1
|
Stevens-Sostre WA, Flores-Aldama L, Bustos D, Li J, Morais-Cabral JH, Delemotte L, Robertson GA. An intracellular hydrophobic nexus critical for hERG1 channel slow deactivation. Biophys J 2024; 123:2024-2037. [PMID: 38219015 PMCID: PMC11309987 DOI: 10.1016/j.bpj.2024.01.010] [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: 08/28/2023] [Revised: 11/17/2023] [Accepted: 01/09/2024] [Indexed: 01/15/2024] Open
Abstract
Slow deactivation is a critical property of voltage-gated K+ channels encoded by the human Ether-à-go-go-Related Gene 1 (hERG). hERG1 channel deactivation is modulated by interactions between intracellular N-terminal Per-Arnt-Sim (PAS) and C-terminal cyclic nucleotide-binding homology (CNBh) domains. The PAS domain is multipartite, comprising a globular domain (gPAS; residues 26-135) and an N-terminal PAS-cap that is further subdivided into an initial unstructured "tip" (residues 1-12) and an amphipathic α-helical region (residues 13-25). Although the PAS-cap tip has long been considered the effector of slow deactivation, how its position near the gating machinery is controlled has not been elucidated. Here, we show that a triad of hydrophobic interactions among the gPAS, PAS-cap α helix, and the CNBh domains is required to support slow deactivation in hERG1. The primary sequence of this "hydrophobic nexus" is highly conserved among mammalian ERG channels but shows key differences to fast-deactivating Ether-à-go-go 1 (EAG1) channels. Combining sequence analysis, structure-directed mutagenesis, electrophysiology, and molecular dynamics simulations, we demonstrate that polar serine substitutions uncover an intermediate deactivation mode that is also mimicked by deletion of the PAS-cap α helix. Molecular dynamics simulation analyses of the serine-substituted channels show an increase in distance among the residues of the hydrophobic nexus, a rotation of the intracellular gating ring, and a retraction of the PAS-cap tip from its receptor site near the voltage sensor domain and channel gate. These findings provide compelling evidence that the hydrophobic nexus coordinates the respective components of the intracellular gating ring and positions the PAS-cap tip to control hERG1 deactivation gating.
Collapse
Affiliation(s)
- Whitney A Stevens-Sostre
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
| | - Lisandra Flores-Aldama
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
| | - Daniel Bustos
- Centro de Investigación de Estudios Avanzados Del Maule (CIEAM), Vicerrectoría de Investigación y Postgrado, Universidad Católica Del Maule, Talca, Chile; Laboratorio de Bioinformática y Química Computacional (LBQC), Departamento de Medicina Traslacional, Facultad de Medicina, Universidad Católica Del Maule, Talca, Chile
| | - Jin Li
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
| | - João H Morais-Cabral
- Instituto de Investigação e Inovação Em Saude da Universidade Do Porto (i3S); Instituto de Biologia Molecular e Celular, Universidade Do Porto, Porto, Portugal
| | - Lucie Delemotte
- KTH Royal Institute of Technology, Science for Life Laboratory, Stockholm, Sweden
| | - Gail A Robertson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
| |
Collapse
|
2
|
Immadisetty K, Fang X, Ramon GS, Hartle CM, McCoy TP, Center RG, Mirshahi T, Delisle BP, Kekenes-Huskey PM. Prediction of Kv11.1 potassium channel PAS-domain variants trafficking via machine learning. J Mol Cell Cardiol 2023; 180:69-83. [PMID: 37187232 DOI: 10.1016/j.yjmcc.2023.05.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 04/28/2023] [Accepted: 05/09/2023] [Indexed: 05/17/2023]
Abstract
Congenital long QT syndrome (LQTS) is characterized by a prolonged QT-interval on an electrocardiogram (ECG). An abnormal prolongation in the QT-interval increases the risk for fatal arrhythmias. Genetic variants in several different cardiac ion channel genes, including KCNH2, are known to cause LQTS. Here, we evaluated whether structure-based molecular dynamics (MD) simulations and machine learning (ML) could improve the identification of missense variants in LQTS-linked genes. To do this, we investigated KCNH2 missense variants in the Kv11.1 channel protein shown to have wild type (WT) like or class II (trafficking-deficient) phenotypes in vitro. We focused on KCNH2 missense variants that disrupt normal Kv11.1 channel protein trafficking, as it is the most common phenotype for LQTS-associated variants. Specifically, we used computational techniques to correlate structural and dynamic changes in the Kv11.1 