1
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Wang Y, Wei Y, Ren M, Sajja VS, Wilder DM, Arun P, Gist ID, Long JB, Yang F. Blast Exposure Alters Synaptic Connectivity in the Mouse Auditory Cortex. J Neurotrauma 2024. [PMID: 38047526 DOI: 10.1089/neu.2023.0348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2023] Open
Abstract
Blast exposure can cause auditory deficits that have a lasting, significant impact on patients. Although the effects of blast on auditory functions localized to the ear have been well documented, the impact of blast on central auditory processing is largely undefined. Understanding the structural and functional alterations in the central nervous system (CNS) associated with blast injuries is crucial for unraveling blast-induced pathophysiological pathways and advancing development of therapeutic interventions. In this study, we used electrophysiology in combination with optogenetics assay, proteomic analysis, and morphological evaluation to investigate the impairment of synaptic connectivity in the auditory cortex (AC) of mice following blast exposure. Our results show that the long-range functional connectivity between the medial geniculate nucleus (MGN) and AC was impaired in the acute phase of blast injury. We also identified impaired synaptic transmission and dendritic spine alterations within 7 days of blast exposure, which recovered at 28 days post-blast. Additionally, proteomic analysis identified a few differentially expressed proteins in the cortex that are involved in synaptic signaling and plasticity. These findings collectively suggest that blast-induced alterations in the sound signaling network in the auditory cortex may underlie hearing deficits in the acute and sub-acute phases after exposure to shockwaves. This study may shed light on the perturbations underlying blast-induced auditory dysfunction and provide insights into the potential therapeutic windows for improving auditory outcomes in blast-exposed individuals.
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Affiliation(s)
- Ying Wang
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Yanling Wei
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Ming Ren
- Lieber Institute for Brain Development, Johns Hopkins Medical Center, Baltimore, Maryland, USA
| | - Venkatasivasai S Sajja
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Donna M Wilder
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Peethambaran Arun
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Irene D Gist
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Joseph B Long
- Blast-Induced Neurotrauma Branch, Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, Maryland, USA
| | - Feng Yang
- Lieber Institute for Brain Development, Johns Hopkins Medical Center, Baltimore, Maryland, USA
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2
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Ouahed JD, Griffith A, Collen LV, Snapper SB. Breaking Down Barriers: Epithelial Contributors to Monogenic IBD Pathogenesis. Inflamm Bowel Dis 2024:izad319. [PMID: 38280053 DOI: 10.1093/ibd/izad319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Indexed: 01/29/2024]
Abstract
Monogenic causes of inflammatory bowel diseases (IBD) are increasingly being discovered. To date, much attention has been placed in those resulting from inborn errors of immunity. Therapeutic efforts have been largely focused on offering personalized immune modulation or curative bone marrow transplant for patients with IBD and underlying immune disorders. To date, less emphasis has been placed on monogenic causes of IBD that pertain to impairment of the intestinal epithelial barrier. Here, we provide a comprehensive review of monogenic causes of IBD that result in impaired intestinal epithelial barrier that are categorized into 6 important functions: (1) epithelial cell organization, (2) epithelial cell intrinsic functions, (3) epithelial cell apoptosis and necroptosis, (4) complement activation, (5) epithelial cell signaling, and (6) control of RNA degradation products. We illustrate how impairment of any of these categories can result in IBD. This work reviews the current understanding of the genes involved in maintaining the intestinal barrier, the inheritance patterns that result in dysfunction, features of IBD resulting from these disorders, and pertinent translational work in this field.
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Affiliation(s)
- Jodie D Ouahed
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
| | - Alexandra Griffith
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
| | - Lauren V Collen
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
| | - Scott B Snapper
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
- Division of Gastroenterology, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, USA
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3
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Kioumourtzoglou D, Black HL, Al Tobi M, Livingstone R, Petrie JR, Boyle JG, Gould GW, Bryant NJ. Phosphorylation of Syntaxin 4 by the Insulin Receptor Drives Exocytic SNARE Complex Formation to Deliver GLUT4 to the Cell Surface. Biomolecules 2023; 13:1738. [PMID: 38136609 PMCID: PMC10741561 DOI: 10.3390/biom13121738] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 11/24/2023] [Accepted: 11/29/2023] [Indexed: 12/24/2023] Open
Abstract
A major consequence of insulin binding its receptor on fat and muscle cells is the stimulation of glucose transport into these tissues. This is achieved through an increase in the exocytic trafficking rate of the facilitative glucose transporter GLUT4 from intracellular stores to the cell surface. Delivery of GLUT4 to the cell surface requires the formation of functional SNARE complexes containing Syntaxin 4, SNAP23, and VAMP2. Insulin stimulates the formation of these complexes and concomitantly causes phosphorylation of Syntaxin 4. Here, we use a combination of biochemistry and cell biological approaches to provide a mechanistic link between these observations. We present data to support the hypothesis that Tyr-115 and Tyr-251 of Syntaxin 4 are direct substrates of activated insulin receptors, and that these residues modulate the protein's conformation and thus regulate the rate at which Syntaxin 4 forms SNARE complexes that deliver GLUT4 to the cell surface. This report provides molecular details on how the cell regulates SNARE-mediated membrane traffic in response to an external stimulus.
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Affiliation(s)
| | - Hannah L. Black
- Department of Biology, University of York, Heslington YO10 5DD, UK; (D.K.)
| | - Mohammed Al Tobi
- Institute of Molecular Cell and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK; (M.A.T.)
| | - Rachel Livingstone
- Institute of Molecular Cell and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK; (M.A.T.)
| | - John R. Petrie
- Institute of Cardiovascular and Medical Sciences, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
| | - James G. Boyle
- School of Medicine, Dentistry & Nursing, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK;
| | - Gwyn W. Gould
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 ORE, UK
| | - Nia J. Bryant
- Department of Biology, University of York, Heslington YO10 5DD, UK; (D.K.)
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4
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Yan C, Jiang J, Yang Y, Geng X, Dong W. The function of VAMP2 in mediating membrane fusion: An overview. Front Mol Neurosci 2022; 15:948160. [PMID: 36618823 PMCID: PMC9816800 DOI: 10.3389/fnmol.2022.948160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 12/05/2022] [Indexed: 12/24/2022] Open
Abstract
Vesicle-associated membrane protein 2 (VAMP2, also known as synaptobrevin-2), encoded by VAMP2 in humans, is a key component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex. VAMP2 combined with syntaxin-1A (SYX-1A) and synaptosome-associated protein 25 (SNAP-25) produces a force that induces the formation of fusion pores, thereby mediating the fusion of synaptic vesicles and the release of neurotransmitters. VAMP2 is largely unstructured in the absence of interaction partners. Upon interaction with other SNAREs, the structure of VAMP2 stabilizes, resulting in the formation of four structural domains. In this review, we highlight the current knowledge of the roles of the VAMP2 domains and the interaction between VAMP2 and various fusion-related proteins in the presynaptic cytoplasm during the fusion process. Our summary will contribute to a better understanding of the roles of the VAMP2 protein in membrane fusion.
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Affiliation(s)
- Chong Yan
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
| | - Jie Jiang
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
| | - Yuan Yang
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
| | - Xiaoqi Geng
- Department of Neurosurgery, Neurosurgical Clinical Research Center of Sichuan Province, Affiliated Hospital of Southwest Medical University, Luzhou, China,*Correspondence: Xiaoqi Geng,
| | - Wei Dong
- Key Laboratory of Medical Electrophysiology, Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China,Wei Dong,
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5
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Peer M, Yuan H, Zhang Y, Korbula K, Novick P, Dong G. Double NPY motifs at the N-terminus of the yeast t-SNARE Sso2 synergistically bind Sec3 to promote membrane fusion. eLife 2022; 11:82041. [PMID: 35979953 PMCID: PMC9427108 DOI: 10.7554/elife.82041] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Accepted: 07/29/2022] [Indexed: 11/29/2022] Open
Abstract
Exocytosis is an active vesicle trafficking process by which eukaryotes secrete materials to the extracellular environment and insert membrane proteins into the plasma membrane. The final step of exocytosis in yeast involves the assembly of two t-SNAREs, Sso1/2 and Sec9, with the v-SNARE, Snc1/2, on secretory vesicles. The rate-limiting step in this process is the formation of a binary complex of the two t-SNAREs. Despite a previous report of acceleration of binary complex assembly by Sec3, it remains unknown how Sso2 is efficiently recruited to the vesicle-docking site marked by Sec3. Here, we report a crystal structure of the pleckstrin homology (PH) domain of Sec3 in complex with a nearly full-length version of Sso2 lacking only its C-terminal transmembrane helix. The structure shows a previously uncharacterized binding site for Sec3 at the N-terminus of Sso2, consisting of two highly conserved triple residue motifs (NPY: Asn-Pro-Tyr). We further reveal that the two NPY motifs bind Sec3 synergistically, which together with the previously reported binding interface constitute dual-site interactions between Sso2 and Sec3 to drive the fusion of secretory vesicles at target sites on the plasma membrane.
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Affiliation(s)
- Maximilian Peer
- Vienna Biocenter, Medical University of Vienna, Vienna, Austria
| | - Hua Yuan
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, United States
| | - Yubo Zhang
- Vienna Biocenter, Medical University of Vienna, Vienna, Austria
| | | | - Peter Novick
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, United States
| | - Gang Dong
- Medical Unviersity of Vienna, Vienna, Austria
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6
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Brasher MI, Chafe SC, McDonald PC, Nemirovsky O, Gorshtein G, Gerbec ZJ, Brown WS, Grafinger OR, Marchment M, Matus E, Dedhar S, Coppolino MG. Syntaxin4-Munc18c Interaction Promotes Breast Tumor Invasion and Metastasis by Regulating MT1-MMP Trafficking. Mol Cancer Res 2022; 20:434-445. [PMID: 34876482 PMCID: PMC9306282 DOI: 10.1158/1541-7786.mcr-20-0527] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 11/18/2020] [Accepted: 11/24/2021] [Indexed: 01/07/2023]
Abstract
Invasion of neighboring extracellular matrix (ECM) by malignant tumor cells is a hallmark of metastatic progression. This invasion can be mediated by subcellular structures known as invadopodia, the function of which depends upon soluble N-ethylmaleimide-sensitive factor-activating protein receptor (SNARE)-mediated vesicular transport of cellular cargo. Recently, it has been shown the SNARE Syntaxin4 (Stx4) mediates trafficking of membrane type 1-matrix metalloproteinase (MT1-MMP) to invadopodia, and that Stx4 is regulated by Munc18c in this context. Here, it is observed that expression of a construct derived from the N-terminus of Stx4, which interferes with Stx4-Munc18c interaction, leads to perturbed trafficking of MT1-MMP, and reduced invadopodium-based invasion in vitro, in models of triple-negative breast cancer (TNBC). Expression of Stx4 N-terminus also led to increased survival and markedly reduced metastatic burden in multiple TNBC models in vivo. The findings are the first demonstration that disrupting Stx4-Munc18c interaction can dramatically alter metastatic progression in vivo, and suggest that this interaction warrants further investigation as a potential therapeutic target. IMPLICATIONS Disrupting the interaction of Syntaxin4 and Munc18c may be a useful approach to perturb trafficking of MT1-MMP and reduce metastatic potential of breast cancers.
