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Davis J, Cornwell JD, Campagna N, Guo J, Li W, Yang T, Wang T, Zhang S. Rescue of expression and function of long QT syndrome-causing mutant hERG channels by enhancing channel stability in the plasma membrane. J Biol Chem 2024; 300:107526. [PMID: 38960041 PMCID: PMC11325228 DOI: 10.1016/j.jbc.2024.107526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2024] [Revised: 06/21/2024] [Accepted: 06/23/2024] [Indexed: 07/05/2024] Open
Abstract
The human ether-a-go-go-related gene (hERG) encodes the Kv11.1 (or hERG) channel that conducts the rapidly activating delayed rectifier potassium current (IKr). Naturally occurring mutations in hERG impair the channel function and cause long QT syndrome type 2. Many missense hERG mutations lead to a lack of channel expression on the cell surface, representing a major mechanism for the loss-of-function of mutant channels. While it is generally thought that a trafficking defect underlies the lack of channel expression on the cell surface, in the present study, we demonstrate that the trafficking defective mutant hERG G601S can reach the plasma membrane but is unstable and quickly degrades, which is akin to WT hERG channels under low K+ conditions. We previously showed that serine (S) residue at 624 in the innermost position of the selectivity filter of hERG is involved in hERG membrane stability such that substitution of serine 624 with threonine (S624T) enhances hERG stability and renders hERG insensitive to low K+ culture. Here, we report that the intragenic addition of S624T substitution to trafficking defective hERG mutants G601S, N470D, and P596R led to a complete rescue of the function of these otherwise loss-of-function mutant channels to a level similar to the WT channel, representing the most effective rescue means for the function of mutant hERG channels. These findings not only provide novel insights into hERG mutation-mediated channel dysfunction but also point to the critical role of S624 in hERG stability on the plasma membrane.
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Affiliation(s)
- Jordan Davis
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - James D Cornwell
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Noah Campagna
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Jun Guo
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Wentao Li
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Tonghua Yang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Tingzhong Wang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Shetuan Zhang
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.
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2
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Maurissen TL, Kawatou M, López-Dávila V, Minatoya K, Yamashita JK, Woltjen K. Modeling mutation-specific arrhythmogenic phenotypes in isogenic human iPSC-derived cardiac tissues. Sci Rep 2024; 14:2586. [PMID: 38297132 PMCID: PMC10831092 DOI: 10.1038/s41598-024-52871-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 01/24/2024] [Indexed: 02/02/2024] Open
Abstract
Disease modeling using human induced pluripotent stem cells (hiPSCs) from patients with genetic disease is a powerful approach for dissecting pathophysiology and drug discovery. Nevertheless, isogenic controls are required to precisely compare phenotypic outcomes from presumed causative mutations rather than differences in genetic backgrounds. Moreover, 2D cellular models often fail to exhibit authentic disease phenotypes resulting in poor validation in vitro. Here we show that a combination of precision gene editing and bioengineered 3D tissue models can establish advanced isogenic hiPSC-derived cardiac disease models, overcoming these drawbacks. To model inherited cardiac arrhythmias we selected representative N588D and N588K missense mutations affecting the same codon in the hERG potassium channel gene KCNH2, which are reported to cause long (LQTS) and short (SQTS) QT syndromes, respectively. We generated compound heterozygous variants in normal hiPSCs, and differentiated cardiomyocytes (CMs) and mesenchymal cells (MCs) to form 3D cardiac tissue sheets (CTSs). In hiPSC-derived CM monolayers and 3D CTSs, electrophysiological analysis with multielectrode arrays showed prolonged and shortened repolarization, respectively, compared to the isogenic controls. When pharmacologically inhibiting the hERG channels, mutant 3D CTSs were differentially susceptible to arrhythmic events than the isogenic controls. Thus, this strategy offers advanced disease models that can reproduce clinically relevant phenotypes and provide solid validation of gene mutations in vitro.
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Affiliation(s)
- Thomas L Maurissen
- Department of Life Science Frontiers, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, 606-8507, Japan
- Roche Pharma Research and Early Development, Cardiovascular, Metabolism, Immunology, Infectious Diseases and Ophthalmology, Roche Innovation Center Basel, F. Hoffmann-La Roche Ltd., Basel, Switzerland
| | - Masahide Kawatou
- Department of Cell Growth and Differentiation, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, 606-8507, Japan
- Department of Cardiovascular Surgery, Kyoto University Graduate School of Medicine, Kyoto, 606-8507, Japan
| | - Víctor López-Dávila
- Department of Cell Growth and Differentiation, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, 606-8507, Japan
- Gourmey, Paris, France
| | - Kenji Minatoya
- Department of Cardiovascular Surgery, Kyoto University Graduate School of Medicine, Kyoto, 606-8507, Japan
| | - Jun K Yamashita
- Department of Cell Growth and Differentiation, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, 606-8507, Japan.
- Department of Cellular and Tissue Communications, Graduate School of Medicine, University of Tokyo, Tokyo, Japan.
| | - Knut Woltjen
- Department of Life Science Frontiers, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, 606-8507, Japan.
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3
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Veldhuizen J, Mann HF, Karamanova N, Van Horn WD, Migrino RQ, Brafman D, Nikkhah M. Modeling long QT syndrome type 2 on-a-chip via in-depth assessment of isogenic gene-edited 3D cardiac tissues. SCIENCE ADVANCES 2022; 8:eabq6720. [PMID: 36525500 PMCID: PMC9757749 DOI: 10.1126/sciadv.abq6720] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Accepted: 11/16/2022] [Indexed: 06/09/2023]
Abstract
Long QT syndrome (LQTS) is a cardiovascular disease characterized by QT interval prolongation that can lead to sudden cardiac death. Many mutations with heterogeneous mechanisms have been identified in KCNH2, the gene that encodes for hERG (Kv11.1), which lead to onset of LQTS type 2 (LQTS2). In this work, we developed a LQTS2-diseased tissue-on-a-chip model, using 3D coculture of isogenic stem cell-derived cardiomyocytes (CMs) and cardiac fibroblasts (CFs) within an organotypic microfluidic chip technology. Primarily, we created a hiPSC line with R531W mutation in KCNH2 using CRISPR-Cas9 gene-editing technique and characterized the resultant differentiated CMs and CFs. A deficiency in hERG trafficking was identified in KCNH2-edited hiPSC-CMs, revealing a possible mechanism of R531W mutation in LQTS2 pathophysiology. Following creation of a 3D LQTS2 tissue-on-a-chip, the tissues were extensively characterized, through analysis of calcium handling and response to β-agonist. Furthermore, attempted phenotypic rescue via pharmacological intervention of LQTS2 on a chip was investigated.
