1
|
Szeto A, Cecati M, Ahmed R, McCabe PM, Mendez AJ. Oxytocin reduces adipose tissue inflammation in obese mice. Lipids Health Dis 2020; 19:188. [PMID: 32819381 PMCID: PMC7441653 DOI: 10.1186/s12944-020-01364-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 08/10/2020] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND Obesity and adipose tissue expansion is characterized by a chronic state of systemic inflammation that contributes to disease. The neuropeptide, oxytocin, working through its receptor has been shown to attenuate inflammation in sepsis, wound healing, and cardiovascular disease. The current study examined the effects of chronic oxytocin infusions on adipose tissue inflammation in a murine model of obesity, the leptin receptor-deficient (db/db) mouse. METHODS The effect of obesity on oxytocin receptor protein and mRNA expression in adipose tissue was evaluated by Western blotting and real-time polymerase chain reaction. Mice were implanted with osmotic minipumps filled with oxytocin or vehicle for 8 weeks. At study endpoint adipose tissue inflammation was assessed by measurement of cytokine and adipokine mRNA tissue levels, adipocyte size and macrophage infiltration via histopathology, and plasma levels of adiponectin and serum amyloid A as markers of systemic inflammation. RESULTS The expression of adipose tissue oxytocin receptor was increased in obese db/db mice compared to lean controls. In adipose tissue oxytocin infusion reduced adipocyte size, macrophage infiltration, IL-6 and TNFα mRNA expression, and increased the expression of the anti-inflammatory adipokine, adiponectin. In plasma, oxytocin infusion reduced the level of serum amyloid A, a marker of systemic inflammation, and increased circulating adiponectin. CONCLUSIONS In an animal model of obesity and diabetes chronic oxytocin treatment led to a reduction in visceral adipose tissue inflammation and plasma markers of systemic inflammation, which may play a role in disease progression.
Collapse
Affiliation(s)
- Angela Szeto
- Department of Psychology, University of Miami, PO Box 248185, Coral Gables, FL, 33124, USA
| | - Monia Cecati
- Department of Medicine and Diabetes Research Institute, University of Miami Miller School of Medicine, 1450 N.W. 10th Avenue, Miami, FL, 33136, USA
| | - Raisa Ahmed
- Department of Psychology, University of Miami, PO Box 248185, Coral Gables, FL, 33124, USA
| | - Philip M McCabe
- Department of Psychology, University of Miami, PO Box 248185, Coral Gables, FL, 33124, USA
| | - Armando J Mendez
- Department of Medicine and Diabetes Research Institute, University of Miami Miller School of Medicine, 1450 N.W. 10th Avenue, Miami, FL, 33136, USA.
| |
Collapse
|
2
|
Kim SH, Bennett PR, Terzidou V. Advances in the role of oxytocin receptors in human parturition. Mol Cell Endocrinol 2017; 449:56-63. [PMID: 28119132 DOI: 10.1016/j.mce.2017.01.034] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Revised: 01/16/2017] [Accepted: 01/21/2017] [Indexed: 12/26/2022]
Abstract
Oxytocin (OT) is a neurohypophysial hormone which has been found to play a central role in the regulation of human parturition. The most established role of oxytocin/oxytocin receptor (OT/OTR) system in human parturition is the initiation of uterine contractions, however, recent evidence have demonstrated that it may have a more complex role including initiation of inflammation, regulation of miRNA expression, as well as mediation of other non-classical oxytocin actions via receptor crosstalk with other G protein-coupled receptors (GPCRs). In this review we highlight both established and newly emerging roles of OT/OTR system in human parturition and discuss the expanding potential for OTRs as pharmacological targets in the management of preterm labour.
