51
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A synthetic ion transporter that disrupts autophagy and induces apoptosis by perturbing cellular chloride concentrations. Nat Chem 2017. [PMID: 28644464 DOI: 10.1038/nchem.2706] [Citation(s) in RCA: 193] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Perturbations in cellular chloride concentrations can affect cellular pH and autophagy and lead to the onset of apoptosis. With this in mind, synthetic ion transporters have been used to disturb cellular ion homeostasis and thereby induce cell death; however, it is not clear whether synthetic ion transporters can also be used to disrupt autophagy. Here, we show that squaramide-based ion transporters enhance the transport of chloride anions in liposomal models and promote sodium chloride influx into the cytosol. Liposomal and cellular transport activity of the squaramides is shown to correlate with cell death activity, which is attributed to caspase-dependent apoptosis. One ion transporter was also shown to cause additional changes in lysosomal pH, which leads to impairment of lysosomal enzyme activity and disruption of autophagic processes. This disruption is independent of the initiation of apoptosis by the ion transporter. This study provides the first experimental evidence that synthetic ion transporters can disrupt both autophagy and induce apoptosis.
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52
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Beck A, Fecher-Trost C, Wolske K, Philipp SE, Flockerzi V, Wissenbach U. Identification of Sidt2 as a lysosomal cation-conducting protein. FEBS Lett 2017; 591:76-87. [PMID: 27987306 DOI: 10.1002/1873-3468.12528] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 11/25/2016] [Accepted: 12/01/2016] [Indexed: 12/18/2022]
Abstract
A screen to identify lysosomal-expressed ion channels led to the discovery of the human Sidt2 protein. Sidt2 is expressed within lysosomal organelles but as a result of heterologous overexpression the protein is also detectable within the plasma membrane of human embryonic kidney cells. The overexpressed protein leads to cell depolarization upon sodium addition. Accordingly in whole-cell patch clamp experiments a spontaneous noninactivating monovalent cation current can be detected in Sidt2-overexpressing cells. Strong overexpression of Sidt2 in HEK293 cells is attended by a significant reduction/loss of detectable lysosomes, indicating that the overexpressed protein leads to lysosomal dysfunction, a hallmark of Alzheimer's disease. Sidt2 is located on chromosome 11q23, a locus repeatedly found by chromosomal mapping of Alzheimer's disease-related genes.
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Affiliation(s)
- Andreas Beck
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg/Saar, Germany
| | - Claudia Fecher-Trost
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg/Saar, Germany
| | - Karin Wolske
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg/Saar, Germany
| | - Stephan E Philipp
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg/Saar, Germany
| | - Veit Flockerzi
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg/Saar, Germany
| | - Ulrich Wissenbach
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg/Saar, Germany
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53
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Lysosomal Re-acidification Prevents Lysosphingolipid-Induced Lysosomal Impairment and Cellular Toxicity. PLoS Biol 2016; 14:e1002583. [PMID: 27977664 PMCID: PMC5169359 DOI: 10.1371/journal.pbio.1002583] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 11/11/2016] [Indexed: 12/20/2022] Open
Abstract
Neurodegenerative lysosomal storage disorders (LSDs) are severe and untreatable, and mechanisms underlying cellular dysfunction are poorly understood. We found that toxic lipids relevant to three different LSDs disrupt multiple lysosomal and other cellular functions. Unbiased drug discovery revealed several structurally distinct protective compounds, approved for other uses, that prevent lysosomal and cellular toxicities of these lipids. Toxic lipids and protective agents show unexpected convergence on control of lysosomal pH and re-acidification as a critical component of toxicity and protection. In twitcher mice (a model of Krabbe disease [KD]), a central nervous system (CNS)-penetrant protective agent rescued myelin and oligodendrocyte (OL) progenitors, improved motor behavior, and extended lifespan. Our studies reveal shared principles relevant to several LSDs, in which diverse cellular and biochemical disruptions appear to be secondary to disruption of lysosomal pH regulation by specific lipids. These studies also provide novel protective strategies that confer therapeutic benefits in a mouse model of a severe LSD.
