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Gubič Š, Montalbano A, Sala C, Becchetti A, Hendrickx LA, Van Theemsche KM, Pinheiro-Junior EL, Altadonna GC, Peigneur S, Ilaš J, Labro AJ, Pardo LA, Tytgat J, Tomašič T, Arcangeli A, Peterlin Mašič L. Immunosuppressive effects of new thiophene-based K V1.3 inhibitors. Eur J Med Chem 2023; 259:115561. [PMID: 37454520 DOI: 10.1016/j.ejmech.2023.115561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 06/08/2023] [Accepted: 06/08/2023] [Indexed: 07/18/2023]
Abstract
Voltage-gated potassium channel KV1.3 inhibitors have been shown to be effective in preventing T-cell proliferation and activation by affecting intracellular Ca2+ homeostasis. Here, we present the structure-activity relationship, KV1.3 inhibition, and immunosuppressive effects of new thiophene-based KV1.3 inhibitors with nanomolar potency on K+ current in T-lymphocytes and KV1.3 inhibition on Ltk- cells. The new KV1.3 inhibitor trans-18 inhibited KV1.3 -mediated current in phytohemagglutinin (PHA)-activated T-lymphocytes with an IC50 value of 26.1 nM and in mammalian Ltk- cells with an IC50 value of 230 nM. The KV1.3 inhibitor trans-18 also had nanomolar potency against KV1.3 in Xenopus laevis oocytes (IC50 = 136 nM). The novel thiophene-based KV1.3 inhibitors impaired intracellular Ca2+ signaling as well as T-cell activation, proliferation, and colony formation.
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Affiliation(s)
- Špela Gubič
- University of Ljubljana, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Aškerčeva cesta 7, 1000, Ljubljana, Slovenia
| | - Alberto Montalbano
- University of Florence, Department of Experimental and Clinical Medicine, I-50134, Florence, Italy
| | - Cesare Sala
- University of Florence, Department of Experimental and Clinical Medicine, I-50134, Florence, Italy
| | - Andrea Becchetti
- University of Milano-Bicocca, Department of Biotechnology and Biosciences, Piazza della Scienza 2, I-20126, Milano, Italy
| | - Louise Antonia Hendrickx
- University of Leuven, Toxicology and Pharmacology, Campus Gasthuisberg, Onderwijs en Navorsing 2, Herestraat 49, PO Box 922, 3000, Leuven, Belgium
| | - Kenny M Van Theemsche
- University of Antwerp, Department of Biomedical Sciences, Campus Drie Eiken, Universiteisplein 1, 2610, Wilrijk, Belgium; Ghent University, Department of Basic and Applied Medical Sciences, Corneel Heymanslaan 10, 9000, Ghent, Belgium
| | - Ernesto Lopes Pinheiro-Junior
- University of Leuven, Toxicology and Pharmacology, Campus Gasthuisberg, Onderwijs en Navorsing 2, Herestraat 49, PO Box 922, 3000, Leuven, Belgium
| | | | - Steve Peigneur
- University of Leuven, Toxicology and Pharmacology, Campus Gasthuisberg, Onderwijs en Navorsing 2, Herestraat 49, PO Box 922, 3000, Leuven, Belgium
| | - Janez Ilaš
- University of Ljubljana, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Aškerčeva cesta 7, 1000, Ljubljana, Slovenia
| | - Alain J Labro
- Ghent University, Department of Basic and Applied Medical Sciences, Corneel Heymanslaan 10, 9000, Ghent, Belgium
| | - Luis A Pardo
- Max-Planck Institute for Experimental Medicine, AG Oncophysiology, Hermann-Rein-Str. 3, 37075, Göttingen, Germany
| | - Jan Tytgat
- University of Leuven, Toxicology and Pharmacology, Campus Gasthuisberg, Onderwijs en Navorsing 2, Herestraat 49, PO Box 922, 3000, Leuven, Belgium
| | - Tihomir Tomašič
- University of Ljubljana, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Aškerčeva cesta 7, 1000, Ljubljana, Slovenia
| | - Annarosa Arcangeli
- University of Florence, Department of Experimental and Clinical Medicine, I-50134, Florence, Italy.
| | - Lucija Peterlin Mašič
- University of Ljubljana, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Aškerčeva cesta 7, 1000, Ljubljana, Slovenia.
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2
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Gubič Š, Hendrickx LA, Shi X, Toplak Ž, Možina Š, Theemsche KMV, Pinheiro-Junior EL, Peigneur S, Labro AJ, Pardo LA, Tytgat J, Tomašič T, Peterlin Mašič L. Correction: Gubič et al. Design of New Potent and Selective Thiophene-Based K V1.3 Inhibitors and Their Potential for Anticancer Activity. Cancers 2022, 14, 2595. Cancers (Basel) 2023; 15:cancers15112925. [PMID: 37297027 DOI: 10.3390/cancers15112925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 05/10/2023] [Indexed: 06/12/2023] Open
Abstract
In the original publication [...].
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Affiliation(s)
- Špela Gubič
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva 7, 1000 Ljubljana, Slovenia
| | - Louise Antonia Hendrickx
- Campus Gasthuisberg, University of Leuven, Toxicology and Pharmacology, Onderwijs en Navorsing 2, Herestraat 49, 3000 Leuven, Belgium
| | - Xiaoyi Shi
- AG Oncophysiology, Max-Planck Institute for Multidisciplinary Sciences, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
| | - Žan Toplak
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva 7, 1000 Ljubljana, Slovenia
| | - Štefan Možina
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva 7, 1000 Ljubljana, Slovenia
| | - Kenny M Van Theemsche
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium
- Department of Basic and Applied Medical Sciences, Ghent University, Corneel Heymanslaan 10 (Entrance 36), 9000 Ghent, Belgium
| | - Ernesto Lopes Pinheiro-Junior
- Campus Gasthuisberg, University of Leuven, Toxicology and Pharmacology, Onderwijs en Navorsing 2, Herestraat 49, 3000 Leuven, Belgium
| | - Steve Peigneur
- Campus Gasthuisberg, University of Leuven, Toxicology and Pharmacology, Onderwijs en Navorsing 2, Herestraat 49, 3000 Leuven, Belgium
| | - Alain J Labro
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium
- Department of Basic and Applied Medical Sciences, Ghent University, Corneel Heymanslaan 10 (Entrance 36), 9000 Ghent, Belgium
| | - Luis A Pardo
- AG Oncophysiology, Max-Planck Institute for Multidisciplinary Sciences, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
| | - Jan Tytgat
- Campus Gasthuisberg, University of Leuven, Toxicology and Pharmacology, Onderwijs en Navorsing 2, Herestraat 49, 3000 Leuven, Belgium
| | - Tihomir Tomašič
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva 7, 1000 Ljubljana, Slovenia
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Sieliwonczyk E, Alaerts M, Simons E, Snyders D, Nijak A, Vandendriessche B, Schepers D, Akdeniz D, Van Craenenbroeck E, Knaepen K, Rabaut L, Heidbuchel H, Van Laer L, Saenen J, Labro AJ, Loeys B. Clinical and functional characterisation of a recurrent KCNQ1 variant in the Belgian population. Orphanet J Rare Dis 2023; 18:23. [PMID: 36721196 PMCID: PMC9887867 DOI: 10.1186/s13023-023-02618-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Accepted: 01/15/2023] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND The c.1124_1127delTTCA p.(Ile375Argfs*43) pathogenic variant is the most frequently identified molecular defect in the KCNQ1 gene in the cardiogenetics clinic of the Antwerp University Hospital. This variant was observed in nine families presenting with either Jervell-Lange-Nielsen syndrome or long QT syndrome (LQTS). Here, we report on the molecular, clinical and functional characterization of the KCNQ1 c.1124_1127delTTCA variant. RESULTS Forty-one heterozygous variant harboring individuals demonstrated a predominantly mild clinical and electrophysiological phenotype, compared to individuals harboring other KCNQ1 pathogenic variants (5% symptomatic before 40 years of age, compared to 24% and 29% in p.(Tyr111Cys) and p.(Ala341Val) variant carriers, respectively, 33% with QTc ≤ 440 ms compared to 10% in p.(Tyr111Cys) and p.(Ala341Val) variant carriers). The LQTS phenotype was most comparable to that observed for the Swedish p.(Arg518*) founder mutation (7% symptomatic at any age, compared to 17% in p.(Arg518*) variant carriers, 33% with QTc ≤ 440 ms compared to 16% in p.(Arg518*) variant carriers). Surprisingly, short tandem repeat analysis did not reveal a common haplotype for all families. One KCNQ1 c.1124_1127delTTCA harboring patient was diagnosed with Brugada syndrome (BrS). The hypothesis of a LQTS/BrS overlap syndrome was supported by electrophysiological evidence for both loss-of-function and gain-of-function (acceleration of channel kinetics) in a heterologous expression system. However, BrS phenotypes were not identified in other affected individuals and allelic KCNQ1 expression testing in patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) showed nonsense mediated decay of the c.1124_1127delTTCA allele. CONCLUSIONS The c.1124_1127delTTCA frameshift variant shows a high prevalence in our region, despite not being confirmed as a founder mutation. This variant leads to a mild LQTS phenotype in the heterozygous state. Despite initial evidence for a gain-of-function effect based on in vitro electrophysiological assessment in CHO cells and expression of the KCNQ1 c.1124_1127delTTCA allele in patient blood cells, additional testing in iPSC-CMs showed lack of expression of the mutant allele. This suggests haploinsufficiency as the pathogenic mechanism. Nonetheless, as inter-individual differences in allele expression in (iPSC-) cardiomyocytes have not been assessed, a modifying effect on the BrS phenotype through potassium current modulation cannot be excluded.
