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Díaz-Rodríguez SM, Ivorra I, Espinosa J, Vegar C, Herrero-Turrión MJ, López DE, Gómez-Nieto R, Alberola-Die A. Enhanced Membrane Incorporation of H289Y Mutant GluK1 Receptors from the Audiogenic Seizure-Prone GASH/Sal Model: Functional and Morphological Impacts on Xenopus Oocytes. Int J Mol Sci 2023; 24:16852. [PMID: 38069190 PMCID: PMC10706347 DOI: 10.3390/ijms242316852] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 11/21/2023] [Accepted: 11/23/2023] [Indexed: 12/18/2023] Open
Abstract
Epilepsy is a neurological disorder characterized by abnormal neuronal excitability, with glutamate playing a key role as the predominant excitatory neurotransmitter involved in seizures. Animal models of epilepsy are crucial in advancing epilepsy research by faithfully replicating the diverse symptoms of this disorder. In particular, the GASH/Sal (genetically audiogenic seizure-prone hamster from Salamanca) model exhibits seizures resembling human generalized tonic-clonic convulsions. A single nucleotide polymorphism (SNP; C9586732T, p.His289Tyr) in the Grik1 gene (which encodes the kainate receptor GluK1) has been previously identified in this strain. The H289Y mutation affects the amino-terminal domain of GluK1, which is related to the subunit assembly and trafficking. We used confocal microscopy in Xenopus oocytes to investigate how the H289Y mutation, compared to the wild type (WT), affects the expression and cell-surface trafficking of GluK1 receptors. Additionally, we employed the two-electrode voltage-clamp technique to examine the functional effects of the H289Y mutation. Our results indicate that this mutation increases the expression and incorporation of GluK1 receptors into an oocyte's membrane, enhancing kainate-evoked currents, without affecting their functional properties. Although further research is needed to fully understand the molecular mechanisms responsible for this epilepsy, the H289Y mutation in GluK1 may be part of the molecular basis underlying the seizure-prone circuitry in the GASH/Sal model.
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Affiliation(s)
- Sandra M. Díaz-Rodríguez
- Neuroscience Institute of Castilla y León (INCyL), University of Salamanca, E-37007 Salamanca, Spain; (S.M.D.-R.); (M.J.H.-T.); (R.G.-N.)
- Institute of Biomedical Research of Salamanca (IBSAL), E-37007 Salamanca, Spain
| | - Isabel Ivorra
- Department of Physiology, Genetics and Microbiology, University of Alicante, E-03690 Alicante, Spain; (I.I.); (J.E.); (C.V.); (A.A.-D.)
| | - Javier Espinosa
- Department of Physiology, Genetics and Microbiology, University of Alicante, E-03690 Alicante, Spain; (I.I.); (J.E.); (C.V.); (A.A.-D.)
| | - Celia Vegar
- Department of Physiology, Genetics and Microbiology, University of Alicante, E-03690 Alicante, Spain; (I.I.); (J.E.); (C.V.); (A.A.-D.)
| | - M. Javier Herrero-Turrión
- Neuroscience Institute of Castilla y León (INCyL), University of Salamanca, E-37007 Salamanca, Spain; (S.M.D.-R.); (M.J.H.-T.); (R.G.-N.)
- Institute of Biomedical Research of Salamanca (IBSAL), E-37007 Salamanca, Spain
- Neurological Tissue Bank INCYL (BTN-INCYL), University of Salamanca, E-37007 Salamanca, Spain
| | - Dolores E. López
- Neuroscience Institute of Castilla y León (INCyL), University of Salamanca, E-37007 Salamanca, Spain; (S.M.D.-R.); (M.J.H.-T.); (R.G.-N.)
- Institute of Biomedical Research of Salamanca (IBSAL), E-37007 Salamanca, Spain
| | - Ricardo Gómez-Nieto
- Neuroscience Institute of Castilla y León (INCyL), University of Salamanca, E-37007 Salamanca, Spain; (S.M.D.-R.); (M.J.H.-T.); (R.G.-N.)
- Institute of Biomedical Research of Salamanca (IBSAL), E-37007 Salamanca, Spain
| | - Armando Alberola-Die
- Department of Physiology, Genetics and Microbiology, University of Alicante, E-03690 Alicante, Spain; (I.I.); (J.E.); (C.V.); (A.A.-D.)
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2
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Wu D, Xu L, Cai WM, Zhan SY, Wan G, Xu Y, Shi YS. A splicing-dependent ER retention signal regulates surface expression of the mechanosensitive TMEM63B cation channel. J Biol Chem 2022; 299:102781. [PMID: 36496074 PMCID: PMC9830214 DOI: 10.1016/j.jbc.2022.102781] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 11/25/2022] [Accepted: 11/29/2022] [Indexed: 12/12/2022] Open
Abstract
TMEM63B is a mechanosensitive cation channel activated by hypoosmotic stress and mechanic stimulation. We recently reported a brain-specific alternative splicing of exon 4 in TMEM63B. The short variant lacking exon 4, which constitutes the major isoform in the brain, exhibits enhanced responses to hypoosmotic stimulation compared to the long isoform containing exon 4. However, the mechanisms affecting this differential response are unclear. Here, we showed that the short isoform exhibited stronger cell surface expression compared to the long variant. Using mutagenesis screening of the coding sequence of exon 4, we identified an RXR-type endoplasmic reticulum (ER) retention signal (RER). We found that this motif was responsible for binding to the COPI retrieval vesicles, such that the longer TMEM63B isoforms were more likely to be retrotranslocated to the ER than the short isoforms. In addition, we demonstrated long TMEM63Bs could form heterodimers with short isoforms and reduce their surface expression. Taken together, our findings revealed an ER retention signal in the alternative splicing domain of TMEM63B that regulates the surface expression of TMEM63B protein and channel function.
