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Kaji I, Thiagarajah JR, Goldenring JR. Modeling the cell biology of monogenetic intestinal epithelial disorders. J Cell Biol 2024; 223:e202310118. [PMID: 38683247 PMCID: PMC11058565 DOI: 10.1083/jcb.202310118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 04/02/2024] [Accepted: 04/15/2024] [Indexed: 05/01/2024] Open
Abstract
Monogenetic variants are responsible for a range of congenital human diseases. Variants in genes that are important for intestinal epithelial function cause a group of disorders characterized by severe diarrhea and loss of nutrient absorption called congenital diarrheas and enteropathies (CODEs). CODE-causing genes include nutrient transporters, enzymes, structural proteins, and vesicular trafficking proteins in intestinal epithelial cells. Several severe CODE disorders result from the loss-of-function in key regulators of polarized endocytic trafficking such as the motor protein, Myosin VB (MYO5B), as well as STX3, STXBP2, and UNC45A. Investigations of the cell biology and pathophysiology following loss-of-function in these genes have led to an increased understanding of both homeostatic and pathological vesicular trafficking in intestinal epithelial cells. Modeling different CODEs through investigation of changes in patient tissues, coupled with the development of animal models and patient-derived enteroids, has provided critical insights into the enterocyte differentiation and function. Linking basic knowledge of cell biology with the phenotype of specific patient variants is a key step in developing effective treatments for rare monogenetic diseases. This knowledge can also be applied more broadly to our understanding of common epithelial disorders.
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Affiliation(s)
- Izumi Kaji
- Section of Surgical Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA
- Epithelial Biology Center, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Jay R. Thiagarajah
- Division of Gastroenterology, Hepatology and Nutrition, Boston Children’s Hospital, Harvard Medical School, Boston, MA, USA
- Congenital Enteropathy Program, Boston Children’s Hospital, Boston, MA, USA
- Harvard Digestive Disease Center, Boston, MA, USA
| | - James R. Goldenring
- Section of Surgical Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA
- Epithelial Biology Center, Vanderbilt University School of Medicine, Nashville, TN, USA
- Nashville VA Medical Center, Nashville, TN, USA
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2
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Huang M, Chow CH, Gurdita A, Harada H, Pham Truong VQB, Eide S, Sun HS, Feng ZP, Monnier PP, Wallace VA, Sugita S. SNAP-25, but not SNAP-23, is essential for photoreceptor development, survival, and function in mice. Commun Biol 2024; 7:34. [PMID: 38182732 PMCID: PMC10770054 DOI: 10.1038/s42003-023-05760-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 12/29/2023] [Indexed: 01/07/2024] Open
Abstract
SNARE-mediated vesicular transport is thought to play roles in photoreceptor glutamate exocytosis and photopigment delivery. However, the functions of Synaptosomal-associated protein (SNAP) isoforms in photoreceptors are unknown. Here, we revisit the expression of SNAP-23 and SNAP-25 and generate photoreceptor-specific knockout mice to investigate their roles. Although we find that SNAP-23 shows weak mRNA expression in photoreceptors, SNAP-23 removal does not affect retinal morphology or vision. SNAP-25 mRNA is developmentally regulated and undergoes mRNA trafficking to photoreceptor inner segments at postnatal day 9 (P9). SNAP-25 knockout photoreceptors develop normally until P9 but degenerate by P14 resulting in severe retinal thinning. Photoreceptor loss in SNAP-25 knockout mice is associated with abolished electroretinograms and vision loss. We find mistrafficked photopigments, enlarged synaptic vesicles, and abnormal synaptic ribbons which potentially underlie photoreceptor degeneration. Our results conclude that SNAP-25, but not SNAP-23, mediates photopigment delivery and synaptic functioning required for photoreceptor development, survival, and function.
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Affiliation(s)
- Mengjia Huang
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Chun Hin Chow
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Akshay Gurdita
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, M5S 1A8, Canada
- Donald K. Johnson Eye Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
| | - Hidekiyo Harada
- Donald K. Johnson Eye Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
| | - Victor Q B Pham Truong
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, M5S 1A8, Canada
- Donald K. Johnson Eye Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
| | - Sarah Eide
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Hong-Shuo Sun
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
- Department of Anatomy, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Zhong-Ping Feng
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Philippe P Monnier
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
- Donald K. Johnson Eye Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
- Department of Ophthalmology & Vision Sciences, University of Toronto, Toronto, ON, M5T 3A9, Canada
| | - Valerie A Wallace
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, M5S 1A8, Canada
- Donald K. Johnson Eye Institute, University Health Network, Toronto, ON, M5T 0S8, Canada
- Department of Ophthalmology & Vision Sciences, University of Toronto, Toronto, ON, M5T 3A9, Canada
| | - Shuzo Sugita
- Division of Experimental & Translational Neuroscience, Krembil Brain Institute, University Health Network, Toronto, ON, M5T 0S8, Canada.