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Affiliation(s)
- Megan I. Brasher
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Shawn C. Chafe
- Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, British Columbia, Canada
| | - Paul C. McDonald
- Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, British Columbia, Canada
| | - Oksana Nemirovsky
- Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, British Columbia, Canada
| | - Genya Gorshtein
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Zachary J. Gerbec
- Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, British Columbia, Canada
| | - Wells S. Brown
- Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, British Columbia, Canada
| | - Olivia R. Grafinger
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Matthew Marchment
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Esther Matus
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Shoukat Dedhar
- Department of Integrative Oncology, BC Cancer Research Institute, Vancouver, British Columbia, Canada.,Department of Biochemistry and Molecular Biology, Faculty of Medicine, The University of British Columbia, Vancouver, British Columbia, Canada
| | - Marc G. Coppolino
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.,Corresponding Author: Marc G. Coppolino, Department of Molecular and Cellular Biology, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G 2W1, Canada. E-mail:
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7
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Ouahed J, Kelsen JR, Spessott WA, Kooshesh K, Sanmillan ML, Dawany N, Sullivan KE, Hamilton KE, Slowik V, Nejentsev S, Neves JF, Flores H, Chung WK, Wilson A, Anyane-Yeboa K, Wou K, Jain P, Field M, Tollefson S, Dent MH, Li D, Naito T, McGovern DPB, Kwong AC, Taliaferro F, Ordovas-Montanes J, Horwitz BH, Kotlarz D, Klein C, Evans J, Dorsey J, Warner N, Elkadri A, Muise AM, Goldsmith J, Thompson B, Engelhardt KR, Cant AJ, Hambleton S, Barclay A, Toth-Petroczy A, Vuzman D, Carmichael N, Bodea C, Cassa CA, Devoto M, Maas RL, Behrens EM, Giraudo CG, Snapper SB. Variants in STXBP3 are Associated with Very Early Onset Inflammatory Bowel Disease, Bilateral Sensorineural Hearing Loss and Immune Dysregulation. J Crohns Colitis 2021; 15:1908-1919. [PMID: 33891011 PMCID: PMC8575043 DOI: 10.1093/ecco-jcc/jjab077] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
BACKGROUND AND AIMS Very early onset inflammatory bowel disease [VEOIBD] is characterized by intestinal inflammation affecting infants and children less than 6 years of age. To date, over 60 monogenic aetiologies of VEOIBD have been identified, many characterized by highly penetrant recessive or dominant variants in underlying immune and/or epithelial pathways. We sought to identify the genetic cause of VEOIBD in a subset of patients with a unique clinical presentation. METHODS Whole exome sequencing was performed on five families with ten patients who presented with a similar constellation of symptoms including medically refractory infantile-onset IBD, bilateral sensorineural hearing loss and, in the majority, recurrent infections. Genetic aetiologies of VEOIBD were assessed and Sanger sequencing was performed to confirm novel genetic findings. Western analysis on peripheral blood mononuclear cells and functional studies with epithelial cell lines were employed. RESULTS In each of the ten patients, we identified damaging heterozygous or biallelic variants in the Syntaxin-Binding Protein 3 gene [STXBP3], a protein known to regulate intracellular vesicular trafficking in the syntaxin-binding protein family of molecules, but not associated to date with either VEOIBD or sensorineural hearing loss. These mutations interfere with either intron splicing or protein stability and lead to reduced STXBP3 protein expression. Knock-down of STXBP3 in CaCo2 cells resulted in defects in cell polarity. CONCLUSION Overall, we describe a novel genetic syndrome and identify a critical role for STXBP3 in VEOIBD, sensorineural hearing loss and immune dysregulation.
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Affiliation(s)
- Jodie Ouahed
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA
| | - Judith R Kelsen
- Division of Gastroenterology, Hepatology, and Nutrition, The Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Waldo A Spessott
- Department of Microbiology and Immunology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, 19107, USA
| | - Kameron Kooshesh
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
| | - Maria L Sanmillan
- Department of Microbiology and Immunology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, 19107, USA
| | - Noor Dawany
- Department of Biomedical Health Informatics, The Children's Hospital of Philadelphia, Philadelphia, PA, 19104, USA
| | - Kathleen E Sullivan
- Division of Allergy and Immunology, The Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Kathryn E Hamilton
- Division of Gastroenterology, Hepatology, and Nutrition, The Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Voytek Slowik
- Department of Medicine, Division of Gastroenterology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Sergey Nejentsev
- Division of Gastroenterology, Hepatology, and Nutrition, Children's Mercy Kansas City, Kansas City, MO, 64108, USA.,Department of Medicine, University of Cambridge, Cambridge, CB2 0QQ, UK
| | - João Farela Neves
- Department of Molecular Cell Biology and Immunology, Amsterdam University Medical Centers, Amsterdam, the Netherlands.,Primary Immunodeficiencies Unit; Hospital Dona Estefânia-CHLC, EPE, Lisbon, 1169, Portugal
| | - Helena Flores
- CEDOC, Chronic Diseases Research Center, NOVA Medical School, Lisbon, 1150, Portugal
| | - Wendy K Chung
- Gastroenterology Unit, Hospital Dona Estefânia-CHLC, EPE, Lisbon, 1169, Portugal
| | - Ashley Wilson
- Gastroenterology Unit, Hospital Dona Estefânia-CHLC, EPE, Lisbon, 1169, Portugal
| | - Kwame Anyane-Yeboa
- Gastroenterology Unit, Hospital Dona Estefânia-CHLC, EPE, Lisbon, 1169, Portugal
| | - Karen Wou
- Gastroenterology Unit, Hospital Dona Estefânia-CHLC, EPE, Lisbon, 1169, Portugal
| | - Preti Jain
- Department of Pediatrics, Columbia University Medical Center, New York, NY, 10032, USA.,Department of Medicine, Columbia University Medical Center, New York, NY, 10032, USA
| | - Michael Field
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA
| | - Sophia Tollefson
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA
| | - Maiah H Dent
- Department of Genetics, Yale University, New Haven, CT, 06510, USA
| | - Dalin Li
- F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, 90048, USA
| | - Takeo Naito
- F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, 90048, USA
| | - Dermot P B McGovern
- F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, 90048, USA
| | - Andrew C Kwong
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA.,Biological and Biomedical Sciences, Harvard Medical School, Boston, MA, 02115, USA.,Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA
| | - Faith Taliaferro
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA.,Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA
| | - Jose Ordovas-Montanes
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA.,Broad Institute of MIT and Harvard, Cambridge, MA, 02142, USA.,Program in Immunology, Harvard Medical School, Boston, MA, 02115, USA.,Harvard Stem Cell Institute, Cambridge, MA, 02138, USA
| | - Bruce H Horwitz
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA.,Division of Emergency Medicine, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA
| | - Daniel Kotlarz
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA.,Dr. von Hauner Children's Hospital, Department of Pediatrics, University Hospital LMU Munich, Munich, 80337, Germany
| | - Christoph Klein
- Dr. von Hauner Children's Hospital, Department of Pediatrics, University Hospital LMU Munich, Munich, 80337, Germany
| | - Jonathan Evans
- Department of Pediatrics, Nemours Children's Specialty Care, Jacksonville, FL 32207, USA
| | - Jill Dorsey
- Department of Pediatrics, Nemours Children's Specialty Care, Jacksonville, FL 32207, USA
| | - Neil Warner
- SickKids Inflammatory Bowel Disease Center and Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, ON, Canada.,Department of Pediatrics and Biochemistry, University of Toronto, Hospital for Sick Children, Toronto, ON, M5G 1X8, Canada
| | - Abdul Elkadri
- SickKids Inflammatory Bowel Disease Center and Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, ON, Canada.,Department of Pediatrics and Biochemistry, University of Toronto, Hospital for Sick Children, Toronto, ON, M5G 1X8, Canada
| | - Aleixo M Muise
- SickKids Inflammatory Bowel Disease Center and Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, ON, Canada.,Department of Pediatrics and Biochemistry, University of Toronto, Hospital for Sick Children, Toronto, ON, M5G 1X8, Canada
| | - Jeffrey Goldsmith
- Department of Pathology, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA
| | - Benjamin Thompson
- Primary Immunodeficiency Group, III Theme, Institute of Cellular Medicine, Newcastle University, Newcastle, NE2 4HH, UK
| | - Karin R Engelhardt
- Primary Immunodeficiency Group, III Theme, Institute of Cellular Medicine, Newcastle University, Newcastle, NE2 4HH, UK
| | - Andrew J Cant
- Primary Immunodeficiency Group, III Theme, Institute of Cellular Medicine, Newcastle University, Newcastle, NE2 4HH, UK.,Children's Immunology Service, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle, NE1 4LP, UK
| | - Sophie Hambleton
- Primary Immunodeficiency Group, III Theme, Institute of Cellular Medicine, Newcastle University, Newcastle, NE2 4HH, UK.,Children's Immunology Service, Great North Children's Hospital, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle, NE1 4LP, UK
| | - Andrew Barclay
- Department of Paediatric Gastroenterology, Royal Hospital for Children, Glasgow, G51 4TF, UK
| | - Agnes Toth-Petroczy
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA.,Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.,Center for Systems Biology Dresden, Dresden, Germany
| | - Dana Vuzman
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
| | - Nikkola Carmichael
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
| | - Corneliu Bodea
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
| | - Christopher A Cassa
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
| | - Marcella Devoto
- Division of Human Genetics, The Children's Hospital of Philadelphia, Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.,Department of Translational and Precision Medicine, University Sapienza, Rome 00185, Italy.,CNR-IRGB, Cagliari 09042, Italy
| | - Richard L Maas
- Brigham Genomic Medicine Program, Division of Genetics, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
| | - Edward M Behrens
- Division of Rheumatology, The Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Claudio G Giraudo
- Department of Microbiology and Immunology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, 19107, USA
| | - Scott B Snapper
- Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Boston Children's Hospital, and Harvard Medical School, Boston, MA, 02115, USA.,Division of Gastroenterology, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA, 02115, USA
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8
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Complexin-2 redistributes to the membrane of muscle cells in response to insulin and contributes to GLUT4 translocation. Biochem J 2021; 478:407-422. [DOI: 10.1042/bcj20200542] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 12/11/2020] [Accepted: 01/04/2021] [Indexed: 11/17/2022]
Abstract
Insulin stimulates glucose uptake in muscle cells by rapidly redistributing vesicles containing GLUT4 glucose transporters from intracellular compartments to the plasma membrane (PM). GLUT4 vesicle fusion requires the formation of SNARE complexes between vesicular VAMP and PM syntaxin4 and SNAP23. SNARE accessory proteins usually regulate vesicle fusion processes. Complexins aide in neuro-secretory vesicle-membrane fusion by stabilizing trans-SNARE complexes but their participation in GLUT4 vesicle fusion is unknown. We report that complexin-2 is expressed and homogeneously distributed in L6 rat skeletal muscle cells. Upon insulin stimulation, a cohort of complexin-2 redistributes to the PM. Complexin-2 knockdown markedly inhibited GLUT4 translocation without affecting proximal insulin signalling of Akt/PKB phosphorylation and actin fiber remodelling. Similarly, complexin-2 overexpression decreased maximal GLUT4 translocation suggesting that the concentration of complexin-2 is finely tuned to vesicle fusion. These findings reveal an insulin-dependent regulation of GLUT4 insertion into the PM involving complexin-2.
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9
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Whitten AE, Jarrott RJ, Hu SH, Duff AP, King GJ, Martin JL, Christie MP. Studying Munc18:Syntaxin Interactions Using Small-Angle Scattering. Methods Mol Biol 2019; 1860:115-144. [PMID: 30317501 DOI: 10.1007/978-1-4939-8760-3_7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The interaction between the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein syntaxin (Sx) and regulatory partner Sec/Munc18 (SM) protein is a critical step in vesicle fusion. The exact role played by SM proteins, whether positive or negative, has been the topic of much debate. High-resolution structures of the SM:Sx complex have shown that SM proteins can bind syntaxin in a closed fusion incompetent state. However, in vitro and in vivo experiments also point to a positive regulatory role for SM proteins that is inconsistent with binding syntaxin in a closed conformation. Here we present protocols we used for the expression and purification of the SM proteins Munc18a and Munc18c and syntaxins 1 and 4 along with procedures used for small-angle X-ray and neutron scattering that showed that syntaxins can bind in an open conformation to SM proteins. We also describe methods for chemical cross-linking experiments and detail how this information can be combined with scattering data to obtain low-resolution structural models for SM:Sx protein complexes.
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Affiliation(s)
- Andrew E Whitten
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Russell J Jarrott
- Griffith Institute for Drug Discovery, Griffith University, Nathan, QLD, Australia
| | - Shu-Hong Hu
- Griffith Institute for Drug Discovery, Griffith University, Nathan, QLD, Australia
| | - Anthony P Duff
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Gordon J King
- Centre for Microscopy and Microanalysis, The University of Queensland, St Lucia, QLD, Australia
| | - Jennifer L Martin
- Griffith Institute for Drug Discovery, Griffith University, Nathan, QLD, Australia
| | - Michelle P Christie
- Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, VIC, Australia.
