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Altube MJ, Cutro A, Bakas L, Morilla MJ, Disalvo EA, Romero EL. Nebulizing novel multifunctional nanovesicles: the impact of macrophage-targeted-pH-sensitive archaeosomes on a pulmonary surfactant. J Mater Chem B 2017; 5:8083-8095. [PMID: 32264647 DOI: 10.1039/c7tb01694h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In this study, a NE-U22 vibrating mesh Omron nebulizer was used to deliver the Lissamine™ rhodamine B 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (Rh-PE) and 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS)/p-xylene-bis-pyridinium bromide (DPX) double-labelled macrophage-targeted pH-sensitive archaeosomes (ApH, 174 ± 48 nm, -30 ± 13 mV unilamellar nanovesicles made of dioleoyl-sn-glycero-3-phosphoethanolamine: [total polar archaeolipids from the hyperhalophile archaebacteria Halorubrum tebenquichense]: cholesteryl hemisuccinate 4.2 : 2.8 : 3 w : w : w) to J774A.1 cells covered by a Prosurf pulmonary surfactant (PS) monolayer at or below the equilibrium surface pressure πe. The uptake and cytoplasmic drug release from ApH were assessed by flow cytometry of Rh-PE and HPTS fluorescence, respectively. Despite being soft matter, nanovesicles are submitted to the dismantling interactions of shear stress of nebulization and contact with the surfactant barrier, and at least a fraction of nebulized ApH was found to be stable enough to execute higher cytoplasmic delivery than archaeolipid-lacking vesicles. Nebulized ApH increased the PS tensioactivity to just below πe, which was beyond the physiological range; this finding indicated that changes in lung surfactant function induced by nebulized nanovesicles were less likely to occur in vivo. The cytoplasmic delivery from ApH slightly decreased across monolayers at πe; this suggested that nanovesicles crossed the PS in a fashion inversely related to monolayer compression. Laurdan generalized polarization and fluorescence anisotropy were used to reveal that nanovesicles neither depleted B and C proteins of the PS nor increased the fluidity of the PS. Together with the feasibility of the cytoplasmic drug delivery upon nebulization, our results suggest that ApH are structurally unique nanovesicles that would not induce biophysical changes leading to PS inactivation and open the door to deeper future translational studies.
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Affiliation(s)
- Maria Julia Altube
- Nanomedicine Research Program-2, Science and Technology Department, National University of Quilmes, Bernal, Buenos Aires, Argentina.
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2
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Klemens CA, Edinger RS, Kightlinger L, Liu X, Butterworth MB. Ankyrin G Expression Regulates Apical Delivery of the Epithelial Sodium Channel (ENaC). J Biol Chem 2016; 292:375-385. [PMID: 27895120 DOI: 10.1074/jbc.m116.753616] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 11/11/2016] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) is the limiting entry point for Na+ reabsorption in the distal kidney nephron and is regulated by numerous hormones, including the mineralocorticoid hormone aldosterone. Previously we identified ankyrin G (AnkG), a cytoskeletal protein involved in vesicular transport, as a novel aldosterone-induced protein that can alter Na+ transport in mouse cortical collecting duct cells. However, the mechanisms underlying AnkG regulation of Na+ transport were unknown. Here we report that AnkG expression directly regulates Na+ transport by altering ENaC activity in the apical membrane. Increasing AnkG expression increased ENaC activity while depleting AnkG reduced ENaC-mediated Na+ transport. These changes were due to a change in ENaC directly rather than through alterations to the Na+ driving force created by Na+/K+-ATPase. Using a constitutively open mutant of ENaC, we demonstrate that the augmentation of Na+ transport is caused predominantly by increasing the number of ENaCs at the surface. To determine the mechanism of AnkG action on ENaC surface number, changes in rates of internalization, recycling, and membrane delivery were investigated. AnkG did not alter ENaC delivery to the membrane from biosynthetic pathways or removal by endocytosis. However, AnkG did alter ENaC insertion from constitutive recycling pathways. These findings provide a mechanism to account for the role of AnkG in the regulation of Na+ transport in the distal kidney nephron.
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Affiliation(s)
- Christine A Klemens
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Robert S Edinger
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Lindsay Kightlinger
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Xiaoning Liu
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Michael B Butterworth
- From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
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Lucas R, Yue Q, Alli A, Duke BJ, Al-Khalili O, Thai TL, Hamacher J, Sridhar S, Lebedyeva I, Su H, Tzotzos S, Fischer B, Gameiro AF, Loose M, Chakraborty T, Shabbir W, Aufy M, Lemmens-Gruber R, Eaton DC, Czikora I. The Lectin-like Domain of TNF Increases ENaC Open Probability through a Novel Site at the Interface between the Second Transmembrane and C-terminal Domains of the α-Subunit. J Biol Chem 2016; 291:23440-23451. [PMID: 27645999 DOI: 10.1074/jbc.m116.718163] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Indexed: 12/29/2022] Open
Abstract
Regulation of the epithelial sodium channel (ENaC), which regulates fluid homeostasis and blood pressure, is complex and remains incompletely understood. The TIP peptide, a mimic of the lectin-like domain of TNF, activates ENaC by binding to glycosylated residues in the extracellular loop of ENaC-α, as well as to a hitherto uncharacterized internal site. Molecular docking studies suggested three residues, Val567, Glu568, and Glu571, located at the interface between the second transmembrane and C-terminal domains of ENaC-α, as a critical site for binding of the TIP peptide. We generated Ala replacement mutants in this region of ENaC-α and examined its interaction with TIP peptide (3M, V567A/E568A/E571A; 2M, V567A/E568A; and 1M, E571A). 3M and 2M ENaC-α, but not 1M ENaC-α, displayed significantly reduced binding capacity to TIP peptide and to TNF. When overexpressed in H441 cells, 3M mutant ENaC-α formed functional channels with similar gating and density characteristics as the WT subunit and efficiently associated with the β and γ subunits in the plasma membrane. We subsequently assayed for increased open probability time and membrane expression, both of which define ENaC activity, following addition of TIP peptide. TIP peptide increased open probability time in H441 cells overexpressing wild type and 1M ENaC-α channels, but not 3M or 2M ENaC-α channels. On the other hand, TIP peptide-mediated reduction in ENaC ubiquitination was similar in cells overexpressing either WT or 3M ENaC-α subunits. In summary, this study has identified a novel site in ENaC-α that is crucial for activation of the open probability of the channel, but not membrane expression, by the lectin-like domain of TNF.
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Affiliation(s)
- Rudolf Lucas
- From the Vascular Biology Center, .,the Department of Pharmacology and Toxicology, and.,the Division of Pulmonary and Critical Care Medicine, Medical College of Georgia, Augusta, Georgia 30912
| | - Qiang Yue
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Abdel Alli
- the Department of Physiology, Emory University, Atlanta, Georgia 30322.,the Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida 32610
| | | | - Otor Al-Khalili
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Tiffany L Thai
- the Department of Physiology, Emory University, Atlanta, Georgia 30322
| | - Jürg Hamacher
- the Department of Pulmonology, Saarland University, D-66421 Homburg, Germany
| | | | - Iryna Lebedyeva
- the Department of Chemistry, Augusta University, Augusta, Georgia 30912
| | - Huabo Su
- From the Vascular Biology Center
| | - Susan Tzotzos
- Apeptico Research and Development, 1150 Vienna, Austria
| | | | | | - Maria Loose
- the Institute for Medical Microbiology, Justus-Liebig University, 35390 Giessen, Germany, and
| | - Trinad Chakraborty
- the Institute for Medical Microbiology, Justus-Liebig University, 35390 Giessen, Germany, and
| | - Waheed Shabbir
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Mohammed Aufy
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Rosa Lemmens-Gruber
- the Department of Pharmacology and Toxicology, University Vienna, 1010 Vienna, Austria
| | - Douglas C Eaton
- the Department of Physiology, Emory University, Atlanta, Georgia 30322,
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Hanukoglu I, Hanukoglu A. Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases. Gene 2016; 579:95-132. [PMID: 26772908 PMCID: PMC4756657 DOI: 10.1016/j.gene.2015.12.061] [Citation(s) in RCA: 250] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Revised: 12/20/2015] [Accepted: 12/22/2015] [Indexed: 01/24/2023]
Abstract
The epithelial sodium channel (ENaC) is composed of three homologous subunits and allows the flow of Na(+) ions across high resistance epithelia, maintaining body salt and water homeostasis. ENaC dependent reabsorption of Na(+) in the kidney tubules regulates extracellular fluid (ECF) volume and blood pressure by modulating osmolarity. In multi-ciliated cells, ENaC is located in cilia and plays an essential role in the regulation of epithelial surface liquid volume necessary for cilial transport of mucus and gametes in the respiratory and reproductive tracts respectively. The subunits that form ENaC (named as alpha, beta, gamma and delta, encoded by genes SCNN1A, SCNN1B, SCNN1G, and SCNN1D) are members of the ENaC/Degenerin superfamily. The earliest appearance of ENaC orthologs is in the genomes of the most ancient vertebrate taxon, Cyclostomata (jawless vertebrates) including lampreys, followed by earliest representatives of Gnathostomata (jawed vertebrates) including cartilaginous sharks. Among Euteleostomi (bony vertebrates), Actinopterygii (ray finned-fishes) branch has lost ENaC genes. Yet, most animals in the Sarcopterygii (lobe-finned fish) branch including Tetrapoda, amphibians and amniotes (lizards, crocodiles, birds, and mammals), have four ENaC paralogs. We compared the sequences of ENaC orthologs from 20 species and established criteria for the identification of ENaC orthologs and paralogs, and their distinction from other members of the ENaC/Degenerin superfamily, especially ASIC family. Differences between ENaCs and ASICs are summarized in view of their physiological functions and tissue distributions. Structural motifs that are conserved throughout vertebrate ENaCs are highlighted. We also present a comparative overview of the genotype-phenotype relationships in inherited diseases associated with ENaC mutations, including multisystem pseudohypoaldosteronism (PHA1B), Liddle syndrome, cystic fibrosis-like disease and essential hypertension.