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Affiliation(s)
- Ewa Sieliwonczyk
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium. .,Medical Genetics (MEDGEN), GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium.
| | - Maaike Alaerts
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Medical Genetics (MEDGEN), GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
| | - Eline Simons
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Dirk Snyders
- grid.5284.b0000 0001 0790 3681Experimental Neurobiology Unit, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Aleksandra Nijak
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Bert Vandendriessche
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Dorien Schepers
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Medical Genetics (MEDGEN), GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Experimental Neurobiology Unit, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Dogan Akdeniz
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Emeline Van Craenenbroeck
- grid.5284.b0000 0001 0790 3681Department of Cardiology, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Cardiovascular Research, GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
| | - Katleen Knaepen
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Laura Rabaut
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Hein Heidbuchel
- grid.5284.b0000 0001 0790 3681Department of Cardiology, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Cardiovascular Research, GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
| | - Lut Van Laer
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Medical Genetics (MEDGEN), GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
| | - Johan Saenen
- grid.5284.b0000 0001 0790 3681Department of Cardiology, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Cardiovascular Research, GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
| | - Alain J. Labro
- grid.5284.b0000 0001 0790 3681Experimental Neurobiology Unit, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium ,grid.5342.00000 0001 2069 7798Department of Basic and Applied Medical Sciences, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Bart Loeys
- grid.5284.b0000 0001 0790 3681Center of Medical Genetics, Faculty of Medicine and Health Sciences, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium ,grid.5284.b0000 0001 0790 3681Medical Genetics (MEDGEN), GENCOR, Faculty of Medicine and Health Sciences, University of Antwerp, Antwerp, Belgium
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4
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Déri S, Hartai T, Virág L, Jost N, Labro AJ, Varró A, Baczkó I, Nattel S, Ördög B. MiRP2 rescues long QT syndrome type 5. J Mol Cell Cardiol 2022. [DOI: 10.1016/j.yjmcc.2022.08.175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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5
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Coonen L, Martinez-Morales E, Van De Sande DV, Snyders DJ, Cortes DM, Cuello LG, Labro AJ. The nonconducting W434F mutant adopts upon membrane depolarization an inactivated-like state that differs from wild-type Shaker-IR potassium channels. Sci Adv 2022; 8:eabn1731. [PMID: 36112676 PMCID: PMC9481120 DOI: 10.1126/sciadv.abn1731] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 08/01/2022] [Indexed: 06/15/2023]
Abstract
Voltage-gated K+ (Kv) channels mediate the flow of K+ across the cell membrane by regulating the conductive state of their activation gate (AG). Several Kv channels display slow C-type inactivation, a process whereby their selectivity filter (SF) becomes less or nonconductive. It has been proposed that, in the fast inactivation-removed Shaker-IR channel, the W434F mutation epitomizes the C-type inactivated state because it functionally accelerates this process. By introducing another pore mutation that prevents AG closure, P475D, we found a way to record ionic currents of the Shaker-IR-W434F-P475D mutant at hyperpolarized membrane potentials as the W434F-mutant SF recovers from its inactivated state. This W434F conductive state lost its high K+ over Na+ selectivity, and even NMDG+ can permeate, features not observed in a wild-type SF. This indicates that, at least during recovery from inactivation, the W434F-mutant SF transitions to a widened and noncationic specific conformation.
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Affiliation(s)
- Laura Coonen
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Evelyn Martinez-Morales
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dieter V. Van De Sande
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - D. Marien Cortes
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Luis G. Cuello
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Alain J. Labro
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, 9000 Ghent, Belgium
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6
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Van Theemsche KM, Heymans JG, Popovic NZ, Martinez-Morales E, Snyders DJ, Labro AJ. Offsetting Voltage-Dependent Kv1.5 Channel Opening Through Charged Residue Substitutions on Top of the First Transmembrane Segment. Bioelectricity 2022. [DOI: 10.1089/bioe.2022.0005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Kenny M. Van Theemsche
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Joni G. Heymans
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
| | - Nikola Z. Popovic
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
| | | | - Dirk J. Snyders
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Alain J. Labro
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
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7
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Simons E, Nijak A, Vandendriessche B, Van De Sande D, Sieliwonczyk E, Labro AJ, Saenen J, Snyders D, Schepers D, Loeys B, Alaerts M. Modeling of an SCN5A founder mutation in iPSC-derived cardiomyocytes. Cardiovasc Res 2022. [DOI: 10.1093/cvr/cvac066.118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation - Flanders (FWO)
Introduction
SCN5A encodes the α-subunit of voltage-gated cardiac sodium channel Nav1.5. Mutations in SCN5A are identified in about 20% of patients with Brugada syndrome (BrS), an inherited cardiac arrhythmia. We have identified an SCN5A founder mutation (c.4813+3_4813+6dupGGGT), leading to a loss-of-function of Nav1.5 in 25 different families. Mutation carriers show variable expression of the phenotype: from asymptomatic to syncopes and sudden cardiac death. We used induced pluripotent stem cell derived cardiomyocytes (iPSC-CM) to investigate the underlying pathophysiology.
Material & Methods
Dermal fibroblasts of six patients with different disease severity, and two unrelated healthy control individuals were reprogrammed using a commercially available reprogramming kit. iPSC-CMs were differentiated following a published protocol. We performed several differentiation rounds and investigated expression of cardiac markers using qPCR and immunocytochemistry and electrophysiological properties using patch-clamping.
Results
All iPSC-CMs expressed the tested markers. We observed reduction in sodium current density in patient iPSC-CMs compared to the control cells. However, our data display variability in AP characteristics between the differentiation batches, as well as between clones generated from one donor.
Conclusions
We established iPSC-CM models for a unique Belgian SCN5A founder mutation. Despite the observed variability, we could detect expected differences in electrophysiological properties of patient cells compared to controls.
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Affiliation(s)
- E Simons
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
| | - A Nijak
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
| | - B Vandendriessche
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
| | - D Van De Sande
- University of Antwerp, Laboratory of Molecular Biophysics, Physiology & Pharmacology , Antwerp , Belgium
| | - E Sieliwonczyk
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
| | - A J Labro
- University of Antwerp, Laboratory of Molecular Biophysics, Physiology & Pharmacology , Antwerp , Belgium
| | - J Saenen
- University Hospital Antwerp, Department of Cardiology , Antwerp , Belgium
| | - D Snyders
- University of Antwerp, Laboratory of Molecular Biophysics, Physiology & Pharmacology , Antwerp , Belgium
| | - D Schepers
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
| | - B Loeys
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
| | - M Alaerts
- University of Antwerp, Center of Medical Genetics , Antwerp , Belgium
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8
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Nijak A, Simons E, Vandendriessche B, Van de Sande D, Fransen E, Sieliwończyk E, Van Gucht I, Van Craenenbroeck E, Saenen J, Heidbuchel H, Ponsaerts P, Labro AJ, Snyders D, De Vos W, Schepers D, Alaerts M, Loeys BL. Morpho-functional comparison of differentiation protocols to create iPSC-derived cardiomyocytes. Biol Open 2022; 11:274508. [PMID: 35195246 PMCID: PMC8890088 DOI: 10.1242/bio.059016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 12/15/2021] [Indexed: 11/30/2022] Open
Abstract
Cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) offer an attractive platform for cardiovascular research. Patient-specific iPSC-CMs are very useful for studying disease development, and bear potential for disease diagnostics, prognosis evaluation and development of personalized treatment. Several monolayer-based serum-free protocols have been described for the differentiation of iPSCs into cardiomyocytes, but data on their performance are scarce. In this study, we evaluated two protocols that are based on temporal modulation of the Wnt/β-catenin pathway for iPSC-CM differentiation from four iPSC lines, including two control individuals and two patients carrying an SCN5A mutation. The SCN5A gene encodes the cardiac voltage-gated sodium channel (Nav1.5) and loss-of-function mutations can cause the cardiac arrhythmia Brugada syndrome. We performed molecular characterization of the obtained iPSC-CMs by immunostaining for cardiac specific markers and by expression analysis of selected cardiac structural and ionic channel protein-encoding genes with qPCR. We also investigated cell growth morphology, contractility and survival of the iPSC-CMs after dissociation. Finally, we performed electrophysiological characterization of the cells, focusing on the action potential (AP) and calcium transient (CT) characteristics using patch-clamping and optical imaging, respectively. Based on our comprehensive morpho-functional analysis, we concluded that both tested protocols result in a high percentage of contracting CMs. Moreover, they showed acceptable survival and cell quality after dissociation (>50% of cells with a smooth cell membrane, possible to seal during patch-clamping). Both protocols generated cells presenting with typical iPSC-CM AP and CT characteristics, although one protocol (that involves sequential addition of CHIR99021 and Wnt-C59) rendered iPSC-CMs, which were more accessible for patch-clamp and calcium transient experiments and showed an expression pattern of cardiac-specific markers more similar to this observed in human heart left ventricle samples. Summary: In this study, we evaluated two protocols that are based on temporal modulation of the Wnt/β -catenin pathway for iPSC-CM differentiation from four iPSC lines. We show that both protocols were successful in the generation of contracting iPSC-CMs. However, one of the tested protocols rendered cells that were more accessible for patch-clamp experiments and showed an expression pattern of cardiac-specific markers more similar to this of human heart left ventricle samples.