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Affiliation(s)
- Dan Wu
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China; Guangdong Institute of Intelligence Science and Technology, Zhuhai, China
| | - Lushan Xu
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China; Clinical College of Traditional Chinese and Western Medicine, Nanjing University of Chinese Medicine, Nanjing, China
| | - Wen-Min Cai
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China
| | - Shi-Yu Zhan
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China
| | - Guoqiang Wan
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China; Institute for Brain Sciences, Nanjing University, Nanjing, China
| | - Yun Xu
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China; Institute for Brain Sciences, Nanjing University, Nanjing, China.
| | - Yun Stone Shi
- Department of Neurology, Drum Tower Hospital, Ministry of Education Key -Laboratory of Model Animal for Disease Study, Model Animal Research Center, Jiangsu Key Laboratory of Molecular Medicine, Medical School, Nanjing University, Nanjing, China; Guangdong Institute of Intelligence Science and Technology, Zhuhai, China; Institute for Brain Sciences, Nanjing University, Nanjing, China.
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3
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Biomarker Discovery for Meta-Classification of Melanoma Metastatic Progression Using Transfer Learning. Genes (Basel) 2022; 13:genes13122303. [PMID: 36553569 PMCID: PMC9777873 DOI: 10.3390/genes13122303] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 12/02/2022] [Indexed: 12/12/2022] Open
Abstract
Melanoma is considered to be the most serious and aggressive type of skin cancer, and metastasis appears to be the most important factor in its prognosis. Herein, we developed a transfer learning-based biomarker discovery model that could aid in the diagnosis and prognosis of this disease. After applying it to the ensemble machine learning model, results revealed that the genes found were consistent with those found using other methodologies previously applied to the same TCGA (The Cancer Genome Atlas) data set. Further novel biomarkers were also found. Our ensemble model achieved an AUC of 0.9861, an accuracy of 91.05, and an F1 score of 90.60 using an independent validation data set. This study was able to identify potential genes for diagnostic classification (C7 and GRIK5) and diagnostic and prognostic biomarkers (S100A7, S100A7, KRT14, KRT17, KRT6B, KRTDAP, SERPINB4, TSHR, PVRL4, WFDC5, IL20RB) in melanoma. The results show the utility of a transfer learning approach for biomarker discovery in melanoma.
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Khanra N, Brown PMGE, Perozzo AM, Bowie D, Meyerson JR. Architecture and structural dynamics of the heteromeric GluK2/K5 kainate receptor. eLife 2021; 10:e66097. [PMID: 33724189 PMCID: PMC7997659 DOI: 10.7554/elife.66097] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 03/05/2021] [Indexed: 12/15/2022] Open
Abstract
Kainate receptors (KARs) are L-glutamate-gated ion channels that regulate synaptic transmission and modulate neuronal circuits. KARs have strict assembly rules and primarily function as heteromeric receptors in the brain. A longstanding question is how KAR heteromer subunits organize and coordinate together to fulfill their signature physiological roles. Here we report structures of the GluK2/GluK5 heteromer in apo, antagonist-bound, and desensitized states. The receptor assembles with two copies of each subunit, ligand binding domains arranged as two heterodimers and GluK5 subunits proximal to the channel. Strikingly, during desensitization, GluK2, but not GluK5, subunits undergo major structural rearrangements to facilitate channel closure. We show how the large conformational differences between antagonist-bound and desensitized states are mediated by the linkers connecting the pore helices to the ligand binding domains. This work presents the first KAR heteromer structure, reveals how its subunits are organized, and resolves how the heteromer can accommodate functionally distinct closed channel structures.
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Affiliation(s)
- Nandish Khanra
- Department of Physiology and Biophysics, Weill Cornell Medical CollegeNew YorkUnited States
| | - Patricia MGE Brown
- Department of Pharmacology and Therapeutics, McGill UniversityMontréalCanada
| | - Amanda M Perozzo
- Department of Pharmacology and Therapeutics, McGill UniversityMontréalCanada
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill UniversityMontréalCanada
| | - Joel R Meyerson
- Department of Physiology and Biophysics, Weill Cornell Medical CollegeNew YorkUnited States
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Litwin DB, Paudyal N, Carrillo E, Berka V, Jayaraman V. The structural arrangement and dynamics of the heteromeric GluK2/GluK5 kainate receptor as determined by smFRET. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2020; 1862:183001. [PMID: 31194959 PMCID: PMC6899175 DOI: 10.1016/j.bbamem.2019.05.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 05/14/2019] [Accepted: 05/31/2019] [Indexed: 01/08/2023]
Abstract
Kainate receptors, which are glutamate activated excitatory neurotransmitter receptors, predominantly exist as heteromers of GluK2 and GluK5 subunits in the mammalian central nervous system. There are currently no structures of the full-length heteromeric kainate receptors. Here, we have used single molecule FRET to determine the specific arrangement of the GluK2 and GluK5 subunits within the dimer of dimers configuration in a full-length receptor. Additionally, we have also studied the dynamics and conformational heterogeneity of the amino-terminal and agonist-binding domain interfaces associated with the resting and desensitized states of the full-length heteromeric kainate receptor using FRET-based methods. The smFRET data are compared to similar experiments performed on the homomeric kainate receptor to provide insight into the differences in conformational dynamics that distinguish the two functionally. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.