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Affiliation(s)
- Jaimeson Veldhuizen
- School of Biological and Health Systems Engineering (SBHSE), Arizona State University, Tempe, AZ 85287, USA
| | - Helen F. Mann
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Nina Karamanova
- Phoenix Veterans Affairs Health Care System, Phoenix, AZ 85012, USA
| | - Wade D. Van Horn
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
- Biodesign Center for Personalized Diagnostics, Arizona State University, Tempe, AZ 85287, USA
| | - Raymond Q. Migrino
- Phoenix Veterans Affairs Health Care System, Phoenix, AZ 85012, USA
- University of Arizona College of Medicine, Phoenix, AZ 85004, USA
| | - David Brafman
- School of Biological and Health Systems Engineering (SBHSE), Arizona State University, Tempe, AZ 85287, USA
| | - Mehdi Nikkhah
- School of Biological and Health Systems Engineering (SBHSE), Arizona State University, Tempe, AZ 85287, USA
- Biodesign Center for Personalized Diagnostics, Arizona State University, Tempe, AZ 85287, USA
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4
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Gu K, Qian D, Qin H, Cui C, Fernando WCHA, Wang D, Wang J, Cao K, Chen M. A novel mutation in KCNH2 yields loss-of-function of hERG potassium channel in long QT syndrome 2. Pflugers Arch 2021; 473:219-229. [PMID: 33449212 DOI: 10.1007/s00424-021-02518-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 12/24/2020] [Accepted: 01/07/2021] [Indexed: 12/16/2022]
Abstract
Mutations in hERG (human ether-à-go-go-related gene) potassium channel are closely associated with long QT syndromes. By direct Sanger sequencing, we identified a novel KCNH2 mutation W410R in the patient with long QT syndrome 2 (LQT2). However, the electrophysiological functions of this mutation remain unknown. In comparison to hERGWT channels, hERGW410R channels have markedly decreased total and surface expressions. W410R mutation dramatically reduces hERG channel currents (IKr) and shifts its steady-state activation curve to depolarization. Moreover, hERGW410R channels make dominant-negative effects on hERGWT channels. Significantly, we find hERG channel blocker E-4031 could partially rescue the function of hERGW410R channels by increasing the membrane expression. By using in silico model, we reveal that hERGW410R channels obviously elongate the repolarization of human ventricular myocyte action potentials. Collectively, W410R mutation decreases the currents of hERG channel, because of diminished membrane expression of mutant channels, that subsequently leads to elongated repolarization of cardiomyocyte, which might induce the pathogenesis of LQT2. Furthermore, E-4031 could partially rescue the decreased activity of hERGW410R channels. Thus, our work identifies a novel loss-of-function mutation in KCNH2 gene, which might provide a rational basis for the management of LQT2.
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Affiliation(s)
- Kai Gu
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China
| | - Duoduo Qian
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China
| | - Huiyuan Qin
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China
| | - Chang Cui
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China
| | - W C Hewith A Fernando
- Department of Physiology, Nanjing Medical University, 101 Longmian Ave, Nanjing, 211166, China
| | - Daowu Wang
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China.,State Key Laboratory of Reproductive Medicine, the Centre for Clinical Reproductive Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, 210029, China
| | - Juejin Wang
- Department of Physiology, Nanjing Medical University, 101 Longmian Ave, Nanjing, 211166, China.
| | - Kejiang Cao
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China.
| | - Minglong Chen
- Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China.
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5
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Simpson KE, Venkateshappa R, Pang ZK, Faizi S, Tibbits GF, Claydon TW. Utility of Zebrafish Models of Acquired and Inherited Long QT Syndrome. Front Physiol 2021; 11:624129. [PMID: 33519527 PMCID: PMC7844309 DOI: 10.3389/fphys.2020.624129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 12/21/2020] [Indexed: 01/12/2023] Open
Abstract
Long-QT Syndrome (LQTS) is a cardiac electrical disorder, distinguished by irregular heart rates and sudden death. Accounting for ∼40% of cases, LQTS Type 2 (LQTS2), is caused by defects in the Kv11.1 (hERG) potassium channel that is critical for cardiac repolarization. Drug block of hERG channels or dysfunctional channel variants can result in acquired or inherited LQTS2, respectively, which are typified by delayed repolarization and predisposition to lethal arrhythmia. As such, there is significant interest in clear identification of drugs and channel variants that produce clinically meaningful perturbation of hERG channel function. While toxicological screening of hERG channels, and phenotypic assessment of inherited channel variants in heterologous systems is now commonplace, affordable, efficient, and insightful whole organ models for acquired and inherited LQTS2 are lacking. Recent work has shown that zebrafish provide a viable in vivo or whole organ model of cardiac electrophysiology. Characterization of cardiac ion currents and toxicological screening work in intact embryos, as well as adult whole hearts, has demonstrated the utility of the zebrafish model to contribute to the development of therapeutics that lack hERG-blocking off-target effects. Moreover, forward and reverse genetic approaches show zebrafish as a tractable model in which LQTS2 can be studied. With the development of new tools and technologies, zebrafish lines carrying precise channel variants associated with LQTS2 have recently begun to be generated and explored. In this review, we discuss the present knowledge and questions raised related to the use of zebrafish as models of acquired and inherited LQTS2. We focus discussion, in particular, on developments in precise gene-editing approaches in zebrafish to create whole heart inherited LQTS2 models and evidence that zebrafish hearts can be used to study arrhythmogenicity and to identify potential anti-arrhythmic compounds.