channel protein PAS domain (PASD) with Kv11.1 channel protein trafficking phenotypes. These simulations unveiled several molecular features, including the numbers of hydrating waters and hydrogen bonding pairs, as well as folding free energy scores, that are predictive of trafficking. We then used statistical and machine learning (ML) (Decision tree (DT), Random forest (RF), and Support vector machine (SVM)) techniques to classify variants using these simulation-derived features. Together with bioinformatics data, such as sequence conservation and folding energies, we were able to predict with reasonable accuracy (≈75%) which KCNH2 variants do not traffic normally. We conclude that structure-based simulations of KCNH2 variants localized to the Kv11.1 channel PASD led to an improvement in classification accuracy. Therefore, this approach should be considered to complement the classification of variant of unknown significance (VUS) in the Kv11.1 channel PASD.
Collapse
Affiliation(s)
| | - Xuan Fang
- Stritch School of Medicine, Loyola University Chicago, Maywood, IL, USA
| | | | | | | | | | | | | | | |
Collapse
|
3
|
Meier S, Grundland A, Dobrev D, Volders PG, Heijman J. In silico analysis of the dynamic regulation of cardiac electrophysiology by K v 11.1 ion-channel trafficking. J Physiol 2023; 601:2711-2731. [PMID: 36752166 PMCID: PMC10313819 DOI: 10.1113/jp283976] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 01/30/2023] [Indexed: 02/09/2023] Open
Abstract
Cardiac electrophysiology is regulated by continuous trafficking and internalization of ion channels occurring over minutes to hours. Kv 11.1 (also known as hERG) underlies the rapidly activating delayed-rectifier K+ current (IKr ), which plays a major role in cardiac ventricular repolarization. Experimental characterization of the distinct temporal effects of genetic and acquired modulators on channel trafficking and gating is challenging. Computer models are instrumental in elucidating these effects, but no currently available model incorporates ion-channel trafficking. Here, we present a novel computational model that reproduces the experimentally observed production, forward trafficking, internalization, recycling and degradation of Kv 11.1 channels, as well as their modulation by temperature, pentamidine, dofetilide and extracellular K+ . The acute effects of these modulators on channel gating were also incorporated and integrated with the trafficking model in the O'Hara-Rudy human ventricular cardiomyocyte model. Supraphysiological dofetilide concentrations substantially increased Kv 11.1 membrane levels while also producing a significant channel block. However, clinically relevant concentrations did not affect trafficking. Similarly, severe hypokalaemia reduced Kv 11.1 membrane levels based on long-term culture data, but had limited effect based on short-term data. By contrast, clinically relevant elevations in temperature acutely increased IKr due to faster kinetics, while after 24 h, IKr was decreased due to reduced Kv 11.1 membrane levels. The opposite was true for lower temperatures. Taken together, our model reveals a complex temporal regulation of cardiac electrophysiology by temperature, hypokalaemia, and dofetilide through competing effects on channel gating and trafficking, and provides a framework for future studies assessing the role of impaired trafficking in cardiac arrhythmias. KEY POINTS: Kv 11.1 channels underlying the rapidly activating delayed-rectifier K+ current are important for ventricular repolarization and are continuously shuttled from the cytoplasm to the plasma membrane and back over minutes to hours. Kv 11.1 gating and trafficking are modulated by temperature, drugs and extracellular K+ concentration but experimental characterization of their combined effects is challenging. Computer models may facilitate these analyses, but no currently available model incorporates ion-channel trafficking. We introduce a new two-state ion-channel trafficking model able to reproduce a wide range of experimental data, along with the effects of modulators of Kv 11.1 channel functioning and trafficking. The model reveals complex dynamic regulation of ventricular repolarization by temperature, extracellular K+ concentration and dofetilide through opposing acute (millisecond) effects on Kv 11.1 gating and long-term (hours) modulation of Kv 11.1 trafficking. This in silico trafficking framework provides a tool to investigate the roles of acute and long-term processes on arrhythmia promotion and maintenance.
