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Khvotchev M, Soloviev M. SNARE Modulators and SNARE Mimetic Peptides. Biomolecules 2022; 12:biom12121779. [PMID: 36551207 PMCID: PMC9776023 DOI: 10.3390/biom12121779] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 11/22/2022] [Accepted: 11/26/2022] [Indexed: 12/03/2022] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptor (SNARE) proteins play a central role in most forms of intracellular membrane trafficking, a key process that allows for membrane and biocargo shuffling between multiple compartments within the cell and extracellular environment. The structural organization of SNARE proteins is relatively simple, with several intrinsically disordered and folded elements (e.g., SNARE motif, N-terminal domain, transmembrane region) that interact with other SNAREs, SNARE-regulating proteins and biological membranes. In this review, we discuss recent advances in the development of functional peptides that can modify SNARE-binding interfaces and modulate SNARE function. The ability of the relatively short SNARE motif to assemble spontaneously into stable coiled coil tetrahelical bundles has inspired the development of reduced SNARE-mimetic systems that use peptides for biological membrane fusion and for making large supramolecular protein complexes. We evaluate two such systems, based on peptide-nucleic acids (PNAs) and coiled coil peptides. We also review how the self-assembly of SNARE motifs can be exploited to drive on-demand assembly of complex re-engineered polypeptides.
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Affiliation(s)
- Mikhail Khvotchev
- Department of Biochemistry, Center for Neuroscience, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
- Correspondence: (M.K.); (M.S.)
| | - Mikhail Soloviev
- Department of Biological Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
- Correspondence: (M.K.); (M.S.)
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2
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Involvement of SNARE Protein Interaction for Non-classical Release of DAMPs/Alarmins Proteins, Prothymosin Alpha and S100A13. Cell Mol Neurobiol 2020; 41:1817-1828. [PMID: 32856232 DOI: 10.1007/s10571-020-00950-y] [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: 05/15/2020] [Accepted: 08/19/2020] [Indexed: 12/30/2022]
Abstract
Prothymosin alpha (ProTα) is involved in multiple cellular processes. Upon serum-free stress, ProTα lacking a signal peptide sequence is non-classically released from C6 glioma cells as a complex with Ca2+-binding cargo protein S100A13. Thus, ProTα and S100A13 are conceived to be members of damage-associated molecular patterns (DAMPs)/alarmins. However, it remains to be determined whether stress-induced release of ProTα and S100A13 involves SNARE proteins in the mechanisms underlying membrane tethering of the multiprotein complex. In the present study, we used C6 glioma cells as a model of ProTα release. In pull-down assay, p40 synaptotagmin-1 (Syt-1), a vesicular SNARE, formed a hetero-oligomeric complex with homodimeric S100A13 in a Ca2+-dependent manner. The interaction between p40 Syt-1 and S100A13 was also Ca2+-dependent in surface plasmon resonance (SPR). Immunoprecipitation using conditioned medium (CM) revealed that p40 Syt-1 was co-released with ProTα and S100A13 upon serum-free stress. In in situ proximity ligation assay (PLA), Syt-1 interacted with S100A13 upon serum-free stress in C6 glioma cells. The intracellular delivery of anti-Syt-1 IgG blocked serum free-induced release of ProTα and S100A13. Serum free-induced ProTα-EGFP release was significantly blocked by botulinum neurotoxin/C1 (BoNT/C1), which cleaves target SNARE syntaxin-1 (Stx-1). In immunocytochemistry, the cellular loss of ProTα-EGFP, S100A13, and Syt-1 was also blocked by BoNT/C1. Furthermore, the intracellular delivery of anti-Stx-1 IgG or Stx-1 siRNA treatment blocked Syt-1, S100A13 and ProTα release from C6 glioma cells. All these findings suggest that SNARE proteins play roles in stress-induced non-classical release of DAMPs/alarmins proteins, ProTα and S100A13 from C6 glioma cells.
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Malik AR, Willnow TE. Excitatory Amino Acid Transporters in Physiology and Disorders of the Central Nervous System. Int J Mol Sci 2019; 20:ijms20225671. [PMID: 31726793 PMCID: PMC6888459 DOI: 10.3390/ijms20225671] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 11/07/2019] [Accepted: 11/11/2019] [Indexed: 12/12/2022] Open
Abstract
Excitatory amino acid transporters (EAATs) encompass a class of five transporters with distinct expression in neurons and glia of the central nervous system (CNS). EAATs are mainly recognized for their role in uptake of the amino acid glutamate, the major excitatory neurotransmitter. EAATs-mediated clearance of glutamate released by neurons is vital to maintain proper glutamatergic signalling and to prevent toxic accumulation of this amino acid in the extracellular space. In addition, some EAATs also act as chloride channels or mediate the uptake of cysteine, required to produce the reactive oxygen speciesscavenger glutathione. Given their central role in glutamate homeostasis in the brain, as well as their additional activities, it comes as no surprise that EAAT dysfunctions have been implicated in numerous acute or chronic diseases of the CNS, including ischemic stroke and epilepsy, cerebellar ataxias, amyotrophic lateral sclerosis, Alzheimer’s disease and Huntington’s disease. Here we review the studies in cellular and animal models, as well as in humans that highlight the roles of EAATs in the pathogenesis of these devastating disorders. We also discuss the mechanisms regulating EAATs expression and intracellular trafficking and new exciting possibilities to modulate EAATs and to provide neuroprotection in course of pathologies affecting the CNS.
