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Wang J, Liu H, Sun Z, Zou X, Zhang Z, Wei X, Pan L, Stalin A, Zhao W, Chen Y. The Inhibitory Effect of Magnolol on the Human TWIK1 Channel Is Related to G229 and T225 Sites. Molecules 2023; 28:6815. [PMID: 37836658 PMCID: PMC10574557 DOI: 10.3390/molecules28196815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 09/01/2023] [Accepted: 09/25/2023] [Indexed: 10/15/2023] Open
Abstract
TWIK1 (K2P1.1/KCNK1) belongs to the potassium channels of the two-pore domain. Its current is very small and difficult to measure. In this work, we used a 100 mM NH4+ extracellular solution to increase TWIK1 current in its stable cell line expressed in HEK293. Then, the inhibition of magnolol on TWIK1 was observed via a whole-cell patch clamp experiment, and it was found that magnolol had a significant inhibitory effect on TWIK1 (IC50 = 6.21 ± 0.13 μM). By molecular docking and alanine scanning mutagenesis, the IC50 of TWIK1 mutants G229A, T225A, I140A, L223A, and S224A was 20.77 ± 3.20, 21.81 ± 7.93, 10.22 ± 1.07, 9.55 ± 1.62, and 7.43 ± 3.20 μM, respectively. Thus, we conclude that the inhibition of the TWIK1 channel by magnolol is related to G229 and T225 on the P2- pore helix.
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Affiliation(s)
- Jintao Wang
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Huan Liu
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Zhuolin Sun
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Xinyi Zou
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Zixuan Zhang
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Xiaofeng Wei
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Lanying Pan
- Shulan International Medical College, Zhejiang Shuren University, Hangzhou 310015, China
| | - Antony Stalin
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, China;
| | - Wei Zhao
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
| | - Yuan Chen
- Zhejiang Provincial Key Laboratory of Resources Protection and Innovation of Traditional Chinese Medicine, College of Food and Health, Zhejiang Agriculture and Forestry University, Hangzhou 311300, China; (J.W.); (H.L.); (Z.S.); (X.Z.); (Z.Z.); (X.W.); (W.Z.)
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2
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Abstract
Lysosomes are acidic membrane-bound organelles that use hydrolytic enzymes to break down material through pathways such as endocytosis, phagocytosis, mitophagy, and autophagy. To function properly, intralysosomal environments are strictly controlled by a set of integral membrane proteins such as ion channels and transporters. Potassium ion (K+) channels are a large and diverse family of membrane proteins that control K+ flux across both the plasma membrane and intracellular membranes. In the plasma membrane, they are essential in both excitable and non-excitable cells for the control of membrane potential and cell signaling. However, our understanding of intracellular K+ channels is very limited. In this review, we summarize the recent development in studies of K+ channels in the lysosome. We focus on their characterization, potential roles in maintaining lysosomal membrane potential and lysosomal function, and pathological implications.
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Affiliation(s)
- Peng Huang
- Collaborative Innovation Center for Biomedicine, School of Clinical Medicine, Shanghai University of Medicine and Health Sciences, Shanghai, China
| | - Mengnan Xu
- Department of Physiology and Biophysics, Dalhousie University, Sir Charles Tupper Medical Building, Halifax, NS, Canada
| | - Yi Wu
- Collaborative Innovation Center for Biomedicine, School of Clinical Medicine, Shanghai University of Medicine and Health Sciences, Shanghai, China
| | - Alia Kazim Rizvi Syeda
- Department of Physiology and Biophysics, Dalhousie University, Sir Charles Tupper Medical Building, Halifax, NS, Canada
| | - Xian-Ping Dong
- Department of Physiology and Biophysics, Dalhousie University, Sir Charles Tupper Medical Building, Halifax, NS, Canada.
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3
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Wang Y, Wang C, He Q, Chen G, Yu J, Cang J, Zhong M. Inhibition of sphingosine-1-phosphate receptor 3 suppresses ATP-induced NLRP3 inflammasome activation in macrophages via TWIK2-mediated potassium efflux. Front Immunol 2023; 14:1090202. [PMID: 36798132 PMCID: PMC9927198 DOI: 10.3389/fimmu.2023.1090202] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2022] [Accepted: 01/16/2023] [Indexed: 02/04/2023] Open
Abstract
Background Inhibition of sphingosine kinase 1 (SphK1), which catalyzes bioactive lipid sphingosine-1-phosphate (S1P), attenuates NLRP3 inflammasome activation. S1P exerts most of its function by binding to S1P receptors (S1PR1-5). The roles of S1P receptors in NLRP3 inflammasome activation remain unclear. Materials and methods The mRNA expressions of S1PRs in bone marrow-derived macrophages (BMDMs) were measured by real-time quantitative polymerase chain reaction (qPCR) assays. BMDMs were primed with LPS and stimulated with NLRP3 activators, including ATP, nigericin, and imiquimod. Interleukin-1β (IL-1β) in the cell culture supernatant was detected by enzyme-linked immunosorbent assay (ELISA). Intracellular potassium was labeled with a potassium indicator and was measured by confocal microscopy. Protein expression in whole-cell or plasma membrane fraction was measured by Western blot. Cecal ligation and puncture (CLP) was induced in C57BL/6J mice. Mortality, lung wet/dry ratio, NLRP3 activation, and bacterial loads were measured. Results Macrophages expressed all five S1PRs in the resting state. The mRNA expression of S1PR3 was upregulated after lipopolysaccharide (LPS) stimulation. Inhibition of S1PR3 suppressed NLRP3 and pro-IL-1β in macrophages primed with LPS. Inhibition of S1PR3 attenuated ATP-induced NLRP3 inflammasome activation, enhanced nigericin-induced NLRP3 activation, and did not affect imiquimod-induced NLRP3 inflammasome activation. In addition, inhibition of S1PR3 suppressed ATP-induced intracellular potassium efflux. Inhibition of S1PR3 did not affect the mRNA or protein expression of TWIK2 in LPS-primed BMDMs. ATP stimulation induced TWIK2 expression in the plasma membrane of LPS-primed BMDMs, and inhibition of S1PR3 impeded the membrane expression of TWIK2 induced by ATP. Compared with CLP mice treated with vehicle, CLP mice treated with the S1PR3 antagonist, TY52156, had aggravated pulmonary edema, increased bacterial loads in the lung, liver, spleen, and blood, and a higher seven-day mortality rate. Conclusions Inhibition of S1PR3 suppresses the expression of NLRP3 and pro-IL-1β during LPS priming, and attenuates ATP-induced NLRP3 inflammasome activation by impeding membrane trafficking of TWIK2 and potassium efflux. Although inhibition of S1PR3 decreases IL-1β maturation in the lungs, it leads to higher bacterial loads and mortality in CLP mice.
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Affiliation(s)
- Yingqin Wang
- Department of Anesthesiology, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Chen Wang
- Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Qiaolan He
- Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Guannan Chen
- Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Jie Yu
- Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Jing Cang
- Department of Anesthesiology, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Ming Zhong
- Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai, China.,Shanghai Key Laboratory of Lung Inflammation and Injury, Shanghai, China.,Shanghai Institute of Infectious Disease and Biosecurity, School of Public Health, Fudan University, Shanghai, China
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4
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Turney TS, Li V, Brohawn SG. Structural Basis for pH-gating of the K + channel TWIK1 at the selectivity filter. Nat Commun 2022; 13:3232. [PMID: 35680900 PMCID: PMC9184524 DOI: 10.1038/s41467-022-30853-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Accepted: 05/20/2022] [Indexed: 11/11/2022] Open
Abstract
TWIK1 (K2P1.1, KCNK1) is a widely expressed pH-gated two-pore domain K+ channel (K2P) that contributes to cardiac rhythm generation and insulin release from pancreatic beta cells. TWIK1 displays unique properties among K2Ps including low basal activity and inhibition by extracellular protons through incompletely understood mechanisms. Here, we present cryo-EM structures of TWIK1 in lipid nanodiscs at high and low pH that reveal a previously undescribed gating mechanism at the K+ selectivity filter. At high pH, TWIK1 adopts an open conformation. At low pH, protonation of an extracellular histidine results in a cascade of conformational changes that close the channel by sealing the top of the selectivity filter, displacing the helical cap to block extracellular ion access pathways, and opening gaps for lipid block of the intracellular cavity. These data provide a mechanistic understanding for extracellular pH-gating of TWIK1 and illustrate how diverse mechanisms have evolved to gate the selectivity filter of K+ channels.
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Affiliation(s)
- Toby S Turney
- Biophysics Graduate Program, University of California Berkeley, Berkeley, CA, 94720, USA
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
- California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA, 94720, USA
| | - Vivian Li
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
- California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA, 94720, USA
| | - Stephen G Brohawn
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA.
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA.
- California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA, 94720, USA.
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5
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Wu XY, Lv JY, Zhang SQ, Yi X, Xu ZW, Zhi YX, Zhao BX, Pang JX, Yung KKL, Liu SW, Zhou PZ. ML365 inhibits TWIK2 channel to block ATP-induced NLRP3 inflammasome. Acta Pharmacol Sin 2022; 43:992-1000. [PMID: 34341510 DOI: 10.1038/s41401-021-00739-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 06/30/2021] [Indexed: 02/06/2023] Open
Abstract
Dysregulation of NLRP3 inflammasome results in uncontrolled inflammation, which participates in various chronic diseases. TWIK2 potassium channel mediates potassium efflux that has been reported to be an essential upstream mechanism for ATP-induced NLRP3 inflammasome activation. Thus, TWIK2 potassium channel could be a potential drug target for NLRP3-related inflammatory diseases. In the present study we investigated the effects of known K2P channel modulators on TWIK2 channel expressed in a heterologous system. In order to increase plasma membrane expression and thus TWIK2 currents, a mutant channel with three mutations (TWIK2I289A/L290A/Y308A) in the C-terminus was expressed in COS-7 cells. TWIK2 currents were assessed using whole-cell voltage-clamp recording. Among 6 known K2P channel modulators tested (DCPIB, quinine, fluoxetine, ML365, ML335, and TKDC), ML365 was the most potent TWIK2 channel blocker with an IC50 value of 4.07 ± 1.5 μM. Furthermore, ML365 selectively inhibited TWIK2 without affecting TWIK1 or THIK1 channels. We showed that ML365 (1, 5 μM) concentration-dependently inhibited ATP-induced NLRP3 inflammasome activation in LPS-primed murine BMDMs, whereas it did not affect nigericin-induced NLRP3, or non-canonical, AIM2 and NLRC4 inflammasomes activation. Knockdown of TWIK2 significantly impaired the inhibitory effect of ML365 on ATP-induced NLRP3 inflammasome activation. Moreover, we demonstrated that pre-administration of ML365 (1, 10, 25 mg/kg, ip) dose-dependently ameliorated LPS-induced endotoxic shock in mice. In a preliminary pharmacokinetic study conducted in rats, ML365 showed good absolute oral bioavailability with F value of 22.49%. In conclusion, ML365 provides a structural reference for future design of selective TWIK2 channel inhibitors in treating related inflammatory diseases.
