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Chan M, Sahakyan H, Eldstrom J, Sastre D, Wang Y, Dou Y, Pourrier M, Vardanyan V, Fedida D. A generic binding pocket for small molecule IKs activators at the extracellular inter-subunit interface of KCNQ1 and KCNE1 channel complexes. eLife 2023; 12:RP87038. [PMID: 37707495 PMCID: PMC10501768 DOI: 10.7554/elife.87038] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/15/2023] Open
Abstract
The cardiac IKs ion channel comprises KCNQ1, calmodulin, and KCNE1 in a dodecameric complex which provides a repolarizing current reserve at higher heart rates and protects from arrhythmia syndromes that cause fainting and sudden death. Pharmacological activators of IKs are therefore of interest both scientifically and therapeutically for treatment of IKs loss-of-function disorders. One group of chemical activators are only active in the presence of the accessory KCNE1 subunit and here we investigate this phenomenon using molecular modeling techniques and mutagenesis scanning in mammalian cells. A generalized activator binding pocket is formed extracellularly by KCNE1, the domain-swapped S1 helices of one KCNQ1 subunit and the pore/turret region made up of two other KCNQ1 subunits. A few residues, including K41, A44 and Y46 in KCNE1, W323 in the KCNQ1 pore, and Y148 in the KCNQ1 S1 domain, appear critical for the binding of structurally diverse molecules, but in addition, molecular modeling studies suggest that induced fit by structurally different molecules underlies the generalized nature of the binding pocket. Activation of IKs is enhanced by stabilization of the KCNQ1-S1/KCNE1/pore complex, which ultimately slows deactivation of the current, and promotes outward current summation at higher pulse rates. Our results provide a mechanistic explanation of enhanced IKs currents by these activator compounds and provide a map for future design of more potent therapeutically useful molecules.
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Affiliation(s)
- Magnus Chan
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
| | - Harutyun Sahakyan
- Laboratory of Computational Modeling of Biological Processes, Institute of Molecular BiologyYerevanArmenia
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
| | - Daniel Sastre
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
| | - Yundi Wang
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
| | - Ying Dou
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
| | - Marc Pourrier
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
| | - Vitya Vardanyan
- Molecular Neuroscience Group, Institute of Molecular BiologyYerevanArmenia
| | - David Fedida
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British ColumbiaVancouverCanada
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Li N, Li YJ, Guo XJ, Wu SH, Jiang WF, Zhang DL, Wang KW, Li L, Sun YM, Xu YJ, Yang YQ, Qiu XB. Discovery of TBX20 as a Novel Gene Underlying Atrial Fibrillation. BIOLOGY 2023; 12:1186. [PMID: 37759586 PMCID: PMC10525918 DOI: 10.3390/biology12091186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 08/25/2023] [Accepted: 08/28/2023] [Indexed: 09/29/2023]
Abstract
Atrial fibrillation (AF), the most prevalent type of sustained cardiac dysrhythmia globally, confers strikingly enhanced risks for cognitive dysfunction, stroke, chronic cardiac failure, and sudden cardiovascular demise. Aggregating studies underscore the crucial roles of inherited determinants in the occurrence and perpetuation of AF. However, due to conspicuous genetic heterogeneity, the inherited defects accounting for AF remain largely indefinite. Here, via whole-genome genotyping with genetic markers and a linkage assay in a family suffering from AF, a new AF-causative locus was located at human chromosome 7p14.2-p14.3, a ~4.89 cM (~4.43-Mb) interval between the markers D7S526 and D7S2250. An exome-wide sequencing assay unveiled that, at the defined locus, the mutation in the TBX20 gene, NM_001077653.2: c.695A>G; p.(His232Arg), was solely co-segregated with AF in the family. Additionally, a Sanger sequencing assay of TBX20 in another family suffering from AF uncovered a novel mutation, NM_001077653.2: c.862G>C; p.(Asp288His). Neither of the two mutations were observed in 600 unrelated control individuals. Functional investigations demonstrated that the two mutations both significantly reduced the transactivation of the target gene KCNH2 (a well-established AF-causing gene) and the ability to bind the promoter of KCNH2, while they had no effect on the nuclear distribution of TBX20. Conclusively, these findings reveal a new AF-causative locus at human chromosome 7p14.2-p14.3 and strongly indicate TBX20 as a novel AF-predisposing gene, shedding light on the mechanism underlying AF and suggesting clinical significance for the allele-specific treatment of AF patients.
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Affiliation(s)
- Ning Li
- Department of Cardiology, Putuo Hospital, Shanghai University of Traditional Chinese Medicine, Shanghai 200062, China;
| | - Yan-Jie Li
- Department of Cardiology, Shanghai Chest Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China; (Y.-J.L.); (S.-H.W.); (W.-F.J.)
| | - Xiao-Juan Guo
- Department of Cardiology, Shanghai Fifth People’s Hospital, Fudan University, Shanghai 200240, China; (X.-J.G.); (Y.-J.X.)
- Center for Complex Cardiac Arrhythmias of Minhang District, Shanghai Fifth People′s Hospital, Fudan University, Shanghai 200240, China
| | - Shao-Hui Wu
- Department of Cardiology, Shanghai Chest Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China; (Y.-J.L.); (S.-H.W.); (W.-F.J.)
| | - Wei-Feng Jiang
- Department of Cardiology, Shanghai Chest Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China; (Y.-J.L.); (S.-H.W.); (W.-F.J.)
| | - Dao-Liang Zhang
- Cardiac Arrhythmia Center, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen 518057, China;
| | - Kun-Wei Wang
- Department of Cardiology, Tongji Hospital, Tongji University School of Medicine, Shanghai 200065, China;
| | - Li Li
- Key Laboratory of Arrhythmias, Ministry of Education of China, Tongji University School of Medicine, Shanghai 200092, China;
| | - Yu-Min Sun
- Department of Cardiology, Shanghai Jing’an District Central Hospital, Fudan University, Shanghai 200040, China;
| | - Ying-Jia Xu
- Department of Cardiology, Shanghai Fifth People’s Hospital, Fudan University, Shanghai 200240, China; (X.-J.G.); (Y.-J.X.)