Collapse
Affiliation(s)
- Sung Hye Kim
- Imperial College London, Parturition Research Group, Institute of Reproductive and Developmental Biology, Hammersmith Hospital Campus, Du Cane Road, East Acton, London W12 0NN, UK
| | - Phillip R Bennett
- Imperial College London, Parturition Research Group, Institute of Reproductive and Developmental Biology, Hammersmith Hospital Campus, Du Cane Road, East Acton, London W12 0NN, UK
| | - Vasso Terzidou
- Imperial College London, Parturition Research Group, Institute of Reproductive and Developmental Biology, Hammersmith Hospital Campus, Du Cane Road, East Acton, London W12 0NN, UK; Academic Department of Obstetrics & Gynaecology, Imperial College School of Medicine, Chelsea and Westminster Hospital, 369 Fulham Road, London SW10 9NH, UK.
| |
Collapse
|
3
|
Loke SY, Tanaka K, Ong WY. Comprehensive gene expression analyses of the rat prefrontal cortex after oxysterol treatment. J Neurochem 2013; 124:770-81. [DOI: 10.1111/jnc.12142] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Revised: 01/03/2013] [Accepted: 01/04/2013] [Indexed: 02/06/2023]
Affiliation(s)
- Sau-Yeen Loke
- Department of Anatomy; National University of Singapore; Singapore
| | - Kazuhiro Tanaka
- Department of Physiology; National University of Singapore; Singapore
| | - Wei-Yi Ong
- Department of Anatomy; National University of Singapore; Singapore
- Neurobiology and Ageing Research Programme; National University of Singapore; Singapore
| |
Collapse
|
4
|
Szeto A, Nation DA, Mendez AJ, Dominguez-Bendala J, Brooks LG, Schneiderman N, McCabe PM. Oxytocin attenuates NADPH-dependent superoxide activity and IL-6 secretion in macrophages and vascular cells. Am J Physiol Endocrinol Metab 2008; 295:E1495-501. [PMID: 18940936 PMCID: PMC2603556 DOI: 10.1152/ajpendo.90718.2008] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Oxytocin is synthesized and released in the heart and vasculature, tissues that also express oxytocin receptors. Although it has been established this intrinsic cardiovascular oxytocin system is important in normal homeostatic cardiac and vascular regulation, a role for this system in cardiovascular pathophysiology has not been investigated. The current study examined the influence of oxytocin on mechanisms in atherogenesis, oxidative stress, and inflammation in cultured human vascular cells, THP-1 monocytes, and macrophages. Oxytocin receptor protein and mRNA expression, NADPH-dependent superoxide activity, and interleukin-6 secretion were measured. Results demonstrated oxytocin receptor protein and mRNA in THP-1 monocytes and macrophages. Incubation of cells at physiological levels of oxytocin significantly decreased basal and stimulated NADPH-dependent superoxide activity in vascular cells, monocytes, and macrophages by 24-48%. Oxytocin also attenuated interleukin-6 secretion from stimulated THP-1 macrophages and endothelial cells by 56 and 26%, respectively. These findings suggest that oxytocin attenuates vascular oxidative stress and inflammation, two important pathophysiological processes in atherosclerosis. The fact that oxytocin receptors are found in monocytes and macrophages, and oxytocin decreases both superoxide production and release of a proinflammatory cytokine from these cells, suggests a potentially larger role for oxytocin in the attenuation of disease.
Collapse
Affiliation(s)
- Angela Szeto
- Dept. of Psychology, Univ. of Miami, Coral Gables, FL 33124, USA
| | | | | | | | | | | | | |
Collapse
|
5
|
Ndiaye K, Poole DH, Pate JL. Expression and regulation of functional oxytocin receptors in bovine T lymphocytes. Biol Reprod 2007; 78:786-93. [PMID: 18094352 DOI: 10.1095/biolreprod.107.065938] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The corpus luteum (CL) produces oxytocin (OXT), which has been proposed to regulate the pulsatile release of prostaglandin F2alpha during luteolysis in ruminants. This action of OXT is mediated via oxytocin receptors (OXTRs) present on uterine epithelial cells. It is hypothesized that luteal OXT acts as a paracrine regulator of resident immune cells. In the present study, OXTR mRNA expression in bovine lymphocytes was analyzed, as well as its regulation during the estrous cycle. OXTR transcripts were observed in freshly purified bovine peripheral blood mononuclear cells and T lymphocytes. OXTR mRNA in bovine lymphocytes on Day 3 was numerically greater than but not significantly different from that of Day 19 of the estrous cycle (P=0.091). In cultured T cells, estradiol (E2) treatment significantly increased the steady-state concentrations of OXTR mRNA, but the stimulatory effect of E2 was inhibited by the addition of progesterone (P4). Each of the major T cell subsets (CD4+, CD8+, and gamma delta+) expressed OXTR mRNA, with no significant difference in expression among them. Western blot analyses demonstrated the presence of the bovine OXTR protein at about 45 kDa in lymphocytes, as well as expression of the 14-kDa precursor of OXT. When lymphocytes were treated with OXT, intracellular concentrations of calcium ([Ca2+]i) were rapidly and dramatically increased. This study demonstrated that bovine lymphocytes express OXTRs and that this expression can be regulated in a steroid-dependent manner. Furthermore, OXT elicited a functional [Ca2+]i response in T lymphocytes, supporting the possibility that OXT within the CL could act as a paracrine or autocrine regulator of resident T lymphocytes.