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Affiliation(s)
- Anna R. Malik
- Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland
- Correspondence:
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Ibata K, Kono M, Narumi S, Motohashi J, Kakegawa W, Kohda K, Yuzaki M. Activity-Dependent Secretion of Synaptic Organizer Cbln1 from Lysosomes in Granule Cell Axons. Neuron 2019; 102:1184-1198.e10. [PMID: 31072786 DOI: 10.1016/j.neuron.2019.03.044] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2019] [Revised: 03/18/2019] [Accepted: 03/27/2019] [Indexed: 12/18/2022]
Abstract
Synapse formation is achieved by various synaptic organizers. Although this process is highly regulated by neuronal activity, the underlying molecular mechanisms remain largely unclear. Here we show that Cbln1, a synaptic organizer of the C1q family, is released from lysosomes in axons but not dendrites of cerebellar granule cells in an activity- and Ca2+-dependent manner. Exocytosed Cbln1 was retained on axonal surfaces by binding to its presynaptic receptor neurexin. Cbln1 further diffused laterally along the axonal surface and accumulated at boutons by binding postsynaptic δ2 glutamate receptors. Cbln1 exocytosis was insensitive to tetanus neurotoxin, accompanied by cathepsin B release, and decreased by disrupting lysosomes. Furthermore, overexpression of lysosomal sialidase Neu1 not only inhibited Cbln1 and cathepsin B exocytosis in vitro but also reduced axonal bouton formation in vivo. Our findings imply that co-release of Cbln1 and cathepsin B from lysosomes serves as a new mechanism of activity-dependent coordinated synapse modification.
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Affiliation(s)
- Keiji Ibata
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan; Department of Physiology, St. Marianna University School of Medicine, Kanagawa 216-8511, Japan
| | - Maya Kono
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan; Department of Neurosurgery, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Sakae Narumi
- Department of Physiology, St. Marianna University School of Medicine, Kanagawa 216-8511, Japan
| | - Junko Motohashi
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Wataru Kakegawa
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Kazuhisa Kohda
- Department of Physiology, St. Marianna University School of Medicine, Kanagawa 216-8511, Japan
| | - Michisuke Yuzaki
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan.
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5
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Su JF, Wei J, Li PS, Miao HH, Ma YC, Qu YX, Xu J, Qin J, Li BL, Song BL, Xu ZP, Luo J. Numb directs the subcellular localization of EAAT3 through binding the YxNxxF motif. J Cell Sci 2016; 129:3104-14. [PMID: 27358480 DOI: 10.1242/jcs.185496] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 06/24/2016] [Indexed: 11/20/2022] Open
Abstract
Excitatory amino acid transporter type 3 (EAAT3, also known as SLC1A1) is a high-affinity, Na(+)-dependent glutamate carrier that localizes primarily within the cell and at the apical plasma membrane. Although previous studies have reported proteins and sequence regions involved in EAAT3 trafficking, the detailed molecular mechanism by which EAAT3 is distributed to the correct location still remains elusive. Here, we identify that the YVNGGF sequence in the C-terminus of EAAT3 is responsible for its intracellular localization and apical sorting in rat hepatoma cells CRL1601 and Madin-Darby canine kidney (MDCK) cells, respectively. We further demonstrate that Numb, a clathrin adaptor protein, directly binds the YVNGGF motif and regulates the localization of EAAT3. Mutation of Y503, N505 and F508 within the YVNGGF motif to alanine residues or silencing Numb by use of small interfering RNA (siRNA) results in the aberrant localization of EAAT3. Moreover, both Numb and the YVNGGF motif mediate EAAT3 endocytosis in CRL1601 cells. In summary, our study suggests that Numb is a pivotal adaptor protein that mediates the subcellular localization of EAAT3 through binding the YxNxxF (where x stands for any amino acid) motif.
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Affiliation(s)
- Jin-Feng Su
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Zhejiang University, Hangzhou 310058, China
| | - Jian Wei
- College of Life Sciences, Wuhan University, Wuhan 430072, China
| | - Pei-Shan Li
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Hong-Hua Miao
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Yong-Chao Ma
- College of Life Sciences, Wuhan University, Wuhan 430072, China
| | - Yu-Xiu Qu
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Jie Xu
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Jie Qin
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Bo-Liang Li
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Bao-Liang Song
- College of Life Sciences, Wuhan University, Wuhan 430072, China
| | - Zheng-Ping Xu
- Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Zhejiang University, Hangzhou 310058, China
| | - Jie Luo
- College of Life Sciences, Wuhan University, Wuhan 430072, China
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Bjørn-Yoshimoto WE, Underhill SM. The importance of the excitatory amino acid transporter 3 (EAAT3). Neurochem Int 2016; 98:4-18. [PMID: 27233497 DOI: 10.1016/j.neuint.2016.05.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 05/09/2016] [Accepted: 05/17/2016] [Indexed: 12/21/2022]
Abstract
The neuronal excitatory amino acid transporter 3 (EAAT3) is fairly ubiquitously expressed in the brain, though it does not necessarily maintain the same function everywhere. It is important in maintaining low local concentrations of glutamate, where its predominant post-synaptic localization can buffer nearby glutamate receptors and modulate excitatory neurotransmission and synaptic plasticity. It is also the main neuronal cysteine uptake system acting as the rate-limiting factor for the synthesis of glutathione, a potent antioxidant, in EAAT3 expressing neurons, while on GABAergic neurons, it is important in supplying glutamate as a precursor for GABA synthesis. Several diseases implicate EAAT3, and modulation of this transporter could prove a useful therapeutic approach. Regulation of EAAT3 could be targeted at several points for functional modulation, including the level of transcription, trafficking and direct pharmacological modulation, and indeed, compounds and experimental treatments have been identified that regulate EAAT3 function at different stages, which together with observations of EAAT3 regulation in patients is giving us insight into the endogenous function of this transporter, as well as the consequences of altered function. This review summarizes work done on elucidating the role and regulation of EAAT3.
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Affiliation(s)
- Walden E Bjørn-Yoshimoto
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 København Ø, Denmark
| | - Suzanne M Underhill
- National Institute of Mental Health, National Institutes of Health, 35 Convent Drive Room 3A: 210 MSC3742, Bethesda, MD 20892-3742, USA.
