1
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Kenakin T. Know your molecule: pharmacological characterization of drug candidates to enhance efficacy and reduce late-stage attrition. Nat Rev Drug Discov 2024; 23:626-644. [PMID: 38890494 DOI: 10.1038/s41573-024-00958-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/23/2024] [Indexed: 06/20/2024]
Abstract
Despite advances in chemical, computational and biological sciences, the rate of attrition of drug candidates in clinical development is still high. A key point in the small-molecule discovery process that could provide opportunities to help address this challenge is the pharmacological characterization of hit and lead compounds, culminating in the selection of a drug candidate. Deeper characterization is increasingly important, because the 'quality' of drug efficacy, at least for G protein-coupled receptors (GPCRs), is now understood to be much more than activation of commonly evaluated pathways such as cAMP signalling, with many more 'efficacies' of ligands that could be harnessed therapeutically. Such characterization is being enabled by novel assays to characterize the complex behaviour of GPCRs, such as biased signalling and allosteric modulation, as well as advances in structural biology, such as cryo-electron microscopy. This article discusses key factors in the assessments of the pharmacology of hit and lead compounds in the context of GPCRs as a target class, highlighting opportunities to identify drug candidates with the potential to address limitations of current therapies and to improve the probability of them succeeding in clinical development.
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Affiliation(s)
- Terry Kenakin
- Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
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2
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Yan W, Zhu H, Yu B, Ma X, Liang H, Zhao S, Deng K. Effects of two inhibitors of metabolic glutamate receptor 5 on expression of endogenous homer scaffold protein 1 in the auditory cortex of mice with tinnitus. Bioengineered 2021; 12:7156-7164. [PMID: 34546852 PMCID: PMC8806735 DOI: 10.1080/21655979.2021.1979354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 09/07/2021] [Indexed: 10/29/2022] Open
Abstract
Tinnitus is deemed as the result of abnormal neural activities in the brain, and Homer proteins are expressed in the brain that convey nociception. The expression of Homer in tinnitus has not been studied. We hypothesized that expression of Homer in the auditory cortex was altered after tinnitus treatment. Mice were injected with sodium salicylate to induce tinnitus. Expression of Homer was detected by quantitative real-time polymerase chain reaction, western blotting, and immunohistochemistry assays. We found that Homer1 expression was upregulated in the auditory cortex of mice with tinnitus, while expression of Homer2 or Homer3 exhibited no significant alteration. Effects of two inhibitors of metabolic glutamate receptor 5 (mGluR5), noncompetitive 2-Methyl-6-(phenylethynyl)-pyridine (MPEP) and competitive α-methyl-4-carboxyphenylglycine (MCPG), on the tinnitus scores of the mice and on Homer1 expression were detected. MPEP significantly reduced tinnitus scores and suppressed Homer1 expression in a concentration dependent manner. MCPG had no significant effects on tinnitus scores or Homer1 expression. In conclusion, Homer1 expression was upregulated in the auditory cortex of mice after tinnitus, and was suppressed by noncompetitive mGluR5 inhibitor MPEP, but not competitive mGluR5 inhibitor MCPG.
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Affiliation(s)
- Weiwei Yan
- The First Clinical College, Hubei University of Chinese Medicine, Wuhan, Hubei, China
| | - Hongfei Zhu
- Department of Anesthesiology, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
| | - Bianbian Yu
- Department of Otorhinolaryngology, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
| | - Xin Ma
- Department of Otorhinolaryngology, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
| | - Hang Liang
- Department of Anesthesiology, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
| | - Shuyan Zhao
- Department of Anesthesiology, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
| | - Kebin Deng
- Department of Otorhinolaryngology, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
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3
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Hámor PU, Schwendt M. Metabotropic Glutamate Receptor Trafficking and its Role in Drug-Induced Neurobehavioral Plasticity. Brain Plast 2021; 7:61-76. [PMID: 34868874 PMCID: PMC8609495 DOI: 10.3233/bpl-210120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/06/2021] [Indexed: 12/18/2022] Open
Abstract
Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system that guides developmental and experience-dependent changes in many cellular substrates and brain circuits, through the process collectively referred to as neurobehavioral plasticity. Regulation of cell surface expression and membrane trafficking of glutamate receptors represents an important mechanism that assures optimal excitatory transmission, and at the same time, also allows for fine-tuning neuronal responses to glutamate. On the other hand, there is growing evidence implicating dysregulated glutamate receptor trafficking in the pathophysiology of several neuropsychiatric disorders. This review provides up-to-date information on the molecular determinants regulating trafficking and surface expression of metabotropic glutamate (mGlu) receptors in the rodent and human brain and discusses the role of mGluR trafficking in maladaptive synaptic plasticity produced by addictive drugs. As substantial evidence links glutamatergic dysfunction to the progression and the severity of drug addiction, advances in our understanding of mGluR trafficking may provide opportunities for the development of novel pharmacotherapies of addiction and other neuropsychiatric disorders.
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Affiliation(s)
- Peter U. Hámor
- Department of Psychology, University of Florida, Gainesville, FL, USA
- Center for Addiction Research and Education, University of Florida, Gainesville, FL, USA
| | - Marek Schwendt
- Department of Psychology, University of Florida, Gainesville, FL, USA
- Center for Addiction Research and Education, University of Florida, Gainesville, FL, USA
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4
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Gregory KJ, Goudet C. International Union of Basic and Clinical Pharmacology. CXI. Pharmacology, Signaling, and Physiology of Metabotropic Glutamate Receptors. Pharmacol Rev 2020; 73:521-569. [PMID: 33361406 DOI: 10.1124/pr.119.019133] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Metabotropic glutamate (mGlu) receptors respond to glutamate, the major excitatory neurotransmitter in the mammalian brain, mediating a modulatory role that is critical for higher-order brain functions such as learning and memory. Since the first mGlu receptor was cloned in 1992, eight subtypes have been identified along with many isoforms and splice variants. The mGlu receptors are transmembrane-spanning proteins belonging to the class C G protein-coupled receptor family and represent attractive targets for a multitude of central nervous system disorders. Concerted drug discovery efforts over the past three decades have yielded a wealth of pharmacological tools including subtype-selective agents that competitively block or mimic the actions of glutamate or act allosterically via distinct sites to enhance or inhibit receptor activity. Herein, we review the physiologic and pathophysiological roles for individual mGlu receptor subtypes including the pleiotropic nature of intracellular signal transduction arising from each. We provide a comprehensive analysis of the in vitro and in vivo pharmacological properties of prototypical and commercially available orthosteric agonists and antagonists as well as allosteric modulators, including ligands that have entered clinical trials. Finally, we highlight emerging areas of research that hold promise to facilitate rational design of highly selective mGlu receptor-targeting therapeutics in the future. SIGNIFICANCE STATEMENT: The metabotropic glutamate receptors are attractive therapeutic targets for a range of psychiatric and neurological disorders. Over the past three decades, intense discovery efforts have yielded diverse pharmacological tools acting either competitively or allosterically, which have enabled dissection of fundamental biological process modulated by metabotropic glutamate receptors and established proof of concept for many therapeutic indications. We review metabotropic glutamate receptor molecular pharmacology and highlight emerging areas that are offering new avenues to selectively modulate neurotransmission.
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Affiliation(s)
- Karen J Gregory
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology, Monash University, Parkville, Victoria, Australia (K.J.G.) and Institut de Génomique Fonctionnelle (IGF), University of Montpellier, Centre National de la Recherche Scientifique (CNRS), Institut National de la Sante et de la Recherche Medicale (INSERM), Montpellier, France (C.G.)
| | - Cyril Goudet
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences and Department of Pharmacology, Monash University, Parkville, Victoria, Australia (K.J.G.) and Institut de Génomique Fonctionnelle (IGF), University of Montpellier, Centre National de la Recherche Scientifique (CNRS), Institut National de la Sante et de la Recherche Medicale (INSERM), Montpellier, France (C.G.)
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5
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Lee S, Park S, Lee H, Han S, Song JM, Han D, Suh YH. Nedd4 E3 ligase and beta-arrestins regulate ubiquitination, trafficking, and stability of the mGlu7 receptor. eLife 2019; 8:44502. [PMID: 31373553 PMCID: PMC6690720 DOI: 10.7554/elife.44502] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 08/01/2019] [Indexed: 12/23/2022] Open
Abstract
The metabotropic glutamate receptor 7 (mGlu7) is a class C G protein-coupled receptor that modulates excitatory neurotransmitter release at the presynaptic active zone. Although post-translational modification of cellular proteins with ubiquitin is a key molecular mechanism governing protein degradation and function, mGlu7 ubiquitination and its functional consequences have not been elucidated yet. Here, we report that Nedd4 ubiquitin E3 ligase and β-arrestins regulate ubiquitination of mGlu7 in heterologous cells and rat neurons. Upon agonist stimulation, β-arrestins recruit Nedd4 to mGlu7 and facilitate Nedd4-mediated ubiquitination of mGlu7. Nedd4 and β-arrestins regulate constitutive and agonist-induced endocytosis of mGlu7 and are required for mGlu7-dependent MAPK signaling in neurons. In addition, Nedd4-mediated ubiquitination results in the degradation of mGlu7 by both the ubiquitin-proteasome system and the lysosomal degradation pathway. These findings provide a model in which Nedd4 and β-arrestin act together as a complex to regulate mGlu7 surface expression and function at presynaptic terminals.