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54
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Shi B, Huang QQ, Birkett R, Doyle R, Dorfleutner A, Stehlik C, He C, Pope RM. SNAPIN is critical for lysosomal acidification and autophagosome maturation in macrophages. Autophagy 2016; 13:285-301. [PMID: 27929705 DOI: 10.1080/15548627.2016.1261238] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
We previously observed that SNAPIN, which is an adaptor protein in the SNARE core complex, was highly expressed in rheumatoid arthritis synovial tissue macrophages, but its role in macrophages and autoimmunity is unknown. To identify SNAPIN's role in these cells, we employed siRNA to silence the expression of SNAPIN in primary human macrophages. Silencing SNAPIN resulted in swollen lysosomes with impaired CTSD (cathepsin D) activation, although total CTSD was not reduced. Neither endosome cargo delivery nor lysosomal fusion with endosomes or autophagosomes was inhibited following the forced silencing of SNAPIN. The acidification of lysosomes and accumulation of autolysosomes in SNAPIN-silenced cells was inhibited, resulting in incomplete lysosomal hydrolysis and impaired macroautophagy/autophagy flux. Mechanistic studies employing ratiometric color fluorescence on living cells demonstrated that the reduction of SNAPIN resulted in a modest reduction of H+ pump activity; however, the more critical mechanism was a lysosomal proton leak. Overall, our results demonstrate that SNAPIN is critical in the maintenance of healthy lysosomes and autophagy through its role in lysosome acidification and autophagosome maturation in macrophages largely through preventing proton leak. These observations suggest an important role for SNAPIN and autophagy in the homeostasis of macrophages, particularly long-lived tissue resident macrophages.
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Affiliation(s)
- Bo Shi
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Qi-Quan Huang
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Robert Birkett
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Renee Doyle
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Andrea Dorfleutner
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Christian Stehlik
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Congcong He
- b Department of Cell and Molecular Biology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
| | - Richard M Pope
- a Division of Rheumatology , Feinberg School of Medicine, Northwestern University , Chicago , IL , USA
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55
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Circu ML, Dykes SS, Carroll J, Kelly K, Galiano F, Greer A, Cardelli J, El-Osta H. A Novel High Content Imaging-Based Screen Identifies the Anti-Helminthic Niclosamide as an Inhibitor of Lysosome Anterograde Trafficking and Prostate Cancer Cell Invasion. PLoS One 2016; 11:e0146931. [PMID: 26784896 PMCID: PMC4718621 DOI: 10.1371/journal.pone.0146931] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 12/23/2015] [Indexed: 01/22/2023] Open
Abstract
Lysosome trafficking plays a significant role in tumor invasion, a key event for the development of metastasis. Previous studies from our laboratory have demonstrated that the anterograde (outward) movement of lysosomes to the cell surface in response to certain tumor microenvironment stimulus, such as hepatocyte growth factor (HGF) or acidic extracellular pH (pHe), increases cathepsin B secretion and tumor cell invasion. Anterograde lysosome trafficking depends on sodium-proton exchanger activity and can be reversed by blocking these ion pumps with Troglitazone or EIPA. Since these drugs cannot be advanced into the clinic due to toxicity, we have designed a high-content assay to discover drugs that block peripheral lysosome trafficking with the goal of identifying novel drugs that inhibit tumor cell invasion. An automated high-content imaging system (Cellomics) was used to measure the position of lysosomes relative to the nucleus. Among a total of 2210 repurposed and natural product drugs screened, 18 "hits" were identified. One of the compounds identified as an anterograde lysosome trafficking inhibitor was niclosamide, a marketed human anti-helminthic drug. Further studies revealed that niclosamide blocked acidic pHe, HGF, and epidermal growth factor (EGF)-induced anterograde lysosome redistribution, protease secretion, motility, and invasion of DU145 castrate resistant prostate cancer cells at clinically relevant concentrations. In an effort to identify the mechanism by which niclosamide prevented anterograde lysosome movement, we found that this drug exhibited no significant effect on the level of ATP, microtubules or actin filaments, and had minimal effect on the PI3K and MAPK pathways. Niclosamide collapsed intralysosomal pH without disruption of the lysosome membrane, while bafilomycin, an agent that impairs lysosome acidification, was also found to induce JLA in our model. Taken together, these data suggest that niclosamide promotes juxtanuclear lysosome aggregation (JLA) via modulation of pathways involved in lysosome acidification. In conclusion, we have designed a validated reproducible high-content assay to screen for drugs that inhibit lysosome trafficking and reduce tumor invasion and we summarize the action of one of these drugs.
