cells and ECL cells expressed Sstr2, and these two cell types accounted for almost all of the Sstr2-expressing epithelial cells. Somatostatin inhibits gastric acid secretion. The presence of SSTR2 on both parietal and ECL cells suggests that somatostatin acting on SSTR2 may reduce acid secretion by both acting directly on parietal cells and by reducing histamine release from ECL cells. In the small and large intestine, subpopulations of neurons in the myenteric and submucosal plexuses expressed Sstr2, and many of the Sstr2-expressing myenteric neurons also showed SSTR2(a) immunostaining. Most of Sstr2-expressing neurons in the myenteric plexus showed nitric oxide synthase (NOS) immunoreactivity. Previous studies have shown that NOS neurons are descending interneurons and anally projecting, inhibitory motor neurons. Thus, somatostatin acting at SSTR2 receptors on NOS neurons might modulate descending relaxation.
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Affiliation(s)
- Jeremy P Allen
- Department of Neurobiology, The Babraham Institute, Babraham, Cambridge, CB2 4AT, United Kingdom
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22
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Vasilaki A, Mouratidou M, Schulz S, Thermos K. Somatostatin mediates nitric oxide production by activating sst(2) receptors in the rat retina. Neuropharmacology 2002; 43:899-909. [PMID: 12384175 DOI: 10.1016/s0028-3908(02)00181-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Somatostatin and its receptors (ssts) are found in the retina. Recent evidence suggested the involvement of sst(2A) and sst(2B) receptors in the regulation of nitric oxide (NO) (). In this study, we investigated further the localization of sst(1), sst(3)-sst(5), and the possible involvement of all subtypes, present in the rat retina, in the regulation of NO production. Polyclonal antibodies raised against sst(1), sst(3-5) were applied to 10-14 micro m cryostat sections of rat retinas fixed in paraformaldehyde. NADPH-diaphorase reactivity was assessed histochemically. The levels of NO in rat retinal explants were assessed by the production of its stable metabolites NO(2)(-) and NO(3)(-). sst(1) immunofluorescence was detected mainly in the retinal pigment epithelium, blood vessels of the inner retina, where it was colocalized with NADPH-diaphorase, and in processes of the inner plexiform layer (IPL). sst(4) immunohistochemistry was found in ganglion cell bodies, where it was colocalized with NADPH-diaphorase, processes of the IPL and ganglion cell layer, and optic nerve fibers. sst(3) or sst(5) immunostain was not detected. Somatostatin increased NO production and this effect was mimicked only by the sst(2) specific analog L-779976. The sst(2) antagonist CYN-154806 blocked the L-779976 increase of NO production. These results present conclusive evidence that somatostatin's role in the retina involves the regulation of NO by an sst(2) mechanism.
