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Kaziannis S, Broser M, van Stokkum IHM, Dostal J, Busse W, Munhoven A, Bernardo C, Kloz M, Hegemann P, Kennis JTM. Multiple retinal isomerizations during the early phase of the bestrhodopsin photoreaction. Proc Natl Acad Sci U S A 2024; 121:e2318996121. [PMID: 38478688 PMCID: PMC10962995 DOI: 10.1073/pnas.2318996121] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Accepted: 02/13/2024] [Indexed: 03/27/2024] Open
Abstract
Bestrhodopsins constitute a class of light-regulated pentameric ion channels that consist of one or two rhodopsins in tandem fused with bestrophin ion channel domains. Here, we report on the isomerization dynamics in the rhodopsin tandem domains of Phaeocystis antarctica bestrhodopsin, which binds all-trans retinal Schiff-base (RSB) absorbing at 661 nm and, upon illumination, converts to the meta-stable P540 state with an unusual 11-cis RSB. The primary photoproduct P682 corresponds to a mixture of highly distorted 11-cis and 13-cis RSB directly formed from the excited state in 1.4 ps. P673 evolves from P682 in 500 ps and contains highly distorted 13-cis RSB, indicating that the 11-cis fraction in P682 converts to 13-cis. Next, P673 establishes an equilibrium with P595 in 1.2 µs, during which RSB converts to 11-cis and then further proceeds to P560 in 48 µs and P540 in 1.0 ms while remaining 11-cis. Hence, extensive isomeric switching occurs on the early ground state potential energy surface (PES) on the hundreds of ps to µs timescale before finally settling on a metastable 11-cis photoproduct. We propose that P682 and P673 are trapped high up on the ground-state PES after passing through either of two closely located conical intersections that result in 11-cis and 13-cis RSB. Co-rotation of C11=C12 and C13=C14 bonds results in a constricted conformational landscape that allows thermal switching between 11-cis and 13-cis species of highly strained RSB chromophores. Protein relaxation may release RSB strain, allowing it to evolve to a stable 11-cis isomeric configuration in microseconds.
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Affiliation(s)
- Spyridon Kaziannis
- The Extreme Light Infrastructure ERIC, Dolní Břežany252 41, Czech Republic
- Department of Physics, University of Ioannina, IoanninaGr-45110, Greece
| | - Matthias Broser
- Faculty of Life Sciences, Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, BerlinD-10115, Germany
| | - Ivo H. M. van Stokkum
- Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam1081 HV, The Netherlands
| | - Jakub Dostal
- The Extreme Light Infrastructure ERIC, Dolní Břežany252 41, Czech Republic
| | - Wayne Busse
- Faculty of Life Sciences, Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, BerlinD-10115, Germany
| | - Arno Munhoven
- Faculty of Life Sciences, Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, BerlinD-10115, Germany
| | - Cesar Bernardo
- The Extreme Light Infrastructure ERIC, Dolní Břežany252 41, Czech Republic
| | - Miroslav Kloz
- The Extreme Light Infrastructure ERIC, Dolní Břežany252 41, Czech Republic
| | - Peter Hegemann
- Faculty of Life Sciences, Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, BerlinD-10115, Germany
| | - John T. M. Kennis
- Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam1081 HV, The Netherlands
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2
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The mechanisms of chromogranin B-regulated Cl- homeostasis. Biochem Soc Trans 2022; 50:1659-1672. [PMID: 36511243 DOI: 10.1042/bst20220435] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 11/25/2022] [Accepted: 12/01/2022] [Indexed: 12/15/2022]
Abstract
Chloride is the most abundant inorganic anions in almost all cells and in human circulation systems. Its homeostasis is therefore important for systems physiology and normal cellular activities. This topic has been extensively studied with chloride loaders and extruders expressed in both cell surfaces and intracellular membranes. With the newly discovered, large-conductance, highly selective Cl- channel formed by membrane-bound chromogranin B (CHGB), which differs from all other known anion channels of conventional transmembrane topology, and is distributed in plasma membranes, endomembrane systems, endosomal, and endolysosomal compartments in cells expressing it, we will discuss the potential physiological importance of the CHGB channels to Cl- homeostasis, cellular excitability and volume control, and cation uptake or release at the cellular and subcellular levels. These considerations and CHGB's association with human diseases make the CHGB channel a possible druggable target for future molecular therapeutics.
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3
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Lee JM, Gadhe CG, Kang H, Pae AN, Lee CJ. Glutamate Permeability of Chicken Best1. Exp Neurobiol 2022; 31:277-288. [PMID: 36351838 PMCID: PMC9659495 DOI: 10.5607/en22038] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2022] [Revised: 10/28/2022] [Accepted: 10/28/2022] [Indexed: 07/28/2023] Open
Abstract
Bestrophin-1 (Best1) is a calcium (Ca2+)-activated chloride (Cl-) channel which has a phylogenetically conserved channel structure with an aperture and neck in the ion-conducting pathway. Mammalian mouse Best1 (mBest1) has been known to have a permeability for large organic anions including gluconate, glutamate, and D-serine, in addition to several small monovalent anions, such as Cl‑, bromine (Br-), iodine (I-), and thiocyanate (SCN-). However, it is still unclear whether non-mammalian Best1 has a glutamate permeability through the ion-conducting pathway. Here, we report that chicken Best1 (cBest1) is permeable to glutamate in a Ca2+-dependent manner. The molecular docking and molecular dynamics simulation showed a glutamate binding at the aperture and neck of cBest1 and a glutamate permeation through the ion-conducting pore, respectively. Moreover, through electrophysiological recordings, we calculated the permeability ratio of glutamate to Cl- (PGlutamate/PCl) as 0.28 based on the reversal potential shift by ion substitution from Cl- to glutamate in the internal solution. Finally, we directly detected the Ca2+-dependent glutamate release through cBest1 using the ultrasensitive two-cell sniffer patch technique. Our results propose that Best1 homologs from non-mammalian (cBest1) to mammalian (mBest1) have a conserved permeability for glutamate.
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Affiliation(s)
- Jung Moo Lee
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea
- Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea
| | | | - Hyunji Kang
- Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea
- IBS School, University of Science and Technology, Daejeon 34113, Korea
| | - Ae Nim Pae
- Brain Science Institute, Korea Institute of Science and Technology, Seoul 02792, Korea
- KIST School, University of Science and Technology, Seoul 02792, Korea
| | - C. Justin Lee
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 02841, Korea
- Center for Cognition and Sociality, Institute for Basic Science, Daejeon 34126, Korea
- IBS School, University of Science and Technology, Daejeon 34113, Korea
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4
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Owji AP, Kittredge A, Zhang Y, Yang T. Structure and Function of the Bestrophin family of calcium-activated chloride channels. Channels (Austin) 2021; 15:604-623. [PMID: 34612806 PMCID: PMC8496536 DOI: 10.1080/19336950.2021.1981625] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Bestrophins are a family of calcium-activated chloride channels (CaCCs) with relevance to human physiology and a myriad of eye diseases termed "bestrophinopathies". Since the identification of bestrophins as CaCCs nearly two decades ago, extensive studies from electrophysiological and structural biology perspectives have sought to define their key channel features including calcium sensing, gating, inactivation, and anion selectivity. The initial X-ray crystallography studies on the prokaryotic homolog of Best1, Klebsiella pneumoniae (KpBest), and the Best1 homolog from Gallus gallus (chicken Best1, cBest1), laid the foundational groundwork for establishing the architecture of Best1. Recent progress utilizing single-particle cryogenic electron microscopy has further elucidated the molecular mechanism of gating in cBest1 and, separately, the structure of Best2 from Bos taurus (bovine Best2, bBest2). Meanwhile, whole-cell patch clamp, planar lipid bilayer, and other electrophysiologic analyses using these models as well as the human Best1 (hBest1) have provided ample evidence describing the functional properties of the bestrophin channels. This review seeks to consolidate these structural and functional results to paint a broad picture of the underlying mechanisms comprising the bestrophin family's structure-function relationship.
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Affiliation(s)
- Aaron P Owji
- Department of Pharmacology, Columbia University, NY, USA
| | - Alec Kittredge
- Department of Pharmacology, Columbia University, NY, USA
| | - Yu Zhang
- Department of Ophthalmology, Columbia University, NY, USA
| | - Tingting Yang
- Department of Ophthalmology, Columbia University, NY, USA
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Ravichandran G, Raju SV, Sarkar P, N. T. S, Al Olayan EM, Aloufi AS, Elokaby MA, Arshad A, Mala K, Arockiaraj J. Bestrophin‐derived peptide,
WP17
, elicits cell wall disruption‐mediated bactericidal activity against
Micrococcus luteus
and anti‐neoplastic effect against murine melanoma cells. Pept Sci (Hoboken) 2021. [DOI: 10.1002/pep2.24220] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Gayathri Ravichandran
- SRM Research Institute, SRM Institute of Science and Technology Chennai Tamil Nadu India
| | - Stefi V. Raju
- SRM Research Institute, SRM Institute of Science and Technology Chennai Tamil Nadu India
| | - Purabi Sarkar
- SRM Research Institute, SRM Institute of Science and Technology Chennai Tamil Nadu India
| | - Saraswathi N. T.
