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Signoret-Genest J, Barnet M, Gabrielli F, Aissouni Y, Artola A, Dallel R, Antri M, Tovote P, Monconduit L. Compromised trigemino-coerulean coupling in migraine sensitization can be prevented by blocking beta-receptors in the locus coeruleus. J Headache Pain 2023; 24:165. [PMID: 38062355 PMCID: PMC10704784 DOI: 10.1186/s10194-023-01691-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 11/11/2023] [Indexed: 12/18/2023] Open
Abstract
BACKGROUND Migraine is a disabling neurological disorder, characterized by recurrent headaches. During migraine attacks, individuals often experience sensory symptoms such as cutaneous allodynia which indicates the presence of central sensitization. This sensitization is prevented by oral administration of propranolol, a common first-line medication for migraine prophylaxis, that also normalized the activation of the locus coeruleus (LC), considered as the main origin of descending noradrenergic pain controls. We hypothesized that the basal modulation of trigeminal sensory processing by the locus coeruleus is shifted towards more facilitation in migraineurs and that prophylactic action of propranolol may be attributed to a direct action in LC through beta-adrenergic receptors. METHODS We used simultaneous in vivo extracellular recordings from the trigeminocervical complex (TCC) and LC of male Sprague-Dawley rats to characterize the relationship between these two areas following repeated meningeal inflammatory soup infusions. Von Frey Hairs and air-puff were used to test periorbital mechanical allodynia. RNAscope and patch-clamp recordings allowed us to examine the action mechanism of propranolol. RESULTS We found a strong synchronization between TCC and LC spontaneous activities, with a precession of the LC, suggesting the LC drives TCC excitability. Following repeated dural-evoked trigeminal activations, we observed a disruption in coupling of activity within LC and TCC. This suggested an involvement of the two regions' interactions in the development of sensitization. Furthermore, we showed the co-expression of alpha-2A and beta-2 adrenergic receptors within LC neurons. Finally propranolol microinjections into the LC prevented trigeminal sensitization by desynchronizing and decreasing LC neuronal activity. CONCLUSIONS Altogether these results suggest that trigemino-coerulean coupling plays a pivotal role in migraine progression, and that propranolol's prophylactic effects involve, to some extent, the modulation of LC activity through beta-2 adrenergic receptors. This insight reveals new mechanistic aspects of LC control over sensory processing.
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Affiliation(s)
- Jérémy Signoret-Genest
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
- Institute of Clinical Neurobiology, University Hospital Würzburg, 97078, Würzburg, Germany
- Department of Psychiatry, Center of Mental Health, University Hospital Würzburg, 97078, Würzburg, Germany
| | - Maxime Barnet
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
| | - François Gabrielli
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
| | - Youssef Aissouni
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
| | - Alain Artola
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
| | - Radhouane Dallel
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
| | - Myriam Antri
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France
| | - Philip Tovote
- Institute of Clinical Neurobiology, University Hospital Würzburg, 97078, Würzburg, Germany
| | - Lénaïc Monconduit
- Université Clermont Auvergne, CHU Clermont-Ferrand, Inserm/UCA U1107, Neuro-Dol: Trigeminal Pain and Migraine, Faculté de Chirurgie Dentaire, 2 Rue de Braga, 63100, Clermont-Ferrand, France.
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Interaction kinetics between p115-RhoGEF and Gα 13 are determined by unique molecular interactions affecting agonist sensitivity. Commun Biol 2022; 5:1287. [PMID: 36434027 PMCID: PMC9700851 DOI: 10.1038/s42003-022-04224-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 11/04/2022] [Indexed: 11/27/2022] Open
Abstract
The three RH-RhoGEFs (Guanine nucleotide exchange factors) p115-RhoGEF, LARG (leukemia-associated RhoGEF) and PDZ-RhoGEF link G-protein coupled receptors (GPCRs) with RhoA signaling through activation of Gα12/13. In order to find functional differences in signaling between the different RH-RhoGEFs we examined their interaction with Gα13 in high spatial and temporal resolution, utilizing a FRET-based single cell assay. We found that p115-RhoGEF interacts significantly shorter with Gα13 than LARG and PDZ-RhoGEF, while narrowing the structural basis for these differences down to a single amino acid in the rgRGS domain of p115-RhoGEF. The mutation of this amino acid led to an increased interaction time with Gα13 and an enhanced agonist sensitivity, comparable to LARG, while mutating the corresponding amino acid in Gα13 the same effect could be achieved. While the rgRGS domains of RH-RhoGEFs showed GAP (GTPase-activating protein) activity towards Gα13 in vitro, our approach suggests higher GAP activity of p115-RhoGEF in intact cells.
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Copits BA, Gowrishankar R, O'Neill PR, Li JN, Girven KS, Yoo JJ, Meshik X, Parker KE, Spangler SM, Elerding AJ, Brown BJ, Shirley SE, Ma KKL, Vasquez AM, Stander MC, Kalyanaraman V, Vogt SK, Samineni VK, Patriarchi T, Tian L, Gautam N, Sunahara RK, Gereau RW, Bruchas MR. A photoswitchable GPCR-based opsin for presynaptic inhibition. Neuron 2021; 109:1791-1809.e11. [PMID: 33979635 PMCID: PMC8194251 DOI: 10.1016/j.neuron.2021.04.026] [Citation(s) in RCA: 55] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 04/21/2021] [Accepted: 04/26/2021] [Indexed: 12/12/2022]
Abstract
Optical manipulations of genetically defined cell types have generated significant insights into the dynamics of neural circuits. While optogenetic activation has been relatively straightforward, rapid and reversible synaptic inhibition has proven more elusive. Here, we leveraged the natural ability of inhibitory presynaptic GPCRs to suppress synaptic transmission and characterize parapinopsin (PPO) as a GPCR-based opsin for terminal inhibition. PPO is a photoswitchable opsin that couples to Gi/o signaling cascades and is rapidly activated by pulsed blue light, switched off with amber light, and effective for repeated, prolonged, and reversible inhibition. PPO rapidly and reversibly inhibits glutamate, GABA, and dopamine release at presynaptic terminals. Furthermore, PPO alters reward behaviors in a time-locked and reversible manner in vivo. These results demonstrate that PPO fills a significant gap in the neuroscience toolkit for rapid and reversible synaptic inhibition and has broad utility for spatiotemporal control of inhibitory GPCR signaling cascades.
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Affiliation(s)
- Bryan A Copits
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA.
| | - Raaj Gowrishankar
- Center of Excellence in the Neurobiology of Addiction, Pain, and Emotion, Departments of Anesthesiology and Pain Medicine, and Pharmacology, University of Washington, Seattle, WA, USA
| | - Patrick R O'Neill
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA; Shirley and Stefan Hatos Center for Neuropharmacology, Semel Institute, Department of Psychiatry and Biobehavioral Sciences, University of California Los Angeles, Los Angeles, CA
| | - Jun-Nan Li
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Kasey S Girven
- Center of Excellence in the Neurobiology of Addiction, Pain, and Emotion, Departments of Anesthesiology and Pain Medicine, and Pharmacology, University of Washington, Seattle, WA, USA
| | - Judy J Yoo
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Xenia Meshik
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Kyle E Parker
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Skylar M Spangler
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Abigail J Elerding
- Center of Excellence in the Neurobiology of Addiction, Pain, and Emotion, Departments of Anesthesiology and Pain Medicine, and Pharmacology, University of Washington, Seattle, WA, USA
| | - Bobbie J Brown
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Sofia E Shirley
- Center of Excellence in the Neurobiology of Addiction, Pain, and Emotion, Departments of Anesthesiology and Pain Medicine, and Pharmacology, University of Washington, Seattle, WA, USA
| | - Kelly K L Ma
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Alexis M Vasquez
- Department of Pharmacology, University of California San Diego, San Diego, CA, USA
| | - M Christine Stander
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Vani Kalyanaraman
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Sherri K Vogt
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Vijay K Samineni
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Tommaso Patriarchi
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Lin Tian
- Department of Biochemistry and Molecular Medicine, University of California Davis, Davis, CA, USA
| | - N Gautam
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA
| | - Roger K Sunahara
- Department of Pharmacology, University of California San Diego, San Diego, CA, USA
| | - Robert W Gereau
- Washington University Pain Center, Washington University School of Medicine, St. Louis, MO, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA; Department of Neuroscience, Washington University School of Medicine, St. Louis, MO, USA
| | - Michael R Bruchas
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO, USA; Department of Neuroscience, Washington University School of Medicine, St. Louis, MO, USA; Center of Excellence in the Neurobiology of Addiction, Pain, and Emotion, Departments of Anesthesiology and Pain Medicine, and Pharmacology, University of Washington, Seattle, WA, USA.
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Gadgaard C, Jensen AA. Functional characterization of 5-HT 1A and 5-HT 1B serotonin receptor signaling through G-protein-activated inwardly rectifying K + channels in a fluorescence-based membrane potential assay. Biochem Pharmacol 2020; 175:113870. [PMID: 32088264 DOI: 10.1016/j.bcp.2020.113870] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Accepted: 02/18/2020] [Indexed: 11/15/2022]
Abstract
The 5-HT1A and 5-HT1B serotonin receptors are abundantly expressed in the CNS and constitute validated as well as putative drug targets in a variety of psychiatric and cognitive disorders, alcoholism/addiction, pain and migraine. In the present study we have characterized the functional properties of human 5-HT1A and 5-HT1B stably co-expressed with the human G-protein-activated inwardly rectifying K+ channel 2 (GIRK2) in HEK293 cells in the fluorescence-based FLIPR® Membrane Potential Blue (FMP) assay. Serotonin and other agonists induced robust decreases in fluorescence levels in the 5-HT1A/GIRK2- and 5-HT1B/GIRK2-HEK293 cells in a concentration-dependent manner in the assay, and these responses could be inhibited by selective 5-HT1A/5-HT1B antagonists and by the Gαi/o-protein inhibitor pertussis toxin (PTX). Five additional stable HEK293 cell lines co-expressing 5-HT1A or 5-HT1B with GIRK2 and one of the PTX-insensitive Gαi/o-subunit mutants Gαi1C351I, Gαi2C352I and Gαo1C351I were constructed, and 5-HT1A/5-HT1B-mediated responses through these specific Gαi/o-subunits were measured in these cells pretreated with PTX in the FMP assay. The functional properties of 16 reference 5-HT1 agonists were characterized at the seven cell lines, which constitutes the most detailed pharmacological profiling and comparison of 5-HT1A and 5-HT1B receptor signaling in the same assay published to date. We propose that this approach to assay 5-HT1-mediated signaling through endogenous Gαi/o-proteins in HEK293 cells or through specific Gαi/o-subunits in a fairly high-throughput manner holds some advantages to other functional assays for Gαi/o-coupled receptors. The assay will facilitate detailed profiling of the Gαi/o- and Gβγ-mediated signaling of 5-HT1A and 5-HT1B at the molecular level, and it could also be used to identify novel modulators for the receptors.
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Affiliation(s)
- Camilla Gadgaard
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen Ø, Denmark
| | - Anders A Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen Ø, Denmark.
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Ilyaskina OS, Lemoine H, Bünemann M. Lifetime of muscarinic receptor-G-protein complexes determines coupling efficiency and G-protein subtype selectivity. Proc Natl Acad Sci U S A 2018; 115:5016-5021. [PMID: 29686069 PMCID: PMC5948956 DOI: 10.1073/pnas.1715751115] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
G-protein-coupled receptors (GPCRs) are essential for the detection of extracellular stimuli by cells and transfer the encoded information via the activation of functionally distinct subsets of heterotrimeric G proteins into intracellular signals. Despite enormous achievements toward understanding GPCR structures, major aspects of the GPCR-G-protein selectivity mechanism remain unresolved. As this can be attributed to the lack of suitable and broadly applicable assays, we set out to develop a quantitative FRET-based assay to study kinetics and affinities of G protein binding to activated GPCRs in membranes of permeabilized cells in the absence of nucleotides. We measured the association and dissociation kinetics of agonist-induced binding of Gi/o, Gq/11, Gs, and G12/13 proteins to muscarinic M1, M2, and M3 receptors in the absence of nucleotides between fluorescently labeled G proteins and receptors expressed in mammalian cells. Our results show a strong quantitative correlation between not the on-rates of G-protein-M3-R interactions but rather the affinities of Gq and Go proteins to M3-Rs, their GPCR-G-protein lifetime and their coupling efficiencies determined in intact cells, suggesting that the G-protein subtype-specific affinity to the activated receptor in the absence of nucleotides is, in fact, a major determinant of the coupling efficiency. Our broadly applicable FRET-based assay represents a fast and reliable method to quantify the intrinsic affinity and relative coupling selectivity of GPCRs toward all G-protein subtypes.