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Affiliation(s)
- Magdalena L. Circu
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - Samantha S. Dykes
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - Jennifer Carroll
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - Kinsey Kelly
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - Floyd Galiano
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - Adam Greer
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - James Cardelli
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
| | - Hazem El-Osta
- Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America
- * E-mail:
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56
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Flannagan RS, Heit B, Heinrichs DE. Antimicrobial Mechanisms of Macrophages and the Immune Evasion Strategies of Staphylococcus aureus. Pathogens 2015; 4:826-68. [PMID: 26633519 PMCID: PMC4693167 DOI: 10.3390/pathogens4040826] [Citation(s) in RCA: 128] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 11/17/2015] [Accepted: 11/24/2015] [Indexed: 12/21/2022] Open
Abstract
Habitually professional phagocytes, including macrophages, eradicate microbial invaders from the human body without overt signs of infection. Despite this, there exist select bacteria that are professional pathogens, causing significant morbidity and mortality across the globe and Staphylococcus aureus is no exception. S. aureus is a highly successful pathogen that can infect virtually every tissue that comprises the human body causing a broad spectrum of diseases. The profound pathogenic capacity of S. aureus can be attributed, in part, to its ability to elaborate a profusion of bacterial effectors that circumvent host immunity. Macrophages are important professional phagocytes that contribute to both the innate and adaptive immune response, however from in vitro and in vivo studies, it is evident that they fail to eradicate S. aureus. This review provides an overview of the antimicrobial mechanisms employed by macrophages to combat bacteria and describes the immune evasion strategies and some representative effectors that enable S. aureus to evade macrophage-mediated killing.
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Affiliation(s)
- Ronald S Flannagan
- Department of Microbiology and Immunology, the University of Western Ontario, London, ON N6A 5C1, Canada.
| | - Bryan Heit
- Department of Microbiology and Immunology, the University of Western Ontario, London, ON N6A 5C1, Canada.
- Centre for Human Immunology, the University of Western Ontario, London, ON N6A 5C1, Canada.
| | - David E Heinrichs
- Department of Microbiology and Immunology, the University of Western Ontario, London, ON N6A 5C1, Canada.
- Centre for Human Immunology, the University of Western Ontario, London, ON N6A 5C1, Canada.
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57
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Guan L, Rizzello L, Battaglia G. Polymersomes and their applications in cancer delivery and therapy. Nanomedicine (Lond) 2015; 10:2757-80. [DOI: 10.2217/nnm.15.110] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Polymersomes have been proposed as a platform for drug delivery systems since late 90s. They are exploited to deliver hydrophilic and/or hydrophobic therapeutic and diagnostic agents. The relatively robust membrane, the colloidal stability, along with a significant biocompatibility and easy ligands conjugation methods make polymersomes primary candidates for therapeutic drugs delivery in cancer clinical treatments. In addition, they represent an optimal choice as imaging tools in noninvasive diagnostic. As a result, polymersomes have been proposed and widely studied for anticancer treatments. However, there are not sufficient clinic translation data of human studies yet. In this critical review, we will discuss such topics, focusing on the self-assembly of membrane-forming copolymers, on their tunable physicochemical properties and on the consequential applications of these biocompatible polymersomes in drug delivery and cancer therapy.
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Affiliation(s)
- Lijuan Guan
- Department of Chemistry, University College London, London, WC1H 0AJ, UK
- MRC Center for Medical Molecular Virology, University College London, London, WC1H 0AJ, UK
| | - Loris Rizzello
- Department of Chemistry, University College London, London, WC1H 0AJ, UK
- MRC Center for Medical Molecular Virology, University College London, London, WC1H 0AJ, UK
| | - Giuseppe Battaglia
- Department of Chemistry, University College London, London, WC1H 0AJ, UK
- MRC Center for Medical Molecular Virology, University College London, London, WC1H 0AJ, UK
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58
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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.
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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
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59
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Doria F, Folini M, Grande V, Cimino-Reale G, Zaffaroni N, Freccero M. Naphthalene diimides as red fluorescent pH sensors for functional cell imaging. Org Biomol Chem 2015; 13:570-6. [DOI: 10.1039/c4ob02054e] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Water-soluble naphthalene diimides have been designed and synthesized as cell permeable pH “turned-on” fluorescent sensors for cellular applications.