Collapse
Affiliation(s)
- Stefan Meier
- Department of Cardiology, Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine, and Life Sciences, Maastricht University and Maastricht University Medical Center+, Maastricht, The Netherlands
| | - Adaïa Grundland
- Department of Cardiology, Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine, and Life Sciences, Maastricht University and Maastricht University Medical Center+, Maastricht, The Netherlands
- Department of Data Science and Knowledge Engineering, Faculty of Science and Engineering, Maastricht University, Maastricht, The Netherlands
| | - Dobromir Dobrev
- Institute of Pharmacology, West German Heart and Vascular Center, University of Duisburg-Essen, Essen, Germany
- Department of Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal, Montréal, Quebec, Canada
| | - Paul G.A. Volders
- Department of Cardiology, Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine, and Life Sciences, Maastricht University and Maastricht University Medical Center+, Maastricht, The Netherlands
| | - Jordi Heijman
- Department of Cardiology, Cardiovascular Research Institute Maastricht (CARIM), Faculty of Health, Medicine, and Life Sciences, Maastricht University and Maastricht University Medical Center+, Maastricht, The Netherlands
| |
Collapse
|
4
|
Conformation-sensitive antibody reveals an altered cytosolic PAS/CNBh assembly during hERG channel gating. Proc Natl Acad Sci U S A 2021; 118:2108796118. [PMID: 34716268 DOI: 10.1073/pnas.2108796118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 09/22/2021] [Indexed: 11/18/2022] Open
Abstract
The human ERG (hERG) K+ channel has a crucial function in cardiac repolarization, and mutations or channel block can give rise to long QT syndrome and catastrophic ventricular arrhythmias. The cytosolic assembly formed by the Per-Arnt-Sim (PAS) and cyclic nucleotide binding homology (CNBh) domains is the defining structural feature of hERG and related KCNH channels. However, the molecular role of these two domains in channel gating remains unclear. We have previously shown that single-chain variable fragment (scFv) antibodies can modulate hERG function by binding to the PAS domain. Here, we mapped the scFv2.12 epitope to a site overlapping with the PAS/CNBh domain interface using NMR spectroscopy and mutagenesis and show that scFv binding in vitro and in the cell is incompatible with the PAS interaction with CNBh. By generating a fluorescently labeled scFv2.12, we demonstrate that association with the full-length hERG channel is state dependent. We detect Förster resonance energy transfer (FRET) with scFv2.12 when the channel gate is open but not when it is closed. In addition, state dependence of scFv2.12 FRET signal disappears when the R56Q mutation, known to destabilize the PAS-CNBh interaction, is introduced in the channel. Altogether, these data are consistent with an extensive structural alteration of the PAS/CNBh assembly when the cytosolic gate opens, likely favoring PAS domain dissociation from the CNBh domain.
