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Taniguchi S, Berenger F, Doi Y, Mimura A, Yamanishi Y, Okiyoneda T. Ligand-based virtual-screening identified a novel CFTR ligand which improves the defective cell surface expression of misfolded ABC transporters. Front Pharmacol 2024; 15:1370676. [PMID: 38666024 PMCID: PMC11043560 DOI: 10.3389/fphar.2024.1370676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2024] [Accepted: 04/01/2024] [Indexed: 04/28/2024] Open
Abstract
Cystic fibrosis (CF) is a monogenetic disease caused by the mutation of CFTR, a cAMP-regulated Cl- channel expressing at the apical plasma membrane (PM) of epithelia. ∆F508-CFTR, the most common mutant in CF, fails to reach the PM due to its misfolding and premature degradation at the endoplasmic reticulum (ER). Recently, CFTR modulators have been developed to correct CFTR abnormalities, with some being used as therapeutic agents for CF treatment. One notable example is Trikafta, a triple combination of CFTR modulators (TEZ/ELX/IVA), which significantly enhances the functionality of ΔF508-CFTR on the PM. However, there's room for improvement in its therapeutic effectiveness since TEZ/ELX/IVA doesn't fully stabilize ΔF508-CFTR on the PM. To discover new CFTR modulators, we conducted a virtual screening of approximately 4.3 million compounds based on the chemical structures of existing CFTR modulators. This effort led us to identify a novel CFTR ligand named FR3. Unlike clinically available CFTR modulators, FR3 appears to operate through a distinct mechanism of action. FR3 enhances the functional expression of ΔF508-CFTR on the apical PM in airway epithelial cell lines by stabilizing NBD1. Notably, FR3 counteracted the degradation of mature ΔF508-CFTR, which still occurs despite the presence of TEZ/ELX/IVA. Furthermore, FR3 corrected the defective PM expression of a misfolded ABCB1 mutant. Therefore, FR3 may be a potential lead compound for addressing diseases resulting from the misfolding of ABC transporters.
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Affiliation(s)
- Shogo Taniguchi
- Department of Biomedical Sciences, School of Biological and Environmental Sciences, Kwansei Gakuin University, Nishinomiya, Japan
| | - Francois Berenger
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan
| | - Yukako Doi
- Department of Biomedical Sciences, School of Biological and Environmental Sciences, Kwansei Gakuin University, Nishinomiya, Japan
| | - Ayana Mimura
- Department of Biomedical Sciences, School of Biological and Environmental Sciences, Kwansei Gakuin University, Nishinomiya, Japan
| | - Yoshihiro Yamanishi
- Department of Complex Systems Science, Graduate School of Informatics, Nagoya University, Graduate School of Informatics, Nagoya University, Nagoya, Japan
| | - Tsukasa Okiyoneda
- Department of Biomedical Sciences, School of Biological and Environmental Sciences, Kwansei Gakuin University, Nishinomiya, Japan
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2
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Campagna N, Wall E, Lee K, Guo J, Li W, Yang T, Baranchuk A, El-Diasty M, Zhang S. Differential Effects of Remdesivir and Lumacaftor on Homomeric and Heteromeric hERG Channels. Mol Pharmacol 2023; 104:164-173. [PMID: 37419691 DOI: 10.1124/molpharm.123.000708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 05/31/2023] [Accepted: 06/08/2023] [Indexed: 07/09/2023] Open
Abstract
The human ether-a-go-go-related gene (hERG) encodes for the pore-forming subunit of the channel that conducts the rapidly activating delayed K+ current (IKr) in the heart. The hERG channel is important for cardiac repolarization, and reduction of its expression in the plasma membrane due to mutations causes long QT syndrome type 2 (LQT2). As such, promoting hERG membrane expression is a strategy to rescue mutant channel function. In the present study, we applied patch clamp, western blots, immunocytochemistry, and quantitative reverse transcription polymerase chain reaction techniques to investigate the rescue effects of two drugs, remdesivir and lumacaftor, on trafficking-defective mutant hERG channels. As our group has recently reported that the antiviral drug remdesivir increases wild-type (WT) hERG current and surface expression, we studied the effects of remdesivir on trafficking-defective LQT2-causing hERG mutants G601S and R582C expressed in HEK293 cells. We also investigated the effects of lumacaftor, a drug used to treat cystic fibrosis, that promotes CFTR protein trafficking and has been shown to rescue membrane expression of some hERG mutations. Our results show that neither remdesivir nor lumacaftor rescued the current or cell-surface expression of homomeric mutants G601S and R582C. However, remdesivir decreased while lumacaftor increased the current and cell-surface expression of heteromeric channels formed by WT hERG and mutant G601S or R582C hERG. We concluded that drugs can differentially affect homomeric WT and heteromeric WT+G601S (or WT+R582C) hERG channels. These findings extend our understanding of drug-channel interaction and may have clinical implications for patients with hERG mutations. SIGNIFICANCE STATEMENT: Various naturally occurring mutations in a cardiac potassium channel called hERG can impair channel function by decreasing cell-surface channel expression, resulting in cardiac electrical disturbances and even sudden cardiac death. Promotion of cell-surface expression of mutant hERG channels represents a strategy to rescue channel function. This work demonstrates that drugs such as remdesivir and lumacaftor can differently affect homomeric and heteromeric mutant hERG channels, which have biological and clinical implications.
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Affiliation(s)
- Noah Campagna
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Erika Wall
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Kevin Lee
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Jun Guo
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Wentao Li
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Tonghua Yang
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Adrian Baranchuk
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Mohammad El-Diasty
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
| | - Shetuan Zhang
- Department of Biomedical and Molecular Sciences (N.C., E.W., K.L., J.G., W.L., T.Y., S.Z.); Division of Cardiology, Department of Medicine (A.B.); and Division of Cardiac Surgery, Department of Surgery (M.E.-D.), Queen's University, Kingston, Ontario, Canada
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3
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Nguyen NH, Brodsky JL. The cellular pathways that maintain the quality control and transport of diverse potassium channels. BIOCHIMICA ET BIOPHYSICA ACTA. GENE REGULATORY MECHANISMS 2023; 1866:194908. [PMID: 36638864 PMCID: PMC9908860 DOI: 10.1016/j.bbagrm.2023.194908] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 12/20/2022] [Accepted: 01/03/2023] [Indexed: 01/12/2023]
Abstract
Potassium channels are multi-subunit transmembrane proteins that permit the selective passage of potassium and play fundamental roles in physiological processes, such as action potentials in the nervous system and organismal salt and water homeostasis, which is mediated by the kidney. Like all ion channels, newly translated potassium channels enter the endoplasmic reticulum (ER) and undergo the error-prone process of acquiring post-translational modifications, folding into their native conformations, assembling with other subunits, and trafficking through the secretory pathway to reach their final destinations, most commonly the plasma membrane. Disruptions in these processes can result in detrimental consequences, including various human diseases. Thus, multiple quality control checkpoints evolved to guide potassium channels through the secretory pathway and clear potentially toxic, aggregation-prone misfolded species. We will summarize current knowledge on the mechanisms underlying potassium channel quality control in the secretory pathway, highlight diseases associated with channel misfolding, and suggest potential therapeutic routes.
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Affiliation(s)
- Nga H Nguyen
- Department of Biological Sciences, University of Pittsburgh, A320 Langley Hall, Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA 15260, USA
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, A320 Langley Hall, Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA 15260, USA.