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Affiliation(s)
- Israel Hanukoglu
- Laboratory of Cell Biology, Faculty of Natural Sciences, Ariel University, Ariel, Israel.
| | - Aaron Hanukoglu
- Division of Pediatric Endocrinology, E. Wolfson Medical Center, Holon, Israel; Sackler School of Medicine, Tel-Aviv University, Tel Aviv, Israel
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Czikora I, Alli A, Bao HF, Kaftan D, Sridhar S, Apell HJ, Gorshkov B, White R, Zimmermann A, Wendel A, Pauly-Evers M, Hamacher J, Garcia-Gabay I, Fischer B, Verin A, Bagi Z, Pittet JF, Shabbir W, Lemmens-Gruber R, Chakraborty T, Lazrak A, Matthay MA, Eaton DC, Lucas R. A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation. Am J Respir Crit Care Med 2014; 190:522-32. [PMID: 25029038 DOI: 10.1164/rccm.201405-0833oc] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
RATIONALE Alveolar liquid clearance is regulated by Na(+) uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na(+)-K(+)-ATPase in type II alveolar epithelial cells. Dysfunction of these Na(+) transporters during pulmonary inflammation can contribute to pulmonary edema. OBJECTIVES In this study, we sought to determine the precise mechanism by which the TIP peptide, mimicking the lectin-like domain of tumor necrosis factor (TNF), stimulates Na(+) uptake in a homologous cell system in the presence or absence of the bacterial toxin pneumolysin (PLY). METHODS We used a combined biochemical, electrophysiological, and molecular biological in vitro approach and assessed the physiological relevance of the lectin-like domain of TNF in alveolar liquid clearance in vivo by generating triple-mutant TNF knock-in mice that express a mutant TNF with deficient Na(+) uptake stimulatory activity. MEASUREMENTS AND MAIN RESULTS TIP peptide directly activates ENaC, but not the Na(+)-K(+)-ATPase, upon binding to the carboxy-terminal domain of the α subunit of the channel. In the presence of PLY, a mediator of pneumococcal-induced pulmonary edema, this binding stabilizes the ENaC-PIP2-MARCKS complex, which is necessary for the open probability conformation of the channel and preserves ENaC-α protein expression, by means of blunting the protein kinase C-α pathway. Triple-mutant TNF knock-in mice are more prone than wild-type mice to develop edema with low-dose intratracheal PLY, correlating with reduced pulmonary ENaC-α subunit expression. CONCLUSIONS These results demonstrate a novel TNF-mediated mechanism of direct ENaC activation and indicate a physiological role for the lectin-like domain of TNF in the resolution of alveolar edema during inflammation.
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Cerecedo D, Martínez-Vieyra I, Alonso-Rangel L, Benítez-Cardoza C, Ortega A. Epithelial sodium channel modulates platelet collagen activation. Eur J Cell Biol 2014; 93:127-36. [PMID: 24679405 DOI: 10.1016/j.ejcb.2014.02.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 01/30/2014] [Accepted: 02/24/2014] [Indexed: 12/14/2022] Open
Abstract
Activated platelets adhere to the exposed subendothelial extracellular matrix and undergo a rapid cytoskeletal rearrangement resulting in shape change and release of their intracellular dense and alpha granule contents to avoid hemorrhage. A central step in this process is the elevation of the intracellular Ca(2+) concentration through its release from intracellular stores and on throughout its influx from the extracellular space. The Epithelial sodium channel (ENaC) is a highly selective Na(+) channel involved in mechanosensation, nociception, fluid volume homeostasis, and control of arterial blood pressure. The present study describes the expression, distribution, and participation of ENaC in platelet migration and granule secretion using pharmacological inhibition with amiloride. Our biochemical and confocal analysis in suspended and adhered platelets suggests that ENaC is associated with Intermediate filaments (IF) and with Dystrophin-associated proteins (DAP) via α-syntrophin and β-dystroglycan. Migration assays, quantification of soluble P-selectin, and serotonin release suggest that ENaC is dispensable for migration and alpha and dense granule secretion, whereas Na(+) influx through this channel is fundamental for platelet collagen activation.
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Affiliation(s)
- Doris Cerecedo
- Laboratorio de Hematobiología, Escuela Nacional de Medicina y Homeopatía (ENMH), Instituto Politécnico Nacional (IPN), Mexico City, Mexico.
| | - Ivette Martínez-Vieyra
- Laboratorio de Hematobiología, Escuela Nacional de Medicina y Homeopatía (ENMH), Instituto Politécnico Nacional (IPN), Mexico City, Mexico
| | - Lea Alonso-Rangel
- Laboratorio de Hematobiología, Escuela Nacional de Medicina y Homeopatía (ENMH), Instituto Politécnico Nacional (IPN), Mexico City, Mexico
| | - Claudia Benítez-Cardoza
- Laboratorio de Bioquímica, Escuela Nacional de Medicina y Homeopatía (ENMH), Instituto Politécnico Nacional (IPN), Mexico City, Mexico
| | - Arturo Ortega
- Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del IPN (Cinvestav-IPN), Mexico City, Mexico
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Sasaki S, Yui N, Noda Y. Actin directly interacts with different membrane channel proteins and influences channel activities: AQP2 as a model. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:514-20. [PMID: 23770358 DOI: 10.1016/j.bbamem.2013.06.004] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Revised: 06/01/2013] [Accepted: 06/06/2013] [Indexed: 11/26/2022]
Abstract
The interplay between actin and 10 membrane channel proteins that have been shown to directly bind to actin are reviewed. The 10 membrane channel proteins covered in this review are aquaporin 2 (AQP2), cystic fibrosis transmembrane conductance regulator (CFTR), ClC2, short form of ClC3 (sClC3), chloride intracellular channel 1 (CLIC1), chloride intracellular channel 5 (CLIC5), epithelial sodium channel (ENaC), large-conductance calcium-activated potassium channel (Maxi-K), transient receptor potential vanilloid 4 (TRPV4), and voltage-dependent anion channel (VDAC), with particular attention to AQP2. In regard to AQP2, most reciprocal interactions between actin and AQP2 occur during intracellular trafficking, which are largely mediated through indirect binding. Actin and the actin cytoskeleton work as cables, barriers, stabilizers, and force generators for motility. However, as with ENaC, the effects of actin cytoskeleton on channel gating should be investigated further. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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Affiliation(s)
- Sei Sasaki
- Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
| | - Naofumi Yui
- Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8519, Japan
| | - Yumi Noda
- Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo 113-8519, Japan
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Kashlan OB, Kleyman TR. Epithelial Na(+) channel regulation by cytoplasmic and extracellular factors. Exp Cell Res 2012; 318:1011-9. [PMID: 22405998 DOI: 10.1016/j.yexcr.2012.02.024] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Accepted: 02/24/2012] [Indexed: 11/30/2022]
Abstract
Electrogenic Na(+) transport across high resistance epithelial is mediated by the epithelial Na(+) channel (ENaC). Our understanding of the mechanisms of ENaC regulation has continued to evolve over the two decades following the cloning of ENaC subunits. This review highlights many of the cellular and extracellular factors that regulate channel trafficking or gating.
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Affiliation(s)
- Ossama B Kashlan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
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9
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The plasma membrane potential and the organization of the actin cytoskeleton of epithelial cells. Int J Cell Biol 2012; 2012:121424. [PMID: 22315611 PMCID: PMC3272338 DOI: 10.1155/2012/121424] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2011] [Accepted: 10/08/2011] [Indexed: 12/22/2022] Open
Abstract
The establishment and maintenance of the polarized epithelial phenotype require a characteristic organization of the cytoskeletal components. There are many cellular effectors involved in the regulation of the cytoskeleton of epithelial cells. Recently, modifications in the plasma membrane potential (PMP) have been suggested to participate in the modulation of the cytoskeletal organization of epithelia. Here, we review evidence showing that changes in the PMP of diverse epithelial cells promote characteristic modifications in the cytoskeletal organization, with a focus on the actin cytoskeleton. The molecular paths mediating these effects may include voltage-sensitive integral membrane proteins and/or peripheral proteins sensitive to surface potentials. The voltage dependence of the cytoskeletal organization seems to have implications in several physiological processes, including epithelial wound healing and apoptosis.
