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Park NK, Park SJ, Park YG, Moon SH, Woo J, Kim HJ, Kim SJ, Choi SW. Translation reinitiation in c.453delC frameshift mutation of KCNH2 producing functional hERG K+ channels with mild dominant negative effect in the heterozygote patient-derived iPSC cardiomyocytes. Hum Mol Genet 2024; 33:110-121. [PMID: 37769355 DOI: 10.1093/hmg/ddad165] [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: 03/16/2023] [Revised: 08/16/2023] [Accepted: 09/25/2023] [Indexed: 09/30/2023] Open
Abstract
The c.453delC (p.Thr152Profs*14) frameshift mutation in KCNH2 is associated with an elevated risk of Long QT syndrome (LQTS) and fatal arrhythmia. Nevertheless, the loss-of-function mechanism underlying this mutation remains unexplored and necessitates an understanding of electrophysiology. To gain insight into the mechanism of the LQT phenotype, we conducted whole-cell patch-clamp and immunoblot assays, utilizing both a heterologous expression system and patient-derived induced pluripotent stem cell-cardiomyocytes (iPSC-CMs) with 453delC-KCNH2. We also explored the site of translational reinitiation by employing LC/MS mass spectrometry. Contrary to the previous assumption of early termination of translation, the findings of this study indicate that the 453delC-KCNH2 leads to an N-terminally truncated hERG channel, a potential from a non-canonical start codon, with diminished expression and reduced current (IhERG). The co-expression with wildtype KCNH2 produced heteromeric hERG channel with mild dominant-negative effect. Additionally, the heterozygote patient-derived iPSC-CMs exhibited prolonged action potential duration and reduced IhERG, which was ameliorated with the use of a hERG activator, PD-118057. The results of our study offer novel insights into the mechanisms involved in congenital LQTS associated with the 453delC mutation of KCNH2. The mutant results in the formation of less functional N-terminal-truncated channels with reduced amount of membrane expression. A hERG activator is capable of correcting abnormalities in both the heterologous expression system and patient-derived iPSC-CMs.
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Affiliation(s)
- Na Kyeong Park
- Department of Physiology, Seoul National University College of Medicine, 103, Daehak-ro, Seoul 03080, Korea
| | - Soon-Jung Park
- Stem Cell Research Institute, T&R Biofab Co. Ltd, 237, Sangidaehak-ro, Siheung 15073, Korea
| | - Yun-Gwi Park
- Department of Animal Science and Technology, Chung-Ang University, 4726, Seodong-daero, Anseong 17546, Korea
| | - Sung-Hwan Moon
- Department of Animal Science and Technology, Chung-Ang University, 4726, Seodong-daero, Anseong 17546, Korea
| | - JooHan Woo
- Department of Physiology, Dongguk University College of Medicine, 123, Dongdae-ro, Gyeongju 38066, Korea
| | - Hyun Jong Kim
- Department of Physiology, Dongguk University College of Medicine, 123, Dongdae-ro, Gyeongju 38066, Korea
| | - Sung Joon Kim
- Department of Physiology, Seoul National University College of Medicine, 103, Daehak-ro, Seoul 03080, Korea
- Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, 103, Daehak-ro, Seoul 03080, Korea
| | - Seong Woo Choi
- Department of Physiology, Dongguk University College of Medicine, 123, Dongdae-ro, Gyeongju 38066, Korea
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Usuda K, Hayashi K, Nakajima T, Kurata Y, Cui S, Kusayama T, Tsuda T, Tada H, Kato T, Sakata K, Usui S, Fujino N, Tanaka Y, Kaneko Y, Kurabayashi M, Tange S, Saito T, Ohta K, Yamagishi M, Takamura M. Mechanisms of fever-induced QT prolongation and torsades de pointes in patients with KCNH2 mutation. Europace 2023; 25:euad161. [PMID: 37386841 PMCID: PMC10310978 DOI: 10.1093/europace/euad161] [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: 11/24/2022] [Accepted: 05/13/2023] [Indexed: 07/01/2023] Open
Abstract
AIMS Patients with particular mutations of type-2 long QT syndrome (LQT2) are at an increased risk for malignant arrhythmia during fever. This study aimed to determine the mechanism by which KCNH2 mutations cause fever-induced QT prolongation and torsades de pointes (TdP). METHODS AND RESULTS We evaluated three KCNH2 mutations, G584S, D609G, and T613M, in the Kv11.1 S5-pore region, identified in patients with marked QT prolongation and TdP during fever. We also evaluated KCNH2 M124T and R269W, which are not associated with fever-induced QT prolongation. We characterized the temperature-dependent changes in the electrophysiological properties of the mutant Kv11.1 channels by patch-clamp recording and computer simulation. The average tail current densities (TCDs) at 35°C for G584S, WT+D609G, and WT+T613M were significantly smaller and less increased with rising temperature from 35°C to 40°C than those for WT, M124T, and R269W. The ratios of the TCDs at 40°C to 35°C for G584S, WT+D609G, and WT+T613M were significantly smaller than for WT, M124T, and R269W. The voltage dependence of the steady-state inactivation curve for WT, M124T, and R269W showed a significant positive shift with increasing temperature; however, that for G584S, WT+D609G, and WT+T613M showed no significant change. Computer simulation demonstrated that G584S, WT+D609G, and WT+T613M caused prolonged action potential durations and early afterdepolarization formation at 40°C. CONCLUSION These findings indicate that KCNH2 G584S, D609G, and T613M in the S5-pore region reduce the temperature-dependent increase in TCDs through an enhanced inactivation, resulting in QT prolongation and TdP at a febrile state in patients with LQT2.
