1
|
He H, Guzman RE, Cao D, Sierra-Marquez J, Yin F, Fahlke C, Peng J, Stauber T. The molecular and phenotypic spectrum of CLCN4-related epilepsy. Epilepsia 2021; 62:1401-1415. [PMID: 33951195 DOI: 10.1111/epi.16906] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 04/01/2021] [Accepted: 04/01/2021] [Indexed: 01/02/2023]
Abstract
OBJECTIVE This study was undertaken to expand the phenotypic and genetic spectrum of CLCN4-related epilepsy and to investigate genotype-phenotype correlations. METHODS We systematically reviewed the phenotypic and genetic spectrum of newly diagnosed and previously reported patients with CLCN4-related epilepsy. Three novel variants identified in four patients reported in this study were evaluated through in silico prediction and functional analysis by Western blot, immunofluorescence, and electrophysiological measurements. RESULTS Epilepsy was diagnosed in 54.55% (24/44) of individuals with CLCN4-related disorders and was drug-resistant in most cases. Of 24 patients, 15 had epileptic encephalopathy and four died at an early age; 69.57% of patients had seizure onset within the first year of life. Myoclonic seizures are the most common seizure type, and 56.25% of patients presented multiple seizure types. Notably, seizure outcome was favorable in individuals with only one seizure type. All patients showed intellectual disability, which was severe in 65.22% of patients. Additional common features included language delay, behavioral disorders, and dysmorphic features. Five patients benefitted from treatment with lamotrigine. Most variants, which were mainly missense (79.17%), were inherited (70.83%). Whereas frameshift, intragenic deletion, or inherited variants were associated with milder phenotypes, missense or de novo variants led to more severe phenotypes. All evaluated CLCN4 variants resulted in loss of function with reduced ClC-4 currents. Nonetheless, genotype-phenotype relationships for CLCN4-related epilepsy are not straightforward, as phenotypic variability was observed in recurrent variants and within single families. SIGNIFICANCE Pathogenic CLCN4 variants contribute significantly to the genetic etiology of epilepsy. The phenotypic spectrum of CLCN4-related epilepsy includes drug-resistant seizures, cognitive and language impairment, behavioral disorders, and congenital anomalies. Notably, the mutation type and the number of seizure types correlate with the severity of the phenotype, suggesting its use for clinical prognosis. Lamotrigine can be considered a therapeutic option.
Collapse
Affiliation(s)
- Hailan He
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, China
| | - Raul E Guzman
- Institute of Biological Information Processing (IBI-1), Molecular and Cell Physiology, Jülich Research Center, Jülich, Germany
| | - Dezhi Cao
- Neurology Department, Shenzhen Children's Hospital, Shenzhen, China
| | - Juan Sierra-Marquez
- Institute of Biological Information Processing (IBI-1), Molecular and Cell Physiology, Jülich Research Center, Jülich, Germany
| | - Fei Yin
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Christoph Fahlke
- Institute of Biological Information Processing (IBI-1), Molecular and Cell Physiology, Jülich Research Center, Jülich, Germany
| | - Jing Peng
- Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, China.,Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Tobias Stauber
- Institute of Chemistry and Biochemistry, Berlin Free University, Berlin, Germany.,Department of Human Medicine and Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| |
Collapse
|
2
|
Bose S, He H, Stauber T. Neurodegeneration Upon Dysfunction of Endosomal/Lysosomal CLC Chloride Transporters. Front Cell Dev Biol 2021; 9:639231. [PMID: 33708769 PMCID: PMC7940362 DOI: 10.3389/fcell.2021.639231] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2020] [Accepted: 02/03/2021] [Indexed: 12/15/2022] Open
Abstract
The regulation of luminal ion concentrations is critical for the function of, and transport between intracellular organelles. The importance of the acidic pH in the compartments of the endosomal-lysosomal pathway has been well-known for decades. Besides the V-ATPase, which pumps protons into their lumen, a variety of ion transporters and channels is involved in the regulation of the organelles' complex ion homeostasis. Amongst these are the intracellular members of the CLC family, ClC-3 through ClC-7. They localize to distinct but overlapping compartments of the endosomal-lysosomal pathway, partially with tissue-specific expression. Functioning as 2Cl−/H+ exchangers, they can support the vesicular acidification and accumulate luminal Cl−. Mutations in the encoding genes in patients and mouse models underlie severe phenotypes including kidney stones with CLCN5 and osteopetrosis or hypopigmentation with CLCN7. Dysfunction of those intracellular CLCs that are expressed in neurons lead to neuronal defects. Loss of endosomal ClC-3, which heteromerizes with ClC-4, results in neurodegeneration. Mutations in ClC-4 are associated with epileptic encephalopathy and intellectual disability. Mice lacking the late endosomal ClC-6 develop a lysosomal storage disease with reduced pain sensitivity. Human gene variants have been associated with epilepsy, and a gain-of-function mutation causes early-onset neurodegeneration. Dysfunction of the lysosomal ClC-7 leads to a lysosomal storage disease and neurodegeneration in mice and humans. Reduced luminal chloride, as well as altered calcium regulation, has been associated with lysosomal storage diseases in general. This review discusses the properties of endosomal and lysosomal Cl−/H+ exchange by CLCs and how various alterations of ion transport by CLCs impact organellar ion homeostasis and function in neurodegenerative disorders.
