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Manori B, Vaknin A, Vaňková P, Nitzan A, Zaidel-Bar R, Man P, Giladi M, Haitin Y. Chloride intracellular channel (CLIC) proteins function as fusogens. Nat Commun 2024; 15:2085. [PMID: 38453905 PMCID: PMC10920813 DOI: 10.1038/s41467-024-46301-z] [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: 08/27/2023] [Accepted: 02/19/2024] [Indexed: 03/09/2024] Open
Abstract
Chloride Intracellular Channel (CLIC) family members uniquely transition between soluble and membrane-associated conformations. Despite decades of extensive functional and structural studies, CLICs' function as ion channels remains debated, rendering our understanding of their physiological role incomplete. Here, we expose the function of CLIC5 as a fusogen. We demonstrate that purified CLIC5 directly interacts with the membrane and induces fusion, as reflected by increased liposomal diameter and lipid and content mixing between liposomes. Moreover, we show that this activity is facilitated by acidic pH, a known trigger for CLICs' transition to a membrane-associated conformation, and that increased exposure of the hydrophobic inter-domain interface is crucial for this process. Finally, mutation of a conserved hydrophobic interfacial residue diminishes the fusogenic activity of CLIC5 in vitro and impairs excretory canal extension in C. elegans in vivo. Together, our results unravel the long-sought physiological role of these enigmatic proteins.
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Grants
- 1721/16 Israel Science Foundation (ISF)
- 1653/21 Israel Science Foundation (ISF)
- 3308/20 Israel Science Foundation (ISF)
- 01214 Israel Cancer Research Fund (Israel Cancer Research Fund, Inc.)
- 19202 Israel Cancer Research Fund (Israel Cancer Research Fund, Inc.)
- 20230029 Israel Cancer Association (ICA)
- CZ.1.05/1.1.00/02.0109 Ministerstvo školstva, vedy, výskumu a športu Slovenskej republiky (Ministry of Education, Science, Research and Sport of the Slovak Republic)
- 731077 EC | Horizon 2020 Framework Programme (EU Framework Programme for Research and Innovation H2020)
- The Claire and Amedee Maratier Institute for the Study of Blindness and Visual Disorders, Faculty of Medicine, Tel-Aviv University.
- The Czech Infrastructure for Integrative Structural Biology (CIISB) grant (LM2023042).
- The Kahn Foundation's Orion project, Tel Aviv Sourasky Medical Center, Israel. The Claire and Amedee Maratier Institute for the Study of Blindness and Visual Disorders, Faculty of Medicine, Tel-Aviv University.
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Affiliation(s)
- Bar Manori
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Alisa Vaknin
- School of Chemistry, Raymond & Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, 6997801, Tel Aviv, Israel
| | - Pavla Vaňková
- Institute of Biotechnology of the Czech Academy of Sciences, Division BioCeV, Prumyslova 595, 252 50, Vestec, Czech Republic
| | - Anat Nitzan
- Department of Cell and Developmental Biology, Faculty of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Ronen Zaidel-Bar
- Department of Cell and Developmental Biology, Faculty of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Petr Man
- Institute of Microbiology of the Czech Academy of Sciences, Division BioCeV, Prumyslova 595, 252 50, Vestec, Czech Republic
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel.
- Tel Aviv Sourasky Medical Center, Tel Aviv, 6423906, Israel.
| | - Yoni Haitin
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel.
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, 6997801, Israel.
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2
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Ott E, Hoff S, Indorf L, Ditengou FA, Müller J, Renschler G, Lienkamp SS, Kramer-Zucker A, Bergmann C, Epting D. A novel role for the chloride intracellular channel protein Clic5 in ciliary function. Sci Rep 2023; 13:17647. [PMID: 37848494 PMCID: PMC10582032 DOI: 10.1038/s41598-023-44235-y] [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: 12/05/2022] [Accepted: 10/05/2023] [Indexed: 10/19/2023] Open
Abstract
CLIC5 belongs to a family of ion channels with six members reported so far. In vertebrates, the CLIC5 gene encodes two different isoforms, CLIC5A and CLIC5B. In addition to its ion channel activity, there is evidence for further functions of CLIC5A, such as the remodeling of the actin cytoskeleton during the formation of a functional glomerulus in the vertebrate kidney. However, its specific role is still incompletely understood and a specific functional role for CLIC5B has not been described yet. Here we report our findings on the differential expression and functions of Clic5a and Clic5b during zebrafish kidney development. Whole-mount in situ hybridization studies revealed specific expression of clic5a in the eye and pronephric glomerulus, and clic5b is expressed in the gut, liver and the pronephric tubules. Clic5 immunostainings revealed that Clic5b is localized in the cilia. Whereas knockdown of Clic5a resulted in leakiness of the glomerular filtration barrier, Clic5b deficient embryos displayed defective ciliogenesis, leading to ciliopathy-associated phenotypes such as ventral body curvature, otolith deposition defects, altered left-right asymmetry and formation of hydrocephalus and pronephric cysts. In addition, Clic5 deficiency resulted in dysregulation of cilia-dependent Wnt signalling pathway components. Mechanistically, we identified a Clic5-dependent activation of the membrane-cytoskeletal linker proteins Ezrin/Radixin/Moesin (ERM) in the pronephric tubules of zebrafish. In conclusion, our in vivo data demonstrates a novel role for Clic5 in regulating essential ciliary functions and identified Clic5 as a positive regulator of ERM phosphorylation.
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Affiliation(s)
- Elisabeth Ott
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany
| | - Sylvia Hoff
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany
| | - Lara Indorf
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany
| | - Franck Anicet Ditengou
- Bio Imaging Core Light Microscopy (BiMiC), Medical Faculty-Institute for Disease Modeling and Targeted Medicine (IMITATE), 79106, Freiburg, Germany
| | - Julius Müller
- Limbach Genetics, Medizinische Genetik Mainz, 55128, Mainz, Germany
| | - Gina Renschler
- Limbach Genetics, Medizinische Genetik Mainz, 55128, Mainz, Germany
| | - Soeren S Lienkamp
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany
- Center for Biological Signaling Studies (BIOSS), 79104, Freiburg, Germany
| | - Albrecht Kramer-Zucker
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany
| | - Carsten Bergmann
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany
- Limbach Genetics, Medizinische Genetik Mainz, 55128, Mainz, Germany
| | - Daniel Epting
- Department of Medicine IV, Faculty of Medicine, Medical Center-University of Freiburg, 79106, Freiburg, Germany.
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3
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Chen GL, Li J, Zhang J, Zeng B. To Be or Not to Be an Ion Channel: Cryo-EM Structures Have a Say. Cells 2023; 12:1870. [PMID: 37508534 PMCID: PMC10378246 DOI: 10.3390/cells12141870] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 07/13/2023] [Accepted: 07/16/2023] [Indexed: 07/30/2023] Open
Abstract
Ion channels are the second largest class of drug targets after G protein-coupled receptors. In addition to well-recognized ones like voltage-gated Na/K/Ca channels in the heart and neurons, novel ion channels are continuously discovered in both excitable and non-excitable cells and demonstrated to play important roles in many physiological processes and diseases such as developmental disorders, neurodegenerative diseases, and cancer. However, in the field of ion channel discovery, there are an unignorable number of published studies that are unsolid and misleading. Despite being the gold standard of a functional assay for ion channels, electrophysiological recordings are often accompanied by electrical noise, leak conductance, and background currents of the membrane system. These unwanted signals, if not treated properly, lead to the mischaracterization of proteins with seemingly unusual ion-conducting properties. In the recent ten years, the technical revolution of cryo-electron microscopy (cryo-EM) has greatly advanced our understanding of the structures and gating mechanisms of various ion channels and also raised concerns about the pore-forming ability of some previously identified channel proteins. In this review, we summarize cryo-EM findings on ion channels with molecular identities recognized or disputed in recent ten years and discuss current knowledge of proposed channel proteins awaiting cryo-EM analyses. We also present a classification of ion channels according to their architectures and evolutionary relationships and discuss the possibility and strategy of identifying more ion channels by analyzing structures of transmembrane proteins of unknown function. We propose that cross-validation by electrophysiological and structural analyses should be essentially required for determining molecular identities of novel ion channels.
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Affiliation(s)
- Gui-Lan Chen
- Key Laboratory of Medical Electrophysiology, Ministry of Education & Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou 646000, China
| | - Jian Li
- College of Pharmaceutical Sciences, Gannan Medical University, Ganzhou 341000, China
| | - Jin Zhang
- School of Basic Medical Sciences, Nanchang University, Nanchang 330031, China
| | - Bo Zeng
- Key Laboratory of Medical Electrophysiology, Ministry of Education & Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou 646000, China
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4
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Huang JJ, Lin J, Chen X, Zhu W. Identification of chloride intracellular channels as prognostic factors correlated with immune infiltration in hepatocellular carcinoma using bioinformatics analysis. Medicine (Baltimore) 2021; 100:e27739. [PMID: 34766585 PMCID: PMC10545300 DOI: 10.1097/md.0000000000027739] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 09/21/2021] [Accepted: 10/22/2021] [Indexed: 12/28/2022] Open
Abstract
ABSTRACT Chloride intracellular channel (CLIC) proteins are novel Cl-channels with 6 family members (CLIC1-6) that are known to play crucial roles in multiple physiological functions, such as neurological, cardiovascular, pulmonary, and auditory functions, and in various malignancies, including hepatocellular carcinoma (HCC). However, considerable challenges exist in identifying appropriate CLICs as therapeutic target molecules and prognostic biomarkers for HCC because the transformation of soluble or integral membrane protein forms, and specific pharmacological agents (agonists and antagonists) for distinct CLICs remains enigmatic.To address this issue and the possible molecular basis and the signaling networks activated by CLICs in HCC, we examined the transcriptional, promoter methylation, DNA mutation, survival, and immune infiltration data of CLICs in patients with HCC using the ONCOMINE, UALCAN, GEPIA, cBioPortal, and TIMER databases.The data showed that the expression levels of CLIC family members were differed between tumor and normal tissues. High expression levels of CLIC1 and CLIC3 were associated with advanced cancer stage in HCC patients. Low CLIC1 expression was associated with a better overall survival (OS). The DNA methylation levels of the CLIC1-3 and CLIC5-6 promoters in tumor tissue with HCC were significantly lower in HCC tissues than in normal tissues. Patients with CLIC1 alterations had a shorter OS than patients with unaltered CLIC1. Moreover, the expression levels of CLICs correlated with the infiltration of 6 different immune cells (B cells, CD4+ T cells, CD8+ T cells, neutrophils, macrophages, and dendritic cells).These results indicate that the increased mRNA expression and decreased promoter DNA methylation level of CLICs may play crucial roles in HCC tumorigenesis. The expression of CLIC family members was significantly correlated with the tumor immune status. High CLIC1 and CLIC3 expression levels could serve as biomarkers for identifying advanced-stage HCC. Moreover, a CLIC1 mutation rate of 18% was also observed and CLIC1 genetic alterations were significantly associated with lower OS in HCC patients.