- Center for Complex Cardiac Arrhythmias of Minhang District, Shanghai Fifth People′s Hospital, Fudan University, Shanghai 200240, China
| | - Yi-Qing Yang
- Department of Cardiology, Shanghai Fifth People’s Hospital, Fudan University, Shanghai 200240, China; (X.-J.G.); (Y.-J.X.)
- Center for Complex Cardiac Arrhythmias of Minhang District, Shanghai Fifth People′s Hospital, Fudan University, Shanghai 200240, China
- Cardiovascular Research Laboratory, Shanghai Fifth People’s Hospital, Fudan University, Shanghai 200240, China
- Central Laboratory, Shanghai Fifth People’s Hospital, Fudan University, Shanghai 200240, China
| | - Xing-Biao Qiu
- Department of Cardiology, Shanghai Chest Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200030, China; (Y.-J.L.); (S.-H.W.); (W.-F.J.)
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3
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Alameh M, Oliveira-Mendes BR, Kyndt F, Rivron J, Denjoy I, Lesage F, Schott JJ, De Waard M, Loussouarn G. A need for exhaustive and standardized characterization of ion channels activity. The case of K V11.1. Front Physiol 2023; 14:1132533. [PMID: 36860515 PMCID: PMC9968853 DOI: 10.3389/fphys.2023.1132533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Accepted: 01/30/2023] [Indexed: 02/16/2023] Open
Abstract
hERG, the pore-forming subunit of the rapid component of the delayed rectifier K+ current, plays a key role in ventricular repolarization. Mutations in the KCNH2 gene encoding hERG are associated with several cardiac rhythmic disorders, mainly the Long QT syndrome (LQTS) characterized by prolonged ventricular repolarization, leading to ventricular tachyarrhythmias, sometimes progressing to ventricular fibrillation and sudden death. Over the past few years, the emergence of next-generation sequencing has revealed an increasing number of genetic variants including KCNH2 variants. However, the potential pathogenicity of the majority of the variants remains unknown, thus classifying them as variants of uncertain significance or VUS. With diseases such as LQTS being associated with sudden death, identifying patients at risk by determining the variant pathogenicity, is crucial. The purpose of this review is to describe, on the basis of an exhaustive examination of the 1322 missense variants, the nature of the functional assays undertaken so far and their limitations. A detailed analysis of 38 hERG missense variants identified in Long QT French patients and studied in electrophysiology also underlies the incomplete characterization of the biophysical properties for each variant. These analyses lead to two conclusions: first, the function of many hERG variants has never been looked at and, second, the functional studies done so far are excessively heterogeneous regarding the stimulation protocols, cellular models, experimental temperatures, homozygous and/or the heterozygous condition under study, a context that may lead to conflicting conclusions. The state of the literature emphasizes how necessary and important it is to perform an exhaustive functional characterization of hERG variants and to standardize this effort for meaningful comparison among variants. The review ends with suggestions to create a unique homogeneous protocol that could be shared and adopted among scientists and that would facilitate cardiologists and geneticists in patient counseling and management.
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Affiliation(s)
- Malak Alameh
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France,Labex ICST, INSERM, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d’Azur, Valbonne, France
| | - Barbara Ribeiro Oliveira-Mendes
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France,*Correspondence: Barbara Ribeiro Oliveira-Mendes,
| | - Florence Kyndt
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France
| | - Jordan Rivron
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France
| | - Isabelle Denjoy
- Service de Cardiologie et CNMR Maladies Cardiaques Héréditaires Rares, Hôpital Bichat, Paris, France
| | - Florian Lesage
- Labex ICST, INSERM, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d’Azur, Valbonne, France
| | - Jean-Jacques Schott
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France
| | - Michel De Waard
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France,Labex ICST, INSERM, CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Université Côte d’Azur, Valbonne, France
| | - Gildas Loussouarn
- CNRS, INSERM, l’institut du thorax, Nantes Université, CHU Nantes, Nantes, France
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Liao QQ, Dong QQ, Zhang H, Shu HP, Tu YC, Yao LJ. Contributions of SGK3 to transporter-related diseases. Front Cell Dev Biol 2022; 10:1007924. [PMID: 36531961 PMCID: PMC9753149 DOI: 10.3389/fcell.2022.1007924] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Accepted: 11/09/2022] [Indexed: 02/09/2024] Open
Abstract
Serum- and glucocorticoid-induced kinase 3 (SGK3), which is ubiquitously expressed in mammals, is regulated by estrogens and androgens. SGK3 is activated by insulin and growth factors through signaling pathways involving phosphatidylinositol-3-kinase (PI3K), 3-phosphoinositide-dependent kinase-1 (PDK-1), and mammalian target of rapamycin complex 2 (mTORC2). Activated SGK3 can activate ion channels (TRPV5/6, SOC, Kv1.3, Kv1.5, Kv7.1, BKCa, Kir2.1, Kir2.2, ENaC, Nav1.5, ClC-2, and ClC Ka), carriers and receptors (Npt2a, Npt2b, NHE3, GluR1, GluR6, SN1, EAAT1, EAAT2, EAAT4, EAAT5, SGLT1, SLC1A5, SLC6A19, SLC6A8, and NaDC1), and Na+/K+-ATPase, promoting the transportation of calcium, phosphorus, sodium, glucose, and neutral amino acids in the kidney and intestine, the absorption of potassium and neutral amino acids in the renal tubules, the transportation of glutamate and glutamine in the nervous system, and the transportation of creatine. SGK3-sensitive transporters contribute to a variety of physiological and pathophysiological processes, such as maintaining calcium and phosphorus homeostasis, hydro-salinity balance and acid-base balance, cell proliferation, muscle action potential, cardiac and neural electrophysiological disturbances, bone density, intestinal nutrition absorption, immune function, and multiple substance metabolism. These processes are related to kidney stones, hypophosphorous rickets, multiple syndromes, arrhythmia, hypertension, heart failure, epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, glaucoma, ataxia idiopathic deafness, and other diseases.