Collapse
Affiliation(s)
- Shroddha Bose
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Hailan He
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.,Department of Pediatrics, Xiangya Hospital, Central South University, Changsha, China
| | - Tobias Stauber
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.,Department of Human Medicine and Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| |
Collapse
|
3
|
Osei-Owusu J, Yang J, Leung KH, Ruan Z, Lü W, Krishnan Y, Qiu Z. Proton-activated chloride channel PAC regulates endosomal acidification and transferrin receptor-mediated endocytosis. Cell Rep 2021; 34:108683. [PMID: 33503418 PMCID: PMC7869721 DOI: 10.1016/j.celrep.2020.108683] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Revised: 11/19/2020] [Accepted: 12/29/2020] [Indexed: 12/13/2022] Open
Abstract
During vesicular acidification, chloride (Cl−), as the counterion, provides the electrical shunt for proton pumping by the vacuolar H+ ATPase. Intracellular CLC transporters mediate Cl− influx to the endolysosomes through their 2Cl−/H+ exchange activity. However, whole-endolysosomal patch-clamp recording also revealed a mysterious conductance releasing Cl− from the lumen. It remains unknown whether CLCs or other Cl− channels are responsible for this activity. Here, we show that the newly identified proton-activated Cl− (PAC) channel traffics from the plasma membrane to endosomes via the classical YxxL motif. PAC deletion abolishes the endosomal Cl− conductance, raises luminal Cl− level, lowers luminal pH, and increases transferrin receptor-mediated endocytosis. PAC overexpression generates a large endosomal Cl− current with properties similar to those of endogenous conductance, hypo-acidifies endosomal pH, and reduces transferrin uptake. We propose that the endosomal Cl− PAC channel functions as a low pH sensor and prevents hyper-acidification by releasing Cl− from the lumen. Osei-Owusu et al. show that the recently identified proton-activated chloride (PAC) channel traffics from the plasma membrane to endosomes and forms an intracellular organelle Cl− channel. PAC functions as a low pH sensor in endosomes and prevents luminal hyper-acidification.
Collapse
Affiliation(s)
- James Osei-Owusu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Junhua Yang
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ka Ho Leung
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA; Grossman Institute of Neuroscience, Quantitative Biology and Human Behavior, The University of Chicago, Chicago, IL 60637, USA
| | - Zheng Ruan
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI 49503, USA
| | - Wei Lü
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI 49503, USA
| | - Yamuna Krishnan
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA; Grossman Institute of Neuroscience, Quantitative Biology and Human Behavior, The University of Chicago, Chicago, IL 60637, USA
| | - Zhaozhu Qiu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| |
Collapse
|
4
|
Sun H, Shen L, Qin Y, Liu X, Hao K, Li Y, Wang J, Yang J, Wang F. CLC-Nt1 affects Potato Virus Y infection via regulation of endoplasmic reticulum luminal Ph. THE NEW PHYTOLOGIST 2018; 220:539-552. [PMID: 30022473 DOI: 10.1111/nph.15310] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2018] [Accepted: 06/04/2018] [Indexed: 06/08/2023]
Abstract
Chloride channel (CLC) proteins are important anion transporters conserved in organisms ranging from bacteria and yeast to plants and animals. According to sequence comparison, some plant CLCs are predicted to function as Cl- /H+ antiporters, but not Cl- channels. However, no direct evidence was provided to verify the role of these plant CLCs in regulating the pH of the intracellular compartment. We identified tobacco CLC-Nt1 interacting with the Potato virus Y (PVY) 6K2 protein. To investigate its physiological function, homologous genes of CLC-Nt1 in Nicotiana benthamiana were knocked out using the CRISPR/Cas9 system. Complementation experiments were subsequently performed by expression of wild-type or point-mutated CLC-Nt1 in knockout mutants. The data presented herein demonstrate that CLC-Nt1 is localized at endoplasmic reticulum (ER). Using a pH-sensitive fluorescent protein (pHluorin), we found that loss of CLC-Nt1 function resulted in a decreased ER luminal pH. Secreted GFP (secGFP) was retained mostly in ER in knockout mutants, indicating that CLC-Nt1 is also involved in protein secretion. PVY infection induced a rise in ER luminal pH, which was dependent on functional CLC-Nt1. By contrast, loss of CLC-Nt1 function inhibited PVY intracellular replication and systemic infection. We propose that PVY alters ER luminal pH for infection in a CLC-Nt1-dependent manner.