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Affiliation(s)
- Olga S Ilyaskina
- Department of Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, University of Marburg, 35032 Marburg, Germany
| | - Horst Lemoine
- Department of Laser Medicine, Heinrich Heine University, 40225 Düsseldorf, Germany
| | - Moritz Bünemann
- Department of Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, University of Marburg, 35032 Marburg, Germany;
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Mui RK, Fernandes RN, Garver HG, Van Rooijen N, Galligan JJ. Macrophage-dependent impairment of α 2-adrenergic autoreceptor inhibition of Ca 2+ channels in sympathetic neurons from DOCA-salt but not high-fat diet-induced hypertensive rats. Am J Physiol Heart Circ Physiol 2018; 314:H863-H877. [PMID: 29351460 DOI: 10.1152/ajpheart.00536.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
DOCA-salt and obesity-related hypertension are associated with inflammation and sympathetic nervous system hyperactivity. Prejunctional α2-adrenergic receptors (α2ARs) provide negative feedback to norepinephrine release from sympathetic nerves through inhibition of N-type Ca2+ channels. Increased neuronal norepinephrine release in DOCA-salt and obesity-related hypertension occurs through impaired α2AR signaling; however, the mechanisms involved are unclear. Mesenteric arteries are resistance arteries that receive sympathetic innervation from the superior mesenteric and celiac ganglia (SMCG). We tested the hypothesis that macrophages impair α2AR-mediated inhibition of Ca2+ channels in SMCG neurons from DOCA-salt and high-fat diet (HFD)-induced hypertensive rats. Whole cell patch-clamp methods were used to record Ca2+ currents from SMCG neurons maintained in primary culture. We found that DOCA-salt, but not HFD-induced, hypertension caused macrophage accumulation in mesenteric arteries, increased SMCG mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-α, and impaired α2AR-mediated inhibition of Ca2+ currents in SMCG neurons. α2AR dysfunction did not involve changes in α2AR expression, desensitization, or downstream signaling factors. Oxidative stress impaired α2AR-mediated inhibition of Ca2+ currents in SMCG neurons and resulted in receptor internalization in human embryonic kidney-293T cells. Systemic clodronate-induced macrophage depletion preserved α2AR function and lowered blood pressure in DOCA-salt rats. HFD caused hypertension without obesity in Sprague-Dawley rats and hypertension with obesity in Dahl salt-sensitive rats. HFD-induced hypertension was not associated with inflammation in SMCG and mesenteric arteries or α2AR dysfunction in SMCG neurons. These results suggest that macrophage-mediated α2AR dysfunction in the mesenteric circulation may only be relevant to mineralocorticoid-salt excess. NEW & NOTEWORTHY Here, we identify a contribution of macrophages to hypertension development through impaired α2-adrenergic receptor (α2AR)-mediated inhibition of sympathetic nerve terminal Ca2+ channels in DOCA-salt hypertensive rats. Impaired α2AR function may involve oxidative stress-induced receptor internalization. α2AR dysfunction may be unique to mineralocorticoid-salt excess, as it does not occur in obesity-related hypertension.
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Affiliation(s)
- Ryan K Mui
- Department of Physiology, Michigan State University , East Lansing, Michigan
| | - Roxanne N Fernandes
- Department of Pharmacology and Toxicology, Michigan State University , East Lansing, Michigan
| | - Hannah G Garver
- Department of Pharmacology and Toxicology, Michigan State University , East Lansing, Michigan
| | - Nico Van Rooijen
- Department of Molecular Cell Biology, Vrije Universiteit Medical Center , Amsterdam , The Netherlands
| | - James J Galligan
- Department of Pharmacology and Toxicology, Michigan State University , East Lansing, Michigan.,Neuroscience Program, Michigan State University , East Lansing, Michigan
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Shioda N, Yabuki Y, Wang Y, Uchigashima M, Hikida T, Sasaoka T, Mori H, Watanabe M, Sasahara M, Fukunaga K. Endocytosis following dopamine D 2 receptor activation is critical for neuronal activity and dendritic spine formation via Rabex-5/PDGFRβ signaling in striatopallidal medium spiny neurons. Mol Psychiatry 2017; 22:1205-1222. [PMID: 27922607 DOI: 10.1038/mp.2016.200] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 09/28/2016] [Accepted: 10/04/2016] [Indexed: 02/06/2023]
Abstract
Aberrant dopamine D2 receptor (D2R) activity is associated with neuropsychiatric disorders, making those receptors targets for antipsychotic drugs. Here, we report that novel signaling through the intracellularly localized D2R long isoform (D2LR) elicits extracellular signal-regulated kinase (ERK) activation and dendritic spine formation through Rabex-5/platelet-derived growth factor receptor-β (PDGFRβ)-mediated endocytosis in mouse striatum. We found that D2LR directly binds to and activates Rabex-5, promoting early-endosome formation. Endosomes containing D2LR and PDGFRβ are then transported to the Golgi apparatus, where those complexes trigger Gαi3-mediated ERK signaling. Loss of intracellular D2LR-mediated ERK activation decreased neuronal activity and dendritic spine density in striatopallidal medium spiny neurons (MSNs). In addition, dendritic spine density in striatopallidal MSNs significantly increased following treatment of striatal slices from wild-type mice with quinpirole, a D2R agonist, but those changes were lacking in D2LR knockout mice. Moreover, intracellular D2LR signaling mediated effects of a typical antipsychotic drug, haloperidol, in inducing catalepsy behavior. Taken together, intracellular D2LR signaling through Rabex-5/PDGFRβ is critical for ERK activation, dendritic spine formation and neuronal activity in striatopallidal MSNs of mice.
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Affiliation(s)
- N Shioda
- Department of Biofunctional Analysis Laboratory of Molecular Biology, Gifu Pharmaceutical University, Gifu, Japan
| | - Y Yabuki
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan
| | - Y Wang
- Department of Pharmacology, Beckman Institute, University of Illinois, Urbana, IL, USA
| | - M Uchigashima
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - T Hikida
- Department of Research and Drug Discovery, Medical Innovation Center, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - T Sasaoka
- Department of Comparative and Experimental Medicine, Brain Research Institute, Niigata University, Niigata, Japan
| | - H Mori
- Department of Molecular Neuroscience, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan
| | - M Watanabe
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - M Sasahara
- Department of Pathology, Graduate School of Medicine and Pharmaceutical Sciences for Research, University of Toyama, Toyama, Japan
| | - K Fukunaga
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Japan
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Chishiki K, Kamakura S, Hayase J, Sumimoto H. Ric-8A, an activator protein of Gαi, controls mammalian epithelial cell polarity for tight junction assembly and cystogenesis. Genes Cells 2017; 22:293-309. [PMID: 28185378 DOI: 10.1111/gtc.12477] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Accepted: 01/11/2017] [Indexed: 01/04/2023]
Abstract
Correct cyst morphogenesis of epithelial cells requires apical-basal polarization, which is partly regulated by mitotic spindle orientation, a process dependent on the heterotrimeric G protein subunit Gαi and its binding protein LGN. Here, we show that in three-dimensional culture of mammalian epithelial Madin-Darby canine kidney (MDCK) cells, the Gαi-activating protein Ric-8A is crucial for orientation of the mitotic spindle and formation of normal cysts that comprise a single layer of polarized cells with their apical surfaces lining an inner lumen. Consistent with the involvement of LGN, cystogenesis can be well organized by ADP-ribosylated Gαi, retaining the ability to interact with LGN, but not by the interaction-defective mutant protein Gαi2 (N150I). In monolayer culture of MDCK cells, functional tight junction (TJ) assembly, a process associated with epithelial cell polarization, is significantly delayed in Ric-8A-depleted cells as well as in Gαi-depleted cells in a mitosis-independent manner. Ric-8A knockdown results in a delayed cortical delivery of Gαi and the apical membrane protein gp135, and an increased formation of intercellular lumens surrounded by membranes rich in Gαi3 and gp135. TJ development also involves LGN and its related protein AGS3. Thus, Ric-8A regulates mammalian epithelial cell polarity for TJ assembly and cystogenesis probably in concert with Gαi and LGN/AGS3.
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Affiliation(s)
- Kanako Chishiki
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka, 812-8582, Japan
| | - Sachiko Kamakura
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka, 812-8582, Japan
| | - Junya Hayase
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka, 812-8582, Japan
| | - Hideki Sumimoto
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka, 812-8582, Japan
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Chishiki K, Kamakura S, Hayase J, Yuzawa S, Sumimoto H. Ric-8A-mediated stabilization of the trimeric G protein subunit Gαi is inhibited by pertussis toxin-catalyzed ADP-ribosylation. Biochem Biophys Res Commun 2017; 483:941-945. [PMID: 28082199 DOI: 10.1016/j.bbrc.2017.01.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2016] [Accepted: 01/09/2017] [Indexed: 11/26/2022]
Abstract
The heterotrimeric G protein subunit Gαi can be activated by G protein-coupled receptors and the cytosolic protein Ric-8A, the latter of which is also known to prevent ubiquitin-dependent degradation of Gαi. Here we show that the amounts of the three Gαi-related proteins Gαi1, Gαi2, and Gαi3, but not that of Gαq, are rapidly decreased by cell treatment with pertussis toxin (PTX). The decrease appears to be due to ADP-ribosylation of Gαi, because PTX treatment does not affect the amount of a mutant Gαi2 carrying alanine substitution for Cys352, the residue that is ADP-ribosylated by the toxin. The presence of endogenous and exogenous Ric-8A increases Gαi stability as shown in cells treated with the protein synthesis inhibitor cycloheximide; however, Ric-8A fails to efficiently stabilize ADP-ribosylated Gαi. The failure agrees with the inability of Ric-8A to bind to ADP-ribosylated Gαi both in vitro and in vivo. Thus PTX appears to exert its pathological effects at least in part by converting Gαi to an unstable ADP-ribosylated form, in addition to the well-known inability of ADP-ribosylated Gαi to transduce signals triggered by G protein-coupled receptors.
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Affiliation(s)
- Kanako Chishiki
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan
| | - Sachiko Kamakura
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan
| | - Junya Hayase
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan
| | - Satoru Yuzawa
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan
| | - Hideki Sumimoto
- Department of Biochemistry, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan.
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Tarchini B, Tadenev ALD, Devanney N, Cayouette M. A link between planar polarity and staircase-like bundle architecture in hair cells. Development 2016; 143:3926-3932. [PMID: 27660326 DOI: 10.1242/dev.139089] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 09/14/2016] [Indexed: 01/14/2023]
Abstract
Sensory perception in the inner ear relies on the hair bundle, the highly polarized brush of movement detectors that crowns hair cells. We previously showed that, in the mouse cochlea, the edge of the forming bundle is defined by the 'bare zone', a microvilli-free sub-region of apical membrane specified by the Insc-LGN-Gαi protein complex. We now report that LGN and Gαi also occupy the very tip of stereocilia that directly abut the bare zone. We demonstrate that LGN and Gαi are both essential for promoting the elongation and differential identity of stereocilia across rows. Interestingly, we also reveal that total LGN-Gαi protein amounts are actively balanced between the bare zone and stereocilia tips, suggesting that early planar asymmetry of protein enrichment at the bare zone confers adjacent stereocilia their tallest identity. We propose that LGN and Gαi participate in a long-inferred signal that originates outside the bundle to model its staircase-like architecture, a property that is essential for direction sensitivity to mechanical deflection and hearing.