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Fan Q, Wang YE, Zhao X, Loo JSC, Zuo YY. Adverse biophysical effects of hydroxyapatite nanoparticles on natural pulmonary surfactant. ACS NANO 2011; 5:6410-6. [PMID: 21761867 PMCID: PMC4854525 DOI: 10.1021/nn2015997] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Inhaled nanoparticles (NPs) must first interact with the pulmonary surfactant (PS) lining layer that covers the entire internal surface of the respiratory tract and plays an important role in surface tension reduction and host defense. Interactions with the PS film determine the subsequent clearance, retention, and translocation of the inhaled NPs and hence their potential toxicity. To date, little is known how NPs interact with PS, and whether or not NPs have adverse effects on the biophysical function of PS. We found a time-dependent toxicological effect of hydroxyapatite NPs (HA-NPs) on a natural PS, Infasurf, and the time scale of surfactant inhibition after particle exposure was comparable to the turnover period of surfactant metabolism. Using a variety of in vitro biophysicochemical characterization techniques, we have determined the inhibition mechanism to be due to protein adsorption onto the HA-NPs. Consequently, depletion of surfactant proteins from phospholipid vesicles caused conversion of original large vesicles into much smaller vesicles with poor surface activity. These small vesicles, in turn, inhibited biophysical function of surfactant films after adsorption at the air-water interface. Cytotoxicity study found that the HA-NPs at the studied concentration were benign to human bronchial epithelial cells, thereby highlighting the importance of evaluating biophysical effect of NPs on PS. The NP-PS interaction mechanism revealed by this study may not only provide new insight into the toxicological study of nanoparticles but also shed light on the feasibility of NP-based pulmonary drug delivery.
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Affiliation(s)
- Qihui Fan
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
| | - Yi E. Wang
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
| | - Xinxin Zhao
- School of Materials Science & Engineering, Nanyang Technological University, Singapore 639798
| | - Joachim S. C. Loo
- School of Materials Science & Engineering, Nanyang Technological University, Singapore 639798
| | - Yi Y. Zuo
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
- Address correspondence to
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Assef YA, Ozu M, Marino GI, Galizia L, Kotsias BA. ENaC channels in oocytes from Xenopus laevis and their regulation by xShroom1 protein. Cell Physiol Biochem 2011; 28:259-66. [PMID: 21865733 DOI: 10.1159/000331738] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/08/2011] [Indexed: 11/19/2022] Open
Abstract
Shroom is a family of related proteins linked to the actin cytoskeleton. xShroom1 is constitutively expressed in X. oocytes and is required for the expression of amiloride sensitive sodium channels (ENaC). Oocytes were injected with α, β, and γ mENaC and xShroom1 sense or antisense oligonucleotides. We used voltage clamp techniques to study the amiloride-sensitive Na(+) currents (INa((amil))). We observed a marked reduction in INa((amil)) in oocytes co-injected with xShroom1 antisense. Oocytes expressing a DEG mutant β-mENaC subunit (β-S518K) with an open probability of 1 had enhanced INa((amil)) although these currents were also reduced when co-injected with xShroom1 antisense. Addition of low concentration (20 ng/ml) of trypsin which activates the membrane-resident ENaC channels led to a slow increase in INa((amil)) in oocytes with xShroom1 sense but had no effect on the currents in oocytes coinjected with ENaC and xShroom1 antisense. The same results were obtained with higher concentrations of trypsin (2 μg/ml) exposed during 2.5 min. In addition, fluorescence positive staining of plasma membrane in the oocytes expressing α, β and γ mENaC and xShroom1 sense were observed but not in oocytes coinjected with ENaC and xShroom1 antisense oligonucleotides. On this basis, we suggest that xShroom1-dependent ENaC inhibition may be through the number of channels inserted in the membrane.
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Affiliation(s)
- Yanina A Assef
- Laboratorio de Canales Iónicos, Instituto de Investigaciones Médicas Alfredo Lanari, University of Buenos Aires, IDIM- CONICET, Buenos Aires, Argentina
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Sarker M, Rose J, McDonald M, Morrow MR, Booth V. Modifications to surfactant protein B structure and lipid interactions under respiratory distress conditions: consequences of tryptophan oxidation. Biochemistry 2010; 50:25-36. [PMID: 21128671 DOI: 10.1021/bi101426s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
These studies detail the altered structure-function relationships caused by oxidation of surfactant protein B (SP-B), a mode of damage thought to be important in acute respiratory distress syndrome (ARDS), a common and frequently fatal condition. An 18-residue fragment comprising the N-terminal helix of SP-B was investigated in oxidized and unmodified forms by solution and solid-state nuclear magnetic resonance (NMR), circular dichroism (CD), and molecular dynamics (MD) simulation. Taken together, the results indicate that tryptophan oxidation causes substantial disruptions in helical structure and lipid interactions. The structural modifications induced by tryptophan oxidation were severe, with a reduction in helical extent from approximately three helical turns to, at most, one turn, and were observed in a variety of solvent environments, including sodium dodecyl sulfate (SDS) micelles, dodecyl phosphocholine (DPC) micelles, and a 40% hexafluoro-2-propanol (HFIP) aqueous solution. The unmodified peptide takes on an orientation within lipid bilayers that is tilted approximately 30° away from an in-plane position. Tryptophan oxidation causes significant modifications to the peptide-lipid interactions, and the peptide likely shifts to a more in-plane orientation within the lipids. Interestingly, the character of the disruptions to peptide-lipid interactions caused by tryptophan oxidation was highly dependent on the charge of the lipid headgroup.
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Affiliation(s)
- Muzaddid Sarker
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, Canada
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13
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Intact cytoskeleton is required for small G protein dependent activation of the epithelial Na+ channel. PLoS One 2010; 5:e8827. [PMID: 20098689 PMCID: PMC2809106 DOI: 10.1371/journal.pone.0008827] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Accepted: 01/04/2010] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND The Epithelial Na(+) Channel (ENaC) plays a central role in control of epithelial surface hydration and vascular volume. Similar to other ion channels, ENaC activity is regulated, in part, by cortical cytoskeleton. Besides, the cytoskeleton is an established target for small G proteins signaling. Here we studied whether ENaC activity is modulated by changes in the state of the cytoskeleton and whether cytoskeletal elements are involved in small G protein mediated increase of ENaC activity. METHODS AND FINDINGS First, the functional importance of the cytoskeleton was established with whole-cell patch clamp experiments recording ENaC reconstituted in CHO cells. Pretreatment with Cytochalasin D (CytD; 10 microg/ml; 1-2 h) or colchicine (500 microM; 1-3 h) to disassembly F-actin and destroy microtubules, respectively, significantly decreased amiloride sensitive current. However, acute application of CytD induced rapid increase in macroscopic current. Single channel measurements under cell-attached conditions revealed similar observations. CytD rapidly increased ENaC activity in freshly isolated rat collecting duct, polarized epithelial mouse mpkCCD(c14) cells and HEK293 cells transiently transfected with ENaC subunits. In contrast, colchicine did not have an acute effect on ENaC activity. Small G proteins RhoA, Rac1 and Rab11a markedly increase ENaC activity. 1-2 h treatment with colchicine or CytD abolished effects of these GTPases. Interestingly, when cells were coexpressed with ENaC and RhoA, short-term treatment with CytD decreased ENaC activity. CONCLUSIONS We conclude that cytoskeleton is involved in regulation of ENaC and is necessary for small G protein mediated increase of ENaC activity.
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Simon A, Shenton F, Hunter I, Banks RW, Bewick GS. Amiloride-sensitive channels are a major contributor to mechanotransduction in mammalian muscle spindles. J Physiol 2009; 588:171-85. [PMID: 19917568 DOI: 10.1113/jphysiol.2009.182683] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
We investigated whether channels of the epithelial sodium/amiloride-sensitive degenerin (ENaC/DEG) family are a major contributor to mechanosensory transduction in primary mechanosensory afferents, using adult rat muscle spindles as a model system. Stretch-evoked afferent discharge was reduced in a dose-dependent manner by amiloride and three analogues - benzamil, 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and hexamethyleneamiloride (HMA), reaching > or = 85% inhibition at 1 mm. Moreover, firing was slightly but significantly increased by ENaC delta subunit agonists (icilin and capsazepine). HMA's profile of effects was distinct from that of the other drugs. Amiloride, benzamil and EIPA significantly decreased firing (P < 0.01 each) at 1 microm, while 10 microm HMA was required for highly significant inhibition (P < 0.0001). Conversely, amiloride, benzamil and EIPA rarely blocked firing entirely at 1 mm, whereas 1 mm HMA blocked 12 of 16 preparations. This pharmacology suggests low-affinity ENaCs are the important spindle mechanotransducer. In agreement with this, immunoreactivity to ENaC alpha, beta and gamma subunits was detected both by Western blot and immunocytochemistry. Immunofluorescence intensity ratios for ENaC alpha, beta or gamma relative to the vesicle marker synaptophysin in the same spindle all significantly exceeded controls (P < 0.001). Ratios for the related brain sodium channel ASIC2 (BNaC1alpha) were also highly significantly greater (P < 0.005). Analysis of confocal images showed strong colocalisation within the terminal of ENaC/ASIC2 subunits and synaptophysin. This study implicates ENaC and ASIC2 in mammalian mechanotransduction. Moreover, within the terminals they colocalise with synaptophysin, a marker for the synaptic-like vesicles which regulate afferent excitability in these mechanosensitive endings.
