1
|
McCullock TW, Kammermeier PJ. The evidence for and consequences of metabotropic glutamate receptor heterodimerization. Neuropharmacology 2021; 199:108801. [PMID: 34547332 DOI: 10.1016/j.neuropharm.2021.108801] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 09/07/2021] [Accepted: 09/17/2021] [Indexed: 12/15/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) are an essential component of the mammalian central nervous system. These receptors modulate neuronal excitability in response to extracellular glutamate through the activation of intracellular heterotrimeric G proteins. Like most other class C G protein-coupled receptors, mGluRs function as obligate dimer proteins, meaning they need to form dimer complexes before becoming functional receptors. All mGluRs possess the ability to homodimerize, but studies over the past ten years have demonstrated these receptors are also capable of forming heterodimers in specific patterns. These mGluR heterodimers appear to have their own unique biophysical behavior and pharmacology with both native and synthetic compounds with few rules having been identified that allow for prediction of the consequences of any particular mGluR pair forming heterodimers. Here, we review the relevant literature demonstrating the existence and consequences of mGluR heterodimerization. By collecting biophysical and pharmacological data of several mGluR heterodimers we demonstrate the lack of generalizable behavior of these complexes indicating that each individual dimeric pair needs to be investigated independently. Additionally, by combining sequence alignment and structural analysis, we propose that interactions between the β4-A Helix Loop and the D Helix in the extracellular domain of these receptors are the structural components that dictate heterodimerization compatibility. Finally, we discuss the potential implications of mGluR heterodimerization from the viewpoints of further developing our understanding of neuronal physiology and leveraging mGluRs as a therapeutic target for the treatment of pathophysiology.
Collapse
Affiliation(s)
- Tyler W McCullock
- Department of Pharmacology and Physiology, University of Rochester Medical Center, 601 Elmwood Ave, Box 711, Rochester, NY, 14642, USA.
| | - Paul J Kammermeier
- Department of Pharmacology and Physiology, University of Rochester Medical Center, 601 Elmwood Ave, Box 711, Rochester, NY, 14642, USA.
| |
Collapse
|
2
|
Defining the Homo- and Heterodimerization Propensities of Metabotropic Glutamate Receptors. Cell Rep 2021; 31:107605. [PMID: 32375054 PMCID: PMC7271767 DOI: 10.1016/j.celrep.2020.107605] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 03/10/2020] [Accepted: 04/10/2020] [Indexed: 01/02/2023] Open
Abstract
The eight metabotropic glutamate receptors (mGluRs) serve critical modulatory roles throughout the nervous system. The molecular diversity of mGluRs is thought to be further expanded by the formation of heterodimers, but the co-expression of mGluR subtypes at the cellular level and the relative propensities of heterodimer formation are not well known. Here, we analyze single-cell RNA sequencing data and find that cortical pyramidal cells express multiple mGluR subtypes with distinct profiles for different receptor combinations. We then develop quantitative, fluorescence-based assays to define the relative homo- and heterodimer propensities across group-I, -II, and -III mGluRs. We find a strong preference for heterodimerization in a number of cases, including mGluR2 with mGluR3, which we confirm in frontal cortex using in situ RNA hybridization and co-immunoprecipitation. Together, our findings support the biological relevance of mGluR heterodimerization and highlight the complex landscape of mGluR populations in the brain.