Collapse
|
5
|
Oliveira‐Mendes B, Feliciangeli S, Ménard M, Chatelain F, Alameh M, Montnach J, Nicolas S, Ollivier B, Barc J, Baró I, Schott J, Probst V, Kyndt F, Denjoy I, Lesage F, Loussouarn G, De Waard M. A standardised hERG phenotyping pipeline to evaluate KCNH2 genetic variant pathogenicity. Clin Transl Med 2021; 11:e609. [PMID: 34841674 PMCID: PMC8609418 DOI: 10.1002/ctm2.609] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 09/22/2021] [Accepted: 09/28/2021] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND AIMS Mutations in KCNH2 cause long or short QT syndromes (LQTS or SQTS) predisposing to life-threatening arrhythmias. Over 1000 hERG variants have been described by clinicians, but most remain to be characterised. The objective is to standardise and accelerate the phenotyping process to contribute to clinician diagnosis and patient counselling. In silico evaluation was also included to characterise the structural impact of the variants. METHODS We selected 11 variants from known LQTS patients and two variants for which diagnosis was problematic. Using the Gibson assembly strategy, we efficiently introduced mutations in hERG cDNA despite GC-rich sequences. A pH-sensitive fluorescent tag was fused to hERG for efficient evaluation of channel trafficking. An optimised 35-s patch-clamp protocol was developed to evaluate hERG channel activity in transfected cells. R software was used to speed up analyses. RESULTS In the present work, we observed a good correlation between cell surface expression, assessed by the pH-sensitive tag, and current densities. Also, we showed that the new biophysical protocol allows a significant gain of time in recording ion channel properties and provides extensive information on WT and variant channel biophysical parameters, that can all be recapitulated in a single parameter defined herein as the repolarisation power. The impacts of the variants on channel structure were also reported where structural information was available. These three readouts (trafficking, repolarisation power and structural impact) define three pathogenicity indexes that may help clinical diagnosis. CONCLUSIONS Fast-track characterisation of KCNH2 genetic variants shows its relevance to discriminate mutants that affect hERG channel activity from variants with undetectable effects. It also helped the diagnosis of two new variants. This information is meant to fill a patient database, as a basis for personalised medicine. The next steps will be to further accelerate the process using an automated patch-clamp system.
Collapse
Affiliation(s)
| | - Sylvain Feliciangeli
- Labex ICST, Université Côte d'Azur, INSERMCentre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et CellulaireValbonneFrance
| | - Mélissa Ménard
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | - Frank Chatelain
- Labex ICST, Université Côte d'Azur, INSERMCentre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et CellulaireValbonneFrance
| | - Malak Alameh
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | - Jérôme Montnach
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | | | | | - Julien Barc
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | - Isabelle Baró
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| | | | - Vincent Probst
- CHU Nantes, l'Institut du Thorax, INSERM, CNRSUNIV NantesNantesFrance
| | - Florence Kyndt
- CHU Nantes, l'Institut du Thorax, INSERM, CNRSUNIV NantesNantesFrance
| | - Isabelle Denjoy
- Service de Cardiologie et CNMR Maladies Cardiaques Héréditaires RaresHôpital BichatParisFrance
| | - Florian Lesage
- Labex ICST, Université Côte d'Azur, INSERMCentre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et CellulaireValbonneFrance
| | | | - Michel De Waard
- l'Institut du ThoraxInserm UMR 1087/CNRS UMR 6291NantesFrance
| |
Collapse
|
6
|
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.
Collapse
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.