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Affiliation(s)
- Juan-Jun Huang
- Department of Infectious Diseases, The Affiliated Ganzhou Hospital of Nanchang University, Ganzhou, Jiangxi, PR China
| | - Jing Lin
- Central Laboratory, The Affiliated Ganzhou Hospital of Nanchang University, Ganzhou, Jiangxi, PR China
| | - Xiaoli Chen
- Central Laboratory, The Affiliated Ganzhou Hospital of Nanchang University, Ganzhou, Jiangxi, PR China
| | - Wei Zhu
- Central Laboratory, The Affiliated Ganzhou Hospital of Nanchang University, Ganzhou, Jiangxi, PR China
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5
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Turkewitz DR, Moghaddasi S, Alghalayini A, D'Amario C, Ali HM, Wallach M, Valenzuela SM. Comparative study of His- and Non-His-tagged CLIC proteins, reveals changes in their enzymatic activity. Biochem Biophys Rep 2021; 26:101015. [PMID: 34036185 PMCID: PMC8138732 DOI: 10.1016/j.bbrep.2021.101015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 04/15/2021] [Accepted: 05/02/2021] [Indexed: 10/29/2022] Open
Abstract
The chloride intracellular ion channel protein (CLIC) family are a unique set of ion channels that can exist as soluble and integral membrane proteins. New evidence has emerged that demonstrates CLICs' possess oxidoreductase enzymatic activity and may function as either membrane-spanning ion channels or as globular enzymes. To further characterize the enzymatic profile of members of the CLIC family and to expand our understanding of their functions, we expressed and purified recombinant CLIC1, CLIC3, and a non-functional CLIC1-Cys24A mutant using a Histidine tag, bacterial protein expression system. We demonstrate that the presence of the six-polyhistidine tag at the amino terminus of the proteins led to a decrease in their oxidoreductase enzymatic activity compared to their non-His-tagged counterparts, when assessed using 2-hydroxyethyl disulfide as a substrate. These results strongly suggest the six-polyhistidine tag alters CLIC's structure at the N-terminus, which also contains the enzyme active site. It also raises the need for caution in use of His-tagged proteins when assessing oxidoreductase protein enzymatic function.
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Affiliation(s)
- Daniel R Turkewitz
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia
| | - Saba Moghaddasi
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia
| | - Amani Alghalayini
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia.,ARC Research Hub for Integrated Device for End-user Analysis at Low-levels (IDEAL), Faculty of Science, University of Technology Sydney, NSW, 2007, Australia
| | - Claudia D'Amario
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia
| | - Hala M Ali
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia
| | - Michael Wallach
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia
| | - Stella M Valenzuela
- School of Life Sciences, University of Technology Sydney, Sydney, NSW, 2007, Australia.,ARC Research Hub for Integrated Device for End-user Analysis at Low-levels (IDEAL), Faculty of Science, University of Technology Sydney, NSW, 2007, Australia
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6
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Zheng S, Jiang J, Lee A, Barboiu M. A Voltage‐Responsive Synthetic Cl−‐Channel Regulated by pH. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202008393] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Shao‐Ping Zheng
- Lehn Institute of Functional Materials School of Chemistry Sun Yat-Sen University Guangzhou 510275 China
- Institut Europeen des Membranes Adaptive Supramolecular Nanosystems Group University of Montpellier ENSCM-CNRS Place E. Bataillon CC047 34095 Montpellier France
| | - Ji‐Jun Jiang
- Lehn Institute of Functional Materials School of Chemistry Sun Yat-Sen University Guangzhou 510275 China
| | - Arie Lee
- Institut Europeen des Membranes Adaptive Supramolecular Nanosystems Group University of Montpellier ENSCM-CNRS Place E. Bataillon CC047 34095 Montpellier France
| | - Mihail Barboiu
- Lehn Institute of Functional Materials School of Chemistry Sun Yat-Sen University Guangzhou 510275 China
- Institut Europeen des Membranes Adaptive Supramolecular Nanosystems Group University of Montpellier ENSCM-CNRS Place E. Bataillon CC047 34095 Montpellier France
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7
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Zheng S, Jiang J, Lee A, Barboiu M. A Voltage‐Responsive Synthetic Cl−‐Channel Regulated by pH. Angew Chem Int Ed Engl 2020; 59:18920-18926. [DOI: 10.1002/anie.202008393] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 08/10/2020] [Indexed: 12/11/2022]
Affiliation(s)
- Shao‐Ping Zheng
- Lehn Institute of Functional Materials School of Chemistry Sun Yat-Sen University Guangzhou 510275 China
- Institut Europeen des Membranes Adaptive Supramolecular Nanosystems Group University of Montpellier ENSCM-CNRS Place E. Bataillon CC047 34095 Montpellier France
| | - Ji‐Jun Jiang
- Lehn Institute of Functional Materials School of Chemistry Sun Yat-Sen University Guangzhou 510275 China
| | - Arie Lee
- Institut Europeen des Membranes Adaptive Supramolecular Nanosystems Group University of Montpellier ENSCM-CNRS Place E. Bataillon CC047 34095 Montpellier France
| | - Mihail Barboiu
- Lehn Institute of Functional Materials School of Chemistry Sun Yat-Sen University Guangzhou 510275 China
- Institut Europeen des Membranes Adaptive Supramolecular Nanosystems Group University of Montpellier ENSCM-CNRS Place E. Bataillon CC047 34095 Montpellier France
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8
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Ferofontov A, Vankova P, Man P, Giladi M, Haitin Y. Conserved cysteine dioxidation enhances membrane interaction of human Cl - intracellular channel 5. FASEB J 2020; 34:9925-9940. [PMID: 32725932 DOI: 10.1096/fj.202000399r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 04/21/2020] [Accepted: 04/30/2020] [Indexed: 11/11/2022]
Abstract
The human chloride intracellular channel (hCLIC) family is thought to transition between globular and membrane-associated forms by exposure of a hydrophobic surface. However, the molecular identity of this surface, and the triggering events leading to its exposure, remain elusive. Here, by combining biochemical and structural approaches, together with mass spectrometry (MS) analyses, we show that hCLIC5 is inherently flexible. X-ray crystallography revealed the existence of a globular conformation, while small-angle X-ray scattering showed additional elongated forms consisting of exposure of the conserved hydrophobic inter-domain interface to the bulk phase. Tryptophan fluorescence measurements demonstrated that the transition to the membrane-associated form is enhanced by the presence of oxidative environment and lipids. Using MS, we identified a dose-dependent oxidation of a highly conserved cysteine residue, known to play a key role in the structurally related omega-class of glutathione-S-transferases. Hydrogen/deuterium exchange MS analysis revealed that oxidation of this cysteine facilitates the exposure of the conserved hydrophobic inter-domain interface. Together, our results pinpoint an oxidation of a specific cysteine residue as a triggering mechanism initializing the molecular commitment for membrane interaction in the CLIC family.
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Affiliation(s)
- Alisa Ferofontov
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel
| | - Pavla Vankova
- Division BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Vestec, Czech Republic.,Department of Biochemistry, Faculty of Science, Charles University, Prague, Czech Republic
| | - Petr Man
- Division BioCeV, Institute of Microbiology of the Czech Academy of Sciences, Vestec, Czech Republic
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel
| | - Yoni Haitin
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, Israel.,Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
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9
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Ferofontov A, Strulovich R, Marom M, Giladi M, Haitin Y. Inherent flexibility of CLIC6 revealed by crystallographic and solution studies. Sci Rep 2018; 8:6882. [PMID: 29720717 PMCID: PMC5931990 DOI: 10.1038/s41598-018-25231-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 04/16/2018] [Indexed: 12/22/2022] Open
Abstract
Chloride intracellular channels (CLICs) are a family of unique proteins, that were suggested to adopt both soluble and membrane-associated forms. Moreover, following this unusual metamorphic change, CLICs were shown to incorporate into membranes and mediate ion conduction in vitro, suggesting multimerization upon membrane insertion. Here, we present a 1.8 Å resolution crystal structure of the CLIC domain of mouse CLIC6 (mCLIC6). The structure reveals a monomeric arrangement and shows a high degree of structural conservation with other CLICs. Small-angle X-ray scattering (SAXS) analysis of mCLIC6 demonstrated that the overall solution structure is similar to the crystallographic conformation. Strikingly, further analysis of the SAXS data using ensemble optimization method unveiled additional elongated conformations, elucidating high structural plasticity as an inherent property of the protein. Moreover, structure-guided perturbation of the inter-domain interface by mutagenesis resulted in a population shift towards elongated conformations of mCLIC6. Additionally, we demonstrate that oxidative conditions induce an increase in mCLIC6 hydrophobicity along with mild oligomerization, which was enhanced by the presence of membrane mimetics. Together, these results provide mechanistic insights into the metamorphic nature of mCLIC6.
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Affiliation(s)
- Alisa Ferofontov
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Roi Strulovich
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Milit Marom
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel
| | - Yoni Haitin
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv, 6997801, Israel. .,Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, 6997801, Israel.
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10
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Gururaja Rao S, Ponnalagu D, Patel NJ, Singh H. Three Decades of Chloride Intracellular Channel Proteins: From Organelle to Organ Physiology. CURRENT PROTOCOLS IN PHARMACOLOGY 2018; 80:11.21.1-11.21.17. [PMID: 30040212 PMCID: PMC6060641 DOI: 10.1002/cpph.36] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Intracellular organelles are membranous structures central for maintaining cellular physiology and the overall health of the cell. To maintain cellular function, intracellular organelles are required to tightly regulate their ionic homeostasis. Any imbalance in ionic concentrations can disrupt energy production (mitochondria), protein degradation (lysosomes), DNA replication (nucleus), or cellular signaling (endoplasmic reticulum). Ionic homeostasis is also important for volume regulation of intracellular organelles and is maintained by cation and anion channels as well as transporters. One of the major classes of ion channels predominantly localized to intracellular membranes is chloride intracellular channel proteins (CLICs). They are non-canonical ion channels with six homologs in mammals, existing as either soluble or integral membrane protein forms, with dual functions as enzymes and channels. Provided in this overview is a brief introduction to CLICs, and a summary of recent information on their localization, biophysical properties, and physiological roles. © 2018 by John Wiley & Sons, Inc.
