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Zünkler BJ, Wos-Maganga M, Bohnet S, Kleinau A, Manns D, Chatterjee S. Intracellular Binding of Terfenadine Competes with Its Access to Pancreatic ß-cell ATP-Sensitive K + Channels and Human ether-à-go-go-Related Gene Channels. J Membr Biol 2023; 256:63-77. [PMID: 35763054 PMCID: PMC9884252 DOI: 10.1007/s00232-022-00252-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 06/02/2022] [Indexed: 02/07/2023]
Abstract
Most blockers of both hERG (human ether-à-go-go-related gene) channels and pancreatic ß-cell ATP-sensitive K+ (KATP) channels access their binding sites from the cytoplasmic side of the plasma membrane. It is unknown whether binding to intracellular components competes with binding of these substances to K+ channels. The whole-cell configuration of the patch-clamp technique, a laser-scanning confocal microscope, and fluorescence correlation spectroscopy (FCS) were used to study hERG channels expressed in HEK (human embryonic kidney) 293 cells and KATP channels from the clonal insulinoma cell line RINm5F. When applied via the pipette solution in the whole-cell configuration, terfenadine blocked both hERG and KATP currents with much lower potency than after application via the bath solution, which was not due to P-glycoprotein-mediated efflux of terfenadine. Such a difference was not observed with dofetilide and tolbutamide. 37-68% of hERG/EGFP (enhanced green-fluorescent protein) fusion proteins expressed in HEK 293 cells were slowly diffusible as determined by laser-scanning microscopy in the whole-cell configuration and by FCS in intact cells. Bath application of a green-fluorescent sulphonylurea derivative (Bodipy-glibenclamide) induced a diffuse fluorescence in the cytosol of RINm5F cells under whole-cell patch-clamp conditions. These observations demonstrate the presence of intracellular binding sites for hERG and KATP channel blockers not dialyzable by the patch-pipette solution. Intracellular binding of terfenadine was not influenced by a mutated hERG (Y652A) channel. In conclusion, substances with high lipophilicity are not freely diffusible inside the cell but steep concentration gradients might exist within the cell and in the sub-membrane space.
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Affiliation(s)
- Bernd J Zünkler
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany.
- Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technische Universität Braunschweig, Mendelssohnstr. 1, 38106, Braunschweig, Germany.
| | - Maria Wos-Maganga
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Stefanie Bohnet
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Anne Kleinau
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Detlef Manns
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
| | - Shivani Chatterjee
- Federal Institute for Drugs and Medical Devices, Kurt-Georg-Kiesinger-Allee 3, 53175, Bonn, Germany
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Li Q, Chai L, Dong G, Zhang X, Du L. NBD-Based Environment-Sensitive Fluorescent Probes for the Human Ether-a-Go-Go-Related Gene Potassium Channel. Front Mol Biosci 2021; 8:666605. [PMID: 34055884 PMCID: PMC8160426 DOI: 10.3389/fmolb.2021.666605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Accepted: 04/26/2021] [Indexed: 11/13/2022] Open
Abstract
Three environment-sensitive probes were developed for the hERG channel based on the nitrobenzoxadiazole fluorophore herein. After careful evaluation, probes M1 and M3 were found to have a high affinity for imaging the hERG channel in the cell-based experiment. Compared with other fluorescent labeling technologies (such as fluorescent proteins), these probes afford a convenient and economical method to determine hERG channel in vitro and in cellulo. Therefore, these probes are expected to be applicable for usage in physiological and pathological studies of hERG channels and have the potential to establish a screening system for hERG channels.
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Affiliation(s)
- Qi Li
- Department of Medicinal Chemistry, Key Laboratory of Chemical Biology (MOE), School of Pharmacy, Shandong University, Jinan, China
| | - Lijuan Chai
- Department of Internal Medicine, Hospital of Shandong University, Jinan, China
| | - Gaopan Dong
- Department of Medicinal Chemistry, Key Laboratory of Chemical Biology (MOE), School of Pharmacy, Shandong University, Jinan, China
| | - Xiaomeng Zhang
- Department of Medicinal Chemistry, Key Laboratory of Chemical Biology (MOE), School of Pharmacy, Shandong University, Jinan, China
| | - Lupei Du
- Department of Medicinal Chemistry, Key Laboratory of Chemical Biology (MOE), School of Pharmacy, Shandong University, Jinan, China
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Osterbur Badhey ML, Bertalovitz AC, McDonald TV. Express with caution: Epitope tags and cDNA variants effects on hERG channel trafficking, half-life and function. J Cardiovasc Electrophysiol 2017; 28:1070-1082. [PMID: 28544109 PMCID: PMC5671924 DOI: 10.1111/jce.13259] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 05/19/2017] [Accepted: 05/19/2017] [Indexed: 01/14/2023]
Abstract
INTRODUCTION Genetic mutations in KCNH2, which encodes hERG, the alpha subunit of the potassium channel responsible for the IKr current, cause long QT syndrome (LQTS), an inherited cardiac arrhythmia disorder. Electrophysiology techniques are used to correlate genotype with molecular phenotype to determine which mutations identified in patients diagnosed with LQTS are disease causing, and which are benign. These investigations are usually done using heterologous expression in cell lines, and often, epitope fusion tags are used to enable isolation and identification of the protein of interest. METHODS AND RESULTS Here, we demonstrate through electrophysiology techniques and immunohistochemistry, that both N-terminal and C-terminal myc fusion tags may perturb hERG protein channel expression and kinetics of the IKr current. We also characterize the impact of 2 previously reported inadvertent cDNA variants on hERG channel expression and half-life. CONCLUSION Our results underscore the importance of careful characterization of the impact of epitope fusion tags and of confirming complete sequence accuracy prior to genotype-phenotype studies for ion channel proteins such as hERG.