Collapse
Affiliation(s)
- Kalidou Ndiaye
- Department of Animal Sciences, The Ohio State University/Ohio Agricultural Research and Development Center, Wooster, Ohio 44691, USA
| | | | | |
Collapse
|
6
|
Carnazzi E, Aumelas A, Mouillac B, Breton C, Guillou L, Barberis C, Seyer R. Design, synthesis and pharmacological characterization of a potent radioiodinated and photoactivatable peptidic oxytocin antagonist. J Med Chem 2001; 44:3022-30. [PMID: 11520211 DOI: 10.1021/jm010125u] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using a segment strategy, we have synthesized four iodinated photoactivatable cyclic peptidic ligands of oxytocin, bearing a beta-mercapto-betabeta-cyclopentamethylene propionic group (Pmp) on their N-terminus. All the syntheses were RP-HPLC monitored, and the compounds were HPLC purified. They were characterized by 1H NMR, MALDI-TOF, or FAB mass spectrometries. The affinities of Pmp-Tyr(Me)-Ile-Thr-Asn-Cys-Gly-Orn-Phe(3I,4N3)-NH2 (20), Pmp-Tyr-Ile-Thr-Asn-Cys-Gly-Orn-Phe(3I,4N3)-NH2 (21), Pmp-Tyr(Me)-Ile-Thr-Asn-Cys-Pro-Orn-Phe(3I,4N3)-NH2 (22), and Pmp-Tyr-Ile-Thr-Asn-Cys-Pro-Orn-Phe(3I,4N3)-NH2 (23) were evaluated as inhibition constants (K(i), in nM) for the human oxytocin receptor expressed in Chinese hamster ovary cells by displacement of a radioiodinated disulfide-cyclized antagonist (Elands et al. Eur. J. Pharmacol. 1987, 147, 197-207). The most potent of them, compound 22, was synthesized by another method in order to allow its radiolabeling by 125I. Its dissociation constant (K(d)) for the human oxytocin receptor, directly measured in saturation studies, was 0.25 +/- 0.04 nM, and its antagonist properties were determined by inactivation of phospholipase C, thus obtaining an inactivation constant (K(inact)) of 0.18 +/- 0.02 nM, evaluated by inositol phosphate accumulation. This compound is a very good tool for the mapping of peptidic antagonist binding sites in the human oxytocin receptor.
Collapse
MESH Headings
- Animals
- Binding, Competitive
- CHO Cells
- Chromatography, High Pressure Liquid
- Cricetinae
- Drug Design
- Humans
- In Vitro Techniques
- Inositol Phosphates/biosynthesis
- Iodine Radioisotopes
- Magnetic Resonance Spectroscopy
- Peptides, Cyclic/chemical synthesis
- Peptides, Cyclic/chemistry
- Peptides, Cyclic/pharmacology
- Photolysis
- Radioligand Assay
- Receptors, Oxytocin/antagonists & inhibitors
- Spectrometry, Mass, Fast Atom Bombardment
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
- Structure-Activity Relationship
Collapse
Affiliation(s)
- E Carnazzi
- CNRS UPR 9023 and INSERM U 469, CCIPE, 141, rue de la Cardonille, 34094 Montpellier Cedex 5, France.