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4
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Li JV, Ng CA, Cheng D, Zhou Z, Yao M, Guo Y, Yu ZY, Ramaswamy Y, Ju LA, Kuchel PW, Feneley MP, Fatkin D, Cox CD. Modified N-linked glycosylation status predicts trafficking defective human Piezo1 channel mutations. Commun Biol 2021; 4:1038. [PMID: 34489534 PMCID: PMC8421374 DOI: 10.1038/s42003-021-02528-w] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Accepted: 08/05/2021] [Indexed: 02/06/2023] Open
Abstract
Mechanosensitive channels are integral membrane proteins that sense mechanical stimuli. Like most plasma membrane ion channel proteins they must pass through biosynthetic quality control in the endoplasmic reticulum that results in them reaching their destination at the plasma membrane. Here we show that N-linked glycosylation of two highly conserved asparagine residues in the 'cap' region of mechanosensitive Piezo1 channels are necessary for the mature protein to reach the plasma membrane. Both mutation of these asparagines (N2294Q/N2331Q) and treatment with an enzyme that hydrolyses N-linked oligosaccharides (PNGaseF) eliminates the fully glycosylated mature Piezo1 protein. The N-glycans in the cap are a pre-requisite for N-glycosylation in the 'propeller' regions, which are present in loops that are essential for mechanotransduction. Importantly, trafficking-defective Piezo1 variants linked to generalized lymphatic dysplasia and bicuspid aortic valve display reduced fully N-glycosylated Piezo1 protein. Thus the N-linked glycosylation status in vitro correlates with efficient membrane trafficking and will aid in determining the functional impact of Piezo1 variants of unknown significance.
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Affiliation(s)
- Jinyuan Vero Li
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
| | - Chai-Ann Ng
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Delfine Cheng
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Zijing Zhou
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
| | - Mingxi Yao
- Mechanobiology Institute, National University of Singapore, Singapore, Singapore
| | - Yang Guo
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Ze-Yan Yu
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Yogambha Ramaswamy
- School of Biomedical Engineering, Faculty of Engineering, The University of Sydney, Camperdown, NSW, Australia
| | - Lining Arnold Ju
- School of Biomedical Engineering, Faculty of Engineering, The University of Sydney, Camperdown, NSW, Australia
| | - Philip W Kuchel
- School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia
| | - Michael P Feneley
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
- Department of Cardiology, St Vincent's Hospital, Sydney, Australia
| | - Diane Fatkin
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
| | - Charles D Cox
- Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Sydney, Australia.
- St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia.
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5
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Shenkman M, Lederkremer GZ. Compartmentalization and Selective Tagging for Disposal of Misfolded Glycoproteins. Trends Biochem Sci 2019; 44:827-836. [PMID: 31133362 DOI: 10.1016/j.tibs.2019.04.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Revised: 04/18/2019] [Accepted: 04/24/2019] [Indexed: 01/08/2023]
Abstract
The ability of mammalian cells to correctly identify and degrade misfolded secretory proteins, most of them bearing N-glycans, is crucial for their correct function and survival. An inefficient disposal mechanism results in the accumulation of misfolded proteins and consequent endoplasmic reticulum (ER) stress. N-glycan processing creates a code that reveals the folding status of each molecule, enabling continued folding attempts or targeting of the doomed glycoprotein for disposal. We review here the main steps involved in the accurate processing of unfolded glycoproteins. We highlight recent data suggesting that the processing is not stochastic, but that there is selective accelerated glycan trimming on misfolded glycoprotein molecules.
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Affiliation(s)
- Marina Shenkman
- School of Molecular Cell Biology and Biotechnology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Gerardo Z Lederkremer
- School of Molecular Cell Biology and Biotechnology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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Feng P, Zhao L, Guo F, Zhang B, Fang L, Zhan G, Xu X, Fang Q, Liang Z, Li B. The enhancement of cardiotoxicity that results from inhibiton of CYP 3A4 activity and hERG channel by berberine in combination with statins. Chem Biol Interact 2018; 293:115-123. [PMID: 30086269 DOI: 10.1016/j.cbi.2018.07.022] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 05/25/2018] [Accepted: 07/23/2018] [Indexed: 11/24/2022]
Abstract
Metabolism of most endogenous and exogenous compounds is usually produced by the oxidation of cytochrome P450. Due to drug-drug interactions caused by the inhibition or induction of cytochrome P450 enzymes, changes in drug metabolism are the major causes of drug toxicity, CYP3A4 is one of the key isozymes, and involved in the metabolism of over 60% of clinical drugs. Human ether-a-go-go related genes (hERG) potassium channel is the most important target of many drugs and plays an important role in cardiac repolarization. Blockade of this channel may lead to long QT syndrome (LQTS), leading to sudden cardiac death. Therefore, it is necessary to evaluate the inhibitory properties of drugs on cytochrome P450 enzymes and hERG channel. We primarily evaluate the safety of berberine in combination with statins. Based on these findings, berberine in combination with statins has a greater inhibitory effect on CYP3A4 activity and CYP3A4 protein and mRNA expression than berberine alone. Simvastatin and atorvastatin reduce hERG current by accelerating channel inactivation. At the same time, the inhibitory effect of berberine and statin combination increased on hERG current by reducing the time constant of inactivation than the single drug alone. These results indicate that berberine in combination with statins can increase cardiotoxicity by inhibiting CYP3A4 and hERG channel.
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Affiliation(s)
- Panfeng Feng
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Lei Zhao
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Fengfeng Guo
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Bo Zhang
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Li Fang
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Ge Zhan
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Xueqi Xu
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Qing Fang
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China
| | - Zhaoguang Liang
- First Affiliated Hospital of Harbin Medical University, Harbin, 150086, China.
| | - Baoxin Li
- Department of Pharmacology, Harbin Medical University, Harbin, 150086, China.
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7
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Hall AR, Anderson CL, Smith JL, Mirshahi T, Elayi CS, January CT, Delisle BP. Visualizing Mutation-Specific Differences in the Trafficking-Deficient Phenotype of Kv11.1 Proteins Linked to Long QT Syndrome Type 2. Front Physiol 2018; 9:584. [PMID: 29875689 PMCID: PMC5974211 DOI: 10.3389/fphys.2018.00584] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 05/02/2018] [Indexed: 02/05/2023] Open
Abstract
KCNH2 encodes the Kv11.1 α-subunit that underlies the rapidly activating delayed-rectifier K+ current in the heart. Loss-of-function KCNH2 mutations cause long QT syndrome type 2 (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channel protein to the cell surface membrane. Several trafficking-deficient LQT2 mutations (e.g., G601S) generate Kv11.1 proteins that are sequestered in a microtubule-dependent quality control (QC) compartment in the transitional endoplasmic reticulum (ER). We tested the hypothesis that the QC mechanisms that regulate LQT2-linked Kv11.1 protein trafficking are mutation-specific. Confocal imaging analyses of HEK293 cells stably expressing the trafficking-deficient LQT2 mutation F805C showed that, unlike G601S-Kv11.1 protein, F805C-Kv11.1 protein was concentrated in several transitional ER subcompartments. The microtubule depolymerizing drug nocodazole differentially affected G601S- and F805C-Kv11.1 protein immunostaining. Nocodazole caused G601S-Kv11.1 protein to distribute into peripheral reticular structures, and it increased the diffuse immunostaining of F805C-Kv11.1 protein around the transitional ER subcompartments. Proteasome inhibition also affected the immunostaining of G601S- and F805C-Kv11.1 protein differently. Incubating cells in MG132 minimally impacted G601S-Kv11.1 immunostaining, but it dramatically increased the diffuse immunostaining of F805C-Kv11.1 protein in the transitional ER. Similar results were seen after incubating cells in the proteasome inhibitor lactacystin. Differences in the cellular distribution of G601S-Kv11.1 and F805C-Kv11.1 protein persisted in transfected human inducible pluripotent stem cell derived cardiomyocytes. These are the first data to visually demonstrate mutation-specific differences in the trafficking-deficient LQT2 phenotype, and this study has identified a novel way to categorize trafficking-deficient LQT2 mutations based on differences in intracellular retention.