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10
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Gutierrez BA, Chavez MA, Rodarte AI, Ramos MA, Dominguez A, Petrova Y, Davalos AJ, Costa RM, Elizondo R, Tuvim MJ, Dickey BF, Burns AR, Heidelberger R, Adachi R. Munc18-2, but not Munc18-1 or Munc18-3, controls compound and single-vesicle-regulated exocytosis in mast cells. J Biol Chem 2018; 293:7148-7159. [PMID: 29599294 DOI: 10.1074/jbc.ra118.002455] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 03/20/2018] [Indexed: 11/06/2022] Open
Abstract
Mast cells (MCs) play pivotal roles in many inflammatory conditions including infections, anaphylaxis, and asthma. MCs store immunoregulatory compounds in their large cytoplasmic granules and, upon stimulation, secrete them via regulated exocytosis. Exocytosis in many cells requires the participation of Munc18 proteins (also known as syntaxin-binding proteins), and we found that mature MCs express all three mammalian isoforms: Munc18-1, -2, and -3. To study their functions in MC effector responses and test the role of MC degranulation in anaphylaxis, we used conditional knockout (cKO) mice in which each Munc18 protein was deleted exclusively in MCs. Using recordings of plasma membrane capacitance for high-resolution analysis of exocytosis in individual MCs, we observed an almost complete absence of exocytosis in Munc18-2-deficient MCs but intact exocytosis in MCs lacking Munc18-1 or Munc18-3. Stereological analysis of EM images of stimulated MCs revealed that the deletion of Munc18-2 also abolishes the homotypic membrane fusion required for compound exocytosis. We confirmed the severe defect in regulated exocytosis in the absence of Munc18-2 by measuring the secretion of mediators stored in MC granules. Munc18-2 cKO mice had normal morphology, development, and distribution of their MCs, indicating that Munc18-2 is not essential for the migration, retention, and maturation of MC-committed progenitors. Despite that, we found that Munc18-2 cKO mice were significantly protected from anaphylaxis. In conclusion, MC-regulated exocytosis is required for the anaphylactic response, and Munc18-2 is the sole Munc18 isoform that mediates membrane fusion during MC degranulation.
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Affiliation(s)
- Berenice A Gutierrez
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030; Escuela de Ingeniería y Ciencias, Tecnologico de Monterrey, Monterrey NL 64849 México
| | - Miguel A Chavez
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030; Escuela de Medicina y Ciencias de la Salud, Tecnologico de Monterrey, Monterrey NL 64710 México
| | - Alejandro I Rodarte
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030; Escuela de Medicina y Ciencias de la Salud, Tecnologico de Monterrey, Monterrey NL 64710 México
| | - Marco A Ramos
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Andrea Dominguez
- Escuela de Medicina y Ciencias de la Salud, Tecnologico de Monterrey, Monterrey NL 64710 México
| | - Youlia Petrova
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Alfredo J Davalos
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Renan M Costa
- Graduate School of Biomedical Sciences, Houston, Texas 77030
| | - Ramon Elizondo
- Escuela de Medicina y Ciencias de la Salud, Tecnologico de Monterrey, Monterrey NL 64710 México
| | - Michael J Tuvim
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Burton F Dickey
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
| | - Alan R Burns
- College of Optometry, University of Houston, Houston, Texas 77204
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center, Houston, Texas 77030
| | - Roberto Adachi
- Department of Pulmonary Medicine, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030.
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11
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Christie MP, Hu SH, Whitten AE, Rehman A, Jarrott RJ, King GJ, Collins BM, Martin JL. Revisiting interaction specificity reveals neuronal and adipocyte Munc18 membrane fusion regulatory proteins differ in their binding interactions with partner SNARE Syntaxins. PLoS One 2017; 12:e0187302. [PMID: 29088285 PMCID: PMC5663490 DOI: 10.1371/journal.pone.0187302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Accepted: 10/17/2017] [Indexed: 01/01/2023] Open
Abstract
The efficient delivery of cellular cargo relies on the fusion of cargo-carrying vesicles with the correct membrane at the correct time. These spatiotemporal fusion events occur when SNARE proteins on the vesicle interact with cognate SNARE proteins on the target membrane. Regulatory Munc18 proteins are thought to contribute to SNARE interaction specificity through interaction with the SNARE protein Syntaxin. Neuronal Munc18a interacts with Syntaxin1 but not Syntaxin4, and adipocyte Munc18c interacts with Syntaxin4 but not Syntaxin1. Here we show that this accepted view of specificity needs revision. We find that Munc18c interacts with both Syntaxin4 and Syntaxin1, and appears to bind “non-cognate” Syntaxin1 a little more tightly than Syntaxin4. Munc18a binds Syntaxin1 and Syntaxin4, though it interacts with its cognate Syntaxin1 much more tightly. We also observed that when bound to non-cognate Munc18c, Syntaxin1 captures its neuronal SNARE partners SNAP25 and VAMP2, and Munc18c can bind to pre-formed neuronal SNARE ternary complex. These findings reveal that Munc18a and Munc18c bind Syntaxins differently. Munc18c relies principally on the Syntaxin N-peptide interaction for binding Syntaxin4 or Syntaxin1, whereas Munc18a can bind Syntaxin1 tightly whether or not the Syntaxin1 N-peptide is present. We conclude that Munc18a and Munc18c differ in their binding interactions with Syntaxins: Munc18a has two tight binding modes/sites for Syntaxins as defined previously but Munc18c has just one that requires the N-peptide. These results indicate that the interactions between Munc18 and Syntaxin proteins, and the consequences for in vivo function, are more complex than can be accounted for by binding specificity alone.
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Affiliation(s)
- Michelle P. Christie
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
- * E-mail: (MPC); (JLM)
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Andrew E. Whitten
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Russell J. Jarrott
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Gordon J. King
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Brett M. Collins
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, Queensland, Australia
- Griffith Institute for Drug Discovery, Griffith University, Nathan, Queensland, Australia
- * E-mail: (MPC); (JLM)
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12
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Morey C, Kienle CN, Klöpper TH, Burkhardt P, Fasshauer D. Evidence for a conserved inhibitory binding mode between the membrane fusion assembly factors Munc18 and syntaxin in animals. J Biol Chem 2017; 292:20449-20460. [PMID: 29046354 DOI: 10.1074/jbc.m117.811182] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 10/10/2017] [Indexed: 12/30/2022] Open
Abstract
The membrane fusion necessary for vesicle trafficking is driven by the assembly of heterologous SNARE proteins orchestrated by the binding of Sec1/Munc18 (SM) proteins to specific syntaxin SNARE proteins. However, the precise mode of interaction between SM proteins and SNAREs is debated, as contrasting binding modes have been found for different members of the SM protein family, including the three vertebrate Munc18 isoforms. While different binding modes could be necessary, given their roles in different secretory processes in different tissues, the structural similarity of the three isoforms makes this divergence perplexing. Although the neuronal isoform Munc18a is well-established to bind tightly to both the closed conformation and the N-peptide of syntaxin 1a, thereby inhibiting SNARE complex formation, Munc18b and -c, which have a more widespread distribution, are reported to mainly interact with the N-peptide of their partnering syntaxins and are thought to instead promote SNARE complex formation. We have reinvestigated the interaction between Munc18c and syntaxin 4 (Syx4). Using isothermal titration calorimetry, we found that Munc18c, like Munc18a, binds to both the closed conformation and the N-peptide of Syx4. Furthermore, using a novel kinetic approach, we found that Munc18c, like Munc18a, slows down SNARE complex formation through high-affinity binding to syntaxin. This strongly suggests that secretory Munc18s in general control the accessibility of the bound syntaxin, probably preparing it for SNARE complex assembly.
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Affiliation(s)
- Czuee Morey
- From the Département des neurosciences fondamentales, Université de Lausanne, Rue du Bugnon 9, CH-1005 Lausanne, Switzerland
| | - C Nickias Kienle
- From the Département des neurosciences fondamentales, Université de Lausanne, Rue du Bugnon 9, CH-1005 Lausanne, Switzerland
| | - Tobias H Klöpper
- Whitehat Life Sciences Ltd., 20 Wenlock Road, N1 7GU London, United Kingdom, and
| | - Pawel Burkhardt
- the Marine Biological Association, Citadel Hill Marine Laboratory, Plymouth PL1 2PB, United Kingdom
| | - Dirk Fasshauer
- From the Département des neurosciences fondamentales, Université de Lausanne, Rue du Bugnon 9, CH-1005 Lausanne, Switzerland,
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13
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Rehman A, Hu SH, Tnimov Z, Whitten AE, King GJ, Jarrott RJ, Norwood SJ, Alexandrov K, Collins BM, Christie MP, Martin JL. The nature of the Syntaxin4 C-terminus affects Munc18c-supported SNARE assembly. PLoS One 2017; 12:e0183366. [PMID: 28841669 PMCID: PMC5571939 DOI: 10.1371/journal.pone.0183366] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 08/02/2017] [Indexed: 11/18/2022] Open
Abstract
Vesicular transport of cellular cargo requires targeted membrane fusion and formation of a SNARE protein complex that draws the two apposing fusing membranes together. Insulin-regulated delivery and fusion of glucose transporter-4 storage vesicles at the cell surface is dependent on two key proteins: the SNARE integral membrane protein Syntaxin4 (Sx4) and the soluble regulatory protein Munc18c. Many reported in vitro studies of Munc18c:Sx4 interactions and of SNARE complex formation have used soluble Sx4 constructs lacking the native transmembrane domain. As a consequence, the importance of the Sx4 C-terminal anchor remains poorly understood. Here we show that soluble C-terminally truncated Sx4 dissociates more rapidly from Munc18c than Sx4 where the C-terminal transmembrane domain is replaced with a T4-lysozyme fusion. We also show that Munc18c appears to inhibit SNARE complex formation when soluble C-terminally truncated Sx4 is used but does not inhibit SNARE complex formation when Sx4 is C-terminally anchored (by a C-terminal His-tag bound to resin, by a C-terminal T4L fusion or by the native C-terminal transmembrane domain in detergent micelles). We conclude that the C-terminus of Sx4 is critical for its interaction with Munc18c, and that the reported inhibitory role of Munc18c may be an artifact of experimental design. These results support the notion that a primary role of Munc18c is to support SNARE complex formation and membrane fusion.
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Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Zakir Tnimov
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Andrew E. Whitten
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Gordon J. King
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Russell J. Jarrott
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Suzanne J. Norwood
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Kirill Alexandrov
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Brett M. Collins
- Division of Cell Biology and Molecular Medicine, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
| | - Michelle P. Christie
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
- * E-mail: (MPC); (JLM)
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Brisbane, QLD, Australia
- * E-mail: (MPC); (JLM)
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14
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Brasher MI, Martynowicz DM, Grafinger OR, Hucik A, Shanks-Skinner E, Uniacke J, Coppolino MG. Interaction of Munc18c and syntaxin4 facilitates invadopodium formation and extracellular matrix invasion of tumor cells. J Biol Chem 2017; 292:16199-16210. [PMID: 28798239 DOI: 10.1074/jbc.m117.807438] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Revised: 08/08/2017] [Indexed: 12/17/2022] Open
Abstract
Tumor cell invasion involves targeted localization of proteins required for interactions with the extracellular matrix and for proteolysis. The localization of many proteins during these cell-extracellular matrix interactions relies on membrane trafficking mediated in part by SNAREs. The SNARE protein syntaxin4 (Stx4) is involved in the formation of invasive structures called invadopodia; however, it is unclear how Stx4 function is regulated during tumor cell invasion. Munc18c is known to regulate Stx4 activity, and here we show that Munc18c is required for Stx4-mediated invadopodium formation and cell invasion. Biochemical and microscopic analyses revealed a physical association between Munc18c and Stx4, which was enhanced during invadopodium formation, and that a reduction in Munc18c expression decreases invadopodium formation. We also found that an N-terminal Stx4-derived peptide associates with Munc18c and inhibits endogenous interactions of Stx4 with synaptosome-associated protein 23 (SNAP23) and vesicle-associated membrane protein 2 (VAMP2). Furthermore, expression of the Stx4 N-terminal peptide decreased invadopodium formation and cell invasion in vitro Of note, cells expressing the Stx4 N-terminal peptide exhibited impaired trafficking of membrane type 1 matrix metalloproteinase (MT1-MMP) and EGF receptor (EGFR) to the cell surface during invadopodium formation. Our findings implicate Munc18c as a regulator of Stx4-mediated trafficking of MT1-MMP and EGFR, advancing our understanding of the role of SNARE function in the localization of proteins that drive tumor cell invasion.