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Affiliation(s)
- Qian-Qian Liao
- Department of Nephrology, Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, China
| | - Qing-Qing Dong
- Department of Nephrology, Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, China
- Department of Nephrology, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Hui Zhang
- Department of Nephrology, Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, China
| | - Hua-Pan Shu
- Department of Nephrology, Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, China
| | - Yu-Chi Tu
- Department of Nephrology, Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, China
| | - Li-Jun Yao
- Department of Nephrology, Tongji Medical College, Union Hospital, Huazhong University of Science and Technology, Wuhan, China
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How Dysregulated Ion Channels and Transporters Take a Hand in Esophageal, Liver, and Colorectal Cancer. Rev Physiol Biochem Pharmacol 2020; 181:129-222. [PMID: 32875386 DOI: 10.1007/112_2020_41] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Over the last two decades, the understanding of how dysregulated ion channels and transporters are involved in carcinogenesis and tumor growth and progression, including invasiveness and metastasis, has been increasing exponentially. The present review specifies virtually all ion channels and transporters whose faulty expression or regulation contributes to esophageal, hepatocellular, and colorectal cancer. The variety reaches from Ca2+, K+, Na+, and Cl- channels over divalent metal transporters, Na+ or Cl- coupled Ca2+, HCO3- and H+ exchangers to monocarboxylate carriers and organic anion and cation transporters. In several cases, the underlying mechanisms by which these ion channels/transporters are interwoven with malignancies have been fully or at least partially unveiled. Ca2+, Akt/NF-κB, and Ca2+- or pH-dependent Wnt/β-catenin signaling emerge as cross points through which ion channels/transporters interfere with gene expression, modulate cell proliferation, trigger epithelial-to-mesenchymal transition, and promote cell motility and metastasis. Also miRs, lncRNAs, and DNA methylation represent potential links between the misexpression of genes encoding for ion channels/transporters, their malfunctioning, and cancer. The knowledge of all these molecular interactions has provided the basis for therapeutic strategies and approaches, some of which will be broached in this review.
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Wang Y, Eldstrom J, Fedida D. Gating and Regulation of KCNQ1 and KCNQ1 + KCNE1 Channel Complexes. Front Physiol 2020; 11:504. [PMID: 32581825 PMCID: PMC7287213 DOI: 10.3389/fphys.2020.00504] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 04/24/2020] [Indexed: 12/20/2022] Open
Abstract
The IKs channel complex is formed by the co-assembly of Kv7.1 (KCNQ1), a voltage-gated potassium channel, with its β-subunit, KCNE1 and the association of numerous accessory regulatory molecules such as PIP2, calmodulin, and yotiao. As a result, the IKs potassium current shows kinetic and regulatory flexibility, which not only allows IKs to fulfill physiological roles as disparate as cardiac repolarization and the maintenance of endolymph K+ homeostasis, but also to cause significant disease when it malfunctions. Here, we review new areas of understanding in the assembly, kinetics of activation and inactivation, voltage-sensor pore coupling, unitary events and regulation of this important ion channel complex, all of which have been given further impetus by the recent solution of cryo-EM structural representations of KCNQ1 alone and KCNQ1+KCNE3. Recently, the stoichiometric ratio of KCNE1 to KCNQ1 subunits has been confirmed to be variable up to a ratio of 4:4, rather than fixed at 2:4, and we will review the results and new methodologies that support this conclusion. Significant advances have been made in understanding differences between KCNQ1 and IKs gating using voltage clamp fluorimetry and mutational analysis to illuminate voltage sensor activation and inactivation, and the relationship between voltage sensor translation and pore domain opening. We now understand that the KCNQ1 pore can open with different permeabilities and conductance when the voltage sensor is in partially or fully activated positions, and the ability to make robust single channel recordings from IKs channels has also revealed the complicated pore subconductance architecture during these opening steps, during inactivation, and regulation by 1−4 associated KCNE1 subunits. Experiments placing mutations into individual voltage sensors to drastically change voltage dependence or prevent their movement altogether have demonstrated that the activation of KCNQ1 alone and IKs can best be explained using allosteric models of channel gating. Finally, we discuss how the intrinsic gating properties of KCNQ1 and IKs are highly modulated through the impact of intracellular signaling molecules and co-factors such as PIP2, protein kinase A, calmodulin and ATP, all of which modulate IKs current kinetics and contribute to diverse IKs channel complex function.
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Affiliation(s)
- Yundi Wang
- Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, BC, Canada
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, BC, Canada
| | - David Fedida
- Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, BC, Canada
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Lindner M, Gilhooley MJ, Palumaa T, Morton AJ, Hughes S, Hankins MW. Expression and Localization of Kcne2 in the Vertebrate Retina. Invest Ophthalmol Vis Sci 2020; 61:33. [PMID: 32191288 PMCID: PMC7401445 DOI: 10.1167/iovs.61.3.33] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To characterize the retinal expression and localization of Kcne2, an ancillary (β) ion-channel subunit with an important role in fine-tuning cellular excitability. Methods We analyzed available single-cell transcriptome data from tens of thousands of murine retinal cells for cell-type-specific expression of Kcne2 using state-of-the-art bioinformatics techniques. This evidence at the transcriptome level was complemented with a comprehensive immunohistochemical characterization of mouse retina (C57BL/6, ages 8-12 weeks) employing co-labeling techniques and cell-type-specific antibody markers. We furthermore examined how conserved the Kcne2 localization pattern in the retina was across species by performing immunostaining on zebrafish, cowbird, sheep, mice, and macaque. Results Kcne2 is distinctly expressed in cone photoreceptors and rod bipolar cells. At a subcellular level, the bulk of Kcne2 immunoreactivity can be observed in the outer plexiform layer. Here, it localizes into cone pedicles and likely the postsynaptic membrane of the rod bipolar cells. Thus, the vast majority of Kcne2 immunoreactivity is observed in a thin band in the outer plexiform layer. In addition to this, faint Kcne2 immunoreactivity can also be observed in cone inner segments and the somata of a small subset of cone ON bipolar cells. Strikingly, the localization of Kcne2 in the outer plexiform layer was preserved among all of the species studied, spanning at least 300 million years of evolution of the vertebrate kingdom. Conclusions The data we present here suggest an important and specific role for Kcne2 in the highly specialized photoreceptor-bipolar cell synapse.
