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Saed B, Ramseier NT, Perera T, Anderson J, Burnett J, Gunasekara H, Burgess A, Jing H, Hu YS. Increased vesicular dynamics and nanoscale clustering of IL-2 after T cell activation. Biophys J 2024:S0006-3495(24)00209-1. [PMID: 38532626 DOI: 10.1016/j.bpj.2024.03.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 12/04/2023] [Accepted: 03/22/2024] [Indexed: 03/28/2024] Open
Abstract
T cells coordinate intercellular communication through the meticulous regulation of cytokine secretion. Direct visualization of vesicular transport and intracellular distribution of cytokines provides valuable insights into the temporal and spatial mechanisms involved in regulation. Employing Jurkat E6-1 T cells and interleukin-2 (IL-2) as a model system, we investigated vesicular dynamics using single-particle tracking and the nanoscale distribution of intracellular IL-2 in fixed T cells using superresolution microscopy. Live-cell imaging revealed that in vitro activation resulted in increased vesicular dynamics. Direct stochastic optical reconstruction microscopy and 3D structured illumination microscopy revealed nanoscale clustering of IL-2. In vitro activation correlated with spatial accumulation of IL-2 nanoclusters into more pronounced and elongated clusters. These observations provide visual evidence that accelerated vesicular transport and spatial concatenation of IL-2 clusters at the nanoscale may constitute a potential mechanism for modulating cytokine release by Jurkat T cells.
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Affiliation(s)
- Badeia Saed
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois
| | - Neal T Ramseier
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois
| | - Thilini Perera
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois
| | - Jesse Anderson
- Department of Chemical Engineering, College of Engineering, University of Illinois Chicago, Chicago, Illinois
| | | | - Hirushi Gunasekara
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois
| | - Alyssa Burgess
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois
| | - Haoran Jing
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois
| | - Ying S Hu
- Department of Chemistry, College of Liberal Arts and Sciences, University of Illinois Chicago, Chicago, Illinois.
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2
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Nguyen-Tu MS, Harris J, Martinez-Sanchez A, Chabosseau P, Hu M, Georgiadou E, Pollard A, Otero P, Lopez-Noriega L, Leclerc I, Sakamoto K, Schmoll D, Smith DM, Carling D, Rutter GA. Opposing effects on regulated insulin secretion of acute vs chronic stimulation of AMP-activated protein kinase. Diabetologia 2022; 65:997-1011. [PMID: 35294578 PMCID: PMC9076735 DOI: 10.1007/s00125-022-05673-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Accepted: 12/13/2021] [Indexed: 11/26/2022]
Abstract
AIMS/HYPOTHESIS Although targeted in extrapancreatic tissues by several drugs used to treat type 2 diabetes, the role of AMP-activated protein kinase (AMPK) in the control of insulin secretion is still debatable. Previous studies have used pharmacological activators of limited selectivity and specificity, and none has examined in primary pancreatic beta cells the actions of the latest generation of highly potent and specific activators that act via the allosteric drug and metabolite (ADaM) site. METHODS AMPK was activated acutely in islets isolated from C57BL6/J mice, and in an EndoC-βH3 cell line, using three structurally distinct ADaM site activators (991, PF-06409577 and RA089), with varying selectivity for β1- vs β2-containing complexes. Mouse lines expressing a gain-of-function mutation in the γ1 AMPK subunit (D316a) were generated to examine the effects of chronic AMPK stimulation in the whole body, or selectively in the beta cell. RESULTS Acute (1.5 h) treatment of wild-type mouse islets with 991, PF-06409577 or RA089 robustly stimulated insulin secretion at high glucose concentrations (p<0.01, p<0.05 and p<0.001, respectively), despite a lowering of glucose-induced intracellular free Ca2+ dynamics in response to 991 (AUC, p<0.05) and to RA089 at the highest dose (25 μmol/l) at 5.59 min (p<0.05). Although abolished in the absence of AMPK, the effects of 991 were observed in the absence of the upstream kinase, liver kinase B1, further implicating 'amplifying' pathways. In marked contrast, chronic activation of AMPK, either globally or selectively in the beta cell, achieved using a gain-of-function mutant, impaired insulin release in vivo (p<0.05 at 15 min following i.p. injection of 3 mmol/l glucose) and in vitro (p<0.01 following incubation of islets with 17 mmol/l glucose), and lowered glucose tolerance (p<0.001). CONCLUSIONS/INTERPRETATION AMPK activation exerts complex, time-dependent effects on insulin secretion. These observations should inform the design and future clinical use of AMPK modulators.
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Affiliation(s)
- Marie-Sophie Nguyen-Tu
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Joseph Harris
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Aida Martinez-Sanchez
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Pauline Chabosseau
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Ming Hu
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Eleni Georgiadou
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Alice Pollard
- MRC- London Institute of Medical Sciences, Imperial College London, London, UK
- Structure Biophysics and Fragments, Discovery Sciences, AstraZeneca R&D, Cambridge, UK
| | - Pablo Otero
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Livia Lopez-Noriega
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Isabelle Leclerc
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
| | - Kei Sakamoto
- Novo Nordisk Center for Basic Metabolic Research, Copenhagen, Denmark
| | - Dieter Schmoll
- Sanofi-Aventis Deutschland GmbH, Frankfurt am Main, Germany
| | - David M Smith
- Emerging Innovations Unit, Discovery Sciences, AstraZeneca R&D , Cambridge, UK
| | - David Carling
- MRC- London Institute of Medical Sciences, Imperial College London, London, UK
| | - Guy A Rutter
- Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK.
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Republic of Singapore.
- CR-CHUM, University of Montréal, Montréal, QC, Canada.
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3
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Yau B, Hays L, Liang C, Laybutt DR, Thomas HE, Gunton JE, Williams L, Hawthorne WJ, Thorn P, Rhodes CJ, Kebede MA. A fluorescent timer reporter enables sorting of insulin secretory granules by age. J Biol Chem 2020; 295:8901-8911. [PMID: 32341128 PMCID: PMC7335792 DOI: 10.1074/jbc.ra120.012432] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2020] [Revised: 03/21/2020] [Indexed: 01/03/2023] Open
Abstract
Within the pancreatic β-cells, insulin secretory granules (SGs) exist in functionally distinct pools, displaying variations in motility as well as docking and fusion capability. Current therapies that increase insulin secretion do not consider the existence of these distinct SG pools. Accordingly, these approaches are effective only for a short period, with a worsening of glycemia associated with continued decline in β-cell function. Insulin granule age is underappreciated as a determinant for why an insulin granule is selected for secretion and may explain why newly synthesized insulin is preferentially secreted from β-cells. Here, using a novel fluorescent timer protein, we aimed to investigate the preferential secretion model of insulin secretion and identify how granule aging is affected by variation in the β-cell environment, such as hyperglycemia. We demonstrate the use of a fluorescent timer construct, syncollin-dsRedE5TIMER, which changes its fluorescence from green to red over 18 h, in both microscopy and fluorescence-assisted organelle-sorting techniques. We confirm that the SG-targeting construct localizes to insulin granules in β-cells and does not interfere with normal insulin SG behavior. We visualize insulin SG aging behavior in MIN6 and INS1 β-cell lines and in primary C57BL/6J mouse and nondiabetic human islet cells. Finally, we separated young and old insulin SGs, revealing that preferential secretion of younger granules occurs in glucose-stimulated insulin secretion. We also show that SG population age is modulated by the β-cell environment in vivo in the db/db mouse islets and ex vivo in C57BL/6J islets exposed to different glucose environments.
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Affiliation(s)
- Belinda Yau
- Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia; School of Life and Environmental Sciences, Faculty of Science, University of Sydney, Sydney, New South Wales, Australia
| | - Lori Hays
- STEM-Department of Biology, Edmonds Community College, Lynnwood, Washington, USA
| | - Cassandra Liang
- Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - D Ross Laybutt
- Garvan Institute of Medical Research, Sydney, New South Wales, Australia; St. Vincent's Clinical School, University of New South Wales Sydney, Sydney, New South Wales, Australia
| | - Helen E Thomas
- St. Vincent's Institute, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, University of Melbourne, Fitzroy, Victoria, Australia
| | - Jenny E Gunton
- Faculty of Medicine and Health, the University of Sydney, Sydney, New South Wales, Australia; The Westmead Institute for Medical Research, University of Sydney, Westmead, New South Wales, Australia
| | - Lindy Williams
- Faculty of Medicine and Health, the University of Sydney, Sydney, New South Wales, Australia; National Pancreas and Islet Transplant Unit (NPITU), Westmead Hospital, Sydney, New South Wales, Australia
| | - Wayne J Hawthorne
- Faculty of Medicine and Health, the University of Sydney, Sydney, New South Wales, Australia; National Pancreas and Islet Transplant Unit (NPITU), Westmead Hospital, Sydney, New South Wales, Australia
| | - Peter Thorn
- Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia; Discipline of Physiology, School of Medical Sciences, Faculty of Medicine and Health, Charles Perkins Centre, University of Sydney, Camperdown, New South Wales, Australia
| | - Christopher J Rhodes
- Research and Early Development, Cardiovascular, Renal and Metabolic Diseases, BioPharmaceuticals R&D, AstraZeneca Ltd, Gaithersburg, Maryland, USA; Pacific Northwest Research Institute, Seattle, Washington, USA
| | - Melkam A Kebede
- Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia; School of Life and Environmental Sciences, Faculty of Science, University of Sydney, Sydney, New South Wales, Australia.
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4
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Hummer BH, Maslar D, Soltero-Gutierrez M, de Leeuw NF, Asensio CS. Differential sorting behavior for soluble and transmembrane cargoes at the trans-Golgi network in endocrine cells. Mol Biol Cell 2019; 31:157-166. [PMID: 31825717 PMCID: PMC7001476 DOI: 10.1091/mbc.e19-10-0561] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Regulated secretion of neuropeptides and peptide hormones by secretory granules (SGs) is central to physiology. Formation of SGs occurs at the trans-Golgi network (TGN) where their soluble cargo aggregates to form a dense core, but the mechanisms controlling the sorting of regulated secretory cargoes (soluble and transmembrane) away from constitutively secreted proteins remain unclear. Optimizing the use of the retention using selective hooks method in (neuro-)endocrine cells, we now quantify TGN budding kinetics of constitutive and regulated secretory cargoes. We further show that, by monitoring two cargoes simultaneously, it becomes possible to visualize sorting to the constitutive and regulated secretory pathways in real time. Further analysis of the localization of SG cargoes immediately after budding from the TGN revealed that, surprisingly, the bulk of two studied transmembrane SG cargoes (phogrin and VMAT2) does not sort directly onto SGs during budding, but rather exit the TGN into nonregulated vesicles to get incorporated to SGs at a later step. This differential behavior of soluble and transmembrane cargoes suggests a more complex model of SG biogenesis than anticipated.