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Affiliation(s)
- A Vasilaki
- University of Crete, Faculty of Medicine, Department of Basic Sciences, Laboratory of Pharmacology, Heraclion, Crete, Greece
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23
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Hutchinson DS, Bengtsson T, Evans BA, Summers RJ. Mouse beta 3a- and beta 3b-adrenoceptors expressed in Chinese hamster ovary cells display identical pharmacology but utilize distinct signalling pathways. Br J Pharmacol 2002; 135:1903-14. [PMID: 11959793 PMCID: PMC1573318 DOI: 10.1038/sj.bjp.0704654] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. This study characterizes the mouse beta(3a)-adrenoceptor (AR) and the splice variant of the beta(3)-AR (beta(3b)-AR) expressed in Chinese hamster ovary cells (CHO-K1). 2. Stable clones with high (approximately 1200), medium (approximately 500) or low receptor expression (approximately 100 fmol mg protein(-1)) were determined by saturation binding with [(125)I]-(-)-cyanopindolol. Competition binding studies showed no significant differences in affinity of beta-AR ligands for either receptor. 3. Several functional responses of each receptor were measured, namely extracellular acidification rate (EAR; cytosensor microphysiometer), cyclic AMP accumulation, and Erk1/2 phosphorylation. The beta(3)-AR agonists BRL37344, CL316243, GR265162X, L755507, SB251023, the non-conventional partial beta-AR agonist CGP12177 and the beta-AR agonist (-)-isoprenaline caused concentration-dependent increases in EAR in cells expressing either splice variant. CL316243 caused concentration-dependent increases in cyclic AMP accumulation and Erk1/2 phosphorylation in cells expressing either receptor. 4. PTX treatment increased maximum EAR and cyclic AMP responses to CL316243 in cells expressing the beta(3b)-AR but not in cells expressing the beta(3a)-AR at all levels of receptor expression. 5. CL316243 increased Erk1/2 phosphorylation with pEC(50) values and maximum responses that were not significantly different in cells expressing either splice variant. Erk1/2 phosphorylation was insensitive to PTX or H89 (PKA inhibitor) but was inhibited by LY294002 (PI3K gamma inhibitor), PP2 (c-Src inhibitor), genistein (tyrosine kinase inhibitor) and PD98059 (MEK inhibitor). 6. The adenylate cyclase activators forskolin or cholera toxin failed to increase Erk1/2 levels although both treatments markedly increased cyclic AMP accumulation in both beta(3a)- or beta(3b)-AR transfected cells. 7. These results suggest that in CHO-K1 cells, the beta(3b)-AR, can couple to both G(s) and G(i) to stimulate and inhibit cyclic AMP production respectively, while the beta(3a)-AR, couples solely to G(s) to increase cyclic AMP levels. However, the increase in Erk1/2 phosphorylation following receptor activation is not dependent upon coupling of the receptors to G(i) or the generation of cyclic AMP.
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Affiliation(s)
- Dana S Hutchinson
- Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia
- The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Tore Bengtsson
- The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Bronwyn A Evans
- Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia
| | - Roger J Summers
- Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia
- Author for correspondence:
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24
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Hannon JP, Petrucci C, Fehlmann D, Viollet C, Epelbaum J, Hoyer D. Somatostatin sst2 receptor knock-out mice: localisation of sst1-5 receptor mRNA and binding in mouse brain by semi-quantitative RT-PCR, in situ hybridisation histochemistry and receptor autoradiography. Neuropharmacology 2002; 42:396-413. [PMID: 11897118 DOI: 10.1016/s0028-3908(01)00186-1] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The peptide hormone/neurotransmitter somatostatin (somatotropin release inhibiting factor; SRIF) and its receptors (sst(1)-sst(5)) appear to regulate many physiological functions in the CNS. Semi-quantitative analysis of the densities of mRNA expression for sst(1-5) receptors and SRIF receptor binding sites were established in sst(2) receptor knock-out (KO) mice. Patterns of sst(1-5) receptor mRNA expression were largely conserved for sst(1,3,4) and sst(5) selective oligonucleotide probes; whereas sst(2) signals were completely absent in KO mouse brain. Autoradiographic analysis demonstrated [(125)I]LTT SRIF(28), [(125)I]CGP 23996 (two radioligands known to label all five recombinant SRIF receptors) and [(125)I]Tyr(3)-octreotide (sst(2) and sst(5) receptor selective) binding in wild type (WT) mouse brain sections; yet no specific binding of [(125)I]Tyr(3)-octreotide in KO mice. In contrast, [(125)I]LTT SRIF(28) and [(125)I]CGP 23996 binding was still present in a number of brain areas in KO mice, although to a lesser degree than in those regions where [(125)I]Tyr(3)-octreotide binding was found, in WT animals. The present data suggest first, that both sst(2) receptor protein and mRNA were completely absent in the brain of these KO animals. Second, there was little evidence of compensatory regulation, at the mRNA level, of the other SRIF receptors as a consequence of the sst(2) KO. Third, the absence of any [(125)I]Tyr(3)-octreotide binding, in KO mice, suggests that this particular ligand is selective for the sst(2) receptor subtype (under the conditions utilised); or that sst(5) receptors are only marginally expressed in brain. Fourth, there were regions where the binding of [(125)I]LTT SRIF(28) and [(125)I]CGP 23996 were moderately affected by the sst(2) KO, suggesting that additional SRIF receptors may well contribute to the binding of the aforementioned radioligands. Finally, since the relative distribution of these two ligands were not entirely superimposable, it suggests that their respective selectivity profiles towards the different SRIF receptor subtypes in situ are not identical.