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Affiliation(s)
- Sanghyeon Lee
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea.,Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Sunha Park
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea.,Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Hyojin Lee
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea.,Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Seulki Han
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea.,Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Jae-Man Song
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea.,Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Dohyun Han
- Proteomics Core Facility, Biomedical Research Institute, Seoul National University Hospital, Seoul, Republic of Korea
| | - Young Ho Suh
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, Republic of Korea.,Neuroscience Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea
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6
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Thakur R, Naik A, Panda A, Raghu P. Regulation of Membrane Turnover by Phosphatidic Acid: Cellular Functions and Disease Implications. Front Cell Dev Biol 2019; 7:83. [PMID: 31231646 PMCID: PMC6559011 DOI: 10.3389/fcell.2019.00083] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 05/03/2019] [Indexed: 01/23/2023] Open
Abstract
Phosphatidic acid (PA) is a simple glycerophospholipid with a well-established role as an intermediate in phospholipid biosynthesis. In addition to its role in lipid biosynthesis, PA has been proposed to act as a signaling molecule that modulates several aspects of cell biology including membrane transport. PA can be generated in eukaryotic cells by several enzymes whose activity is regulated in the context of signal transduction and enzymes that can metabolize PA thus terminating its signaling activity have also been described. Further, several studies have identified PA binding proteins and changes in their activity are proposed to be mediators of the signaling activity of this lipid. Together these enzymes and proteins constitute a PA signaling toolkit that mediates the signaling functions of PA in cells. Recently, a number of novel genetic models for the analysis of PA function in vivo and analytical methods to quantify PA levels in cells have been developed and promise to enhance our understanding of PA functions. Studies of several elements of the PA signaling toolkit in a single cell type have been performed and are presented to provide a perspective on our understanding of the biochemical and functional organization of pools of PA in a eukaryotic cell. Finally, we also provide a perspective on the potential role of PA in human disease, synthesizing studies from model organisms, human disease genetics and analysis using recently developed PLD inhibitors.
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Affiliation(s)
- Rajan Thakur
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Amruta Naik
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Aniruddha Panda
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, Bengaluru, India
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7
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Sanderson TM, Bradley CA, Georgiou J, Hong YH, Ng AN, Lee Y, Kim HD, Kim D, Amici M, Son GH, Zhuo M, Kim K, Kaang BK, Kim SJ, Collingridge GL. The Probability of Neurotransmitter Release Governs AMPA Receptor Trafficking via Activity-Dependent Regulation of mGluR1 Surface Expression. Cell Rep 2018; 25:3631-3646.e3. [PMID: 30590038 PMCID: PMC6315206 DOI: 10.1016/j.celrep.2018.12.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 09/28/2018] [Accepted: 12/03/2018] [Indexed: 12/14/2022] Open
Abstract
A major mechanism contributing to synaptic plasticity involves alterations in the number of AMPA receptors (AMPARs) expressed at synapses. Hippocampal CA1 synapses, where this process has been most extensively studied, are highly heterogeneous with respect to their probability of neurotransmitter release, P(r). It is unknown whether there is any relationship between the extent of plasticity-related AMPAR trafficking and the initial P(r) of a synapse. To address this question, we induced metabotropic glutamate receptor (mGluR) dependent long-term depression (mGluR-LTD) and assessed AMPAR trafficking and P(r) at individual synapses, using SEP-GluA2 and FM4-64, respectively. We found that either pharmacological or synaptic activation of mGluR1 reduced synaptic SEP-GluA2 in a manner that depends upon P(r); this process involved an activity-dependent reduction in surface mGluR1 that selectively protects high-P(r) synapses from synaptic weakening. Consequently, the extent of postsynaptic plasticity can be pre-tuned by presynaptic activity.
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Affiliation(s)
- Thomas M Sanderson
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Neuroscience Research Institute, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea; School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK; Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Clarrisa A Bradley
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Neuroscience & Mental Health Program, The Hospital for Sick Children, Toronto, ON, Canada
| | - John Georgiou
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Yun Hwa Hong
- Neuroscience Research Institute, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea; Department of Physiology, Seoul National University College of Medicine, 28, Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea
| | - Ai Na Ng
- School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
| | - Yeseul Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
| | - Hee-Dae Kim
- Department of Brain and Cognitive Sciences, DGIST, and Korea Brain Institute (KBRI), Daegu, 41068, Korea
| | - Doyeon Kim
- Department of Brain and Cognitive Sciences, DGIST, and Korea Brain Institute (KBRI), Daegu, 41068, Korea
| | - Mascia Amici
- School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
| | - Gi Hoon Son
- Department of Biomedical Sciences, Korea University College of Medicine, Seoul 136-705, Seoul, Korea
| | - Min Zhuo
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Biological Sciences, College of Natural Sciences, Seoul National University, Building 504, Room 202, 599 Gwanangno, Gwanak-gu 151-747, Seoul, Korea; Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, 710049, China
| | - Kyungjin Kim
- Department of Brain and Cognitive Sciences, DGIST, and Korea Brain Institute (KBRI), Daegu, 41068, Korea
| | - Bong-Kiun Kaang
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Department of Biological Sciences, College of Natural Sciences, Seoul National University, Building 504, Room 202, 599 Gwanangno, Gwanak-gu 151-747, Seoul, Korea; Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, 710049, China
| | - Sang Jeong Kim
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Neuroscience Research Institute, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea; Department of Physiology, Seoul National University College of Medicine, 28, Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea.
| | - Graham L Collingridge
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK; Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada; Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada.
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8
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Suh YH, Chang K, Roche KW. Metabotropic glutamate receptor trafficking. Mol Cell Neurosci 2018; 91:10-24. [PMID: 29604330 DOI: 10.1016/j.mcn.2018.03.014] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 03/07/2018] [Accepted: 03/26/2018] [Indexed: 01/14/2023] Open
Abstract
The metabotropic glutamate receptors (mGlu receptors) are G protein-coupled receptors that bind to the excitatory neurotransmitter glutamate and are important in the modulation of neuronal excitability, synaptic transmission, and plasticity in the central nervous system. Trafficking of mGlu receptors in and out of the synaptic plasma membrane is a fundamental mechanism modulating excitatory synaptic function through regulation of receptor abundance, desensitization, and signaling profiles. In this review, we cover the regulatory mechanisms determining surface expression and endocytosis of mGlu receptors, with particular focus on post-translational modifications and receptor-protein interactions. The literature we review broadens our insight into the precise events defining the expression of functional mGlu receptors at synapses, and will likely contribute to the successful development of novel therapeutic targets for a variety of developmental, neurological, and psychiatric disorders.
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Affiliation(s)
- Young Ho Suh
- Department of Biomedical Sciences, Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, South Korea.
| | - Kai Chang
- Receptor Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Katherine W Roche
- Receptor Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
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9
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Group I Metabotropic Glutamate Receptors (mGluRs): Ins and Outs. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1112:163-175. [DOI: 10.1007/978-981-13-3065-0_12] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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10
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Nisar SP, Lordkipanidzé M, Jones ML, Dawood BB, Murden S, Cunningham MR, Mumford AD, Wilde JT, Watson SP, Lowe GC, Mundell SJ. A novel thromboxane A2 receptor N42S variant results in reduced surface expression and platelet dysfunction. Thromb Haemost 2017; 111:923-32. [DOI: 10.1160/th13-08-0672] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 12/19/2013] [Indexed: 11/05/2022]
Abstract
SummaryA small number of thromboxane receptor variants have been described in patients with a bleeding history that result in platelet dysfunction. We have identified a patient with a history of significant bleeding, who expresses a novel heterozygous thromboxane receptor variant that predicts an asparagine to serine substitution (N42S). This asparagine is conserved across all class A GPCRs, suggesting a vital role for receptor structure and function. We investigated the functional consequences of the TP receptor heterozygous N42S substitution by performing platelet function studies on platelet-rich plasma taken from the patient and healthy controls. We investigated the N42S mutation by expressing the wild-type (WT) and mutant receptor in human embryonic kidney (HEK) cells. Aggregation studies showed an ablation of arachidonic acid responses in the patient, whilst there was right-ward shift of the U46619 concentration response curve (CRC). Thromboxane generation was unaffected. Calcium mobilisation studies in cells lines showed a rightward shift of the U46619 CRC in N42S–expressing cells compared to WT. Radioligand binding studies revealed a reduction in BMax in platelets taken from the patient and in N42S–expressing cells, whilst cell studies confirmed poor surface expression. We have identified a novel thromboxane receptor variant, N42S, which results in platelet dysfunction due to reduced surface expression. It is associated with a significant bleeding history in the patient in whom it was identified. This is the first description of a naturally occurring variant that results in the substitution of this highly conserved residue and confirms the importance of this residue for correct GPCR function.