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Affiliation(s)
- Kyle E. Simpson
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Ravichandra Venkateshappa
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Zhao Kai Pang
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Shoaib Faizi
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Glen F. Tibbits
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
- Department of Cardiovascular Science, British Columbia Children’s Hospital, Vancouver, BC, Canada
| | - Tom W. Claydon
- Molecular Cardiac Physiology Group, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
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6
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Huo J, Guo X, Lu Q, Qiang H, Liu P, Bai L, Huang CLH, Zhang Y, Ma A. NS1643 enhances ionic currents in a G604S-WT hERG co-expression system associated with long QT syndrome 2. Clin Exp Pharmacol Physiol 2017; 44:1125-1133. [PMID: 28741726 DOI: 10.1111/1440-1681.12820] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 06/27/2017] [Accepted: 07/17/2017] [Indexed: 12/19/2022]
Affiliation(s)
- JianHua Huo
- Department of Cardiovascular Medicine; First Affiliated Hospital of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University); Ministry of Education; Xi'an Shaanxi China
| | - Xueyan Guo
- Shaanxi Provincial People's Hospital; Xi'an Shaanxi China
| | - Qun Lu
- Department of Cardiovascular Medicine; First Affiliated Hospital of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University); Ministry of Education; Xi'an Shaanxi China
| | - Hua Qiang
- Department of Cardiovascular Medicine; First Affiliated Hospital of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University); Ministry of Education; Xi'an Shaanxi China
| | - Ping Liu
- Department of Cardiovascular Medicine; First Affiliated Hospital of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University); Ministry of Education; Xi'an Shaanxi China
| | - Ling Bai
- Department of Cardiovascular Medicine; First Affiliated Hospital of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University); Ministry of Education; Xi'an Shaanxi China
| | | | - Yanmin Zhang
- Department of Pediatric Cardiology; Childrens Research Institute; affiliate children's hospital of Xi'an Jiaotong University; Xi'an Shaanxi China
| | - Aiqun Ma
- Department of Cardiovascular Medicine; First Affiliated Hospital of Xi'an Jiaotong University; Key Laboratory of Environment and Genes Related to Diseases (Xi'an Jiaotong University); Ministry of Education; Xi'an Shaanxi China
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7
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Calcaterra NE, Hoeppner DJ, Wei H, Jaffe AE, Maher BJ, Barrow JC. Schizophrenia-Associated hERG channel Kv11.1-3.1 Exhibits a Unique Trafficking Deficit that is Rescued Through Proteasome Inhibition for High Throughput Screening. Sci Rep 2016; 6:19976. [PMID: 26879421 PMCID: PMC4754628 DOI: 10.1038/srep19976] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 12/22/2015] [Indexed: 12/24/2022] Open
Abstract
The primate-specific brain voltage-gated potassium channel isoform Kv11.1-3.1 has been identified as a novel therapeutic target for the treatment of schizophrenia. While this ether-a-go-go related K + channel has shown clinical relevance, drug discovery efforts have been hampered due to low and inconsistent activity in cell-based assays. This poor activity is hypothesized to result from poor trafficking via the lack of an intact channel-stabilizing Per-Ant-Sim (PAS) domain. Here we characterize Kv11.1-3.1 cellular localization and show decreased channel expression and cell surface trafficking relative to the PAS-domain containing major isoform, Kv11.1-1A. Using small molecule inhibition of proteasome degradation, cellular expression and plasma membrane trafficking are rescued. These findings implicate the importance of the unfolded-protein response and endoplasmic reticulum associated degradation pathways in the expression and regulation of this schizophrenia risk factor. Utilizing this identified phenomenon, an electrophysiological and high throughput in-vitro fluorescent assay platform has been developed for drug discovery in order to explore a potentially new class of cognitive therapeutics.
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Affiliation(s)
| | | | - Huijun Wei
- Lieber Institute for Brain Development, Baltimore, MD 21205
| | - Andrew E Jaffe
- Lieber Institute for Brain Development, Baltimore, MD 21205.,Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205
| | - Brady J Maher
- Lieber Institute for Brain Development, Baltimore, MD 21205.,Departments of Psychiatry and Behavioral Sciences, Baltimore, MD 21205.,Departments of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - James C Barrow
- Departments of Pharmacology and Molecular Sciences, Baltimore, MD 21205.,Lieber Institute for Brain Development, Baltimore, MD 21205
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Large-scale mutational analysis of Kv11.1 reveals molecular insights into type 2 long QT syndrome. Nat Commun 2014; 5:5535. [PMID: 25417810 PMCID: PMC4243539 DOI: 10.1038/ncomms6535] [Citation(s) in RCA: 134] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 10/09/2014] [Indexed: 12/23/2022] Open
Abstract
It has been suggested that deficient protein trafficking to the cell membrane is the dominant mechanism associated with type 2 Long QT syndrome (LQT2) caused by Kv11.1 potassium channel missense mutations, and that for many mutations the trafficking defect can be corrected pharmacologically. However, this inference was based on expression of a small number of Kv11.1 mutations. We performed a comprehensive analysis of 167 LQT2-linked missense mutations in four Kv11.1 structural domains and found that deficient protein trafficking is the dominant mechanism for all domains except for the distal carboxy-terminus. Also, most pore mutations--in contrast to intracellular domain mutations--were found to have severe dominant-negative effects when co-expressed with wild-type subunits. Finally, pharmacological correction of the trafficking defect in homomeric mutant channels was possible for mutations within all structural domains. However, pharmacological correction is dramatically improved for pore mutants when co-expressed with wild-type subunits to form heteromeric channels.
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9
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Jang JH, Jung J, Kim AR, Cho YM, Kim MY, Lee SY, Choi JY, Lee JH, Choi BY. Identification of Novel Functional Null Allele of SLC26A4 Associated with Enlarged Vestibular Aqueduct and Its Possible Implication. Audiol Neurootol 2014; 19:319-26. [DOI: 10.1159/000366190] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 07/28/2014] [Indexed: 11/19/2022] Open
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10
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Veale EL, Hassan M, Walsh Y, Al-Moubarak E, Mathie A. Recovery of current through mutated TASK3 potassium channels underlying Birk Barel syndrome. Mol Pharmacol 2013; 85:397-407. [PMID: 24342771 DOI: 10.1124/mol.113.090530] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
TASK3 (TWIK-related acid-sensitive K(+) channel 3) potassium channels are members of the two-pore-domain potassium channel family. They are responsible for background leak potassium currents found in many cell types. TASK3 channels are genetically imprinted, and a mutation in TASK3 (G236R) is responsible for Birk Barel mental retardation dysmorphism syndrome, a maternally transmitted developmental disorder. This syndrome may arise from a neuronal migration defect during development caused by dysfunctional TASK3 channels. Through the use of whole-cell electrophysiologic recordings, we have found that, although G236R mutated TASK3 channels give rise to a functional current, this current is significantly smaller in an outward direction when compared with wild-type (WT) TASK3 channels. In contrast to WT TASK3 channels, the current is inwardly rectifying. Furthermore, the current through mutated channels is differentially sensitive to a number of regulators, such as extracellular acidification, extracellular zinc, and activation of Gαq-coupled muscarinic (M3) receptors, compared with WT TASK3 channels. The reduced outward current through mutated TASK3_G236R channels can be overcome, at least in part, by both a gain-of-function additional mutation of TASK3 channels (A237T) or by application of the nonsteroidal anti-inflammatory drug flufenamic acid (FFA; 2-{[3-(trifluoromethyl)phenyl]amino}benzoic acid). FFA produces a significantly greater enhancement of current through mutated channels than through WT TASK3 channels. We propose that pharmacologic enhancement of mutated TASK3 channel current during development may, therefore, provide a potentially useful therapeutic strategy in the treatment of Birk Barel syndrome.
