1
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Falcone FH, Wan D, Barwary N, Sagi-Eisenberg R. RBL cells as models for in vitro studies of mast cells and basophils. Immunol Rev 2018; 282:47-57. [DOI: 10.1111/imr.12628] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Franco H. Falcone
- Division of Molecular Therapeutics and Formulation; School of Pharmacy; University of Nottingham; Nottingham UK
| | - Daniel Wan
- Division of Molecular Therapeutics and Formulation; School of Pharmacy; University of Nottingham; Nottingham UK
| | - Nafal Barwary
- Division of Molecular Therapeutics and Formulation; School of Pharmacy; University of Nottingham; Nottingham UK
| | - Ronit Sagi-Eisenberg
- Department of Cell and Developmental Biology; Sackler Faculty of Medicine; Tel Aviv University; Tel Aviv Israel
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2
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Moreira B, Tuoriniemi J, Kouchak Pour N, Mihalčíková L, Safina G. Surface Plasmon Resonance for Measuring Exocytosis from Populations of PC12 Cells: Mechanisms of Signal Formation and Assessment of Analytical Capabilities. Anal Chem 2017; 89:3069-3077. [DOI: 10.1021/acs.analchem.6b04811] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Beatriz Moreira
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Jani Tuoriniemi
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Naghmeh Kouchak Pour
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Lýdia Mihalčíková
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
| | - Gulnara Safina
- Department
of Chemistry and Molecular Biology, University of Gothenburg, Kemigården
4, 412 96 Gothenburg, Sweden
- Division
of Biological Physics, Department of Physics, Chalmers University of Technology, Kemigården 1, 412 96 Gothenburg, Sweden
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3
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Bretou M, Jouannot O, Fanget I, Pierobon P, Larochette N, Gestraud P, Guillon M, Emiliani V, Gasman S, Desnos C, Lennon-Duménil AM, Darchen F. Cdc42 controls the dilation of the exocytotic fusion pore by regulating membrane tension. Mol Biol Cell 2014; 25:3195-209. [PMID: 25143404 PMCID: PMC4196869 DOI: 10.1091/mbc.e14-07-1229] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
On exocytosis, membrane fusion starts with the formation of a narrow fusion pore that must expand to allow the release of secretory compounds. The GTPase Cdc42 promotes fusion pore dilation in neuroendocrine cells by controlling membrane tension. Membrane fusion underlies multiple processes, including exocytosis of hormones and neurotransmitters. Membrane fusion starts with the formation of a narrow fusion pore. Radial expansion of this pore completes the process and allows fast release of secretory compounds, but this step remains poorly understood. Here we show that inhibiting the expression of the small GTPase Cdc42 or preventing its activation with a dominant negative Cdc42 construct in human neuroendocrine cells impaired the release process by compromising fusion pore enlargement. Consequently the mode of vesicle exocytosis was shifted from full-collapse fusion to kiss-and-run. Remarkably, Cdc42-knockdown cells showed reduced membrane tension, and the artificial increase of membrane tension restored fusion pore enlargement. Moreover, inhibiting the motor protein myosin II by blebbistatin decreased membrane tension, as well as fusion pore dilation. We conclude that membrane tension is the driving force for fusion pore dilation and that Cdc42 is a key regulator of this force.
