1
|
Tang C, Ksiazek I, Siccardi N, Gapp B, Weber D, Wirsching J, Beck V, Reist M, Gaudet L, Stuber N, Surber SS, Mao X, Nicholson TB, Carbone W, Beibel M, Roma G, Gubser Keller C, Bassilana F. UTS2B Defines a Novel Enteroendocrine Cell Population and Regulates GLP-1 Secretion Through SSTR5 in Male Mice. Endocrinology 2019; 160:2849-2860. [PMID: 31556942 DOI: 10.1210/en.2019-00549] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 09/20/2019] [Indexed: 12/25/2022]
Abstract
The gut-pancreas axis plays a key role in the regulation of glucose homeostasis and may be therapeutically exploited to treat not only type 2 diabetes but also hypoglycemia and hyperinsulinemia. We identify a novel enteroendocrine cell type expressing the peptide hormone urotensin 2B (UTS2B). UTS2B inhibits glucagon-like peptide-1 (GLP-1) secretion in mouse intestinal crypts and organoids, not by signaling through its cognate receptor UTS2R but through the activation of the somatostatin receptor (SSTR) 5. Circulating UTS2B concentrations in mice are physiologically regulated during starvation, further linking this peptide hormone to metabolism. Furthermore, administration of UTS2B to starved mice demonstrates that it is capable of regulating blood glucose and plasma concentrations of GLP-1 and insulin in vivo. Altogether, our results identify a novel cellular source of UTS2B in the gut, which acts in a paracrine manner to regulate GLP-1 secretion through SSTR5. These findings uncover a fine-tuning mechanism mediated by a ligand-receptor pair in the regulation of gut hormone secretion, which can potentially be exploited to correct metabolic unbalance caused by overactivation of the gut-pancreas axis.
Collapse
Affiliation(s)
- Cong Tang
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Iwona Ksiazek
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Noemie Siccardi
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Berangere Gapp
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Delphine Weber
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | | | - Valerie Beck
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Matthias Reist
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Laurent Gaudet
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Nathalie Stuber
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | | | - Xiaohong Mao
- Novartis Institutes for BioMedical Research, Cambridge, Massachusetts
| | | | - Walter Carbone
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Martin Beibel
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Guglielmo Roma
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | | | | |
Collapse
|
2
|
Olsen C, Memarzadeh K, Ulu A, Carr HS, Bean AJ, Frost JA. Regulation of Somatostatin Receptor 2 Trafficking by C-Tail Motifs and the Retromer. Endocrinology 2019; 160:1031-1043. [PMID: 30822353 PMCID: PMC6462214 DOI: 10.1210/en.2018-00865] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 02/25/2019] [Indexed: 12/15/2022]
Abstract
The Gi-coupled somatostatin receptor 2 (SST2) is a G protein-coupled receptor (GPCR) that mediates many of somatostatin's neuroendocrine actions. Upon stimulation, SST2 is rapidly internalized and transported to early endosomes before being recycled to the plasma membrane. However, little is known about the intracellular itinerary of SST2 after it moves to the early endosomal compartment or the cytoplasmic proteins that regulate its trafficking. As postsynaptic density protein/discs large 1/zonula occludens-1 (PDZ) domain interactions often regulate the trafficking and signaling potential of GPCRs, we examined the role of the SST2 PDZ ligand and additional C-terminal residues in controlling its intracellular trafficking. We determined that SST2 can recycle to the plasma membrane via multiple pathways, including a LAMP1/Rab7-positive late endosome to the trans-Golgi network (TGN) pathway. Trafficking from the late endosome to the TGN is often regulated by the retromer complex of endosomal coat proteins, and disrupting the retromer components sorting nexins 1/2 inhibits the budding of SST2 from late endosomes. Moreover, trafficking through the late endosomal/TGN pathway is dependent on an intact PDZ ligand and C-terminal tail, as truncating either the 3 or 10 C-terminal amino acids of SST2 alters the pathway through which it recycles to the plasma membrane. Moreover, addition of these amino acids to a heterologous receptor is sufficient to redirect it from a degradation pathway to a recycling itinerary. Our results demonstrate that endosomal trafficking of SST2 is dependent on numerous regulatory mechanisms controlled by its C terminus and the retromer machinery.
Collapse
Affiliation(s)
- Courtney Olsen
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
- MD Anderson UTHealth Graduate School of Biomedical Sciences, Houston, Texas
| | - Kimiya Memarzadeh
- MD Anderson UTHealth Graduate School of Biomedical Sciences, Houston, Texas
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, Texas
| | - Arzu Ulu
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | - Heather S Carr
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
| | - Andrew J Bean
- MD Anderson UTHealth Graduate School of Biomedical Sciences, Houston, Texas
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, Texas
- Department of Pediatrics, University of Texas MD Anderson Cancer Center, Houston, Texas
| | - Jeffrey A Frost
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, Texas
- MD Anderson UTHealth Graduate School of Biomedical Sciences, Houston, Texas
| |
Collapse
|
3
|
Rodriguez M, Frost JA, Schonbrunn A. Real-Time Signaling Assays Demonstrate Somatostatin Agonist Bias for Ion Channel Regulation in Somatotroph Tumor Cells. J Endocr Soc 2018; 2:779-793. [PMID: 30151433 PMCID: PMC6106105 DOI: 10.1210/js.2018-00115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 06/11/2018] [Indexed: 11/19/2022] Open
Abstract
Acromegaly is a neuroendocrine disorder caused by excess secretion of GH by somatotroph tumor cells. It is often treated with somatostatin receptor (SSTR) 2 agonists, which suppress GH secretion. SOM230 is a somatostatin analogue that targets multiple SSTRs and was recently approved for patients with treatment-resistant acromegaly. Previous reports indicate that SOM230 may function as a biased agonist, suggesting that its ability to selectively activate SSTR-dependent signaling events may contribute to its therapeutic efficacy. To better understand how SOM230 modulates Sstr2A function, which is the most commonly expressed SSTR in somatotrophs, we used real-time assays to study SOM230-dependent signaling in rat pituitary tumor cells. We observed that SOM230 suppressed cAMP production in a Gαi-dependent manner, similar to conventional Sstr2A agonists. However, it did not cause receptor internalization as would be expected for an Sstr2A agonist. Surprisingly, SOM230 did not cause membrane hyperpolarization, which is an important mechanism by which Sstr2a activation suppresses intracellular calcium (Ca2+) accumulation and GH secretion. In fact, SOM230 inhibited the ability of conventional somatostatin analogues to control membrane potential. However, SOM230 still inhibited intracellular Ca2+ accumulation in a novel, Gβγ-dependent manner. These studies show that SOM230 exhibits strong agonist bias in regulating signaling pathways downstream of Sstr2A that control GH secretion.
Collapse
Affiliation(s)
- Melissa Rodriguez
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas
| | - Jeffrey A Frost
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas
| | - Agnes Schonbrunn
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas
| |
Collapse
|
4
|
Therapeutic uses of somatostatin and its analogues: Current view and potential applications. Pharmacol Ther 2015; 152:98-110. [PMID: 25956467 DOI: 10.1016/j.pharmthera.2015.05.007] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Accepted: 04/28/2015] [Indexed: 01/22/2023]
Abstract
Somatostatin is an endogeneous cyclic tetradecapeptide hormone that exerts multiple biological activities via five ubiquitously distributed receptor subtypes. Classified as a broad inhibitory neuropeptide, somatostatin has anti-secretory, anti-proliferative and anti-angiogenic effects. The clinical use of native somatostatin is limited by a very short half-life (1 to 3min) and the broad spectrum of biological responses. Thus stable, receptor-selective agonists have been developed. The majority of these somatostatin therapeutic agonists bind strongly to two of the five receptor subtypes, although recently an agonist of wider affinity has been introduced. Somatostatin agonists are established in the treatment of acromegaly with recently approved indications in the therapy of neuroendocrine tumours. Potential therapeutic uses for somatostatin analogues include diabetic complications like retinopathy, nephropathy and obesity, due to inhibition of IGF-1, VEGF together with insulin secretion and effects upon the renin-angiotensin-aldosterone system. Wider uses in anti-neoplastic therapy may also be considered and recent studies have further revealed anti-inflammatory and anti-nociceptive effects. This review provides a comprehensive, current view of the biological functions of somatostatin and potential therapeutic uses, informed by the wide range of pharmacological advances reported since the last published review in 2004 by P. Dasgupta. The pharmacology of somatostatin receptors is explained, the current uses of somatostatin agonists are discussed, and the potential future of therapeutic applications is explored.
Collapse
|
5
|
Horváth K, Boros M, Bagoly T, Sándor V, Kilár F, Kemény A, Helyes Z, Szolcsányi J, Pintér E. Analgesic topical capsaicinoid therapy increases somatostatin-like immunoreactivity in the human plasma. Neuropeptides 2014; 48:371-8. [PMID: 25455106 DOI: 10.1016/j.npep.2014.10.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 10/02/2014] [Accepted: 10/07/2014] [Indexed: 01/26/2023]
Abstract
The aim of the present study was to evaluate the therapeutic potential of local capsaicinoid (EMSPOMA(®) cream) treatment on chronic low back pain in patients with degenerative spine diseases and to investigate the possible mechanism of action of the therapy. The qualitative and quantitative analyses of capsaicinoids in EMSPOMA(®) cream were performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In the clinical study 20 patients with degenerative spine diseases were involved in a self-controlled examination. During the 21 day therapy they received 30 min daily treatment with capsaicinoid (EMSPOMA(®)) cream to the lumbar region of the back. The pain (VASs, Oswestry Disability Index) and the mobility of the lumbar region of the spine (Schober's, Domján's L and R test) were detected at baseline and at the end of the 1st, 2nd and 3rd weeks. The plasma level of somatostatin-like immunoreactivity (SST-LI) was measured by radioimmunoassay (RIA) before and after the treatment on the first and the last day of the therapy. Nonivamide (0.01%) was identified as the only capsaicinoid molecule in the cream. In the clinical study the 21 day local nonivamide treatment reduced the pain sensation. Oswestry Disability Index decreased from 39 ± 3.9% to 32.5 ± 4.4%. VASs showed 37.29%-59.51% improvement. In the plasma level of SST-LI threefold elevation was observed after the first nonivamide treatment. We conclude that nonivamide treatment exerts analgesic action in chronic low back pain and causes the release of the antinociceptive and anti-inflammatory neuropeptide somatostatin which may play pivotal role in the pain-relieving effect.