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6
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Riel EB, Jürs BC, Cordeiro S, Musinszki M, Schewe M, Baukrowitz T. The versatile regulation of K2P channels by polyanionic lipids of the phosphoinositide and fatty acid metabolism. J Gen Physiol 2022; 154:212926. [PMID: 34928298 PMCID: PMC8693234 DOI: 10.1085/jgp.202112989] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 12/01/2021] [Indexed: 12/29/2022] Open
Abstract
Work over the past three decades has greatly advanced our understanding of the regulation of Kir K+ channels by polyanionic lipids of the phosphoinositide (e.g., PIP2) and fatty acid metabolism (e.g., oleoyl-CoA). However, comparatively little is known regarding the regulation of the K2P channel family by phosphoinositides and by long-chain fatty acid–CoA esters, such as oleoyl-CoA. We screened 12 mammalian K2P channels and report effects of polyanionic lipids on all tested channels. We observed activation of members of the TREK, TALK, and THIK subfamilies, with the strongest activation by PIP2 for TRAAK and the strongest activation by oleoyl-CoA for TALK-2. By contrast, we observed inhibition for members of the TASK and TRESK subfamilies. Our results reveal that TASK-2 channels have both activatory and inhibitory PIP2 sites with different affinities. Finally, we provided evidence that PIP2 inhibition of TASK-1 and TASK-3 channels is mediated by closure of the recently identified lower X-gate as critical mutations within the gate (i.e., L244A, R245A) prevent PIP2-induced inhibition. Our findings establish that K+ channels of the K2P family are highly sensitive to polyanionic lipids, extending our knowledge of the mechanisms of lipid regulation and implicating the metabolism of these lipids as possible effector pathways to regulate K2P channel activity.
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Affiliation(s)
- Elena B Riel
- Institute of Physiology, Kiel University, Kiel, Germany
| | - Björn C Jürs
- Institute of Physiology, Kiel University, Kiel, Germany.,Medical School Hamburg, University of Applied Sciences and Medical University, Hamburg, Germany
| | | | | | - Marcus Schewe
- Institute of Physiology, Kiel University, Kiel, Germany
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7
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Oliveira‐Mendes B, Feliciangeli S, Ménard M, Chatelain F, Alameh M, Montnach J, Nicolas S, Ollivier B, Barc J, Baró I, Schott J, Probst V, Kyndt F, Denjoy I, Lesage F, Loussouarn G, De Waard M. A standardised hERG phenotyping pipeline to evaluate KCNH2 genetic variant pathogenicity. Clin Transl Med 2021; 11:e609. [PMID: 34841674 PMCID: PMC8609418 DOI: 10.1002/ctm2.609] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 09/22/2021] [Accepted: 09/28/2021] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND AIMS Mutations in KCNH2 cause long or short QT syndromes (LQTS or SQTS) predisposing to life-threatening arrhythmias. Over 1000 hERG variants have been described by clinicians, but most remain to be characterised. The objective is to standardise and accelerate the phenotyping process to contribute to clinician diagnosis and patient counselling. In silico evaluation was also included to characterise the structural impact of the variants. METHODS We selected 11 variants from known LQTS patients and two variants for which diagnosis was problematic. Using the Gibson assembly strategy, we efficiently introduced mutations in hERG cDNA despite GC-rich sequences. A pH-sensitive fluorescent tag was fused to hERG for efficient evaluation of channel trafficking. An optimised 35-s patch-clamp protocol was developed to evaluate hERG channel activity in transfected cells. R software was used to speed up analyses. RESULTS In the present work, we observed a good correlation between cell surface expression, assessed by the pH-sensitive tag, and current densities. Also, we showed that the new biophysical protocol allows a significant gain of time in recording ion channel properties and provides extensive information on WT and variant channel biophysical parameters, that can all be recapitulated in a single parameter defined herein as the repolarisation power. The impacts of the variants on channel structure were also reported where structural information was available. These three readouts (trafficking, repolarisation power and structural impact) define three pathogenicity indexes that may help clinical diagnosis. CONCLUSIONS Fast-track characterisation of KCNH2 genetic variants shows its relevance to discriminate mutants that affect hERG channel activity from variants with undetectable effects. It also helped the diagnosis of two new variants. This information is meant to fill a patient database, as a basis for personalised medicine. The next steps will be to further accelerate the process using an automated patch-clamp system.
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Affiliation(s)
| | - Sylvain Feliciangeli
- Labex ICST, Université Côte d'Azur, INSERMCentre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et CellulaireValbonneFrance
| | - Mélissa Ménard
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | - Frank Chatelain
- Labex ICST, Université Côte d'Azur, INSERMCentre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et CellulaireValbonneFrance
| | - Malak Alameh
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | - Jérôme Montnach
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | | | | | - Julien Barc
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | - Isabelle Baró
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | | | - Vincent Probst
- CHU Nantes, l'Institut du Thorax, INSERM, CNRSUNIV NantesNantesFrance
| | - Florence Kyndt
- CHU Nantes, l'Institut du Thorax, INSERM, CNRSUNIV NantesNantesFrance
| | - Isabelle Denjoy
- Service de Cardiologie et CNMR Maladies Cardiaques Héréditaires RaresHôpital BichatParisFrance
| | - Florian Lesage
- Labex ICST, Université Côte d'Azur, INSERMCentre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et CellulaireValbonneFrance
| | | | - Michel De Waard
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
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8
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Khoubza L, Chatelain FC, Feliciangeli S, Lesage F, Bichet D. Physiological roles of heteromerization: focus on the two-pore domain potassium channels. J Physiol 2021; 599:1041-1055. [PMID: 33347640 DOI: 10.1113/jp279870] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 12/07/2020] [Indexed: 12/28/2022] Open
Abstract
Potassium channels form the largest family of ion channels with more than 80 members involved in cell excitability and signalling. Most of them exist as homomeric channels, whereas specific conditions are required to obtain heteromeric channels. It is well established that heteromerization of voltage-gated and inward rectifier potassium channels affects their function, increasing the diversity of the native potassium currents. For potassium channels with two pore domains (K2P ), homomerization has long been considered the rule, their polymodal regulation by a wide diversity of physical and chemical stimuli being responsible for the adaptation of the leak potassium currents to cellular needs. This view has recently evolved with the accumulation of evidence of heteromerization between different K2P subunits. Several functional intragroup and intergroup heteromers have recently been identified, which contribute to the functional heterogeneity of this family. K2P heteromerization is involved in the modulation of channel expression and trafficking, promoting functional and signalling diversity. As illustrated in the Abstract Figure, heteromerization of TREK1 and TRAAK provides the cell with more possibilities of regulation. It is becoming increasingly evident that K2P heteromers contribute to important physiological functions including neuronal and cardiac excitability. Since heteromerization also affects the pharmacology of K2P channels, this understanding helps to establish K2P heteromers as new therapeutic targets for physiopathological conditions.
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Affiliation(s)
- Lamyaa Khoubza
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France
| | - Franck C Chatelain
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France
| | - Sylvain Feliciangeli
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France.,Inserm, 101 rue de Tolbiac, 75013, Paris, France
| | - Florian Lesage
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France.,Inserm, 101 rue de Tolbiac, 75013, Paris, France
| | - Delphine Bichet
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, 660 route des Lucioles 06650 Valbonne, France
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9
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Abstract
Two-pore domain potassium channels are formed by subunits that each contain two pore-loops moieties. Whether the channels are expressed in yeast or the human central nervous system, two subunits come together to form a single potassium selective pore. TOK1, the first two-domain channel was cloned from Saccharomyces cerevisiae in 1995 and soon thereafter, 15 distinct K2P subunits were identified in the human genome. The human K2P channels are stratified into six K2P subfamilies based on sequence as well as physiological or pharmacological similarities. Functional K2P channels pass background (or "leak") K+ currents that shape the membrane potential and excitability of cells in a broad range of tissues. In the years since they were first described, classical functional assays, latterly coupled with state-of-the-art structural and computational studies have revealed the mechanistic basis of K2P channel gating in response to specific physicochemical or pharmacological stimuli. The growing appreciation that K2P channels can play a pivotal role in the pathophysiology of a growing spectrum of diseases makes a compelling case for K2P channels as targets for drug discovery. Here, we summarize recent advances in unraveling the structure, function, and pharmacology of the K2P channels.
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Affiliation(s)
- Jordie M Kamuene
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA
| | - Yu Xu
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA
| | - Leigh D Plant
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA.
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10
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Nematian-Ardestani E, Abd-Wahab F, Chatelain FC, Sun H, Schewe M, Baukrowitz T, Tucker SJ. Selectivity filter instability dominates the low intrinsic activity of the TWIK-1 K2P K + channel. J Biol Chem 2019; 295:610-618. [PMID: 31806709 DOI: 10.1074/jbc.ra119.010612] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 12/04/2019] [Indexed: 12/24/2022] Open
Abstract
Two-pore domain K+ (K2P) channels have many important physiological functions. However, the functional properties of the TWIK-1 (K2P1.1/KCNK1) K2P channel remain poorly characterized because heterologous expression of this ion channel yields only very low levels of functional activity. Several underlying reasons have been proposed, including TWIK-1 retention in intracellular organelles, inhibition by posttranslational sumoylation, a hydrophobic barrier within the pore, and a low open probability of the selectivity filter (SF) gate. By evaluating these potential mechanisms, we found that the latter dominates the low intrinsic functional activity of TWIK-1. Investigating this further, we observed that the low activity of the SF gate appears to arise from the inefficiency of K+ in stabilizing an active (i.e. conductive) SF conformation. In contrast, other permeant ion species, such as Rb+, NH4 +, and Cs+, strongly promoted a pH-dependent activated conformation. Furthermore, many K2P channels are activated by membrane depolarization via an SF-mediated gating mechanism, but we found here that only very strong nonphysiological depolarization produces voltage-dependent activation of heterologously expressed TWIK-1. Remarkably, we also observed that TWIK-1 Rb+ currents are potently inhibited by intracellular K+ (IC50 = 2.8 mm). We conclude that TWIK-1 displays unique SF gating properties among the family of K2P channels. In particular, the apparent instability of the conductive conformation of the TWIK-1 SF in the presence of K+ appears to dominate the low levels of intrinsic functional activity observed when the channel is expressed at the cell surface.
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Affiliation(s)
- Ehsan Nematian-Ardestani
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Firdaus Abd-Wahab
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Franck C Chatelain
- Université Côte d'Azur, Centre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et Cellulaire, Labex ICST, 06560 Valbonne, France
| | - Han Sun
- Department of Structural Biology, Leibniz-Forschungsinstitut für Molekulare Pharmakologie, 13125 Berlin, Germany
| | - Marcus Schewe
- Institute of Physiology, Christian-Albrechts University of Kiel, 24118 Kiel, Germany
| | - Thomas Baukrowitz
- Institute of Physiology, Christian-Albrechts University of Kiel, 24118 Kiel, Germany
| | - Stephen J Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom.