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Affiliation(s)
- Aleksandra Nijak
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium
| | - Eline Simons
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium
| | - Bert Vandendriessche
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium
| | - Dieter Van de Sande
- Laboratory of Molecular Biophysics, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, Antwerp 2610, Belgium
| | - Erik Fransen
- StatUa Center of Statistics, University of Antwerp 2650, Antwerp, Belgium
| | - Ewa Sieliwończyk
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium
| | - Ilse Van Gucht
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium
| | - Emeline Van Craenenbroeck
- Department of Cardiology, Faculty of Medicine and Health Sciences, University of Antwerp and Antwerp University Hospital, Antwerp 2650, Belgium
| | - Johan Saenen
- Department of Cardiology, Faculty of Medicine and Health Sciences, University of Antwerp and Antwerp University Hospital, Antwerp 2650, Belgium
| | - Hein Heidbuchel
- Department of Cardiology, Faculty of Medicine and Health Sciences, University of Antwerp and Antwerp University Hospital, Antwerp 2650, Belgium
| | - Peter Ponsaerts
- Laboratory of Experimental Hematology, Vaccine & Infectious Disease Institute, Department of Biomedical Sciences, University of Antwerp, Antwerp 2610, Belgium
| | - Alain J Labro
- Laboratory of Molecular Biophysics, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, Antwerp 2610, Belgium.,Department of Basic and Applied Medical Sciences, Faculty of Medicine and Health Sciences, Ghent University, Ghent 9000, Belgium
| | - Dirk Snyders
- Laboratory of Molecular Biophysics, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, Antwerp 2610, Belgium
| | - Winnok De Vos
- Laboratory of Cell Biology and Histology, Faculty of Veterinary Sciences, University of Antwerp, Antwerp 2610, Belgium
| | - Dorien Schepers
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium.,Laboratory of Molecular Biophysics, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, Antwerp 2610, Belgium
| | - Maaike Alaerts
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium
| | - Bart L Loeys
- Center of Medical Genetics, Faculty of Medicine and Health Sciences, University of Antwerp & Antwerp University Hospital, Antwerp 2650, Belgium.,Department of Human Genetics, Radboud University Medical Centre, Nijmegen 6525, The Netherlands
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9
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Coonen L, Martinez-Morales E, Cuello LG, Snyders DJ, Labro AJ. The recovery from the C-type inactivated state differs between Shaker and Shaker-W434F K+channels. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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10
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Arora R, Van Theemsche KM, Van Remoortel S, Snyders DJ, Labro AJ, Timmermans JP. Constitutive, Basal, and β-Alanine-Mediated Activation of the Human Mas-Related G Protein-Coupled Receptor D Induces Release of the Inflammatory Cytokine IL-6 and Is Dependent on NF-κB Signaling. Int J Mol Sci 2021; 22:ijms222413254. [PMID: 34948051 PMCID: PMC8703779 DOI: 10.3390/ijms222413254] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 12/03/2021] [Accepted: 12/04/2021] [Indexed: 12/14/2022] Open
Abstract
G protein-coupled receptors (GPCRs) have emerged as key players in regulating (patho)physiological processes, including inflammation. Members of the Mas-related G protein coupled receptors (MRGPRs), a subfamily of GPCRs, are largely expressed by sensory neurons and known to modulate itch and pain. Several members of MRGPRs are also expressed in mast cells, macrophages, and in cardiovascular tissue, linking them to pseudo-allergic drug reactions and suggesting a pivotal role in the cardiovascular system. However, involvement of the human Mas-related G-protein coupled receptor D (MRGPRD) in the regulation of the inflammatory mediator interleukin 6 (IL-6) has not been demonstrated to date. By stimulating human MRGPRD-expressing HeLa cells with the agonist β-alanine, we observed a release of IL-6. β-alanine-induced signaling through MRGPRD was investigated further by probing downstream signaling effectors along the Gαq/Phospholipase C (PLC) pathway, which results in an IkB kinases (IKK)-mediated canonical activation of nuclear factor kappa-B (NF-κB) and stimulation of IL-6 release. This IL-6 release could be blocked by a Gαq inhibitor (YM-254890), an IKK complex inhibitor (IKK-16), and partly by a PLC inhibitor (U-73122). Additionally, we investigated the constitutive (ligand-independent) and basal activity of MRGPRD and concluded that the observed basal activity of MRGPRD is dependent on the presence of fetal bovine serum (FBS) in the culture medium. Consequently, the dynamic range for IL-6 detection as an assay for β-alanine-mediated activation of MRGPRD is substantially increased by culturing the cells in FBS free medium before treatment. Overall, the observation that MRGPRD mediates the release of IL-6 in an in vitro system, hints at a role as an inflammatory mediator and supports the notion that IL-6 can be used as a marker for MRGPRD activation in an in vitro drug screening assay.
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Affiliation(s)
- Rohit Arora
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (R.A.); (S.V.R.)
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
| | - Kenny M. Van Theemsche
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
| | - Samuel Van Remoortel
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (R.A.); (S.V.R.)
| | - Dirk J. Snyders
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
| | - Alain J. Labro
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
- Department of Basic and Applied Medical Sciences, Ghent University, 9000 Ghent, Belgium
- Correspondence: (A.J.L.); (J.-P.T.); Tel.: +32-9-3320034 (A.J.L.); +32-3-2653327 (J.-P.T.)
| | - Jean-Pierre Timmermans
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (R.A.); (S.V.R.)
- Correspondence: (A.J.L.); (J.-P.T.); Tel.: +32-9-3320034 (A.J.L.); +32-3-2653327 (J.-P.T.)
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11
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Van de Sande DV, Kopljar I, Maaike A, Teisman A, Gallacher DJ, Bart L, Snyders DJ, Leybaert L, Lu HR, Labro AJ. The resting membrane potential of hSC-CM in a syncytium is more hyperpolarised than that of isolated cells. Channels (Austin) 2021; 15:239-252. [PMID: 33465001 PMCID: PMC7817136 DOI: 10.1080/19336950.2021.1871815] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 11/20/2020] [Accepted: 12/31/2020] [Indexed: 01/11/2023] Open
Abstract
Human-induced pluripotent stem cell (hiPSC) and stem cell (hSC) derived cardiomyocytes (CM) are gaining popularity as in vitro model for cardiology and pharmacology studies. A remaining flaw of these cells, as shown by single-cell electrophysiological characterization, is a more depolarized resting membrane potential (RMP) compared to native CM. Most reports attribute this to a lower expression of the Kir2.1 potassium channel that generates the IK1 current. However, most RMP recordings are obtained from isolated hSC/hiPSC-CMs whereas in a more native setting these cells are interconnected with neighboring cells by connexin-based gap junctions, forming a syncytium. Hereby, these cells are electrically connected and the total pool of IK1 increases. Therefore, the input resistance (Ri) of interconnected cells is lower than that of isolated cells. During patch clamp experiments pipettes need to be well attached or sealed to the cell, which is reflected in the seal resistance (Rs), because a nonspecific ionic current can leak through this pipette-cell contact or seal and balance out small currents within the cell such as IK1. By recording the action potential of isolated hSC-CMs and that of hSC-CMs cultured in small monolayers, we show that the RMP of hSC-CMs in monolayer is approximately -20 mV more hyperpolarized compared to isolated cells. Accordingly, adding carbenoxolone, a connexin channel blocker, isolates the cell that is patch clamped from its neighboring cells of the monolayer and depolarizes the RMP. The presented data show that the recorded RMP of hSC-CMs in a syncytium is more negative than that determined from isolated hSC/hiPSC-CMs, most likely because the active pool of Kir2.1 channels increased.
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Affiliation(s)
| | - Ivan Kopljar
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Alaerts Maaike
- Centre of Medical Genetics, University of Antwerp, Antwerp, Belgium
| | - Ard Teisman
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - David J. Gallacher
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Loeys Bart
- Centre of Medical Genetics, University of Antwerp, Antwerp, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Luc Leybaert
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
| | - Hua Rong Lu
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Alain J. Labro
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
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12
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Déri S, Borbás J, Hartai T, Hategan L, Csányi B, Visnyovszki Á, Madácsy T, Maléth J, Hegedűs Z, Nagy I, Arora R, Labro AJ, Környei L, Varró A, Sepp R, Ördög B. Impaired cytoplasmic domain interactions cause co-assembly defect and loss of function in the p.Glu293Lys KNCJ2 variant isolated from an Andersen-Tawil syndrome patient. Cardiovasc Res 2021; 117:1923-1934. [PMID: 32810216 DOI: 10.1093/cvr/cvaa249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 07/16/2020] [Accepted: 08/12/2020] [Indexed: 02/07/2023] Open
Abstract
AIMS Subunit interactions at the cytoplasmic domain interface (CD-I) have recently been shown to control gating in inward rectifier potassium channels. Here we report the novel KCNJ2 variant p.Glu293Lys that has been found in a patient with Andersen-Tawil syndrome type 1 (ATS1), causing amino acid substitution at the CD-I of the inward rectifier potassium channel subunit Kir2.1. Neither has the role of Glu293 in gating control been investigated nor has a pathogenic variant been described at this position. This study aimed to assess the involvement of Glu293 in CD-I subunit interactions and to establish the pathogenic role of the p.Glu293Lys variant in ATS1. METHODS AND RESULTS The p.Glu293Lys variant produced no current in homomeric form and showed dominant-negative effect over wild-type (WT) subunits. Immunocytochemical labelling showed the p.Glu293Lys subunits to distribute in the subsarcolemmal space. Salt bridge prediction indicated the presence of an intersubunit salt bridge network at the CD-I of Kir2.1, with the involvement of Glu293. Subunit interactions were studied by the NanoLuc® Binary Technology (NanoBiT) split reporter assay. Reporter constructs carrying NanoBiT tags on the intracellular termini produced no bioluminescent signal above background with the p.Glu293Lys variant in homomeric configuration and significantly reduced signals in cells co-expressing WT and p.Glu293Lys subunits simultaneously. Extracellularly presented reporter tags, however, generated comparable bioluminescent signals with heteromeric WT and p.Glu293Lys subunits and with homomeric WT channels. CONCLUSIONS Loss of function and dominant-negative effect confirm the causative role of p.Glu293Lys in ATS1. Co-assembly of Kir2.1 subunits is impaired in homomeric channels consisting of p.Glu293Lys subunits and is partially rescued in heteromeric complexes of WT and p.Glu293Lys Kir2.1 variants. These data point to an important role of Glu293 in mediating subunit assembly, as well as in gating of Kir2.1 channels.
