1
|
Mao LM, Mathur N, Mahmood T, Rajan S, Chu XP, Wang JQ. Phosphorylation and regulation of group II metabotropic glutamate receptors (mGlu2/3) in neurons. Front Cell Dev Biol 2022; 10:1022544. [PMID: 36407098 PMCID: PMC9669598 DOI: 10.3389/fcell.2022.1022544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 10/18/2022] [Indexed: 11/05/2022] Open
Abstract
Group II metabotropic glutamate (mGlu) receptors (mGlu2/3) are Gαi/o-coupled receptors and are primarily located on presynaptic axonal terminals in the central nervous system. Like ionotropic glutamate receptors, group II mGlu receptors are subject to regulation by posttranslational phosphorylation. Pharmacological evidence suggests that several serine/threonine protein kinases possess the ability to regulate mGlu2/3 receptors. Detailed mapping of phosphorylation residues has revealed that protein kinase A (PKA) phosphorylates mGlu2/3 receptors at a specific serine site on their intracellular C-terminal tails in heterologous cells or neurons, which underlies physiological modulation of mGlu2/3 signaling. Casein kinases promote mGlu2 phosphorylation at a specific site. Tyrosine protein kinases also target group II receptors to induce robust phosphorylation. A protein phosphatase was found to specifically bind to mGlu3 receptors and dephosphorylate the receptor at a PKA-sensitive site. This review summarizes recent progress in research on group II receptor phosphorylation and the phosphorylation-dependent regulation of group II receptor functions. We further explore the potential linkage of mGlu2/3 phosphorylation to various neurological and neuropsychiatric disorders, and discuss future research aimed at analyzing novel biochemical and physiological properties of mGlu2/3 phosphorylation.
Collapse
Affiliation(s)
- Li-Min Mao
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Nirav Mathur
- Department of Anesthesiology, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Tayyibah Mahmood
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Sri Rajan
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Xiang-Ping Chu
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - John Q. Wang
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States,Department of Anesthesiology, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States,*Correspondence: John Q. Wang,
| |
Collapse
|
2
|
Klotz L, Enz R. MGluR7 is a presynaptic metabotropic glutamate receptor at ribbon synapses of inner hair cells. FASEB J 2021; 35:e21855. [PMID: 34644430 DOI: 10.1096/fj.202100672r] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2021] [Revised: 07/15/2021] [Accepted: 07/29/2021] [Indexed: 01/17/2023]
Abstract
Glutamate is the most pivotal excitatory neurotransmitter in the central nervous system. Metabotropic glutamate receptors (mGluRs) dimerize and can couple to inhibitory intracellular signal cascades, thereby protecting glutamatergic neurons from excessive excitation and cell death. MGluR7 is correlated with age-related hearing deficits and noise-induced hearing loss; however its exact localization in the cochlea is unknown. Here, we analyzed the expression and localization of mGluR7a and mGluR7b in mouse cochlear wholemounts in detail, using confocal microscopy and 3D reconstructions. We observed a presynaptic localization of mGluR7a at inner hair cells (IHCs), close to the synaptic ribbon. To detect mGluR7b, newly generated antibodies were characterized and showed co-localization with mGluR7a at IHC ribbon synapses. Compared to the number of synaptic ribbons, the numbers of mGluR7a and mGluR7b puncta were reduced at higher frequencies (48 to 64 kHz) and in older animals (6 and 12 months). Previously, we reported a presynaptic localization of mGluR4 and mGluR8b at this synapse type. This enables the possibility for the formation of homo- and/or heterodimeric receptors composed of mGluR4, mGluR7a, mGluR7b and mGluR8b at IHC ribbon synapses. These receptor complexes might represent new molecular targets suited for pharmacological concepts to protect the cochlea against noxious stimuli and excitotoxicity.
Collapse
Affiliation(s)
- Lisa Klotz
- Institute for Biochemistry, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| | - Ralf Enz
- Institute for Biochemistry, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany
| |
Collapse
|
3
|
Wu Z, Yang L, Li H, Zhou S. Krüppel-homolog 1 exerts anti-metamorphic and vitellogenic functions in insects via phosphorylation-mediated recruitment of specific cofactors. BMC Biol 2021; 19:222. [PMID: 34625063 PMCID: PMC8499471 DOI: 10.1186/s12915-021-01157-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Accepted: 09/24/2021] [Indexed: 11/23/2022] Open
Abstract
Background The zinc-finger transcription factor Krüppel-homolog 1 (Kr-h1) exerts a dual regulatory role during insect development by preventing precocious larval/nymphal metamorphosis and in stimulating aspects of adult reproduction such as vitellogenesis. However, how Kr-h1 functions both as a transcriptional repressor in juvenile metamorphosis and an activator in adult reproduction remains elusive. Here, we use the insect Locusta migratoria to dissect the molecular mechanism by which Kr-h1 functions as activator and repressor at these distinct developmental stages. Results We report that the kinase PKCα triggers Kr-h1 phosphorylation at the amino acid residue Ser154, a step essential for its dual functions. During juvenile stage, phosphorylated Kr-h1 recruits a corepressor, C-terminal binding protein (CtBP). The complex of phosphorylated Kr-h1 and CtBP represses the transcription of Ecdysone induced protein 93F (E93) and consequently prevents the juvenile-to-adult transition. In adult insects, phosphorylated Kr-h1 recruits a coactivator, CREB-binding protein (CBP), and promotes vitellogenesis by inducing the expression of Ribosomal protein L36. Furthermore, Kr-h1 phosphorylation with the concomitant inhibition of E93 transcription is evolutionarily conserved across insect orders. Conclusion Our results suggest that Kr-h1 phosphorylation is indispensable for the recruitment of transcriptional cofactors, and for its anti-metamorphic and vitellogenic actions in insects. Our data shed new light on the understanding of Kr-h1 regulation and function in JH-regulated insect metamorphosis and reproduction. Supplementary Information The online version contains supplementary material available at 10.1186/s12915-021-01157-3.
Collapse
Affiliation(s)
- Zhongxia Wu
- State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, School of Life Sciences, Henan University, Kaifeng, 475004, China
| | - Libin Yang
- State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, School of Life Sciences, Henan University, Kaifeng, 475004, China
| | - Huihui Li
- State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, School of Life Sciences, Henan University, Kaifeng, 475004, China
| | - Shutang Zhou
- State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, School of Life Sciences, Henan University, Kaifeng, 475004, China.
| |
Collapse
|
4
|
Dyakin VV, Wisniewski TM, Lajtha A. Racemization in Post-Translational Modifications Relevance to Protein Aging, Aggregation and Neurodegeneration: Tip of the Iceberg. Symmetry (Basel) 2021; 13:455. [PMID: 34350031 PMCID: PMC8330555 DOI: 10.3390/sym13030455] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Homochirality of DNA and prevalent chirality of free and protein-bound amino acids in a living organism represents the challenge for modern biochemistry and neuroscience. The idea of an association between age-related disease, neurodegeneration, and racemization originated from the studies of fossils and cataract disease. Under the pressure of new results, this concept has a broader significance linking protein folding, aggregation, and disfunction to an organism's cognitive and behavioral functions. The integrity of cognitive function is provided by a delicate balance between the evolutionarily imposed molecular homo-chirality and the epigenetic/developmental impact of spontaneous and enzymatic racemization. The chirality of amino acids is the crucial player in the modulation the structure and function of proteins, lipids, and DNA. The collapse of homochirality by racemization is the result of the conformational phase transition. The racemization of protein-bound amino acids (spontaneous and enzymatic) occurs through thermal activation over the energy barrier or by the tunnel transfer effect under the energy barrier. The phase transition is achieved through the intermediate state, where the chirality of alpha carbon vanished. From a thermodynamic consideration, the system in the homo-chiral (single enantiomeric) state is characterized by a decreased level of entropy. The oscillating protein chirality is suggesting its distinct significance in the neurotransmission and flow of perceptual information, adaptive associative learning, and cognitive laterality. The common pathological hallmarks of neurodegenerative disorders include protein misfolding, aging, and the deposition of protease-resistant protein aggregates. Each of the landmarks is influenced by racemization. The brain region, cell type, and age-dependent racemization critically influence the functions of many intracellular, membrane-bound, and extracellular proteins including amyloid precursor protein (APP), TAU, PrP, Huntingtin, α-synuclein, myelin basic protein (MBP), and collagen. The amyloid cascade hypothesis in Alzheimer's disease (AD) coexists with the failure of amyloid beta (Aβ) targeting drug therapy. According to our view, racemization should be considered as a critical factor of protein conformation with the potential for inducing order, disorder, misfolding, aggregation, toxicity, and malfunctions.