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Affiliation(s)
- Megan I Brasher
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - David M Martynowicz
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Olivia R Grafinger
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Andrea Hucik
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Emma Shanks-Skinner
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - James Uniacke
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Marc G Coppolino
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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15
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Gene-wide Association Study Reveals RNF122 Ubiquitin Ligase as a Novel Susceptibility Gene for Attention Deficit Hyperactivity Disorder. Sci Rep 2017; 7:5407. [PMID: 28710364 PMCID: PMC5511183 DOI: 10.1038/s41598-017-05514-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Accepted: 05/31/2017] [Indexed: 01/07/2023] Open
Abstract
Attention Deficit Hyperactivity Disorder (ADHD) is a common childhood-onset neurodevelopmental condition characterized by pervasive impairment of attention, hyperactivity, and/or impulsivity that can persist into adulthood. The aetiology of ADHD is complex and multifactorial and, despite the wealth of evidence for its high heritability, genetic studies have provided modest evidence for the involvement of specific genes and have failed to identify consistent and replicable results. Due to the lack of robust findings, we performed gene-wide and pathway enrichment analyses using pre-existing GWAS data from 607 persistent ADHD subjects and 584 controls, produced by our group. Subsequently, expression profiles of genes surpassing a follow-up threshold of P-value < 1e-03 in the gene-wide analyses were tested in peripheral blood mononucleated cells (PBMCs) of 45 medication-naive adults with ADHD and 39 healthy unrelated controls. We found preliminary evidence for genetic association between RNF122 and ADHD and for its overexpression in adults with ADHD. RNF122 encodes for an E3 ubiquitin ligase involved in the proteasome-mediated processing, trafficking, and degradation of proteins that acts as an essential mediator of the substrate specificity of ubiquitin ligation. Thus, our findings support previous data that place the ubiquitin-proteasome system as a promising candidate for its involvement in the aetiology of ADHD.
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16
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Ren H, Elgner F, Himmelsbach K, Akhras S, Jiang B, Medvedev R, Ploen D, Hildt E. Identification of syntaxin 4 as an essential factor for the hepatitis C virus life cycle. Eur J Cell Biol 2017. [PMID: 28624237 DOI: 10.1016/j.ejcb.2017.06.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Although there is evidence that multivesicular bodies (MVBs) are involved in the release of hepatitis C virus (HCV), many aspects of HCV release are still not fully understood. The amount of α-taxilin that prevents SNARE (soluble N-ethylmaleimidesensitive factor attachment protein receptor) complex formation by binding to free syntaxin 4 is reduced in HCV-positive cells. Therefore, it was analyzed whether the t-SNARE protein syntaxin 4 which mediates vesicles fusion is involved in the HCV life cycle. HCV-positive cells possess an increased amount of syntaxin 4 protein, although the amount of syntaxin 4-specific transcripts is decreased in HCV-positive Huh7.5 cells and in HCV-infected primary human hepatocytes. In HCV-positive cells a significant longer half-life of syntaxin 4 was found that overcompensates for the decreased expression and leads to the elevated level of syntaxin 4. Overexpression of syntaxin 4 reduces the intracellular amount of infectious viral particles by facilitating viral release, while silencing of syntaxin 4 expression using specific siRNAs inhibits the release of HCV particles and so leads to an increase in the intracellular amount of infectious viral particles. This indicates that HCV uses a SNARE-dependent pathway for viral release. Confocal immunofluorescence microscopy revealed a colocalization of syntaxin 4 with a MVB-specific marker, exosomes and HCV core, which suggests a fraction of syntaxin 4 is associated with exosomes loaded with HCV. Altogether, it is assumed that syntaxin 4 is a novel essential cellular factor for the release of HCV.
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Affiliation(s)
- Huimei Ren
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany
| | - Fabian Elgner
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany
| | | | - Sami Akhras
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany
| | - Bingfu Jiang
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany
| | - Regina Medvedev
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany
| | - Daniela Ploen
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany
| | - Eberhard Hildt
- Paul-Ehrlich-Institut, Department of Virology, Langen, Germany; DZIF-German Center for Infection Research, Braunschweig, Germany.
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17
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Yu H, Rathore SS, Shen C, Liu Y, Ouyang Y, Stowell MH, Shen J. Reconstituting Intracellular Vesicle Fusion Reactions: The Essential Role of Macromolecular Crowding. J Am Chem Soc 2015; 137:12873-83. [PMID: 26431309 DOI: 10.1021/jacs.5b08306] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Intracellular vesicle fusion is mediated by SNAREs and Sec1/Munc18 (SM) proteins. Despite intensive efforts, the SNARE-SM mediated vesicle fusion reaction has not been faithfully reconstituted in biochemical assays. Here, we present an unexpected discovery that macromolecular crowding is required for reconstituting the vesicle fusion reaction in vitro. Macromolecular crowding is known to profoundly influence the kinetic and thermodynamic behaviors of macromolecules, but its role in membrane transport processes such as vesicle fusion remains unexplored. We introduced macromolecular crowding agents into reconstituted fusion reactions to mimic the crowded cellular environment. In this crowded assay, SNAREs and SM proteins acted in concert to drive efficient membrane fusion. In uncrowded assays, by contrast, SM proteins failed to associate with the SNAREs and the fusion rate decreased more than 30-fold, close to undetectable levels. The activities of SM proteins were strictly specific to their cognate SNARE isoforms and sensitive to biologically relevant mutations, further supporting that the crowded fusion assay accurately recapitulates the vesicle fusion reaction. Using this crowded fusion assay, we also showed that the SNARE-SM mediated fusion reaction can be modulated by two additional factors: NSF and α-SNAP. These findings suggest that the vesicle fusion machinery likely has been evolutionarily selected to function optimally in the crowded milieu of the cell. Accordingly, macromolecular crowding should constitute an integral element of any reconstituted fusion assay.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Shailendra S Rathore
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Chong Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Yinghui Liu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Yan Ouyang
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Michael H Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
| | - Jingshi Shen
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder , Boulder, Colorado 80309, United States
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18
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Xie L, Zhu D, Dolai S, Liang T, Qin T, Kang Y, Xie H, Huang YC, Gaisano HY. Syntaxin-4 mediates exocytosis of pre-docked and newcomer insulin granules underlying biphasic glucose-stimulated insulin secretion in human pancreatic beta cells. Diabetologia 2015; 58:1250-9. [PMID: 25762204 DOI: 10.1007/s00125-015-3545-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Accepted: 02/03/2015] [Indexed: 10/23/2022]
Abstract
AIMS/HYPOTHESIS Of the four exocytotic syntaxins (Syns), much is now known about the role of Syn-1A (pre-docked secretory granules [SGs]) and Syn-3 (newcomer SGs) in insulin exocytosis. Some work was reported on Syn-4's role in biphasic glucose-stimulated insulin secretion (GSIS), but its precise role in insulin SG exocytosis remains unclear. In this paper we examine this role in human beta cells. METHODS Endogenous function of Syn-4 in human islets was assessed by knocking down its expression with lentiviral single hairpin RNA (lenti-shRNA)-RFP. Biphasic GSIS was determined by islet perifusion assay. Single-cell analysis of exocytosis of red fluorescent protein (RFP)-positive beta cells (exhibiting near-total depletion of Syn-4) was by patch clamp capacitance measurements (Cm) and total internal reflection fluorescence microscopy (TIRFM), the latter to further assess single SG behaviour. Co-immunoprecipitations were conducted on INS-1 cells to assess exocytotic complexes. RESULTS Syn-4 knockdown (KD) of 77% in human islets caused a concomitant reduction in cognate Munc18c expression (46%) without affecting expression of other exocytotic proteins; this resulted in reduction of GSIS in the first phase (by 42%) and the second phase (by 40%). Cm of RFP-tagged Syn-4-KD beta cells showed severe inhibition in the readily releasable pool (by 71%) and mobilisation from reserve pools (by 63%). TIRFM showed that Syn-4-KD-induced inhibition of first-phase GSIS was attributed to reduction in exocytosis of both pre-docked and newcomer SGs (which undergo minimal residence or docking time at the plasma membrane before fusion). Second-phase inhibition was attributed to reduction in newcomer SGs. Stx-4 co-immunoprecipitated Munc18c, VAMP2 and VAMP8, suggesting that these exocytotic complexes may be involved in exocytosis of pre-docked and newcomer SGs. CONCLUSIONS/INTERPRETATION Syn-4 is involved in distinct molecular machineries that influence exocytosis of both pre-docked and newcomer SGs in a manner functionally redundant to Syn-1A and Syn-3, respectively; this underlies Syn-4's role in mediating portions of first-phase and second-phase GSIS.
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Affiliation(s)
- Li Xie
- Department of Medicine, Faculty of Medicine, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, ON, Canada, M5S 1A8
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19
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Odemuyiwa SO, Ilarraza R, Davoine F, Logan MR, Shayeganpour A, Wu Y, Majaesic C, Adamko DJ, Moqbel R, Lacy P. Cyclin-dependent kinase 5 regulates degranulation in human eosinophils. Immunology 2015; 144:641-8. [PMID: 25346443 DOI: 10.1111/imm.12416] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 10/03/2014] [Accepted: 10/17/2014] [Indexed: 12/19/2022] Open
Abstract
Degranulation from eosinophils in response to secretagogue stimulation is a regulated process that involves exocytosis of granule proteins through specific signalling pathways. One potential pathway is dependent on cyclin-dependent kinase 5 (Cdk5) and its effector molecules, p35 and p39, which play a central role in neuronal cell exocytosis by phosphorylating Munc18, a regulator of SNARE binding. Emerging evidence suggests a role for Cdk5 in exocytosis in immune cells, although its role in eosinophils is not known. We sought to examine the expression of Cdk5 and its activators in human eosinophils, and to assess the role of Cdk5 in eosinophil degranulation. We used freshly isolated human eosinophils and analysed the expression of Cdk5, p35, p39 and Munc18c by Western blot, RT-PCR, flow cytometry and immunoprecipitation. Cdk5 kinase activity was determined following eosinophil activation. Cdk5 inhibitors were used (roscovitine, AT7519 and small interfering RNA) to determine its role in eosinophil peroxidase (EPX) secretion. Cdk5 was expressed in association with Munc18c, p35 and p39, and phosphorylated following human eosinophil activation with eotaxin/CCL11, platelet-activating factor, and secretory IgA-Sepharose. Cdk5 inhibitors (roscovitine, AT7519) reduced EPX release when cells were stimulated by PMA or secretory IgA. In assays using small interfering RNA knock-down of Cdk5 expression in human eosinophils, we observed inhibition of EPX release. Our findings suggest that in activated eosinophils, Cdk5 is phosphorylated and binds to Munc18c, resulting in Munc18c release from syntaxin-4, allowing SNARE binding and vesicle fusion, with subsequent eosinophil degranulation. Our work identifies a novel role for Cdk5 in eosinophil mediator release by agonist-induced degranulation.
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Affiliation(s)
- Solomon O Odemuyiwa
- Pulmonary Research Group, Department of Medicine, University of Alberta, Edmonton, AB, Canada; Department of Paediatrics, University of Alberta, Edmonton, AB, Canada
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20
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Archbold JK, Whitten AE, Hu SH, Collins BM, Martin JL. SNARE-ing the structures of Sec1/Munc18 proteins. Curr Opin Struct Biol 2014; 29:44-51. [DOI: 10.1016/j.sbi.2014.09.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 09/09/2014] [Accepted: 09/12/2014] [Indexed: 10/24/2022]
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21
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Rehman A, Archbold JK, Hu SH, Norwood SJ, Collins BM, Martin JL. Reconciling the regulatory role of Munc18 proteins in SNARE-complex assembly. IUCRJ 2014; 1:505-513. [PMID: 25485130 PMCID: PMC4224468 DOI: 10.1107/s2052252514020727] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/15/2014] [Indexed: 06/04/2023]
Abstract
Membrane fusion is essential for human health, playing a vital role in processes as diverse as neurotransmission and blood glucose control. Two protein families are key: (1) the Sec1p/Munc18 (SM) and (2) the soluble N-ethylmaleimide-sensitive attachment protein receptor (SNARE) proteins. Whilst the essential nature of these proteins is irrefutable, their exact regulatory roles in membrane fusion remain controversial. In particular, whether SM proteins promote and/or inhibit the SNARE-complex formation required for membrane fusion is not resolved. Crystal structures of SM proteins alone and in complex with their cognate SNARE proteins have provided some insight, however, these structures lack the transmembrane spanning regions of the SNARE proteins and may not accurately reflect the native state. Here, we review the literature surrounding the regulatory role of mammalian Munc18 SM proteins required for exocytosis in eukaryotes. Our analysis suggests that the conflicting roles reported for these SM proteins may reflect differences in experimental design. SNARE proteins appear to require C-terminal immobilization or anchoring, for example through a transmembrane domain, to form a functional fusion complex in the presence of Munc18 proteins.