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Affiliation(s)
- Basile Tarchini
- The Jackson Laboratory, Bar Harbor, ME 04609, USA .,Department of Medicine, Tufts University, Boston, MA 02111, USA.,Graduate School of Biomedical Science and Engineering (GSBSE), University of Maine, Orono, ME 04469, USA.,Cellular Neurobiology Research Unit, Institut de recherches cliniques de Montréal (IRCM), Montreal, Quebec, Canada H2W 1R7
| | | | | | - Michel Cayouette
- Cellular Neurobiology Research Unit, Institut de recherches cliniques de Montréal (IRCM), Montreal, Quebec, Canada H2W 1R7 .,Department of Medicine, Université de Montréal, Montreal, Quebec, Canada H3T 1J4.,Department of Anatomy and Cell Biology, and Division of Experimental Medicine, McGill University, Montreal, Quebec, Canada H3A 0G4
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11
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Weichert D, Banerjee A, Hiller C, Kling RC, Hübner H, Gmeiner P. Molecular Determinants of Biased Agonism at the Dopamine D2 Receptor. J Med Chem 2015; 58:2703-17. [DOI: 10.1021/jm501889t] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Dietmar Weichert
- Department of Chemistry and
Pharmacy, Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19, 91052 Erlangen, Germany
| | - Ashutosh Banerjee
- Department of Chemistry and
Pharmacy, Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19, 91052 Erlangen, Germany
| | - Christine Hiller
- Department of Chemistry and
Pharmacy, Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19, 91052 Erlangen, Germany
| | - Ralf C. Kling
- Department of Chemistry and
Pharmacy, Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19, 91052 Erlangen, Germany
| | - Harald Hübner
- Department of Chemistry and
Pharmacy, Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19, 91052 Erlangen, Germany
| | - Peter Gmeiner
- Department of Chemistry and
Pharmacy, Medicinal Chemistry, Emil Fischer Center, Friedrich Alexander University, Schuhstraße 19, 91052 Erlangen, Germany
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12
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Gozalo-Marcilla M, Gasthuys F, Schauvliege S. Partial intravenous anaesthesia in the horse: a review of intravenous agents used to supplement equine inhalation anaesthesia. Part 2: opioids and alpha-2 adrenoceptor agonists. Vet Anaesth Analg 2015; 42:1-16. [DOI: 10.1111/vaa.12196] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Accepted: 09/13/2013] [Indexed: 01/04/2023]
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Wolters V, Krasel C, Brockmann J, Bünemann M. Influence of gαq on the dynamics of m3-acetylcholine receptor-g-protein-coupled receptor kinase 2 interaction. Mol Pharmacol 2014; 87:9-17. [PMID: 25316767 DOI: 10.1124/mol.114.094722] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
G-protein-coupled receptor kinase 2 (GRK2) is a serine/threonine kinase with an important function in the desensitization of G-protein-coupled receptors. Based on its ability to bind G-protein βγ subunits as well as activated Gαq subunits, it can be considered as an effector for G-proteins. The recruitment of GRK2 to activated receptors is well known to be mediated by Gβγ together with negatively charged membrane phospholipids. In the current study, we address the role of Gαq on the interaction of GRK2 with activated Gq-protein-coupled receptors. Therefore, we established new Förster resonance energy transfer (FRET)-based assays to study the interaction of GRK2 with the M3-acetylcholine (M3-ACh) receptor as well as Gq-protein subunits with high spatiotemporal resolution in single living human embryonic kidney 293T cells. M3-ACh receptor stimulation with 10 µM acetylcholine resulted in distinct changes in FRET, which reflects interaction of the respective proteins. GRK2 mutants with reduced binding affinity toward Gαq [GRK2(D110A)] and Gβγ [GRK2(R587Q)] were used to determine the specific role of Gq-protein-binding by GRK2. Comparison of absolute FRET amplitudes demonstrated that Gαq enhances the extent and stability of the GRK2-M3-ACh receptor interaction, and that not only Gβγ but also Gαq can target GRK2 to the membrane. This reveals an important role of Gαq in efficient recruitment of GRK2 to M3-ACh receptors. Furthermore, interactions between Gαq and GRK2 were associated with a prolongation of the interaction between GRK2 and the M3-ACh receptor and enhanced arrestin recruitment by these receptors, indicating that Gαq influences signaling and desensitization.
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Affiliation(s)
- Valerie Wolters
- Institute for Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, Philipps-University Marburg, Marburg, Germany (V.W., C.K., M.B.); and Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany (J.B.)
| | - Cornelius Krasel
- Institute for Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, Philipps-University Marburg, Marburg, Germany (V.W., C.K., M.B.); and Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany (J.B.)
| | - Jörg Brockmann
- Institute for Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, Philipps-University Marburg, Marburg, Germany (V.W., C.K., M.B.); and Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany (J.B.)
| | - Moritz Bünemann
- Institute for Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, Philipps-University Marburg, Marburg, Germany (V.W., C.K., M.B.); and Department of Pharmacology and Toxicology, University of Würzburg, Würzburg, Germany (J.B.)
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Costante R, Pinnen F, Stefanucci A, Mollica A. Potent Biphalin Analogs with µ/δ Mixed Opioid Activity:In VivoandIn VitroBiological Evaluation. Arch Pharm (Weinheim) 2014; 347:305-12. [DOI: 10.1002/ardp.201300380] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 12/11/2013] [Accepted: 12/17/2013] [Indexed: 02/03/2023]
Affiliation(s)
- Roberto Costante
- Dipartimento di Farmacia; Università di Chieti-Pescara “G. d'Annunzio”; Chieti Italy
| | - Francesco Pinnen
- Dipartimento di Farmacia; Università di Chieti-Pescara “G. d'Annunzio”; Chieti Italy
| | | | - Adriano Mollica
- Dipartimento di Farmacia; Università di Chieti-Pescara “G. d'Annunzio”; Chieti Italy
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15
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Millan MJ, Mannoury la Cour C, Chanrion B, Dupuis DS, Di Cara B, Audinot V, Cussac D, Newman-Tancredi A, Kamal M, Boutin JA, Jockers R, Marin P, Bockaert J, Muller O, Dekeyne A, Lavielle G. S32212, a novel serotonin type 2C receptor inverse agonist/α2-adrenoceptor antagonist and potential antidepressant: I. A mechanistic characterization. J Pharmacol Exp Ther 2011; 340:750-64. [PMID: 22178752 DOI: 10.1124/jpet.111.187468] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Although most antidepressants suppress serotonin (5-HT) and/or noradrenaline reuptake, blockade of 5-HT(2C) receptors and α(2)-adrenoceptors likewise enhances monoaminergic transmission. These sites are targeted by the urea derivative N- [4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-1,2-dihydro-3-H-benzo[e]indole-3-carboxamide (S32212). S32212 was devoid of affinity for monoamine reuptake sites, yet displayed pronounced affinity (pK(i), 8.2) for constitutively active human 5-HT(2CINI) (h5-HT(2CINI)) receptors, behaving as an inverse agonist in reducing basal Gα(q) activation, [(3)H]inositol-phosphate production, and the spontaneous association of h5-HT(2CINI)-Renilla luciferase receptors with β-arrestin2-yellow fluorescent protein. Furthermore, upon 18-h pretreatment, S32212 enhanced the plasma membrane expression of h5-HT(2CINI) receptors as visualized by confocal microscopy and quantified by enzyme-linked immunosorbent assay. Its actions were prevented by the neutral antagonist 6-chloro-5-methyl-N-[6-(2-methylpyridin-3-yloxy)pyridin-3-yl]indoline-1-carboxamide (SB242,084), which also impeded the induction by long-term exposure to S32212 of otherwise absent Ca(2+) mobilization in mouse cortical neurones. In vivo, S32212 blunted the inhibitory influence of the 5-HT(2C) agonist 2-(3-chlorobenzyloxy)-6-(1-piperazinyl)pyrazine (CP809,101) on ventrotegmental dopaminergic neurones. S32212 also blocked 5-HT-induced Gα(q) and phospholipase C activation at the h5-HT(2A) and, less potently, h5-HT(2B) receptors and suppressed the discriminative stimulus properties of the 5-HT(2A) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane in rats. S32212 manifested marked affinity for human α(2A)- (pK(i) 7.2), α(2B)- (pK(i) 8.2), and α(2C)- (pK(i) 7.4) adrenoceptors, at which it abolished noradrenaline-induced recruitment of Gα(i3), Gα(o), adenylyl cyclase, and extracellular-regulated kinase1/2. Moreover, S32212 dose-dependently abolished the discriminative stimulus effects of the α(2)-adrenoceptor agonist (S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(1',2',3',4'-tetrahydronaphthalene)] (S18616). Finally, S32212 displayed negligible affinity for α(1A)-adrenoceptors, histamine H(1) receptors, and muscarinic M(1) receptors. In conclusion, S32212 behaves as an inverse agonist at h5-HT(2C) receptors and as an antagonist at human α(2)-adrenoceptors (and h5-HT(2A) receptors). Its promising profile in preclinical models potentially relevant to the treatment of depression is described in J Pharmacol Exp Ther 340:765-780, 2012.
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Affiliation(s)
- Mark J Millan
- Institut de Recherches Servier, Centre de Recherches de Croissy, Psychopharmacology Department, 125 Chemin de Ronde, 78290 Croissy/Seine, France.
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16
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Yoshiura S, Ohta N, Matsuzaki F. Tre1 GPCR signaling orients stem cell divisions in the Drosophila central nervous system. Dev Cell 2011; 22:79-91. [PMID: 22178499 DOI: 10.1016/j.devcel.2011.10.027] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 09/14/2011] [Accepted: 10/26/2011] [Indexed: 11/20/2022]
Abstract
During development, directional cell division is a major mechanism for establishing the orientation of tissue growth. Drosophila neuroblasts undergo asymmetric divisions perpendicular to the overlying epithelium to produce descendant neurons on the opposite side, thereby orienting initial neural tissue growth. However, the mechanism remains elusive. We provide genetic evidence that extrinsic GPCR signaling determines the orientation of cortical polarity underlying asymmetric divisions of neuroblasts relative to the epithelium. The GPCR Tre1 activates the G protein oα subunit in neuroblasts by interacting with the epithelium to recruit Pins, which regulates spindle orientation. Because Pins associates with the Par-complex via Inscuteable, Tre1 consequently recruits the polarity complex to orthogonally orient the polarity axis to the epithelium. Given the universal role of the Par complex in cellular polarization, we propose that the GPCR-Pins system is a comprehensive mechanism controlling tissue polarity by orienting polarized stem cells and their divisions.
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Affiliation(s)
- Shigeki Yoshiura
- RIKEN Center for Developmental Biology, 2-2-3 Minatojima-Minamimachi, Chuo-ku, Kobe 650-0047, Japan
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18
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Millan MJ. From the cell to the clinic: a comparative review of the partial D₂/D₃receptor agonist and α2-adrenoceptor antagonist, piribedil, in the treatment of Parkinson's disease. Pharmacol Ther 2010; 128:229-73. [PMID: 20600305 DOI: 10.1016/j.pharmthera.2010.06.002] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/02/2010] [Indexed: 12/16/2022]
Abstract
Though L-3,4-dihydroxyphenylalanine (L-DOPA) is universally employed for alleviation of motor dysfunction in Parkinson's disease (PD), it is poorly-effective against co-morbid symptoms like cognitive impairment and depression. Further, it elicits dyskinesia, its pharmacokinetics are highly variable, and efficacy wanes upon long-term administration. Accordingly, "dopaminergic agonists" are increasingly employed both as adjuncts to L-DOPA and as monotherapy. While all recognize dopamine D(2) receptors, they display contrasting patterns of interaction with other classes of monoaminergic receptor. For example, pramipexole and ropinirole are high efficacy agonists at D(2) and D(3) receptors, while pergolide recognizes D(1), D(2) and D(3) receptors and a broad suite of serotonergic receptors. Interestingly, several antiparkinson drugs display modest efficacy at D(2) receptors. Of these, piribedil displays the unique cellular signature of: 1), signal-specific partial agonist actions at dopamine D(2)and D(3) receptors; 2), antagonist properties at α(2)-adrenoceptors and 3), minimal interaction with serotonergic receptors. Dopamine-deprived striatal D(2) receptors are supersensitive in PD, so partial agonism is sufficient for relief of motor dysfunction while limiting undesirable effects due to "over-dosage" of "normosensitive" D(2) receptors elsewhere. Further, α(2)-adrenoceptor antagonism reinforces adrenergic, dopaminergic and cholinergic transmission to favourably influence motor function, cognition, mood and the integrity of dopaminergic neurones. In reviewing the above issues, the present paper focuses on the distinctive cellular, preclinical and therapeutic profile of piribedil, comparisons to pramipexole, ropinirole and pergolide, and the core triad of symptoms that characterises PD-motor dysfunction, depressed mood and cognitive impairment. The article concludes by highlighting perspectives for clarifying the mechanisms of action of piribedil and other antiparkinson agents, and for optimizing their clinical exploitation.