Collapse
Affiliation(s)
- Victor V. Dyakin
- Virtual Reality Perception Lab (VRPL), The Nathan S. Kline Institute for Psychiatric Research (NKI), Orangeburg, NY 10962, USA
| | - Thomas M. Wisniewski
- Departments of Neurology, Pathology and Psychiatry, Center for Cognitive Neurology, New York University School of Medicine, New York, NY 10016, USA
| | - Abel Lajtha
- Center for Neurochemistry, The Nathan S. Kline Institute for Psychiatric Research (NKI), Orangeburg, NY 10962, USA
| |
Collapse
|
5
|
Rai D, Akagi T, Shimohata A, Ishii T, Gangi M, Maruyama T, Wada-Kiyama Y, Ogiwara I, Kaneda M. Involvement of the C-terminal domain in cell surface localization and G-protein coupling of mGluR6. J Neurochem 2020; 158:837-848. [PMID: 33067823 DOI: 10.1111/jnc.15217] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Revised: 05/25/2020] [Accepted: 10/11/2020] [Indexed: 01/05/2023]
Abstract
Metabotropic glutamate receptor 6, mGluR6, interacts with scaffold proteins and Gβγ subunits via its intracellular C-terminal domain (CTD). The mGluR6 pathway is critically involved in the retinal processing of visual signals. We herein investigated whether the CTD (residues 840-871) was necessary for mGluR6 cell surface localization and G-protein coupling using mGluR6-CTD mutants with immunocytochemistry, surface biotinylation assays, and electrophysiological approaches. We used 293T cells and primary hippocampal neurons as model systems. We examined C-terminally truncated mGluR6 and showed that the removal of up to residue 858 did not affect surface localization or glutamate-induced G-protein-mediated responses, whereas a 15-amino acid deletion (Δ857-871) impaired these functions. However, a 21-amino acid deletion (Δ851-871) restored surface localization and glutamate-dependent responses, which were again attenuated when the entire CTD was removed. The sequence alignment of group III mGluRs showed conserved amino acids resembling an ER retention motif in the CTD. These results suggest that the intracellular CTD is required for the cell surface transportation and receptor function of mGluR6, whereas it may contain regulatory elements for intracellular trafficking and signaling.
Collapse
Affiliation(s)
- Dilip Rai
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | - Takumi Akagi
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | | | - Toshiyuki Ishii
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | - Mie Gangi
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | - Takuma Maruyama
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | | | - Ikuo Ogiwara
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | | |
Collapse
|
6
|
Isozumi N, Ohki S. Met872 is the key residue determining the novel binominal binding of metabotropic glutamate receptor 7 to calmodulin. Biochem Biophys Res Commun 2019; 520:640-644. [PMID: 31627896 DOI: 10.1016/j.bbrc.2019.10.053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 10/04/2019] [Indexed: 11/16/2022]
Abstract
Two mGluR7-derived peptides corresponding to residues 856 to 879 and 856 to 875 are known to bind to Ca2+-saturated calmodulin (Ca2+/CaM), and their binding manners are thought to differ. Met872 function is believed as one of the anchor residues for CaM-binding only in the shorter peptide. To uncover the role of Met872 in CaM-binding, we prepared a mutant of the long peptide, mGluR7 (M872A), in which Met872 was replaced with Ala. We used the mutant together with the two peptides to perform NMR-titration experiments to monitor interaction with stable isotope-labeled CaM. Interaction of Ca2+/CaM with mGluR7 (M872A) caused a spectrum that differed from that of Ca2+/CaM with the long peptide, suggesting that Met872 of mGluR7 could be involved in CaM-binding even in the long peptide. Analyses of all NMR data suggested that the binding between Ca2+/CaM and mGluR7 occurs in some conformational equilibrium manner. The unique CaM-binding properties caused by Met872 may be related to mGluR7's function.
Collapse
Affiliation(s)
- Noriyoshi Isozumi
- Center for Nano Materials and Technology (CNMT), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa, 923-1292, Japan.
| | - Shinya Ohki
- Center for Nano Materials and Technology (CNMT), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa, 923-1292, Japan
| |
Collapse
|
7
|
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.
Collapse
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.
| |
Collapse
|
8
|
Role of post-translational modifications on structure, function and pharmacology of class C G protein-coupled receptors. Eur J Pharmacol 2015; 763:233-40. [PMID: 25981296 DOI: 10.1016/j.ejphar.2015.05.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Revised: 03/06/2015] [Accepted: 05/11/2015] [Indexed: 11/22/2022]
Abstract
G protein-coupled receptors are divided into three classes (A, B and C) based on homology of their seven transmembrane domains. Class C is the smallest class with 22 human receptor subtypes including eight metabotropic glutamate (mGlu1-8) receptors, two GABAB receptors (GABAB1 and GABAB2), three taste receptors (T1R1-3), one calcium-sensing (CaS) receptor, one GPCR, class C, group 6, subtype A (GPRC6) receptor, and seven orphan receptors. G protein-coupled receptors undergo a number of post-translational modifications, which regulate their structure, function and/or pharmacology. Here, we review the existence of post-translational modifications in class C G protein-coupled receptors and their regulatory roles, with particular focus on glycosylation, phosphorylation, ubiquitination, SUMOylation, disulphide bonding and lipidation.
Collapse
|
9
|
Two distinct calmodulin binding sites in the third intracellular loop and carboxyl tail of angiotensin II (AT(1A)) receptor. PLoS One 2013; 8:e65266. [PMID: 23755207 PMCID: PMC3673938 DOI: 10.1371/journal.pone.0065266] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Accepted: 04/24/2013] [Indexed: 11/25/2022] Open
Abstract
In this study, we present data that support the presence of two distinct calmodulin binding sites within the angiotensin II receptor (AT1A), at juxtamembrane regions of the N-terminus of the third intracellular loop (i3, amino acids 214–231) and carboxyl tail of the receptor (ct, 302–317). We used bioluminescence resonance energy transfer assays to document interactions of calmodulin with the AT1A holo-receptor and GST-fusion protein pull-downs to demonstrate that i3 and ct interact with calmodulin in a Ca2+-dependent fashion. The former is a 1–12 motif and the latter belongs to 1-5-10 calmodulin binding motif. The apparent Kd of calmodulin for i3 is 177.0±9.1 nM, and for ct is 79.4±7.9 nM as assessed by dansyl-calmodulin fluorescence. Replacement of the tryptophan (W219) for alanine in i3, and phenylalanine (F309 or F313) for alanine in ct reduced their binding affinities for calmodulin, as predicted by computer docking simulations. Exogenously applied calmodulin attenuated interactions between G protein βγ subunits and i3 and ct, somewhat more so for ct than i3. Mutations W219A, F309A, and F313A did not alter Gβγ binding, but reduced the ability of calmodulin to compete with Gβγ, suggesting that calmodulin and Gβγ have overlapping, but not identical, binding requirements for i3 and ct. Calmodulin interference with the Gβγ binding to i3 and ct regions of the AT1A receptor strongly suggests that calmodulin plays critical roles in regulating Gβγ-dependent signaling of the receptor.
Collapse
|
10
|
Ullmer C, Zoffmann S, Bohrmann B, Matile H, Lindemann L, Flor P, Malherbe P. Functional monoclonal antibody acts as a biased agonist by inducing internalization of metabotropic glutamate receptor 7. Br J Pharmacol 2013; 167:1448-66. [PMID: 22747985 DOI: 10.1111/j.1476-5381.2012.02090.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
BACKGROUND AND PURPOSE The mGlu(7) receptors are strategically located at the site of vesicle fusion where they modulate the release of the main excitatory and inhibitory neurotransmitters. Consequently, they are implicated in the underlying pathophysiology of CNS diseases such as epilepsy and stress-related psychiatric disorders. Here, we characterized a selective, potent and functional anti-mGlu(7) monoclonal antibody, MAB1/28, that triggers receptor internalization. EXPERIMENTAL APPROACH MAB1/28's activity was investigated using Western blot and direct immunofluorescence on live cells, in vitro pharmacology by functional cAMP and [(35) S]-GTPγ binding assays, the kinetics of IgG-induced internalization by image analysis, and the activation of the ERK1/2 by elisa. KEY RESULTS mGlu(7) /mGlu(6) chimeric studies located the MAB1/28 binding site at the extracellular amino-terminus of mGlu(7) . MAB1/28 potently antagonized both orthosteric and allosteric agonist-induced inhibition of cAMP accumulation. The potency of the antagonistic actions was similar to the potency in triggering receptor internalization. The internalization mechanism occurred via a pertussis toxin-insensitive pathway and did not require Gα(i) protein activation. MAB1/28 activated ERK1/2 with potency similar to that for receptor internalization. The requirement of a bivalent receptor binding mode for receptor internalizations suggests that MAB1/28 modulates mGlu(7) dimers. CONCLUSIONS AND IMPLICATIONS We obtained evidence for an allosteric-biased agonist activity triggered by MAB1/28, which activates a novel IgG-mediated GPCR internalization pathway that is not utilized by small molecule, orthosteric or allosteric agonists. Thus, MAB1/28 provides an invaluable biological tool for probing mGlu(7) function and selective activation of its intracellular trafficking.