Collapse
Affiliation(s)
- Katalin Horváth
- Zsigmondy Vilmos Harkány Medicinal Spa Hospital, 1 Zsigmondy Street, Harkány 7815, Hungary
| | - Melinda Boros
- Department of Pharmacology and Pharmacotherapy, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary
| | - Teréz Bagoly
- Department of Pharmacology and Pharmacotherapy, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary
| | - Viktor Sándor
- MTA-PTE Molecular Interactions in Separation Science Research Group, 12 Szigeti Street, Pécs 7624, Hungary; Szentágothai Research Center, University of Pécs, 20 Ifjúság Street, Pécs 7624, Hungary
| | - Ferenc Kilár
- Department of Bioanalysis, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary; Szentágothai Research Center, University of Pécs, 20 Ifjúság Street, Pécs 7624, Hungary
| | - Agnes Kemény
- Department of Pharmacology and Pharmacotherapy, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary; Szentágothai Research Center, University of Pécs, 20 Ifjúság Street, Pécs 7624, Hungary
| | - Zsuzsanna Helyes
- Department of Pharmacology and Pharmacotherapy, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary; Szentágothai Research Center, University of Pécs, 20 Ifjúság Street, Pécs 7624, Hungary
| | - János Szolcsányi
- Department of Pharmacology and Pharmacotherapy, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary
| | - Erika Pintér
- Department of Pharmacology and Pharmacotherapy, University of Pécs, 12 Szigeti Street, Pécs 7624, Hungary; Szentágothai Research Center, University of Pécs, 20 Ifjúság Street, Pécs 7624, Hungary.
| |
Collapse
|
6
|
Reubi JC, Schonbrunn A. Illuminating somatostatin analog action at neuroendocrine tumor receptors. Trends Pharmacol Sci 2013; 34:676-88. [PMID: 24183675 DOI: 10.1016/j.tips.2013.10.001] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 09/26/2013] [Accepted: 10/03/2013] [Indexed: 02/08/2023]
Abstract
Somatostatin analogs for the diagnosis and therapy of neuroendocrine tumors (NETs) have been used in clinical applications for more than two decades. Five somatostatin receptor subtypes have been identified and molecular mechanisms of somatostatin receptor signaling and regulation have been elucidated. These advances increased understanding of the biological role of each somatostatin receptor subtype, their distribution in NETs, as well as agonist-specific regulation of receptor signaling, internalization, and phosphorylation, particularly for the sst2 receptor subtype, which is the primary target of current somatostatin analog therapy for NETs. Various hypotheses exist to explain differences in patient responsiveness to somatostatin analog inhibition of tumor secretion and growth as well as differences in the development of tumor resistance to therapy. In addition, we now have a better understanding of the action of both first generation (octreotide, lanreotide, Octreoscan) and second generation (pasireotide) FDA-approved somatostatin analogs, including the biased agonistic character of some agonists. The increased understanding of somatostatin receptor pharmacology provides new opportunities to design more sophisticated assays to aid the future development of somatostatin analogs with increased efficacy.
Collapse
Affiliation(s)
- Jean Claude Reubi
- Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Berne, Berne, Switzerland.
| | | |
Collapse
|
7
|
Theodoropoulou M, Stalla GK. Somatostatin receptors: from signaling to clinical practice. Front Neuroendocrinol 2013; 34:228-52. [PMID: 23872332 DOI: 10.1016/j.yfrne.2013.07.005] [Citation(s) in RCA: 241] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 06/13/2013] [Accepted: 07/12/2013] [Indexed: 02/08/2023]
Abstract
Somatostatin is a peptide with a potent and broad antisecretory action, which makes it an invaluable drug target for the pharmacological management of pituitary adenomas and neuroendocrine tumors. Somatostatin receptors (SSTR1, 2A and B, 3, 4 and 5) belong to the G protein coupled receptor family and have a wide expression pattern in both normal tissues and solid tumors. Investigating the function of each SSTR in several tumor types has provided a wealth of information about the common but also distinct signaling cascades that suppress tumor cell proliferation, survival and angiogenesis. This provided the rationale for developing multireceptor-targeted somatostatin analogs and combination therapies with signaling-targeted agents such as inhibitors of the mammalian (or mechanistic) target of rapamycin (mTOR). The ability of SSTR to internalize and the development of rabiolabeled somatostatin analogs have improved the diagnosis and treatment of neuroendocrine tumors.
Collapse
Affiliation(s)
- Marily Theodoropoulou
- Department of Endocrinology, Max Planck Institute of Psychiatry, Kraepelinstrasse 10, 80804 Munich, Germany.
| | | |
Collapse
|
8
|
Wang J, Cao DY, Guo Y, Ma SJ, Luo R, Pickar JG, Zhao Y. Octreotide inhibits capsaicin-induced activation of C and Aδ afferent fibres in rat hairy skin in vivo. Clin Exp Pharmacol Physiol 2012; 38:521-7. [PMID: 21595740 DOI: 10.1111/j.1440-1681.2011.05542.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
1. The present study investigated whether the somatostatin receptor (SSTR) agonist, octreotide, could inhibit the activation of dorsal skin afferent fibres induced by local injection of capsaicin in the rat. 2. Single unit activity from Aδ mechano-heat sensitive (AMH; n = 41) and C mechano-heat sensitive (CMH; n = 30) afferents was recorded after their isolation in thin filaments from the dorsal cutaneous nerve branches. The effect of subcutaneous octreotide injection on the change in discharge rate and mechanical threshold induced by capsaicin was determined. 3. Capsaicin (0.05%) injection into the edge of the receptive field of both AMH and CMH units increased their discharge rate and decreased their mechanical threshold. Pre-injection of octreotide inhibited these responses, and co-application of SSTR antagonist, cyclosomatostatin, reversed the inhibitory effect of octreotide. 4. The present study provides electrophysiological evidence that the signal evoked by the somatostatin receptor inhibits the activation and mechanical sensitization evoked by capsaicin in the terminals in small-diameter sensory neurons.
Collapse
Affiliation(s)
- Jun Wang
- Department of Physiology and Pathophysiology, Xi'an Jiaotong University School of Medicine, Shaanxi, China
| | | | | | | | | | | | | |
Collapse
|
9
|
Abstract
Endocrine pituitary cells are neuronlike; they express numerous voltage-gated sodium, calcium, potassium, and chloride channels and fire action potentials spontaneously, accompanied by a rise in intracellular calcium. In some cells, spontaneous electrical activity is sufficient to drive the intracellular calcium concentration above the threshold for stimulus-secretion and stimulus-transcription coupling. In others, the function of these action potentials is to maintain the cells in a responsive state with cytosolic calcium near, but below, the threshold level. Some pituitary cells also express gap junction channels, which could be used for intercellular Ca(2+) signaling in these cells. Endocrine cells also express extracellular ligand-gated ion channels, and their activation by hypothalamic and intrapituitary hormones leads to amplification of the pacemaking activity and facilitation of calcium influx and hormone release. These cells also express numerous G protein-coupled receptors, which can stimulate or silence electrical activity and action potential-dependent calcium influx and hormone release. Other members of this receptor family can activate calcium channels in the endoplasmic reticulum, leading to a cell type-specific modulation of electrical activity. This review summarizes recent findings in this field and our current understanding of the complex relationship between voltage-gated ion channels, ligand-gated ion channels, gap junction channels, and G protein-coupled receptors in pituitary cells.
Collapse
Affiliation(s)
- Stanko S Stojilkovic
- Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Building 49, Room 6A-36, 49 Convent Drive, Bethesda, Maryland 20892-4510, USA.
| | | | | |
Collapse
|
10
|
Luo R, Guo Y, Cao DY, Pickar JG, Li L, Wang J, Zhao Y. Local effects of octreotide on glutamate-evoked activation of Aδ and C afferent fibers in rat hairy skin. Brain Res 2010; 1322:50-8. [DOI: 10.1016/j.brainres.2010.01.058] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Revised: 01/19/2010] [Accepted: 01/22/2010] [Indexed: 10/19/2022]
|
11
|
Tonic inhibition of somatostatin on C and Aδ afferent fibers in rat dorsal skin in vivo. Brain Res 2009; 1288:50-9. [DOI: 10.1016/j.brainres.2009.06.088] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2009] [Revised: 06/11/2009] [Accepted: 06/30/2009] [Indexed: 11/18/2022]
|
12
|
Bell GI, Yasuda K, Kong H, Law SF, Raynor K, Reisine T. Molecular biology of somatostatin receptors. CIBA FOUNDATION SYMPOSIUM 2007; 190:65-79; discussion 80-8. [PMID: 7587653 DOI: 10.1002/9780470514733.ch5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The diverse physiological effects of somatostatin are mediated by a family of cell surface receptors that bind somatostatin selectively and with high affinity. The somatostatin receptors are members of the seven transmembrane segment receptor superfamily and molecular cloning studies have identified five types, designated sstr1-5. The human somatostatin receptors vary in size from 364 (sstr5) to 418 (sstr3) amino acids with 46-61% amino acid identity between receptors, and 105 amino acids are invariant. The sequences of the seven putative alpha-helical membrane-spanning domains are more highly conserved than those of the extracellular N- and intracellular C-terminal domains. Two forms of sstr2 have been identified in the mouse, sstr2A and sstr2B, which differ in size and sequence of the intracellular C-terminal domain. These two forms of sstr2 are products of a common gene and are generated by alternative splicing with sstr2A and sstr2B being the products of the unspliced and spliced forms, respectively, of sstr2 mRNA. Thus, functional diversity within the somatostatin receptor family may result from the expression of multiple types as well as from alternative splicing. The five somatostatin receptors have distinct patterns of expression in the central nervous system and peripheral tissues. They have also been expressed in vitro and shown to have different pharmacological properties. Somatostatin analogues selective for sstr2, sstr3 and sstr5 have been identified which will facilitate in vivo studies of the functions of these somatostatin receptors. Such studies to date suggest that sstr2 mediates inhibition of growth hormone secretion and sstr5 mediates inhibition of insulin secretion. The molecular cloning and functional characterization of the somatostatin receptor family is a first step in elucidating the diverse effects of somatostatin on cellular functions.