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Affiliation(s)
| | | | | | - Noah F de Leeuw
- Department of Physics and Astronomy, University of Denver, Denver, CO 80210
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5
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Midorikawa M. Real-time imaging of synaptic vesicle exocytosis by total internal reflection fluorescence (TIRF) microscopy. Neurosci Res 2018; 136:1-5. [DOI: 10.1016/j.neures.2018.01.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 01/29/2018] [Indexed: 12/15/2022]
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6
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Klein O, Roded A, Hirschberg K, Fukuda M, Galli SJ, Sagi-Eisenberg R. Imaging FITC-dextran as a Reporter for Regulated Exocytosis. J Vis Exp 2018. [PMID: 29985342 DOI: 10.3791/57936] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Regulated exocytosis is a process by which cargo, which is stored in secretory granules (SGs), is released in response to a secretory trigger. Regulated exocytosis is fundamental for intercellular communication and is a key mechanism for the secretion of neurotransmitters, hormones, inflammatory mediators, and other compounds, by a variety of cells. At least three distinct mechanisms are known for regulated exocytosis: full exocytosis, where a single SG fully fuses with the plasma membrane, kiss-and-run exocytosis, where a single SG transiently fuses with the plasma membrane, and compound exocytosis, where several SGs fuse with each other, prior to or after SG fusion with the plasma membrane. The type of regulated exocytosis undertaken by a cell is often dictated by the type of secretory trigger. However, in many cells, a single secretory trigger can activate multiple modes of regulated exocytosis simultaneously. Despite their abundance and importance across cell types and species, the mechanisms that determine the different modes of secretion are largely unresolved. One of the main challenges in investigating the different modes of regulated exocytosis, is the difficulty in distinguishing between them as well as exploring them separately. Here we describe the use of fluorescein isothiocyanate (FITC)-dextran as an exocytosis reporter, and live cell imaging, to differentiate between the different pathways of regulated exocytosis, focusing on compound exocytosis, based on the robustness and duration of the exocytic events.
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Affiliation(s)
- Ofir Klein
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University
| | - Amit Roded
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University
| | - Koret Hirschberg
- Department of Pathology, Sackler Faculty of Medicine, Tel Aviv University
| | - Mitsunori Fukuda
- Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University
| | - Stephen J Galli
- Departments of Pathology and of Microbiology and Immunology and Sean N. Parker Center for Allergy and Asthma Research, School of Medicine, Stanford University
| | - Ronit Sagi-Eisenberg
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University;
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7
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Xu Y, Toomre DK, Bogan JS, Hao M. Excess cholesterol inhibits glucose-stimulated fusion pore dynamics in insulin exocytosis. J Cell Mol Med 2017; 21:2950-2962. [PMID: 28544529 PMCID: PMC5661106 DOI: 10.1111/jcmm.13207] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 03/28/2017] [Indexed: 01/06/2023] Open
Abstract
Type 2 diabetes is caused by defects in both insulin sensitivity and insulin secretion. Glucose triggers insulin secretion by causing exocytosis of insulin granules from pancreatic β-cells. High circulating cholesterol levels and a diminished capacity of serum to remove cholesterol from β-cells are observed in diabetic individuals. Both of these effects can lead to cholesterol accumulation in β-cells and contribute to β-cell dysfunction. However, the molecular mechanisms by which cholesterol accumulation impairs β-cell function remain largely unknown. Here, we used total internal reflection fluorescence microscopy to address, at the single-granule level, the role of cholesterol in regulating fusion pore dynamics during insulin exocytosis. We focused particularly on the effects of cholesterol overload, which is relevant to type 2 diabetes. We show that excess cholesterol reduced the number of glucose-stimulated fusion events, and modulated the proportion of full fusion and kiss-and-run fusion events. Analysis of single exocytic events revealed distinct fusion kinetics, with more clustered and compound exocytosis observed in cholesterol-overloaded β-cells. We provide evidence for the involvement of the GTPase dynamin, which is regulated in part by cholesterol-induced phosphatidylinositol 4,5-bisphosphate enrichment in the plasma membrane, in the switch between full fusion and kiss-and-run fusion. Characterization of insulin exocytosis offers insights into the role that elevated cholesterol may play in the development of type 2 diabetes.
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Affiliation(s)
- Yingke Xu
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Department of Bioengineering, Key Laboratory of Biomedical Engineering of Ministry of Education, Zhejiang University, Hangzhou, China
| | - Derek K Toomre
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA
| | - Jonathan S Bogan
- Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.,Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Mingming Hao
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA.,Department of Biochemistry, Weill Cornell Medical College, New York, NY, USA
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8
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Schifferer M, Yushchenko DA, Stein F, Bolbat A, Schultz C. A Ratiometric Sensor for Imaging Insulin Secretion in Single β Cells. Cell Chem Biol 2017; 24:525-531.e4. [PMID: 28366620 PMCID: PMC5404835 DOI: 10.1016/j.chembiol.2017.03.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Revised: 12/14/2016] [Accepted: 03/02/2017] [Indexed: 01/03/2023]
Abstract
Despite the urgent need for assays to visualize insulin secretion there is to date no reliable method available for measuring insulin release from single cells. To address this need, we developed a genetically encoded reporter termed RINS1 based on proinsulin superfolder GFP (sfGFP) and mCherry fusions for monitoring insulin secretion. RINS1 expression in MIN6 β cells resulted in proper processing yielding single-labeled insulin species. Unexpectedly, glucose or drug stimulation of insulin secretion in β cells led to the preferential release of the insulin-sfGFP construct, while the mCherry-fused C-peptide remained trapped in exocytic granules. This physical separation was used to monitor glucose-stimulated insulin secretion ratiometrically by total internal reflection fluorescence microscopy in single MIN6 and primary mouse β cells. Further, RINS1 enabled parallel monitoring of pulsatile insulin release in tolbutamide-treated β cells, demonstrating the potential of RINS1 for investigations of antidiabetic drug candidates at the single-cell level.
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Affiliation(s)
- Martina Schifferer
- Interdisciplinary Chemistry Group, Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Dmytro A Yushchenko
- Interdisciplinary Chemistry Group, Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany; Group of Chemical Biology, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo namesti 2, 16610 Prague 6, Czech Republic
| | - Frank Stein
- Interdisciplinary Chemistry Group, Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Andrey Bolbat
- Interdisciplinary Chemistry Group, Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Carsten Schultz
- Interdisciplinary Chemistry Group, Cell Biology & Biophysics Unit, European Molecular Biology Laboratory (EMBL), Meyerhofstrasse 1, 69117 Heidelberg, Germany; Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97237, USA.
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9
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Gandasi NR, Vestö K, Helou M, Yin P, Saras J, Barg S. Survey of Red Fluorescence Proteins as Markers for Secretory Granule Exocytosis. PLoS One 2015; 10:e0127801. [PMID: 26091288 PMCID: PMC4474633 DOI: 10.1371/journal.pone.0127801] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 04/18/2015] [Indexed: 12/18/2022] Open
Abstract
Fluorescent proteins (FPs) have proven to be valuable tools for high-resolution imaging studies of vesicle transport processes, including exo- and endocytosis. Since the pH of the vesicle lumen changes between acidic and neutral during these events, pH-sensitive FPs with near neutral pKa, such as pHluorin, are particularly useful. FPs with pKa>6 are readily available in the green spectrum, while red-emitting pH-sensitive FPs are rare and often not well characterized as reporters of exo- or endocytosis. Here we tested a panel of ten orange/red and two green FPs in fusions with neuropeptide Y (NPY) for use as secreted vesicle marker and reporter of dense core granule exocytosis and release. We report relative brightness, bleaching rate, targeting accuracy, sensitivity to vesicle pH, and their performance in detecting exocytosis in live cells. Tandem dimer (td)-mOrange2 was identified as well-targeted, bright, slowly bleaching and pH-sensitive FP that performed similar to EGFP. Single exocytosis events were readily observed, which allowed measurements of fusion pore lifetime and the dynamics of the exocytosis protein syntaxin at the release site during membrane fusion and cargo release.
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Affiliation(s)
- Nikhil R. Gandasi
- Institute of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123, Uppsala, Sweden
| | - Kim Vestö
- Institute of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123, Uppsala, Sweden
| | - Maria Helou
- Institute of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123, Uppsala, Sweden
| | - Peng Yin
- Institute of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123, Uppsala, Sweden
| | - Jan Saras
- Institute of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123, Uppsala, Sweden
| | - Sebastian Barg
- Institute of Medical Cell Biology, Uppsala University, Box 571, Husargatan 3, 75123, Uppsala, Sweden
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10
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Houy S, Croisé P, Gubar O, Chasserot-Golaz S, Tryoen-Tóth P, Bailly Y, Ory S, Bader MF, Gasman S. Exocytosis and endocytosis in neuroendocrine cells: inseparable membranes! Front Endocrinol (Lausanne) 2013; 4:135. [PMID: 24106488 PMCID: PMC3788349 DOI: 10.3389/fendo.2013.00135] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Accepted: 09/13/2013] [Indexed: 12/23/2022] Open
Abstract
Although much has been learned concerning the mechanisms of secretory vesicle formation and fusion at donor and acceptor membrane compartments, relatively little attention has been paid toward understanding how cells maintain a homeostatic membrane balance through vesicular trafficking. In neurons and neuroendocrine cells, release of neurotransmitters, neuropeptides, and hormones occurs through calcium-regulated exocytosis at the plasma membrane. To allow recycling of secretory vesicle components and to preserve organelles integrity, cells must initiate and regulate compensatory membrane uptake. This review relates the fate of secretory granule membranes after full fusion exocytosis in neuroendocrine cells. In particular, we focus on the potential role of lipids in preserving and sorting secretory granule membranes after exocytosis and we discuss the potential mechanisms of membrane retrieval.