- Department of Physiology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada.
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3
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Fernández G, Krapacher F, Ferreras S, Quassollo G, Mari MM, Pisano MV, Montemerlo A, Rubianes MD, Bregonzio C, Arias C, Paglini MG. Lack of Cdk5 activity is involved on Dopamine Transporter expression and function: Evidences from an animal model of Attention-Deficit Hyperactivity Disorder. Exp Neurol 2021; 346:113866. [PMID: 34537209 DOI: 10.1016/j.expneurol.2021.113866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 09/08/2021] [Accepted: 09/14/2021] [Indexed: 11/29/2022]
Abstract
Attention deficit/Hyperactivity disorder (ADHD) is one of the most diagnosed psychiatric disorders nowadays. The core symptoms of the condition include hyperactivity, impulsiveness and inattention. The main pharmacological treatment consists of psychostimulant drugs affecting Dopamine Transporter (DAT) function. We have previously shown that genetically modified mice lacking p35 protein (p35KO), which have reduced Cdk5 activity, present key hallmarks resembling those described in animal models useful for studying ADHD. The p35KO mouse displays spontaneous hyperactivity and shows a calming effect of methylphenidate or amphetamine treatment. Interestingly, dopaminergic neurotransmission is altered in these mice as they have an increased Dopamine (DA) content together with a low DA turnover. This led us to hypothesize that the lack of Cdk5 activity affects DAT expression and/or function in this animal model. In this study, we performed biochemical assays, cell-based approaches, quantitative fluorescence analysis and functional studies that allowed us to demonstrate that p35KO mice exhibit decreased DA uptake and reduced cell surface DAT expression levels in the striatum (STR). These findings are supported by in vitro observations in which the inhibition of Cdk5 activity in N2a cells induced a significant increase in constitutive DAT endocytosis with a concomitant increase in DAT localization to recycling endosomes. Taken together, these data provide evidences regarding the role of Cdk5/p35 in DAT expression and function, thus contributing to the knowledge of DA neurotransmission physiology and also providing therapeutic options for the treatment of DA pathologies such as ADHD.
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Affiliation(s)
- Guillermo Fernández
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Favio Krapacher
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Soledad Ferreras
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Gonzalo Quassollo
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Macarena Mariel Mari
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - María Victoria Pisano
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Antonella Montemerlo
- Instituto de Investigaciones en Fisicoquímica de Córdoba, INFIQC-CONICET, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - María Dolores Rubianes
- Instituto de Investigaciones en Fisicoquímica de Córdoba, INFIQC-CONICET, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Claudia Bregonzio
- Instituto de Farmacología Experimental Córdoba, IFEC-CONICET, Departamento de Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - Carlos Arias
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina; Instituto de Investigaciones Psicológicas, IIPSI-CONICET, Facultad de Psicología, Universidad Nacional de Córdoba, Córdoba, Argentina
| | - María Gabriela Paglini
- Laboratory of Neurophysiology, Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina; Instituto de Virología "Dr. J. M. Vanella", Facultad de Ciencias Médicas, Universidad Nacional de Córdoba, Córdoba, Argentina.
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Engevik AC, Kaji I, Goldenring JR. The Physiology of the Gastric Parietal Cell. Physiol Rev 2020; 100:573-602. [PMID: 31670611 PMCID: PMC7327232 DOI: 10.1152/physrev.00016.2019] [Citation(s) in RCA: 97] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 10/10/2019] [Accepted: 10/13/2019] [Indexed: 12/11/2022] Open
Abstract
Parietal cells are responsible for gastric acid secretion, which aids in the digestion of food, absorption of minerals, and control of harmful bacteria. However, a fine balance of activators and inhibitors of parietal cell-mediated acid secretion is required to ensure proper digestion of food, while preventing damage to the gastric and duodenal mucosa. As a result, parietal cell secretion is highly regulated through numerous mechanisms including the vagus nerve, gastrin, histamine, ghrelin, somatostatin, glucagon-like peptide 1, and other agonists and antagonists. The tight regulation of parietal cells ensures the proper secretion of HCl. The H+-K+-ATPase enzyme expressed in parietal cells regulates the exchange of cytoplasmic H+ for extracellular K+. The H+ secreted into the gastric lumen by the H+-K+-ATPase combines with luminal Cl- to form gastric acid, HCl. Inhibition of the H+-K+-ATPase is the most efficacious method of preventing harmful gastric acid secretion. Proton pump inhibitors and potassium competitive acid blockers are widely used therapeutically to inhibit acid secretion. Stimulated delivery of the H+-K+-ATPase to the parietal cell apical surface requires the fusion of intracellular tubulovesicles with the overlying secretory canaliculus, a process that represents the most prominent example of apical membrane recycling. In addition to their unique ability to secrete gastric acid, parietal cells also play an important role in gastric mucosal homeostasis through the secretion of multiple growth factor molecules. The gastric parietal cell therefore plays multiple roles in gastric secretion and protection as well as coordination of physiological repair.