Collapse
|
3
|
Fisher NM, AlHashim A, Buch AB, Badivuku H, Samman MM, Weiss KM, Cestero GI, Does MD, Rook JM, Lindsley CW, Conn PJ, Gogliotti RG, Niswender CM. A GRM7 mutation associated with developmental delay reduces mGlu7 expression and produces neurological phenotypes. JCI Insight 2021; 6:143324. [PMID: 33476302 PMCID: PMC7934925 DOI: 10.1172/jci.insight.143324] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 01/13/2021] [Indexed: 12/29/2022] Open
Abstract
The metabotropic glutamate receptor 7 (mGlu7) is a G protein–coupled receptor that has been recently linked to neurodevelopmental disorders. This association is supported by the identification of GRM7 variants in patients with autism spectrum disorder, attention deficit hyperactivity disorder, and severe developmental delay. One GRM7 mutation previously reported in 2 patients results in a single amino acid change, I154T, within the mGlu7 ligand-binding domain. Here, we report 2 new patients with this mutation who present with severe developmental delay and epilepsy. Functional studies of the mGlu7-I154T mutant reveal that this substitution resulted in significant loss of mGlu7 protein expression in HEK293A cells and in mice. We show that this occurred posttranscriptionally at the level of protein expression and trafficking. Similar to mGlu7–global KO mice, mGlu7-I154T animals exhibited reduced motor coordination, deficits in contextual fear learning, and seizures. This provides functional evidence that a disease-associated mutation affecting the mGlu7 receptor was sufficient to cause neurological dysfunction in mice and further validates GRM7 as a disease-causing gene in the human population.
Collapse
Affiliation(s)
- Nicole M Fisher
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA
| | | | - Aditi B Buch
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA
| | - Hana Badivuku
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA
| | | | - Kelly M Weiss
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA
| | - Gabriela I Cestero
- Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Mark D Does
- Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Jerri M Rook
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA
| | - Craig W Lindsley
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA.,Department of Chemistry and.,Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee, USA
| | - P Jeffrey Conn
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA.,Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee, USA.,Vanderbilt Kennedy Center, Vanderbilt University Medical Center, Nashville, Tennessee USA
| | - Rocco G Gogliotti
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA.,Department of Molecular Pharmacology and Neuroscience, Loyola University Chicago, Maywood, Illinois, USA
| | - Colleen M Niswender
- Department of Pharmacology and.,Warren Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, Tennessee, USA.,Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee, USA.,Vanderbilt Kennedy Center, Vanderbilt University Medical Center, Nashville, Tennessee USA
| |
Collapse
|
4
|
Dasgupta A, Lim YJ, Kumar K, Baby N, Pang KLK, Benoy A, Behnisch T, Sajikumar S. Group III metabotropic glutamate receptors gate long-term potentiation and synaptic tagging/capture in rat hippocampal area CA2. eLife 2020; 9:e55344. [PMID: 32310084 PMCID: PMC7170650 DOI: 10.7554/elife.55344] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Accepted: 04/08/2020] [Indexed: 12/17/2022] Open
Abstract
Metabotropic glutamate receptors (mGluRs) play an important role in synaptic plasticity and memory and are largely classified based on amino acid sequence homology and pharmacological properties. Among group III metabotropic glutamate receptors, mGluR7 and mGluR4 show high relative expression in the rat hippocampal area CA2. Group III metabotropic glutamate receptors are known to down-regulate cAMP-dependent signaling pathways via the activation of Gi/o proteins. Here, we provide evidence that inhibition of group III mGluRs by specific antagonists permits an NMDA receptor- and protein synthesis-dependent long-lasting synaptic potentiation in the apparently long-term potentiation (LTP)-resistant Schaffer collateral (SC)-CA2 synapses. Moreover, long-lasting potentiation of these synapses transforms a transient synaptic potentiation of the entorhinal cortical (EC)-CA2 synapses into a stable long-lasting LTP, in accordance with the synaptic tagging/capture hypothesis (STC). Furthermore, this study also sheds light on the role of ERK/MAPK protein signaling and the downregulation of STEP protein in the group III mGluR inhibition-mediated plasticity in the hippocampal CA2 region, identifying them as critical molecular players. Thus, the regulation of group III mGluRs provides a conducive environment for the SC-CA2 synapses to respond to events that could lead to activity-dependent synaptic plasticity.