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Affiliation(s)
- Sébastien Houy
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Pauline Croisé
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Olga Gubar
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Sylvette Chasserot-Golaz
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Petra Tryoen-Tóth
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Yannick Bailly
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Stéphane Ory
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Marie-France Bader
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
| | - Stéphane Gasman
- Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, Strasbourg, France
- *Correspondence: Stéphane Gasman, Institut des Neurosciences Cellulaires et Intégratives (INCI), Centre National de la Recherche Scientifique (CNRS UPR 3212), Université de Strasbourg, 5 rue Blaise Pascal, Strasbourg 67084, France e-mail:
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11
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Gurbaxani B, Dostalek M, Gardner I. Are endosomal trafficking parameters better targets for improving mAb pharmacokinetics than FcRn binding affinity? Mol Immunol 2013; 56:660-74. [PMID: 23917469 DOI: 10.1016/j.molimm.2013.05.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Revised: 05/09/2013] [Accepted: 05/14/2013] [Indexed: 12/21/2022]
Abstract
F.W.R. Brambell deduced the existence of a protective receptor for IgG, the neonatal Fc receptor (FcRn), long before its discovery in the early to mid-1990s. With the coincident, explosive development of IgG-based drugs, FcRn became a popular target for tuning the pharmacokinetics of monoclonal antibodies (mAbs). One aspect of Brambell's initial observation, however, that is seldom discussed since the discovery of the receptor, is the compliance in the mechanism that Brambell observed (saturating at 10s-100s of μM concentration), vs. the comparative stiffness of the receptor kinetics (saturating in the nM range for most species). Although some studies reported that increasing the already very high Fc-FcRn affinity at pH 6.0 further improved mAb half-life, in fact the results were mixed, with later studies increasingly implicating non-FcRn-dependent mechanisms as determinants of mAb pharmacokinetics. Mathematical modelling of the FcRn system has also indicated that the processes determining the pharmacokinetics of mAbs have more nuances than had at first been hypothesised. We propose, in keeping with the latest modelling and experimental evidence reviewed here, that the dynamics of endosomal sorting and trafficking have important roles in the compliant salvage mechanism that Brambell first observed nearly 50 years ago, and therefore also in the pharmacokinetics of mAbs. These ideas lead to many open questions regarding the endosomal trafficking of both FcRn and mAbs and also to what properties of a mAb can be altered to achieve an improvement in pharmacokinetics.
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Affiliation(s)
- Brian Gurbaxani
- Chronic Viral Diseases Branch, Division of High-Consequence Pathogens and Pathology, National Centre for Emerging and Zoonotic Infectious Diseases, Centres for Disease Control and Prevention, Atlanta, GA, USA.
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12
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Extracellular calcium influx activates adenylate cyclase 1 and potentiates insulin secretion in MIN6 cells. Biochem J 2013; 450:365-73. [PMID: 23282092 DOI: 10.1042/bj20121022] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Intracellular cAMP and Ca(2+) are important second messengers that regulate insulin secretion in pancreatic β-cells; however, the molecular mechanism underlying their mutual interaction for exocytosis is not fully understood. In the present study, we investigated the interplay between intracellular cAMP and Ca(2+) concentrations ([cAMP](i) and [Ca(2+)](i) respectively) in the pancreatic β-cell line MIN6 using total internal reflection fluorescence microscopy. For measuring [cAMP](i), we developed a genetically encoded yellow fluorescent biosensor for cAMP [Flamindo (fluorescent cAMP indicator)], which changes fluorescence intensity with cAMP binding. Application of high-KCl or glucose to MIN6 cells induced the elevation of [cAMP](i) and exocytosis. Furthermore, application of an L-type Ca(2+) channel agonist or ionomycin to induce extracellular Ca(2+) influx evoked the elevation of [cAMP](i), whereas application of carbachol or thapsigargin, which mobilize Ca(2+) from internal stores, did not evoke the elevation of [cAMP](i). We performed RT (reverse transcription)-PCR analysis and found that Ca(2+)-sensitive Adcy1 (adenylate cyclase 1) was expressed in MIN6 cells. Knockdown of endogenous ADCY1 by small interference RNA significantly suppressed glucose-induced exocytosis and the elevation of both [cAMP](i) and [Ca(2+)](i). Taken together, the findings of the present study demonstrate that ADCY1 plays an important role in the control of pancreatic β-cell cAMP homoeostasis and insulin secretion.
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13
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Properties of ribbon and non-ribbon release from rod photoreceptors revealed by visualizing individual synaptic vesicles. J Neurosci 2013; 33:2071-86. [PMID: 23365244 DOI: 10.1523/jneurosci.3426-12.2013] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Vesicle release from rod photoreceptors is regulated by Ca(2+) entry through L-type channels located near synaptic ribbons. We characterized sites and kinetics of vesicle release in salamander rods by using total internal reflection fluorescence microscopy to visualize fusion of individual synaptic vesicles. A small number of vesicles were loaded by brief incubation with FM1-43 or a dextran-conjugated, pH-sensitive form of rhodamine, pHrodo. Labeled organelles matched the diffraction-limited size of fluorescent microspheres and disappeared rapidly during stimulation. Consistent with fusion, depolarization-evoked vesicle disappearance paralleled electrophysiological release kinetics and was blocked by inhibiting Ca(2+) influx. Rods maintained tonic release at resting membrane potentials near those in darkness, causing depletion of membrane-associated vesicles unless Ca(2+) entry was inhibited. This depletion of release sites implies that sustained release may be rate limited by vesicle delivery. During depolarizing stimulation, newly appearing vesicles approached the membrane at ∼800 nm/s, where they paused for ∼60 ms before fusion. With fusion, vesicles advanced ∼18 nm closer to the membrane. Release events were concentrated near ribbons, but lengthy depolarization also triggered release from more distant non-ribbon sites. Consistent with greater contributions from non-ribbon sites during lengthier depolarization, damaging the ribbon by fluorophore-assisted laser inactivation (FALI) of Ribeye caused only weak inhibition of exocytotic capacitance increases evoked by 200-ms depolarizing test steps, whereas FALI more strongly inhibited capacitance increases evoked by 25 ms steps. Amplifying release by use of non-ribbon sites when rods are depolarized in darkness may improve detection of decrements in release when they hyperpolarize to light.
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Loder MK, Tsuboi T, Rutter GA. Live-cell imaging of vesicle trafficking and divalent metal ions by total internal reflection fluorescence (TIRF) microscopy. Methods Mol Biol 2013; 950:13-26. [PMID: 23086867 DOI: 10.1007/978-1-62703-137-0_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Total internal reflection fluorescence (TIRF) microscopy is an especially powerful tool for visualizing live cellular events. Fluorescent molecules alone provide broad information about the expression and localization of proteins and other molecules; however, the temporal and spatial resolution is confounded by signal from outside the area of interest and the intensity of the illumination required. TIRF overcomes this limitation by using the reflective properties of a laser beam to illuminate a narrow (<100 nm) strip at the surface of a cell with a relatively low powered evanescent wave, thus making it possible to measure events occurring specifically at the plasma membrane such as exocytosis, single molecule interactions, and ionic changes during signal transduction. Here we describe some of the methods for using TIRF microscopy to study the processes involved in exocytosis from excitable cells (i.e., neurons, endocrine, neuroendocrine, and exocrine cells) and the release of physiologically active substances (i.e., neurotransmitters, hormones, and mucus).The failure of regulated exocytosis is associated with various diseases such as allergy, brain dysfunction, and endocrine illness. Diabetes mellitus, which is due to an absolute (type I) or relative (type II) deficiency of insulin secretion from pancreatic β-cells, is a major area of therapeutic interest. Insulin is stored in dense core vesicles with Zn(2+) ions in pancreatic β-cells. Insulin secretion is regulated by plasma glucose concentration which acts through intracellular metabolism to influence intracellular [Ca(2+)]. However, the precise molecular mechanisms controlling insulin granule movement towards, and fusion at, the plasma membrane remain only partially understood. To tackle this problem, we have used live cell imaging techniques to image regulated exocytosis in single living β-cells alongside intracellular Ca(2+) and Zn(2+) concentrations.
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Affiliation(s)
- Merewyn K Loder
- Section of Cell Biology, Division of Diabetes Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, Imperial College London, London, UK
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15
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16
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Seino S. Cell signalling in insulin secretion: the molecular targets of ATP, cAMP and sulfonylurea. Diabetologia 2012; 55:2096-108. [PMID: 22555472 DOI: 10.1007/s00125-012-2562-9] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 03/09/2012] [Indexed: 12/25/2022]
Abstract
Clarification of the molecular mechanisms of insulin secretion is crucial for understanding the pathogenesis and pathophysiology of diabetes and for development of novel therapeutic strategies for the disease. Insulin secretion is regulated by various intracellular signals generated by nutrients and hormonal and neural inputs. In addition, a variety of glucose-lowering drugs including sulfonylureas, glinide-derivatives, and incretin-related drugs such as dipeptidyl peptidase IV (DPP-4) inhibitors and glucagon-like peptide 1 (GLP-1) receptor agonists are used for glycaemic control by targeting beta cell signalling for improved insulin secretion. There has been a remarkable increase in our understanding of the basis of beta cell signalling over the past two decades following the application of molecular biology, gene technology, electrophysiology and bioimaging to beta cell research. This review discusses cell signalling in insulin secretion, focusing on the molecular targets of ATP, cAMP and sulfonylurea, an essential metabolic signal in glucose-induced insulin secretion (GIIS), a critical signal in the potentiation of GIIS, and the commonly used glucose-lowering drug, respectively.
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Affiliation(s)
- S Seino
- Division of Diabetes and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe, 650-0017, Japan.
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17
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Seino S, Shibasaki T, Minami K. Dynamics of insulin secretion and the clinical implications for obesity and diabetes. J Clin Invest 2011; 121:2118-25. [PMID: 21633180 DOI: 10.1172/jci45680] [Citation(s) in RCA: 250] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Insulin secretion is a highly dynamic process regulated by various factors including nutrients, hormones, and neuronal inputs. The dynamics of insulin secretion can be studied at different levels: the single β cell, pancreatic islet, whole pancreas, and the intact organism. Studies have begun to analyze cellular and molecular mechanisms underlying dynamics of insulin secretion. This review focuses on our current understanding of the dynamics of insulin secretion in vitro and in vivo and discusses their clinical relevance.
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Affiliation(s)
- Susumu Seino
- Division of Diabetes and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, Kobe, Japan.