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Affiliation(s)
- Marine Bretou
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France Institut National de la Santé et de la Recherche Médicale, U932, Institut Curie, 75005 Paris, France
| | - Ouardane Jouannot
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
| | - Isabelle Fanget
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
| | - Paolo Pierobon
- Institut National de la Santé et de la Recherche Médicale, U932, Institut Curie, 75005 Paris, France
| | - Nathanaël Larochette
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
| | - Pierre Gestraud
- Institut Curie, Paris 75248, France Institut National de la Santé et de la Recherche Médicale, U900, Paris 75248, France Ecole des Mines ParisTech, Fontainebleau, 77300 France
| | - Marc Guillon
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
| | - Valentina Emiliani
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
| | - Stéphane Gasman
- Centre National de la Recherche Scientifique/UPR3212, Institut des Neurosciences Cellulaires et Intégratives, Université Strasbourg, 67084 Strasbourg, France
| | - Claire Desnos
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
| | - Ana-Maria Lennon-Duménil
- Institut National de la Santé et de la Recherche Médicale, U932, Institut Curie, 75005 Paris, France
| | - François Darchen
- Université Paris Descartes, Sorbonne Paris Cité, Centre National de la Recherche Scientifique, UMR 8250, 75270 Paris Cedex 06, France
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4
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Mackenzie KD, Duffield MD, Peiris H, Phillips L, Zanin MP, Teo EH, Zhou XF, Keating DJ. Huntingtin-associated protein 1 regulates exocytosis, vesicle docking, readily releasable pool size and fusion pore stability in mouse chromaffin cells. J Physiol 2013; 592:1505-18. [PMID: 24366265 DOI: 10.1113/jphysiol.2013.268342] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Huntingtin-associated protein 1 (HAP1) was initially established as a neuronal binding partner of huntingtin, mutations in which underlie Huntington's disease. Subcellular localization and protein interaction data indicate that HAP1 may be important in vesicle trafficking and cell signalling. In this study, we establish that HAP1 is important in several steps of exocytosis in adrenal chromaffin cells. Using carbon-fibre amperometry, we measured single vesicle exocytosis in chromaffin cells obtained from HAP1(-/-) and HAP1(+/+) littermate mice. Numbers of Ca(2+)-dependent and Ca(2+)-independent full fusion events in HAP1(-/-) cells are significantly decreased compared with those in HAP1(+/+) cells. We observed no change in the frequency of 'kiss-and-run' fusion events or in Ca(2+) entry. Whereas release per full fusion event is unchanged in HAP1(-/-) cells, early fusion pore duration is prolonged, as indicated by the increased duration of pre-spike foot signals. Kiss-and-run events have a shorter duration, indicating opposing roles for HAP1 in the stabilization of the fusion pore during full fusion and transient fusion, respectively. We use electron microscopy to demonstrate a reduction in the number of vesicles docked at the plasma membrane of HAP1(-/-) cells, where membrane capacitance measurements reveal the readily releasable pool of vesicles to be reduced in size. Our study therefore illustrates that HAP1 regulates exocytosis by influencing the morphological docking of vesicles at the plasma membrane, the ability of vesicles to be released rapidly upon stimulation, and the early stages of fusion pore formation.
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Affiliation(s)
- Kimberly D Mackenzie
- Department of Human Physiology, School of Medicine, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.
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5
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Bost A, Pasche M, Schirra C, Becherer U. Super-resolution microscopy in studying neuroendocrine cell function. Front Neurosci 2013; 7:222. [PMID: 24324394 PMCID: PMC3839409 DOI: 10.3389/fnins.2013.00222] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 11/04/2013] [Indexed: 12/13/2022] Open
Abstract
The last two decades have seen a tremendous development in high resolution microscopy techniques giving rise to acronyms such as TIRFM, SIM, PALM, STORM, and STED. The goal of all these techniques is to overcome the physical resolution barrier of light microscopy in order to resolve precise protein localization and possibly their interaction in cells. Neuroendocrine cell function is to secrete hormones and peptides on demand. This fine-tuned multi-step process is mediated by a large array of proteins. Here, we review the new microscopy techniques used to obtain high resolution and how they have been applied to increase our knowledge of the molecular mechanisms involved in neuroendocrine cell secretion. Further the limitations of these methods are discussed and insights in possible new applications are provided.
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Affiliation(s)
- Anneka Bost
- Physiologisches Institut, Universität des Saarlandes Homburg/Saar, Germany
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6
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Opposing actions of environmental enrichment and Alzheimer's disease on the expression of hippocampal microRNAs in mouse models. Transl Psychiatry 2013; 3:e304. [PMID: 24022509 PMCID: PMC3784766 DOI: 10.1038/tp.2013.77] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Accepted: 07/19/2013] [Indexed: 12/18/2022] Open
Abstract
Alzheimer's disease (AD) is the most common form of dementia in the elderly. Although there are no drugs that modify the disease process, exposure to an enriched environment (EE) can slow the disease progression. Here, we characterize the effects of AD and EE on the post-transcriptional regulators, microRNAs (miRNAs), which may contribute to the detrimental and beneficial effects of AD and EE, respectively, on synaptic plasticity-related proteins and AD pathology. We found for the first time miRNAs that were inversely regulated in AD and EE, and may affect synaptic proteins and modulators, molecular factors associated with AD pathology, and survival and neuroprotective factors. MiRNAs that were upregulated only in 3xTgAD mice model of AD compared with their control mice were localized to synapses, predicted to downregulate essential synaptic proteins and are highly associated with regulating apoptosis, AD-associated processes and axon guidance. Studying the progressive change in miRNAs modulation during aging of 3xTgAD mice, we identified miRNAs that were regulated in earlier stages of AD, suggesting them as potential AD biomarkers. Last, we characterized AD- and EE-related effects in the mouse hippocampus on tomosyn protein levels, an inhibitor of the synaptic transmission machinery. While EE reduced tomosyn levels, tomosyn levels were increased in old 3xTgAD mice, suggesting a role for tomosyn in the impairment of synaptic transmission in AD. Interestingly, we found that miR-325 regulates the expression levels of tomosyn as demonstrated by a luciferase reporter assay, and that miR-325 was downregulated in AD and upregulated following EE. These findings improve our understanding of the molecular and cellular processes in AD pathology, following EE, and the interplay between the two processes, and open new avenues for the studies of understanding and controlling AD.