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Affiliation(s)
- J P Hannon
- Nervous System Research, Novartis Pharma AG, CH-4002 Basel, Switzerland
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25
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Abstract
Somatostatin (SRIF) is a multigene family of peptides. SRIF-14 is conserved with identical primary structure in species across the vertebrates. The presence of multiple SRIF genes has been demonstrated in a number of fish species. Notably, three distinct SRIF genes have been identified in goldfish. One of these genes, which encodes [Pro(2)]SRIF-14, has also been identified in sturgeon and African lungfish, and is closely associated with the amphibian [Pro(2),Met(13)]SRIF-14 gene and mammalian cortistatin gene. The main neuroendocrine role of SRIF-14 peptide that has been determined in fish is the inhibition of pituitary growth hormone secretion. The functions of SRIF-14 variant or larger forms of SRIF peptide and the regulation of SRIF gene expression remain to be explored. Type one and two SRIF receptors have been identified from goldfish and type three SRIF receptor from an electric fish. Fish SRIF receptors display considerable homology to mammalian counterparts in terms of primary structure and negative coupling to adenylate cyclase. The identification of the multiple gene family of SRIF peptides and multiple types of SRIF receptors in fish opens a new avenue for the study of physiological roles of SRIF, and the molecular and cellular mechanisms of SRIF actions in fish.
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Affiliation(s)
- X Lin
- Department of Biological Sciences, University of Alberta, Alberta T6G 2E9, Edmonton, Canada
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26
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Helboe L, Møller M. Localization of somatostatin receptors at the light and electron microscopial level by using antibodies raised against fusion proteins. PROGRESS IN HISTOCHEMISTRY AND CYTOCHEMISTRY 2001; 35:3-64. [PMID: 10904940 DOI: 10.1016/s0079-6336(00)80005-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Somatostatin mediates its multiple biological effects via specific plasma membrane receptors belonging to the family of G-protein coupled receptors with seven putative membrane-spanning domains. Five somatostatin receptor subtypes (sst1-sst5) have been cloned in human, mouse, and rat. We have raised specific antibodies against the five human somatostatin receptors by using the fusion protein technique. DNA sequences encoding C-terminal parts of the somatostatin receptors were inserted into a pGEX-2T plasmid vector. E. coli bacteria were transformed with the recombinant plasmid and fusion proteins were expressed and purified using the glutathione S-transferase Gene Fusion System. The fusion proteins were emulsified with Freund's complete adjuvant and polyclonal antibodies were raised in rabbits. The antisera were tested for specificity in Western blot analysis of membrane preparations from cell lines expressing the receptors and in membrane preparations of brain tissues. The receptors were visualized at the light microscopical level in paraformaldehyde fixed tissue sections by use of biotin labelled secondary antibodies as well as by amplification with biotinylated tyramide. The final step in the immunohistochemical visualization of the receptors was done by both peroxidase labelled streptavidin/biotin and different fluorophores. At the electron microscopical level, some of the receptors could be visualized in tissues fixed with a combination of paraformaldehyde and low concentrations of glutaraldehyde. In the hamster brain, sst2 receptors labelling was observed in both neuronal processes and perikarya. The staining was present in neo-, and allocortical areas of the forebrain, the hypothalamus, brain stem, and spinal cord. In the rat and human, sst1 receptor was shown to be an auto receptor on somatostatinergic neurons located in the hypothalamus. In the retina both sst1 and sst2 receptors were present. sst1 receptors were confined to amacrine cells, few ganglionic cells, and Müller cell-end feet. sst2 receptors were more widespread than the sst1 receptors. sst2-immunoreactivity was present in dopaminergic amacrine cells, the Müller cell-end feet, and in the inner segments of the cone photoreceptors. Thus, the availability of subtype specific antibodies against the five somatostatin receptors makes it possible to identify the receptors involved in the multiple somatostatinergic system in the body.