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Affiliation(s)
- Amy C Engevik
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - Izumi Kaji
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - James R Goldenring
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
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5
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Diverse exocytic pathways for mast cell mediators. Biochem Soc Trans 2018; 46:235-247. [PMID: 29472369 DOI: 10.1042/bst20170450] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 12/23/2017] [Accepted: 01/04/2018] [Indexed: 12/14/2022]
Abstract
Mast cells play pivotal roles in innate and adaptive immunities but are also culprits in allergy, autoimmunity, and cardiovascular diseases. Mast cells respond to environmental changes by initiating regulated exocytosis/secretion of various biologically active compounds called mediators (e.g. proteases, amines, and cytokines). Many of these mediators are stored in granules/lysosomes and rely on intricate degranulation processes for release. Mast cell stabilizers (e.g. sodium cromoglicate), which prevent such degranulation processes, have therefore been clinically employed to treat asthma and allergic rhinitis. However, it has become increasingly clear that different mast cell diseases often involve multiple mediators that rely on overlapping but distinct mechanisms for release. This review illustrates existing evidence that highlights the diverse exocytic pathways in mast cells. We also discuss strategies to delineate these pathways so as to identify unique molecular components which could serve as new drug targets for more effective and specific treatments against mast cell-related diseases.
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6
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Jakhanwal S, Lee CT, Urlaub H, Jahn R. An activated Q-SNARE/SM protein complex as a possible intermediate in SNARE assembly. EMBO J 2017; 36:1788-1802. [PMID: 28483813 DOI: 10.15252/embj.201696270] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 03/23/2017] [Accepted: 03/24/2017] [Indexed: 01/15/2023] Open
Abstract
Assembly of the SNARE proteins syntaxin1, SNAP25, and synaptobrevin into a SNARE complex is essential for exocytosis in neurons. For efficient assembly, SNAREs interact with additional proteins but neither the nature of the intermediates nor the sequence of protein assembly is known. Here, we have characterized a ternary complex between syntaxin1, SNAP25, and the SM protein Munc18-1 as a possible acceptor complex for the R-SNARE synaptobrevin. The ternary complex binds synaptobrevin with fast kinetics, resulting in the rapid formation of a fully zippered SNARE complex to which Munc18-1 remains tethered by the N-terminal domain of syntaxin1. Intriguingly, only one of the synaptobrevin truncation mutants (Syb1-65) was able to bind to the syntaxin1:SNAP25:Munc18-1 complex, suggesting either a cooperative zippering mechanism that proceeds bidirectionally or the progressive R-SNARE binding via an SM template. Moreover, the complex is resistant to disassembly by NSF Based on these findings, we consider the ternary complex as a strong candidate for a physiological intermediate in SNARE assembly.
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Affiliation(s)
- Shrutee Jakhanwal
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Chung-Tien Lee
- Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center, Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.,Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center, Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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7
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Heijnen H, van der Sluijs P. Platelet secretory behaviour: as diverse as the granules … or not? J Thromb Haemost 2015; 13:2141-51. [PMID: 26391322 DOI: 10.1111/jth.13147] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 09/05/2015] [Indexed: 12/19/2022]
Abstract
Platelets play a central role in the arrest of bleeding after damage to a blood vessel and in the development of thrombosis. Platelets rapidly respond after interaction with sub-endothelial components and release cargo from their storage granules. The three principal granule types of platelets are α-granules, dense granules and lysosomes. Timed release of granule contents and regulated expression of critical receptors are essential for maintenance of the platelet thrombus, yet also have important functions beyond hemostasis (i.e. inflammatory reactions and immune responses). α-granules store adhesive molecules such as von Willebrand factor and fibrinogen, growth factors and inflammatory and angiogenic mediators, which play crucial roles in inflammatory responses and tumor genesis. The α-granules comprise a group of subcellular compartments with a unique composition and ultrastructure. Recent studies have suggested that differential secretory kinetics of α-granule subtypes is responsible for a thematic release of adhesive and inflammatory mediators. In addition, new results indicate that activation-dependent synthesis and release of cytokines also contribute to the inflammatory role of platelets. We will discuss the various methods that platelets use to regulate secretory processes and how these relate to potential differential secretion patterns, thereby promoting adhesiveness and/or inflammatory functions. We will focus on the heterogenic granule population, open canalicular system (OCS) plasticity, the role of contractile and mechanobiological forces, and the fusogenic machinery.