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Affiliation(s)
- Emma L Veale
- Medway School of Pharmacy, University of Kent and University of Greenwich, Kent, United Kingdom
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Balijepalli SY, Lim E, Concannon SP, Chew CL, Holzem KE, Tester DJ, Ackerman MJ, Delisle BP, Balijepalli RC, January CT. Mechanism of loss of Kv11.1 K+ current in mutant T421M-Kv11.1-expressing rat ventricular myocytes: interaction of trafficking and gating. Circulation 2012; 126:2809-18. [PMID: 23136156 DOI: 10.1161/circulationaha.112.118018] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Type 2 long QT syndrome involves mutations in the human ether a-go-go-related gene (hERG or KCNH2). T421M, an S1 domain mutation in the Kv11.1 channel protein, was identified in a resuscitated patient. We assessed its biophysical, protein trafficking, and pharmacological mechanisms in adult rat ventricular myocytes. METHODS AND RESULTS Isolated adult rat ventricular myocytes were infected with wild-type (WT)-Kv11.1- and T421M-Kv11.1-expressing adenovirus and analyzed with the use of patch clamp, Western blot, and confocal imaging techniques. Expression of WT-Kv11.1 or T421M-Kv11.1 produced peak tail current (I(Kv11.1)) of 8.78±1.18 and 1.91±0.22 pA/pF, respectively. Loss of mutant I(Kv11.1) resulted from (1) a partially trafficking-deficient channel protein with reduced cell surface expression and (2) altered channel gating with a positive shift in the voltage dependence of activation and altered kinetics of activation and deactivation. Coexpression of WT+T421M-Kv11.1 resulted in heterotetrameric channels that remained partially trafficking deficient with only a minimal increase in peak I(Kv11.1) density, whereas the voltage dependence of channel gating became WT-like. In the adult rat ventricular myocyte model, both WT-Kv11.1 and T421M-Kv11.1 channels responded to β-adrenergic stimulation by increasing I(Kv11.1). CONCLUSIONS The T421M-Kv11.1 mutation caused a loss of I(Kv11.1) through interactions of abnormal protein trafficking and channel gating. Furthermore, for coexpressed WT+T421M-Kv11.1 channels, different dominant-negative interactions govern protein trafficking and ion channel gating, and these are likely to be reflected in the clinical phenotype. Our results also show that WT and mutant Kv11.1 channels responded to β-adrenergic stimulation.
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12
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Kaufman ES. Mutation location matters in long QT syndrome type 2 (but behavior matters more). Heart Rhythm 2012; 10:68-9. [PMID: 23041577 DOI: 10.1016/j.hrthm.2012.10.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Indexed: 11/18/2022]
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13
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Liu L, Hayashi K, Kaneda T, Ino H, Fujino N, Uchiyama K, Konno T, Tsuda T, Kawashiri MA, Ueda K, Higashikata T, Shuai W, Kupershmidt S, Higashida H, Yamagishi M. A novel mutation in the transmembrane nonpore region of the KCNH2 gene causes severe clinical manifestations of long QT syndrome. Heart Rhythm 2012; 10:61-7. [PMID: 23010577 DOI: 10.1016/j.hrthm.2012.09.053] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND Long QT syndrome (LQTS) is characterized by prolonged ventricular repolarization and variable clinical course with arrhythmia-related syncope and sudden death. Mutations in the nonpore region of the LQTS-associated KCNH2 gene (also known as hERG) are mostly associated with coassembly or trafficking abnormalities, resulting in haplotype insufficiency and milder clinical phenotypes compared with mutations in the pore domain. OBJECTIVE To investigate the effect of a nonpore mutation on the channel current, which was identified from an LQTS family with severe clinical phenotypes. METHODS Two members of a Japanese family with LQTS were searched for mutations in KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, and KCNJ2 genes by using automated DNA sequencing. We characterized the electrophysiological properties and glycosylation pattern of the mutant channels by using patch clamp recording and Western blot analysis. RESULTS In the LQTS patient with torsades de pointes and cardiopulmonary arrest, we identified the novel T473P mutation in the transmembrane nonpore region of KCNH2. The proband's father carried the same mutation and showed prolonged corrected QT interval and frequent torsades de pointes in the presence of hypokalemia following the administration of garenoxacin. Patch clamp analysis in heterologous cells showed that hERG T473P channels generated no current and exhibited a dominant negative effect when coexpressed with wild-type protein. Only incompletely glycosylated hERG T473P channels were observed by using Western blot analysis, suggesting impaired trafficking. CONCLUSIONS These results demonstrated that a trafficking-deficient mutation in the transmembrane nonpore region of KCNH2 causes a dominant negative effect and a severe clinical course in affected patients.
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Affiliation(s)
- Li Liu
- Department of Biophysical Genetics, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan
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Isoform-specific dominant-negative effects associated with hERG1 G628S mutation in long QT syndrome. PLoS One 2012; 7:e42552. [PMID: 22876326 PMCID: PMC3411645 DOI: 10.1371/journal.pone.0042552] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Accepted: 07/09/2012] [Indexed: 11/25/2022] Open
Abstract
Background Mutations in the human ether-a-go-go-related gene 1 (hERG1) cause type 2 long QT syndrome (LQT2). The hERG1 gene encodes a K+ channel with properties similar to the rapidly activating delayed rectifying K+ current in the heart. Several hERG1 isoforms with unique structural and functional properties have been identified. To date, the pathogenic mechanisms of LQT2 mutations have been predominantly described in the context of the hERG1a isoform. In the present study, we investigated the functional consequences of the LQT2 mutation G628S in the hERG1b and hERG1aUSO isoforms. Methods A double-stable, mammalian expression system was developed to characterize isoform-specific dominant-negative effects of G628S-containing channels when co-expressed at equivalent levels with wild-type hERG1a. Western blot and co-immunoprecipitation studies were performed to study the trafficking and co-assembly of wild-type and mutant hERG1 isoforms. Patch-clamp electrophysiology was performed to characterize hERG1 channel function and the isoform-specific dominant-negative effects associated with the G628S mutation. Conclusions The non-functional hERG1a-G628S and hERG1b-G628S channels co-assembled with wild-type hERG1a and dominantly suppressed hERG1 current. In contrast, G628S-induced dominant-negative effects were absent in the context of the hERG1aUSO isoform. hERG1aUSO-G628S channels did not appreciably associate with hERG1a and did not significantly suppress hERG1 current when co-expressed at equivalent ratios or at ratios that approximate those found in cardiac tissue. These results suggest that the dominant-negative effects of LQT2 mutations may primarily occur in the context of the hERG1a and hERG1b isoforms.
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Kinoshita K, Yamaguchi Y, Nishide K, Kimoto K, Nonobe Y, Fujita A, Asano K, Tabata T, Mori H, Inoue H, Hata Y, Fukurotani K, Nishida N. A novel missense mutation causing a G487R substitution in the S2-S3 loop of human ether-à-go-go-related gene channel. J Cardiovasc Electrophysiol 2012; 23:1246-53. [PMID: 22764740 DOI: 10.1111/j.1540-8167.2012.02383.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
INTRODUCTION Mutations of human ether-à-go-go-related gene (hERG), which encodes a cardiac K(+) channel responsible for the acceleration of the repolarizing phase of an action potential and the prevention of premature action potential regeneration, often cause severe arrhythmic disorders. We found a novel missense mutation of hERG that results in a G487R substitution in the S2-S3 loop of the channel subunit [hERG(G487R)] from a family and determined whether this mutant gene could induce an abnormality in channel function. METHODS AND RESULTS We made whole-cell voltage-clamp recordings from HEK-293T cells transfected with wild-type hERG [hERG(WT)], hERG(G487R), or both. We measured hERG channel-mediated current as the "tail" of a depolarization-elicited current. The current density of the tail current and its voltage- and time-dependences were not different among all the cell groups. The time-courses of deactivation, inactivation, and recovery from inactivation and their voltage-dependences were not different among all the cell groups. Furthermore, we performed immunocytochemical analysis using an anti-hERG subunit antibody. The ratio of the immunoreactivity of the plasma membrane to that of the cytoplasm was not different between cells transfected with hERG(WT), hERG(G487R), or both. CONCLUSION hERG(G487R) can produce functional channels with normal gating kinetics and cell-surface expression efficiency with or without the aid of hERG(WT). Therefore, neither the heterozygous nor homozygous inheritance of hERG(G487R) is thought to cause severe cardiac disorders. hERG(G487R) would be a candidate for a rare variant or polymorphism of hERG with an amino acid substitution in the unusual region of the channel subunit.