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Tao-Cheng JH, Pham A, Yang Y, Winters CA, Gallant PE, Reese TS. Syntaxin 4 is concentrated on plasma membrane of astrocytes. Neuroscience 2014; 286:264-71. [PMID: 25485479 DOI: 10.1016/j.neuroscience.2014.11.054] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Revised: 11/25/2014] [Accepted: 11/25/2014] [Indexed: 01/30/2023]
Abstract
Syntaxins are a family of transmembrane proteins that participate in SNARE complexes to mediate membrane fusion events including exocytosis. Different syntaxins are thought to participate in exocytosis in different compartments of the nervous system such as the axon, the soma/dendrites or astrocytes. It is well known that exocytosis of synaptic vesicles at axonal presynaptic terminals involves syntaxin 1 but distributions of syntaxins on neuronal somal and dendritic, postsynaptic or astroglial plasma membranes are less well characterized. Here, we use pre-embedding immunogold labeling to compare the distribution of two plasma membrane-enriched syntaxins (1 and 4) in dissociated rat hippocampal cultures as well as in perfusion-fixed mouse brains. Comparison of Western blots of neuronal cultures, consisting of a mixture of hippocampal neurons and glia, with glial cultures, consisting of mostly astrocytes, shows that syntaxin 1 is enriched in neuronal cultures, whereas syntaxin 4 is enriched in glial cultures. Electron microscopy (EM)-immunogold labeling shows that syntaxin 1 is most abundant at the plasma membranes of axons and terminals, while syntaxin 4 is most abundant at astroglial plasma membranes. This differential distribution was evident even at close appositions of membranes at synapses, where syntaxin 1 was localized to the plasma membrane of the presynaptic terminal, including that at the active zone, while syntaxin 4 was localized to nearby peri-synaptic astroglial processes. These results show that syntaxin 4 is available to support exocytosis in astroglia.
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Affiliation(s)
- J-H Tao-Cheng
- EM Facility, NINDS, NIH, Bethesda, MD, United States.
| | - A Pham
- Laboratory of Neurobiology, NINDS, NIH, Bethesda, MD, United States
| | - Y Yang
- Laboratory of Neurobiology, NINDS, NIH, Bethesda, MD, United States
| | - C A Winters
- Laboratory of Neurobiology, NINDS, NIH, Bethesda, MD, United States
| | - P E Gallant
- Laboratory of Neurobiology, NINDS, NIH, Bethesda, MD, United States
| | - T S Reese
- Laboratory of Neurobiology, NINDS, NIH, Bethesda, MD, United States
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Bianchi MG, Bardelli D, Chiu M, Bussolati O. Changes in the expression of the glutamate transporter EAAT3/EAAC1 in health and disease. Cell Mol Life Sci 2014; 71:2001-15. [PMID: 24162932 PMCID: PMC11113519 DOI: 10.1007/s00018-013-1484-0] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 09/17/2013] [Accepted: 09/19/2013] [Indexed: 12/14/2022]
Abstract
Excitatory amino acid transporters (EAATs) are high-affinity Na(+)-dependent carriers of major importance in maintaining glutamate homeostasis in the central nervous system. EAAT3, the human counterpart of the rodent excitatory amino acid carrier 1 (EAAC1), is encoded by the SLC1A1 gene. EAAT3/EAAC1 is ubiquitously expressed in the brain, mostly in neurons but also in other cell types, such as oligodendrocyte precursors. While most of the glutamate released in the synapses is taken up by the "glial-type" EAATs, EAAT2 (GLT-1 in rodents) and EAAT1 (GLAST), the functional role of EAAT3/EAAC1 is related to the subtle regulation of glutamatergic transmission. Moreover, because it can also transport cysteine, EAAT3/EAAC1 is believed to be important for the synthesis of intracellular glutathione and subsequent protection from oxidative stress. In contrast to other EAATs, EAAT3/EAAC1 is mostly intracellular, and several mechanisms have been described for the rapid regulation of the membrane trafficking of the transporter. Moreover, the carrier interacts with several proteins, and this interaction modulates transport activity. Much less is known about the slow regulatory mechanisms acting on the expression of the transporter, although several recent reports have identified changes in EAAT3/EAAC1 protein level and activity related to modulation of its expression at the gene level. Moreover, EAAT3/EAAC1 expression is altered in pathological conditions, such as hypoxia/ischemia, multiple sclerosis, schizophrenia, and epilepsy. This review summarizes these results and provides an overall picture of changes in EAAT3/EAAC1 expression in health and disease.
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Affiliation(s)
- Massimiliano G. Bianchi
- Unit of General Pathology, Department of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy
- Unit of Occupational Medicine, Department of Clinical and Experimental Medicine, University of Parma, Parma, Italy
| | - Donatella Bardelli
- Unit of General Pathology, Department of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy
| | - Martina Chiu
- Unit of General Pathology, Department of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy
| | - Ovidio Bussolati
- Unit of General Pathology, Department of Biomedical, Biotechnological and Translational Sciences (SBiBiT), University of Parma, Via Volturno 39, 43125 Parma, Italy
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Neuroprotective properties of the excitatory amino acid carrier 1 (EAAC1). Amino Acids 2013; 45:133-42. [PMID: 23462929 DOI: 10.1007/s00726-013-1481-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 02/23/2013] [Indexed: 01/09/2023]
Abstract
Extracellular glutamate should be maintained at low levels to conserve optimal neurotransmission and prevent glutamate neurotoxicity in the brain. Excitatory amino acid transporters (EAATs) play a pivotal role in removing extracellular glutamate in the central nervous system (CNS). Excitatory amino acid carrier 1 (EAAC1) is a high-affinity Na⁺-dependent neuronal EAAT that is ubiquitously expressed in the brain. However, most glutamate released in the synapses is cleared by glial EAATs, but not by EAAC1 in vivo. In the CNS, EAAC1 is widely distributed in somata and dendrites but not in synaptic terminals. The contribution of EAAC1 to the control of extracellular glutamate levels seems to be negligible in the brain. However, EAAC1 can transport not only extracellular glutamate but also cysteine into the neurons. Cysteine is an important substrate for glutathione (GSH) synthesis in the brain. GSH has a variety of neuroprotective functions, while its depletion induces neurodegeneration. Therefore, EAAC1 might exert a critical role for neuroprotection in neuronal GSH metabolism rather than glutamatergic neurotransmission, while EAAC1 dysfunction would cause neurodegeneration. Despite the potential importance of EAAC1 in the brain, previous studies have mainly focused on the glutamate neurotoxicity induced by glial EAAT dysfunction. In recent years, however, several studies have revealed regulatory mechanisms of EAAC1 functions in the brain. This review will summarize the latest information on the EAAC1-regulated neuroprotective functions in the CNS.