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11
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Oishi A, Karamitri A, Gerbier R, Lahuna O, Ahmad R, Jockers R. Orphan GPR61, GPR62 and GPR135 receptors and the melatonin MT 2 receptor reciprocally modulate their signaling functions. Sci Rep 2017; 7:8990. [PMID: 28827538 PMCID: PMC5566548 DOI: 10.1038/s41598-017-08996-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 07/14/2017] [Indexed: 01/14/2023] Open
Abstract
Understanding the function of orphan G protein-coupled receptors (GPCRs), whose cognate ligand is unknown, is of major importance as GPCRs are privileged drug targets for many diseases. Recent phylogenetic studies classified three orphan receptors, GPR61, GPR62 and GPR135 among the melatonin receptor subfamily, but their capacity to bind melatonin and their biochemical functions are not well characterized yet. We show here that GPR61, GPR62 and GPR135 do not bind [3H]-melatonin nor 2-[125I]iodomelatonin and do not respond to melatonin in several signaling assays. In contrast, the three receptors show extensive spontaneous ligand-independent activities on the cAMP, inositol phosphate and ß-arrestin pathways with distinct pathway-specific profiles. Spontaneous ß-arrestin recruitment internalizes all three GPRs in the endosomal compartment. Co-expression of the melatonin binding MT2 receptor with GPR61, GPR62 or GPR135 has several consequences such as (i) the formation of receptor heteromers, (ii) the inhibition of melatonin-induced ß-arrestin2 recruitment to MT2 and (iii) the decrease of elevated cAMP levels upon melatonin stimulation in cells expressing spontaneously active GPR61 and GPR62. Collectively, these data show that GPR61, GPR62 and GPR135 are unable to bind melatonin, but show a reciprocal regulatory interaction with MT2 receptors.
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Affiliation(s)
- Atsuro Oishi
- Inserm, U1016, Institut Cochin, Paris, France.,CNRS UMR, 8104, Paris, France.,University Paris Descartes, Paris, France
| | - Angeliki Karamitri
- Inserm, U1016, Institut Cochin, Paris, France.,CNRS UMR, 8104, Paris, France.,University Paris Descartes, Paris, France
| | - Romain Gerbier
- Inserm, U1016, Institut Cochin, Paris, France.,CNRS UMR, 8104, Paris, France.,University Paris Descartes, Paris, France
| | - Olivier Lahuna
- Inserm, U1016, Institut Cochin, Paris, France.,CNRS UMR, 8104, Paris, France.,University Paris Descartes, Paris, France
| | - Raise Ahmad
- Inserm, U1016, Institut Cochin, Paris, France.,CNRS UMR, 8104, Paris, France.,University Paris Descartes, Paris, France
| | - Ralf Jockers
- Inserm, U1016, Institut Cochin, Paris, France. .,CNRS UMR, 8104, Paris, France. .,University Paris Descartes, Paris, France.
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12
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Bhattacharyya S. Inside story of Group I Metabotropic Glutamate Receptors (mGluRs). Int J Biochem Cell Biol 2016; 77:205-12. [PMID: 26987586 DOI: 10.1016/j.biocel.2016.03.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 03/10/2016] [Accepted: 03/11/2016] [Indexed: 12/31/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) are G-protein coupled receptors (GPCRs) that are activated by the neurotransmitter glutamate in the central nervous system. Among the eight subtypes, mGluR1 and mGluR5 belong to the group I family. These receptors play important roles in the brain and are believed to be involved in multiple forms of experience dependent synaptic plasticity including learning and memory. In addition, group I mGluRs also have been implicated in various neuropsychiatric disorders like Fragile X syndrome, autism etc. The normal signaling depends on the precise location of these receptors in specific region of the neuron and the process of receptor trafficking plays a crucial role in controlling this localization. Intracellular trafficking could also regulate the desensitization, resensitization, down-regulation and intracellular signaling of these receptors. In this review I focus on the current understanding of group I mGluR regulation in the central nervous system and also their role in neuropsychiatric disorders.
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Affiliation(s)
- Samarjit Bhattacharyya
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge city, Sector-81, SAS Nagar, PO: 140306, Punjab, India.
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13
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Millar RP, Babwah AV. KISS1R: Hallmarks of an Effective Regulator of the Neuroendocrine Axis. Neuroendocrinology 2015; 101:193-210. [PMID: 25765628 DOI: 10.1159/000381457] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 03/04/2015] [Indexed: 11/19/2022]
Abstract
Kisspeptin (KP) is now well recognized as a potent stimulator of gonadotropin-releasing hormone (GnRH) secretion and thereby a major regulator of the neuroendocrine-reproductive axis. KP signals via KISS1R, a G protein-coupled receptor (GPCR) that activates the G proteins Gαq/11. Modulation of the interaction of KP with KISS1R is therefore a potential new therapeutic target for stimulating (in infertility) or inhibiting (in hormone-dependent diseases) the reproductive hormone cascade. Major efforts are underway to target KISS1R in the treatment of sex steroid hormone-dependent disorders and to stimulate endogenous hormonal responses along the neuroendocrine axis as part of in vitro fertilization protocols. The development of analogs modulating KISS1R signaling will be aided by an understanding of the intracellular pathways and dynamics of KISS1R signaling under normal and pathological conditions. This review focuses on KISS1R recruitment of intracellular signaling (Gαq/11- and β-arrestin-dependent) pathways that mediate GnRH secretion and the respective roles of rapid desensitization, internalization, and recycling of resensitized receptors in maintaining an active population of KISS1R at the cell surface to facilitate prolonged KP signaling. Additionally, this review summarizes and discusses the major findings of an array of studies examining the desensitization of KP signaling in man, domestic and laboratory animals. This discussion highlights the major effects of ligand efficacy and concentration and the physiological, developmental, and metabolic status of the organism on KP signaling. Finally, the potential for the utilization of KP and analogs in stimulating and inhibiting the reproductive hormone cascade as an alternative to targeting the downstream GnRH receptor is discussed.
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Affiliation(s)
- Robert P Millar
- Mammal Research Institute, University of Pretoria, Pretoria, South Africa
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14
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Patel YM, Lordkipanidzé M, Lowe GC, Nisar SP, Garner K, Stockley J, Daly ME, Mitchell M, Watson SP, Austin SK, Mundell SJ. A novel mutation in the P2Y12 receptor and a function-reducing polymorphism in protease-activated receptor 1 in a patient with chronic bleeding. J Thromb Haemost 2014; 12:716-25. [PMID: 24612435 DOI: 10.1111/jth.12539] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 01/27/2014] [Indexed: 11/29/2022]
Abstract
BACKGROUND The study of patients with bleeding problems is a powerful approach in determining the function and regulation of important proteins in human platelets. We have identified a patient with a chronic bleeding disorder expressing a homozygous P2RY(12) mutation, predicting an arginine to cysteine (R122C) substitution in the G-protein-coupled P2Y(12) receptor. This mutation is found within the DRY motif, which is a highly conserved region in G-protein-coupled receptors (GPCRs) that is speculated to play a critical role in regulating receptor conformational states. OBJECTIVES To determine the functional consequences of the R122C substitution for P2Y(12) function. PATIENT/METHODS We performed a detailed phenotypic analysis of an index case and affected family members. An analysis of the variant R122C P2Y(12) stably expressed in cells was also performed. RESULTS ADP-stimulated platelet aggregation was reduced as a result of a significant impairment of P2Y(12) activity in the patient and family members. Cell surface R122C P2Y(12) expression was reduced both in cell lines and in platelets; in cell lines, this was as a consequence of agonist-independent internalization followed by subsequent receptor trafficking to lysosomes. Strikingly, members of this family also showed reduced thrombin-induced platelet activation, owing to an intronic polymorphism in the F2R gene, which encodes protease-activated receptor 1 (PAR-1), that has been shown to be associated with reduced PAR-1 receptor activity. CONCLUSIONS Our study is the first to demonstrate a patient with deficits in two stimulatory GPCR pathways that regulate platelet activity, further indicating that bleeding disorders constitute a complex trait.
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Affiliation(s)
- Y M Patel
- Department of Cardiology, Cardiovascular Division, King's College London, The Rayne Institute, St Thomas' Hospital, London, UK
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15
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Neuronal phenotype dependency of agonist-induced internalization of the 5-HT(1A) serotonin receptor. J Neurosci 2014; 34:282-94. [PMID: 24381289 DOI: 10.1523/jneurosci.0186-13.2014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Selective serotonin reuptake inhibitors (SSRI) are aimed at increasing brain 5-HT tone; however, this expected effect has a slow onset after starting SSRI treatment because of initial activation of 5-HT(1A) autoreceptor-mediated negative feedback of 5-HT release. After chronic SSRI treatment, 5-HT(1A) autoreceptors desensitize, which allows 5-HT tone elevation. Because 5-HT(1A) receptor (5-HT(1A)R) internalization has been proposed as a possible mechanism underlying 5-HT(1A) autoreceptor desensitization, we examined whether this receptor could internalize under well controlled in vitro conditions in the LLC-CPK1 cell line and in raphe or hippocampal neurons from rat embryos. To this goal, cells were transfected with recombinant lentiviral vectors encoding N-terminal tagged 5-HT(1A)R, and exposed to various pharmacological conditions. Constitutive endocytosis and plasma membrane recycling of tagged-5-HT(1A)R was observed in LLC-PK1 cells as well as in neurons. Acute exposure (for 1 h) to the full 5-HT(1A)R agonists, 5-HT and 5-carboxamido-tryptamine, but not the partial agonist 8-OH-DPAT, triggered internalization of tagged 5-HT(1A)R in serotonergic neurons only. In contrast, sustained exposure (for 24 h) to all agonists induced tagged-5-HT(1A)R endocytosis in raphe serotonergic neurons and a portion of hippocampal neurons, but not LLC-PK1 cells and partial agonist displayed an effect only in serotonergic neurons. In all cases, agonist-induced tagged 5-HT(1A)R endocytosis was prevented by the 5-HT(1A)R antagonist, WAY-100635, which was inactive on its own. These data showed that agonist-induced 5-HT(1A)R internalization does exist in neurons and depends on agonist efficacy and neuronal phenotype. Its differential occurrence in serotonergic neurons supports the idea that 5-HT(1A)R internalization might underlie 5-HT(1A) autoreceptor desensitization under SSRI antidepressant therapy.