Collapse
Affiliation(s)
- G I Bell
- Howard Hughes Medical Institute, University of Chicago, IL 60637, USA
| | | | | | | | | | | |
Collapse
|
13
|
Pintér E, Helyes Z, Szolcsányi J. Inhibitory effect of somatostatin on inflammation and nociception. Pharmacol Ther 2006; 112:440-56. [PMID: 16764934 DOI: 10.1016/j.pharmthera.2006.04.010] [Citation(s) in RCA: 170] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2006] [Accepted: 04/27/2006] [Indexed: 10/24/2022]
Abstract
The present review focuses on promising new opportunities for anti-inflammatory and analgesic therapy. The theoretical background is an original observation based on our own experimental results. These data demonstrate that somatostatin is released from capsaicin-sensitive, peptidergic sensory nerve endings in response to noxious heat and chemical stimuli such as vanilloids, protons or lipoxygenase products. It reaches distant parts of the body via the circulation and exerts systemic anti-inflammatory and analgesic effects. Somatostatin binds to G-protein-coupled membrane receptors (sst(1)-sst(5)) and diminishes neurogenic inflammation by prejunctional action on sensory-efferent nerve terminals, as well as by postjunctional mechanisms on target cells. It decreases the release of pro-inflammatory neuropeptides from sensory nerve endings and also acts on receptors of vascular endothelial, inflammatory and immune cells. Analgesic effect is mediated by an inhibitory action on peripheral terminals of nociceptive neurons, since circulating somatostatin cannot exert central action. Somatostatin itself is not suitable for drug development because of its broad spectrum and short elimination half life, stable, receptor-selective agonists have been synthesized and investigated. The present overview is aimed at summarizing the physiological importance of somatostatin and sst receptors, pharmacological significance of synthetic agonists and their potential in the development of novel anti-inflammatory and analgesic drugs. These compounds might provide novel perspectives in the pharmacotherapy of acute and chronic painful inflammatory diseases, as well as neuropathic conditions.
Collapse
Affiliation(s)
- Erika Pintér
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Pécs, H-7624 Pécs, Szigeti u. 12, Hungary.
| | | | | |
Collapse
|
14
|
Abstract
Somatostatin (SST) peptide is produced by various SST-secreting cells throughout the body and acts as a neurotransmitter or paracrine/autocrine regulator in response to ions, nutrients, peptides hormones and neurotransmitters. SST is also widely distributed in the periphery to regulate the inflammatory and immune cells in response to hormones, growth factors, cytokines and other secretive molecules. SST peptides are considered the most important physiologic regulator of the islet cell, gastrointestinal cell and immune cell functions, and the importance of SST production levels has been implicated in several diseases including diabetes. The expression of SST receptors has also been found in T lymphocytes and primary immunologic organs. Interaction of SST and its receptors is also involved in T-cell proliferation and thymocyte selection. SSTR gene-ablated mice developed diabetes with morphologic, physiologic and immunologic alterations in the endocrine pancreas. Increased levels of mononuclear cell infiltration of the islets are associated with the increased levels of antigen-presenting cells located in the islets and peripancreatic lymph nodes. Increased levels of SST were also found in antigen-presenting cells and are associated with a significant increase of CD8 expression levels on CD4(+)/CD8(+) immature thymocytes. These findings highlight the crucial role of this neuroendocrine peptide and its receptors in regulating autoimmune functions.
Collapse
Affiliation(s)
- Xaio-Ping Wang
- The Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA.
| | | | | |
Collapse
|
15
|
Carlton SM, Zhou S, Du J, Hargett GL, Ji G, Coggeshall RE. Somatostatin modulates the transient receptor potential vanilloid 1 (TRPV1) ion channel. Pain 2004; 110:616-627. [PMID: 15288402 DOI: 10.1016/j.pain.2004.04.042] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2004] [Revised: 04/14/2004] [Accepted: 04/26/2004] [Indexed: 11/24/2022]
Abstract
Activation of peripheral somatostatin receptors (SSTRs) inhibits sensitization of nociceptors, thus having a short term or phasic effect [Pain 90 (2001) 233] as well as maintaining a tonic inhibitory control over nociceptors [J Neurosci 21 (2001) 4042]. The present study provides several lines of evidence that an important mechanism underlying SSTR modulation of nociceptors is regulation of the transient receptor potential vanilloid 1 ion channel (TRPV1, formerly the VR1 receptor). Double labeling of L5 dorsal root ganglion cells demonstrates that approximately 60% of SSTR2a-labeled cells are positive for TRPV1. Conversely, approximately 33% of TRPV1-labeled cells are positive for SSTR2a. In vivo behavioral studies demonstrate that intraplantar injection of 20.0 but not 2.0 microM octreotide (OCT, SSTR agonist) significantly reduces capsaicin (CAP, a ligand for TRPV1) -induced flinching and lifting/licking behaviors. This occurs through local activation of SSTRs in the injected hindpaw and is reversed following co-application of the SSTR antagonist cyclo-somatostatin (c-SOM). In vitro studies using a skin-nerve preparation demonstrate that activation of peripheral SSTRs on nociceptors with 20.0 microM OCT significantly reduces CAP-induced activity and can prevent CAP-induced desensitization. Furthermore, blockade of peripheral SSTRs with c-SOM dramatically enhances CAP-induced behaviors and nociceptor activity, demonstrating SSTR-induced tonic inhibitory modulation of TRPV1. Finally, TRPV1 does not appear to be under tonic opioid receptor control since the opioid antagonist naloxone does not change CAP-induced excitation and does not effect OCT-induced inhibition of CAP responses. These data strongly suggest that SSTRs modulate nociceptors through phasic and tonic regulation of peripheral TRPV1 receptors.
Collapse
Affiliation(s)
- Susan M Carlton
- Department of Anatomy and Neurosciences, Marine Biomedical Institute, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1069, USA
| | | | | | | | | | | |
Collapse
|
16
|
Hyde GN, Seale AP, Grau EG, Borski RJ. Cortisol rapidly suppresses intracellular calcium and voltage-gated calcium channel activity in prolactin cells of the tilapia (Oreochromis mossambicus). Am J Physiol Endocrinol Metab 2004; 286:E626-33. [PMID: 14656715 DOI: 10.1152/ajpendo.00088.2003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cortisol was previously shown to rapidly (10-20 min) reduce the release of prolactin (PRL) from pituitary glands of tilapia (Oreochromis mossambicus). This inhibition of PRL release by cortisol is accompanied by rapid reductions in (45)Ca(2+) and cAMP accumulation. Cortisol's early actions occur through a protein synthesis-independent pathway and are mimicked by a membrane-impermeable analog. The signaling pathway that mediates rapid, nongenomic membrane effects of glucocorticoids is poorly understood. Using the advantageous characteristics of the teleost pituitary gland from which a nearly pure population of PRL cells can be isolated and incubated in defined medium, we examined whether cortisol rapidly reduces intracellular free calcium (Ca(i)(2+)) and suppresses L-type voltage-gated ion channel activity in events that lead to reduced PRL release. Microspectrofluorometry, used in combination with the Ca(2+)-sensitive dye fura 2 revealed that cortisol reversibly reduces basal and hyposmotically induced Ca(i)(2+) within seconds (P < 0.001) in dispersed pituitary cells. Somatostatin, a peptide known to inhibit PRL release through a membrane receptor-coupled mechanism, similarly reduces Ca(i)(2+). Under depolarizing [K(+)], the L-type calcium channel agonist BAY K 8644, a factor known to delay the closing of L-type Ca(2+) channels, stimulates PRL release in a concentration-dependent fashion (P < 0.01). Cortisol (and somatostatin) blocks BAY K 8644-induced PRL release (P < 0.01; 30 min), well within the time course over which its actions occur, independent of protein synthesis and at the level of the plasma membrane. Results indicate that cortisol inhibits tilapia PRL release through rapid reductions in Ca(i)(2+) that likely involve an attenuation of Ca(2+) entry through L-type voltage-gated Ca(2+) channels. These results provide further evidence that glucocorticoids rapidly modulate hormone secretion via a membrane-associated mechanism similar to that observed with the fast effects of peptides and neurotransmitters.