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Affiliation(s)
- Mark J Millan
- Dept of Psychopharmacology, Institut de Recherches Servier, 125 Chemin de Ronde, 78290 Croissy/Seine (Paris), France.
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Stewart GD, Valant C, Dowell SJ, Mijaljica D, Devenish RJ, Scammells PJ, Sexton PM, Christopoulos A. Determination of adenosine A1 receptor agonist and antagonist pharmacology using Saccharomyces cerevisiae: implications for ligand screening and functional selectivity. J Pharmacol Exp Ther 2009; 331:277-86. [PMID: 19641164 DOI: 10.1124/jpet.109.158667] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The budding yeast, Saccharomyces cerevisiae, is a convenient system for coupling heterologous G protein-coupled receptors (GPCRs) to the pheromone response pathway to facilitate empirical ligand screening and/or GPCR mutagenesis studies. However, few studies have applied this system to define GPCR-G protein-coupling preferences and furnish information on ligand affinities, efficacies, and functional selectivity. We thus used different S. cerevisiae strains, each expressing a specific human Galpha/yeast Gpa1 protein chimera, and determined the pharmacology of various ligands of the coexpressed human adenosine A(1) receptor. These assays, in conjunction with the application of quantitative models of agonism and antagonism, revealed that (-)-N(6)-(2-phenylisopropyl)adenosine was a high-efficacy agonist that selectively coupled to Gpa/1Galpha(o), Gpa1/Galpha(i1/2), and Gpa1/Galpha(i3), whereas the novel compound, 5'-deoxy-N(6)-(endo-norborn-2-yl)-5'-(2-fluorophenylthio)adenosine (VCP-189), was a lower-efficacy agonist that selectively coupled to Gpa1/Galpha(i) proteins; the latter finding suggested that VCP-189 might be functionally selective. The affinity of the antagonist, 8-cyclopentyl-1,3-dipropylxanthine, was also determined at the various strains. Subsequent experiments performed in mammalian Chinese hamster ovary cells monitoring cAMP formation/inhibition, intracellular calcium mobilization, phosphorylation of extracellular signal-regulated kinase 1 and 2 or (35)S-labeled guanosine 5'-(gamma-thio)triphosphate binding, were in general agreement with the yeast data regarding agonist efficacy estimation and antagonist affinity estimation, but revealed that the apparent functional selectivity of VCP-189 could be explained by differences in stimulus-response coupling between yeast and mammalian cells. Our results suggest that this yeast system is a useful tool for quantifying ligand affinity and relative efficacy, but it may lack the sensitivity required to detect functional selectivity of low-efficacy agonists.
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Affiliation(s)
- Gregory D Stewart
- Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia
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Bennett KA, Langmead CJ, Wise A, Milligan G. Growth hormone secretagogues and growth hormone releasing peptides act as orthosteric super-agonists but not allosteric regulators for activation of the G protein Galpha(o1) by the Ghrelin receptor. Mol Pharmacol 2009; 76:802-11. [PMID: 19625579 DOI: 10.1124/mol.109.056101] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Some growth hormone secretagogues act as agonists at the ghrelin receptor and have been described as "ago-allosteric" ligands because of an ability to also modulate the maximum efficacy and potency of ghrelin (Holst et al., 2005). In membranes prepared from cells coexpressing the human ghrelin receptor and the G protein Galpha(o1), N-[1(R)-1, 2-dihydro-1-ethanesulfonylspiro-3H-indole-3,4'-piperidin)-1'-yl]carbonyl-2-(phenylmethoxy)-ethyl-2-amino-2-methylpropanamide (MK-677), growth hormone-releasing peptide 6 (GHRP-6), and the 2(R)-hydroxypropyl derivative of 3-amino-3-methyl-N-(2,3,4,5-tetrahydro-2-oxo-1-([2'-(1H-tetrazol-5-yl) (1,1'-biphenyl)-4-yl]methyl)-1H-1-benzazepin-3(R)-yl)-butanamide (L-692,585) each functioned as direct agonists, and each displayed higher efficacy than ghrelin. The effect of multiple, fixed concentrations of each of these ligands on the function and concentration-dependence of ghrelin and the effect of multiple, fixed concentrations of ghrelin on the action of MK-677, GHRP-6, and L-692,585 was analyzed globally according to a modified version of an operational model of allosterism that accounts for allosteric modulation of affinity, efficacy, and allosteric agonism. Each of the data sets was best fit by a model of simple competition between a partial and a full agonist. Both positive and negative allosteric modulators are anticipated to alter the kinetics of binding of an orthosteric agonist. However, none of the proposed ago-allosteric regulators tested had any effect on the dissociation kinetics of (125)I-[His]-ghrelin, and GHRP-6 and MK-677 were able to fully displace (125)I-[His]-ghrelin from the receptor. At least in the system tested, each of the ligands acted in a simple competitive fashion with ghrelin as demonstrated by analysis according to a model whereby ghrelin is a partial agonist with respect to each of the synthetic agonists tested.
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Affiliation(s)
- Kirstie A Bennett
- Molecular Pharmacology Group, Neuroscience and Molecular Pharmacology, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
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Tso PH, Morris CJ, Yung LY, Ip NY, Wong YH. Multiple Gi Proteins Participate in Nerve Growth Factor-Induced Activation of c-Jun N-terminal Kinases in PC12 Cells. Neurochem Res 2008; 34:1101-12. [DOI: 10.1007/s11064-008-9880-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/23/2008] [Indexed: 01/21/2023]
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Margas W, Sedeek K, Ruiz-Velasco V. Coupling specificity of NOP opioid receptors to pertussis-toxin-sensitive Galpha proteins in adult rat stellate ganglion neurons using small interference RNA. J Neurophysiol 2008; 100:1420-32. [PMID: 18562551 PMCID: PMC2544458 DOI: 10.1152/jn.90405.2008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2008] [Accepted: 06/15/2008] [Indexed: 01/18/2023] Open
Abstract
The opioid receptor-like 1 (NOP or ORL1) receptor is a G-protein-coupled receptor the endogenous ligand of which is the heptadecapeptide, nociceptin (Noc). NOP receptors are known to modulate pain processing at spinal, supraspinal, and peripheral levels. Previous work has demonstrated that NOP receptors inhibit N-type Ca2+ channel currents in rat sympathetic stellate ganglion (SG) neurons via pertussis toxin (PTX)-sensitive Galphai/o subunits. However, the identification of the specific Galpha subunit that mediates the Ca2+ current modulation is unknown. The purpose of the present study was to examine coupling specificity of Noc-activated NOP receptors to N-type Ca2+ channels in SG neurons. Small interference RNA (siRNA) transfection was employed to block the expression of PTX-sensitive Galpha subunits. RT-PCR results showed that siRNA specifically decreased the expression of the intended Galpha subunit. Evaluation of cell surface protein expression and Ca2+ channel modulation were assessed by immunofluorescence staining and electrophysiological recordings, respectively. Furthermore, the presence of mRNA of the intended siRNA target Galpha protein was examined by RT-PCR experiments. Fluorescence imaging showed that Galphai1, Galphai3, and Galphao were expressed in SG neurons. The transfection of Galphai1-specific siRNA resulted in a significant decrease in Noc-mediated Ca2+ current inhibition, while silencing of either Galphai3 or Galphao was without effect. Taken together, these results suggest that in SG neurons Galphai1 subunits selectively couple NOP receptors to N-type Ca2+ channels.
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Affiliation(s)
- Wojciech Margas
- Department of Anesthesiology, Penn State University College of Medicine, Hershey, PA 17033-0850, USA
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Yung LY, Tso PH, Wu EH, Yu JC, Ip NY, Wong YH. Nerve growth factor-induced stimulation of p38 mitogen-activated protein kinase in PC12 cells is partially mediated via Gi/o proteins. Cell Signal 2008; 20:1538-44. [DOI: 10.1016/j.cellsig.2008.04.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 04/10/2008] [Accepted: 04/11/2008] [Indexed: 12/21/2022]
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Hase M, Yokomizo T, Shimizu T, Nakamura M. Characterization of an orphan G protein-coupled receptor, GPR20, that constitutively activates Gi proteins. J Biol Chem 2008; 283:12747-55. [PMID: 18347022 DOI: 10.1074/jbc.m709487200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GPR20 was isolated as an orphan G protein-coupled receptor from genomic DNA by PCR amplification. Although GPR20 was closely related to nucleotide or lipid receptors, the functional role of this receptor, as well as its endogenous ligand, remains unclear. Here we demonstrate that GPR20 is constitutively active in the absence of ligand, leading to continuous activation of its coupled G proteins. When GPR20 was exogenously expressed in HEK293 cells, both the basal level and the prostaglandin E(2)-induced production of cAMP were significantly decreased. A remarkable increase in [(35)S]guanosine 5'-(gamma-thio)triphosphate (GTPgammaS) binding to membrane preparations was also observed in GPR20-expressing cells. These effects of GPR20 overexpression were diminished in cells treated with pertussis toxin, suggesting that the expression of GPR20 results in the activation of G(i/o) proteins. Involvement of GPR20 in the activation of G(i/o) proteins was also supported by evidence that the disruption of a conserved DRY motif in GPR20 attenuated both [(35)S]GTPgammaS incorporation and inhibition of the prostaglandin E(2)-induced cAMP production. Knockdown of GPR20 in PC12h cells resulted in an elevation of the basal cAMP level, suggesting that the endogenous GPR20 achieves a constitutively or spontaneously active conformation. Furthermore, enhancement of [(3)H]thymidine incorporation was also observed in the GPR20-silencing cells, implying that the GPR20 expression seems to attenuate PC12h cell growth. Taken together, these data indicate that GPR20 constitutively activates G(i) proteins without ligand stimulation. The receptor may be involved in cellular processes, including control of intracellular cAMP levels and mitogenic signaling.
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Affiliation(s)
- Momoko Hase
- Department of Biochemistry and Molecular Biology, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Brown SL, Jala VR, Raghuwanshi SK, Nasser MW, Haribabu B, Richardson RM. Activation and regulation of platelet-activating factor receptor: role of G(i) and G(q) in receptor-mediated chemotactic, cytotoxic, and cross-regulatory signals. THE JOURNAL OF IMMUNOLOGY 2006; 177:3242-9. [PMID: 16920964 DOI: 10.4049/jimmunol.177.5.3242] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycerolphosphocholine; PAF) induces leukocyte accumulation and activation at sites of inflammation via the activation of a specific cell surface receptor (PAFR). PAFR couples to both pertussis toxin-sensitive and pertussis toxin-insensitive G proteins to activate leukocytes. To define the role(s) of G(i) and G(q) in PAF-induced leukocyte responses, two G-protein-linked receptors were generated by fusing G alpha(i3) (PAFR-G alpha(i3)) or G alpha(q) (PAFR-G alpha(q)) at the C terminus of PAFR. Rat basophilic leukemia cell line (RBL-2H3) stably expressing wild-type PAFR, PAFR-G alpha(i3), or PAFR-G alpha(q) was generated and characterized. All receptor variants bound PAF with similar affinities to mediate G-protein activation, intracellular Ca2+ mobilization, phosphoinositide (PI) hydrolysis, and secretion of beta-hexosaminidase. PAFR-G alpha(i3) and PAFR-G alpha(q) mediated greater GTPase activity in isolated membranes than PAFR but lower PI hydrolysis and secretion in whole cells. PAFR and PAFR-G alpha(i3), but not PAFR-G alpha(q), mediated chemotaxis to PAF. All three receptors underwent phosphorylation and desensitization upon exposure to PAF but only PAFR translocated beta arrestin to the cell membrane and internalized. In RBL-2H3 cells coexpressing the PAFRs along with CXCR1, IL-8 (CXCL8) cross-desensitized Ca2+ mobilization to PAF by all the receptors but only PAFR-G alpha(i3) activation cross-inhibited the response of CXCR1 to CXCL8. Altogether, the data indicate that G(i) exclusively mediates chemotactic and cross-regulatory signals of the PAFR, but both G(i) and G(q) activate PI hydrolysis and exocytosis by this receptor. Because chemotaxis and cross-desensitization are exclusively mediated by G(i), the data suggest that differential activation of both G(i) and G(q) by PAFR likely mediate specific as well as redundant signaling pathways.