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18
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Suzuki T, Kondo C, Kanamori T, Inouye S. Video rate bioluminescence imaging of secretory proteins in living cells: localization, secretory frequency, and quantification. Anal Biochem 2011; 415:182-9. [PMID: 21477579 DOI: 10.1016/j.ab.2011.03.039] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Accepted: 03/31/2011] [Indexed: 11/16/2022]
Abstract
We have developed a method of video rate bioluminescence imaging to investigate protein secretion from a single mammalian cell and analyzed the localization, secretory frequency, and quantification of secreted protein. By detecting the luminescence signals from the Gaussia luciferase (GLase) reaction using a high-speed electron-multiplying charge-coupled device (EM-CCD) camera, video rate imaging was performed with a time resolution within 500 ms/image over 30 min in living cells. As a model study, we applied the method to visualize the glucose-stimulated insulin secretion from clustered pancreatic MIN6 β cells using the fused protein of GLase with preproinsulin. High-quality video images clearly showed that the glucose-stimulated insulin secretion from the clustered MIN6 β cells oscillated within a period of a few minutes over 10 min. In addition, the glibenclamide-induced insulin secretion from the clustered MIN6 β cells was visualized, suggesting that bioluminescence video rate imaging is a useful method for validating drug action in living cells.
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Affiliation(s)
- Takahiro Suzuki
- Department of Biochemistry, School of Dentistry, Aichi-Gakuin University, Nagoya 464-8650, Japan
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19
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Suzuki Y, Urano T. Novel Situations of Endothelial Injury in Stroke — Mechanisms of Stroke and Strategy of Drug Development: Novel Mechanism of the Expression and Amplification of Cell Surface–Associated Fibrinolytic Activity Demonstrated by Real-Time Imaging Analysis. J Pharmacol Sci 2011; 116:19-24. [DOI: 10.1254/jphs.10r23fm] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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20
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Dominguez V, Raimondi C, Somanath S, Bugliani M, Loder MK, Edling CE, Divecha N, da Silva-Xavier G, Marselli L, Persaud SJ, Turner MD, Rutter GA, Marchetti P, Falasca M, Maffucci T. Class II phosphoinositide 3-kinase regulates exocytosis of insulin granules in pancreatic beta cells. J Biol Chem 2010; 286:4216-25. [PMID: 21127054 PMCID: PMC3039383 DOI: 10.1074/jbc.m110.200295] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Phosphoinositide 3-kinases (PI3Ks) are critical regulators of pancreatic β cell mass and survival, whereas their involvement in insulin secretion is more controversial. Furthermore, of the different PI3Ks, the class II isoforms were detected in β cells, although their role is still not well understood. Here we show that down-regulation of the class II PI3K isoform PI3K-C2α specifically impairs insulin granule exocytosis in rat insulinoma cells without affecting insulin content, the number of insulin granules at the plasma membrane, or the expression levels of key proteins involved in insulin secretion. Proteolysis of synaptosomal-associated protein of 25 kDa, a process involved in insulin granule exocytosis, is impaired in cells lacking PI3K-C2α. Finally, our data suggest that the mRNA for PI3K-C2α may be down-regulated in islets of Langerhans from type 2 diabetic compared with non-diabetic individuals. Our results reveal a critical role for PI3K-C2α in β cells and suggest that down-regulation of PI3K-C2α may be a feature of type 2 diabetes.
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Affiliation(s)
- Veronica Dominguez
- From the Queen Mary University of London, Barts and The London School of Medicine and Dentistry, Blizard Institute of Cell and Molecular Science, Centre for Diabetes, London E1 2AT, United Kingdom
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21
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Ott S, Henkel AW, Henkel MK, Redzic ZB, Kornhuber J, Wiltfang J. Pre-aggregated Aβ1-42 peptide increases tau aggregation and hyperphosphorylation after short-term application. Mol Cell Biochem 2010; 349:169-77. [PMID: 21113648 DOI: 10.1007/s11010-010-0671-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Accepted: 11/15/2010] [Indexed: 12/16/2022]
Abstract
Neuritic amyloid plaques and neurofibrillary tangles, consisting of hyperphosphorylated tau protein, are the hallmarks of Alzheimer disease. It is not clear so far, how both structures are functionally and physiologically connected. We have investigated the role of Aβ1-42 on hyperphosphorylation and aggregation of tau in SY5Y cells by transfection and overexpression with two tau constructs, a shortened wildtype tau (2N4R) and a point mutation tau (P301L), found in fronto-temporal dementia. It was found that the tau protein becomes hyperphosphorylated and forms large aggregates inside cells, visualized by immunofluorescence, after short incubation of 90 min with preaggregated Aβ1-42. In Addition, Aβ1-42 caused a decrease of tau solubility in both tau constructs in this relatively short time period. Taken together, these experiments suggest that pathological preaggregated Aβ1-42 in physiological concentrations quickly induces hyperphosphorylation and pathological structural changes of tau protein and thereby directly linking the 'amyloid hypothesis' to tau pathology, observed in Alzheimer disease.
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Affiliation(s)
- Sabine Ott
- Department of Psychiatry and Psychotherapy, University Hospital of Erlangen, Erlangen, Germany
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22
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Takahashi N, Hatakeyama H, Okado H, Noguchi J, Ohno M, Kasai H. SNARE conformational changes that prepare vesicles for exocytosis. Cell Metab 2010; 12:19-29. [PMID: 20620992 DOI: 10.1016/j.cmet.2010.05.013] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Revised: 04/28/2010] [Accepted: 05/26/2010] [Indexed: 11/25/2022]
Abstract
When cells release hormones and neurotransmitters through exocytosis, cytosolic Ca(2+) triggers the fusion of secretory vesicles with the plasma membrane. It is well known that this fusion requires assembly of a SNARE protein complex. However, the timing of SNARE assembly relative to vesicle fusion--essential for understanding exocytosis--has not been demonstrated. To investigate this timing, we constructed a probe that detects the assembly of two plasma membrane SNAREs, SNAP25 and syntaxin-1A, through fluorescence resonance energy transfer (FRET). With two-photon imaging, we simultaneously measured FRET signals and insulin exocytosis in beta cells from the pancreatic islet of Langerhans. In some regions of the cell, we found that the SNARE complex was preassembled, which enabled rapid exocytosis. In other regions, SNARE assembly followed Ca(2+) influx, and exocytosis was slower. Thus, SNARE proteins exist in multiple stable preparatory configurations, from which Ca(2+) may trigger exocytosis through distinct mechanisms and with distinct kinetics.
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Affiliation(s)
- Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
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23
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Moreno A, SantoDomingo J, Fonteriz RI, Lobatón CD, Montero M, Alvarez J. A confocal study on the visualization of chromaffin cell secretory vesicles with fluorescent targeted probes and acidic dyes. J Struct Biol 2010; 172:261-9. [PMID: 20600953 DOI: 10.1016/j.jsb.2010.06.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2010] [Revised: 06/14/2010] [Accepted: 06/16/2010] [Indexed: 12/24/2022]
Abstract
Secretory vesicles have low pH and have been classically identified as those labelled by a series of acidic fluorescent dyes such as acridine orange or neutral red, which accumulate into the vesicles according to the pH gradient. More recently, several fusion proteins containing enhanced green fluorescent protein (EGFP) and targeted to the secretory vesicles have been engineered. Both targeted fluorescent proteins and acidic dyes have been used, separately or combined, to monitor the dynamics of secretory vesicle movements and their fusion with the plasma membrane. We have now investigated in detail the degree of colocalization of both types of probes using several fusion proteins targeted to the vesicles (synaptobrevin2-EGFP, Cromogranin A-EGFP and neuropeptide Y-EGFP) and several acidic dyes (acridine orange, neutral red and lysotracker red) in chromaffin cells, PC12 cells and GH(3) cells. We find that all the acidic dyes labelled the same population of vesicles. However, that population was largely different from the one labelled by the targeted proteins, with very little colocalization among them, in all the cell types studied. Our data show that the vesicles containing the proteins more characteristic of the secretory vesicles are not labelled by the acidic dyes, and vice versa. Peptide glycyl-L-phenylalanine 2-naphthylamide (GPN) produced a rapid and selective disruption of the vesicles labelled by acidic dyes, suggesting that they could be mainly lysosomes. Therefore, these labelling techniques distinguish two clearly different sets of acidic vesicles in neuroendocrine cells. This finding should be taken into account whenever vesicle dynamics is studied using these techniques.
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Affiliation(s)
- Alfredo Moreno
- Instituto de Biología y Genética Molecular, Departamento de Bioquímica y Biología Molecular y Fisiología, Facultad de Medicina, Universidad de Valladolid and Consejo Superior de Investigaciones Científicas, Ramón y Cajal, 7, E-47005 Valladolid, Spain
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24
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Surface analysis of membrane dynamics. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:766-76. [DOI: 10.1016/j.bbamem.2009.09.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 09/18/2009] [Accepted: 09/20/2009] [Indexed: 11/18/2022]
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25
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Anantharam A, Onoa B, Edwards RH, Holz RW, Axelrod D. Localized topological changes of the plasma membrane upon exocytosis visualized by polarized TIRFM. ACTA ACUST UNITED AC 2010; 188:415-28. [PMID: 20142424 PMCID: PMC2819686 DOI: 10.1083/jcb.200908010] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Imaging of individual secretory granules reveals how exocytosis curves the membrane. Total internal reflection fluorescence microscopy (TIRFM) images the plasma membrane–cytosol interface and has allowed insights into the behavior of individual secretory granules before and during exocytosis. Much less is known about the dynamics of the other partner in exocytosis, the plasma membrane. In this study, we report the implementation of a TIRFM-based polarization technique to detect rapid submicrometer changes in plasma membrane topology as a result of exocytosis. A theoretical analysis of the technique is presented together with image simulations of predicted topologies of the postfusion granule membrane–plasma membrane complex. Experiments on diI-stained bovine adrenal chromaffin cells using polarized TIRFM demonstrate rapid and varied submicrometer changes in plasma membrane topology at sites of exocytosis that occur immediately upon fusion. We provide direct evidence for a persistent curvature in the exocytotic region that is altered by inhibition of dynamin guanosine triphosphatase activity and is temporally distinct from endocytosis measured by VMAT2-pHluorin.
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Affiliation(s)
- Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA.