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7
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Neuron-specific expression of tomosyn1 in the mouse hippocampal dentate gyrus impairs spatial learning and memory. Neuromolecular Med 2013; 15:351-63. [PMID: 23519441 DOI: 10.1007/s12017-013-8223-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 02/16/2013] [Indexed: 01/20/2023]
Abstract
Tomosyn, a syntaxin-binding protein, is known to inhibit vesicle priming and synaptic transmission via interference with the formation of SNARE complexes. Using a lentiviral vector, we specifically overexpressed tomosyn1 in hippocampal dentate gyrus neurons in adult mice. Mice were then subjected to spatial learning and memory tasks and electrophysiological measurements from hippocampal slices. Tomosyn1-overexpression significantly impaired hippocampus-dependent spatial memory while tested in the Morris water maze. Further, tomosyn1-overexpressing mice utilize swimming strategies of lesser cognitive ability in the Morris water maze compared with control mice. Electrophysiological measurements at mossy fiber-CA3 synapses revealed impaired paired-pulse facilitation in the mossy fiber of tomosyn1-overexpressing mice. This study provides evidence for novel roles for tomosyn1 in hippocampus-dependent spatial learning and memory, potentially via decreased synaptic transmission in mossy fiber-CA3 synapses. Moreover, it provides new insight regarding the role of the hippocampal dentate gyrus and mossy fiber-CA3 synapses in swimming strategy preference, and in learning and memory.
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8
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Pasche M, Matti U, Hof D, Rettig J, Becherer U. Docking of LDCVs is modulated by lower intracellular [Ca2+] than priming. PLoS One 2012; 7:e36416. [PMID: 22590540 PMCID: PMC3349663 DOI: 10.1371/journal.pone.0036416] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 03/31/2012] [Indexed: 11/23/2022] Open
Abstract
Many regulatory steps precede final membrane fusion in neuroendocrine cells. Some parts of this preparatory cascade, including fusion and priming, are dependent on the intracellular Ca(2+) concentration ([Ca(2+)](i)). However, the functional implications of [Ca(2+)](i) in the regulation of docking remain elusive and controversial due to an inability to determine the modulatory effect of [Ca(2+)](i). Using a combination of TIRF-microscopy and electrophysiology we followed the movement of large dense core vesicles (LDCVs) close to the plasma membrane, simultaneously measuring membrane capacitance and [Ca(2+)](i). We found that a free [Ca(2+)](i) of 700 nM maximized the immediately releasable pool and minimized the lateral mobility of vesicles, which is consistent with a maximal increase of the pool size of primed LDCVs. The parameters that reflect docking, i.e. axial mobility and the fraction of LDCVs residing at the plasma membrane for less than 5 seconds, were strongly decreased at a free [Ca(2+)](i) of 500 nM. These results provide the first evidence that docking and priming occur at different free intracellular Ca(2+) concentrations, with docking efficiency being the most robust at 500 nM.