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Affiliation(s)
- Shubha Gururaja Rao
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Devasena Ponnalagu
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Neel J Patel
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Harpreet Singh
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
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11
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Argenzio E, Moolenaar WH. Emerging biological roles of Cl- intracellular channel proteins. J Cell Sci 2017; 129:4165-4174. [PMID: 27852828 DOI: 10.1242/jcs.189795] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Cl- intracellular channels (CLICs) are a family of six evolutionary conserved cytosolic proteins that exist in both soluble and membrane-associated forms; however, their functions have long been elusive. Soluble CLICs adopt a glutathione S-transferase (GST)-fold, can induce ion currents in artificial membranes and show oxidoreductase activity in vitro, but there is no convincing evidence of CLICs having such activities in vivo. Recent studies have revealed a role for CLIC proteins in Rho-regulated cortical actin dynamics as well as vesicular trafficking and integrin recycling, the latter of which are under the control of Rab GTPases. In this Commentary, we discuss the emerging roles of CLIC proteins in these processes and the lessons learned from gene-targeting studies. We also highlight outstanding questions regarding the molecular function(s) of these important but still poorly understood proteins.
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Affiliation(s)
- Elisabetta Argenzio
- Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam 1066CX, The Netherlands
| | - Wouter H Moolenaar
- Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam 1066CX, The Netherlands
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12
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Brum AM, van der Leije CS, Schreuders-Koedam M, Verhoeven J, Janssen M, Dekkers DH, Demmers JA, Eijken M, van de Peppel J, van Leeuwen JP, van der Eerden BC. Identification of Chloride Intracellular Channel Protein 3 as a Novel Gene Affecting Human Bone Formation. JBMR Plus 2017; 1:16-26. [PMID: 30283877 PMCID: PMC6124162 DOI: 10.1002/jbm4.10003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 03/09/2017] [Indexed: 12/14/2022] Open
Abstract
Osteoporosis is a common skeletal disorder characterized by low bone mass leading to increased bone fragility and fracture susceptibility. The bone building cells, osteoblasts, are derived from mesenchymal stromal cells (MSCs); however, with increasing age osteogenic differentiation is diminished and more adipocytes are seen in the bone marrow, suggesting a shift in MSC lineage commitment. Identification of specific factors that stimulate osteoblast differentiation from human MSCs may deliver therapeutic targets to treat osteoporosis. The aim of this study was to identify novel genes involved in osteoblast differentiation of human bone marrow–derived MSCs (hMSCs). We identified the gene chloride intracellular channel protein 3 (CLIC3) to be strongly upregulated during MSC‐derived osteoblast differentiation. Lentiviral overexpression of CLIC3 in hMSCs caused a 60% increase of matrix mineralization. Conversely, knockdown of CLIC3 in hMSCs using two short‐hairpin RNAs (shRNAs) against CLIC3 resulted in a 69% to 76% reduction in CLIC3 mRNA expression, 53% to 37% less alkaline phosphatase (ALP) activity, and 78% to 88% less matrix mineralization compared to scrambled control. Next, we used an in vivo human bone formation model in which hMSCs lentivirally transduced with the CLIC3 overexpression construct were loaded onto a scaffold (hydroxyapatite‐tricalcium‐phosphate), implanted under the skin of NOD‐SCID mice, and analyzed for bone formation 8 weeks later. CLIC3 overexpression led to a 15‐fold increase in bone formation (0.33% versus 5.05% bone area relative to scaffold). Using a Clic3‐His‐tagged pull‐down assay and liquid chromatography–mass spectrometry (LS/MS)‐based proteomics analysis in lysates of osteogenically differentiated hMSCs, we showed that CLIC3 interacts with NIMA‐related kinase 9 (NEK9) and phosphatidylserine synthase 1 (PTDSS1) in vitro, and this finding was supported by immunofluorescent analysis. In addition, inhibition of NEK9 or PTDSS1 gene expression by shRNAs inhibited osteoblast differentiation and mineralization. In conclusion, we successfully identified CLIC3 to be a lineage‐specific gene regulating osteoblast differentiation and bone formation through its interaction with NEK9 and PTDSS1. © The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.
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Affiliation(s)
- Andrea M Brum
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
| | - Cindy S van der Leije
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
| | - Marijke Schreuders-Koedam
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
| | - Jeroen Verhoeven
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
| | | | - Dick Hw Dekkers
- Proteomics Center Erasmus University Medical Center Rotterdam The Netherlands
| | - Jeroen Aa Demmers
- Proteomics Center Erasmus University Medical Center Rotterdam The Netherlands
| | | | - Jeroen van de Peppel
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
| | - Johannes Ptm van Leeuwen
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
| | - Bram Cj van der Eerden
- Department of Internal Medicine School of Molecular Medicine Erasmus University Medical Center Rotterdam the Netherlands
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13
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Ulmasov B, Bruno J, Oshima K, Cheng YW, Holly SP, Parise LV, Egan TM, Edwards JC. CLIC1 null mice demonstrate a role for CLIC1 in macrophage superoxide production and tissue injury. Physiol Rep 2017; 5:e13169. [PMID: 28275112 PMCID: PMC5350177 DOI: 10.14814/phy2.13169] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 01/16/2017] [Accepted: 01/17/2017] [Indexed: 12/23/2022] Open
Abstract
We generated and studied CLIC1 null (C1KO) mice to investigate the physiological role of this protein. C1KO and matched wild-type (WT) mice were studied in two models of acute toxic tissue injury. CLIC1 expression is upregulated following acute injury of WT kidney and pancreas and is absent in C1KOs. Acute tissue injury is attenuated in the C1KOs and this correlates with an absence of the rise in tissue reactive oxygen species (ROS) that is seen in WT mice. Infiltration of injured tissue by inflammatory cells was comparable between WT and C1KOs. Absence of CLIC1 increased PMA-induced superoxide production by isolated peritoneal neutrophils but dramatically decreased PMA-induced superoxide production by peritoneal macrophages. CLIC1 is expressed in both neutrophils and macrophages in a peripheral pattern consistent with either plasma membrane or the cortical cytoskeleton in resting cells and redistributes away from the periphery following PMA stimulation in both cell types. Absence of CLIC1 had no effect on redistribution or dephosphorylation of Ezrin/ERM cytoskeleton in macrophages. Plasma membrane chloride conductance is altered in the absence of CLIC1, but not in a way that would be expected to block superoxide production. NADPH oxidase redistributes from an intracellular compartment to the plasma membrane when WT macrophages are stimulated to produce superoxide and this redistribution fails to occur in C1KO macrophages. We conclude that the role of CLIC1 in macrophage superoxide production is to support redistribution of NADPH oxidase to the plasma membrane, and not through major effects on ERM cytoskeleton or by acting as a plasma membrane chloride channel.
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Affiliation(s)
- Barbara Ulmasov
- Department of Internal Medicine, Saint Louis University, St. Louis, Missouri
| | - Jonathan Bruno
- Department of Internal Medicine, Saint Louis University, St. Louis, Missouri
- UNC Kidney Center, University of North Carolina, Chapel Hill, North Carolina
| | - Kiyoko Oshima
- Department of Pathology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Yao-Wen Cheng
- UNC Kidney Center, University of North Carolina, Chapel Hill, North Carolina
| | - Stephen P Holly
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina
| | - Leslie V Parise
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina
| | - Terrance M Egan
- Department of Pharmacology and Physiology, Saint Louis University, St. Louis, Missouri
| | - John C Edwards
- Department of Internal Medicine, Saint Louis University, St. Louis, Missouri
- UNC Kidney Center, University of North Carolina, Chapel Hill, North Carolina
- Department of Pharmacology and Physiology, Saint Louis University, St. Louis, Missouri
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14
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Tavasoli M, Al-Momany A, Wang X, Li L, Edwards JC, Ballermann BJ. Both CLIC4 and CLIC5A activate ERM proteins in glomerular endothelium. Am J Physiol Renal Physiol 2016; 311:F945-F957. [PMID: 27582103 DOI: 10.1152/ajprenal.00353.2016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 08/25/2016] [Indexed: 01/17/2023] Open
Abstract
The chloride intracellular channel (CLIC) 5A is expressed at very high levels in renal glomeruli, in both endothelial cells (EC) and podocytes. CLIC5A stimulates Rac1- and phosphatidylinositol (4,5)-bisphosphate-dependent ERM (ezrin, radixin, moesin) activation. ERM proteins, in turn, function in lumen formation and in the development of actin-based cellular projections. In mice lacking CLIC5A, ERM phosphorylation is profoundly reduced in podocytes, but preserved in glomerular EC. Since glomerular EC also express CLIC4, we reasoned that, if CLIC4 activates ERM proteins like CLIC5A, then CLIC4 could compensate for the CLIC5A loss in glomerular EC. In glomeruli of CLIC5-deficient mice, CLIC4 expression was upregulated and colocalized with moesin and ezrin in glomerular EC, but not in podocytes. In cultured glomerular EC, CLIC4 silencing reduced ERM phosphorylation and cytoskeletal association, and expression of exogenous CLIC4 or CLIC5A rescued ERM de-phosphorylation due to CLIC4 silencing. In mice lacking either CLIC4 or CLIC5, ERM phosphorylation was retained in glomerular EC, but, in mice lacking both CLIC4 and CLIC5, glomerular EC ERM phosphorylation was profoundly reduced. Although glomerular EC fenestrae developed normally in dual CLIC4/CLIC5-deficient mice, the density of fenestrae declined substantially by 8 mo of age, along with the deposition of subendothelial electron-lucent material. The dual CLIC4/CLIC5-deficient mice developed spontaneous proteinuria, glomerular cell proliferation, and matrix deposition. Thus CLIC4 stimulates ERM activation and can compensate for CLIC5A in glomerular EC. The findings indicate that CLIC4/CLIC5A-mediated ERM activation is required for maintenance of the glomerular capillary architecture.