Collapse
Affiliation(s)
- C Ullmer
- DTA CV and Metabolism, Discovery Research CV & Metabolic Diseases, F. Hoffmann-La Roche AG, pRED, Pharma Research & Early Development, Basel, Switzerland.
| | | | | | | | | | | | | |
Collapse
|
11
|
Enz R. Structure of metabotropic glutamate receptor C-terminal domains in contact with interacting proteins. Front Mol Neurosci 2012; 5:52. [PMID: 22536173 PMCID: PMC3332230 DOI: 10.3389/fnmol.2012.00052] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Accepted: 04/02/2012] [Indexed: 01/22/2023] Open
Abstract
Metabotropic glutamate receptors (mGluRs) regulate intracellular signal pathways that control several physiological tasks, including neuronal excitability, learning, and memory. This is achieved by the formation of synaptic signal complexes, in which mGluRs assemble with functionally related proteins such as enzymes, scaffolds, and cytoskeletal anchor proteins. Thus, mGluR associated proteins actively participate in the regulation of glutamatergic neurotransmission. Importantly, dysfunction of mGluRs and interacting proteins may lead to impaired signal transduction and finally result in neurological disorders, e.g., night blindness, addiction, epilepsy, schizophrenia, autism spectrum disorders and Parkinson's disease. In contrast to solved crystal structures of extracellular N-terminal domains of some mGluR types, only a few studies analyzed the conformation of intracellular receptor domains. Intracellular C-termini of most mGluR types are subject to alternative splicing and can be further modified by phosphorylation and SUMOylation. In this way, diverse interaction sites for intracellular proteins that bind to and regulate the glutamate receptors are generated. Indeed, most of the known mGluR binding partners interact with the receptors' C-terminal domains. Within the last years, different laboratories analyzed the structure of these domains and described the geometry of the contact surface between mGluR C-termini and interacting proteins. Here, I will review recent progress in the structure characterization of mGluR C-termini and provide an up-to-date summary of the geometry of these domains in contact with binding partners.
Collapse
Affiliation(s)
- Ralf Enz
- Emil-Fischer-Zentrum, Institut für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg Erlangen, Germany
| |
Collapse
|
12
|
Diversity of metabotropic glutamate receptor-interacting proteins and pathophysiological functions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 970:63-79. [PMID: 22351051 DOI: 10.1007/978-3-7091-0932-8_3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
In the mammalian brain, the large majority of excitatory synapses express pre- and postsynaptic glutamate receptors. These are ion channels and G protein-coupled membrane proteins that are organized into functional signaling complexes. Here, we will review the nature and pathophysiological functions of the scaffolding proteins associated to these receptors, focusing on the G protein-coupled subtypes.
Collapse
|
13
|
Plouffe B, Yang X, Tiberi M. The third intracellular loop of D1 and D5 dopaminergic receptors dictates their subtype-specific PKC-induced sensitization and desensitization in a receptor conformation-dependent manner. Cell Signal 2011; 24:106-18. [PMID: 21893192 DOI: 10.1016/j.cellsig.2011.08.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Revised: 08/05/2011] [Accepted: 08/17/2011] [Indexed: 01/11/2023]
Abstract
We previously showed that phorbol-12-myristate-13-acetate (PMA) mediates a robust PKC-dependent sensitization and desensitization of the highly homologous human Gs protein and adenylyl cyclase (AC)-linked D1 (hD1R) and D5 (hD5R) dopaminergic receptors, respectively. Here, we demonstrate using forskolin-mediated AC stimulation that PMA-mediated hD1R sensitization and hD5R desensitization is not associated with changes in AC activity. We next employed a series of chimeric hD1R and hD5R to delineate the underlying structural determinants dictating the subtype-specific regulation of human D1-like receptors by PMA. We first used chimeric receptors in which the whole terminal region (TR) spanning from the extracellular face of transmembrane domain 6 to the end of cytoplasmic tail (CT) or CT alone were exchanged between hD1R and hD5R. CT and TR swaps lead to chimeric hD1R and hD5R retaining PMA-induced sensitization and desensitization of wild type parent receptors. In striking contrast, hD1R sensitization and hD5R desensitization mediated by PMA are correspondingly switched to PMA-induced receptor desensitization and sensitization following the IL3 swap between hD1R and hD5R. Cell treatment with the PKC blocker, Gö6983, inhibits PMA-induced regulation of these chimeric receptors in a similar fashion to wild type receptors. Further studies with chimeras constructed by exchanging IL3 and TR show that PMA-induced regulation of these chimeras remains fully switched relative to their respective wild type parent receptor. Interestingly, results obtained with the exchange of IL3 and TR also reveal that the D1-like subtype-specific regulation by PMA, while fully dictated by IL3, can be modulated in a receptor conformation-dependent manner. Overall, our results strongly suggest that IL3 is the critical determinant underlying the subtype-specific regulation of human D1-like receptor responsiveness by PKC.
Collapse
Affiliation(s)
- Bianca Plouffe
- Ottawa Hospital Research Institute, Department of Medicine, University of Ottawa, Ottawa, ON, Canada
| | | | | |
Collapse
|
14
|
Mao LM, Guo ML, Jin DZ, Fibuch EE, Choe ES, Wang JQ. Post-translational modification biology of glutamate receptors and drug addiction. Front Neuroanat 2011; 5:19. [PMID: 21441996 PMCID: PMC3062099 DOI: 10.3389/fnana.2011.00019] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Accepted: 03/03/2011] [Indexed: 01/26/2023] Open
Abstract
Post-translational covalent modifications of glutamate receptors remain a hot topic. Early studies have established that this family of receptors, including almost all ionotropic and metabotropic glutamate receptor subtypes, undergoes active phosphorylation at serine, threonine, or tyrosine residues in their intracellular domains. Recent evidence identifies several glutamate receptor subtypes to be direct substrates for palmitoylation at cysteine residues. Other modifications such as ubiquitination and sumoylation at lysine residues also occur to certain glutamate receptors. These modifications are dynamic and reversible in nature and are regulatable by changing synaptic inputs. The regulated modifications significantly impact the receptor in many ways, including interrelated changes in biochemistry (synthesis, subunit assembling, and protein–protein interactions), subcellular redistribution (trafficking, endocytosis, synaptic delivery, and clustering), and physiology, usually associated with changes in synaptic plasticity. Glutamate receptors are enriched in the striatum and cooperate closely with dopamine to regulate striatal signaling. Emerging evidence shows that modification processes of striatal glutamate receptors are sensitive to addictive drugs, such as psychostimulants (cocaine and amphetamine). Altered modifications are believed to be directly linked to enduring receptor/synaptic plasticity and drug-seeking. This review summarizes several major types of modifications of glutamate receptors and analyzes the role of these modifications in striatal signaling and in the pathogenesis of psychostimulant addiction.