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Affiliation(s)
- Anna Simon
- School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
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16
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Del Mónaco SM, Marino GI, Assef YA, Damiano AE, Kotsias BA. Cell migration in BeWo cells and the role of epithelial sodium channels. J Membr Biol 2009; 232:1-13. [PMID: 19911219 DOI: 10.1007/s00232-009-9206-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Accepted: 09/23/2009] [Indexed: 01/08/2023]
Abstract
Cell migration/proliferation processes associated with wound healing were measured in BeWo cells at 6 h, when mitosis is still scarce. Cells were cultured in medium with 1% fetal bovine serum to minimize proliferation. BeWo cell migration covered 20.6 +/- 7.0%, 38.0 +/- 5.4%, 16.6 +/- 4.8% and 13.7 +/- 3.6% of the wound when cultivated under control, aldosterone (100 nM, 12 h), aldosterone plus amiloride (10 muM) and amiloride treatments, respectively. When BeWo cells were treated with aldosterone, there was an increase in wound healing (P < 0.05), which was prevented by adding the ENaC blocker amiloride (P < 0.05, n = 16). Immunocytochemistry studies showed that the three ENaC subunits showed greater expression at the leading edge of the wound 3 h after injury, supporting the notion that these proteins participate in a postinjury signal. Antisense oligonucleotides directed against the alpha-ENaC subunit decreased the migratory response of the cells compared to the sense treated cells or the cells without oligonucleotides (P < 0.001, n = 16): 30.2 +/- 3.7%, 17.6 +/- 1.3%, 27.5 +/- 1.5% and 20.2 +/- 1.5% reinvasion of the wound with aldosterone, aldosterone plus antisense, aldosterone plus sense treatments and control conditions, respectively. Aldosterone and amiloride influence wound healing in BeWo cells, probably by their effects upon ENaCs, transmitting a signal to the cell cytoplasm for the release of several agents that promote cell migration.
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Affiliation(s)
- Silvana M Del Mónaco
- Laboratorio de Canales Iónicos, Instituto de Investigaciones Médicas A. Lanari, Universidad de Buenos Aires, C. de Malvinas 3150, 1427 Buenos Aires, Argentina
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17
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Saad SMI, Policova Z, Acosta EJ, Hair ML, Neumann AW. Mixed DPPC/DPPG monolayers at very high film compression. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:10907-10912. [PMID: 19507830 DOI: 10.1021/la901250z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A drop shape technique using a constrained sessile drop constellation (ADSA-CSD) has been introduced as a superior technique for studying spread films specially at high collapse pressures [Saad et al. Langmuir 2008, 24, 10843-10850]. It has been shown that ADSA-CSD has certain advantages including the need only for small quantities of liquid and insoluble surfactants, the ability to measure very low surface tension values, easier deposition procedure, and leak-proof design. Here, this technique was applied to investigate mixed DPPC/DPPG monolayers to characterize the role of such molecules in maintaining stable film properties and surface activity of lung surfactant preparations. Results of compression isotherms were obtained for different DPPC/DPPG mixture ratios: 90/10, 80/20, 70/30, 60/40, and 50/50 in addition to pure DPPC and pure DPPG at room temperature of 24 degrees C. The ultimate collapse pressure of DPPC/DPPG mixtures was found to be 70.5 mJ/m2 (similar to pure DPPC) for the cases of low DPPG content (up to 20%). Increasing the DPPG content in the mixture (up to 40%) caused a slight decrease in the ultimate collapse pressure. However, further increase of DPPG in the mixture (50% or more) caused a sharp decrease in the ultimate collapse pressure to a value of 59.9 mJ/m2 (similar to pure DPPG). The change in film elasticity was also tracked for the range of mixture ratios studied. The physical reasons for such changes and the interaction between DPPC and DPPG molecules are discussed. The results also show a change in the film hysteresis upon successive compression and expansion cycles for different mixture ratios.
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Affiliation(s)
- Sameh M I Saad
- Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, Ontario, Canada M5S 3G8
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18
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Vandivier RW, Richens TR, Horstmann SA, deCathelineau AM, Ghosh M, Reynolds SD, Xiao YQ, Riches DW, Plumb J, Vachon E, Downey GP, Henson PM. Dysfunctional cystic fibrosis transmembrane conductance regulator inhibits phagocytosis of apoptotic cells with proinflammatory consequences. Am J Physiol Lung Cell Mol Physiol 2009; 297:L677-86. [PMID: 19633071 DOI: 10.1152/ajplung.00030.2009] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Cystic fibrosis (CF) is caused by mutated CF transmembrane conductance regulator (CFTR) and is characterized by robust airway inflammation and accumulation of apoptotic cells. Phagocytosis of apoptotic cells (efferocytosis) is a pivotal regulator of inflammation, because it prevents postapoptotic necrosis and actively suppresses release of a variety of proinflammatory mediators, including IL-8. Because CF is associated with accumulation of apoptotic cells, inappropriate levels of IL-8, and robust inflammation, we sought to determine whether CFTR deficiency specifically impairs efferocytosis and its regulation of inflammatory mediator release. Here we show that CFTR deficiency directly interferes with efferocytosis by airway epithelium, an effect that is not due to altered binding of apoptotic cells to epithelial cells or altered expression of efferocytosis receptors. In contrast, expression of RhoA, a known negative regulator of efferocytosis, is substantially increased in CFTR-deficient cells, and inhibitors of RhoA or its downstream effector Rho kinase normalize efferocytosis in these cells. Impaired efferocytosis appears to be mediated through an amiloride-sensitive ion channel, because amiloride restores phagocytic competency in CFTR-deficient cells. Finally, ineffective efferocytosis in CFTR-deficient cells appears to have proinflammatory consequences, because apoptotic cells enhance IL-8 release by these cells, but not by wild-type controls. Therefore, in CF, dysregulated efferocytosis may lead to accumulation of apoptotic cells and impaired regulation of the inflammatory response and, ultimately, may suggest a new therapeutic target.
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Affiliation(s)
- R William Vandivier
- Division of Pulmonary Sciences and Critical Care Medicine, Univ. of Colorado Denver, Research Bldg. 2, 12700 E. 19th Ave. Box C272, Aurora, CO 80045, USA.
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19
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ENaC Proteins in Vascular Smooth Muscle Mechanotransduction. CURRENT TOPICS IN MEMBRANES 2007; 59:127-53. [DOI: 10.1016/s1063-5823(06)59006-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/05/2023]
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Mazzochi C, Benos DJ, Smith PR. Interaction of epithelial ion channels with the actin-based cytoskeleton. Am J Physiol Renal Physiol 2006; 291:F1113-22. [PMID: 16926444 DOI: 10.1152/ajprenal.00195.2006] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The interaction of ion channels with the actin-based cytoskeleton in epithelial cells not only maintains the polarized expression of ion channels within specific membrane domains, it also functions in the intracellular trafficking and regulation of channel activity. Initial evidence supporting an interaction between epithelial ion channels and the actin-based cytoskeleton came from patch-clamp studies examining the effects of cytochalasins on channel activity. Cytochalasins were shown to either activate or inactivate epithelial ion channels. An interaction between the actin-based cytoskeleton and epithelial ion channels was further supported by the fact that the addition of monomeric or filamentous actin to excised patches had an effect on channel activity comparable to that of cytochalasins. Through the recent application of molecular and proteomic approaches, we now know that the interactions between epithelial ion channels and actin can either be direct or indirect, the latter being mediated through scaffolding or actin-binding proteins that serve as links between the channels and the actin-based cytoskeleton. This review discusses recent advances in our understanding of the interactions between epithelial ion channels and the actin-based cytoskeleton, and the roles these interactions play in regulating the cell surface expression, activity, and intracellular trafficking of epithelial ion channels.