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Affiliation(s)
- H Heijnen
- Department of Clinical Chemistry and Hematology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - P van der Sluijs
- Department of Cell Biology, University Medical Center Utrecht, Utrecht, the Netherlands
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8
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Xu H, Arnold MG, Kumar SV. Differential Effects of Munc18s on Multiple Degranulation-Relevant Trans-SNARE Complexes. PLoS One 2015; 10:e0138683. [PMID: 26384026 PMCID: PMC4575180 DOI: 10.1371/journal.pone.0138683] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Accepted: 09/02/2015] [Indexed: 11/24/2022] Open
Abstract
Mast cell exocytosis, which includes compound degranulation and vesicle-associated piecemeal degranulation, requires multiple Q- and R- SNAREs. It is not clear how these SNAREs pair to form functional trans-SNARE complexes and how these trans-SNARE complexes are selectively regulated for fusion. Here we undertake a comprehensive examination of the capacity of two Q-SNARE subcomplexes (syntaxin3/SNAP-23 and syntaxin4/SNAP-23) to form fusogenic trans-SNARE complexes with each of the four granule-borne R-SNAREs (VAMP2, 3, 7, 8). We report the identification of at least six distinct trans-SNARE complexes under enhanced tethering conditions: i) VAMP2/syntaxin3/SNAP-23, ii) VAMP2/syntaxin4/SNAP-23, iii) VAMP3/syntaxin3/SNAP-23, iv) VAMP3/syntaxin4/SNAP-23, v) VAMP8/syntaxin3/SNAP-23, and vi) VAMP8/syntaxin4/SNAP-23. We show for the first time that Munc18a operates synergistically with SNAP-23-based non-neuronal SNARE complexes (i to iv) in lipid mixing, in contrast to Munc18b and c, which exhibit no positive effect on any SNARE combination tested. Pre-incubation with Munc18a renders the SNARE-dependent fusion reactions insensitive to the otherwise inhibitory R-SNARE cytoplasmic domains, suggesting a protective role of Munc18a for its cognate SNAREs. Our findings substantiate the recently discovered but unexpected requirement for Munc18a in mast cell exocytosis, and implicate post-translational modifications in Munc18b/c activation.
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Affiliation(s)
- Hao Xu
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America
- * E-mail:
| | - Matthew Grant Arnold
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America
| | - Sushmitha Vijay Kumar
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States of America
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Yu H, Zhou J, Takahashi H, Yao W, Suzuki Y, Yuan X, Yoshimura SH, Zhang Y, Liu Y, Emmett N, Bond V, Wang D, Ding X, Takeyasu K, Yao X. Spatial control of proton pump H,K-ATPase docking at the apical membrane by phosphorylation-coupled ezrin-syntaxin 3 interaction. J Biol Chem 2014; 289:33333-42. [PMID: 25301939 PMCID: PMC4246090 DOI: 10.1074/jbc.m114.581280] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 10/08/2014] [Indexed: 11/06/2022] Open
Abstract
The digestive function of the stomach depends on acidification of the gastric lumen. Acid secretion into the lumen is triggered by activation of a cAMP-dependent protein kinase (PKA) cascade, which ultimately results in the insertion of gastric H,K-ATPases into the apical plasma membranes of parietal cells. A coupling protein is ezrin whose phosphorylation at Ser-66 by PKA is required for parietal cell activation. However, little is known regarding the molecular mechanism(s) by which ezrin operates in gastric acid secretion. Here we show that phosphorylation of Ser-66 induces a conformational change of ezrin that enables its association with syntaxin 3 (Stx3) and provides a spatial cue for H,K-ATPase trafficking. This conformation-dependent association is specific for Stx3, and the binding interface is mapped to the N-terminal region. Biochemical analyses show that inhibition of ezrin phosphorylation at Ser-66 prevents ezrin-Stx3 association and insertion of H,K-ATPase into the apical plasma membrane of parietal cells. Using atomic force microscopic analyses, our study revealed that phosphorylation of Ser-66 induces unfolding of ezrin molecule to allow Stx3 binding to its N terminus. Given the essential role of Stx3 in polarized secretion, our study presents the first evidence in which phosphorylation-induced conformational rearrangement of the ezrin molecule provides a spatial cue for polarized membrane trafficking in epithelial cells.