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Affiliation(s)
- Koshi Kinoshita
- Department of Legal Medicine Second, Graduate School of Medical and Pharmaceutical Sciences, University of Toyama, Toyama, Japan
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Maljevic S, Naros G, Yalçin Ö, Blazevic D, Loeffler H, Cağlayan H, Steinlein OK, Lerche H. Temperature and pharmacological rescue of a folding-defective, dominant-negative KV 7.2 mutation associated with neonatal seizures. Hum Mutat 2012; 32:E2283-93. [PMID: 21913284 DOI: 10.1002/humu.21554] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Benign familial neonatal seizures (BFNS) are a dominant epilepsy syndrome caused by mutations in the voltage-gated potassium channels K(V) 7.2 and K(V) 7.3. We examined the molecular pathomechanism of a BFNS-causing mutation (p.N258S) in the extracellular S5-H5 loop of K(V) 7.2. Wild type (WT) and mutant channels, expressed in both Xenopus laevis oocytes and CHO cells, were studied using electrophysiological techniques. The results revealed a pronounced loss-of-function with a dominant-negative effect of the mutant on WT K(V) 7.2 and K(V) 7.3 channels. Since single-channel recordings of K(V) 7.3-K(V) 7.2 and K(V) 7.3-N285S concatemers showed similar properties for both constructs, we hypothesized that the observed reduction in current amplitude was due to a folding and trafficking defect, which was confirmed by biochemical and immunocytochemical experiments revealing a reduced number of mutant channels in the surface membrane. Furthermore, rescuing experiments revealed that upon specific incubation of transfected CHO cells-either at lower temperatures of <30°C or in presence of the agonist retigabine (RTG)-the N258S-derived currents increased fivefold in contrast to the WT. The obtained results represent a first example of temperature and pharmacological rescue of a K(V) 7 mutation and suggest a folding and trafficking deficiency as the cause of reduced current amplitudes with a dominant-negative effect of N258S mutant proteins.
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Affiliation(s)
- Snezana Maljevic
- Neurological Clinic and Institute of Applied Physiology, University of Ulm, Germany
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17
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Wang Y, Huang X, Zhou J, Yang X, Li D, Mao H, Sun HH, Liu N, Lian J. Trafficking-deficient G572R-hERG and E637K-hERG activate stress and clearance pathways in endoplasmic reticulum. PLoS One 2012; 7:e29885. [PMID: 22242185 PMCID: PMC3252338 DOI: 10.1371/journal.pone.0029885] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 12/07/2011] [Indexed: 02/01/2023] Open
Abstract
Background Long QT syndrome type 2 (LQT2) is the second most common type of all long QT syndromes. It is well-known that trafficking deficient mutant human ether-a-go-go-related gene (hERG) proteins are often involved in LQT2. Cells respond to misfolded and trafficking-deficient proteins by eliciting the unfolded protein response (UPR) and Activating Transcription Factor (ATF6) has been identified as a key regulator of the mammalian UPR. In this study, we investigated the role of ER chaperone proteins (Calnexin and Calreticulin) in the processing of G572R-hERG and E637K-hERG mutant proteins. Methods pcDNA3-WT-hERG, pcDNA3-G572R-hERG and pcDNA3-E637K-hERG plasmids were transfected into U2OS and HEK293 cells. Confocal microscopy and western blotting were used to analyze subcellular localization and protein expression. Interaction between WT or mutant hERGs and Calnexin/Calreticulin was tested by coimmunoprecipitation. To assess the role of the ubiquitin proteasome pathway in the degradation of mutant hERG proteins, transfected HEK293 cells were treated with proteasome inhibitors and their effects on the steady state protein levels of WT and mutant hERGs were examined. Conclusion Our results showed that levels of core-glycosylated immature forms of G572R-hERG and E637K-hERG in association with Calnexin and Calreticulin were higher than that in WT-hERG. Both mutant hERG proteins could activate the UPR by upregulating levels of active ATF6. Furthermore, proteasome inhibition increased the levels of core-glycosylated immature forms of WT and mutant hERGs. In addition, interaction between mutant hERGs and Calnexin/Calreticulin was stronger after proteasome inhibition, compared to WT-hERG. These results suggest that trafficking-deficient G572R-hERG and E637K-hERG mutant proteins can activate ER stress pathways and are targeted to the proteasome for degradation. Calnexin and Calreticulin play important roles in these processes.
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Affiliation(s)
- Ying Wang
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
| | - Xiaoyan Huang
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
| | - Jianqing Zhou
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
| | - Xi Yang
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
| | - Di Li
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
| | - Haiyan Mao
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
| | - Huan Huan Sun
- Department of Surgery, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Ningsheng Liu
- Department of Pathology, Nanjing Medical University, Nanjing, China
- * E-mail: (JL); (NL)
| | - Jiangfang Lian
- Ningbo Medical Center, LiHuiLi Hospital School of Medicine, Ningbo University, Ningbo, China
- * E-mail: (JL); (NL)
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Mihic A, Chauhan VS, Gao X, Oudit GY, Tsushima RG. Trafficking defect and proteasomal degradation contribute to the phenotype of a novel KCNH2 long QT syndrome mutation. PLoS One 2011; 6:e18273. [PMID: 21483829 PMCID: PMC3069070 DOI: 10.1371/journal.pone.0018273] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Accepted: 02/25/2011] [Indexed: 12/26/2022] Open
Abstract
The Kv11.1 (hERG) K+ channel plays a fundamental role in cardiac repolarization. Missense mutations in KCNH2, the gene encoding Kv11.1, cause long QT syndrome (LQTS) and frequently cause channel trafficking-deficiencies. This study characterized the properties of a novel KCNH2 mutation discovered in a LQT2 patient resuscitated from a ventricular fibrillation arrest. Proband genotyping was performed by SSCP and DNA sequencing. The electrophysiological and biochemical properties of the mutant channel were investigated after expression in HEK293 cells. The proband manifested a QTc of 554 ms prior to electrolyte normalization. Mutation analysis revealed an autosomal dominant frameshift mutation at proline 1086 (P1086fs+32X; 3256InsG). Co-immunoprecipitation demonstrated that wild-type Kv11.1 and mutant channels coassemble. Western blot showed that the mutation did not produce mature complex-glycosylated Kv11.1 channels and coexpression resulted in reduced channel maturation. Electrophysiological recordings revealed mutant channel peak currents to be similar to untransfected cells. Co-expression of channels in a 1∶1 ratio demonstrated dominant negative suppression of peak Kv11.1 currents. Immunocytochemistry confirmed that mutant channels were not present at the plasma membrane. Mutant channel trafficking rescue was attempted by incubation at reduced temperature or with the pharmacological agents E-4031. These treatments did not significantly increase peak mutant currents or induce the formation of mature complex-glycosylated channels. The proteasomal inhibitor lactacystin increased the protein levels of the mutant channels demonstrating proteasomal degradation, but failed to induce mutant Kv11.1 protein trafficking. Our study demonstrates a novel dominant-negative Kv11.1 mutation, which results in degraded non-functional channels leading to a LQT2 phenotype.