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Affiliation(s)
- Mahtab Tavasoli
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Abass Al-Momany
- Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada; and
| | - Xin Wang
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Laiji Li
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - John C Edwards
- Department of Internal Medicine, St. Louis University, St. Louis, Missouri
| | - Barbara J Ballermann
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada; .,Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada; and
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15
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Tavasoli M, Li L, Al-Momany A, Zhu LF, Adam BA, Wang Z, Ballermann BJ. The chloride intracellular channel 5A stimulates podocyte Rac1, protecting against hypertension-induced glomerular injury. Kidney Int 2016; 89:833-47. [PMID: 26924049 DOI: 10.1016/j.kint.2016.01.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Revised: 07/02/2015] [Accepted: 10/15/2015] [Indexed: 11/16/2022]
Abstract
Glomerular capillary hypertension elicits podocyte remodeling and is a risk factor for the progression of glomerular disease. Ezrin, which links podocalyxin to actin in podocytes, is activated through the chloride intracellular channel 5A (CLIC5A)-dependent phosphatidylinositol 4,5 bisphosphate (PI[4,5]P2) accumulation. Because Rac1 is involved in podocyte actin remodeling and can promote PI[4,5]P2 production we determined whether CLIC5A-dependent PI[4,5]P2 generation and ezrin activation are mediated by Rac1. In COS7 cells, CLIC5A expression stimulated Rac1 but not Cdc42 or Rho activity. CLIC5A also stimulated phosphorylation of the Rac1 effector Pak1 in COS7 cells and in cultured mouse podocytes. CLIC5A-induced PI[4,5]P2 accumulation and Pak1 and ezrin phosphorylation were all Rac1 dependent. In DOCA/Salt hypertension, phosphorylated Pak increased in podocytes of wild-type, but not CLIC5-deficient mice. In DOCA/salt hypertensive mice lacking CLIC5, glomerular capillary microaneurysms were more frequent and albuminuria was greater than in wild-type mice. Thus, augmented hypertension-induced glomerular capillary injury in mice lacking CLIC5 results from abrogation of Rac1-dependent Pak and ezrin activation, perhaps reducing the tensile strength of the podocyte actin cytoskeleton.
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Affiliation(s)
- Mahtab Tavasoli
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Laiji Li
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Abass Al-Momany
- Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Lin-Fu Zhu
- Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Benjamin A Adam
- Department of Pathology and Laboratory Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Zhixiang Wang
- Department of Medical Genetics, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Barbara J Ballermann
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada; Department of Surgery, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
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16
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Pedersen SF, Okada Y, Nilius B. Biophysics and Physiology of the Volume-Regulated Anion Channel (VRAC)/Volume-Sensitive Outwardly Rectifying Anion Channel (VSOR). Pflugers Arch 2016; 468:371-83. [DOI: 10.1007/s00424-015-1781-6] [Citation(s) in RCA: 113] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 12/19/2015] [Accepted: 12/21/2015] [Indexed: 01/25/2023]
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17
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Pedersen SF, Klausen TK, Nilius B. The identification of a volume-regulated anion channel: an amazing Odyssey. Acta Physiol (Oxf) 2015; 213:868-81. [PMID: 25565132 DOI: 10.1111/apha.12450] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Revised: 12/05/2014] [Accepted: 01/05/2015] [Indexed: 01/03/2023]
Abstract
The volume-regulated anion channel (VRAC) plays a pivotal role in cell volume regulation in essentially all cell types studied. Additionally, VRAC appears to contribute importantly to a wide range of other cellular functions and pathological events, including cell motility, cell proliferation, apoptosis and excitotoxic glutamate release in stroke. Although biophysically, pharmacologically and functionally thoroughly described, VRAC has until very recently remained a genetic orphan. The search for the molecular identity of VRAC has been long and has yielded multiple potential candidates, all of which eventually turned out to have properties not fully compatible with those of VRAC. Recently, two groups have independently identified the protein leucine-rich repeats containing 8A (LRRC8A), belonging to family of proteins (LRRC8A-E) distantly related to pannexins, as the likely pore-forming subunit of VRAC. In this brief review, we summarize the history of the discovery of VRAC, outline its basic biophysical and pharmacological properties, link these to several cellular functions in which VRAC appears to play important roles, and sketch the amazing search for the molecular identity of this channel. Finally, we describe properties of the LRRC8 proteins, highlight some features of the LRRC8A knockout mouse and discuss the impact of the discovery of LRRC8 as VRAC on future research.
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Affiliation(s)
- S. F. Pedersen
- Section for Cell and Developmental Biology; Department of Biology; Faculty of Science; University of Copenhagen; Copenhagen Denmark
| | - T. K. Klausen
- Section for Cell and Developmental Biology; Department of Biology; Faculty of Science; University of Copenhagen; Copenhagen Denmark
| | - B. Nilius
- Laboratory of Ion Channel Research; Department of Cellular and Molecular Medicine; KU Leuven, Campus Gasthuisberg; Leuven Belgium
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18
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Al-Momany A, Li L, Alexander RT, Ballermann BJ. Clustered PI(4,5)P₂ accumulation and ezrin phosphorylation in response to CLIC5A. J Cell Sci 2014; 127:5164-78. [PMID: 25344252 DOI: 10.1242/jcs.147744] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
CLIC5A (encoded by CLIC5) is a component of the ezrin-NHERF2-podocalyxin complex in renal glomerular podocyte foot processes. We explored the mechanism(s) by which CLIC5A regulates ezrin function. In COS-7 cells, CLIC5A augmented ezrin phosphorylation without changing ezrin abundance, increased the association of ezrin with the cytoskeletal fraction and enhanced actin polymerization and the formation of cell surface projections. CLIC5A caused the phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] reporter RFP-PH-PLC to translocate from the cytosol to discrete plasma membrane clusters at the cell surface, where it colocalized with CLIC5A. Transiently expressed HA-PIP5Kα colocalized with GFP-CLIC5A and was pulled from cell lysates by GST-CLIC5A, and silencing of endogenous PIP5Kα abrogated CLIC5A-dependent ERM phosphorylation. N- and C-terminal deletion mutants of CLIC5A, which failed to associate with the plasma membrane, failed to colocalize with PIP5Kα, did not alter the abundance of PI(4,5)P2 plasma membrane clusters and failed to enhance ezrin phosphorylation. Relative to wild-type mice, in CLIC5-deficient mice, the phosphorylation of glomerular ezrin was diminished and the cytoskeletal association of both ezrin and NHERF2 was reduced. Therefore, the mechanism of CLIC5A action involves clustered plasma membrane PI(4,5)P2 accumulation through an interaction of CLIC5A with PI(4,5)P2-generating kinases, in turn facilitating ezrin activation and actin-dependent cell surface remodeling.
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Affiliation(s)
- Abass Al-Momany
- Department of Physiology, University of Alberta, Edmonton, AL T6G 2V2, Canada
| | - Laiji Li
- Department of Medicine (Nephrology), University of Alberta, Edmonton, AL T6G 2V2, Canada
| | - R Todd Alexander
- Department of Pediatrics, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AL T6G 2V2, Canada
| | - Barbara J Ballermann
- Department of Physiology, University of Alberta, Edmonton, AL T6G 2V2, Canada Department of Medicine (Nephrology), University of Alberta, Edmonton, AL T6G 2V2, Canada
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19
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Averaimo S, Abeti R, Savalli N, Brown LJ, Curmi PMG, Breit SN, Mazzanti M. Point mutations in the transmembrane region of the clic1 ion channel selectively modify its biophysical properties. PLoS One 2013; 8:e74523. [PMID: 24058583 PMCID: PMC3776819 DOI: 10.1371/journal.pone.0074523] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 08/02/2013] [Indexed: 12/16/2022] Open
Abstract
Chloride intracellular Channel 1 (CLIC1) is a metamorphic protein that changes from a soluble cytoplasmic protein into a transmembrane protein. Once inserted into membranes, CLIC1 multimerises and is able to form chloride selective ion channels. Whilst CLIC1 behaves as an ion channel both in cells and in artificial lipid bilayers, its structure in the soluble form has led to some uncertainty as to whether it really is an ion channel protein. CLIC1 has a single putative transmembrane region that contains only two charged residues: arginine 29 (Arg29) and lysine 37 (Lys37). As charged residues are likely to have a key role in ion channel function, we hypothesized that mutating them to neutral alanine to generate K37A and R29A CLIC1 would alter the electrophysiological characteristics of CLIC1. By using three different electrophysiological approaches: i) single channel Tip-Dip in artificial bilayers using soluble recombinant CLIC1, ii) cell-attached and iii) whole-cell patch clamp recordings in transiently transfected HEK cells, we determined that the K37A mutation altered the single-channel conductance while the R29A mutation affected the single-channel open probability in response to variation in membrane potential. Our results show that mutation of the two charged amino acids (K37 and R29) in the putative transmembrane region of CLIC1 alters the biophysical properties of the ion channel in both artificial bilayers and cells. Hence these charged residues are directly involved in regulating its ion channel activity. This strongly suggests that, despite its unusual structure, CLIC1 itself is able to form a chloride ion channel.
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Affiliation(s)
- Stefania Averaimo
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
- * E-mail:
| | - Rosella Abeti
- Department of Molecular Neuroscience, University College London, Institute of Neurology, London, United Kingdom
| | - Nicoletta Savalli
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
| | - Louise J. Brown
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, Australia
| | - Paul M. G. Curmi
- School of Physics, University of New South Wales, Sydney, Australia
- St Vincent’s Centre for Applied Medical Research, St Vincent’s Hospital, Sydney, Australia
| | - Samuel N. Breit
- St Vincent’s Centre for Applied Medical Research, St Vincent’s Hospital, Sydney, Australia
| | - Michele Mazzanti
- Dipartimento di Bioscienze, Università degli Studi di Milano, Milan, Italy
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20
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Jiang L, Phang JM, Yu J, Harrop SJ, Sokolova AV, Duff AP, Wilk KE, Alkhamici H, Breit SN, Valenzuela SM, Brown LJ, Curmi PMG. CLIC proteins, ezrin, radixin, moesin and the coupling of membranes to the actin cytoskeleton: a smoking gun? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:643-57. [PMID: 23732235 DOI: 10.1016/j.bbamem.2013.05.025] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 05/20/2013] [Accepted: 05/21/2013] [Indexed: 12/20/2022]
Abstract
The CLIC proteins are a highly conserved family of metazoan proteins with the unusual ability to adopt both soluble and integral membrane forms. The physiological functions of CLIC proteins may include enzymatic activity in the soluble form and anion channel activity in the integral membrane form. CLIC proteins are associated with the ERM proteins: ezrin, radixin and moesin. ERM proteins act as cross-linkers between membranes and the cortical actin cytoskeleton. Both CLIC and ERM proteins are controlled by Rho family small GTPases. CLIC proteins, ERM and Rho GTPases act in a concerted manner to control active membrane processes including the maintenance of microvillar structures, phagocytosis and vesicle trafficking. All of these processes involve the interaction of membranes with the underlying cortical actin cytoskeleton. The relationships between Rho GTPases, CLIC proteins, ERM proteins and the membrane:actin cytoskeleton interface are reviewed. Speculative models are proposed involving the formation of localised multi-protein complexes on the membrane surface that assemble via multiple weak interactions. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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Affiliation(s)
- Lele Jiang
- St Vincent's Centre for Applied Medical Research, St Vincent's Hospital, Sydney, NSW 2010, Australia
| | - Juanita M Phang
- School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia
| | - Jiang Yu
- School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia
| | - Stephen J Harrop
- School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia
| | - Anna V Sokolova
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Anthony P Duff
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
| | - Krystyna E Wilk
- School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia
| | - Heba Alkhamici
- School of Medical and Molecular Biosciences, The University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Samuel N Breit
- St Vincent's Centre for Applied Medical Research, St Vincent's Hospital, Sydney, NSW 2010, Australia
| | - Stella M Valenzuela
- School of Medical and Molecular Biosciences, The University of Technology Sydney, Sydney, NSW 2007, Australia
| | - Louise J Brown
- Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
| | - Paul M G Curmi
- St Vincent's Centre for Applied Medical Research, St Vincent's Hospital, Sydney, NSW 2010, Australia; School of Physics, The University of New South Wales, Sydney, NSW 2052, Australia.