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Wang Y, Eldstrom J, Fedida D. The I Ks Ion Channel Activator Mefenamic Acid Requires KCNE1 and Modulates Channel Gating in a Subunit-Dependent Manner. Mol Pharmacol 2019; 97:132-144. [PMID: 31722973 DOI: 10.1124/mol.119.117952] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 11/04/2019] [Indexed: 01/05/2023] Open
Abstract
The pairing of KCNQ1 and KCNE1 subunits together mediates the cardiac slow delayed rectifier current (I Ks ), which is partly responsible for cardiomyocyte repolarization and physiologic shortening of the cardiac action potential. Mefenamic acid, a nonsteroidal anti-inflammatory drug, has been identified as an I Ks activator. Here, we provide a biophysical and pharmacological characterization of mefenamic acid's effect on I Ks Using whole-cell patch clamp, we show that mefenamic acid enhances I Ks activity in both a dose- and stoichiometry-dependent fashion by changing the slowly activating and deactivating I Ks current into an almost linear current with instantaneous onset and slowed tail current decay, sensitive to the I Ks blocker (3R,4S)-(+)-N-[3-hydroxy-2,2-dimethyl-6-(4,4,4-trifluorobutoxy) chroman-4-yl]-N-methylmethanesulfonamide (HMR1556). Both single channels, which reveal no change in the maximum conductance, and whole-cell studies, which reveal a dramatically altered conductance-voltage relationship despite increasingly longer interpulse intervals, suggest mefenamic acid decreases the voltage sensitivity of the I Ks channel and shifts channel gating kinetics toward more negative potentials. Modeling studies revealed that changes in voltage sensor activation kinetics are sufficient to reproduce the dose and frequency dependence of mefenamic acid action on I Ks channels. Mutational analysis showed that mefenamic acid's effect on I Ks required residue K41 and potentially other surrounding residues on the extracellular surface of KCNE1, and explains why the KCNQ1 channel alone is insensitive to up to 1 mM mefenamic acid. Given that mefenamic acid can enhance all I Ks channel complexes containing different ratios of KCNQ1 to KCNE1, it may provide a promising therapeutic approach to treating life-threatening cardiac arrhythmia syndromes. SIGNIFICANCE STATEMENT: The channels which generate the cardiac slow delayed rectifier K+ current (I Ks ) are composed of KCNQ1 and KCNE1 subunits. Due to the critical role played by I Ks in heartbeat regulation, enhancing I Ks current has been identified as a promising therapeutic strategy to treat various heart rhythm diseases. Most I Ks activators, unfortunately, only work on KCNQ1 alone and not the physiologically relevant I Ks channel. We have demonstrated that mefenamic acid can enhance I Ks in a dose- and stoichiometry-dependent fashion, regulated by its interactions with KCNE1.
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Affiliation(s)
- Yundi Wang
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - David Fedida
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
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Zou M, Alzahrani AS, Al-Odaib A, Alqahtani MA, Babiker O, Al-Rijjal RA, BinEssa HA, Kattan WE, Al-Enezi AF, Al Qarni A, Al-Faham MSA, Baitei EY, Alsagheir A, Meyer BF, Shi Y. Molecular Analysis of Congenital Hypothyroidism in Saudi Arabia: SLC26A7 Mutation Is a Novel Defect in Thyroid Dyshormonogenesis. J Clin Endocrinol Metab 2018; 103:1889-1898. [PMID: 29546359 DOI: 10.1210/jc.2017-02202] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Accepted: 03/07/2018] [Indexed: 12/21/2022]
Abstract
CONTEXT Congenital hypothyroidism (CH) is the most common neonatal endocrine disorder, affecting one in 3000 to 4000 newborns. Since the introduction of a newborn screening program in 1988, more than 300 cases have been identified. The underlying genetic defects have not been systematically studied. OBJECTIVE To identify the mutation spectrum of CH-causing genes. METHODS Fifty-five patients from 47 families were studied by next-generation exome sequencing. RESULTS Mutations were identified in 52.7% of patients (29 of 55) in the following 11 genes: TG, TPO, DUOX2, SLC26A4, SLC26A7, TSHB, TSHR, NKX2-1, PAX8, CDCA8, and HOXB3. Among 30 patients with thyroid dyshormonogenesis, biallelic TG mutations were found in 12 patients (40%), followed by biallelic mutations in TPO (6.7%), SLC26A7 (6.7%), and DUOX2 (3.3%). Monoallelic SLC26A4 mutations were found in two patients, one of them coexisting with two tandem biallelic deletions in SLC26A7. In 25 patients with thyroid dysgenesis, biallelic mutations in TSHR were found in six patients (24%). Biallelic mutations in TSHB, PAX 8, NKX2-1, or HOXB3 were found once in four different patients. A monoallelic CDCA8 mutation was found in one patient. Most mutations were novel, including three TG, two TSHR, and one each in DUOX2, TPO, SLC26A7, TSHB, NKX2-1, PAX8, CDCA8, and HOXB3. SLC26A7 and HOXB3 were novel genes associated with thyroid dyshormonogenesis and dysgenesis, respectively. CONCLUSIONS TG and TSHR mutations are the most common genetic defects in Saudi patients with CH. The prevalence of other disease-causing mutations is low, reflecting the consanguineous nature of the population. SLC26A7 mutations appear to be associated with thyroid dyshormonogenesis.