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Affiliation(s)
- Anton Mihic
- Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Vijay S. Chauhan
- Division of Cardiology, University Health Network, Toronto, Ontario, Canada
| | - Xiaodong Gao
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Gavin Y. Oudit
- Department of Medicine, Mazankowski Alberta Heart Institute and Division of Cardiology, University of Alberta, Edmonton, Alberta, Canada
- * E-mail: (GYO); (RGT)
| | - Robert G. Tsushima
- Department of Biology, York University, Toronto, Ontario, Canada
- * E-mail: (GYO); (RGT)
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19
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Zarraga IG, Zhang L, Stump MR, Gong Q, Vincent GM, Zhou Z. Nonsense-mediated mRNA decay caused by a frameshift mutation in a large kindred of type 2 long QT syndrome. Heart Rhythm 2011; 8:1200-6. [PMID: 21419236 DOI: 10.1016/j.hrthm.2011.03.039] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 03/10/2011] [Indexed: 12/26/2022]
Abstract
BACKGROUND Nonsense and frameshift mutations are common in congenital long QT syndrome type 2 (LQT2). We previously demonstrated that hERG nonsense mutations cause degradation of mutant mRNA by nonsense-mediated mRNA decay (NMD) and are associated with mild clinical phenotypes. The impact of NMD on the expression of hERG frameshift mutations and their phenotypic severity is not clear. OBJECTIVE The purpose of this study was to examine the role of NMD in the pathogenesis of a hERG frameshift mutation, P926AfsX14, identified in a large LQT2 kindred and characterize genotype-phenotype correlations. METHODS Genetic screening was performed among family members. Phenotyping was performed by assessment of ECGs and LQTS-related cardiac events. The functional effect of P926AfsX14 was studied using hERG cDNA and minigene constructs expressed in HEK293 cells. RESULTS Significant cardiac events occurred in carriers of the P926AfsX14 mutation. When expressed from cDNA, the P926AfsX14 mutant channel was only mildly defective. However, when expressed from a minigene, the P926AfsX14 mutation caused a significant reduction in mutant mRNA, protein, and hERG current. Inhibition of NMD by RNA interference knockdown of up-frameshift protein 1 partially restored expression of mutant mRNA and protein and led to a significant increase in hERG current in the mutant cells. These results suggest that NMD is involved in the pathogenic mechanism of the P926AfsX14 mutation. CONCLUSION Our findings suggest that the hERG frameshift mutation P926AfsX14 primarily results in degradation of mutant mRNA by the NMD pathway rather than production of truncated proteins. When combined with environmental triggers and genetic modifiers, LQT2 frameshift mutations associated with NMD can manifest with a severe clinical phenotype.
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Affiliation(s)
- Ignatius Gerardo Zarraga
- Division of Cardiovascular Medicine, Department of Medicine, Oregon Health & Science University, Portland, Oregon, USA
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20
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Abstract
Inherited arrhythmia syndromes comprise an increasingly complex group of diseases involving mutations in multiple genes encoding ion channels, ion channel accessory subunits and channel interacting proteins, and various regulatory elements. These mutations serve to disrupt normal electrophysiology in the heart, leading to increased arrhythmogenic risk and death. These diseases have added impact as they often affect young people, sometimes without warning. Although originally thought to alter ion channel function, it is now increasingly recognized that mutations may alter ion channel protein and messenger RNA processing, to reduce the number of channels reaching the surface membrane. For many of these mutations, it is also known that several interventions may restore protein processing of mutant channels to increase their surface membrane expression toward normal. In this article, we reviewed inherited arrhythmia syndromes, focusing on long QT syndrome type 2, and discuss the complex biology of ion channel trafficking and pharmacological rescue of disease-causing mutant channels. Pharmacological rescue of misprocessed mutant channel proteins, or their transcripts providing appropriate small molecule drugs can be developed, has the potential for novel clinical therapies in some patients with inherited arrhythmia syndromes.
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21
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Stump MR, Gong Q, Zhou Z. Multiple splicing defects caused by hERG splice site mutation 2592+1G>A associated with long QT syndrome. Am J Physiol Heart Circ Physiol 2010; 300:H312-8. [PMID: 21057041 DOI: 10.1152/ajpheart.00818.2010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Long QT syndrome type 2 (LQT2) is caused by mutations in the human ether-a-go-go-related gene (hERG). Cryptic splice site activation in hERG has recently been identified as a novel pathogenic mechanism of LQT2. In this report, we characterize a hERG splice site mutation, 2592+1G>A, which occurs at the 5' splice site of intron 10. Reverse transcription-PCR analyses using hERG minigenes transfected into human embryonic kidney-293 cells and HL-1 cardiomyocytes revealed that the 2592+1G>A mutation disrupted normal splicing and caused multiple splicing defects: the activation of cryptic splice sites within exon 10 and intron 10 and complete intron 10 retention. We performed functional and biochemical analyses of the major splice product, hERGΔ24, in which 24 amino acids within the cyclic nucleotide binding domain of the hERG channel COOH-terminus is deleted. Patch-clamp experiments revealed that the splice mutant did not generate hERG current. Western blot and immunostaining studies showed that mutant channels did not traffic to the cell surface. Coexpression of wild-type hERG and hERGΔ24 resulted in significant dominant-negative suppression of hERG current via the intracellular retention of the wild-type channels. Our results demonstrate that 2592+1G>A causes multiple splicing defects, consistent with the pathogenic mechanisms of long QT syndrome.