| | | | | | | | | | | | | |
Collapse
|
7
|
Breton C, Chellil H, Kabbaj-Benmansour M, Carnazzi E, Seyer R, Phalipou S, Morin D, Durroux T, Zingg H, Barberis C, Mouillac B. Direct identification of human oxytocin receptor-binding domains using a photoactivatable cyclic peptide antagonist: comparison with the human V1a vasopressin receptor. J Biol Chem 2001; 276:26931-41. [PMID: 11337500 DOI: 10.1074/jbc.m102073200] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Understanding of the molecular determinants responsible for antagonist binding to the oxytocin receptor should provide important insights that facilitate rational design of potential therapeutic agents for the treatment of preterm labor. To study ligand/receptor interactions, we used a novel photosensitive radioiodinated antagonist of the human oxytocin receptor, d(CH(2))(5) [Tyr(Me)(2),Thr(4),Orn(8),Phe(3(125)I,4N(3))-NH(2)9]vasotocin. This ligand had an equivalent high affinity for human oxytocin and V(1a) vasopressin receptors expressed in Chinese hamster ovary cells. Taking advantage of this dual specificity, we conducted photoaffinity labeling experiments on both receptors. Photolabeled oxytocin and V(1a) receptors appeared as a unique protein band at 70-75 kDa and two labeled protein bands at 85-90 and 46 kDa, respectively. To identify contact sites between the antagonist and the receptors, the labeled 70-75- and the 46-kDa proteins were cleaved with CNBr and digested with Lys-C and Arg-C endoproteinases. The fragmentation patterns allowed the identification of a covalently labeled region in the oxytocin receptor transmembrane domain III consisting of the residues Leu(114)-Val(115)-Lys(116). Analysis of contact sites in the V(1a) receptor led to the identification of the homologous region consisting of the residues Val(126)-Val(127)-Lys(128). Binding domains were confirmed by mutation of several CNBr cleavage sites in the oxytocin receptor and of one Lys-C cleavage site in the V(1a) receptor. The results are in agreement with previous experimental data and three-dimensional models of agonist and antagonist binding to members of the oxytocin/vasopressin receptor family.
Collapse
Affiliation(s)
- C Breton
- U469 INSERM and the UPR 9023 CNRS, 141 rue de la Cardonille, 34094 Montpellier cedex 5, France
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
8
|
Abstract
The neurohypophysial peptide oxytocin (OT) and OT-like hormones facilitate reproduction in all vertebrates at several levels. The major site of OT gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to a variety of stimuli such as suckling, parturition, or certain kinds of stress, the processed OT peptide is released from the posterior pituitary into the systemic circulation. Such stimuli also lead to an intranuclear release of OT. Moreover, oxytocinergic neurons display widespread projections throughout the central nervous system. However, OT is also synthesized in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. The OT receptor is a typical class I G protein-coupled receptor that is primarily coupled via G(q) proteins to phospholipase C-beta. The high-affinity receptor state requires both Mg(2+) and cholesterol, which probably function as allosteric modulators. The agonist-binding region of the receptor has been characterized by mutagenesis and molecular modeling and is different from the antagonist binding site. The function and physiological regulation of the OT system is strongly steroid dependent. However, this is, unexpectedly, only partially reflected by the promoter sequences in the OT receptor gene. The classical actions of OT are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation. While the essential role of OT for the milk let-down reflex has been confirmed in OT-deficient mice, OT's role in parturition is obviously more complex. Before the onset of labor, uterine sensitivity to OT markedly increases concomitant with a strong upregulation of OT receptors in the myometrium and, to a lesser extent, in the decidua where OT stimulates the release of PGF(2 alpha). Experiments with transgenic mice suggest that OT acts as a luteotrophic hormone opposing the luteolytic action of PGF(2 alpha). Thus, to initiate labor, it might be essential to generate sufficient PGF(2 alpha) to overcome the luteotrophic action of OT in late gestation. OT also plays an important role in many other reproduction-related functions, such as control of the estrous cycle length, follicle luteinization in the ovary, and ovarian steroidogenesis. In the male, OT is a potent stimulator of spontaneous erections in rats and is involved in ejaculation. OT receptors have also been identified in other tissues, including the kidney, heart, thymus, pancreas, and adipocytes. For example, in the rat, OT is a cardiovascular hormone acting in concert with atrial natriuretic peptide to induce natriuresis and kaliuresis. The central actions of OT range from the modulation of the neuroendocrine reflexes to the establishment of complex social and bonding behaviors related to the reproduction and care of the offspring. OT exerts potent antistress effects that may facilitate pair bonds. Overall, the regulation by gonadal and adrenal steroids is one of the most remarkable features of the OT system and is, unfortunately, the least understood. One has to conclude that the physiological regulation of the OT system will remain puzzling as long as the molecular mechanisms of genomic and nongenomic actions of steroids have not been clarified.
