51
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Anoctamins support calcium-dependent chloride secretion by facilitating calcium signaling in adult mouse intestine. Pflugers Arch 2014; 467:1203-13. [PMID: 24974903 DOI: 10.1007/s00424-014-1559-2] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Revised: 06/12/2014] [Accepted: 06/17/2014] [Indexed: 12/13/2022]
Abstract
Intestinal epithelial electrolyte secretion is activated by increase in intracellular cAMP or Ca(2+) and opening of apical Cl(-) channels. In infants and young animals, but not in adults, Ca(2+)-activated chloride channels may cause secretory diarrhea during rotavirus infection. While detailed knowledge exists concerning the contribution of cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) channels, analysis of the role of Ca(2+)-dependent Cl(-) channels became possible through identification of the anoctamin (TMEM16) family of proteins. We demonstrate expression of several anoctamin paralogues in mouse small and large intestines. Using intestinal-specific mouse knockout models for anoctamin 1 (Ano1) and anoctamin 10 (Ano10) and a conventional knockout model for anoctamin 6 (Ano6), we demonstrate the role of anoctamins for Ca(2+)-dependent Cl(-) secretion induced by the muscarinic agonist carbachol (CCH). Ano1 is preferentially expressed in the ileum and large intestine, where it supports Ca(2+)-activated Cl(-) secretion. In contrast, Ano10 is essential for Ca(2+)-dependent Cl(-) secretion in jejunum, where expression of Ano1 was not detected. Although broadly expressed, Ano6 has no role in intestinal cholinergic Cl(-) secretion. Ano1 is located in a basolateral compartment/membrane rather than in the apical membrane, where it supports CCH-induced Ca(2+) increase, while the essential and possibly only apical Cl(-) channel is CFTR. These results define a new role of Ano1 for intestinal Ca(2+)-dependent Cl(-) secretion and demonstrate for the first time a contribution of Ano10 to intestinal transport.
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52
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Abstract
TMEM16 proteins, also known as anoctamins, are involved in a variety of functions that include ion transport, phospholipid scrambling, and regulation of other membrane proteins. The first two members of the family, TMEM16A (anoctamin-1, ANO1) and TMEM16B (anoctamin-2, ANO2), function as Ca2+-activated Cl- channels (CaCCs), a type of ion channel that plays important functions such as transepithelial ion transport, smooth muscle contraction, olfaction, phototransduction, nociception, and control of neuronal excitability. Genetic ablation of TMEM16A in mice causes impairment of epithelial Cl- secretion, tracheal abnormalities, and block of gastrointestinal peristalsis. TMEM16A is directly regulated by cytosolic Ca2+ as well as indirectly by its interaction with calmodulin. Other members of the anoctamin family, such as TMEM16C, TMEM16D, TMEM16F, TMEM16G, and TMEM16J, may work as phospholipid scramblases and/or ion channels. In particular, TMEM16F (ANO6) is a major contributor to the process of phosphatidylserine translocation from the inner to the outer leaflet of the plasma membrane. Intriguingly, TMEM16F is also associated with the appearance of anion/cation channels activated by very high Ca2+ concentrations. Furthermore, a TMEM16 protein expressed in Aspergillus fumigatus displays both ion channel and lipid scramblase activity. This finding suggests that dual function is an ancestral characteristic of TMEM16 proteins and that some members, such as TMEM16A and TMEM16B, have evolved to a pure channel function. Mutations in anoctamin genes (ANO3, ANO5, ANO6, and ANO10) cause various genetic diseases. These diseases suggest the involvement of anoctamins in a variety of cell functions whose link with ion transport and/or lipid scrambling needs to be clarified.