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16
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Akama KT, Thompson LI, Milner TA, McEwen BS. Post-synaptic density-95 (PSD-95) binding capacity of G-protein-coupled receptor 30 (GPR30), an estrogen receptor that can be identified in hippocampal dendritic spines. J Biol Chem 2013; 288:6438-50. [PMID: 23300088 DOI: 10.1074/jbc.m112.412478] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The estrogen 17β-estradiol (E2) modulates dendritic spine plasticity in the cornu ammonis 1 (CA1) region of the hippocampus, and GPR30 (G-protein coupled estrogen receptor 1 (GPER1)) is an estrogen-sensitive G-protein-coupled receptor (GPCR) that is expressed in the mammalian brain and in specific subregions that are responsive to E2, including the hippocampus. The subcellular localization of hippocampal GPR30, however, remains unclear. Here, we demonstrate that GPR30 immunoreactivity is detected in dendritic spines of rat CA1 hippocampal neurons in vivo and that GPR30 protein can be found in rat brain synaptosomes. GPR30 immunoreactivity is identified at the post-synaptic density (PSD) and in the adjacent peri-synaptic zone, and GPR30 can associate with the spine scaffolding protein PSD-95 both in vitro and in vivo. This PSD-95 binding capacity of GPR30 is specific and determined by the receptor C-terminal tail that is both necessary and sufficient for PSD-95 interaction. The interaction with PSD-95 functions to increase GPR30 protein levels residing at the plasma membrane surface. GPR30 associates with the N-terminal tandem pair of PDZ domains in PSD-95, suggesting that PSD-95 may be involved in clustering GPR30 with other receptors in the hippocampus. We demonstrate that GPR30 has the potential to associate with additional post-synaptic GPCRs, including the membrane progestin receptor, the corticotropin releasing hormone receptor, and the 5HT1a serotonin receptor. These data demonstrate that GPR30 is well positioned in the dendritic spine compartment to integrate E2 sensitivity directly onto multiple inputs on synaptic activity and might begin to provide a molecular explanation as to how E2 modulates dendritic spine plasticity.
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Affiliation(s)
- Keith T Akama
- Laboratory of Neuroendocrinology, The Rockefeller University, Weill Cornell Medical College, New York, New York 10065, USA
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17
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Iacovelli L, Nicoletti F, De Blasi A. Molecular mechanisms that desensitize metabotropic glutamate receptor signaling: an overview. Neuropharmacology 2012; 66:24-30. [PMID: 22659473 DOI: 10.1016/j.neuropharm.2012.05.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 05/06/2012] [Accepted: 05/08/2012] [Indexed: 01/10/2023]
Abstract
The purpose of the present article is to review our actual knowledge on the desensitization of metabotropic glutamate receptors based on the literature available so far, with the attempt to emphasize all converging data and to give a possible explanation to those evidences that still remain controversial. 1. We review our knowledge on the regulation of mGlu receptors based on the available literature 2. We report converging data and we comment on issues that still remain controversial. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.
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Affiliation(s)
- Luisa Iacovelli
- Dept. of Physiology and Pharmacology "V. Erspamer", University of Rome "Sapienza", P.le Aldo Moro 5, 00185 Rome, Italy.
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18
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Oh P, Horner T, Witkiewicz H, Schnitzer JE. Endothelin induces rapid, dynamin-mediated budding of endothelial caveolae rich in ET-B. J Biol Chem 2012; 287:17353-17362. [PMID: 22457360 DOI: 10.1074/jbc.m111.338897] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Clathrin-independent trafficking pathways for internalizing G protein-coupled receptors (GPCRs) remain undefined. Clathrin-mediated endocytosis of receptors including ligand-engaged GPCRs can be very rapid and comprehensive (<10 min). Caveolae-mediated endocytosis of ligands and antibodies has been reported to be much slower in cell culture (≫10 min). Little is known about the role of physiological ligands and specific GPCRs in regulating caveolae trafficking. Here, we find that one receptor for endothelin, ET-B but not ET-A, resides on endothelial cell surfaces in both tissue and cell culture primarily concentrated within caveolae. Reconstituted cell-free budding assays show that endothelins (ETs) induce the fission of caveolae from endothelial plasma membranes purified from rat lungs. Electron microcopy of lung tissue sections and tissue subcellular fractionation both show that endothelin administered intravascularly in rats also induces a significant loss of caveolae at the luminal surface of lung vascular endothelium. Endothelial cells in culture show that ET stimulates very rapid internalization of caveolae and cargo including caveolin, caveolae-targeting antibody, and itself. The ET-B inhibitor BQ788, but not the ET-A inhibitor BQ123, blocks the ET-induced budding of caveolae. Both the pharmacological inhibitor Dynasore and the genetic dominant negative K44A mutant of dynamin prevent this induced budding and internalization of caveolae. Also shRNA lentivirus knockdown of caveolin-1 expression prevents rapid internalization of ET and ET-B. It appears that endothelin can engage ET-B already highly concentrated in caveolae of endothelial cells to induce very rapid caveolae fission and endocytosis. This transport requires active dynamin function. Caveolae trafficking may occur more rapidly than previously documented when it is stimulated by a specific ligand to signaling receptors already located in caveolae before ligand engagement.
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Affiliation(s)
- Phil Oh
- Proteogenomics Research Institute for Systems Medicine, San Diego, California 92121
| | - Thierry Horner
- Proteogenomics Research Institute for Systems Medicine, San Diego, California 92121
| | - Halina Witkiewicz
- Proteogenomics Research Institute for Systems Medicine, San Diego, California 92121
| | - Jan E Schnitzer
- Proteogenomics Research Institute for Systems Medicine, San Diego, California 92121.
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Carrel D, Simon A, Emerit MB, Rivals I, Leterrier C, Biard M, Hamon M, Darmon M, Lenkei Z. Axonal Targeting of the 5-HT1B Serotonin Receptor Relies on Structure-Specific Constitutive Activation. Traffic 2011; 12:1501-20. [DOI: 10.1111/j.1600-0854.2011.01260.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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20
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Hu JH, Park JM, Park S, Xiao B, Dehoff MH, Kim S, Hayashi T, Schwarz MK, Huganir RL, Seeburg PH, Linden DJ, Worley PF. Homeostatic scaling requires group I mGluR activation mediated by Homer1a. Neuron 2010; 68:1128-42. [PMID: 21172614 PMCID: PMC3013614 DOI: 10.1016/j.neuron.2010.11.008] [Citation(s) in RCA: 194] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2010] [Indexed: 01/02/2023]
Abstract
Homeostatic scaling is a non-Hebbian form of neural plasticity that maintains neuronal excitability and informational content of synaptic arrays in the face of changes of network activity. Here, we demonstrate that homeostatic scaling is dependent on group I metabotropic glutamate receptor activation that is mediated by the immediate early gene Homer1a. Homer1a is transiently upregulated during increases in network activity and evokes agonist-independent signaling of group I mGluRs that scales down the expression of synaptic AMPA receptors. Homer1a effects are dynamic and play a role in the induction of scaling. Similar to mGluR-LTD, Homer1a-dependent scaling involves a reduction of tyrosine phosphorylation of GluA2 (GluR2), but is distinct in that it exploits a unique signaling property of group I mGluR to confer cell-wide, agonist-independent activation of the receptor. These studies reveal an elegant interplay of mechanisms that underlie Hebbian and non-Hebbian plasticity.
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Affiliation(s)
- Jia-Hua Hu
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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21
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Mundell S, Kelly E. Adenosine receptor desensitization and trafficking. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:1319-28. [PMID: 20550943 DOI: 10.1016/j.bbamem.2010.06.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 04/30/2010] [Revised: 05/28/2010] [Accepted: 06/06/2010] [Indexed: 11/26/2022]
Abstract
As with the majority of G-protein-coupled receptors, all four of the adenosine receptor subtypes are known to undergo agonist-induced regulation in the form of desensitization and trafficking. These processes can limit the ability of adenosine receptors to couple to intracellular signalling pathways and thus reduce the ability of adenosine receptor agonists as well as endogenous adenosine to produce cellular responses. In addition, since adenosine receptors couple to multiple signalling pathways, these pathways may desensitize differentially, while the desensitization of one pathway could even trigger signalling via another. Thus, the overall picture of adenosine receptor regulation can be complex. For all adenosine receptor subtypes, there is evidence to implicate arrestins in agonist-induced desensitization and trafficking, but there is also evidence for other possible forms of regulation, including second messenger-dependent kinase regulation, heterologous effects involving G proteins, and the involvement of non-clathrin trafficking pathways such as caveolae. In this review, the evidence implicating these mechanisms is summarized for each adenosine receptor subtype, and we also discuss those issues of adenosine receptor regulation that remain to be resolved as well as likely directions for future research in this field.