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Affiliation(s)
- Filippo Doria
- Dipartimento di Chimica
- Università di Pavia
- 27100 Pavia
- Italy
| | - Marco Folini
- Molecular Pharmacology Unit
- Department of Experimental Oncology and Molecular Medicine
- Fondazione IRCCS Istituto Nazionale dei Tumori
- Milano
- Italy
| | | | - Graziella Cimino-Reale
- Molecular Pharmacology Unit
- Department of Experimental Oncology and Molecular Medicine
- Fondazione IRCCS Istituto Nazionale dei Tumori
- Milano
- Italy
| | - Nadia Zaffaroni
- Molecular Pharmacology Unit
- Department of Experimental Oncology and Molecular Medicine
- Fondazione IRCCS Istituto Nazionale dei Tumori
- Milano
- Italy
| | - Mauro Freccero
- Dipartimento di Chimica
- Università di Pavia
- 27100 Pavia
- Italy
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60
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Lin PH, Duann P, Komazaki S, Park KH, Li H, Sun M, Sermersheim M, Gumpper K, Parrington J, Galione A, Evans AM, Zhu MX, Ma J. Lysosomal two-pore channel subtype 2 (TPC2) regulates skeletal muscle autophagic signaling. J Biol Chem 2014; 290:3377-89. [PMID: 25480788 PMCID: PMC4319008 DOI: 10.1074/jbc.m114.608471] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Postnatal skeletal muscle mass is regulated by the balance between anabolic protein synthesis and catabolic protein degradation, and muscle atrophy occurs when protein homeostasis is disrupted. Autophagy has emerged as critical in clearing dysfunctional organelles and thus in regulating protein turnover. Here we show that endolysosomal two-pore channel subtype 2 (TPC2) contributes to autophagy signaling and protein homeostasis in skeletal muscle. Muscles derived from Tpcn2−/− mice exhibit an atrophic phenotype with exacerbated autophagy under starvation. Compared with wild types, animals lacking TPC2 demonstrated an enhanced autophagy flux characterized by increased accumulation of autophagosomes upon combined stress induction by starvation and colchicine treatment. In addition, deletion of TPC2 in muscle caused aberrant lysosomal pH homeostasis and reduced lysosomal protease activity. Association between mammalian target of rapamycin and TPC2 was detected in skeletal muscle, allowing for appropriate adjustments to cellular metabolic states and subsequent execution of autophagy. TPC2 therefore impacts mammalian target of rapamycin reactivation during the process of autophagy and contributes to maintenance of muscle homeostasis.
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Affiliation(s)
- Pei-Hui Lin
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210,
| | - Pu Duann
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Shinji Komazaki
- Department of Anatomy, Saitama Medical University, Saitama 350-0495, Japan
| | - Ki Ho Park
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Haichang Li
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Mingzhai Sun
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Mathew Sermersheim
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - Kristyn Gumpper
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210
| | - John Parrington
- Department of Pharmacology, University of Oxford, Oxford OX1 3QT, United Kingdom
| | - Antony Galione
- Department of Pharmacology, University of Oxford, Oxford OX1 3QT, United Kingdom
| | - A Mark Evans
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom, and
| | - Michael X Zhu
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center, Houston, Texas 77030
| | - Jianjie Ma
- From the Department of Surgery, Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio 43210,
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61
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Geilfus CM, Mühling KH, Kaiser H, Plieth C. Bacterially produced Pt-GFP as ratiometric dual-excitation sensor for in planta mapping of leaf apoplastic pH in intact Avena sativa and Vicia faba. PLANT METHODS 2014; 10:31. [PMID: 25313311 PMCID: PMC4194361 DOI: 10.1186/1746-4811-10-31] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 09/20/2014] [Indexed: 05/24/2023]
Abstract
BACKGROUND Ratiometric analysis with H(+)-sensitive fluorescent sensors is a suitable approach for monitoring apoplastic pH dynamics. For the acidic range, the acidotropic dual-excitation dye Oregon Green 488 is an excellent pH sensor. Long lasting (hours) recordings of apoplastic pH in the near neutral range, however, are more problematic because suitable pH indicators that combine a good pH responsiveness at a near neutral pH with a high photostability are lacking. The fluorescent pH reporter protein from Ptilosarcus gurneyi (Pt-GFP) comprises both properties. But, as a genetically encoded indicator and expressed by the plant itself, it can be used almost exclusively in readily transformed plants. In this study we present a novel approach and use purified recombinant indicators for measuring ion concentrations in the apoplast of crop plants such as Vicia faba L. and Avena sativa L. RESULTS Pt-GFP was purified using a bacterial expression system and subsequently loaded through stomata into the leaf apoplast of intact plants. Imaging verified the apoplastic localization of Pt-GFP and excluded its presence in the symplast. The pH-dependent emission signal stood out clearly from the background. PtGFP is highly photostable, allowing ratiometric measurements over hours. By using this approach, a chloride-induced alkalinizations of the apoplast was demonstrated for the first in oat. CONCLUSIONS Pt-GFP appears to be an excellent sensor for the quantification of leaf apoplastic pH in the neutral range. The presented approach encourages to also use other genetically encoded biosensors for spatiotemporal mapping of apoplastic ion dynamics.