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11
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Nematian-ardestani E, Abd-wahab MF, Chatelain FC, Sun H, Schewe M, Baukrowitz T, Tucker SJ. Selectivity filter instability dominates the low intrinsic activity of the TWIK-1 K2P K + Channel.. [DOI: 10.1101/735704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
ABSTRACTTwo-pore domain (K2P) K+ channels have many important physiological functions. However, the functional properties of the TWIK-1 (K2P1.1/KCNK1) K2P channel remain poorly characterized because heterologous expression of this ion channel yields only very low levels of functional activity. Several underlying reasons have been proposed, including TWIK-1 retention in intracellular organelles, inhibition by post-translational sumoylation, a hydrophobic barrier within the pore, and a low open probability of the selectivity filter (SF) gate. By evaluating these various potential mechanisms, we found that the latter dominates the low intrinsic functional activity of TWIK-1. Investigating the underlying mechanism, we observed that the low activity of the SF gate appears to arise from the inefficiency of K+ in stabilizing an active (i.e. conductive) SF conformation. In contrast, other permeant ion species, such as Rb+, NH4+, and Cs+, strongly promoted a pH-dependent activated conformation. Furthermore, many K2P channels are activated by membrane depolarization via a SF-mediated gating mechanism, but we found here that only very strong, non-physiological depolarization produces voltage-dependent activation of heterologously expressed TWIK-1. Remarkably, we also observed that TWIK-1 Rb+ currents are potently inhibited by intracellular K+ (IC50 = 2.8 mM). We conclude that TWIK-1 displays unique SF gating properties among the family of K2P channels. In particular, the apparent instability of the conductive conformation of the TWIK-1 SF in the presence of K+ appears to dominate the low levels of intrinsic functional activity observed when the channel is expressed at the cell surface.
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Choi JH, Yarishkin O, Kim E, Bae Y, Kim A, Kim SC, Ryoo K, Cho CH, Hwang EM, Park JY. TWIK-1/TASK-3 heterodimeric channels contribute to the neurotensin-mediated excitation of hippocampal dentate gyrus granule cells. Exp Mol Med 2018; 50:1-13. [PMID: 30416196 PMCID: PMC6230555 DOI: 10.1038/s12276-018-0172-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Revised: 07/16/2018] [Accepted: 07/23/2018] [Indexed: 01/15/2023] Open
Abstract
Two-pore domain K+ (K2P) channels have been shown to modulate neuronal excitability. The physiological role of TWIK-1, the first identified K2P channel, in neuronal cells is largely unknown, and we reported previously that TWIK-1 contributes to the intrinsic excitability of dentate gyrus granule cells (DGGCs) in mice. In the present study, we investigated the coexpression of TWIK-1 and TASK-3, another K2P member, in DGGCs. Immunohistochemical staining data showed that TASK-3 proteins were highly localized in the proximal dendrites and soma of DGGCs, and this localization is similar to the expression pattern of TWIK-1. TWIK-1 was shown to associate with TASK-3 in DGGCs of mouse hippocampus and when both genes were overexpressed in COS-7 cells. shRNA-mediated gene silencing demonstrated that TWIK-1/TASK-3 heterodimeric channels displayed outwardly rectifying currents and contributed to the intrinsic excitability of DGGCs. Neurotensin-neurotensin receptor 1 (NT-NTSR1) signaling triggered the depolarization of DGGCs by inhibiting TWIK-1/TASK-3 heterodimeric channels, causing facilitated excitation of DGGCs. Taken together, our study clearly showed that TWIK-1/TASK-3 heterodimeric channels contribute to the intrinsic excitability of DGGCs and that their activities are regulated by NT-NTSR1 signaling.
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Affiliation(s)
- Jae Hyouk Choi
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul, 02792, Republic of Korea.,Division of Bio-Medical Science and Technology, KIST School, Korea University of Science and Technology, Seoul, 02792, Republic of Korea
| | - Oleg Yarishkin
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul, 02792, Republic of Korea
| | - Eunju Kim
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul, 02792, Republic of Korea.,School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea
| | - Yeonju Bae
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea
| | - Ajung Kim
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul, 02792, Republic of Korea.,KHU-KIST Department of Converging Science and Technology, Kyung Hee University, Seoul, 02447, Republic of Korea
| | - Seung-Chan Kim
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul, 02792, Republic of Korea.,School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea
| | - Kanghyun Ryoo
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea
| | - Chang-Hoon Cho
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea
| | - Eun Mi Hwang
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul, 02792, Republic of Korea. .,Division of Bio-Medical Science and Technology, KIST School, Korea University of Science and Technology, Seoul, 02792, Republic of Korea. .,KHU-KIST Department of Converging Science and Technology, Kyung Hee University, Seoul, 02447, Republic of Korea.
| | - Jae-Yong Park
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul, 02841, Republic of Korea.
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13
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Cho CH, Hwang EM, Park JY. Emerging Roles of TWIK-1 Heterodimerization in the Brain. Int J Mol Sci 2017; 19:E51. [PMID: 29295556 PMCID: PMC5796001 DOI: 10.3390/ijms19010051] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 12/20/2017] [Accepted: 12/22/2017] [Indexed: 12/29/2022] Open
Abstract
Two-pore domain K⁺ (K2P) channels play essential roles in regulating resting membrane potential and cellular excitability. Although TWIK-1 (TWIK-tandem of pore domains in a weak inward rectifying K⁺ channel) was the first identified member of the K2P channel family, it is only in recent years that the physiological roles of TWIK-1 have been studied in depth. A series of reports suggest that TWIK-1 may underlie diverse functions, such as intrinsic excitability of neurons, astrocytic passive conductance, and astrocytic glutamate release, as a homodimer or heterodimer with other K2P isotypes. Here, we summarize expression patterns and newly identified functions of TWIK-1 in the brain.
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Affiliation(s)
- Chang-Hoon Cho
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul 136-703, Korea.
| | - Eun Mi Hwang
- Korea Institute of Science and Technology (KIST), Center for Functional Connectomics, Seoul 02792, Korea.
- KHU-KIST Department of Converging Science and Technology, Kyung Hee University, Seoul 02447, Korea.
| | - Jae-Yong Park
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul 136-703, Korea.
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Oakes V, Furini S, Pryde D, Domene C. Exploring the Dynamics of the TWIK-1 Channel. Biophys J 2017; 111:775-784. [PMID: 27558721 PMCID: PMC5002071 DOI: 10.1016/j.bpj.2016.07.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 05/13/2016] [Accepted: 07/11/2016] [Indexed: 01/02/2023] Open
Abstract
Potassium channels in the two-pore domain family (K2P) have various structural attributes that differ from those of other K(+) channels, including a dimeric assembly constituted of nonidentical domains and an expansive extracellular cap. Crystallization of the prototypical K2P channel, TWIK-1, finally revealed the structure of these characteristics in atomic detail, allowing computational studies to be undertaken. In this study, we performed molecular-dynamics simulations for a cumulative time of ∼1 μs to discern the mechanism of ion transport throughout TWIK-1. We observed the free passage of ions beneath the extracellular cap and identified multiple high-occupancy sites in close proximity to charged residues on the protein surface. Despite the overall topological similarity of the x-ray structure of the selectivity filter to other K(+) channels, the structure diverges significantly in molecular-dynamics simulations as a consequence of nonconserved residues in both pore domains contributing to the selectivity filter (T118 and L228). The behavior of such residues has been linked to channel inactivation and the phenomenon of dynamic selectivity, where TWIK-1 displays robust Na(+) inward flux in response to subphysiological K(+) concentrations.
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Affiliation(s)
- Victoria Oakes
- Department of Chemistry, King's College London, London, United Kingdom
| | - Simone Furini
- Department of Medical Biotechnologies, University of Siena, Siena, Italy
| | - David Pryde
- Worldwide Medicinal Chemistry, Pfizer Neuroscience and Pain Research Unit, Cambridge, United Kingdom
| | - Carmen Domene
- Department of Chemistry, King's College London, London, United Kingdom; Chemistry Research Laboratory, Mansfield Road, University of Oxford, Oxford, United Kingdom.
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15
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Recombinant tandem of pore-domains in a Weakly Inward rectifying K + channel 2 (TWIK2) forms active lysosomal channels. Sci Rep 2017; 7:649. [PMID: 28381826 PMCID: PMC5428834 DOI: 10.1038/s41598-017-00640-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 03/07/2017] [Indexed: 12/27/2022] Open
Abstract
Recombinant TWIK2 channels produce weak basal background K+ currents. Current amplitudes depend on the animal species the channels have been isolated from and on the heterologous system used for their re-expression. Here we show that this variability is due to a unique cellular trafficking. We identified three different sequence signals responsible for the preferential expression of TWIK2 in the Lamp1-positive lysosomal compartment. Sequential inactivation of tyrosine-based (Y308ASIP) and di-leucine-like (E266LILL and D282EDDQVDIL) trafficking motifs progressively abolishes the targeting of TWIK2 to lysosomes, and promotes its functional relocation at the plasma membrane. In addition, TWIK2 contains two N-glycosylation sites (N79AS and N85AS) on its luminal side, and glycosylation is necessary for expression in lysosomes. As shown by electrophysiology and electron microscopy, TWIK2 produces functional background K+ currents in the endolysosomes, and its expression affects the number and mean size of the lysosomes. These results show that TWIK2 is expressed in lysosomes, further expanding the registry of ion channels expressed in these organelles.
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16
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Miller SJ, Zhang PW, Glatzer J, Rothstein JD. Astroglial transcriptome dysregulation in early disease of an ALS mutant SOD1 mouse model. J Neurogenet 2016; 31:37-48. [DOI: 10.1080/01677063.2016.1260128] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Sean J. Miller
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- The Brain Science Institute, Johns Hopkins University, Baltimore, MD, USA
- Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Ping-wu Zhang
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- The Brain Science Institute, Johns Hopkins University, Baltimore, MD, USA
| | - Jenna Glatzer
- The Brain Science Institute, Johns Hopkins University, Baltimore, MD, USA
| | - Jeffrey D. Rothstein
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- The Brain Science Institute, Johns Hopkins University, Baltimore, MD, USA
- Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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17
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Seifert G, Henneberger C, Steinhäuser C. Diversity of astrocyte potassium channels: An update. Brain Res Bull 2016; 136:26-36. [PMID: 27965079 DOI: 10.1016/j.brainresbull.2016.12.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 12/08/2016] [Accepted: 12/09/2016] [Indexed: 01/08/2023]
Abstract
Astrocyte K+ channels and the K+ currents they mediate dwarf all other transmembrane conductances in these cells. This defining feature of astrocytes and its functional implications have been investigated intensely over the past decades. Nonetheless, many aspects of astrocyte K+ handling and signaling remain incompletely understood. In this review, we provide an update on the diversity of K+ channels expressed by astrocytes and new functional implications. We focus on inwardly-rectifying K+ channels (particularly Kir4.1), two-pore K+ channels and voltage and Ca2+-dependent K+ channels. We further discuss new insights into the involvement of these K+ channels in K+ buffering, control of synaptic transmission, regulation of the vasculature and in diseases of the central nervous system.