- Molecular Biophysics Lab School of Chemical and Biotechnology, SASTRA Deemed to be University Thanjavur Tamil Nadu India
| | - Ebtesam M. Al Olayan
- Department of Zoology College of Science, King Saud University Riyadh Saudi Arabia
| | - Abeer S. Aloufi
- Department of Zoology College of Science, King Saud University Riyadh Saudi Arabia
| | - Mohamed A. Elokaby
- Aquaculture Division National Institute of Oceanography and Fisheries (NIOF) Alexandria Egypt
| | - Aziz Arshad
- International Institute of Aquaculture and Aquatic Sciences (I‐AQUAS) Universiti Putra Malaysia Port Dickson Negeri Sembilan Malaysia
- Department of Aquaculture, Faculty of Agriculture University Putra Malaysia Serdang Selangor Malaysia
| | - Kanchana Mala
- Department of Medical Research Medical College Hospital & Research Centre, SRM Institute of Science & Technology Chennai Tamil Nadu India
| | - Jesu Arockiaraj
- SRM Research Institute, SRM Institute of Science and Technology Chennai Tamil Nadu India
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Mak M, Beattie KD, Basta A, Randall D, Chen ZH, Spooner-Hart R. Triangulation of methods using insect cell lines to investigate insecticidal mode-of-action. PEST MANAGEMENT SCIENCE 2021; 77:492-501. [PMID: 32815275 DOI: 10.1002/ps.6046] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 07/29/2020] [Accepted: 08/19/2020] [Indexed: 06/11/2023]
Abstract
BACKGROUND This study investigated three in vitro models to assist in elucidating possible mode-of-action, which could be adopted to evaluate insecticidal activity of complex, unknown, or multi-constituent formulations. We used a combination of absorbance spectrometry, confocal scanning laser microscopy and microelectrode ion flux estimation (MIFE) to provide insight into potential target sites for insecticides. This study used two insect cell lines and evaluated three pyrethroid insecticides. RESULTS We observed that the two cell lines produced distinctly different responses. Drosophila melanogaster D.mel-S2 cell line was a useful model to monitor ion flux changes, resulting from insecticides with neural toxicity; however, it was less useful to determine some metabolic pathway indicators of toxic stress. Conversely, the Spodoptera frugiperda Sf9 cell line produced acute reactive oxygen species (ROS) in response to insecticide treatments, but was not highly responsive in electrophysiological experiments. We also showed that the natural, multi-constituent botanical extract of pyrethrum elicited different Na+ , Cl- and Ca2+ ion fluxes than its synthetic, single constituent analogues, α-cypermethrin and esfenvalerate. These two methods used in combination with absorbance spectrometry measuring cell growth inhibition plus cell mortality assays shed some light on cytotoxic responses in differing model cell lines. CONCLUSION This research highlights the importance of using multiple cell types and interdisciplinary methods to provide a better insight into mode of insecticidal action. This is especially pertinent to novel biopesticide discovery, as the underlying mechanisms for toxicity in initial screening processes are likely to be unknown.
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Affiliation(s)
- Michelle Mak
- School of Science, Western Sydney University, Penrith, Australia
| | - Karren D Beattie
- School of Science, Western Sydney University, Penrith, Australia
| | - Albert Basta
- School of Science, Western Sydney University, Penrith, Australia
| | - David Randall
- School of Science, Western Sydney University, Penrith, Australia
| | - Zhong-Hua Chen
- School of Science, Western Sydney University, Penrith, Australia
- Hawkesbury Institute for the Environment, Western Sydney University, Penrith, Australia
| | - Robert Spooner-Hart
- Hawkesbury Institute for the Environment, Western Sydney University, Penrith, Australia
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Sensing through Non-Sensing Ocular Ion Channels. Int J Mol Sci 2020; 21:ijms21186925. [PMID: 32967234 PMCID: PMC7554890 DOI: 10.3390/ijms21186925] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 09/17/2020] [Accepted: 09/18/2020] [Indexed: 12/12/2022] Open
Abstract
Ion channels are membrane-spanning integral proteins expressed in multiple organs, including the eye. In the eye, ion channels are involved in various physiological processes, like signal transmission and visual processing. A wide range of mutations have been reported in the corresponding genes and their interacting subunit coding genes, which contribute significantly to an array of blindness, termed ocular channelopathies. These mutations result in either a loss- or gain-of channel functions affecting the structure, assembly, trafficking, and localization of channel proteins. A dominant-negative effect is caused in a few channels formed by the assembly of several subunits that exist as homo- or heteromeric proteins. Here, we review the role of different mutations in switching a “sensing” ion channel to “non-sensing,” leading to ocular channelopathies like Leber’s congenital amaurosis 16 (LCA16), cone dystrophy, congenital stationary night blindness (CSNB), achromatopsia, bestrophinopathies, retinitis pigmentosa, etc. We also discuss the various in vitro and in vivo disease models available to investigate the impact of mutations on channel properties, to dissect the disease mechanism, and understand the pathophysiology. Innovating the potential pharmacological and therapeutic approaches and their efficient delivery to the eye for reversing a “non-sensing” channel to “sensing” would be life-changing.
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Abstract
During morphogenesis, cells communicate with each other to shape tissues and organs. Several lines of recent evidence indicate that ion channels play a key role in cellular signaling and tissue morphogenesis. However, little is known about the scope of specific ion-channel types that impinge upon developmental pathways. The Drosophila melanogaster wing is an excellent model in which to address this problem as wing vein patterning is acutely sensitive to changes in developmental pathways. We conducted a screen of 180 ion channels expressed in the wing using loss-of-function mutant and RNAi lines. Here we identify 44 candidates that significantly impacted development of the Drosophila melanogaster wing. Calcium, sodium, potassium, chloride, and ligand-gated cation channels were all identified in our screen, suggesting that a wide variety of ion channel types are important for development. Ion channels belonging to the pickpocket family, the ionotropic receptor family, and the bestrophin family were highly represented among the candidates of our screen. Seven new ion channels with human orthologs that have been implicated in human channelopathies were also identified. Many of the human orthologs of the channels identified in our screen are targets of common general anesthetics, anti-seizure and anti-hypertension drugs, as well as alcohol and nicotine. Our results confirm the importance of ion channels in morphogenesis and identify a number of ion channels that will provide the basis for future studies to understand the role of ion channels in development.
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Okada Y, Okada T, Sato-Numata K, Islam MR, Ando-Akatsuka Y, Numata T, Kubo M, Shimizu T, Kurbannazarova RS, Marunaka Y, Sabirov RZ. Cell Volume-Activated and Volume-Correlated Anion Channels in Mammalian Cells: Their Biophysical, Molecular, and Pharmacological Properties. Pharmacol Rev 2019; 71:49-88. [PMID: 30573636 DOI: 10.1124/pr.118.015917] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
There are a number of mammalian anion channel types associated with cell volume changes. These channel types are classified into two groups: volume-activated anion channels (VAACs) and volume-correlated anion channels (VCACs). VAACs can be directly activated by cell swelling and include the volume-sensitive outwardly rectifying anion channel (VSOR), which is also called the volume-regulated anion channel; the maxi-anion channel (MAC or Maxi-Cl); and the voltage-gated anion channel, chloride channel (ClC)-2. VCACs can be facultatively implicated in, although not directly activated by, cell volume changes and include the cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, the Ca2+-activated Cl- channel (CaCC), and the acid-sensitive (or acid-stimulated) outwardly rectifying anion channel. This article describes the phenotypical properties and activation mechanisms of both groups of anion channels, including accumulating pieces of information on the basis of recent molecular understanding. To that end, this review also highlights the molecular identities of both anion channel groups; in addition to the molecular identities of ClC-2 and CFTR, those of CaCC, VSOR, and Maxi-Cl were recently identified by applying genome-wide approaches. In the last section of this review, the most up-to-date information on the pharmacological properties of both anion channel groups, especially their half-maximal inhibitory concentrations (IC50 values) and voltage-dependent blocking, is summarized particularly from the standpoint of pharmacological distinctions among them. Future physiologic and pharmacological studies are definitely warranted for therapeutic targeting of dysfunction of VAACs and VCACs.
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Affiliation(s)
- Yasunobu Okada
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Toshiaki Okada
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Kaori Sato-Numata
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Md Rafiqul Islam
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Yuhko Ando-Akatsuka
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Tomohiro Numata
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Machiko Kubo
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Takahiro Shimizu
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Ranohon S Kurbannazarova
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Yoshinori Marunaka
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Ravshan Z Sabirov
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
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10
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Miller AN, Vaisey G, Long SB. Molecular mechanisms of gating in the calcium-activated chloride channel bestrophin. eLife 2019; 8:43231. [PMID: 30628889 PMCID: PMC6342527 DOI: 10.7554/elife.43231] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Accepted: 01/02/2019] [Indexed: 11/13/2022] Open
Abstract
Bestrophin (BEST1-4) ligand-gated chloride (Cl-) channels are activated by calcium (Ca2+). Mutation of BEST1 causes retinal disease. Partly because bestrophin channels have no sequence or structural similarity to other ion channels, the molecular mechanisms underlying gating are unknown. Here, we present a series of cryo-electron microscopy structures of chicken BEST1, determined at 3.1 Å resolution or better, that represent the channel’s principal gating states. Unlike other channels, opening of the pore is due to the repositioning of tethered pore-lining helices within a surrounding protein shell that dramatically widens a neck of the pore through a concertina of amino acid rearrangements. The neck serves as both the activation and the inactivation gate. Ca2+ binding instigates opening of the neck through allosteric means whereas inactivation peptide binding induces closing. An aperture within the otherwise wide pore controls anion permeability. The studies define a new molecular paradigm for gating among ligand-gated ion channels.
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Affiliation(s)
- Alexandria N Miller
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - George Vaisey
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States.,Louis V. Gerstner Jr. Graduate School of Biomedical Sciences, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Stephen B Long
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
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11
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Zhang Y, Kittredge A, Ward N, Ji C, Chen S, Yang T. ATP activates bestrophin ion channels through direct interaction. Nat Commun 2018; 9:3126. [PMID: 30087350 PMCID: PMC6081419 DOI: 10.1038/s41467-018-05616-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 07/09/2018] [Indexed: 11/13/2022] Open
Abstract
Human Bestrophin1 (hBest1) is a Ca2+-activated Cl- channel in retinal pigment epithelium (RPE) essential for retina physiology, and its mutation results in retinal degenerative diseases that have no available treatments. Here, we discover that hBest1's channel activity in human RPE is significantly enhanced by adenosine triphosphate (ATP) in a dose-dependent manner. We further demonstrate a direct interaction between ATP and bestrophins, and map the ATP-binding motif on hBest1 to an intracellular loop adjacent to the channel activation gate. Importantly, a disease-causing mutation of hBest1 located within the ATP-binding motif, p.I201T, diminishes ATP-dependent activation of the channel in patient-derived RPE, while the corresponding mutants in bestrophin homologs display defective ATP binding and a conformational change in the ATP-binding motif. Taken together, our results identify ATP as a critical activator of bestrophins, and reveal the molecular mechanism of an hBest1 patient-specific mutation.
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Affiliation(s)
- Yu Zhang
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Alec Kittredge
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Nancy Ward
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Changyi Ji
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Shoudeng Chen
- Molecular Imaging Center, Department of Experimental Medicine, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, Guangzhou, 519000, China
| | - Tingting Yang
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA.