| |
Collapse
|
7
|
Jenewein T, Kanner SA, Bauer D, Hertel B, Colecraft HM, Moroni A, Thiel G, Kauferstein S. The mutation L69P in the PAS domain of the hERG potassium channel results in LQTS by trafficking deficiency. Channels (Austin) 2021; 14:163-174. [PMID: 32253972 PMCID: PMC7188350 DOI: 10.1080/19336950.2020.1751522] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The congenital long QT syndrome (LQTS) is a cardiac disorder characterized by a prolonged QT interval on the electrocardiogram and an increased susceptibility to ventricular arrhythmias and sudden cardiac death. A frequent cause for LQTS is mutations in the KCNH2 gene (also known as the human ether-a-go-go-related gene or hERG), which reduce or modulate the potassium current IKr and hence alter cardiac repolarization. In a patient with a clinically diagnosed LQTS, we identified the mutation L69P in the N-terminal PAS (Per-Arnt-Sim) domain of hERG. Functional expression in HEK293 cells shows that a homotetrameric hERG channel reconstituted with only mutant subunits exhibits a drastically reduced surface expression of the channel protein thus leading to a diminished hERG current. Unlike many other mutations in the hERG-PAS domain the negative impact of the L69P substitution cannot be rescued by facilitated protein folding at a lower incubation temperature. Further, co-expression of wt and mutant monomers does not restore either wt like surface expression or the full hERG current. These results indicate L69P is a dominant negative mutation, with deficits which most likely occurs at the level of protein folding and subsequently inhibits trafficking to the plasma membrane. The functional deficits of the mutant channel support the clinical diagnosis of a LQTS.
Collapse
Affiliation(s)
- Tina Jenewein
- Institute of Legal Medicine, University of Frankfurt, Frankfurt Am Main, Germany
| | - Scott A Kanner
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Daniel Bauer
- Computational Biology and Simulation Group, Department of Biology, Technische Universita ̈t Darmstadt, Darmstadt, Germany
| | - Brigitte Hertel
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Henry M Colecraft
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, New York, NY, USA
| | - Anna Moroni
- Department of Biosciences and CNR IBF-Mi, University of Milano, Milano, Italy
| | - Gerhard Thiel
- Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany
| | - Silke Kauferstein
- Institute of Legal Medicine, University of Frankfurt, Frankfurt Am Main, Germany
| |
Collapse
|
8
|
Ng CA, Farr J, Young P, Windley MJ, Perry MD, Hill AP, Vandenberg JI. Heterozygous KCNH2 variant phenotyping using Flp-In HEK293 and high-throughput automated patch clamp electrophysiology. Biol Methods Protoc 2021; 6:bpab003. [PMID: 33884304 PMCID: PMC8046900 DOI: 10.1093/biomethods/bpab003] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 03/10/2021] [Accepted: 03/16/2021] [Indexed: 11/13/2022] Open
Abstract
KCNH2 is one of the 59 medically actionable genes recommended by the American College of Medical Genetics for reporting of incidental findings from clinical genomic sequencing. However, half of the reported KCNH2 variants in the ClinVar database are classified as variants of uncertain significance. In the absence of strong clinical phenotypes, there is a need for functional phenotyping to help decipher the significance of variants identified incidentally. Here, we report detailed methods for assessing the molecular phenotype of any KCNH2 missense variant. The key components of the assay include quick and cost-effective generation of a bi-cistronic vector to co-express Wild-type (WT) and any KCNH2 variant allele, generation of stable Flp-In HEK293 cell lines and high-throughput automated patch clamp electrophysiology analysis of channel function. Stable cell lines take 3–4 weeks to produce and can be generated in bulk, which will then allow up to 30 variants to be phenotyped per week after 48 h of channel expression. This high-throughput functional genomics assay will enable a much more rapid assessment of the extent of loss of function of any KCNH2 variant.