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Affiliation(s)
- L Helboe
- Inst. Med. Anat., Section B, Panum Institute, Copenhagen, Denmark
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27
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Abstract
Somatostatin, and the recently discovered neuropeptide cortistatin, exert their physiological actions via a family of six G protein-coupled receptors (sst1, sst2A, sst2B, sst3, sst4, sst5). Following the cloning of somatostatin receptors significant advances have been made in our understanding of their molecular, pharmacological and signaling properties although much progress remains to be done to define their physiological role in vivo. In this review, the present knowledge regarding neuroanatomical localization, signal transduction pathways, desensitization and internalization properties of somatostatin receptors is summarized. Evidence that somatostatin receptors can form homo- and heterodimers and can physically interact with members of the SSTRIP/Shank/ProSAP1/CortBP1 family is also discussed.
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Affiliation(s)
- Z Csaba
- Inserm U549, IFR Broca-Sainte Anne, Centre Paul Broca, Paris, France
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28
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Lin X, Otto CJ, Cardenas R, Peter RE. Somatostatin family of peptides and its receptors in fish. Can J Physiol Pharmacol 2000. [DOI: 10.1139/y00-100] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Somatostatin (SRIF or SS) is a phylogenetically ancient, multigene family of peptides. SRIF-14 is conserved with identical primary structure in species of all classes of vertebrates. The presence of multiple SRIF genes has been demonstrated in a number of fish species and could extend to tetrapods. Three distinct SRIF genes have been identified in goldfish. One of these genes, which encodes [Pro2]SRIF-14, is also present in sturgeon and African lungfish, and is closely associated with amphibian [Pro2,Met13]SRIF-14 gene and mammalian cortistatin gene. The post-translational processing of SRIF precursors could result in multiple forms of mature SRIF peptides, with differential abundance and tissue- or cell type-specific patterns. The main neuroendocrine role of SRIF-14 peptide that has been determined in fish is the inhibition of pituitary growth hormone secretion. The functions of SRIF-14 variant or larger forms of SRIF peptide and the regulation of SRIF gene expression remain to be explored. Type 1 and type 2 SRIF receptors have been identified from goldfish and a type 3 SRIF receptor has been identified from an electric fish. Fish SRIF receptors display considerable homology with mammalian counterparts in terms of primary structure and negative coupling to adenylate cyclase. Although additional types of receptors remain to be determined, identification of the multiple gene family of SRIF peptides and multiple types of SRIF receptors opens a new avenue for the study of physiological roles of SRIF, and the molecular and cellular mechanisms of SRIF action in fish.Key words: somatostatin, somatostatin receptor, growth hormone, fish.