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Affiliation(s)
- Minjing Zou
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Ali S Alzahrani
- Department of Medicine, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Ali Al-Odaib
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | | | - Omer Babiker
- Department of Medicine, King Abdulaziz Hospital, National Guard Health Affairs, Al Ahsa, Saudi Arabia
| | - Roua A Al-Rijjal
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Huda A BinEssa
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Walaa E Kattan
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Anwar F Al-Enezi
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Ali Al Qarni
- Department of Pediatrics, King Abdulaziz Hospital, National Guard Health Affairs, Al Ahsa, Saudi Arabia
| | - Manar S A Al-Faham
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Essa Y Baitei
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Afaf Alsagheir
- Department of Pediatrics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Brian F Meyer
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
| | - Yufei Shi
- Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
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Pedersen PJ, Thomsen KB, Flak JB, Tejada MA, Hauser F, Trachsel D, Buhl R, Kalbfleisch T, DePriest MS, MacLeod JN, Calloe K, Klaerke DA. Molecular cloning and functional expression of the K + channel K V7.1 and the regulatory subunit KCNE1 from equine myocardium. Res Vet Sci 2017; 113:79-86. [PMID: 28917093 DOI: 10.1016/j.rvsc.2017.09.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2017] [Revised: 08/05/2017] [Accepted: 09/07/2017] [Indexed: 10/18/2022]
Abstract
BACKGROUND The voltage-gated K+-channel KV7.1 and the subunit KCNE1, encoded by the KCNQ1 and KCNE1 genes, respectively, are responsible for termination of the cardiac action potential. In humans, mutations in these genes can predispose patients to arrhythmias and sudden cardiac death (SCD). AIM To characterize equine KV7.1/KCNE1 currents and compare them to human KV7.1/KCNE1 currents to determine whether KV7.1/KCNE1 plays a similar role in equine and human hearts. METHODS mRNA encoding KV7.1 and KCNE1 was isolated from equine hearts, sequenced, and cloned into expression vectors. The channel subunits were heterologously expressed in Xenopus laevis oocytes or CHO-K1 cells and characterized using voltage-clamp techniques. RESULTS Equine KV7.1/KCNE1 expressed in CHO-K1 cells exhibited electrophysiological properties that are overall similar to the human orthologs; however, a slower deactivation was found which could result in more open channels at fast rates. CONCLUSION The results suggest that the equine KV7.1/KCNE1 channel may be important for cardiac repolarization and this could indicate that horses are susceptible to SCD caused by mutations in KCNQ1 and KCNE1.
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Affiliation(s)
- Philip J Pedersen
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Kirsten B Thomsen
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Jon B Flak
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Maria A Tejada
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Frank Hauser
- Center for Functional and Comparative Insect Genomics, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Dagmar Trachsel
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Rikke Buhl
- Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Taastrup, Denmark
| | - Theodore Kalbfleisch
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Louisville, Louisville, KY, United States
| | - Michael Scott DePriest
- Department of Biochemistry and Molecular Genetics, School of Medicine, University of Louisville, Louisville, KY, United States
| | - James N MacLeod
- Maxwell H., Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, United States
| | - Kirstine Calloe
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
| | - Dan A Klaerke
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
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11
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Abstract
Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.
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Affiliation(s)
- Christopher L-H Huang
- Physiological Laboratory and the Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
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12
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Liu L, Tian J, Lu C, Chen X, Fu Y, Xu B, Zhu C, Sun Y, Zhang Y, Zhao Y, Li Y. Electrophysiological Characteristics of the LQT2 Syndrome Mutation KCNH2-G572S and Regulation by Accessory Protein KCNE2. Front Physiol 2016; 7:650. [PMID: 28082916 PMCID: PMC5187237 DOI: 10.3389/fphys.2016.00650] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 12/12/2016] [Indexed: 01/18/2023] Open
Abstract
Mutations in hERG cause long QT syndrome type 2 which is characterized by a prolonged QT interval on electrocardiogram and predisposition to life-threatening ventricular tachyarrhythmia, syncope, and sudden death. hERG-G572S induces trafficking defects of hERG channel protein from Golgi to the plasma membrane and results in a dominant negative suppression of hERG current density. As an accessory β subunit, KCNE2 promotes hERG migration from Golgi to cellular membrane. In this study, we investigated the rescue effect of KCNE2 in a G572S mutation of hERG. Transfection was performed into HEK293 cells. Patch clamp technique, western blotting analyses and confocal microscopic examination were used. Results showed that KCNE2 had a significantly enhanced effect on G572S mutation current. The increase of current was largest at KCNH2:KCNE2 of 1:3. Confocal images showed co-expressing G572S and KCNE2 could cause a substantial up-regulated membrane protein (155 kDa) expression. Expression of membrane protein accumulated markedly with increasing ratio of KCNH2:KCNE2. G572S defective mutant could be restored by both KCNE2 and lower temperature (27°C), which suggested that the lower temperature could be the favorable circumstances for the rescue function of KCNE2. In this study, we successfully set up “the action potential” on the HEK 293 cells by genetically engineered to express Kir2.1, Nav1.5, and Kv11.1, wherein on reaching over an excitation threshold by current injection. The results suggested that KCNE2 could shorten action potential duration which was prolonged by G572S. These findings described electrophysiological characteristics of the LQT2 syndrome mutation KCNH2-G572S and regulation by accessory protein KCNE2, and provided a clue about LQT2 and relative rescue mechanism.