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12
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Oh SJ, Lee CJ. Distribution and Function of the Bestrophin-1 (Best1) Channel in the Brain. Exp Neurobiol 2017; 26:113-121. [PMID: 28680296 PMCID: PMC5491579 DOI: 10.5607/en.2017.26.3.113] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 06/08/2017] [Accepted: 06/08/2017] [Indexed: 12/29/2022] Open
Abstract
Bestrophin-1 (Best1) is a calcium-activated anion channel identified from retinal pigment epithelium where human mutations are associated with Best's macular degeneration. Best1 is known to be expressed in a variety of tissues including the brain, and is thought to be involved in many physiological processes. This review focuses on the current state of knowledge on aspects of expression and function of Best1 in the brain. Best1 protein is observed in cortical and hippocampal astrocytes, in cerebellar Bergmann glia and lamellar astrocytes, in thalamic reticular neurons, in meninges and in the epithelial cells of the choroid plexus. The most prominent feature of Best1 is its significant permeability to glutamate and GABA in addition to chloride ions because glutamate and GABA are important transmitters in the brain. Under physiological conditions, both Best1-mediated glutamate release and tonic GABA release from astrocytes modulate neuronal excitability, synaptic transmission and synaptic plasticity. Under pathological conditions such as neuroinflammation and neurodegeneration, reactive astrocytes phenotypically switch from GABA-negative to GABA-producing and redistribute Best1 from the perisynaptic microdomains to the soma and processes to tonically release GABA via Best1. This implicates that tonic GABA release from reactive astrocyte via redistributed Best1 is a common phenomenon that occur in various pathological conditions with astrogliosis such as traumatic brain injury, neuroinflammation, neurodegeneration, and hypoxic and ischemic insults. These properties of Best1, including the permeation and release of glutamate and GABA and its redistribution in reactive astrocytes, promise us exciting discoveries of novel brain functions to be uncovered in the future.
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Affiliation(s)
- Soo-Jin Oh
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Convergence Research Center for Diagnosis, Treatment and Care System of Dementia, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Center for Glia-Neuron Interaction, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
| | - C Justin Lee
- Center for Neuroscience, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.,Center for Glia-Neuron Interaction, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea
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13
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Duan Z, Kong F, Zhang L, Li W, Zhang J, Peng L. A bestrophin-like protein modulates the proton motive force across the thylakoid membrane in Arabidopsis. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2016; 58:848-858. [PMID: 26947269 PMCID: PMC5074266 DOI: 10.1111/jipb.12475] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 03/03/2016] [Indexed: 05/20/2023]
Abstract
During photosynthesis, photosynthetic electron transport generates a proton motive force (pmf) across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is composed of an electric potential (ΔΨ) and an osmotic component (ΔpH). Partitioning between these components in chloroplasts is strictly regulated in response to fluctuating environments. However, our knowledge of the molecular mechanisms that regulate pmf partitioning is limited. Here, we report a bestrophin-like protein (AtBest), which is critical for pmf partitioning. While the ΔpH component was slightly reduced in atbest, the ΔΨ component was much greater in this mutant than in the wild type, resulting in less efficient activation of nonphotochemical quenching (NPQ) upon both illumination and a shift from low light to high light. Although no visible phenotype was observed in the atbest mutant in the greenhouse, this mutant exhibited stronger photoinhibition than the wild type when grown in the field. AtBest belongs to the bestrophin family proteins, which are believed to function as chloride (Cl- ) channels. Thus, our findings reveal an important Cl- channel required for ion transport and homeostasis across the thylakoid membrane in higher plants. These processes are essential for fine-tuning photosynthesis under fluctuating environmental conditions.
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Affiliation(s)
- Zhikun Duan
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fanna Kong
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Lin Zhang
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Wenjing Li
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | - Jiao Zhang
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | - Lianwei Peng
- Key Laboratory of Photobiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
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14
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Mislocalisation of BEST1 in iPSC-derived retinal pigment epithelial cells from a family with autosomal dominant vitreoretinochoroidopathy (ADVIRC). Sci Rep 2016; 6:33792. [PMID: 27653836 PMCID: PMC5031956 DOI: 10.1038/srep33792] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 08/26/2016] [Indexed: 12/31/2022] Open
Abstract
Autosomal dominant vitreoretinochoroidopathy (ADVIRC) is a rare, early-onset retinal dystrophy characterised by distinct bands of circumferential pigmentary degeneration in the peripheral retina and developmental eye defects. ADVIRC is caused by mutations in the Bestrophin1 (BEST1) gene, which encodes a transmembrane protein thought to function as an ion channel in the basolateral membrane of retinal pigment epithelial (RPE) cells. Previous studies suggest that the distinct ADVIRC phenotype results from alternative splicing of BEST1 pre-mRNA. Here, we have used induced pluripotent stem cell (iPSC) technology to investigate the effects of an ADVIRC associated BEST1 mutation (c.704T > C, p.V235A) in patient-derived iPSC-RPE. We found no evidence of alternate splicing of the BEST1 transcript in ADVIRC iPSC-RPE, however in patient-derived iPSC-RPE, BEST1 was expressed at the basolateral membrane and the apical membrane. During human eye development we show that BEST1 is expressed more abundantly in peripheral RPE compared to central RPE and is also expressed in cells of the developing retina. These results suggest that higher levels of mislocalised BEST1 expression in the periphery, from an early developmental stage, could provide a mechanism that leads to the distinct clinical phenotype observed in ADVIRC patients.
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15
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Boedtkjer E, Matchkov VV, Boedtkjer DMB, Aalkjaer C. Negative News: Cl− and HCO3− in the Vascular Wall. Physiology (Bethesda) 2016; 31:370-83. [DOI: 10.1152/physiol.00001.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Cl− and HCO3− are the most prevalent membrane-permeable anions in the intra- and extracellular spaces of the vascular wall. Outwardly directed electrochemical gradients for Cl− and HCO3− permit anion channel opening to depolarize vascular smooth muscle and endothelial cells. Transporters and channels for Cl− and HCO3− also modify vascular contractility and structure independently of membrane potential. Transport of HCO3− regulates intracellular pH and thereby modifies the activity of enzymes, ion channels, and receptors. There is also evidence that Cl− and HCO3− transport proteins affect gene expression and protein trafficking. Considering the extensive implications of Cl− and HCO3− in the vascular wall, it is critical to understand how these ions are transported under physiological conditions and how disturbances in their transport can contribute to disease development. Recently, sensing mechanisms for Cl− and HCO3− have been identified in the vascular wall where they modify ion transport and vasomotor function, for instance, during metabolic disturbances. This review discusses current evidence that transport (e.g., via NKCC1, NBCn1, Ca2+-activated Cl− channels, volume-regulated anion channels, and CFTR) and sensing (e.g., via WNK and RPTPγ) of Cl− and HCO3− influence cardiovascular health and disease.
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Affiliation(s)
| | | | - Donna M. B. Boedtkjer
- Department of Biomedicine, Aarhus University, Denmark
- Department of Clinical Medicine, Aarhus University, Denmark; and
| | - Christian Aalkjaer
- Department of Biomedicine, Aarhus University, Denmark
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark
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16
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Dam VS, Boedtkjer DMB, Aalkjaer C, Matchkov V. The bestrophin- and TMEM16A-associated Ca(2+)- activated Cl(–) channels in vascular smooth muscles. Channels (Austin) 2015; 8:361-9. [PMID: 25478625 PMCID: PMC4203738 DOI: 10.4161/chan.29531] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The presence of Ca2+-activated Cl– currents (ICl(Ca)) in vascular smooth muscle cells (VSMCs) is well established. ICl(Ca) are supposedly important for arterial contraction by linking changes in [Ca2+]i and membrane depolarization. Bestrophins and some members of the TMEM16 protein family were recently associated with ICl(Ca). Two distinct ICl(Ca) are characterized in VSMCs; the cGMP-dependent ICl(Ca) dependent upon bestrophin expression and the ‘classical’ Ca2+-activated Cl– current, which is bestrophin-independent. Interestingly, TMEM16A is essential for both the cGMP-dependent and the classical ICl(Ca). Furthermore, TMEM16A has a role in arterial contraction while bestrophins do not. TMEM16A’s role in the contractile response cannot be explained however only by a simple suppression of the depolarization by Cl– channels. It is suggested that TMEM16A expression modulates voltage-gated Ca2+ influx in a voltage-independent manner and recent studies also demonstrate a complex role of TMEM16A in modulating other membrane proteins.
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17
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Leblanc N, Forrest AS, Ayon RJ, Wiwchar M, Angermann JE, Pritchard HAT, Singer CA, Valencik ML, Britton F, Greenwood IA. Molecular and functional significance of Ca(2+)-activated Cl(-) channels in pulmonary arterial smooth muscle. Pulm Circ 2015; 5:244-68. [PMID: 26064450 DOI: 10.1086/680189] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 07/22/2014] [Indexed: 12/31/2022] Open
Abstract
Increased peripheral resistance of small distal pulmonary arteries is a hallmark signature of pulmonary hypertension (PH) and is believed to be the consequence of enhanced vasoconstriction to agonists, thickening of the arterial wall due to remodeling, and increased thrombosis. The elevation in arterial tone in PH is attributable, at least in part, to smooth muscle cells of PH patients being more depolarized and displaying higher intracellular Ca(2+) levels than cells from normal subjects. It is now clear that downregulation of voltage-dependent K(+) channels (e.g., Kv1.5) and increased expression and activity of voltage-dependent (Cav1.2) and voltage-independent (e.g., canonical and vanilloid transient receptor potential [TRPC and TRPV]) Ca(2+) channels play an important role in the functional remodeling of pulmonary arteries in PH. This review focuses on an anion-permeable channel that is now considered a novel excitatory mechanism in the systemic and pulmonary circulations. It is permeable to Cl(-) and is activated by a rise in intracellular Ca(2+) concentration (Ca(2+)-activated Cl(-) channel, or CaCC). The first section outlines the biophysical and pharmacological properties of the channel and ends with a description of the molecular candidate genes postulated to encode for CaCCs, with particular emphasis on the bestrophin and the newly discovered TMEM16 and anoctamin families of genes. The second section provides a review of the various sources of Ca(2+) activating CaCCs, which include stimulation by mobilization from intracellular Ca(2+) stores and Ca(2+) entry through voltage-dependent and voltage-independent Ca(2+) channels. The third and final section summarizes recent findings that suggest a potentially important role for CaCCs and the gene TMEM16A in PH.