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Affiliation(s)
- Keisuke Usuda
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Kenshi Hayashi
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Tadashi Nakajima
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Yasutaka Kurata
- Department of Physiology, Kanazawa Medical University, Uchinada, Japan
| | - Shihe Cui
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Takashi Kusayama
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Toyonobu Tsuda
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Hayato Tada
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Takeshi Kato
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Kenji Sakata
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Soichiro Usui
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Noboru Fujino
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
| | - Yoshihiro Tanaka
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
- Department of Preventive Medicine Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
| | - Yoshiaki Kaneko
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Masahiko Kurabayashi
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Shoichi Tange
- Department of Cardiovascular Medicine, Maebashi Red Cross Hospital, Maebashi, Japan
| | - Takekatsu Saito
- Department of Pediatrics, Kanazawa University, Kanazawa, Japan
| | - Kunio Ohta
- Department of Pediatrics, Kanazawa University, Kanazawa, Japan
| | | | - Masayuki Takamura
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, 13-1, Takara-machi, Kanazawa Ishikawa 920-8641, Japan
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Ledford HA, Ren L, Thai PN, Park S, Timofeyev V, Sirish P, Xu W, Emigh AM, Priest JR, Perez MV, Ashley EA, Yarov-Yarovoy V, Yamoah EN, Zhang XD, Chiamvimonvat N. Disruption of protein quality control of the human ether-à-go-go related gene K + channel results in profound long QT syndrome. Heart Rhythm 2021; 19:281-292. [PMID: 34634443 DOI: 10.1016/j.hrthm.2021.10.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 09/20/2021] [Accepted: 10/04/2021] [Indexed: 11/04/2022]
Abstract
BACKGROUND Long QT syndrome (LQTS) is a hereditary disease that predisposes patients to life-threatening cardiac arrhythmias and sudden cardiac death. Our previous study of the human ether-à-go-go related gene (hERG)-encoded K+ channel (Kv11.1) supports an association between hERG and RING finger protein 207 (RNF207) variants in aggravating the onset and severity of LQTS, specifically T613M hERG (hERGT613M) and RNF207 frameshift (RNF207G603fs) mutations. However, the underlying mechanistic underpinning remains unknown. OBJECTIVE The purpose of the present study was to test the role of RNF207 in the function of hERG-encoded K+ channel subunits. METHODS Whole-cell patch-clamp experiments were performed in human embryonic kidney (HEK 293) cells and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) together with immunofluorescent confocal and high resolution microscopy, auto-ubiquitinylation assays, and co-immunoprecipitation experiments to test the functional interactions between hERG and RNF207. RESULTS Here, we demonstrated that RNF207 serves as an E3 ubiquitin ligase and targets misfolded hERGT613M proteins for degradation. RNF207G603fs exhibits decreased activity and hinders the normal degradation pathway; this increases the levels of hERGT613M subunits and their dominant-negative effect on the wild-type subunits, ultimately resulting in decreased current density. Similar findings are shown for hERGA614V, a known dominant-negative mutant subunit. Finally, the presence of RNF207G603fs with hERGT613M results in significantly prolonged action potential durations and reduced hERG current in human-induced pluripotent stem cell-derived cardiomyocytes. CONCLUSION Our study establishes RNF207 as an interacting protein serving as a ubiquitin ligase for hERG-encoded K+ channel subunits. Normal function of RNF207 is critical for the quality control of hERG subunits and consequently cardiac repolarization. Moreover, our study provides evidence for protein quality control as a new paradigm in life-threatening cardiac arrhythmias in patients with LQTS.
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Affiliation(s)
- Hannah A Ledford
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California
| | - Lu Ren
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California
| | - Phung N Thai
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California
| | - Seojin Park
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California; Department of Physiology and Cell Biology, University of Nevada, Reno, Reno, Nevada
| | - Valeriy Timofeyev
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California
| | - Padmini Sirish
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California; Department of Veterans Affairs, Northern California Health Care System, Mather, California
| | - Wilson Xu
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California
| | - Aiyana M Emigh
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, California
| | - James R Priest
- Division of Cardiovascular Medicine, Department of Medicine, Stanford University, Stanford, California
| | - Marco V Perez
- Division of Cardiovascular Medicine, Department of Medicine, Stanford University, Stanford, California
| | - Euan A Ashley
- Division of Cardiovascular Medicine, Department of Medicine, Stanford University, Stanford, California
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, California
| | - Ebenezer N Yamoah
- Department of Physiology and Cell Biology, University of Nevada, Reno, Reno, Nevada
| | - Xiao-Dong Zhang
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California; Department of Veterans Affairs, Northern California Health Care System, Mather, California
| | - Nipavan Chiamvimonvat
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, Davis, California; Department of Veterans Affairs, Northern California Health Care System, Mather, California.
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Folding and misfolding of potassium channel monomers during assembly and tetramerization. Proc Natl Acad Sci U S A 2021; 118:2103674118. [PMID: 34413192 DOI: 10.1073/pnas.2103674118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics and folding of potassium channel pore domain monomers are connected to the kinetics of tetramer assembly. In all-atom molecular dynamics simulations of Kv1.2 and KcsA channels, monomers adopt multiple nonnative conformations while the three helices remain folded. Consistent with this picture, NMR studies also find the monomers to be dynamic and structurally heterogeneous. However, a KcsA construct with a disulfide bridge engineered between the two transmembrane helices has an NMR spectrum with well-dispersed peaks, suggesting that the monomer can be locked into a native-like conformation that is similar to that observed in the folded tetramer. During tetramerization, fluoresence resonance energy transfer (FRET) data indicate that monomers rapidly oligomerize upon insertion into liposomes, likely forming a protein-dense region. Folding within this region occurs along separate fast and slow routes, with τfold ∼40 and 1,500 s, respectively. In contrast, constructs bearing the disulfide bond mainly fold via the faster pathway, suggesting that maintaining the transmembrane helices in their native orientation reduces misfolding. Interestingly, folding is concentration independent despite the tetrameric nature of the channel, indicating that the rate-limiting step is unimolecular and occurs after monomer association in the protein-dense region. We propose that the rapid formation of protein-dense regions may help with the assembly of multimeric membrane proteins by bringing together the nascent components prior to assembly. Finally, despite its name, the addition of KcsA's C-terminal "tetramerization" domain does not hasten the kinetics of tetramerization.
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Xu B, Li K, Liu F, Kong L, Yang J, Zhou B, Lv T, Liu Y, She F, He R, Zhang P. Mexiletine Shortened QT Interval and Reduced Ventricular Arrhythmias in a Pedigree of Type 2 Long QT Syndrome Combined with Left Ventricular Non-Compaction. Int Heart J 2021; 62:427-431. [PMID: 33731522 DOI: 10.1536/ihj.20-518] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In this study, we present a case of a 22-year-old female with a family history of syncope, suffering from recurrent syncope since childhood. She had an obvious prolonged QTc interval of up to 651 ms, a bifid T wave pattern on electrocardiogram, and torsade de pointes, corresponding to a syncope episode. Additionally, her echocardiogram showed left ventricular non-compaction in the apex. After treatment with mexiletine, the QTc interval has been observed to shorten immediately, and the T wave morphology recovered. A similar effect was also observed in her mother and young sister. Administration of propranolol prolonged her QTc interval. Target sequencing of candidate genes revealed a missense mutation in the pore area of the hERG protein, coded by KCNH2. We diagnosed this as a case of type 2 long QT syndrome in which mexiletine could be effective in shortening the QTc interval.