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Affiliation(s)
- Li Liu
- Department of Cardiology, General Hospital of People's Liberation ArmyBeijing, China; The Third Department of Internal Medicine, Beijing Municipal Corps Hospital of Chinese People's Armed Police ForceBeijing, China
| | - Jinwen Tian
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Caiyi Lu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Xi Chen
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yicheng Fu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Bin Xu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Chao Zhu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yanmei Sun
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yu Zhang
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Ying Zhao
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yang Li
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
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13
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Goodchild SJ, Macdonald LC, Fedida D. Sequence of gating charge movement and pore gating in HERG activation and deactivation pathways. Biophys J 2016; 108:1435-1447. [PMID: 25809256 DOI: 10.1016/j.bpj.2015.02.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 02/08/2015] [Accepted: 02/18/2015] [Indexed: 12/26/2022] Open
Abstract
KV11.1 voltage-gated K(+) channels are noted for unusually slow activation, fast inactivation, and slow deactivation kinetics, which tune channel activity to provide vital repolarizing current during later stages of the cardiac action potential. The bulk of charge movement in human ether-a-go-go-related gene (hERG) is slow, as is return of charge upon repolarization, suggesting that the rates of hERG channel opening and, critically, that of deactivation might be determined by slow voltage sensor movement, and also by a mode-shift after activation. To test these ideas, we compared the kinetics and voltage dependence of ionic activation and deactivation with gating charge movement. At 0 mV, gating charge moved ∼threefold faster than ionic current, which suggests the presence of additional slow transitions downstream of charge movement in the physiological activation pathway. A significant voltage sensor mode-shift was apparent by 24 ms at +60 mV in gating currents, and return of charge closely tracked pore closure after pulses of 100 and 300 ms duration. A deletion of the N-terminus PAS domain, mutation R4AR5A or the LQT2-causing mutation R56Q gave faster-deactivating channels that displayed an attenuated mode-shift of charge. This indicates that charge movement is perturbed by N- and C-terminus interactions, and that these domain interactions stabilize the open state and limit the rate of charge return. We conclude that slow on-gating charge movement can only partly account for slow hERG ionic activation, and that the rate of pore closure has a limiting role in the slow return of gating charges.
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Affiliation(s)
- Samuel J Goodchild
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Logan C Macdonald
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada
| | - David Fedida
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, British Columbia, Canada.
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14
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Murray CI, Westhoff M, Eldstrom J, Thompson E, Emes R, Fedida D. Unnatural amino acid photo-crosslinking of the IKs channel complex demonstrates a KCNE1:KCNQ1 stoichiometry of up to 4:4. eLife 2016; 5. [PMID: 26802629 PMCID: PMC4807126 DOI: 10.7554/elife.11815] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 01/22/2016] [Indexed: 12/20/2022] Open
Abstract
Cardiac repolarization is determined in part by the slow delayed rectifier current (IKs), through the tetrameric voltage-gated ion channel, KCNQ1, and its β-subunit, KCNE1. The stoichiometry between α and β-subunits has been controversial with studies reporting either a strict 2 KCNE1:4 KCNQ1 or a variable ratio up to 4:4. We used IKs fusion proteins linking KCNE1 to one (EQ), two (EQQ) or four (EQQQQ) KCNQ1 subunits, to reproduce compulsory 4:4, 2:4 or 1:4 stoichiometries. Whole cell and single-channel recordings showed EQQ and EQQQQ to have increasingly hyperpolarized activation, reduced conductance, and shorter first latency of opening compared to EQ - all abolished by the addition of KCNE1. As well, using a UV-crosslinking unnatural amino acid in KCNE1, we found EQQQQ and EQQ crosslinking rates to be progressively slowed compared to KCNQ1, which demonstrates that no intrinsic mechanism limits the association of up to four β-subunits within the IKs complex. DOI:http://dx.doi.org/10.7554/eLife.11815.001 The membrane that surrounds heart muscle cells contains specialized channels that can open and close to control the movements of charged ions into and out of the cell. This ion flow generates the electrical signals that stimulate the heart muscle to contract for each heart beat. Different ion channels influence different steps in the initiation and termination of each electrical signal. For example, the IKs ion channel complex helps to return the cell to a resting state so the heart muscle can relax. This allows chambers of the heart to fill with blood before the next beat pumps blood throughout the body. Mutations that affect IKs cause serious heart conditions that affect heart rhythm, such as Long QT Syndrome. The IKs complex consists of channels that are each made of four copies of a protein called KCNQ1, through which potassium ions exit the cell. This channel opens in response to changes in the voltage across the cell membrane (known as the “membrane potential”). A small protein subunit called KCNE1 also makes up part of the complex, but it was not clear how many KCNE1 molecules combine with KCNQ1 to form a working channel complex. Several previous studies have reported two different results: that the KCNQ1 channel complex only exists with two KCNE1 molecules, or that the association is flexible, allowing the complex to contain up to four KCNE1 subunits. Murray et al. have now constructed IKs fusion channels out of different numbers of KCNQ1 and KCNE1 molecules to investigate how different KCNQ1:KCNE1 ratios affect how the channel works. Measuring the responses of these modified channels in mammalian cells revealed that channels with four KCNE1 subunits conducted ions better than channels with one or two KCNE1s. The channels containing fewer KCNE1s also opened at lower membrane potentials and after a shorter delay following a change in the membrane potential. Further experiments also supported the theory that up to four independent KCNE1 subunits may be easily added to the IKs ion channel complex. Murray et al. suggest that by being able to form channel complexes containing different numbers of KCNE1 subunits, cells can more flexibly control the rate at which ions flow out of the heart cells to tune the electrical signals that trigger each heart beat. The next challenges will be to determine the composition of the IKs channel complex in adult heart cells and to investigate how the complex might change with disease. DOI:http://dx.doi.org/10.7554/eLife.11815.002
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Affiliation(s)
- Christopher I Murray
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Maartje Westhoff
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Jodene Eldstrom
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Emely Thompson
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - Robert Emes
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
| | - David Fedida
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
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15
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Pedersen PJ, Thomsen KB, Olander ER, Hauser F, Tejada MDLA, Poulsen KL, Grubb S, Buhl R, Calloe K, Klaerke DA. Molecular Cloning and Functional Expression of the Equine K+ Channel KV11.1 (Ether à Go-Go-Related/KCNH2 Gene) and the Regulatory Subunit KCNE2 from Equine Myocardium. PLoS One 2015; 10:e0138320. [PMID: 26376488 PMCID: PMC4574097 DOI: 10.1371/journal.pone.0138320] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 08/28/2015] [Indexed: 11/18/2022] Open
Abstract
The KCNH2 and KCNE2 genes encode the cardiac voltage-gated K+ channel KV11.1 and its auxiliary β subunit KCNE2. KV11.1 is critical for repolarization of the cardiac action potential. In humans, mutations or drug therapy affecting the KV11.1 channel are associated with prolongation of the QT intervals on the ECG and increased risk of ventricular tachyarrhythmia and sudden cardiac death—conditions known as congenital or acquired Long QT syndrome (LQTS), respectively. In horses, sudden, unexplained deaths are a well-known problem. We sequenced the cDNA of the KCNH2 and KCNE2 genes using RACE and conventional PCR on mRNA purified from equine myocardial tissue. Equine KV11.1 and KCNE2 cDNA had a high homology to human genes (93 and 88%, respectively). Equine and human KV11.1 and KV11.1/KCNE2 were expressed in Xenopus laevis oocytes and investigated by two-electrode voltage-clamp. Equine KV11.1 currents were larger compared to human KV11.1, and the voltage dependence of activation was shifted to more negative values with V1/2 = -14.2±1.1 mV and -17.3±0.7, respectively. The onset of inactivation was slower for equine KV11.1 compared to the human homolog. These differences in kinetics may account for the larger amplitude of the equine current. Furthermore, the equine KV11.1 channel was susceptible to pharmacological block with terfenadine. The physiological importance of KV11.1 was investigated in equine right ventricular wedge preparations. Terfenadine prolonged action potential duration and the effect was most pronounced at slow pacing. In conclusion, these findings indicate that horses could be disposed to both congenital and acquired LQTS.