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Affiliation(s)
- Huijuan Yu
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027
| | - Jiajia Zhou
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027, Morehouse School of Medicine, Atlanta, Georgia 30310, and
| | - Hirohide Takahashi
- Laboratory of Plasma Membrane, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
| | - William Yao
- Morehouse School of Medicine, Atlanta, Georgia 30310, and
| | - Yuki Suzuki
- Laboratory of Plasma Membrane, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
| | - Xiao Yuan
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027
| | - Shige H Yoshimura
- Laboratory of Plasma Membrane, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
| | - Yin Zhang
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027, Graduate School, Beijing University of Chinese Medicine, Beijing 100086, China
| | - Ya Liu
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027
| | | | - Vincent Bond
- Morehouse School of Medicine, Atlanta, Georgia 30310, and
| | - Dongmei Wang
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027
| | - Xia Ding
- Graduate School, Beijing University of Chinese Medicine, Beijing 100086, China
| | - Kunio Takeyasu
- Laboratory of Plasma Membrane, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan,
| | - Xuebiao Yao
- From the Anhui Key Laboratory for Cellular Dynamics and Chemical Biology, University of Science and Technology of China School of Life Science, Hefei, China 230027,
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10
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Caceres PS, Mendez M, Ortiz PA. Vesicle-associated membrane protein 2 (VAMP2) but Not VAMP3 mediates cAMP-stimulated trafficking of the renal Na+-K+-2Cl- co-transporter NKCC2 in thick ascending limbs. J Biol Chem 2014; 289:23951-62. [PMID: 25008321 PMCID: PMC4156046 DOI: 10.1074/jbc.m114.589333] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In the kidney, epithelial cells of the thick ascending limb (TAL) reabsorb NaCl via the apical Na+/K+/2Cl− co-transporter NKCC2. Steady-state surface NKCC2 levels in the apical membrane are maintained by a balance between exocytic delivery, endocytosis, and recycling. cAMP is the second messenger of hormones that enhance NaCl absorption. cAMP stimulates NKCC2 exocytic delivery via protein kinase A (PKA), increasing steady-state surface NKCC2. However, the molecular mechanism involved has not been studied. We found that several members of the SNARE family of membrane fusion proteins are expressed in TALs. Here we report that NKCC2 co-immunoprecipitates with VAMP2 in rat TALs, and they co-localize in discrete domains at the apical surface. cAMP stimulation enhanced VAMP2 exocytic delivery to the plasma membrane of renal cells, and stimulation of PKA enhanced VAMP2-NKCC2 co-immunoprecipitation in TALs. In vivo silencing of VAMP2 but not VAMP3 in TALs blunted cAMP-stimulated steady-state surface NKCC2 expression and completely blocked cAMP-stimulated NKCC2 exocytic delivery. VAMP2 was not involved in constitutive NKCC2 delivery. We concluded that VAMP2 but not VAMP3 selectively mediates cAMP-stimulated NKCC2 exocytic delivery and surface expression in TALs. We also demonstrated that cAMP stimulation enhances VAMP2 exocytosis and promotes VAMP2 interaction with NKCC2.
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Affiliation(s)
- Paulo S Caceres
- From the Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan 48202 and the Department of Physiology, Wayne State University, Detroit, Michigan 48202
| | - Mariela Mendez
- From the Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan 48202 and
| | - Pablo A Ortiz
- From the Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan 48202 and the Department of Physiology, Wayne State University, Detroit, Michigan 48202
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11
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Truchet S, Chat S, Ollivier-Bousquet M. Milk secretion: The role of SNARE proteins. J Mammary Gland Biol Neoplasia 2014; 19:119-30. [PMID: 24264376 DOI: 10.1007/s10911-013-9311-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Accepted: 11/13/2013] [Indexed: 12/21/2022] Open
Abstract
During lactation, polarized mammary epithelial secretory cells (MESCs) secrete huge quantities of the nutrient molecules that make up milk, i.e. proteins, fat globules and soluble components such as lactose and minerals. Some of these nutrients are only produced by the MESCs themselves, while others are to a great extent transferred from the blood. MESCs can thus be seen as a crossroads for both the uptake and the secretion with cross-talks between intracellular compartments that enable spatial and temporal coordination of the secretion of the milk constituents. Although the physiology of lactation is well understood, the molecular mechanisms underlying the secretion of milk components remain incompletely characterized. Major milk proteins, namely caseins, are secreted by exocytosis, while the milk fat globules are released by budding, being enwrapped by the apical plasma membrane. Prolactin, which stimulates the transcription of casein genes, also induces the production of arachidonic acid, leading to accelerated casein transport and/or secretion. Because of their ability to form complexes that bridge two membranes and promote their fusion, SNARE (Soluble N-ethylmaleimide-Sensitive Factor Attachment Protein Receptor) proteins are involved in almost all intracellular trafficking steps and exocytosis. As SNAREs can bind arachidonic acid, they could be the effectors of the secretagogue effect of prolactin in MESCs. Indeed, some SNAREs have been observed between secretory vesicles and lipid droplets suggesting that these proteins could not only orchestrate the intracellular trafficking of milk components but also act as key regulators for both the coupling and coordination of milk product secretion in response to hormones.
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Affiliation(s)
- Sandrine Truchet
- INRA, UR1196 Génomique et Physiologie de la Lactation, 78352, Jouy-en-Josas Cedex, France,
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van der Sluijs P, Zibouche M, van Kerkhof P. Late steps in secretory lysosome exocytosis in cytotoxic lymphocytes. Front Immunol 2013; 4:359. [PMID: 24302923 PMCID: PMC3831147 DOI: 10.3389/fimmu.2013.00359] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 10/22/2013] [Indexed: 12/16/2022] Open
Abstract
Natural Killer cells are a subset of cytotoxic lymphocytes that are important in host defense against infections and transformed cells. They exert this function through recognition of target cells by cell surface receptors, which triggers a signaling program that results in a re-orientation of the microtubule organizing center and secretory lysosomes toward the target cell. Upon movement of secretory lysosomes to the plasma membrane and subsequent fusion, toxic proteins are released by secretory lysosomes in the immunological synapse which then enter and kill the target cell. In this minireview we highlight recent progress in our knowledge of late steps in this specialized secretion pathway and address important open questions.