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Affiliation(s)
- Normand Leblanc
- Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA
| | - Abigail S Forrest
- Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA
| | - Ramon J Ayon
- Department of Medicine, University of Illinois, Chicago, Illinois, USA
| | - Michael Wiwchar
- Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA
| | - Jeff E Angermann
- School of Community Health Sciences, University of Nevada, Reno, Nevada, USA
| | - Harry A T Pritchard
- Vascular Biology Research Centre, Institute of Cardiovascular and Cell Sciences, St. George's University of London, London, United Kingdom
| | - Cherie A Singer
- Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, USA
| | - Maria L Valencik
- Department of Biochemistry and Molecular Biology, University of Nevada School of Medicine, Reno, Nevada, USA
| | - Fiona Britton
- Department of Physiology, School of Medical Sciences, University of New South Wales, Sydney, Australia
| | - Iain A Greenwood
- Vascular Biology Research Centre, Institute of Cardiovascular and Cell Sciences, St. George's University of London, London, United Kingdom
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18
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Bestrophin 1 is indispensable for volume regulation in human retinal pigment epithelium cells. Proc Natl Acad Sci U S A 2015; 112:E2630-9. [PMID: 25941382 DOI: 10.1073/pnas.1418840112] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
In response to cell swelling, volume-regulated anion channels (VRACs) participate in a process known as regulatory volume decrease (RVD). Only recently, first insight into the molecular identity of mammalian VRACs was obtained by the discovery of the leucine-rich repeats containing 8A (LRRC8A) gene. Here, we show that bestrophin 1 (BEST1) but not LRRC8A is crucial for volume regulation in human retinal pigment epithelium (RPE) cells. Whole-cell patch-clamp recordings in RPE derived from human-induced pluripotent stem cells (hiPSC) exhibit an outwardly rectifying chloride current with characteristic functional properties of VRACs. This current is severely reduced in hiPSC-RPE cells derived from macular dystrophy patients with pathologic BEST1 mutations. Disruption of the orthologous mouse gene (Best1(-/-)) does not result in obvious retinal pathology but leads to a severe subfertility phenotype in agreement with minor endogenous expression of Best1 in murine RPE but highly abundant expression in mouse testis. Sperm from Best1(-/-) mice showed reduced motility and abnormal sperm morphology, indicating an inability in RVD. Together, our data suggest that the molecular identity of VRACs is more complex--that is, instead of a single ubiquitous channel, VRACs could be formed by cell type- or tissue-specific subunit composition. Our findings provide the basis to further examine VRAC diversity in normal and diseased cell physiology, which is key to exploring novel therapeutic approaches in VRAC-associated pathologies.
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19
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Bulley S, Jaggar JH. Cl⁻ channels in smooth muscle cells. Pflugers Arch 2014; 466:861-72. [PMID: 24077695 DOI: 10.1007/s00424-013-1357-2] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 09/09/2013] [Accepted: 09/09/2013] [Indexed: 10/26/2022]
Abstract
In smooth muscle cells (SMCs), the intracellular chloride ion (Cl−) concentration is high due to accumulation by Cl−/HCO3− exchange and Na+–K+–Cl− cotransportation. The equilibrium potential for Cl− (ECl) is more positive than physiological membrane potentials (Em), with Cl− efflux inducing membrane depolarization. Early studies used electrophysiology and nonspecific antagonists to study the physiological relevance of Cl− channels in SMCs. More recent reports have incorporated molecular biological approaches to identify and determine the functional significance of several different Cl− channels. Both "classic" and cGMP-dependent calcium (Ca2+)-activated (ClCa) channels and volume-sensitive Cl− channels are present, with TMEM16A/ANO1, bestrophins, and ClC-3, respectively, proposed as molecular candidates for these channels. The cystic fibrosis transmembrane conductance regulator (CFTR) has also been described in SMCs. This review will focus on discussing recent progress made in identifying each of these Cl− channels in SMCs, their physiological functions, and contribution to diseases that modify contraction, apoptosis, and cell proliferation.
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20
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Kane Dickson V, Pedi L, Long SB. Structure and insights into the function of a Ca(2+)-activated Cl(-) channel. Nature 2014; 516:213-8. [PMID: 25337878 DOI: 10.1038/nature13913] [Citation(s) in RCA: 154] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 10/06/2014] [Indexed: 01/22/2023]
Abstract
Bestrophin calcium-activated chloride channels (CaCCs) regulate the flow of chloride and other monovalent anions across cellular membranes in response to intracellular calcium (Ca(2+)) levels. Mutations in bestrophin 1 (BEST1) cause certain eye diseases. Here we present X-ray structures of chicken BEST1-Fab complexes, at 2.85 Å resolution, with permeant anions and Ca(2+). Representing, to our knowledge, the first structure of a CaCC, the eukaryotic BEST1 channel, which recapitulates CaCC function in liposomes, is formed from a pentameric assembly of subunits. Ca(2+) binds to the channel's large cytosolic region. A single ion pore, approximately 95 Å in length, is located along the central axis and contains at least 15 binding sites for anions. A hydrophobic neck within the pore probably forms the gate. Phenylalanine residues within it may coordinate permeating anions via anion-π interactions. Conformational changes observed near the 'Ca(2+) clasp' hint at the mechanism of Ca(2+)-dependent gating. Disease-causing mutations are prevalent within the gating apparatus.
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Affiliation(s)
- Veronica Kane Dickson
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Leanne Pedi
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Stephen B Long
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
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21
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Abstract
Human Bestrophin 1 (hBest1) is a calcium-activated chloride channel that regulates neuronal excitability, synaptic activity, and retinal homeostasis. Mutations in hBest1 cause the autosomal-dominant Best macular dystrophy (BMD). Because hBest1 mutations cause BMD, but a knockout does not, we wondered if hBest1 mutants exert a dominant negative effect through interaction with other calcium-activated chloride channels, such as hBest2, 3, or 4, or transmembrane member 16A (TMEM16A), a member of another channel family. The subunit architecture of Best channels is debated, and their ability to form heteromeric channel assemblies is unclear. Using single-molecule subunit analysis, we find that each of hBest1, 2, 3, and 4 forms a homotetrameric channel. Despite considerable conservation among hBests, hBest1 has little or no interaction with other hBests or mTMEM16A. We identify the domain responsible for assembly specificity. This domain also plays a role in channel function. Our results indicate that Best channels preferentially self-assemble into homotetramers.
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22
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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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23
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Duran C, Chien LT, Hartzell HC. Drosophila bestrophin-1 currents are regulated by phosphorylation via a CaMKII dependent mechanism. PLoS One 2013; 8:e58875. [PMID: 23554946 PMCID: PMC3595206 DOI: 10.1371/journal.pone.0058875] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 02/07/2013] [Indexed: 11/19/2022] Open
Abstract
Cell swelling induced by hypo-osmotic stress results in activation of volume-regulated anion channels (VRAC) that drive a compensatory regulatory volume decrease. We have previously shown that the Best1 gene in Drosophila encodes a VRAC that is also activated by increases in intracellular Ca2+. The role of Best1 as a VRAC has recently been independently confirmed by the Clapham lab in an unbiased RNAi screen. Although dBest1 is clearly a volume-regulated channel, its mechanisms of regulation remain unknown. Here we investigate Drosophila Best1 (dBest1) regulation using the Drosophila S2 cell model system. Because dBest1 activates slowly after establishing whole-cell recording, we tested the hypothesis that the channel is activated by phosphorylation. Two experiments indicate that phosphorylation is required for dBest1 activation: nonspecific protein kinase inhibitors or intracellular perfusion with the non-hydrolyzable ATP analog AMP-PNP dramatically reduce the amplitude of dBest1 currents. Furthermore, intracellular perfusion with ATP-γ-S augments channel activation. The kinase responsible for dBest1 activation is likely Ca2+/calmodulin dependent kinase II (CaMKII), because specific inhibitors of this kinase dramatically inhibit dBest1 current activation. Neither specific PKA inhibitors nor inactive control inhibitors have effects on dBest1currents. Our results demonstrate that dBest1 currents are regulated by phosphorylation via a CaMKII dependent mechanism.
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Affiliation(s)
- Charity Duran
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Li-Ting Chien
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - H. Criss Hartzell
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia, United States of America
- * E-mail:
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24
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Channel-mediated astrocytic glutamate release via Bestrophin-1 targets synaptic NMDARs. Mol Brain 2013; 6:4. [PMID: 23324492 PMCID: PMC3577500 DOI: 10.1186/1756-6606-6-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Accepted: 01/14/2013] [Indexed: 11/16/2022] Open
Abstract
Background Astrocytes regulate neuronal excitability and synaptic activity by releasing gliotransmitters such as glutamate. Our recent study demonstrated that astrocytes release glutamate upon GPCR activation via Ca2+ activated anion channel, Bestrophin-1 (Best1). The target of Best1-mediated astrocytic glutamate has been shown to be the neuronal NMDA receptors (NMDAR). However, whether it targets synaptically or extra-synaptically localized NMDAR is not known. Findings We recorded spontaneous miniature excitatory postsynaptic currents (mEPSCs) from CA1 pyramidal cells to test whether Best1-mediated astrocytic glutamate targets synaptic NMDAR. An agonist of protease activated receptor 1 (PAR1) was used to induce astrocytic Ca2+ increase and glutamate release. Firstly, we found that activation of PAR1 and subsequent release of glutamate from astrocyte does not alone increase the frequency of mEPSCs. Secondly, we found that mEPSC rise time is variable depending on the different electrotonic distances from the somatic recording site to the synaptic region where each mEPSC occurs. Two subgroups of mEPSC from CA1 pyramidal neuron by rise time were selected and analyzed. One group is fast rising mEPSCs with a rise time of 1 ~ 5 ms, representing synaptic activities arising from proximal dendrites. The other group is slowly rising mEPSCs with a rise time of 5 ~ 10 ms, representing synaptic events arising from glutamate release at synapses located in the distal dendrites. We used cell-type specific Best1 gene silencing system by Cre-loxP cleavage to dissociate the effect of neuronal and astrocytic Best1. Astrocytic Best1-mediated glutamate release by PAR1 activation did not affect decay kinetics, frequency, and amplitude of fast rising mEPSC. In contrast, PAR1 activation resulted in an NMDA receptor component to be present on slowly rising mEPSC, but did not alter frequency or amplitude. Conclusions Our results indicate that astrocytic glutamate via Best1 channel targets and activates synaptic NMDARs.