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Affiliation(s)
- Gerald Seifert
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany.
| | - Christian Henneberger
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany; German Center of Neurodegenerative Diseases (DZNE), Bonn, Germany; Institute of Neurology, University College London, London, United Kingdom
| | - Christian Steinhäuser
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany.
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18
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Afzali AM, Ruck T, Herrmann AM, Iking J, Sommer C, Kleinschnitz C, Preuβe C, Stenzel W, Budde T, Wiendl H, Bittner S, Meuth SG. The potassium channels TASK2 and TREK1 regulate functional differentiation of murine skeletal muscle cells. Am J Physiol Cell Physiol 2016; 311:C583-C595. [PMID: 27488672 DOI: 10.1152/ajpcell.00363.2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Accepted: 08/02/2016] [Indexed: 12/18/2022]
Abstract
Two-pore domain potassium (K2P) channels influence basic cellular parameters such as resting membrane potential, cellular excitability, or intracellular Ca2+-concentration [Ca2+]i While the physiological importance of K2P channels in different organ systems (e.g., heart, central nervous system, or immune system) has become increasingly clear over the last decade, their expression profile and functional role in skeletal muscle cells (SkMC) remain largely unknown. The mouse SkMC cell line C2C12, wild-type mouse muscle tissue, and primary mouse muscle cells (PMMs) were analyzed using quantitative PCR, Western blotting, and immunohistochemical stainings as well as functional analysis including patch-clamp measurements and Ca2+ imaging. Mouse SkMC express TWIK-related acid-sensitive K+ channel (TASK) 2, TWIK-related K+ channel (TREK) 1, TREK2, and TWIK-related arachidonic acid stimulated K+ channel (TRAAK). Except TASK2 all mentioned channels were upregulated in vitro during differentiation from myoblasts to myotubes. TASK2 and TREK1 were also functionally expressed and upregulated in PMMs isolated from mouse muscle tissue. Inhibition of TASK2 and TREK1 during differentiation revealed a morphological impairment of myoblast fusion accompanied by a downregulation of maturation markers. TASK2 and TREK1 blockade led to a decreased K+ outward current and a decrease of ACh-dependent Ca2+ influx in C2C12 cells as potential underlying mechanisms. K2P-channel expression was also detected in human muscle tissue by immunohistochemistry pointing towards possible relevance for human muscle cell maturation and function. In conclusion, our findings for the first time demonstrate the functional expression of TASK2 and TREK1 in muscle cells with implications for differentiation processes warranting further investigations in physiologic and pathophysiologic scenarios.
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Affiliation(s)
- Ali M Afzali
- Department of Neurology, University of Münster, Münster, Germany
| | - Tobias Ruck
- Department of Neurology, University of Münster, Münster, Germany;
| | | | - Janette Iking
- Department of Neurology, University of Münster, Münster, Germany
| | - Claudia Sommer
- Department of Neurology, University Hospital of Würzburg, Würzburg, Germany
| | | | - Corinna Preuβe
- Department of Neuropathology, Charité-Universitätsmedizin, Berlin, Germany
| | - Werner Stenzel
- Department of Neuropathology, Charité-Universitätsmedizin, Berlin, Germany
| | - Thomas Budde
- Institute of Physiology I, University of Münster, Münster, Germany; and
| | - Heinz Wiendl
- Department of Neurology, University of Münster, Münster, Germany
| | - Stefan Bittner
- Department of Neurology, University Medical Center of the Johannes Gutenberg-University Mainz, Mainz, Germany
| | - Sven G Meuth
- Department of Neurology, University of Münster, Münster, Germany
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19
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Christensen AH, Chatelain FC, Huttner IG, Olesen MS, Soka M, Feliciangeli S, Horvat C, Santiago CF, Vandenberg JI, Schmitt N, Olesen SP, Lesage F, Fatkin D. The two-pore domain potassium channel, TWIK-1, has a role in the regulation of heart rate and atrial size. J Mol Cell Cardiol 2016; 97:24-35. [PMID: 27103460 DOI: 10.1016/j.yjmcc.2016.04.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 04/11/2016] [Accepted: 04/14/2016] [Indexed: 12/24/2022]
Abstract
The two-pore domain potassium (K(+)) channel TWIK-1 (or K2P1.1) contributes to background K(+) conductance in diverse cell types. TWIK-1, encoded by the KCNK1 gene, is present in the human heart with robust expression in the atria, however its physiological significance is unknown. To evaluate the cardiac effects of TWIK-1 deficiency, we studied zebrafish embryos after knockdown of the two KCNK1 orthologues, kcnk1a and kcnk1b. Knockdown of kcnk1a or kcnk1b individually caused bradycardia and atrial dilation (p<0.001 vs. controls), while ventricular stroke volume was preserved. Combined knockdown of both kcnk1a and kcnk1b resulted in a more severe phenotype, which was partially reversed by co-injection of wild-type human KCNK1 mRNA, but not by a dominant negative variant of human KCNK1 mRNA. To determine whether genetic variants in KCNK1 might cause atrial fibrillation (AF), we sequenced protein-coding regions in two independent cohorts of patients (373 subjects) and identified three non-synonymous variants, p.R171H, p.I198M and p.G236S, that were all located in highly conserved amino acid residues. In transfected mammalian cells, zebrafish and wild-type human TWIK-1 channels had a similar cellular distribution with predominant localization in the endosomal compartment. Two-electrode voltage-clamp experiments using Xenopus oocytes showed that both zebrafish and wild-type human TWIK-1 channels produced K(+) currents that are sensitive to external K(+) concentration as well as acidic pH. There were no effects of the three KCNK1 variants on cellular localization, current amplitude or reversal potential at pH7.4 or pH6. Our data indicate that TWIK-1 has a highly conserved role in cardiac function and is required for normal heart rate and atrial morphology. Despite the functional importance of TWIK-1 in the atrium, genetic variation in KCNK1 is not a common primary cause of human AF.
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Affiliation(s)
- Alex Hørby Christensen
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Franck C Chatelain
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, and Université de Nice Sophia-Antipolis, Sophia-Antipolis, Valbonne, France
| | - Inken G Huttner
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia; Faculty of Medicine, University of New South Wales, Kensington, New South Wales, Australia
| | - Morten Salling Olesen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark
| | - Magdalena Soka
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Sylvain Feliciangeli
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, and Université de Nice Sophia-Antipolis, Sophia-Antipolis, Valbonne, France
| | - Claire Horvat
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Celine F Santiago
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Jamie I Vandenberg
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia; Faculty of Medicine, University of New South Wales, Kensington, New South Wales, Australia
| | - Nicole Schmitt
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark
| | - Søren-Peter Olesen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark
| | - Florian Lesage
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, and Université de Nice Sophia-Antipolis, Sophia-Antipolis, Valbonne, France
| | - Diane Fatkin
- Molecular Cardiology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia; Faculty of Medicine, University of New South Wales, Kensington, New South Wales, Australia; Cardiology Department, St Vincent's Hospital, Darlinghurst, New South Wales, Australia.
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20
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Mixing and matching TREK/TRAAK subunits generate heterodimeric K2P channels with unique properties. Proc Natl Acad Sci U S A 2016; 113:4200-5. [PMID: 27035965 DOI: 10.1073/pnas.1522748113] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The tandem of pore domain in a weak inwardly rectifying K(+) channel (Twik)-related acid-arachidonic activated K(+) channel (TRAAK) and Twik-related K(+) channels (TREK) 1 and TREK2 are active as homodimers gated by stretch, fatty acids, pH, and G protein-coupled receptors. These two-pore domain potassium (K2P) channels are broadly expressed in the nervous system where they control excitability. TREK/TRAAK KO mice display altered phenotypes related to nociception, neuroprotection afforded by polyunsaturated fatty acids, learning and memory, mood control, and sensitivity to general anesthetics. These channels have emerged as promising targets for the development of new classes of anesthetics, analgesics, antidepressants, neuroprotective agents, and drugs against addiction. Here, we show that the TREK1, TREK2, and TRAAK subunits assemble and form active heterodimeric channels with electrophysiological, regulatory, and pharmacological properties different from those of homodimeric channels. Heteromerization occurs between all TREK variants produced by alternative splicing and alternative translation initiation. These results unveil a previously unexpected diversity of K2P channels that will be challenging to analyze in vivo, but which opens new perspectives for the development of clinically relevant drugs.
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21
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Du Y, Kiyoshi CM, Wang Q, Wang W, Ma B, Alford CC, Zhong S, Wan Q, Chen H, Lloyd EE, Bryan RM, Zhou M. Genetic Deletion of TREK-1 or TWIK-1/TREK-1 Potassium Channels does not Alter the Basic Electrophysiological Properties of Mature Hippocampal Astrocytes In Situ. Front Cell Neurosci 2016; 10:13. [PMID: 26869883 PMCID: PMC4738265 DOI: 10.3389/fncel.2016.00013] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 01/14/2016] [Indexed: 01/03/2023] Open
Abstract
We have recently shown that a linear current-to-voltage (I-V) relationship of membrane conductance (passive conductance) reflects the intrinsic property of K+ channels in mature astrocytes. While passive conductance is known to underpin a highly negative and stable membrane potential (VM) essential for the basic homeostatic function of astrocytes, a complete repertoire of the involved K+ channels remains elusive. TREK-1 two-pore domain K+ channel (K2P) is highly expressed in astrocytes, and covalent association of TREK-1 with TWIK-1, another highly expressed astrocytic K2P, has been reported as a mechanism underlying the trafficking of heterodimer TWIK-1/TREK-1 channel to the membrane and contributing to astrocyte passive conductance. To decipher the individual contribution of TREK-1 and address whether the appearance of passive conductance is conditional to the co-expression of TWIK-1/TREK-1 in astrocytes, TREK-1 single and TWIK-1/TREK-1 double gene knockout mice were used in the present study. The relative quantity of mRNA encoding other astrocyte K+ channels, such as Kir4.1, Kir5.1, and TREK-2, was not altered in these gene knockout mice. Whole-cell recording from hippocampal astrocytes in situ revealed no detectable changes in astrocyte passive conductance, VM, or membrane input resistance (Rin) in either kind of gene knockout mouse. Additionally, TREK-1 proteins were mainly located in the intracellular compartments of the hippocampus. Altogether, genetic deletion of TREK-1 alone or together with TWIK-1 produced no obvious alteration in the basic electrophysiological properties of hippocampal astrocytes. Thus, future research focusing on other K+ channels may shed light on this long-standing and important question in astrocyte physiology.