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Affiliation(s)
- Szilvia Déri
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Dóm tér 12, 6720 Szeged, Hungary
| | - János Borbás
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Teodóra Hartai
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
| | - Lidia Hategan
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Beáta Csányi
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Ádám Visnyovszki
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
| | - Tamara Madácsy
- 1st Department of Internal Medicine, University of Szeged, Korányi fasor 8-10, 6720 Szeged, Hungary, Hungary
| | - József Maléth
- 1st Department of Internal Medicine, University of Szeged, Korányi fasor 8-10, 6720 Szeged, Hungary, Hungary
| | - Zoltán Hegedűs
- Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, 6726 Szeged, Hungary
- Department of Biochemistry and Medical Chemistry, University of Pécs, Szigeti út 12, 7624 Pécs, Hungary
| | - István Nagy
- Institute of Biochemistry, Biological Research Centre the Hungarian Academy of Sciences, Temesvári krt. 62, 6726 Szeged, Hungary
- Seqomics Biotechnology Ltd, Vállalkozók útja 7, 6782 Mórahalom, Hungary
| | - Rohit Arora
- Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium
| | - Alain J Labro
- Department of Biomedical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium
- Department of Basic Medical Sciences, University of Ghent, C. Heymanslaan 10, 9000 Ghent, Belgium
| | - László Környei
- Gottsegen György National Institute of Cardiology, Haller u. 9, 1096 Budapest, Hungary
| | - András Varró
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Dóm tér 12, 6720 Szeged, Hungary
- MTA-SZTE Research Group for Cardiovascular Pharmacology, Hungarian Academy of Sciences, Dóm tér 12, 6720 Szeged, Hungary
| | - Róbert Sepp
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Balázs Ördög
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
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13
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Nijak A, Labro AJ, De Wilde H, Dewals W, Peigneur S, Tytgat J, Snyders D, Sieliwonczyk E, Simons E, Van Craenenbroeck E, Schepers D, Van Laer L, Saenen J, Loeys B, Alaerts M. Compound Heterozygous SCN5A Mutations in Severe Sodium Channelopathy With Brugada Syndrome: A Case Report. Front Cardiovasc Med 2020; 7:117. [PMID: 32850980 PMCID: PMC7396896 DOI: 10.3389/fcvm.2020.00117] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 06/04/2020] [Indexed: 12/16/2022] Open
Abstract
Aims: Brugada syndrome (BrS) is an inherited cardiac arrhythmia with an increased risk for sudden cardiac death (SCD). About 20% of BrS cases are explained by mutations in the SCN5A gene, encoding the main cardiac sodium Nav1.5 channel. Here we present a severe case of cardiac sodium channelopathy with BrS caused by SCN5A compound heterozygous mutations. We performed a genetic analysis of SCN5A in a male proband who collapsed during cycling at the age of 2 years. Because of atrial standstill, he received a pacemaker, and at the age of 3 years, he experienced a collapse anew with left-sided brain stroke. A later ECG taken during a fever unmasked a characteristic BrS type-1 pattern. The functional effect of the detected genetic variants was investigated. Methods and Results: Next-generation sequencing allowed the detection of two SCN5A variants in trans: c.4813+3_4813+6dupGGGT-a Belgian founder mutation-and c.4711 T>C, p.Phe1571Leu. A familial segregation analysis showed the presence of the founder mutation in the proband's affected father and paternal aunt and the de novo occurrence of the p.Phe1571Leu. The functional effect of the founder mutation was previously described as a loss-of-function. We performed a functional analysis of the p.Phe571Leu variant in HEK293 cells alone or co-expressed with the β1-subunit. Compared to the SCN5A wild type, p.Phe1571Leu displayed a hyperpolarizing shift in the voltage dependence of inactivation (loss-of-function), while the activation parameters were unaffected. Using the peptide toxin nemertide α-1, the variant's loss-of-function effect could be restored due to a toxin-dependent reduction of channel inactivation. Conclusion: This is the first report providing support for the pathogenicity of the p.Phe1571Leu SCN5A variant which, together with the c.4813+3_4813+6dupGGGT founder mutation, explains the severity of the phenotype of cardiac sodium channelopathy with BrS in the presented case.
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Affiliation(s)
- Aleksandra Nijak
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Alain J Labro
- Laboratory of Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Hans De Wilde
- Department of Paediatric Cardiology, Antwerp University Hospital, Antwerp, Belgium.,Department of Invasive Cardiology and Electrophysiology, Ghent University Hospital, Ghent, Belgium
| | - Wendy Dewals
- Department of Paediatric Cardiology, Antwerp University Hospital, Antwerp, Belgium
| | - Steve Peigneur
- Toxicology and Pharmacology, University of Leuven (KU Leuven), Leuven, Belgium
| | - Jan Tytgat
- Toxicology and Pharmacology, University of Leuven (KU Leuven), Leuven, Belgium
| | - Dirk Snyders
- Laboratory of Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Ewa Sieliwonczyk
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Eline Simons
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | | | - Dorien Schepers
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Lut Van Laer
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Johan Saenen
- Department of Cardiology, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
| | - Bart Loeys
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium.,Department of Human Genetics, Radboud University Medical Centre, Nijmegen, Netherlands
| | - Maaike Alaerts
- Center of Medical Genetics, Antwerp University Hospital, University of Antwerp, Antwerp, Belgium
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14
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Van Theemsche KM, Van de Sande DV, Snyders DJ, Labro AJ. Hydrophobic Drug/Toxin Binding Sites in Voltage-Dependent K + and Na + Channels. Front Pharmacol 2020; 11:735. [PMID: 32499709 PMCID: PMC7243439 DOI: 10.3389/fphar.2020.00735] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 05/04/2020] [Indexed: 12/26/2022] Open
Abstract
In the Nav channel family the lipophilic drugs/toxins binding sites and the presence of fenestrations in the channel pore wall are well defined and categorized. No such classification exists in the much larger Kv channel family, although certain lipophilic compounds seem to deviate from binding to well-known hydrophilic binding sites. By mapping different compound binding sites onto 3D structures of Kv channels, there appear to be three distinct lipid-exposed binding sites preserved in Kv channels: the front and back side of the pore domain, and S2-S3/S3-S4 clefts. One or a combination of these sites is most likely the orthologous equivalent of neurotoxin site 5 in Nav channels. This review describes the different lipophilic binding sites and location of pore wall fenestrations within the Kv channel family and compares it to the knowledge of Nav channels.
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Affiliation(s)
- Kenny M Van Theemsche
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Dieter V Van de Sande
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Alain J Labro
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
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15
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Moeller L, Labro AJ, Snyders DJ, Blunck R. Choosing the Correct Stoichiometry from Single Subunit Counting Data. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.1518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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16
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Van de Sande DV, Kopljar I, Teisman A, Gallacher DJ, Snyders DJ, Lu HR, Labro AJ. Pharmacological Profile of the Sodium Current in Human Stem Cell-Derived Cardiomyocytes Compares to Heterologous Nav1.5+β1 Model. Front Pharmacol 2019; 10:1374. [PMID: 31920633 PMCID: PMC6917651 DOI: 10.3389/fphar.2019.01374] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 10/29/2019] [Indexed: 12/20/2022] Open
Abstract
The cardiac Nav1.5 mediated sodium current (INa) generates the upstroke of the action potential in atrial and ventricular myocytes. Drugs that modulate this current can therefore be antiarrhythmic or proarrhythmic, which requires preclinical evaluation of their potential drug-induced inhibition or modulation of Nav1.5. Since Nav1.5 assembles with, and is modulated by, the auxiliary β1-subunit, this subunit can also affect the channel’s pharmacological response. To investigate this, the effect of known Nav1.5 inhibitors was compared between COS-7 cells expressing Nav1.5 or Nav1.5+β1 using whole-cell voltage clamp experiments. For the open state class Ia blockers ajmaline and quinidine, and class Ic drug flecainide, the affinity did not differ between both models. For class Ib drugs phenytoin and lidocaine, which are inactivated state blockers, the affinity decreased more than a twofold when β1 was present. Thus, β1 did not influence the affinity for the class Ia and Ic compounds but it did so for the class Ib drugs. Human stem cell-derived cardiomyocytes (hSC-CMs) are a promising translational cell source for in vitro models that express a representative repertoire of channels and auxiliary proteins, including β1. Therefore, we subsequently evaluated the same drugs for their response on the INa in hSC-CMs. Consequently, it was expected and confirmed that the drug response of INa in hSC-CMs compares best to INa expressed by Nav1.5+β1.