Collapse
MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/antagonists & inhibitors
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Animals
- Anti-Inflammatory Agents/pharmacology
- Calcium/metabolism
- Calcium Channel Agonists/pharmacology
- Calcium Channel Blockers
- Calcium Channels, L-Type/drug effects
- Calcium Radioisotopes
- Cyclic AMP/metabolism
- Electrophoresis, Polyacrylamide Gel
- Fura-2
- Hormone Antagonists/pharmacology
- Hydrocortisone/pharmacology
- In Vitro Techniques
- Ion Channel Gating/drug effects
- Ion Channel Gating/physiology
- Male
- Osmotic Pressure
- Pituitary Gland, Anterior/cytology
- Pituitary Gland, Anterior/drug effects
- Pituitary Gland, Anterior/metabolism
- Prolactin/physiology
- Somatostatin/pharmacology
- Tilapia/physiology
Collapse
Affiliation(s)
- Gregory N Hyde
- Department of Zoology, North Carolina State University, Box 7617, Raleigh, NC 27695-7617, USA
| | | | | | | |
Collapse
|
17
|
Elberg G, Hipkin RW, Schonbrunn A. Homologous and heterologous regulation of somatostatin receptor 2. Mol Endocrinol 2002; 16:2502-14. [PMID: 12403839 DOI: 10.1210/me.2002-0207] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
We previously demonstrated that phosphorylation of somatostatin receptor 2A (sst2A) is rapidly increased in transfected cells both by agonist and by the protein kinase C (PKC) activator phorbol myristate acetate (PMA). Here, we investigate whether PKC-mediated receptor phosphorylation is involved in the homologous or heterologous regulation of endogenous sst2 receptors in AR42J pancreatic acinar cells upon stimulation by agonist or by cholecystokinin (CCK) or bombesin (BBS). Somatostatin, PMA, CCK, and BBS all increased sst2A receptor phosphorylation 5- to 10-fold within minutes. Somatostatin binding also caused rapid internalization of the ligand-receptor complex, and PMA, CCK, and BBS all stimulated this internalization further. Additionally, sst2 receptor-mediated inhibition of adenylyl cyclase was desensitized by all treatments. Somatostatin, as well as peptidic (SMS201-995) and nonpeptidic (L-779,976) sst2 receptor agonists increased the EC(50) for somatostatin inhibition 20-fold. In contrast, pretreatment with BBS, CCK, or PMA caused a modest 2-fold increase in the EC(50) for cyclase inhibition. Whereas the PKC inhibitor GF109203X abolished sst2A receptor phosphorylation by CCK, BBS, and PMA, it did not alter the effect of somatostatin, demonstrating that these reactions were catalyzed by different kinases. Consistent with a functional role for PKC-mediated receptor phosphorylation, GF109203X prevented PMA stimulation of sst2 receptor internalization. Surprisingly, however, GF109203X did not inhibit BBS and CCK stimulation of sst2A receptor endocytosis. These results demonstrate that homologous and heterologous hormones induce sst2A receptor phosphorylation by PKC-independent and -dependent mechanisms, respectively, and produce distinct effects on receptor signaling and internalization. In addition, the heterologous hormones also modulate sst2 receptor internalization by a novel mechanism that is independent of receptor phosphorylation.
Collapse
Affiliation(s)
- Gerard Elberg
- Department of Integrative Biology and Pharmacology, University of Texas Health Sciences Center Houston, Houston, Texas 77225, USA
| | | | | |
Collapse
|
18
|
Norman M, Moldovan S, Seghers V, Wang XP, DeMayo FJ, Brunicardi FC. Sulfonylurea receptor knockout causes glucose intolerance in mice that is not alleviated by concomitant somatostatin subtype receptor 5 knockout. Ann Surg 2002; 235:767-74. [PMID: 12035032 PMCID: PMC1422505 DOI: 10.1097/00000658-200206000-00003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To examine the long-term effects of Sur KO, SSTR5 KO, and double Sur/SSTR5 KO on insulin secretion and glucose regulation. SUMMARY BACKGROUND DATA The sulfonylurea receptor (Sur) and somatostatin receptor type 5 (SSTR5) play an integral role in the regulatory pathways of the endocrine pancreas. Sur knockout (KO) and SSTR5 KO mice were generated in the authors' laboratories and crossbred to generate Sur/SSTR5 KO mice. All mice were genotyped by Southern blotting and polymerase chain reaction analysis. METHODS One-year-old Sur KO, Sur/SSTR5 KO, SSTR5 KO, and age-matched wild-type control mice underwent single-pass perfusion of isolated pancreata with low and high glucose concentration (n = 4-6/group). Another group of mice also underwent intraperitoneal glucose tolerance tests with 1.2 g glucose/kg body weight (n = 4/group per time point). RESULTS Sur1 KO and Sur/SSTR5 KO mice had profoundly decreased insulin secretion in vitro, whereas SSTR5 KO had increased insulin secretion compared with wild-type mice. Sur1 KO and Sur/SSTR5 mice had increased glucose response in vivo compared with wild-type mice. Sur1 KO and Sur/SSTR5 KO mice exhibit glucose intolerance and SSTR5 KO mice show increased insulin response in vitro. CONCLUSIONS Sur1 KO causes glucose intolerance and SSTR5 KO causes increased insulin secretion. However, Sur/SSTR5 double ablation does not alleviate the diabetic state of the Sur1 KO.
Collapse
Affiliation(s)
- Michael Norman
- Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, Texas 77030, USA
| | | | | | | | | | | |
Collapse
|
19
|
Borski RJ, Hyde GN, Fruchtman S. Signal transduction mechanisms mediating rapid, nongenomic effects of cortisol on prolactin release. Steroids 2002; 67:539-48. [PMID: 11960633 DOI: 10.1016/s0039-128x(01)00197-0] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
While the mechanisms governing genomically mediated glucocorticoid actions are becoming increasingly understood, relatively little is known with regard to the cell signaling pathways that transduce rapid glucocorticoid actions. Studies of the cultured tilapia rostral pars distalis (RPD), a naturally segregated region of the fish pituitary gland that contains a 95-99% pure population of prolactin (PRL) cells and is easily dissected and maintained in a completely defined, serum-free media, indicate that physiological concentrations of cortisol rapidly inhibit PRL release. The attenuative action of cortisol on PRL release occurs within 10-20 min, is insensitive to the protein synthesis inhibitor, cycloheximide, and mimicked by its membrane impermeable analog, cortisol-21 hemisuccinate-conjugated bovine serum albumin (BSA). Cortisol and somatostatin, a peptide known to work through membrane receptors to inhibit PRL release, rapidly and reversibly reduces intracellular free Ca(2+) (Ca(i)(2+)), and inhibits 45Ca(2+) influx and BAYK-8644 induced PRL release. Preliminary investigations show cortisol, but not somatostatin, suppresses phospholipase C (PLC) activity in PRL cell membrane preparations. In addition, cortisol and somatostatin reduce intracellular cAMP and membrane adenylyl cyclase activity. These findings indicate that the acute inhibitory effects of cortisol on PRL release occur through a nongenomic mechanism involving interactions with the plasma membrane and inhibition of both the Ca(2+) and cAMP signal transduction pathways. Cortisol may reduce Ca(i)(2+) by inhibiting influx through L-type voltage-gated channels and possibly release through a PLC/inositol triphosphate sensitive intracellular Ca(2+) pool. In addition, it is also likely the steroid inhibits adenylyl cyclase activity in events leading to reduced cAMP production and the subsequent release of PRL.
Collapse
Affiliation(s)
- Russell J Borski
- Department of Zoology, North Carolina State University, Raleigh, NC, USA.
| | | | | |
Collapse
|
20
|
Brasselet S, Guillen S, Vincent JP, Mazella J. Beta-arrestin is involved in the desensitization but not in the internalization of the somatostatin receptor 2A expressed in CHO cells. FEBS Lett 2002; 516:124-8. [PMID: 11959117 DOI: 10.1016/s0014-5793(02)02517-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The interaction of beta-arrestin-1 with the somatostatin receptor type 2A (sst2A) was monitored using both biochemical and confocal imaging approaches. We show that, using transient transfection of either beta-arrestin-1 or its dominant negative Delta-arrestin-1 in CHO cells stably transfected with the sst2A, beta-arrestin-1 is colocalized with the receptor in endosomal vesicles after somatostatin-induced sequestration. However, this interaction leads to a role of beta-arrestin-1 in the desensitization of the sst2A rather than in the internalization process of the receptor-ligand complex.
Collapse
Affiliation(s)
- Sabrina Brasselet
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, UMR 6097, 660 route des Lucioles, 06560, Valbonne, France
| | | | | | | |
Collapse
|
21
|
Kuzhikandathil EV, Oxford GS. Dominant-negative mutants identify a role for GIRK channels in D3 dopamine receptor-mediated regulation of spontaneous secretory activity. J Gen Physiol 2000; 115:697-706. [PMID: 10828244 PMCID: PMC2232885 DOI: 10.1085/jgp.115.6.697] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human D3 dopamine receptor can activate G-protein-coupled inward rectifier potassium channels (GIRKs), inhibit P/Q-type calcium channels, and inhibit spontaneous secretory activity in AtT-20 neuroendocrine cells (Kuzhikandathil, E.V., W. Yu, and G.S. Oxford. 1998. Mol. Cell. Neurosci. 12:390-402; Kuzhikandathil, E.V., and G.S. Oxford. 1999. J. Neurosci. 19:1698-1707). In this study, we evaluate the role of GIRKs in the D3 receptor-mediated inhibition of secretory activity in AtT-20 cells. The absence of selective blockers for GIRKs has precluded a direct test of the hypothesis that they play an important role in inhibiting secretory activity. However, the tetrameric structure of these channels provides a means of disrupting endogenous GIRK function using a dominant negative approach. To develop a dominant-negative GIRK mutant, the K(+) selectivity amino acid sequence -GYG- in the putative pore domain of the human GIRK2 channels was mutated to -AAA-, -GLG-, or -GFG-. While the mutation of -GYG- to -GFG- did not affect channel function, both the -AAA- and -GLG- GIRK2 mutants were nonfunctional. This suggests that the aromatic ring of the tyrosine residue rather than its hydroxyl group is involved in maintaining the pore architecture of human GIRK2 channels. When expressed in AtT-20 cells, the nonfunctional AAA-GIRK2 and GLG-GIRK2 acted as effective dominant-negative mutants and significantly attenuated endogenous GIRK currents. Furthermore, these dominant-negative mutants interfered with the D3 receptor-mediated inhibition of secretion in AtT-20 cells, suggesting they are centrally involved in the signaling pathway of this secretory response. These results indicate that dominant-negative GIRK mutants are effective molecular tools to examine the role of GIRK channels in vivo.
Collapse
Affiliation(s)
- Eldo V. Kuzhikandathil
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Gerry S. Oxford
- Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| |
Collapse
|
22
|
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.