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Affiliation(s)
- C Mazzochi
- Department of Cell Biology, MCLM 704, University of Alabama at Birmingham, 1530 3rd Ave. South, Birmingham, AL 35294-0005, USA
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21
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Satlin LM, Carattino MD, Liu W, Kleyman TR. Regulation of cation transport in the distal nephron by mechanical forces. Am J Physiol Renal Physiol 2006; 291:F923-31. [PMID: 16849691 DOI: 10.1152/ajprenal.00192.2006] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Thiazide and loop diuretics induce renal K(+) secretion, often leading to renal K(+) wasting and hypokalemia. This phenomenon has been proposed to reflect an increase in delivery to and reabsorption of Na(+) by the distal nephron, with a resultant increase in the driving force for passive K(+) efflux across the apical membrane. Recent studies suggest that cellular mechanisms that lead to enhanced rates of Na(+) reabsorption as well as K(+) secretion in response to increases tubular flow rates are more complex. Increases in tubular flow rates directly enhance the activity of apical membrane Na(+) channels and indirectly activate a class of K(+) channels, referred to as maxi-K, that are functionally inactive under low flow states. This review addresses the role of biomechanical forces, generated by variations in urinary flow rate and tubular fluid volume, in the regulation of transepithelial Na(+) and K(+) transport in the distal nephron. The question of why the distal nephron has evolved to include a component of flow-dependent K(+) secretion is also addressed.
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Affiliation(s)
- Lisa M Satlin
- Renal-Electrolyte Div, Univ. of Pittsburgh, A919 Scaife Hall, 3550 Terrace St, Pittsburgh, PA 15261, USA
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22
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Mazzochi C, Bubien JK, Smith PR, Benos DJ. The carboxyl terminus of the alpha-subunit of the amiloride-sensitive epithelial sodium channel binds to F-actin. J Biol Chem 2005; 281:6528-38. [PMID: 16356937 DOI: 10.1074/jbc.m509386200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activity of the amiloride-sensitive epithelial sodium channel (ENaC) is modulated by F-actin. However, it is unknown if there is a direct interaction between alpha-ENaC and actin. We have investigated the hypothesis that the actin cytoskeleton directly binds to the carboxyl terminus of alpha-ENaC using a combination of confocal microscopy, co-immunoprecipitation, and protein binding studies. Confocal microscopy of Madin-Darby canine kidney cell monolayers stably transfected with wild type, rat isoforms of alpha-, beta-, and gamma-ENaC revealed co-localization of alpha-ENaC with the cortical F-actin cytoskeleton both at the apical membrane and within the subapical cytoplasm. F-actin was found to co-immunoprecipitate with alpha-ENaC from whole cell lysates of this cell line. Gel overlay assays demonstrated that F-actin specifically binds to the carboxyl terminus of alpha-ENaC. A direct interaction between F-actin and the COOH terminus of alpha-ENaC was further corroborated by F-actin co-sedimentation studies. This is the first study to report a direct and specific biochemical interaction between F-actin and ENaC.
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Affiliation(s)
- Christopher Mazzochi
- Department of Physiology and Biophysics and Department of Cell Biology, The University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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23
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Chifflet S, Hernández JA, Grasso S. A possible role for membrane depolarization in epithelial wound healing. Am J Physiol Cell Physiol 2005; 288:C1420-30. [PMID: 15897322 DOI: 10.1152/ajpcell.00259.2004] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Linear narrow wounds produced on cultured bovine corneal endothelial monolayers heal by actin cable formation at the wound border and lamellar crawling of cells into the injured area. We report the novel finding that membrane potential depolarization occurs at the leading edge of wounds and gradually extends inward toward the neighboring cells. We have determined that the replacement of extracellular Na+by choline and the incorporation of phenamil, an inhibitor of the epithelial Na+channel (ENaC), provoke a decrease in the actin cable and depolarization areas and in the lamellar activity of the wound edges. To the contrary, extracellular Li+can successfully replace Na+in the determination of the depolarization and cytoskeletal responses. This finding supports the idea that membrane depolarization, not the increase in intracellular Na+concentration, is responsible for the formation of the actin cable, a result that is in agreement with previous evidence showing that nonspecific depolarization of the plasma membrane potential (PMP) of epithelial cells may promote characteristic cytoskeletal rearrangements per se (Chifflet S, Hernández JA, Grasso S, and Cirillo A. Exp Cell Res 282: 1–13, 2003). We suggest that spontaneous depolarization of the PMP of the cells at the wound borders determined by a rise in the ENaC activity of these cells constitutes an additional factor in the intermediate cellular processes leading to wound healing in some epithelia.
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Affiliation(s)
- Silvia Chifflet
- Departomento de Bioquímica, Facultad de Medicina, Universidad de la República, Gral Flores 2125, 11800 Montevideo, Uruguay.
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24
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Kashlan OB, Sheng S, Kleyman TR. On the interaction between amiloride and its putative alpha-subunit epithelial Na+ channel binding site. J Biol Chem 2005; 280:26206-15. [PMID: 15908426 DOI: 10.1074/jbc.m503500200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epithelial Na+ channel (ENaC) belongs to the structurally conserved ENaC/Degenerin superfamily. These channels are blocked by amiloride and its analogues. Several amino acid residues have been implicated in amiloride binding. Primary among these are alphaSer-583, betaGly-525, and gammaGly-542, which are present at a homologous site within the three subunits of ENaC. Mutations of the beta and gamma glycines greatly weakened amiloride block, but, surprisingly, mutation of the serine of the alpha subunit resulted in moderate (<5-fold) weakening of amiloride K(i). We investigated the role of alphaSer-583 in amiloride binding by systematically mutating alphaSer-583 and analyzing the mutant channels with two-electrode voltage clamp. We observed that most mutations had moderate effects on amiloride block, whereas those introducing rings showed dramatic effects on amiloride block. In addition, mutations introducing a beta-methyl group at this site altered the electric field of ENaC, affecting both amiloride binding and the voltage dependence of channel gating. We also found that the His mutation, in addition to greatly weakening amiloride binding, appends a voltage-sensitive gate within the pore of ENaC at low pH. Because diverse residues at alpha583, such as Asn, Gln, Ser, Gly, Thr, and Ala, have similar amiloride binding affinities, our results suggest that the wild type Ser side chain is not important for amiloride binding. However, given that some alphaSer-583 mutations affect the electrical properties of the channel whereas those introducing rings greatly weaken amiloride block, we conclude that amiloride binds at or near this site and that alphaSer-583 may have a role in ion permeation through ENaC.
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Affiliation(s)
- Ossama B Kashlan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pennsylvania 15261, USA
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25
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Butterworth MB, Edinger RS, Johnson JP, Frizzell RA. Acute ENaC stimulation by cAMP in a kidney cell line is mediated by exocytic insertion from a recycling channel pool. ACTA ACUST UNITED AC 2005; 125:81-101. [PMID: 15623897 PMCID: PMC2217480 DOI: 10.1085/jgp.200409124] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Acute hormonal regulation of the epithelial sodium channel (ENaC) in tight epithelia increases transcellular Na+ transport via trafficking of intracellular channels to the apical surface. The fate of the channels removed from the apical surface following agonist washout is less clear. By repetitively stimulating polarized mouse cortical collecting duct (mCCD, MPKCCD14) epithelia, we evaluated the hypothesis that ENaC recycles through an intracellular pool to be available for reinsertion into the apical membrane. Short circuit current (ISC), membrane capacitance (CT), and conductance (GT) were recorded from mCCD epithelia mounted in modified Ussing chambers. Surface biotinylation of ENaC demonstrated an increase in channel number in the apical membrane following cAMP stimulation. This increase was accompanied by a 83 ± 6% (n = 31) increase in ISC and a 15.3 ± 1.5% (n = 15) increase in CT. Selective membrane permeabilization demonstrated that the CT increase was due to an increase in apical membrane capacitance. ISC and CT declined to basal levels on stimulus washout. Repetitive cAMP stimulation and washout (∼1 h each cycle) resulted in response fatigue; ΔISC decreased ∼10% per stimulation–recovery cycle. When channel production was blocked by cycloheximide, ΔISC decreased ∼15% per stimulation cycle, indicating that newly synthesized ENaC contributed a relatively small fraction of the channels mobilized to the apical membrane. Selective block of surface ENaC by benzamil demonstrated that channels inserted from a subapical pool made up >90% of the stimulated ISC, and that on restimulation a large proportion of channels retrieved from the apical surface were reinserted into the apical membrane. Channel recycling was disrupted by brefeldin A, which inhibited ENaC exocytosis, by chloroquine, which inhibited ENaC endocytosis and recycling, and by latrunculin A, which blocked ENaC exocytosis. A compartment model featuring channel populations in the apical membrane and intracellular recycling pool provided an adequate kinetic description of the ISC responses to repetitive stimulation. The model supports the concept of ENaC recycling in response to repetitive cAMP stimulation.
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Affiliation(s)
- Michael B Butterworth
- Department of Cell Biology and Physiology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA.