Collapse
Affiliation(s)
- G Gimpl
- Institut für Biochemie, Johannes Gutenberg Universität, Mainz, Germany.
| | | |
Collapse
|
9
|
Kojro E, Postina R, Gilbert S, Bender F, Krause G, Fahrenholz F. Structural requirements for V2 vasopressin receptor proteolytic cleavage. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 266:538-48. [PMID: 10561596 DOI: 10.1046/j.1432-1327.1999.00892.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ligand-induced proteolytic cleavage of the V2 vasopressin receptor transiently expressed in COS cells was investigated. After incubation of the cell membranes with a photoreactive ligand possessing full agonistic properties for V2 receptors, approximately 90% of the porcine and bovine V2 vasopressin receptors were cleaved in the upper part of transmembrane helix 2 at a heptapeptide sequence conserved in both vasopressin and oxytocin receptors. The oxytocin receptor was completely resistant to proteolysis after binding the same photoreactive ligand, which is only a partial agonist for this receptor. Chimeric V2/oxytocin receptors obtained by transfer of extracellular domains of the oxytocin receptor into the V2 receptor showed an increase in binding affinity for oxytocin versus vasopressin and a diminished cleavage. The proteolysis-resistant chimeric V2/oxytocin receptor, which contains the first three extracellular domains of the oxytocin receptor, stimulated cAMP accumulation to a larger extent in response to vasopressin than the wild-type receptor and showed impaired desensitization of the adenylate cyclase system. Our data indicate that the proteolytic cleavage of the V2 receptor requires a defined conformation, especially of the first two extracellular domains that is induced by agonist binding. Furthermore, the results suggest that the proteolytic V2 receptor cleavage might play a role in signal termination at elevated hormone concentrations.
Collapse
MESH Headings
- Adenylyl Cyclases/metabolism
- Amino Acid Sequence
- Animals
- COS Cells
- Cattle
- Cloning, Molecular
- Cyclic AMP/metabolism
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- Enzyme Activation
- Humans
- Ligands
- Microscopy, Fluorescence
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Point Mutation
- Protein Binding
- Protein Conformation
- Protein Structure, Tertiary
- Proteins/metabolism
- Receptors, Oxytocin/chemistry
- Receptors, Vasopressin/chemistry
- Sequence Homology, Amino Acid
- Swine
- Time Factors
- Transfection
- Type C Phospholipases/metabolism
Collapse
Affiliation(s)
- E Kojro
- Institut für Biohemie, Johannes Gutenberg-Universität, Mainz, Germany
| | | | | | | | | | | |
Collapse
|
10
|
Affiliation(s)
- T Kimura
- Department of Obstetrics and Gynecology, Osaka University Medical School, Japan
| | | |
Collapse
|
11
|
Postina R, Kojro E, Fahrenholz F. Identification of neurohypophysial hormone receptor domains involved in ligand binding and G protein coupling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 449:371-85. [PMID: 10026828 DOI: 10.1007/978-1-4615-4871-3_48] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Chimeric vasopressin V2/OT receptors were constructed and investigated to identify receptor regions involved in ligand binding or G protein coupling. The fusion sites for one series of hybrid receptors were either located at the C-terminal end of the third extracellular domain or in the centre of the third transmembrane helix, respectively. In each pair of the resulting symmetrical hybrids only one receptor was able to bind arginine vasopressin (AVP) and/or oxytocin (OT). In both cases a major part of the vasopressin V2 receptor (V2R) was needed for ligand binding. A chimeric OT/V2 receptor including OT receptor (OTR) sequences from its N-terminus to the middle of transmembrane region three showed both high-affinity OT binding (Ki = 3 nM) and activation of the adenylyl cyclase. In contrast, a hybrid containing OTR sequences reaching from transmembrane helix five to its C-terminus showed the V2 receptor's ligand binding profile and was unable to couple to G alpha s. These results indicate (i) that the third and/or the fourth intracellular domain of the V2R are involved in G protein coupling and (ii) for high-affinity OT binding the N-terminal third of the OTR plays an important role. By detailed binding studies on a second series of chimeric V2/OT receptors with AVP, OT and the two hybrid hormone derivatives arginine vasotocin and oxypressin it was further demonstrated that the first two extracellular domains of the OTR are involved