Collapse
Affiliation(s)
- Ananya Dasgupta
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
- Life Sciences Institute Neurobiology Programme, National University of SingaporeSingaporeSingapore
| | - Yu Jia Lim
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
| | - Krishna Kumar
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
- Life Sciences Institute Neurobiology Programme, National University of SingaporeSingaporeSingapore
| | - Nimmi Baby
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
- Life Sciences Institute Neurobiology Programme, National University of SingaporeSingaporeSingapore
| | - Ka Lam Karen Pang
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
- Life Sciences Institute Neurobiology Programme, National University of SingaporeSingaporeSingapore
| | - Amrita Benoy
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
- Life Sciences Institute Neurobiology Programme, National University of SingaporeSingaporeSingapore
| | - Thomas Behnisch
- Institutes of Brain Science, State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan UniversityShanghaiChina
| | - Sreedharan Sajikumar
- Department of Physiology, Yong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
- Life Sciences Institute Neurobiology Programme, National University of SingaporeSingaporeSingapore
| |
Collapse
|
5
|
Correa AMB, Guimarães JDS, Dos Santos E Alhadas E, Kushmerick C. Control of neuronal excitability by Group I metabotropic glutamate receptors. Biophys Rev 2017; 9:835-845. [PMID: 28836161 PMCID: PMC5662043 DOI: 10.1007/s12551-017-0301-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Accepted: 07/27/2017] [Indexed: 12/12/2022] Open
Abstract
Metabotropic glutamate (mGlu) receptors couple through G proteins to regulate a large number of cell functions. Eight mGlu receptor isoforms have been cloned and classified into three Groups based on sequence, signal transduction mechanisms and pharmacology. This review will focus on Group I mGlu receptors, comprising the isoforms mGlu1 and mGlu5. Activation of these receptors initiates both G protein-dependent and -independent signal transduction pathways. The G-protein-dependent pathway involves mainly Gαq, which can activate PLCβ, leading initially to the formation of IP3 and diacylglycerol. IP3 can release Ca2+ from cellular stores resulting in activation of Ca2+-dependent ion channels. Intracellular Ca2+, together with diacylglycerol, activates PKC, which has many protein targets, including ion channels. Thus, activation of the G-protein-dependent pathway affects cellular excitability though several different effectors. In parallel, G protein-independent pathways lead to activation of non-selective cationic currents and metabotropic synaptic currents and potentials. Here, we provide a survey of the membrane transport proteins responsible for these electrical effects of Group I metabotropic glutamate receptors.
Collapse
Affiliation(s)
- Ana Maria Bernal Correa
- Graduate Program in Physiology and Pharmacology, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil
| | | | | | - Christopher Kushmerick
- Graduate Program in Physiology and Pharmacology, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
- Departamento de Fisiologia e Biofísica - ICB, UFMG, Av. Pres. Antônio Carlos, 6627 - Pampulha, Belo Horizonte, MG, 31270-901, Brazil.
| |
Collapse
|
6
|
Mechanism of Assembly and Cooperativity of Homomeric and Heteromeric Metabotropic Glutamate Receptors. Neuron 2016; 92:143-159. [PMID: 27641494 DOI: 10.1016/j.neuron.2016.08.036] [Citation(s) in RCA: 122] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 07/19/2016] [Accepted: 08/19/2016] [Indexed: 11/23/2022]
Abstract
G protein-coupled receptors (GPCRs) mediate cellular responses to a wide variety of extracellular stimuli. GPCR dimerization may expand signaling diversity and tune functionality, but little is known about the mechanisms of subunit assembly and interaction or the signaling properties of heteromers. Using single-molecule subunit counting on class C metabotropic glutamate receptors (mGluRs), we map dimerization determinants and define a heterodimerization profile. Intersubunit fluorescence resonance energy transfer measurements reveal that interactions between ligand-binding domains control the conformational rearrangements underlying receptor activation. Selective liganding with photoswitchable tethered agonists conjugated to one or both subunits of covalently linked mGluR2 homodimers reveals that receptor activation is highly cooperative. Strikingly, this cooperativity is asymmetric in mGluR2/mGluR3 heterodimers. Our results lead to a model of cooperative activation of mGluRs that provides a framework for understanding how class C GPCRs couple extracellular binding to dimer reorganization and G protein activation.