Collapse
Affiliation(s)
- Hangjun Sun
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| | - Lili Shen
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| | - Yuanxia Qin
- College of Plant Protection, Shenyang Agricultural University, Shenyang, 110866, China
| | - Xiaowei Liu
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| | - Kaiqiang Hao
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan Agricultural University, Kunming, 650201, China
| | - Ying Li
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| | - Jie Wang
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| | - Jinguang Yang
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| | - Fenglong Wang
- Key Laboratory of Tobacco Pest Monitoring Controlling & Integrated Management, Tobacco Research Institute of Chinese Academy of Agricultural Sciences, Qingdao, 266101, China
| |
Collapse
|
5
|
Jentsch TJ, Pusch M. CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease. Physiol Rev 2018; 98:1493-1590. [DOI: 10.1152/physrev.00047.2017] [Citation(s) in RCA: 214] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo- or heteromeric dimers that sometimes require accessory β-subunits for function. CLC proteins come in two flavors: anion channels and anion/proton exchangers. Structures of these two CLC protein classes are surprisingly similar. Extensive structure-function analysis identified residues involved in ion permeation, anion-proton coupling and gating and led to attractive biophysical models. In mammals, ClC-1, -2, -Ka/-Kb are plasma membrane Cl−channels, whereas ClC-3 through ClC-7 are 2Cl−/H+-exchangers in endolysosomal membranes. Biological roles of CLCs were mostly studied in mammals, but also in plants and model organisms like yeast and Caenorhabditis elegans. CLC Cl−channels have roles in the control of electrical excitability, extra- and intracellular ion homeostasis, and transepithelial transport, whereas anion/proton exchangers influence vesicular ion composition and impinge on endocytosis and lysosomal function. The surprisingly diverse roles of CLCs are highlighted by human and mouse disorders elicited by mutations in their genes. These pathologies include neurodegeneration, leukodystrophy, mental retardation, deafness, blindness, myotonia, hyperaldosteronism, renal salt loss, proteinuria, kidney stones, male infertility, and osteopetrosis. In this review, emphasis is laid on biophysical structure-function analysis and on the cell biological and organismal roles of mammalian CLCs and their role in disease.
Collapse
Affiliation(s)
- Thomas J. Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Michael Pusch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| |
Collapse
|
6
|
Abeyrathne PD, Chami M, Stahlberg H. Biochemical and biophysical approaches to study the structure and function of the chloride channel (ClC) family of proteins. Biochimie 2016; 128-129:154-62. [PMID: 27554851 DOI: 10.1016/j.biochi.2016.08.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 08/19/2016] [Indexed: 11/30/2022]
Abstract
The chloride channel (ClC) protein family comprises both chloride (Cl(-)) channels and chloride/proton (Cl(-)/H(+)) antiporters. In prokaryotes and eukaryotes, these proteins mediate the movement of Cl(-) ions across the membrane. In eukaryotes, ClC proteins play a role in the stabilization of membrane potential, epithelial ion transport, hippocampal neuroprotection, cardiac pacemaker activity and vesicular acidification. Moreover, mutations in the genes encoding ClC proteins can cause genetic disease in humans. In prokaryotes, the Cl(-)/H(+) antiporters, such as ClC-ec1 found in Escherichia coli promote proton expulsion in the extreme acid-resistance response common to enteric bacteria. To date, structural and functional studies of the prokaryotic protein have revealed unique structural features, including complicated transmembrane topology with 18 α-helices in each subunit and an anion-coordinating region in each subunit. Several different approaches such as X-ray crystallography, NMR, biochemical studies, and molecular dynamics simulations have been applied to the study of ClC proteins. Continued study of the unique structure and function of this diverse family of proteins has the potential to lead to the development of novel therapeutic targets for neuronal, renal, bone, and food-borne diseases.