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Affiliation(s)
- Douglas B Litwin
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA; MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Nabina Paudyal
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA; MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Elisa Carrillo
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Vladimir Berka
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Vasanthi Jayaraman
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
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Hong X, Jeyifous O, Ronilo M, Marshall J, Green WN, Standley S. A novel function for the ER retention signals in the C-terminus of kainate receptor subunit, GluK5. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2018; 1866:459-473. [PMID: 30339823 DOI: 10.1016/j.bbamcr.2018.10.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Revised: 10/10/2018] [Accepted: 10/11/2018] [Indexed: 11/30/2022]
Abstract
Classically, endoplasmic reticulum (ER) retention signals in secreted integral membrane proteins impose the requirement to assemble with other cognate subunits to form functional assemblies before they can exit the ER. We report that GluK5 has two ER retention signals in its cytoplasmic C-terminus: an arginine-based signal and a di-leucine motif previously thought to be an endocytic motif. GluK5 assembles with GluK2, but surprisingly GluK2 association does little to block the ER retention signals. We find instead that the ER retention signals are blocked by two proteins involved in intracellular trafficking, SAP97 and CASK. We show that SAP97, in the presence of CASK and the receptor complex, assumes an extended conformation. In the extended conformation, SAP97 makes its SH3 and GuK domains available to bind and sterically mask the ER retention signals in the GluK5 C-terminus. SAP97 and CASK are also necessary for sorting receptor cargoes into the local dendritic secretory pathway in neurons. We show that the ER retention signals of GluK5 play a vital role in sorting the receptor complex in the local dendritic secretory pathway in neurons. These data suggest a new role for ER retention signals in trafficking integral membrane proteins in neurons. SIGNIFICANCE: We present evidence that the ER retention signals in the kainate receptors containing GluK5 impose a requirement for sorting into local dendritic secretory pathways in neurons, as opposed to traversing the somatic Golgi apparatus. There are two ER retention signals in the C-terminus of GluK5. We show that both are blocked by physical association with SAP97 and CASK. The SH3 and GuK domains of SAP97, in the presence of CASK, bind directly to each ER retention signal and form a complex. These results support an entirely new function for ER retention signals in the C-termini of neuronal receptors, such as NMDA and kainate receptors, and define a mechanism for selective entry of receptors into local secretory pathways.
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Affiliation(s)
- Xiaoqi Hong
- Graduate College of Biomedical Sciences, Western University of Health Sciences, Pomona, CA 91711, United States of America
| | - Okunola Jeyifous
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, United States of America
| | - Mason Ronilo
- Graduate College of Biomedical Sciences, Western University of Health Sciences, Pomona, CA 91711, United States of America
| | - John Marshall
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, RI 02912, United States of America
| | - William N Green
- Department of Neurobiology, University of Chicago, Chicago, IL 60637, United States of America
| | - Steve Standley
- Graduate College of Biomedical Sciences, Western University of Health Sciences, Pomona, CA 91711, United States of America.
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Scholefield CL, Atlason PT, Jane DE, Molnár E. Assembly and Trafficking of Homomeric and Heteromeric Kainate Receptors with Impaired Ligand Binding Sites. Neurochem Res 2018; 44:585-599. [PMID: 30302614 PMCID: PMC6420462 DOI: 10.1007/s11064-018-2654-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 09/27/2018] [Accepted: 10/01/2018] [Indexed: 10/28/2022]
Abstract
Kainate receptors (KARs) are a subfamily of ionotropic glutamate receptors (iGluRs) mediating excitatory synaptic transmission. Cell surface expressed KARs modulate the excitability of neuronal networks. The transfer of iGluRs from the endoplasmic reticulum (ER) to the cell surface requires occupation of the agonist binding sites. Here we used molecular modelling to produce a range of ligand binding domain (LBD) point mutants of GluK1-3 KAR subunits with and without altered agonist efficacy to further investigate the role of glutamate binding in surface trafficking and activation of homomeric and heteromeric KARs using endoglycosidase digestion, cell surface biotinylation and imaging of changes in intracellular Ca2+ concentration [Ca2+]i. Mutations of conserved amino acid residues in the LBD that disrupt agonist binding to GluK1-3 (GluK1-T675V, GluK2-A487L, GluK2-T659V and GluK3-T661V) reduced both the total expression levels and cell surface delivery of all of these mutant subunits compared to the corresponding wild type in transiently transfected human embryonic kidney 293 (HEK293) cells. In contrast, the exchange of non-conserved residues in the LBD that convert antagonist selectivity of GluK1-3 (GluK1-T503A, GluK2-A487T, GluK3-T489A, GluK1-N705S/S706N, GluK2-S689N/N690S, GluK3-N691S) did not alter the biosynthesis and trafficking of subunit proteins. Co-assembly of mutant GluK2 with an impaired LBD and wild type GluK5 subunits enables the cell surface expression of both subunits. However, [Ca2+]i imaging indicates that the occupancy of both GluK2 and GluK5 LBDs is required for the full activation of GluK2/GluK5 heteromeric KAR channels.
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Affiliation(s)
- Caroline L Scholefield
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Palmi T Atlason
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - David E Jane
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Elek Molnár
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK.
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Lomash RM, Sheng N, Li Y, Nicoll RA, Roche KW. Phosphorylation of the kainate receptor (KAR) auxiliary subunit Neto2 at serine 409 regulates synaptic targeting of the KAR subunit GluK1. J Biol Chem 2017; 292:15369-15377. [PMID: 28717010 DOI: 10.1074/jbc.m117.787903] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 07/09/2017] [Indexed: 11/06/2022] Open
Abstract
Synaptic strength at excitatory synapses is determined by the presence of glutamate receptors (i.e. AMPA, NMDA, and kainate receptors) at the synapse. Synaptic strength is modulated by multiple factors including assembly of different receptor subunits, interaction with auxiliary subunits, and post-translational modifications of either the receptors or their auxiliary subunits. Using mass spectrometry, we found that the intracellular region of neuropilin and tolloid-like proteins (Neto) 1 and Neto2, the auxiliary subunits of kainate receptor (KARs), are phosphorylated by multiple kinases in vitro Specifically, Neto2 was phosphorylated at serine 409 (Ser-409) by Ca2+/calmodulin-dependent protein kinase II (CaMKII) and protein kinase A (PKA) both in vitro and in heterologous cells. Interestingly, we observed a substantial increase in Neto2 Ser-409 phosphorylation in the presence of CaMKII, and this phosphorylation was reduced in the presence of the KAR subunit GluK1 or GluK2. We also found endogenous phosphorylation of Neto2 at Ser-409 in the brain. Moreover, Neto2 Ser-409 phosphorylation inhibited synaptic targeting of GluK1 because, unlike WT Neto2 and the phosphodeficient mutant Neto2 S409A, the Neto2 S409D phosphomimetic mutant impeded GluK1 trafficking to synapses. These results support a molecular mechanism by which Neto2 phosphorylation at Ser-409 helps restrict GluK1 targeting to the synapse.