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53
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The calcium-activated chloride channel Anoctamin 1 contributes to the regulation of renal function. Kidney Int 2014; 85:1369-81. [PMID: 24476694 DOI: 10.1038/ki.2013.535] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 10/16/2013] [Accepted: 11/14/2013] [Indexed: 01/14/2023]
Abstract
The role of calcium-activated chloride channels for renal function is unknown. By immunohistochemistry we demonstrate dominant expression of the recently identified calcium-activated chloride channels, Anoctamin 1 (Ano1, TMEM16A) in human and mouse proximal tubular epithelial (PTE) cells, with some expression in podocytes and other tubular segments. Ano1-null mice had proteinuria and numerous large reabsorption vesicles in PTE cells. Selective knockout of Ano1 in podocytes (Ano1-/-/Nphs2-Cre) did not impair renal function, whereas tubular knockout in Ano1-/-/Ksp-Cre mice increased urine protein excretion and decreased urine electrolyte concentrations. Purinergic stimulation activated calcium-dependent chloride currents in isolated proximal tubule epithelial cells from wild-type but not from Ano1-/-/Ksp-Cre mice. Ano1 currents were activated by acidic pH, suggesting parallel stimulation of Ano1 chloride secretion with activation of the proton-ATPase. Lack of calcium-dependent chloride secretion in cells from Ano1-/-/Ksp-Cre mice was paralleled by attenuated proton secretion and reduced endosomal acidification, which compromised proximal tubular albumin uptake. Tubular knockout of Ano1 enhanced serum renin and aldosterone concentrations, probably leading to enhanced compensatory distal tubular reabsorption, thus maintaining normal blood pressure levels. Thus, Ano1 has a role in proximal tubular proton secretion and protein reabsorption. The results correspond to regulation of the proton-ATPase by the Ano1-homolog Ist2 in yeast.
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Wolf W, Meese K, Seedorf M. Ist2 in the yeast cortical endoplasmic reticulum promotes trafficking of the amino acid transporter Bap2 to the plasma membrane. PLoS One 2014; 9:e85418. [PMID: 24416406 PMCID: PMC3885692 DOI: 10.1371/journal.pone.0085418] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 11/26/2013] [Indexed: 11/18/2022] Open
Abstract
The equipment of the plasma membrane in Saccharomyces cerevisiae with specific nutrient transporters is highly regulated by transcription, translation and protein trafficking allowing growth in changing environments. The activity of these transporters depends on a H+ gradient across the plasma membrane generated by the H+-ATPase Pma1. We found that the polytopic membrane protein Ist2 in the cortical endoplasmic reticulum (ER) is required for efficient leucine uptake during the transition from fermentation to respiration. Experiments employing tandem fluorescence timer protein tag showed that Ist2 was necessary for efficient trafficking of newly synthesized leucine transporter Bap2 from the ER to the plasma membrane. This finding explains the growth defect of ist2Δ mutants during nutritional challenges and illustrates the important role of physical coupling between cortical ER and plasma membrane.
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Affiliation(s)
- Wendelin Wolf
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH-Allianz, Heidelberg, Germany
| | - Klaus Meese
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH-Allianz, Heidelberg, Germany
| | - Matthias Seedorf
- Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), DKFZ-ZMBH-Allianz, Heidelberg, Germany
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55
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Wong XM, Younger S, Peters CJ, Jan YN, Jan LY. Subdued, a TMEM16 family Ca²⁺-activated Cl⁻channel in Drosophila melanogaster with an unexpected role in host defense. eLife 2013; 2:e00862. [PMID: 24192034 PMCID: PMC3814000 DOI: 10.7554/elife.00862] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
TMEM16A and TMEM16B are calcium-activated chloride channels (CaCCs) with important functions in mammalian physiology. Whether distant relatives of the vertebrate TMEM16 families also form CaCCs is an intriguing open question. Here we report that a TMEM16 family member from Drosophila melanogaster, Subdued (CG16718), is a CaCC. Amino acid substitutions of Subdued alter the ion selectivity and kinetic properties of the CaCC channels heterologously expressed in HEK 293T cells. This Drosophila channel displays characteristics of classic CaCCs, thereby providing evidence for evolutionarily conserved biophysical properties in the TMEM16 family. Additionally, we show that knockout flies lacking subdued gene activity more readily succumb to death caused by ingesting the pathogenic bacteria Serratia marcescens, suggesting that subdued has novel functions in Drosophila host defense. DOI: http://dx.doi.org/10.7554/eLife.00862.001.