Collapse
Affiliation(s)
- Priyanka D Abeyrathne
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland.
| | - Mohamed Chami
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland
| | - Henning Stahlberg
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, WRO-1508 Mattenstrasse 26, CH-4058, Basel, Switzerland
| |
Collapse
|
7
|
Seifert W, Posor Y, Schu P, Stenbeck G, Mundlos S, Klaassen S, Nürnberg P, Haucke V, Kornak U, Kühnisch J. The progressive ankylosis protein ANK facilitates clathrin- and adaptor-mediated membrane traffic at the trans-Golgi network-to-endosome interface. Hum Mol Genet 2016; 25:3836-3848. [PMID: 27466194 DOI: 10.1093/hmg/ddw230] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Revised: 07/01/2016] [Accepted: 07/01/2016] [Indexed: 12/19/2022] Open
Abstract
Dominant or recessive mutations in the progressive ankylosis gene ANKH have been linked to familial chondrocalcinosis (CCAL2), craniometaphyseal dysplasia (CMD), mental retardation, deafness and ankylosis syndrome (MRDA). The function of the encoded membrane protein ANK in cellular compartments other than the plasma membrane is unknown. Here, we show that ANK localizes to the trans-Golgi network (TGN), clathrin-coated vesicles and the plasma membrane. ANK functionally interacts with clathrin and clathrin associated adaptor protein (AP) complexes as loss of either protein causes ANK dispersion from the TGN to cytoplasmic endosome-like puncta. Consistent with its subcellular localization, loss of ANK results in reduced formation of tubular membrane carriers from the TGN, perinuclear accumulation of early endosomes and impaired transferrin endocytosis. Our data indicate that clathrin/AP-mediated cycling of ANK between the TGN, endosomes, and the cell surface regulates membrane traffic at the TGN/endosomal interface. These findings suggest that dysfunction of Golgi-endosomal membrane traffic may contribute to ANKH-associated pathologies.
Collapse
Affiliation(s)
- Wenke Seifert
- Institute of Vegetative Anatomy, Charité - Universitätsmedizin Berlin, Germany
| | - York Posor
- Department of Molecular Pharmacology and Cell Biology, Leibniz-Institut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Peter Schu
- Department of Cellular Biochemistry, Universitätsmedizin Georg-August University, Göttingen, Germany
| | - Gudrun Stenbeck
- College of Health and Life Sciences, Brunel University, Uxbridge, United Kingdom
| | - Stefan Mundlos
- Institute for Medical and Human Genetics, Charité - Universitätsmedizin Berlin, Germany.,FG Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.,Berlin-Brandenburg Center for Regenerative Therapies, Charité - Universitätsmedizin Berlin, Germany
| | - Sabine Klaassen
- Experimental and Clinical Research Center (ECRC)
- Max-Delbrück-Centrum for Molecular Medicine (MDC), Charité - Universitätsmedizin Berlin, Berlin, Germany.,Department of Pediatric Cardiology, Charité - Universitätsmedizin Berlin, Germany and
| | - Peter Nürnberg
- Cologne Center for Genomics (CCG), University of Cologne, Germany
| | - Volker Haucke
- Department of Molecular Pharmacology and Cell Biology, Leibniz-Institut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Uwe Kornak
- Institute for Medical and Human Genetics, Charité - Universitätsmedizin Berlin, Germany.,FG Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.,Berlin-Brandenburg Center for Regenerative Therapies, Charité - Universitätsmedizin Berlin, Germany
| | - Jirko Kühnisch
- Institute for Medical and Human Genetics, Charité - Universitätsmedizin Berlin, Germany .,FG Development and Disease, Max-Planck-Institute for Molecular Genetics, Berlin, Germany.,Experimental and Clinical Research Center (ECRC)
- Max-Delbrück-Centrum for Molecular Medicine (MDC), Charité - Universitätsmedizin Berlin, Berlin, Germany
| |
Collapse
|
8
|
Saha S, Prakash V, Halder S, Chakraborty K, Krishnan Y. A pH-independent DNA nanodevice for quantifying chloride transport in organelles of living cells. NATURE NANOTECHNOLOGY 2015; 10:645-51. [PMID: 26098226 DOI: 10.1038/nnano.2015.130] [Citation(s) in RCA: 156] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2014] [Accepted: 05/22/2015] [Indexed: 05/24/2023]
Abstract
The concentration of chloride ions in the cytoplasm and subcellular organelles of living cells spans a wide range (5-130 mM), and is tightly regulated by intracellular chloride channels or transporters. Chloride-sensitive protein reporters have been used to study the role of these chloride regulators, but they are limited to a small range of chloride concentrations and are pH-sensitive. Here, we show that a DNA nanodevice can precisely measure the activity and location of subcellular chloride channels and transporters in living cells in a pH-independent manner. The DNA nanodevice, called Clensor, is composed of sensing, normalizing and targeting modules, and is designed to localize within organelles along the endolysosomal pathway. It allows fluorescent, ratiometric sensing of chloride ions across the entire physiological regime. We used Clensor to quantitate the resting chloride concentration in the lumen of acidic organelles in Drosophila melanogaster. We showed that lumenal lysosomal chloride, which is implicated in various lysosomal storage diseases, is regulated by the intracellular chloride transporter DmClC-b.