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Affiliation(s)
- Marika L Osterbur Badhey
- Department of Molecular Pharmacology, Department of Medicine, Division of Cardiology, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Alexander C Bertalovitz
- Department of Molecular Pharmacology, Department of Medicine, Division of Cardiology, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Thomas V McDonald
- Department of Molecular Pharmacology, Department of Medicine, Division of Cardiology, Albert Einstein College of Medicine, Bronx, New York, USA
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Ooi A, Wong A, Esau L, Lemtiri-Chlieh F, Gehring C. A Guide to Transient Expression of Membrane Proteins in HEK-293 Cells for Functional Characterization. Front Physiol 2016; 7:300. [PMID: 27486406 PMCID: PMC4949579 DOI: 10.3389/fphys.2016.00300] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 06/28/2016] [Indexed: 01/17/2023] Open
Abstract
The human embryonic kidney 293 (HEK-293) cells are commonly used as host for the heterologous expression of membrane proteins not least because they have a high transfection efficiency and faithfully translate and process proteins. In addition, their cell size, morphology and division rate, and low expression of native channels are traits that are particularly attractive for current-voltage measurements. Nevertheless, the heterologous expression of complex membrane proteins such as receptors and ion channels for biological characterization and in particular for single-cell applications such as electrophysiology remains a challenge. Expression of functional proteins depends largely on careful step-by-step optimization that includes the design of expression vectors with suitable identification tags, as well as the selection of transfection methods and detection parameters appropriate for the application. Here, we use the heterologous expression of a plant potassium channel, the Arabidopsis thaliana guard cell outward-rectifying K(+) channel, AtGORK (At5G37500) in HEK-293 cells as an example, to evaluate commonly used transfection reagents and fluorescent detection methods, and provide a detailed methodology for optimized transient transfection and expression of membrane proteins for in vivo studies in general and for single-cell applications in particular. This optimized protocol will facilitate the physiological and cellular characterization of complex membrane proteins.
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Affiliation(s)
- Amanda Ooi
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology Thuwal, Saudi Arabia
| | - Aloysius Wong
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and TechnologyThuwal, Saudi Arabia; Institute of Integrative Biology of the Cell, Centre National de la Recherche Scientifique, Le Commissariat à l'Energie Atomique et aux Energies Alternatives, Paris-Sud UniversityGif-Sur-Yvette, France
| | - Luke Esau
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology Thuwal, Saudi Arabia
| | - Fouad Lemtiri-Chlieh
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology Thuwal, Saudi Arabia
| | - Chris Gehring
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology Thuwal, Saudi Arabia
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Tanaka H, Takahashi Y, Hamaguchi S, Iida-Tanaka N, Oka T, Nishio M, Ohtsuki A, Namekata I. Effect of Terfenadine and Pentamidine on the hERG Channel and Its Intracellular Trafficking: Combined Analysis with Automated Voltage Clamp and Confocal Microscopy. Biol Pharm Bull 2014; 37:1826-30. [DOI: 10.1248/bpb.b14-00417] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Hikaru Tanaka
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
| | - Yukiko Takahashi
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
| | - Shogo Hamaguchi
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
| | | | - Takayuki Oka
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
| | - Masato Nishio
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
| | - Atsushi Ohtsuki
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
| | - Iyuki Namekata
- Department of Pharmacology, Toho University Faculty of Pharmaceutical Sciences
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Genetic suppression of atrial fibrillation using a dominant-negative ether-a-go-go-related gene mutant. Heart Rhythm 2011; 9:265-72. [PMID: 21907172 DOI: 10.1016/j.hrthm.2011.09.008] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Accepted: 09/02/2011] [Indexed: 12/31/2022]
Abstract
BACKGROUND Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Gene therapy-dependent modulation of atrial electrophysiology may provide a more specific alternative to pharmacological and ablative treatment strategies. OBJECTIVE We hypothesized that genetic inactivation of atrial repolarizing ether-a-go-go-related gene (ERG) K(+) currents using a dominant-negative mutant would provide rhythm control in AF. METHODS Ten domestic swine underwent pacemaker implantation and were subjected to atrial burst pacing to induce persistent AF. Animals were then randomized to receive either AdCERG-G627S to suppress ERG/I(Kr) currents or green fluorescent protein (AdGFP) as control. Adenoviruses were applied using a novel hybrid technique combining atrial virus injection and epicardial electroporation to increase transgene expression. RESULTS In pigs treated with AdCERG-G627S, the onset of persistent AF was prevented (n = 2) or significantly delayed compared with AdGFP controls (12 ± 2.1 vs. 6.2 ± 1.3 days; P < .001) during 14-day follow-up. Effective refractory periods were prolonged in the AdCERG-G627S group compared with AdGFP animals (221.5 ± 4.7 ms vs. 197.0 ± 4.7 ms; P < .006). Impairment of left ventricular ejection fraction (LVEF) during AF was prevented by AdCERG-G627S application (LVEF(CERG-G627S) = 62.1% ± 4.0% vs. LVEF(GFP) = 30.3% ± 9.1%; P < .001). CONCLUSION Inhibition of ERG function using atrial AdCERG-G627S gene transfer suppresses or delays the onset of persistent AF by prolongation of atrial refractoriness in a porcine model. Targeted gene therapy represents an alternative to pharmacological or ablative treatment of AF.