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Affiliation(s)
- Mathias Pasche
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Ulf Matti
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Detlef Hof
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Jens Rettig
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
| | - Ute Becherer
- Physiologisches Institut, Universität des Saarlandes, Homburg/Saar, Germany
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9
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Myrip couples the capture of secretory granules by the actin-rich cell cortex and their attachment to the plasma membrane. J Neurosci 2012; 32:2564-77. [PMID: 22396429 DOI: 10.1523/jneurosci.2724-11.2012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Exocytosis of secretory granules (SGs) requires their delivery to the actin-rich cell cortex followed by their attachment to the plasma membrane (PM). How these reactions are executed and coordinated is still unclear. Myrip, which is also known as Slac-2c, binds to the SG-associated GTPase Rab27 and is thought to promote the delivery of SGs to the PM by recruiting the molecular motor myosin Va. Myrip also interacts with actin and the exocyst complex, suggesting that it may exert multiple roles in the secretory process. By combining total internal reflection fluorescence microscopy, single-particle tracking, a photoconversion-based assay, and mathematical modeling, we show that, in human enterochromaffin cells, Myrip (1) inhibits a class of SG motion characterized by fast and directed movement, suggesting that it facilitates the dissociation of SGs from microtubules; (2) enhances their motion toward the PM and the probability of SG attachment to the PM; and (3) increases the characteristic time of immobilization at the PM, indicating that it is a component of the molecular machinery that tether SGs to the PM. Remarkably, while the first two effects of Myrip depend on its ability to recruit myosin Va on SGs, the third is myosin Va independent but relies on the C-terminal domain of Myrip. We conclude that Myrip couples the retention of SGs in the cell cortex, their transport to the PM, and their attachment to the PM, and thus promotes secretion. These three steps of the secretory process are thus intimately coordinated.
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10
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The munc13-4-rab27 complex is specifically required for tethering secretory lysosomes at the plasma membrane. Blood 2011; 118:1570-8. [PMID: 21693760 DOI: 10.1182/blood-2011-02-339523] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cytotoxic T lymphocytes (CTLs) kill target cells through the polarized release of lytic molecules from secretory lysosomes. Loss of munc13-4 function inhibits this process and causes familial hemophagocytic lymphohistiocytosis type 3 (FHL3). munc13-4 binds rab27a, but the necessity of the complex remains enigmatic, because studies in knockout models suggest separate functions. In the present study, we describe a noncanonical rab27a-binding motif in the N-terminus of munc13-4. Point mutants in this sequence have severely impaired rab27a binding, allowing dissection of rab27a requirements in munc13-4 function. The munc13-4-rab27a complex is not needed for secretory lysosome maturation, as shown by complementation in CTLs from FHL3 patients and in a mast cell line silenced for munc13-4. In contrast, fusion of secretory lysosomes with, and content release at the plasma membrane during degranulation, strictly required the munc13-4-rab27a complex. Total internal reflection fluorescence microscopy imaging revealed that the complex corrals motile secretory lysosomes beneath the plasma membrane during degranulation and controls their docking. The propensity to stall motility of secretory lysosomes is lost in cells expressing munc13-4 point mutants that do not bind rab27. In summary, these results uncovered a mechanism for tethering secretory lysosomes to the plasma membrane that is essential for degranulation in immune cells.
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11
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Williams AL, Bielopolski N, Meroz D, Lam AD, Passmore DR, Ben-Tal N, Ernst SA, Ashery U, Stuenkel EL. Structural and functional analysis of tomosyn identifies domains important in exocytotic regulation. J Biol Chem 2011; 286:14542-53. [PMID: 21330375 DOI: 10.1074/jbc.m110.215624] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tomosyn is a 130-kDa cytosolic R-SNARE protein that associates with Q-SNAREs and reduces exocytotic activity. Two paralogous genes, tomosyn-1 and -2, occur in mammals and produce seven different isoforms via alternative splicing. Here, we map the structural differences between the yeast homologue of m-tomosyn-1, Sro7, and tomosyn genes/isoforms to identify domains critical to the regulation of exocytotic activity to tomosyn that are outside the soluble N-ethylmaleimide-sensitive attachment receptor motif. Homology modeling of m-tomosyn-1 based on the known structure of yeast Sro7 revealed a highly conserved functional conformation but with tomosyn containing three additional loop domains that emanate from a β-propeller core. Notably, deletion of loops 1 and 3 eliminates tomosyn inhibitory activity on secretion without altering its soluble N-ethylmaleimide-sensitive attachment receptor pairing with syntaxin1A. By comparison, deletion of loop 2, which contains the hypervariable splice region, did not reduce the ability of tomosyn to inhibit regulated secretion. However, exon variation within the hypervariable splice region resulted in significant differences in protein accumulation of tomosyn-2 isoforms. Functional analysis of s-tomosyn-1, m-tomosyn-1, m-tomosyn-2, and xb-tomosyn-2 demonstrated that they exert similar inhibitory effects on elevated K(+)-induced secretion in PC12 cells, although m-tomosyn-2 was novel in strongly augmenting basal secretion. Finally, we report that m-tomosyn-1 is a target substrate for SUMO 2/3 conjugation and that mutation of this small ubiquitin-related modifier target site (Lys-730) enhances m-tomosyn-1 inhibition of secretion without altering interaction with syntaxin1A. Together these results suggest that multiple domains outside the R-SNARE of tomosyn are critical to the efficacy of inhibition by tomosyn on exocytotic secretion.