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Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Julia K. Archbold
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Suzanne J. Norwood
- Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Brett M. Collins
- Division of Molecular Cell Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD 4072, Australia
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22
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Yu H, Rathore SS, Gulbranson DR, Shen J. The N- and C-terminal domains of tomosyn play distinct roles in soluble N-ethylmaleimide-sensitive factor attachment protein receptor binding and fusion regulation. J Biol Chem 2014; 289:25571-80. [PMID: 25063806 DOI: 10.1074/jbc.m114.591487] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tomosyn negatively regulates SNARE-dependent exocytic pathways including insulin secretion, GLUT4 exocytosis, and neurotransmitter release. The molecular mechanism of tomosyn, however, has not been fully elucidated. Here, we reconstituted SNARE-dependent fusion reactions in vitro to recapitulate the tomosyn-regulated exocytic pathways. We then expressed and purified active full-length tomosyn and examined how it regulates the reconstituted SNARE-dependent fusion reactions. Using these defined fusion assays, we demonstrated that tomosyn negatively regulates SNARE-mediated membrane fusion by inhibiting the assembly of the ternary SNARE complex. Tomosyn recognizes the t-SNARE complex and prevents its pairing with the v-SNARE, therefore arresting the fusion reaction at a pre-docking stage. The inhibitory function of tomosyn is mediated by its C-terminal domain (CTD) that contains an R-SNARE-like motif, confirming previous studies carried out using truncated tomosyn fragments. Interestingly, the N-terminal domain (NTD) of tomosyn is critical (but not sufficient) to the binding of tomosyn to the syntaxin monomer, indicating that full-length tomosyn possesses unique features not found in the widely studied CTD fragment. Finally, we showed that the inhibitory function of tomosyn is dominant over the stimulatory activity of the Sec1/Munc18 protein in fusion. We suggest that tomosyn uses its CTD to arrest SNARE-dependent fusion reactions, whereas its NTD is required for the recruitment of tomosyn to vesicle fusion sites through syntaxin interaction.
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Affiliation(s)
- Haijia Yu
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Shailendra S Rathore
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Daniel R Gulbranson
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
| | - Jingshi Shen
- From the Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309
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23
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Hellewell AL, Foresti O, Gover N, Porter MY, Hewitt EW. Analysis of familial hemophagocytic lymphohistiocytosis type 4 (FHL-4) mutant proteins reveals that S-acylation is required for the function of syntaxin 11 in natural killer cells. PLoS One 2014; 9:e98900. [PMID: 24910990 PMCID: PMC4049605 DOI: 10.1371/journal.pone.0098900] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 05/08/2014] [Indexed: 11/25/2022] Open
Abstract
Natural killer (NK) cell secretory lysosome exocytosis and cytotoxicity are impaired in familial hemophagocytic lymphohistiocytosis type 4 (FHL-4), a disorder caused by mutations in the gene encoding the SNARE protein syntaxin 11. We show that syntaxin 11 binds to SNAP23 in NK cells and that this interaction is reduced by FHL-4 truncation and frameshift mutation proteins that delete all or part of the SNARE domain of syntaxin 11. In contrast the FHL-4 mutant proteins bound to the Sec-1/Munc18-like (SM) protein Munc18-2. We demonstrate that the C-terminal cysteine rich region of syntaxin 11, which is deleted in the FHL-4 mutants, is S-acylated. This posttranslational modification is required for the membrane association of syntaxin 11 and for its polarization to the immunological synapse in NK cells conjugated to target cells. Moreover, we show that Munc18-2 is recruited by syntaxin 11 to intracellular membranes in resting NK cells and to the immunological synapse in activated NK cells. This recruitment of Munc18-2 is abolished by deletion of the C-terminal cysteine rich region of syntaxin 11. These results suggest a pivotal role for S-acylation in the function of syntaxin 11 in NK cells.
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Affiliation(s)
- Andrew L. Hellewell
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Ombretta Foresti
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Nicola Gover
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Morwenna Y. Porter
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Eric W. Hewitt
- School of Molecular and Cellular Biology and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
- * E-mail:
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24
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Insulin stimulates syntaxin4 SNARE complex assembly via a novel regulatory mechanism. Mol Cell Biol 2014; 34:1271-9. [PMID: 24469400 DOI: 10.1128/mcb.01203-13] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Insulin stimulates glucose transport into fat and muscle cells by increasing the exocytic trafficking rate of the GLUT4 facilitative glucose transporter from intracellular stores to the plasma membrane. Delivery of GLUT4 to the plasma membrane is mediated by formation of functional SNARE complexes containing syntaxin4, SNAP23, and VAMP2. Here we have used an in situ proximity ligation assay to integrate these two observations by demonstrating for the first time that insulin stimulation causes an increase in syntaxin4-containing SNARE complex formation in adipocytes. Furthermore, we demonstrate that insulin brings about this increase in SNARE complex formation by mobilizing a pool of syntaxin4 held in an inactive state under basal conditions. Finally, we have identified phosphorylation of the regulatory protein Munc18c, a direct target of the insulin receptor, as a molecular switch to coordinate this process. Hence, this report provides molecular detail of how the cell alters membrane traffic in response to an external stimulus, in this case, insulin.
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25
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Rehman A, Jarrott RJ, Whitten AE, King GJ, Hu SH, Christie MP, Collins BM, Martin JL. Milligram quantities of homogeneous recombinant full-length mouse Munc18c from Escherichia coli cultures. PLoS One 2013; 8:e83499. [PMID: 24391775 PMCID: PMC3877047 DOI: 10.1371/journal.pone.0083499] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Accepted: 11/05/2013] [Indexed: 12/24/2022] Open
Abstract
Vesicle fusion is an indispensable cellular process required for eukaryotic cargo delivery. The Sec/Munc18 protein Munc18c is essential for insulin-regulated trafficking of glucose transporter4 (GLUT4) vesicles to the cell surface in muscle and adipose tissue. Previously, our biophysical and structural studies have used Munc18c expressed in SF9 insect cells. However to maximize efficiency, minimize cost and negate any possible effects of post-translational modifications of Munc18c, we investigated the use of Escherichia coli as an expression host for Munc18c. We were encouraged by previous reports describing Munc18c production in E. coli cultures for use in in vitro fusion assay, pulldown assays and immunoprecipitations. Our approach differs from the previously reported method in that it uses a codon-optimized gene, lower temperature expression and autoinduction media. Three N-terminal His-tagged constructs were engineered, two with a tobacco etch virus (TEV) or thrombin protease cleavage site to enable removal of the fusion tag. The optimized protocol generated 1–2 mg of purified Munc18c per L of culture at much reduced cost compared to Munc18c generated using insect cell culture. The purified recombinant Munc18c protein expressed in bacteria was monodisperse, monomeric, and functional. In summary, we developed methods that decrease the cost and time required to generate functional Munc18c compared with previous insect cell protocols, and which generates sufficient purified protein for structural and biophysical studies.
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Affiliation(s)
- Asma Rehman
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Russell J. Jarrott
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Andrew E. Whitten
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Gordon J. King
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Shu-Hong Hu
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Michelle P. Christie
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Brett M. Collins
- Division of Molecular Cell Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
| | - Jennifer L. Martin
- Division of Chemistry and Structural Biology, University of Queensland, Institute for Molecular Bioscience, Brisbane, Australia
- * E-mail:
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26
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Abstract
Mutations in either syntaxin 11 (Stx11) or Munc18-2 abolish cytotoxic T lymphocytes (CTL) and natural killer cell (NK) cytotoxicity, and give rise to familial hemophagocytic lymphohistiocytosis (FHL4 or FHL5, respectively). Although Munc18-2 is known to interact with Stx11, little is known about the molecular mechanisms governing the specificity of this interaction or how in vitro IL-2 activation leads to compensation of CTL and NK cytotoxicity. To understand how mutations in Munc18-2 give rise to disease, we have solved the structure of human Munc18-2 at 2.6 Å resolution and mapped 18 point mutations. The four surface mutations identified (R39P, L130S, E132A, P334L) map exclusively to the predicted syntaxin and soluble N-ethylmaleimide-sensitive factor accessory protein receptor binding sites of Munc18-2. We find that Munc18-2 binds the N-terminal peptide of Stx11 with a ~20-fold higher affinity than Stx3, suggesting a potential role in selective binding. Upon IL-2 activation, levels of Stx3 are increased, favoring Munc18-2 binding when Stx11 is absent. Similarly, Munc18-1, expressed in IL-2-activated CTL, is capable of binding Stx11. These findings provide potential explanations for restoration of Munc18-Stx function and cytotoxicity in IL-2-activated cells.
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27
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Comparative studies of Munc18c and Munc18-1 reveal conserved and divergent mechanisms of Sec1/Munc18 proteins. Proc Natl Acad Sci U S A 2013; 110:E3271-80. [PMID: 23918365 DOI: 10.1073/pnas.1311232110] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Sec1/Munc18 (SM) family proteins are essential for every vesicle fusion pathway. The best-characterized SM protein is the synaptic factor Munc18-1, but it remains unclear whether its functions represent conserved mechanisms of SM proteins or specialized activities in neurotransmitter release. To address this question, we dissected Munc18c, a functionally distinct SM protein involved in nonsynaptic exocytic pathways. We discovered that Munc18c binds to the trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex and strongly accelerates the fusion rate. Further analysis suggests that Munc18c recognizes both vesicle-rooted SNARE and target membrane-associated SNAREs, and promotes trans-SNARE zippering at the postdocking stage of the fusion reaction. The stimulation of fusion by Munc18c is specific to its cognate SNARE isoforms. Because Munc18-1 regulates fusion in a similar manner, we conclude that one conserved function of SM proteins is to bind their cognate trans-SNARE complexes and accelerate fusion kinetics. Munc18c also binds syntaxin-4 monomer but does not block target membrane-associated SNARE assembly, in agreement with our observation that six- to eightfold increases in Munc18c expression do not inhibit insulin-stimulated glucose uptake in adipocytes. Thus, the inhibitory "closed" syntaxin binding mode demonstrated for Munc18-1 is not conserved in Munc18c. Unexpectedly, we found that Munc18c recognizes the N-terminal region of the vesicle-rooted SNARE, whereas Munc18-1 requires the C-terminal sequences, suggesting that the architecture of the SNARE/SM complex likely differs across fusion pathways. Together, these comparative studies of two distinct SM proteins reveal conserved as well as divergent mechanisms of SM family proteins in intracellular vesicle fusion.
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28
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Lam PP, Ohno M, Dolai S, He Y, Qin T, Liang T, Zhu D, Kang Y, Liu Y, Kauppi M, Xie L, Wan WC, Bin NR, Sugita S, Olkkonen VM, Takahashi N, Kasai H, Gaisano HY. Munc18b is a major mediator of insulin exocytosis in rat pancreatic β-cells. Diabetes 2013; 62:2416-28. [PMID: 23423569 PMCID: PMC3712044 DOI: 10.2337/db12-1380] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Sec1/Munc18 proteins facilitate the formation of trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes that mediate fusion of secretory granule (SG) with plasma membrane (PM). The capacity of pancreatic β-cells to exocytose insulin becomes compromised in diabetes. β-Cells express three Munc18 isoforms of which the role of Munc18b is unknown. We found that Munc18b depletion in rat islets disabled SNARE complex formation formed by syntaxin (Syn)-2 and Syn-3. Two-photon imaging analysis revealed in Munc18b-depleted β-cells a 40% reduction in primary exocytosis (SG-PM fusion) and abrogation of almost all sequential SG-SG fusion, together accounting for a 50% reduction in glucose-stimulated insulin secretion (GSIS). In contrast, gain-of-function expression of Munc18b wild-type and, more so, dominant-positive K314L/R315L mutant promoted the assembly of cognate SNARE complexes, which caused potentiation of biphasic GSIS. We found that this was attributed to a more than threefold enhancement of both primary exocytosis and sequential SG-SG fusion, including long-chain fusion (6-8 SGs) not normally (2-3 SG fusion) observed. Thus, Munc18b-mediated exocytosis may be deployed to increase secretory efficiency of SGs in deeper cytosolic layers of β-cells as well as additional primary exocytosis, which may open new avenues of therapy development for diabetes.