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Affiliation(s)
- Dieter V Van de Sande
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Ivan Kopljar
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium.,Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Ard Teisman
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - David J Gallacher
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Dirk J Snyders
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Hua Rong Lu
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Alain J Labro
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
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17
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Arora R, Van Remoortel S, Van Raemdonck G, Baggerman G, Buckinx R, Snyders DJ, Labro AJ, Timmermans J. Activation of Human Mas‐related G Protein‐coupled Receptor F (MRGPRF) by the Cysteine Protease Cathepsin S: Implication in Neuro‐Immune Communication Within the Gut. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.585.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Rohit Arora
- Veterinary Sciences, Lab Cell Biology & HistologyUniversity of AntwerpWilrijkAntwerpBelgium
| | - Samuel Van Remoortel
- Veterinary Sciences, Lab Cell Biology & HistologyUniversity of AntwerpWilrijkAntwerpBelgium
| | | | | | - Roeland Buckinx
- Veterinary Sciences, Lab Cell Biology & HistologyUniversity of AntwerpWilrijkAntwerpBelgium
| | - Dirk J Snyders
- Biomedical Sciences, Lab Molecular, Cellular and Network ExcitabilityUniversity of AntwerpWilrijkAntwerpBelgium
| | - Alain J Labro
- Biomedical Sciences, Lab Molecular, Cellular and Network ExcitabilityUniversity of AntwerpWilrijkAntwerpBelgium
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18
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Kopljar I, Grottesi A, de Block T, Rainier JD, Tytgat J, Labro AJ, Snyders DJ. Voltage-sensor conformation shapes the intra-membrane drug binding site that determines gambierol affinity in Kv channels. Neuropharmacology 2016; 107:160-167. [PMID: 26956727 DOI: 10.1016/j.neuropharm.2016.03.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 02/13/2016] [Accepted: 03/04/2016] [Indexed: 01/02/2023]
Abstract
Marine ladder-shaped polyether toxins are implicated in neurological symptoms of fish-borne food poisonings. The toxin gambierol, produced by the marine dinoflagellate Gambierdiscus toxicus, belongs to the group of ladder-shaped polyether toxins and inhibits Kv3.1 channels with nanomolar affinity through a mechanism of gating modification. Binding determinants for gambierol localize at the lipid-exposed interface of the pore forming S5 and S6 segments, suggesting that gambierol binds outside of the permeation pathway. To explore a possible involvement of the voltage-sensing domain (VSD), we made different chimeric channels between Kv3.1 and Kv2.1, exchanging distinct parts of the gating machinery. Our results showed that neither the electro-mechanical coupling nor the S1-S3a region of the VSD affect gambierol sensitivity. In contrast, the S3b-S4 part of the VSD (paddle motif) decreased gambierol sensitivity in Kv3.1 more than 100-fold. Structure determination by homology modeling indicated that the position of the S3b-S4 paddle and its primary structure defines the shape and∖or the accessibility of the binding site for gambierol, explaining the observed differences in gambierol affinity between the channel chimeras. Furthermore, these findings explain the observed difference in gambierol affinity for the closed and open channel configurations of Kv3.1, opening new possibilities for exploring the VSDs as selectivity determinants in drug design.
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Affiliation(s)
- Ivan Kopljar
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium
| | | | - Tessa de Block
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium
| | - Jon D Rainier
- Department of Chemistry, University of Utah, Salt Lake City, UT, 84112-0850, USA
| | - Jan Tytgat
- Toxicology and Pharmacology, University of Leuven Campus Gasthuisberg, 3000, Leuven, Belgium
| | - Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium.
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Stas JI, Bocksteins E, Labro AJ, Snyders DJ. Modulation of Closed-State Inactivation in Kv2.1/Kv6.4 Heterotetramers as Mechanism for 4-AP Induced Potentiation. PLoS One 2015; 10:e0141349. [PMID: 26505474 PMCID: PMC4623978 DOI: 10.1371/journal.pone.0141349] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 10/06/2015] [Indexed: 12/26/2022] Open
Abstract
The voltage-gated K+ (Kv) channel subunits Kv2.1 and Kv2.2 are expressed in almost every tissue. The diversity of Kv2 current is increased by interacting with the electrically silent Kv (KvS) subunits Kv5-Kv6 and Kv8-Kv9, into functional heterotetrameric Kv2/KvS channels. These Kv2/KvS channels possess unique biophysical properties and display a more tissue-specific expression pattern, making them more desirable pharmacological and therapeutic targets. However, little is known about the pharmacological properties of these heterotetrameric complexes. We demonstrate that Kv5.1, Kv8.1 and Kv9.3 currents were inhibited differently by the channel blocker 4-aminopyridine (4-AP) compared to Kv2.1 homotetramers. In contrast, Kv6.4 currents were potentiated by 4-AP while displaying moderately increased affinities for the channel pore blockers quinidine and flecainide. We found that the 4-AP induced potentiation of Kv6.4 currents was caused by modulation of the Kv6.4-mediated closed-state inactivation: suppression by 4-AP of the Kv2.1/Kv6.4 closed-state inactivation recovered a population of Kv2.1/Kv6.4 channels that was inactivated at resting conditions, i.e. at a holding potential of -80 mV. This modulation also resulted in a slower initiation and faster recovery from closed-state inactivation. Using chimeric substitutions between Kv6.4 and Kv9.3 subunits, we demonstrated that the lower half of the S6 domain (S6c) plays a crucial role in the 4-AP induced potentiation. These results demonstrate that KvS subunits modify the pharmacological response of Kv2 subunits when assembled in heterotetramers and illustrate the potential of KvS subunits to provide unique pharmacological properties to the heterotetramers, as is the case for 4-AP on Kv2.1/Kv6.4 channels.
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Affiliation(s)
- Jeroen I. Stas
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Alain J. Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
- * E-mail:
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Martinez-Morales E, Snyders DJ, Labro AJ. Mutations in the S6 gate isolate a late step in the activation pathway and reduce 4-AP sensitivity in shaker K(v) channel. Biophys J 2014; 106:134-44. [PMID: 24411245 DOI: 10.1016/j.bpj.2013.11.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Revised: 10/28/2013] [Accepted: 11/12/2013] [Indexed: 01/12/2023] Open
Abstract
Kv channels detect changes in the membrane potential via their voltage-sensing domains (VSDs) that control the status of the S6 bundle crossing (BC) gate. The movement of the VSDs results in a transfer of the S4 gating charges across the cell membrane but only the last 10-20% of the total gating charge movement is associated with BC gate opening, which involves cooperative transition(s) in the subunits. Substituting the proline residue P475 in the S6 of the Shaker channel by a glycine or alanine causes a considerable shift in the voltage-dependence of the cooperative transition(s) of BC gate opening, effectively isolating the late gating charge component from the other gating charge that originates from earlier VSD movements. Interestingly, both mutations also abolished Shaker's sensitivity to 4-aminopyridine, which is a pharmacological tool to isolate the late gating charge component. The alanine substitution (that would promote a α-helical configuration compared to proline) resulted in the largest separation of both gating charge components; therefore, BC gate flexibility appears to be important for enabling the late cooperative step of channel opening.
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Affiliation(s)
- Evelyn Martinez-Morales
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium
| | - Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium.
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21
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Stas JI, Bocksteins E, Labro AJ, Snyders DJ. Diversity in the Pharmacological Profile of Heterotetrameric KV2/KVS Channels for Channel Blockers. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.3024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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22
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Martinez-Morales E, Labro AJ, Snyders DJ. Offsetting the Electric Field Sensed by KV Channels through Residue Substitutions on Top of S1. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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23
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Kopljar I, Labro AJ, de Block T, Rainier JD, Tytgat J, Snyders DJ. The ladder-shaped polyether toxin gambierol anchors the gating machinery of Kv3.1 channels in the resting state. ACTA ACUST UNITED AC 2013; 141:359-69. [PMID: 23401573 PMCID: PMC3581691 DOI: 10.1085/jgp.201210890] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Voltage-gated potassium (Kv) and sodium (Nav) channels are key determinants of cellular excitability and serve as targets of neurotoxins. Most marine ciguatoxins potentiate Nav channels and cause ciguatera seafood poisoning. Several ciguatoxins have also been shown to affect Kv channels, and we showed previously that the ladder-shaped polyether toxin gambierol is a potent Kv channel inhibitor. Most likely, gambierol acts via a lipid-exposed binding site, located outside the K+ permeation pathway. However, the mechanism by which gambierol inhibits Kv channels remained unknown. Using gating and ionic current analysis to investigate how gambierol affected S6 gate opening and voltage-sensing domain (VSD) movements, we show that the resting (closed) channel conformation forms the high-affinity state for gambierol. The voltage dependence of activation was shifted by >120 mV in the depolarizing direction, precluding channel opening in the physiological voltage range. The (early) transitions between the resting and the open state were monitored with gating currents, and provided evidence that strong depolarizations allowed VSD movement up to the activated-not-open state. However, for transition to the fully open (ion-conducting) state, the toxin first needed to dissociate. These dissociation kinetics were markedly accelerated in the activated-not-open state, presumably because this state displayed a much lower affinity for gambierol. A tetrameric concatemer with only one high-affinity binding site still displayed high toxin sensitivity, suggesting that interaction with a single binding site prevented the concerted step required for channel opening. We propose a mechanism whereby gambierol anchors the channel’s gating machinery in the resting state, requiring more work from the VSD to open the channel. This mechanism is quite different from the action of classical gating modifier peptides (e.g., hanatoxin). Therefore, polyether toxins open new opportunities in structure–function relationship studies in Kv channels and in drug design to modulate channel function.