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26
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Zheng M, Wang Q, Teng Y, Wang X, Wang F, Chen T, Samaj J, Lin J, Logan DC. The speed of mitochondrial movement is regulated by the cytoskeleton and myosin in Picea wilsonii pollen tubes. PLANTA 2010; 231:779-91. [PMID: 20033230 DOI: 10.1007/s00425-009-1086-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 12/04/2009] [Indexed: 05/23/2023]
Abstract
Strategic control of mitochondrial movements and cellular distribution is essential for correct cell function and survival. However, despite being a vital process, mitochondrial movement in plant cells is a poorly documented phenomenon. To investigate the roles of actin filaments and microtubules on mitochondrial movements, Picea wilsonii pollen tubes were treated with two microtubule-disrupting drugs, two actin-disrupting drugs and a myosin inhibitor. Following these treatments, mitochondrial movements were characterized by multiangle evanescent wave microscopy and laser-scanning confocal microscopy. The results showed that individual mitochondria underwent three classes of linear movement: high-speed movement (instantaneous velocities >5.0 microm/s), low-speed movement (instantaneous velocities <5.0 microm/s) and variable-speed movement (instantaneous velocities ranging from 0.16 to 10.35 microm/s). 10 nM latrunculin B induced fragmentation of actin filaments and completely inhibited mitochondrial vectorial movement. Jasplakinolide treatment induced a 28% reduction in chondriome motility, and dramatically inhibition of high-speed and variable-speed movements. Treatment with 2,3-butanedione 2-monoxime caused a 61% reduction of chondriome motility, and the complete inhibition of high-speed and low-speed movements. In contrast to actin-disrupting drugs, microtubule-disrupting drugs caused mild effects on mitochondrial movement. Taxol increased the speed of mitochondrial movement in cortical cytoplasm. Oryzalin induced curved mitochondrial trajectories with similar velocities as in the control pollen tubes. These results suggest that mitochondrial movement at low speeds in pollen tubes is driven by myosin, while high-speed and variable-speed movements are powered both by actin filament dynamics and myosin. In addition, microtubule dynamics has profound effects on mitochondrial velocity, trajectory and positioning via its role in directing the arrangement of actin filaments.
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Affiliation(s)
- Maozhong Zheng
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Xiangshan, 100093, Beijing, China
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27
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Feranchak AP, Lewis MA, Kresge C, Sathe M, Bugde A, Luby-Phelps K, Antich PP, Fitz JG. Initiation of purinergic signaling by exocytosis of ATP-containing vesicles in liver epithelium. J Biol Chem 2010; 285:8138-47. [PMID: 20071341 DOI: 10.1074/jbc.m109.065482] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Extracellular ATP represents an important autocrine/paracrine signaling molecule within the liver. The mechanisms responsible for ATP release are unknown, and alternative pathways have been proposed, including either conductive ATP movement through channels or exocytosis of ATP-enriched vesicles, although direct evidence from liver cells has been lacking. Utilizing dynamic imaging modalities (confocal and total internal reflection fluorescence microscopy and luminescence detection utilizing a high sensitivity CCD camera) at different scales, including confluent cell populations, single cells, and the intracellular submembrane space, we have demonstrated in a model liver cell line that (i) ATP release is not uniform but reflects point source release by a defined subset of cells; (ii) ATP within cells is localized to discrete zones of high intensity that are approximately 1 mum in diameter, suggesting a vesicular localization; (iii) these vesicles originate from a bafilomycin A(1)-sensitive pool, are depleted by hypotonic exposure, and are not rapidly replenished from recycling of endocytic vesicles; and (iv) exocytosis of vesicles in response to cell volume changes depends upon a complex series of signaling events that requires intact microtubules as well as phosphoinositide 3-kinase and protein kinase C. Collectively, these findings are most consistent with an essential role for exocytosis in regulated release of ATP and initiation of purinergic signaling in liver cells.
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Affiliation(s)
- Andrew P Feranchak
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9030, USA.
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28
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Burchfield JG, Lopez JA, Mele K, Vallotton P, Hughes WE. Exocytotic vesicle behaviour assessed by total internal reflection fluorescence microscopy. Traffic 2010; 11:429-39. [PMID: 20070611 DOI: 10.1111/j.1600-0854.2010.01039.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The regulated trafficking or exocytosis of cargo-containing vesicles to the cell surface is fundamental to all cells. By coupling the technology of fluorescently tagged fusion proteins with total internal reflection fluorescence microscopy (TIRFM), it is possible to achieve the high spatio-temporal resolution required to study the dynamics of sub-plasma membrane vesicle trafficking and exocytosis. TIRFM has been used in a number of cell types to visualize and dissect the various steps of exocytosis revealing how molecules identified via genetic and/or biochemical approaches are involved in the regulation of this process. Here, we summarize the contribution of TIRFM to our understanding of the mechanism of exocytosis and discuss the novel methods of analysis that are required to exploit the large volumes of data that can be produced using this technique.
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Affiliation(s)
- James G Burchfield
- The Garvan Institute of Medical Research, 384 Victoria Street, Sydney, New South Wales 2010, Australia
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29
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Tsuboi T, Kitaguchi T, Karasawa S, Fukuda M, Miyawaki A. Age-dependent preferential dense-core vesicle exocytosis in neuroendocrine cells revealed by newly developed monomeric fluorescent timer protein. Mol Biol Cell 2010; 21:87-94. [PMID: 19889833 PMCID: PMC2801723 DOI: 10.1091/mbc.e09-08-0722] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Revised: 10/13/2009] [Accepted: 10/28/2009] [Indexed: 11/11/2022] Open
Abstract
Although it is evident that only a few secretory vesicles accumulating in neuroendocrine cells are qualified to fuse with the plasma membrane and release their contents to the extracellular space, the molecular mechanisms that regulate their exocytosis are poorly understood. For example, it has been controversial whether secretory vesicles are exocytosed randomly or preferentially according to their age. Using a newly developed protein-based fluorescent timer, monomeric Kusabira Green Orange (mK-GO), which changes color with a predictable time course, here we show that small GTPase Rab27A effectors regulate age-dependent exocytosis of secretory vesicles in PC12 cells. When the vesicles were labeled with mK-GO-tagged neuropeptide Y or tissue-type plasminogen activator, punctate structures with green or red fluorescence were observed. Application of high [K(+)] stimulation induced exocytosis of new (green) fluorescent secretory vesicles but not of old (red) vesicles. Overexpression or depletion of rabphilin and synaptotagmin-like protein4-a (Slp4-a), which regulate exocytosis positively and negatively, respectively, disturbed the age-dependent exocytosis of the secretory vesicles in different manners. Our results suggest that coordinate functions of the two effectors of Rab27A, rabphilin and Slp4-a, are required for regulated secretory pathway.
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Affiliation(s)
- Takashi Tsuboi
- *Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Meguro, Tokyo 153-8902, Japan
- Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, Wako, Saitama 351-0198, Japan
| | - Tetsuya Kitaguchi
- Life Function and Dynamics, Exploratory Research for Advanced Technology, Japan Science and Technology Agency, Wako, Saitama 351-0198, Japan
| | - Satoshi Karasawa
- Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, Wako, Saitama 351-0198, Japan
- Amalgaam Co., Ltd., Itabashi, Tokyo 173-0004, Japan; and
| | - Mitsunori Fukuda
- Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan
| | - Atsushi Miyawaki
- Laboratory for Cell Function and Dynamics, Advanced Technology Development Group, Brain Science Institute, RIKEN, Wako, Saitama 351-0198, Japan
- Life Function and Dynamics, Exploratory Research for Advanced Technology, Japan Science and Technology Agency, Wako, Saitama 351-0198, Japan
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30
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Isolation and culture of mouse pancreatic islets for ex vivo imaging studies with trappable or recombinant fluorescent probes. Methods Mol Biol 2010; 633:171-84. [PMID: 20204627 DOI: 10.1007/978-1-59745-019-5_12] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The endocrine pancreas contains small clusters of 1,000-2,000 neuroendocrine cells termed islets of Langerhans. By secreting insulin, glucagon, or other hormones as circumstances dictate, islets play a central role in the control of glucose homeostasis in mammals. Islets are dispersed throughout the exocrine tissue and comprise only 1-2% of the volume of the whole organ; human pancreas contains about 10(6) islets whereas rodents have approximately 2 x 10(3) islets. The isolation of islets from the exocrine tissue usually begins with digestion of the pancreas with collagenase. Collagenase-containing medium is either injected into the pancreatic duct, and the organ left to digest in situ, or added after isolation of the pancreas and its dissection into small pieces ex vivo. Islets can then be separated from the exocrine tissue by gradient density or by handpicking. The islets obtained can either be used intact, for example, to measure insulin or glucagon secretion or be dispersed into single cells with a Ca(2+)-free medium or with trypsin/dispase. The latter facilitates the introduction of recombinant or trappable probes and microimaging studies of, for example, changes in cytosolic-free Ca(2+) concentration or the dynamics of individual organelles or proteins.
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Okayama M, Arakawa T, Tanimura A, Mizoguchi I, Tajima Y, Takuma T. Role of VAMP8/endobrevin in constitutive exocytotic pathway in HeLa cells. Cell Struct Funct 2009; 34:115-25. [PMID: 19738360 DOI: 10.1247/csf.09013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
To evaluate the role of VAMP8/endobrevin in constitutive exocytosis, we have examined the exocytotic pathways of VAMP8 and human growth hormone, both GFP-tagged, by total internal reflection fluorescence microscopy (TIRF-M). Human GH-GFP and VAMP8-GFP were similarly expressed in small round vesicles and elongated tubular vesicles in HeLa cells, and were mostly exocytosed at the peripheral area of the cells. VAMP8-GFP gave 2 types of exocytotic images: a burst type and a non-burst type. The burst type showed a sharp transient increase in the peak fluorescence intensity and a much slower decrease in the average intensity in the active windows, where exocytosis took place, as observed in the "full-fusion" type of exocytosis. The non-burst type showed a relatively long-lasting fusion to the plasma membrane with little transfer of VAMP8-GFP to the plasma membrane, as observed in the so-called "kiss-and-run" type of exocytosis. Endogenous VAMP8 and hGH-GFP were colocalized on the same vesicles at least in part. However, the constitutive exocytosis of hGH-GFP and CLuc, a secreted luciferase from Cypridina noctiluca, was normal, even when siRNAs for VAMP8 and VAMP3 robustly decreased their proteins. These results suggest that VAMP8 is not essential for constitutive exocytosis, although it can be involved in the exocytosis.