Collapse
Affiliation(s)
- Li-Min Mao
- Department of Basic Medical Science, School of Medicine, University of Missouri-Kansas City Kansas City, MO, USA
| | | | | | | | | | | |
Collapse
|
15
|
Isozumi N, Iida Y, Nakatomi A, Nemoto N, Yazawa M, Ohki S. Conformation of the calmodulin-binding domain of metabotropic glutamate receptor subtype 7 and its interaction with calmodulin. J Biochem 2011; 149:463-74. [PMID: 21258069 DOI: 10.1093/jb/mvr006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Calmodulin (CaM), a Ca(2+)-binding protein, is a well-known regulator of various cellular functions. One of the targets of CaM is metabotropic glutamate receptor 7 (mGluR7), which serves as a low-pass filter for glutamate in the pre-synaptic terminal to regulate neurotransmission. Surface plasmon resonance (SPR), circular dichroism (CD) spectroscopy and nuclear magnetic spectroscopy (NMR) were performed to study the structure of the peptides corresponding to the CaM-binding domain of mGluR7 and their interaction with CaM. Unlike well-known CaM-binding peptides, mGluR7 has a random coil structure even in the presence of trifluoroethanol. Moreover, NMR data suggested that the complex between Ca(2+)/CaM and the mGluR7 peptide has multiple conformations. The mGluR7 peptide has been found to interact with CaM even in the absence of Ca(2+), and the binding is directed toward the C-domain of apo-CaM rather than the N-domain. We propose a possible mechanism for the activation of mGluR7 by CaM. A pre-binding occurs between apo-CaM and mGluR7 in the resting state of cells. Then, the Ca(2+)/CaM-mGluR7 complex is formed once Ca(2+) influx occurs. The weak interaction at lower Ca(2+) concentrations is likely to bind CaM to mGluR7 for the fast complex formation in response to the elevation of Ca(2+) concentration.
Collapse
Affiliation(s)
- Noriyoshi Isozumi
- School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
| | | | | | | | | | | |
Collapse
|
16
|
Maurice P, Guillaume JL, Benleulmi-Chaachoua A, Daulat AM, Kamal M, Jockers R. GPCR-Interacting Proteins, Major Players of GPCR Function. PHARMACOLOGY OF G PROTEIN COUPLED RECEPTORS 2011; 62:349-80. [DOI: 10.1016/b978-0-12-385952-5.00001-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
|
17
|
|
18
|
Suh YH, Pelkey KA, Lavezzari G, Roche PA, Huganir RL, McBain CJ, Roche KW. Corequirement of PICK1 binding and PKC phosphorylation for stable surface expression of the metabotropic glutamate receptor mGluR7. Neuron 2008; 58:736-48. [PMID: 18549785 DOI: 10.1016/j.neuron.2008.03.028] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2007] [Revised: 02/14/2008] [Accepted: 03/28/2008] [Indexed: 10/22/2022]
Abstract
The presynaptic metabotropic glutamate receptor (mGluR) mGluR7 modulates excitatory neurotransmission by regulating neurotransmitter release and plays a critical role in certain forms of synaptic plasticity. Although the dynamic regulation of mGluR7 surface expression governs a form of metaplasticity in the hippocampus, little is known about the molecular mechanisms regulating mGluR7 trafficking. We now show that mGluR7 surface expression is stabilized by both PKC phosphorylation and by receptor binding to the PDZ domain-containing protein PICK1. Phosphorylation of mGluR7 on serine 862 (S862) inhibits CaM binding, thereby increasing mGluR7 surface expression and receptor binding to PICK1. Furthermore, in mice lacking PICK1, PKC-dependent increases in mGluR7 phosphorylation and surface expression are diminished, and mGluR7-dependent plasticity at mossy fiber-interneuron hippocampal synapses is impaired. These data support a model in which PICK1 binding and PKC phosphorylation act together to stabilize mGluR7 on the cell surface in vivo.
Collapse
Affiliation(s)
- Young Ho Suh
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA
| | | | | | | | | | | | | |
Collapse
|
19
|
Kim CH, Lee J, Lee JY, Roche KW. Metabotropic glutamate receptors: phosphorylation and receptor signaling. J Neurosci Res 2008; 86:1-10. [PMID: 17663464 DOI: 10.1002/jnr.21437] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) play important roles in neurotransmission, neuronal development, synaptic plasticity, and neurological disorders. Recent studies have revealed a sophisticated interplay between mGluRs and protein kinases: activation of mGluRs regulates the activity of a number of kinases, and direct phosphorylation of mGluRs affects receptor signaling, trafficking, and desensitization. Here we review the emerging literature on mGluR phosphorylation, signaling, and synaptic function.
Collapse
Affiliation(s)
- Chul Hoon Kim
- Department of Pharmacology, Brain Research Institute, Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea.
| | | | | | | |
Collapse
|
20
|
Scheschonka A, Findlow S, Schemm R, El Far O, Caldwell JH, Crump MP, Holden-Dye K, O'Connor V, Betz H, Werner JM. Structural determinants of calmodulin binding to the intracellular C-terminal domain of the metabotropic glutamate receptor 7A. J Biol Chem 2007; 283:5577-88. [PMID: 18089570 DOI: 10.1074/jbc.m709505200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calmodulin (CaM) binds in a Ca2+-dependent manner to the intracellular C-terminal domains of most group III metabotropic glutamate receptors (mGluRs). Here we combined mutational and biophysical approaches to define the structural basis of CaM binding to mGluR 7A. Ca2+/CaM was found to interact with mGluR 7A primarily via its C-lobe at a 1:1 CaM:C-tail stoichiometry. Pulldown experiments with mutant CaM and mGluR 7A C-tail constructs and high resolution NMR with peptides corresponding to the CaM binding region of mGluR 7A allowed us to define hydrophobic and ionic interactions required for Ca2+/CaM binding and identified a 1-8-14 CaM-binding motif. The Ca2+/CaM.mGluR 7A peptide complex displays a classical wraparound structure that closely resembles that formed by Ca2+/CaM upon binding to smooth muscle myosin light chain kinase. Our data provide insight into how Ca2+/CaM regulates group III mGluR signaling via competition with intracellular proteins for receptor-binding sites.
Collapse
Affiliation(s)
- Astrid Scheschonka
- Department of Neurochemistry, Max Planck Institute for Brain Research, 60528 Frankfurt, Germany
| | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Martín R, Torres M, Sánchez-Prieto J. mGluR7 inhibits glutamate release through a PKC-independent decrease in the activity of P/Q-type Ca2+ channels and by diminishing cAMP in hippocampal nerve terminals. Eur J Neurosci 2007; 26:312-22. [PMID: 17650109 DOI: 10.1111/j.1460-9568.2007.05660.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The modulation of calcium channels by metabotropic glutamate receptors (mGluRs) is a key event in the fine-tuning of neurotransmitter release. Here we report that, in hippocampal nerve terminals from adult rats, the inhibition of glutamate release by the group III mGluR agonist L-2-amino-4-phosphonobutyrate (L-AP4) is largely mediated by mGluR7. In this preparation, P/Q-type Ca(2+) channels support the major component of glutamate release while the remaining release is supported by N-type Ca(2+) channels. The release associated with P/Q channels was modulated by mGluR7, either in the presence of omega-conotoxin-GVIA or after decreasing the extracellular Ca(2+) concentration [Ca(2+)](o) to abolish the contribution of N-type Ca(2+) channels. Under these conditions, L-AP4 (1 mm) reduced the evoked glutamate release by 35 +/- 2%. This inhibition was largely prevented by pertussis toxin, but it was insensitive to inhibitors of protein kinase C (bisindolylmaleimide) and protein kinase A (H-89). Furthermore, this inhibition was associated with a reduction in the Ca(2+) influx mediated by P/Q channels in the absence of any detectable change in cAMP levels. However, L-AP4 decreased the levels of cAMP in the presence of forskolin. The activation of this additional signalling pathway was very efficient in counteracting the facilitation of glutamate release induced by forskolin. Thus, mGluR7 mediates the inhibition of glutamate release at hippocampal nerve terminals primarily by inhibiting P/Q-type Ca(2+) channels, although augmenting the levels of cAMP reveals the ability of the receptor to decrease cAMP.
Collapse
Affiliation(s)
- Ricardo Martín
- Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense, Madrid 28040, Spain
| | | | | |
Collapse
|
22
|
Enz R. The trick of the tail: protein-protein interactions of metabotropic glutamate receptors. Bioessays 2007; 29:60-73. [PMID: 17187376 DOI: 10.1002/bies.20518] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
It was initially believed that G-protein-coupled receptors, such as metabotropic glutamate receptors, could simply be described as individual proteins that are associated with intracellular signal cascades via G-proteins. This view is no longer tenable. Today we know that metabotropic glutamate receptors (mGluRs) can dimerize and bind to a variety of proteins in addition to trimeric G-proteins. These newly identified protein interactions led to the discovery of new regulatory mechanisms that are independent of and sometimes synergistic with the classical G-protein-coupled second messenger pathways. Notably, several of these mechanisms connect mGluR-mediated signaling to other receptor classes, thereby creating a network of different receptor types and associated signal cascades. The intracellular C-termini of mGluRs play a key role in the regulation of these networks, and various new protein interactions of these domains were described recently. Because mGluRs are involved in a variety of physiological and pathophysiological processes, some of the proteins interacting with this receptor class have potential as valuable pharmaceutical targets. This review will give a comprehensive overview of proteins interacting with mGluR C-termini, highlight new evolving regulatory mechanisms for glutamatergic signal transduction and discuss possibilities for future drug development.