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Matchkov VV, Secher Dam V, Bødtkjer DMB, Aalkjær C. Transport and Function of Chloride in Vascular Smooth Muscles. J Vasc Res 2013; 50:69-87. [DOI: 10.1159/000345242] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2012] [Accepted: 10/16/2012] [Indexed: 12/12/2022] Open
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François A, Grauso M, Demondion E, Bozzolan F, Debernard S, Lucas P. Bestrophin-encoded Ca²⁺-activated Cl⁻ channels underlie a current with properties similar to the native current in the moth Spodoptera littoralis olfactory receptor neurons. PLoS One 2012; 7:e52691. [PMID: 23300744 PMCID: PMC3530479 DOI: 10.1371/journal.pone.0052691] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2012] [Accepted: 11/20/2012] [Indexed: 11/19/2022] Open
Abstract
Responses of insect olfactory receptor neurons (ORNs) involve an entry of Ca2+ through olfactory heterodimeric receptor complexes. In moths, the termination of ORN responses was found to strongly depend on the external Ca2+ concentration through the activation of unknown Ca2+-dependent Cl− channels. We thus investigated the molecular identity of these Cl− channels. There is compelling evidence that bestrophins form Cl− channels when expressed in heterologous systems. Here we provide evidence that antennae of the moth Spodoptera littoralis express three transcripts encoding proteins with hallmarks of bestrophins. One of these transcripts, SlitBest1b, is expressed in ORNs. The heterologous expression of SlitBest1b protein in CHO-K1 cells yielded a Ca2+-activated Cl− current that shares electrophysiological properties with the native Ca2+-activated Cl− current of ORNs. Both currents are anionic, present similar dependence on the intracellular Ca2+ concentration, partly inactivate over time, have the same anion permeability sequence, the same sequence of inhibitory efficiency of blockers, the same almost linear I–V relationships and finally both currents do not depend on the cell volume. Therefore, our data suggest that SlitBest1b is a good candidate for being a molecular component of the olfactory Ca2+-activated Cl− channel and is likely to constitute part of the insect olfactory transduction pathway. A different function (e.g. regulation of other proteins, maintenance of the anionic homeostasis in the sensillar lymph) and a different role (e.g. involvement in the olfactory system development) cannot be excluded however.
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Affiliation(s)
- Adrien François
- Institut National de la Recherche Agronomique, UMR 1272 Physiologie de l’Insecte : Signalisation et Communication, Versailles, France
- Université Pierre et Marie Curie, UMR 1272 Physiologie de l’Insecte: Signalisation et Communication, Paris, France
| | - Marta Grauso
- Institut National de la Recherche Agronomique, UMR 1272 Physiologie de l’Insecte : Signalisation et Communication, Versailles, France
| | - Elodie Demondion
- Institut National de la Recherche Agronomique, UMR 1272 Physiologie de l’Insecte : Signalisation et Communication, Versailles, France
| | - Françoise Bozzolan
- Université Pierre et Marie Curie, UMR 1272 Physiologie de l’Insecte: Signalisation et Communication, Paris, France
| | - Stéphane Debernard
- Université Pierre et Marie Curie, UMR 1272 Physiologie de l’Insecte: Signalisation et Communication, Paris, France
| | - Philippe Lucas
- Institut National de la Recherche Agronomique, UMR 1272 Physiologie de l’Insecte : Signalisation et Communication, Versailles, France
- * E-mail:
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Diykov D, Jenson LJ, Bloomquist JR. Voltage-sensitive chloride ion channels in Anopheles gambiae Sua-1B cells. INVERTEBRATE NEUROSCIENCE 2012; 13:57-62. [DOI: 10.1007/s10158-012-0143-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Accepted: 10/29/2012] [Indexed: 01/21/2023]
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Oh SJ, Han KS, Park H, Woo DH, Kim HY, Traynelis SF, Lee CJ. Protease activated receptor 1-induced glutamate release in cultured astrocytes is mediated by Bestrophin-1 channel but not by vesicular exocytosis. Mol Brain 2012; 5:38. [PMID: 23062602 PMCID: PMC3539998 DOI: 10.1186/1756-6606-5-38] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Accepted: 10/09/2012] [Indexed: 11/27/2022] Open
Abstract
Background Glutamate is the major transmitter that mediates the principal form of excitatory synaptic transmission in the brain. It has been well established that glutamate is released via Ca2+-dependent exocytosis of glutamate-containing vesicles in neurons. However, whether astrocytes exocytose to release glutamate under physiological condition is still unclear. Findings We report a novel form of glutamate release in astrocytes via the recently characterized Ca2+-activated anion channel, Bestrophin-1 (Best1) by Ca2+ dependent mechanism through the channel pore. We demonstrate that upon activation of protease activated receptor 1 (PAR1), an increase in intracellular Ca2+ concentration leads to an opening of Best1 channels and subsequent release of glutamate in cultured astrocytes. Conclusions These results provide strong molecular evidence for potential astrocyte-neuron interaction via Best1-mediated glutamate release.
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Affiliation(s)
- Soo-Jin Oh
- Korea Institute of Science and Technology, Seoul, South Korea
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Liang L, Woodward OM, Chen Z, Cotter R, Guggino WB. A novel role of protein tyrosine kinase2 in mediating chloride secretion in human airway epithelial cells. PLoS One 2011; 6:e21991. [PMID: 21765932 PMCID: PMC3135607 DOI: 10.1371/journal.pone.0021991] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2011] [Accepted: 06/14/2011] [Indexed: 11/25/2022] Open
Abstract
Ca2+ activated Cl− channels (CaCC) are up-regulated in cystic fibrosis (CF) airway surface epithelia. The presence and functional properties of CaCC make it a possible therapeutic target to compensate for the deficiency of Cl− secretion in CF epithelia. CaCC is activated by an increase in cytosolic Ca2+, which not only activates epithelial CaCCs, but also inhibits epithelial Na+ hyperabsorption, which may also be beneficial in CF. Our previous study has shown that spiperone, a known antipsychotic drug, activates CaCCs and stimulates Cl− secretion in polarized human non-CF and CF airway epithelial cell monolayers in vitro, and in Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) knockout mice in vivo. Spiperone activates CaCC not by acting in its well-known role as an antagonist of either 5-HT2 or D2 receptors, but through a protein tyrosine kinase-coupled phospholipase C-dependent pathway. Moreover, spiperone independently activates CFTR through a novel mechanism. Herein, we performed a mass spectrometry analysis and identified the signaling molecule that mediates the spiperone effect in activating chloride secretion through CaCC and CFTR. Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor protein tyrosine kinase, which belongs to the focal adhesion kinase family. The inhibition of PYK2 notably reduced the ability of spiperone to increase intracellular Ca2+ and Cl− secretion. In conclusion, we have identified the tyrosine kinase, PYK2, as the modulator, which plays a crucial role in the activation of CaCC and CFTR by spiperone. The identification of this novel role of PYK2 reveals a new signaling pathway in human airway epithelial cells.
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Affiliation(s)
- Lihua Liang
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Owen M. Woodward
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Zhaohui Chen
- Department of Pharmacology and Molecular Science, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Robert Cotter
- Department of Pharmacology and Molecular Science, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - William B. Guggino
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland
- * E-mail: .
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Roberts SK, Milnes J, Caddick M. Characterisation of AnBEST1, a functional anion channel in the plasma membrane of the filamentous fungus, Aspergillus nidulans. Fungal Genet Biol 2011; 48:928-38. [PMID: 21596151 DOI: 10.1016/j.fgb.2011.05.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Revised: 05/03/2011] [Accepted: 05/04/2011] [Indexed: 11/29/2022]
Abstract
Two distant homologues of the bestrophin gene family have been identified in the filamentous fungus, Aspergillus nidulans (anbest1 and anbest2). AnBEST1 was functionally characterised using the patch clamp technique and was shown to be an anion selective channel permeable to citrate. Furthermore, AnBEST1 restored the growth of the pdr12Δ yeast mutant on inhibitory concentrations of extracellular propionate, benzoate and sorbate, also consistent with carboxylated organic anion permeation of AnBEST1. Similar to its animal counterparts, AnBEST1 currents were activated by elevated cytosolic Ca(2+) with a K(d) of 1.60μM. Single channel currents showed long (>10s) open and closed times with a unitary conductance of 16.3pS. Transformation of A. nidulans with GFP-tagged AnBEST1 revealed that AnBEST1 localised to the plasma membrane. An anbest1 null mutant was generated to investigate the possibility that AnBEST1 mediated organic anion efflux across the plasma membrane. Although organic anion efflux was reduced from anbest1 null mutants, this phenotype was linked to the restoration of uracil/uridine-requiring A. nidulans strains to uracil/uridine prototrophy. In conclusion, this study identifies a new family of organic anion-permeable channels in filamentous fungi. We also reveal that uracil/uridine-requiring Aspergillus strains exhibit altered organic anion metabolism which could have implications for the interpretation of physiological studies using auxotrophic Aspergillus strains.
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Affiliation(s)
- Stephen K Roberts
- Division of Biomedical and Life Sciences, School of Health and Medicine, Lancaster University, Lancaster, UK.
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Duran C, Thompson CH, Xiao Q, Hartzell HC. Chloride channels: often enigmatic, rarely predictable. Annu Rev Physiol 2010; 72:95-121. [PMID: 19827947 DOI: 10.1146/annurev-physiol-021909-135811] [Citation(s) in RCA: 241] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Until recently, anion (Cl(-)) channels have received considerably less attention than cation channels. One reason for this may be that many Cl(-) channels perform functions that might be considered cell-biological, like fluid secretion and cell volume regulation, whereas cation channels have historically been associated with cellular excitability, which typically happens more rapidly. In this review, we discuss the recent explosion of interest in Cl(-) channels, with special emphasis on new and often surprising developments over the past five years. This is exemplified by the findings that more than half of the ClC family members are antiporters, and not channels, as was previously thought, and that bestrophins, previously prime candidates for Ca(2+)-activated Cl(-) channels, have been supplanted by the newly discovered anoctamins and now hold a tenuous position in the Cl(-) channel world.
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Affiliation(s)
- Charity Duran
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA
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Davidson AE, Millar ID, Urquhart JE, Burgess-Mullan R, Shweikh Y, Parry N, O'Sullivan J, Maher GJ, McKibbin M, Downes SM, Lotery AJ, Jacobson SG, Brown PD, Black GC, Manson FD. Missense mutations in a retinal pigment epithelium protein, bestrophin-1, cause retinitis pigmentosa. Am J Hum Genet 2009; 85:581-92. [PMID: 19853238 PMCID: PMC2775838 DOI: 10.1016/j.ajhg.2009.09.015] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Revised: 09/16/2009] [Accepted: 09/24/2009] [Indexed: 10/20/2022] Open
Abstract
Bestrophin-1 is preferentially expressed at the basolateral membrane of the retinal pigmented epithelium (RPE) of the retina. Mutations in the BEST1 gene cause the retinal dystrophies vitelliform macular dystrophy, autosomal-dominant vitreochoroidopathy, and autosomal-recessive bestrophinopathy. Here, we describe four missense mutations in bestrophin-1, three that we believe are previously unreported, in patients diagnosed with autosomal-dominant and -recessive forms of retinitis pigmentosa (RP). The physiological function of bestrophin-1 remains poorly understood although its heterologous expression induces a Cl--specific current. We tested the effect of RP-causing variants on Cl- channel activity and cellular localization of bestrophin-1. Two (p.L140V and p.I205T) produced significantly decreased chloride-selective whole-cell currents in comparison to those of wild-type protein. In a model system of a polarized epithelium, two of three mutations (p.L140V and p.D228N) caused mislocalization of bestrophin-1 from the basolateral membrane to the cytoplasm. Mutations in bestrophin-1 are increasingly recognized as an important cause of inherited retinal dystrophy.