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Raffel DM, Chen W, Jung YW, Jang KS, Gu G, Cozzi NV. Radiotracers for cardiac sympathetic innervation: transport kinetics and binding affinities for the human norepinephrine transporter. Nucl Med Biol 2013; 40:331-7. [PMID: 23306137 DOI: 10.1016/j.nucmedbio.2012.11.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Revised: 11/16/2012] [Accepted: 11/28/2012] [Indexed: 02/07/2023]
Abstract
INTRODUCTION Most radiotracers for imaging of cardiac sympathetic innervation are substrates of the norepinephrine transporter (NET). The goal of this study was to characterize the NET transport kinetics and binding affinities of several sympathetic nerve radiotracers, including [(11)C]-(-)-meta-hydroxyephedrine, [(11)C]-(-)-epinephrine, and a series of [(11)C]-labeled phenethylguanidines under development in our laboratory. For comparison, the NET transport kinetics and binding affinities of some [(3)H]-labeled biogenic amines were also determined. METHODS Transport kinetics studies were performed using rat C6 glioma cells stably transfected with the human norepinephrine transporter (C6-hNET cells). For each radiolabeled NET substrate, saturation transport assays with C6-hNET cells measured the Michaelis-Menten transport constants Km and Vmax for NET transport. Competitive inhibition binding assays with homogenized C6-hNET cells and [(3)H]mazindol provided estimates of binding affinities (KI) for NET. RESULTS Km, Vmax and KI values were determined for each NET substrate with a high degree of reproducibility. Interestingly, C6-hNET transport rates for 'tracer concentrations' of substrate, given by the ratio Vmax/Km, were found to be highly correlated with neuronal transport rates measured previously in isolated rat hearts (r(2)=0.96). This suggests that the transport constants Km and Vmax measured using the C6-hNET cells accurately reflect in vivo transport kinetics. CONCLUSION The results of these studies show how structural changes in NET substrates influence NET binding and transport constants, providing valuable insights that can be used in the design of new tracers with more optimal kinetics for quantifying regional sympathetic nerve density.
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Affiliation(s)
- David M Raffel
- Division of Nuclear Medicine, Department of Radiology, 2276 Medical Sciences I Building, University of Michigan Medical School, 1301 Catherine Street, SPC 5610, Ann Arbor, MI 48109, USA.
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Aoyama K, Nakaki T. Inhibition of GTRAP3-18 may increase neuroprotective glutathione (GSH) synthesis. Int J Mol Sci 2012; 13:12017-12035. [PMID: 23109897 PMCID: PMC3472789 DOI: 10.3390/ijms130912017] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 08/06/2012] [Accepted: 09/10/2012] [Indexed: 01/24/2023] Open
Abstract
Glutathione (GSH) is a tripeptide consisting of glutamate, cysteine, and glycine; it has a variety of functions in the central nervous system. Brain GSH depletion is considered a preclinical sign in age-related neurodegenerative diseases, and it promotes the subsequent processes toward neurotoxicity. A neuroprotective mechanism accomplished by increasing GSH synthesis could be a promising approach in the treatment of neurodegenerative diseases. In neurons, cysteine is the rate-limiting substrate for GSH synthesis. Excitatory amino acid carrier 1 (EAAC1) is a neuronal cysteine/glutamate transporter in the brain. EAAC1 translocation to the plasma membrane promotes cysteine uptake, leading to GSH synthesis, while being negatively regulated by glutamate transport associated protein 3-18 (GTRAP3-18). Our recent studies have suggested GTRAP3-18 as an inhibitory factor for neuronal GSH synthesis. Inhibiting GTRAP3-18 function is an endogenous mechanism to increase neuron-specific GSH synthesis in the brain. This review gives an overview of EAAC1-mediated GSH synthesis, and its regulatory mechanisms by GTRAP3-18 in the brain, and a potential approach against neurodegeneration.
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Affiliation(s)
| | - Toshio Nakaki
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +81-3-3964-1211; Fax: +81-3-3964-0602
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Suh YH, Yoshimoto-Furusawa A, Weih KA, Tessarollo L, Roche KW, Mackem S, Roche PA. Deletion of SNAP-23 results in pre-implantation embryonic lethality in mice. PLoS One 2011; 6:e18444. [PMID: 21479242 PMCID: PMC3066230 DOI: 10.1371/journal.pone.0018444] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Accepted: 02/28/2011] [Indexed: 11/18/2022] Open
Abstract
SNARE-mediated membrane fusion is a pivotal event for a wide-variety of biological processes. SNAP-25, a neuron-specific SNARE protein, has been well-characterized and mouse embryos lacking Snap25 are viable. However, the phenotype of mice lacking SNAP-23, the ubiquitously expressed SNAP-25 homolog, remains unknown. To reveal the importance of SNAP-23 function in mouse development, we generated Snap23-null mice by homologous recombination. We were unable to obtain newborn SNAP-23-deficient mice, and analysis of pre-implantation embryos from Snap23Δ/wt matings revealed that Snap23-null blastocysts were dying prior to implantation at embryonic day E3.5. Thus these data reveal a critical role for SNAP-23 during embryogenesis.