Collapse
Affiliation(s)
- Ralf Enz
- Emil-Fischer-Zentrum, Institut für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fahrstrasse 17, 91054 Erlangen, Germany.
| |
Collapse
|
23
|
Bertaso F, Lill Y, Airas JM, Espeut J, Blahos J, Bockaert J, Fagni L, Betz H, El-Far O. MacMARCKS interacts with the metabotropic glutamate receptor type 7 and modulates G protein-mediated constitutive inhibition of calcium channels. J Neurochem 2006; 99:288-98. [PMID: 16987251 DOI: 10.1111/j.1471-4159.2006.04121.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
We have previously shown that the interaction of Ca2+/calmodulin with the metabotropic glutamate receptor type 7 (mGluR7) promotes the G-protein-mediated inhibition of voltage-sensitive Ca2+ channels (VSCCs) seen upon agonist activation. Here, we performed a yeast two-hybrid screen of a new-born rat brain cDNA library using the cytoplasmic C-terminal tail of mGluR7 as bait and identified macrophage myristoylated alanine-rich c-kinase substrate (MacMARCKS) as a binding protein. The interaction was confirmed in vitro and in vivo by pull-down assays, immunoprecipitation, and colocalization of mGluR7 and MacMARCKS in transfected HEK293 cells and cultured cerebellar granule cells. Binding of MacMARCKS to mGluR7 was antagonized by Ca2+/calmodulin. In neurons, cotransfection of MacMARCKS with mGluR7, but not mGluR7 mutants unable to bind MacMARCKS, reduced the G-protein-mediated tonic inhibition of VSCCs in the absence of mGluR7 agonist. These results suggest that competitive interactions of Ca2+/calmodulin and MacMARCKS with mGluR7 control the tonic inhibition of VSCCs by G-proteins.
Collapse
Affiliation(s)
- Federica Bertaso
- CNRS, UMR5203, Montpellier; INSERM, U661, Montpellier, University Montpellier I & II, Montpellier, France
| | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Tang Z, El Far O, Betz H, Scheschonka A. Pias1 Interaction and Sumoylation of Metabotropic Glutamate Receptor 8. J Biol Chem 2005; 280:38153-9. [PMID: 16144832 DOI: 10.1074/jbc.m508168200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Group III presynaptic metabotropic glutamate receptors (mGluRs) play a central role in regulating presynaptic activity through G-protein effects on ion channels and signal transducing enzymes. Like all Class C G-protein-coupled receptors, mGluR8 has an extended intracellular C-terminal domain (CTD) presumed to allow for modulation of downstream signaling. In a yeast two-hybrid screen of an adult rat brain cDNA library with the CTDs of mGluR8a and 8b (mGluR8-C) as baits, we identified sumo1 and four different components of the sumoylation cascade (ube2a, Pias1, Piasgamma, Piasxbeta) as interacting proteins. Binding assays using recombinant GST fusion proteins confirmed that Pias1 interacts not only with mGluR8-C but also with all group III mGluR CTDs. Pias1 binding to mGluR8-C required a region N-terminal to a consensus sumoylation motif and was not affected by arginine substitution of the conserved lysine 882 within this motif. Co-transfection of fluorescently tagged mGluR8a-C, sumo1, and enzymes of the sumoylation cascade into HEK293 cells showed that mGluR8a-C can be sumoylated in vivo. Arginine substitution of lysine 882 within the consensus sumoylation motif, but not other conserved lysines within the CTD, abolished in vivo sumoylation. Our results are consistent with post-translational sumoylation providing a novel mechanism of group III mGluR regulation.
Collapse
Affiliation(s)
- Zhongshu Tang
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, 60528 Frankfurt, Germany
| | | | | | | |
Collapse
|
25
|
Turner JH, Raymond JR. Interaction of calmodulin with the serotonin 5-hydroxytryptamine2A receptor. A putative regulator of G protein coupling and receptor phosphorylation by protein kinase C. J Biol Chem 2005; 280:30741-50. [PMID: 15970592 DOI: 10.1074/jbc.m501696200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The 5-hydroxytryptamine2A (5-HT2A) receptor is a G(q/11)-coupled serotonin receptor that activates phospholipase C and increases diacylglycerol formation. In this report, we demonstrated that calmodulin (CaM) co-immunoprecipitates with the 5-HT2A receptor in NIH-3T3 fibroblasts in an agonist-dependent manner and that the receptor contains two putative CaM binding regions. The putative CaM binding regions of the 5-HT2A receptor are localized to the second intracellular loop and carboxyl terminus. In an in vitro binding assay peptides encompassing the putative second intracellular loop (i2) and carboxyl-terminal (ct) CaM binding regions bound CaM in a Ca2+-dependent manner. The i2 peptide bound with apparent higher affinity and shifted the mobility of CaM in a nondenaturing gel shift assay. Fluorescence emission spectral analyses of dansyl-CaM showed apparent K(D) values of 65 +/- 30 nM for the i2 peptide and 168 +/- 38 nM for the ct peptide. The ct CaM-binding domain overlaps with a putative protein kinase C (PKC) site, which was readily phosphorylated by PKC in vitro. CaM binding and phosphorylation of the ct peptide were found to be antagonistic, suggesting a putative role for CaM in the regulation of 5-HT2A receptor phosphorylation and desensitization. Finally, we showed that CaM decreases 5-HT2A receptor-mediated [35S]GTPgammaS binding to NIH-3T3 cell membranes, supporting a possible role for CaM in regulating receptor-G protein coupling. These data indicate that the serotonin 5-HT2A receptor contains two high affinity CaM-binding domains that may play important roles in signaling and function.
Collapse
Affiliation(s)
- Justin H Turner
- Medical and Research Services, Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina 29425-2227, USA
| | | |
Collapse
|
26
|
Sohn UD, Park JH, Lee TS, Shin CY, Jeong JH, Kim JH, Je HD, Dartt DA, Zoukhri D, Choi HC, Lee KY. Differential regulation by Ca(2+) of calmodulin- and PKC-dependent contractile pathways in cat lower oesophageal sphincter. ACTA ACUST UNITED AC 2004; 23:307-17. [PMID: 15255815 DOI: 10.1111/j.1474-8673.2004.00302.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
1. In the present investigation we examined the regulation of calmodulin (CaM)- and protein kinase C (PKC)-dependent pathways by cytosolic Ca(2+) in the contraction of cat lower oesophageal sphincter (LES). 2. Force developed in response to increasing doses of acetylcholine (ACh) was directly related to the increase of the [Ca(2+)](i) measured by fura-2. Thapsigargin, which depletes Ca(2+) stores, reduced the contraction and the [Ca(2+)](i). In addition, contraction in response to maximal ACh was reduced by the CaM inhibitor CGS9343B but not by the PKC inhibitor chelerythrine. The contraction in response to submaximal ACh was reduced by chelerythrine but not by CGS9343B. 3. In permeabilized cells, the contraction in response to low Ca(2+) (0.54 microm) was also reduced by CGS9343B. 4. The response to high Ca(2+) (1.0 microm) was reduced by CGS9343B. ACh also inhibited PKC activation induced by diacylglycerol, which activation is inhibited by the N-myristoylated peptide inhibitor derived from pseudosubstrate sequences of PKCalphabetagamma (myr-PKC-alphabetagamma), but not of myr-PKC-alpha. 5. These data are consistent with the view that activated CaM-dependent pathways inhibit PKC-dependent pathways, this switch mechanism might be regulated by Ca(2+) in the LES.
Collapse
Affiliation(s)
- U D Sohn
- Department of Pharmacology, College of Pharmacy, Chung Ang University, Seoul 156-756, Korea
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
27
|
Fagni L, Ango F, Perroy J, Bockaert J. Identification and functional roles of metabotropic glutamate receptor-interacting proteins. Semin Cell Dev Biol 2004; 15:289-98. [PMID: 15125892 DOI: 10.1016/j.semcdb.2003.12.018] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
In the mammalian brain, a majority of excitatory synapses use glutamate as a neurotransmitter. Glutamate activates ligand-gated channels (ionotropic receptors) and G protein-coupled (metabotropic) receptors. During the past decade, a number of intracellular proteins have been described to interact with these receptors. These proteins not only scaffold the glutamate receptors at the pre- and post-synaptic membranes, but also regulate their subcellular targeting and intracellular signaling. Thus, identification of these proteins has been essential for further understanding the functions of glutamate receptors. Here we will focus on those proteins that interact with the subgroup of metabotropic glutamate (mGlu) receptors, and review the methods used for their identification, as well as their functional roles in neurons.