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Korte J, Fröhlich T, Kohn M, Kaspers B, Arnold GJ, Härtle S. 2D DIGE analysis of the bursa of Fabricius reveals characteristic proteome profiles for different stages of chicken B-cell development. Proteomics 2012; 13:119-33. [PMID: 23135993 DOI: 10.1002/pmic.201200177] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 09/14/2012] [Accepted: 10/05/2012] [Indexed: 11/09/2022]
Abstract
Antibody producing B-cells are an essential component of the immune system. In contrast to human and mice where B-cells develop in the bone marrow, chicken B-cells develop in defined stages in the bursa of Fabricius, a gut associated lymphoid tissue. In order to gain a better understanding of critical biological processes like immigration of B-cell precursors into the bursa anlage, their differentiation and final emigration from the bursa we analyzed the proteome dynamics of this organ during embryonic and posthatch development. Samples were taken from four representative developmental stages (embryonic day (ED) 10, ED18, day 2, and day 28) and compared in an extensive 2D DIGE approach comprising six biological replicates per time point. Cluster analysis and PCA demonstrated high reliability and reproducibility of the obtained data set and revealed distinctive proteome profiles for the selected time points, which precisely reflect the differentiation processes. One hundred fifty three protein spots with significantly different intensities were identified by MS. We detected alterations in the abundance of several proteins assigned to retinoic acid metabolism (e.g. retinal-binding protein 5) and the actin-cytoskeleton (e.g. vinculin and gelsolin). By immunohistochemistry, desmin was identified as stromal cell protein associated with the maturation of B-cell follicles. Strongest protein expression difference (10.8-fold) was observed for chloride intracellular channel 2. This protein was thus far not associated with B-cell biology but our data suggest an important function in bursa B-cell development.
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Affiliation(s)
- Julia Korte
- Department for Veterinary Science, Institute for Animal Physiology, Ludwig-Maximilians-Universität München, Munich, Germany
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22
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Board PG, Menon D. Glutathione transferases, regulators of cellular metabolism and physiology. Biochim Biophys Acta Gen Subj 2012. [PMID: 23201197 DOI: 10.1016/j.bbagen.2012.11.019] [Citation(s) in RCA: 233] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
BACKGROUND The cytosolic glutathione transferases (GSTs) comprise a super family of proteins that can be categorized into multiple classes with a mixture of highly specific and overlapping functions. SCOPE OF REVIEW The review covers the genetics, structure and function of the human cytosolic GSTs with particular attention to their emerging roles in cellular metabolism. MAJOR CONCLUSIONS All the catalytically active GSTs contribute to the glutathione conjugation or glutathione dependant-biotransformation of xenobiotics and many catalyze glutathione peroxidase or thiol transferase reactions. GSTs also catalyze glutathione dependent isomerization reactions required for the synthesis of several prostaglandins and steroid hormones and the catabolism of tyrosine. An increasing body of work has implicated several GSTs in the regulation of cell signaling pathways mediated by stress-activated kinases like Jun N-terminal kinase. In addition, some members of the cytosolic GST family have been shown to form ion channels in intracellular membranes and to modulate ryanodine receptor Ca(2+) channels in skeletal and cardiac muscle. GENERAL SIGNIFICANCE In addition to their well established roles in the conjugation and biotransformation of xenobiotics, GSTs have emerged as significant regulators of pathways determining cell proliferation and survival and as regulators of ryanodine receptors that are essential for muscle function. This article is part of a Special Issue entitled Cellular functions of glutathione.
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Affiliation(s)
- Philip G Board
- John Curtin School of Medical Research, Australian National University, Canberra, Australia
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Abstract
Luminal acidification is of pivotal importance for the physiology of the secretory and endocytic pathways and its diverse trafficking events. Acidification by the proton-pumping V-ATPase requires charge compensation by counterion currents that are commonly attributed to chloride. The molecular identification of intracellular chloride transporters and the improvement of methodologies for measuring intraorganellar pH and chloride have facilitated the investigation of the physiology of vesicular chloride transport. New data question the requirement of chloride for pH regulation of various organelles and furthermore ascribe functions to chloride that are beyond merely electrically shunting the proton pump. This review surveys the currently established and proposed intracellular chloride transporters and gives an overview of membrane-trafficking steps that are affected by the perturbation of chloride transport. Finally, potential mechanisms of membrane-trafficking modulation by chloride are discussed and put into the context of organellar ion homeostasis in general.
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Affiliation(s)
- Tobias Stauber
- Physiology and Pathology of Ion Transport, Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin, 13125 Berlin, Germany.
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He G, Ma Y, Chou SY, Li H, Yang C, Chuang JZ, Sung CH, Ding A. Role of CLIC4 in the host innate responses to bacterial lipopolysaccharide. Eur J Immunol 2011; 41:1221-30. [PMID: 21469130 DOI: 10.1002/eji.201041266] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2010] [Revised: 01/11/2011] [Accepted: 02/15/2011] [Indexed: 11/08/2022]
Abstract
Chloride intracellular channel (CLIC) 4 has diverse functions in membrane trafficking, apoptosis, angiogenesis and cell differentiation. CLIC4 is abundantly expressed in macrophages, but its role in innate immune functions is unclear. Here, we show that primary murine macrophages express increased amounts of CLIC4 after exposure to bacterial lipopolysaccharide (LPS). Endogenous CLIC4 level was significantly elevated in the brain, heart, lung, kidney, liver and spleen after LPS injection of mice. Stable macrophage lines overexpressing CLIC4 produced more TNF, IL-6, IL-12 and CCL5 than mock transfectants when exposed to LPS. To explore the role of CLIC4 in vivo, we generated CLIC4-null mice. These mice were protected from LPS-induced death, and had reduced serum levels of inflammatory cytokines. Upon infection with Listeria monocytogenes, CLIC4-deficient mice were impaired in their ability to clear infection, and their macrophages responded to Listeria by producing less inflammatory cytokines and chemokines than the WT controls. When challenged with LPS in vitro, deletion of clic4 gene had little effect on MAPK and NF-κB activation, but led to a reduced accumulation of phosphorylated interferon response factor 3 (IRF3) within macrophages. Conversely, overexpression of CLIC4 enhanced LPS-mediated IRF3. Thus, these findings suggest that CLIC4 is an LPS-induced product that can serve as a positive regulator of LPS signaling.
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Affiliation(s)
- Guoan He
- Department of Microbiology and Immunology, Weill Cornell Medical College, NY 10065, USA
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Littler DR, Brown LJ, Breit SN, Perrakis A, Curmi PMG. Structure of human CLIC3 at 2 A resolution. Proteins 2010; 78:1594-600. [PMID: 20146363 DOI: 10.1002/prot.22675] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- D R Littler
- Department of Molecular Carcinogenesis, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
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Bradford EM, Miller ML, Prasad V, Nieman ML, Gawenis LR, Berryman M, Lorenz JN, Tso P, Shull GE. CLIC5 mutant mice are resistant to diet-induced obesity and exhibit gastric hemorrhaging and increased susceptibility to torpor. Am J Physiol Regul Integr Comp Physiol 2010; 298:R1531-42. [PMID: 20357015 DOI: 10.1152/ajpregu.00849.2009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Chloride intracellular channel 5 (CLIC5) and other CLIC isoforms have been implicated in a number of biological processes, but their specific functions are poorly understood. The association of CLIC5 with ezrin and the actin cytoskeleton led us to test its possible involvement in gastric acid secretion. Clic5 mutant mice exhibited only a minor reduction in acid secretion, Clic5 mRNA was expressed at only low levels in stomach, and Clic5 mutant parietal cells were ultrastructurally normal, negating the hypothesis that CLIC5 plays a major role in acid secretion. However, the mutants exhibited gastric hemorrhaging in response to fasting, reduced monocytes and granulocytes suggestive of immune dysfunction, behavioral and social disorders suggestive of neurological dysfunction, and evidence of a previously unidentified metabolic defect. Wild-type and mutant mice were maintained on normal and high-fat diets; plasma levels of various hormones, glucose, and lipids were determined; and body composition was studied by quantitative magnetic resonance imaging. Clic5 mutants were lean, hyperphagic, and highly resistant to diet-induced obesity. Plasma insulin and glucose levels were reduced, and leptin levels were very low; however, plasma triglycerides, cholesterol, phospholipids, and fatty acids were normal. Indirect calorimetry revealed increased peripheral metabolism and greater reliance on carbohydrate metabolism. Because Clic5 mutants were unable to maintain energy reserves, they also exhibited increased susceptibility to fasting-induced torpor, as indicated by telemetric measurements showing episodes of reduced body temperature and heart rate. These data reveal a requirement for CLIC5 in the maintenance of normal systemic energy metabolism.
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Affiliation(s)
- Emily M Bradford
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, Cincinnati, OH 45267-0524, USA
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Wegner B, Al-Momany A, Kulak SC, Kozlowski K, Obeidat M, Jahroudi N, Paes J, Berryman M, Ballermann BJ. CLIC5A, a component of the ezrin-podocalyxin complex in glomeruli, is a determinant of podocyte integrity. Am J Physiol Renal Physiol 2010; 298:F1492-503. [PMID: 20335315 DOI: 10.1152/ajprenal.00030.2010] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The chloride intracellular channel 5A (CLIC5A) protein, one of two isoforms produced by the CLIC5 gene, was isolated originally as part of a cytoskeletal protein complex containing ezrin from placental microvilli. Whether CLIC5A functions as a bona fide ion channel is controversial. We reported previously that a CLIC5 transcript is enriched approximately 800-fold in human renal glomeruli relative to most other tissues. Therefore, this study sought to explore CLIC5 expression and function in glomeruli. RT-PCR and Western blots show that CLIC5A is the predominant CLIC5 isoform expressed in glomeruli. Confocal immunofluorescence and immunogold electron microscopy reveal high levels of CLIC5A protein in glomerular endothelial cells and podocytes. In podocytes, CLIC5A localizes to the apical plasma membrane of foot processes, similar to the known distribution of podocalyxin and ezrin. Ezrin and podocalyxin colocalize with CLIC5A in glomeruli, and podocalyxin coimmunoprecipitates with CLIC5A from glomerular lysates. In glomeruli of jitterbug (jbg/jbg) mice, which lack the CLIC5A protein, ezrin and phospho-ERM levels in podocytes are markedly lower than in wild-type mice. Transmission electron microscopy reveals patchy broadening and effacement of podocyte foot processes as well as vacuolization of glomerular endothelial cells. These ultrastructural changes are associated with microalbuminuria at baseline and increased susceptibility to adriamycin-induced glomerular injury compared with wild-type mice. Together, the data suggest that CLIC5A is required for the development and/or maintenance of the proper glomerular endothelial cell and podocyte architecture. We postulate that the interaction between podocalyxin and subjacent filamentous actin, which requires ezrin, is compromised in podocytes of CLIC5A-deficient mice, leading to dysfunction under unfavorable genetic or environmental conditions.