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Affiliation(s)
- Christoph-Martin Geilfus
- />Institute of Plant Nutrition and Soil Science, Christian-Albrechts-Universität zu Kiel, Hermann-Rodewald-Str. 2, 24118 Kiel, Germany
| | - Karl H Mühling
- />Institute of Plant Nutrition and Soil Science, Christian-Albrechts-Universität zu Kiel, Hermann-Rodewald-Str. 2, 24118 Kiel, Germany
| | - Hartmut Kaiser
- />Botanisches Institut, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 3-9, 24118 Kiel, Germany
| | - Christoph Plieth
- />Zentrum für Biochemie und Molekularbiologie, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 3-9, 24118 Kiel, Germany
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62
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Zhao L, Wang Z, Xi Z, Xu D, Chen S, Liu Y. The Reaction of Arsenite with Proteins Relies on Solution Conditions. Inorg Chem 2014; 53:3054-61. [DOI: 10.1021/ic402891t] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Linhong Zhao
- CAS Key
Laboratory of Soft Matter Chemistry, CAS High Magnetic Field Laboratory,
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026 China
| | - Zhen Wang
- CAS Key
Laboratory of Soft Matter Chemistry, CAS High Magnetic Field Laboratory,
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026 China
| | - Zhaoyong Xi
- CAS Key
Laboratory of Soft Matter Chemistry, CAS High Magnetic Field Laboratory,
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026 China
| | - Dechen Xu
- CAS Key
Laboratory of Soft Matter Chemistry, CAS High Magnetic Field Laboratory,
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026 China
| | - Siming Chen
- CAS Key
Laboratory of Soft Matter Chemistry, CAS High Magnetic Field Laboratory,
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026 China
| | - Yangzhong Liu
- CAS Key
Laboratory of Soft Matter Chemistry, CAS High Magnetic Field Laboratory,
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026 China
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63
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Lu Y, Hao B, Graeff R, Yue J. NAADP/TPC2/Ca(2+) Signaling Inhibits Autophagy. Commun Integr Biol 2014; 6:e27595. [PMID: 24753792 PMCID: PMC3984295 DOI: 10.4161/cib.27595] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 12/19/2013] [Accepted: 12/19/2013] [Indexed: 12/21/2022] Open
Abstract
Nicotinic adenine acid dinucleotide phosphate (NAADP) is one of the most potent endogenous Ca2+ mobilizing messengers. NAADP mobilizes Ca2+ from an acidic lysosome-related store, which can be subsequently amplified into global Ca2+ waves by calcium-induced calcium release (CICR) from ER/SR via Ins(1,4,5)P3 receptors or ryanodine receptors. A body of evidence indicates that 2 pore channel 2 (TPC2), a new member of the superfamily of voltage-gated ion channels containing 12 putative transmembrane segments, is the long sought after NAADP receptor. Activation of NAADP/TPC2/Ca2+ signaling inhibits the fusion between autophagosome and lysosome by alkalizing the lysosomal pH, thereby arresting autophagic flux. In addition, TPC2 is downregulated during neural differentiation of mouse embryonic stem (ES) cells, and TPC2 downregulation actually facilitates the neural lineage entry of ES cells. Here we propose the mechanism underlying how NAADP-induced Ca2+ release increases lysosomal pH and discuss the role of TPC2 in neural differentiation of mouse ES cells.
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Affiliation(s)
- Yingying Lu
- Department of Physiology; University of Hong Kong; Hong Kong, PR China
| | - Baixia Hao
- Department of Physiology; University of Hong Kong; Hong Kong, PR China
| | - Richard Graeff
- Department of Physiology; University of Hong Kong; Hong Kong, PR China
| | - Jianbo Yue
- Department of Physiology; University of Hong Kong; Hong Kong, PR China
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64
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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.