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Affiliation(s)
- Yixing Du
- Department of Neuroscience, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Neurology, The First Affiliated Hospital of Nanjing Medical UniversityNanjing, China
| | - Conrad M Kiyoshi
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Qi Wang
- Department of Neuroscience, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Neurology, Meitan General HospitalXibahe Nanli, Beijing, China
| | - Wei Wang
- Department of Physiology, Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology Wuhan, China
| | - Baofeng Ma
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Catherine C Alford
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Shiying Zhong
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Qi Wan
- Department of Neurology, The First Affiliated Hospital of Nanjing Medical University Nanjing, China
| | - Haijun Chen
- Department of Biological Science, University at Albany, State University of New York Albany, NY, USA
| | - Eric E Lloyd
- Department of Anesthesiology, Baylor College of Medicine Houston, TX, USA
| | - Robert M Bryan
- Department of Anesthesiology, Baylor College of Medicine Houston, TX, USA
| | - Min Zhou
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
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22
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New Insights on Astrocyte Ion Channels: Critical for Homeostasis and Neuron-Glia Signaling. J Neurosci 2016; 35:13827-35. [PMID: 26468182 DOI: 10.1523/jneurosci.2603-15.2015] [Citation(s) in RCA: 137] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Initial biophysical studies on glial cells nearly 50 years ago identified these cells as being electrically silent. These first studies also demonstrated a large K(+) conductance, which led to the notion that glia may regulate extracellular K(+) levels homeostatically. This view has now gained critical support from the study of multiple disease models discussed herein. Dysfunction of a major astrocyte K(+) channel, Kir4.1, appears as an early pathological event underlying neuronal phenotypes in several neurodevelopmental and neurodegenerative diseases. An expanding list of other astrocyte ion channels, including the calcium-activated ion channel BEST-1, hemichannels, and two-pore domain K(+) channels, all contribute to astrocyte biology and CNS function and underpin new forms of crosstalk between neurons and glia. Once considered merely the glue that holds the brain together, it is now increasingly recognized that astrocytes contribute in several fundamental ways to neuronal function. Emerging new insights and future perspectives of this active research area are highlighted within. SIGNIFICANCE STATEMENT The critical role of astrocyte potassium channels in CNS homeostasis has been reemphasized by recent studies conducted in animal disease models. Emerging evidence also supports the signaling role mediated by astrocyte ion channels such as BEST1, hemichannels, and two-pore channels, which enable astrocytes to interact with neurons and regulate synaptic transmission and plasticity. This minisymposium highlights recent developments and future perspectives of these research areas.
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23
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The K+ channel KIR2.1 functions in tandem with proton influx to mediate sour taste transduction. Proc Natl Acad Sci U S A 2015; 113:E229-38. [PMID: 26627720 DOI: 10.1073/pnas.1514282112] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Sour taste is detected by a subset of taste cells on the tongue and palate epithelium that respond to acids with trains of action potentials. Entry of protons through a Zn(2+)-sensitive proton conductance that is specific to sour taste cells has been shown to be the initial event in sour taste transduction. Whether this conductance acts in concert with other channels sensitive to changes in intracellular pH, however, is not known. Here, we show that intracellular acidification generates excitatory responses in sour taste cells, which can be attributed to block of a resting K(+) current. We identify KIR2.1 as the acid-sensitive K(+) channel in sour taste cells using pharmacological and RNA expression profiling and confirm its contribution to sour taste with tissue-specific knockout of the Kcnj2 gene. Surprisingly, acid sensitivity is not conferred on sour taste cells by the specific expression of Kir2.1, but by the relatively small magnitude of the current, which makes the cells exquisitely sensitive to changes in intracellular pH. Consistent with a role of the K(+) current in amplifying the sensory response, entry of protons through the Zn(2+)-sensitive conductance produces a transient block of the KIR2.1 current. The identification in sour taste cells of an acid-sensitive K(+) channel suggests a mechanism for amplification of sour taste and may explain why weak acids that produce intracellular acidification, such as acetic acid, taste more sour than strong acids.
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24
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Wang W, Kiyoshi CM, Du Y, Ma B, Alford CC, Chen H, Zhou M. mGluR3 Activation Recruits Cytoplasmic TWIK-1 Channels to Membrane that Enhances Ammonium Uptake in Hippocampal Astrocytes. Mol Neurobiol 2015; 53:6169-6182. [PMID: 26553349 DOI: 10.1007/s12035-015-9496-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Accepted: 10/16/2015] [Indexed: 12/29/2022]
Abstract
TWIK-1 two-pore domain K+ channels are highly expressed in mature hippocampal astrocytes. While the TWIK-1 activity is readily detectable on astrocyte membrane, the majority of channels are retained in the intracellular compartments, which raises an intriguing question of whether the membrane TWIK-1 channels could be dynamically regulated for functions yet unknown. Here, the regulation of TWIK-1 membrane expression by Gi/Go-coupled metabotropic glutamate receptor 3 (mGluR3) and its functional impact on ammonium uptake has been studied. Activation of mGluR3 induced a marked translocation of TWIK-1 channels from the cytoplasm to the membrane surface. Consistent with our early observation that membrane TWIK-1 behaves as nonselective monovalent cation channel, mGluR3-mediated TWIK-1 membrane expression was associated with a depolarizing membrane potential (V M). As TWIK-1 exhibits a discernibly high permeability to ammonium (NH4+), a critical substrate in glutamate-glutamine cycle for neurotransmitter replenishment, regulation of NH4+ uptake capacity by TWIK-1 membrane expression was determined by response of astrocyte V M to bath application of 5 mM NH4Cl. Stimulation of mGluR3 potentiated NH4+-induced V M depolarization by ∼30 % in wild type, but not in TWIK-1 knockout astrocytes. Furthermore, activation of mGluR3 mediated a coordinated translocation of TWIK-1 channels with recycling endosomes toward astrocyte membrane and the mGluR3-mediated potentiation of NH4+ uptake required a functional Rab-mediated trafficking pathway. Altogether, we demonstrate that the activation of mGluR3 up-regulates the membrane expression of TWIK-1 that in turn enhances NH4+ uptake in astrocytes, a mechanism potentially important for functional coupling of astrocyte glutamate-glutamine cycle with the replenishment of neurotransmitters in neurons.
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Affiliation(s)
- Wei Wang
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA. .,Department of Physiology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, 430030, China. .,Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, China.
| | - Conrad M Kiyoshi
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Yixing Du
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Baofeng Ma
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Catherine C Alford
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Haijun Chen
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, USA
| | - Min Zhou
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
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25
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Huang SS, Chen CL, Huang FW, Johnson FE, Huang JS. Ethanol Enhances TGF-β Activity by Recruiting TGF-β Receptors From Intracellular Vesicles/Lipid Rafts/Caveolae to Non-Lipid Raft Microdomains. J Cell Biochem 2015; 117:860-71. [PMID: 26419316 DOI: 10.1002/jcb.25389] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 09/28/2015] [Indexed: 12/16/2022]
Abstract
Regular consumption of moderate amounts of ethanol has important health benefits on atherosclerotic cardiovascular disease (ASCVD). Overindulgence can cause many diseases, particularly alcoholic liver disease (ALD). The mechanisms by which ethanol causes both beneficial and harmful effects on human health are poorly understood. Here we demonstrate that ethanol enhances TGF-β-stimulated luciferase activity with a maximum of 0.5-1% (v/v) in Mv1Lu cells stably expressing a luciferase reporter gene containing Smad2-dependent elements. In Mv1Lu cells, 0.5% ethanol increases the level of P-Smad2, a canonical TGF-β signaling sensor, by ∼ 2-3-fold. Ethanol (0.5%) increases cell-surface expression of the type II TGF-β receptor (TβR-II) by ∼ 2-3-fold from its intracellular pool, as determined by I(125) -TGF-β-cross-linking/Western blot analysis. Sucrose density gradient ultracentrifugation and indirect immunofluorescence staining analyses reveal that ethanol (0.5% and 1%) also displaces cell-surface TβR-I and TβR-II from lipid rafts/caveolae and facilitates translocation of these receptors to non-lipid raft microdomains where canonical signaling occurs. These results suggest that ethanol enhances canonical TGF-β signaling by increasing non-lipid raft microdomain localization of the TGF-β receptors. Since TGF-β plays a protective role in ASCVD but can also cause ALD, the TGF-β enhancer activity of ethanol at low and high doses appears to be responsible for both beneficial and harmful effects. Ethanol also disrupts the location of lipid raft/caveolae of other membrane proteins (e.g., neurotransmitter, growth factor/cytokine, and G protein-coupled receptors) which utilize lipid rafts/caveolae as signaling platforms. Displacement of these membrane proteins induced by ethanol may result in a variety of pathologies in nerve, heart and other tissues.
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Affiliation(s)
| | - Chun-Lin Chen
- Department of Biological Science, National Sun Yat-sen University, Kaohsiung, 804, Taiwan.,Doctoral Degree Program in Marine Biotechnology, National Sun Yat-sen University and Academia Sinica, Kaohsiung, 804, Taiwan
| | - Franklin W Huang
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts, 02115.,Harvard Medical School, Boston, Massachusetts, 02115
| | - Frank E Johnson
- Department of Surgery, Saint Louis University School of Medicine, St. Louis, Missouri, 63104
| | - Jung San Huang
- Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Doisy Research Center, St. Louis, Missouri, 63104
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26
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Chen H, Zuo D, Zhang J, Zhou M, Ma L. Classification of 2-pore domain potassium channels based on rectification under quasi-physiological ionic conditions. Channels (Austin) 2015; 8:503-8. [PMID: 25616686 DOI: 10.4161/19336950.2014.973779] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
It is generally expected that 2-pore domain K(+) (K2P) channels are open or outward rectifiers in asymmetric physiological K(+) gradients, following the Goldman-Hodgkin-Katz (GHK) current equation. Although cloned K2P channels have been extensively studied, their current-voltage (I-V) relationships are not precisely characterized and previous definitions are contradictory. Here we study all the functional channels from 6 mammalian K2P subfamilies in transfected Chinese hamster ovary cells with patch-clamp technique, and examine whether their I-V relationships are described by the GHK current equation. K2P channels display 2 distinct types of I-V curves in asymmetric physiological K(+) gradients. Two K2P isoforms in the TWIK subfamily conduct large inward K(+) currents and have a nearly linear I-V curve. Ten isoforms from 5 other K2P subfamilies conduct small inward K(+) currents and exhibit open rectification, but fits with the GHK current equation cannot precisely reveal the differences in rectification among K2P channels. The Rectification Index, a ratio of limiting I-V slopes for outward and inward currents, is used to quantitatively describe open rectification of each K2P isoform, which is previously qualitatively defined as strong or weak open rectification. These results systematically and precisely classify K2P channels and suggest that TWIK K(+) channels have a unique feature in regulating cellular function.