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Affiliation(s)
- Bihe Xu
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University.,School of Medicine, Tsinghua University
| | - Kun Li
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Fang Liu
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Lingyun Kong
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Jing Yang
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Boda Zhou
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Tingting Lv
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University.,School of Medicine, Tsinghua University
| | - Yuanwei Liu
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Fei She
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Rong He
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University
| | - Ping Zhang
- Department of Cardiology, Beijing Tsinghua Changgung Hospital, School of Clinical Medicine, Tsinghua University.,School of Medicine, Tsinghua University
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High-throughput phenotyping of heteromeric human ether-à-go-go-related gene potassium channel variants can discriminate pathogenic from rare benign variants. Heart Rhythm 2020; 17:492-500. [DOI: 10.1016/j.hrthm.2019.09.020] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Indexed: 12/19/2022]
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7
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Perissinotti L, Guo J, Kudaibergenova M, Lees-Miller J, Ol'khovich M, Sharapova A, Perlovich GL, Muruve DA, Gerull B, Noskov SY, Duff HJ. The Pore-Lipid Interface: Role of Amino-Acid Determinants of Lipophilic Access by Ivabradine to the hERG1 Pore Domain. Mol Pharmacol 2019; 96:259-271. [PMID: 31182542 DOI: 10.1124/mol.118.115642] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 05/28/2019] [Indexed: 12/14/2022] Open
Abstract
Abnormal cardiac electrical activity is a common side effect caused by unintended block of the promiscuous drug target human ether-à-go-go-related gene (hERG1), the pore-forming domain of the delayed rectifier K+ channel in the heart. hERG1 block leads to a prolongation of the QT interval, a phase of the cardiac cycle that underlies myocyte repolarization detectable on the electrocardiogram. Even newly released drugs such as heart-rate lowering agent ivabradine block the rapid delayed rectifier current IKr, prolong action potential duration, and induce potentially lethal arrhythmia known as torsades de pointes. In this study, we describe a critical drug-binding pocket located at the lateral pore surface facing the cellular membrane. Mutations of the conserved M651 residue alter ivabradine-induced block but not by the common hERG1 blocker dofetilide. As revealed by molecular dynamics simulations, binding of ivabradine to a lipophilic pore access site is coupled to a state-dependent reorientation of aromatic residues F557 and F656 in the S5 and S6 helices. We show that the M651 mutation impedes state-dependent dynamics of F557 and F656 aromatic cassettes at the protein-lipid interface, which has a potential to disrupt drug-induced block of the channel. This fundamentally new mechanism coupling the channel dynamics and small-molecule access from the membrane into the hERG1 intracavitary site provides a simple rationale for the well established state-dependence of drug blockade. SIGNIFICANCE STATEMENT: The drug interference with the function of the cardiac hERG channels represents one of the major sources of drug-induced heart disturbances. We found a novel and a critical drug-binding pocket adjacent to a lipid-facing surface of the hERG1 channel, which furthers our molecular understanding of drug-induced QT syndrome.
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Affiliation(s)
- Laura Perissinotti
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Jiqing Guo
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Meruyert Kudaibergenova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - James Lees-Miller
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Marina Ol'khovich
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Angelica Sharapova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - German L Perlovich
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Daniel A Muruve
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Brenda Gerull
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Sergei Yu Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
| | - Henry J Duff
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada (L.P., M.K., S.Y.N.); Libin Cardiovascular Institute of Alberta (J.G., J.-L.M., H.J.D.) and Snyder Institute for Chronic Diseases (D.A.M.), Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russian Federation (M.O., A.S., G.L.P.); Department of Cardiac Sciences and Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada (B.G.); and Comprehensive Heart Failure Center and Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany (B.G.)
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Bohnen MS, Peng G, Robey SH, Terrenoire C, Iyer V, Sampson KJ, Kass RS. Molecular Pathophysiology of Congenital Long QT Syndrome. Physiol Rev 2017; 97:89-134. [PMID: 27807201 PMCID: PMC5539372 DOI: 10.1152/physrev.00008.2016] [Citation(s) in RCA: 113] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Ion channels represent the molecular entities that give rise to the cardiac action potential, the fundamental cellular electrical event in the heart. The concerted function of these channels leads to normal cyclical excitation and resultant contraction of cardiac muscle. Research into cardiac ion channel regulation and mutations that underlie disease pathogenesis has greatly enhanced our knowledge of the causes and clinical management of cardiac arrhythmia. Here we review the molecular determinants, pathogenesis, and pharmacology of congenital Long QT Syndrome. We examine mechanisms of dysfunction associated with three critical cardiac currents that comprise the majority of congenital Long QT Syndrome cases: 1) IKs, the slow delayed rectifier current; 2) IKr, the rapid delayed rectifier current; and 3) INa, the voltage-dependent sodium current. Less common subtypes of congenital Long QT Syndrome affect other cardiac ionic currents that contribute to the dynamic nature of cardiac electrophysiology. Through the study of mutations that cause congenital Long QT Syndrome, the scientific community has advanced understanding of ion channel structure-function relationships, physiology, and pharmacological response to clinically employed and experimental pharmacological agents. Our understanding of congenital Long QT Syndrome continues to evolve rapidly and with great benefits: genotype-driven clinical management of the disease has improved patient care as precision medicine becomes even more a reality.
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Affiliation(s)
- M S Bohnen
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - G Peng
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - S H Robey
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - C Terrenoire
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - V Iyer
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - K J Sampson
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - R S Kass
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
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9
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Ramakrishna H, O’Hare M, Mookadam F, Gutsche JT, Shah R, Augoustides JG. Sudden Cardiac Death and Disorders of the QT Interval: Anesthetic Implications and Focus on Perioperative Management. J Cardiothorac Vasc Anesth 2015; 29:1723-33. [DOI: 10.1053/j.jvca.2015.07.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Indexed: 12/19/2022]
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POULSEN KRISTIANL, HOTAIT MOSTAFA, CALLOE KIRSTINE, KLAERKE DANA, REBEIZ ABDALLAH, NEMER GEORGES, TEJADA MARIAA, REFAAT MARWANM. The Mutation P.T613a in the Pore Helix of the Kv11.1 Potassium Channel is Associated with Long QT Syndrome. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2015; 38:1304-9. [DOI: 10.1111/pace.12693] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 06/15/2015] [Accepted: 06/28/2015] [Indexed: 11/30/2022]
Affiliation(s)
- KRISTIAN L. POULSEN
- Department of Veterinary Clinical and Animal Science; University of Copenhagen; Frederiksberg C Denmark
| | - MOSTAFA HOTAIT
- Cardiology Division, Department of Internal Medicine; American University of Beirut; Beirut Lebanon
| | - KIRSTINE CALLOE
- Department of Veterinary Clinical and Animal Science; University of Copenhagen; Frederiksberg C Denmark
| | - DAN A. KLAERKE
- Department of Veterinary Clinical and Animal Science; University of Copenhagen; Frederiksberg C Denmark
| | - ABDALLAH REBEIZ
- Cardiology Division, Department of Internal Medicine; American University of Beirut; Beirut Lebanon
| | - GEORGES NEMER
- Department of Biochemistry and Molecular Genetics; American University of Beirut; Beirut Lebanon
| | - MARIA A. TEJADA
- Department of Veterinary Clinical and Animal Science; University of Copenhagen; Frederiksberg C Denmark
| | - MARWAN M. REFAAT
- Cardiology Division, Department of Internal Medicine; American University of Beirut; Beirut Lebanon
- Department of Biochemistry and Molecular Genetics; American University of Beirut; Beirut Lebanon
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Sahu ID, Kroncke BM, Zhang R, Dunagan MM, Smith HJ, Craig A, McCarrick RM, Sanders CR, Lorigan GA. Structural investigation of the transmembrane domain of KCNE1 in proteoliposomes. Biochemistry 2014; 53:6392-401. [PMID: 25234231 PMCID: PMC4196734 DOI: 10.1021/bi500943p] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
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KCNE1 is a single-transmembrane protein
of the KCNE family that modulates the function of voltage-gated potassium
channels, including KCNQ1. Hereditary mutations in KCNE1 have been
linked to diseases such as long QT syndrome (LQTS), atrial fibrillation,
sudden infant death syndrome, and deafness. The transmembrane domain
(TMD) of KCNE1 plays a key role in mediating the physical association
with KCNQ1 and in subsequent modulation of channel gating kinetics
and conductance. However, the mechanisms associated with these roles
for the TMD remain poorly understood, highlighting a need for experimental
structural studies. A previous solution NMR study of KCNE1 in LMPG
micelles revealed a curved transmembrane domain, a structural feature
proposed to be critical to KCNE1 function. However, this curvature
potentially reflects an artifact of working in detergent micelles.