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Affiliation(s)
- Alice E. Davidson
- Genetic Medicine, The University of Manchester, Manchester Academic Heath Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
| | - Ian D. Millar
- Faculty of Life Sciences, The University of Manchester, Manchester, UK
| | - Jill E. Urquhart
- National Genetics Reference Laboratory, St. Mary's Hospital, Manchester, UK
| | - Rosemary Burgess-Mullan
- Genetic Medicine, The University of Manchester, Manchester Academic Heath Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
| | - Yusrah Shweikh
- Genetic Medicine, The University of Manchester, Manchester Academic Heath Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
| | - Neil Parry
- Manchester Royal Eye Hospital, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
| | - James O'Sullivan
- National Genetics Reference Laboratory, St. Mary's Hospital, Manchester, UK
| | - Geoffrey J. Maher
- Genetic Medicine, The University of Manchester, Manchester Academic Heath Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
| | | | | | | | - Samuel G. Jacobson
- Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, PA, USA
| | - Peter D. Brown
- Faculty of Life Sciences, The University of Manchester, Manchester, UK
| | - Graeme C.M. Black
- Genetic Medicine, The University of Manchester, Manchester Academic Heath Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
- Manchester Royal Eye Hospital, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
| | - Forbes D.C. Manson
- Genetic Medicine, The University of Manchester, Manchester Academic Heath Science Centre, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK
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Abstract
In mammalian brain, neurons and astrocytes are reported to express various chloride and anion channels, but the evidence for functional expression of Ca(2+)-activated anion channel (CAAC) and its molecular identity have been lacking. Here we report electrophysiological evidence for the CAAC expression and its molecular identity by mouse Bestrophin 1 (mBest1) in astrocytes of the mouse brain. Using Ca(2+) imaging and perforated-patch-clamp analysis, we demonstrate that astrocytes displayed an inward current at holding potential of -70 mV that was dependent on an increase in intracellular Ca(2+) after G(alphaq)-coupled receptor activation. This current was mediated mostly by anions and was sensitive to well known anion channel blockers such as niflumic acid, 5-nitro-2(3-phenylpropylamino)-benzoic acid, and flufenamic acid. To find the molecular identity of the anion channel responsible for the CAAC current, we analyzed the expression of candidate genes and found that the mRNA for mouse mBest1 is predominantly expressed in acutely dissociated or cultured astrocytes. Whole-cell patch-clamp analysis using HEK293T cells heterologously expressing full-length mBest1 showed a Ca(2+)-dependent current mediated by mBest1, with a complete impairment of the current by a putative pore mutation, W93C. Furthermore, mBest1-mediated CAAC from cultured astrocytes was significantly reduced by expression of mBest1-specific short hairpin RNA (shRNA), suggesting that the CAAC is mediated by a channel encoded by mBest1. Finally, hippocampal CA1 astrocytes in hippocampal slice also showed mBest1-mediated CAAC because it was inhibited by mBest1-specific shRNA. Collectively, these data provide molecular evidence that the mBest1 channel is responsible for CAAC function in astrocytes.
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Xiao Q, Yu K, Cui YY, Hartzell HC. Dysregulation of human bestrophin-1 by ceramide-induced dephosphorylation. J Physiol 2009; 587:4379-91. [PMID: 19635817 DOI: 10.1113/jphysiol.2009.176800] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Best vitelliform macular dystrophy is an inherited autosomal dominant, juvenile onset form of macular degeneration caused by mutations in a chloride ion channel, human bestrophin-1 (hBest1). Mutations in Best1 have also been linked to several other forms of retinopathy. In addition to mutations, hBest1 dysfunction might come about by disruption of other processes that regulate Best1 function. Here we show that hBest1 chloride channel activity is regulated by ceramide and phosphorylation. We have identified a protein kinase C (PKC) phosphorylation site (serine 358) in hBest1 that is important for sustained channel function. Channel activity is maintained by PKC activators, protein phosphatase inhibitors, or pseudo-phosphorylation by substitution of glutamic acid for serine 358. When ceramide levels are elevated by exogenous addition of ceramide to the bath, by addition of bacterial sphingomyelinase, or by hypertonic stress, S358 is rapidly dephosphorylated. The dephosphorylation is mediated by protein phosphatase 2A. Hypertonic stress-induced dephosphorylation is blocked by a dihydroceramide, an inactive form of ceramide, and manumycin, an inhibitor of neutral sphingomyelinase. Our results support a model in which ceramide accumulation during early stages of retinopathy inhibits hBest1 function, leading to abnormal fluid transport across the retina, and enhanced inflammation.
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Affiliation(s)
- Qinghuan Xiao
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322, USA
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Qu Z, Cheng W, Cui Y, Cui Y, Zheng J. Human disease-causing mutations disrupt an N-C-terminal interaction and channel function of bestrophin 1. J Biol Chem 2009; 284:16473-16481. [PMID: 19372599 PMCID: PMC2713530 DOI: 10.1074/jbc.m109.002246] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2009] [Revised: 04/01/2009] [Indexed: 11/06/2022] Open
Abstract
Mutations in the human bestrophin 1 (hBest1) chloride channel cause Best vitelliform macular dystrophy. Although mutations in its transmembrane domains were found to alter biophysical properties of the channel, the mechanism for disease-causing mutations in its N and C termini remains elusive. We hypothesized that these mutations lead to channel dysfunction through disruption of an N-C-terminal interaction. Here, we present data demonstrating that hBest1 N and C termini indeed interact both in vivo and in vitro. In addition, using a spectrum-based fluorescence resonance energy transfer method, we showed that functional hBest1 channels in the plasma membrane were multimers. Disease-causing mutations in the N terminus (R19C, R25C, and K30C) and the C terminus (G299E, D301N, and D312N) caused channel dysfunction and disruption of the N-C interaction. Consistent with the functional and biochemical results, mutants D301N and D312N clearly reduced fluorescence resonance energy transfer signal, indicating that the N-C interaction was indeed perturbed. These results suggest that hBest1 functions as a multimer in the plasma membrane, and disruption of the N-C interaction by mutations leads to hBest1 channel dysfunction.
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Affiliation(s)
- Zhiqiang Qu
- From the Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322; Department of Physiology, Qingdao University School of Medicine, Qingdao, Shandong 266071, China.
| | - Wei Cheng
- Department of Physiology and Membrane Biology, University of California, School of Medicine, Davis, California 95616
| | - Yuanyuan Cui
- From the Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Yuanyuan Cui
- Department of Physiology and Membrane Biology, University of California, School of Medicine, Davis, California 95616
| | - Jie Zheng
- Department of Physiology and Membrane Biology, University of California, School of Medicine, Davis, California 95616
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O'Driscoll KE, Leblanc N, Hatton WJ, Britton FC. Functional properties of murine bestrophin 1 channel. Biochem Biophys Res Commun 2009; 384:476-81. [PMID: 19426717 DOI: 10.1016/j.bbrc.2009.05.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Accepted: 05/01/2009] [Indexed: 11/27/2022]
Abstract
Bestrophins form Ca2+-activated Cl- channels when they are expressed heterologously. Here we report the functional characterization of murine bestrophin 1 (mBest1). We isolated mBest1 transcript from mouse heart and analyzed the biophysical properties and expression of this channel protein using a tetracycline inducible system. mBest1 expression is localized at the membrane of transfected HEK cells, in agreement with its role as a channel. Whole-cell patch clamp experiments revealed a calcium sensitive, time independent chloride current. mBest1 current displayed slight voltage dependence, exhibited an anion permeability sequence of SCN- > I- > Cl- and was sensitive to DIDS and niflumic acid. Anion replacement studies were also performed on mBest2 and mBest3 and differences were observed in their relative permeability and slope conductance to SCN-. Our study provides the first characterization of the biophysical properties of mBest1 and a framework for the elucidation of the physiological role of bestrophins.
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Affiliation(s)
- Kate E O'Driscoll
- Department of Physiology and Cell Biology, University of Nevada, School of Medicine, 1664 N. Virginia Street, Reno, NV 89557, USA
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Marmorstein AD, Cross HE, Peachey NS. Functional roles of bestrophins in ocular epithelia. Prog Retin Eye Res 2009; 28:206-26. [PMID: 19398034 DOI: 10.1016/j.preteyeres.2009.04.004] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
There are four members of the bestrophin family of proteins in the human genome, of which two are known to be expressed in the eye. The gene BEST1 (formerly VMD2) which encodes the protein bestrophin-1 (Best1) was first identified in 1998. Mutations in this gene have now been associated with four clinically distinguishable human eye diseases, collectively referred to as "bestrophinopathies". Over the last decade, laboratories have sought to understand how Best1 mutations could result in eye diseases that range in presentation from macular degeneration to nanophthalmos. The majority of our knowledge comes from studies that have sought to understand how Best1 mutations or dysfunction could induce the classical symptoms of the most common of these diseases: Best vitelliform macular dystrophy (BVMD). BVMD is a dominant trait that is characterized electrophysiologically by a diminished electrooculogram light peak with a normal clinical electroretinogram. This together with the localization of Best1 to the retinal pigment epithelium (RPE) basolateral plasma membrane and data from heterologous expression studies, have led to the proposal that Best1 generates the light peak, and that bestrophins are a family of Ca(2+) activated Cl(-) channels (CaCCs). However, data from Best1 knock-out and knock-in mice, coupled with the recent discovery of a recessive bestrophinopathy suggest that Best1 does not generate the light peak. Recently Best2 was found to be expressed in non-pigmented epithelia in the ciliary body. However, aqueous dynamics in Best2 knock-out mice do not support a role for Best2 as a Cl(-) channel. Thus, the purported CaCC function of the bestrophins and how loss of this function relates to clinical disease needs to be reassessed. In this article, we examine data obtained from tissue-type and animal models and discuss the current state of bestrophin research, what roles Best1 and Best2 may play in ocular epithelia and ocular electrophysiology, and how perturbation of these functions may result in disease.