Collapse
Affiliation(s)
- Sonali Saha
- National Centre for Biological Sciences, TIFR, GKVK, Bellary Road, Bangalore 560065, India
| | - Ved Prakash
- Department of Chemistry, University of Chicago, 929E, 57th Street, E305A, GCIS, Chicago, Illinois 60637, USA
| | - Saheli Halder
- National Centre for Biological Sciences, TIFR, GKVK, Bellary Road, Bangalore 560065, India
| | - Kasturi Chakraborty
- Department of Chemistry, University of Chicago, 929E, 57th Street, E305A, GCIS, Chicago, Illinois 60637, USA
| | - Yamuna Krishnan
- 1] National Centre for Biological Sciences, TIFR, GKVK, Bellary Road, Bangalore 560065, India [2] Department of Chemistry, University of Chicago, 929E, 57th Street, E305A, GCIS, Chicago, Illinois 60637, USA
| |
Collapse
|
9
|
Stauber T, Weinert S, Jentsch TJ. Cell biology and physiology of CLC chloride channels and transporters. Compr Physiol 2013; 2:1701-44. [PMID: 23723021 DOI: 10.1002/cphy.c110038] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Proteins of the CLC gene family assemble to homo- or sometimes heterodimers and either function as Cl(-) channels or as Cl(-)/H(+)-exchangers. CLC proteins are present in all phyla. Detailed structural information is available from crystal structures of bacterial and algal CLCs. Mammals express nine CLC genes, four of which encode Cl(-) channels and five 2Cl(-)/H(+)-exchangers. Two accessory β-subunits are known: (1) barttin and (2) Ostm1. ClC-Ka and ClC-Kb Cl(-) channels need barttin, whereas Ostm1 is required for the function of the lysosomal ClC-7 2Cl(-)/H(+)-exchanger. ClC-1, -2, -Ka and -Kb Cl(-) channels reside in the plasma membrane and function in the control of electrical excitability of muscles or neurons, in extra- and intracellular ion homeostasis, and in transepithelial transport. The mainly endosomal/lysosomal Cl(-)/H(+)-exchangers ClC-3 to ClC-7 may facilitate vesicular acidification by shunting currents of proton pumps and increase vesicular Cl(-) concentration. ClC-3 is also present on synaptic vesicles, whereas ClC-4 and -5 can reach the plasma membrane to some extent. ClC-7/Ostm1 is coinserted with the vesicular H(+)-ATPase into the acid-secreting ruffled border membrane of osteoclasts. Mice or humans lacking ClC-7 or Ostm1 display osteopetrosis and lysosomal storage disease. Disruption of the endosomal ClC-5 Cl(-)/H(+)-exchanger leads to proteinuria and Dent's disease. Mouse models in which ClC-5 or ClC-7 is converted to uncoupled Cl(-) conductors suggest an important role of vesicular Cl(-) accumulation in these pathologies. The important functions of CLC Cl(-) channels were also revealed by human diseases and mouse models, with phenotypes including myotonia, renal loss of salt and water, deafness, blindness, leukodystrophy, and male infertility.