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Affiliation(s)
- Miki Okayama
- Department of Orthodontics, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan
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Zheng M, Beck M, Müller J, Chen T, Wang X, Wang F, Wang Q, Wang Y, Baluška F, Logan DC, Šamaj J, Lin J. Actin turnover is required for myosin-dependent mitochondrial movements in Arabidopsis root hairs. PLoS One 2009; 4:e5961. [PMID: 19536333 PMCID: PMC2694364 DOI: 10.1371/journal.pone.0005961] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Accepted: 05/19/2009] [Indexed: 12/04/2022] Open
Abstract
Background Previous studies have shown that plant mitochondrial movements are myosin-based along actin filaments, which undergo continuous turnover by the exchange of actin subunits from existing filaments. Although earlier studies revealed that actin filament dynamics are essential for many functions of the actin cytoskeleton, there are little data connecting actin dynamics and mitochondrial movements. Methodology/Principal Findings We addressed the role of actin filament dynamics in the control of mitochondrial movements by treating cells with various pharmaceuticals that affect actin filament assembly and disassembly. Confocal microscopy of Arabidopsis thaliana root hairs expressing GFP-FABD2 as an actin filament reporter showed that mitochondrial distribution was in agreement with the arrangement of actin filaments in root hairs at different developmental stages. Analyses of mitochondrial trajectories and instantaneous velocities immediately following pharmacological perturbation of the cytoskeleton using variable-angle evanescent wave microscopy and/or spinning disk confocal microscopy revealed that mitochondrial velocities were regulated by myosin activity and actin filament dynamics. Furthermore, simultaneous visualization of mitochondria and actin filaments suggested that mitochondrial positioning might involve depolymerization of actin filaments on the surface of mitochondria. Conclusions/Significance Base on these results we propose a mechanism for the regulation of mitochondrial speed of movements, positioning, and direction of movements that combines the coordinated activity of myosin and the rate of actin turnover, together with microtubule dynamics, which directs the positioning of actin polymerization events.
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Affiliation(s)
- Maozhong Zheng
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
| | - Martina Beck
- Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University Bonn, Department of Plant Cell Biology, Bonn, Germany
| | - Jens Müller
- Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University Bonn, Department of Plant Cell Biology, Bonn, Germany
| | - Tong Chen
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Xiaohua Wang
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
| | - Feng Wang
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
| | - Qinli Wang
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
| | - Yuqing Wang
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
| | - František Baluška
- Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University Bonn, Department of Plant Cell Biology, Bonn, Germany
- Institute of Botany, Slovak Academy of Sciences, Bratislava, Slovak Republic
| | - David C. Logan
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Jozef Šamaj
- Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University Bonn, Department of Plant Cell Biology, Bonn, Germany
- Institute of Plant Genetics and Biotechnology, Slovak Academy of Sciences, Nitra, Slovak Republic
- Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic
| | - Jinxing Lin
- Key Laboratory of Photosynthesis and Molecular Environmental Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing, China
- * E-mail:
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Rutter GA, Leclerc I, Tsuboi T, Xavier GDS, Diraison F, Qian Q. Imaging glucose-regulated insulin secretion and gene expression in single islet beta-cells: control by AMP-activated protein kinase. Cell Biochem Biophys 2009; 40:179-90. [PMID: 15289653 DOI: 10.1385/cbb:40:3:179] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The mechanisms by which changes in glucose concentration regulate gene expression and insulin secretion in pancreatic islet beta-cells are only partly understood. Here we describe the development of new technologies for examining these processes at the level of single living beta-cells. We also present recent findings, made using these and other techniques, which implicate a role for adenosine 5'-monophosphate-activated protein kinase in glucose signaling in these cells.
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Affiliation(s)
- Guy A Rutter
- Henry Wellcome Laboratories of Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University Walk, University of Bristol, United Kingdom.
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Torii S, Saito N, Kawano A, Hou N, Ueki K, Kulkarni RN, Takeuchi T. Gene silencing of phogrin unveils its essential role in glucose-responsive pancreatic beta-cell growth. Diabetes 2009; 58:682-92. [PMID: 19073770 PMCID: PMC2646067 DOI: 10.2337/db08-0970] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Phogrin and IA-2, autoantigens in insulin-dependent diabetes, have been shown to be involved in insulin secretion in pancreatic beta-cells; however, implications at a molecular level are confusing from experiment to experiment. We analyzed biological functions of phogrin in beta-cells by an RNA interference technique. RESEARCH DESIGN AND METHODS Adenovirus-mediated expression of short hairpin RNA specific for phogrin (shPhogrin) was conducted using cultured beta-cell lines and mouse islets. Both glucose-stimulated insulin secretion and cell proliferation rate were determined in the phogrin-knockdown cells. Furthermore, protein expression was profiled in these cells. To see the binding partner of phogrin in beta-cells, coimmunoprecipitation analysis was carried out. RESULTS Adenoviral expression of shPhogrin efficiently decreased its endogenous expression in pancreatic beta-cells. Silencing of phogrin in beta-cells abrogated the glucose-mediated mitogenic effect, which was accompanied by a reduction in the level of insulin receptor substrate 2 (IRS2) protein, without any changes in insulin secretion. Phogrin formed a complex with insulin receptor at the plasma membrane, and their interaction was promoted by high-glucose stimulation that in turn led to stabilization of IRS2 protein. Corroboratively, phogrin knockdown had no additional effect on the proliferation of beta-cell line derived from the insulin receptor-knockout mouse. CONCLUSIONS Phogrin is involved in beta-cell growth via regulating stability of IRS2 protein by the molecular interaction with insulin receptor. We propose that phogrin and IA-2 function as an essential regulator of autocrine insulin action in pancreatic beta-cells.
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Affiliation(s)
- Seiji Torii
- Secretion Biology Lab, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma, Japan
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Michael DJ, Tapechum S, Rohan JG, Johnson JM, Chow RH. Fluorescent cargo proteins in peptidergic endocrine cells: cell type determines secretion kinetics at exocytosis. Ann N Y Acad Sci 2009; 1152:7-17. [PMID: 19161372 DOI: 10.1111/j.1749-6632.2008.04006.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Fluorescent fusion proteins are an important tool for the study of vesicle trafficking and exocytosis, especially when combined with newer types of microscopy. We previously reported that the design of a vesicle-targeted fluorescent fusion construct strongly influences the kinetics of fluorescence change at exocytosis. In the present study we demonstrate that the cell in which a construct is expressed also affects the kinetics of fluorescence change at exocytosis. We fused enhanced green fluorescent protein to the carboxy terminus of the vesicular cargo protein rodent islet amyloid polypeptide. The two proteins were separated by a "linker" sequence of 18 amino acids. We then compared kinetics of fluorescence change at exocytosis for this fluorescent cargo protein expressed in three different types of peptidergic endocrine cell: pancreatic alpha cell, pancreatic beta cell, and adrenal chromaffin cell. In resting cells of all three types, fluorescent spots of similar size and membrane-proximal density appeared near the plasma membrane as expected if the probe is stored in large dense-core secretory vesicles. Upon stimulation, the fluorescent spots displayed sudden changes in fluorescence intensity that were consistent with exocytosis. In beta and alpha cells the fluorescent spots consistently brightened and persisted, whereas in chromaffin cells the fluorescent spots always dispersed rapidly. Thus, for fluorescent cargo proteins in peptidergic endocrine cells, cell type influences the kinetics of fluorescence change at exocytosis. Together with our previous findings, this observation strongly highlights the fact that the behavior of vesicle-targeted fluorescent cargo may be unrelated to that of native cargo, and it emphasizes the need for caution in interpreting fluorescence kinetics in terms of an exocytosis mechanism.
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Affiliation(s)
- Darren J Michael
- Department of Physiology and Biophysics, Keck School of Medicine, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California, USA
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de Wit J, Toonen RF, Verhage M. Matrix-dependent local retention of secretory vesicle cargo in cortical neurons. J Neurosci 2009; 29:23-37. [PMID: 19129381 PMCID: PMC6664920 DOI: 10.1523/jneurosci.3931-08.2009] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 11/21/2008] [Accepted: 11/23/2008] [Indexed: 11/21/2022] Open
Abstract
Neurons secrete many diffusible signals from synaptic and other secretory vesicles. We characterized secretion of guidance cues, neuropeptides, neurotrophins, and proteases from single secretory vesicles using pHluorin-tagged cargo in cortical neurons. Stimulation triggered transient and persistent fusion events. Transient events represented full release followed by cargo diffusion or incomplete release followed by vesicle retrieval, as previously observed in neuroendocrine cells. Unexpectedly, we also observed that certain cargo, such as Semaphorin 3A (Sema3A), was delivered at the cell surface as stable deposits. Stable deposits and transient events were observed for single cargo and both were SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) and calcium dependent. The ratio between stable and transient events did not depend on cargo size, subcellular localization (synaptic vs extrasynaptic secretion), or the presence of the extracellular matrix. Instead, the ratio is cargo specific and depends on an interaction with the vesicle matrix through a basic domain in the cargo protein. Inhibition of this interaction through deletion of the basic domain in Sema3A abolished stable deposits and rendered all events transient. Strikingly, cargo favoring transient release was stably deposited after corelease with cargo favoring stable deposit. These data argue against cargo diffusion after exocytosis as a general principle. Instead, the vesicle matrix retains secreted signals, probably for focal signaling at the cell surface.
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Affiliation(s)
- Joris de Wit
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam (VUA) and VUA Medical Center, 1081 HV Amsterdam, The Netherlands
| | - Ruud F. Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam (VUA) and VUA Medical Center, 1081 HV Amsterdam, The Netherlands
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam (VUA) and VUA Medical Center, 1081 HV Amsterdam, The Netherlands
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Torii S. Expression and function of IA-2 family proteins, unique neuroendocrine-specific protein-tyrosine phosphatases. Endocr J 2009; 56:639-48. [PMID: 19550073 DOI: 10.1507/endocrj.k09e-157] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
IA-2 (also known as islet cell antigen ICA-512) and IA-2 beta (also known as phogrin, phosphatase homologue in granules of insulinoma) are major autoantigens in insulin-dependent diabetes mellitus (IDDM). Autoantibodies against both proteins are expressed years before clinical onset, and they become predictive markers for high-risk subjects. However, the role of these genes in the IDDM pathogenesis has been reported fairly negative by recent studies. IA-2 and IA-2 beta are type I transmembrane proteins that possess one inactive protein-tyrosine phosphatase (PTP) domain in the cytoplasmic region, and act as one of the constituents of regulated secretory pathways in various neuroendocrine cell types including pancreatic beta-cells. Existence of IA-2 homologues in different species suggests a fundamental role in neuroendocrine function. Studies of knockout animals have shown their involvement in maintaining hormone content, however, their specific steps in the secretory pathway IA-2 functions as well as their molecular mechanisms in the hormone content regulation are still unknown. More recent studies have suggested a novel function showing that they contribute to pancreatic beta-cell growth. This review attempts to show the possible biological functions of IA-2 family, focusing on their expression and localization in the neuroendocrine cells.