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Affiliation(s)
- Antionette L Williams
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109, USA
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12
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Gutiérrez-Martín Y, Bustillo D, Gómez-Villafuertes R, Sánchez-Nogueiro J, Torregrosa-Hetland C, Binz T, Gutiérrez LM, Miras-Portugal MT, Artalejo AR. P2X7 receptors trigger ATP exocytosis and modify secretory vesicle dynamics in neuroblastoma cells. J Biol Chem 2011; 286:11370-81. [PMID: 21292765 PMCID: PMC3064193 DOI: 10.1074/jbc.m110.139410] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Previously, we reported that purinergic ionotropic P2X7 receptors negatively regulate neurite formation in Neuro-2a (N2a) mouse neuroblastoma cells through a Ca2+/calmodulin-dependent kinase II-related mechanism. In the present study we used this cell line to investigate a parallel though faster P2X7 receptor-mediated signaling pathway, namely Ca2+-regulated exocytosis. Selective activation of P2X7 receptors evoked exocytosis as assayed by high resolution membrane capacitance measurements. Using dual-wavelength total internal reflection microscopy, we have observed both the increase in near-membrane Ca2+ concentration and the exocytosis of fluorescently labeled vesicles in response to P2X7 receptor stimulation. Moreover, activation of P2X7 receptors also affects vesicle motion in the vertical and horizontal directions, thus, involving this receptor type in the control of early steps (docking and priming) of the secretory pathway. Immunocytochemical and RT-PCR experiments evidenced that N2a cells express the three neuronal SNAREs as well as vesicular nucleotide and monoamine (VMAT-1 and VMAT-2) transporters. Biochemical measurements indicated that ionomycin induced a significant release of ATP from N2a cells. Finally, P2X7 receptor stimulation and ionomycin increased the incidence of small transient inward currents, reminiscent of postsynaptic quantal events observed at synapses. Small transient inward currents were dependent on extracellular Ca2+ and were abolished by Brilliant Blue G, suggesting they were mediated by P2X7 receptors. Altogether, these results suggest the existence of a positive feedback mechanism mediated by P2X7 receptor-stimulated exocytotic release of ATP that would act on P2X7 receptors on the same or neighbor cells to further stimulate its own release and negatively control N2a cell differentiation.
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13
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Stevens DR, Schirra C, Becherer U, Rettig J. Vesicle pools: lessons from adrenal chromaffin cells. Front Synaptic Neurosci 2011; 3:2. [PMID: 21423410 PMCID: PMC3059608 DOI: 10.3389/fnsyn.2011.00002] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Accepted: 01/17/2011] [Indexed: 11/30/2022] Open
Abstract
The adrenal chromaffin cell serves as a model system to study fast Ca2+-dependent exocytosis. Membrane capacitance measurements in combination with Ca2+ uncaging offers a temporal resolution in the millisecond range and reveals that catecholamine release occurs in three distinct phases. Release of a readily releasable (RRP) and a slowly releasable (SRP) pool are followed by sustained release, due to maturation, and release of vesicles which were not release-ready at the start of the stimulus. Trains of depolarizations, a more physiological stimulus, induce release from a small immediately releasable pool of vesicles residing adjacent to calcium channels, as well as from the RRP. The SRP is poorly activated by depolarization. A sequential model, in which non-releasable docked vesicles are primed to a slowly releasable state, and then further mature to the readily releasable state, has been proposed. The docked state, dependent on membrane proximity, requires SNAP-25, synaptotagmin, and syntaxin. The ablation or modification of SNAP-25 and syntaxin, components of the SNARE complex, as well as of synaptotagmin, the calcium sensor, and modulators such complexins and Snapin alter the properties and/or magnitudes of different phases of release, and in particular can ablate the RRP. These results indicate that the composition of the SNARE complex and its interaction with modulatory molecules drives priming and provides a molecular basis for different pools of releasable vesicles.