Collapse
Affiliation(s)
- Tobias Stauber
- Leibniz-Institut für Molekulare Pharmakologie FMP and Max-Delbrück-Centrum für Molekulare Medizin MDC, Berlin, Germany
| | | | | |
Collapse
|
10
|
Hur J, Jeong H, Park J, Jeon S. Chloride channel 4 is required for nerve growth factor-induced TrkA signaling and neurite outgrowth in PC12 cells and cortical neurons. Neuroscience 2013; 253:389-97. [DOI: 10.1016/j.neuroscience.2013.09.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Revised: 08/26/2013] [Accepted: 09/03/2013] [Indexed: 10/26/2022]
|
11
|
Guzman RE, Grieschat M, Fahlke C, Alekov AK. ClC-3 is an intracellular chloride/proton exchanger with large voltage-dependent nonlinear capacitance. ACS Chem Neurosci 2013; 4:994-1003. [PMID: 23509947 DOI: 10.1021/cn400032z] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The chloride/proton exchangers ClC-3, ClC-4 and ClC-5 are localized in distinct intracellular compartments and regulate their luminal acidity. We used electrophysiology combined with fluorescence pH measurements to compare the functions of these three transporters. Since the expression of WT ClC-3 in the surface membrane was negligible, we removed an N-terminal retention signal for standard electrophysiological characterization of this isoform. This construct (ClC-313-19A) mediated outwardly rectifying coupled Cl(-)/H(+) antiport resembling the properties of ClC-4 and ClC-5. In addition, ClC-3 exhibited large electric capacitance, exceeding the nonlinear capacitances of ClC-4 and ClC-5. Mutations of the proton glutamate, a conserved residue at the internal side of the protein, decreased ion transport but increased nonlinear capacitances in all three isoforms. This suggests that nonlinear capacitances in mammalian ClC transporters are regulated in a similar manner. However, the voltage dependence and the amplitudes of these capacitances differed strongly between the investigated isoforms. Our results indicate that ClC-3 is specialized in mainly performing incomplete capacitive nontransporting cycles, that ClC-4 is an effective coupled transporter, and that ClC-5 displays an intermediate phenotype. Mathematical modeling showed that such functional differences would allow differential regulation of luminal acidification and chloride concentration in intracellular compartments.
Collapse
Affiliation(s)
- Raul E. Guzman
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany
- Institute of Complex Systems, Zelluläre Biophysik, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Matthias Grieschat
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany
| | - Christoph Fahlke
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany
- Institute of Complex Systems, Zelluläre Biophysik, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Alexi K. Alekov
- Institut für Neurophysiologie, Medizinische Hochschule Hannover, D-30625 Hannover, Germany
| |
Collapse
|
12
|
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.
Collapse
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.
| | | |
Collapse
|
13
|
van Weering JRT, Verkade P, Cullen PJ. SNX-BAR-mediated endosome tubulation is co-ordinated with endosome maturation. Traffic 2011; 13:94-107. [PMID: 21973056 DOI: 10.1111/j.1600-0854.2011.01297.x] [Citation(s) in RCA: 123] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Endosomal sorting is essential for cell homeostasis. Proteins targeted for degradation are retained in the maturing endosome vacuole while others are recycled to the cell surface or sorted to the biosynthetic pathway via tubular transport carriers. Sorting nexin (SNX) proteins containing a BAR (for Bin-Amphiphysin-Rvs) domain are key regulators of phosphoinositide-mediated, tubular-based endosomal sorting, but how such sorting is co-ordinated with endosomal maturation is not known. Here, using well-defined Rab GTPases as endosomal compartment markers, we have analyzed the localization of SNX1 [endosome-to-trans-Golgi network (TGN) transport as part of the SNX-BAR-retromer complex], SNX4 (cargo-recycling from endosomes to the plasma membrane) and SNX8 (endosomes-to-TGN trafficking in a retromer-independent manner). We show that these SNX-BARs are primarily localized to early endosomes, but display the highest frequency of tubule formation at the moment of early-to-late endosome transition: the Rab5-to-Rab7 switch. Perturbing this switch shifts SNX-BAR tubulation to early endosomes, resulting in SNX1-decorated tubules that lack retromer components VPS26 and VPS35, suggesting that both early and late endosomal characteristics of the endosome are important for SNX-BAR-retromer-tubule formation. We also establish that SNX4, but not SNX1 and SNX8, is associated with the Rab11-recycling endosomes and that a high frequency of SNX4-mediated tubule formation is observed as endosomes undergo Rab4-to-Rab11 transition. Our study therefore provides evidence for fine-tuning between the processes of endosomal maturation and the formation of endosomal tubules. As tubulation is required for SNX1-, SNX4- and SNX8-mediated sorting, these data reveal a previously unrecognized co-ordination between maturation and tubular-based sorting.