Collapse
Affiliation(s)
- Laurent Fagni
- Laboratory of Functional Genomics, CNRS UPR 2580, CCIPE, 141 Rue de la Cardonille, 34094 Montpellier Cedex 05, France.
| | | | | | | |
Collapse
|
28
|
Kline LW, Ji J, Wang GJ, Sutherland SK, Pang PKT, Benishin CG. Protein Kinase C Masks Nitric Oxide Synthase Activity in Vascular Smooth Muscle under Basal Conditions. J Cardiovasc Pharmacol 2004; 43:281-7. [PMID: 14716218 DOI: 10.1097/00005344-200402000-00018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Under basal conditions there is no observable nitric oxide synthase (NOS) activity in vascular smooth muscle (VSM). Pretreatment of endothelium-denuded aortic rings from Sprague-Dawley rats with 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), (0.1 micromol/L) significantly attenuated phenylephrine (PE)-induced contractile responses in a dose-dependent manner. In the presence of 10 micromol/L Nomega-nitro-L-arginine (L-NNA) or 0.1 mmol/L aminoguanidine (AG), the inhibition of contractions at 10 nmol/L PE by H-7 was blocked by 88% or 52%, respectively. The blockade by antagonists was completely reversed by l-arginine but not by d-arginine, and alone they did not significantly alter PE-induced contraction of endothelium-denuded aorta. Methylene blue (MB, 50 micromol/L) also inhibited the action of H-7. The inhibitory effect of H-7 occurred after 5 minutes and was reversible. PE-induced contraction was also inhibited by the selective protein kinase C inhibitors calphostin C (10 micromol/L), and bisindolylmaleimide IV (Bis-IV, 10 micromol/L), but not by the selective protein kinase A inhibitor H-89 (0.1 micromol/L). These results indicate protein kinase C inhibits NOS activity in VSM under basal conditions. Incubation of tissues with either H-7 or calphostin C stimulates NO production, and immunocytochemical studies reveal the presence of NOS in VSM under basal conditions.
Collapse
Affiliation(s)
- Loren W Kline
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
| | | | | | | | | | | |
Collapse
|
29
|
Croci C, Sticht H, Brandstätter JH, Enz R. Group I Metabotropic Glutamate Receptors Bind to Protein Phosphatase 1C. J Biol Chem 2003; 278:50682-90. [PMID: 14519764 DOI: 10.1074/jbc.m305764200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The modulation of neurotransmitter receptors by kinases and phosphatases represents a key mechanism in controlling synaptic signal transduction. However, molecular determinants involved in the specific targeting and interactions of these enzymes are largely unknown. Here, we identified both catalytic gamma-isoforms of protein phosphatase 1C (PP1gamma1 and PP1gamma2) as binding partners of the group I metabotropic glutamate receptors type 1a, 5a, and 5b in yeast cells and pull-down assays, using recombinant and native protein preparations. The tissue distribution of interacting proteins was compared, and protein phosphatase 1C was detected in dendrites of retinal bipolar cells expressing the respective interacting glutamate receptors. We mapped interacting domains within binding partners and identified five amino acids in the intracellular C termini of the metabotropic glutamate receptors type 1a, 5a, 5b, and 7b being both necessary and sufficient to bind protein phosphatase 1C. Furthermore, we show a dose-dependent competition of these C termini in binding the enzyme. Based on our data, we investigated the structure of the identified amino acids bound to protein phosphatase 1C by homology-based molecular modeling. In summary, these results provide a molecular description of the interaction between protein phosphatase 1C and metabotropic glutamate receptors and thereby increase our understanding of glutamatergic signal transduction.
Collapse
Affiliation(s)
- Cristina Croci
- Emil-Fischer-Zentrum, Institut für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fahrstr. 17, Erlangen 91054, Germany
| | | | | | | |
Collapse
|
30
|
Enz R, Croci C. Different binding motifs in metabotropic glutamate receptor type 7b for filamin A, protein phosphatase 1C, protein interacting with protein kinase C (PICK) 1 and syntenin allow the formation of multimeric protein complexes. Biochem J 2003; 372:183-91. [PMID: 12570872 PMCID: PMC1223362 DOI: 10.1042/bj20021750] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2002] [Revised: 02/03/2003] [Accepted: 02/05/2003] [Indexed: 11/17/2022]
Abstract
Metabotropic glutamate receptor (mGluR) type 7-mediated neurotransmission depends critically on its regulation by associated molecules, such as kinases, phosphatases and structural proteins. The splice variants mGluR7a and mGluR7b are defined by different intracellular C-termini, and simultaneous or exclusive binding of interacting proteins to these domains modulates mGluR7-mediated signalling. However, molecular determinants defining binding regions for associated proteins within mGluR7 C-termini are mostly unknown. In the present study, we have mapped the binding domains of four proteins [filamin A, protein phosphatase (PP) 1C, protein interacting with protein kinase C (PICK) 1 and syntenin] interacting with the mGluR7b variant, and show that the alternatively spliced distal part of the mGluR7b C-terminus was sufficient for the interactions. By individual substitution of all mGluR7b isoform-specific amino acids with alanine and construction of a series of deletion constructs, residues important for the interactions were identified and binding regions could be defined. Interestingly, mGluR7b contains an unusual PP1C-binding motif, located at the N-terminus of the binding domains for PICK1 and syntenin. Consistently, binding of PP1C and PICK1 or PP1C and syntenin to mGluR7b was not competitive. Furthermore, PICK1, but not PP1C, interacted physically with syntenin. Our results represent a molecular description of the binding mechanisms of four mGluR7-associated proteins, and indicate the formation of ternary protein complexes composed of mGluR7b, PP1C, PICK1 and syntenin.
Collapse
Affiliation(s)
- Ralf Enz
- Emil-Fischer Zentrum, Institut für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fahrstrasse 17, D-91054 Erlangen, Germany.
| | | |
Collapse
|
31
|
El Far O, Betz H. G-protein-coupled receptors for neurotransmitter amino acids: C-terminal tails, crowded signalosomes. Biochem J 2002; 365:329-36. [PMID: 12006104 PMCID: PMC1222699 DOI: 10.1042/bj20020481] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2002] [Accepted: 05/08/2002] [Indexed: 11/17/2022]
Abstract
G-protein-coupled receptors (GPCRs) represent a superfamily of highly diverse integral membrane proteins that transduce external signals to different subcellular compartments, including nuclei, via trimeric G-proteins. By differential activation of diffusible G(alpha) and membrane-bound G(beta)gamma subunits, GPCRs might act on both cytoplasmic/intracellular and plasma-membrane-bound effector systems. The coupling efficiency and the plasma membrane localization of GPCRs are regulated by a variety of interacting proteins. In this review, we discuss recently disclosed protein interactions found with the cytoplasmic C-terminal tail regions of two types of presynaptic neurotransmitter receptors, the group III metabotropic glutamate receptors and the gamma-aminobutyric acid type-B receptors (GABA(B)Rs). Calmodulin binding to mGluR7 and other group III mGluRs may provide a Ca(2+)-dependent switch for unidirectional (G(alpha)) versus bidirectional (G(alpha) and G(beta)gamma) signalling to downstream effector proteins. In addition, clustering of mGluR7 by PICK1 (protein interacting with C-kinase 1), a polyspecific PDZ (PSD-95/Dlg1/ZO-1) domain containing synaptic organizer protein, sheds light on how higher-order receptor complexes with regulatory enzymes (or 'signalosomes') could be formed. The interaction of GABA(B)Rs with the adaptor protein 14-3-3 and the transcription factor ATF4 (activating transcription factor 4) suggests novel regulatory pathways for G-protein signalling, cytoskeletal reorganization and nuclear gene expression: processes that may all contribute to synaptic plasticity.