Collapse
Affiliation(s)
- Chai-Ann Ng
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, Darlinghurst, New South Wales 2010, Australia
| | - Jessica Farr
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,School of Computer Science and Engineering, UNSW Sydney, Kensington, New South Wales 2052, Australia
| | - Paul Young
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia
| | - Monique J Windley
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia
| | - Matthew D Perry
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, Darlinghurst, New South Wales 2010, Australia
| | - Adam P Hill
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, Darlinghurst, New South Wales 2010, Australia
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, Darlinghurst, New South Wales 2010, Australia
| |
Collapse
|
9
|
Perry MD, Ng CA, Mangala MM, Ng TYM, Hines AD, Liang W, Xu MJO, Hill AP, Vandenberg JI. Pharmacological activation of IKr in models of long QT Type 2 risks overcorrection of repolarization. Cardiovasc Res 2021; 116:1434-1445. [PMID: 31628797 DOI: 10.1093/cvr/cvz247] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 08/21/2019] [Accepted: 10/09/2019] [Indexed: 12/11/2022] Open
Abstract
AIMS Current treatment for congenital long QT syndrome Type 2 (cLQTS2), an electrical disorder that increases the risk of life-threatening cardiac arrhythmias, is aimed at reducing the incidence of arrhythmia triggers (beta-blockers) or terminating the arrhythmia after onset (implantable cardioverter-defibrillator). An alternative strategy is to target the underlying disease mechanism, which is reduced rapid delayed rectifier current (IKr) passed by Kv11.1 channels. Small molecule activators of Kv11.1 have been identified but the extent to which these can restore normal cardiac signalling in cLQTS2 backgrounds remains unclear. Here, we examined the ability of ICA-105574, an activator of Kv11.1 that impairs transition to the inactivated state, to restore function to heterozygous Kv11.1 channels containing either inactivation enhanced (T618S, N633S) or expression deficient (A422T) mutations. METHODS AND RESULTS ICA-105574 effectively restored Kv11.1 current from heterozygous inactivation enhanced or expression defective mutant channels in heterologous expression systems. In a human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model of cLQTS2 containing the expression defective Kv11.1 mutant A422T, cardiac repolarization, estimated from the duration of calcium transients in isolated cells and the rate corrected field potential duration (FPDc) in culture monolayers of cells, was significantly prolonged. The Kv11.1 activator ICA-105574 was able to reverse the prolonged repolarization in a concentration-dependent manner. However, at higher doses, ICA-105574 produced a shortening of the FPDc compared to controls. In vitro and in silico analysis suggests that this overcorrection occurs as a result of a temporal redistribution of the peak IKr to much earlier in the plateau phase of the action potential, which results in early repolarization. CONCLUSION Kv11.1 activators, which target the primary disease mechanism, provide a possible treatment option for cLQTS2, with the caveat that there may be a risk of overcorrection that could itself be pro-arrhythmic.
Collapse
Affiliation(s)
- Matthew D Perry
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, New South Wales, Australia
| | - Chai-Ann Ng
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, New South Wales, Australia
| | - Melissa M Mangala
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia
| | - Timothy Y M Ng
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, New South Wales, Australia
| | - Adam D Hines
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,Queensland Brain Institute, The University of Queensland, St. Lucia 4072, Queensland, Australia
| | - Whitney Liang
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia
| | - Michelle J O Xu
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, New South Wales, Australia
| | - Adam P Hill
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, New South Wales, Australia
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, Australia.,St Vincent's Clinical School, UNSW Sydney, New South Wales, Australia
| |
Collapse
|
10
|
A rapid solubility assay of protein domain misfolding for pathogenicity assessment of rare DNA sequence variants. Genet Med 2020; 22:1642-1652. [PMID: 32475984 PMCID: PMC7529867 DOI: 10.1038/s41436-020-0842-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 05/11/2020] [Accepted: 05/12/2020] [Indexed: 02/08/2023] Open
Abstract
PURPOSE DNA sequencing technology has unmasked a vast number of uncharacterized single-nucleotide variants in disease-associated genes, and efficient methods are needed to determine pathogenicity and enable clinical care. METHODS We report an E. coli-based solubility assay for assessing the effects of variants on protein domain stability for three disease-associated proteins. RESULTS First, we examined variants in the Kv11.1 channel PAS domain (PASD) associated with inherited long QT syndrome type 2 and found that protein solubility correlated well with reported in vitro protein stabilities. A comprehensive solubility analysis of 56 Kv11.1 PASD variants revealed that disruption of membrane trafficking, the dominant loss-of-function disease mechanism, is largely determined by domain stability. We further validated this assay by using it to identify second-site suppressor PASD variants that improve domain stability and Kv11.1 protein trafficking. Finally, we applied this assay to several cancer-linked P53 tumor suppressor DNA-binding domain and myopathy-linked Lamin A/C Ig-like domain variants, which also correlated well with reported protein stabilities and functional analyses. CONCLUSION This simple solubility assay can aid in determining the likelihood of pathogenicity for sequence variants due to protein misfolding in structured domains of disease-associated genes as well as provide insights into the structural basis of disease.