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Affiliation(s)
| | - Nengyin Sheng
- Departments of Cellular and Molecular Pharmacology and
| | - Yan Li
- Protein/Peptide Sequencing Facility, NINDS, National Institutes of Health, Bethesda, Maryland 20892 and
| | - Roger A Nicoll
- Departments of Cellular and Molecular Pharmacology and.,Physiology, University of California, San Francisco, California 94143
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Watanabe-Iida I, Konno K, Akashi K, Abe M, Natsume R, Watanabe M, Sakimura K. Determination of kainate receptor subunit ratios in mouse brain using novel chimeric protein standards. J Neurochem 2015; 136:295-305. [DOI: 10.1111/jnc.13384] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 09/04/2015] [Accepted: 10/01/2015] [Indexed: 12/01/2022]
Affiliation(s)
- Izumi Watanabe-Iida
- Department of Cellular Neurobiology; Brain Research Institute; Niigata University; Niigata Japan
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
| | - Kohtarou Konno
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
- Department of Anatomy; Hokkaido University School of Medicine; Sapporo Japan
| | - Kaori Akashi
- Department of Cellular Neurobiology; Brain Research Institute; Niigata University; Niigata Japan
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
| | - Manabu Abe
- Department of Cellular Neurobiology; Brain Research Institute; Niigata University; Niigata Japan
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
| | - Rie Natsume
- Department of Cellular Neurobiology; Brain Research Institute; Niigata University; Niigata Japan
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
| | - Masahiko Watanabe
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
- Department of Anatomy; Hokkaido University School of Medicine; Sapporo Japan
| | - Kenji Sakimura
- Department of Cellular Neurobiology; Brain Research Institute; Niigata University; Niigata Japan
- CREST; Japan Science and Technology Agency; Chiyoda-ku Japan
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SAP97 blocks the RXR ER retention signal of NMDA receptor subunit GluN1-3 through its SH3 domain. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:489-99. [PMID: 25499266 DOI: 10.1016/j.bbamcr.2014.11.030] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 11/14/2014] [Accepted: 11/30/2014] [Indexed: 11/21/2022]
Abstract
SAP97 is directly involved in exporting NMDA receptors with a specific subunit composition from the endoplasmic reticulum (ER). Characterization of the interactions between SAP97 and an NMDA receptor splice variant, GluN1-3, and of the effects on forward trafficking revealed that an ER-level interaction blocked the RXR ER-retention motif in the GluN1-3 cytoplasmic C-terminus in the context of both reporter molecules and full-length receptors. Binding of SAP97 to the PDZ-binding domain of GluN1-3 was required, but the blockade of ER-retention was mediated by the SH3-GuK domains coupled with the action of the N-terminus of SAP97. While other domains of SAP97 were involved in forward trafficking of GluN1-3 out of the ER, the SH3 domain was necessary and sufficient to block the ER retention. This is the first direct evidence for the masking of ER-retention signals by PDZ domain-containing proteins, and provides detailed underlying mechanistic requirements. Such a mechanism could be central to modulating the ER exit of receptors into local, non-conventional or conventional, secretory pathways in neurons.
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11
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Pahl S, Tapken D, Haering SC, Hollmann M. Trafficking of kainate receptors. MEMBRANES 2014; 4:565-95. [PMID: 25141211 PMCID: PMC4194049 DOI: 10.3390/membranes4030565] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2014] [Revised: 08/04/2014] [Accepted: 08/12/2014] [Indexed: 11/17/2022]
Abstract
Ionotropic glutamate receptors (iGluRs) mediate the vast majority of excitatory neurotransmission in the central nervous system of vertebrates. In the protein family of iGluRs, kainate receptors (KARs) comprise the probably least well understood receptor class. Although KARs act as key players in the regulation of synaptic network activity, many properties and functions of these proteins remain elusive until now. Especially the precise pre-, extra-, and postsynaptic localization of KARs plays a critical role for neuronal function, as an unbalanced localization of KARs would ultimately lead to dysregulated neuronal excitability. Recently, important advances in the understanding of the regulation of surface expression, function, and agonist-dependent endocytosis of KARs have been achieved. Post-translational modifications like PKC-mediated phosphorylation and SUMOylation have been reported to critically influence surface expression and endocytosis, while newly discovered auxiliary proteins were shown to shape the functional properties of KARs.
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Affiliation(s)
- Steffen Pahl
- Department of Biochemistry I, Ruhr University Bochum, Universitätsstr. 150, 44780 Bochum, Germany.
| | - Daniel Tapken
- Department of Biochemistry I, Ruhr University Bochum, Universitätsstr. 150, 44780 Bochum, Germany.
| | - Simon C Haering
- Department of Biochemistry I, Ruhr University Bochum, Universitätsstr. 150, 44780 Bochum, Germany.
| | - Michael Hollmann
- Department of Biochemistry I, Ruhr University Bochum, Universitätsstr. 150, 44780 Bochum, Germany.
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12
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Davies MN, Volta M, Pidsley R, Lunnon K, Dixit A, Lovestone S, Coarfa C, Harris RA, Milosavljevic A, Troakes C, Al-Sarraj S, Dobson R, Schalkwyk LC, Mill J. Functional annotation of the human brain methylome identifies tissue-specific epigenetic variation across brain and blood. Genome Biol 2012; 13:R43. [PMID: 22703893 PMCID: PMC3446315 DOI: 10.1186/gb-2012-13-6-r43] [Citation(s) in RCA: 498] [Impact Index Per Article: 41.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2012] [Revised: 05/21/2012] [Accepted: 06/15/2012] [Indexed: 01/13/2023] Open
Abstract
Background Dynamic changes to the epigenome play a critical role in establishing and maintaining cellular phenotype during differentiation, but little is known about the normal methylomic differences that occur between functionally distinct areas of the brain. We characterized intra- and inter-individual methylomic variation across whole blood and multiple regions of the brain from multiple donors. Results Distinct tissue-specific patterns of DNA methylation were identified, with a highly significant over-representation of tissue-specific differentially methylated regions (TS-DMRs) observed at intragenic CpG islands and low CG density promoters. A large proportion of TS-DMRs were located near genes that are differentially expressed across brain regions. TS-DMRs were significantly enriched near genes involved in functional pathways related to neurodevelopment and neuronal differentiation, including BDNF, BMP4, CACNA1A, CACA1AF, EOMES, NGFR, NUMBL, PCDH9, SLIT1, SLITRK1 and SHANK3. Although between-tissue variation in DNA methylation was found to greatly exceed between-individual differences within any one tissue, we found that some inter-individual variation was reflected across brain and blood, indicating that peripheral tissues may have some utility in epidemiological studies of complex neurobiological phenotypes. Conclusions This study reinforces the importance of DNA methylation in regulating cellular phenotype across tissues, and highlights genomic patterns of epigenetic variation across functionally distinct regions of the brain, providing a resource for the epigenetics and neuroscience research communities.