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Affiliation(s)
- Allison R. Hall
- Department of Physiology, University of Kentucky, Lexington, KY, United States
| | - Corey L. Anderson
- Cellular and Molecular Arrhythmia Research Program, University of Wisconsin–Madison, Madison, WI, United States
| | - Jennifer L. Smith
- Department of Physiology, University of Kentucky, Lexington, KY, United States
| | - Tooraj Mirshahi
- Department of Molecular and Functional Genomics, Genomic Medicine Institute, Geisinger Clinic, Danville, PA, United States
| | - Claude S. Elayi
- Department of Cardiology, Gill Heart Institute, University of Kentucky, Lexington, KY, United States
| | - Craig T. January
- Cellular and Molecular Arrhythmia Research Program, University of Wisconsin–Madison, Madison, WI, United States
| | - Brian P. Delisle
- Department of Physiology, University of Kentucky, Lexington, KY, United States
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8
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Smith JL, Tester DJ, Hall AR, Burgess DE, Hsu CC, Elayi SC, Anderson CL, January CT, Luo JZ, Hartzel DN, Mirshahi UL, Murray MF, Mirshahi T, Ackerman MJ, Delisle BP. Functional Invalidation of Putative Sudden Infant Death Syndrome-Associated Variants in the KCNH2-Encoded Kv11.1 Channel. Circ Arrhythm Electrophysiol 2018; 11:e005859. [PMID: 29752375 PMCID: PMC11081002 DOI: 10.1161/circep.117.005859] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 03/12/2018] [Indexed: 12/14/2022]
Abstract
BACKGROUND Heterologous functional validation studies of putative long-QT syndrome subtype 2-associated variants clarify their pathological potential and identify disease mechanism(s) for most variants studied. The purpose of this study is to clarify the pathological potential for rare nonsynonymous KCNH2 variants seemingly associated with sudden infant death syndrome. METHODS Genetic testing of 292 sudden infant death syndrome cases identified 9 KCNH2 variants: E90K, R181Q, A190T, G294V, R791W, P967L, R1005W, R1047L, and Q1068R. Previous studies show R181Q-, P967L-, and R1047L-Kv11.1 channels function similar to wild-type Kv11.1 channels, whereas Q1068R-Kv11.1 channels accelerate inactivation gating. We studied the biochemical and biophysical properties for E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels expressed in human embryonic kidney 293 cells; examined the electronic health records of patients who were genotype positive for the sudden infant death syndrome-linked KCNH2 variants; and simulated their functional impact using computational models of the human ventricular action potential. RESULTS Western blot and voltage-clamping analyses of cells expressing E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels demonstrated these variants express and generate peak Kv11.1 current levels similar to cells expressing wild-type-Kv11.1 channels, but R791W- and R1005W-Kv11.1 channels accelerated deactivation and activation gating, respectively. Electronic health records of patients with the sudden infant death syndrome-linked KCNH2 variants showed that the patients had median heart rate-corrected QT intervals <480 ms and none had been diagnosed with long-QT syndrome or experienced cardiac arrest. Simulating the impact of dysfunctional gating variants predicted that they have little impact on ventricular action potential duration. CONCLUSIONS We conclude that these rare Kv11.1 missense variants are not long-QT syndrome subtype 2-causative variants and therefore do not represent the pathogenic substrate for sudden infant death syndrome in the variant-positive infants.
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Affiliation(s)
- Jennifer L Smith
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington (J.L.S., A.R.H., D.E.B., B.P.D.)
| | - David J Tester
- Departments of Cardiovascular Diseases, Pediatrics, and Molecular Pharmacology & Experimental Therapeutics, Divisions of Heart Rhythm Services and Pediatric Cardiology, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN (D.J.T., M.J.A.)
| | - Allison R Hall
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington (J.L.S., A.R.H., D.E.B., B.P.D.)
| | - Don E Burgess
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington (J.L.S., A.R.H., D.E.B., B.P.D.)
| | - Chun-Chun Hsu
- School of Respiratory Therapy, College of Medicine, Taipei Medical University, Taiwan (C.-C.H.)
| | - Samy Claude Elayi
- University of Kentucky, Gill Heart Institute and VAMC, Cardiology, Lexington (S.C.E.)
| | - Corey L Anderson
- Cellular and Molecular Arrhythmias Research Program, Department of Medicine, University of Wisconsin, Madison (C.L.A., C.T.J.)
| | - Craig T January
- Cellular and Molecular Arrhythmias Research Program, Department of Medicine, University of Wisconsin, Madison (C.L.A., C.T.J.)
| | - Jonathan Z Luo
- Department of Molecular and Functional Genomics and Genomic Medicine Institute, Geisinger Clinic, Danville, PA (J.Z.L., D.N.H., U.L.M., M.F.M., T.M.)
| | - Dustin N Hartzel
- Department of Molecular and Functional Genomics and Genomic Medicine Institute, Geisinger Clinic, Danville, PA (J.Z.L., D.N.H., U.L.M., M.F.M., T.M.)
| | - Uyenlinh L Mirshahi
- Department of Molecular and Functional Genomics and Genomic Medicine Institute, Geisinger Clinic, Danville, PA (J.Z.L., D.N.H., U.L.M., M.F.M., T.M.)
| | - Michael F Murray
- Department of Molecular and Functional Genomics and Genomic Medicine Institute, Geisinger Clinic, Danville, PA (J.Z.L., D.N.H., U.L.M., M.F.M., T.M.)
| | - Tooraj Mirshahi
- Department of Molecular and Functional Genomics and Genomic Medicine Institute, Geisinger Clinic, Danville, PA (J.Z.L., D.N.H., U.L.M., M.F.M., T.M.)
| | - Michael J Ackerman
- Departments of Cardiovascular Diseases, Pediatrics, and Molecular Pharmacology & Experimental Therapeutics, Divisions of Heart Rhythm Services and Pediatric Cardiology, Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN (D.J.T., M.J.A.)
| | - Brian P Delisle
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington (J.L.S., A.R.H., D.E.B., B.P.D.).
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9
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Kanner SA, Jain A, Colecraft HM. Development of a High-Throughput Flow Cytometry Assay to Monitor Defective Trafficking and Rescue of Long QT2 Mutant hERG Channels. Front Physiol 2018; 9:397. [PMID: 29725305 PMCID: PMC5917007 DOI: 10.3389/fphys.2018.00397] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 04/04/2018] [Indexed: 11/24/2022] Open
Abstract
Long QT Syndrome (LQTS) is an acquired or inherited disorder characterized by prolonged QT interval, exertion-triggered arrhythmias, and sudden cardiac death. One of the most prevalent hereditary LQTS subtypes, LQT2, results from loss-of-function mutations in the hERG channel, which conducts IKr, the rapid component of the delayed rectifier K+ current, critical for cardiac repolarization. The majority of LQT2 mutations result in Class 2 deficits characterized by impaired maturation and trafficking of hERG channels. Here, we have developed a high-throughput flow cytometric assay to analyze the surface and total expression of wild-type (WT) and mutant hERG channels with single-cell resolution. To test our method, we focused on 16 LQT2 mutations in the hERG Per-Arnt-Sim (PAS) domain that were previously studied via a widely used biochemical approach that compares levels of 135-kDa immature and 155-kDa fully glycosylated hERG protein to infer surface expression. We confirmed that LQT2 mutants expressed in HEK293 cells displayed a decreased surface density compared to WT hERG, and were differentially rescued by low temperature. However, we also uncovered some notable differences from the findings obtained via the biochemical approach. In particular, three mutations (N33T, R56Q, and A57P) with apparent WT-like hERG glycosylation patterns displayed up to 50% decreased surface expression. Furthermore, despite WT-like levels of complex glycosylation, these mutants have impaired forward trafficking, and exhibit varying half-lives at the cell surface. The results highlight utility of the surface labeling/flow cytometry approach to quantitatively assess trafficking deficiencies associated with LQT2 mutations, to discern underlying mechanisms, and to report on interventions that rescue deficits in hERG surface expression.