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Affiliation(s)
- Stuart Mundell
- Department of Physiology and Pharmacology, University of Bristol, Bristol, UK
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22
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Abstract
The kisspeptin/GPR54 signaling system positively regulates GnRH secretion, thereby acting as an important regulator of the hypothalamic-pituitary-gonadal axis. It also negatively regulates tumor metastases and placental trophoblast invasion. GPR54 is a G(q/11)-coupled GPCR and activation by kisspeptin stimulates PIP(2) hydrolysis and inositol phosphate (IP) formation, Ca(2+) mobilization, arachidonic acid release, and ERK1/2 and p38 MAP kinase phosphorylation. Recently, we reported that GPR54 displays constitutive activity and internalization in the heterologous human embryonic kidney 293 cell system. Given the physiological and clinical importance of GPR54 as well as other GPCRs, we present assays for measuring constitutive receptor internalization and activity. Specifically, we describe the use of immunofluorescence coupled to confocal imaging, flow cytometry and indirect receptor radiolabeling to measure constitutive receptor internalization, and IP turnover in intact cells to measure constitutive activity. While we use the FLAG-tagged GPR54 molecule as an example to describe these assays, the assays can be applied to a wide range of GPCRs.
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23
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Pampillo M, Camuso N, Taylor JE, Szereszewski JM, Ahow MR, Zajac M, Millar RP, Bhattacharya M, Babwah AV. Regulation of GPR54 signaling by GRK2 and {beta}-arrestin. Mol Endocrinol 2009; 23:2060-74. [PMID: 19846537 DOI: 10.1210/me.2009-0013] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Kisspeptin and its receptor, GPR54, are major regulators of the hypothalamic-pituitary-gonadal axis as well as regulators of human placentation and tumor metastases. GPR54 is a G(q/11)-coupled G protein-coupled receptor (GPCR), and activation by kisspeptin stimulates phosphatidy linositol 4, 5-biphosphate hydrolysis, Ca(2+) mobilization, arachidonic acid release, and ERK1/2 MAPK phosphorylation. Physiological evidence suggests that GPR54 undergoes agonist-dependent desensitization, but underlying molecular mechanisms are unknown. Furthermore, very little has been reported on the early events that regulate GPR54 signaling. The lack of information in these important areas led to this study. Here we report for the first time on the role of GPCR serine/threonine kinase (GRK)2 and beta-arrestin in regulating GPR54 signaling in human embryonic kidney (HEK) 293 cells, a model cell system for studying the molecular regulation of GPCRs, and genetically modified MDA MB-231 cells, an invasive breast cancer cell line expressing about 75% less beta-arrestin-2 than the control cell line. Our study reveals that in HEK 293 cells, GPR54 is expressed both at the plasma membrane and intracellularly and also that plasma membrane expression is regulated by cytoplasmic tail sequences. We also demonstrate that GPR54 exhibits constitutive activity, internalization, and association with GRK2 and beta- arrestins-1 and 2 through sequences in the second intracellular loop and cytoplasmic tail of the receptor. We also show that GRK2 stimulates the desensitization of GPR54 in HEK 293 cells and that beta-arrestin-2 mediates GPR54 activation of ERK1/2 in MDA-MB-231 cells. The significance of these findings in developing molecular-based therapies for treating certain endocrine-related disorders is discussed.
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Affiliation(s)
- Macarena Pampillo
- Children's Health Research Institute, Department of Obstetrics and Gynaecology, The University of Western Ontario, London, Canada
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24
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Olive MF. Metabotropic glutamate receptor ligands as potential therapeutics for addiction. ACTA ACUST UNITED AC 2009; 2:83-98. [PMID: 19630739 DOI: 10.2174/1874473710902010083] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
There is now compelling evidence that the excitatory amino acid neurotransmitter glutamate plays a pivotal role in drug addiction and alcoholism. As a result, there has been increasing interest in developing glutamate-based therapies for the treatment of addictive disorders. Receptors for glutamate are primarily divided into two classes: ionotropic glutamate receptors (iGluRs) that mediate fast excitatory glutamate transmission, and metabotropic glutamate receptors (mGluRs), which are G-protein coupled receptors that mediate slower, modulatory glutamate transmission. Most iGluR antagonists, while showing some efficacy in animal models of addiction, exhibit serious side effects when tested in humans. mGluR ligands, on the other hand, which have been advanced to testing in clinical trials for various medical conditions, have demonstrated the ability to reduce drug reward, reinforcement, and relapse-like behaviors in animal studies. mGluR ligands that have been shown to be primarily effective are Group I (mGluR1 and mGluR5) negative allosteric modulators and Group II (mGluR2 and mGluR3) orthosteric presynaptic autoreceptor agonists. In this review, we will summarize findings from animal studies suggesting that these mGluR ligands may be of potential benefit in reducing on-going drug self-administration and may aid in the prevention of relapse. The neuroanatomical distribution of mGluR1, mGluR2/3, and mGluR5 receptors and the pharmacological properties of Group I negative allosteric modulators and Group II agonists will also be overviewed. Finally, we will discuss the current status of mGluR ligands in human clinical trials.
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Affiliation(s)
- M Foster Olive
- Center for Drug and Alcohol Programs, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, 67 President Street, MSC 861, Charleston, SC 29425, USA.
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25
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Clement JP, Randall AD, Brown JT. Metabotropic glutamate receptor 1 activity generates persistent,N-methyl-d-aspartate receptor-dependent depression of hippocampal pyramidal cell excitability. Eur J Neurosci 2009; 29:2347-62. [DOI: 10.1111/j.1460-9568.2009.06780.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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26
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Ferraguti F, Crepaldi L, Nicoletti F. Metabotropic glutamate 1 receptor: current concepts and perspectives. Pharmacol Rev 2009; 60:536-81. [PMID: 19112153 DOI: 10.1124/pr.108.000166] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Almost 25 years after the first report that glutamate can activate receptors coupled to heterotrimeric G-proteins, tremendous progress has been made in the field of metabotropic glutamate receptors. Now, eight members of this family of glutamate receptors, encoded by eight different genes that share distinctive structural features have been identified. The first cloned receptor, the metabotropic glutamate (mGlu) receptor mGlu1 has probably been the most extensively studied mGlu receptor, and in many respects it represents a prototypical subtype for this family of receptors. Its biochemical, anatomical, physiological, and pharmacological characteristics have been intensely investigated. Together with subtype 5, mGlu1 receptors constitute a subgroup of receptors that couple to phospholipase C and mobilize Ca(2+) from intracellular stores. Several alternatively spliced variants of mGlu1 receptors, which differ primarily in the length of their C-terminal domain and anatomical localization, have been reported. Use of a number of genetic approaches and the recent development of selective antagonists have provided a means for clarifying the role played by this receptor in a number of neuronal systems. In this article we discuss recent advancements in the pharmacology and concepts about the intracellular transduction and pathophysiological role of mGlu1 receptors and review earlier data in view of these novel findings. The impact that this new and better understanding of the specific role of these receptors may have on novel treatment strategies for a variety of neurological and psychiatric disorders is considered.
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Affiliation(s)
- Francesco Ferraguti
- Department of Pharmacology, Innsbruck Medical University, Peter-Mayr Strasse 1a, Innsbruck A-6020, Austria.
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27
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Metabotropic glutamate receptors (mGlus) and cellular transformation. Neuropharmacology 2008; 55:396-402. [PMID: 18554669 DOI: 10.1016/j.neuropharm.2008.04.021] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2008] [Accepted: 04/24/2008] [Indexed: 12/20/2022]
Abstract
Although the glutamatergic system usually functions in the CNS, expression has been observed in non-neuronal tissues and a subset of cancers. Metabotropic glutamate receptors (mGlus) are highly "druggable" GPCRs and thus a priority for validation as therapeutic targets. We have previously reported that the aberrant expression of mGlu1 is sufficient to induce spontaneous melanoma development in vivo. We isolated and characterized several stable mGlu1-mouse melanocytic clones and demonstrated that these clones are transformed and tumorigenic. We hypothesize that expression of mGlus may not be uncommon in the pathogenesis of tumors other than melanoma, and that activity of an otherwise normal glutamate receptor in an ectopic cellular environment involves signaling pathways which dysregulate cell growth, ultimately leading to tumorigenesis. As most human cancers are of epithelial origin (carcinomas), in this review, the possibility that mGlu1 could function as a complete oncogene and transform epithelial cells is also discussed.