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Affiliation(s)
- Matthew N Davies
- Institute of Psychiatry, King's College London, De Crespigny Park, London, UK
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13
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Abstract
Ionotropic glutamate receptors assemble as homo- or heterotetramers. One well-studied heteromeric complex is formed by the kainate receptor subunits GluK2 and GluK5. Retention motifs prevent trafficking of GluK5 homomers to the plasma membrane, but coassembly with GluK2 yields functional heteromeric receptors. Additional control over GluK2/GluK5 assembly seems to be exerted by the aminoterminal domains, which preferentially assemble into heterodimers as isolated domains. However,the stoichiometry of the full-length GluK2/GluK5 receptor complex has yet to be determined, as is the case for all non-NMDA glutamate receptors. Here, we address this question, using a single-molecule imaging technique that enables direct counting of the number of each GluK subunit type in homomeric and heteromeric receptors in the plasma membranes of live cells. We show that GluK2 and GluK5 assemble with 2:2 stoichiometry. This is an important step toward understanding the assembly mechanism, architecture, and functional consequences of heteromer formation in ionotropic glutamate receptors.
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Affiliation(s)
- Andreas Reiner
- Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, California 94720
| | - Ryan J. Arant
- Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, California 94720
| | - Ehud Y. Isacoff
- Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, California 94720
- Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
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14
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González-González IM, Konopacki FA, Rocca DL, Doherty AJ, Jaafari N, Wilkinson KA, Henley JM. Kainate receptor trafficking. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/wmts.23] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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15
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Huyghe D, Veran J, Labrousse VF, Perrais D, Mulle C, Coussen F. Endocytosis of the glutamate receptor subunit GluK3 controls polarized trafficking. J Neurosci 2011; 31:11645-54. [PMID: 21832194 PMCID: PMC6623111 DOI: 10.1523/jneurosci.2206-11.2011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 06/16/2011] [Accepted: 06/16/2011] [Indexed: 11/21/2022] Open
Abstract
Kainate receptors (KARs) are widely expressed in the brain and are present at both presynaptic and postsynaptic sites. GluK3-containing KARs are thought to compose presynaptic autoreceptors that facilitate hippocampal mossy fiber synaptic transmission. Here we identify molecular mechanisms that underlie the polarized trafficking of KARs composed of the GluK3b splice variant. Endocytosis followed by degradation is driven by a dileucine motif on the cytoplasmic C-terminal domain of GluK3b in heterologous cells, in cultured hippocampal neurons, and in dentate granule cells from organotypic slice cultures. The internalization of GluK3b is clathrin and dynamin2 dependent. GluK3b is differentially endocytosed in dendrites as compared to the axons. These data suggest that the polarized trafficking of KARs in neurons could be controlled by the regulation of receptor endocytosis.
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Affiliation(s)
- Deborah Huyghe
- University of Bordeaux, Interdisciplinary Institute for Neuroscience, and
- CNRS UMR 5297, F-33000 Bordeaux, France
| | - Julien Veran
- University of Bordeaux, Interdisciplinary Institute for Neuroscience, and
- CNRS UMR 5297, F-33000 Bordeaux, France
| | - Virginie F. Labrousse
- University of Bordeaux, Interdisciplinary Institute for Neuroscience, and
- CNRS UMR 5297, F-33000 Bordeaux, France
| | - David Perrais
- University of Bordeaux, Interdisciplinary Institute for Neuroscience, and
- CNRS UMR 5297, F-33000 Bordeaux, France
| | - Christophe Mulle
- University of Bordeaux, Interdisciplinary Institute for Neuroscience, and
- CNRS UMR 5297, F-33000 Bordeaux, France
| | - Françoise Coussen
- University of Bordeaux, Interdisciplinary Institute for Neuroscience, and
- CNRS UMR 5297, F-33000 Bordeaux, France
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16
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Nasu-Nishimura Y, Jaffe H, Isaac JTR, Roche KW. Differential regulation of kainate receptor trafficking by phosphorylation of distinct sites on GluR6. J Biol Chem 2010; 285:2847-56. [PMID: 19920140 PMCID: PMC2807338 DOI: 10.1074/jbc.m109.081141] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2009] [Indexed: 11/06/2022] Open
Abstract
Kainate receptors are widely expressed in the brain, and are present at pre- and postsynaptic sites where they play a prominent role in synaptic plasticity and the regulation of network activity. Within individual neurons, kainate receptors of different subunit compositions are targeted to various locations where they serve distinct functional roles. Despite this complex targeting, relatively little is known about the molecular mechanisms regulating kainate receptor subunit trafficking. Here we investigate the role of phosphorylation in the trafficking of the GluR6 kainate receptor subunit. We identify two specific residues on the GluR6 C terminus, Ser(846) and Ser(868), which are phosphorylated by protein kinase C (PKC) and dramatically regulate GluR6 surface expression. By using GluR6 containing phosphomimetic and nonphosphorylatable mutations for these sites expressed in heterologous cells or in neurons lacking endogenous GluR6, we show that phosphorylation of Ser(846) or Ser(868) regulates receptor trafficking through the biosynthetic pathway. Additionally, Ser(846) phosphorylation dynamically regulates endocytosis of GluR6 at the plasma membrane. Our findings thus demonstrate that phosphorylation of PKC sites on GluR6 regulates surface expression of GluR6 at distinct intracellular trafficking pathways, providing potential molecular mechanisms for the PKC-dependent regulation of synaptic kainate receptor function observed during various forms of synaptic plasticity.