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Affiliation(s)
- Peter van der Sluijs
- Department of Cell Biology, University Medical Center Utrecht , Utrecht , Netherlands
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Munc18b is an essential gene in mice whose expression is limiting for secretion by airway epithelial and mast cells. Biochem J 2012; 446:383-94. [PMID: 22694344 PMCID: PMC3430001 DOI: 10.1042/bj20120057] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Airway mucin secretion and MC (mast cell) degranulation must be tightly controlled for homoeostasis of the lungs and immune system respectively. We found the exocytic protein Munc18b to be highly expressed in mouse airway epithelial cells and MCs, and localized to the apical pole of airway secretory cells. To address its functions, we created a mouse with a severely hypomorphic Munc18b allele such that protein expression in heterozygotes was reduced by ~50%. Homozygous mutant mice were not viable, but heterozygotes showed a ~50% reduction in stimulated release of mucin from epithelial cells and granule contents from MCs. The defect in MCs affected only regulated secretion and not constitutive or transporter-mediated secretion. The severity of passive cutaneous anaphylaxis was also reduced by ~50%, showing that reduction of Munc18b expression results in an attenuation of physiological responses dependent on MC degranulation. The Munc18b promoter is controlled by INR (initiator), Sp1 (specificity protein 1), Ets, CRE (cAMP-response element), GRE (glucocorticoid-response element), GATA and E-box elements in airway epithelial cells; however, protein levels did not change during mucous metaplasia induced by allergic inflammation. Taken together, the results of the present study identify Munc18b as an essential gene that is a limiting component of the exocytic machinery of epithelial cells and MCs.
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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Zhu D, Zhang Y, Lam PPL, Dolai S, Liu Y, Cai EP, Choi D, Schroer SA, Kang Y, Allister EM, Qin T, Wheeler MB, Wang CC, Hong WJ, Woo M, Gaisano HY. Dual role of VAMP8 in regulating insulin exocytosis and islet β cell growth. Cell Metab 2012; 16:238-49. [PMID: 22841572 DOI: 10.1016/j.cmet.2012.07.001] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Revised: 04/17/2012] [Accepted: 06/26/2012] [Indexed: 12/22/2022]
Abstract
Optimal insulin secretion required to maintain glucose homeostasis is the summation of total pancreatic islet β cell mass and intrinsic secretory capacity of individual β cells, which are regulated by distinct mechanisms that could be amplified by glucagon-like-peptide-1 (GLP-1). Because of these actions of GLP-1 on islet β cells, GLP-1 has been deployed to treat diabetes. We employed SNARE protein VAMP8-null mice to demonstrate that VAMP8 mediates insulin granule recruitment to the plasma membrane, which partly accounts for GLP-1 potentiation of glucose-stimulated insulin secretion. VAMP8-null mice also exhibited increased islet β cell mass from increased β cell mitosis, with β cell proliferative activity greatly amplified by GLP-1. Thus, despite the β cell exocytotic defect, VAMP8-null mice have an increased total insulin secretory capacity, which improved glucose homeostasis. We conclude that these VAMP8-mediated events partly underlie the therapeutic actions of GLP-1 on insulin secretion and β cell growth.
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Affiliation(s)
- Dan Zhu
- Department of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
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Ares GR, Caceres PS, Ortiz PA. Molecular regulation of NKCC2 in the thick ascending limb. Am J Physiol Renal Physiol 2011; 301:F1143-59. [PMID: 21900458 DOI: 10.1152/ajprenal.00396.2011] [Citation(s) in RCA: 136] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The kidney plays an essential role in blood pressure regulation by controlling short-term and long-term NaCl and water balance. The thick ascending limb of the loop of Henle (TAL) reabsorbs 25-30% of the NaCl filtered by the glomeruli in a process mediated by the apical Na(+)-K(+)-2Cl(-) cotransporter NKCC2, which allows Na(+) and Cl(-) entry from the tubule lumen into TAL cells. In humans, mutations in the gene coding for NKCC2 result in decreased or absent activity characterized by severe salt and volume loss and decreased blood pressure (Bartter syndrome type 1). Opposite to Bartter's syndrome, enhanced NaCl absorption by the TAL is associated with human hypertension and animal models of salt-sensitive hypertension. TAL NaCl reabsorption is subject to exquisite control by hormones like vasopressin, parathyroid, glucagon, and adrenergic agonists (epinephrine and norepinephrine) that stimulate NaCl reabsorption. Atrial natriuretic peptides or autacoids like nitric oxide and prostaglandins inhibit NaCl reabsorption, promoting salt excretion. In general, the mechanism by which hormones control NaCl reabsorption is mediated directly or indirectly by altering the activity of NKCC2 in the TAL. Despite the importance of NKCC2 in renal physiology, the molecular mechanisms by which hormones, autacoids, physical factors, and intracellular ions regulate NKCC2 activity are largely unknown. During the last 5 years, it has become apparent that at least three molecular mechanisms determine NKCC2 activity. As such, membrane trafficking, phosphorylation, and protein-protein interactions have recently been described in TALs and heterologous expression systems as mechanisms that modulate NKCC2 activity. The focus of this review is to summarize recent data regarding NKCC2 regulation and discuss their potential implications in physiological control of TAL function, renal physiology, and blood pressure regulation.