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Affiliation(s)
- Seiji Torii
- Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
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Calì C, Marchaland J, Spagnuolo P, Gremion J, Bezzi P. Regulated exocytosis from astrocytes physiological and pathological related aspects. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2009; 85:261-93. [PMID: 19607976 DOI: 10.1016/s0074-7742(09)85020-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Astrocytes have traditionally been considered ancillary, satellite cells of the nervous system. However, it is a very recent acquisition that glial cells generate signaling loops which are integral to the brain circuitry and participate, interactively with neuronal networks, in the processing of information. Such a conceptual breakthrough makes this field of investigation one of the hottest in neuroscience, as it calls for a revision of past theories of brain function as well as for new strategies of experimental exploration of brain function. Glial cells are electrically not excitable, and it was only the use of optical recording techniques together with calcium sensitive dyes, that allowed the chemical excitability of glial cells to become apparent. Studies using these new techniques have shown for the first time that glial cells are activated by surrounding synaptic activity and translate neuronal signals into their own calcium code. Intracellular calcium concentration([Ca2+]i) elevations in glial cells have then shown to underlie spatial transfer of information in the glial network, accompanied by release of chemical transmitters (gliotransmitters) such as glutamate and back-signaling to neurons. As a consequence, optical imaging techniques applied to cell cultures or intact tissue have become a state-of-the-art technology for studying glial cell signaling. The molecular mechanisms leading to release of "gliotransmitters," especially glutamate, from glia are under debate. Accumulating evidence clearly indicates that astrocytes secrete numerous transmitters by Ca(2+)-dependent exocytosis. This review will discuss the mechanisms underlying the release of chemical transmitters from astrocytes with a particular emphasis to the regulated exocytosis processes.
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Affiliation(s)
- Corrado Calì
- Department of Cellular Biology and Morphology (DBCM), Faculty of Medicine, University of Lausanne, rue du Bugnon 9, 1005 Lausanne, Switzerland
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Unique secretory dynamics of tissue plasminogen activator and its modulation by plasminogen activator inhibitor-1 in vascular endothelial cells. Blood 2008; 113:470-8. [PMID: 18922856 DOI: 10.1182/blood-2008-03-144279] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We analyzed the secretory dynamics of tissue plasminogen activator (tPA) in EA.hy926 cells, an established vascular endothelial cell (VEC) line producing GFP-tagged tPA, using total internal reflection-fluorescence (TIR-F) microscopy. tPA-GFP was detected in small granules in EA.hy926 cells, the distribution of which was indistinguishable from intrinsically expressed tPA. Its secretory dynamics were unique, with prolonged (> 5 minutes) retention of the tPA-GFP on the cell surface, appearing as fluorescent spots in two-thirds of the exocytosis events. The rapid disappearance (mostly by 250 ms) of a domain-deletion mutant of tPA-GFP possessing only the signal peptide and catalytic domain indicates that the amino-terminal heavy chain of tPA-GFP is essential for binding to the membrane surface. The addition of PAI-1 dose-dependently facilitated the dissociation of membrane-retained tPA and increased the amounts of tPA-PAI-1 high-molecular-weight complexes in the medium. Accordingly, suppression of PAI-1 synthesis in EA.hy926 cells by siRNA prolonged the dissociation of tPA-GFP, whereas a catalytically inactive mutant of tPA-GFP not forming complexes with PAI-1 remained on the membrane even after PAI-1 treatment. Our results provide new insights into the relationship between exocytosed, membrane-retained tPA and PAI-1, which would modulate cell surface-associated fibrinolytic potential.
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Ravier MA, Tsuboi T, Rutter GA. Imaging a target of Ca2+ signalling: dense core granule exocytosis viewed by total internal reflection fluorescence microscopy. Methods 2008; 46:233-8. [PMID: 18854212 PMCID: PMC2597054 DOI: 10.1016/j.ymeth.2008.09.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2008] [Accepted: 09/12/2008] [Indexed: 12/20/2022] Open
Abstract
Ca2+ ions are the most ubiquitous second messenger found in all cells, and play a significant role in controlling regulated secretion from neurons, endocrine, neuroendocrine and exocrine cells. Here, we describe microscopic techniques to image regulated secretion, a target of Ca2+ signalling. The first of these, total internal reflection fluorescence (TIRF), is well suited for optical sectioning at cell–substrate regions with an unusually thin region of fluorescence excitation (<150 nm). It is thus particularly useful for studies of regulated hormone secretion. A brief summary of this approach is provided, as well as a description of the physical basis for the technique and the tools to implement TIRF using a standard fluorescence microscope. We also detail the different fluorescent probes which can be used to detect secretion and how to analyze the data obtained. A comparison between TIRF and other imaging modalities including confocal and multiphoton microscopy is also included.
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Affiliation(s)
- Magalie A Ravier
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30 Avenue Hippocrate 55, B-1200 Brussels, Belgium
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41
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Review: Molecular mechanism of docking of dense-core vesicles to the plasma membrane in neuroendocrine cells. Med Mol Morphol 2008; 41:68-75. [DOI: 10.1007/s00795-008-0400-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2008] [Accepted: 03/04/2008] [Indexed: 02/06/2023]
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Baltrusch S, Lenzen S. Monitoring of glucose-regulated single insulin secretory granule movement by selective photoactivation. Diabetologia 2008; 51:989-96. [PMID: 18389213 DOI: 10.1007/s00125-008-0979-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Accepted: 02/07/2008] [Indexed: 10/22/2022]
Abstract
AIMS/HYPOTHESIS Fluorescence microscopy opens new perspectives for the analysis of insulin secretory granule movement. In this study, we examined whether recently developed photoactivatable/photoconvertible proteins are a useful tool for studying this process at the single granule level in insulin-secreting cells after glucose stimulation. METHODS Plasmids were generated for expression of fusion proteins of the granule membrane phosphatase phogrin or the granule cargo protein neuropeptide Y (NPY) with the photoactivatable green fluorescent protein mutant A206K (PA-GFP-A206K), the photoconvertible protein Dendra2 and the fluorescent protein mCherry. Transfected insulin-secreting MIN6 cells were analysed by fluorescence microscopy. RESULTS Point-resolved 405 nm light exposure during image acquisition of MIN6 cells transiently transfected with Phogrin-PA-GFP-A206K or NPY-PA-GFP-A206K as well as of stable MIN6-Phogrin-Dendra2 cells resulted in selective visualisation of few granules by green or red fluorescence, respectively. Movement of these granules was analysed by an automated tracking method from confocal 3D image series. The high spatiotemporal resolution facilitated an elongated tracking of single granules. Interestingly, the track speed and track displacement of granules after 1 h starvation and subsequent glucose stimulation was lower in cells pre-cultured for 48 h at 3 mmol/l glucose than in cells pre-cultured at 25 mmol/l glucose. CONCLUSIONS/INTERPRETATION Targeting of the granule membrane or its cargo with a photoactivatable/photoconvertible protein allows in-depth visualisation and tracking of single insulin granules in dependence upon glucose. This technique may also open the way to elucidating the regulation of granule movement velocity within the pancreatic beta cell with respect to secretory defects in type 2 diabetes.
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Affiliation(s)
- S Baltrusch
- Institute of Clinical Biochemistry, Hannover Medical School, 30623, Hannover, Germany.
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Tomas A, Meda P, Regazzi R, Pessin JE, Halban PA. Munc 18-1 and granuphilin collaborate during insulin granule exocytosis. Traffic 2008; 9:813-32. [PMID: 18208509 DOI: 10.1111/j.1600-0854.2008.00709.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Munc 18-1 is a member of the Sec/Munc family of syntaxin-binding proteins known to bind to the plasma membrane Q-SNARE syntaxin1 and whose precise role in regulated exocytosis remains controversial. Here, we show that Munc 18-1 plays a positive role in regulated insulin secretion from pancreatic beta cells. Munc 18-1 depletion caused a loss in the secretory capacity of both transiently transfected INS 1E cells and a stable clone with tetracycline-regulated Munc 18-1 RNA interference. In addition, Munc 18-1-depleted cells exhibited defective docking of insulin granules to the plasma membrane and accumulated insulin in the trans Golgi network. Furthermore, glucose stimulation after Munc 18-1 depletion resulted in the rapid formation of autophagosomes. In contrast, overexpression of Munc 18-1 had no effect on insulin secretion. Although there was no detectable interaction between Munc 18-1 and Munc-18-interacting protein 1 or calcium/calmodulin-dependent serine protein kinase, Munc 18-1 associated with the granular protein granuphilin. This association was regulated by glucose and was required for the specific interaction of insulin granules with syntaxin1. We conclude that Munc 18-1 and granuphilin collaborate in the docking of insulin granules to the plasma membrane in an initial fusion-incompetent state, with Munc 18-1 subsequently playing a positive role in a later stage of insulin granule exocytosis.
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Affiliation(s)
- Alejandra Tomas
- Department of Genetic Medicine and Development, University of Geneva Medical School, 1211 Geneva 4, Switzerland.
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Abstract
Total internal reflection fluorescence microscopy (TIRFM), also known as evanescent wave microscopy, is used in a wide range of applications, particularly to view single molecules attached to planar surfaces and to study the position and dynamics of molecules and organelles in living culture cells near the contact regions with the glass coverslip. TIRFM selectively illuminates fluorophores only in a very thin (less than 100 nm deep) layer near the substrate, thereby avoiding excitation of fluorophores outside this subresolution optical section. This chapter reviews the history, current applications in cell biology and biochemistry, basic optical theory, combinations with numerous other optical and spectroscopic approaches, and a range of setup methods, both commercial and custom.
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Affiliation(s)
- Daniel Axelrod
- Departments of Physics and Biophysics, University of Michigan, Ann Arbor, Michigan 48109, USA
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45
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Min L, Leung YM, Tomas A, Watson RT, Gaisano HY, Halban PA, Pessin JE, Hou JC. Dynamin is functionally coupled to insulin granule exocytosis. J Biol Chem 2007; 282:33530-33536. [PMID: 17848579 DOI: 10.1074/jbc.m703402200] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The insulin granule integral membrane protein marker phogrin-green fluorescent protein was co-localized with insulin in Min6B1 beta-cell secretory granules but did not undergo plasma membrane translocation following glucose stimulation. Surprisingly, although expression of a dominant-interfering dynamin mutant (Dyn/K44A) inhibited transferrin receptor endocytosis, it had no effect on phogringreen fluorescent protein localization in the basal or secretagogue-stimulated state. By contrast, co-expression of Dyn/K44A with human growth hormone as an insulin secretory marker resulted in a marked inhibition of human growth hormone release by glucose, KCl, and a combination of multiple secretagogues. Moreover, serial pulse depolarization stimulated an increase in cell surface capacitance that was also blocked in cells expressing Dyn/K44A. Similarly, small interference RNA-mediated knockdown of dynamin resulted in marked inhibition of glucose-stimulated insulin secretion. Together, these data suggest the presence of a selective kiss and run mechanism of insulin release. Moreover, these data indicate a coupling between endocytosis and exocytosis in the regulation of beta-cell insulin secretion.