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Affiliation(s)
| | - Howard Jaffe
- From NINDS, National Institutes of Health, Bethesda, Maryland 20892
| | - John T. R. Isaac
- From NINDS, National Institutes of Health, Bethesda, Maryland 20892
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17
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UBXD4, a UBX-containing protein, regulates the cell surface number and stability of alpha3-containing nicotinic acetylcholine receptors. J Neurosci 2009; 29:6883-96. [PMID: 19474315 DOI: 10.1523/jneurosci.4723-08.2009] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Adaptor proteins are likely to modulate spatially and temporally the trafficking of a number of membrane proteins, including neuronal nicotinic acetylcholine receptors (nAChRs). A yeast two-hybrid screen identified a novel UBX-containing protein, UBXD4, as one of the cytosolic proteins that interact directly with the alpha3 and alpha4 nAChR subunits. The function of UBX-containing proteins is largely unknown. Immunoprecipitation and confocal microscopy confirmed the interaction of UBXD4 with alpha3-containing nAChRs (alpha3* nAChRs) expressed in HEK293 cells, PC12 cells, and rat cortical neurons. Overexpression of UBXD4 in differentiated PC12 cells (dPC12) increased nAChR cell surface expression, especially that of the alpha3beta2 subtype. These findings were corroborated by electrophysiology, immunofluorescent staining, and biotinylation of surface receptors. Silencing of UBXD4 led to a significant reduction of alpha3* nAChRs in rat cortical neurons and dPC12 cells. Biochemical and immunofluorescence studies of endogenous UBXD4 showed that the protein is located in both the ER and cis-Golgi compartments. Our investigations also showed that the alpha3 subunit is ubiquitinated and that UBXD4 can interfere with its ubiquitination and consequent degradation by the proteasome. Our data suggest that UBXD4 modulates the distribution of alpha3* nAChRs between specialized intracellular compartments and the plasma membrane. This effect is achieved by controlling the stability of the alpha3 subunit and, consequently, the number of receptors at the cell surface.
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18
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Coussen F. Molecular determinants of kainate receptor trafficking. Neuroscience 2008; 158:25-35. [PMID: 18358623 DOI: 10.1016/j.neuroscience.2007.12.052] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2007] [Revised: 12/21/2007] [Accepted: 12/26/2007] [Indexed: 11/19/2022]
Abstract
Glutamate receptors of the kainate subtype are ionotropic receptors that play a key role in the modulation of neuronal network activity. The role of kainate receptors depends on their precise membrane and subcellular localization in presynaptic, extrasynaptic and postsynaptic domains. These receptors are composed of the combination of five subunits, three of them having several splice variants. The subunits and splice variants show great divergence in their C-terminal cytoplasmic tail domains, which have been implicated in intracellular trafficking of homomeric and heteromeric receptors. Differential trafficking of kainate receptors to specific neuronal compartments likely relies on interactions between the different kainate receptor subunits with distinct subsets of protein partners that interact with C-terminal domains. These C-terminal domains have also been implicated in the degradation of kainate receptors. Finally, the phosphorylation of the C-terminal domain regulates receptor trafficking and function. This review summarizes our knowledge on the regulation of membrane delivery and trafficking of kainate receptors implicating C-terminal domains of the different isoforms and focuses on the identification and characterization of the function of interacting partners.
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Affiliation(s)
- F Coussen
- CNRS UMR 5091, Laboratoire "Physiologie Cellulaire de la Synapse," Bordeaux Neuroscience Institute, University of Bordeaux 2, Bordeaux, France.
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19
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Coleman SK, Möykkynen T, Cai C, von Ossowski L, Kuismanen E, Korpi ER, Keinänen K. Isoform-specific early trafficking of AMPA receptor flip and flop variants. J Neurosci 2006; 26:11220-9. [PMID: 17065461 PMCID: PMC6674648 DOI: 10.1523/jneurosci.2301-06.2006] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Flip and flop splice variants of AMPA receptor subunits are expressed in distinct but partly overlapping patterns and impart different desensitization kinetics to cognate receptor channels. In the absence of specific antibodies, isoform-specific differences in trafficking or localization of native flip and flop subunits remain uncharacterized. We report that in several transfected cell lines, transport of homomeric glutamate receptor (GluR)-D(flop) receptors is largely blocked at the endoplasmic reticulum (ER) exit, whereas GluR-D(flip) undergoes complex glycosylation and reaches the plasma membrane at >10x higher levels than GluR-D(flop), as determined by immunofluorescence, patch-clamp recordings and biochemical assays. The transport difference between flip and flop is independent of activity, is primarily determined by amino acid residue 780 (Leu in flop, Val in flip), and is manifested even in the secretion of the soluble ligand-binding domain, suggesting it is independent of oligomerization. Coexpression with stargazin or with the flip isoform rescues the surface expression of GluR-D(flop) near to the level exhibited by GluR-D(flip). Our results demonstrate that the extracellular flip/flop region, via interactions with ER luminal splice form-specific protein(s), plays a hitherto unappreciated and important role in AMPA-receptor trafficking.
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MESH Headings
- Animals
- COS Cells
- Cells, Cultured
- Chlorocebus aethiops
- DNA, Recombinant/classification
- DNA, Recombinant/genetics
- DNA, Recombinant/metabolism
- Genetic Variation/physiology
- Humans
- Mice
- Protein Isoforms/classification
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- Protein Transport/physiology
- Rats
- Receptors, AMPA/classification
- Receptors, AMPA/genetics
- Receptors, AMPA/metabolism
- Receptors, Glutamate/classification
- Receptors, Glutamate/genetics
- Receptors, Glutamate/metabolism
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Affiliation(s)
- Sarah K. Coleman
- Department of Biological and Environmental Sciences, Division of Biochemistry, Viikki Biocenter, and
| | - Tommi Möykkynen
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, University of Helsinki, FIN-00014 Helsinki, Finland
| | - Chunlin Cai
- Department of Biological and Environmental Sciences, Division of Biochemistry, Viikki Biocenter, and
| | - Lotta von Ossowski
- Department of Biological and Environmental Sciences, Division of Biochemistry, Viikki Biocenter, and
| | - Esa Kuismanen
- Department of Biological and Environmental Sciences, Division of Biochemistry, Viikki Biocenter, and
| | - Esa R. Korpi
- Institute of Biomedicine, Pharmacology, Biomedicum Helsinki, University of Helsinki, FIN-00014 Helsinki, Finland
| | - Kari Keinänen
- Department of Biological and Environmental Sciences, Division of Biochemistry, Viikki Biocenter, and
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20
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Abstract
Kainate receptors are composed of several subunits and splice variants, but the relevance of this diversity is still not well understood. The subunits and splice variants show great divergence in their C-terminal cytoplasmic tail region, which has been identified as a region of interaction with a number of protein partners. Differential trafficking of kainate receptors to neuronal compartments is likely to rely on interactions with distinct subsets of protein partners. This review summarizes our knowledge of the regulation of trafficking of kainate receptors and focuses on the identification and characterization of functions of interacting partners.