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Affiliation(s)
- Binytha Wegner
- Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
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28
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Two decades with dimorphic Chloride Intracellular Channels (CLICs). FEBS Lett 2010; 584:2112-21. [DOI: 10.1016/j.febslet.2010.03.013] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 03/08/2010] [Accepted: 03/08/2010] [Indexed: 01/11/2023]
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29
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Chloride channels of intracellular membranes. FEBS Lett 2010; 584:2102-11. [PMID: 20100480 DOI: 10.1016/j.febslet.2010.01.037] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Revised: 01/13/2010] [Accepted: 01/19/2010] [Indexed: 11/20/2022]
Abstract
Proteins implicated as intracellular chloride channels include the intracellular ClC proteins, the bestrophins, the cystic fibrosis transmembrane conductance regulator, the CLICs, and the recently described Golgi pH regulator. This paper examines current hypotheses regarding roles of intracellular chloride channels and reviews the evidence supporting a role in intracellular chloride transport for each of these proteins.
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Littler DR, Harrop SJ, Goodchild SC, Phang JM, Mynott AV, Jiang L, Valenzuela SM, Mazzanti M, Brown LJ, Breit SN, Curmi PMG. The enigma of the CLIC proteins: Ion channels, redox proteins, enzymes, scaffolding proteins? FEBS Lett 2010; 584:2093-101. [PMID: 20085760 DOI: 10.1016/j.febslet.2010.01.027] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Revised: 01/13/2010] [Accepted: 01/13/2010] [Indexed: 12/13/2022]
Abstract
Chloride intracellular channel proteins (CLICs) are distinct from most ion channels in that they have both soluble and integral membrane forms. CLICs are highly conserved in chordates, with six vertebrate paralogues. CLIC-like proteins are found in other metazoans. CLICs form channels in artificial bilayers in a process favoured by oxidising conditions and low pH. They are structurally plastic, with CLIC1 adopting two distinct soluble conformations. Phylogenetic and structural data indicate that CLICs are likely to have enzymatic function. The physiological role of CLICs appears to be maintenance of intracellular membranes, which is associated with tubulogenesis but may involve other substructures.
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Affiliation(s)
- Dene R Littler
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
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Singh H, Ashley RH. CLIC4 (p64H1) and its putative transmembrane domain form poorly selective, redox-regulated ion channels. Mol Membr Biol 2009; 24:41-52. [PMID: 17453412 DOI: 10.1080/09687860600927907] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Despite being synthesized in the cytosol without a leader sequence, the soluble 253-residue mammalian protein CLIC4 (Chloride Intracellular Channel 4, or p64H1), a structural homologue of Omega-type glutathione-S-transferase, autoinserts into membranes to form an integral membrane protein with ion channel activity. A predicted transmembrane domain (TMD) near the N-terminus of CLIC4 could mediate membrane insertion, and contribute to oligomeric pores, with minimal reorganization of the soluble protein structure. We tested this idea by reconstituting recombinant CLIC4 in planar bilayers containing phosphatidyethanolamine, phosphatidylserine and cholesterol, recording ion channels with a maximum conductance of approximately 15 pS in KCl under both oxidizing and reducing conditions. The channels discriminated poorly between anions and cations, incompatible with the current "CLIC" nomenclature, and their conductance was modified by the trans (external or luminal) redox potential, as previously observed for CLIC1. We then reconstituted a truncated version of the protein, limited to the first 61 residues containing the predicted TMD. This included a single trans cysteine residue in the putative pore-forming subunits, at the external entrance to the pore. The truncated protein formed non-selective channels with a reduced conductance, but they retained their trans-redox sensitivity, and could still be blocked or inactivated by trans (not cis) thiol-reative dithiobisnitrobenzoic acid. We suggest that oligomers containing the putative TMD are essential components of the CLIC4 pore. However, the pore is inherently non-selective, and any ionic selectivity in CLIC4 (and other membrane CLICs) may be attributable to other regions of the protein, including the channel vestibules.
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Affiliation(s)
- Harpreet Singh
- Biomedical Sciences, College of Medicine, University of Edinburgh, Edinburgh, UK
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Meng X, Wang G, Viero C, Wang Q, Mi W, Su XD, Wagenknecht T, Williams AJ, Liu Z, Yin CC. CLIC2-RyR1 interaction and structural characterization by cryo-electron microscopy. J Mol Biol 2009; 387:320-34. [PMID: 19356589 DOI: 10.1016/j.jmb.2009.01.059] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2008] [Revised: 01/18/2009] [Accepted: 01/27/2009] [Indexed: 11/18/2022]
Abstract
Chloride intracellular channel 2 (CLIC2), a newly discovered small protein distantly related to the glutathione transferase (GST) structural family, is highly expressed in cardiac and skeletal muscle, although its physiological function in these tissues has not been established. In the present study, [3H]ryanodine binding, Ca2+ efflux from skeletal sarcoplasmic reticulum (SR) vesicles, single channel recording, and cryo-electron microscopy were employed to investigate whether CLIC2 can interact with skeletal ryanodine receptor (RyR1) and modulate its channel activity. We found that: (1) CLIC2 facilitated [3H]ryanodine binding to skeletal SR and purified RyR1, by increasing the binding affinity of ryanodine for its receptor without significantly changing the apparent maximal binding capacity; (2) CLIC2 reduced the maximal Ca2+ efflux rate from skeletal SR vesicles; (3) CLIC2 decreased the open probability of RyR1 channel, through increasing the mean closed time of the channel; (4) CLIC2 bound to a region between domains 5 and 6 in the clamp-shaped region of RyR1; (5) and in the same clamp region, domains 9 and 10 became separated after CLIC2 binding, indicating CLIC2 induced a conformational change of RyR1. These data suggest that CLIC2 can interact with RyR1 and modulate its channel activity. We propose that CLIC2 functions as an intrinsic stabilizer of the closed state of RyR channels.
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Affiliation(s)
- Xing Meng
- Wadsworth Center, New York State Department of Health, Albany, NY 12201, USA
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Mihm M, Baker PJ, Fleming LM, Monteiro AM, O'Shaughnessy PJ. Differentiation of the bovine dominant follicle from the cohort upregulates mRNA expression for new tissue development genes. Reproduction 2008; 135:253-65. [DOI: 10.1530/rep-06-0193] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This study was designed to identify genes that regulate the transition from FSH- to LH-dependent development in the bovine dominant follicle (DF). Serial analysis of gene expression (SAGE) was used to compare the transcriptome of granulosa cells isolated from the most oestrogenic growing cohort follicle (COH), the newly selected DF and its largest subordinate follicle (SF) which is destined for atresia. Follicle diameter, follicular fluid oestradiol (E) and E:progesterone ratio confirmed follicle identity. Results show that there are 93 transcript species differentially expressed in DF granulosa cells, but only 8 of these encode proteins known to be involved in DF development. Most characterised transcripts upregulated in the DF are from tissue development genes that regulate cell differentiation, proliferation, apoptosis, signalling and tissue remodelling. Semiquantitative real-time PCR analysis confirmed seven genes with upregulated (P≤0.05) mRNA expression in DF compared with both COH and SF granulosa cells. Thus, the new genes identified by SAGE and real-time PCR, which show enhanced mRNA expression in the DF, may regulate proliferation (cyclin D2;CCND2), prevention of apoptosis or DNA damage (growth arrest and DNA damage-inducible, β;GADD45B), RNA synthesis (splicing factor, arginine/serine rich 9;SFRS9) and unknown processes associated with enhanced steroidogenesis (ovary-specific acidic protein; DQ004742) in granulosa cells of DF at the onset of LH-dependent development. Further studies are required to show whether the expression of identified genes is dysregulated when abnormalities occur during DF selection or subsequent development.
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35
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Littler DR, Harrop SJ, Brown LJ, Pankhurst GJ, Mynott AV, Luciani P, Mandyam RA, Mazzanti M, Tanda S, Berryman MA, Breit SN, Curmi PMG. Comparison of vertebrate and invertebrate CLIC proteins: The crystal structures ofCaenorhabditis elegans EXC-4 andDrosophila melanogaster DmCLIC. Proteins 2008; 71:364-78. [DOI: 10.1002/prot.21704] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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36
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Cromer BA, Gorman MA, Hansen G, Adams JJ, Coggan M, Littler DR, Brown LJ, Mazzanti M, Breit SN, Curmi PM, Dulhunty AF, Board PG, Parker MW. Structure of the Janus Protein Human CLIC2. J Mol Biol 2007; 374:719-31. [DOI: 10.1016/j.jmb.2007.09.041] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Revised: 09/12/2007] [Accepted: 09/12/2007] [Indexed: 10/22/2022]
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37
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Edwards JC, Cohen C, Xu W, Schlesinger PH. c-Src control of chloride channel support for osteoclast HCl transport and bone resorption. J Biol Chem 2006; 281:28011-22. [PMID: 16831863 PMCID: PMC1808340 DOI: 10.1074/jbc.m605865200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Bone degradation by osteoclasts depends upon active transport of hydrogen ions to solubilize bone mineral. This transport is supported by the parallel actions of a proton ATPase and a chloride channel located in the osteoclast ruffled membrane. We have previously identified a novel chloride channel, p62, which appears to be the avian counterpart to CLIC-5b and is expressed coincident with the appearance of acid secretion as avian osteoclasts differentiate in culture. In this article, we show that suppression of CLIC-5b in differentiating avian osteoclasts results in decreased acidification by vesicles derived from these cells and decreased ability of the cells to resorb bone. Acidification is rescued by the presence of valinomycin, consistent with a selective loss of chloride channel but not proton pump activity. Osteoclast bone resorption is known to be dependent on the expression of the tyrosine kinase, c-Src. We show that CLIC-5b from osteoclasts has affinity for both Src SH2 and SH3 domains. We find that suppression of expression of Src in developing osteoclasts results in decreased vesicular acidification, which is rescued by valinomycin, consistent with the loss of chloride conductance in the proton pump-containing vesicles. Suppression of c-Src causes no change in the steady state level of CLIC-5b expression, but does result in failure of proton pump and CLIC-5b to colocalize in cultured osteoclast precursors. We conclude that suppression of c-Src interferes with osteoclast bone resorption by disrupting functional co-localization of proton pump and CLIC-5b.