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28
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Vercauteren FGG, Flores G, Ma W, Chabot JG, Geenen L, Clerens S, Fazel A, Bergeron JJM, Srivastava LK, Arckens L, Quirion R. An organelle proteomic method to study neurotransmission-related proteins, applied to a neurodevelopmental model of schizophrenia. Proteomics 2008; 7:3569-79. [PMID: 17907268 DOI: 10.1002/pmic.200700379] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Limited information is currently available on molecular events that underlie schizophrenia-like behaviors in animal models. Accordingly, we developed an organelle proteomic approach enabling the study of neurotransmission-related proteins in the prefrontal cortex (PFC) of postpubertal (postnatal day 60 (PD60)) neonatally ventral hippocampal (nVH) lesioned rats, an extensively used neurodevelopmental model of schizophrenia-like behaviors. The PFC was chosen because of its purported role in the etiology of the disease. Statistical analysis of 392 reproducible spots on 2-D organelle proteomic patterns revealed significant changes in intensity of 18 proteinous spots in plasma membrane-enriched fractions obtained from postpubertal nVH lesioned rats compared to controls. Mass spectrometric analysis and database searching allowed the identification of a single protein in each of the nine differential spots, including proteins of low abundance, such as neurocalcin delta. Most of the identified dysregulated proteins, including clathrin light chain B, syntaxin binding protein 1b and visinin-like protein 1 are known to be linked to various neurotransmitter systems and to play key roles in plasma membrane receptor expression and recycling as well as synaptic vesicle exocytosis/recycling. Organelle proteomic approaches have hence proved to be most useful to identify key proteins linked to a given behavior in animal models of brain diseases.
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Affiliation(s)
- Freya G G Vercauteren
- Department of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Québec, Canada
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29
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Kelly E, Bailey CP, Henderson G. Agonist-selective mechanisms of GPCR desensitization. Br J Pharmacol 2007; 153 Suppl 1:S379-88. [PMID: 18059321 DOI: 10.1038/sj.bjp.0707604] [Citation(s) in RCA: 281] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The widely accepted model of G protein-coupled receptor (GPCR) regulation describes a system where the agonist-activated receptors couple to G proteins to induce a cellular response, and are subsequently phosphorylated by a family of kinases called the G protein-coupled receptor kinases (GRKs). The GRK-phosphorylated receptor then acts as a substrate for the binding of a family of proteins called arrestins, which uncouple the receptor and G protein so desensitizing the agonist-induced response. Other kinases, principally the second messenger-dependent protein kinases, are also known to play a role in the desensitization of many GPCR responses. It is now clear that there are subtle and complex interactions between GRKs and second messenger-dependent protein kinases in the regulation of GPCR function. Functional selectivity describes the ability of agonists to stabilize different active conformations of the same GPCR. With regard to desensitization, distinct agonist-activated conformations of a GPCR could undergo different molecular mechanisms of desensitization. An example of this is the mu opioid receptor (MOPr), where the agonists morphine and [D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO) induce desensitization of the MOPr by different mechanisms, largely protein kinase C (PKC)- or GRK-dependent, respectively. This can be best explained by supposing that these two agonists stabilize distinct conformations of the MOPr, which are nevertheless able to couple to the relevant G-proteins and produce similar responses, yet are sufficiently different to trigger different regulatory processes. There is evidence that other GPCRs also undergo agonist-selective desensitization, but the full therapeutic consequences of this phenomenon await further detailed study.
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Affiliation(s)
- E Kelly
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol, UK.
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30
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Wang M, Bianchi R, Chuang SC, Zhao W, Wong RKS. Group I metabotropic glutamate receptor-dependent TRPC channel trafficking in hippocampal neurons. J Neurochem 2007; 101:411-21. [PMID: 17402970 DOI: 10.1111/j.1471-4159.2006.04377.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The group I metabotropic glutamate receptor agonist (S)-3,5-dihydroxyphenylglycine (DHPG) elicited two phases of synchronized neuronal (epileptiform) discharges in hippocampal slices: an initial phase of short duration discharges followed by a phase of prolonged discharges. We assessed the involvement of transient receptor potential canonical (TRPC) channels in these responses. Pre-treatment of hippocampal slices with TRPC channel blockers, 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride (SKF96365) or 2-aminoethoxydiphenyl borate, did not affect the short epileptiform discharges but blocked the prolonged epileptiform discharges. SKF96365 suppressed ongoing DHPG-induced prolonged epileptiform discharges. Western blot analysis showed that the total TRPC4 or TRPC5 proteins in hippocampal slices were unchanged following DHPG. DHPG increased TRPC4 and TRPC5 in the cytoplasmic compartment and decreased these proteins in the plasma membrane. Translocation of TRPC4 and TRPC5 was suppressed when the epileptiform discharges were blocked by ionotropic glutamate receptor blockers. Translocation of TRPC4 and TRPC5 was also prevented in slices from phospholipase C (PLC) beta1 knockout mice, even when synchronized discharges were elicited by the convulsant 4-aminopyridine. The results suggest that TRPC channels are involved in generating DHPG-induced prolonged epileptiform discharges. This function of TRPC channels is associated with a neuronal activity- and PLCbeta1-dependent translocation of TRPC4 and TRPC5 proteins from the plasmalemma to the cytoplasmic compartment.
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Affiliation(s)
- Min Wang
- Department of Physiology and Pharmacology, Robert F. Furchgott Center for Neural and Behavioral Science, State University of New York Downstate Medical Center, Brooklyn, New York, USA
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31
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Walwyn W, Evans CJ, Hales TG. Beta-arrestin2 and c-Src regulate the constitutive activity and recycling of mu opioid receptors in dorsal root ganglion neurons. J Neurosci 2007; 27:5092-104. [PMID: 17494695 PMCID: PMC6672367 DOI: 10.1523/jneurosci.1157-07.2007] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 03/30/2007] [Accepted: 04/01/2007] [Indexed: 11/21/2022] Open
Abstract
Beta-arrestins bind to agonist-activated G-protein-coupled receptors regulating signaling events and initiating endocytosis. In beta-arrestin2-/- (beta arr2-/-) mice, a complex phenotype is observed that includes altered sensitivity to morphine. However, little is known of how beta-arrestin2 affects mu receptor signaling. We investigated the coupling of mu receptors to voltage-gated Ca2+ channels (VGCCs) in beta arr2+/+ and beta arr2-/- dorsal root ganglion neurons. A lack of beta-arrestin2 reduced the maximum inhibition of VGCCs by morphine and DAMGO (D-Ala2-N-Me-Phe4-glycol5-enkephalin) without affecting agonist potency, the onset of receptor desensitization, or the functional contribution of N-type VGCCs. The reduction in inhibition was accompanied by increased naltrexone-sensitive constitutive inhibitory coupling of mu receptors to VGCCs. Agonist-independent mu receptor inhibitory coupling was insensitive to CTAP (Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2), a neutral antagonist that inhibited the inverse agonist action of naltrexone. These functional changes were accompanied by diminished constitutive recycling and increased cell-surface mu receptor expression in beta arr2-/- compared with beta arr2+/+ neurons. Such changes could not be explained by the classical role of beta-arrestins in agonist-induced endocytosis. The localization of the nonreceptor tyrosine kinase c-Src appeared disrupted in beta arr2-/- neurons, and there was reduced activation of c-Src by DAMGO. Using the Src inhibitor PP2 [4-amino-5-(4-chlorophenyl)-(t-butyl)pyrazolo[3,4-d]pyrimidine], we demonstrated that defective Src signaling mimics the beta arr2-/- cellular phenotype of reduced mu agonist efficacy, increased constitutive mu receptor activity, and reduced constitutive recycling. We propose that beta-arrestin2 is required to target c-Src to constitutively active mu receptors, resulting in their internalization, providing another dimension to the complex role of beta-arrestin2 and c-Src in G-protein-coupled receptor function.
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MESH Headings
- Analgesics, Opioid/pharmacology
- Animals
- Arrestins/genetics
- Arrestins/metabolism
- CSK Tyrosine-Protein Kinase
- Calcium Channels/drug effects
- Calcium Channels/metabolism
- Calcium Signaling/drug effects
- Calcium Signaling/physiology
- Cells, Cultured
- Endocytosis/drug effects
- Endocytosis/physiology
- Female
- Ganglia, Spinal/metabolism
- Male
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Neurons, Afferent/drug effects
- Neurons, Afferent/metabolism
- Nociceptors/drug effects
- Nociceptors/metabolism
- Pain/metabolism
- Pain/physiopathology
- Patch-Clamp Techniques
- Protein Transport/drug effects
- Protein Transport/physiology
- Protein-Tyrosine Kinases/metabolism
- Receptors, G-Protein-Coupled/drug effects
- Receptors, G-Protein-Coupled/metabolism
- Receptors, Opioid, mu/drug effects
- Receptors, Opioid, mu/metabolism
- Signal Transduction/drug effects
- Signal Transduction/physiology
- beta-Arrestin 2
- beta-Arrestins
- src-Family Kinases
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Affiliation(s)
- Wendy Walwyn
- Department of Psychiatry and Biobehavioral Sciences, Hatos Center, University of California, Los Angeles, Los Angeles, California 90095, and
| | - Christopher J. Evans
- Department of Psychiatry and Biobehavioral Sciences, Hatos Center, University of California, Los Angeles, Los Angeles, California 90095, and
| | - Tim G. Hales
- Departments of Pharmacology and Physiology, and Anesthesiology and Critical Care Medicine, The George Washington University, Washington, DC 20037
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32
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Abstract
G protein-coupled receptors (GPCRs) mediate cellular responses to diverse extracellular stimuli to play a vital role in the control of physiology and behaviour. GPCR trafficking is of fundamental importance for the regulation of GPCRs signaling. In this mini review, we will discuss some of the recent findings on the mechanisms that regulate GPCR trafficking, which include (i) large dense-core vesicle (LDCV)-associated GPCR delivery which could be a general cell biological mechanism for rapid modulation of membrane receptors in response to certain stimuli; (ii) lateral diffusion of GPCRs in the plasma membrane for rapid change of the number of neurotransmitter receptors during synaptic plasticity and (iii) constitutive internalization of GPCRs, that contributes to receptor resensitization and distribution, including axonal polarization.