Collapse
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:
| |
Collapse
|
23
|
Smith RG, Van der Ploeg LH, Howard AD, Feighner SD, Cheng K, Hickey GJ, Wyvratt MJ, Fisher MH, Nargund RP, Patchett AA. Peptidomimetic regulation of growth hormone secretion. Endocr Rev 1997; 18:621-45. [PMID: 9331545 DOI: 10.1210/edrv.18.5.0316] [Citation(s) in RCA: 268] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- R G Smith
- Merck Research Laboratories, Rahway, New Jersey 07065, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Chen L, Fitzpatrick VD, Vandlen RL, Tashjian AH. Both overlapping and distinct signaling pathways for somatostatin receptor subtypes SSTR1 and SSTR2 in pituitary cells. J Biol Chem 1997; 272:18666-72. [PMID: 9228036 DOI: 10.1074/jbc.272.30.18666] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
To elucidate the signaling events mediated by specific somatostatin receptor (SSTR) subtypes, we expressed SSTR1 and SSTR2 individually in rat pituitary GH12C1 and F4C1 cells, which lack endogenous somatostatin receptors. In transfected GH12C1 cells, both SSTR1 and SSTR2 coupled to inhibition of Ca2+ influx and hyperpolarization of membrane potential via a pertussis toxin (PTx)-sensitive mechanism. These effects reflected modulation of ion channel activities which are important for regulation of hormone secretion. Somatostatin analogs MK678 and CH275 acted as subtype selective agonists as expected. In transfected F4C1 cells, both SSTR1 and SSTR2 mediated somatostatin-induced inhibition of adenylyl cyclase via a PTx-sensitive pathway. In addition, activation of SSTR2 in F4C1 cells, but not SSTR1, stimulated phospholipase C (PLC) activity and an increase in [Ca2+]i due to release of Ca2+ from intracellular stores. Unlike adenylyl cyclase inhibition, the PLC-mediated response was only partially sensitive to PTx. To determine the structural determinants in SSTR2 necessary for activation of PLC, we constructed chimeric receptors in which domains of SSTR2 were introduced into SSTR1. Chimeric receptors containing only the third intracellular loop, or all three intracellular loops from SSTR2, mediated inhibition of adenylyl cyclase, but failed to stimulate PLC activity as did wild-type SSTR2. Furthermore, the C-terminal tail of SSTR2 was not required for coupling to PLC. Thus, by expressing individual somatostatin receptor subtypes in pituitary cells, we have identified both overlapping and distinct signaling pathways for SSTR1 and SSTR2, and have shown that sequences other than simply the intracellular domains are required for SSTR2 to couple to the PLC signaling pathway.
Collapse
Affiliation(s)
- L Chen
- Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115, USA
| | | | | | | |
Collapse
|
25
|
Hipkin RW, Friedman J, Clark RB, Eppler CM, Schonbrunn A. Agonist-induced desensitization, internalization, and phosphorylation of the sst2A somatostatin receptor. J Biol Chem 1997; 272:13869-76. [PMID: 9153246 DOI: 10.1074/jbc.272.21.13869] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Cellular responsiveness to the inhibitory peptide somatostatin (SRIF) or its clinically used analogs can desensitize with agonist exposure. While desensitization of other seven-transmembrane domain receptors is mediated by receptor phosphorylation and/or internalization, the mechanisms mediating SRIF receptor (sst) desensitization are unknown. Therefore, we investigated the susceptibility of the sst2A receptor isotype to ligand-induced desensitization, internalization, and phosphorylation in GH-R2 cells, a clone of pituitary tumor cells overexpressing this receptor. A 30-min exposure of cells to either SRIF or the analog SMS 201-995 (SMS) reduced both the potency and efficacy of agonist inhibition of adenylyl cyclase. Internalization of receptor-bound ligand was rapid (t1/2 = 4 min) and temperature-dependent. SRIF and SMS increased the phosphorylation of the 71-kDa sst2A protein 25-fold within 15 min. Receptor phosphorylation was dependent on both the concentration and time of agonist exposure and was not affected by pertussis toxin pretreatment, indicating that receptor occupancy rather than second messenger formation was required. Receptor phosphorylation was also stimulated by phorbol 12-myristate 13-acetate activation of protein kinase C. Both ligand-stimulated and phorbol 12-myristate 13-acetate-stimulated receptor phosphorylation occurred primarily on serine. These studies are the first demonstration of agonist-dependent desensitization, internalization, and phosphorylation of the sst2A receptor and suggest that phosphorylation may mediate the homologous and heterologous regulation of this receptor.
Collapse
Affiliation(s)
- R W Hipkin
- Department of Pharmacology, University of Texas Medical School, Houston, Texas 77225, USA
| | | | | | | | | |
Collapse
|
26
|
Piros ET, Hales TG, Evans CJ. Functional analysis of cloned opioid receptors in transfected cell lines. Neurochem Res 1996; 21:1277-85. [PMID: 8947917 DOI: 10.1007/bf02532368] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Opioids modulate numerous central and peripheral processes including pain perception neuroendocrine secretion and the immune response. The opioid signal is transduced from receptors through G proteins to various different effectors. Heterogeneity exists at all levels of the transduction process. There are numerous endogenous ligands with differing selectivities for at least three distinct opioid receptors (mu, delta, kappa). G proteins activated by opioid receptors are generally of the pertussis toxin-sensitive Gi/Go class, but there are also opioid actions that are thought to involve Gq and cholera toxin-sensitive G proteins. To further complicate the issue, the actions of opioid receptors may be mediated by G-protein alpha subunits and/or beta gamma subunits. Subsequent to G protein activation several effectors are known to orchestrate the opioid signal. For example activation of opioid receptors increases phosphatidyl inositol turnover, activates K+ channels and reduces adenylyl cyclase and Ca2+ channel activities. Each of these effectors shows considerable heterogeneity. In this review we examine the opioid signal transduction mechanism. Several important questions arise: Why do opioid ligands with similar binding affinities have different potencies in functional assays? To which Ca2+ channel subtypes do opioid receptors couple? Do opioid receptors couple to Ca2+ channels through direct G protein interactions? Does the opioid-induced inhibition of vesicular release occur through modulation of multiple effectors? We are attempting to answer these questions by expressing cloned opioid receptors in GH3 cells. Using this well characterized system we can study the entire opioid signal transduction process from ligand-receptor interaction to G protein-effector coupling and subsequent inhibition of vesicular release.
Collapse
MESH Headings
- Animals
- Cell Line
- Cyclic AMP/metabolism
- GTP-Binding Proteins/metabolism
- Humans
- Inositol Phosphates/metabolism
- Models, Biological
- Narcotics/pharmacology
- Receptors, Opioid/biosynthesis
- Receptors, Opioid/physiology
- Receptors, Opioid, delta/biosynthesis
- Receptors, Opioid, delta/physiology
- Receptors, Opioid, kappa/biosynthesis
- Receptors, Opioid, kappa/physiology
- Receptors, Opioid, mu/biosynthesis
- Receptors, Opioid, mu/physiology
- Recombinant Proteins/biosynthesis
- Signal Transduction
- Transfection/methods
Collapse
Affiliation(s)
- E T Piros
- Department of Psychiatry and Biobehavioral Sciences, University of California, School of Medicine, Los Angeles 90095, USA
| | | | | |
Collapse
|
27
|
Abstract
The regulation of GH secretion involves finely balanced systems with multiple components. As our knowledge of the physiology of GH regulation expands, so does our understanding of the bases for GH diseases. We now can identify several cellular loci that cause GH deficiency or GH excess. In addition, the recent increased understanding of GH physiology has resulted in an increase in potential therapies for growth disorders.
Collapse
Affiliation(s)
- L Cuttler
- Department of Pediatrics, Case Western Reserve University, Rainbow Babies and Children's Hospital, Cleveland, Ohio, USA
| |
Collapse
|
28
|
Xi D, Kurtz DT, Ramsdell JS. Maitotoxin-elevated cytosolic free calcium in GH4C1 rat pituitary cells nimodipine-sensitive and -insensitive mechanisms. Biochem Pharmacol 1996; 51:759-69. [PMID: 8602871 DOI: 10.1016/0006-2952(95)02392-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Maitotoxin includes an extracellular Ca2+-dependent membrane depolarization predominantly via activation of L-type voltage-dependent Ca2+ channels (L-VDCC) in GH4C1 rat pituitary cells. In contract to studies employing intracellular dyes, electrophysiological studies have indicated that maitotoxin activates voltage-independent conductances. In the present study, we used fura-2 calcium digital analysis to investigate the actions of very low concentrations of maitotoxin on cytosolic free calcium ([Ca2+]i) in GH4C1 cells in an effort to distinguish different calcium entry mechanisms. Maitotoxin at concentrations as low as 0.01 ng/mL elevated [Ca2+]i 35 +/- 3% and induced membrane depolarization. The concentration dependency for maitotoxin-elevated [Ca2+]i was biphasic with the first phase maximal at 0.05 to 0.5 ng/mL and the minimum EC50 of the second phase about 2.0 ng/mL. Nimodipine (100 nM), a dihydropyridine antagonist of L-VDCC, prevented the [Ca+2]i increase and depolarization induced by up to 0.1 ng/mL maitotoxin, but not at higher concentration (0.5 ng/mL) of maitotoxin. This indicates that lower concentrations (0.1 ng/mL) of maitotoxin require L-VDCC, whereas higher concentrations (>-0.5 ng/mL) of maitotoxin may require additional ionic mechanisms. Maitotoxin (0.5 ng/mL) induced 45Ca2+ uptake and depolarization in Ltk-cells which lack VDCC. Reducing extracellular Cl- from 123 to 5.8 microM increased the magnitude of membrane depolarization by maitotoxin (0.5 ng/mL), which suggests that a Cl- conductance participated in depolarization induced by higher maitotoxin concentrations. Taken together, our results indicate that maitotoxin activates at least two ionic mechanisms. At lower concentrations of maitotoxin, the primary ionic mechanism requires the activation of L-VDCC; however, at higher maitotoxin concentrations, additional ionic mechanisms are involve in the entry of extracellular Ca2+. This latter mechanism may represent the voltage-independent pathway evident under voltage clamp conditions.