Collapse
Affiliation(s)
- Oussama El Far
- Max-Planck Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt/Main, Germany
| | | |
Collapse
|
32
|
Yamauchi T. Molecular constituents and phosphorylation-dependent regulation of the post-synaptic density. MASS SPECTROMETRY REVIEWS 2002; 21:266-286. [PMID: 12533800 DOI: 10.1002/mas.10033] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The post-synaptic density (PSD) contains receptors with associated signaling- and scaffolding-proteins that organize signal-transduction pathways near the post-synaptic membrane. The PSD plays an important role in synaptic plasticity, and protein phosphorylation is critical to the regulation of PSD function, including learning and memory. Recently, studies have investigated the protein constituents of the PSD and substrate proteins for various protein kinases by proteomic analysis. The present review focuses on the molecular properties of PSD proteins, and substrates of protein kinases and their regulation by phosphorylation in order to understand the role of PSD in synaptic plasticity.
Collapse
Affiliation(s)
- Takashi Yamauchi
- Department of Biochemistry, Faculty of Pharmaceutical Sciences, The University of Tokushima, Shomachi 1, Tokushima 770-8505, Japan.
| |
Collapse
|
33
|
Sorensen SD, Macek TA, Cai Z, Saugstad JA, Conn PJ. Dissociation of protein kinase-mediated regulation of metabotropic glutamate receptor 7 (mGluR7) interactions with calmodulin and regulation of mGluR7 function. Mol Pharmacol 2002; 61:1303-12. [PMID: 12021391 DOI: 10.1124/mol.61.6.1303] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Presynaptic metabotropic glutamate receptors (mGluRs) often act as feedback inhibitors of synaptic transmission and serve important roles in defining the activity of glutamatergic synapses. Recent investigations have begun to identify novel interactions of presynaptic mGluRs, especially mGluR7, with multiple protein kinases and putative regulatory proteins that probably serve to further shape the overall activity of glutamatergic synapses. In the present study, we report that in addition to protein kinase C (PKC), cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG) can inhibit calmodulin (CaM) interactions with the carboxyl-terminal tail of mGluR7. These actions are mediated by PKC-, PKA-, or PKG-dependent phosphorylation of mGluR7 at a single serine residue, Ser(862), in the carboxyl terminus of the receptor. Mutation of this residue inhibits kinase-mediated phosphorylation of the mGluR7 carboxyl terminus and reverses kinase-mediated inhibition of CaM binding to mGluR7. However, PKC-mediated inhibition of the functional coupling of mGluR7 to G protein-coupled inward rectifier potassium (GIRK) currents in a heterologous expression system is not affected by mutating Ser(862). Furthermore, mutation of Ser(862) to glutamate to mimic receptor phosphorylation and inhibit CaM interactions with mGluR7 does not affect receptor function. These studies demonstrate that the ability of these second messenger-dependent kinases to inhibit mGluR7-mediated activation of GIRK current is not dependent on the phosphorylation of Ser(862) or the regulation of CaM binding to mGluR7. Furthermore, our studies suggest that CaM binding is not required for mGluR7-mediated activation of GIRK current.
Collapse
Affiliation(s)
- Scott D Sorensen
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
| | | | | | | | | |
Collapse
|
34
|
Enz R. The metabotropic glutamate receptor mGluR7b binds to the catalytic gamma-subunit of protein phosphatase 1. J Neurochem 2002; 81:1130-40. [PMID: 12065625 DOI: 10.1046/j.1471-4159.2002.00922.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Correct targeting of enzymes represents an important biological mechanism to control post-translational modifications of neurotransmitter receptors. The metabotropic glutamate receptor type 7 (mGluR7) exists in two splice variants (mGluR7a and mGluR7b), defined by different C-termini that are phosphorylated by protein kinase C (PKC). Recently, the search for mGluR7a binding partners yielded several proteins that interacted with its C-terminus. Here, a yeast two-hybrid screen using the mGluR7b C-terminus identified both variants of the catalytic gamma-subunit of protein phosphatase 1 (PP1gamma1 and PP1gamma2) as binding partners. The minimal interacting region of PP1gamma1/2 contained the core domain and was homologous to a region of PP1alpha that is needed for functional expression. Although this core domain is highly conserved within the protein phosphatase family, PP1alpha1 and PP1beta did not interact with mGluR7b. Binding between PP1gamma1 and mGluR7b might be regulated by alternative splicing, as the variant-specific distal part of the mGluR7b C-terminus mediated the interaction. Within this domain, amino acids involved in the binding to PP1gamma1 were mapped and biochemical assays using recombinant and native proteins verified the proposed interaction. Finally, the expression pattern of PP1gamma1, PP1gamma2 and mGluR7b was analysed in various CNS regions. In summary, these results suggest a regulation of mGluR7b by PP1gamma.
Collapse
Affiliation(s)
- Ralf Enz
- Emil-Fischer Zentrum, Institut für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
| |
Collapse
|
35
|
Tebar F, Lladó A, Enrich C. Role of calmodulin in the modulation of the MAPK signalling pathway and the transactivation of epidermal growth factor receptor mediated by PKC. FEBS Lett 2002; 517:206-10. [PMID: 12062438 DOI: 10.1016/s0014-5793(02)02624-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We have recently shown that calmodulin (CaM) regulates the trafficking of epidermal growth factor receptor (EGFR) as well as the mitogen-activated protein kinase (MAPK) signalling pathway. However, the overall regulation of the MAPK pathway is achieved through a complex interplay of other several upstream effectors including G-proteins, EGF, EGFR, protein kinase C (PKC), phosphatidylinositol-3-kinase and CaM. In order to understand the role of CaM in the PKC-mediated transactivation of EGFR we have analysed the effect of a CaM antagonist, N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide, on the 12-O-tetradecanoylphorbol-13-acetate-mediated activation of EGFR and the subsequent MAPK activation. The results show that CaM interferes with MAPK activation and the transactivation of EGFR mediated by PKC.
Collapse
Affiliation(s)
- Francesc Tebar
- Departament de Biologia Cellular, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain
| | | | | |
Collapse
|
36
|
Abstract
A yeast two-hybrid screen identified Filamin-A as a binding partner of the metabotropic glutamate receptor type 7b (mGluR7b) splice variant. In addition, Filamin-A interacted with mGluR4a, mGluR5a, mGluR5b, mGluR7a and mGluR8a. Domain mapping revealed that alternative splicing of mGluR4, mGluR7 and mGluR8 C-termini regulated the interaction. A conserved tyrosine within mGluR C-termini was identified to mediate the binding to Filamin-A. Protein interactions were verified in biochemical assays using recombinant and native proteins. Finally, co-expression of Filamin-A and mGluR7 splice variants was shown in brain regions. These findings suggest that Filamin-A may physically link metabotropic glutamate receptors to the actin cytoskeleton.
Collapse
Affiliation(s)
- Ralf Enz
- Institut für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fahrstrasse 17, D-91054 Erlangen, Germany.
| |
Collapse
|
37
|
Saugstad JA, Yang S, Pohl J, Hall RA, Conn PJ. Interaction between metabotropic glutamate receptor 7 and alpha tubulin. J Neurochem 2002; 80:980-8. [PMID: 11953448 PMCID: PMC2925652 DOI: 10.1046/j.0022-3042.2002.00778.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) mediate a variety of responses to glutamate in the central nervous system. A primary role for group-III mGluRs is to inhibit neurotransmitter release from presynaptic terminals, but the molecular mechanisms that regulate presynaptic trafficking and activity of group-III mGluRs are not well understood. Here, we describe the interaction of mGluR7, a group-III mGluR and presynaptic autoreceptor, with the cytoskeletal protein, alpha tubulin. The mGluR7 carboxy terminal (CT) region was expressed as a GST fusion protein and incubated with rat brain extract to purify potential mGluR7-interacting proteins. These studies yielded a single prominent mGluR7 CT-associated protein of 55 kDa, which subsequent microsequencing analysis revealed to be alpha tubulin. Coimmunoprecipitation assays confirmed that full-length mGluR7 and alpha tubulin interact in rat brain as well as in BHK cells stably expressing mGluR7a, a splice variant of mGluR7. In addition, protein overlay experiments showed that the CT domain of mGluR7a binds specifically to purified tubulin and calmodulin, but not to bovine serum albumin. Further pull-down studies revealed that another splice variant mGluR7b also interacts with alpha tubulin, indicating that the binding region is not localized to the splice-variant regions of either mGluR7a (900-915) or mGluR7b (900-923). Indeed, deletion mutagenesis experiments revealed that the alpha tubulin-binding site is located within amino acids 873-892 of the mGluR7 CT domain, a region known to be important for regulation of mGluR7 trafficking. Interestingly, activation of mGluR7a in cells results in an immediate and significant decrease in alpha tubulin binding. These data suggest that the mGluR7/alpha tubulin interaction may provide a mechanism to control access of the CT domain to regulatory molecules, or alternatively, that this interaction may lead to morphological changes in the presynaptic membrane in response to receptor activation.