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Affiliation(s)
- Matthew R Stump
- Division of Cardiovascular Medicine, Department of Medicine, Oregon Health and Science University, Portland, Oregon 97239, USA
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22
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Schulze-Bahr E. Making sense in a nonsense reading frame: suppression of cardiac sodium channel dysfunction. Cardiovasc Res 2009; 83:423-4. [PMID: 19528082 DOI: 10.1093/cvr/cvp196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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23
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Chen J, Sroubek J, Krishnan Y, Li Y, Bian J, McDonald TV. PKA phosphorylation of HERG protein regulates the rate of channel synthesis. Am J Physiol Heart Circ Physiol 2009; 296:H1244-54. [PMID: 19234087 DOI: 10.1152/ajpheart.01252.2008] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Acute changes in cAMP and protein kinase A (PKA) signaling can regulate ion channel protein activities such as gating. Effects on channels due to chronic PKA signaling, as in stress or disease states, are less understood. We examined the effects of prolonged PKA activity on the human ether-a-go-go-related gene (HERG) K(+) channel in stably transfected human embryonic kidney (HEK)293 cells. Sustained elevation of cAMP by either chlorophenylthiol (CPT)-cAMP or forskolin increased the HERG channel protein abundance two- to fourfold within 24 h, with measurable difference as early as 4 h. The cAMP-induced augmentation was not due to changes in transcription and was specific for HERG compared with other cardiac K(+) channels (Kv1.4, Kv1.5, Kir2.1, and KvLQT1). PKA activity was necessary for the effect on HERG protein and did not involve other cAMP signaling pathways. Direct PKA phosphorylation of the HERG protein was responsible for the cAMP-induced augmentation. Enhanced abundance of HERG protein was detected in endoplasmic reticulum-enriched, Golgi, and plasma membrane without significant changes in trafficking rates or patterns. An increase in the K(+) current density carried by the HERG channel was also observed, but with a delay, suggesting that traffic to the surface is rate-limiting traffic. Acceleration of the HERG protein synthesis rate was the primary factor in the cAMP/PKA effect with lesser effects on protein stability. These results provide evidence for a novel mechanism whereby phosphorylation of a nascent protein dictates its rate of synthesis, resetting its steady-state abundance.
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Affiliation(s)
- Jian Chen
- Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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24
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Yao Y, Teng S, Li N, Zhang Y, Boyden PA, Pu J. Aminoglycoside antibiotics restore functional expression of truncated HERG channels produced by nonsense mutations. Heart Rhythm 2009; 6:553-60. [PMID: 19324319 DOI: 10.1016/j.hrthm.2009.01.017] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 01/11/2009] [Indexed: 11/17/2022]
Abstract
BACKGROUND Pharmacologic restoration of the trafficking defects of HERG missense mutations has been documented. However, whether correction of HERG nonsense mutations is possible is unknown. OBJECTIVE The purpose of this study was to investigate the effect of aminoglycoside antibiotics on the expression of nonsense mutants expected to produce truncated HERG channels. METHODS HERG channel and mutant currents were recorded by whole-cell patch clamp techniques. Pharmacologic rescue was applied by culturing the cells in 400 microg/mL G-418 or gentamicin for 24 hours. RESULTS Current densities were significantly reduced in cells expressing R1014X and W927X mutants compared to those of cells expressing wild-type (WT) HERG. R863X and E698X mutants failed to generate any typical HERG currents. Mean peak tail current density of R1014X mutant was significantly lower than that of WT (3.9 +/- 1.4 pA/pF, n = 8, vs 47.8 +/- 6.3 pA/pF, n = 12, P <.05) and increased to 12.7 +/- 3.3 pA/pF (n = 7, P <.05) and 18.3 +/- 3.7 pA/pF (n = 8, P <.05) after G-418 and gentamicin treatment. The voltage dependence of activation of R1014X was also restored after drug treatment. Furthermore, expression of full-length proteins for R1014X induced by drugs was detected by western blot and confocal imaging. Similar results were observed in W927X. For R863X and E698X, however, gentamicin treatment had no effect. In the cells cotransfected with WT/R1014X, gentamicin and G-418 demonstrated different results: gentamicin, but not G-418, increased the current density by 2.2-fold (n = 12, P <.05). CONCLUSION The study findings provide proof of principle that interventions designed to read through premature stop mutations may at least partially reverse the LQT2 phenotype in vitro.
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Affiliation(s)
- Yan Yao
- Center for Arrhythmia Diagnosis and Treatment, Cardiovascular Institute and Fu Wai Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China
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Amin AS, Herfst LJ, Delisle BP, Klemens CA, Rook MB, Bezzina CR, Underkofler HAS, Holzem KM, Ruijter JM, Tan HL, January CT, Wilde AAM. Fever-induced QTc prolongation and ventricular arrhythmias in individuals with type 2 congenital long QT syndrome. J Clin Invest 2008; 118:2552-61. [PMID: 18551196 DOI: 10.1172/jci35337] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Accepted: 05/07/2008] [Indexed: 11/17/2022] Open
Abstract
Type 2 congenital long QT syndrome (LQT-2) is linked to mutations in the human ether a-go-go-related gene (HERG) and is characterized by rate-corrected QT interval (QTc) prolongation, ventricular arrhythmias, syncope, and sudden death. Recognized triggers of these cardiac events include emotional and acoustic stimuli. Here we investigated the repeated occurrence of fever-induced polymorphic ventricular tachycardia and ventricular fibrillation in 2 LQT-2 patients with A558P missense mutation in HERG. ECG analysis showed increased QTc with fever in both patients. WT, A558P, and WT+A558P HERG were expressed heterologously in HEK293 cells and were studied using biochemical and electrophysiological techniques. A558P proteins showed a trafficking-deficient phenotype. WT+A558P coexpression caused a dominant-negative effect, selectively accelerated the rate of channel inactivation, and reduced the temperature-dependent increase in the WT current. Thus, the WT+A558P current did not increase to the same extent as the WT current, leading to larger current density differences at higher temperatures. A similar temperature-dependent phenotype was seen for coexpression of the trafficking-deficient LQT-2 F640V mutation. We postulate that the weak increase in the HERG current density in WT-mutant coassembled channels contributes to the development of QTc prolongation and arrhythmias at febrile temperatures and suggest that fever is a potential trigger of life-threatening arrhythmias in LQT-2 patients.
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Affiliation(s)
- Ahmad S Amin
- Heart Failure Research Center, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
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The G604S-hERG mutation alters the biophysical properties and exerts a dominant-negative effect on expression of hERG channels in HEK293 cells. Pflugers Arch 2008; 456:917-28. [DOI: 10.1007/s00424-008-0454-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2007] [Revised: 01/02/2008] [Accepted: 01/11/2008] [Indexed: 10/22/2022]
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Gong Q, Zhang L, Moss AJ, Vincent GM, Ackerman MJ, Robinson JC, Jones MA, Tester DJ, Zhou Z. A splice site mutation in hERG leads to cryptic splicing in human long QT syndrome. J Mol Cell Cardiol 2008; 44:502-9. [PMID: 18272172 DOI: 10.1016/j.yjmcc.2008.01.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2007] [Revised: 01/09/2008] [Accepted: 01/10/2008] [Indexed: 10/22/2022]
Abstract
Mutations in the human ether-a-go-go-related gene (hERG) cause type 2 long QT syndrome. In this study, we investigated the pathogenic mechanism of the hERG splice site mutation 2398+1G>C and the genotype-phenotype relationship of mutation carriers in three unrelated kindreds with long QT syndrome. The effect of 2398+1G>C on mRNA splicing was studied by analysis of RNA isolated from lymphocytes of index patients and using minigenes expressed in HEK293 cells and neonatal rat ventricular myocytes. RT-PCR analysis revealed that the 2398+1G>C mutation disrupted the normal splicing and activated a cryptic splice donor site in intron 9, leading to the inclusion of 54 nt of the intron 9 sequence in hERG mRNA. The cryptic splicing resulted in an in-frame insertion of 18 amino acids in the middle of the cyclic nucleotide binding domain. In patch clamp experiments the splice mutant did not generate hERG current. Western blot and immunostaining studies showed that the mutant expressed an immature form of hERG protein that failed to reach the plasma membrane. Coexpression of the mutant and wild-type channels led to a dominant negative suppression of wild-type channel function by intracellular retention of heteromeric channels. Our results demonstrate that 2398+1G>C activates a cryptic site and generates a full-length hERG protein with an insertion of 18 amino acids, which leads to a trafficking defect of the mutant channel.