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Affiliation(s)
- Stephan L Brown
- Department of Biochemistry, Meharry Medical College, Nashville, TN 37208, USA
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26
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Clark MJ, Furman CA, Gilson TD, Traynor JR. Comparison of the relative efficacy and potency of mu-opioid agonists to activate Galpha(i/o) proteins containing a pertussis toxin-insensitive mutation. J Pharmacol Exp Ther 2006; 317:858-64. [PMID: 16436499 DOI: 10.1124/jpet.105.096818] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pertussis toxin (PTX)-insensitive mutants of Galpha(i/o) proteins expressed in C6mu cells were used to examine the hypothesis that there are agonist-specific conformational states of the mu-opioid receptor with coupling preferences to different Galpha(i/o) subtypes, as measured by the degree of stimulation of [(35)S]guanosine 5'-O-(3-thio)triphosphate (GTPgammaS) binding. Binding of [(35)S]GTPgammaS to endogenous Galpha(i/o) proteins stimulated by the full mu-opioid agonist [d-Ala(2),MePhe(4),Gly(5)-ol]enkephalin (DAMGO) was completely blocked by overnight treatment with 100 ng/ml PTX. Treatment for 4 h with lower concentrations led to a PTX-dependent reduction in the maximal effect of DAMGO but no alteration in the potency of DAMGO or morphine nor in the relative maximal effect (relative efficacy) of the partial agonists morphine and buprenorphine compared with the full agonist DAMGO. Using PTX-insensitive Galpha mutants in which the PTX-sensitive cysteine was replaced with isoleucine, the potency for a series of mu-opioid agonists was highest in cells expressing Galpha(i3) and Galpha(o) and lowest with Galpha(i1) and Galpha(i2), with no significant change in the order of potency, namely, etorphine >> endomorphin-1 = DAMGO = endomorphin-2 = fentanyl = morphine >> meperidine. The order of agonist relative efficacy, etorphine = DAMGO = endomorphin-1 = endomorphin-2 = fentanyl > or = morphine > or = meperidine > buprenorphine > or = nalbuphine, was also the same across all of the PTX-insensitive Galpha(i/o) subtypes. Highest relative efficacy to stimulate [(35)S]GTPgammaS binding was seen with Galpha(i3). Consequently, reported observations of agonist-directed trafficking at mu-opioid receptors most likely involve non-PTX-sensitive Galpha protein mechanisms.
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Affiliation(s)
- Mary J Clark
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109-0632, USA
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27
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Fitzsimons CP, Gompels UA, Verzijl D, Vischer HF, Mattick C, Leurs R, Smit MJ. Chemokine-directed trafficking of receptor stimulus to different g proteins: selective inducible and constitutive signaling by human herpesvirus 6-encoded chemokine receptor U51. Mol Pharmacol 2005; 69:888-98. [PMID: 16332987 DOI: 10.1124/mol.105.015222] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The human herpes virus 6 (HHV-6)-encoded chemokine receptor U51 constitutively activates phospholipase C (PLC) and inhibits cAMP-responsive element (CRE)-mediated gene transcription via the activation of G(q/11) proteins. Yet, chemokines known to bind U51 differentially regulate U51 coupling to G proteins. CCL5/RANTES induced pertussis toxin (PTX)-insensitive increases in PLC activity and changes in intracellular free calcium concentration ([Ca2+]i), whereas both CCL2/MCP-1 and CCL11/eotaxin failed to stimulate PLC activity or increase [Ca2+]i. In contrast, all three chemokines counteracted the effects of U51 on CRE activity via the activation of PTX-sensitive G(i/o) proteins. For each of the tested chemokines, coexpression of U51 with a variety of G alpha subunits, however, revealed a distinct profile for preferred G-protein coupling, which could be shifted by modulation of the relative expression of G proteins. These findings are consistent with a chemokine-selective trafficking of receptor stimulus to distinct G proteins and suggest that the constitutive activity of U51 and the chemokine-induced signaling involve different active states of the receptor. By virtue of its ability to constitutively activate signaling pathways, its G-protein promiscuity, and the chemokine-directed trafficking of receptor stimulus, U51 can be considered a sensitive and versatile virally encoded signaling device, potentially of importance in HHV-6-related pathologies.
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Affiliation(s)
- Carlos P Fitzsimons
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Vrije Universiteit Amsterdam, The Netherlands
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28
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Benians A, Nobles M, Hosny S, Tinker A. Regulators of G-protein signaling form a quaternary complex with the agonist, receptor, and G-protein. A novel explanation for the acceleration of signaling activation kinetics. J Biol Chem 2005; 280:13383-94. [PMID: 15677457 DOI: 10.1074/jbc.m410163200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulators of G-protein signaling (RGS) proteins modulate signaling through heterotrimeric G-proteins. They act to enhance the intrinsic GTPase activity of the Galpha subunit but paradoxically have also been shown to enhance receptor-stimulated activation. To study this paradox, we used a G-protein gated K+ channel to report the dynamics of the G-protein cycle and fluorescence resonance energy transfer techniques with cyan and yellow fluorescent protein-tagged proteins to report physical interaction. Our data show that the acceleration of the activation kinetics is dissociated from deactivation kinetics and dependent on receptor and RGS type, G-protein isoform, and RGS expression levels. By using fluorescently tagged proteins, fluorescence resonance energy transfer microscopy showed a stable physical interaction between the G-protein alpha subunit and RGS (RGS8 and RGS7) that is independent of the functional state of the G-protein. RGS8 does not directly interact with G-protein-coupled receptors. Our data show participation of the RGS in the ternary complex between agonist-receptor and G-protein to form a "quaternary complex." Thus we propose a novel model for the action of RGS proteins in the G-protein cycle in which the RGS protein appears to enhance the "kinetic efficacy" of the ternary complex, by direct association with the G-protein alpha subunit.
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Affiliation(s)
- Amy Benians
- BHF Laboratories and Department of Medicine, University College London, Room 420, 4th Floor, 5 University Street, London WC1E 6JJ, United Kingdom
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29
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Abstract
Discovery of "regulators of G-protein signaling" (RGS) as GTPase-activating proteins for heterotrimeric G proteins has provided a highly sought "missing link," reconciling past discrepancies between the in vitro GTPase activity of purified G proteins and the kinetics of physiological responses mediated by G-protein signaling in vivo. With the number of RGS genes in the mammalian genome at more than 30, associating specific RGS proteins to specific G-protein-coupled receptor (GPCR) signaling events has become a focus of RGS investigators. The ubiquitous expression of multiple RGS proteins has complicated this effort, yet the outlook has been encouraged with the identification of RGS9 as the determinant mediating rapid recovery of the transducin-dependent photoresponse. G-protein-gated inwardly rectifying potassium (GIRK) channels that mediate inhibitory synaptic transmission via GPCR activation of pertussis toxin-sensitive G proteins are similarly accelerated by RGS proteins when reconstituted in heterologous cell expression systems and fully reproduce the gating properties of native GIRK channels in neurons and cardiomyocytes. The endogenous neuronal and cardiac RGS protein(s) that accelerate GPCR-->GIRK channel-gating kinetics are currently not known. This article describes methods used to measure the receptor-dependent GIRK channel-gating parameters reconstituted in Chinese hamster ovary (CHO-K1) cells and Xenopus oocytes, as well as rat atrial myocytes and rat cerebellar granule neurons as model cells with native GPCR-->GIRK channel signaling. Applications of these methods for structure-function-based studies of RGS proteins, G proteins, and GPCRs are discussed. We also describe single cell reverse transcriptase polymerase chain reaction methods developed to profile atrial myocyte and neuronal RGS expression to identify specific RGS proteins for targeted knockdown or knockout.
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Affiliation(s)
- Craig A Doupnik
- Department of Physiology and Biophysics, University of South Florida College of Medicine, Tampa 33612, USA
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30
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Bünemann M, Frank M, Lohse MJ. Gi protein activation in intact cells involves subunit rearrangement rather than dissociation. Proc Natl Acad Sci U S A 2003; 100:16077-82. [PMID: 14673086 PMCID: PMC307695 DOI: 10.1073/pnas.2536719100] [Citation(s) in RCA: 326] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2003] [Indexed: 11/18/2022] Open
Abstract
G protein-coupled receptors transduce diverse extracellular signals, such as neurotransmitters, hormones, chemokines, and sensory stimuli, into intracellular responses through activation of heterotrimeric G proteins. G proteins play critical roles in determining specificity and kinetics of subsequent biological responses by modulation of effector proteins. We have developed a fluorescence resonance energy transfer (FRET)-based assay to directly measure mammalian G protein activation in intact cells and found that Gi proteins activate within 1-2 s, which is considerably slower than activation kinetics of the receptors themselves. More importantly, FRET measurements demonstrated that Galphai- and Gbetagamma-subunits do not dissociate during activation, as has been previously postulated. Based on FRET measurements between Galphai-yellow fluorescent protein and Gbetagamma-subunits that were fused to cyan fluorescent protein at various positions, we conclude that, instead, G protein subunits undergo a molecular rearrangement during activation. The detection of a persistent heterotrimeric composition during G protein activation will impact the understanding of how G proteins achieve subtype-selective coupling to effectors. This finding will be of particular interest for unraveling Gbetagamma-induced signaling pathways.
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Affiliation(s)
- Moritz Bünemann
- Department of Pharmacology and Toxicology, University of Würzburg, Versbacherstrasse 9, 97078 Würzburg, Germany.
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31
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Bakker RA, Casarosa P, Timmerman H, Smit MJ, Leurs R. Constitutively active Gq/11-coupled receptors enable signaling by co-expressed G(i/o)-coupled receptors. J Biol Chem 2003; 279:5152-61. [PMID: 14610092 DOI: 10.1074/jbc.m309200200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Co-expression of guanine nucleotide-binding regulatory (G) protein-coupled receptors (GPCRs), such as the G(i/o)-coupled human 5-hydroxytryptamine receptor 1B (5-HT(1B)R), with the G(q/11)-coupled human histamine 1 receptor (H1R) results in an overall increase in agonist-independent signaling, which can be augmented by 5-HT(1B)R agonists and inhibited by a selective inverse 5-HT(1B)R agonist. Interestingly, inverse H1R agonists inhibit constitutively H1R-mediated as well as 5-HT(1B)R agonist-induced signaling in cells co-expressing both receptors. This phenomenon is not solely characteristic of 5-HT(1B)R; it is also evident with muscarinic M2 and adenosine A1 receptors and is mimicked by mastoparan-7, an activator of G(i/o) proteins, or by over-expression of Gbetagamma subunits. Likewise, expression of the G(q/11)-coupled human cytomegalovirus (HCMV)-encoded chemokine receptor US28 unmasks a functional coupling of G(i/o)-coupled CCR1 receptors that is mediated via the constitutive activity of receptor US28. Consequently, constitutively active G(q/11)-coupled receptors, such as the H1R and HCMV-encoded chemokine receptor US28, constitute a regulatory switch for signal transduction by G(i/o)-coupled receptors, which may have profound implications in understanding the role of both constitutive GPCR activity and GPCR cross-talk in physiology as well as in the observed pathophysiology upon HCMV infection.