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Affiliation(s)
- Ivan Kopljar
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610 Antwerp, Belgium
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Martinez-Morales E, Kopljar I, Labro AJ, Snyders DJ. 1-Butanol and Gambierol:Low and High Affinity Compounds that Immobilize Charge Movement in Shaker and Kv3.1 Potassium Channels. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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25
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Cortes DM, Labro AJ, Cuello LG. Structural and Functional Consequences of Replacing Glycine 77 with a L-Alanine at the KcsA Selectivity Filter. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.2578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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26
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Abderemane-Ali F, Es-Salah-Lamoureux Z, Delemotte L, Kasimova MA, Labro AJ, Snyders DJ, Fedida D, Tarek M, Baró I, Loussouarn G. Dual Effect of PIP2 on Shaker K+ Channels. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.2567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Labro AJ, Lacroix JJ, Villalba-Galea CA, Snyders DJ, Bezanilla F. Molecular mechanism for depolarization-induced modulation of Kv channel closure. ACTA ACUST UNITED AC 2012; 140:481-93. [PMID: 23071266 PMCID: PMC3483114 DOI: 10.1085/jgp.201210817] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage-dependent potassium (Kv) channels provide the repolarizing power that shapes the action potential duration and helps control the firing frequency of neurons. The K+ permeation through the channel pore is controlled by an intracellularly located bundle-crossing (BC) gate that communicates with the voltage-sensing domains (VSDs). During prolonged membrane depolarizations, most Kv channels display C-type inactivation that halts K+ conduction through constriction of the K+ selectivity filter. Besides triggering C-type inactivation, we show that in Shaker and Kv1.2 channels (expressed in Xenopus laevis oocytes), prolonged membrane depolarizations also slow down the kinetics of VSD deactivation and BC gate closure during the subsequent membrane repolarization. Measurements of deactivating gating currents (reporting VSD movement) and ionic currents (BC gate status) showed that the kinetics of both slowed down in two distinct phases with increasing duration of the depolarizing prepulse. The biphasic slowing in VSD deactivation and BC gate closure was strongly correlated in time and magnitude. Simultaneous recordings of ionic currents and fluorescence from a probe tracking VSD movement in Shaker directly demonstrated that both processes were synchronized. Whereas the first slowing originates from a stabilization imposed by BC gate opening, the subsequent slowing reflects the rearrangement of the VSD toward its relaxed state (relaxation). The VSD relaxation was observed in the Ciona intestinalis voltage-sensitive phosphatase and in its isolated VSD. Collectively, our results show that the VSD relaxation is not kinetically related to C-type inactivation and is an intrinsic property of the VSD. We propose VSD relaxation as a general mechanism for depolarization-induced slowing of BC gate closure that may enable Kv1.2 channels to modulate the firing frequency of neurons based on the depolarization history.
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Affiliation(s)
- Alain J Labro
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
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28
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Abstract
Kv channels form voltage-dependent potassium selective pores in the outer cell membrane and are composed out of four α-subunits, each having six membrane-spanning α-helices (S1–S6). The α-subunits tetramerize such that the S5–S6 pore domains co-assemble into a centrally located K+ pore which is surrounded by four operational voltage-sensing domains (VSD) that are each formed by the S1–S4 segments. Consequently, each subunit is capable of responding to changes in membrane potential and dictates whether the pore should be conductive or not. K+ permeation through the pore can be sealed off by two separate gates in series: (a) at the inner S6 bundle crossing (BC gate) and (b) at the level of the selectivity filter (SF gate) located at the extracellular entrance of the pore. Within the last years a general consensus emerged that a direct communication between the S4S5-linker and the bottom part of S6 (S6c) constitutes the coupling with the VSD thus making the BC gate the main voltage-controllable activation gate. While the BC gate listens to the VSD, the SF changes its conformation depending on the status of the BC gate. Through the eyes of an entering K+ ion, the operation of the BC gate apparatus can be compared with the iris-like motion of the diaphragm from a camera whereby its diameter widens. Two main gating motions have been proposed to create this BC gate widening: (1) tilting of the helix whereby the S6 converts from a straight α-helix to a tilted one or (2) swiveling of the S6c whereby the S6 remains bent. Such motions require a flexible hinge that decouples the pre- and post-hinge segment. Roughly at the middle of the S6 there exists a highly conserved glycine residue and a tandem proline motif that seem to fulfill the role of a gating hinge which allows for tilting/swiveling/rotations of the post-hinge S6 segment. In this review we delineate our current view on the operation of the BC gate for controlling K+ permeation in Kv channels.
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Affiliation(s)
- Alain J Labro
- Department of Biomedical Sciences, University of Antwerp Antwerp, Belgium
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Abderemane-Ali F, Es-Salah-Lamoureux Z, Delemotte L, Kasimova MA, Labro AJ, Snyders DJ, Fedida D, Tarek M, Baró I, Loussouarn G. Dual effect of phosphatidylinositol (4,5)-bisphosphate PIP(2) on Shaker K(+) [corrected] channels. J Biol Chem 2012; 287:36158-67. [PMID: 22932893 DOI: 10.1074/jbc.m112.382085] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphatidylinositol (4,5)-bisphosphate (PIP(2)) is a phospholipid of the plasma membrane that has been shown to be a key regulator of several ion channels. Functional studies and more recently structural studies of Kir channels have revealed the major impact of PIP(2) on the open state stabilization. A similar effect of PIP(2) on the delayed rectifiers Kv7.1 and Kv11.1, two voltage-gated K(+) channels, has been suggested, but the molecular mechanism remains elusive and nothing is known on PIP(2) effect on other Kv such as those of the Shaker family. By combining giant-patch ionic and gating current recordings in COS-7 cells, and voltage-clamp fluorimetry in Xenopus oocytes, both heterologously expressing the voltage-dependent Shaker channel, we show that PIP(2) exerts 1) a gain-of-function effect on the maximal current amplitude, consistent with a stabilization of the open state and 2) a loss-of-function effect by positive-shifting the activation voltage dependence, most likely through a direct effect on the voltage sensor movement, as illustrated by molecular dynamics simulations.
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Kopljar I, Labro AJ, Rainier JD, Tytgat J, Snyders DJ. 110. Voltage Sensor Trapping in Voltage-Gated K-Channels by the Marine Neurotoxin Gambierol. Toxicon 2012. [DOI: 10.1016/j.toxicon.2012.04.111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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31
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Bocksteins E, Labro AJ, Snyders DJ, Mohapatra DP. The electrically silent Kv6.4 subunit confers hyperpolarized gating charge movement in Kv2.1/Kv6.4 heterotetrameric channels. PLoS One 2012; 7:e37143. [PMID: 22615922 PMCID: PMC3355112 DOI: 10.1371/journal.pone.0037143] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Accepted: 04/18/2012] [Indexed: 12/20/2022] Open
Abstract
The voltage-gated K(+) (Kv) channel subunit Kv6.4 does not form functional homotetrameric channels but co-assembles with Kv2.1 to form functional Kv2.1/Kv6.4 heterotetrameric channels. Compared to Kv2.1 homotetramers, Kv6.4 exerts a ~40 mV hyperpolarizing shift in the voltage-dependence of Kv2.1/Kv6.4 channel inactivation, without a significant effect on activation gating. However, the underlying mechanism of this Kv6.4-induced modulation of Kv2.1 channel inactivation, and whether the Kv6.4 subunit participates in the voltage-dependent gating of heterotetrameric channels is not well understood. Here we report distinct gating charge movement of Kv2.1/Kv6.4 heterotetrameric channels, compared to Kv2.1 homotetramers, as revealed by gating current recordings from mammalian cells expressing these channels. The gating charge movement of Kv2.1/Kv6.4 heterotetrameric channels displayed an extra component around the physiological K(+) equilibrium potential, characterized by a second sigmoidal relationship of the voltage-dependence of gating charge movement. This distinct gating charge displacement reflects movement of the Kv6.4 voltage-sensing domain and has a voltage-dependency that matches the hyperpolarizing shift in Kv2.1/Kv6.4 channel inactivation. These results provide a mechanistic basis for the modulation of Kv2.1 channel inactivation gating kinetics by silent Kv6.4 subunits.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerpen, Belgium
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, United States of America
| | - Alain J. Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerpen, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerpen, Belgium
- * E-mail: (DPM); (DJS)
| | - Durga P. Mohapatra
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, United States of America
- * E-mail: (DPM); (DJS)
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Bocksteins E, Labro AJ, Snyders DJ, Mohapatra DP. The Silent K+ Channel Subunit, KV6.4. Influences the Gating Charge Movement of KV2.1 in a Heterotetrameric Channel Complex. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.2907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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33
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Veys K, Labro AJ, Snyders DJ. Electrophysiological and Gene Expression Profiling at Single Cell Level through an Improved Whole Cell Patch Clamp Quantitative Real-Time PCR Technique. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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34
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Labro AJ, Cortes DM, Gagnon DG, Snyders DJ, Cuello LG. The Role of the 2nd Threonine Within the TTVGYGD Sequence of Kv-Channels in C-Type Inactivation Gating, Ion Selectivity and Permeation. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022] Open
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35
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Lacroix JJ, Labro AJ, Bezanilla F. Properties of deactivation gating currents in Shaker channels. Biophys J 2011; 100:L28-30. [PMID: 21354387 DOI: 10.1016/j.bpj.2011.01.043] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Revised: 01/19/2011] [Accepted: 01/24/2011] [Indexed: 10/18/2022] Open
Abstract
The charge versus voltage relation of voltage-sensor domains shifts in the voltage axis depending on the initial voltage. Here we show that in nonconducting W434F Shaker K(+) channels, a large portion of this charge-voltage shift is apparent due to a dramatic slowing of the deactivation gating currents, Ig(D) (with τ up to 80 ms), which develops with a time course of ∼1.8 s. This slowing in Ig(D) adds up to the slowing due to pore opening and is absent in the presence of 4-aminopyridine, a compound that prevents the last gating step that leads to pore opening. A remaining 10-15 mV negative shift in the voltage dependence of both the kinetics and the charge movement persists independently of the depolarizing prepulse duration and remains in the presence of 4-aminopyridine, suggesting the existence of an intrinsic offset in the local electric field seen by activated channels. We propose a new (to our knowledge) kinetic model that accounts for these observations.