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Affiliation(s)
- Philip Juul Pedersen
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Kirsten Brolin Thomsen
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Emma Rie Olander
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Frank Hauser
- Center for Functional and Comparative Insect Genomics, Department of Biology, Faculty of Science, University of Copenhagen, Copenhagen, Denmark
| | - Maria de los Angeles Tejada
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Kristian Lundgaard Poulsen
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Soren Grubb
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Rikke Buhl
- Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Taastrup, Denmark
| | - Kirstine Calloe
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
- * E-mail:
| | - Dan Arne Klaerke
- Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
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16
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Nielsen JB, Bentzen BH, Olesen MS, David JP, Olesen SP, Haunsø S, Svendsen JH, Schmitt N. Gain-of-function mutations in potassium channel subunit KCNE2 associated with early-onset lone atrial fibrillation. Biomark Med 2014; 8:557-70. [PMID: 24796621 DOI: 10.2217/bmm.13.137] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
AIMS Atrial fibrillation (AF) is the most common cardiac arrhythmia. Disturbances in cardiac potassium conductance are considered as one of the disease mechanisms in AF. We aimed to investigate if mutations in potassium-channel β-subunits KCNE2 and KCNE3 are associated with early-onset lone AF. METHODS & RESULTS The coding regions of KCNE2 and KCNE3 were bidirectionally sequenced in 192 unrelated patients diagnosed with early-onset lone AF (<40 years). Two nonsynonymous missense mutations were identified in KCNE2 (M23L and I57T). Both mutations were absent in a healthy control group (n=1500 alleles). Electrophysiological investigations were performed for both mutations in combination with candidate pore-forming α-subunits KV7.1, KV11.1, KV4.3 and KV1.5. A significant gain-of-function effect was observed upon coexpression with KV7.1 and KV7.1+KCNE1. Confocal imaging found no differences in subcellular localization. No disease-suspected mutations were identified in KCNE3. CONCLUSION We identified two KCNE2 gain-of-function missense mutations that seem to increase the susceptibility of early-onset lone AF. These results confirm previous findings indicating that gain-of-function in the slow delayed rectifier potassium current might be involved in the pathogenesis of AF.
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Affiliation(s)
- Jonas Bille Nielsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia (DARC), Copenhagen, Denmark
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17
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Pan Y, Laird JG, Yamaguchi DM, Baker SA. A di-arginine ER retention signal regulates trafficking of HCN1 channels from the early secretory pathway to the plasma membrane. Cell Mol Life Sci 2014; 72:833-43. [PMID: 25142030 PMCID: PMC4309907 DOI: 10.1007/s00018-014-1705-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Revised: 07/14/2014] [Accepted: 08/12/2014] [Indexed: 12/25/2022]
Abstract
Hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels carry Ih, which contributes to neuronal excitability and signal transmission in the nervous system. Controlling the trafficking of HCN1 is an important aspect of its regulation, yet the details of this process are poorly understood. Here, we investigated how the C-terminus of HCN1 regulates trafficking by testing for its ability to redirect the localization of a non-targeted reporter in transgenic Xenopus laevis photoreceptors. We found that HCN1 contains an ER localization signal and through a series of deletion constructs, identified the responsible di-arginine ER retention signal. This signal is located in the intrinsically disordered region of the C-terminus of HCN1. To test the function of the ER retention signal in intact channels, we expressed wild type and mutant HCN1 in HEK293 cells and found this signal negatively regulates surface expression of HCN1. In summary, we report a new mode of regulating HCN1 trafficking: through the use of a di-arginine ER retention signal that monitors processing of the channel in the early secretory pathway.