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Affiliation(s)
- Young Ho Suh
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- Receptor Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States of America
- Neuroscience Graduate Program, Department of Pharmacology, Ajou University School of Medicine, Suwon, South Korea
| | - Aki Yoshimoto-Furusawa
- Cancer and Developmental Biology Laboratory, Center for Cancer Research (CCR), NCI-Frederick, National Institutes of Health, Frederick, Maryland, United States of America
| | - Karis A. Weih
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Lino Tessarollo
- Mouse Cancer Genetics Program, Center for Cancer Research (CCR), NCI-Frederick, National Institutes of Health, Frederick, Maryland, United States of America
| | - Katherine W. Roche
- Receptor Biology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Susan Mackem
- Cancer and Developmental Biology Laboratory, Center for Cancer Research (CCR), NCI-Frederick, National Institutes of Health, Frederick, Maryland, United States of America
| | - Paul A. Roche
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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Bianchi MG, Gatti R, Torielli L, Padoani G, Gazzola GC, Bussolati O. The glutamate transporter excitatory amino acid carrier 1 associates with the actin-binding protein alpha-adducin. Neuroscience 2010; 169:584-95. [PMID: 20493242 DOI: 10.1016/j.neuroscience.2010.05.029] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Revised: 04/26/2010] [Accepted: 05/14/2010] [Indexed: 11/28/2022]
Abstract
Excitatory amino acid carrier 1 (EAAC1) belongs to the family of the Na(+)-dependent glutamate carriers. Although the association between defective EAAC1 function and neurologic disease has been repeatedly studied, EAAC1 regulation is not yet fully understood. We have reported that in C6 glioma cells both the activity and membrane targeting of EAAC1 require the integrity of actin cytoskeleton. Here we show that, in the same model, EAAC1 partially co-localizes with actin filaments at the level of cell processes. Moreover, perinuclear spots in which EAAC1 co-localizes with the actin binding protein alpha-adducin are observed in some cells and, consistently, faint co-immunoprecipitation bands between EAAC1 and alpha-adducin are detected. Co-localization and partial co-immunoprecipitation of EAAC1 and adducin are still detectable after cell treatment with phorbol esters, a condition that leads to a protein kinase C (PKC)-dependent increase of EAAC1 expression on the membrane and to the phosphorylation of adducin. A co-immunoprecipitation band was also detected in protein extracts of rat hippocampus. The amount of adducin co-immunoprecipitated with EAAC1 increases after the treatment of C6 cells with retinoic acid, a differentiating agent that induces EAAC1 overexpression in this cell model. Moreover, in clones of C6 cells transfected with a hemagglutinin (HA)-tagged adducin, the bands of EAAC1 immunoprecipitated by an anti-HA antiserum were proportional to EAAC1 expression. These results suggest the existence of a pool of EAAC1 transporters associated with the actin binding protein alpha-adducin in a PKC-insensitive manner.
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Affiliation(s)
- M G Bianchi
- Unit of General and Clinical Pathology, Department of Experimental Medicine, University of Parma, Parma, Italy
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Gillitzer A, Peluso M, Bültmann A, Münch G, Gawaz M, Ungerer M. Effect of dominant negative SNAP-23 expression on platelet function. J Thromb Haemost 2008; 6:1757-63. [PMID: 18665925 DOI: 10.1111/j.1538-7836.2008.03108.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND The protein SNAP-23 is part of the secretory pathway in platelets. It is, however, not entirely clear to what extent this protein contributes to the secretory function of platelets. Therefore, we overexpressed a dominant negative mutant with a novel technology that allows the creation of intact transgene-expressing platetets. RESULTS Overexpression of a dominant negative SNAP-23 mutant that inhibited the binding of the native protein to the docking site within the secretory machinery resulted in significant suppression of the agonist-dependent surface recruitment of P-selectin and CD40L. Simultaneously, release from dense granules was clearly suppressed in the presence of this construct. Also agonist-dependent surface expression of fibrinogen receptor markers CD41 and CD61 was reduced, and agonist-triggered aggregation was inhibited. CONCLUSION The dominant negative inhibition of SNAP-23 resulted in clear effects on platelet functions. The novel method using recombinant culture-derived platelets allowed the rapid clarification of the functional importance of this protein in intact platelets.
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15
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Ng EL, Tang BL. Rab GTPases and their roles in brain neurons and glia. ACTA ACUST UNITED AC 2008; 58:236-46. [PMID: 18485483 DOI: 10.1016/j.brainresrev.2008.04.006] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 02/29/2008] [Accepted: 04/06/2008] [Indexed: 12/19/2022]
Affiliation(s)
- Ee Ling Ng
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, 8 Medical Drive, Singapore 117597, Singapore
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16
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Plasma membrane expression of the neuronal glutamate transporter EAAC1 is regulated by glial factors: evidence for different regulatory pathways associated with neuronal maturation. Neurochem Int 2008; 52:1373-82. [PMID: 18400334 DOI: 10.1016/j.neuint.2008.02.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2007] [Revised: 02/15/2008] [Accepted: 02/21/2008] [Indexed: 11/21/2022]
Abstract
At the glutamatergic synapse the neurotransmitter is removed from the synaptic cleft by high affinity amino acid transporters located on neurons (EAAC1) and astrocytes (GLAST and GLT1), and a coordinated action of these cells is necessary in order to regulate glutamate extracellular concentration. We show here that treatment of neuronal cultures with glial soluble factors (GCM) is associated with a redistribution of EAAC1 and GLAST to the cell membrane and we analysed the effect of membrane cholesterol depletion on this regulation. In enriched neuronal culture (90% neurons and 10% astrocytes), GCM treatment for 10 days increases EAAC1 and GLAST cell surface expression with no change in total expression. In opposite, GLT1 surface expression is not modified by GCM but total expression is increased. When cholesterol is acutely depleted from the membrane by 10 mM methyl-beta-cyclodextrin (beta5-MCD, 30 min), glutamate transport activity and cell surface expressions of EAAC1 and GLAST are decreased in the enriched neuronal culture treated by GCM. In pure neuronal culture addition of GCM also increases EAAC1 cell membrane expression but surprisingly acute treatment with beta5-MCD decreases glutamate uptake activity but not EAAC1 cell membrane expression. By immunocytochemistry a modification in the distribution of EAAC1 within neurons was undetectable whatever the treatment but we show that EAAC1 was no more co localized with Thy-1 in the enriched neuronal culture treated by GCM suggesting that GCM have stimulated polarity formation in neurons, an index of maturation. In conclusion we suggest that different regulatory mechanisms are involved after GCM treatment, glutamate transporter trafficking to and from the plasma membrane in enriched neuronal culture and modulation of EAAC1 intrinsic activity and/or association with regulatory proteins at the cell membrane in the pure neuronal culture. These different regulatory pathways of EAAC1 are associated with different neuronal maturation stages.