Collapse
|
7
|
Selective Disruption of Metabotropic Glutamate Receptor 5-Homer Interactions Mimics Phenotypes of Fragile X Syndrome in Mice. J Neurosci 2016; 36:2131-47. [PMID: 26888925 DOI: 10.1523/jneurosci.2921-15.2016] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
UNLABELLED Altered function of the Gq-coupled, Group 1 metabotropic glutamate receptors, specifically mGlu5, is implicated in multiple mouse models of autism and intellectual disability. mGlu5 dysfunction has been most well characterized in the fragile X syndrome mouse model, the Fmr1 knock-out (KO) mouse, where pharmacological and genetic reduction of mGlu5 reverses many phenotypes. mGlu5 is less associated with its scaffolding protein Homer in Fmr1 KO mice, and restoration of mGlu5-Homer interactions by genetic deletion of a short, dominant negative of Homer, H1a, rescues many phenotypes of Fmr1 KO mice. These results suggested that disruption of mGlu5-Homer leads to phenotypes of FXS. To test this idea, we examined mice with a knockin mutation of mGlu5 (F1128R; mGlu5(R/R)) that abrogates binding to Homer. Although FMRP levels were normal, mGlu5(R/R) mice mimicked multiple phenotypes of Fmr1 KO mice, including reduced mGlu5 association with the postsynaptic density, enhanced constitutive mGlu5 signaling to protein synthesis, deficits in agonist-induced translational control, protein synthesis-independent LTD, neocortical hyperexcitability, audiogenic seizures, and altered behaviors, including anxiety and sensorimotor gating. These results reveal new roles for the Homer scaffolds in regulation of mGlu5 function and implicate a specific molecular mechanism in a complex brain disease. SIGNIFICANCE STATEMENT Abnormal function of the metabotropic, or Gq-coupled, glutamate receptor 5 (mGlu5) has been implicated in neurodevelopmental disorders, including a genetic cause of intellectual disability and autism called fragile X syndrome. In brains of a mouse model of fragile X, mGlu5 is less associated with its binding partner Homer, a scaffolding protein that regulates mGlu5 localization to synapses and its ability to activate biochemical signaling pathways. Here we show that a mouse expressing a mutant mGlu5 that cannot bind to Homer is sufficient to mimic many of the biochemical, neurophysiological, and behavioral symptoms observed in the fragile X mouse. This work provides strong evidence that Homer-mGlu5 binding contributes to symptoms associated with neurodevelopmental disorders.
Collapse
|
8
|
Donaldson LF, Beazley-Long N. Alternative RNA splicing: contribution to pain and potential therapeutic strategy. Drug Discov Today 2016; 21:1787-1798. [PMID: 27329269 PMCID: PMC5405051 DOI: 10.1016/j.drudis.2016.06.017] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 05/31/2016] [Accepted: 06/14/2016] [Indexed: 12/19/2022]
Abstract
Alternative pre-mRNA splicing generates multiple proteins from a single gene. Control of alternative splicing is a likely therapy in cancer and other disorders. Key molecules in pain pathways – GPCRs and channels – are alternatively spliced. It is proposed that alternative splicing may be a therapeutic target in pain.
Since the sequencing of metazoan genomes began, it has become clear that the number of expressed proteins far exceeds the number of genes. It is now estimated that more than 98% of human genes give rise to multiple proteins through alternative pre-mRNA splicing. In this review, we highlight the known alternative splice variants of many channels, receptors, and growth factors that are important in nociception and pain. Recently, pharmacological control of alternative splicing has been proposed as potential therapy in cancer, wet age-related macular degeneration, retroviral infections, and pain. Thus, we also consider the effects that known splice variants of molecules key to nociception/pain have on nociceptive processing and/or analgesic action, and the potential for control of alternative pre-mRNA splicing as a novel analgesic strategy.