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Affiliation(s)
- Yuan Pan
- Department of Biochemistry, Carver College of Medicine, University of Iowa, 51 Newton Road, Biochemistry, 4-712 BSB, Iowa City, IA, 52242, USA
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18
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Schmitt N, Grunnet M, Olesen SP. Cardiac potassium channel subtypes: new roles in repolarization and arrhythmia. Physiol Rev 2014; 94:609-53. [PMID: 24692356 DOI: 10.1152/physrev.00022.2013] [Citation(s) in RCA: 160] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
About 10 distinct potassium channels in the heart are involved in shaping the action potential. Some of the K+ channels are primarily responsible for early repolarization, whereas others drive late repolarization and still others are open throughout the cardiac cycle. Three main K+ channels drive the late repolarization of the ventricle with some redundancy, and in atria this repolarization reserve is supplemented by the fairly atrial-specific KV1.5, Kir3, KCa, and K2P channels. The role of the latter two subtypes in atria is currently being clarified, and several findings indicate that they could constitute targets for new pharmacological treatment of atrial fibrillation. The interplay between the different K+ channel subtypes in both atria and ventricle is dynamic, and a significant up- and downregulation occurs in disease states such as atrial fibrillation or heart failure. The underlying posttranscriptional and posttranslational remodeling of the individual K+ channels changes their activity and significance relative to each other, and they must be viewed together to understand their role in keeping a stable heart rhythm, also under menacing conditions like attacks of reentry arrhythmia.
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19
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Wang QI, Ohno S, Ding WG, Fukuyama M, Miyamoto A, Itoh H, Makiyama T, Wu J, Bai J, Hasegawa K, Shinohara T, Takahashi N, Shimizu A, Matsuura H, Horie M. Gain-of-function KCNH2 mutations in patients with Brugada syndrome. J Cardiovasc Electrophysiol 2014; 25:522-530. [PMID: 24400717 DOI: 10.1111/jce.12361] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Revised: 12/15/2013] [Accepted: 12/23/2013] [Indexed: 12/19/2022]
Abstract
BACKGROUND Brugada syndrome (BrS) is an inherited disease characterized by right precordial ST segment elevation on electrocardiograms (ECGs) that predisposes patients to sudden cardiac death as a result of polymorphic ventricular tachyarrhythmia or ventricular fibrillation (VF). In BrS patients, except for SCN5A, mutations in other responsible genes are poorly elucidated. METHODS AND RESULTS We identified 4 KCNH2 mutations, T152I, R164C, W927G, and R1135H, in 236 consecutive probands with BrS or Brugada-like ECG. Three of these mutation carriers showed QTc intervals shorter than 360 milliseconds and 1 experienced VF. We performed patch-clamp analyses on I(Kr) reconstituted with the KCNH2 mutations in Chinese hamster ovary cells and compared the phenotypes of the patients with different genotypes. Three mutations, R164C, W927G, and R1135H, increased I(Kr) densities. Three mutations, T152I, R164C, and W927G, caused a negative shift in voltage-dependent activation curves. Only the R1135H mutant channel prolonged the deactivation time constants. We also identified 20 SCN5A and 5 CACNA1C mutation carriers in our cohort. Comparison of probands' phenotypes with 3 different genotypes revealed that KCNH2 mutation carriers showed shorter QTc intervals and SCN5A mutation carriers had longer QRS durations. CONCLUSIONS All KCNH2 mutations that we identified in probands with BrS exerted gain-of-function effects on I(Kr) channels, which may partially explain the ECG findings in our patients.
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Affiliation(s)
- Q I Wang
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Seiko Ohno
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Wei-Guang Ding
- Division of Physiology, Shiga University of Medical Science, Otsu, Japan
| | - Megumi Fukuyama
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Akashi Miyamoto
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Hideki Itoh
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Takeru Makiyama
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Jie Wu
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Jiayu Bai
- Division of Physiology, Shiga University of Medical Science, Otsu, Japan
| | - Kanae Hasegawa
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
| | - Tetsuji Shinohara
- Department of Cardiology and Clinical Examination, Oita University Faculty of Medicine, Yufu, Japan
| | - Naohiko Takahashi
- Department of Cardiology and Clinical Examination, Oita University Faculty of Medicine, Yufu, Japan
| | - Akihiko Shimizu
- Faculty of Health Sciences, Yamaguchi Graduate School of Medicine, Ube, Japan
| | - Hiroshi Matsuura
- Division of Physiology, Shiga University of Medical Science, Otsu, Japan
| | - Minoru Horie
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
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20
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Pan Y, Bhattarai S, Modestou M, Drack AV, Chetkovich DM, Baker SA. TRIP8b is required for maximal expression of HCN1 in the mouse retina. PLoS One 2014; 9:e85850. [PMID: 24409334 PMCID: PMC3883711 DOI: 10.1371/journal.pone.0085850] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Accepted: 10/31/2013] [Indexed: 01/04/2023] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are cation-selective channels present in retina, brain and heart. The activity of HCN channels contributes to signal integration, cell excitability and pacemaker activity. HCN1 channels expressed in photoreceptors participate in keeping light responses transient and are required for normal mesopic vision. The subcellular localization of HCN1 varies among cell types. In photoreceptors HCN1 is concentrated in the inner segments while in other retinal neurons, HCN1 is evenly distributed though the cell. This is in contrast to hippocampal neurons where HCN1 is concentrated in a subset of dendrites. A key regulator of HCN1 trafficking and activity is tetratricopeptide repeat-containing Rab8b interacting protein (TRIP8b). Multiple splice isoforms of TRIP8b are expressed throughout the brain and can differentially regulate the surface expression and activity of HCN1. The purpose of the present study was to determine which isoforms of TRIP8b are expressed in the retina and to test if loss of TRIP8b alters HCN1 expression or trafficking. We found that TRIP8b colocalizes with HCN1 in multiple retina neurons and all major splice isoforms of TRIP8b are expressed in the retina. Photoreceptors express three different isoforms. In TRIP8b knockout mice, the ability of HCN1 to traffic to the surface of retinal neurons is unaffected. However, there is a large decrease in the total amount of HCN1. We conclude that TRIP8b in the retina is needed to achieve maximal expression of HCN1.
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Affiliation(s)
- Yuan Pan
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Sajag Bhattarai
- Department of Ophthalmology and Visual Sciences, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Modestos Modestou
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Arlene V. Drack
- Department of Ophthalmology and Visual Sciences, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Dane M. Chetkovich
- The Ken & Ruth Davee Department of Neurology and Clinical Neurosciences and Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America
| | - Sheila A. Baker
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Department of Ophthalmology and Visual Sciences, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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