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Affiliation(s)
- Tobias Stauber
- Leibniz-Institut für Molekulare Pharmakologie FMP and Max-Delbrück-Centrum für Molekulare Medizin MDC, Berlin, Germany
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Li G, Zhu D, Xue L, Jiang H. Quinoline-Based Fluorescent Probe for Ratiometric Detection of Lysosomal pH. Org Lett 2013; 15:5020-3. [DOI: 10.1021/ol4023547] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Guoping Li
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China, and College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Dongjian Zhu
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China, and College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Lin Xue
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China, and College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
| | - Hua Jiang
- Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China, and College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China
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66
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Collaco AM, Geibel P, Lee BS, Geibel JP, Ameen NA. Functional vacuolar ATPase (V-ATPase) proton pumps traffic to the enterocyte brush border membrane and require CFTR. Am J Physiol Cell Physiol 2013; 305:C981-96. [PMID: 23986201 DOI: 10.1152/ajpcell.00067.2013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Vacuolar ATPases (V-ATPases) are highly conserved proton pumps that regulate organelle pH. Epithelial luminal pH is also regulated by cAMP-dependent traffic of specific subunits of the V-ATPase complex from endosomes into the apical membrane. In the intestine, cAMP-dependent traffic of cystic fibrosis transmembrane conductance regulator (CFTR) channels and the sodium hydrogen exchanger (NHE3) in the brush border regulate luminal pH. V-ATPase was found to colocalize with CFTR in intestinal CFTR high expresser (CHE) cells recently. Moreover, apical traffic of V-ATPase and CFTR in rat Brunner's glands was shown to be dependent on cAMP/PKA. These observations support a functional relationship between V-ATPase and CFTR in the intestine. The current study examined V-ATPase and CFTR distribution in intestines from wild-type, CFTR(-/-) mice and polarized intestinal CaCo-2BBe cells following cAMP stimulation and inhibition of CFTR/V-ATPase function. Coimmunoprecipitation studies examined V-ATPase interaction with CFTR. The pH-sensitive dye BCECF determined proton efflux and its dependence on V-ATPase/CFTR in intestinal cells. cAMP increased V-ATPase/CFTR colocalization in the apical domain of intestinal cells and redistributed the V-ATPase Voa1 and Voa2 trafficking subunits from the basolateral membrane to the brush border membrane. Voa1 and Voa2 subunits were localized to endosomes beneath the terminal web in untreated CFTR(-/-) intestine but redistributed to the subapical cytoplasm following cAMP treatment. Inhibition of CFTR or V-ATPase significantly decreased pHi in cells, confirming their functional interdependence. These data establish that V-ATPase traffics into the brush border membrane to regulate proton efflux and this activity is dependent on CFTR in the intestine.
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Affiliation(s)
- Anne M Collaco
- Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut
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Lockwood TD. Lysosomal metal, redox and proton cycles influencing the CysHis cathepsin reaction. Metallomics 2013; 5:110-24. [PMID: 23302864 DOI: 10.1039/c2mt20156a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In the 1930's pioneers discovered that maximal autolysis in tissue homogenates requires metal chelator, sulfhydryl reducing agent and acid pH. However, metals, reducing equivalents and protons (MR&P) have been overlooked as combined catalytic controls. Three categories of lysosomal machinery drive three distinguishable cycles importing and exporting MR&P. Zn(2+) preemptively inhibits CysHis catalysis under otherwise optimal protonation and reduction. Protein-bound cell Zn(2+) concentration is 200-2000 times the non-sequestered inhibitory concentration. Following autophagy, lysosomal proteolysis liberates much inhibitory Zn(2+). The vacuolar proton pump is the driving force for Zn(2+) export, as well as protonation of the peptidolytic mechanism. Other machinery of lysosomal cycles includes proton-driven Zn(2+) exporters (e.g. SLC11A1), Zn(2+) channels (e.g. TRPML-1), lysosomal thiol reductase, etc. The CysHis dyad is a sensor of the vacuolar environment of MR&P, an integrator of these simultaneous variables, and a catalytic responder. Rate-determination can shift between autophagic substrate acquisition (swallowing) and substrate degradation (digesting). Zn(2+) recycling from degraded proteins to new proteins is a fourth cycle that might pace lysosomal function under some conditions. Heritable insufficient or excess functions of CysHis cathepsins are associated with dysfunctional inflammation and immunity/auto-immunity, including diabetic pathogenesis.