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Abstract
Maturity-onset diabetes of the young (MODY) is a monogenic form of type 2 diabetes mellitus that is characterized by impairment of glucose-stimulated insulin secretion from pancreatic beta-cells. We previously reported that heterozygous mutations of the hepatocyte nuclear factor (HNF)-1alpha gene cause a form of MODY (MODY3). We have subsequently found that collectrin, a recently cloned kidney-specific gene of unknown function, is a novel target of HNF-1alpha in pancreatic beta-cells. In addition, we have demonstrated that collectrin forms a complex with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex by direct interaction with snapin, a protein that is thought to be involved in neurotransmission by binding to synaptosomal-associated protein, 25 KD (SNAP25). Collectrin favours the formation of SNARE complexes and controls insulin exocytosis.
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Affiliation(s)
- K Yamagata
- Department of Metabolic Medicine, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.
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19
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Zhang Y, Wada J. Collectrin, a homologue of ACE2, its transcriptional control and functional perspectives. Biochem Biophys Res Commun 2007; 363:1-5. [PMID: 17825789 DOI: 10.1016/j.bbrc.2007.08.136] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2007] [Accepted: 08/20/2007] [Indexed: 11/29/2022]
Abstract
Collectrin is a type I membrane protein and shares significant homology with C-terminal domain of angiotensin-converting enzyme-2 (ACE2). However, collectrin lacks catalytic domain and it suggests the presence of uncharacterized physiological functions of collectrin. Collectrin is transcriptionally regulated by hepatocyte nuclear factor-alpha and -beta and is highly expressed on renal proximal tubules and collecting ducts as well as pancreatic beta-cells. Recent in vitro and in vivo studies demonstrated interesting physiological roles of collectrin related to insulin secretion, formation of primary cilia, renal cyst formation and amino acid transport. The common underlying molecular mechanism may be suggested by the evidence that collectrin binds to SNARE complex by interacting with snapin. Collectrin is involved in the process of vesicle transport and membrane fusion and thus it delivers insulin for exocytosis or various membrane proteins to apical plasmalemma and primary cilia. Collectrin may be the new therapeutic target for various pathological processes such as diabetes, polycystic kidney disease, hypertension and aminoaciduria.
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Affiliation(s)
- Yanling Zhang
- Department of Nephrology, Third Hospital Hebei Medical University, Shijiazhuang 050051, PR China.
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González MI, Susarla BTS, Fournier KM, Sheldon AL, Robinson MB. Constitutive endocytosis and recycling of the neuronal glutamate transporter, excitatory amino acid carrier 1. J Neurochem 2007; 103:1917-31. [PMID: 17868307 DOI: 10.1111/j.1471-4159.2007.04881.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The neuronal glutamate transporter, excitatory amino acid carrier 1 (EAAC1), has a diverse array of physiologic and metabolic functions. There is evidence that there is a relatively large intracellular pool of EAAC1 both in vivo and in vitro, that EAAC1 cycles on and off the plasma membrane, and that EAAC1 cell surface expression can be rapidly regulated by intracellular signals. Despite the possible relevance of EAAC1 trafficking to both physiologic and pathologic processes, the cellular machinery involved has not been defined. In the present study, we found that agents that disrupt clathrin-dependent endocytosis or plasma membrane cholesterol increased steady-state levels of biotinylated EAAC1 in C6 glioma cells and primary neuronal cultures. Acute depletion of cholesterol increased the V(max) for EAAC1-mediated activity and had no effect on Na(+)-dependent glycine transport in the same system. These agents also impaired endocytosis as measured using a reversible biotinylating reagent. Co-expression with dominant-negative variants of dynamin or the clathrin adaptor, epidermal growth factor receptor pathway substrate clone 15, increased the steady-state levels of biotinylated myc-EAAC1. EAAC1 immunoreactivity was found in a subcellular fraction enriched in early endosome antigen 1 (EEA1) isolated by differential centrifugation and partially co-localized with EEA1. Co-expression of a dominant-negative variant of Rab11 (Rab11 S25N) reduced steady-state levels of biotinylated myc-EAAC1 and slowed constitutive delivery of myc-EAAC1 to the plasma membrane. Together, these observations suggest that EAAC1 is constitutively internalized via a clathrin- and dynamin-dependent pathway into early endosomes and that EAAC1 is trafficked back to the cell surface via the endocytic recycling compartment in a Rab11-dependent mechanism. As one defines the machinery required for constitutive trafficking of EAAC1, it may be possible to determine how intracellular signals regulate EAAC1 cell surface expression.