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Affiliation(s)
- Scott A Kanner
- Doctoral Program in Neurobiology and Behavior, Columbia University College of Physicians and Surgeons, New York, NY, United States
| | - Ananya Jain
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY, United States
| | - Henry M Colecraft
- Doctoral Program in Neurobiology and Behavior, Columbia University College of Physicians and Surgeons, New York, NY, United States.,Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY, United States.,Department of Pharmacology, Columbia University College of Physicians and Surgeons, New York, NY, United States
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10
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Yu D, Lv L, Fang L, Zhang B, Wang J, Zhan G, Zhao L, Zhao X, Li B. Inhibitory effects and mechanism of dihydroberberine on hERG channels expressed in HEK293 cells. PLoS One 2017; 12:e0181823. [PMID: 28763460 PMCID: PMC5538702 DOI: 10.1371/journal.pone.0181823] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 07/09/2017] [Indexed: 12/20/2022] Open
Abstract
The human ether-a-go-go-related gene (hERG) potassium channel conducts rapid delayed rectifier potassium currents (IKr) and contributes to phase III cardiac action potential repolarization. Drugs inhibit hERG channels by binding to aromatic residues in hERG helixes. Berberine (BBR) has multiple actions, and its hydrogenated derivative dihydroberberine (DHB) is a potential candidate for developing new drugs. Previous studies have demonstrated that BBR blocks hERG channels and prolongs action potential duration (APD). Our present study aimed to investigate the effects and mechanism of DHB on hERG channels. Protein expression and the hERG current were analyzed using western blotting and patch-clamp, respectively. DHB inhibited the hERG current concentration-dependently after instantaneous perfusion, accelerated channel inactivation by directly binding tyrosine (Tyr652) and phenylalanine (Phe656), and decreased mature (155-kDa) and simultaneously increased immature (135-kDa) hERG expression, respectively. This suggests disruption of forward trafficking of hERG channels. Besides, DHB remarkably reduced heat shock protein 90 (Hsp90) expression and its interaction with hERG, indicating that DHB disrupted hERG trafficking by impairing channel folding. Meanwhie, DHB enhanced the expression of cleaved activating transcription factor-6 (ATF-6), a biomarker of unfolded protein response (UPR). Expression of calnexin and calreticulin, chaperones activated by ATF-6 to facilitate channel folding, were also increased, which indicating UPR activation. Additionally, the degradation rate of mature 155-kDa hERG increased following DHB exposure. In conclusion, we demonstrated that DHB acutely blocked hERG channels by binding the aromatic Tyr652 and Phe656. DHB may decrease hERG plasma membrane expression through two pathways involving disruption of forward trafficking of immature hERG channels and enhanced degradation of mature hERG channels. Furthermore, forward trafficking was disrupted by impaired channel folding associated with altered interactions between hERG proteins and chaperones. Finally, trafficking inhibition activated UPR, and mature hERG channel degradation was increased by DHB.
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Affiliation(s)
- Dahai Yu
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Lin Lv
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Li Fang
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Bo Zhang
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Junnan Wang
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Ge Zhan
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Lei Zhao
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Xin Zhao
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
| | - Baoxin Li
- Department of Pharmacology, College of Pharmacy, Harbin Medical University, Harbin, Heilongjiang Province, People's Republic of China
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11
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Liu L, Tian J, Lu C, Chen X, Fu Y, Xu B, Zhu C, Sun Y, Zhang Y, Zhao Y, Li Y. Electrophysiological Characteristics of the LQT2 Syndrome Mutation KCNH2-G572S and Regulation by Accessory Protein KCNE2. Front Physiol 2016; 7:650. [PMID: 28082916 PMCID: PMC5187237 DOI: 10.3389/fphys.2016.00650] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Accepted: 12/12/2016] [Indexed: 01/18/2023] Open
Abstract
Mutations in hERG cause long QT syndrome type 2 which is characterized by a prolonged QT interval on electrocardiogram and predisposition to life-threatening ventricular tachyarrhythmia, syncope, and sudden death. hERG-G572S induces trafficking defects of hERG channel protein from Golgi to the plasma membrane and results in a dominant negative suppression of hERG current density. As an accessory β subunit, KCNE2 promotes hERG migration from Golgi to cellular membrane. In this study, we investigated the rescue effect of KCNE2 in a G572S mutation of hERG. Transfection was performed into HEK293 cells. Patch clamp technique, western blotting analyses and confocal microscopic examination were used. Results showed that KCNE2 had a significantly enhanced effect on G572S mutation current. The increase of current was largest at KCNH2:KCNE2 of 1:3. Confocal images showed co-expressing G572S and KCNE2 could cause a substantial up-regulated membrane protein (155 kDa) expression. Expression of membrane protein accumulated markedly with increasing ratio of KCNH2:KCNE2. G572S defective mutant could be restored by both KCNE2 and lower temperature (27°C), which suggested that the lower temperature could be the favorable circumstances for the rescue function of KCNE2. In this study, we successfully set up “the action potential” on the HEK 293 cells by genetically engineered to express Kir2.1, Nav1.5, and Kv11.1, wherein on reaching over an excitation threshold by current injection. The results suggested that KCNE2 could shorten action potential duration which was prolonged by G572S. These findings described electrophysiological characteristics of the LQT2 syndrome mutation KCNH2-G572S and regulation by accessory protein KCNE2, and provided a clue about LQT2 and relative rescue mechanism.
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Affiliation(s)
- Li Liu
- Department of Cardiology, General Hospital of People's Liberation ArmyBeijing, China; The Third Department of Internal Medicine, Beijing Municipal Corps Hospital of Chinese People's Armed Police ForceBeijing, China
| | - Jinwen Tian
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Caiyi Lu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Xi Chen
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yicheng Fu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Bin Xu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Chao Zhu
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yanmei Sun
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yu Zhang
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Ying Zhao
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
| | - Yang Li
- Department of Cardiology, General Hospital of People's Liberation Army Beijing, China
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12
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Grandi E, Sanguinetti MC, Bartos DC, Bers DM, Chen-Izu Y, Chiamvimonvat N, Colecraft HM, Delisle BP, Heijman J, Navedo MF, Noskov S, Proenza C, Vandenberg JI, Yarov-Yarovoy V. Potassium channels in the heart: structure, function and regulation. J Physiol 2016; 595:2209-2228. [PMID: 27861921 DOI: 10.1113/jp272864] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Accepted: 07/18/2016] [Indexed: 12/22/2022] Open
Abstract
This paper is the outcome of the fourth UC Davis Systems Approach to Understanding Cardiac Excitation-Contraction Coupling and Arrhythmias Symposium, a biannual event that aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2016 symposium was 'K+ Channels and Regulation'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies and challenges on the topic of cardiac K+ channels. This paper summarizes the topics of formal presentations and informal discussions from the symposium on the structural basis of voltage-gated K+ channel function, as well as the mechanisms involved in regulation of K+ channel gating, expression and membrane localization. Given the critical role for K+ channels in determining the rate of cardiac repolarization, it is hardly surprising that essentially every aspect of K+ channel function is exquisitely regulated in cardiac myocytes. This regulation is complex and highly interrelated to other aspects of myocardial function. K+ channel regulatory mechanisms alter, and are altered by, physiological challenges, pathophysiological conditions, and pharmacological agents. An accompanying paper focuses on the integrative role of K+ channels in cardiac electrophysiology, i.e. how K+ currents shape the cardiac action potential, and how their dysfunction can lead to arrhythmias, and discusses K+ channel-based therapeutics. A fundamental understanding of K+ channel regulatory mechanisms and disease processes is fundamental to reveal new targets for human therapy.