Collapse
Affiliation(s)
- D Xi
- Marine Biotoxins Program of the U.S. Marine Fisheries Services, Charleston, SC 29412, USA
| | | | | |
Collapse
|
29
|
Abstract
The diverse biological effects of somatostatin (SST) are mediated through a family of G protein coupled receptors of which 5 members have been recently identified by molecular cloning. This review focuses on the molecular biology, pharmacology, expression, and function of these receptors with particular emphasis on the human (h) homologs. hSSTRs are encoded by a family of 5 genes which map to separate chromosomes and which, with one exception, are intronless. SSTR2 gives rise to spliced variants, SSTR2A and 2B. hSSTR1-4 display weak selectivity for SST-14 binding whereas hSSTR5 is SST-28 selective. Based on structural similarity and reactivity for octapeptide and hexapeptide SST analogs, hSSTR2,3, and 5 belong to a similar SSTR subclass. hSSTR1 and 4 react poorly with these analogs and belong to a separate subclass. All 5 hSSTRs are functionally coupled to inhibition of adenylyl cyclase via pertussis toxin sensitive GTP binding proteins. Some of the subtypes are also coupled to tyrosine phosphatase (SSTR1,2), Ca2+ channels (SSTR2), Na+/H+ exchanger (SSTR1), PLA-2 (SSTR4), and MAP kinase (SSTR4). mRNA for SSTR1-5 is widely expressed in brain and peripheral organs and displays an overlapping but characteristic pattern that is subtype-selective, and tissue- and species-specific. Pituitary and islet tumors express several SSTR genes suggesting that multiple SSTR subtypes are coexpressed in the same cell. Structure-function studies indicate that the core residues in SST-14 ligand Phe6-Phe11 dock within a ligand binding pocket located in TMDs 3-7 which is lined by hydrophobic and charged amino acid residues.
Collapse
Affiliation(s)
- Y C Patel
- Fraser Laboratories, Department of Medicine, McGill University, Royal Victoria Hospital, Montreal, Quebec, Canada
| | | | | | | | | | | |
Collapse
|
30
|
Rodriguez-Pascual F, Miras-Portugal MT, Torres M. Cyclic GMP-dependent protein kinase activation mediates inhibition of catecholamines secretion and Ca2+ influx in bovine chromaffin cells. Neuroscience 1995; 67:149-57. [PMID: 7477895 DOI: 10.1016/0306-4522(95)00035-h] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The effects of the membrane-permeable cGMP analogue, 8-bromoguanosine 3':5'-cyclic monophosphate on acetylcholine-evoked catecholamine secretion and cytosolic calcium increases were studied in chromaffin cells from the bovine adrenal gland. Preincubation with 100 microM 8-bromoguanosine 3':5'-cyclic monophosphate during 10 and 30 min decreased the acetylcholine-evoked catecholamine release by 16 +/- 3% and 27 /+- 5%, respectively. The cytosolic calcium increases triggered by acetylcholine and 30 mM KCl were also inhibited by 30 min of preincubation with this compound by 27 +/- 4 and 34 /+- 12%, respectively. Changes in membrane potential induced by acetylcholine and KCl were not affected by preincubation with 8-bromoguanosine 3':5'-cyclic monophosphate. The cyclic GMP-dependent protein kinase inhibitor N-[2-(methylamino)ethyl]-5-isoquinoline sulfonamide dihydrochloride-at l micron abolished the inhibitory effect of 8-bromoguanosine 3':5'-cyclic monophosphate on acetylcholine-evoked calcium increase. By contrast, a potent and selective inhibitor against cyclic AMP-dependent protein kinase, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide did not block the 8-bromoguanosine 3':5'-cyclic monophosphate effect. Additionally, 8-bromoguanosine 3':5'-cyclic monophosphate stimulated histone F2b phosphorylation by a partial purified cGMP-dependent protein kinase from chromaffin cells. The extent of histone phosphorylation was reduced by N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride and 8-(4-chlorophenylthio)-guanosine 3':5'-cyclic monophosphorothioate, Rp-isomer, a specific inhibitor against cyclic GMP-dependent protein kinase, whereas it was not modified by N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline sulfonamide. The results suggest that the inhibitory effects of 8-bromoguanosine 3':5' cyclic monophosphate on chromaffin cells are mediated through the activation of cGMP-dependent protein kinase.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- F Rodriguez-Pascual
- Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain
| | | | | |
Collapse
|
31
|
Cordido F, Peñalva A, Peino R, Casanueva FF, Dieguez C. Effect of combined administration of growth hormone (GH)-releasing hormone, GH-releasing peptide-6, and pyridostigmine in normal and obese subjects. Metabolism 1995; 44:745-8. [PMID: 7783658 DOI: 10.1016/0026-0495(95)90187-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Growth hormone (GH) secretion in response to all provocative stimuli is decreased in patients with obesity. Recently, we found that the combined administration of GH-releasing hormone (GHRH) and the hexapeptide GH-releasing peptide-6 (GHRP-6) induced a large increase in plasma GH levels. To gain further insight into the disrupted mechanism of GH regulation in obesity, we investigated whether the inhibition of somatostatinergic tone with pyridostigmine could further increase the GH response to combined administration of GHRH and GHRP-6. In normal subjects, administration of GHRH plus GHRP-6 induced a marked increase in plasma GH with a peak at 30 minutes (mean +/- SEM, 76.7 +/- 9.7 micrograms/L), which was similar to that obtained after pretreatment with pyridostigmine (74.7 +/- 9.4 micrograms/L). In obese patients, combined administration of GHRH plus GHRP-6 induced a clear increase in GH secretion with a peak at 15 minutes of 42.2 +/- 10.0 micrograms/L, which was also unaffected after pretreatment with pyridostigmine (38.4 +/- 5.8 micrograms/L). The GH response was lower in obese patients than in controls as assessed by the area under the curve after administration of both GHRH plus GHRP-6 (1,846 +/- 396 v 4,773 +/- 653, P < .01) and pyridostigmine plus GHRH plus GHRP-6 (1,989 +/- 372 v 5,098 +/- 679, P < .005). In conclusion, these data suggest that GHRP-6 can behave as a functional somatostatin antagonist, and that somatotrope responsiveness to the combined administration of GHRH plus GHRP-6 is largely independent of somatostatinergic tone.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- F Cordido
- Faculty of Medicine, University of Santiago de Compostela, Spain
| | | | | | | | | |
Collapse
|
32
|
Tatsuno I, Arimura A. Pituitary adenylate cyclase-activating polypeptide (PACAP) mobilizes intracellular free calcium in cultured rat type-2, but not type-1, astrocytes. Brain Res 1994; 662:1-10. [PMID: 7859060 DOI: 10.1016/0006-8993(94)90790-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We investigated the effects of pituitary adenylate cyclase-activating polypeptide (PACAP38) on cytosolic free calcium ([Ca2+]i) at a single cell level in both type-1 and type-2 cultured rat astrocytes using a calcium-sensitive fluorescent dye, fura-2. Type-1 astrocytes were relatively silent during the 20 min observation of baseline [Ca2+]i and PACAP38 did not alter [Ca2+]i in type-1 astrocytes at concentrations up to 1 microM. In contrast, type-2 astrocytes could be divided into three subtypes (silent type, randomly-firing type and oscillatory type) based on the observation of baseline [Ca2+]i. Of 166 type-2 astrocytes tested, 145 (87.4%) were the silent type (stable basal [Ca2+]i levels) and 13 (7.8%) were the randomly-firing type (random increases in [Ca2+]i). PACAP38 could stimulate [Ca2+]i in subpopulations of all three subtypes. In the silent type-2 astrocytes (4 experiments with 255 cells/experiment), 54.4 +/- 3.6% of the total number responded to PACAP38. The half maximal concentration (ED50) of PACAP38 was 2.89 +/- 1.89 nM. Removing Ca2+ from the superfusion media did not alter the PACAP38-induced increase of [Ca2+]i. Neither 1-30 microM of forskolin nor 1-10 mM of dibutyryl cyclic AMP increased [Ca2+]i in the same type-2 astrocytes which responded to PACAP38. These findings suggest that PACAP increases [Ca2+]i in type-2, not type-1, rat astrocytes by mobilizing Ca2+ from intracellular stores, and that this action is not linked to activation of the cyclic AMP second messenger system.
Collapse
Affiliation(s)
- I Tatsuno
- US-Japan Biomedical Research Laboratories, Tulane University Hebert Center, Belle Chasse, LA 70037
| | | |
Collapse
|
33
|
Chen C, Vincent JD, Clarke IJ. Ion channels and the signal transduction pathways in the regulation of growth hormone secretion. Trends Endocrinol Metab 1994; 5:227-33. [PMID: 18407212 DOI: 10.1016/1043-2760(94)p3080-q] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The secretion of GH from pituitary somatotrophs is mainly regulated by alterations in the levels of intracellular free Ca(2+) concentrations ([Ca(2+)](i)) that depend on the influx of Ca(2+) through voltage-gated Ca(2+) channels in the cell membrane. Hypothalamic stimulatory and inhibitory factors bind to specific receptors on the cell membrane to regulate membrane potential and activate second-messenger systems. The receptors are G-protein coupled, and activated G proteins directly influence membrane ion channels to regulate Ca(2+) influx. The function of cAMP-dependent protein kinase A is also modulated by receptor-coupled G proteins leading to the phosphorylation of Ca(2+) channel proteins and further alteration of Ca(2+) influx.
Collapse
Affiliation(s)
- C Chen
- Prince Henry's Institute of Medical Research, Clayton, Victoria 3168, Australia
| | | | | |
Collapse
|
34
|
Albert PR. Heterologous expression of G protein-linked receptors in pituitary and fibroblast cell lines. VITAMINS AND HORMONES 1994; 48:59-109. [PMID: 7941429 DOI: 10.1016/s0083-6729(08)60496-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- P R Albert
- Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
| |
Collapse
|
35
|
Patel Y, Panetta R, Escher E, Greenwood M, Srikant C. Expression of multiple somatostatin receptor genes in AtT-20 cells. Evidence for a novel somatostatin-28 selective receptor subtype. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)42285-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
36
|
Zerek-Mełeń G, Pawlikowski M, Winczyk K, Lachowicz-Ochedalska A, Legowska A, Kwaśny H, Przybylski J, Szadowska A. Effects of new somatostatin analogs on the cell proliferation of colonic crypts and colonic cancers in rats. Neuropeptides 1993; 25:57-60. [PMID: 8105412 DOI: 10.1016/0143-4179(93)90069-m] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The antiproliferative activity of two new somatostatin (SS) analogs: ASS-51 and ASS-52 have been tested in this study. We assessed their ability to inhibit the DNA synthesis in normal colon crypt cells and in the cells of chemically (dimethylhydrazine)-induced colon cancer in the rats. The incorporation of bromodeoxyuridine (BrDU) into appropriate cell nuclei was used as an index of DNA synthesis. It was found that: 1) Only ASS-51 significantly decreases the colon crypt cell proliferation in the rat when compared to controls. Since both analogs were previously shown to inhibit GH release, these data indicate that the antiproliferogenic effect of ASS-51 is independent of the inhibition of GH release. 2) Both examined analogs did not significantly effect the BrDU incorporation into cell nuclei of chemically-induced colon cancer.