Double electron electron resonance (DEER) measurements were conducted
on KCNE1 in LMPG micelles, POPC/POPG proteoliposomes, and POPC/POPG
lipodisq nanoparticles to directly compare the structure of the TMD
in a variety of different membrane environments. Experimentally derived
DEER distances coupled with simulated annealing molecular dynamic
simulations were used to probe the bilayer structure of the TMD of
KCNE1. The results indicate that the structure is helical in proteoliposomes
and is slightly curved, which is consistent with the previously determined
solution NMR structure in micelles. The evident resilience of the
curvature in the KCNE1 TMD leads us to hypothesize that the curvature
is likely to be maintained upon binding of the protein to the KCNQ1
channel.
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Affiliation(s)
- Indra D Sahu
- Department of Chemistry and Biochemistry, Miami University , Oxford, Ohio 45056, United States
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12
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Abstract
Many ion channels, both selective and nonselective, have reentrant pore loops that contribute to the architecture of the permeation pathway. It is a fundamental feature of these diverse channels, regardless of whether they are gated by changes of membrane potential or by neurotransmitters, and is critical to function of the channel. Misfolding of the pore loop leads to loss of trafficking and expression of these channels on the cell surface. Mature tetrameric potassium channels contain an α-helix within the pore loop. We systematically mutated the "pore helix" residues of the channel Kv1.3 and assessed the ability of the monomer to fold into a tertiary reentrant loop. Our results show that pore loop residues form a canonical α-helix in the monomer early in biogenesis and that disruption of tertiary folding is caused by hydrophilic substitutions only along one face of this α-helix. These results provide insight into the determinants of the reentrant pore conformation, which is essential for ion channel function.
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13
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Pakladok T, Hosseinzadeh Z, Almilaji A, Lebedeva A, Shumilina E, Alesutan I, Lang F. Up-regulation of hERG K⁺ channels by B-RAF. PLoS One 2014; 9:e87457. [PMID: 24475291 PMCID: PMC3903650 DOI: 10.1371/journal.pone.0087457] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 12/26/2013] [Indexed: 11/19/2022] Open
Abstract
Human ether-a-go-go related-gene K⁺ channels (hERG) participate in the regulation of tumor cell proliferation and apoptosis. HERG channel activity is up-regulated by growth factors. Kinases sensitive to growth factor signaling include the serine/threonine protein kinase B-RAF. The present study thus explored whether B-RAF influences hERG channel expression and activity. To this end, hERG channels were expressed in Xenopus oocytes with or without wild-type B-RAF, hERG channel activity was determined utilizing dual-electrode voltage clamp and hERG protein abundance in the cell membrane was analyzed utilizing confocal microscopy as well as chemiluminescence. Moreover, in rhabdomyosarcoma RD cells the effect of B-RAF inhibitor PLX-4720 on hERG-mediated current was quantified by whole-cell patch clamp and hERG cell surface protein abundance by utilizing biotinylation of cell surface proteins as well as flow cytometry. As a result, co-expression of wild-type B-RAF in hERG-expressing Xenopus oocytes significantly increased hERG channel activity and hERG channel protein abundance in the cell membrane. Treatment for 24 hours of B-RAF and hERG-expressing Xenopus oocytes with B-RAF inhibitor PLX-4720 (10 µM) significantly decreased hERG-mediated current and hERG cell surface expression. Similarly, in rhabdomyosarcoma RD cells, treatment for 24 hours with B-RAF inhibitor PLX-4720 significantly decreased hERG cell membrane protein abundance and hERG-mediated current. In conclusion, B-RAF is a powerful regulator of hERG channel activity and cell surface hERG protein abundance.
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Affiliation(s)
| | | | - Ahmad Almilaji
- Department of Physiology, University of Tübingen, Tübingen, Germany
| | - Aleksandra Lebedeva
- Department of Physiology, University of Tübingen, Tübingen, Germany
- Department of Immunology, Institute of Experimental Medicine, St. Petersburg, Russia
| | | | - Ioana Alesutan
- Department of Physiology, University of Tübingen, Tübingen, Germany
| | - Florian Lang
- Department of Physiology, University of Tübingen, Tübingen, Germany
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Transmembrane segments form tertiary hairpins in the folding vestibule of the ribosome. J Mol Biol 2013; 426:185-98. [PMID: 24055377 DOI: 10.1016/j.jmb.2013.09.013] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 08/30/2013] [Accepted: 09/11/2013] [Indexed: 11/21/2022]
Abstract
Folding of membrane proteins begins in the ribosome as the peptide is elongated. During this process, the nascent peptide navigates along 100Å of tunnel from the peptidyltransferase center to the exit port. Proximal to the exit port is a "folding vestibule" that permits the nascent peptide to compact and explore conformational space for potential tertiary folding partners. The latter occurs for cytosolic subdomains but has not yet been shown for transmembrane segments. We now demonstrate, using an accessibility assay and an improved intramolecular crosslinking assay, that the helical transmembrane S3b-S4 hairpin ("paddle") of a voltage-gated potassium (Kv) channel, a critical region of the Kv voltage sensor, forms in the vestibule. S3-S4 hairpin interactions are detected at an early stage of Kv biogenesis. Moreover, this vestibule hairpin is consistent with a closed-state conformation of the Kv channel in the plasma membrane.