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Affiliation(s)
- John C. Edwards
- From the UNC Kidney Center and the Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, the
- Department of Medicine, St. Louis University School of Medicine, St. Louis, Missouri 63104, and the
| | - Christopher Cohen
- Department of Physiology and Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Weibing Xu
- Department of Physiology and Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Paul H. Schlesinger
- Department of Physiology and Cell Biology, Washington University School of Medicine, St. Louis, Missouri 63110
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Berry KL, Hobert O. Mapping Functional Domains of Chloride Intracellular Channel (CLIC) Proteins in Vivo. J Mol Biol 2006; 359:1316-33. [PMID: 16737711 DOI: 10.1016/j.jmb.2006.04.046] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2006] [Revised: 04/06/2006] [Accepted: 04/20/2006] [Indexed: 10/24/2022]
Abstract
Chloride intracellular channel (CLIC) proteins are small proteins distantly related to the omega family of glutathione S-transferases (GSTs). CLIC proteins are expressed in a wide variety of tissues in multicellular organisms and are targeted to specific cellular membranes. Members of this family are capable in vitro of changing conformation from a globular, soluble state to a membrane-inserted state in which they provide chloride conductance. The structural basis for in vivo CLIC protein function, however, is not well understood. We have mapped the functional domains of CLIC family members using an in vivo assay for membrane localization and function of CLIC proteins in the nematode Caenorhabditis elegans. A<70 amino acid N-terminal domain is a key determinant of membrane localization and function of invertebrate CLIC proteins. This domain, which we term the ''PTM'' domain, named after an amphipathic putative transmembrane helix contained within it, directs distinct C. elegans CLIC homologs to distinct subcellular membranes. We find that within the PTM region, the cysteine residues required for GST-type activity are unnecessary for invertebrate CLIC function, but that specific residues within the proposed transmembrane helix are necessary for correct targeting and protein function. We find that among all tested invertebrate CLIC proteins, function appears to be completely conserved despite striking differences in the charged residues contained within the amphipathic helix. This indicates that these residues do not contribute to anion selectivity as previously suggested. We find that outside the PTM region, the remaining three-quarters of CLIC protein sequence is functionally equivalent not only among vertebrate and invertebrate CLIC proteins, but also among the more distantly related GST-omega and GST-sigma proteins. The PTM region thus provides both targeting information and CLIC functional specificity, possibly adapting GST-type proteins to function as ion channels.
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Affiliation(s)
- Katherine L Berry
- Department of Biochemistry and Molecular Biophysics Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY 10032, USA
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Abstract
Numerous Cl- channels have been identified in the kidney using physiological approaches and thus are thought to be involved in a range of physiological processes, including vectorial transepithelial Cl- transport, cell volume regulation, and vesicular acidification. In addition, expression of genes from several Cl- channel gene families has also been observed. However, the molecular characteristics of a number of Cl- channels within the kidney are still unknown, and the physiological roles of Cl- channels identified by molecular means remain to be determined. A gene knockout approach using mice might shed further light on the characteristics of these various Cl- channels. In addition, study of diseases involving Cl- channels (channelopathies) might clarify the physiological role of specific Cl- channels. To date, more is known about CLC Cl- channels than any other Cl- channels within the kidney. This review focuses on the physiological roles of CLC Cl- channels within the kidney, particularly kidney-specific ClC-K Cl- channels, as well as the recently identified maxi anion channel in macula densa, which is involved in tubulo-glomerular feedback.
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Affiliation(s)
- Shinichi Uchida
- Department of Nephrology, Graduate School of Medicine, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
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40
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Paroutis P, Touret N, Grinstein S. The pH of the secretory pathway: measurement, determinants, and regulation. Physiology (Bethesda) 2004; 19:207-15. [PMID: 15304635 DOI: 10.1152/physiol.00005.2004] [Citation(s) in RCA: 316] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The luminal pH of the secretory pathway plays a critical role in the posttranslational modification and sorting of proteins and lipids. The pH of each one of the organelles that constitute the pathway is unique, becoming more acidic as the biosynthetic cargo approaches its destination. The methods used for measurement of pH in the secretory pathway, its determinants, and its regulation are the subjects of this review.
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Affiliation(s)
- Paul Paroutis
- Cell Biology Program, Hospital for Sick Children, Toronto M5G 1X8 Ontario, Canada
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41
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Myers K, Somanath PR, Berryman M, Vijayaraghavan S. Identification of chloride intracellular channel proteins in spermatozoa. FEBS Lett 2004; 566:136-40. [PMID: 15147883 DOI: 10.1016/j.febslet.2004.04.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2004] [Revised: 04/02/2004] [Accepted: 04/07/2004] [Indexed: 10/26/2022]
Abstract
We have identified for the first time the presence of chloride intracellular channel (CLIC) proteins in bovine epididymal spermatozoa. CLIC1 was discovered during microsequencing of proteins that co-purified with protein phosphatase 1, PP1gamma2, in sperm extracts. In addition to CLIC1, Western blot showed that two additional CLIC family members, CLIC4 and CLIC5, are also present in spermatozoa. CLIC fusion proteins, GST-CLIC1, GST-CLIC4 and GST-CLIC5, were all able to bind to PP1gamma2 in sperm extracts during pull-down assays. Immunofluorescence microscopy revealed that each of the three isoforms occupies a distinct location within the cell. Given that PP1gamma2 is a key enzyme regulating sperm motility, PP1gamma2-binding proteins, such as the CLIC proteins, are likely to play significant roles in sperm function.
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Affiliation(s)
- Kimberley Myers
- Department of Biological Sciences, Kent State University, Kent, OH 44242, USA
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Berryman M, Bruno J, Price J, Edwards JC. CLIC-5A functions as a chloride channel in vitro and associates with the cortical actin cytoskeleton in vitro and in vivo. J Biol Chem 2004; 279:34794-801. [PMID: 15184393 DOI: 10.1074/jbc.m402835200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CLIC-5A is a member of the chloride intracellular channel protein family, which is comprised of six related human genes encoding putative chloride channels. In this study, we found that reconstitution of purified recombinant CLIC-5A into artificial liposomes resulted in a dose-dependent chloride efflux that was sensitive to the chloride channel blocker IAA-94. CLIC-5A was originally isolated as a component of an ezrin-containing cytoskeletal complex from human placental microvilli. Here we show that similar protein complexes can be isolated using either immobilized CLIC-5A or the C-terminal F-actin-binding domain of ezrin and that actin polymerization is required for de novo assembly of these complexes. To investigate the behavior of CLIC-5A in vivo, JEG-3 placental choriocarcinoma cells were stably transfected with epitope-tagged CLIC-5A. In fixed cells, CLIC-5A displayed a polarized distribution and colocalized with ezrin in apical microvilli. Microvillar localization of CLIC-5A was retained after Triton X-100 extraction and was disrupted by treatment with latrunculin B. In transient transfections assays, we mapped a region between residues 20 and 54 of CLIC-5A that is required for targeting of CLIC-5A to microvilli in JEG-3 cells. Interestingly, expression of CLIC-5A in JEG-3 cells did not enhance the rate of iodide efflux in intact cells, suggesting that if CLIC-5A is a chloride channel, its channel activity may be restricted to intracellular membrane compartments in these cells. Regardless of its role in ion transport, CLIC-5A, like ezrin, may play an important role in the assembly or maintenance of F-actin-based structures at the cell cortex.
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Affiliation(s)
- Mark Berryman
- Department of Biomedical Sciences, Ohio University College of Osteopathic Medicine and the Molecular and Cellular Biology Program, Athens, OH 45701, USA.
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Abstract
Cellular functions of Cl- channels are poorly understood, in contrast to well-established roles of cation channels. Recently, important achievements in Cl- channel research have been sequentially reported, including cloning of many Cl- channel cDNAs, linkage of gene abnormalities to human inherited disorders, analysis of knock-out mouse phenotype, analysis of crystal structure, and regulation by protein-protein interaction. Intracellular membrane Cl- channels are important for acidification of intracellular vesicles: ClC-5 functions for re-absorption of low-molecular-weight proteins in renal proximal tubule, and ClC-7 for absorption of bone matrix by osteoclasts. Abnormal functions of these channels result in Dent's disease characterized by proteinuria and kidney stones and by osteopetrosis, respectively. Plasma membrane Cl- channels, ClC-K1, ClC-K2, and ClC-3B, are expressed predominantly in epithelial cells and are important for uni-directional Cl- transport across the epithelia. Abnormalities of these channels are also related to human diseases: abnormal ClC-K1 to diabetes insipidus and abnormal ClC-K2 to Bartter's syndrome.
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Affiliation(s)
- Tetsushi Furukawa
- Department of Bio-informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Japan
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Friedli M, Guipponi M, Bertrand S, Bertrand D, Neerman-Arbez M, Scott HS, Antonarakis SE, Reymond A. Identification of a novel member of the CLIC family, CLIC6, mapping to 21q22.12. Gene 2003; 320:31-40. [PMID: 14597386 DOI: 10.1016/s0378-1119(03)00830-8] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Five members of the newly identified chloride intracellular channel (CLIC) gene family of intracellular chloride channels (CLIC1-CLIC5) have previously been described in humans. Here we report the molecular cloning and initial characterisation of two splice forms of a novel member of this family, CLIC6, mapping to human chromosome 21. Two essential features distinguish CLIC6 from other members of the family. The CLIC6 protein is significantly longer and the CLIC6 gene contains a GC rich segment, which encodes a 10 amino acid motif repeated 14 times in the amino-terminus. Surprisingly, the repeat is conserved in the lagomorphs, but not in the rodents lineage. The putative bovine orthologue of CLIC5, p64, also exhibits a repeated motif, which is different from that of CLIC6. Attempts to functionally characterise CLIC6 by voltage clamp failed to show any chloride channel activity. Hence, the exact function of this protein remains unknown.