Collapse
Affiliation(s)
- G Zerek-Mełeń
- Institute of Endocrinology, Medical University of Lódź, Poland
| | | | | | | | | | | | | | | |
Collapse
|
37
|
Yajima Y, Akita Y, Katada T, Saito T. Somatostatin induces release of the alpha subunits of pertussis toxin-sensitive G proteins in native membranes and in intact GH4C1 rat pituitary cells. Mol Cell Endocrinol 1993; 92:143-52. [PMID: 8100541 DOI: 10.1016/0303-7207(93)90001-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Incubation of GH4C1 rat pituitary cell membranes with the poorly hydrolyzable GTP analogue, GTP gamma S, produces a decrease in the pertussis toxin-catalyzed ADP-ribosylation of 40-kDa protein in the membrane pellet and the release of an alpha-like substrate from the membrane into the supernatant fraction; these effects do not occur with the inactive GDP analogue, GDP beta S. The resolved supernatant fraction from GTP gamma S-stimulated membranes is significantly activated to pertussis toxin-catalyzed [32P]ADP-ribosylation by the addition of purified beta gamma complex. Immunoblot analysis identifies the released pertussis toxin substrate as alpha subunits of Gi2, Gi3, and G(o) in the resolved supernatant. The physiological agonist, somatostatin, also stimulates the release of Gi2 and G(o) alpha subunits but not Gi3 from GH4C1 cell membranes in the presence of a low concentration of GTP gamma S (20 nM). The effects of somatostatin are inhibited by pretreatment of GH4C1 cells with pertussis toxin. Furthermore, the addition of somatostatin to intact GH4C1 cells decreases the level of Gi2 alpha subunits in the crude membrane whereas immunoblot analysis of the 274,000 x g supernatant (cytosolic fraction) clearly shows the presence of Gi2 alpha subunits. These data indicate that pertussis toxin-sensitive G proteins in GH4C1 cells dissociate into alpha subunits and beta gamma complex with the release of the alpha subunits from the membranes upon somatostatin activation.
Collapse
Affiliation(s)
- Y Yajima
- Department of Molecular Biology, Tokyo Metropolitan Institute of Medical Science, Japan
| | | | | | | |
Collapse
|
38
|
Leszczynski D, Josephs MD, Fournier RS, Foegh ML. Angiopeptin, the octapeptide analogue of somatostatin, decreases rat heart endothelial cell adhesiveness for mononuclear cells. REGULATORY PEPTIDES 1993; 43:131-40. [PMID: 8095098 DOI: 10.1016/0167-0115(93)90147-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The effect of angiopeptin, a stable analogue of somatostatin, was studied on basal and interleukin-1-beta-induced endothelial cell adhesiveness for mononuclear cells, and compared to the effect of somatostatin. Angiopeptin and somatostatin decreased basal and interleukin-1-beta-induced endothelial cell adhesiveness for mononuclear cells. The decreased mononuclear cells adhesion to endothelial cells exposed to angiopeptin and somatostatin is not due to modulation of the expression of intrecellular adhesion molecule-1 because neither angiopeptin nor somatostatin decreased basal and interleukin-1-beta-induced expression of this adhesion molecule. The effect of angiopeptin in inhibiting endothelial cell adhesiveness for mononuclear cells was abolished by addition of dibutyryl-cyclic AMP. Angiopeptin induced a transient decrease in basal and interleukin-1-beta-induced cyclic AMP levels in endothelial cells. Exposure of unstimulated and interleukin-1-beta-activated endothelial cells to KT5720, a specific inhibitor of cyclic AMP-dependent protein kinase, decreased endothelial cell adhesiveness for mononuclear cells. Thus, angiopeptin most likely diminishes endothelial adhesiveness for mononuclear cells by affecting the cyclic AMP-dependent protein kinase signal transduction pathway. The findings suggest that angiopeptin and somatostatin may modify the development of the immune response by attenuating endothelial cell adhesiveness for mononuclear cells. Angiopeptin may have a potential clinical application as a modulator of some aspects of the immune response due to its long half-life and prolonged inhibitory effect on interleukin-1-beta induced endothelial adhesiveness for mononuclear cells.
Collapse
Affiliation(s)
- D Leszczynski
- Department of Surgery, Georgetown University Medical Center, Washington, DC
| | | | | | | |
Collapse
|
39
|
Abstract
A new class of small synthetic peptides has been developed which specifically release GH. They consist of 6-7 amino acids and release GH in animals as well as humans. So far 3 of these peptides have been administered to humans, i.e., GHRP-6, GHRP-1 and GHRP-2. As in rats, these 3 peptides have been found to be increasingly more effective in releasing GH in humans. All 3 GHRPs release GH more efficaciously than GHRH 1-44 NH2 in humans. Particularly note-worthy is that GHRP-6, GHRP-1 AND GHRP-2 all release GH after oral administration. Near maximal amounts of GH can be released after GHRP-1 and GHRP-2 oral administration. In the present studies, the GH responses and serum irGHRP levels after i.v., s.c. and oral administration have been determined in normal younger men and/or women. By each route of administration GH was very effectively released. Additionally, GH release was induced by oral GHRP-6 in children with various degrees of GH deficiency. Noteworthy is the synergistic release of GH induced by the combined i.v. bolus administration of 1 microgram/kg of GHRP-1 + GHRH 1-44NH2. Thus, these results demonstrate GHRPs' potential importance at the theoretical as well as pharmaceutical level.
Collapse
Affiliation(s)
- C Y Bowers
- Tulane University Medical Center, New Orleans, LA 70112
| |
Collapse
|
40
|
Leszczynski D, Zhao Y, Cathapermal S, Nilsson J, Foegh ML. Rat heart smooth muscle cells express high and low affinity receptors for somatostatin-14, which are involved in regulation of cell proliferation. Life Sci 1993; 53:1663-74. [PMID: 7901726 DOI: 10.1016/0024-3205(93)90203-f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We demonstrate that rat heart coronary artery smooth muscle cells express specific binding sites (receptors) for somatostatin-14. The sigmoidal shape kinetics of the somatostatin-14 binding by the cells suggests the presence of either an allosteric binding site or binding sites with different affinities towards the ligand. Scatchard analysis reveals presence of high affinity (Kd = 0.039 x 10(-9)M) and low affinity (Kd = 0.602 x 10(-9)M) binding sites. Somatostatin-14 and Angiopeptin can displace each other from the binding sites. The concentrations of Angiopeptin required to displace 28%-48% of bound somatostatin-14 (10(-9)M) are in the range of 10(-4)-10(-3)M. The concentrations of somatostatin-14 required to displace 8-27% of bound Angiopeptin (10(-6)M) are in the range of 10(-6)-10(-5)M. Thus, somatostatin-14 seems to possess much higher binding affinity than Angiopeptin. Binding of somatostatin-14 and Angiopeptin to rat smooth muscle cells triggers intracellular event(s) leading to inhibition of smooth muscle cell proliferation. Exposure of smooth muscle cells to somatostatin-14 and Angiopeptin decreases amount of phosphorylated tyrosine residues. The effect of somatostatin-14 and Angiopeptin on the expression of phosphotyrosine precedes and is most likely responsible, at least in part, for the inhibition of smooth muscle cell proliferation. This demonstrates that rat heart smooth muscle cells express physiologically active receptor(s) for somatostatin-14.
Collapse
Affiliation(s)
- D Leszczynski
- Department of Surgery, Georgetown University Medical Center, Washington, DC
| | | | | | | | | |
Collapse
|
41
|
Shin SH, Soukup C, Pang SC, Kubiseski TJ, Flynn TG. Measurement of prolactin release and cytosolic calcium in estradiol-primed lactotrophs. Life Sci 1993; 53:1605-16. [PMID: 8231638 DOI: 10.1016/0024-3205(93)90184-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We have developed a perifusion system that can measure both changes of cytosolic free calcium concentration [Ca2+]i and prolactin release simultaneously from cultured lactotrophs. This model incorporated a commonly-used perifusion system to a spectrofluorometer. Indo-1 loaded cells were injected into Sephadex G-150 matrix in the cuvette at a site where the emitting light of the fluorometer projects. During perifusion periods, the perifusate was collected in a fraction collector, while optical density of the emitting light at 405 nm was recorded. The [Ca2+]i was calculated based on an ionomycin and Mn2+ quenching technique. As expected, TRH (1 mumol/l) stimulated prolactin release from cultured lactotrophs in this system. We further observed that prolactin releases as induced by TRH and ionomycin were not proportional with changes of the [Ca2+]i, suggesting that changes of [Ca2+]i is not the sole final pathway of intracellular transduction systems for prolactin release.
Collapse
Affiliation(s)
- S H Shin
- Department of Physiology, Queen's University, Kingston, Ontario, Canada
| | | | | | | | | |
Collapse
|
42
|
Xi D, Van Dolah F, Ramsdell J. Maitotoxin induces a calcium-dependent membrane depolarization in GH4C1 pituitary cells via activation of type L voltage-dependent calcium channels. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)74000-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
43
|
Strowbridge BW, Bean AJ, Spencer DD, Roth RH, Shepherd GM, Robbins RJ. Low levels of somatostatin-like immunoreactivity in neocortex resected from presumed seizure foci in epileptic patients. Brain Res 1992; 587:164-8. [PMID: 1356061 DOI: 10.1016/0006-8993(92)91441-g] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The concentration of somatostatin-like immunoreactivity (SS-LI) was determined by radioimmunoassay in neocortical tissue resected from 20 patients with pharmacologically intractable complex partial seizures. Most resections included either the anterior temporal pole neocortex (15 cases) or cingulate gyrus neocortex (3 cases). The concentration of SS-LI was lowest in cortical tissue immediately adjacent to cortical tumors. Preoperative electrical recordings suggested that this tissue was the seizure focus. In vitro recordings showed that this tissue also exhibited abnormal hyperexcitable synaptic responses. Higher levels of SS-LI, similar to normal values previously reported in human cortex, were present in non-focal temporal neocortical tissue (resected from patients in whom the seizure focus was in the ipsilateral hippocampus) in which no hyperexcitable synaptic activity was present in vitro. The functional loss of inhibitory transmitters suggested by the low SS-LI levels might provide a theoretical basis for the hyperexcitability observed in vivo and in vitro.