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MESH Headings
- Animals
- COS Cells
- DNA/chemistry
- DNA, Complementary/metabolism
- Enzyme Activation
- Enzyme-Linked Immunosorbent Assay
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Protein alpha Subunits, Gi-Go/physiology
- GTP-Binding Protein alpha Subunits, Gq-G11/metabolism
- Genes, Reporter
- Humans
- Inositol Phosphates/metabolism
- Intercellular Signaling Peptides and Proteins
- Ligands
- Models, Biological
- Peptides
- Protein Binding
- Protein Structure, Tertiary
- Receptor, Adenosine A1/metabolism
- Receptor, Muscarinic M2/metabolism
- Receptor, Serotonin, 5-HT1B/chemistry
- Receptor, Serotonin, 5-HT1B/metabolism
- Receptors, G-Protein-Coupled/metabolism
- Signal Transduction
- Transcription, Genetic
- Wasp Venoms/metabolism
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Affiliation(s)
- Remko A Bakker
- Leiden/Amsterdam Center for Drug Research, Division of Medicinal Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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32
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Abstract
The endothelium is more than just a passive vessel lining. New advances have revealed and expanded the multifactorial role of the endothelium in the homeostatic regulation of the microvasculature, including control of primary hemostasis, blood coagulation and fibrinolysis, platelet and leukocyte interactions with the vessel wall, lipoprotein metabolism, presentation of histocompatibility antigens, regulation of vascular tone and growth, and regulation of blood pressure. It possesses numerous receptors and releases compounds that affect the regulation of vascular tone and contribute to vascular permeability. Many crucial vasoactive endogenous compounds are formed in the endothelial cells to control the functions of vascular smooth muscle cells and circulating blood cells. Gap junctions facilitate the exchange of metabolites, ions, and other messenger molecules among endothelial cells and smooth muscle cells, and regulate cell growth. Among the numerous regulatory systems affecting microvascular function are the cholinergic and adrenergic (α1, α2, and β) systems. Flow-metabolism coupling is affected by a variety of signaling systems, including adenosine, oxygen, carbon dioxide, lactate, nitric oxide, and others. Agents such as the angiotensin system and endothelin, as well as others, play a role in autoregulation (maintenance of constant flow in the face of changing pressure). All of these are discussed in detail.
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Affiliation(s)
- Danja Striimper
- University of Münster, University Hospital Maastrich, The Netherlands
| | - Marcel Durieux
- University of Münster; Department of Anesthesiology, University Hospital Maastrich, The Netherlands
| | - Paul Roekaerts
- Department of Anesthesiology, University Hospital Maastrich, The Netherlands
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33
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Bahia DS, Sartania N, Ward RJ, Cavalli A, Jones TLZ, Druey KM, Milligan G. Concerted stimulation and deactivation of pertussis toxin-sensitive G proteins by chimeric G protein-coupled receptor-regulator of G protein signaling 4 fusion proteins: analysis of the contribution of palmitoylated cysteine residues to the GAP activity of RGS4. J Neurochem 2003; 85:1289-98. [PMID: 12753087 DOI: 10.1046/j.1471-4159.2003.01769.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Agonists stimulated high-affinity GTPase activity in membranes of HEK293 cells following coexpression of the alpha 2A-adrenoceptor and a pertussis toxin-resistant mutant of Go1 alpha. Enzyme kinetic analysis of Vmax and Km failed to detect regulation of the effect of agonist by a GTPase activating protein. This did occur, however, when cells were also transfected to express RGS4. Both elements of a fusion protein in which the N-terminus of RGS4 was linked to the C-terminal tail of the alpha 2A-adrenoceptor were functional, as it was able to provide concerted stimulation and deactivation of the G protein. By contrast, the alpha 2A-adrenoceptor-RGS4 fusion protein stimulated but did not enhance deactivation of a form of Go1 alpha that is resistant to the effects of regulator of G protein signaling (RGS) proteins. Employing this model system, mutation of Asn128 but not Asn88 eliminated detectable GTPase activating protein activity of RGS4 against Go1 alpha. Mutation of all three cysteine residues that are sites of post-translational acylation in RGS4 also eliminated GTPase activating protein activity but this was not achieved by less concerted mutation of these sites. These studies demonstrate that a fusion protein between a G protein-coupled receptor and an RGS protein is fully functional in providing both enhanced guanine nucleotide exchange and GTP hydrolysis of a coexpressed G protein. They also provide a direct means to assess, in mammalian cells, the effects of mutation of the RGS protein on function in circumstances in which the spatial relationship and orientation of the RGS to its target G protein is defined and maintained.
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Affiliation(s)
- Daljit S Bahia
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
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34
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Kammermeier PJ, Davis MI, Ikeda SR. Specificity of metabotropic glutamate receptor 2 coupling to G proteins. Mol Pharmacol 2003; 63:183-91. [PMID: 12488551 DOI: 10.1124/mol.63.1.183] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Metabotropic glutamate receptor 2 (mGluR2) is a class 3 G protein-coupled receptor and an important mediator of synaptic activity in the central nervous system. Previous work demonstrated that mGluR2 couples to pertussis toxin (PTX)-sensitive G proteins. However, the specificity of mGluR2 coupling to individual members of the G(i/o) family is not known. Using heterologously expressed mGluR2 in rat sympathetic neurons from the superior cervical ganglion (SCG), the mGluR2/G protein coupling profile was characterized by reconstituting coupling in PTX-treated cells expressing PTX-insensitive mutant Galpha proteins and Gbetagamma. By employing this method, it was demonstrated that mGluR2 coupled strongly with Galphaob, Galphai1, Galphai2, and Galphai3, although coupling to Galphaoa was less efficient. In addition, mGluR2 did not seem to couple to the most divergent member of the G(i/o) family, Galphaz, although Galphaz coupled strongly to the endogenous alpha2 adrenergic receptor. To determine which Galpha proteins may be natively expressed in SCG neurons, the presence of mRNA for various Galpha proteins was tested using reverse transcription-polymerase chain reaction. Strong bands were detected for all members of the G(i/o) family (Galphao, Galphai1, Galphai2, Galphai3, Galphaz) as well as for Galpha11 and Galphas. A weak signal was detected for Galphaq and no Galpha15 mRNA was detected.
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Affiliation(s)
- Paul J Kammermeier
- Laboratory of Molecular Physiology, National Institutes of Health, National Institute on Alcohol Abuse and Alcoholism, Rockville, Maryland, USA.
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35
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Zhang Q, Pacheco MA, Doupnik CA. Gating properties of GIRK channels activated by Galpha(o)- and Galpha(i)-coupled muscarinic m2 receptors in Xenopus oocytes: the role of receptor precoupling in RGS modulation. J Physiol 2002; 545:355-73. [PMID: 12456817 PMCID: PMC2290703 DOI: 10.1113/jphysiol.2002.032151] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
'Regulators of G protein Signalling' (RGSs) accelerate the activation and deactivation kinetics of G protein-gated inwardly rectifying K(+) (GIRK) channels. In an apparent paradox, RGSs do not reduce steady-state GIRK current amplitudes as expected from the accelerated rate of deactivation when reconstituted in Xenopus oocytes. We present evidence here that this kinetic anomaly is dependent on the degree of G protein-coupled receptor (GPCR) precoupling, which varies with different Galpha(i/o)-RGS complexes. The gating properties of GIRK channels (Kir3.1/Kir3.2a) activated by muscarinic m2 receptors at varying levels of G protein expression were examined with or without the co-expression of either RGS4 or RGS7 in Xenopus oocytes. Different levels of specific m2 receptor-Galpha coupling were established by uncoupling endogenous pertussis toxin (PTX)-sensitive Galpha(i/o) subunits with PTX, while expressing varying amounts of a single PTX-insensitive subunit (Galpha(i1(C351G)), Galpha(i2(C352G)), Galpha(i3(C351G)), Galpha(oA(C351G)), or Galpha(oB(C351G))). Co-expression of each of the PTX-insensitive Galpha(i/o) subunits rescued acetylcholine (ACh)-elicited GIRK currents (I(K,ACh)) in a concentration-dependent manner, with Galpha(o) isoforms being more effective than Galpha(i) isoforms. Receptor-independent 'basal' GIRK currents (I(K,basal)) were reduced with increasing expression of PTX-insensitive Galpha subunits and were accompanied by a parallel rise in I(K,ACh). These effects together are indicative of increased Gbetagamma scavenging by the expressed Galpha subunit and the subsequent formation of functionally coupled m2 receptor-G protein heterotrimers (Galpha((GDP))betagamma). Co-expression of RGS4 accelerated all the PTX-insensitive Galpha(i/o)-coupled GIRK currents to a similar extent, yet reduced I(K,ACh) amplitudes 60-90 % under conditions of low Galpha(i/o) coupling. Kinetic analysis indicated the RGS4-dependent reduction in steady-state GIRK current was fully explained by the accelerated deactivation rate. Thus kinetic inconsistencies associated with RGS4-accelerated GIRK currents occur at a critical threshold of G protein coupling. In contrast to RGS4, RGS7 selectively accelerated Galpha(o)-coupled GIRK currents. Co-expression of Gbeta5, in addition to enhancing the kinetic effects of RGS7, caused a significant reduction (70-85 %) in steady-state GIRK currents indicating RGS7-Gbeta5 complexes disrupt Galpha(o) coupling. Altogether these results provide further evidence for a GPCR-Galphabetagamma-GIRK signalling complex that is revealed by the modulatory affects of RGS proteins on GIRK channel gating. Our functional experiments demonstrate that the formation of this signalling complex is markedly dependent on the concentration and composition of G protein-RGS complexes.
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Affiliation(s)
- Qingli Zhang
- Department of Physiology and Biophysics, University of South Florida College of Medicine, Tampa, Florida 33612-4799, USA
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36
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Leaney JL, Benians A, Graves FM, Tinker A. A novel strategy to engineer functional fluorescent inhibitory G-protein alpha subunits. J Biol Chem 2002; 277:28803-9. [PMID: 12048213 DOI: 10.1074/jbc.m204683200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Signaling studies in living cells would be greatly facilitated by the development of functional fluorescently tagged G-protein alpha subunits. We have designed G(i/o)alpha subunits fused to the cyan fluorescent protein and assayed their function by studying the following two signal transduction pathways: the regulation of G-protein-gated inwardly rectifying K(+) channels (Kir3.0 family) and adenylate cyclase. Palmitoylation and myristoylation consensus sites were removed from G(i/o) alpha subunits (G(i1)alpha, G(i2)alpha, G(i3)alpha, and G(oA)alpha) and a mutation introduced at Cys(-4) rendering the subunit resistant to pertussis toxin. This construct was fused in-frame with cyan fluorescent protein containing a short peptide motif from GAP43 that directs palmitoylation and thus membrane targeting. Western blotting confirmed G(i/o)alpha protein expression. Confocal microscopy and biochemical fractionation studies revealed membrane localization. Each mutant G(i/o) alpha subunit significantly reduced basal current density when transiently expressed in a stable cell line expressing Kir3.1 and Kir3.2A, consistent with the sequestration of the Gbetagamma dimer by the mutant Galpha subunit. Moreover, each subunit was able to support A1-mediated and D2S-mediated channel activation when transiently expressed in pertussis toxin-treated cells. Overexpression of tagged G(i3)alpha and G(oA)alpha alpha subunits reduced receptor-mediated and forskolin-induced cAMP mobilization.