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Affiliation(s)
- David R Stevens
- Physiologisches Institut, Universität des Saarlandes Homburg, Saarland, Germany
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14
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Gottfried I, Ehrlich M, Ashery U. HIP1 exhibits an early recruitment and a late stage function in the maturation of coated pits. Cell Mol Life Sci 2009; 66:2897-911. [PMID: 19626275 PMCID: PMC11115706 DOI: 10.1007/s00018-009-0077-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2009] [Accepted: 06/12/2009] [Indexed: 11/26/2022]
Abstract
Huntingtin interacting protein 1 (HIP1) is an accessory protein of the clathrin-mediated endocytosis (CME) pathway, yet its precise role and the step at which it becomes involved are unclear. We employed live-cell imaging techniques to focus on the early steps of CME and characterize HIP1 dynamics. We show that HIP1 is highly colocalized with clathrin at the plasma membrane and shares similar dynamics with a subpopulation of clathrin assemblies. Employing transferrin receptor fused to pHluorin, we distinguished between open pits to which HIP1 localizes and newly internalized vesicles that are devoid of HIP1. Moreover, shRNA knockdown of clathrin compromised HIP1 membranal localization, unlike the reported behavior of Sla2p. HIP1 fragment, lacking its ANTH and Talin-like domains, inhibits internalization of transferrin, but retains colocalization with membranal clathrin assemblies. These data demonstrate HIP1's role in pits maturation and formation of the coated vesicle, and its strong dependence on clathrin for membranal localization.
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Affiliation(s)
- Irit Gottfried
- Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel
| | - Marcelo Ehrlich
- Department of Cell Research and Immunology, Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
| | - Uri Ashery
- Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel
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15
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Kofer-Geles M, Gottfried I, Haklai R, Elad-Zefadia G, Kloog Y, Ashery U. Rasosomes spread Ras signals from plasma membrane 'hotspots'. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:1691-702. [PMID: 19695294 DOI: 10.1016/j.bbamcr.2009.08.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 07/28/2009] [Accepted: 08/10/2009] [Indexed: 12/31/2022]
Abstract
Ras proteins regulate cell growth, differentiation, and apoptosis from various cellular platforms. We have recently identified a novel potential signaling platform, the rasosome, which moves rapidly near the plasma membrane (PM) and in the cytosol, carrying multiple copies of palmitoylated Ras proteins. In the present study we demonstrate that rasosomes are unique entities distinct from PM nanoclusters or from endocytotic compartments. In addition, we examine whether rasosomes can act as regulated Ras signaling platforms. We show that a single rasosome simultaneously carries different types of Ras molecules in their active and inactive state, suggesting that rasosomes can upload and download Ras signals. Total internal reflection fluorescence (TIRF) microscopy combined with fast time-lapse and a new spatial analysis algorithm demonstrate that rasosome movement near the PM is restricted to distinctive areas, rasosomal 'hotspots', localized between actin filament cages. In addition, Ras-binding domain of Raf-1 (RBD) is recruited to Ras in rasosomal hotspots as revealed by bimolecular fluorescence complementation experiments. Interestingly, epidermal growth factor stimulates H/NRas activation on rasosomes and the subsequent recruitment of RBD to rasosomes. Moreover, we show that rasosomes are loaded with Ras downstream effectors and modulators. These findings establish that physiological stimulation originating from PM hotspots is transduced to rasosomes, which appear to serve as robust Ras signaling platforms that spread signals across the cell.
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Affiliation(s)
- Merav Kofer-Geles
- Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
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Ashery U, Bielopolski N, Barak B, Yizhar O. Friends and foes in synaptic transmission: the role of tomosyn in vesicle priming. Trends Neurosci 2009; 32:275-82. [PMID: 19307030 PMCID: PMC2713869 DOI: 10.1016/j.tins.2009.01.004] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 01/06/2009] [Accepted: 01/07/2009] [Indexed: 12/24/2022]
Abstract
Priming is the process by which vesicles become available for fusion at nerve terminals and is modulated by numerous proteins and second messengers. One of the prominent members of this diverse family is tomosyn. Tomosyn has been identified as a syntaxin-binding protein; it inhibits vesicle priming, but its mode of action is not fully understood. The inhibitory activity of tomosyn depends on its N-terminal WD40-repeat domain and is regulated by the binding of its SNARE motif to syntaxin. Here, we describe new physiological information on the function of tomosyn and address possible interpretations of these results in the framework of the recently described crystal structure of the yeast tomosyn homolog Sro7. We also present possible molecular scenarios for vesicle priming and the involvement of tomosyn in these processes.
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Affiliation(s)
- Uri Ashery
- Department of Neurobiology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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