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15
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Biogenesis of the pore architecture of a voltage-gated potassium channel. Proc Natl Acad Sci U S A 2011; 108:3240-5. [PMID: 21300900 DOI: 10.1073/pnas.1017097108] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The pore domain of voltage-gated potassium (Kv) channels consists of transmembrane helices S5 and S6, the turret, the pore helix, the selectivity filter, and the loop preceding S6, with a tertiary reentrant structure between S5 and S6. Using biogenic intermediates, mass tagging (pegylation), and a molecular tape measure, we explored the possibility that the first stages of pore formation occur prior to oligomerization of the transmembrane core. Pegylation of introduced cysteines shows that the pore helix, but not the turret, forms a compact secondary structure in the terminal 20 Å of the ribosomal tunnel. We assessed the tertiary fold of the pore loop in monomeric constructs by determining the relative accessibilities of select cysteines using the kinetics of pegylation. Turret residues are accessible at the extracellular surface. In contrast, pore helix residues are less accessible. All-atom molecular dynamics simulations of a single Kv monomer in a solvated lipid membrane indicate that secondary and tertiary folds are stable over 650 ns. These results are consistent with acquisition of a tertiary reentrant pore architecture at the monomer stage of Kv biogenesis and begin to define a plausible sequence of folding events in the formation of Kv channels.
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Durdagi S, Duff HJ, Noskov SY. Combined Receptor and Ligand-Based Approach to the Universal Pharmacophore Model Development for Studies of Drug Blockade to the hERG1 Pore Domain. J Chem Inf Model 2011; 51:463-74. [DOI: 10.1021/ci100409y] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Serdar Durdagi
- Department of Biological Sciences, University of Calgary, Institute for Biocomplexity and Informatics Calgary, Alberta, Canada
| | - Henry J. Duff
- Faculty of Medicine, University of Calgary, Libin Cardiovascular Institute of Alberta, Calgary, Alberta, Canada
| | - Sergei Yu. Noskov
- Department of Biological Sciences, University of Calgary, Institute for Biocomplexity and Informatics Calgary, Alberta, Canada
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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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18
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Schmalhofer WA, Swensen AM, Thomas BS, Felix JP, Haedo RJ, Solly K, Kiss L, Kaczorowski GJ, Garcia ML. A Pharmacologically Validated, High-Capacity, Functional Thallium Flux Assay for the Human Ether-à-go-go Related Gene Potassium Channel. Assay Drug Dev Technol 2010; 8:714-26. [DOI: 10.1089/adt.2010.0351] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
| | - Andrew M. Swensen
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey
| | - Brande S. Thomas
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey
| | - John P. Felix
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey
| | - Rodolfo J. Haedo
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey
| | - Kelli Solly
- Department of Automated Biotechnology, Merck Research Laboratories, North Wales, Pennsylvania
| | - Laszlo Kiss
- Department of Automated Biotechnology, Merck Research Laboratories, North Wales, Pennsylvania
| | | | - Maria L. Garcia
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey
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Subbotina J, Yarov-Yarovoy V, Lees-Miller J, Durdagi S, Guo J, Duff HJ, Noskov SY. Structural refinement of the hERG1 pore and voltage-sensing domains with ROSETTA-membrane and molecular dynamics simulations. Proteins 2010; 78:2922-34. [PMID: 20740484 PMCID: PMC2939218 DOI: 10.1002/prot.22815] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The hERG1 gene (Kv11.1) encodes a voltage-gated potassium channel. Mutations in this gene lead to one form of the Long QT Syndrome (LQTS) in humans. Promiscuous binding of drugs to hERG1 is known to alter the structure/function of the channel leading to an acquired form of the LQTS. Expectably, creation and validation of reliable 3D model of the channel have been a key target in molecular cardiology and pharmacology for the last decade. Although many models were built, they all were limited to pore domain. In this work, a full model of the hERG1 channel is developed which includes all transmembrane segments. We tested a template-driven de-novo design with ROSETTA-membrane modeling using side-chain placements optimized by subsequent molecular dynamics (MD) simulations. Although backbone templates for the homology modeled parts of the pore and voltage sensors were based on the available structures of KvAP, Kv1.2 and Kv1.2-Kv2.1 chimera channels, the missing parts are modeled de-novo. The impact of several alignments on the structure of the S4 helix in the voltage-sensing domain was also tested. Herein, final models are evaluated for consistency to the reported structural elements discovered mainly on the basis of mutagenesis and electrophysiology. These structural elements include salt bridges and close contacts in the voltage-sensor domain; and the topology of the extracellular S5-pore linker compared with that established by toxin foot-printing and nuclear magnetic resonance studies. Implications of the refined hERG1 model to binding of blockers and channels activators (potent new ligands for channel activations) are discussed.
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Affiliation(s)
- Julia Subbotina
- Institute for Biocomplexity and Informatics, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | | | - James Lees-Miller
- Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Serdar Durdagi
- Institute for Biocomplexity and Informatics, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Jiqing Guo
- Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Henry J. Duff
- Libin Cardiovascular Institute of Alberta, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Sergei Yu. Noskov
- Institute for Biocomplexity and Informatics, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
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Lian J, Huang N, Zhou J, Ge S, Huang X, Huo J, Liu L, Xu W, Zhang S, Yang X, Zhou J, Huang C. Novel characteristics of a trafficking-defective G572R-hERG channel linked to hereditary long QT syndrome. Can J Cardiol 2010; 26:417-22. [PMID: 20931094 DOI: 10.1016/s0828-282x(10)70439-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND The congenital long QT syndrome is a heterogeneous genetic disease associated with delayed cardiac repolarization, prolonged QT intervals, the development of ventricular arrhythmias and sudden death. Type 2 congenital long QT syndrome (LQT2) results from KCNH2 or hERG gene mutations. hERG encodes the K(v)11.1 alpha subunit of the rapidly activating delayed rectifier K(+) current in the heart. Studies of mutant hERG channels indicate that most LQT2 missense mutations generate trafficking-deficient K(v)11.1 channels. OBJECTIVE To identify the mechanism underlying G572R-hERG by using molecular and electrophysiological analyses. METHODS AND RESULTS To elucidate the electrophysiological properties of the G572R-hERG mutant channels, mutant hERG subunits were heterologously expressed in HEK293 cells alone or in combination with wild-type (WT)-hERG subunits. Patch-clamp techniques were used to record currents, and double immunofluorescence protein tagging and Western blotting were performed to examine the cellular trafficking of mutant subunits. When expressed alone, G572R-hERG subunits were not present in the cell membrane and did not produce detectable currents. When coexpressed with WT-hERG subunits, G572R-hERG decreased current density and altered gating properties of the WT-hERG channel. CONCLUSION The hERG-associated missense mutation G572R, like most LQT2 missense mutations, generates a trafficking-deficient phenotype. Furthermore, G572R-hERG causes a loss of function in hERG by a strong dominant negative effect on the WT-hERG channel.