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Affiliation(s)
- Marco I González
- Departments of Pediatrics and Pharmacology, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Internalization and degradation of the glutamate transporter GLT-1 in response to phorbol ester. Neurochem Int 2007; 52:709-22. [PMID: 17919781 DOI: 10.1016/j.neuint.2007.08.020] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2007] [Revised: 08/09/2007] [Accepted: 08/31/2007] [Indexed: 11/20/2022]
Abstract
Activation of protein kinase C (PKC) decreases the activity and cell surface expression of the predominant forebrain glutamate transporter, GLT-1. In the present study, C6 glioma were used as a model system to define the mechanisms that contribute to this decrease in cell surface expression and to determine the fate of internalized transporter. As was previously observed, phorbol 12-myristate 13-acetate (PMA) caused a decrease in biotinylated GLT-1. This effect was blocked by sucrose or by co-expression with a dominant-negative variant of dynamin 1, and it was attenuated by co-expression with a dominant-negative variant of the clathrin heavy chain. Depletion of cholesterol with methyl-beta-cyclodextrin, co-expression with a dominant-negative caveolin-1 mutant (Cav1/S80E), co-expression with dominant-negative variants of Eps15 (epidermal-growth-factor receptor pathway substrate clone 15), or co-expression with dominant-negative Arf6 (T27N) had no effect on the PMA-induced loss of biotinylated GLT-1. Long-term treatment with PMA caused a time-dependent loss of biotinylated GLT-1 and decreased the levels of GLT-1 protein. Inhibitors of lysosomal degradation (chloroquine or ammonium chloride) or co-expression with a dominant-negative variant of a small GTPase implicated in trafficking to lysosomes (Rab7) prevented the PMA-induced decrease in protein and caused an intracellular accumulation of GLT-1. These results suggest that the PKC-induced redistribution of GLT-1 is dependent upon clathrin-mediated endocytosis. These studies identify a novel mechanism by which the levels of GLT-1 could be rapidly down-regulated via lysosomal degradation. The possibility that this mechanism may contribute to the loss of GLT-1 observed after acute insults to the CNS is discussed.
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Okayama M, Arakawa T, Mizoguchi I, Tajima Y, Takuma T. SNAP-23 is not essential for constitutive exocytosis in HeLa cells. FEBS Lett 2007; 581:4583-8. [PMID: 17825825 DOI: 10.1016/j.febslet.2007.08.046] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2007] [Revised: 08/09/2007] [Accepted: 08/21/2007] [Indexed: 01/28/2023]
Abstract
We applied the small interfering RNA (siRNA) technique and over-expression of a dominant-negative mutant to evaluate the role of SNAP-23, a non-neuronal isoform of SNAP-25, in constitutive exocytosis from HeLa cells. Although the protein level of SNAP-23 was reduced to less than 10% of the control value by siRNA directed against SNAP-23, exocytosis of SEAP (secreted alkaline phosphatase) was normal. Double knockdown of SNAP-23 and syntaxin-4 also failed to inhibit the secretion. Furthermore, over-expression of deltaC8-SNAP-23, a dominant-negative mutant of SNAP-23, did not abrogate SEAP secretion. These results suggest that SNAP-23 is not essential for constitutive exocytosis of SEAP.
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Affiliation(s)
- Miki Okayama
- Department of Orthodontics, School of Dentistry, Health Sciences University of Hokkaido, Tobetsu, Hokkaido 061-0293, Japan
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23
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González MI, Krizman-Genda E, Robinson MB. Caveolin-1 regulates the delivery and endocytosis of the glutamate transporter, excitatory amino acid carrier 1. J Biol Chem 2007; 282:29855-65. [PMID: 17715130 DOI: 10.1074/jbc.m704738200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The sodium-dependent glutamate transporter, excitatory amino acid carrier 1 (EAAC1), has been implicated in the regulation of excitatory signaling and prevention of cell death in the nervous system. There is evidence that EAAC1 constitutively cycles on and off the plasma membrane and that under steady state conditions up to 80% of the transporter is intracellular. As is observed with other neurotransmitter transporters, the activity of EAAC1 is regulated by a variety of molecules, and some of these effects are associated with redistribution of EAAC1 on and off the plasma membrane. In the present study we tested the hypothesis that a structural component of lipid rafts, caveolin-1 (Cav-1), may participate in EAAC1 trafficking. Using C6 glioma cells as a model system, co-expression of Cav-1 S80E (a dominant-negative variant) or small interfering RNA-mediated knock-down of caveolin-1 reduced cell surface expression of myc epitope-tagged EAAC1 or endogenous EAAC1, respectively. Cav-1 S80E slowed the constitutive delivery and endocytosis of myc-EAAC1. In primary cultures derived from caveolin-1 knock-out mice, a similar reduction in delivery and internalization of endogenous EAAC1 was observed. We also found that caveolin-1, caveolin-2, or Cav-1 S80E formed immunoprecipitable complexes with EAAC1 in C6 glioma and/or transfected HEK cells. Together, these data provide strong evidence that caveolin-1 contributes to the trafficking of EAAC1 on and off the plasma membrane and that these effects are associated with formation of EAAC1-caveolin complexes.