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Affiliation(s)
- Gustavo R Ares
- Hypertension and Vascular Research Division, Dept. of Internal Medicine, Henry Ford Hospital, 2799 West Grand Blvd., Detroit, MI 48202, USA
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Fujii T, Morii M, Takeguchi N, Sakai H. [Molecular mechanisms of H(+) and Cl(-) secretion in gastric parietal cells]. Nihon Yakurigaku Zasshi 2011; 138:51-5. [PMID: 21828937 DOI: 10.1254/fpj.138.51] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Shimomura H, Imai A, Nashida T. Evidence for amylase release by cyclin-dependent kinase 5 in the rat parotid. Arch Biochem Biophys 2011; 507:310-4. [DOI: 10.1016/j.abb.2010.12.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 12/13/2010] [Accepted: 12/18/2010] [Indexed: 11/25/2022]
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Zhu L, Crothers J, Zhou R, Forte JG. A possible mechanism for ezrin to establish epithelial cell polarity. Am J Physiol Cell Physiol 2010; 299:C431-43. [PMID: 20505040 DOI: 10.1152/ajpcell.00090.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ezrin is an important membrane/actin cytoskeleton linker protein, especially in epithelia. Ezrin has two important binding domains: an NH(2)-terminal region that binds to plasma membrane and a COOH-terminal region that binds to F-actin only after a conformational activation by phosphorylation at Thr567 of ezrin. The present experiments were undertaken to investigate the detailed cellular changes in the time course of expression of ezrin-T567 mutants (nonphosphorylatable T567A and permanent phospho-mimic T567D) in parietal cells and to assess ezrin distribution and its influence on the elaborate membrane recruitment processes of these cells. T567A mutant and wild-type (WT) ezrin were consistently localized to the apical plasma membrane, even with overexpression. On the other hand, T567D went first to apical membrane at early times and low expression levels, then accumulated mainly at the basal surface after 24 h. Overexpression of WT or T567A led to incorporation of internal membranes to apical vacuoles, while overexpression of T567D led to large incorporation of apical and intracellular membranes (including H-K-ATPase) to the basal surface. Differences in polar distribution of ezrin suggest a role for the linker protein in promoting formation and plasticity of membrane surface projections, forming the basis for a novel theory for ezrin as an organizer and regulator of membrane recruitment. A model simulating the cellular distribution of ezrin and its associated membrane- and F-actin-binding forms is given to predict redistributions observed with phosphorylation and mutant overexpression, and it can easily be modified as more specific information regarding binding constants and specific sites becomes available.
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Affiliation(s)
- Lixin Zhu
- Department of Pediatrics, State University of New York at Buffalo, Buffalo, New York, USA
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Affiliation(s)
- John G. Forte
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720;
| | - Lixin Zhu
- Department of Pediatrics, Digestive Disease and Nutrition Center, The State University of New York, Buffalo, New York 14214;
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Caceres PS, Ares GR, Ortiz PA. cAMP stimulates apical exocytosis of the renal Na(+)-K(+)-2Cl(-) cotransporter NKCC2 in the thick ascending limb: role of protein kinase A. J Biol Chem 2009; 284:24965-71. [PMID: 19592485 PMCID: PMC2757200 DOI: 10.1074/jbc.m109.037135] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The apical renal Na(+)-K(+)-2Cl(-) cotransporter NKCC2 mediates NaCl absorption by the thick ascending limb (TAL) of Henle's loop. cAMP stimulates NKCC2 by enhancing steady-state apical membrane levels of this protein; however, the trafficking and signaling mechanisms by which this occurs have not been studied. Here, we report that stimulation of endogenous cAMP levels with either forskolin/3-isobutyl-1-methylxanthine (IBMX) or the V2 receptor agonist [deamino-Cys(1),d-Arg(8)]vasopressin increases steady-state surface NKCC2 and that the protein kinase A (PKA) inhibitor H-89 blocks this effect. Confocal imaging of apical surface NKCC2 in isolated perfused TALs confirmed a stimulatory effect of cAMP on apical trafficking that was blocked by PKA inhibition. Selective stimulation of PKA with the agonist N(6)-benzoyl-cAMP (500 microm) stimulated steady-state surface NKCC2, whereas the Epac-selective agonist 8-p-chlorophenylthio-2'-O-methyl-cAMP (100 and 250 microm) had no effect. To explore the trafficking mechanism by which cAMP increases apical NKCC2, we measured cumulative apical membrane exocytosis and NKCC2 exocytic insertion in TALs. By monitoring apical FM1-43 fluorescence, we observed rapid stimulation of apical exocytosis (2 min) by forskolin/IBMX. We also found constitutive exocytic insertion of NKCC2 in TALs over time, which was increased by 3-fold in the presence of forskolin/IBMX. PKA inhibition blunted cAMP-stimulated exocytic insertion but did not affect the rate of constitutive exocytosis. We conclude that cAMP stimulates steady-state apical surface NKCC2 by stimulating exocytic insertion and that this process is highly dependent on PKA but not Epac.