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Affiliation(s)
- Patrick P.L. Lam
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Mitsuyo Ohno
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Tokyo, Japan
| | - Subhankar Dolai
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yu He
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tairan Qin
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Dan Zhu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Youhou Kang
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Yunfeng Liu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Maria Kauppi
- National Institute for Health and Welfare, Biomedicum, Helsinki, Finland
| | - Li Xie
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Wilson C.Y. Wan
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - Na-Rhum Bin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Division of Fundamental Neurobiology, University Health Network, Toronto, Ontario, Canada
| | - Shuzo Sugita
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Division of Fundamental Neurobiology, University Health Network, Toronto, Ontario, Canada
| | - Vesa M. Olkkonen
- Minerva Foundation Institute for Medical Research, Biomedicum, Helsinki, Finland
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Tokyo, Japan
| | - Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, University of Tokyo, Tokyo, Japan
- Corresponding authors: Haruo Kasai, , and Herbert Y. Gaisano,
| | - Herbert Y. Gaisano
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Corresponding authors: Haruo Kasai, , and Herbert Y. Gaisano,
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29
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Yu H, Rathore SS, Shen J. Synip arrests soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent membrane fusion as a selective target membrane SNARE-binding inhibitor. J Biol Chem 2013; 288:18885-93. [PMID: 23665562 DOI: 10.1074/jbc.m113.465450] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The vesicle fusion reaction in regulated exocytosis requires the concerted action of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) core fusion engine and a group of SNARE-binding regulatory factors. The regulatory mechanisms of vesicle fusion remain poorly understood in most exocytic pathways. Here, we reconstituted the SNARE-dependent vesicle fusion reaction of GLUT4 exocytosis in vitro using purified components. Using this defined fusion system, we discovered that the regulatory factor synip binds to GLUT4 exocytic SNAREs and inhibits the docking, lipid mixing, and content mixing of the fusion reaction. Synip arrests fusion by binding the target membrane SNARE (t-SNARE) complex and preventing the initiation of ternary SNARE complex assembly. Although synip also interacts with the syntaxin-4 monomer, it does not inhibit the pairing of syntaxin-4 with SNAP-23. Interestingly, synip selectively arrests the fusion reactions reconstituted with its cognate SNAREs, suggesting that the defined system recapitulates the biological functions of the vesicle fusion proteins. We further showed that the inhibitory function of synip is dominant over the stimulatory activity of Sec1/Munc18 proteins. Importantly, the inhibitory function of synip is distinct from how other fusion inhibitors arrest SNARE-dependent membrane fusion and therefore likely represents a novel regulatory mechanism of vesicle fusion.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309, USA
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30
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Lopez JA, Voskoboinik I. Deciphering the syntax of cytotoxic lymphocyte degranulation. Eur J Immunol 2013; 43:46-9. [PMID: 23322694 DOI: 10.1002/eji.201243221] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 12/03/2012] [Accepted: 12/10/2012] [Indexed: 11/09/2022]
Abstract
In the killer lymphocyte, the targeted delivery of perforin- and granzyme-containing cytotoxic granules to the immunological synapse is crucial for the eradication of pathogen-infected or transformed targets. This process is achieved through a tightly controlled and highly efficient granule exocytosis pathway. Mutations in the granule trafficking proteins Munc13-4, syntaxin 11, Munc18-2 or Rab27 leads to a fatal lapse of immune surveillance and can be manifested as haemophagocytic lymphohistiocytosis in humans. Elucidation of the role of these proteins in exocytic trafficking is pivotal for our understanding of their role in health and disease. In this issue of the European Journal of Immunology, D'Orlando et al. [Eur. J. Immunol. 2013. 43: 194-208] make an important step in this direction, as they generate and characterise syntaxin 11 deficient mice. Herein, we discuss the role of syntaxin-11 in soluble NSF (N-ethylmaleimide sensitive fusion) attachment protein receptors complex formation leading to cytotoxic lymphocyte degranulation and its importance in maintaining immune homeostasis.
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Affiliation(s)
- Jamie A Lopez
- Cancer Immunology Program, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Australia
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31
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Yu H, Rathore SS, Davis EM, Ouyang Y, Shen J. Doc2b promotes GLUT4 exocytosis by activating the SNARE-mediated fusion reaction in a calcium- and membrane bending-dependent manner. Mol Biol Cell 2013; 24:1176-84. [PMID: 23427263 PMCID: PMC3623638 DOI: 10.1091/mbc.e12-11-0810] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Reconstitution of GLUT4 vesicle fusion in a defined fusion system shows that the C2-domain factor Doc2b activates the SNARE-dependent fusion reaction by a calcium- and membrane bending–dependent mechanism. Of importance, certain features of Doc2b function appear to be distinct from how synaptotagmin-1 promotes synaptic release. The glucose transporter GLUT4 plays a central role in maintaining body glucose homeostasis. On insulin stimulation, GLUT4-containing vesicles fuse with the plasma membrane, relocating GLUT4 from intracellular reservoirs to the cell surface to uptake excess blood glucose. The GLUT4 vesicle fusion reaction requires soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNAREs) as the core fusion engine and a group of regulatory proteins. In particular, the soluble C2-domain factor Doc2b plays a key role in GLUT4 vesicle fusion, but its molecular mechanism has been unclear. Here we reconstituted the SNARE-dependent GLUT4 vesicle fusion in a defined proteoliposome fusion system. We observed that Doc2b binds to GLUT4 exocytic SNAREs and potently accelerates the fusion kinetics in the presence of Ca2+. The stimulatory activity of Doc2b requires intact Ca2+-binding sites on both the C2A and C2B domains. Using electron microscopy, we observed that Doc2b strongly bends the membrane bilayer, and this membrane-bending activity is essential to the stimulatory function of Doc2b in fusion. These results demonstrate that Doc2b promotes GLUT4 exocytosis by accelerating the SNARE-dependent fusion reaction by a Ca2+- and membrane bending–dependent mechanism. Of importance, certain features of Doc2b function appear to be distinct from how synaptotagmin-1 promotes synaptic neurotransmitter release, suggesting that exocytic Ca2+ sensors may possess divergent mechanisms in regulating vesicle fusion.
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Affiliation(s)
- Haijia Yu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder, Boulder, CO 80309, USA
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Mendez M, Gaisano HY. Role of the SNARE protein SNAP23 on cAMP-stimulated renin release in mouse juxtaglomerular cells. Am J Physiol Renal Physiol 2012; 304:F498-504. [PMID: 23269646 DOI: 10.1152/ajprenal.00556.2012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Renin, the rate-limiting enzyme in the formation of angiotensin II, is synthesized and stored in granules in juxtaglomerular (JG) cells. Therefore, the controlled mechanism involved in renin release is essential for the regulation of blood pressure. Exocytosis of renin-containing granules is likely involved in renin release; a process stimulated by cAMP. We found that the "soluble NSF (N-ethylmaleimide-sensitive factor) attachment protein receptor" (SNARE) protein VAMP2 mediates cAMP-stimulated renin release and exocytosis in JG cells. To mediate exocytosis, VAMP2 must interact with a synaptosome-associated protein (SNAP). In the renal cortex, the isoform SNAP23 is abundantly expressed. We hypothesized that SNAP23 mediates cAMP-stimulated renin release from primary cultures of mouse JG cells. We found that SNAP23 protein is expressed and colocalized with renin-containing granules in primary cultures of mouse JG cell lysates. Thus, we then tested the involvement of SNAP23 in cAMP-stimulated renin release by transducing JG cells with a dominant-negative SNAP23 construct. In control JG cells transduced with a scrambled sequence, increasing cAMP stimulated renin release from 1.3 ± 0.3 to 5.3 ± 1.2% of renin content. In cells transduced with dominant-negative SNAP23, cAMP increased renin from 1.0 ± 0.1 to 3.0 ± 0.6% of renin content, a 50% blockade. Botulinum toxin E, which cleaves and inactivates SNAP23, reduced cAMP-stimulated renin release by 42 ± 17%. Finally, adenovirus-mediated silencing of SNAP23 significantly blocked cAMP-stimulated renin release by 50 ± 13%. We concluded that the SNARE protein SNAP23 mediates cAMP-stimulated renin release. These data show that renin release is a SNARE-dependent process.
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Rizo J, Südhof TC. The Membrane Fusion Enigma: SNAREs, Sec1/Munc18 Proteins, and Their Accomplices—Guilty as Charged? Annu Rev Cell Dev Biol 2012; 28:279-308. [DOI: 10.1146/annurev-cellbio-101011-155818] [Citation(s) in RCA: 318] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Josep Rizo
- Departments of Biophysics, Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390;
| | - Thomas C. Südhof
- Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University Medical School, Stanford, California 94305;
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Abstract
GLUT4 is an insulin-regulated glucose transporter that is responsible for insulin-regulated glucose uptake into fat and muscle cells. In the absence of insulin, GLUT4 is mainly found in intracellular vesicles referred to as GLUT4 storage vesicles (GSVs). Here, we summarise evidence for the existence of these specific vesicles, how they are sequestered inside the cell and how they undergo exocytosis in the presence of insulin. In response to insulin stimulation, GSVs fuse with the plasma membrane in a rapid burst and in the continued presence of insulin GLUT4 molecules are internalised and recycled back to the plasma membrane in vesicles that are distinct from GSVs and probably of endosomal origin. In this Commentary we discuss evidence that this delivery process is tightly regulated and involves numerous molecules. Key components include the actin cytoskeleton, myosin motors, several Rab GTPases, the exocyst, SNARE proteins and SNARE regulators. Each step in this process is carefully orchestrated in a sequential and coupled manner and we are beginning to dissect key nodes within this network that determine vesicle-membrane fusion in response to insulin. This regulatory process clearly involves the Ser/Thr kinase AKT and the exquisite manner in which this single metabolic process is regulated makes it a likely target for lesions that might contribute to metabolic disease.
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Affiliation(s)
- Jacqueline Stöckli
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia
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Rizo J, Rosen MK, Gardner KH. Enlightening molecular mechanisms through study of protein interactions. J Mol Cell Biol 2012; 4:270-83. [PMID: 22735643 DOI: 10.1093/jmcb/mjs036] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The investigation of molecular mechanisms is a fascinating area of current biological research that unites efforts from scientists with very diverse expertise. This review provides a perspective on the characterization of protein interactions as a central aspect of this research. We discuss case studies on the neurotransmitter release machinery that illustrate a variety of principles and emphasize the power of combining nuclear magnetic resonance (NMR) spectroscopy with other biophysical techniques, particularly X-ray crystallography. These studies have shown that: (i) the soluble SNAP receptor (SNARE) proteins form a tight complex that brings the synaptic vesicle and plasma membranes together, which is key for membrane fusion; (ii) the SNARE syntaxin-1 adopts an autoinhibitory closed conformation; (iii) Munc18-1 plays crucial functions through interactions with closed syntaxin-1 and with the SNARE complex; (iv) Munc13s mediate the opening of syntaxin-1; (v) complexins play dual roles through distinct interactions with the SNARE complex; (vi) synaptotagmin-1 acts a Ca(2+) sensor, interacting simultaneously with the membranes and the SNAREs; and (vii) a Munc13 homodimer to Munc13-RIM heterodimer switch modulates neurotransmitter release. Overall, this research underlines the complexities involved in elucidating molecular mechanisms and how these mechanisms can depend critically on an interplay between strong and weak protein interactions.
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Affiliation(s)
- Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA.