in binding to the C-terminal tripeptide of OT. Moreover, the third extracellular domain of the OTR is able to contact the cyclic part of OT and the fourth outer domain does not interact with the two variable amino acid residues of AVP and OT. Thus, the first three extracellular domains of the OTR provide an essential part of the OT binding site. The other part is most probably contributed by the OTR's transmembrane helices 3 and 4. Photoaffinity labeling and ligand binding studies demonstrated that the binding site for the OT antagonist d(CH2)5[Tyr(Me)2, Thr4, Orn8, Tyr9]vasotocin is located in the helices 1, 2 and 7. Our results provide evidence for the existence of separate domains of a peptide hormone receptor involved in binding and selectivity for agonists and peptide antagonists.
Collapse
Affiliation(s)
- R Postina
- Max-Planck-Institut für Biophysik, Frankfurt am Main, Germany
| | | | | |
Collapse
|
12
|
Postina R, Kojro E, Fahrenholz F. Separate agonist and peptide antagonist binding sites of the oxytocin receptor defined by their transfer into the V2 vasopressin receptor. J Biol Chem 1996; 271:31593-601. [PMID: 8940177 DOI: 10.1074/jbc.271.49.31593] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The neurohypophyseal nonapeptide oxytocin (OT) is the main hormone responsible for the initiation of labor; uterus contraction can be enhanced by application of oxytocin or suppressed by oxytocin antagonists. By transfer of domains from the G protein-coupled OT receptor into the related V2 vasopressin receptor, chimeric "gain in function" V2/OT receptors were produced that were able to bind either OT receptor agonists or a competitive peptide antagonist with high affinity. The binding site for the OT antagonist d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr9]vasotocin was found to be formed by transmembrane helices 1, 2, and 7 with a major contribution to binding affinity by the upper part of helix 7. These transmembrane receptor regions could be excluded from participating in OT binding. For agonist binding and selectivity the first three extracellular receptor domains were most important. The interaction of the N-terminal domain and of the first extracellular loop of the OT receptor with the linear C-terminal tripeptidic part of oxytocin was demonstrated. Furthermore, the second extracellular loop of the OT receptor could be identified to interact with the cyclic hormone part. These three domains contribute to OT binding by synergistic interaction with oxytocin but not with the competitive antagonist. Our results provide evidence for the existence of separate domains and different conformations of a peptide hormone receptor involved in binding and selectivity for agonists and peptide antagonists.
Collapse
Affiliation(s)
- R Postina
- Max-Planck-Institut für Biophysik, Kennedyallee 70, 60596 Frankfurt am Main, Federal Republic of Germany
| | | | | |
Collapse
|
13
|
Barbeau D, Bouley R, Escher E. Molecular weight determination of the hepatic vasopressin receptor with a high-affinity photoprobe. INTERNATIONAL JOURNAL OF PEPTIDE AND PROTEIN RESEARCH 1996; 48:364-73. [PMID: 8919057 DOI: 10.1111/j.1399-3011.1996.tb00853.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We report here a study of photoaffinity labeling of the V1a-vasopressin receptor with high-affinity, V1-specific radioiodinated antagonist ligands: one containing an azidophenylalanine residue ([beta,beta-dimethyl-beta-mercaptopropionyl(1), p-azido-Phe2,Val4,Lys8,D-Tyr9] vasopressin), two others containing nitrophenylalanine, and one, highly similar but without a photosensitive function, as control. All analogues competed in the dark for the same binding site with vasopressin. Long-wavelength UV irradiation of rat liver membranes incubated in presence of the radio-iodinated azido photolabel produced a specifically labeled protein band at 53 kDa in SDS-PAGE. Identical experiments with the nitrophenylalanyl peptides produced only non-specific labeling and control experiments with the non-photosensitive analogue produced no labeling at all. Chemical crosslinking of 3H-VP to the same membrane preparation produced a result identical to that of the azido photolabel, confirming the receptor nature of the labeled protein. Deglycosylation of the labeled receptor with endoglycosidase F reduced the observed molecular weight of 53 kDa to 43 kDa. The molecular parameters reported herein of the presumed hepatic vasopressin receptor confirm the values deduced from the molecular cloning of the rat V1a receptor.