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Affiliation(s)
- Thomas D Lockwood
- Dept. of Pharmacology, School of Medicine, Wright State University, Dayton, Ohio 45435, USA.
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Lu Y, Hao BX, Graeff R, Wong CWM, Wu WT, Yue J. Two pore channel 2 (TPC2) inhibits autophagosomal-lysosomal fusion by alkalinizing lysosomal pH. J Biol Chem 2013; 288:24247-63. [PMID: 23836916 PMCID: PMC3745369 DOI: 10.1074/jbc.m113.484253] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Autophagy is an evolutionarily conserved lysosomal degradation pathway, yet the underlying mechanisms remain poorly understood. Nicotinic acid adenine dinucleotide phosphate (NAADP), one of the most potent Ca2+ mobilizing messengers, elicits Ca2+ release from lysosomes via the two pore channel 2 (TPC2) in many cell types. Here we found that overexpression of TPC2 in HeLa or mouse embryonic stem cells inhibited autophagosomal-lysosomal fusion, thereby resulting in the accumulation of autophagosomes. Treatment of TPC2 expressing cells with a cell permeant-NAADP agonist, NAADP-AM, further induced autophagosome accumulation. On the other hand, TPC2 knockdown or treatment of cells with Ned-19, a NAADP antagonist, markedly decreased the accumulation of autophagosomes. TPC2-induced accumulation of autophagosomes was also markedly blocked by ATG5 knockdown. Interestingly, inhibiting mTOR activity failed to increase TPC2-induced autophagosome accumulation. Instead, we found that overexpression of TPC2 alkalinized lysosomal pH, and lysosomal re-acidification abolished TPC2-induced autophagosome accumulation. In addition, TPC2 overexpression had no effect on general endosomal-lysosomal degradation but prevented the recruitment of Rab-7 to autophagosomes. Taken together, our data demonstrate that TPC2/NAADP/Ca2+ signaling alkalinizes lysosomal pH to specifically inhibit the later stage of basal autophagy progression.
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Affiliation(s)
- Yingying Lu
- Department of Physiology, University of Hong Kong, Hong Kong, China
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Wolfe DM, Lee JH, Kumar A, Lee S, Orenstein SJ, Nixon RA. Autophagy failure in Alzheimer's disease and the role of defective lysosomal acidification. Eur J Neurosci 2013; 37:1949-61. [PMID: 23773064 PMCID: PMC3694736 DOI: 10.1111/ejn.12169] [Citation(s) in RCA: 253] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 01/22/2013] [Accepted: 01/28/2013] [Indexed: 12/12/2022]
Abstract
Autophagy is a lysosomal degradative process which recycles cellular waste and eliminates potentially toxic damaged organelles and protein aggregates. The important cytoprotective functions of autophagy are demonstrated by the diverse pathogenic consequences that may stem from autophagy dysregulation in a growing number of neurodegenerative disorders. In many of the diseases associated with autophagy anomalies, it is the final stage of autophagy-lysosomal degradation that is disrupted. In several disorders, including Alzheimer's disease (AD), defective lysosomal acidification contributes to this proteolytic failure. The complex regulation of lysosomal pH makes this process vulnerable to disruption by many factors, and reliable lysosomal pH measurements have become increasingly important in investigations of disease mechanisms. Although various reagents for pH quantification have been developed over several decades, they are not all equally well suited for measuring the pH of lysosomes. Here, we evaluate the most commonly used pH probes for sensitivity and localisation, and identify LysoSensor yellow/blue-dextran, among currently used probes, as having the optimal profile of properties for measuring lysosomal pH. In addition, we review evidence that lysosomal acidification is defective in AD and extend our original findings, of elevated lysosomal pH in presenilin 1 (PS1)-deficient blastocysts and neurons, to additional cell models of PS1 and PS1/2 deficiency, to fibroblasts from AD patients with PS1 mutations, and to neurons in the PS/APP mouse model of AD.