Collapse
Affiliation(s)
- Lucy F Donaldson
- School of Life Sciences and Arthritis Research UK Pain Centre, University of Nottingham, Nottingham NG7 2UH, UK.
| | - Nicholas Beazley-Long
- School of Life Sciences and Arthritis Research UK Pain Centre, University of Nottingham, Nottingham NG7 2UH, UK
| |
Collapse
|
9
|
Chang K, Roche KW. Structural and molecular determinants regulating mGluR5 surface expression. Neuropharmacology 2016; 115:10-19. [PMID: 27211252 DOI: 10.1016/j.neuropharm.2016.04.037] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 02/29/2016] [Accepted: 04/26/2016] [Indexed: 01/29/2023]
Abstract
Trafficking of G protein-coupled receptors (GPCRs) to the plasma membrane is a pivotal process to fulfill their biological functions. Metabotropic glutamate receptors (mGluRs; mGluR1-8) are expressed throughout the CNS and are important for modulating synaptic transmission and plasticity. Group I mGluRs, including mGluR1 and mGluR5, have long intracellular C-terminal tails containing multiple protein binding domains and sites for phosphorylation and ER retention. We have now investigated some of the structural determinants for mGluR5 trafficking to the plasma membrane by studying a series of truncations and ligand binding mutants. We also take advantage of dimer formation between the extracellular domain (ECD) of mGluR5 and design an ECD based surface-binding assay to evaluate dimerization and surface expression of mGluR5 containing various truncations or point mutations. We found that the C terminus is not essential for mGluR5 surface expression. In contrast, the 7th transmembrane domain (TM7) plays a critical role in its surface expression in both heterologous cells and neurons. Furthermore, a ligand binding mutation within the ECD of mGluR5 (Y64A/T174A) that blocks ligand binding impairs both surface expression and dimerization of mGluR5 in neurons. The integrity of both the whole 7TM domain and the C- terminal tail of mGluR5 are also important for stabilizing dimerization with the ECD. Thus multiple domains regulate dimerization and trafficking of mGluR5. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.
Collapse
Affiliation(s)
- Kai Chang
- Receptor Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 35, Room 2C903, Bethesda, MD 20892, USA
| | - Katherine W Roche
- Receptor Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 35, Room 2C903, Bethesda, MD 20892, USA.
| |
Collapse
|
10
|
Nørskov-Lauritsen L, Jørgensen S, Bräuner-Osborne H. N-glycosylation and disulfide bonding affects GPRC6A receptor expression, function, and dimerization. FEBS Lett 2015; 589:588-97. [PMID: 25617829 DOI: 10.1016/j.febslet.2015.01.019] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 12/28/2014] [Accepted: 01/14/2015] [Indexed: 12/20/2022]
Abstract
Investigation of post-translational modifications of receptor proteins is important for our understanding of receptor pharmacology and disease physiology. However, our knowledge about post-translational modifications of class C G protein-coupled receptors and how these modifications regulate expression and function is very limited. Herein, we show that the nutrient-sensing class C G protein-coupled receptor GPRC6A carries seven N-glycans and that one of these sites modulates surface expression whereas mutation of another site affects receptor function. GPRC6A has been speculated to form covalently linked dimers through cysteine disulfide linkage in the extracellular amino-terminal domain and here we show that GPRC6A indeed is a homodimer and that a disulfide bridge between the C131 residues is formed.
Collapse
Affiliation(s)
- Lenea Nørskov-Lauritsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Stine Jørgensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Hans Bräuner-Osborne
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
| |
Collapse
|
11
|
Jong YJI, Sergin I, Purgert CA, O'Malley KL. Location-dependent signaling of the group 1 metabotropic glutamate receptor mGlu5. Mol Pharmacol 2014; 86:774-85. [PMID: 25326002 DOI: 10.1124/mol.114.094763] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Although G protein-coupled receptors are primarily known for converting extracellular signals into intracellular responses, some receptors, such as the group 1 metabotropic glutamate receptor, mGlu5, are also localized on intracellular membranes where they can mediate both overlapping and unique signaling effects. Thus, besides "ligand bias," whereby a receptor's signaling modality can shift from G protein dependence to independence, canonical mGlu5 receptor signaling can also be influenced by "location bias" (i.e., the particular membrane and/or cell type from which it signals). Because mGlu5 receptors play important roles in both normal development and in disorders such as Fragile X syndrome, autism, epilepsy, addiction, anxiety, schizophrenia, pain, dyskinesias, and melanoma, a large number of drugs are being developed to allosterically target this receptor. Therefore, it is critical to understand how such drugs might be affecting mGlu5 receptor function on different membranes and in different brain regions. Further elucidation of the site(s) of action of these drugs may determine which signal pathways mediate therapeutic efficacy.