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Affiliation(s)
- Xiu Ming Wong
- Graduate Program in Chemistry and Chemical Biology, University of California, San Francisco, San Francisco, United States
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56
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Goyal U, Blackstone C. Untangling the web: mechanisms underlying ER network formation. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1833:2492-8. [PMID: 23602970 PMCID: PMC3729797 DOI: 10.1016/j.bbamcr.2013.04.009] [Citation(s) in RCA: 121] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 04/04/2013] [Accepted: 04/08/2013] [Indexed: 12/16/2022]
Abstract
The ER is a continuous membrane system consisting of the nuclear envelope, flat sheets often studded with ribosomes, and a polygonal network of highly-curved tubules extending throughout the cell. Although protein and lipid biosynthesis, protein modification, vesicular transport, Ca(2+)dynamics, and protein quality control have been investigated in great detail, mechanisms that generate the distinctive architecture of the ER have been uncovered only recently. Several protein families including the reticulons and REEPs/DP1/Yop1p harbor hydrophobic hairpin domains that shape high-curvature ER tubules and mediate intramembrane protein interactions. Members of the atlastin/RHD3/Sey1p family of dynamin-related GTPases interact with the ER-shaping proteins and mediate the formation of three-way junctions responsible for the polygonal structure of the tubular ER network, with Lunapark proteins acting antagonistically. Additional classes of tubular ER proteins including some REEPs and the M1 spastin ATPase interact with the microtubule cytoskeleton. Flat ER sheets possess a different complement of proteins such as p180, CLIMP-63 and kinectin implicated in shaping, cisternal stacking and cytoskeletal interactions. The ER is also in constant motion, and numerous signaling pathways as well as interactions among cytoskeletal elements, the plasma membrane, and organelles cooperate to position and shape the ER dynamically. Finally, many proteins involved in shaping the ER network are mutated in the most common forms of hereditary spastic paraplegia, indicating a particular importance for proper ER morphology and distribution in large, highly-polarized cells such as neurons. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Uma Goyal
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Craig Blackstone
- Cell Biology Section, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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57
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Helle SC, Kanfer G, Kolar K, Lang A, Michel AH, Kornmann B. Organization and function of membrane contact sites. BIOCHIMICA ET BIOPHYSICA ACTA (BBA) - MOLECULAR CELL RESEARCH 2013. [DOI: 10.1016.j.bbamcr.2013.01.02810.1016/j.bbamcr.2013.01.028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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58
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Oligomerization and Ca2+/calmodulin control binding of the ER Ca2+-sensors STIM1 and STIM2 to plasma membrane lipids. Biosci Rep 2013; 33:BSR20130089. [PMID: 24044355 PMCID: PMC3814058 DOI: 10.1042/bsr20130089] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Ca2+ (calcium) homoeostasis and signalling rely on physical contacts between Ca2+ sensors in the ER (endoplasmic reticulum) and Ca2+ channels in the PM (plasma membrane). STIM1 (stromal interaction molecule 1) and STIM2 Ca2+ sensors oligomerize upon Ca2+ depletion in the ER lumen, contact phosphoinositides at the PM via their cytosolic lysine (K)-rich domains, and activate Ca2+ channels. Differential sensitivities of STIM1 and STIM2 towards ER luminal Ca2+ have been studied but responses towards elevated cytosolic Ca2+ concentration and the mechanism of lipid binding remain unclear. We found that tetramerization of the STIM1 K-rich domain is necessary for efficient binding to PI(4,5)P2-containing PM-like liposomes consistent with an oligomerization-driven STIM1 activation. In contrast, dimerization of STIM2 K-rich domain was sufficient for lipid binding. Furthermore, the K-rich domain of STIM2, but not of STIM1, forms an amphipathic α-helix. These distinct features of the STIM2 K-rich domain cause an increased affinity for PI(4,5)P2, consistent with the lower activation threshold of STIM2 and a function as regulator of basal Ca2+ levels. Concomitant with higher affinity for PM lipids, binding of CaM (calmodulin) inhibited the interaction of the STIM2 K-rich domain with liposomes in a Ca2+ and PI(4,5)P2 concentration-dependent manner. Therefore we suggest that elevated cytosolic Ca2+ concentration down-regulates STIM2-mediated ER–PM contacts via CaM binding.