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Affiliation(s)
- Eleonora Grandi
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Michael C Sanguinetti
- Department of Internal Medicine, University of Utah, Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT, 84112, USA
| | - Daniel C Bartos
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Ye Chen-Izu
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA.,Department of Internal Medicine, Division of Cardiology, University of California, Davis, CA, 95616, USA
| | - Nipavan Chiamvimonvat
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, CA, 95616, USA
| | - Henry M Colecraft
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, 10032, USA
| | - Brian P Delisle
- Department of Physiology, University of Kentucky, Lexington, KY, 40536, USA
| | - Jordi Heijman
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Faculty of Health, Medicine, and Life Sciences, Maastricht University, Maastricht, The Netherlands
| | - Manuel F Navedo
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Sergei Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB, T2N 1N4, Canada
| | - Catherine Proenza
- Department of Physiology and Biophysics, University of Colorado - Anschutz Medical Campus, Denver, CO, 80045, USA
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, Darlinghurst, NSW, 2010, Australia
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA
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13
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Andrade A, Hope J, Allen A, Yorgan V, Lipscombe D, Pan JQ. A rare schizophrenia risk variant of CACNA1I disrupts Ca V3.3 channel activity. Sci Rep 2016; 6:34233. [PMID: 27756899 PMCID: PMC5069464 DOI: 10.1038/srep34233] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Accepted: 09/07/2016] [Indexed: 02/04/2023] Open
Abstract
CACNA1I is a candidate schizophrenia risk gene. It encodes the pore-forming human CaV3.3 α1 subunit, a subtype of voltage-gated calcium channel that contributes to T-type currents. Recently, two de novo missense variations, T797M and R1346H, of hCaV3.3 were identified in individuals with schizophrenia. Here we show that R1346H, but not T797M, is associated with lower hCaV3.3 protein levels, reduced glycosylation, and lower membrane surface levels of hCaV3.3 when expressed in human cell lines compared to wild-type. Consistent with our biochemical analyses, whole-cell hCaV3.3 currents in cells expressing the R1346H variant were ~50% of those in cells expressing WT hCaV3.3, and neither R1346H nor T797M altered channel biophysical properties. Employing the NEURON simulation environment, we found that reducing hCaV3.3 current densities by 22% or more eliminates rebound bursting in model thalamic reticular nucleus (TRN) neurons. Our analyses suggest that a single copy of Chr22: 39665939G > A CACNA1I has the capacity to disrupt CaV3.3 channel-dependent functions, including rebound bursting in TRN neurons, with potential implications for schizophrenia pathophysiology.
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Affiliation(s)
- A Andrade
- Department of Biological Sciences, College of Life Sciences and Agriculture, University of New Hampshire, Durham, NH 03824, USA.,Brown Institute for Brain Science, Providence, RI 02912, USA
| | - J Hope
- Stanley Center of Psychiatric Research, Broad Institute of Harvard and MIT, 75 Ames Street, Cambridge, MA 02142, USA
| | - A Allen
- Stanley Center of Psychiatric Research, Broad Institute of Harvard and MIT, 75 Ames Street, Cambridge, MA 02142, USA
| | - V Yorgan
- Brown Institute for Brain Science, Providence, RI 02912, USA
| | - D Lipscombe
- Brown Institute for Brain Science, Providence, RI 02912, USA
| | - J Q Pan
- Stanley Center of Psychiatric Research, Broad Institute of Harvard and MIT, 75 Ames Street, Cambridge, MA 02142, USA
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14
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Spence S, Deurinck M, Ju H, Traebert M, McLean L, Marlowe J, Emotte C, Tritto E, Tseng M, Shultz M, Friedrichs GS. Histone Deacetylase Inhibitors Prolong Cardiac Repolarization through Transcriptional Mechanisms. Toxicol Sci 2016; 153:39-54. [PMID: 27255383 DOI: 10.1093/toxsci/kfw104] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Histone deacetylase (HDAC) inhibitors are an emerging class of anticancer agents that modify gene expression by altering the acetylation status of lysine residues of histone proteins, thereby inducing transcription, cell cycle arrest, differentiation, and cell death or apoptosis of cancer cells. In the clinical setting, treatment with HDAC inhibitors has been associated with delayed cardiac repolarization and in rare instances a lethal ventricular tachyarrhythmia known as torsades de pointes. The mechanism(s) of HDAC inhibitor-induced effects on cardiac repolarization is unknown. We demonstrate that administration of structurally diverse HDAC inhibitors to dogs causes delayed but persistent increases in the heart rate corrected QT interval (QTc), an in vivo measure of cardiac repolarization, at timepoints far removed from the Tmax for parent drug and metabolites. Transcriptional profiling of ventricular myocardium from dogs treated with various HDAC inhibitors demonstrated effects on genes involved in protein trafficking, scaffolding and insertion of various ion channels into the cell membrane as well as genes for specific ion channel subunits involved in cardiac repolarization. Extensive in vitro ion channel profiling of various structural classes of HDAC inhibitors (and their major metabolites) by binding and acute patch clamp assays failed to show any consistent correlations with direct ion channel blockade. Drug-induced rescue of an intracellular trafficking-deficient mutant potassium ion channel, hERG (G601S), and decreased maturation (glycosylation) of wild-type hERG expressed by CHO cells in vitro correlated with prolongation of QTc intervals observed in vivo The results suggest that HDAC inhibitor-induced prolongation of cardiac repolarization may be mediated in part by transcriptional changes of genes required for ion channel trafficking and localization to the sarcolemma. These data have broad implications for the development of these drug classes and suggest that the optimal time to assess potentially transcriptionally mediated physiologic effects will be delayed relative to an epigenetic drug's Tmax/Cmax.