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Abstract
Despite daily fasting and feeding, plasma glucose levels are normally maintained within a narrow range owing to the hormones insulin and glucagon. Insulin increases glucose uptake into fat and muscle cells through the regulated trafficking of vesicles that contain glucose transporter type 4 (GLUT4). New insights into insulin signalling reveal that phosphorylation events initiated by the insulin receptor regulate key GLUT4 trafficking proteins, including small GTPases, tethering complexes and the vesicle fusion machinery. These proteins, in turn, control GLUT4 movement through the endosomal system, formation and retention of specialized GLUT4 storage vesicles and targeted exocytosis of these vesicles. Understanding these processes may help to explain the development of insulin resistance in type 2 diabetes and provide new potential therapeutic targets.
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Munc18-1 mutations that strongly impair SNARE-complex binding support normal synaptic transmission. EMBO J 2012; 31:2156-68. [PMID: 22446389 DOI: 10.1038/emboj.2012.72] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Accepted: 02/28/2012] [Indexed: 01/22/2023] Open
Abstract
Synaptic transmission depends critically on the Sec1p/Munc18 protein Munc18-1, but it is unclear whether Munc18-1 primarily operates as a integral part of the fusion machinery or has a more upstream role in fusion complex assembly. Here, we show that point mutations in Munc18-1 that interfere with binding to the free Syntaxin1a N-terminus and strongly impair binding to assembled SNARE complexes all support normal docking, priming and fusion of synaptic vesicles, and normal synaptic plasticity in munc18-1 null mutant neurons. These data support a prevailing role of Munc18-1 before/during SNARE-complex assembly, while its continued association to assembled SNARE complexes is dispensable for synaptic transmission.
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Kadono N, Miyazaki T, Okugawa Y, Nakajima K, Hirai Y. The impact of extracellular syntaxin4 on HaCaT keratinocyte behavior. Biochem Biophys Res Commun 2012; 417:1200-5. [DOI: 10.1016/j.bbrc.2011.12.107] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2011] [Accepted: 12/20/2011] [Indexed: 10/14/2022]
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Han GA, Malintan NT, Saw NMN, Li L, Han L, Meunier FA, Collins BM, Sugita S. Munc18-1 domain-1 controls vesicle docking and secretion by interacting with syntaxin-1 and chaperoning it to the plasma membrane. Mol Biol Cell 2011; 22:4134-49. [PMID: 21900502 PMCID: PMC3204074 DOI: 10.1091/mbc.e11-02-0135] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Munc18-1 plays pleiotropic roles in neurosecretion by acting as 1) a molecular chaperone of syntaxin-1, 2) a mediator of dense-core vesicle docking, and 3) a priming factor for soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated membrane fusion. However, how these functions are executed and whether they are correlated remains unclear. Here we analyzed the role of the domain-1 cleft of Munc18-1 by measuring the abilities of various mutants (D34N, D34N/M38V, K46E, E59K, K46E/E59K, K63E, and E66A) to bind and chaperone syntaxin-1 and to restore the docking and secretion of dense-core vesicles in Munc18-1/-2 double-knockdown cells. We identified striking correlations between the abilities of these mutants to bind and chaperone syntaxin-1 with their ability to restore vesicle docking and secretion. These results suggest that the domain-1 cleft of Munc18-1 is essential for binding to syntaxin-1 and thereby critical for its chaperoning, docking, and secretory functions. Our results demonstrate that the effect of the alleged priming mutants (E59K, D34N/M38V) on exocytosis can largely be explained by their reduced syntaxin-1-chaperoning functions. Finally, our data suggest that the intracellular expression and distribution of syntaxin-1 determines the level of dense-core vesicle docking.
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Affiliation(s)
- Gayoung A Han
- Division of Fundamental Neurobiology, University Health Network, Toronto ON M5T 2S8, Canada
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40
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Primordial neurosecretory apparatus identified in the choanoflagellate Monosiga brevicollis. Proc Natl Acad Sci U S A 2011; 108:15264-9. [PMID: 21876177 DOI: 10.1073/pnas.1106189108] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
SNARE protein-driven secretion of neurotransmitters from synaptic vesicles is at the center of neuronal communication. In the absence of the cytosolic protein Munc18-1, synaptic secretion comes to a halt. Although it is believed that Munc18-1 orchestrates SNARE complexes, its mode of action is still a matter of debate. In particular, it has been challenging to clarify the role of a tight Munc18/syntaxin 1 complex, because this interaction interferes strongly with syntaxin's ability to form a SNARE complex. In this complex, two regions of syntaxin, the N-peptide and the remainder in closed conformation, bind to Munc18 simultaneously. Until now, this binary complex has been reported for neuronal tissues only, leading to the hypothesis that it might be a specialization of the neuronal secretion apparatus. Here we aimed, by comparing the core secretion machinery of the unicellular choanoflagellate Monosiga brevicollis with that of animals, to reconstruct the ancestral function of the Munc18/syntaxin1 complex. We found that the Munc18/syntaxin 1 complex from M. brevicollis is structurally and functionally highly similar to the vertebrate complex, suggesting that it constitutes a fundamental step in the reaction pathway toward SNARE assembly. We thus propose that the primordial secretion machinery of the common ancestor of choanoflagellates and animals has been co-opted for synaptic roles during the rise of animals.
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41
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Schollmeier Y, Krause JM, Kreye S, Malsam J, Söllner TH. Resolving the function of distinct Munc18-1/SNARE protein interaction modes in a reconstituted membrane fusion assay. J Biol Chem 2011; 286:30582-30590. [PMID: 21730064 DOI: 10.1074/jbc.m111.269886] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sec1p/Munc18 proteins and SNAP receptors (SNAREs) are key components of the intracellular membrane fusion machinery. Compartment-specific v-SNAREs on a transport vesicle pair with their cognate t-SNAREs on the target membrane and drive lipid bilayer fusion. In a reconstituted assay that dissects the sequential assembly of t-SNARE (syntaxin 1·SNAP-25) and v-/t-SNARE (VAMP2·syntaxin 1·SNAP-25) complexes, and finally measures lipid bilayer merger, we resolved the inhibitory and stimulatory functions of the Sec1p/Munc18 protein Munc18-1 at the molecular level. Inhibition of membrane fusion by Munc18-1 requires a closed conformation of syntaxin 1. Remarkably, the concurrent preincubation of Munc18-1-inhibited syntaxin 1 liposomes with both VAMP2 liposomes and SNAP-25 at low temperature releases the inhibition and effectively stimulates membrane fusion. VAMP8 liposomes can neither release the inhibition nor exert the stimulatory effect, demonstrating the need for a specific Munc18-1/VAMP2 interaction. In addition, Munc18-1 binds to the N-terminal peptide of syntaxin 1, which is obligatory for a robust stimulation of membrane fusion. In contrast, this interaction is neither required for the inhibitory function of Munc18-1 nor for the release of this block. These results indicate that Munc18-1 and the neuronal SNAREs already have the inherent capability to function as a basic stage-specific off/on switch to control membrane fusion.
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Affiliation(s)
| | | | - Susanne Kreye
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Jörg Malsam
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany
| | - Thomas H Söllner
- Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany.
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42
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Reales E, Sharma N, Low SH, Fölsch H, Weimbs T. Basolateral sorting of syntaxin 4 is dependent on its N-terminal domain and the AP1B clathrin adaptor, and required for the epithelial cell polarity. PLoS One 2011; 6:e21181. [PMID: 21698262 PMCID: PMC3115984 DOI: 10.1371/journal.pone.0021181] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Accepted: 05/22/2011] [Indexed: 12/14/2022] Open
Abstract
Generation of epithelial cell polarity requires mechanisms to sort plasma membrane proteins to the apical and basolateral domains. Sorting involves incorporation into specific vesicular carriers and subsequent fusion to the correct target membranes mediated by specific SNARE proteins. In polarized epithelial cells, the SNARE protein syntaxin 4 localizes exclusively to the basolateral plasma membrane and plays an important role in basolateral trafficking pathways. However, the mechanism of basolateral targeting of syntaxin 4 itself has remained poorly understood. Here we show that newly synthesized syntaxin 4 is directly targeted to the basolateral plasma membrane in polarized Madin-Darby canine kidney (MDCK) cells. Basolateral targeting depends on a signal that is centered around residues 24–29 in the N-terminal domain of syntaxin 4. Furthermore, basolateral targeting of syntaxin 4 is dependent on the epithelial cell-specific clathrin adaptor AP1B. Disruption of the basolateral targeting signal of syntaxin 4 leads to non-polarized delivery to both the apical and basolateral surface, as well as partial intercellular retention in the trans-Golgi network. Importantly, disruption of the basolateral targeting signal of syntaxin 4 leads to the inability of MDCK cells to establish a polarized morphology which suggests that restriction of syntaxin 4 to the basolateral domain is required for epithelial cell polarity.
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Affiliation(s)
- Elena Reales
- Department of Molecular, Cellular, and Developmental Biology and Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California, United States of America
| | - Nikunj Sharma
- Department of Molecular, Cellular, and Developmental Biology and Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California, United States of America
| | - Seng Hui Low
- Department of Molecular, Cellular, and Developmental Biology and Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California, United States of America
| | - Heike Fölsch
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois, United States of America
| | - Thomas Weimbs
- Department of Molecular, Cellular, and Developmental Biology and Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, California, United States of America
- * E-mail:
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Torres J, Funk HM, Zegers MMP, ter Beest MBA. The syntaxin 4 N terminus regulates its basolateral targeting by munc18c-dependent and -independent mechanisms. J Biol Chem 2011; 286:10834-46. [PMID: 21278252 DOI: 10.1074/jbc.m110.186668] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
To generate and maintain epithelial cell polarity, specific sorting of proteins into vesicles destined for the apical and basolateral domain is required. Syntaxin 3 and 4 are apical and basolateral SNARE proteins important for the specificity of vesicle fusion at the apical and basolateral plasma membrane domains, respectively, but how these proteins are specifically targeted to these domains themselves is unclear. Munc18/SM proteins are potential regulators of this process. Like syntaxins, they are crucial for exocytosis and vesicle fusion. However, how munc18c and syntaxin 4 regulate the function of each other is unclear. Here, we investigated the requirement of syntaxin 4 in the delivery of basolateral membrane and secretory proteins, the basolateral targeting of syntaxin 4, and the role of munc18c in this targeting. Depletion of syntaxin 4 resulted in significant reduction of basolateral targeting, suggesting no compensation by other syntaxin forms. Mutational analysis identified amino acids Leu-25 and to a lesser extent Val-26 as essential for correct localization of syntaxin 4. Recently, it was shown that the N-terminal peptide of syntaxin 4 is involved in binding to munc18c. A mutation in this region that affects munc18c binding shows that munc18c binding is required for stabilization of syntaxin 4 at the plasma membrane but not for its correct targeting. We conclude that the N terminus serves two functions in membrane targeting. First, it harbors the sorting motif, which targets syntaxin 4 basolaterally in a munc18c-independent manner and second, it allows for munc18c binding, which stabilizes the protein in a munc18c-dependent manner.
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Affiliation(s)
- Jacqueline Torres
- Department of Surgery, The University of Chicago, Chicago, Illinois 60637, USA
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44
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Possible roles for Munc18-1 domain 3a and Syntaxin1 N-peptide and C-terminal anchor in SNARE complex formation. Proc Natl Acad Sci U S A 2010; 108:1040-5. [PMID: 21193638 DOI: 10.1073/pnas.0914906108] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Munc18-1 and Syntaxin1 are essential proteins for SNARE-mediated neurotransmission. Munc18-1 participates in synaptic vesicle fusion via dual roles: as a docking/chaperone protein by binding closed Syntaxin1, and as a fusion protein that binds SNARE complexes in a Syntaxin1 N-peptide dependent manner. The two roles are associated with a closed-open Syntaxin1 conformational transition. Here, we show that Syntaxin N-peptide binding to Munc18-1 is not highly selective, suggesting that other parts of the SNARE complex are involved in binding to Munc18-1. We also find that Syntaxin1, with an N peptide and a physically anchored C terminus, binds to Munc18-1 and that this complex can participate in SNARE complex formation. We report a Munc18-1-N-peptide crystal structure that, together with other data, reveals how Munc18-1 might transit from a conformation that binds closed Syntaxin1 to one that may be compatible with binding open Syntaxin1 and SNARE complexes. Our results suggest the possibility that structural transitions occur in both Munc18-1 and Syntaxin1 during their binary interaction. We hypothesize that Munc18-1 domain 3a undergoes a conformational change that may allow coiled-coil interactions with SNARE complexes.