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Affiliation(s)
- Jiangfang Lian
- LiHuiLi Hospital, Medical School of Ningbo University, People's Republic of China
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Trigger-specific risk factors and response to therapy in long QT syndrome type 2. Heart Rhythm 2010; 7:1797-805. [PMID: 20850565 DOI: 10.1016/j.hrthm.2010.09.011] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2010] [Accepted: 09/10/2010] [Indexed: 11/22/2022]
Abstract
BACKGROUND Cardiac events in patients with long QT syndrome type 2 (LQT2) are predominately associated with sudden arousal. However, exercise-induced events also occur in this population. OBJECTIVE The purpose of this study was to test the hypothesis that risk factors show a trigger-specific association with cardiac events in LQT2 patients. METHODS The study population consisted of 634 genetically confirmed LQT2 patients from the U.S. portion of the International LQTS Registry. Multivariate Cox proportional hazards regression analysis was used to determine the independent contribution of clinical and genetic risk factors to the first occurrence of trigger-specific cardiac events, categorized as arousal, exercise-induced, and nonarousal/nonexercise, from birth through age 40 years. RESULTS Study patients experienced 204 cardiac events during follow-up, of which 44% were associated with arousal triggers, 13% with exercise activity, and 43% with nonexercise/nonarousal triggers. Risk factors for arousal-triggered cardiac events included gender (female:male > 13 years: hazard ratio [HR] 9.10, P < .001) and the presence of pore-loop mutations (HR 2.19, P = .009). In contrast, non-pore-loop transmembrane mutations were the predominant risk factor for exercise-triggered events (HR 6.84, P < .001), whereas gender was not a significant risk factor for this endpoint. Nonexercise/nonarousal events were associated with heterogeneous causes. Risk factors for this endpoint included gender, mutation location and type, and prolonged QTc (≥ 500 m) Beta-blocker therapy was associated with a pronounced reduction in the risk for exercise-triggered events (HR 0.29, P < .01) but had a nonsignificant effect on the risk for arousal and nonexercise/nonarousal events. CONCLUSION The study findings suggest that management of patients with the LQT2 genotype should use a trigger-specific approach to risk assessment and medical therapy.
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Nagaoka I, Shimizu W, Itoh H, Yamamoto S, Sakaguchi T, Oka Y, Tsuji K, Ashihara T, Ito M, Yoshida H, Ohno S, Makiyama T, Miyamoto Y, Noda T, Kamakura S, Akao M, Horie M. Mutation site dependent variability of cardiac events in Japanese LQT2 form of congenital long-QT syndrome. Circ J 2008; 72:694-9. [PMID: 18441445 DOI: 10.1253/circj.72.694] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND In the LQT2 form of long QT syndrome (LQTS), mutation sites are reported to correlate with clinical phenotypes in Caucasians, but the relationship in Asian patients remains unknown. The present study was designed to determine whether the location of KCNH2 mutations would influence the arrhythmic risk in LQT2 patients. METHODS AND RESULTS In 118 genetically-confirmed LQT2 patients (69 families, 62 KCNH2 mutations), the ECG parameters, Schwartz scores, and the incidence of cardiac events, defined as syncope, aborted cardiac arrest, and sudden cardiac death, were evaluated. To examine the effect of mutation sites, the participants were divided accordingly: pore (n=56) and non-pore (n=62) groups. The corrected QTend interval was significantly greater in the pore than in the non-pore group (QTc; 522+/-63 ms vs 490+/-49 ms, p=0.002). In this study, the clinical course of each of the probands did not differ according to the mutation sites, whereas non-probands carrying the pore site mutation experienced their first cardiac events at significantly younger age than those with the non-pore site mutation (log-rank, p=0.0005). CONCLUSIONS In a Japanese LQT2 cohort, family members with the pore site mutation were at higher arrhythmic risk than those with the non-pore site mutation.
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Affiliation(s)
- Iori Nagaoka
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
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23
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Reiner DJ, Weinshenker D, Tian H, Thomas JH, Nishiwaki K, Miwa J, Gruninger T, Leboeuf B, Garcia LR. Behavioral genetics of caenorhabditis elegans unc-103-encoded erg-like K(+) channel. J Neurogenet 2007; 20:41-66. [PMID: 16807195 DOI: 10.1080/01677060600788826] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The Caenorhabditis elegans unc-103 gene encodes a potassium channel whose sequence is most similar to the ether-a-go-go related gene (erg) type of K+ channels. We find that the n 500 and e 1597 gain-of-function (gf) mutations in unc-103 cause reduced excitation in most muscles, while loss-of-function (lf) mutations cause mild muscle hyper-excitability. Both gf alleles change the same residue near the cytoplasmic end of S6, consistent with this region regulating channel activation. We also report additional dominant-negative and lf alleles of unc-103 that can antagonize or reduce the function of both gf and wild-type alleles. The unc-103 locus contains 6 promoter regions that express unc-103 in different combinations of body-wall and sex-specific muscles, motor-, inter- and sensory-neurons. Each promoter drives transcripts containing a unique first exon, conferring sequence variability to the N-terminus of the UNC-103 protein, while three splice variants introduce variability into the UNC-103 C-terminus. unc-103(0) hermaphrodites prematurely lay embryos that would normally be retained in the uterus and lay eggs under conditions that inhibit egg-laying behavior. In the egg-laying circuit, unc-103 is expressed in vulval muscles and the HSN neurons from different promoters. Supplying the proper UNC-103 isoform to the vulval muscles is sufficient to restore regulation to egg-laying behavior.
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Affiliation(s)
- David J Reiner
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
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Maier G, Palmada M, Rajamanickam J, Shumilina E, Böhmer C, Lang F. Upregulation of HERG channels by the serum and glucocorticoid inducible kinase isoform SGK3. Cell Physiol Biochem 2007; 18:177-86. [PMID: 17167223 DOI: 10.1159/000097666] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/15/2006] [Indexed: 12/30/2022] Open
Abstract
Human ether-a-go-go (HERG) channels participate in the repolarization of the cardiac action potential. Loss of function mutations of HERG lead to delayed cardiac repolarization reflected by prolonged QT interval. HERG channels are regulated through a signaling cascade involving phosphatidylinositol 3 (PI3) kinase. Downstream targets of PI3 kinase include the serum and glucocorticoid inducible kinase (SGK) and protein kinase B (PKB) isoforms. The present study has been performed to explore whether SGK1 and SGK3 participate in the regulation of HERG channel activity. HERG was expressed in Xenopus oocytes with or without additional expression of SGK1 or SGK3. Chemiluminescence was employed to determine HERG plasma membrane protein abundance. Coexpression of SGK3 but not of SGK1 in Xenopus oocytes resulted in an increase of steady state current (I(HERG)) and enhanced cell membrane protein abundance without affecting gating kinetics of the channel. Replacement of serine by alanine at the two SGK consensus sites decreased I(HERG) but neither mutation abolished the stimulating effect of SGK3. In conclusion, SGK3 participates in the regulation of HERG by increasing HERG protein abundance in the plasma membrane and may thus modify the duration of the cardiac action potential.