Collapse
Affiliation(s)
- Jan R T van Weering
- Henry Wellcome Integrated Signalling Laboratories, School of Biochemistry, Medical Sciences Building, University of Bristol, University Walk, Bristol, UK
| | | | | |
Collapse
|
14
|
Wellhauser L, Luna-Chavez C, D'Antonio C, Tainer J, Bear CE. ATP induces conformational changes in the carboxyl-terminal region of ClC-5. J Biol Chem 2010; 286:6733-41. [PMID: 21173145 DOI: 10.1074/jbc.m110.175877] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
ATP binding enhances the activity of ClC-5, the transporter mutated in Dent disease, a disease affecting the renal proximal tubule. Previously, the ATP binding site was revealed in x-ray crystal structures of the cytoplasmic region of this membrane protein. Disruption of this site by mutagenesis (Y617A-ClC-5) reduced the functional expression and ATP-dependent regulation of the full-length transporter in Xenopus oocytes. However, insight into the conformational changes underlying ATP-dependent regulation is lacking. Here, we show that ATP binding induces a change in protein conformation. Specifically, small angle x-ray scattering experiments indicate that ATP binding promotes a clamp-like closure of the isolated ClC-5 carboxyl-terminal region. Limited proteolysis studies show that ATP binding induces conformational compaction of the carboxyl-terminal region in the intact membrane protein as well. In the context of fibroblasts and proximal tubule epithelial cells, disruption of the ATP binding site in full-length ClC-5 (Y617A-ClC-5) led to a defect in processing and trafficking out of the endoplasmic reticulum. These latter findings account for the decrease in functional expression previously reported for this ATP-binding mutant and prompt future study of a model whereby conformational compaction caused by ATP binding promotes biosynthetic maturation.
Collapse
Affiliation(s)
- Leigh Wellhauser
- Programme of Molecular Structure and Function, Research Institute, the Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
| | | | | | | | | |
Collapse
|
15
|
Braun NA, Morgan B, Dick TP, Schwappach B. The yeast CLC protein counteracts vesicular acidification during iron starvation. J Cell Sci 2010; 123:2342-50. [PMID: 20530571 DOI: 10.1242/jcs.068403] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ion gradients across intracellular membranes contribute to the physicochemical environment inside compartments. CLC anion transport proteins that localise to intracellular organelles are anion-proton exchangers involved in anion sequestration or vesicular acidification. By homology, the only CLC protein of Saccharomyces cerevisiae, Gef1, belongs to this family of intracellular exchangers. Gef1 localises to the late Golgi and prevacuole and is essential in conditions of iron limitation. In the absence of Gef1, a multicopper oxidase involved in iron uptake, Fet3, fails to acquire copper ion cofactors. The precise role of the exchanger in this physiological context is unknown. Here, we show that the Gef1-containing compartment is adjusted to a more alkaline pH under iron limitation. This depends on the antiport function of Gef1, because an uncoupled mutant of Gef1 (E230A) results in the acidification of the lumen and fails to support Fet3 maturation. Furthermore, we found that Gef1 antiport activity correlates with marked effects on cellular glutathione homeostasis, raising the possibility that the effect of Gef1 on Fet3 copper loading is related to the control of compartmental glutathione concentration or redox status. Mutational inactivation of a conserved ATP-binding site in the cytosolic cystathione beta-synthetase domain of Gef1 (D732A) suggests that Gef1 activity is regulated by energy metabolism.
Collapse
Affiliation(s)
- Nikolai A Braun
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | | | | | | |
Collapse
|
16
|
Osteogenic role of endosomal chloride channels in MC3T3-E1 cells. Mol Cell Biochem 2010; 342:191-9. [DOI: 10.1007/s11010-010-0483-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Accepted: 05/04/2010] [Indexed: 11/28/2022]
|
17
|
Rickheit G, Wartosch L, Schaffer S, Stobrawa SM, Novarino G, Weinert S, Jentsch TJ. Role of ClC-5 in renal endocytosis is unique among ClC exchangers and does not require PY-motif-dependent ubiquitylation. J Biol Chem 2010; 285:17595-603. [PMID: 20351103 DOI: 10.1074/jbc.m110.115600] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inactivation of the mainly endosomal 2Cl(-)/H(+)-exchanger ClC-5 severely impairs endocytosis in renal proximal tubules and underlies the human kidney stone disorder Dent's disease. In heterologous expression systems, interaction of the E3 ubiquitin ligases WWP2 and Nedd4-2 with a "PY-motif" in the cytoplasmic C terminus of ClC-5 stimulates its internalization from the plasma membrane and may influence receptor-mediated endocytosis. We asked whether this interaction is relevant in vivo and generated mice in which the PY-motif was destroyed by a point mutation. Unlike ClC-5 knock-out mice, these knock-in mice displayed neither low molecular weight proteinuria nor hyperphosphaturia, and both receptor-mediated and fluid-phase endocytosis were normal. The abundances and localizations of the endocytic receptor megalin and of the Na(+)-coupled phosphate transporter NaPi-2a (Npt2) were not changed, either. To explore whether the discrepancy in results from heterologous expression studies might be due to heteromerization of ClC-5 with ClC-3 or ClC-4 in vivo, we studied knock-in mice additionally deleted for those related transporters. Disruption of neither ClC-3 nor ClC-4 led to proteinuria or impaired proximal tubular endocytosis by itself, nor in combination with the PY-mutant of ClC-5. Endocytosis of cells lacking ClC-5 was not impaired further when ClC-3 or ClC-4 was additionally deleted. We conclude that ClC-5 is unique among CLC proteins in being crucial for proximal tubular endocytosis and that PY-motif-dependent ubiquitylation of ClC-5 is dispensable for this role.