Collapse
|
11
|
Brewer KR, Kuenze G, Vanoye CG, George AL, Meiler J, Sanders CR. Structures Illuminate Cardiac Ion Channel Functions in Health and in Long QT Syndrome. Front Pharmacol 2020; 11:550. [PMID: 32431610 PMCID: PMC7212895 DOI: 10.3389/fphar.2020.00550] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Accepted: 04/09/2020] [Indexed: 12/13/2022] Open
Abstract
The cardiac action potential is critical to the production of a synchronized heartbeat. This electrical impulse is governed by the intricate activity of cardiac ion channels, among them the cardiac voltage-gated potassium (Kv) channels KCNQ1 and hERG as well as the voltage-gated sodium (Nav) channel encoded by SCN5A. Each channel performs a highly distinct function, despite sharing a common topology and structural components. These three channels are also the primary proteins mutated in congenital long QT syndrome (LQTS), a genetic condition that predisposes to cardiac arrhythmia and sudden cardiac death due to impaired repolarization of the action potential and has a particular proclivity for reentrant ventricular arrhythmias. Recent cryo-electron microscopy structures of human KCNQ1 and hERG, along with the rat homolog of SCN5A and other mammalian sodium channels, provide atomic-level insight into the structure and function of these proteins that advance our understanding of their distinct functions in the cardiac action potential, as well as the molecular basis of LQTS. In this review, the gating, regulation, LQTS mechanisms, and pharmacological properties of KCNQ1, hERG, and SCN5A are discussed in light of these recent structural findings.
Collapse
Affiliation(s)
- Kathryn R. Brewer
- Center for Structural Biology, Vanderbilt University School of Medicine Basic Sciences, Nashville, TN, United States
- Department of Biochemistry, Vanderbilt University, Nashville, TN, United States
| | - Georg Kuenze
- Center for Structural Biology, Vanderbilt University School of Medicine Basic Sciences, Nashville, TN, United States
- Department of Chemistry, Vanderbilt University, Nashville, TN, United States
| | - Carlos G. Vanoye
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Alfred L. George
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Jens Meiler
- Center for Structural Biology, Vanderbilt University School of Medicine Basic Sciences, Nashville, TN, United States
- Department of Chemistry, Vanderbilt University, Nashville, TN, United States
- Department of Pharmacology, Vanderbilt University School of Medicine Basic Sciences, Nashville, TN, United States
- Institute for Drug Discovery, Leipzig University Medical School, Leipzig, Germany
| | - Charles R. Sanders
- Center for Structural Biology, Vanderbilt University School of Medicine Basic Sciences, Nashville, TN, United States
- Department of Biochemistry, Vanderbilt University, Nashville, TN, United States
| |
Collapse
|
12
|
Marinko J, Huang H, Penn WD, Capra JA, Schlebach JP, Sanders CR. Folding and Misfolding of Human Membrane Proteins in Health and Disease: From Single Molecules to Cellular Proteostasis. Chem Rev 2019; 119:5537-5606. [PMID: 30608666 PMCID: PMC6506414 DOI: 10.1021/acs.chemrev.8b00532] [Citation(s) in RCA: 162] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Indexed: 12/13/2022]
Abstract
Advances over the past 25 years have revealed much about how the structural properties of membranes and associated proteins are linked to the thermodynamics and kinetics of membrane protein (MP) folding. At the same time biochemical progress has outlined how cellular proteostasis networks mediate MP folding and manage misfolding in the cell. When combined with results from genomic sequencing, these studies have established paradigms for how MP folding and misfolding are linked to the molecular etiologies of a variety of diseases. This emerging framework has paved the way for the development of a new class of small molecule "pharmacological chaperones" that bind to and stabilize misfolded MP variants, some of which are now in clinical use. In this review, we comprehensively outline current perspectives on the folding and misfolding of integral MPs as well as the mechanisms of cellular MP quality control. Based on these perspectives, we highlight new opportunities for innovations that bridge our molecular understanding of the energetics of MP folding with the nuanced complexity of biological systems. Given the many linkages between MP misfolding and human disease, we also examine some of the exciting opportunities to leverage these advances to address emerging challenges in the development of therapeutics and precision medicine.