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Affiliation(s)
- Haijun Chen
- a Department of Biological Sciences ; University at Albany; State University of New York ; Albany , NY USA
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27
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Larson VA, Zhang Y, Bergles DE. Electrophysiological properties of NG2(+) cells: Matching physiological studies with gene expression profiles. Brain Res 2015; 1638:138-160. [PMID: 26385417 DOI: 10.1016/j.brainres.2015.09.010] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Revised: 08/31/2015] [Accepted: 09/08/2015] [Indexed: 01/11/2023]
Abstract
NG2(+) glial cells are a dynamic population of non-neuronal cells that give rise to myelinating oligodendrocytes in the central nervous system. These cells express numerous ion channels and neurotransmitter receptors, which endow them with a complex electrophysiological profile that is unique among glial cells. Despite extensive analysis of the electrophysiological properties of these cells, relatively little was known about the molecular identity of the channels and receptors that they express. The generation of new RNA-Seq datasets for NG2(+) cells has provided the means to explore how distinct genes contribute to the physiological properties of these progenitors. In this review, we systematically compare the results obtained through RNA-Seq transcriptional analysis of purified NG2(+) cells to previous physiological and molecular studies of these cells to define the complement of ion channels and neurotransmitter receptors expressed by NG2(+) cells in the mammalian brain and discuss the potential significance of the unique physiological properties of these cells. This article is part of a Special Issue entitled SI:NG2-glia(Invited only).
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Affiliation(s)
- Valerie A Larson
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Ye Zhang
- Department of Neurobiology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Dwight E Bergles
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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28
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Renigunta V, Schlichthörl G, Daut J. Much more than a leak: structure and function of K₂p-channels. Pflugers Arch 2015; 467:867-94. [PMID: 25791628 DOI: 10.1007/s00424-015-1703-7] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 03/09/2015] [Indexed: 11/27/2022]
Abstract
Over the last decade, we have seen an enormous increase in the number of experimental studies on two-pore-domain potassium channels (K2P-channels). The collection of reviews and original articles compiled for this special issue of Pflügers Archiv aims to give an up-to-date summary of what is known about the physiology and pathophysiology of K2P-channels. This introductory overview briefly describes the structure of K2P-channels and their function in different organs. Its main aim is to provide some background information for the 19 reviews and original articles of this special issue of Pflügers Archiv. It is not intended to be a comprehensive review; instead, this introductory overview focuses on some unresolved questions and controversial issues, such as: Do K2P-channels display voltage-dependent gating? Do K2P-channels contribute to the generation of action potentials? What is the functional role of alternative translation initiation? Do K2P-channels have one or two or more gates? We come to the conclusion that we are just beginning to understand the extremely complex regulation of these fascinating channels, which are often inadequately described as 'leak channels'.
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Affiliation(s)
- Vijay Renigunta
- Institute of Physiology and Pathophysiology, Marburg University, 35037, Marburg, Germany
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29
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Sepúlveda FV, Pablo Cid L, Teulon J, Niemeyer MI. Molecular aspects of structure, gating, and physiology of pH-sensitive background K2P and Kir K+-transport channels. Physiol Rev 2015; 95:179-217. [PMID: 25540142 DOI: 10.1152/physrev.00016.2014] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
K(+) channels fulfill roles spanning from the control of excitability to the regulation of transepithelial transport. Here we review two groups of K(+) channels, pH-regulated K2P channels and the transport group of Kir channels. After considering advances in the molecular aspects of their gating based on structural and functional studies, we examine their participation in certain chosen physiological and pathophysiological scenarios. Crystal structures of K2P and Kir channels reveal rather unique features with important consequences for the gating mechanisms. Important tasks of these channels are discussed in kidney physiology and disease, K(+) homeostasis in the brain by Kir channel-equipped glia, and central functions in the hearing mechanism in the inner ear and in acid secretion by parietal cells in the stomach. K2P channels fulfill a crucial part in central chemoreception probably by virtue of their pH sensitivity and are central to adrenal secretion of aldosterone. Finally, some unorthodox behaviors of the selectivity filters of K2P channels might explain their normal and pathological functions. Although a great deal has been learned about structure, molecular details of gating, and physiological functions of K2P and Kir K(+)-transport channels, this has been only scratching at the surface. More molecular and animal studies are clearly needed to deepen our knowledge.
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Affiliation(s)
- Francisco V Sepúlveda
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - L Pablo Cid
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - Jacques Teulon
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - María Isabel Niemeyer
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
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30
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Feliciangeli S, Chatelain FC, Bichet D, Lesage F. The family of K2P channels: salient structural and functional properties. J Physiol 2015; 593:2587-603. [PMID: 25530075 DOI: 10.1113/jphysiol.2014.287268] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 12/10/2014] [Indexed: 12/11/2022] Open
Abstract
Potassium channels participate in many biological functions, from ion homeostasis to generation and modulation of the electrical membrane potential. They are involved in a large variety of diseases. In the human genome, 15 genes code for K(+) channels with two pore domains (K2P ). These channels form dimers of pore-forming subunits that produce background conductances finely regulated by a range of natural and chemical effectors, including signalling lipids, temperature, pressure, pH, antidepressants and volatile anaesthetics. Since the cloning of TWIK1, the prototypical member of this family, a lot of work has been carried out on their structure and biology. These studies are still in progress, but data gathered so far show that K2P channels are central players in many processes, including ion homeostasis, hormone secretion, cell development and excitability. A growing number of studies underline their implication in physiopathological mechanisms, such as vascular and pulmonary hypertension, cardiac arrhythmias, nociception, neuroprotection and depression. This review gives a synthetic view of the most noticeable features of these channels.
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Affiliation(s)
- Sylvain Feliciangeli
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Frank C Chatelain
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Delphine Bichet
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Florian Lesage
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
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31
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O'Kelly I. Endocytosis as a mode to regulate functional expression of two-pore domain potassium (K₂p) channels. Pflugers Arch 2014; 467:1133-42. [PMID: 25413469 PMCID: PMC4428836 DOI: 10.1007/s00424-014-1641-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2014] [Revised: 10/22/2014] [Accepted: 10/24/2014] [Indexed: 11/06/2022]
Abstract
Two-pore domain potassium (K2P) channels are implicated in an array of physiological and pathophysiological roles. As a result of their biophysical properties, these channels produce a background leak K+ current which has a direct effect on cellular membrane potential and activity. The regulation of potassium leak from cells through K2P channels is of critical importance to cell function, development and survival. Controlling the cell surface expression of these channels is one mode to regulate their function and is achieved through a balance between regulated channel delivery to and retrieval from the cell surface. Here, we explore the modes of retrieval of K2P channels from the plasma membrane and observe that K2P channels are endocytosed in both a clathrin-mediated and clathrin-independent manner. K2P channels use a variety of pathways and show altered internalisation and sorting in response to external cues. These pathways working in concert, equip the cell with a range of approaches to maintain steady state levels of channels and to respond rapidly should changes in channel density be required.
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Affiliation(s)
- Ita O'Kelly
- Human Development and Health, Centre for Human Development, Stem Cells and Regeneration, Faculty of Medicine, University of Southampton, Southampton, SO16 6YD, UK, I.M.O'
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Silent but not dumb: how cellular trafficking and pore gating modulate expression of TWIK1 and THIK2. Pflugers Arch 2014; 467:1121-31. [PMID: 25339226 DOI: 10.1007/s00424-014-1631-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 10/09/2014] [Accepted: 10/12/2014] [Indexed: 12/25/2022]
Abstract
Among K2P channels, a few of them turned out to be difficult to express in heterologous systems and were coined "silent subunits". Recent studies have shed light on the mechanisms behind this apparent lack of channel activity at the plasma membrane. For TWIK1 and THIK2 channels, silence is related to a combination of intracellular retention and low intrinsic activity. TWIK1 is constitutively endocytosed from the plasma membrane before being transported to recycling endosomes, whereas THIK2 is restricted to endoplasmic reticulum. These intracellular localizations are related to trafficking signals located in the cytoplasmic parts of the channels. When these motifs are mutated or masked, channels are redistributed at the plasma membrane and produce measurable currents. However, these currents are of modest amplitude. This weak basal activity is due to a hydrophobic barrier in the deep pore that limits water and ions in the conduction pathway. Other silent channels KCNK7, TWIK2, and TASK5 are still under study. Expression and characterization of these K2P channels pave the way for a better understanding of the mechanisms controlling intracellular trafficking of membrane proteins, ion conduction, and channel gating.
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33
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Altered and dynamic ion selectivity of K+ channels in cell development and excitability. Trends Pharmacol Sci 2014; 35:461-9. [PMID: 25023607 DOI: 10.1016/j.tips.2014.06.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Revised: 06/11/2014] [Accepted: 06/12/2014] [Indexed: 12/21/2022]
Abstract
K(+) channels play a key role in regulating cellular excitability. It was thought that the strong K(+) selectivity of these channels was static, only altered by mutations in their selectivity filter, which can cause severe genetic disorders. Recent studies demonstrate that selectivity of K(+) channels can also exhibit dynamic changes. Under acidic conditions or in low extracellular K(+) concentrations, the two-pore domain K(+) channel (K2P) TWIK1 becomes permeable to Na(+), shifting from an inhibitory role to an excitatory role. This phenomenon is responsible for the paradoxical depolarization of human cardiomyocytes in pathological hypokalemia, and therefore may contribute to cardiac arrhythmias. In other cell types, TWIK1 produces depolarizing leak currents under physiological conditions. Dynamic ion selectivity also occurs in other K2P channels. Here we review evidence that dynamic selectivity of K2P channels constitutes a new regulatory mechanism of cellular excitability, whose significance is only now becoming appreciated.
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Aryal P, Abd-Wahab F, Bucci G, Sansom MSP, Tucker SJ. A hydrophobic barrier deep within the inner pore of the TWIK-1 K2P potassium channel. Nat Commun 2014; 5:4377. [PMID: 25001086 PMCID: PMC4102122 DOI: 10.1038/ncomms5377] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 06/11/2014] [Indexed: 12/27/2022] Open
Abstract
Recent X-ray crystal structures of the two-pore domain (K2P) family of potassium channels have revealed a unique structural architecture at the point where the cytoplasmic bundle-crossing gate is found in most other tetrameric K(+) channels. However, despite the apparently open nature of the inner pore in the TWIK-1 (K2P1/KCNK1) crystal structure, the reasons underlying its low levels of functional activity remain unclear. In this study, we use a combination of molecular dynamics simulations and functional validation to demonstrate that TWIK-1 possesses a hydrophobic barrier deep within the inner pore, and that stochastic dewetting of this hydrophobic constriction acts as a major barrier to ion conduction. These results not only provide an important insight into the mechanisms which control TWIK-1 channel activity, but also have important implications for our understanding of how ion permeation may be controlled in similar ion channels and pores.