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Affiliation(s)
- Le Min
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794
| | - Yuk M Leung
- Departments of Medicine and Physiology, University of Toronto, Toronto M5S 1A8, Canada; Department of Physiology, China Medical University, Taichung 404, Taiwan
| | - Alejandra Tomas
- Department of Genetic Medicine and Development, Centre Médical Universitaire, 1 rue Michel-Servet, 1211 Geneva, Switzerland
| | - Robert T Watson
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794
| | - Herbert Y Gaisano
- Departments of Medicine and Physiology, University of Toronto, Toronto M5S 1A8, Canada
| | - Philippe A Halban
- Department of Genetic Medicine and Development, Centre Médical Universitaire, 1 rue Michel-Servet, 1211 Geneva, Switzerland
| | - Jeffrey E Pessin
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794
| | - June Chunqiu Hou
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794.
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Jaiswal JK, Fix M, Takano T, Nedergaard M, Simon SM. Resolving vesicle fusion from lysis to monitor calcium-triggered lysosomal exocytosis in astrocytes. Proc Natl Acad Sci U S A 2007; 104:14151-6. [PMID: 17715060 PMCID: PMC1955787 DOI: 10.1073/pnas.0704935104] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2007] [Indexed: 11/18/2022] Open
Abstract
Optical imaging of individual vesicle exocytosis is providing new insights into the mechanism and regulation of secretion by cells. To study calcium-triggered secretion from astrocytes, we used acridine orange (AO) to label vesicles. Although AO is often used for imaging exocytosis, we found that imaging vesicles labeled with AO can result in their photolysis. Here, we define experimental and analytical approaches that permit us to distinguish unambiguously between fusion, leakage, and lysis of individual vesicles. We have used this approach to demonstrate that lysosomes undergo calcium-triggered exocytosis in astrocytes.
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Affiliation(s)
- Jyoti K. Jaiswal
- *The Rockefeller University, 1230 York Avenue, Box 304, New York, NY 10065; and
| | - Marina Fix
- *The Rockefeller University, 1230 York Avenue, Box 304, New York, NY 10065; and
| | - Takahiro Takano
- Center for Aging and Developmental Biology, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642
| | - Maiken Nedergaard
- Center for Aging and Developmental Biology, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642
| | - Sanford M. Simon
- *The Rockefeller University, 1230 York Avenue, Box 304, New York, NY 10065; and
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Nadrigny F, Li D, Kemnitz K, Ropert N, Koulakoff A, Rudolph S, Vitali M, Giaume C, Kirchhoff F, Oheim M. Systematic colocalization errors between acridine orange and EGFP in astrocyte vesicular organelles. Biophys J 2007; 93:969-80. [PMID: 17416619 PMCID: PMC1913145 DOI: 10.1529/biophysj.106.102673] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Accepted: 01/22/2007] [Indexed: 11/18/2022] Open
Abstract
Dual-color imaging of acridine orange (AO) and EGFP fused to a vesicular glutamate transporter or the vesicle-associated membrane proteins 2 or 3 has been used to visualize a supposedly well-defined subpopulation of glutamatergic astrocytic secretory vesicles undergoing regulated exocytosis. However, AO metachromasy results in the concomitant emission of green and red fluorescence from AO-stained tissue. Therefore, the question arises whether AO and EGFP fluorescence can be distinguished reliably. We used evanescent-field imaging with spectral fluorescence detection as well as fluorescence lifetime imaging microscopy to demonstrate that green fluorescent AO monomers inevitably coexist with red fluorescing AO dimers, at the level of single astroglial vesicles. The green monomer emission spectrally overlaps with that of EGFP and produces a false apparent colocalization on dual-color images. On fluorophore abundance maps calculated from spectrally resolved and unmixed single-vesicle spectral image stacks, EGFP is obscured by the strong green monomer fluorescence, precluding the detection of EGFP. Hence, extreme caution is required when deriving quantitative colocalization information from images of dim fluorescing EGFP-tagged organelles colabeled with bright and broadly emitting dyes like AO. We finally introduce FM4-64/EGFP dual-color imaging as a remedy for imaging a distinct population of astroglial fusion-competent secretory vesicles.
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Tsuboi T, Fukuda M. Synaptotagmin VII modulates the kinetics of dense-core vesicle exocytosis in PC12 cells. Genes Cells 2007; 12:511-9. [PMID: 17397398 DOI: 10.1111/j.1365-2443.2007.01070.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In our previous study, we showed that PC12 cell lines stably expressing synaptotagmin (Syt) VII have greater ability to release hormones Ca(2+)-dependently than the original PC12 cells. However, the precise molecular mechanism of the enhancement of hormone secretion by Syt VII has never been elucidated. In this study, we established a PC12 cell line that stably expresses Syt VII-green fluorescent protein (Syt VII-GFP) or its Ca(2+)-binding-site-deficient mutant (D172N/D303N substitutions; Syt VII-DN-GFP), and examined the effect of Syt VII-GFP expression on the kinetics of dense-core vesicle exocytosis by total internal reflection fluorescence (TIRF) microscopy. Both Syt VII-GFP and Syt VII-DN-GFP co-localized well with dense-core vesicle markers, monomeric red fluorescent protein (mRFP)-tagged neuropeptide Y (NPY-mRFP) and cyan fluorescent protein (CFP)-tagged tissue plasminogen activator (tPA-CFP). Expression of Syt VII-GFP enhanced the number of dense-core vesicle exocytotic events, whereas expression of Syt VII-DN-GFP or knockdown of Syt VII-GFP with specific small interfering RNA (siRNA) attenuated the number of exocytotic events. Monitoring individual tPA-CFP release events revealed that "full release" events are increased in Syt VII-GFP-expressing cells, but not in Syt VII-DN-GFP-expressing or Syt VII-silenced cells. Our data indicate that Syt VII modulates the kinetics of Ca(2+)-dependent dense-core vesicle exocytosis in neuroendocrine PC12 cells, possibly by modulating fusion pore opening.
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Affiliation(s)
- Takashi Tsuboi
- Fukuda Initiative Research Unit, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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Prabhat P, Gan Z, Chao J, Ram S, Vaccaro C, Gibbons S, Ober RJ, Ward ES. Elucidation of intracellular recycling pathways leading to exocytosis of the Fc receptor, FcRn, by using multifocal plane microscopy. Proc Natl Acad Sci U S A 2007; 104:5889-94. [PMID: 17384151 PMCID: PMC1851587 DOI: 10.1073/pnas.0700337104] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The intracellular events on the recycling pathway that lead from sorting endosomes to exocytosis at the plasma membrane are central to cellular function. However, despite intensive study, these processes are poorly characterized in spatial and dynamic terms. The primary reason for this is that, to date, it has not been possible to visualize rapidly moving intracellular compartments in three dimensions in cells. Here, we use a recently developed imaging setup in which multiple planes can be simultaneously imaged within the cell in conjunction with visualization of the plasma membrane plane by using total internal reflection fluorescence microscopy. This has allowed us to track and characterize intracellular events on the recycling pathway that lead to exocytosis of the MHC Class I-related receptor, FcRn. We observe both direct delivery of tubular and vesicular transport containers (TCs) from sorting endosomes to exocytic sites at the plasma membrane, and indirect pathways in which TCs that are not in proximity to sorting endosomes undergo exocytosis. TCs can also interact with different sorting endosomes before exocytosis. Our data provide insight into the intracellular events that precede exocytic fusion.
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Affiliation(s)
- Prashant Prabhat
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
- Department of Electrical Engineering, University of Texas at Dallas, Richardson, TX 75080
| | - Zhuo Gan
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Jerry Chao
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
- Department of Electrical Engineering, University of Texas at Dallas, Richardson, TX 75080
| | - Sripad Ram
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Carlos Vaccaro
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Steven Gibbons
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
| | - Raimund J. Ober
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
- Department of Electrical Engineering, University of Texas at Dallas, Richardson, TX 75080
- To whom correspondence may be addressed. E-mail: or
| | - E. Sally Ward
- *Department of Immunology, University of Texas Southwestern Medical Center, Dallas, TX 75390; and
- To whom correspondence may be addressed. E-mail: or
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Tsuboi T, Kanno E, Fukuda M. The polybasic sequence in the C2B domain of rabphilin is required for the vesicle docking step in PC12 cells. J Neurochem 2007; 100:770-9. [PMID: 17156129 DOI: 10.1111/j.1471-4159.2006.04266.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Rabphilin is generally thought to be involved in the regulation of secretory vesicle exocytosis in neurons and neuroendocrine cells, and it has recently been hypothesized that the C2B domain of rabphilin promotes the docking of dense-core vesicles to the plasma membrane through simultaneous interaction with a vesicle protein, Rab3A/27A, and a plasma membrane protein, SNAP-25 (synaptosome-associated protein of 25 kDa). However, the physiological significance of the rabphilin-SNAP-25 interaction in the vesicle-docking step has never been elucidated. In this study we demonstrated by a mutation analysis that the polybasic sequence (587 KKAKHKTQIKKK 598) in the C2B domain of rabphilin is required for SNAP-25 binding, and that the Asp residues in the Ca(2+)-binding loop 3 (D628 and D630) of the C2B domain are not required. We also investigated the effect of Lys-->Gln (KQ) mutations in the polybasic sequence of the C2B domain on vesicle dynamics by total internal reflection fluorescence microscopy in individual PC12 cells. A rabphilin(KQ) mutant that completely lacks SNAP-25-binding activity significantly decreased the number of plasma-membrane-docked vesicles and strongly inhibited high-KCl-induced dense-core vesicle exocytosis. These results indicate that the polybasic sequence in the C2B domain functions as an effector domain for SNAP-25 and controls the number of 'releasable' vesicles docked to the plasma membrane.
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Affiliation(s)
- Takashi Tsuboi
- Fukuda Initiative Research Unit, RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama, Japan
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