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26
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Mirshamsi S, Laidlaw HA, Spanswick D, Ashford MLJ. Activation of hypothalamic ATP-sensitive K+ channels by the aminoguanidine carboxylate BVT.12777. J Neuroendocrinol 2005; 17:246-54. [PMID: 15842236 DOI: 10.1111/j.1365-2826.2005.01299.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Derivatives of 3-guanidinopropionic acid, such as leptin, reduce body weight in obese, diabetic mice. We have assessed whether one of these analogues, BVT.12777 activates intracellular signalling pathways in the arcuate nucleus in a manner analogous to leptin and insulin. In addition, because these hormones have been shown to activate K(ATP) channels in a subset of arcuate neurones, we examined whether this channel is also a functional endpoint for BVT.12777 in the arcuate nucleus. BVT.12777 transiently increased phosphorylation of MAPK, STAT3, PKB and GSK3, in a manner identical to that observed for leptin and insulin. BVT.12777 also hyperpolarized glucose-responsive neurones by increasing the activity of K(ATP) channels. The increase in K(ATP) activity driven by BVT.12777 was PI3-kinase independent, unlike leptin and insulin activation of this channel, and could also be elicited in isolated patches. However, K(ATP) activity induced by BVT.12777 was dependent on actin filament dynamics, both in intact neurones and isolated patches. Thus, BVT.12777 modulates arcuate neurone K(ATP) activity by re-organization of the cytoskeleton, a mechanism that has also been ascribed to leptin and insulin. Consequently, BVT.12777 appears to act as a leptin and insulin mimetic with respect to at least some elements of arcuate neurone intracellular signalling and the activation of K(ATP) channels. Resistance to leptin and insulin, associated with obesity has, at least in part, been postulated to be due to aberrant intracellular signalling in arcuate neurones. The data presented here indicate that it may be possible to develop drugs, which by-pass up-stream signalling components associated with adiposity hormone resistance, such as PI3-kinase, but can still induce functional outputs from arcuate neurones by targeting downstream components of the leptin and insulin signalling cascades.
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Affiliation(s)
- S Mirshamsi
- Division of Pathology and Neuroscience, University of Dundee, Ninewells Hospital and Medical School, Dundee, UK
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27
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Carattino MD, Sheng S, Kleyman TR. Mutations in the Pore Region Modify Epithelial Sodium Channel Gating by Shear Stress. J Biol Chem 2005; 280:4393-401. [PMID: 15569663 DOI: 10.1074/jbc.m413123200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies have shown that epithelial Na+ channels (ENaCs) are activated by laminar shear stress (LSS). ENaCs with a high intrinsic open probability because of a mutation (betaS518K) or covalent modification of an introduced Cys residue (alphaS580C) in the pre-second transmembrane domain (pre-M2) were not activated by LSS, suggesting that the pre-M2 region participates in conformational rearrangements during channel activation. We examined the role of the pore region of the alpha-subunit in channel gating by studying the kinetics of activation by LSS of wild-type ENaC and channels with Cys mutations in the tract Ser576-Ser592. Whole cell Na+ currents were monitored in oocytes expressing wild-type or mutant ENaCs prior to and following application of LSS. Following a 2.2-s delay, a monoexponential increase in Na+ currents was observed with a time constant (tau) of 8.1 s in oocytes expressing wild-type ENaC. Cys substitutions within the alpha-subunit in the tract Ser580-Ser589 resulted in: (i) a reduction (Ser580-Trp585, Gly587) or increase (Ser589) in delay times preceding channel activation by LSS, (ii) an increase (Gln581, Leu584, Trp585, Phe586, Ser588) or decrease (Ser589) in the rate of channel activation, or (iii) a decrease in the magnitude of the response (Ser583, Gly587, Leu584). Cys substitutions at a putative amiloride-binding site (alphaSer583 or betaGly525) or within the selectivity filter (alphaGly587) resulted in a reduction in the LSS response, and exhibited a multiexponential time course of activation. The corresponding gamma-subunit mutant (alphabetagammaG542C) had a minimal response to LSS and exhibited a high intrinsic open probability. These data suggest that residues in the pore region participate in the sensing and/or transduction of the mechanical stimulus that results in channel activation and are consistent with the hypothesis that the ENaC pore region has a key role in modulating channel gating.
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Affiliation(s)
- Marcelo D Carattino
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, PA 15231, USA
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28
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Staruschenko A, Nichols A, Medina JL, Camacho P, Zheleznova NN, Stockand JD. Rho small GTPases activate the epithelial Na(+) channel. J Biol Chem 2004; 279:49989-94. [PMID: 15448132 DOI: 10.1074/jbc.m409812200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Small G proteins in the Rho family are known to regulate diverse cellular processes, including cytoskeletal organization and cell cycling, and more recently, ion channel activity and activity of phosphatidylinositol 4-phosphate 5-kinase (PI(4)P 5-K). The present study investigates regulation of the epithelial Na(+) channel (ENaC) by Rho GTPases. We demonstrate here that RhoA and Rac1 markedly increase ENaC activity. Activation by RhoA was suppressed by the C3 exoenzyme. Inhibition of the downstream RhoA effector Rho kinase, which is necessary for RhoA activation of PI(4)P 5-K, abolished ENaC activation. Similar to RhoA, overexpression of PI(4)P 5-K increased ENaC activity suggesting that production of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) in response to RhoA-Rho kinase signaling stimulates ENaC. Supporting this idea, inhibition of phosphatidylinositol 4-kinase, but not the RhoA effector phosphatidylinositol 3-kinase and MAPK cascades, markedly attenuated RhoA-dependent activation of ENaC. RhoA increased ENaC activity by increasing the plasma membrane levels of this channel. We conclude that RhoA activates ENaC via Rho kinase and subsequently activates PI(4)P 5-K with concomitant increases in PI(4,5)P(2) levels promoting channel insertion into the plasma membrane.
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Affiliation(s)
- Alexander Staruschenko
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA.
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29
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Berdiev BK, Jovov B, Tucker WC, Naren AP, Fuller CM, Chapman ER, Benos DJ. ENaC subunit-subunit interactions and inhibition by syntaxin 1A. Am J Physiol Renal Physiol 2004; 286:F1100-6. [PMID: 14996668 DOI: 10.1152/ajprenal.00344.2003] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Amiloride-sensitive epithelial Na+ channels (ENaCs) are subject to modulation by many factors. Recent data have also linked the N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) machinery to this regulation of ENaC, but the molecular mechanisms that underlie this modulation are poorly understood. In this study, we demonstrate that syntaxin 1A physically interacts with ENaC and functionally regulates ENaC activity. Syntaxin 1A was able to coimmunoprecipitate in vitro-translated γ-ENaC, but not α- or β-ENaC. Also, using antibodies raised against α-, β-, or γ-ENaC, we detected syntaxin 1A in immunoprecipitates from Madin-Darby canine kidney cells stably transfected with αβγ-ENaC. In bilayers, syntaxin 1A inhibited ENaC, and this syntaxin 1A modulation of ENaC activity was eliminated by truncations of cytoplasmic domains of the ENaC subunits. Our findings provide evidence for a direct physical interaction between ENaC and syntaxin 1A and suggest involvement of ENaC's cytoplasmic domains in functional modulation of ENaC activity by syntaxin 1A.
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Affiliation(s)
- Bakhrom K Berdiev
- Univ. of Alabama at Birmingham, 1918 University Blvd., MCLM 704, Birmingham, AL 35294-0005, USA
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Khalsa PS, Ge W, Uddin MZ, Hadjiargyrou M. Integrin α2β1 affects mechano-transduction in slowly and rapidly adapting cutaneous mechanoreceptors in rat hairy skin. Neuroscience 2004; 129:447-59. [PMID: 15501602 DOI: 10.1016/j.neuroscience.2004.08.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/04/2004] [Indexed: 10/26/2022]
Abstract
The role of a transmembrane protein, integrin alpha2beta1, to modulate the neural responses of cutaneous mechanoreceptors to mechanical indentation was examined using an isolated skin-nerve preparation in a rat model. Skin and its intact innervation were harvested from the medial thigh of the hindlimb and placed in a dish containing synthetic interstitial fluid. Using a standard teased nerve preparation, the neural responses of single slowly or rapidly adapting mechanoreceptors (SA or RA, respectively) were identified and the afferents categorized according to standard protocols (i.e. response to constant stimuli). The most sensitive spot of a mechanoreceptor's receptive field was identified and then stimulated using controlled compressive stress (constant or dynamic loads between threshold and saturation load for SAs and RAs, respectively). Loads were applied before, during, and after passive diffusion into the skin of a function-blocking anti-integrin alpha2 monoclonal antibody (FBmAb) or one of two types of control antibodies (immunoglobulin G or a FBmAb conjugated with a secondary antibody). The sensitivities of both SA and RA mechanoreceptors were profoundly reduced in the presence of the FBmAb, while not changing the waveforms of their action potentials or their adaptation properties. Both control antibodies had no significant effect on mechanoreceptors' sensitivities. Following removal of the FBmAb, the effects in some neurons were partially reversible. Taken together, the data from this study support the hypothesis that integrin alpha2beta1 plays a significant role in modulating mechanoreceptive response to compressive indentation.
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Affiliation(s)
- P S Khalsa
- Department of Biomedical Engineering, State University of New York, HSC T18-031, Stony Brook, NY 11794-8181, USA.