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MESH Headings
- Alternative Splicing
- Amino Acid Sequence
- Animals
- COS Cells
- Cell Line
- Chloride Channels/genetics
- Chlorocebus aethiops
- Chromosome Mapping
- Chromosomes, Human, Pair 21/genetics
- Cloning, Molecular
- DNA, Complementary/chemistry
- DNA, Complementary/genetics
- Female
- Gene Expression
- Green Fluorescent Proteins
- Humans
- Luminescent Proteins/genetics
- Luminescent Proteins/metabolism
- Membrane Potentials/physiology
- Mice
- Mice, Inbred BALB C
- Mice, Inbred C57BL
- Mice, Inbred CBA
- Mice, Inbred Strains
- Microscopy, Fluorescence
- Molecular Sequence Data
- Oocytes/metabolism
- Oocytes/physiology
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Repetitive Sequences, Nucleic Acid/genetics
- Sequence Alignment
- Sequence Analysis, DNA
- Sequence Homology, Amino Acid
- Transfection
- Xenopus
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Affiliation(s)
- Marc Friedli
- Division of Medical Genetics, Centre Médical Universitaire, University of Geneva Medical School, 1 rue Michel-Servet, CH-1211 Geneva 4, Switzerland
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45
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Berryman MA, Goldenring JR. CLIC4 is enriched at cell-cell junctions and colocalizes with AKAP350 at the centrosome and midbody of cultured mammalian cells. ACTA ACUST UNITED AC 2003; 56:159-72. [PMID: 14569596 DOI: 10.1002/cm.10141] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
CLIC4 is a member of the chloride intracellular channel (CLIC) protein family whose principal cellular functions are poorly understood. Recently, we demonstrated that several CLIC proteins, including CLIC4, interact with AKAP350. AKAP350 is concentrated at the Golgi apparatus, centrosome, and midbody and acts as a scaffolding protein for several protein kinases and phosphatases. In this report, we show that endogenous CLIC4 and AKAP350 colocalize at the centrosome and midbody of cultured cells by immunofluorescence microscopy. Unlike AKAP350, CLIC4 is not enriched in the Golgi apparatus but is enriched in mitochondria, actin-based structures at the cell cortex, and the nuclear matrix, indicating that CLIC4-AKAP350 interactions are regulated at specific subcellular sites in vivo. In addition to the centrosome and midbody, CLIC4 colocalizes with AKAP350 and the tight junction protein ZO-1 in the apical region of polarized epithelial cells, suggesting that CLIC4 may play a role in maintaining apical-basolateral membrane polarity during mitosis and cytokinesis. Biochemical studies show that CLIC4 behaves mainly as a soluble cytosolic protein and can associate with proteins of the microtubule cytoskeleton. The localization of CLIC4 to the cortical actin cytoskeleton and its association with AKAP350 at the centrosome and midbody suggests that CLIC4 may be important for regulating cytoskeletal organization during the cell cycle. These findings lead to the conclusion that CLIC4 and possibly other CLIC proteins have alternate cellular functions that are distinct from their proposed roles as chloride channels.
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Affiliation(s)
- Mark A Berryman
- Department of Biomedical Sciences, Molecular and Cellular Biology Program, Ohio University College of Osteopathic Medicine, Athens, OH 45701, USA.
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Osman AA, Saito M, Makepeace C, Permutt MA, Schlesinger P, Mueckler M. Wolframin expression induces novel ion channel activity in endoplasmic reticulum membranes and increases intracellular calcium. J Biol Chem 2003; 278:52755-62. [PMID: 14527944 DOI: 10.1074/jbc.m310331200] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Wolfram syndrome is an autosomal recessive neuro-degenerative disorder associated with juvenile onset non-autoimmune diabetes mellitus and progressive optic atrophy. The disease has been attributed to mutations in the WFS1 gene, which codes for a protein predicted to possess 9-10 transmembrane segments. Little is known concerning the function of the WFS1 protein (wolframin). Endoglycosidase H digestion, immunocytochemistry, and subcellular fractionation studies all indicated that wolframin is localized to the endoplasmic reticulum in rat brain hippocampus and rat pancreatic islet beta-cells, and after ectopic expression in Xenopus oocytes. Reconstitution of wolframin from oocyte membranes into planar lipid bilayers demonstrated that the protein induced a large cation-selective ion channel that was blocked by Mg2+ or Ca2+. Inositol triphosphate was capable of activating channels in the fused bilayers that were similar to channel components induced by wolframin expression. Expression of wolframin also increased cytosolic calcium levels in oocytes. Wolframin thus appears to be important in the regulation of intracellular Ca2+ homeostasis. Disruption of this function may place cells at risk to suffer inappropriate death decisions, thus accounting for the progressive beta-cell loss and neuronal degeneration associated with the disease.
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Affiliation(s)
- Abdullah A Osman
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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47
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Ashley RH. Challenging accepted ion channel biology: p64 and the CLIC family of putative intracellular anion channel proteins (Review). Mol Membr Biol 2003; 20:1-11. [PMID: 12745921 DOI: 10.1080/09687680210042746] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Parchorin, p64 and the related chloride intracellular channel (CLIC) proteins are widely expressed in multicellular organisms and have emerged as candidates for novel, auto-inserting, self-assembling intracellular anion channels involved in a wide variety of fundamental cellular events including regulated secretion, cell division and apoptosis. Although the mammalian phosphoproteins p64 and parchorin (49 and 65K, respectively) have only been indirectly implicated in anion channel activity, two CLIC proteins (CLIC1 and CLIC4, 27 and 29K, respectively) appear to be essential molecular components of anion channels, and CLIC1 can form anion channels in planar lipid bilayers in the absence of other cellular proteins. However, these putative ion channel proteins are controversial because they exist in both soluble and membrane forms, with at least one transmembrane domain. Even more surprisingly, soluble CLICs share the same glutaredoxin fold as soluble omega class glutathione-S-transferases. Working out how these ubiquitous, soluble proteins unfold, insert into membranes and then refold to form integral membrane proteins, and how cells control this potentially dangerous process and make use of the associated ion channels, are challenging prospects. Critical to this future work is the need for better characterization of membrane topology, careful functional analysis of reconstituted and native channels, including their conductances and selectivities, and detailed structure/function studies including targeted mutagenesis to investigate the structure of the putative pore, the role of protein phosphorylation and the role of conserved cysteine residues.
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Affiliation(s)
- R H Ashley
- Department of Biomedical Sciences, University of Edinburgh, UK.
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Shanks RA, Larocca MC, Berryman M, Edwards JC, Urushidani T, Navarre J, Goldenring JR. AKAP350 at the Golgi apparatus. II. Association of AKAP350 with a novel chloride intracellular channel (CLIC) family member. J Biol Chem 2002; 277:40973-80. [PMID: 12163479 DOI: 10.1074/jbc.m112277200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
AKAP350 can scaffold a number of protein kinases and phosphatases at the centrosome and the Golgi apparatus. We performed a yeast two-hybrid screen of a rabbit parietal cell library with a 3.2-kb segment of AKAP350 (nucleotides 3611-6813). This screen yielded a full-length clone of rabbit chloride intracellular channel 1 (CLIC1). CLIC1 belongs to a family of proteins, all of which contain a high degree of homology in their carboxyl termini. All CLIC family members were able to bind a 133-amino acid domain within AKAP350 through the last 120 amino acids in the conserved CLIC carboxyl termini. Antibodies developed against a bovine CLIC, p64, immunoprecipitated AKAP350 from HCA-7 colonic adenocarcinoma cell extracts. Antibodies against CLIC proteins recognized at least five CLIC species including a novel 46-kDa CLIC protein. We isolated the human homologue of bovine p64, CLIC5B, from HCA-7 cell cDNA. A splice variant of CLIC5, the predicted molecular mass of CLIC5B corresponds to the molecular mass of the 46-kDa CLIC immunoreactive protein in HCA-7 cells. Antibodies against CLIC5B colocalized with AKAP350 at the Golgi apparatus with minor staining of the centrosomes. AKAP350 and CLIC5B association with Golgi elements was lost following brefeldin A treatment. Furthermore, GFP-CLIC5B-(178-410) targeted to the Golgi apparatus in HCA-7 cells. The results suggest that AKAP350 associates with CLIC proteins and specifically that CLIC5B interacts with AKAP350 at the Golgi apparatus in HCA-7 cells.
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Affiliation(s)
- Ryan A Shanks
- Department of Medicine, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912, USA
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Proutski I, Karoulias N, Ashley RH. Overexpressed chloride intracellular channel protein CLIC4 (p64H1) is an essential component of novel plasma membrane anion channels. Biochem Biophys Res Commun 2002; 297:317-22. [PMID: 12237120 DOI: 10.1016/s0006-291x(02)02199-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chloride intracellular channel protein CLIC4 is a putative organellar anion channel or channel regulator with an unusual dual cytoplasmic and integral membrane localisation. To investigate its contribution to cellular anion channel activity, the protein was overexpressed in stably transfected HEK-293 cells. Patch-clamp recording revealed CLIC4-associated indanyloxyacetic acid-sensitive (IC(50) approximately 100 microM) plasma membrane currents showing mild outward rectification, and novel low conductance (approximately 1pS) CLIC4-associated anion channels were resolved at the single-channel level. The CLIC4-associated channels were inhibited by anti-CLIC4 antibodies, including a monoclonal antibody directed against a FLAG epitope fused to the C-terminus of CLIC4, but only when these were applied to the cytoplasmic (not the external) face of the membrane. CLIC4 is thus an essential molecular component of novel cellular anion channels and the C-terminus of the integral membrane form of CLIC4 is cytoplasmic.
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Affiliation(s)
- I Proutski
- Department of Biomedical Sciences, University of Edinburgh, UK
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50
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Thévenod F. Ion channels in secretory granules of the pancreas and their role in exocytosis and release of secretory proteins. Am J Physiol Cell Physiol 2002; 283:C651-72. [PMID: 12176723 DOI: 10.1152/ajpcell.00600.2001] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Regulated secretion in exocrine and neuroendocrine cells occurs through exocytosis of secretory granules and the subsequent release of stored small molecules and proteins. The introduction of biophysical techniques with high temporal and spatial resolution, and the identification of Ca(2+)-dependent and -independent "docking" and "fusion" proteins, has greatly enhanced our understanding of exocytosis. The cloning of families of ion channel proteins, including intracellular ion channels, has also revived interest in the role of secretory granule ion channels in exocytotic secretion. Thus secretory granules of pancreatic acinar cell express a ClC-2 Cl(-) channel, a HCO-permeable member of the CLCA Ca(2+)-dependent anion channel family, and a KCNQ1 K(+) channel. Evidence suggests that these channels may facilitate the release of digestive enzymes and/or prevent exocytosed granules from collapsing during "kiss and run" recycling. In pancreatic beta-cells, a granular ClC-3 Cl(-) channel provides a shunt pathway for a vacuolar-type H(+)-ATPase. Acidification "primes" the granules for Ca(2+)-dependent exocytosis and release of insulin. In summary, secretory granules are equipped with specific sets of ion channels, which modulate regulated exocytosis and the release of macromolecules. These channels could represent excellent targets for therapeutic interventions to control exocytotic secretion in relevant diseases, such as pancreatitis, cystic fibrosis, or diabetes mellitus.
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Affiliation(s)
- Frank Thévenod
- School of Biological Sciences, University of Manchester, United Kingdom.
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