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Affiliation(s)
- Joanne L Leaney
- BHF Laboratories, Room 420, 4th Floor, and Centre for Clinical Pharmacology, Department of Medicine, University College London, 5 University Street, London WC1E 6JJ, United Kingdom
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37
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Martin RS, Reynen PH, Calixto JJ, Reyes CL, Chang TK, Dietrich PS, Bonhaus DW, MacLennan SJ. Pharmacological comparison of a recombinant CB1 cannabinoid receptor with its G(alpha 16) fusion product. JOURNAL OF BIOMOLECULAR SCREENING 2002; 7:281-9. [PMID: 12097191 DOI: 10.1177/108705710200700312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The pharmacology of G protein-coupled receptors is widely accepted to depend on the G protein subunit to which the agonist-stimulated receptor couples. In order to investigate whether CB(1) agonist-mediated signal transduction via an engineered G(alpha 16) system is different than that of the G(i/o) coupling normally preferred by the CB(1) receptor, we transfected the human recombinant CB(1) receptor (hCB(1)) or a fusion protein comprising the hCB(1) receptor and G(alpha 16) (hCB(1)-G(alpha 16)) into HEK293 cells. From competition binding studies, the rank order of ligand affinities at the hCB(1)-G(alpha 16) fusion protein was found to be similar to that for hCB(1): HU 210 > CP 55,940 > or = SR 141716A > WIN 55212-2 > anandamide > JWH 015. Agonists increased [(35)S]GTP gamma S binding or inhibited forskolin-stimulated cAMP, presumably by coupling to G(i/o), in cells expressing hCB(1) but not hCB(1)-G(alpha 16). However, an analogous rank order of potencies was observed for these agonists in their ability to evoke increases in intracellular calcium concentration in cells expressing hCB(1)-G(alpha 16) but not hCB(1). These data demonstrate that ligand affinities for the hCB(1) receptor are not affected by fusion to the G(alpha 16) subunit. Furthermore, there is essentially no difference in the function of the hCB(1) receptor when coupled to G(i/o) or G (alpha 16).
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Affiliation(s)
- Renée S Martin
- CNS Therapy Area, Neurobiology Unit, Roche Bioscience, Palo Alto, CA 94304, USA.
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38
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Massotte D, Brillet K, Kieffer B, Milligan G. Agonists activate Gi1 alpha or Gi2 alpha fused to the human mu opioid receptor differently. J Neurochem 2002; 81:1372-82. [PMID: 12068084 DOI: 10.1046/j.1471-4159.2002.00946.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
As preferential coupling of opioid receptor to various inhibitory Galpha subunits is still under debate, we have investigated the selectivity of the human mu opioid receptor fused to a pertussis toxin insensitive C351I Gi1 alpha or C352I Gi2 alpha in stably transfected HEK 293 cells. Overall agonist binding affinities were increased for both fusion constructs when compared to the wild type receptor. [35 S]GTPgammaS binding was performed on pertussis toxin treated cells to monitor coupling efficiency of the fusion constructs. Upon agonist addition hMOR-C351I Gi1 a exhibited an activation profile similar to the non-fused receptor while hMOR-C352I Gi2 alpha was poorly activated. Interestingly no correlation could be drawn between agonist binding affinity and efficacy. Upon agonist addition, forskolin-stimulated cAMP production, as measured using a reporter gene assay, was inhibited by signals transduced via the fused Gi1 alpha and Gi2 alpha mainly. In contrast both fusion constructs were able to initiate ERK-MAPK phosphorylation via coupling to endogenous G proteins only. In conclusion our data indicate that hMOR couples more efficiently to Gi1 alpha than Gi2 alpha and that the coupling efficacy is clearly agonist-dependent.
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Affiliation(s)
- Dominique Massotte
- Département des Récepteurs et Protéines Membranaires, CNRS UPR 9050, Ecole Supérieure de Biotechnologie de Strasbourg, Illkirch-Graffenstaden, France.
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39
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Milligan G. Construction and analysis of function of G protein-coupled receptor-G protein fusion proteins. Methods Enzymol 2002; 343:260-73. [PMID: 11665572 DOI: 10.1016/s0076-6879(02)43141-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Graeme Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
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40
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Moon HE, Bahia DS, Cavalli A, Hoffmann M, Milligan G. Control of the efficiency of agonist-induced information transfer and stability of the ternary complex containing the delta opioid receptor and the alpha subunit of G(i1) by mutation of a receptor/G protein contact interface. Neuropharmacology 2001; 41:321-30. [PMID: 11522323 DOI: 10.1016/s0028-3908(01)00076-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Fusion proteins were constructed between the delta opioid receptor and forms of the alpha subunit of G(i1) in which cysteine(351) was mutated to a range of amino acids. GDP reduced the binding of the agonist [(3)H]DADLE but not the antagonist [(3)H]naltrindole to both the receptor alone and all the delta opioid receptor-Cys(351)XaaG(i1)alpha fusion proteins. For the fusion proteins the pEC(50) for GDP was strongly correlated with the n-octanol/H(2)O partition co-efficient of G protein residue(351). Fusion proteins in which this residue was either isoleucine or glycine had similar observed binding kinetics for [(3)H]DADLE. However, the rate of dissociation of [(3)H]DADLE was substantially greater for the glycine-containing fusion protein than that containing isoleucine, indicating that more hydrophobic residues imbued greater stability to the agonist-receptor-G protein ternary complex. This resulted in a higher affinity of binding of [(3)H]DADLE to the fusion protein containing isoleucine(351). In expectation with the binding data, maximal DADLE-stimulated GTP hydrolysis by the isoleucine(351)-containing fusion protein was two-fold greater and the potency of DADLE seven-fold higher than for the version containing glycine. These results demonstrate that the stability of the ternary complex between delta opioid receptor, G(i1)alpha and an agonist (but not antagonist) ligand is dependent upon the nature of residue(351) of the G protein and that this determines the effectiveness of information flow from the receptor to the G protein.
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Affiliation(s)
- H E Moon
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Davidson Building, Glasgow G12 8QQ, UK
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41
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Fernández-Fernández JM, Abogadie FC, Milligan G, Delmas P, Brown DA. Multiple pertussis toxin-sensitive G-proteins can couple receptors to GIRK channels in rat sympathetic neurons when expressed heterologously, but only native G(i)-proteins do so in situ. Eur J Neurosci 2001; 14:283-92. [PMID: 11553279 DOI: 10.1046/j.0953-816x.2001.01642.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Although many G-protein-coupled neurotransmitter receptors are potentially capable of modulating both voltage-dependent Ca(2+) channels (I(Ca)) and G-protein-gated K(+) channels (I(GIRK)), there is a substantial degree of selectivity in the coupling to one or other of these channels in neurons. Thus, in rat superior cervical ganglion (SCG) neurons, M(2) muscarinic acetylcholine receptors (mAChRs) selectively activate I(GIRK) whereas M(4) mAChRs selectively inhibit I(Ca). One source of selectivity might be that the two receptors couple preferentially to different G-proteins. Using antisense depletion methods, we found that M(2) mAChR-induced activation of I(GIRK) is mediated by G(i) whereas M(4) mAChR-induced inhibition of I(Ca) is mediated by G(oA). Experiments with the beta gamma-sequestering peptides alpha-transducin and beta ARK1(C-ter) indicate that, although both effects are mediated by G-protein beta gamma subunits, the endogenous subunits involved in I(GIRK) inhibition differ from those involved in I(Ca) inhibition. However, this pathway divergence does not result from any fundamental selectivity in receptor-G-protein-channel coupling because both I(GIRK) and I(Ca) modulation can be rescued by heterologously expressed G(i) or G(o) proteins after the endogenously coupled alpha-subunits have been inactivated with Pertussis toxin (PTX). We suggest instead that the divergence in the pathways activated by the endogenous mAChRs results from a differential topographical arrangement of receptor, G-protein and ion channel.
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MESH Headings
- Animals
- Calcium Channels/drug effects
- Calcium Channels/metabolism
- Carbachol/pharmacology
- Cells, Cultured
- Cyclic AMP-Dependent Protein Kinases/genetics
- G Protein-Coupled Inwardly-Rectifying Potassium Channels
- GTP-Binding Protein alpha Subunits, Gi-Go/drug effects
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Proteins/drug effects
- GTP-Binding Proteins/genetics
- GTP-Binding Proteins/metabolism
- Ganglia, Sympathetic/cytology
- Ganglia, Sympathetic/drug effects
- Ganglia, Sympathetic/metabolism
- Immunohistochemistry
- Male
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Mutation/drug effects
- Mutation/physiology
- Neurons/cytology
- Neurons/drug effects
- Neurons/metabolism
- Norepinephrine/pharmacology
- Pertussis Toxin
- Potassium Channels/agonists
- Potassium Channels/drug effects
- Potassium Channels/genetics
- Potassium Channels/metabolism
- Potassium Channels, Inwardly Rectifying
- RNA, Antisense/pharmacology
- Rats
- Rats, Sprague-Dawley
- Receptor, Muscarinic M2
- Receptor, Muscarinic M4
- Receptors, Adrenergic, alpha-2/drug effects
- Receptors, Adrenergic, alpha-2/metabolism
- Receptors, Muscarinic/drug effects
- Receptors, Muscarinic/metabolism
- Transducin/genetics
- Virulence Factors, Bordetella/pharmacology
- beta-Adrenergic Receptor Kinases
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42
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Hein L. Transgenic models of alpha 2-adrenergic receptor subtype function. Rev Physiol Biochem Pharmacol 2001; 142:161-85. [PMID: 11190578 DOI: 10.1007/bfb0117493] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Affiliation(s)
- L Hein
- Institut für Pharmakologie und Toxikologie, Universität Würzburg, Versbacher Strasse 9, 97078 Würzburg, Germany
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43
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Moon HE, Cavalli A, Bahia DS, Hoffmann M, Massotte D, Milligan G. The human delta opioid receptor activates G(i1)alpha more efficiently than G(o1)alpha. J Neurochem 2001; 76:1805-13. [PMID: 11259498 DOI: 10.1046/j.1471-4159.2001.00196.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To assess the relative capacity of the human delta opioid receptor to activate closely related G proteins, fusion proteins were constructed in which the alpha-subunits of either G(i1) or G(o1), containing point mutations to render them insensitive to the actions of pertussis toxin, were linked in-frame with the C-terminus of the receptor. Following transient and stable expression in HEK 293 cells, both constructs bound the antagonist [(3)H]naltrindole with high affinity. D-ala(2),D-leu(5) Enkephalin effectively inhibited forskolin-stimulated adenylyl cyclase activity in intact cells in a concentration-dependent, but pertussis toxin-insensitive, manner. The high-affinity GTPase activity of both constructs was also stimulated by D-ala(2),D-leu(5) enkephalin with similar potency. However, enzyme kinetic analysis of agonist stimulation of GTPase activity demonstrated that the GTP turnover number produced in response to D-ala(2),D-leu(5) enkephalin was more than three times greater for G(i1)alpha than for G(o1)alpha. As the effect of agonist in both cases was to increase V:(max) without increasing the observed K:(m) for GTP, this is consistent with receptor promoting greater guanine nucleotide exchange, and thus activation, of G(i1)alpha compared with G(o1)alpha. An equivalent fusion protein between the human mu opioid receptor-1 and G(i1)alpha produced a similar D-ala(2),D-leu(5) enkephalin-induced GTP turnover number as the delta opioid receptor-G(i1)alpha fusion construct, consistent with agonist occupation of these two opioid receptor subtypes being equally efficiently coupled to activation of G(i1)alpha.
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Affiliation(s)
- H E Moon
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
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44
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Chen H, Lambert NA. Endogenous regulators of G protein signaling proteins regulate presynaptic inhibition at rat hippocampal synapses. Proc Natl Acad Sci U S A 2000; 97:12810-5. [PMID: 11050179 PMCID: PMC18846 DOI: 10.1073/pnas.230260397] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Presynaptic inhibition mediated by G protein-coupled receptors (GPCRs) can develop and decay in a few seconds. This time course is too rapid to be accounted for by the intrinsic GTPase activity of Galpha subunits alone. Here, we test the hypothesis that endogenous regulators of G protein signaling (RGS proteins) are required for rapid, brief presynaptic inhibition. Endogenous G protein alpha subunits were uncoupled from GPCRs by treating cultures with pertussis toxin (PTX). Adenoviral expression of mutant PTX-insensitive (PTX-i) Galpha(i1-3) or Galpha(o) subunits rescued adenosine-induced presynaptic inhibition in cultured hippocampal neurons. Expression of double mutant Galpha(i1) or Galpha(o) subunits that were both PTX-insensitive and unable to bind RGS proteins (PTX/RGS-i) also rescued presynaptic inhibition. Presynaptic inhibition mediated by PTX/RGS-i subunits decayed much more slowly after agonist removal than that mediated by PTX-i subunits or native G proteins. The onset of presynaptic inhibition mediated by PTX/RGS-i Galpha(o) was also slower than that mediated by PTX-i Galpha(o). In contrast, the onset of presynaptic inhibition mediated by PTX/RGS-i Galpha(i1) was similar to that mediated by PTX-i Galpha(i1). These results suggest that endogenous RGS proteins regulate the time course of G protein signaling in mammalian central nervous system presynaptic terminals.