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Affiliation(s)
- F Coussen
- CNRS UMR 5091, Laboratoire Physiologie Cellulaire de la Synapse, Bordeaux Neuroscience Institute, University of Bordeaux, 33077 Bordeaux Cedex, France
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21
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Fleck MW. Glutamate receptors and endoplasmic reticulum quality control: looking beneath the surface. Neuroscientist 2006; 12:232-44. [PMID: 16684968 DOI: 10.1177/1073858405283828] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Glutamate is the principal excitatory neurotransmitter in the mammalian central nervous system. The cellular regulation of glutamate receptor (GluR) ion channel function and expression is important for maintaining or adjusting target cell excitability to meet ever-changing demands, for example, in relation to developmental or use-dependent synaptic plasticity. Dysregulation of GluR function or expression may be a contributing factor in certain forms of epilepsy, stroke/ischemia, head trauma, cognitive impairments, and neurodegenerative disease. Recent years have seen substantial progress in understanding how GluRs operate in terms of their structural and functional properties, their synaptic targeting and membrane anchoring by PDZ-domain proteins, and their activity-dependent cycling at the plasma membrane. Yet precious little is known about the earliest events in GluR biogenesis or the mechanisms in place to ensure the GluRs that reach the cell surface are processed, folded, and oligomerized in an appropriate manner. Indeed, only a minor fraction of the GluR content of cells is expressed at any given time on the cell surface, whereas most of the remaining receptors exist in the endoplasmic reticulum (ER). The functional competence and significance of the ER fraction of receptors are presently unknown, but they are generally thought to represent immature, unassembled, or improperly assembled subunits. Some are ultimately destined for insertion in the plasma membrane. Others may be targeted for proteosomal degradation. Still others might provide a latent pool of fully functional receptors that can be recruited to enhance cell excitability in response to specific signals or under pathological conditions. This review will explore the structural and functional elements that regulate GluR assembly and export from the ER.
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Affiliation(s)
- Mark W Fleck
- Center for Neuropharmacology & Neuroscience, Albany Medical College, NY 12208, USA.
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22
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Abstract
Kainate receptors form a family of ionotropic glutamate receptors that appear to play a special role in the regulation of the activity of synaptic networks. This review first describes briefly the molecular and pharmacological properties of native and recombinant kainate receptors. It then attempts to outline the general principles that appear to govern the function of kainate receptors in the activity of synaptic networks under physiological conditions. It subsequently describes the way that kainate receptors are involved in synaptic integration, synaptic plasticity, the regulation of neurotransmitter release and the control of neuronal excitability, and the manner in which they might play an important role in synaptogenesis and synaptic maturation. These functions require the proper subcellular localization of kainate receptors in specific functional domains of the neuron, necessitating complex cellular and molecular trafficking events. We show that our comprehension of these mechanisms is just starting to emerge. Finally, this review presents evidence that implicates kainate receptors in pathophysiological conditions such as epilepsy, excitotoxicity and pain, and that shows that these receptors represent promising therapeutic targets.
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Affiliation(s)
- Paulo Pinheiro
- CNRS UMR 5091, Laboratoire "Physiologie Cellulaire de la Synapse", Bordeaux Neuroscience Institute, University of Bordeaux, 33077 Bordeaux Cedex, France
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23
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Nasu-Nishimura Y, Hurtado D, Braud S, Tang TTT, Isaac JTR, Roche KW. Identification of an endoplasmic reticulum-retention motif in an intracellular loop of the kainate receptor subunit KA2. J Neurosci 2006; 26:7014-21. [PMID: 16807331 PMCID: PMC6673909 DOI: 10.1523/jneurosci.0573-06.2006] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2006] [Revised: 05/17/2006] [Accepted: 05/18/2006] [Indexed: 11/21/2022] Open
Abstract
Neuronal kainate receptors are typically heteromeric complexes composed of GluR5-7 and KA1-2 subunits. Although GluR5-7 can exist as functional homomeric channels, the KA subunits cannot. KA2 is widely expressed in the CNS, and KA2/GluR6 heteromers are the most prevalent subunit composition in brain. Previous work has identified endoplasmic reticulum (ER)-retention motifs in the C terminus of KA2, which prevent surface expression of KA2 homomers. However, we find that, when these motifs are mutated, only a small fraction of KA2 is surface expressed. We now identify an additional ER retention motif in the intracellular loop region of KA2, which, when mutated together with the C-terminal motifs, significantly increases the level of KA2 surface expression. However, electrophysiological analysis of surface-expressed KA2 homomers indicates that they do not form functional ion channels. In heterologous cells, a large fraction of KA2 remains intracellular even when the trafficking motifs are mutated or when GluR6 is coexpressed. Therefore, we analyzed the trafficking of endogenous KA2 in vivo. We find that native KA2 surface expression is dramatically reduced in GluR6 knock-out mice compared with wild-type mice. In contrast, KA2 trafficking was unaffected in the GluR5 knock-out. Thus, our study demonstrates that trafficking motifs in both the intracellular loop and C terminus regulate KA2 surface expression; however, in neurons, GluR6 oligomerization is required for egress of KA2 from the ER and transport to the cell surface. The combination of these mechanisms likely prevents surface expression of nonfunctional KA2 homomers and ensures a high level of GluR6/KA2 heteromeric kainate receptors.