Collapse
Affiliation(s)
- Yuh-Jiin I Jong
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri
| | - Ismail Sergin
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri
| | - Carolyn A Purgert
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri
| | - Karen L O'Malley
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri
| |
Collapse
|
12
|
Sevastyanova TN, Kammermeier PJ. Cooperative signaling between homodimers of metabotropic glutamate receptors 1 and 5. Mol Pharmacol 2014; 86:492-504. [PMID: 25113912 DOI: 10.1124/mol.114.093468] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Metabotropic glutamate receptors (mGluRs) function as dimers. Recent work suggests that mGluR1 and mGluR5 may physically interact, but the nature and functional consequences of this relationship have not been addressed. In this study, the functional and pharmacological consequences of this interaction were investigated. Using heterologous expression of mGluR cDNA in rat sympathetic neurons from the superior cervical ganglion and inhibition of the native calcium currents as an assay for receptor activation, a functional interdependence between mGluR1 and mGluR5 was demonstrated. In neurons coexpressing these receptors, combining a selective mGluR1 competitive antagonist with either an mGluR1- or mGluR5-selective negative allosteric modulator (NAM) BAY36-7620 [(3aS,6aS)-hexahydro-5-methylene-6a-(2-naphthalenylmethyl)-1H-cyclopenta[c]furan-1-one] or MPEP [2-methyl-6-(phenylethynyl)pyridine hydrochloride], respectively, strongly occluded signaling by both receptors to an approximately equal degree. By contrast, in cells coexpressing mGluR1 and mGluR2, combining the same mGluR1 competitive inhibitor with an mGluR1 or mGluR2 NAM yielded partial and full inhibition of the response, respectively, as expected for independently acting receptors. In neurons expressing mGluR1 and mGluR5, the selective NAMs each strongly inhibited the response to glutamate, suggesting that these receptors do not interact as heterodimers, which would not be inhibited by selective NAMs. Finally, evidence for a similar mGluR1/mGluR5 functional dependence is shown in medium spiny striatal neurons. Together, these data demonstrate cooperative signaling between mGluR1 and mGluR5 in a manner inconsistent with heterodimerization, and thus suggest an interaction between homodimers.
Collapse
Affiliation(s)
- Tatyana N Sevastyanova
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York
| | - Paul J Kammermeier
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York
| |
Collapse
|
13
|
Yin S, Niswender CM. Progress toward advanced understanding of metabotropic glutamate receptors: structure, signaling and therapeutic indications. Cell Signal 2014; 26:2284-97. [PMID: 24793301 DOI: 10.1016/j.cellsig.2014.04.022] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Accepted: 04/27/2014] [Indexed: 12/24/2022]
Abstract
The metabotropic glutamate (mGlu) receptors are a group of Class C seven-transmembrane spanning/G protein-coupled receptors (7TMRs/GPCRs). These receptors are activated by glutamate, one of the standard amino acids and the major excitatory neurotransmitter. By activating G protein-dependent and non-G protein-dependent signaling pathways, mGlus modulate glutamatergic transmission both in the periphery and throughout the central nervous system. Since the discovery of the first mGlu receptor, and especially during the last decade, a great deal of progress has been made in understanding the signaling, structure, pharmacological manipulation and therapeutic indications of the 8 mGlu members.