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Affiliation(s)
- Devin M. Wolfe
- Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY, USA, 10962
| | - Ju-hyun Lee
- Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY, USA, 10962
- Department of Psychiatry, New York University, 550 First Ave, New York, NY, USA 10016
| | - Asok Kumar
- Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY, USA, 10962
- Department of Pathology, New York University, 550 First Ave, New York, NY, USA 10016
| | - Sooyeon Lee
- Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY, USA, 10962
| | - Samantha J. Orenstein
- Department of Developmental and Molecular Biology, Marion Bessin Liver Research Center, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx, NY, USA 10461
| | - Ralph A. Nixon
- Center for Dementia Research, Nathan S. Kline Institute, 140 Old Orangeburg Road, Orangeburg, NY, USA, 10962
- Department of Psychiatry, New York University, 550 First Ave, New York, NY, USA 10016
- Department of Cell Biology, New York University, 550 First Ave, New York, NY, USA 10016
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Lacruz RS, Brookes SJ, Wen X, Jimenez JM, Vikman S, Hu P, White SN, Lyngstadaas SP, Okamoto CT, Smith CE, Paine ML. Adaptor protein complex 2-mediated, clathrin-dependent endocytosis, and related gene activities, are a prominent feature during maturation stage amelogenesis. J Bone Miner Res 2013; 28:672-87. [PMID: 23044750 PMCID: PMC3562759 DOI: 10.1002/jbmr.1779] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Revised: 09/14/2012] [Accepted: 09/18/2012] [Indexed: 12/14/2022]
Abstract
Molecular events defining enamel matrix removal during amelogenesis are poorly understood. Early reports have suggested that adaptor proteins (AP) participate in ameloblast-mediated endocytosis. Enamel formation involves the secretory and maturation stages, with an increase in resorptive function during the latter. Here, using real-time PCR, we show that the expression of clathrin and adaptor protein subunits are upregulated in maturation stage rodent enamel organ cells. AP complex 2 (AP-2) is the most upregulated of the four distinct adaptor protein complexes. Immunolocalization confirms the presence of AP-2 and clathrin in ameloblasts, with strongest reactivity at the apical pole. These data suggest that the resorptive functions of enamel cells involve AP-2 mediated, clathrin-dependent endocytosis, thus implying the likelihood of specific membrane-bound receptor(s) of enamel matrix protein debris. The mRNA expression of other endocytosis-related gene products is also upregulated during maturation including: lysosomal-associated membrane protein 1 (Lamp1); cluster of differentiation 63 and 68 (Cd63 and Cd68); ATPase, H(+) transporting, lysosomal V0 subunit D2 (Atp6v0d2); ATPase, H(+) transporting, lysosomal V1 subunit B2 (Atp6v1b2); chloride channel, voltage-sensitive 7 (Clcn7); and cathepsin K (Ctsk). Immunohistologic data confirms the expression of a number of these proteins in maturation stage ameloblasts. The enamel of Cd63-null mice was also examined. Despite increased mRNA and protein expression in the enamel organ during maturation, the enamel of Cd63-null mice appeared normal. This may suggest inherent functional redundancies between Cd63 and related gene products, such as Lamp1 and Cd68. Ameloblast-like LS8 cells treated with the enamel matrix protein complex Emdogain showed upregulation of AP-2 and clathrin subunits, further supporting the existence of a membrane-bound receptor-regulated pathway for the endocytosis of enamel matrix proteins. These data together define an endocytotic pathway likely used by ameloblasts to remove the enamel matrix during enamel maturation.
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Affiliation(s)
- Rodrigo S Lacruz
- Center for Craniofacial Molecular Biology, Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, CA 90605, USA
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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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Abstract
Lysosomes, the terminal organelles on the endocytic pathway, digest macromolecules and make their components available to the cell as nutrients. Hydrolytic enzymes specific to a wide range of targets reside within the lysosome; these enzymes are activated by the highly acidic pH (between 4.5 and 5.0) in the organelles' interior. Lysosomes generate and maintain their pH gradients by using the activity of a proton-pumping V-type ATPase, which uses metabolic energy in the form of ATP to pump protons into the lysosome lumen. Because this activity separates electric charge and generates a transmembrane voltage, another ion must move to dissipate this voltage for net pumping to occur. This so-called counterion may be either a cation (moving out of the lysosome) or an anion (moving into the lysosome). Recent data support the involvement of ClC-7, a Cl(-)/H(+) antiporter, in this process, although many open questions remain as to this transporter's involvement. Although functional results also point to a cation transporter, its molecular identity remains uncertain. Both the V-ATPase and the counterion transporter are likely to be important players in the mechanisms determining the steady-state pH of the lysosome interior. Exciting new results suggest that lysosomal pH may be dynamically regulated in some cell types.
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Affiliation(s)
- Joseph A Mindell
- Membrane Transport Biophysics Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
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