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Affiliation(s)
- Z-Q D Xu
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
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33
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Pelkey KA, Yuan X, Lavezzari G, Roche KW, McBain CJ. mGluR7 undergoes rapid internalization in response to activation by the allosteric agonist AMN082. Neuropharmacology 2007; 52:108-17. [PMID: 16914173 DOI: 10.1016/j.neuropharm.2006.07.020] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Revised: 07/10/2006] [Accepted: 07/12/2006] [Indexed: 10/24/2022]
Abstract
The G-protein coupled receptor (GPCR) metabotropic glutamate receptor 7 (mGluR7) is widely expressed throughout the nervous system and is implicated in diverse physiological processes ranging from synaptic plasticity to neuroprotection. To date, unequivocally assigning specific functions to mGluR7 has been hampered by a lack of specific pharmacological tools, however, an mGluR7 specific allosteric agonist, AMN082, was recently discovered. Accumulating evidence indicates that in addition to G-protein activation, GPCRs trigger critical intracellular signalling cascades during agonist-induced internalization. Thus, to determine if AMN082 will be useful for evaluating signalling events related to mGluR7 internalization as well as receptor activation we have examined whether AMN082 induces mGluR7 endocytosis. Using an immunofluorescence assay we demonstrate that AMN082 induces robust internalization of mGluR7 overexpressed in dissociated hippocampal neurons. AMN082-induced mGluR7 internalization was resistant to inhibition by a competitive antagonist consistent with the distinct binding site of the allosteric agonist from the glutamate-binding pocket utilized by conventional orthosteric ligands. Finally, as an independent assay of receptor internalization we overexpressed N-terminal pHluorin-tagged mGluR7 in neurons, allowing live imaging of surface receptors in real time. AMN082 treatment produced a rapid loss of surface mGluR7 as indicated by decreased fluorescence confirming the ability of allosteric receptor activation to trigger mGluR7 endocytosis. Thus, AMN082 will be effective for investigating physiological processes related to both mGluR7 activation and internalization such as control of bidirectional plasticity at mossy fiber-st. lucidum interneuron synapses.
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Affiliation(s)
- Kenneth A Pelkey
- Laboratory of Cellular and Synaptic Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Building 35, 35 Lincoln Drive, Bethesda, MD 20892, USA.
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34
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Mundell SJ, Luo J, Benovic JL, Conley PB, Poole AW. Distinct clathrin-coated pits sort different G protein-coupled receptor cargo. Traffic 2006; 7:1420-31. [PMID: 16899088 DOI: 10.1111/j.1600-0854.2006.00469.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Upon activation, many G protein-coupled receptors (GPCRs) internalize by clathrin-mediated endocytosis and are subsequently sorted to undergo recycling or lysosomal degradation. Here we observe that sorting can take place much earlier than previously thought, by entry of different GPCRs into distinct populations of clathrin-coated pit (CCP). These distinct populations were revealed by analysis of two purinergic GPCRs, P2Y(1) and P2Y(12), which enter two populations of CCPs in a mutually exclusive manner. The mechanisms underlying early GPCR sorting involve differential kinase-dependent processes because internalization of P2Y(12) is mediated by GPCR kinases (GRKs) and arrestin, whereas P2Y(1) internalization is GRK- and arrestin-independent but requires protein kinase C. Importantly, the beta(2) adrenoceptor which also internalizes in a GRK-dependent manner also traffics exclusively to P2Y(12)-containing CCPs. Our data therefore reveal distinct populations of CCPs that sort GPCR cargo at the plasma membrane using different kinase-dependent mechanisms.
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MESH Headings
- Antibodies, Monoclonal/metabolism
- Arrestin/metabolism
- Cell Line
- Cell Membrane/metabolism
- Cell Membrane/ultrastructure
- Clathrin/metabolism
- Coated Pits, Cell-Membrane/metabolism
- Endocytosis/physiology
- Humans
- Protein Kinases/genetics
- Protein Kinases/metabolism
- RNA, Small Interfering/genetics
- RNA, Small Interfering/metabolism
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Receptors, G-Protein-Coupled/metabolism
- Receptors, Purinergic P2/genetics
- Receptors, Purinergic P2/metabolism
- Receptors, Purinergic P2Y1
- Receptors, Purinergic P2Y12
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Affiliation(s)
- Stuart J Mundell
- Department of Pharmacology, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.
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35
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Pula G, Mundell SJ, Roberts PJ, Kelly E. Analysis of mGluR1a constitutive internalization using a pulse-chase enzyme-linked immuno-sorbant assay (ELISA). ACTA ACUST UNITED AC 2006; 64:167-81. [PMID: 16112201 DOI: 10.1016/j.jbbm.2005.07.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2005] [Accepted: 07/15/2005] [Indexed: 11/28/2022]
Abstract
The surface expression of G protein-coupled receptors is regulated by internalization. For many receptors, a constitutive level of internalization in the absence of agonist has been reported. The constitutive internalization of metabotropic glutamate receptor 1a (mGluR1a) has been described, but in general little attention has been dedicated to this important aspect of receptor regulation. Here we describe a pulse-chase ELISA method that allows the investigation of mGluR1a constitutive internalization. When investigated by pulse-chase ELISA, the constitutive internalization of mGluR1a was inhibited by dominant negative mutant constructs of arrestin-2 or Eps-15. This observation, besides indicating the arrestin- and clathrin-dependence of mGluR1a constitutive internalization, also confirmed the physiological relevance of the method described in this article. Confocal microscopy experiments to study receptor localization further validated the pulse-chase labelling procedure. The application of the pulse-chase ELISA to mGluR1b, revealed that this splice variant undergoes marginal constitutive internalization. Two COOH-terminal deletion mutants of mGluR1a, DMI (Arg847stop) and DMII (Arg868stop), were also tested for constitutive internalization. Interestingly, only DMII underwent significant constitutive internalization, suggesting that the region between Arg847 and Arg868 might play a regulatory role in mGluR1a trafficking. Taken together, the pulse-chase ELISA appears to be an efficient tool to analyze the constitutive internalization of different mGluR1 splice variants.
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Affiliation(s)
- Giordano Pula
- Department of Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
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36
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Dhami GK, Ferguson SSG. Regulation of metabotropic glutamate receptor signaling, desensitization and endocytosis. Pharmacol Ther 2006; 111:260-71. [PMID: 16574233 DOI: 10.1016/j.pharmthera.2005.01.008] [Citation(s) in RCA: 155] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2005] [Accepted: 01/25/2005] [Indexed: 11/24/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) comprise a unique family of G protein-coupled receptors (GPCR) that can be classified into 3 groups based on G protein coupling specificity and sequence similarity. Group I mGluRs (mGluR1 and mGluR5) are coupled to the heterotrimeric G protein Galpha(q/11) and trigger the release of calcium from intracellular stores. In the present review, we discuss the molecular mechanisms involved in the desensitization and endocytosis of group I mGluRs. Group I mGluRs desensitize in response to both second-messenger-dependent protein kinases and G protein-coupled receptor kinases (GRK). However, GRK2-mediated mGluR1 desensitization appears to be both phosphorylation- and beta-arrestin-independent. In addition to GRK-mediated uncoupling of mGluRs from heterotrimeric G proteins, the huntingtin-interacting protein, optineurin, also contributes to mGluR1 and mGluR5 desensitization. The G protein-uncoupling activity of optineurin appears to be facilitated by the presence of polyglutamine-expanded mutant huntingtin but not wild-type huntingtin. Group I mGluRs also undergo both agonist-dependent and -independent endocytosis in both heterologous cell expression systems and primary neuronal cultures. The present review overviews the current understanding of the contribution of second messenger-dependent protein kinases, beta-arrestins and a novel Ral/phospholipase D2 (PLD2)-mediated endocytic pathway to the regulation of Group I mGluR endocytosis. Overall, the regulation of Group I mGluR desensitization and endocytosis appears to be mediated by the same molecular intermediates as have been described for more typical GPCR such as the beta(2)-adrenergic receptor. However, there appears to be subtle, but important, differences in the mechanisms by which these intermediates are employed to regulate Group I mGluR desensitization and endocytosis.