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Affiliation(s)
- Jérôme J Lacroix
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
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Rodriguez N, Amarouch MY, Montnach J, Piron J, Labro AJ, Charpentier F, Mérot J, Baró I, Loussouarn G. Phosphatidylinositol-4,5-bisphosphate (PIP(2)) stabilizes the open pore conformation of the Kv11.1 (hERG) channel. Biophys J 2010; 99:1110-8. [PMID: 20712994 DOI: 10.1016/j.bpj.2010.06.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2009] [Revised: 05/28/2010] [Accepted: 06/01/2010] [Indexed: 01/30/2023] Open
Abstract
Phosphatidylinositol-4,5-bisphosphate (PIP(2)) is a phospholipid that has been shown to modulate several ion channels, including some voltage-gated channels like Kv11.1 (hERG). From a biophysical perspective, the mechanisms underlying this regulation are not well characterized. From a physiological perspective, it is critical to establish whether the PIP(2) effect is within the physiological concentration range. Using the giant-patch configuration of the patch-clamp technique on COS-7 cells expressing hERG, we confirmed the activating effect of PIP(2). PIP(2) increased the hERG maximal current and concomitantly slowed deactivation. Regarding the molecular mechanism, these increased amplitude and slowed deactivation suggest that PIP(2) stabilizes the channel open state, as it does in KCNE1-KCNQ1. We used kinetic models of hERG to simulate the effects of the phosphoinositide. Simulations strengthened the hypothesis that PIP(2) is more likely stabilizing the channel open state than affecting the voltage sensors. From the physiological aspect, we established that the sensitivity of hERG to PIP(2) comes close to that of KCNE1-KCNQ1 channels, which lies in the range of physiological PIP(2) variations.
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Affiliation(s)
- Nicolas Rodriguez
- Institut National de la Santé et de la Recherche Médicale, Nantes, France
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Labro AJ, Boulet IR, Choveau FS, Mayeur E, Bruyns T, Loussouarn G, Raes AL, Snyders DJ. The S4-S5 linker of KCNQ1 channels forms a structural scaffold with the S6 segment controlling gate closure. J Biol Chem 2010; 286:717-25. [PMID: 21059661 DOI: 10.1074/jbc.m110.146977] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In vivo, KCNQ1 α-subunits associate with the β-subunit KCNE1 to generate the slowly activating cardiac potassium current (I(Ks)). Structurally, they share their topology with other Kv channels and consist out of six transmembrane helices (S1-S6) with the S1-S4 segments forming the voltage-sensing domain (VSD). The opening or closure of the intracellular channel gate, which localizes at the bottom of the S6 segment, is directly controlled by the movement of the VSD via an electromechanical coupling. In other Kv channels, this electromechanical coupling is realized by an interaction between the S4-S5 linker (S4S5(L)) and the C-terminal end of S6 (S6(T)). Previously we reported that substitutions for Leu(353) in S6(T) resulted in channels that failed to close completely. Closure could be incomplete because Leu(353) itself is the pore-occluding residue of the channel gate or because of a distorted electromechanical coupling. To resolve this and to address the role of S4S5(L) in KCNQ1 channel gating, we performed an alanine/tryptophan substitution scan of S4S5(L). The residues with a "high impact" on channel gating (when mutated) clustered on one side of the S4S5(L) α-helix. Hence, this side of S4S5(L) most likely contributes to the electromechanical coupling and finds its residue counterparts in S6(T). Accordingly, substitutions for Val(254) resulted in channels that were partially constitutively open and the ability to close completely was rescued by combination with substitutions for Leu(353) in S6(T). Double mutant cycle analysis supported this cross-talk indicating that both residues come in close contact and stabilize the closed state of the channel.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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Choveau FS, Rodriguez N, Abderemane Ali F, Labro AJ, Rose T, Dahimène S, Boudin H, Le Hénaff C, Escande D, Snyders DJ, Charpentier F, Mérot J, Baró I, Loussouarn G. KCNQ1 channels voltage dependence through a voltage-dependent binding of the S4-S5 linker to the pore domain. J Biol Chem 2010; 286:707-16. [PMID: 20940310 DOI: 10.1074/jbc.m110.146324] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Voltage-dependent potassium (Kv) channels are tetramers of six transmembrane domain (S1-S6) proteins. Crystallographic data demonstrate that the tetrameric pore (S5-S6) is surrounded by four voltage sensor domains (S1-S4). One key question remains: how do voltage sensors (S4) regulate pore gating? Previous mutagenesis data obtained on the Kv channel KCNQ1 highlighted the critical role of specific residues in both the S4-S5 linker (S4S5(L)) and S6 C terminus (S6(T)). From these data, we hypothesized that S4S5(L) behaves like a ligand specifically interacting with S6(T) and stabilizing the closed state. To test this hypothesis, we designed plasmid-encoded peptides corresponding to portions of S4S5(L) and S6(T) of the voltage-gated potassium channel KCNQ1 and evaluated their effects on the channel activity in the presence and absence of the ancillary subunit KCNE1. We showed that S4S5(L) peptides inhibit KCNQ1, in a reversible and state-dependent manner. S4S5(L) peptides also inhibited a voltage-independent KCNQ1 mutant. This inhibition was competitively prevented by a peptide mimicking S6(T), consistent with S4S5(L) binding to S6(T). Val(254) in S4S5(L) is known to contact Leu(353) in S6(T) when the channel is closed, and mutations of these residues alter the coupling between the two regions. The same mutations introduced in peptides altered their effects, further confirming S4S5(L) binding to S6(T). Our results suggest a mechanistic model in which S4S5(L) acts as a voltage-dependent ligand bound to its receptor on S6 at rest. This interaction locks the channel in a closed state. Upon plasma membrane depolarization, S4 pulls S4S5(L) away from S6(T), allowing channel opening.