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Affiliation(s)
- Prafulla Aryal
- 1] Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, UK [2] Department of Biochemistry, University of Oxford, Oxford OX1 3QX, UK [3] OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford OX1 3PT, UK
| | - Firdaus Abd-Wahab
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, UK
| | - Giovanna Bucci
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, UK
| | - Mark S P Sansom
- 1] Department of Biochemistry, University of Oxford, Oxford OX1 3QX, UK [2] OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford OX1 3PT, UK
| | - Stephen J Tucker
- 1] Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, UK [2] OXION Initiative in Ion Channels and Disease, University of Oxford, Oxford OX1 3PT, UK
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35
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Milosavljevic N, Monet M, Léna I, Brau F, Lacas-Gervais S, Feliciangeli S, Counillon L, Poët M. The Intracellular Na+/H+ Exchanger NHE7 Effects a Na+-Coupled, but Not K+-Coupled Proton-Loading Mechanism in Endocytosis. Cell Rep 2014; 7:689-96. [DOI: 10.1016/j.celrep.2014.03.054] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 08/01/2013] [Accepted: 03/20/2014] [Indexed: 12/31/2022] Open
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36
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A disulphide-linked heterodimer of TWIK-1 and TREK-1 mediates passive conductance in astrocytes. Nat Commun 2014; 5:3227. [DOI: 10.1038/ncomms4227] [Citation(s) in RCA: 94] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Accepted: 01/09/2014] [Indexed: 01/22/2023] Open
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37
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Wang W, Putra A, Schools GP, Ma B, Chen H, Kaczmarek LK, Barhanin J, Lesage F, Zhou M. The contribution of TWIK-1 channels to astrocyte K(+) current is limited by retention in intracellular compartments. Front Cell Neurosci 2013; 7:246. [PMID: 24368895 PMCID: PMC3856854 DOI: 10.3389/fncel.2013.00246] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 11/18/2013] [Indexed: 12/04/2022] Open
Abstract
TWIK-1 two-pore domain K+ channels are expressed abundantly in astrocytes. In the present study, we examined the extent to which TWIK-1 contributes to the linear current-voltage (I–V) relationship (passive) K+ membrane conductance, a dominant electrophysiological feature of mature hippocampal astrocytes. Astrocytes from TWIK-1 knockout mice have a more negative resting potential than those from wild type animals and a reduction in both inward rectification and Cs+ permeability. Nevertheless, the overall whole-cell passive conductance is not altered significantly in TWIK-1 knockout astrocytes. The expression of Kir4.1 and TREK-1, two other major astrocytic K+ channels, or of other two-pore K+ channels is not altered in TWIK-1 knockout mice, suggesting that the mild effect of TWIK-1 knockout does not result from compensation by these channels. Fractionation experiments showed that TWIK-1 is primarily localized in intracellular cytoplasmic fractions (55%) and mildly hydrophobic internal compartment fractions (41%), with only 5% in fractions containing plasma membranes. Our study revealed that TWIK-1 proteins are mainly located in the intracellular compartments of hippocampal astrocyte under physiological condition, therefore a minimal contribution of TWIK-1 channels to whole-cell currents is likely attributable to a relatively low level presence of channels in the plasma membrane.
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Affiliation(s)
- Wei Wang
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Adhytia Putra
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | | | - Baofeng Ma
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Haijun Chen
- Department of Biological Sciences, University at Albany, SUNY Albany, NY, USA
| | - Leonard K Kaczmarek
- Department of Pharmacology, Yale University School of Medicine New Haven, CT, USA
| | - Jacques Barhanin
- Centre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia Antipolis Valbonne, France
| | - Florian Lesage
- Centre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia Antipolis Valbonne, France
| | - Min Zhou
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
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38
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Renigunta V, Zou X, Kling S, Schlichthörl G, Daut J. Breaking the silence: functional expression of the two-pore-domain potassium channel THIK-2. Pflugers Arch 2013; 466:1735-45. [DOI: 10.1007/s00424-013-1404-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Accepted: 11/09/2013] [Indexed: 10/26/2022]
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Chatelain FC, Bichet D, Feliciangeli S, Larroque MM, Braud VM, Douguet D, Lesage F. Silencing of the tandem pore domain halothane-inhibited K+ channel 2 (THIK2) relies on combined intracellular retention and low intrinsic activity at the plasma membrane. J Biol Chem 2013; 288:35081-92. [PMID: 24163367 DOI: 10.1074/jbc.m113.503318] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The tandem pore domain halothane-inhibited K(+) channel 1 (THIK1) produces background K(+) currents. Despite 62% amino acid identity with THIK1, THIK2 is not active upon heterologous expression. Here, we show that this apparent lack of activity is due to a unique combination of retention in the endoplasmic reticulum and low intrinsic channel activity at the plasma membrane. A THIK2 mutant containing a proline residue (THIK2-A155P) in its second inner helix (M2) produces K(+)-selective currents with properties similar to THIK1, including inhibition by halothane and insensitivity to extracellular pH variations. Another mutation in the M2 helix (I158D) further increases channel activity and affects current kinetics. We also show that the cytoplasmic amino-terminal region of THIK2 (Nt-THIK2) contains an arginine-rich motif (RRSRRR) that acts as a retention/retrieval signal. Mutation of this motif in THIK2 induces a relocation of the channel to the plasma membrane, resulting in measurable currents, even in the absence of mutations in the M2 helix. Cell surface delivery of a Nt-THIK2-CD161 chimera is increased by mutating the arginines of the retention motif but also by converting the serine embedded in this motif to aspartate, suggesting a phosphorylation-dependent regulation of THIK2 trafficking.
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Affiliation(s)
- Franck C Chatelain
- From the Laboratory of Excellence Ion Channel Science and Therapeutics, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, and Université de Nice Sophia Antipolis, 660 Route des Lucioles, 06560 Valbonne, France
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40
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Pollema-Mays SL, Centeno MV, Ashford CJ, Apkarian AV, Martina M. Expression of background potassium channels in rat DRG is cell-specific and down-regulated in a neuropathic pain model. Mol Cell Neurosci 2013; 57:1-9. [PMID: 23994814 DOI: 10.1016/j.mcn.2013.08.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Revised: 07/30/2013] [Accepted: 08/12/2013] [Indexed: 10/26/2022] Open
Abstract
Neuropathic pain is associated with hyperexcitability of DRG neurons. Despite the importance of leakage potassium channels for neuronal excitability, little is known about their cell-specific expression in DRGs and possible modulation in neuropathic pain. Multiple leakage channels are expressed in DRG neurons, including TASK1, TASK3, TRESK, TRAAK, TWIK1, TREK1 and TREK2 but little is known about their distribution among different cell types. Our immunohistochemical studies show robust TWIK1 expression in large and medium size neurons, without overlap with TRPV1 or IB4 staining. TASK1 and TASK3, on the contrary, are selectively expressed in small cells; TASK1 expression closely overlaps TRPV1-positive cells, while TASK3 is expressed in TRPV1- and IB4-negative cells. We also studied mRNA expression of these channels in L4-L5 DRGs in control conditions and up to 4 weeks after spared nerve injury lesion. We found that TWIK1 expression is much higher than TASK1 and TASK3 and is strongly decreased 1, 2 and 4 weeks after neuropathic injury. TASK3 expression, on the other hand, decreases 1 week after surgery but reverts to baseline by 2weeks; TASK1 shows no significant change at any time point. These data suggest an involvement of TWIK1 in the maintenance of the pain condition.
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Affiliation(s)
- Sarah L Pollema-Mays
- Department of Physiology, Northwestern University Feinberg School of Medicine, 303 E Chicago Ave., Chicago, IL 60611, United States
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41
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The degradation of the inwardly rectifying potassium channel, Kir2.1, depends on the expression level: examination with fluorescent proteins. Brain Res 2013; 1528:8-19. [PMID: 23850646 DOI: 10.1016/j.brainres.2013.07.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2012] [Revised: 07/01/2013] [Accepted: 07/05/2013] [Indexed: 01/24/2023]
Abstract
The expression of ion channels is regulated by their synthesis as well as degradation, and some ion channels are degraded in an expression level-dependent way. Recently, new techniques of fluorescent proteins have been developed and seem to be useful to study protein degradation. To examine the regulation of the degradation of strongly inwardly rectifying potassium channel (Kir2.1) and the usefulness of the fluorescent proteins, we constructed Kir2.1 fusion proteins with SNAP tag and fluorescent timer (FT). The SNAP tag, which covalently binds to a specific membrane-permeable fluorescent dye, enables a pulse-chase experiment with fluorescence. When the SNAP-Kir2.1 proteins were expressed in 293T cells by low and high expression plasmids, the half-life of the fusion protein expressed by a high-expression plasmid was shorter (18.2±1.9 h) than that expressed by a low-expression plasmid (35.1+2.3h). The addition of Ba(2+), a selective blocker of Kir2.1, slowed the degradation, suggesting a current-dependency of degradation. Consistently, patch-clamp recording showed that cultivation in the presence of Ba(2+) increased the whole cell conductance of SNAP-Kir2.1. Since the fluorescence of FT changes gradually changes from green to red, the green/red ratio should allow us to monitor the changes in the degradation rate of FT-Kir2.1. Using this method, we confirmed the slower degradation by Ba(2+). The results suggest a homeostatic regulation of the degradation of Kir2.1 in the 293T cells, and the usefulness of fluorescence-based methods for examining the degradation of ion channels.
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Rapetti-Mauss R, O'Mahony F, Sepulveda FV, Urbach V, Harvey BJ. Oestrogen promotes KCNQ1 potassium channel endocytosis and postendocytic trafficking in colonic epithelium. J Physiol 2013; 591:2813-31. [PMID: 23529131 PMCID: PMC3690688 DOI: 10.1113/jphysiol.2013.251678] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 03/19/2013] [Indexed: 12/23/2022] Open
Abstract
The cAMP-regulated potassium channel KCNQ1:KCNE3 plays an essential role in transepithelial Cl(-) secretion. Recycling of K(+) across the basolateral membrane provides the driving force necessary to maintain apical Cl(-) secretion. The steroid hormone oestrogen (17β-oestradiol; E2), produces a female-specific antisecretory response in rat distal colon through the inhibition of the KCNQ1:KCNE3 channel. It has previously been shown that rapid inhibition of the channel conductance results from E2-induced uncoupling of the KCNE3 regulatory subunit from the KCNQ1 channel pore complex. The purpose of this study was to determine the mechanism required for sustained inhibition of the channel function. We found that E2 plays a role in regulation of KCNQ1 cell membrane abundance by endocytosis. Ussing chamber experiments have shown that E2 inhibits both Cl(-) secretion and KCNQ1 current in a colonic cell line, HT29cl.19A, when cultured as a confluent epithelium. Following E2 treatment, KCNQ1 was retrieved from the plasma membrane by a clathrin-mediated endocytosis, which involved the association between KCNQ1 and the clathrin adaptor, AP-2. Following endocytosis, KCNQ1 was accumulated in early endosomes. Following E2-induced endocytosis, rather than being degraded, KCNQ1 was recycled by a biphasic mechanism involving Rab4 and Rab11. Protein kinase Cδ and AMP-dependent kinase were rapidly phosphorylated in response to E2 on their activating phosphorylation sites, Ser643 and Thr172, respectively (as previously shown). Both kinases are necessary for the E2-induced endocytosis, because E2 failed to induce KCNQ1 internalization following pretreatment with specific inhibitors of both protein kinase Cδ and AMP-dependent kinase. The ubiquitin ligase Nedd4.2 binds KCNQ1 in response to E2 to induce channel internalization. This study has provided the first demonstration of hormonal regulation of KCNQ1 trafficking. In conclusion, we propose that internalization of KCNQ1 is a key event in the sustained antisecretory response to oestrogen.