Collapse
Affiliation(s)
- D Barbeau
- Department of Pharmacology, Faculty of Medicine, Sherbrooke University, Quebec, Canada
| | | | | |
Collapse
|
14
|
Klein U, Jurzak M, Gerstberger R, Fahrenholz F. A new tritiated oxytocin receptor radioligand--synthesis and application for localization of central oxytocin receptors. Peptides 1995; 16:851-7. [PMID: 7479326 DOI: 10.1016/0196-9781(95)00039-m] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A new tritiated oxytocin antagonist radioligand was synthesized by introducing a tritiated propionic acid residue into the free amino group of ornithine in position 8 of the parent peptide [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid), 2-(O-methyl)-tyrosine, 4-threonine, 8-ornithine, 9-tyrosylamide]vasotocin (OTA), that was previously described. The tritiated compound [3H][1-(beta-mercapto-beta,beta-cyclo-pentamethylene propionic acid), 2-(O-methyl)-tyrosine, 4-threonine, 8-(N6-propionyl)-ornithine, 9-tyrosylamide]vasotocin ([3H]PrOTA) was obtained in good yield with high specific activity (100 Ci/mmol). [3H]PrOTA exhibited the same affinity (Kd = 0.8 nM) and selectivity for the myometrial oxytocin receptor as the iodinated antagonist [125I]OTA. Autoradiographic localization of oxytocin receptors in the rat brain showed specific binding sites for [3H]PrOTA within regions of the limbic system, the neocortex, and hypothalamus, which is consistent with the binding pattern obtained with [125I]OTA. The high specific activity in combination with the long half-life of tritium and its low radiotoxicity as compared to iodine-125 makes the new tritiated antagonist a valuable tool for pharmacological studies.
Collapse
Affiliation(s)
- U Klein
- Max-Planck-Institut für Biophysik, Frankfurt, Germany
| | | | | | | |
Collapse
|
15
|
Klein U, Fahrenholz F. Reconstitution of the myometrial oxytocin receptor into proteoliposomes. Dependence of oxytocin binding on cholesterol. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 220:559-67. [PMID: 8125115 DOI: 10.1111/j.1432-1033.1994.tb18656.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The requirements for regaining high-affinity binding of the myometrial oxytocin receptor after detergent solubilization were investigated by reconstitution experiments. Large unilamellar liposomes were prepared by reverse-phase evaporation from different mixtures of phospholipids, cholesterol and cholesteryl hemisuccinate. In the presence of the oxytocin receptor solubilized from myometrial membranes from pregnant guinea pig uterus, liposomes were treated with 3-[(3-cholamidopropyl)-dimethylammonio]-2-hydroxy-1-propanesulfonate (Chapso) throughout the range of detergent concentrations that cause the transformation of lamellar structures to mixed micelles. Detergent removal was achieved using bio-beads SM-2 as adsorbent. The presence of cholesterol was a prerequisite for regaining high-affinity binding of [3H]oxytocin and 125I-oxytocin antagonist to reconstituted proteoliposomes. Binding of [3H]oxytocin but not of the antagonist was dependent on the presence of Mn2+ ions. Reconstitution after lectin chromatography and photoaffinity labeling of reconstituted vesicles resulted in the exclusive labeling of the oxytocin receptor with a molecular mass of 68-80 kDa.
Collapse
Affiliation(s)
- U Klein
- Max-Planck-Institut für Biophysik, Frankfurt, Germany
| | | |
Collapse
|