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24
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Chen BS, Braud S, Badger JD, Isaac JTR, Roche KW. Regulation of NR1/NR2C N-Methyl-D-aspartate (NMDA) Receptors by Phosphorylation*. J Biol Chem 2006; 281:16583-90. [PMID: 16606616 DOI: 10.1074/jbc.m513029200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
NR2C-containing N-methyl-D-aspartate (NMDA) receptors are highly expressed in cerebellar granule cells where they mediate the majority of current in the adult. NMDA receptors composed of NR1/NR2C exhibit a low conductance and reduced sensitivity to Mg(2+), compared with the more commonly studied NR2A- and NR2B-containing receptors. Despite these interesting features, very little is known about the regulation of NR2C function. Here we investigate the role of phosphorylation of NR2C in regulating NMDA receptor trafficking and ion channel properties. We identify a phosphorylation site, serine 1244 (Ser(1244)), near the extreme COOH terminus of NR2C, which is phosphorylated by both cAMP-dependent protein kinase and protein kinase C. This residue is located adjacent to the consensus PDZ ligand, a region that regulates protein-protein interactions and receptor trafficking in NR2A and NR2B. We show that Ser(1244) on NR2C is phosphorylated in vitro, in heterologous cells, and in neurons. Moreover, we demonstrate for the first time that NR2C interacts with the PSD-95 family of PDZ domain-containing proteins but that phosphorylation of Ser(1244) does not influence this PDZ interaction. Furthermore, Ser(1244) phosphorylation does not regulate surface expression of NR1/NR2C receptors. However, we find that this site does regulate the kinetics of the ion channel: a phosphomimetic mutation at Ser(1244) accelerates both the rise and decay of NMDA-evoked currents in excised patches from HEK-293 cells. Therefore, phosphorylation of Ser(1244) does not regulate trafficking but unexpectedly affects ion channel function, suggesting that phosphorylation of Ser(1244) on NR2C may be important in defining the functional properties of NMDA receptor-mediated currents in the cerebellum.
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Affiliation(s)
- Bo-Shiun Chen
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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25
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Jaskolski F, Coussen F, Mulle C. Subcellular localization and trafficking of kainate receptors. Trends Pharmacol Sci 2005; 26:20-6. [PMID: 15629201 DOI: 10.1016/j.tips.2004.11.008] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Glutamate receptors of the kainate type have been identified recently as key players in the modulation of neuronal-network activity. The role of kainate receptors depends on their precise subcellular localization in presynaptic, postsynaptic and extrasynaptic domains. Subcellular localization of kainate receptors has been inferred mainly from electrophysiological studies with the help of selective pharmacological tools and kainate receptor mutant mice. These studies, combined with recent ultrastructural data, highlight the diversity of subcellular localizations of kainate receptors. It is important to understand the molecular mechanisms that underlie the polarized trafficking of kainate receptors in distinct neuronal domains. In this article, we review recent data that shed light on the trafficking and membrane delivery of kainate receptor isoforms, and on the identification of proteins that interact with kainate receptors and might regulate this trafficking.
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Affiliation(s)
- Frédéric Jaskolski
- Laboratoire 'Physiologie Cellulaire de la Synapse', CNRS UMR 5091, Institut François Magendie, Université Bordeaux 2, rue C. Saint-Saëns, 33077 Bordeaux Cedex, France
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26
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Martin S, Henley JM. Activity-dependent endocytic sorting of kainate receptors to recycling or degradation pathways. EMBO J 2004; 23:4749-59. [PMID: 15549132 PMCID: PMC535095 DOI: 10.1038/sj.emboj.7600483] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2004] [Accepted: 10/22/2004] [Indexed: 11/08/2022] Open
Abstract
Kainate receptors (KARs) play important roles in the modulation of neurotransmission and plasticity, but the mechanisms that regulate their surface expression and endocytic sorting remain largely unknown. Here, we show that in cultured hippocampal neurons the surface expression of GluR6-containing KARs is dynamically regulated. Furthermore, internalized KARs are sorted into recycling or degradative pathways depending on the endocytotic stimulus. Kainate activation causes a Ca2+- and PKA-independent but PKC-dependent internalization of KARs that are targeted to lysosomes for degradation. In contrast, NMDAR activation evokes a Ca2+-, PKA- and PKC-dependent endocytosis of KARs to early endosomes with subsequent reinsertion back into the plasma membrane. These results demonstrate that GluR6-containing KARs are subject to activity-dependent endocytic sorting, a process that provides a mechanism for both rapid and chronic changes in the number of functional receptors.
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Affiliation(s)
- Stéphane Martin
- Department of Anatomy, MRC Centre for Synaptic Plasticity, School of Medical Sciences, University Walk, University of Bristol, Bristol, UK
| | - Jeremy M Henley
- Department of Anatomy, MRC Centre for Synaptic Plasticity, School of Medical Sciences, University Walk, University of Bristol, Bristol, UK
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27
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Isaac JTR, Mellor J, Hurtado D, Roche KW. Kainate receptor trafficking: physiological roles and molecular mechanisms. Pharmacol Ther 2004; 104:163-72. [PMID: 15556673 DOI: 10.1016/j.pharmthera.2004.08.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Recently, there has been intense interest in the mechanisms regulating the trafficking and synaptic targeting of kainate receptors in neurons. This topic is still in its infancy when compared with studies of trafficking of other ionotropic glutamate receptors; however, it is already clear that mechanisms exist for subunit- and splice variant-specific trafficking of kainate receptors. There is also enormous diversity of kainate receptor targeting, with the best-studied neurons in this regard being hippocampal CA3 pyramidal neurons and CA1 GABAergic interneurons. This review summarizes the current state of knowledge on this topic, focusing on the molecular mechanisms of kainate receptor trafficking and the potential for these mechanisms to regulate neuronal kainate receptor function.
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Affiliation(s)
- John T R Isaac
- National Institute for Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-3701, USA.
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