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Affiliation(s)
- Alan D Marmorstein
- Department of Ophthalmology and Vision Science, University of Arizona, Tucson, AZ 85711, USA.
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Boon CJ, Klevering BJ, Leroy BP, Hoyng CB, Keunen JE, den Hollander AI. The spectrum of ocular phenotypes caused by mutations in the BEST1 gene. Prog Retin Eye Res 2009; 28:187-205. [DOI: 10.1016/j.preteyeres.2009.04.002] [Citation(s) in RCA: 181] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Marsey LL, Winpenny JP. Bestrophin expression and function in the human pancreatic duct cell line, CFPAC-1. J Physiol 2009; 587:2211-24. [PMID: 19237432 DOI: 10.1113/jphysiol.2008.159087] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Pancreatic duct epithelial cells (PDECs) have been shown to express calcium activated chloride channels (CaCCs) and there is evidence for their involvement in fluid secretion from these cells. The molecular identity of the CaCC in PDECs remains unknown. Recently, the bestrophin family of proteins have been proposed as a potential molecular candidate for CaCCs. Expression of bestrophins is strongly correlated with the function of CaCCs in a variety of tissues. In the present study, the expression of bestrophins has been investigated in the cystic fibrosis pancreatic duct cell line, CFPAC-1. Iodide efflux analysis was used to characterise native CaCCs in CFPAC-1 cell monolayers. Efflux was induced with the addition of UTP (100 microM, 10.2 +/- 1.5 nmol min(-1)), which was blocked by the chloride channel blockers niflumic acid (81%) and DIDS (90%). The UTP-stimulated iodide efflux was shown to be Ca(2+) dependent and cAMP independent. RT-PCR analysis of RNA isolated from CFPAC-1 cells demonstrated positive identification of all four human bestrophin mRNAs. Western blot of CFPAC-1 cell protein isolates with antibodies specific to human bestrophin 1 (hBest1) showed that hBest1 protein was expressed in this cell line. HBest1 was present on the cell surface, demonstrated using biotinylation and confocal imaging, as well as in the cytoplasm. SiRNA-mediated silencing of hBest1 in CFPAC-1 cells reduced the UTP-stimulated iodide efflux by around 40%. This study provides evidence that the bestrophins are expressed in pancreatic duct cells and, more specifically, that hBest1 plays a role in the CaCCs found in these cells.
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Affiliation(s)
- Laura L Marsey
- Biomedicine Group, Biomedical Research Centre, School of Medicine, Health Policy and Practice, Faculty of Health, University of East Anglia, Norwich NR4 7TJ, UK
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Xiao Q, Prussia A, Yu K, Cui YY, Hartzell HC. Regulation of bestrophin Cl channels by calcium: role of the C terminus. ACTA ACUST UNITED AC 2009; 132:681-92. [PMID: 19029375 PMCID: PMC2585866 DOI: 10.1085/jgp.200810056] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Human bestrophin-1 (hBest1), which is genetically linked to several kinds of retinopathy and macular degeneration in both humans and dogs, is the founding member of a family of Cl− ion channels that are activated by intracellular Ca2+. At present, the structures and mechanisms responsible for Ca2+ sensing remain unknown. Here, we have used a combination of molecular modeling, density functional–binding energy calculations, mutagenesis, and patch clamp to identify the regions of hBest1 involved in Ca2+ sensing. We identified a cluster of a five contiguous acidic amino acids in the C terminus immediately after the last transmembrane domain, followed by an EF hand and another regulatory domain that are essential for Ca2+ sensing by hBest1. The cluster of five amino acids (293–308) is crucial for normal channel gating by Ca2+ because all but two of the 35 mutations we made in this region rendered the channel incapable of being activated by Ca2+. Using homology models built on the crystal structure of calmodulin (CaM), an EF hand (EF1) was identified in hBest1. EF1 was predicted to bind Ca2+ with a slightly higher affinity than the third EF hand of CaM and lower affinity than the second EF hand of troponin C. As predicted by the model, the D312G mutation in the putative Ca2+-binding loop (312–323) reduced the apparent Ca2+ affinity by 20-fold. In addition, the D312G and D323N mutations abolished Ca2+-dependent rundown of the current. Furthermore, analysis of truncation mutants of hBest1 identified a domain adjacent to EF1 that is rich in acidic amino acids (350–390) that is required for Ca2+ activation and plays a role in current rundown. These experiments identify a region of hBest1 (312–323) that is involved in the gating of hBest1 by Ca2+ and suggest a model in which Ca2+ binding to EF1 activates the channel in a process that requires the acidic domain (293–308) and another regulatory domain (350–390). Many of the ∼100 disease-causing mutations in hBest1 are located in this region that we have implicated in Ca2+ sensing, suggesting that these mutations disrupt hBest1 channel gating by Ca2+.
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Affiliation(s)
- Qinghuan Xiao
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322, USA
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Chien LT, Hartzell HC. Rescue of volume-regulated anion current by bestrophin mutants with altered charge selectivity. ACTA ACUST UNITED AC 2009; 132:537-46. [PMID: 18955594 PMCID: PMC2571971 DOI: 10.1085/jgp.200810065] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mutations in human bestrophin-1 are linked to various kinds of retinal degeneration. Although it has been proposed that bestrophins are Ca(2+)-activated Cl(-) channels, definitive proof is lacking partly because mice with the bestrophin-1 gene deleted have normal Ca(2+)-activated Cl(-) currents. Here, we provide compelling evidence to support the idea that bestrophin-1 is the pore-forming subunit of a cell volume-regulated anion channel (VRAC) in Drosophila S2 cells. VRAC was abolished by treatment with RNAi to Drosophila bestrophin-1. VRAC was rescued by overexpressing bestrophin-1 mutants with altered biophysical properties and responsiveness to sulfhydryl reagents. In particular, the ionic selectivity of the F81C mutant changed from anionic to cationic when the channel was treated with the sulfhydryl reagent, sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES(-)) (P(Cs)/P(Cl) = 0.25 for native and 2.38 for F81C). The F81E mutant was 1.3 times more permeable to Cs(+) than Cl(-). The finding that VRAC was rescued by F81C and F81E mutants with different biophysical properties shows that bestrophin-1 is a VRAC in S2 cells and not simply a regulator or an auxiliary subunit. F81C overexpressed in HEK293 cells also exhibits a shift of ionic selectivity after MTSES(-) treatment, although the effect is quantitatively smaller than in S2 cells. To test whether bestrophins are VRACs in mammalian cells, we compared VRACs in peritoneal macrophages from wild-type mice and mice with both bestrophin-1 and bestrophin-2 disrupted (best1(-/-)/best2(-/-)). VRACs were identical in wild-type and best1(-/-)/best2(-/-) mice, showing that bestrophins are unlikely to be the classical VRAC in mammalian cells.
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Affiliation(s)
- Li-Ting Chien
- Department of Cell Biology and Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322, USA
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Milenkovic VM, Soria RB, Aldehni F, Schreiber R, Kunzelmann K. Functional assembly and purinergic activation of bestrophins. Pflugers Arch 2009; 458:431-41. [PMID: 19130075 DOI: 10.1007/s00424-008-0626-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 11/21/2008] [Accepted: 12/05/2008] [Indexed: 11/24/2022]
Abstract
Proteins of the bestrophin family produce Ca(2+)-activated Cl(-) currents and regulate voltage-gated Ca(2+) channels. Bestrophin 1 was first identified in the retinal pigment epithelium. Four human paralogs (hBest1-hBest4) exist, and for some bestrophins, dimeric and heterotetrameric structures have been proposed. Here, we demonstrate that hBest1-hBest4 induce Cl(-) conductances of different amplitudes when expressed in HEK293 cells and when activated through purinergic stimulation. hBest1 mutants that are known to cause autosomal dominant macular dystrophy (Best disease) did not produce a Cl(-) current. Bestrophins were colocalized and showed molecular and functional interaction in HEK293 cells, overexpressing hBest1 and hBest2 or hBest4. Interaction was confirmed in airway epithelial cells coexpressing endogenous bestrophins. A fraction of hBest2 and hBest4 was expressed in the membrane, while most of hBest1 was found in the endoplasmic reticulum. Nevertheless, hBest1 has a clear role for the adenosine triphosphate (ATP; or uridine triphosphate)-induced Cl(-) current in both HEK293 and Calu-3 cells. Since native epithelial tissues typically express several bestrophin paralogs, these proteins may exist as heterooligomeric structures.
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Affiliation(s)
- Vladimir M Milenkovic
- Institut für Physiologie, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
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Hartzell HC, Yu K, Xiao Q, Chien LT, Qu Z. Anoctamin/TMEM16 family members are Ca2+-activated Cl- channels. J Physiol 2008; 587:2127-39. [PMID: 19015192 DOI: 10.1113/jphysiol.2008.163709] [Citation(s) in RCA: 202] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Ca(2+)-activated Cl- channels (CaCCs) perform many important functions in cell physiology including secretion of fluids from acinar cells of secretory glands, amplification of olfactory transduction, regulation of cardiac and neuronal excitability, mediation of the fast block to polyspermy in amphibian oocytes, and regulation of vascular tone. Although a number of proteins have been proposed to be responsible for CaCC currents, the anoctamin family (ANO, also known as TMEM16) exhibits characteristics most similar to those expected for the classical CaCC. Interestingly, this family of proteins has previously attracted the interest of both developmental and cancer biologists. Some members of this family are up-regulated in a number of tumours and functional deficiency in others is linked to developmental defects.
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Affiliation(s)
- H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, 615 Michael Street, 535 Whitehead Bldg, Atlanta, GA 30322, USA.