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Affiliation(s)
- Gottlieb Maier
- Department of Physiology, University of Tübingen, Tübingen, Germany
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25
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Millat G, Chevalier P, Restier-Miron L, Da Costa A, Bouvagnet P, Kugener B, Fayol L, Gonzàlez Armengod C, Oddou B, Chanavat V, Froidefond E, Perraudin R, Rousson R, Rodriguez-Lafrasse C. Spectrum of pathogenic mutations and associated polymorphisms in a cohort of 44 unrelated patients with long QT syndrome. Clin Genet 2006; 70:214-27. [PMID: 16922724 DOI: 10.1111/j.1399-0004.2006.00671.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Long QT syndrome (LQTS) is a rare and clinically heterogeneous inherited disorder characterized by a long QT interval on the electrocardiogram, increased risk of syncope and sudden death caused by arrhythmias. This syndrome is mostly caused by mutations in genes encoding various cardiac ion channels. The clinical heterogeneity is usually attributed to variable penetrance. One of the reasons for this variability in expression could be the coexistence of common single nucleotide polymorphisms (SNPs) on LQTS-causing genes and/or unknown genes. Some synonymous and nonsynonymous exonic SNPs identified in LQTS-causing genes may have an effect on the cardiac repolarization process and modulate the clinical expression of a latent LQTS pathogenic mutation. We report the molecular pattern of 44 unrelated patients with LQTS using denaturing high-performance liquid chromatography analysis of the KCNQ1, KCNH2, SCN5A, KCNE1 and KCNE2 genes. Forty-five disease-causing mutations (including 24 novel ones) were identified in this cohort. Most of our patients (84%) showed complex molecular pattern with one mutation (and even two for four patients) associated with several SNPs located in several LQTS genes.
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Affiliation(s)
- G Millat
- Laboratoire de Biochimie et Biologie Moléculaire, Hopital CardioVasculaire et Pneumologique L Pradel, Bron, France, and Unidad de neonatología Servicio de pediatría, Hospital Universitario Río Hortega, Valladolid, Spain.
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26
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Fink M, Giles WR, Noble D. Contributions of inwardly rectifying K+ currents to repolarization assessed using mathematical models of human ventricular myocytes. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2006; 364:1207-22. [PMID: 16608704 DOI: 10.1098/rsta.2006.1765] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Repolarization of the action potential (AP) in cardiac muscle is a major determinant of refractoriness and excitability, and can also strongly modulate excitation-contraction coupling. In clinical cardiac electrophysiology, the Q-T interval, and hence action potential duration, is both an essential marker of normal function and an indicator of risk for arrhythmic events. It is now well known that the termination of the plateau phase of the AP and the repolarization waveform involve a complex interaction of transmembrane ionic currents. These include a slowly inactivating Na+ current, inactivating Ca2+ current, the decline of an electrogenic current due to Na+/Ca2+ exchange and activation of three or four different K+ currents. At present, many of the quantitative aspects of this important physiological and pathophysiological process remain incompletely understood. Recently, three mathematical models of the membrane AP in human ventricle myocyte have been developed and made available on the Internet. In this study, we have implemented these models for the purpose of comparing the K+ currents, which are responsible for terminating the plateau phase of the AP and generating its repolarization. In this paper, our emphasis is on the two highly nonlinear inwardly rectifying potassium currents, (IK1) and (IK,r). A more general goal is to obtain improved understanding of the ionic mechanisms, which underlie all-or-none repolarization and the parameter denoted 'repolarization reserve' in the human ventricle. Further, insights into these fundamental variables can be expected to provide a more rational basis for clinical assessment of the Q-T and Q-TC intervals, and hence provide insights into some of the very substantial efforts in safety pharmacology, which are based on these parameters.
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Affiliation(s)
- Martin Fink
- Department of Bioengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0412, USA
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27
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Yan GX, Lankipalli RS, Kowey PR. Current concepts in the management of long QT syndrome. Expert Opin Ther Pat 2005. [DOI: 10.1517/13543776.12.5.633] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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28
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Yamaguchi M, Shimizu M, Ino H, Terai H, Hayashi K, Kaneda T, Mabuchi H, Sumita R, Oshima T, Hoshi N, Higashida H. Compound heterozygosity for mutations Asp611→Tyr in KCNQ1 and Asp609→Gly in KCNH2 associated with severe long QT syndrome. Clin Sci (Lond) 2005; 108:143-50. [PMID: 15500450 DOI: 10.1042/cs20040220] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
LQTS (long QT syndrome) is an inherited cardiac disorder characterized by prolongation of QT interval, torsades de pointes and sudden death. We have identified two heterozygous missense mutations in the KCNQ1 and KCNH2 (also known as HERG) genes [Asp611→Tyr (D611Y) in KCNQ1 and Asp609→Gly (D609G) in KCNH2] in a 2-year-old boy with LQTS. The aim of the present study was to characterize the contributions of the mutations in the KCNQ1 and KCNH2 genes relative to the clinical manifestations and electrophysiological properties of LQTS. Six of 11 carriers of D611Y in KCNQ1 had long QT intervals. D609G in KCNH2 was detected only in the proband. Studies on the electrophysiological alterations due to the two missense mutations revealed that the D611Y mutation in KCNQ1 did not show a significant suppression of the currents compared with wild-type, but the time constants of current activation in the mutants were increased compared with that in the wild-type. In contrast, the D609G mutation in KCNH2 showed a dominant-negative suppression. Our results suggest that the mild phenotype produced by the D611Y mutation in KCNQ1 became more serious by addition of the D609G mutation in KCNH2 in the proband.
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Affiliation(s)
- Masato Yamaguchi
- Molecular Genetics of Cardiovascular Disorders, Division of Cardiovascular Medicine, Graduate School of Medical Science, Kanazawa University, Kanazawa 920-8640, Japan
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29
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Abstract
This article outlines the up-to-date understanding of the molecular basis of disorders that cause sudden death. Several arrhythmic disorders that cause sudden death have been well-described at the molecular level, including the long QT syndromes and Brugada syndrome; this article reviews the current scientific knowledge of these diseases. Hypertrophic cardiomyopathy, a myocardial disorder that causes sudden death also has been well-studied. Finally, a disorder in which myocardial abnormalities and rhythm abnormalities coexist, arrhythmogenic right ventricular dysplasia, is described.