Collapse
Affiliation(s)
- Shen Yin
- Department of Pharmacology, Vanderbilt University Medical School, Nashville, TN 37232, USA; Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, TN 37232, USA
| | - Colleen M Niswender
- Department of Pharmacology, Vanderbilt University Medical School, Nashville, TN 37232, USA; Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical School, Nashville, TN 37232, USA.
| |
Collapse
|
14
|
Willard SS, Koochekpour S. Glutamate, glutamate receptors, and downstream signaling pathways. Int J Biol Sci 2013; 9:948-59. [PMID: 24155668 PMCID: PMC3805900 DOI: 10.7150/ijbs.6426] [Citation(s) in RCA: 203] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Accepted: 07/11/2013] [Indexed: 12/23/2022] Open
Abstract
Glutamate is a nonessential amino acid, a major bioenergetic substrate for proliferating normal and neoplastic cells, and an excitatory neurotransmitter that is actively involved in biosynthetic, bioenergetic, metabolic, and oncogenic signaling pathways. Glutamate signaling activates a family of receptors consisting of metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs), both of which have been implicated in chronic disabling brain disorders such as Schizophrenia and neurodegenerative diseases like Alzheimer's, Parkinson's, and multiple sclerosis. In this review, we discuss the structural and functional relationship of mGluRs and iGluRs and their downstream signaling pathways. The three groups of mGluRs, the associated second messenger systems, and subsequent activation of PI3K/Akt, MAPK, NFkB, PLC, and Ca/CaM signaling systems will be discussed in detail. The current state of human mGluR1a as one of the most important isoforms of Group I-mGluRs will be highlighted. The lack of studies on the human orthologues of mGluRs family will be outlined. We conclude that upon further study, human glutamate-initiated signaling pathways may provide novel therapeutic opportunities for a variety of non-malignant and malignant human diseases.
Collapse
Affiliation(s)
- Stacey S Willard
- Departments of Cancer Genetics and Urology, Center for Genetics and Pharmacology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY, USA
| | | |
Collapse
|
15
|
Willard SS, Koochekpour S. Glutamate signaling in benign and malignant disorders: current status, future perspectives, and therapeutic implications. Int J Biol Sci 2013; 9:728-42. [PMID: 23983606 PMCID: PMC3753409 DOI: 10.7150/ijbs.6475] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 06/15/2013] [Indexed: 11/05/2022] Open
Abstract
Glutamate, a nonessential amino acid, is the major excitatory neurotransmitter in the central nervous system. As such, glutamate has been shown to play a role in not only neural processes, such as learning and memory, but also in bioenergetics, biosynthetic and metabolic oncogenic pathways. Glutamate has been the target of intense investigation for its involvement not only in the pathogenesis of benign neurodegenerative diseases (NDDs) such as Parkinson's disease, Alzheimer's disease, schizophrenia, multiple sclerosis, and amyotropic lateral sclerosis (ALS), but also in carcinogenesis and progression of malignant diseases. In addition to its intracellular activities, glutamate in secreted form is a phylogenetically conserved cell signaling molecule. Glutamate binding activates multiple major receptor families including the metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs), both of which have been implicated in various signaling pathways in cancer. Inhibition of extracellular glutamate release or glutamate receptor activation via competitive or non-competitive antagonists decreases growth, migration and invasion and induces apoptosis in breast cancer, melanoma, glioma and prostate cancer cells. In this review, we discuss the current state of glutamate signaling research as it relates to benign and malignant diseases. In addition, we provide a synopsis of clinical trials using glutamate antagonists for the treatment of NDD and malignant diseases. We conclude that in addition to its potential role as a metabolic biomarker, glutamate receptors and glutamate-initiated signaling pathways may provide novel therapeutic opportunities for cancer.