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Srivastava A, Romanenko VG, Gonzalez-Begne M, Catalán MA, Melvin JE. A variant of the Ca2+-activated Cl channel Best3 is expressed in mouse exocrine glands. J Membr Biol 2008; 222:43-54. [PMID: 18414923 DOI: 10.1007/s00232-008-9098-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2007] [Accepted: 02/21/2008] [Indexed: 11/27/2022]
Abstract
Fluid secretion by exocrine glands requires the activation of an apical Ca2+-dependent Cl channel, the molecular identity of which is unknown. We found that mouse exocrine glands expressed an alternately spliced variant of Best3, a member of the Bestrophin (Vmd2) Ca2+-activated Cl channel gene family, whereas the heart expressed full-length Best3. The spliced transcript lacked exons 2, 3 and 6 (Best3-Delta2,3,6) and is predicted to generate an in-frame protein missing the entire cytoplasmic N terminus, the initial two transmembrane domains and part of the first intracellular loop. In addition to exocrine glands, the Best3-Delta2,3,6 splice variant transcript was detected in lung, testis and kidney. The parotid gland and heart expressed proteins of the predicted size for Best3-Delta2,3,6 and full-length Best3, respectively, that targeted to the plasma membrane in HEK293 cells. HEK293 cells expressing Best3 displayed Ca2+-dependent Cl(-) currents that were sensitive to the Cl channel blocker DIDS. In contrast, no Ca2+-dependent Cl(-) currents were detected in cells expressing Best3-Delta2,3,6. Cotransfection of Best3-Delta2,3,6 with Best3 or Best2 (also expressed in salivary gland acinar cells) had no significant effects on the currents generated by either of these Ca2+-dependent Cl channels. Our results demonstrate that exocrine glands express a unique splice variant of Best3. Nevertheless, Best3-Delta2,3,6 does not produce Ca2+-dependent Cl(-) currents, nor does it regulate the activity of Best2 or the full-length Best3 channel.
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Affiliation(s)
- Alaka Srivastava
- Center for Oral Biology, Medical Center, University of Rochester School of Medicine and Dentistry, 601 Elmwood Ave., Box 611, Rochester, NY 14642, USA
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Matchkov VV, Larsen P, Bouzinova EV, Rojek A, Boedtkjer DMB, Golubinskaya V, Pedersen FS, Aalkjaer C, Nilsson H. Bestrophin-3 (vitelliform macular dystrophy 2-like 3 protein) is essential for the cGMP-dependent calcium-activated chloride conductance in vascular smooth muscle cells. Circ Res 2008; 103:864-72. [PMID: 18776041 DOI: 10.1161/circresaha.108.178517] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Although the biophysical fingerprints (ion selectivity, voltage-dependence, kinetics, etc) of Ca(2+)-activated Cl(-) currents are well established, their molecular identity is still controversial. Several molecular candidates have been suggested; however, none of them has been fully accepted. We have recently characterized a cGMP-dependent Ca(2+)-activated Cl(-) current with unique characteristics in smooth muscle cells. This novel current has been shown to coexist with a "classic" (cGMP-independent) Ca(2+)-activated Cl(-) current and to have characteristics distinct from those previously known for Ca(2+)-activated Cl(-) currents. Here, we suggest that a bestrophin, a product of the Best gene family, is responsible for the cGMP-dependent Ca(2+)-activated Cl(-) current based on similarities between the membrane currents produced by heterologous expressions of bestrophins and the cGMP-dependent Ca(2+)-activated Cl(-) current. This is supported by similarities in the distribution pattern of the cGMP-dependent Ca(2+)-activated Cl(-) current and bestrophin-3 (the product of Best-3 gene) expression in different smooth muscle. Furthermore, downregulation of Best-3 gene expression with small interfering RNA both in cultured cells and in vascular smooth muscle cells in vivo was associated with a significant reduction of the cGMP-dependent Ca(2+)-activated Cl(-) current, whereas the magnitude of the classic Ca(2+)-activated Cl(-) current was not affected. The majority of previous suggestions that bestrophins are a new Cl(-) channel family were based on heterologous expression in cell culture studies. Our present results demonstrate that at least 1 family member, bestrophin-3, is essential for a well-defined endogenous Ca(2+)-activated Cl(-) current in smooth muscles in the intact vascular wall.
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Affiliation(s)
- Vladimir V Matchkov
- Water and Salt Centre, Institute of Physiology and Biophysics, University of Aarhus, 8000 Aarhus C, Denmark.
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The best disease-linked Cl- channel hBest1 regulates Ca V 1 (L-type) Ca2+ channels via src-homology-binding domains. J Neurosci 2008; 28:5660-70. [PMID: 18509027 DOI: 10.1523/jneurosci.0065-08.2008] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Mutations in the bestrophin-1 (Best1) gene are linked to several kinds of macular degeneration in both humans and dogs. Although bestrophins have been shown clearly to be Cl(-) ion channels, it is controversial whether Cl(-) channel dysfunction can explain the diseases. It has been suggested that bestrophins are multifunctional proteins: they may regulate voltage-gated Ca(2+) channels in addition to functioning as Cl(-) channels. Here, we show that human Best1 gene (hBest1) differentially modulates Ca(V)1.3 (L-type) voltage-gated Ca(2+) channels through association with the Ca(V)beta subunit. In transfected human embryonic kidney 293 cells, hBest1 inhibited Ca(V)1.3. Inhibition of Ca(V)1.3 was not observed in the absence of the beta subunit. Also, the hBest1 C terminus binds to Ca(V)beta subunits, suggesting that the effect of hBest1 was mediated by the Ca(V)beta subunit. The region of hBest1 responsible for the effect was localized to a region (amino acids 330-370) in the cytoplasmic C terminus that contains a predicted src-homology-binding domain that is not present in other bestrophin subtypes. Mutation of Pro(330) and Pro(334) abolished the effects of hBest1 on Ca(V)1.3. The effect was specific to hBest1; it was not observed with mouse Best1 (mBest1), mBest2, or mBest3. Wild-type hBest1 and the disease-causing mutants R92S, G299R, and D312N inhibited Ca(V) currents the same amount, whereas the A146K and G222E mutants were less effective. We propose that hBest1 regulates Ca(V) channels by interacting with the Ca(V)beta subunit and altering channel availability. Our findings reveal a novel function of bestrophin in regulation of Ca(V) channels and suggest a possible mechanism for the role of hBest1 in macular degeneration.
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Hartzell HC, Qu Z, Yu K, Xiao Q, Chien LT. Molecular physiology of bestrophins: multifunctional membrane proteins linked to best disease and other retinopathies. Physiol Rev 2008; 88:639-72. [PMID: 18391176 DOI: 10.1152/physrev.00022.2007] [Citation(s) in RCA: 256] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This article reviews the current state of knowledge about the bestrophins, a newly identified family of proteins that can function both as Cl(-) channels and as regulators of voltage-gated Ca(2+) channels. The founding member, human bestrophin-1 (hBest1), was identified as the gene responsible for a dominantly inherited, juvenile-onset form of macular degeneration called Best vitelliform macular dystrophy. Mutations in hBest1 have also been associated with a small fraction of adult-onset macular dystrophies. It is proposed that dysfunction of bestrophin results in abnormal fluid and ion transport by the retinal pigment epithelium, resulting in a weakened interface between the retinal pigment epithelium and photoreceptors. There is compelling evidence that bestrophins are Cl(-) channels, but bestrophins remain enigmatic because it is not clear that the Cl(-) channel function can explain Best disease. In addition to functioning as a Cl(-) channel, hBest1 also is able to regulate voltage-gated Ca(2+) channels. Some bestrophins are activated by increases in intracellular Ca(2+) concentration, but whether bestrophins are the molecular counterpart of Ca(2+)-activated Cl(-) channels remains in doubt. Bestrophins are also regulated by cell volume and may be a member of the volume-regulated anion channel family.
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Affiliation(s)
- H Criss Hartzell
- Department of Cell Biology, Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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Chien LT, Hartzell HC. Drosophila bestrophin-1 chloride current is dually regulated by calcium and cell volume. ACTA ACUST UNITED AC 2008; 130:513-24. [PMID: 17968025 PMCID: PMC2151665 DOI: 10.1085/jgp.200709795] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mutations in the human bestrophin-1 (hBest1) gene are responsible for Best vitelliform macular dystrophy, however the mechanisms leading to retinal degeneration have not yet been determined because the function of the bestrophin protein is not fully understood. Bestrophins have been proposed to comprise a new family of Cl(-) channels that are activated by Ca(2+). While the regulation of bestrophin currents has focused on intracellular Ca(2+), little is known about other pathways/mechanisms that may also regulate bestrophin currents. Here we show that Cl(-) currents in Drosophila S2 cells, that we have previously shown are mediated by bestrophins, are dually regulated by Ca(2+) and cell volume. The bestrophin Cl(-) currents were activated in a dose-dependent manner by osmotic pressure differences between the internal and external solutions. The increase in the current was accompanied by cell swelling. The volume-regulated Cl(-) current was abolished by treating cells with each of four different RNAi constructs that reduced dBest1 expression. The volume-regulated current was rescued by transfecting with dBest1. Furthermore, cells not expressing dBest1 were severely depressed in their ability to regulate their cell volume. Volume regulation and Ca(2+) regulation can occur independently of one another: the volume-regulated current was activated in the complete absence of Ca(2+) and the Ca(2+)-activated current was activated independently of alterations in cell volume. These two pathways of bestrophin channel activation can interact; intracellular Ca(2+) potentiates the magnitude of the current activated by changes in cell volume. We conclude that in addition to being regulated by intracellular Ca(2+), Drosophila bestrophins are also novel members of the volume-regulated anion channel (VRAC) family that are necessary for cell volume homeostasis.
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Affiliation(s)
- Li-Ting Chien
- Department of Cell Biology, Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322, USA
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Al-Jumaily M, Kozlenkov A, Mechaly I, Fichard A, Matha V, Scamps F, Valmier J, Carroll P. Expression of three distinct families of calcium-activated chloride channel genes in the mouse dorsal root ganglion. Neurosci Bull 2008; 23:293-9. [PMID: 17952139 DOI: 10.1007/s12264-007-0044-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Objective A calcium-activated chloride current (IClCa) has been observed in medium-sized sensory neurons of the dorsal root ganglion (DRG). Axotomy of the sciatic nerve induces a similar current in the majority of medium and large diameter neurons. Our aim is to identify the molecule(s) underlying this current. Methods Using conventional and quantitative RT-PCR, we examined the expression in DRG of members of three families of genes, which have been shown to have IClCa current inducing properties. Results We showed the detection of transcripts representing several members of these families, i.e. chloride channel calcium-activated (CLCA), Bestrophin and Tweety gene families in adult DRG, in the normal state and 3 d after sciatic nerve section, a model for peripheral nerve injury. Conclusion Our analysis revealed that that mBest1 and Tweety2 appear as the best candidates to play a role in the injury-induced IClCa in DRG neurons.
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Affiliation(s)
- Mohammed Al-Jumaily
- The French National Institute for Health and Medical Research, U.583, Montpellier, France.
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