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Affiliation(s)
- Qiuming Gong
- Division of Cardiovascular Medicine, Oregon Health and Science University, Portland, OR , USA
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28
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Abstract
Normal cardiac function requires an appropriate and regular beating rate (cardiac rhythm). When the heart rhythm is too fast or too slow, cardiac function can be impaired, with derangements that vary from mild symptoms to life-threatening complications. Irregularities, particularly those involving excessively fast or slow rates, constitute cardiac 'arrhythmias'. In the past, drug treatment of cardiac arrhythmias has proven difficult, both because of inadequate effectiveness and a risk of serious complications. However, a variety of recent advances have opened up exciting possibilities for the development of novel and superior approaches to arrhythmia therapy. This article will review recent progress and future prospects for treating two particularly important cardiac arrhythmias: atrial fibrillation and ventricular fibrillation.
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Affiliation(s)
- Stanley Nattel
- Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, 5000 Belanger Street, Montreal, Quebec, Canada H1T 1C8.
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Hoda JC, Zaghetto F, Singh A, Koschak A, Striessnig J. Effects of congenital stationary night blindness type 2 mutations R508Q and L1364H on Cav1.4 L-type Ca2+ channel function and expression. J Neurochem 2006; 96:1648-58. [PMID: 16476079 DOI: 10.1111/j.1471-4159.2006.03678.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
At least 48 mutations in the CACNA1F gene encoding retinal Ca(v)1.4 L-type Ca(2+) channels have been linked to X-linked recessive congenital stationary night blindness type 2 (CSNB2). A large number of these are missense mutations encoding full-length alpha1-subunits that can potentially form functional channels. We have previously shown that such missense mutations can confer their phenotype by different pathological mechanisms, such as complete lack of alpha1 subunit protein expression or dramatic changes in channel gating. Here we investigated the functional consequences of CSNB2 missense mutations R508Q and L1364H. We found no (R508Q) or only minor (L1364H) changes in the gating properties of both mutants after heterologous expression in Xenopus laevis oocytes (at 20 degrees C). However, both mutants resulted in altered expression density of Ca(v)1.4 currents. When expressed in the mammalian cell line tsA-201, the current amplitude of L1364H channels was reduced when cells were grown at 30 degrees C and both mutations affected total alpha1 protein expression. This effect was temperature dependent. Our data provide evidence that, in contrast to previously characterized CSNB2 missense mutations, the clinical phenotype of R508Q and L1364H is unlikely to be explained by changes in channel gating. Instead, these mutations affect the protein expression of Ca(v)1.4 Ca(2+) channels.
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Affiliation(s)
- Jean-Charles Hoda
- Abteilung Pharmakologie und Toxikologie, Institut für Pharmazie, Universität Innsbruck, Innsbruck, Austria
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30
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Roepke TK, Abbott GW. Pharmacogenetics and cardiac ion channels. Vascul Pharmacol 2006; 44:90-106. [PMID: 16344000 DOI: 10.1016/j.vph.2005.07.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 07/01/2005] [Indexed: 12/19/2022]
Abstract
Ion channels control electrical excitability in living cells. In mammalian heart, the opposing actions of Na(+) and Ca(2+) ion influx, and K(+) ion efflux, through cardiac ion channels determine the morphology and duration of action potentials in cardiac myocytes, thus controlling the heartbeat. The last decade has seen a leap in our understanding of the molecular genetic origins of inherited cardiac arrhythmia, largely through identification of mutations in cardiac ion channels and the proteins that regulate them. Further, recent advances have shown that 'acquired arrhythmias', which occur more commonly than inherited arrhythmias, arise due to a variety of environmental factors including side effects of therapeutic drugs and often have a significant genetic component. Here, we review the pharmacogenetics of cardiac ion channels-the interplay between genetic and pharmacological factors that underlie human cardiac arrhythmias.
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Affiliation(s)
- Torsten K Roepke
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, 520 East 70th Street, New York, NY 10021, USA
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Gong Q, Jones MA, Zhou Z. Mechanisms of pharmacological rescue of trafficking-defective hERG mutant channels in human long QT syndrome. J Biol Chem 2005; 281:4069-74. [PMID: 16361248 PMCID: PMC1624912 DOI: 10.1074/jbc.m511765200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Long QT syndrome type 2 is caused by mutations in the human ether-a-go-go-related gene (hERG). We previously reported that the N470D mutation is retained in the endoplasmic reticulum (ER) but can be rescued to the plasma membrane by hERG channel blocker E-4031. The mechanisms of ER retention and how E-4031 rescues the N470D mutant are poorly understood. In this study, we investigated the interaction of hERG channels with the ER chaperone protein calnexin. Using coimmunoprecipitation, we showed that the immature forms of both wild type hERG and N470D associated with calnexin. The association required N-linked glycosylation of hERG channels. Pulse-chase analysis revealed that N470D had a prolonged association with calnexin compared with wild type hERG and E-4031 shortened the time course of calnexin association with N470D. To test whether the prolonged association of N470D with calnexin is due to defective folding of mutant channels, we studied hERG channel folding using the trypsin digestion method. We found that N470D and the immature form of wild type hERG were more sensitive to trypsin digestion than the mature form of wild type hERG. In the presence of E-4031, N470D became more resistant to trypsin even when its ER-to-Golgi transport was blocked by brefeldin A. These results suggest that defective folding of N470D contributes to its prolonged association with calnexin and ER retention and that E-4031 may restore proper folding of the N470D channel leading to its cell surface expression.
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Affiliation(s)
- Qiuming Gong
- Division of Cardiovascular Medicine, Department of Medicine, Oregon Health & Science University, Portland, 97239, USA
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32
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Abstract
Long QT syndrome, a rare genetic disorder associated with life-threatening arrhythmias, has provided a wealth of information about fundamental mechanisms underlying human cardiac electrophysiology that has come about because of truly collaborative interactions between clinical and basic scientists. Our understanding of the mechanisms that control the critical plateau and repolarization phases of the human ventricular action potential has been raised to new levels through these studies, which have clarified the manner in which both potassium and sodium channels regulate this critical period of electrical activity.
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Affiliation(s)
- Arthur J Moss
- Heart Research Follow-up Program, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
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