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Affiliation(s)
- Paulo S Caceres
- Hypertension and Vascular Research Division, Henry Ford Hospital, Wayne State University, Detroit, Michigan 48202, USA
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Rodkey TL, Liu S, Barry M, McNew JA. Munc18a scaffolds SNARE assembly to promote membrane fusion. Mol Biol Cell 2008; 19:5422-34. [PMID: 18829865 DOI: 10.1091/mbc.e08-05-0538] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Munc18a is an SM protein required for SNARE-mediated fusion. The molecular details of how Munc18a acts to enhance neurosecretion have remained elusive. Here, we use in vitro fusion assays to characterize how specific interactions between Munc18a and the neuronal SNAREs enhance the rate and extent of fusion. We show that Munc18a interacts directly and functionally with the preassembled t-SNARE complex. Analysis of Munc18a point mutations indicates that Munc18a interacts with helix C of the Syntaxin1a NRD in the t-SNARE complex. Replacement of the t-SNARE SNAP25b with yeast Sec9c had little effect, suggesting that Munc18a has minimal contact with SNAP25b within the t-SNARE complex. A chimeric Syntaxin built of the Syntaxin1a NRD and the H3 domain of yeast Sso1p and paired with Sec9c eliminated stimulation of fusion, suggesting that Munc18a/Syntaxin1a H3 domain contacts are important. Additionally, a Syntaxin1A mutant lacking a flexible linker region that allows NRD movement abolished stimulation of fusion. These experiments suggest that Munc18a binds to the Syntaxin1a NRD and H3 domain within the assembled t-SNARE complex, positioning them for productive VAMP2 binding. In this capacity, Munc18a serves as a platform for trans-SNARE complex assembly that facilitates efficient SNARE-mediated membrane fusion.
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Affiliation(s)
- Travis L Rodkey
- Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77251-1892, USA
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Procino G, Barbieri C, Tamma G, De Benedictis L, Pessin JE, Svelto M, Valenti G. AQP2 exocytosis in the renal collecting duct -- involvement of SNARE isoforms and the regulatory role of Munc18b. J Cell Sci 2008; 121:2097-106. [PMID: 18505797 DOI: 10.1242/jcs.022210] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vasopressin regulates the fusion of the water channel aquaporin 2 (AQP2) to the apical membrane of the renal collecting-duct principal cells and several lines of evidence indicate that SNARE proteins mediate this process. In this work MCD4 renal cells were used to investigate the functional role of a set of Q- and R-SNAREs, together with that of Munc18b as a negative regulator of the formation of the SNARE complex. Both VAMP2 and VAMP3 were associated with immunoisolated AQP2 vesicles, whereas syntaxin 3 (Stx3), SNAP23 and Munc18 were associated with the apical plasma membrane. Co-immunoprecipitation experiments indicated that Stx3 forms complexes with VAMP2, VAMP3, SNAP23 and Munc18b. Protein knockdown coupled to apical surface biotinylation demonstrated that reduced levels of the R-SNAREs VAMP2 and VAMP3, and the Q-SNAREs Stx3 and SNAP23 strongly inhibited AQP2 fusion at the apical membrane. In addition, knockdown of Munc18b promoted a sevenfold increase of AQP2 fused at the plasma membrane without forskolin stimulation. Taken together these findings propose VAMP2, VAMP3, Stx3 and SNAP23 as the complementary set of SNAREs responsible for AQP2-vesicle fusion into the apical membrane, and Munc18b as a negative regulator of SNARE-complex formation in renal collecting-duct principal cells.
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Affiliation(s)
- Giuseppe Procino
- Department of General and Environmental Physiology, University of Bari, Italy
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Affiliation(s)
- James A McNew
- Department of Biochemistry and Cell Biology, Rice University, 6100 Main Street MS-140, Houston, Texas 77251-1892, USA.
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