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Affiliation(s)
- Marco I González
- Department of Pediatrics, Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, Pennsylvania 19104-4318, USA
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Hirano AA, Brandstätter JH, Vila A, Brecha NC. Robust syntaxin-4 immunoreactivity in mammalian horizontal cell processes. Vis Neurosci 2007; 24:489-502. [PMID: 17640443 PMCID: PMC2744743 DOI: 10.1017/s0952523807070198] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2007] [Accepted: 03/12/2007] [Indexed: 12/22/2022]
Abstract
Horizontal cells mediate inhibitory feed-forward and feedback communication in the outer retina; however, mechanisms that underlie transmitter release from mammalian horizontal cells are poorly understood. Toward determining whether the molecular machinery for exocytosis is present in horizontal cells, we investigated the localization of syntaxin-4, a SNARE protein involved in targeting vesicles to the plasma membrane, in mouse, rat, and rabbit retinae using immunocytochemistry. We report robust expression of syntaxin-4 in the outer plexiform layer of all three species. Syntaxin-4 occurred in processes and tips of horizontal cells, with regularly spaced, thicker sandwich-like structures along the processes. Double labeling with syntaxin-4 and calbindin antibodies, a horizontal cell marker, demonstrated syntaxin-4 localization to horizontal cell processes; whereas, double labeling with PKC antibodies, a rod bipolar cell (RBC) marker, showed a lack of co-localization, with syntaxin-4 immunolabeling occurring just distal to RBC dendritic tips. Syntaxin-4 immunolabeling occurred within VGLUT-1-immunoreactive photoreceptor terminals and underneath synaptic ribbons, labeled by CtBP2/RIBEYE antibodies, consistent with localization in invaginating horizontal cell tips at photoreceptor triad synapses. Vertical sections of retina immunostained for syntaxin-4 and peanut agglutinin (PNA) established that the prominent patches of syntaxin-4 immunoreactivity were adjacent to the base of cone pedicles. Horizontal sections through the OPL indicate a one-to-one co-localization of syntaxin-4 densities at likely all cone pedicles, with syntaxin-4 immunoreactivity interdigitating with PNA labeling. Pre-embedding immuno-electron microscopy confirmed the subcellular localization of syntaxin-4 labeling to lateral elements at both rod and cone triad synapses. Finally, co-localization with SNAP-25, a possible binding partner of syntaxin-4, indicated co-expression of these SNARE proteins in the same subcellular compartment of the horizontal cell. Taken together, the strong expression of these two SNARE proteins in the processes and endings of horizontal cells at rod and cone terminals suggests that horizontal cell axons and dendrites are likely sites of exocytotic activity.
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Affiliation(s)
- Arlene A Hirano
- Departments of Neurobiology & Medicine, Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
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25
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Malakauskas SM, Quan H, Fields TA, McCall SJ, Yu MJ, Kourany WM, Frey CW, Le TH. Aminoaciduria and altered renal expression of luminal amino acid transporters in mice lacking novel gene collectrin. Am J Physiol Renal Physiol 2006; 292:F533-44. [PMID: 16985211 DOI: 10.1152/ajprenal.00325.2006] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Defects in renal proximal tubule transport manifest in a number of human diseases. Although variable in clinical presentation, disorders such as Hartnup disease, Dent's disease, and Fanconi syndrome are characterized by wasting of solutes commonly recovered by the proximal tubule. One common feature of these disorders is aminoaciduria. There are distinct classes of amino acid transporters located in the apical and basal membranes of the proximal tubules that reabsorb >95% of filtered amino acids, yet few details are known about their regulation. We present our physiological characterization of a mouse line with targeted deletion of the gene collectrin that is highly expressed in the kidney. Collectrin-deficient mice display a reduced urinary concentrating capacity due to enhanced solute clearance resulting from profound aminoaciduria. The aminoaciduria is generalized, characterized by loss of nearly every amino acid, and results in marked crystalluria. Furthermore, in the kidney, collectrin-deficient mice have decreased plasma membrane populations of amino acid transporter subtypes B(0)AT1, rBAT, and b(0,+)AT, as well as altered cellular distribution of EAAC1. Our data suggest that collectrin is a novel mediator of renal amino acid transport and may provide further insight into the pathogenesis of a number of human disease correlates.
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Sherry DM, Mitchell R, Standifer KM, du Plessis B. Distribution of plasma membrane-associated syntaxins 1 through 4 indicates distinct trafficking functions in the synaptic layers of the mouse retina. BMC Neurosci 2006; 7:54. [PMID: 16839421 PMCID: PMC1555595 DOI: 10.1186/1471-2202-7-54] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Accepted: 07/13/2006] [Indexed: 01/02/2023] Open
Abstract
Background Syntaxins 1 through 4 are SNAP receptor (SNARE) proteins that mediate vesicular trafficking to the plasma membrane. In retina, syntaxins 1 and 3 are expressed at conventional and ribbon synapses, respectively, suggesting that synaptic trafficking functions differ among syntaxin isoforms. To better understand syntaxins in synaptic signaling and trafficking, we further examined the cell- and synapse-specific expression of syntaxins 1 through 4 in the mouse retina by immunolabeling and confocal microscopy. Results Each isoform was expressed in the retina and showed a unique distribution in the synaptic layers of the retina, with little or no colocalization of isoforms. Syntaxin 1 was present in amacrine cell bodies and processes and conventional presynaptic terminals in the inner plexiform layer (IPL). Syntaxin 2 was present in amacrine cells and their processes in the IPL, but showed little colocalization with syntaxin 1 or other presynaptic markers. Syntaxin 3 was found in glutamatergic photoreceptor and bipolar cell ribbon synapses, but was absent from putative conventional glutamatergic amacrine cell synapses. Syntaxin 4 was localized to horizontal cell processes in the ribbon synaptic complexes of photoreceptor terminals and in puncta in the IPL that contacted dopaminergic and CD15-positive amacrine cells. Syntaxins 2 and 4 often were apposed to synaptic active zones labeled for bassoon. Conclusion These results indicate that each syntaxin isoform has unique, non-redundant functions in synaptic signaling and trafficking. Syntaxins 1 and 3 mediate presynaptic transmitter release from conventional and ribbon synapses, respectively. Syntaxins 2 and 4 are not presynaptic and likely mediate post-synaptic trafficking.
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Affiliation(s)
- David M Sherry
- University of Houston, College of Optometry, Houston, TX 77204, USA
- College of Pharmacy, Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77204, USA
| | - Robert Mitchell
- University of Houston, College of Optometry, Houston, TX 77204, USA
| | - Kelly M Standifer
- College of Pharmacy, Department of Pharmacological and Pharmaceutical Sciences, University of Houston, Houston, TX 77204, USA
| | - Brad du Plessis
- University of Houston, College of Optometry, Houston, TX 77204, USA
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