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29
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Selmer IS, Schindler M, Humphrey PP, Emson PC. Immunohistochemical localization of the somatostatin sst(4) receptor in rat brain. Neuroscience 2000; 98:523-33. [PMID: 10869846 DOI: 10.1016/s0306-4522(00)00147-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The biological actions of the neuromodulator somatostatin are mediated through a family of G-protein-coupled receptors, of which five members, sst(1-5), have been identified. Although the messenger RNA distribution of the sst(4) receptor has been reported, no information about the distribution of the receptor protein in the central nervous system is available. We have therefore raised a polyclonal peptide antibody against a rat carboxy-terminal sst(4) peptide. The selectivity of the affinity-purified antibody was demonstrated by western blotting of membrane proteins isolated from Chinese hamster ovary-K1 cells expressing the recombinant sst(4) receptor and from the rat hippocampus. This resulted in both cases in the identification of a single band of approximately 42,000 mol. wt. Furthermore, the sst(4) receptor antibody selectively labelled Chinese hamster ovary-K1 cells expressing the recombinant sst(4) receptor in immunocytochemistry. No cross-reactivity was observed with other recombinant somatostatin receptors. Immunohistochemistry on adult rat brain sections showed the sst(4) receptor to have a widespread distribution. This included labelling of cell bodies as well as processes in the cerebral cortex, hippocampus and several nuclei in the brainstem. All signals were absent following antibody preabsorption with the synthetic sst(4) peptide. This study provides the first detailed analysis of the distribution of sst(4) receptor protein in the rat brain.
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Affiliation(s)
- I S Selmer
- Department of Neurobiology, The Babraham Institute, Babraham Hall, CB2 4AT, Cambridge, UK
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30
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Sellers LA, Alderton F, Carruthers AM, Schindler M, Humphrey PP. Receptor isoforms mediate opposing proliferative effects through gbetagamma-activated p38 or Akt pathways. Mol Cell Biol 2000; 20:5974-85. [PMID: 10913180 PMCID: PMC86074 DOI: 10.1128/mcb.20.16.5974-5985.2000] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The opposing effects on proliferation mediated by G-protein-coupled receptor isoforms differing in their COOH termini could be correlated with the abilities of the receptors to differentially activate p38, implicated in apoptotic events, or phosphatidylinositol 3-kinase (PI 3-K), which provides a source of survival signals. These contrasting growth responses of the somatostatin sst(2) receptor isoforms, which couple to identical Galpha subunit pools (Galpha(i3) > Galpha(i2) >> Galpha(0)), were both inhibited following betagamma sequestration. The sst(2(a)) receptor-mediated ATF-2 activation and inhibition of proliferation induced by basic fibroblast growth factor (bFGF) were dependent on prolonged phosphorylation of p38. In contrast, cell proliferation and the associated transient phosphorylation of Akt and p70(rsk) induced by sst(2(b)) receptors were blocked by the PI 3-K inhibitor LY 294002. Stimulation with bFGF alone had no effect on the activity of either p38 or Akt but markedly enhanced p38 phosphorylation mediated by sst(2(a)) receptors, suggesting that a complex interplay exists between the transduction cascades activated by these distinct receptor types. In addition, although all receptors mediated a sustained activation of extracellular signal-regulated kinases (ERK1 and ERK2), induction of the tumor suppressor p21(cip1) was detected only following amplification of ERK and p38 phosphorylation by concomitant bFGF and sst(2(a)) receptor activation. Expression of constitutively active Akt in the presence of a p38 inhibitor enabled a proliferative response to be detected in sst(2(a)) receptor-expressing cells. These findings demonstrate that the duration of activation and a critical balance between the mitogen-activated protein kinase and PI 3-K pathways are important for controlling cell proliferation and that the COOH termini of the sst(2) receptor isoforms may determine the selection of appropriate betagamma-pairings necessary for interaction with distinct kinase cascades.
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Affiliation(s)
- L A Sellers
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Cambridge CB2 1QJ, United Kingdom
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31
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Selmer I, Schindler M, Allen JP, Humphrey PP, Emson PC. Advances in understanding neuronal somatostatin receptors. REGULATORY PEPTIDES 2000; 90:1-18. [PMID: 10828487 DOI: 10.1016/s0167-0115(00)00108-7] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has long been considered that somatostatin acts as a neuromodulator in the mammalian central nervous system but its precise physiological roles remain elusive. Early studies to identify somatostatin-binding sites revealed a widespread heterogeneous pattern, especially in the CNS. More recently, a family of somatostatin receptors have been identified, of which five genes (sst(1-5)) have been cloned. In this review, we discuss current data describing the localisation of the five receptor types. Recent progress in understanding their function has been made using high-affinity, selective receptor ligands and transgenic animal technology. Finally, the therapeutic potential for somatostatin receptor-selective compounds as analgesics is considered.