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Affiliation(s)
- Stan Spence
- *Preclinical Safety, Novartis Institutes of Biomedical Research, 100 Technology Square, Cambridge, MA 02139
| | - Mark Deurinck
- Preclinical Safety, Novartis Institutes of Biomedical Research, Klybeckstrasse 141, CH-4057, Basel, CH
| | - Haisong Ju
- Preclinical Safety, Novartis Institutes of Biomedical Research, One Health Plaza, East Hanover, NJ 07936-1080
| | - Martin Traebert
- Preclinical Safety, Novartis Institutes of Biomedical Research, Klybeckstrasse 141, CH-4057, Basel, CH
| | - LeeAnne McLean
- Oncology Global Development, Novartis Pharmaceuticals Corporation, One Health Plaza, East Hanover, NJ 07936-1080
| | - Jennifer Marlowe
- *Preclinical Safety, Novartis Institutes of Biomedical Research, 100 Technology Square, Cambridge, MA 02139
| | - Corinne Emotte
- Drug Metabolism and Pharmacokinetics, Novartis Pharmaceuticals Corporation, Fabrikstrasse 14-3.02.08, Basel, CH
| | - Elaine Tritto
- Preclinical Safety, Novartis Institutes of Biomedical Research, Klybeckstrasse 141, CH-4057, Basel, CH
| | - Min Tseng
- Development Sciences, Safety Assessment, Investigative Toxicology, Genentech Inc, 550 Grandview Drive, South San Francisco, CA 94080
| | - Michael Shultz
- Global Discovery Chemistry, Novartis Institutes for BioMedical Research Inc, 250 Massachusetts Avenue, Cambridge, MA 02139
| | - Gregory S Friedrichs
- Preclinical Safety, Novartis Institutes of Biomedical Research, One Health Plaza, East Hanover, NJ 07936-1080
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15
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Calcaterra NE, Hoeppner DJ, Wei H, Jaffe AE, Maher BJ, Barrow JC. Schizophrenia-Associated hERG channel Kv11.1-3.1 Exhibits a Unique Trafficking Deficit that is Rescued Through Proteasome Inhibition for High Throughput Screening. Sci Rep 2016; 6:19976. [PMID: 26879421 PMCID: PMC4754628 DOI: 10.1038/srep19976] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 12/22/2015] [Indexed: 12/24/2022] Open
Abstract
The primate-specific brain voltage-gated potassium channel isoform Kv11.1-3.1 has been identified as a novel therapeutic target for the treatment of schizophrenia. While this ether-a-go-go related K + channel has shown clinical relevance, drug discovery efforts have been hampered due to low and inconsistent activity in cell-based assays. This poor activity is hypothesized to result from poor trafficking via the lack of an intact channel-stabilizing Per-Ant-Sim (PAS) domain. Here we characterize Kv11.1-3.1 cellular localization and show decreased channel expression and cell surface trafficking relative to the PAS-domain containing major isoform, Kv11.1-1A. Using small molecule inhibition of proteasome degradation, cellular expression and plasma membrane trafficking are rescued. These findings implicate the importance of the unfolded-protein response and endoplasmic reticulum associated degradation pathways in the expression and regulation of this schizophrenia risk factor. Utilizing this identified phenomenon, an electrophysiological and high throughput in-vitro fluorescent assay platform has been developed for drug discovery in order to explore a potentially new class of cognitive therapeutics.
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Affiliation(s)
| | | | - Huijun Wei
- Lieber Institute for Brain Development, Baltimore, MD 21205
| | - Andrew E Jaffe
- Lieber Institute for Brain Development, Baltimore, MD 21205.,Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205
| | - Brady J Maher
- Lieber Institute for Brain Development, Baltimore, MD 21205.,Departments of Psychiatry and Behavioral Sciences, Baltimore, MD 21205.,Departments of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - James C Barrow
- Departments of Pharmacology and Molecular Sciences, Baltimore, MD 21205.,Lieber Institute for Brain Development, Baltimore, MD 21205
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16
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Smith JL, Anderson CL, Burgess DE, Elayi CS, January CT, Delisle BP. Molecular pathogenesis of long QT syndrome type 2. J Arrhythm 2016; 32:373-380. [PMID: 27761161 PMCID: PMC5063260 DOI: 10.1016/j.joa.2015.11.009] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 10/21/2015] [Accepted: 11/17/2015] [Indexed: 12/26/2022] Open
Abstract
The molecular mechanisms underlying congenital long QT syndrome (LQTS) are now beginning to be understood. New insights into the etiology and therapeutic strategies are emerging from heterologous expression studies of LQTS-linked mutant proteins, as well as inducible pluripotent stem cell derived cardiomyocytes (iPSC-CMs) from LQTS patients. This review focuses on the major molecular mechanism that underlies LQTS type 2 (LQT2). LQT2 is caused by loss of function (LOF) mutations in KCNH2 (also known as the human Ether-à-go-go-Related Gene or hERG). Most LQT2-linked mutations are missense mutations and functional studies suggest that ~90% of them disrupt the intracellular transport (trafficking) of KCNH2-encoded Kv11.1 proteins to the cell membrane. Trafficking deficient LQT2 mutations disrupt Kv11.1 protein folding and misfolded Kv11.1 proteins are retained in the endoplasmic reticulum (ER) until they are degraded in the ER associated degradation pathway (ERAD). This review focuses on the quality control mechanisms in the ER that contribute to the folding and ERAD of Kv11.1 proteins; the mechanism for ER export of Kv11.1 proteins in the secretory pathway; different subclasses of trafficking deficient LQT2 mutations; and strategies being developed to mitigate or correct trafficking deficient LQT2-related phenotypes.
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Affiliation(s)
- Jennifer L Smith
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
| | - Corey L Anderson
- Cellular and Molecular Arrhythmia Research Program, University of Wisconsin, Madison, WI, USA
| | - Don E Burgess
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
| | - Claude S Elayi
- Department of Cardiology, Gill Heart Institute, University of Kentucky, Lexington, KY, USA
| | - Craig T January
- Cellular and Molecular Arrhythmia Research Program, University of Wisconsin, Madison, WI, USA
| | - Brian P Delisle
- Department of Physiology, Cardiovascular Research Center, Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
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17
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Lin EC, Moungey BM, Lim E, Concannon SP, Anderson CL, Kyle JW, Makielski JC, Balijepalli SY, January CT. Mouse ERG K(+) channel clones reveal differences in protein trafficking and function. J Am Heart Assoc 2014; 3:e001491. [PMID: 25497881 PMCID: PMC4338741 DOI: 10.1161/jaha.114.001491] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background The mouse ether‐a‐go‐go‐related gene 1a (mERG1a, mKCNH2) encodes mERG K+ channels in mouse cardiomyocytes. The mERG channels and their human analogue, hERG channels, conduct IKr. Mutations in hERG channels reduce IKr to cause congenital long‐QT syndrome type 2, mostly by decreasing surface membrane expression of trafficking‐deficient channels. Three cDNA sequences were originally reported for mERG channels that differ by 1 to 4 amino acid residues (mERG‐London, mERG‐Waterston, and mERG‐Nie). We characterized these mERG channels to test the postulation that they would differ in their protein trafficking and biophysical function, based on previous findings in long‐QT syndrome type 2. Methods and Results The 3 mERG and hERG channels were expressed in HEK293 cells and neonatal mouse cardiomyocytes and were studied using Western blot and whole‐cell patch clamp. We then compared our findings with the recent sequencing results in the Welcome Trust Sanger Institute Mouse Genomes Project (WTSIMGP). Conclusions First, the mERG‐London channel with amino acid substitutions in regions of highly ordered structure is trafficking deficient and undergoes temperature‐dependent and pharmacological correction of its trafficking deficiency. Second, the voltage dependence of channel gating would be different for the 3 mERG channels. Third, compared with the WTSIMGP data set, the mERG‐Nie clone is likely to represent the wild‐type mouse sequence and physiology. Fourth, the WTSIMGP analysis suggests that substrain‐specific sequence differences in mERG are a common finding in mice. These findings with mERG channels support previous findings with hERG channel structure–function analyses in long‐QT syndrome type 2, in which sequence changes in regions of highly ordered structure are likely to result in abnormal protein trafficking.