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Affiliation(s)
- Gurpreet K Dhami
- Cell Biology Research Group, Robarts Research Institute, London, Ontario, Canada N6A 5K8
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37
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Zhang X, Wang F, Chen X, Li J, Xiang B, Zhang YQ, Li BM, Ma L. Beta-arrestin1 and beta-arrestin2 are differentially required for phosphorylation-dependent and -independent internalization of delta-opioid receptors. J Neurochem 2005; 95:169-78. [PMID: 16181421 DOI: 10.1111/j.1471-4159.2005.03352.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Beta-arrestins are key negative regulators and scaffolds of G protein-coupled receptor (GPCR) signalling. Beta-arrestin1 and beta-arrestin2 preferentially bind to the phosphorylated GPCRs in response to agonist stimulation, resulting in receptor internalization and desensitization. The critical roles of GPCR kinases (GRKs)-catalyzed receptor phosphorylation and interaction of beta-arrestins with the phosphorylated receptor in receptor internalization are well established. However, emerging evidence suggests that an agonist-stimulated internalization mechanism that is independent of receptor phosphorylation may also be employed in some cases, although the molecular mechanism for the phosphorylation-independent GPCR internalization is not clear. The current study investigated the role of receptor phosphorylation and the involvement of different beta-arrestin subtypes in agonist-induced delta-opioid receptor (DOR) internalization in HEK293 cells. Results from flow cytometry, fluorescence microscopy, and surface biotin labelling experiments showed that elimination of agonist-induced DOR phosphorylation by mutation GRK binding or phosphorylation sites only partially blocked agonist-induced receptor internalization, indicating the presence of an agonist-induced, GRK-independent mechanism for DOR internalization. Fluorescence and co-immunoprecipitation studies indicated that both the wild-type DOR and the phosphorylation-deficient mutant receptor could bind and recruit beta-arrestin1 and beta-arrestin2 to the plasma membrane in an agonist-stimulated manner. Furthermore, internalization of both the wild-type and phosphorylation-deficient receptors was increased by overexpression of either type of beta-arrestins and blocked by dominant-negative mutants of beta-arrestin-mediated internalization, demonstrating that both phosphorylation-dependent and -independent internalization require beta-arrestin. Moreover, double-stranded RNA-mediated interference experiments showed that either beta-arrestin1 or beta-arrestin2 subtype-specific RNAi only partially inhibited agonist-induced internalization of the wild-type DOR. However, agonist-induced internalization of the phosphorylation-deficient DOR was not affected by beta-arrestin1-specific RNAi but was blocked by RNAi against beta-arrestin2 subtype. These data indicate that endogenous beta-arrestin1 functions exclusively in the phosphorylation-dependent receptor internalization, whereas endogenous beta-arrestin2, but not beta-arrestin1, is required for the phosphorylation-independent receptor internalization. These results thus provide the first evidence of different requirement for beta-arrestin isoforms in the agonist induced phosphorylation-dependent and -independent GPCR internalization.
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Affiliation(s)
- Xiaoqing Zhang
- Pharmacology Research Center, Shanghai Medical College, Shanghai, China
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38
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Abstract
In recent years great progress has been made in understanding the function of ionotropic and metabotropic glutamate receptors; their pharmacology and potential therapeutic applications. It should be stressed that there are already N-methyl-D-aspartate (NMDA) antagonists in clinical use, such as memantine, which proves the feasibility of their therapeutic potential. It seems unlikely that competitive NMDA receptor antagonists and high-affinity channel blockers will find therapeutic use due to limiting side-effects, whereas agents acting at the glycineB site, NMDA receptor subtype-selective agents and moderate-affinity channel blockers are far more promising. This is supported by the fact that there are several glycineB antagonists, NMDA moderate-affinity channel blockers and NR2B-selective agents under development. Positive and negative modulators of AMPA receptors such as the AMPAkines and 2,3-benzodiazepines also show more promise than e.g. competitive antagonists. Great progress has also been made in the field of metabotropic glutamate receptors since the discovery of novel, allosteric modulatory sites for these receptors. Selective agents acting at these transmembrane sites have been developed that are more drug-like and have a much better access to the central nervous system than their competitive counterparts. The chapter will critically review preclinical and scarce clinical experience in the development of new ionotropic and metabotropic glutamate receptor modulators according to the following scheme: rational, preclinical findings in animal models and finally clinical experience, where available.
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Affiliation(s)
- C G Parsons
- Max Planck Institute of Psychiatry, Kraepelinstrasse 2-10, 80804 München, Germany
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39
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Soudijn W, van Wijngaarden I, Ijzerman AP. Structure-activity relationships of inverse agonists for G-protein-coupled receptors. Med Res Rev 2005; 25:398-426. [PMID: 15816047 DOI: 10.1002/med.20031] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
It has been recently established that G-protein-coupled receptors (GPCRs) can be constitutively active, i.e., they can be active in the absence of an agonist. This activity can be inhibited by so-called inverse agonists. For a number of GPCRs, such inverse agonists have been developed and studied, now enabling for the first time a study into their structure-activity relationships.
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Affiliation(s)
- Willem Soudijn
- Leiden/Amsterdam Center for Drug Research, PO Box 9502, 2300RA Leiden, The Netherlands
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40
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Boulware MI, Weick JP, Becklund BR, Kuo SP, Groth RD, Mermelstein PG. Estradiol activates group I and II metabotropic glutamate receptor signaling, leading to opposing influences on cAMP response element-binding protein. J Neurosci 2005; 25:5066-78. [PMID: 15901789 PMCID: PMC6724851 DOI: 10.1523/jneurosci.1427-05.2005] [Citation(s) in RCA: 315] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Revised: 04/13/2005] [Accepted: 04/16/2005] [Indexed: 12/12/2022] Open
Abstract
In addition to mediating sexual maturation and reproduction through stimulation of classical intracellular receptors that bind DNA and regulate gene expression, estradiol is also thought to influence various brain functions by acting on receptors localized to the neuronal membrane surface. Many intracellular signaling pathways and modulatory proteins are affected by estradiol via this unconventional route, including regulation of the transcription factor cAMP response element-binding protein (CREB). However, the mechanisms by which estradiol acts at the membrane surface are poorly understood. Because both estradiol and CREB have been implicated in regulating learning and memory, we characterized the effects of estradiol on this transcription factor in cultured rat hippocampal neurons. Within minutes of administration, estradiol triggered mitogen-activated protein kinase (MAPK)-dependent CREB phosphorylation in unstimulated neurons. Furthermore, after brief depolarization, estradiol attenuated L-type calcium channel-mediated CREB phosphorylation. Thus, estradiol exhibited both positive and negative influences on CREB activity. These effects of estradiol were sex specific and traced to membrane-localized estrogen receptors that stimulated group I and II metabotropic glutamate receptor (mGluR) signaling. Activation of estrogen receptor alpha (ERalpha) led to mGluR1a signaling, triggering CREB phosphorylation through phospholipase C regulation of MAPK. In addition, estradiol stimulation of ERalpha or ERbeta triggered mGluR2/3 signaling, decreasing L-type calcium channel-mediated CREB phosphorylation. These results not only characterize estradiol regulation of CREB but also provide two putative signaling mechanisms that may account for many of the unexplained observations regarding the influence of estradiol on nervous system function.
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Affiliation(s)
- Marissa I Boulware
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA
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41
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Bhattacharya M, Babwah AV, Godin C, Anborgh PH, Dale LB, Poulter MO, Ferguson SSG. Ral and phospholipase D2-dependent pathway for constitutive metabotropic glutamate receptor endocytosis. J Neurosci 2005; 24:8752-61. [PMID: 15470141 PMCID: PMC6729950 DOI: 10.1523/jneurosci.3155-04.2004] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
G-protein-coupled receptors play a central role in the regulation of neuronal cell communication. Class 1 metabotropic glutamate receptors (mGluRs) mGluR1a and mGluR5a, which are coupled with the hydrolysis of phosphoinositides, are essential for modulating excitatory neurotransmission at glutamatergic synapses. These receptors are constitutively internalized in heterologous cell cultures, neuronal cultures, and intact neuronal tissues. We show here that the small GTP-binding protein Ral, its guanine nucleotide exchange factor RalGDS (Ral GDP dissociation stimulator), and phospholipase D2 (PLD2) are constitutively associated with class 1 mGluRs and regulate constitutive mGluR endocytosis. Moreover, both Ral and PLD2 are colocalized with mGluRs in endocytic vesicles in both human embryonic kidney 293 (HEK 293) cells and neurons. Ral and PLD2 activity is required for the internalization of class 1 mGluRs but is not required for the internalization of the beta2-adrenergic receptor. Constitutive class 1 mGluR internalization is not dependent on the downstream Ral effector proteins Ral-binding protein 1 and PLD1 or either ADP-ribosylation factors ARF1 or ARF6. The treatment of HEK 293 cells and neurons with small interfering RNA both downregulates PLD2 expression and blocks mGluR1a and mGluR5a endocytosis. The constitutive internalization of mGluR1a and mGluR5a is also attenuated by the treatment of cells with 1-butanol to prevent PLD2-mediated phosphatidic acid formation. We propose that the formation of a mGluR-scaffolded RalGDS/Ral/PLD2 protein complex provides a novel alternative mechanism to beta-arrestins for the constitutive endocytosis of class 1 mGluRs.
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Affiliation(s)
- Moshmi Bhattacharya
- Cell Biology Research Group, Robarts Research Institute, London, Ontario, Canada N6A 5K8
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