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Affiliation(s)
- I Selmer
- Department of Neurobiology, The Babraham Institute, Babraham Hall, CB2 4EF, Cambridge, UK.
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32
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Feniuk W, Jarvie E, Luo J, Humphrey PP. Selective somatostatin sst(2) receptor blockade with the novel cyclic octapeptide, CYN-154806. Neuropharmacology 2000; 39:1443-50. [PMID: 10818260 DOI: 10.1016/s0028-3908(00)00035-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The cyclic octapeptide, CYN-154806, inhibited specific [(125)I]-[Tyr(11)]-SRIF binding to CHO-K1 cell membranes expressing human recombinant somatostatin (SRIF) sst(2) receptors (pIC(50) 8. 58) or rat sst(2(a)) and rat sst(2(b)) receptors (pIC(50) 8.35 and 8. 10, respectively). The affinity of CYN-154806 at other human somatostatin receptor types was at least 100 times lower (pIC(50) 5. 41-6.48). In functional studies, CYN-154806 inhibited SRIF-induced increases in extracellular acidification (EAR) in CHO-K1 cells expressing h sst(2) receptors (pK(B) 7.92) but had no effect on UTP-induced increases in EAR. CYN-154806 also blocked SRIF-induced increases [(35)S]-GTPgammaS binding in CHO-K1 cell membranes expressing h sst(2) receptors as well as rat sst(2(a)) and rat sst(2(b)) receptors (pK(B) 7.81, 7.68 and 7.96, respectively). In marked contrast, no blockade was observed at h sst(5) receptors in concentrations as high 10 microM. The antagonistic activity of CYN-154806 was also studied in isolated tissue preparations that are known to express endogenous SRIF receptors. Thus CYN-154806 blocked SRIF, but not DAMGO-induced inhibition of neurogenic contractions in rat isolated vas deferens and guinea-pig ileum (pK(B) 7.79 and 7.49, respectively). CYN-154806 had no effect on SRIF-28 induced inhibition of neurogenic contractions in guinea-pig vas deferens. The results demonstrate that CYN-154806 is a highly potent specific and selective SRIF sst(2) receptor blocking drug. Furthermore, sst(2) receptors mediate SRIF-induced inhibition of neurogenic contractions in rat vas deferens and guinea-pig ileum but not guinea-pig vas deferens which is thought to be mediated by sst(5) receptors.
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Affiliation(s)
- W Feniuk
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, Tennis Court Road, CB2 1QJ, Cambridge, UK.
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33
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Cole SL, Schindler M. Characterisation of somatostatin sst2 receptor splice variants. JOURNAL OF PHYSIOLOGY, PARIS 2000; 94:217-37. [PMID: 11088000 DOI: 10.1016/s0928-4257(00)00207-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Somatostatin is a peptide with a multitude of functions in the central nervous system and the periphery. It mediates its actions by binding to high-affinity G-protein coupled receptors, genes for five of which (sst1-sst5) have recently been cloned. The somatostatin sst2 receptor exists as two splice variants, sst2(a) and sst2(b) receptors, which differ in length and composition of their intracellular carboxy-termini. In this review, we describe the localisation of the two receptor isoforms in the central nervous system, the periphery and also in tumour tissue. Furthermore, we summarise and discuss the data on the functional properties of the recombinant splice variants that have been generated so far, which include activation of extracellular acidification rates, inhibition of adenylate cyclase and activation of MAP-kinases as well as the transcription factor Elk-1.