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31
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Booth RE, Tong Q, Medina J, Snyder PM, Patel P, Stockand JD. A region directly following the second transmembrane domain in gamma ENaC is required for normal channel gating. J Biol Chem 2003; 278:41367-79. [PMID: 12897071 DOI: 10.1074/jbc.m305400200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We used a yeast one-hybrid complementation screen to identify regions within the cytosolic tails of the mouse alpha, beta, and gamma epithelial Na+ channel (ENaC) important to protein-protein and/or protein-lipid interactions at the plasma membrane. The cytosolic COOH terminus of alphaENaC contained a strongly interactive domain just distal to the second transmembrane region (TM2) between Met610 and Val632. Likewise, gammaENaC contained such a domain just distal to TM2 spanning Gln573-Pro600. Interactive domains were also localized within Met1-Gln54 and the last 17 residues of alpha- and betaENaC, respectively. Confocal images of Chinese hamster ovary cells transfected with enhanced green fluorescent fusion proteins of the cytosolic tails of mENaC subunits were consistent with results in yeast. Fusion proteins of the NH2 terminus of alphaENaC and the COOH termini of all three subunits co-localized with a plasma membrane marker. The functional importance of the membrane interactive domain in the COOH terminus of gammaENaC was established with whole-cell patch clamp experiments of wild type (alpha, beta, and gamma) and mutant (alpha, beta, and gammadeltaQ573-P600) mENaC reconstituted in Chinese hamster ovary cells. Mutant channels had about 13% of the activity of wild type channels with 0.33 +/- 0.14 versus 2.5 +/- 0.80 nA of amiloridesensitive inward current at -80 mV. Single channel analysis of recombinant channels demonstrated that mutant channels had a decrease in Po with 0.16 +/- 0.03 versus 0.67 +/- 0.07 for wild type. Mutant gammaENaC associated normally with the other two subunits in co-immunoprecipitation studies and localized to the plasma membrane in membrane labeling experiments and when visualized with evanescent-field fluorescence microscopy. Similar to deletion of Gln573-Pro600, deletion of Gln573-Arg583 but not Thr584-Pro600 decreased ENaC activity. The current results demonstrate that residues within Gln573-Arg583 of gammaENaC are necessary for normal channel gating.
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Affiliation(s)
- Rachell E Booth
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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Bruns JB, Hu B, Ahn YJ, Sheng S, Hughey RP, Kleyman TR. Multiple epithelial Na+ channel domains participate in subunit assembly. Am J Physiol Renal Physiol 2003; 285:F600-9. [PMID: 12770839 DOI: 10.1152/ajprenal.00095.2003] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial sodium channels (ENaCs) are composed of three structurally related subunits that form a tetrameric channel. The Xenopus laevis oocyte expression system was used to identify regions within the ENaC alpha-subunit that confer a dominant negative phenotype on functional expression of alphabetagamma-ENaC to define domains that have a role in subunit-subunit interactions. Coexpression of full-length mouse alphabetagamma-ENaC with either 1) the alpha-subunit first membrane-spanning domain and short downstream hydrophobic domain (alpha-M1H1); 2) alpha-M1H1 and its downstream hydrophilic extracellular loop (alpha-M1H1-ECL); 3) the membrane-spanning domain of a control type 2 transmembrane protein (glutamyl transpeptidase; gamma-GT) fused to the alpha-ECL (gamma-GT-alpha-ECL); 4) the extracellular domain of a control type 1 transmembrane protein (Tac) fused to the alpha-subunit second membrane-spanning domain and short upstream hydrophobic domain (Tac-alpha-H2M2); or 5) the alpha-subunit cytoplasmic COOH terminus (alpha-Ct) significantly reduced amiloride-sensitive Na+ currents in X. laevis oocytes. Functional expression of Na+ channels was not inhibited when full-length alphabetagamma-ENaC was coexpressed with either 1) the alpha-ECL lacking a signal-anchor sequence, 2) alpha-M1H1 and alpha-Ct expressed as a fusion protein, 3) full-length gamma-GT, or 4) full-length Tac. Furthermore, the expression of ROMK channels was not inhibited when full-length ROMK was coexpressed with either alpha-M1H1-ECL or alpha-Ct. Full-length FLAG-tagged alpha-, beta-, or gamma-ENaC coimmunoprecipitated with myc-tagged alpha-M1H1-ECL, whereas wild-type gamma-GT did not. These data suggest that multiple sites within the alpha-subunit participate in subunit-subunit interactions that are required for proper assembly of the heterooligomeric ENaC complex.
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Affiliation(s)
- James B Bruns
- Department of Medicine, University of Pittsburgh, 15261, USA
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33
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Sheng S, Perry CJ, Kleyman TR. External nickel inhibits epithelial sodium channel by binding to histidine residues within the extracellular domains of alpha and gamma subunits and reducing channel open probability. J Biol Chem 2002; 277:50098-111. [PMID: 12397059 DOI: 10.1074/jbc.m209975200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Epithelial sodium channels (ENaC) are regulated by various intracellular and extracellular factors including divalent cations. We studied the inhibitory effect and mechanism of external Ni(2+) on cloned mouse alpha-beta-gamma ENaC expressed in Xenopus oocytes. Ni(2+) reduced amiloride-sensitive Na(+) currents of the wild type mouse ENaC in a dose-dependent manner. The Ni(2+) block was fast and partially reversible at low concentrations and irreversible at high concentrations. ENaC inhibition by Ni(2+) was accompanied by moderate inward rectification at concentrations higher than 0.1 mm. ENaC currents were also blocked by the histidine-reactive reagent diethyl pyrocarbonate. Pretreatment of the oocytes with the reagent reduced Ni(2+) inhibition of the remaining current. Mutations at alphaHis(282) and gammaHis(239) located within the extracellular loops significantly decreased Ni(2+) inhibition of ENaC currents. The mutation alphaH282D or double mutations alphaH282R/gammaH239R eliminated Ni(2+) block. All mutations at gammaHis(239) eliminated Ni(2+)-induced inward current rectification. Ni(2+) block was significantly enhanced by introduction of a histidine at alphaArg(280). Lowering extracellular pH to 5.5 and 4.4 decreased or eliminated Ni(2+) block. Although alphaH282C-beta-gamma channels were partially inhibited by the sulfhydryl-reactive reagent [2-(trimethylammonium)ethyl] methanethiosulfonate bromide (MTSET), alpha-beta-gamma H239C channels were insensitive to MTSET. From patch clamp studies, Ni(2+) did not affect unitary current but decreased open probability when perfused into the recording pipette. Our results suggest that external Ni(2+) reduces ENaC open probability by binding to a site consisting of alphaHis(282) and gammaHis(239) and that these histidine residues may participate in ENaC gating.
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MESH Headings
- Amiloride/pharmacology
- Amino Acid Sequence
- Animals
- Binding Sites
- Cloning, Molecular
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- Epithelial Sodium Channels
- Histidine/chemistry
- Kinetics
- Magnesium/pharmacology
- Mice
- Models, Biological
- Models, Chemical
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Mutation
- Nickel/pharmacology
- Oocytes/metabolism
- Patch-Clamp Techniques
- Point Mutation
- Protein Binding
- Protein Structure, Tertiary
- RNA, Complementary/metabolism
- Sequence Homology, Amino Acid
- Sodium/metabolism
- Sodium/pharmacology
- Sodium Channels/chemistry
- Sodium Channels/metabolism
- Time Factors
- Xenopus
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Affiliation(s)
- Shaohu Sheng
- Renal-Electrolyte Division, the Department of Medicine, University of Pittsburgh School of Medicine, 3550 Terrace Street, Pittsburgh, PA 15261, USA.
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Hendron E, Patel P, Hausenfluke M, Gamper N, Shapiro MS, Booth RE, Stockand JD. Identification of cytoplasmic domains within the epithelial Na+ channel reactive at the plasma membrane. J Biol Chem 2002; 277:34480-8. [PMID: 12093811 DOI: 10.1074/jbc.m204615200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activity of membrane proteins is controlled, in part, by protein-protein interactions localized to the plasma membrane. In the current study, domains within the epithelial Na(+) channel (ENaC) reactive at the plasma membrane were identified using a novel yeast one-hybrid screen. The cytosolic N terminus of alphaENaC and the cytosolic C termini of alpha-, beta-, and gammaENaC contained domains reactive at the plasma membrane. Fluorescent micrographs of epithelial cells overexpressing fusion proteins of enhanced green fluorescent protein and mENaC cytosolic domains were consistent with those in yeast. A novel membrane reactive domain within the cytosolic C terminus of gamma-mENaC was localized to the 17 amino acids between residues Thr(584)-Pro(600). Two overlapping internalization signals within the C terminus of gamma-mENaC, a WW-binding domain (PY motif) and a tyrosine-based endocytic signal, were additive with respect to decreasing complementation and expression levels of hybrid proteins. Decreases in expression levels of hybrid proteins containing the PY and endocytic motif were reversed with latrunculin A, an inhibitor of endosomal movement. Decreases in complementation and expression levels of hybrid proteins mediated by the combined PY and overlapping endocytic motif proceeded in the absence of established ubiquitination sites within ENaC. In addition, the endocytic motif was active in the absence of the PY motif, demonstrating that these two domains, while possibly interacting, also have discrete functions. The novel domains within the cytosolic N terminus of alphaENaC and the C termini of alpha-, beta-, and gammaENaC identified here are likely to be involved in protein-protein and/or protein-lipid interactions localized to the plasma membrane. We hypothesize that these newly identified domains play a role in modulating ENaC activity.