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Affiliation(s)
- Raphael Rapetti-Mauss
- Department of Molecular Medicine, RCSI-ERC, Beaumont Hospital, PO Box 9063, Dublin 9, Ireland
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Ma L, Xie YP, Zhou M, Chen H. Silent TWIK-1 potassium channels conduct monovalent cation currents. Biophys J 2012; 102:L34-6. [PMID: 22768960 DOI: 10.1016/j.bpj.2012.03.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 02/17/2012] [Accepted: 03/05/2012] [Indexed: 10/28/2022] Open
Abstract
TWIK-1 two-pore domain K(+) channels generally produce nonmeasurable or very low levels of K(+) currents in heterologous expression systems under physiologically ionic conditions. Two controversial mechanisms have been proposed to account for this behavior: TWIK-1 K(+) channels are expressed in the cell surface but silenced by sumoylation at a lysine residue (TWIK-1 K274); constitutive and rapid internalization of TWIK-1 causes TWIK-1 channel silencing. Here we report that TWIK-1 K(+) channels heterologously expressed in Chinese hamster ovary cells, which are silent in physiological K(+) gradients, are able to conduct large monovalent cation currents when extracellular ionic conditions change. These results support the hypothesis that TWIK-1 K(+) channels are expressed in the cell surface but silent, and suggest that the TWIK-1 gating behavior rather than the lack of cell surface expression of TWIK-1 results in nondetectable TWIK-1 K(+) currents in heterologous expression systems.
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Ma L, Zhang X, Zhou M, Chen H. Acid-sensitive TWIK and TASK two-pore domain potassium channels change ion selectivity and become permeable to sodium in extracellular acidification. J Biol Chem 2012; 287:37145-53. [PMID: 22948150 DOI: 10.1074/jbc.m112.398164] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Two-pore domain K(+) channels (K2P) mediate background K(+) conductance and play a key role in a variety of cellular functions. Among the 15 mammalian K2P isoforms, TWIK-1, TASK-1, and TASK-3 K(+) channels are sensitive to extracellular acidification. Lowered or acidic extracellular pH (pH(o)) strongly inhibits outward currents through these K2P channels. However, the mechanism of how low pH(o) affects these acid-sensitive K2P channels is not well understood. Here we show that in Na(+)-based bath solutions with physiological K(+) gradients, lowered pH(o) largely shifts the reversal potential of TWIK-1, TASK-1, and TASK-3 K(+) channels, which are heterologously expressed in Chinese hamster ovary cells, into the depolarizing direction and significantly increases their Na(+) to K(+) relative permeability. Low pH(o)-induced inhibitions in these acid-sensitive K2P channels are more profound in Na(+)-based bath solutions than in channel-impermeable N-methyl-D-glucamine-based bath solutions, consistent with increases in the Na(+) to K(+) relative permeability and decreases in electrochemical driving forces of outward K(+) currents of the channels. These findings indicate that TWIK-1, TASK-1, and TASK-3 K(+) channels change ion selectivity in response to lowered pH(o), provide insights on the understanding of how extracellular acidification modulates acid-sensitive K2P channels, and imply that these acid-sensitive K2P channels may regulate cellular function with dynamic changes in their ion selectivity.
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Affiliation(s)
- Liqun Ma
- Department of Biological Sciences and the Center for Neuroscience Research, University at Albany, State University of New York, Albany, New York 12222, USA
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Gabriel L, Lvov A, Orthodoxou D, Rittenhouse AR, Kobertz WR, Melikian HE. The acid-sensitive, anesthetic-activated potassium leak channel, KCNK3, is regulated by 14-3-3β-dependent, protein kinase C (PKC)-mediated endocytic trafficking. J Biol Chem 2012; 287:32354-66. [PMID: 22846993 DOI: 10.1074/jbc.m112.391458] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The acid-sensitive neuronal potassium leak channel, KCNK3, is vital for setting the resting membrane potential and is the primary target for volatile anesthetics. Recent reports demonstrate that KCNK3 activity is down-regulated by PKC; however, the mechanisms responsible for PKC-induced KCNK3 down-regulation are undefined. Here, we report that endocytic trafficking dynamically regulates KCNK3 activity. Phorbol esters and Group I metabotropic glutamate receptor (mGluR) activation acutely decreased both native and recombinant KCNK3 currents with concomitant KCNK3 surface losses in cerebellar granule neurons and cell lines. PKC-mediated KCNK3 internalization required the presence of both 14-3-3β and a novel potassium channel endocytic motif, because depleting either 14-3-3β protein levels or ablating the endocytic motif completely abrogated PKC-regulated KCNK3 trafficking. These results demonstrate that neuronal potassium leak channels are not static membrane residents but are subject to 14-3-3β-dependent regulated trafficking, providing a straightforward mechanism to modulate neuronal excitability and synaptic plasticity by Group I mGluRs.
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Affiliation(s)
- Luke Gabriel
- Graduate Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts 01604, USA
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46
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Lesage F, Barhanin J. Molecular physiology of pH-sensitive background K(2P) channels. Physiology (Bethesda) 2012; 26:424-37. [PMID: 22170960 DOI: 10.1152/physiol.00029.2011] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Background K(2P) channels are tightly regulated by different stimuli including variations of external and internal pH. pH sensitivity relies on proton-sensing residues that influence channel gating and activity. Gene inactivation in the mouse is a revealing implication of K(2P) channels in many physiological functions ranging from hormone secretion to central respiratory adaptation. Surprisingly, only a few phenotypic traits of these mice have yet been directly related to the pH sensitivity of K(2P) channels.
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Affiliation(s)
- Florian Lesage
- Institut de Pharmacologie Moléculaire et Cellulaire, Unité Mixte de Recherche 6097 Centre National de la Recherche Scientifique, Valbonne, France.
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Abstract
TWIK1 belongs to the family of background K(+) channels with two pore domains. In native and transfected cells, TWIK1 is detected mainly in recycling endosomes. In principal cells in the kidney, TWIK1 gene inactivation leads to the loss of a nonselective cationic conductance, an unexpected effect that was attributed to adaptive regulation of other channels. Here, we show that TWIK1 ion selectivity is modulated by extracellular pH. Although TWIK1 is K(+) selective at neutral pH, it becomes permeable to Na(+) at the acidic pH found in endosomes. Selectivity recovery is slow after restoration of a neutral pH. Such hysteresis makes plausible a role of TWIK1 as a background channel in which selectivity and resulting inhibitory or excitatory influences on cell excitability rely on its recycling rate between internal acidic stores and the plasma membrane. TWIK1(-/-) pancreatic β cells are more polarized than control cells, confirming a depolarizing role of TWIK1 in kidney and pancreatic cells.
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48
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Miller AN, Long SB. Crystal Structure of the Human Two-Pore Domain Potassium Channel K2P1. Science 2012; 335:432-6. [DOI: 10.1126/science.1213274] [Citation(s) in RCA: 244] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Lukashova V, Szabó EZ, Jinadasa T, Mokhov A, Litchfield DW, Orlowski J. CK2 phosphorylation of an acidic Ser/Thr di-isoleucine motif in the Na+/H+ exchanger NHE5 isoform promotes association with beta-arrestin2 and endocytosis. J Biol Chem 2011; 286:11456-68. [PMID: 21296876 DOI: 10.1074/jbc.m110.182881] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Internalization of the Na(+)/H(+) exchanger NHE5 into recycling endosomes is enhanced by the endocytic adaptor proteins β-arrestin1 and -2, best known for their preferential recognition of ligand-activated G protein-coupled receptors (GPCRs). However, the mechanism underlying their atypical association with non-GPCRs, such as NHE5, is unknown. In this study, we identified a highly acidic, serine/threonine-rich, di-isoleucine motif (amino acids 697-723) in the cytoplasmic C terminus of NHE5 that is recognized by β-arrestin2. Gross deletions of this site decreased the state of phosphorylation of NHE5 as well as its binding and responsiveness to β-arrestin2 in intact cells. More refined in vitro analyses showed that this site was robustly phosphorylated by the acidotropic protein kinase CK2, whereas other kinases, such as CK1 or the GPCR kinase GRK2, were considerably less potent. Simultaneous mutation of five Ser/Thr residues within 702-714 to Ala ((702)ST/AA(714)) abolished phosphorylation and binding of β-arrestin2. In transfected cells, the CK2 catalytic α subunit formed a complex with NHE5 and decreased wild-type but not (702)ST/AA(714) NHE5 activity, further supporting a regulatory role for this kinase. The rate of internalization of (702)ST/AA(714) was also diminished and relatively insensitive to overexpression of β-arrestin2. However, unlike in vitro, this mutant retained its ability to form a complex with β-arrestin2 despite its lack of responsiveness. Additional mutations of two di-isoleucine-based motifs (I697A/L698A and I722A/I723A) that immediately flank the acidic cluster, either separately or together, were required to disrupt their association. These data demonstrate that discrete elements of an elaborate sorting signal in NHE5 contribute to β-arrestin2 binding and trafficking along the recycling endosomal pathway.
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Wilkinson KA, Nakamura Y, Henley JM. Targets and consequences of protein SUMOylation in neurons. BRAIN RESEARCH REVIEWS 2010; 64:195-212. [PMID: 20382182 PMCID: PMC3310160 DOI: 10.1016/j.brainresrev.2010.04.002] [Citation(s) in RCA: 104] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2010] [Revised: 03/24/2010] [Accepted: 04/01/2010] [Indexed: 11/26/2022]
Abstract
The post-translational modification of proteins is critical for the spatial and temporal regulation of signalling cascades. This is especially important in the CNS where the processes affecting differentiation, growth, targeting and communication between neurones are highly complex and very tightly regulated. In recent years it has emerged that modification of proteins by members of the SUMO (small ubiquitin-related modifier) family of proteins play key roles in neuronal function. SUMOylation involves the covalent conjugation of a member of the SUMO family to lysine residues in target proteins. Multiple nuclear and perinuclear SUMOylation targets have been reported to be involved in nuclear organisation and transcriptional regulation. In addition, a growing number of extranuclear SUMO substrates have been identified that can have important acute effects on neuronal function. The SUMOylation of both intra- and extranuclear proteins have been implicated in a diverse array of processes that have far-reaching implications for neuronal function and pathophysiology. Here we review the current understanding of the targets and consequences of protein SUMOylation in the brain and examine its established and potential involvement in a wide range of neurological and neurodegenerative diseases.
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Affiliation(s)
- Kevin A. Wilkinson
- Medical Research Council Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
| | - Yasuko Nakamura
- Medical Research Council Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
| | - Jeremy M. Henley
- Medical Research Council Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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