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59
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Clayton EL, Minogue S, Waugh MG. Mammalian phosphatidylinositol 4-kinases as modulators of membrane trafficking and lipid signaling networks. Prog Lipid Res 2013; 52:294-304. [PMID: 23608234 PMCID: PMC3989048 DOI: 10.1016/j.plipres.2013.04.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 04/08/2013] [Indexed: 12/19/2022]
Abstract
The four mammalian phosphatidylinositol 4-kinases modulate inter-organelle lipid trafficking, phosphoinositide signalling and intracellular vesicle trafficking. In addition to catalytic domains required for the synthesis of PI4P, the phosphatidylinositol 4-kinases also contain isoform-specific structural motifs that mediate interactions with proteins such as AP-3 and the E3 ubiquitin ligase Itch, and such structural differences determine isoform-specific roles in membrane trafficking. Moreover, different permutations of phosphatidylinositol 4-kinase isozymes may be required for a single cellular function such as occurs during distinct stages of GPCR signalling and in Golgi to lysosome trafficking. Phosphatidylinositol 4-kinases have recently been implicated in human disease. Emerging paradigms include increased phosphatidylinositol 4-kinase expression in some cancers, impaired functioning associated with neurological pathologies, the subversion of PI4P trafficking functions in bacterial infection and the activation of lipid kinase activity in viral disease. We discuss how the diverse and sometimes overlapping functions of the phosphatidylinositol 4-kinases present challenges for the design of isoform-specific inhibitors in a therapeutic context.
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Affiliation(s)
- Emma L Clayton
- UCL Institute for Liver & Digestive Health, UCL Royal Free Campus, Rowland Hill Street, London NW3 2PF, United Kingdom
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60
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Stefan CJ, Manford AG, Emr SD. ER-PM connections: sites of information transfer and inter-organelle communication. Curr Opin Cell Biol 2013; 25:434-42. [PMID: 23522446 DOI: 10.1016/j.ceb.2013.02.020] [Citation(s) in RCA: 159] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Revised: 02/25/2013] [Accepted: 02/28/2013] [Indexed: 11/18/2022]
Abstract
Eukaryotic cells are divided into distinct membrane-bound organelles with unique identities and specialized metabolic functions. Communication between organelles must take place to regulate the size, shape, and composition of individual organelles, as well as to coordinate transport between organelles. The endoplasmic reticulum (ER) forms an expansive membrane network that contacts and participates in crosstalk with several other organelles in the cell, most notably the plasma membrane (PM). ER-PM junctions have well-established functions in the movement of small molecules, such as lipids and ions, between the ER and PM. Recent discoveries have revealed additional exciting roles for ER-PM junctions in the regulation of cell signaling, ER shape and architecture, and PM domain organization.
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Affiliation(s)
- Christopher J Stefan
- Weill Institute for Cell & Molecular Biology, Department of Molecular Biology & Genetics, Cornell University, Ithaca, NY 14853, United States.
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61
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Helle SCJ, Kanfer G, Kolar K, Lang A, Michel AH, Kornmann B. Organization and function of membrane contact sites. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2526-41. [PMID: 23380708 DOI: 10.1016/j.bbamcr.2013.01.028] [Citation(s) in RCA: 329] [Impact Index Per Article: 29.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Revised: 01/18/2013] [Accepted: 01/21/2013] [Indexed: 11/16/2022]
Abstract
Membrane-bound organelles are a wonderful evolutionary acquisition of the eukaryotic cell, allowing the segregation of sometimes incompatible biochemical reactions into specific compartments with tailored microenvironments. On the flip side, these isolating membranes that crowd the interior of the cell, constitute a hindrance to the diffusion of metabolites and information to all corners of the cell. To ensure coordination of cellular activities, cells use a network of contact sites between the membranes of different organelles. These membrane contact sites (MCSs) are domains where two membranes come to close proximity, typically less than 30nm. Such contacts create microdomains that favor exchange between two organelles. MCSs are established and maintained in durable or transient states by tethering structures, which keep the two membranes in proximity, but fusion between the membranes does not take place. Since the endoplasmic reticulum (ER) is the most extensive cellular membrane network, it is thus not surprising to find the ER involved in most MCSs within the cell. The ER contacts diverse compartments such as mitochondria, lysosomes, lipid droplets, the Golgi apparatus, endosomes and the plasma membrane. In this review, we will focus on the common organizing principles underlying the many MCSs found between the ER and virtually all compartments of the cell, and on how the ER establishes a network of MCSs for the trafficking of vital metabolites and information. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Sebastian C J Helle
- Institute of Biochemistry, ETH Zürich, HPM G16 Schafmattstrasse, Zürich, Switzerland
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62
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Manford A, Stefan C, Yuan H, MacGurn J, Emr S. ER-to-Plasma Membrane Tethering Proteins Regulate Cell Signaling and ER Morphology. Dev Cell 2012; 23:1129-40. [DOI: 10.1016/j.devcel.2012.11.004] [Citation(s) in RCA: 339] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Revised: 10/05/2012] [Accepted: 11/11/2012] [Indexed: 10/27/2022]
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