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Affiliation(s)
- H Chen
- Department of Pharmacology and Toxicology, Medical College of Georgia, and Medical Research Service, Veterans Affairs Medical Center, Augusta, GA 30912, USA
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45
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McAllister G, Stanton JA, Salim K, Handford EJ, Beer MS. Edg2 receptor functionality: gialpha1 coexpression and fusion protein studies. Mol Pharmacol 2000; 58:407-12. [PMID: 10908309 DOI: 10.1124/mol.58.2.407] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Recombinant receptor cell lines are widely used in G-protein-coupled receptor selectivity studies. To unequivocally interpret the results of such studies, it is essential that the host cell line does not endogenously express the receptor of interest and in addition is unresponsive to the receptor's natural ligand. Here we describe an approach to overcome such difficulties associated with orphan receptors or, as in the present case, receptors whose endogenous ligand ubiquitously affects mammalian cells. The functional heterologous assay system described is for the hEdg2 receptor, which uses lysophosphatidic acid as its endogenous ligand. Once activated, this receptor mediates its effects via multiple secondary messenger pathways, including a Gi-coupled pathway. We have transiently expressed a pertussis toxin-insensitive hEdg2 receptor-ratGialpha1 fusion protein into human embryonic kidney cells and have monitored the ability of compounds to stimulate [(35)S]GTPgammaS binding in membranes prepared from these cells after pretreatment with toxin. Because the assay conditions used favor Gi-mediated responses and because endogenous Gialpha subunits are rendered inactive, the response measured is, by definition, fusion protein-mediated. Consequently, we have developed an assay that monitors definitively Edg2 receptor-mediated responses in a mammalian cell line. A limited structure activity relationship study suggests that the lysophospholipid carbon chain has a role in receptor activation and in addition indicates that certain modifications to the phosphate group are tolerated.
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Affiliation(s)
- G McAllister
- Department of Biochemistry, Merck, Sharp & Dohme Research Laboratories, Neuroscience Research Centre, Terlings Park, Harlow, Essex, United Kingdom.
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46
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Endogenous regulator of G-protein signaling proteins modify N-type calcium channel modulation in rat sympathetic neurons. J Neurosci 2000. [PMID: 10844018 DOI: 10.1523/jneurosci.20-12-04489.2000] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Experiments using heterologous overexpression indicate that regulator of G-protein signaling (RGS) proteins play important roles in Gbetagamma-mediated ion channel modulation. However, the roles subserved by endogenous RGS proteins have not been extensively examined because tools for functionally inhibiting natively expressed RGS proteins are lacking. To address this void, we used a strategy in which Galpha(oA) was rendered insensitive to pertussis toxin (PTX) and RGS proteins by site-directed mutagenesis. Either PTX-insensitive (PTX-i) or both PTX- and RGS-insensitive (PTX/RGS-i) mutants of Galpha(oA) were expressed along with Gbeta(1) and Ggamma(2) subunits in rat sympathetic neurons. After overnight treatment with PTX to suppress natively expressed Galpha subunits, voltage-dependent Ca(2+) current inhibition by norepinephrine (NE) (10 microm) was reconstituted in neurons expressing either PTX-i or PTX/RGS-i Galpha(oA). When compared with neurons expressing PTX-i Galpha(oA), the steady-state concentration-response relationships for NE-induced Ca(2+) current inhibition were shifted to lower concentrations in neurons expressing PTX/RGS-i Galpha(oA). In addition to an increase in agonist potency, the expression of PTX/RGS-i Galpha(oA) dramatically retarded the current recovery after agonist removal. Interestingly, the alteration in current recovery was accompanied by a slowing in the onset of current inhibition. Together, our data suggest that endogenous RGS proteins contribute to membrane-delimited Ca(2+) channel modulation by regulating agonist potency and kinetics of G-protein-mediated signaling in neuronal cells.
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47
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Happe HK, Bylund DB, Murrin LC. Alpha(2)-adrenoceptor-stimulated GTP gamma S binding in rat brain: an autoradiographic study. Eur J Pharmacol 2000; 399:17-27. [PMID: 10876018 DOI: 10.1016/s0014-2999(00)00380-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Agonist-stimulated [35S]GTP gamma S binding by alpha(2)-adrenoceptors was examined in rat brain by autoradiography. Epinephrine, norepinephrine, dexmedetomidine and brimonidine stimulated [35S]GTP gamma S binding in a dose-dependent manner. Agonist-stimulated binding was blocked by the specific alpha(2)-adrenoceptor antagonist (1, 4-benzodioxan-2-methoxy-2-yl)-2-imidazoline hydrochloride (RX821002). Each alpha(2)-adrenoceptor agonist stimulated [35S]GTP gamma S binding in the same brain regions, corresponding to alpha(2)-adrenoceptor distribution determined by [125I]para-iodoclonidine autoradiography. The order of antagonist potency (RX821002>idazoxan>rauwolscine>phentolamine>prazosin), and weak inhibition by propranolol and selective serotonin antagonists, indicate that epinephrine-stimulated [35S]GTP gamma S binding is mediated primarily by alpha(2)-adrenoceptors. Several antagonists increased [35S]GTP gamma S binding at very high concentrations, and this effect had anatomic and pharmacologic characteristics of binding mediated by 5-HT(1A) receptors. These studies demonstrate functional linkage of alpha(2)-adrenoceptors to G proteins in tissue sections, thus providing data on neuroanatomic localization and a means to examine drug specificity at alpha(2)-adrenoceptors in different brain regions.
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Affiliation(s)
- H K Happe
- Department of Pharmacology, University of Nebraska Medical Center, 986260 Nebraska Medical Center, Omaha, NE 68198-6260, USA
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48
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Jeong SW, Ikeda SR. Endogenous regulator of G-protein signaling proteins modify N-type calcium channel modulation in rat sympathetic neurons. J Neurosci 2000; 20:4489-96. [PMID: 10844018 PMCID: PMC6772464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023] Open
Abstract
Experiments using heterologous overexpression indicate that regulator of G-protein signaling (RGS) proteins play important roles in Gbetagamma-mediated ion channel modulation. However, the roles subserved by endogenous RGS proteins have not been extensively examined because tools for functionally inhibiting natively expressed RGS proteins are lacking. To address this void, we used a strategy in which Galpha(oA) was rendered insensitive to pertussis toxin (PTX) and RGS proteins by site-directed mutagenesis. Either PTX-insensitive (PTX-i) or both PTX- and RGS-insensitive (PTX/RGS-i) mutants of Galpha(oA) were expressed along with Gbeta(1) and Ggamma(2) subunits in rat sympathetic neurons. After overnight treatment with PTX to suppress natively expressed Galpha subunits, voltage-dependent Ca(2+) current inhibition by norepinephrine (NE) (10 microm) was reconstituted in neurons expressing either PTX-i or PTX/RGS-i Galpha(oA). When compared with neurons expressing PTX-i Galpha(oA), the steady-state concentration-response relationships for NE-induced Ca(2+) current inhibition were shifted to lower concentrations in neurons expressing PTX/RGS-i Galpha(oA). In addition to an increase in agonist potency, the expression of PTX/RGS-i Galpha(oA) dramatically retarded the current recovery after agonist removal. Interestingly, the alteration in current recovery was accompanied by a slowing in the onset of current inhibition. Together, our data suggest that endogenous RGS proteins contribute to membrane-delimited Ca(2+) channel modulation by regulating agonist potency and kinetics of G-protein-mediated signaling in neuronal cells.
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Affiliation(s)
- S W Jeong
- Laboratory of Molecular Physiology, Guthrie Research Institute, Sayre, Pennsylvania 18840, USA
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49
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Rauly I, Ailhaud M, Wurch T, Pauwels PJ. alpha(2A)-adrenoceptor: G(alphai1) protein-mediated pertussis toxin-resistant attenuation of G(s) coupling to the cyclic AMP pathway. Biochem Pharmacol 2000; 59:1531-8. [PMID: 10799649 DOI: 10.1016/s0006-2952(00)00276-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Fusion proteins were constructed between a recombinant human alpha(2A)-adrenoceptor and either a rat wild-type G(alphai1) or putative pertussis toxin-resistant form of the G(alphai1) protein (G(alphai1)Cys(351)Gly). [(3)H]2-[2-(2-Methoxy-1, 4-benzodioxanyl)]imidazoline hydrochloride (RX 821002) saturation binding experiments demonstrated that both fusion proteins were expressed at a similar level as the alpha(2A)-adrenoceptor co-expressed with either a wild-type G(alphai1) or mutant G(alphai1)Cys(351)Gly protein in COS-7 cells, and displayed a ligand binding profile similar to that for the alpha(2A)-adrenoceptor protein. In alpha(2A)-adrenoceptor-transfected COS-7 cells, 5-bromo-6-(2-imidazolin-2-yl-amino) quinoxaline tartrate (brimonidine, 10 microM) induced stimulation (151 +/- 28%) of adenosine 3',5'-cyclic monophosphate (cAMP) formation which was prevented by cholera toxin treatment, demonstrating a direct coupling of the alpha(2A)-adrenoceptor to an endogenous G(alphas) protein in COS-7 cells. Expression of either the wild-type G(alphai1) or mutant G(alphai1)Cys(351)Gly protein in co-expression or fusion with the alpha(2A)-adrenoceptor in COS-7 cells suppressed the brimonidine-induced stimulation of cAMP formation, both in the presence and absence of pertussis toxin pretreatment. Hence, the G(alphai1) protein apparently blocks the G(s)-coupled alpha(2A)-adrenoceptor-mediated pathway in a pertussis toxin-non-sensitive way.
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Affiliation(s)
- I Rauly
- Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, 81106, Castres, France.
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50
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Leaney JL, Tinker A. The role of members of the pertussis toxin-sensitive family of G proteins in coupling receptors to the activation of the G protein-gated inwardly rectifying potassium channel. Proc Natl Acad Sci U S A 2000; 97:5651-6. [PMID: 10779550 PMCID: PMC25883 DOI: 10.1073/pnas.080572297] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Inwardly rectifying potassium (K(+)) channels gated by G proteins (Kir3.x family) are widely distributed in neuronal, atrial, and endocrine tissues and play key roles in generating late inhibitory postsynaptic potentials, slowing the heart rate and modulating hormone release. They are directly activated by G(betagamma) subunits released from G protein heterotrimers of the G(i/o) family upon appropriate receptor stimulation. Here we examine the role of isoforms of pertussis toxin (PTx)-sensitive G protein alpha subunits (G(ialpha1-3) and G(oalphaA)) in mediating coupling between various receptor systems (A(1), alpha(2A), D(2S), M(4), GABA(B)1a+2, and GABA(B)1b+2) and the cloned counterpart of the neuronal channel (Kir3.1+3.2A). The expression of mutant PTx-resistant G(i/oalpha) subunits in PTx-treated HEK293 cells stably expressing Kir3.1+3.2A allows us to selectively investigate that coupling. We find that, for those receptors (A(1), alpha(2A)) known to interact with all isoforms, G(ialpha1-3) and G(oalphaA) can all support a significant degree of coupling to Kir3.1+3.2A. The M(4) receptor appears to preferentially couple to G(ialpha2) while another group of receptors (D(2S), GABA(B)1a+2, GABA(B)1b+2) activates the channel predominantly through G(betagamma) liberated from G(oA) heterotrimers. Interestingly, we have also found a distinct difference in G protein coupling between the two splice variants of GABA(B)1. Our data reveal selective pathways of receptor activation through different G(i/oalpha) isoforms for stimulation of the G protein-gated inwardly rectifying K(+) channel.
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Affiliation(s)
- J L Leaney
- Centre for Clinical Pharmacology, Department of Medicine, University College London, The Rayne Institute, 5 University Street, London WC1E 6JJ, United Kingdom
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