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Affiliation(s)
- S L Cole
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, UK
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34
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Kraus J, Wöltje M, Schönwetter N, Höllt V. Gene structure and regulation of the somatostatin receptor type 2. JOURNAL OF PHYSIOLOGY, PARIS 2000; 94:199-204. [PMID: 11087997 DOI: 10.1016/s0928-4257(00)00205-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The diverse biological effects of the hormone somatostatin are mediated by five genetic different receptor subtypes (sst1-sst5), which belong to the superfamily of G-protein coupled receptors with seven transmembrane domains. The sst2 subtype is unique among the somatostatin receptors in its structure, since it is expressed in two protein variants which differ within their carboxy-terminal ends, generated by alternative splicing. Within the 5' untranslated region of the gene two introns separate three transcriptional units with distinct promoters. Due to the latter feature, the sst2 gene is also unique among all somatostatin receptor genes regarding its transcriptional regulation. The three alternative promoters are tissue specifically active and show alternative responsiveness to extracellular signals. The second sst2 promoter is important for expression of the gene in tissues where somatostatin has essential physiological functions, such as brain, pituitary and gastrointestinal tissues. Furthermore, it contains cis-acting regulatory elements involved in the transcriptional response to elevated cyclic AMP levels and glucocorticoids.
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Affiliation(s)
- J Kraus
- Institut für Pharmakologie und Toxikologie, Universität Magdeburg, Germany.
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35
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Petrucci C, Cervia D, Buzzi M, Biondi C, Bagnoli P. Somatostatin-induced control of cytosolic free calcium in pituitary tumour cells. Br J Pharmacol 2000; 129:471-84. [PMID: 10711345 PMCID: PMC1571859 DOI: 10.1038/sj.bjp.0703075] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
1. In rat pituitary tumour cells (GC cells), spontaneous oscillations of the intracellular concentration of Ca2+ ([Ca2+]i) induce growth hormone (GH) secretion that is inhibited by octreotide, a somatostatin (SRIF) agonist which binds to SRIF subtype (sst) receptor 2. The effects of its functional activation on the control of [Ca2+]i were investigated using fluorimetric measurements of [Ca2+]i. 2. SRIF decreases the basal [Ca2+]i and the [Ca2+]i rise in response to forskolin (FSK) through the inhibition of L-type voltage-dependent Ca2+ channels. 3. Pretreatment with octreotide or with L-Tyr8++ Cyanamid 154806, a sst2 receptor antagonist, abolishes the SRIF-induced inhibition of [Ca2+]i. Octreotide is known to operate through agonist-induced desensitization, while the antagonist operates through receptor blockade. 4. sst1 and sst2 receptor-immunoreactivities (-IRs) are localized to cell membranes. sst2, but not sst1 receptor-IR, internalizes after cell exposure to octreotide. 5. SRIF-induced inhibition of basal [Ca2+]i or FSK-induced Ca2+ entry is blocked by pertussis toxin (PTX). 6. FSK-induced cyclic AMP accumulation is only partially decreased by SRIF or octreotide, indicating that sst2 receptors are coupled to intracellular pathways other than adenylyl cyclase (AC) inhibition. 7. In the presence of H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA), SRIF-induced inhibition of basal [Ca2+]i is still present, although reduced in amplitude. 8. SRIF inhibits [Ca2+]i by activating sst2 receptors. Inhibition of AC activity is only partly responsible for this effect, and other transduction pathways may be involved.