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Affiliation(s)
- Eric C Lin
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Brooke M Moungey
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Evi Lim
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Sarah P Concannon
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Corey L Anderson
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - John W Kyle
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Jonathan C Makielski
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Sadguna Y Balijepalli
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Craig T January
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
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18
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Zhang KP, Yang BF, Li BX. Translational toxicology and rescue strategies of the hERG channel dysfunction: biochemical and molecular mechanistic aspects. Acta Pharmacol Sin 2014; 35:1473-84. [PMID: 25418379 PMCID: PMC4261120 DOI: 10.1038/aps.2014.101] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Accepted: 08/20/2014] [Indexed: 01/08/2023] Open
Abstract
The human ether-à-go-go related gene (hERG) potassium channel is an obligatory anti-target for drug development on account of its essential role in cardiac repolarization and its close association with arrhythmia. Diverse drugs have been removed from the market owing to their inhibitory activity on the hERG channel and their contribution to acquired long QT syndrome (LQTS). Moreover, mutations that cause hERG channel dysfunction may induce congenital LQTS. Recently, an increasing number of biochemical and molecular mechanisms underlying hERG-associated LQTS have been reported. In fact, numerous potential biochemical and molecular rescue strategies are hidden within the biogenesis and regulating network. So far, rescue strategies of hERG channel dysfunction and LQTS mainly include activators, blockers, and molecules that interfere with specific links and other mechanisms. The aim of this review is to discuss the rescue strategies based on hERG channel toxicology from the biochemical and molecular perspectives.
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Affiliation(s)
- Kai-ping Zhang
- Department of Pharmacology, Harbin Medical University, Harbin, China
- The State-Province Key Laboratories of Biomedicine-Pharmaceutics of China (Key Laboratory of Cardiovascular Research, Ministry of Education), China
| | - Bao-feng Yang
- Department of Pharmacology, Harbin Medical University, Harbin, China
- The State-Province Key Laboratories of Biomedicine-Pharmaceutics of China (Key Laboratory of Cardiovascular Research, Ministry of Education), China
| | - Bao-xin Li
- Department of Pharmacology, Harbin Medical University, Harbin, China
- The State-Province Key Laboratories of Biomedicine-Pharmaceutics of China (Key Laboratory of Cardiovascular Research, Ministry of Education), China
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Wang Q, Hu W, Lei M, Wang Y, Yan B, Liu J, Zhang R, Jin Y. MiR-17-5p impairs trafficking of H-ERG K+ channel protein by targeting multiple er stress-related chaperones during chronic oxidative stress. PLoS One 2013; 8:e84984. [PMID: 24386440 PMCID: PMC3875566 DOI: 10.1371/journal.pone.0084984] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Accepted: 11/29/2013] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND To investigate if microRNAs (miRNAs) play a role in regulating h-ERG trafficking in the setting of chronic oxidative stress as a common deleterious factor for many cardiac disorders. METHODS We treated neonatal rat ventricular myocytes and HEK293 cells with stable expression of h-ERG with H2O2 for 12 h and 48 h. Expression of miR-17-5p seed miRNAs was quantified by real-time RT-PCR. Protein levels of chaperones and h-ERG trafficking were measured by Western blot analysis. Luciferase reporter gene assay was used to study miRNA and target interactions. Whole-cell patch-clamp techniques were employed to record h-ERG K(+) current. RESULTS H-ERG trafficking was impaired by H2O2 after 48 h treatment, accompanied by reciprocal changes of expression between miR-17-5p seed miRNAs and several chaperones (Hsp70, Hsc70, CANX, and Golga2), with the former upregulated and the latter downregulated. We established these chaperones as targets for miR-17-5p. Application miR-17-5p inhibitor rescued H2O2-induced impairment of h-ERG trafficking. Upregulation of endogenous by H2O2 or forced miR-17-5p expression either reduced h-ERG current. Sequestration of AP1 by its decoy molecule eliminated the upregulation of miR-17-5p, and ameliorated impairment of h-ERG trafficking. CONCLUSIONS Collectively, deregulation of the miR-17-5p seed family miRNAs can cause severe impairment of h-ERG trafficking through targeting multiple ER stress-related chaperones, and activation of AP1 likely accounts for the deleterious upregulation of these miRNAs, in the setting of prolonged duration of oxidative stress. These findings revealed the role of miRNAs in h-ERG trafficking, which may contribute to the cardiac electrical disturbances associated with oxidative stress.
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Affiliation(s)
- Qi Wang
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Weina Hu
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Mingming Lei
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Yong Wang
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Bing Yan
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Jun Liu
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Ren Zhang
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
| | - Yuanzhe Jin
- The Fourth Affiliated Hospital of China Medical University, Shenyang, Liaoning Province, P. R. China
- * E-mail:
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20
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Bellin M, Casini S, Davis RP, D'Aniello C, Haas J, Ward-van Oostwaard D, Tertoolen LGJ, Jung CB, Elliott DA, Welling A, Laugwitz KL, Moretti A, Mummery CL. Isogenic human pluripotent stem cell pairs reveal the role of a KCNH2 mutation in long-QT syndrome. EMBO J 2013; 32:3161-75. [PMID: 24213244 PMCID: PMC3981141 DOI: 10.1038/emboj.2013.240] [Citation(s) in RCA: 148] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 10/11/2013] [Indexed: 12/16/2022] Open
Abstract
Patient-specific induced pluripotent stem cells (iPSCs) will assist research on genetic cardiac maladies if the disease phenotype is recapitulated in vitro. However, genetic background variations may confound disease traits, especially for disorders with incomplete penetrance, such as long-QT syndromes (LQTS). To study the LQT2-associated c.A2987T (N996I) KCNH2 mutation under genetically defined conditions, we derived iPSCs from a patient carrying this mutation and corrected it. Furthermore, we introduced the same point mutation in human embryonic stem cells (hESCs), generating two genetically distinct isogenic pairs of LQTS and control lines. Correction of the mutation normalized the current (IKr) conducted by the HERG channel and the action potential (AP) duration in iPSC-derived cardiomyocytes (CMs). Introduction of the same mutation reduced IKr and prolonged the AP duration in hESC-derived CMs. Further characterization of N996I-HERG pathogenesis revealed a trafficking defect. Our results demonstrated that the c.A2987T KCNH2 mutation is the primary cause of the LQTS phenotype. Precise genetic modification of pluripotent stem cells provided a physiologically and functionally relevant human cellular context to reveal the pathogenic mechanism underlying this specific disease phenotype. Isogenic pairs of patient-derived iPS- and ES-cell lines reveal the molecular problems contributing to cardiac arrest in long-QT syndrome.