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MESH Headings
- Arrhythmias, Cardiac/genetics
- Arrhythmias, Cardiac/physiopathology
- Arrhythmogenic Right Ventricular Dysplasia/genetics
- Arrhythmogenic Right Ventricular Dysplasia/physiopathology
- Cardiomyopathy, Hypertrophic, Familial/genetics
- Cardiomyopathy, Hypertrophic, Familial/physiopathology
- Child
- Death, Sudden, Cardiac/etiology
- ERG1 Potassium Channel
- Ether-A-Go-Go Potassium Channels
- Humans
- KCNQ Potassium Channels
- KCNQ1 Potassium Channel
- Long QT Syndrome/complications
- Long QT Syndrome/genetics
- Long QT Syndrome/therapy
- NAV1.5 Voltage-Gated Sodium Channel
- Potassium Channels/physiology
- Potassium Channels, Voltage-Gated
- Sodium Channels/physiology
- Syndrome
- Tachycardia, Ventricular/genetics
- Wolff-Parkinson-White Syndrome/physiopathology
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Affiliation(s)
- Jeffrey A Towbin
- Department of Pediatrics (Cardiology), Texas Children's Hospital and Baylor College of Medicine, 6621 Fannin Street, FC. 430.09, Houston, TX 77030, USA.
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30
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Eberhart RC, Su SH, Nguyen KT, Zilberman M, Tang L, Nelson KD, Frenkel P. Bioresorbable polymeric stents: current status and future promise. JOURNAL OF BIOMATERIALS SCIENCE. POLYMER EDITION 2004; 14:299-312. [PMID: 12747671 DOI: 10.1163/156856203321478838] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Metal stents and, more recently, polymer-coated metal stents are used to stabilize dissections, eliminate vessel recoil, and guide remodeling after balloon angioplasty and other treatments for arterial disease. Bioresorbable polymeric stents are being developed to improve the biocompatibility and the drug reservoir capacity of metal stents, and to offer a transient alternative to the permanent metallic stent implant. Following a brief review of metal stent technology, the emerging class of expandable, bioresorbable polymeric stents is described, with emphasis on developments in the authors' laboratory.
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Affiliation(s)
- Robert C Eberhart
- Department of Surgery, University of Texas Southwestern Medical Center at Dallas, 5323 Harry, Hines Boulevard, Dallas, TX 75390-9130, USA.
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31
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Zhu Y, Golden CM, Ye J, Wang XY, Akbarali HI, Huizinga JD. ERG K+ currents regulate pacemaker activity in ICC. Am J Physiol Gastrointest Liver Physiol 2003; 285:G1249-58. [PMID: 12958021 DOI: 10.1152/ajpgi.00149.2003] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Ether-à-go-go-related gene (ERG) K channels have been implicated in the generation of pacemaker activities in the heart. To study the presence and function of ERG K channels in the pacemaker cells of the small intestine [the interstitial cells of Cajal (ICC)], a combination of patch-clamp techniques, tissue and live cell immunohistochemistry, RT-PCR, and in vitro functional studies were performed. Nonenzymatically isolated ICC in culture were identified by vital staining and presence of rhythmic inward currents. RT-PCR showed the presence of ERG mRNA in the intestinal musculature, and immunohistochemistry on tissue and cultured cells demonstrated that protein similar to human ERG was concentrated on ICC in the Auerbach's plexus region. Whole cell ERG K+ currents were evoked on hyperpolarization from 0 mV (but not from -70 mV) up to -120 mV and showed strong inward rectification. The currents were inhibited by E-4031, cisapride, La3+, and Gd3+ but not by 50 microM Ba2+. The ERG K+ inward current had a typical transient component with fast activation and inactivation kinetics followed by significant steady-state current. E-4031 also inhibited tetraethylammonium (TEA)-insensitive outward current indicating that the ERG K+ current is operating at depolarizing potentials. In contrast to TEA, blockers of the ERG K+ currents caused marked increase in tissue excitability as reflected by an increase in slow-wave duration and an increase in superimposed action potential activity. In summary, ERG K channels in ICC contribute to the membrane potential and play a role in regulation of pacemaker activity of the small intestine.
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Affiliation(s)
- Yaohui Zhu
- Intestinal Disease Research Program, McMaster University, Hamilton, Ontario, Canada L8N 3Z5
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32
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Paulussen A, Raes A, Matthijs G, Snyders DJ, Cohen N, Aerssens J. A novel mutation (T65P) in the PAS domain of the human potassium channel HERG results in the long QT syndrome by trafficking deficiency. J Biol Chem 2002; 277:48610-6. [PMID: 12354768 DOI: 10.1074/jbc.m206569200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The congenital long QT syndrome is a cardiac disease characterized by an increased susceptibility to ventricular arrhythmias. The clinical hallmark is a prolongation of the QT interval, which reflects a delay in repolarization caused by mutations in cardiac ion channel genes. Mutations in the HERG (human ether-à-go-go-related gene KCNH2 can cause a reduction in I(Kr), one of the currents responsible for cardiac repolarization. We describe the identification and characterization of a novel missense mutation T65P in the PAS (Per-Arnt-Sim) domain of HERG, resulting in defective trafficking of the protein to the cell membrane. Defective folding of the mutant protein could be restored by decreased cell incubation temperature and pharmacologically by cisapride and E-4031. When trafficking was restored by growing cells at 27 degrees C, the kinetics of the mutated channel resembled that of wild-type channels although the rate of activation, deactivation, and recovery from inactivation were accelerated. No positive evidence for the formation of heterotetramers was obtained by co-expression of wild-type with mutant subunits at 37 degrees C. As a consequence the clinical symptoms may be explained rather by haploinsufficiency than by dominant negative effects. This study is the first to relate a PAS domain mutation in HERG to a trafficking deficiency at body temperature, apart from effects on channel deactivation.
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Affiliation(s)
- Aimée Paulussen
- Department of Pharmacogenomics, Johnson & Johnson Pharmaceutical Research and Development, Beerse B-2340, Belgium.
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33
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Abstract
Genetic screens in Drosophila melanogaster, Caenorhabditis elegans, and Danio rerio clarified the logic of metazoan development by revealing critical unitary steps and pathways to embryogenesis. Can genetic screens similarly organize medicine? We here examine human diseases that resemble mutations in Danio rerio, the zebrafish, the one vertebrate species for which large-scale genetic screens have been performed and extensively analyzed. Zebrafish mutations faithfully phenocopy many human disorders. Each mutation, once cloned, provides candidate genes and pathways for evaluation in the human. The collection of mutations in their entirety potentially provides a medical taxonomy, one based in developmental biology and genetics.
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Affiliation(s)
- Jordan T Shin
- Cardiovascular Research Center and Division of Cardiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
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