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The EGFP/hERG fusion protein alter the electrophysiological properties of hERG channels in HEK293 cells. Cell Biol Int 2011; 35:193-9. [PMID: 21143190 DOI: 10.1042/cbi20100022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
EGFP (enhanced green fluorescent protein) tagged to either the N (amino)-terminus [EGFP/hERG (human ether-a-go-go-related gene)] or C (carboxyl)-terminus (hERG/EGFP) of hERG channel is used to study mutant channel protein trafficking for several years. However, it has been reported that the process can alter hERG channel properties. The aim of the study was to determine whether EGFP tagged to N-terminus of hERG channels would alter the cellular localizations and the electrophysiological properties of hERG channels compared with untagged hERG channels. The hERG channels tagged with or without EGFP were transiently expressed in HEK (human embryonic kidney) 293 cells using a lipofectamine method. HEK 293 cells expressing pCDNA3-hERG or pEGFP-hERG were double immunolabelled with anti-hERG and anti-calnexin (an ER marker protein) followed with FITC- and TRITC (tetramethylrhodamine β-isothiocyanate)-labelled secondary antibodies, respectively. Confocal laser scanning microscope was used to observe the cellular localization of EGFP-tagged hERG channels and untagged hERG channels. Patch-clamp technique was used to record whole cell currents. We found that the EGFP/hERG fusion protein and untagged hERG channels were both expressed not only on the cell surface membrane but also in the cytoplasm of HEK293 cells. The EGFP/hERG appeared to influence the hERG channel gating properties, including reduction of the peak tail current density, more rapid inactivation process, faster recovery from inactivation and faster deactivation kinetics compared with untagged hERG channels. Our results suggest that the EGFP/hERG channel alter the electrophysiological properties of hERG channel, but it does not seem to alter the cellular location of hERG channels. Thus, EGFP tagging to N-terminus might be used for research of subcellular location of hERG channels but not for the channel electrophysiological properties.
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Guasti L, Crociani O, Redaelli E, Pillozzi S, Polvani S, Masselli M, Mello T, Galli A, Amedei A, Wymore RS, Wanke E, Arcangeli A. Identification of a posttranslational mechanism for the regulation of hERG1 K+ channel expression and hERG1 current density in tumor cells. Mol Cell Biol 2008; 28:5043-60. [PMID: 18559421 PMCID: PMC2519704 DOI: 10.1128/mcb.00304-08] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Revised: 03/25/2008] [Accepted: 06/04/2008] [Indexed: 01/19/2023] Open
Abstract
A common feature of tumor cells is the aberrant expression of ion channels on their plasma membrane. The molecular mechanisms regulating ion channel expression in cancer cells are still poorly known. K(+) channels that belong to the human ether-a-go-go-related gene 1 (herg1) family are frequently misexpressed in cancer cells compared to their healthy counterparts. We describe here a posttranslational mechanism for the regulation of hERG1 channel surface expression in cancer cells. This mechanism is based on the activity of hERG1 isoforms containing the USO exon. These isoforms (i) are frequently overexpressed in human cancers, (ii) are retained in the endoplasmic reticulum, and (iii) form heterotetramers with different proteins of the hERG family. (iv) The USO-containing heterotetramers are retained intracellularly and undergo ubiquitin-dependent degradation. This process results in decreased hERG1 current (I(hERG1)) density. We detailed such a mechanism in heterologous systems and confirmed its functioning in tumor cells that endogenously express hERG1 proteins. The silencing of USO-containing hERG1 isoforms induces a higher I(hERG1) density in tumors, an effect that apparently regulates neurite outgrowth in neuroblastoma cells and apoptosis in leukemia cells.
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Affiliation(s)
- Leonardo Guasti
- Department of Experimental Pathology and Oncology, University of Florence, Viale G. B. Morgagni 50, 50134 Florence, Italy
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