Collapse
Affiliation(s)
- Stacey S Willard
- Departments of Cancer Genetics and Urology, Center for Genetics and Pharmacology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA
| | | |
Collapse
|
16
|
Kammermeier PJ. Functional and pharmacological characteristics of metabotropic glutamate receptors 2/4 heterodimers. Mol Pharmacol 2012; 82:438-47. [PMID: 22653971 DOI: 10.1124/mol.112.078501] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Metabotropic glutamate receptors (mGluRs) were thought until recently to function mainly as stable homodimers, but recent work suggests that heteromerization is possible. Despite the growth in available compounds targeting mGluRs, little is known about the pharmacological profile of mGluR heterodimers. Here, this question was addressed for the mGluR2/4 heterodimer, examined by coexpressing both receptors in isolated sympathetic neurons from the rat superior cervical ganglion (SCG), a native neuronal system with a null mGluR background. Under conditions that favor mGluR2/4 heterodimer formation, activation of the receptor was not evident with the mGluR2-selective agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) or with the mGluR4 selective agonist L-(+)-2-amino-4-phosphonobutyric acid (L-AP4); however, full activation was apparent when both ligands were applied together, confirming that mGluR dimers require ligand binding in both subunits for full activation. Properties of allosteric modulators were also examined, including the findings that negative allosteric modulators (NAMs) have two binding sites per dimer and that positive allosteric modulators (PAMs) have only a single site per dimer. In SCG neurons, mGluR2/4 dimers were not inhibited by the mGluR2-selective NAM (Z)-1-[2-cycloheptyloxy-2-(2,6-dichlorophenyl)ethenyl]-1H-1,2,4-triazole (Ro 64-5229), supporting the two-site model. Furthermore, application of the mGluR4 selective PAMs N-(4-chloro-3-methoxyphenyl)-2-pyridinecarboxamide (VU0361737) or N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC) and combined application of mGluR4 PAMs with the mGluR2 selective PAM biphenyl indanone-A failed to potentiate glutamate responses through mGluR2/4, suggesting that mGluR2/4 heterodimers are not modulatable by PAMs that are currently available.
Collapse
Affiliation(s)
- Paul J Kammermeier
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York, USA.
| |
Collapse
|
17
|
Taman A, Ribeiro P. Characterization of a truncated metabotropic glutamate receptor in a primitive metazoan, the parasitic flatworm Schistosoma mansoni. PLoS One 2011; 6:e27119. [PMID: 22069494 PMCID: PMC3206071 DOI: 10.1371/journal.pone.0027119] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 10/11/2011] [Indexed: 11/26/2022] Open
Abstract
A novel glutamate-binding protein was identified in Schistosoma mansoni. The protein (SmGBP) is related to metabotropic glutamate receptors from other species and has a predicted glutamate binding site located within a Venus Flytrap module but it lacks the heptahelical transmembrane segment that normally characterizes these receptors. The SmGBP cDNA was cloned, verified by 5' and 3' Rapid Amplification of cDNA Ends (RACE) and shown to be polyadenylated at the 3'end, suggesting the transcript is full-length. The cloned cDNA was subsequently expressed in bacteria and shown to encode a functional glutamate-binding protein. Other studies, using a specific peptide antibody, determined that SmGBP exists in two forms, a monomer of the expected size and a stable but non-covalent dimer. The monomer and dimer are both present in the membrane fraction of S. mansoni and are resistant to extraction with high-salt, alkaline pH and urea, suggesting SmGBP is either an integral membrane protein or a peripheral protein that is tightly associated with the membrane. Surface biotinylation experiments combined with western blot analyses and confocal immunolocalization revealed that SmGBP localized to the surface membranes of adult male schistosomes, especially the dorsal tubercles. In contrast, we detected little or no expression of SmGBP either in the females or larval stages. A comparative quantitative PCR analysis confirmed that the level of SmGBP expression is several-fold higher in male worms than cercariae, and it is barely detectable in adult females. Together, the results identify SmGBP as a new type of schistosome glutamate receptor that is both gender- and stage-specific. The high-level expression of this protein in the male tubercles suggests a possible role in host-parasite interaction.
Collapse
Affiliation(s)
- Amira Taman
- Institute of Parasitology, McGill University, Macdonald Campus, Sainte Anne de Bellevue, Quebec, Canada
| | - Paula Ribeiro
- Institute of Parasitology, McGill University, Macdonald Campus, Sainte Anne de Bellevue, Quebec, Canada
| |
Collapse
|