Collapse
Affiliation(s)
- Gesa Rickheit
- Leibniz-Institut für Molekulare Pharmakologie and Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Strasse 10, D-13125 Berlin, Germany
| | | | | | | | | | | | | |
Collapse
|
18
|
Ishiguro T, Avila H, Lin SY, Nakamura T, Yamamoto M, Boyd DD. Gene trapping identifies chloride channel 4 as a novel inducer of colon cancer cell migration, invasion and metastases. Br J Cancer 2010; 102:774-82. [PMID: 20087350 PMCID: PMC2837579 DOI: 10.1038/sj.bjc.6605536] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Revised: 11/30/2009] [Accepted: 12/15/2009] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND To date, there are few reports on gene products contributing to colon cancer progression. METHODS We used a gene trap comprised of an enhanced retroviral mutagen (ERM) cassette that includes a tetracycline-responsive promoter upstream of a haemagglutinin (HA) tag and a splice donor site. Integration of the ERM within an endogenous gene yields a tetracycline-regulated HA-tagged transcript. We transduced RKO colon cancer cells expressing a tetracycline trans-activator-off with the ERM-encoding retrovirus and screened for enhanced migration. RESULTS One clone showed fivefold enhanced migration with tetracycline withdrawal. Rapid amplification of cDNA ends identified the trapped gene as the chloride channel 4 (CLCN4) exchanger. Stable expression of a CLCN4 cDNA enhanced motility, whereas cells knocked down or null for this transcript showed reduced migration/invasion. CLCN4-overexpressing RKO colon cancer cells were more resistant than controls to proton load-induced cytotoxicity, consistent with the H(+)-extruding function of this antiporter. Intra-splenic delivery of RKO-CLCN4 transfectants, but not controls, yielded liver metastases, and transcript levels were higher in colon cancer metastases to the liver when compared with primary tumours. CONCLUSIONS CLCN4 is a novel driver of colon cancer progression.
Collapse
Affiliation(s)
- T Ishiguro
- Cancer Biology Department, MD Anderson Cancer Center, Houston, TX, USA
| | - H Avila
- Cancer Biology Department, MD Anderson Cancer Center, Houston, TX, USA
| | - S-Y Lin
- Systems Biology Department, MD Anderson Cancer Center, Houston, TX, USA
| | - T Nakamura
- Surgical Oncology Department, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - M Yamamoto
- Second Department of Surgery, Hamamatsu University School of Medicine, Hamanatsu, Japan
| | - D D Boyd
- Cancer Biology Department, MD Anderson Cancer Center, Houston, TX, USA
| |
Collapse
|
19
|
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.
Collapse
|
20
|
ClC transporters: discoveries and challenges in defining the mechanisms underlying function and regulation of ClC-5. Pflugers Arch 2010; 460:543-57. [PMID: 20049483 DOI: 10.1007/s00424-009-0769-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Revised: 11/27/2009] [Accepted: 11/30/2009] [Indexed: 02/03/2023]
Abstract
The involvement of several members of the chloride channel (ClC) family of membrane proteins in human disease highlights the need to define the mechanisms underlying their function and the consequences of disease-causing mutations. Despite the utility of high-resolution structural models, our understanding of the molecular basis for function of the chloride channels and transporters in the family remains incomplete. In this review, we focus on recent discoveries regarding molecular mechanisms underlying the regulated chloride:proton antiporter activity of ClC-5, the protein mutated in the Dent's disease-a kidney disease presenting with proteinuria and renal failure in severe cases. We discuss the putative role of ClC-5 in receptor-mediated endocytosis and protein uptake by the proximal renal tubule and the possible molecular and cellular consequences of disease-causing mutations. However, validation of these models will require future study of the intrinsic function of this transporter, in situ, in the membranes of recycling endosomes in proximal tubule epithelial cells.
Collapse
|