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Affiliation(s)
- Cristina Petrucci
- Department of Physiology and Biochemistry ‘G. Moruzzi', University of Pisa, Via S. Zeno, 31-56127 Pisa, Italy
| | - Davide Cervia
- Department of Physiology and Biochemistry ‘G. Moruzzi', University of Pisa, Via S. Zeno, 31-56127 Pisa, Italy
| | - Marco Buzzi
- Department of Biology, University of Ferrara, 44100 Ferrara, Italy
| | - Carla Biondi
- Department of Biology, University of Ferrara, 44100 Ferrara, Italy
| | - Paola Bagnoli
- Department of Physiology and Biochemistry ‘G. Moruzzi', University of Pisa, Via S. Zeno, 31-56127 Pisa, Italy
- Author for correspondence:
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36
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Schindler M, Humphrey PP, Löhrke S, Friauf E. Immunohistochemical localization of the somatostatin sst2(b) receptor splice variant in the rat central nervous system. Neuroscience 1999; 90:859-74. [PMID: 10218786 DOI: 10.1016/s0306-4522(98)00483-7] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Somatostatin is a neuromodulator in the mammalian CNS. To date, genes for at least five different somatotrophin release inhibiting factor receptors, termed sst1-sst5, have been cloned. The rat sst2 receptor exists in two splice variants, sst(alpha)a) and sst2(b), which differ in their carboxy-termini. When heterologously expressed in Chinese hamster ovary-K1 cells, these splice variants show little difference in their operational characteristics. Recently, the distribution of the sst2(a) receptor was documented, yet at present no data are available about the distribution of the sst2(b) receptor in the CNS. Here, we present the characterization of a novel polyclonal anti-peptide antibody that is selective for the sst2(b) receptor splice variant. The antibody was raised against the unique intracellular carboxy-terminal portion of the receptor protein. Using this affinity-purified antibody in western blotting experiments, the sst2(b) receptor expressed in Chinese hamster ovary-K1 cells was shown to be a glycoprotein with a molecular weight centred at about 85,000. The antibody showed no cross-reactivity to any of the recombinant human sst1-5 receptors, the rat sst2(a) receptor or wild-type Chinese hamster ovary-K1 cells. Employing immunohistochemistry, we investigated the distribution of the sst2(b) receptor in the brain and spinal cord of adult rats. A distinct distribution was found throughout the rostrocaudal axis of the CNS. Somatodendritic as well as axonal staining was observed. Somatodendritic labelling was particularly obvious in the olfactory bulb, cerebral cortex, hippocampal formation, mesencephalic trigeminal nucleus and cerebellum, as well as in cranial and spinal motor areas. The results show that the distribution of the sst2(b) receptor partially overlaps with that of the sst2(b) receptor, although there were differences in a number of brain areas. The location of the sst2(b) receptor implies that it may mediate a modulatory role of somatostatin inhibitory releasing factor on sensory as well as motor functions.
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Affiliation(s)
- M Schindler
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, UK
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37
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Alderton F, Fan TP, Schindler M, Humphrey PP. Rat somatostatin sst2(a) and sst2(b) receptor isoforms mediate opposite effects on cell proliferation. Br J Pharmacol 1998; 125:1630-3. [PMID: 9886753 PMCID: PMC1565767 DOI: 10.1038/sj.bjp.0702282] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We have investigated the actions of somatostatin (SRIF) and angiopeptin on cell proliferation of CHO-K1 cells expressing the recently cloned rat sst2(b) receptor (CHOsst2(b)) and compared these to their effects in cells expressing the sst2(a) receptor (CHOsst2(a)). In contrast to the sst2(a) receptor, the sst2(b) receptor did not mediate inhibition of bFGF (10 ng ml(-1))-stimulated re-growth and cell proliferation. Rather, SRIF (0.1-1000 nM) and angiopeptin (0.1-1000 nM) stimulated basal re-growth and proliferation of CHOsst2(b) cells in a concentration-dependent manner (estimated pEC50 values of 7.8 and 7.9, respectively). The opposite effects of SRIF on cell proliferation mediated through the two sst2 receptor isoforms were both abolished by 18 h pre-treatment with pertussis toxin. The proliferative effect via the sst2(b) receptor was also abolished by the tyrosine kinase inhibitor, genistein. In conclusion, the present study shows that the rat sst2(a) and sst2(b) receptor splice variants mediate opposite effects on cell proliferation.
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Affiliation(s)
- F Alderton
- Glaxo Institute of Applied Pharmacology, University of Cambridge
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