Collapse
Affiliation(s)
- Julie A Saugstad
- Robert S. Dow Neurobiology Laboratories, Legacy Research, Portland, Oregon, USA.
| | | | | | | | | |
Collapse
|
38
|
Lin X, Gelman IH. Calmodulin and cyclin D anchoring sites on the Src-suppressed C kinase substrate, SSeCKS. Biochem Biophys Res Commun 2002; 290:1368-75. [PMID: 11820772 DOI: 10.1006/bbrc.2002.6357] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
SSeCKS and its human orthologue, Gravin, are large scaffolding proteins that are thought to facilitate mitogenic control by anchoring key signal mediators such as protein kinase (PK) C, PKA, the plasma membrane associated isoform of alpha-1,4-galactosyltransferase (GalTase), beta2-adrenergic receptor, and cyclins. SSeCKS is also a major PKC substrate and phosphatidylserine-dependent PKC binding protein whose phosphorylation sites shares homology with a site in the MARCKS protein that encodes phosphorylation-sensitive calmodulin (CaM) binding activity. In the present study, we mapped the in vitro binding sites for CaM and cyclins on SSeCKS. Four CaM binding sites were identified by binding assays that conform to the so-called 1-5-10 motif. Notably, CaM binding was antagonized by prephosphorylation of SSeCKS by PKC. We also identified two major cyclin binding (CY) sites that overlap a major PKC phosphorylation site in SSeCKS (Ser(507/515)), and showed that cyclin D binding is attenuated if SSeCKS is prephosphorylated by PKC. These data suggest that the scaffolding activities of SSeCKS are modulated by mitogenically stimulated kinases such as PKC.
Collapse
Affiliation(s)
- Xueying Lin
- Department of Medicine and Ruttenberg Cancer Center, Mount Sinai School of Medicine, Box 1090, One Gustave L. Levy Place, New York, New York 10029-6574, USA
| | | |
Collapse
|
39
|
Hermans E, Challiss RA. Structural, signalling and regulatory properties of the group I metabotropic glutamate receptors: prototypic family C G-protein-coupled receptors. Biochem J 2001; 359:465-84. [PMID: 11672421 PMCID: PMC1222168 DOI: 10.1042/0264-6021:3590465] [Citation(s) in RCA: 208] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In 1991 a new type of G-protein-coupled receptor (GPCR) was cloned, the type 1a metabotropic glutamate (mGlu) receptor, which, despite possessing the defining seven-transmembrane topology of the GPCR superfamily, bore little resemblance to the growing number of other cloned GPCRs. Subsequent studies have shown that there are eight mammalian mGlu receptors that, together with the calcium-sensing receptor, the GABA(B) receptor (where GABA is gamma-aminobutyric acid) and a subset of pheromone, olfactory and taste receptors, make up GPCR family C. Currently available data suggest that family C GPCRs share a number of structural, biochemical and regulatory characteristics, which differ markedly from those of the other GPCR families, most notably the rhodopsin/family A GPCRs that have been most widely studied to date. This review will focus on the group I mGlu receptors (mGlu1 and mGlu5). This subgroup of receptors is widely and differentially expressed in neuronal and glial cells within the brain, and receptor activation has been implicated in the control of an array of key signalling events, including roles in the adaptative changes needed for long-term depression or potentiation of neuronal synaptic connectivity. In addition to playing critical physiological roles within the brain, the mGlu receptors are also currently the focus of considerable attention because of their potential as drug targets for the treatment of a variety of neurological and psychiatric disorders.
Collapse
Affiliation(s)
- E Hermans
- Laboratoire de Pharmacologie, Université Catholique de Louvain (54.10), B-1200 Brussels, Belgium.
| | | |
Collapse
|
40
|
El Far O, Bofill-Cardona E, Airas JM, O'Connor V, Boehm S, Freissmuth M, Nanoff C, Betz H. Mapping of calmodulin and Gbetagamma binding domains within the C-terminal region of the metabotropic glutamate receptor 7A. J Biol Chem 2001; 276:30662-9. [PMID: 11395497 DOI: 10.1074/jbc.m102573200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ca(2+)/calmodulin (Ca(2+)/CaM) and the betagamma subunits of heterotrimeric G-proteins (Gbetagamma) have recently been shown to interact in a mutually exclusive fashion with the intracellular C terminus of the presynaptic metabotropic glutamate receptor 7 (mGluR 7). Here, we further characterized the core CaM and Gbetagamma binding sequences. In contrast to a previous report, we find that the CaM binding motif localized in the N-terminal region of the cytoplasmic tail domain of mGluR 7 is conserved in the related group III mGluRs 4A and 8 and allows these receptors to also bind Ca(2+)/CaM. Mutational analysis of the Ca(2+)/CaM binding motif is consistent with group III receptors containing a conventional CaM binding site formed by an amphipathic alpha-helix. Substitutions adjacent to the core CaM target sequence selectively prevent Gbetagamma binding, suggesting that the CaM-dependent regulation of signal transduction involves determinants that overlap with but are different from those mediating Gbetagamma recruitment. In addition, we present evidence that Gbetagamma uses distinct nonoverlapping interfaces for interaction with the mGluR 7 C-terminal tail and the effector enzyme adenylyl cyclase II, respectively. Although Gbetagamma-mediated signaling is abolished in receptors lacking the core CaM binding sequence, alpha subunit activation, as assayed by agonist-dependent GTPgammaS binding, was not affected. This suggests that Ca(2+)/CaM may alter the mode of group III mGluR signaling from mono- (alpha) to bidirectional (alpha and betagamma) activation of downstream effector cascades.
Collapse
Affiliation(s)
- O El Far
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, Frankfurt 60528, Germany
| | | | | | | | | | | | | | | |
Collapse
|
41
|
Cai Z, Saugstad JA, Sorensen SD, Ciombor KJ, Zhang C, Schaffhauser H, Hubalek F, Pohl J, Duvoisin RM, Conn PJ. Cyclic AMP-dependent protein kinase phosphorylates group III metabotropic glutamate receptors and inhibits their function as presynaptic receptors. J Neurochem 2001; 78:756-66. [PMID: 11520896 PMCID: PMC3799790 DOI: 10.1046/j.1471-4159.2001.00468.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent evidence suggests that the functions of presynaptic metabotropic glutamate receptors (mGluRs) are tightly regulated by protein kinases. We previously reported that cAMP-dependent protein kinase (PKA) directly phosphorylates mGluR2 at a single serine residue (Ser843) on the C-terminal tail region of the receptor, and that phosphorylation of this site inhibits coupling of mGluR2 to GTP-binding proteins. This may be the mechanism by which the adenylyl cyclase activator forskolin inhibits presynaptic mGluR2 function at the medial perforant path-dentate gyrus synapse. We now report that PKA also directly phosphorylates several group III mGluRs (mGluR4a, mGluR7a, and mGluR8a), as well as mGluR3 at single conserved serine residues on their C-terminal tails. Furthermore, activation of PKA by forskolin inhibits group III mGluR-mediated responses at glutamatergic synapses in the hippocampus. Interestingly, beta-adrenergic receptor activation was found to mimic the inhibitory effect of forskolin on both group II and III mGluRs. These data suggest that a common PKA-dependent mechanism may be involved in regulating the function of multiple presynaptic group II and group III mGluRs. Such regulation is not limited to the pharmacological activation of adenylyl cyclase but can also be elicited by the stimulation of endogenous G(s)-coupled receptors, such as beta-adrenergic receptors.
Collapse
Affiliation(s)
- Zhaohui Cai
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Julie A. Saugstad
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Scott D. Sorensen
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Kelly J. Ciombor
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Congxiao Zhang
- Dyson Vision Research Institute, Weill Medical College, Cornell University, New York, USA
| | - Hervé Schaffhauser
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Frantisek Hubalek
- Microchemical Facilities, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Jan Pohl
- Microchemical Facilities, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Robert M. Duvoisin
- Dyson Vision Research Institute, Weill Medical College, Cornell University, New York, USA
| | - P. Jeffrey Conn
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA
- Department of Neuroscience, Merck Research Laboratories, West Point, Philadelphia, USA
| |
Collapse
|