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45
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Syntaxin N-terminal peptide motif is an initiation factor for the assembly of the SNARE-Sec1/Munc18 membrane fusion complex. Proc Natl Acad Sci U S A 2010; 107:22399-406. [PMID: 21139055 DOI: 10.1073/pnas.1012997108] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Intracellular membrane fusion is mediated by the concerted action of N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and Sec1/Munc18 (SM) proteins. During fusion, SM proteins bind the N-terminal peptide (N-peptide) motif of the SNARE subunit syntaxin, but the function of this interaction is unknown. Here, using FRET-based biochemical reconstitution and Caenorhabditis elegans genetics, we show that the N-peptide of syntaxin-1 recruits the SM protein Munc18-1/nSec1 to the SNARE bundle, facilitating their assembly into a fusion-competent complex. The recruitment is achieved through physical tethering rather than allosteric activation of Munc18-1. Consistent with the recruitment role, the N-peptide is not spatially constrained along syntaxin-1, and it is functional when translocated to another SNARE subunit SNAP-25 or even when simply anchored in the target membrane. The N-peptide function is restricted to an early initiation stage of the fusion reaction. After association, Munc18-1 and the SNARE bundle together drive membrane merging without further involving the N-peptide. Thus, the syntaxin N-peptide is an initiation factor for the assembly of the SNARE-SM membrane fusion complex.
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46
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Weber-Boyvat M, Aro N, Chernov KG, Nyman T, Jäntti J. Sec1p and Mso1p C-terminal tails cooperate with the SNAREs and Sec4p in polarized exocytosis. Mol Biol Cell 2010; 22:230-44. [PMID: 21119007 PMCID: PMC3020918 DOI: 10.1091/mbc.e10-07-0592] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
It is shown that Sec1p C-terminal tail is needed for proper Sec1p-SNARE complex interaction. Furthermore, evidence is provided that the Mso1p C terminus collaborates with the GTP-bound form of Sec4p in the bud. These results reveal a role for the Sec1p C-terminal tail in SNARE complex binding and suggest Mso1p as an effector for Sec4p. The Sec1/Munc18 protein family members perform an essential, albeit poorly understood, function in association with soluble n-ethylmaleimide sensitive factor adaptor protein receptor (SNARE) complexes in membrane fusion. The Saccharomyces cerevisiae Sec1p has a C-terminal tail that is missing in its mammalian homologues. Here we show that deletion of the Sec1p tail (amino acids 658–724) renders cells temperature sensitive for growth, reduces sporulation efficiency, causes a secretion defect, and abolishes Sec1p-SNARE component coimmunoprecipitation. The results show that the Sec1p tail binds preferentially ternary Sso1p-Sec9p-Snc2p complexes and it enhances ternary SNARE complex formation in vitro. The bimolecular fluorescence complementation (BiFC) assay results suggest that, in the SNARE-deficient sso2–1 Δsso1 cells, Mso1p, a Sec1p binding protein, helps to target Sec1p(1–657) lacking the C-terminal tail to the sites of secretion. The results suggest that the Mso1p C terminus is important for Sec1p(1–657) targeting. We show that, in addition to Sec1p, Mso1p can bind the Rab-GTPase Sec4p in vitro. The BiFC results suggest that Mso1p acts in close association with Sec4p on intracellular membranes in the bud. This association depends on the Sec4p guanine nucleotide exchange factor Sec2p. Our results reveal a novel binding mode between the Sec1p C-terminal tail and the SNARE complex, and suggest a role for Mso1p as an effector of Sec4p.
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Affiliation(s)
- Marion Weber-Boyvat
- Cell and Molecular Biology Program Research Program in Structural Biology and Biophysics, Institute of Biotechnology, FI-0001 University of Helsinki, Finland
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Peng RW, Abellan E, Fussenegger M. Differential effect of exocytic SNAREs on the production of recombinant proteins in mammalian cells. Biotechnol Bioeng 2010; 108:611-20. [PMID: 21246508 DOI: 10.1002/bit.22986] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Revised: 09/29/2010] [Accepted: 10/18/2010] [Indexed: 01/09/2023]
Abstract
Mammalian cells play a dominant role in the industrial production of biopharmaceutical proteins. However, the productivity of producer cells is often hindered by a bottleneck in the saturated secretory pathway, where a sophisticated mechanism of vesicle trafficking is mediated by numerous proteins and their complexes, among which are the cross-kingdom conserved SNAREs [soluble NSF (N-ethylmaleimide-sensitive factor) receptor]. The SNAREs assemble into complexes by means of four interactive α-helices and, thus, trigger the fusion of transport vesicles with the respective target membranes. We report that the transgenic expression of exocytic SNAREs, which control the fusion of secretory vesicles to the plasma membrane, differentially impacts the secretory capacity of HEK-293, HeLa, and CHO-K1 cells. While other exocytic SNAREs have no effect or a negative effect, SNAP-23 [synaptosome-associated protein of 23 kDa] and VAMP8 [vesicle-associated membrane protein 8] specifically increase the production of recombinant proteins when they are ectopically and stably expressed in mammalian cells. The targeted and effective intervention in the secretory capacity of SNARE proteins is a novel engineering strategy, which could lead to the development of new therapies by increasing the production of biopharmaceutical proteins or by boosting the secretion of cell implants in cell therapy initiatives.
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Affiliation(s)
- Ren-Wang Peng
- Department of Biosystems Science and Engineering (D-BSSE), ETH Zurich, Basel, Switzerland
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48
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Munc18b regulates core SNARE complex assembly and constitutive exocytosis by interacting with the N-peptide and the closed-conformation C-terminus of syntaxin 3. Biochem J 2010; 431:353-61. [PMID: 20695848 DOI: 10.1042/bj20100145] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The interaction between SM (Sec1/Munc18) and SNARE (soluble N-ethylmaleimide-sensitive factor-attachment receptor) proteins constitutes the core eukaryotic membrane fusion machinery which manages exocytosis by mediating fusion of constitutively exocytic vesicles with the plasma membrane. However, mechanistic details on the nature and the physiological impact of SM-SNARE interactions remain largely elusive. Detailed characterization of the interaction profiles between Munc18b and its cognate SNAREs, Stx3 (syntaxin 3), SNAP-23 (soluble N-ethylmaleimide-attachment protein 23) and VAMP8 (vesicle-associated membrane protein 8), revealed that Munc18b binds Stx3, VAMP8 and the assembled core SNARE complex consisting of Stx3, SNAP-23 and VAMP8. Dissection of the Munc18b-Stx3 heterodimer suggested that Munc18b interacts with Stx3's conserved N-peptide as well as with its closed-conformation C-terminus encompassing the Habc domain, a linker and the SNARE (H3) motif. Deletion of the Habc domain or mutations interrupting the intramolecular binding of the Habc and H3 domains abrogated the Munc18b-Stx3 interaction. Although only the N-peptide deletion mutant, but not the soluble wild-type Stx3, is assembled into the core SNARE complex in the presence of Munc18b in vitro, ectopic expression of this SM protein increases constitutive exocytosis in mammalian cells. Our results suggest that Munc18b is functionally coupled to the assembly of exocytic SNARE complexes and increases exocytosis by interacting with the N-peptide and closed-conformation C-terminus of Stx3, thereby neutralizing the secretion-inhibitory effect of this SNARE.
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Han GA, Malintan NT, Collins BM, Meunier FA, Sugita S. Munc18-1 as a key regulator of neurosecretion. J Neurochem 2010; 115:1-10. [PMID: 20681955 DOI: 10.1111/j.1471-4159.2010.06900.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Munc18-1 plays essential roles in neurosecretion by interacting with syntaxin-1 and controlling the formation of the soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) complex. At least three important functions of Munc18-1 have been proposed: (i) molecular chaperone of syntaxin-1 for appropriate localization and expression of syntaxin-1, (ii) priming/stimulation of the SNARE-mediated membrane fusion, and (iii) docking of large dense-core vesicles to the plasma membrane. Similarly, at least two different binding modes have been proposed for the interaction between Munc18-1 and syntaxin-1: (i) binary binding to a 'closed' conformation of syntaxin-1, and (ii) binding to the N-terminal peptide of syntaxin-1, which is thought to enable an interaction with the quaternary SNARE complex and/or further stabilize the binary interaction between Munc18-1 and closed syntaxin-1. Recent structural analyses have identified critical Munc18-1 residues implicated in these different modes of binding. These have recently been tested functionally in rescue experiments using Munc18-1 null neurons, chromaffin cells and Munc18-1/-2 knockdown PC12 cells, allowing remarkable progress to be made in the structural/functional understanding of Munc18-1. In this review, we summarize these recent advances and attempt to propose an updated model of the pleiotropic functions of Munc18-1 in neuroexocytosis.
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Affiliation(s)
- Gayoung A Han
- Division of Fundamental Neurobiology, University Health Network, Toronto, Ontario, Canada
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Boström P, Andersson L, Vind B, Håversen L, Rutberg M, Wickström Y, Larsson E, Jansson PA, Svensson MK, Brånemark R, Ling C, Beck-Nielsen H, Borén J, Højlund K, Olofsson SO. The SNARE protein SNAP23 and the SNARE-interacting protein Munc18c in human skeletal muscle are implicated in insulin resistance/type 2 diabetes. Diabetes 2010; 59:1870-8. [PMID: 20460426 PMCID: PMC2911056 DOI: 10.2337/db09-1503] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Accepted: 04/30/2010] [Indexed: 12/18/2022]
Abstract
OBJECTIVE Our previous studies suggest that the SNARE protein synaptosomal-associated protein of 23 kDa (SNAP23) is involved in the link between increased lipid levels and insulin resistance in cardiomyocytes. The objective was to determine whether SNAP23 may also be involved in the known association between lipid accumulation in skeletal muscle and insulin resistance/type 2 diabetes in humans, as well as to identify a potential regulator of SNAP23. RESEARCH DESIGN AND METHODS We analyzed skeletal muscle biopsies from patients with type 2 diabetes and healthy, insulin-sensitive control subjects for expression (mRNA and protein) and intracellular localization (subcellular fractionation and immunohistochemistry) of SNAP23, and for expression of proteins known to interact with SNARE proteins. Insulin resistance was determined by a euglycemic hyperinsulinemic clamp. Potential mechanisms for regulation of SNAP23 were also investigated in the skeletal muscle cell line L6. RESULTS We showed increased SNAP23 levels in skeletal muscle from patients with type 2 diabetes compared with that from lean control subjects. Moreover, SNAP23 was redistributed from the plasma membrane to the microsomal/cytosolic compartment in the patients with the type 2 diabetes. Expression of the SNARE-interacting protein Munc18c was higher in skeletal muscle from patients with type 2 diabetes. Studies in L6 cells showed that Munc18c promoted the expression of SNAP23. CONCLUSIONS We have translated our previous in vitro results into humans by showing that there is a change in the distribution of SNAP23 to the interior of the cell in skeletal muscle from patients with type 2 diabetes. We also showed that Munc18c is a potential regulator of SNAP23.
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Affiliation(s)
- Pontus Boström
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Linda Andersson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Birgitte Vind
- Diabetes Research Centre, Department of Endocrinology, Odense University Hospital, Odense, Denmark
| | - Liliana Håversen
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Mikael Rutberg
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Ylva Wickström
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Erik Larsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Per-Anders Jansson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Maria K. Svensson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Richard Brånemark
- Department of Orthopedic Surgery, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Charlotte Ling
- Department of Clinical Sciences CRC, University Hospital of Malmö, Lund University, Sweden
| | - Henning Beck-Nielsen
- Diabetes Research Centre, Department of Endocrinology, Odense University Hospital, Odense, Denmark
| | - Jan Borén
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
| | - Kurt Højlund
- Diabetes Research Centre, Department of Endocrinology, Odense University Hospital, Odense, Denmark
| | - Sven-Olof Olofsson
- Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Sahlgrenska University Hospital, Göteborg, Sweden
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