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Labro AJ, Boulet IR, Mayeur E, Timmermans JP, Snyders D. The LQT1 Phenotype of the KCNQ1 H258R Mutant is Unmasked by Faster Stimulation Rates. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.1833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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Labro AJ, Boulet IR, Raes AL, Snyders DJ. Substitution Scan of the S4-S5 Linker Region in KCNQ1 Channel: Structural Scaffold for Critical Protein Interactions. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Labro AJ, Boulet IR, Timmermans JP, Ottschytsch N, Snyders DJ. The rate-dependent biophysical properties of the LQT1 H258R mutant are counteracted by a dominant negative effect on channel trafficking. J Mol Cell Cardiol 2009; 48:1096-104. [PMID: 19913547 DOI: 10.1016/j.yjmcc.2009.10.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Revised: 10/28/2009] [Accepted: 10/28/2009] [Indexed: 01/17/2023]
Abstract
The long QT syndrome (LQTS) is a cardiac disorder caused by a prolonged ventricular repolarization. The co-assembly of the pore-forming human KCNQ1 alpha-subunits with the modulating hKCNE1 beta-subunits generates I(Ks)in vivo, explaining why mutations in the hKCNQ1 gene underlie the LQT1 form of congenital LQT. Here we describe the functional defects of the LQT1 mutation H258R located in the S4-S5 linker, a segment important for channel gating. Mutant subunits with this arginine substitution generated no or barely detectable currents in a homotetrameric condition, but did generate I(Ks)-like currents in association with hKCNE1. Compared to the WT hKCNQ1/hKCNE1 complex, the H258R/hKCNE1 complex displayed accelerated activation kinetics, slowed channel closure and a hyperpolarizing shift of the voltage-dependence of activation, thus predicting an increased K(+) current. However, current density analysis combined with subcellular localization indicated that the H258R subunit exerted a dominant negative effect on channel trafficking to the plasma membrane. The co-expression hKCNQ1/H258R/hKCNE1, mimicking the heterozygous state of a patient, displayed similar properties. During repetitive stimulation the mutant yielded more current compared to WT at 1 Hz but this effect was counteracted by the trafficking defect at faster frequencies. These rate-dependent effects may be relevant given the larger contribution of I(Ks) to the "repolarization reserve" at higher action potential rates. The combination of complex kinetics that counteract the trafficking problem represents a particular mechanism underlying LQT1.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp (UA), Universiteitsplein 1, 2610 Antwerp, Belgium
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Bocksteins E, Labro AJ, Mayeur E, Bruyns T, Timmermans JP, Adriaensen D, Snyders DJ. Conserved negative charges in the N-terminal tetramerization domain mediate efficient assembly of Kv2.1 and Kv2.1/Kv6.4 channels. J Biol Chem 2009; 284:31625-34. [PMID: 19717558 DOI: 10.1074/jbc.m109.039479] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated potassium (Kv) channels are transmembrane tetramers of individual alpha-subunits. Eight different Shaker-related Kv subfamilies have been identified in which the tetramerization domain T1, located on the intracellular N terminus, facilitates and controls the assembly of both homo- and heterotetrameric channels. Only the Kv2 alpha-subunits are able to form heterotetramers with members of the silent Kv subfamilies (Kv5, Kv6, Kv8, and Kv9). The T1 domain contains two subdomains, A and B box, which presumably determine subfamily specificity by preventing incompatible subunits to assemble. In contrast, little is known about the involvement of the A/B linker sequence. Both Kv2 and silent Kv subfamilies contain a fully conserved and negatively charged sequence (CDD) in this linker that is lacking in the other subfamilies. Neutralizing these aspartates in Kv2.1 by mutating them to alanines did not affect the gating properties, but reduced the current density moderately. However, charge reversal arginine substitutions strongly reduced the current density of these homotetrameric mutant Kv2.1 channels and immunocytochemistry confirmed the reduced expression at the plasma membrane. Förster resonance energy transfer measurements using confocal microscopy showed that the latter was not due to impaired trafficking, but to a failure to assemble the tetramer. This was further confirmed with co-immunoprecipitation experiments. The corresponding arginine substitution in Kv6.4 prevented its heterotetrameric interaction with Kv2.1. These results indicate that these aspartates (especially the first one) in the A/B box linker of the T1 domain are required for efficient assembly of both homotetrameric Kv2.1 and heterotetrameric Kv2.1/silent Kv6.4 channels.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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Labro AJ, Raes AL, Grottesi A, Van Hoorick D, Sansom MSP, Snyders DJ. Kv channel gating requires a compatible S4-S5 linker and bottom part of S6, constrained by non-interacting residues. ACTA ACUST UNITED AC 2009; 132:667-80. [PMID: 19029374 PMCID: PMC2585865 DOI: 10.1085/jgp.200810048] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Voltage-dependent K+ channels transfer the voltage sensor movement into gate opening or closure through an electromechanical coupling. To test functionally whether an interaction between the S4-S5 linker (L45) and the cytoplasmic end of S6 (S6T) constitutes this coupling, the L45 in hKv1.5 was replaced by corresponding hKv2.1 sequence. This exchange was not tolerated but could be rescued by also swapping S6T. Exchanging both L45 and S6T transferred hKv2.1 kinetics to an hKv1.5 background while preserving the voltage dependence. A one-by-one residue substitution scan of L45 and S6T in hKv1.5 further shows that S6T needs to be α-helical and forms a “crevice” in which residues I422 and T426 of L45 reside. These residues transfer the mechanical energy onto the S6T crevice, whereas other residues in S6T and L45 that are not involved in the interaction maintain the correct structure of the coupling.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology, and Pharmacology, Department of Biomedical Sciences, University of Antwerp, 2610 Antwerp, Belgium
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Labro AJ, Grottesi A, Sansom MSP, Raes AL, Snyders DJ. A Kv channel with an altered activation gate sequence displays both “fast” and “slow” activation kinetics. Am J Physiol Cell Physiol 2008; 294:C1476-84. [DOI: 10.1152/ajpcell.00479.2007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Kv1–4 families of K+ channels contain a tandem proline motif (P XP) in the S6 helix that is crucial for channel gating. In human Kv1.5, replacing the first proline by an alanine resulted in a nonfunctional channel. This mutant was rescued by introducing another proline at a nearby position, changing the sequence into AVPP. This resulted in a channel that activated quickly (ms range) upon the first depolarization. However, thereafter, the channel became trapped in another gating mode that was characterized by slow activation kinetics (s range) with a shallow voltage dependence. The switch in gating mode was observed even with very short depolarization steps, but recovery to the initial “fast” mode was extremely slow. Computational modeling suggested that switching occurred during channel deactivation. To test the effect of the altered P XP sequence on the mobility of the S6 helix, we used molecular dynamics simulations of the isolated S6 domain of wild type (WT) and mutants starting from either a closed or open conformation. The WT S6 helix displayed movements around the P XP region with simulations starting from either state. However, the S6 with a AVPP sequence displayed flexibility only when started from the closed conformation and was rigid when started from the open state. These results indicate that the region around the P XP motif may serve as a “hinge” and that changing the sequence to AVPP results in channels that deactivate to a state with an alternate configuration that renders them “reluctant” to open subsequently.
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Abstract
Co-assembly of KCNQ1 alpha-subunits with KCNE1 beta-subunits results in the channel complex underlying the cardiac IKs current in vivo. Like other voltage-gated K+ channels, KCNQ1 has a tetrameric configuration. The S6 segment of each subunit lines the ion channel pore with the lower part forming the activation gate. To determine residues involved in protein-protein interactions in the C-terminal part of S6 (S6T), alanine and tryptophan perturbation scans were performed from residue 348-362 in the KCNQ1 channel. Several residues were identified to be relevant in channel gating, as substitutions affected the activation and/or deactivation process. Some mutations (F351A and V355W) drastically altered the gating characteristics of the resultant KCNQ1 channel, to the point of mimicking the IKs current. Furthermore, mutagenesis of residue L353 to an alanine or a charged residue impaired normal channel closure upon hyperpolarization, generating a constitutively open phenotype. This indicates that the L353 residue is essential for stabilizing the closed conformation of the channel gate. These findings together with the identification of several LQT1 mutations in the S6 C-terminus of KCNQ1 underscore the relevance of this region in KCNQ1 and IKs channel gating.
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Affiliation(s)
- Inge R Boulet
- Laboratory for Molecular Biophysics, Pharmacology and Physiology, University of Antwerp, Department of Biomedical Sciences, Antwerp, Belgium
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Abstract
Human ether-a-go-go-related gene (HERG) potassium channels contribute to the repolarization of the cardiac action potential and display unique gating properties with slow activation and fast inactivation kinetics. Deletions in the N-terminal 'proximal' domain (residues 135-366) have been shown to induce hyperpolarizing shifts in the voltage dependence of activation, suggesting that it modulates activation. However, we did not observe a hyperpolarizing shift with a subtotal deletion designed to preserve the local charge distribution, and other deletions narrowed the region to the KIKER containing sequence 362-372. Replacing the positively charged residues of this sequence by negative ones (EIEEE) resulted in a -45 mV shift of the voltage dependence of activation. The shifts were intermediate for individual charge reversals, whereas E365R resulted in a positive shift. Furthermore, the shifts in the voltage dependence were strongly correlated with the net charge of the KIKER region. The apparent speeding of the activation was attributable to the shifted voltage dependence of activation. Additionally, the introduction of negative charges accelerated the intermediate voltage-independent forward rate constant. We propose that the modulatory effects of the proximal domain on HERG gating are largely electrostatic, localized to the charged KIKER sequence.
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Affiliation(s)
- J B Saenen
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp Belgium
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Abstract
Voltage-gated K(+) channels play a central role in the modulation of excitability. In these channels, the voltage-dependent movement of the voltage sensor (primarily S4) is coupled to the (S6) gate that opens the permeation pathway. Because of the tetrameric structure, such coupling could occur within each subunit or between adjacent subunits. To discriminate between these possibilities, we analyzed various combinations of a S4 mutation (R401N) and a S6 mutation (P511G) in hKv1.5, incorporated into tandem constructs to constrain subunit stoichiometry. R401N shifted the voltage dependence of activation to negative potentials while P511G did the opposite. When both mutations were introduced in the same alpha-subunit of the tandem, the positive shift of P511G was compensated by the negative shift of R401N. With each mutation in a separate subunit of a tandem, this compensation did not occur. This suggests that for Kv channels, the coupling between voltage sensing and gating reflects primarily an intrasubunit interaction.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp 2610, Belgium
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Abstract
The recent crystallization of a voltage-gated K+ channel has given insight into the structure of these channels but has not resolved the issues of the location and the operation of the gate. The conserved PXP motif in the S6 segment of Shaker channels has been proposed to contribute to the intracellular gating structure. To investigate the role of this motif in the destabilization of the alpha-helix, both prolines were replaced to promote an alpha-helix (alanine) or to allow a flexible configuration (glycine). These substitutions were nonfunctional or resulted in drastically altered channel gating, highlighting an important role of these prolines. Combining these mutations with a proline substitution scan demonstrated that proline residues in the midsection of S6 are required for functionality, but not necessarily at the positions conserved throughout evolution. These results indicate that the destabilization or bending of the S6 alpha-helix caused by the PXP motif apparently creates a flexible "hinge" that allows movement of the lower S6 segment during channel gating and opening.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium
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