Collapse
Affiliation(s)
- B W Strowbridge
- Section of Neurobiology, Yale University School of Medicine, New Haven, CT 06520
| | | | | | | | | | | |
Collapse
|
44
|
Lachowicz A, Stepień H, Kunert-Radek J, Pawlikowski M. Effects of somatostatin on inositol-1,4,5-trisphosphate content in mouse spleen lymphocytes. ACTA ACUST UNITED AC 1992; 101:661-4. [PMID: 1351438 DOI: 10.1016/0300-9629(92)90340-v] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. The effects of somatostatin-14 (SS) and diazepam in vitro on the content of inositol-1,4,5-trisphosphate (IP3) in mouse spleen lymphocytes were investigated. 2. It was found that the exposure of mouse spleen lymphocytes in vitro to SS sharply diminished their IP3 level. 3. Diazepam had no effect on lymphocytes IP3 content. 4. The inhibition of phosphatydyloinositol (PI) breakdown was suggested as one of the mechanisms of the physiological SS action.
Collapse
Affiliation(s)
- A Lachowicz
- Institute of Endocrinology, Medical Academy of Lódź, Poland
| | | | | | | |
Collapse
|
45
|
Scherübl H, Hescheler J, Schultz G, Kliemann D, Zink A, Ziegler R, Raue F. Inhibition of Ca2+-induced calcitonin secretion by somatostatin: Roles of voltage dependent Ca2+ channels and G-proteins. Cell Signal 1992; 4:77-85. [PMID: 1349229 DOI: 10.1016/0898-6568(92)90009-w] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Somatostatin has recently been applied therapeutically for hypercalcitonemia in patients with calcitonin-producing tumours. Using calcitonin-secreting cells (C-cells) of the medullary thyroid carcinoma cell line rMTC 44-2, we investigated the inhibitory action of somatostatin on calcitonin release, cytosolic Ca2+ and Ca2+ channel currents. The Ca(2+)-induced rises of the cytosolic Ca2+ and calcitonin secretion were greatly inhibited by somatostatin or its stable analogue octreotide. The effects of somatostatin were pertussis toxin-sensitive. Under voltage clamp conditions, C-cells exhibited slowly inactivating Ca2+ channel currents. Bath application of 100 nM somatostatin reversibly reduced the Ca2+ channel current by about 30%. The Ca2+ channel current and its inhibition by somatostatin were not affected by intracellularly applied cyclic AMP. Moreover, pretreating the cells with pertussis toxin had no effect on the control Ca2+ channel currents but greatly abolished its inhibition by somatostatin. The data show that somatostatin suppresses the Ca(2+)-stimulated calcitonin secretion by inhibiting voltage-dependent Ca2+ channel currents and by lowering cytosolic Ca2+. These actions of somatostatin involve pertussis toxin-sensitive G-proteins and occur independently of changes in the cyclic AMP concentration.
Collapse
Affiliation(s)
- H Scherübl
- Pharmakologisches Institut der Freien Universität Berlin, Germany
| | | | | | | | | | | | | |
Collapse
|
46
|
Lachowicz A, Pawlikowski M. Effects of somatostatin-14 and its analogs on the (Ca,Mg)ATPase in the rat anterior pituitary. Biochem Biophys Res Commun 1991; 178:1492-7. [PMID: 1678601 DOI: 10.1016/0006-291x(91)91062-h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The effects of somatostatin-14 and its biologically active analogs, RC-160 and SMS 201-995, on (Ca,Mg)ATPase activity in vitro were studied in homogenates of anterior pituitary cells. It was found that somatostatin inhibited the (Ca,Mg)ATPase activity in the anterior pituitary and somatostatin analogs exerted slight biphasic effects on the calcium pump activity. The effects of specific brain (Ca,Mg)ATPase inhibitors, VOSO4 and LaCl3, were also studied in vitro. Neither VOSO4 nor LaCl3 enhance the inhibition of calcium pump activity caused by somatostatin. It is suggested that somatostatin may mediate its action in pituitary cells, among others, by the regulation of (Ca,Mg)ATPase activity.
Collapse
Affiliation(s)
- A Lachowicz
- Department of Experimental Endocrinology, Medical Academy of Lodz, Poland
| | | |
Collapse
|
47
|
White RE, Schonbrunn A, Armstrong DL. Somatostatin stimulates Ca(2+)-activated K+ channels through protein dephosphorylation. Nature 1991; 351:570-3. [PMID: 1710783 DOI: 10.1038/351570a0] [Citation(s) in RCA: 220] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The neuropeptide somatostatin inhibits secretion from electrically excitable cells in the pituitary, pancreas, gut and brain. In mammalian pituitary tumour cells somatostatin inhibits secretion through two distinct pertussis toxin-sensitive mechanisms. One involves inhibition of adenylyl cyclase, the other an unidentified cyclic AMP-independent mechanism that reduces Ca2+ influx by increasing membrane conductance to potassium. Here we demonstrate that the predominant electrophysiological effect of somatostatin on metabolically intact pituitary tumour cells is a large, sustained increase in the activity of the large-conductance Ca(2+)- and voltage-activated K+ channels (BK). This action of somatostatin does not involve direct effects of Ca2+, cAMP or G proteins on the channels. Our results indicate instead that somatostatin stimulates BK channel activity through protein dephosphorylation.
Collapse
Affiliation(s)
- R E White
- Laboratory of Cellular and Molecular Pharmacology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709
| | | | | |
Collapse
|
48
|
Robbins RJ, Brines ML, Kim JH, Adrian T, de Lanerolle N, Welsh S, Spencer DD. A selective loss of somatostatin in the hippocampus of patients with temporal lobe epilepsy. Ann Neurol 1991; 29:325-32. [PMID: 1675046 DOI: 10.1002/ana.410290316] [Citation(s) in RCA: 152] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Although neuropeptides have been demonstrated to be hippocampal neuromodulators in laboratory animals, their role in human hippocampal physiology or pathophysiology remains to be defined. The concentrations of somatostatin, cholecystokinin octapeptide, vasoactive intestinal polypeptide, and dynorphin A 1-17 were determined in hippocampal tissue resected from patients with cryptogenic temporal lobe epilepsy, a common seizure disorder originating in or near the hippocampus. Control tissue was obtained from cadavera or epilepsy patients in whom the hippocampus was removed during the resection of temporal lobe tumors. Peptide determinations were performed on extracts of punch biopsy specimens taken from six different hippocampal regions. A significant decrease in immunoreactive somatostatin concentration was identified in the dentate gyrus and in region cornu ammonis 4 of cryptogenic temporal lobe epilepsy specimens. No significant changes were present in any other hippocampal region or in the levels of other peptides. In situ hybridization studies performed on cryostat sections from similar patients confirmed a marked loss of neurons expressing the somatostatin gene, which was restricted to the dentate hilus. The density of specific 125I-somatostatin binding to cryostat sections, as determined by semiquantitative in vitro autoradiography, was significantly increased in the dentate gyrus of the cryptogenic epilepsy patients, compared with tumor control specimens. We conclude that a loss of somatostatin-producing interneurons with an upregulation of dentate somatostatin receptors is a specific and characteristic element in the pathophysiology of human cryptogenic temporal lobe epilepsy.
Collapse
Affiliation(s)
- R J Robbins
- Neuroendocrinology Program, Yale University School of Medicine, New Haven, CT 06510
| | | | | | | | | | | | | |
Collapse
|
49
|
Somatostatin inhibits insulin secretion by a G-protein-mediated decrease in Ca2+ entry through voltage-dependent Ca2+ channels in the beta cell. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(17)35249-3] [Citation(s) in RCA: 96] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
|
50
|
Donoghue DJ, Scanes CG. Possible involvement of adenylyl cyclase-cAMP-protein kinase a pathway in somatostatin inhibition of growth hormone release from chicken pituitary cells. Gen Comp Endocrinol 1991; 81:113-9. [PMID: 1709126 DOI: 10.1016/0016-6480(91)90131-o] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Somatostatin (SRIF) reduces growth hormone releasing hormone (GRF)-stimulated growth hormone (GH) release from avian and mammalian adenohypophyseal cells. The present studies examined the intracellular mechanisms mediating SRIF inhibition of GRF-stimulated GH release from chicken pituitary cells. Increases (P less than 0.05) in GH release were observed in the presence of (1) GRF; (2) the adenylyl cyclase stimulator, forskolin; (3) a cAMP analog, 8-bromo-cAMP; (4) the phosphodiesterase inhibitor 3-isobutyl-l-methyl-xanthine (IBMX) combined with GRF; (5) a tumor-promoting phorbol ester and protein kinase C activator, phorbol 12-myristate, 13-acetate (PMA); (6) a diacylglycerol analog, 1,2-dioctanoyl-glycerol (DiC8); and (7) a calcium ionophore, A23187, alone and in combination with PMA. Somatostatin (10 ng/ml) reduced the release of GH stimulated by GRF, forskolin, and 8-bromo cAMP and the GRF-provoked release of GH in the presence of IBMX (P less than 0.05). Somatostatin, however, did not influence GH release in the presence of the protein kinase C activators, PMA or DiC8, or the calcium ionophore A23187. These data suggest that SRIF inhibits GRF-provoked GH release by reducing the ability of the cAMP-protein kinase A but not of the calcium or protein kinase C intracellular message pathways to stimulate GH release.
Collapse
Affiliation(s)
- D J Donoghue
- Department of Animal Science, Rutgers State University of New Jersey, New Brunswick 08903
| | | |
Collapse
|