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Affiliation(s)
- Milena Bellin
- Department of Anatomy and Embryology, Leiden University Medical Center, Leiden, The Netherlands
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21
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Ayon RJ, Fernandez RA, Yuan JXJ. Mutant hERG channel traffic jam. Focus on "Pharmacological correction of long QT-linked mutations in KCNH2 (hERG) increases the trafficking of Kv11.1 channels stored in the transitional endoplasmic reticulum". Am J Physiol Cell Physiol 2013; 305:C916-8. [PMID: 23986200 DOI: 10.1152/ajpcell.00256.2013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Ramon J Ayon
- Division of Pulmonary, Critical Care, Sleep and Allergy Medicine, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois; Institute for Personalized Respiratory Medicine, University of Illinois at Chicago, Chicago, Illinois; Department of Pharmacology, University of Illinois at Chicago, Chicago, Illinois; and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois
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22
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Smith JL, Reloj AR, Nataraj PS, Bartos DC, Schroder EA, Moss AJ, Ohno S, Horie M, Anderson CL, January CT, Delisle BP. Pharmacological correction of long QT-linked mutations in KCNH2 (hERG) increases the trafficking of Kv11.1 channels stored in the transitional endoplasmic reticulum. Am J Physiol Cell Physiol 2013; 305:C919-30. [PMID: 23864605 DOI: 10.1152/ajpcell.00406.2012] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
KCNH2 encodes Kv11.1 and underlies the rapidly activating delayed rectifier K(+) current (IKr) in the heart. Loss-of-function KCNH2 mutations cause the type 2 long QT syndrome (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channels. Drugs that bind to Kv11.1 and block IKr (e.g., E-4031) can act as pharmacological chaperones to increase the trafficking and functional expression for most LQT2 channels (pharmacological correction). We previously showed that LQT2 channels are selectively stored in a microtubule-dependent compartment within the endoplasmic reticulum (ER). We tested the hypothesis that pharmacological correction promotes the trafficking of LQT2 channels stored in this compartment. Confocal analyses of cells expressing the trafficking-deficient LQT2 channel G601S showed that the microtubule-dependent ER compartment is the transitional ER. Experiments with E-4031 and the protein synthesis inhibitor cycloheximide suggested that pharmacological correction promotes the trafficking of G601S stored in this compartment. Treating cells in E-4031 or ranolazine (a drug that blocks IKr and has a short half-life) for 30 min was sufficient to cause pharmacological correction. Moreover, the increased functional expression of G601S persisted 4-5 h after drug washout. Coexpression studies with a dominant-negative form of Rab11B, a small GTPase that regulates Kv11.1 trafficking, prevented the pharmacological correction of G601S trafficking from the transitional ER. These data suggest that pharmacological correction quickly increases the trafficking of LQT2 channels stored in the transitional ER via a Rab11B-dependent pathway, and we conclude that the pharmacological chaperone activity of drugs like ranolazine might have therapeutic potential.
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Affiliation(s)
- Jennifer L Smith
- Center for Muscle Biology, Department of Physiology, University of Kentucky, Lexington, Kentucky
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23
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Mechanistic basis for type 2 long QT syndrome caused by KCNH2 mutations that disrupt conserved arginine residues in the voltage sensor. J Membr Biol 2013; 246:355-64. [PMID: 23546015 DOI: 10.1007/s00232-013-9539-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Accepted: 03/19/2013] [Indexed: 01/24/2023]
Abstract
KCNH2 encodes the Kv11.1 channel, which conducts the rapidly activating delayed rectifier K+ current (I Kr) in the heart. KCNH2 mutations cause type 2 long QT syndrome (LQT2), which increases the risk for life-threatening ventricular arrhythmias. LQT2 mutations are predicted to prolong the cardiac action potential (AP) by reducing I Kr during repolarization. Kv11.1 contains several conserved basic amino acids in the fourth transmembrane segment (S4) of the voltage sensor that are important for normal channel trafficking and gating. This study sought to determine the mechanism(s) by which LQT2 mutations at conserved arginine residues in S4 (R531Q, R531W or R534L) alter Kv11.1 function. Western blot analyses of HEK293 cells transiently expressing R531Q, R531W or R534L suggested that only R534L inhibited Kv11.1 trafficking. Voltage-clamping experiments showed that R531Q or R531W dramatically altered Kv11.1 current (I Kv11.1) activation, inactivation, recovery from inactivation and deactivation. Coexpression of wild type (to mimic the patients' genotypes) mostly corrected the changes in I Kv11.1 activation and inactivation, but deactivation kinetics were still faster. Computational simulations using a human ventricular AP model showed that accelerating deactivation rates was sufficient to prolong the AP, but these effects were minimal compared to simply reducing I Kr. These are the first data to demonstrate that coexpressing wild type can correct activation and inactivation dysfunction caused by mutations at a critical voltage-sensing residue in Kv11.1. We conclude that some Kv11.1 mutations might accelerate deactivation to cause LQT2 but that the ventricular AP duration is much more sensitive to mutations that decrease I Kr. This likely explains why most LQT2 mutations are nonsense or trafficking-deficient.
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Krishnan Y, Li Y, Zheng R, Kanda V, McDonald TV. Mechanisms underlying the protein-kinase mediated regulation of the HERG potassium channel synthesis. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1823:1273-84. [PMID: 22613764 DOI: 10.1016/j.bbamcr.2012.05.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Revised: 05/10/2012] [Accepted: 05/10/2012] [Indexed: 12/11/2022]
Abstract
The HERG (human ether-a-go-go related gene) potassium channel aids in the repolarization of the cardiomyocyte membrane at the end of each action potential. We have previously shown that sustained protein kinase A or C (PKA and PKC) activity specifically enhances channel synthesis over the course of hours to days in heterologous expression and cardiac myocytes. The kinase-mediated augmentation of the channel is post-transcriptional and occurs near or at the endoplasmic reticulum. Here we report our further investigations into the mechanisms of kinase-mediated augmentation of HERG channel protein. We show that HERG channel phosphorylation alone is not sufficient for the PKA-dependent increase to occur. In vitro translation studies indicate that an additional factor is required for the process. Pharmacologic inhibitors suggest that the channel augmentation is not due to kinase-mediated alteration in proteasome or lysosome activity. PKA activation had no effect on stability of HERG mRNA and polyribosomal profiling showed that kinase activity did not elevate translation from low to high rates. Transcriptional inhibition results suggest that the additional cellular factor is a PKA-regulated protein. Together, these findings suggest that PKA-mediated augmentation of HERG abundance is more complex than previously appreciated involving enhancement of already active translation rates, phosphorylation of the channel protein and at least one other cyclic-AMP/PKA-responsive protein. Further exploration of molecular components of this regulatory pathway will be necessary to determine exact mechanism and the biomedical impact of this process in vivo.
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Affiliation(s)
- Yamini Krishnan
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY, USA
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25
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Okubo J, Takita J, Chen Y, Oki K, Nishimura R, Kato M, Sanada M, Hiwatari M, Hayashi Y, Igarashi T, Ogawa S. Aberrant activation of ALK kinase by a novel truncated form ALK protein in neuroblastoma. Oncogene 2012; 31:4667-76. [PMID: 22249260 DOI: 10.1038/onc.2011.616] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Anaplastic lymphoma kinase (ALK) was originally identified from a rare subtype of non-Hodgkin's lymphomas carrying t(2;5)(p23;q35) translocation, where ALK was constitutively activated as a result of a fusion with nucleophosmin (NPM). Aberrant ALK fusion proteins were also generated in inflammatory fibrosarcoma and a subset of non-small-cell lung cancers, and these proteins are implicated in their pathogenesis. Recently, ALK has been demonstrated to be constitutively activated by gene mutations and/or amplifications in sporadic as well as familial cases of neuroblastoma. Here we describe another mechanism of aberrant ALK activation observed in a neuroblastoma-derived cell line (NB-1), in which a short-form ALK protein (ALK(del2-3)) having a truncated extracellular domain is overexpressed because of amplification of an abnormal ALK gene that lacks exons 2 and 3. ALK(del2-3) was autophosphorylated in NB-1 cells as well as in ALK(del2-3)-transduced cells and exhibited enhanced in vitro kinase activity compared with the wild-type kinase. ALK(del2-3)-transduced NIH3T3 cells exhibited increased colony-forming capacity in soft agar and tumorigenicity in nude mice. RNAi-mediated ALK knockdown resulted in the growth suppression of ALK(del2-3)-expressing cells, arguing for the oncogenic role of this mutant. Our findings provide a novel insight into the mechanism of deregulation of the ALK kinase and its roles in neuroblastoma pathogenesis.
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Affiliation(s)
- J Okubo
- Department of Pediatrics, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
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