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Affiliation(s)
- Eunan Hendron
- Department of Physiology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-2900, USA
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Brockway LM, Zhou ZH, Bubien JK, Jovov B, Benos DJ, Keyser KT. Rabbit retinal neurons and glia express a variety of ENaC/DEG subunits. Am J Physiol Cell Physiol 2002; 283:C126-34. [PMID: 12055080 DOI: 10.1152/ajpcell.00457.2001] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Some members of the epithelial Na+ channel/degenerin (ENaC/DEG) family of ion channels have been detected in mammalian brain. Therefore, we examined the RNA and protein expression of these channels in another part of the central nervous system, the rabbit retina. We next sought to demonstrate physiological evidence for an amiloride-sensitive current in Müller glia, which, on the basis of a previous study, are thought to express alpha-ENaC (Golestaneh N, de Kozak Y, Klein C, and Mirshahi M. Glia 33: 160-168, 2001). RT-PCR of retinal RNA revealed the presence of alpha-, beta-, gamma-, and delta-ENaC as well as acid-sensing ion channel (ASIC)1, ASIC2, ASIC3, and ASIC4. Immunohistochemical localization with antibodies against alpha-ENaC and beta-ENaC showed labeling in Müller cells and neurons, respectively. The presence of alpha-ENaC, beta-ENaC, and ASIC1 was detected by Western blotting. Cultured Müller cells were whole cell patch clamped. These cells exhibited an inward Na+ current that was blocked by amiloride. These data demonstrate for the first time both the expression of a variety of ENaC and ASIC subunits in the rabbit retina as well as distinct cellular expression patterns of specific subunits in neurons and glia.
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Affiliation(s)
- L M Brockway
- Vision Science Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
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Diemel RV, Snel MME, Waring AJ, Walther FJ, van Golde LMG, Putz G, Haagsman HP, Batenburg JJ. Multilayer formation upon compression of surfactant monolayers depends on protein concentration as well as lipid composition. An atomic force microscopy study. J Biol Chem 2002; 277:21179-88. [PMID: 11923286 DOI: 10.1074/jbc.m111758200] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The determinants for the formation of multilayers upon compression of surfactant monolayers were investigated by compressing films, beyond the squeeze-out plateau, to a surface tension of 22 millinewtons/m. Atomic force microscopy was used to visualize the topography of lipid films containing varying amounts of native surfactant protein B (SP-B). These films were compared with films containing synthetic peptides based on the N terminus of human SP-B: monomeric mSP-B-(1-25) or dimeric dSP-B-(1-25). The formation of typical hexagonal network structures as well as the height of protrusions were shown to depend on the concentration of SP-B. Protrusions of bilayer height were formed from physiologically relevant concentrations of 0.2-0.4 mol % (4.5-8.5 wt %) SP-B upwards. Much higher concentrations of SP-B-(1-25) peptides were needed to obtain network structures, and protrusion heights were not equal to those found for films with native SP-B. A striking observation was that while protrusions formed in films of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/1,2-dipalmitoyl-sn-glycero-3-(phospho-rac-(1-glycerol)) (DPPG) (80/20) had single bilayer thickness, those formed in DPPC/1-palmitoyl-2-oleoyl-sn-glycero-3-(phospho-rac-(1-glycerol)) (80/20) had various heights of multilayers, whereas those seen in DPPC/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/DPPG (60/20/20) were mainly of bilayer height. For the first time direct observations by atomic force microscopy show (i) that a certain minimal concentration of SP-B is required for the formation of layered protrusions upon film compression, (ii) that protrusion height depends on whether the phospholipids contain an unsaturated fatty acyl chain, and (iii) that protrusion height also depends on whether the unsaturated acyl chain is present in phosphatidylcholine or in phosphatidylglycerol.
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Affiliation(s)
- Robert V Diemel
- Department of Biochemistry and Cell Biology, Graduate School of Animal Health, Faculty of Veterinary Medicine, Utrecht University, PO Box 80176, 3508 TD Utrecht, The Netherlands
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37
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Rao US, Steimle RE, Balachandran P. Activation of large conductance sodium channels upon expression of amiloride-sensitive sodium channel in Sf9 insect cells. J Biol Chem 2002; 277:4900-5. [PMID: 11733494 DOI: 10.1074/jbc.m108258200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The amiloride-sensitive epithelial sodium channels (ENaC) mediate Na(+) reabsorption in epithelial tissues including distal nephron, colon, lung, and secretory glands and plays a critical role in pathophysiology of hypertension and cystic fibrosis. The ENaC is a multimeric protein composed of alpha-ENaC, beta-ENaC, and gamma-ENaC subunits. To study the biochemical properties of the channel, the subunit cDNAs of rat colon ENaC (rENaC) were subcloned into baculoviruses, and the corresponding proteins were expressed in Sf9 insect cells. The functional characteristics of the expressed rENaC were studied in planar lipid bilayers. The results show that expression of alpha-rENaC and alphabetagamma-rENaC in Sf9 insect cells results in the generation of cation-selective large conductance channels. Although the large conductance channels observed in the alpha-rENaC-containing membranes were unaffected by amiloride, the large conductance channels found in alphabetagamma-rENaC complex-containing membranes exhibited voltage-dependent flickering in the presence of micromolar amiloride. Possible implications of these observations are discussed.
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Affiliation(s)
- U Subrahmanyeswara Rao
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA.
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38
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Volk KA, Snyder PM, Stokes JB. Regulation of epithelial sodium channel activity through a region of the carboxyl terminus of the alpha -subunit. Evidence for intracellular kinase-mediated reactions. J Biol Chem 2001; 276:43887-93. [PMID: 11571309 DOI: 10.1074/jbc.m108714200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) is a heteromultimer composed of three subunits, each having two membrane-spanning domains with intracellular amino and carboxyl termini. Several hormones and proteins regulate channel activity, but the molecular nature of this regulation is unknown. We conducted experiments to determine a possible new site within the carboxyl terminus of the alpha-subunit involved in enhanced channel activity through endogenous kinases. When an alpha-subunit that was truncated to remove a PY motif was expressed in Xenopus oocytes with wild type human beta- and gamma-ENaC subunits, channel activity was greatly enhanced. The removal of the entire intracellular carboxyl terminus of the alpha-subunit eliminated this enhanced basal activity. Using several point mutations, we localized this site to two amino acid residues (Pro(595)-Gly(596)) near the second membrane-spanning domain. The nonspecific kinase inhibitor staurosporine inhibits basal channel activity of wild type ENaC but was ineffective in inhibiting channels mutated at this site. The major effect of these mutations was not on channel kinetics but was largely, if not entirely, on the number of active channels on the cell surface. This region is potentially important in effecting kinase-mediated increases in ENaC activity.
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Affiliation(s)
- K A Volk
- Department of Internal Medicine, University of Iowa College of Medicine and the Veterans Affairs Medical Center, Iowa City, Iowa 52246, USA
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Baines DL, MacGregor GG, Kemp PJ. Fatty acid modulation and sequence identity of fetal guinea pig alveolar type II cell amiloride-sensitive Na+ channel. Biochem Biophys Res Commun 2001; 288:727-35. [PMID: 11676504 DOI: 10.1006/bbrc.2001.5828] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Removal of fetal lung fluid at birth is crucial to survival. In vivo, a reversal in the direction of vectorial, amiloride-sensitive Na+) transport can be stimulated by ETYA, a nonmetabolizable analogue of the naturally occurring unsaturated fatty acid, arachidonate. Using the patch-clamp technique, fetal guinea pig alveolar type II pneumocyte single Na+ channel activity was robustly activated by 10 microM arachidonate, ETYA, oleate and stearate; this was unaffected by cyclooxygenase and 5'lipoxygenase inhibitors. The Na+ channel expressed in fetal guinea pig alveolar epithelial type II pneumocytes has biophysical properties compatible with species-specific coexpression of a novel variant of alphaENaC with betaENaC. gammaENaC is either not expressed in this tissue or shares very little homology with the rat and human gamma subunit. Thus, dramatic stimulation of this channel by arachidonate explains the in vivo observation of gestation-dependent reversal of fetal transepithelial driving force and may, therefore, be of physiological significance during the transition to breathing air at birth.
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Affiliation(s)
- D L Baines
- Lung Membrane Transport Group, Tayside Institute of Child Health, University of Dundee, Dundee, DD1 9SY, United Kingdom
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