Collapse
Affiliation(s)
- Justin
T. Marinko
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
| | - Hui Huang
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
| | - Wesley D. Penn
- Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - John A. Capra
- Center
for Structural Biology, Vanderbilt University, Nashville, Tennessee 37240, United States
- Department
of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37245, United States
| | - Jonathan P. Schlebach
- Department
of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Charles R. Sanders
- Department
of Biochemistry, Vanderbilt University, Nashville, Tennessee 37240, United States
| |
Collapse
|
13
|
Mutation-specific peripheral and ER quality control of hERG channel cell-surface expression. Sci Rep 2019; 9:6066. [PMID: 30988392 PMCID: PMC6465299 DOI: 10.1038/s41598-019-42331-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 03/28/2019] [Indexed: 12/11/2022] Open
Abstract
Impaired functional plasma membrane (PM) expression of the hERG K+-channel is associated with Long-QT syndrome type-2 (LQT2) and increased risk of cardiac arrhythmia. Reduced PM-expression is primarily attributed to retention and degradation of misfolded channels by endoplasmic reticulum (ER) protein quality control (QC) systems. However, as the molecular pathogenesis of LQT2 was defined using severely-misfolded hERG variants with limited PM-expression, the potential contribution of post-ER (peripheral) QC pathways to the disease phenotype remains poorly established. Here, we investigate the cellular processing of mildly-misfolded Per-Arnt-Sim (PAS)-domain mutant hERGs, which display incomplete ER-retention and PM-expression defects at physiological temperature. We show that the attenuated PM-expression of hERG is dictated by mutation-specific contributions from both the ER and peripheral QC systems. At the ER, PAS-mutants experience inefficient conformational maturation coupled with rapid ubiquitin-dependent proteasomal degradation. In post-ER compartments, they are rapidly endocytosed from the PM via a ubiquitin-independent mechanism and rapidly targeted for lysosomal degradation. Conformational destabilization underlies aberrant cellular processing at both ER- and post-ER compartments, since conformational correction by a hERG-specific pharmacochaperone or low-temperatures can restore WT-like trafficking. Our results demonstrate that the post-ER QC alone or jointly with the ER QC determines the loss-of-PM-expression phenotype of a subset of LQT2 mutations.
Collapse
|
14
|
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.
Collapse
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
| |
Collapse
|
15
|
Landstrom AP, Fernandez E, Rosenfeld JA, Yang Y, Dailey-Schwartz AL, Miyake CY, Allen HD, Penny DJ, Kim JJ. Amino acid-level signal-to-noise analysis of incidentally identified variants in genes associated with long QT syndrome during pediatric whole exome sequencing reflects background genetic noise. Heart Rhythm 2018; 15:1042-1050. [PMID: 29501670 DOI: 10.1016/j.hrthm.2018.02.031] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Indexed: 10/17/2022]
Abstract
BACKGROUND Due to rapid expansion of clinical genetic testing, an increasing number of genetic variants of undetermined significance and unclear diagnostic value are being identified in children. Variants found in genes associated with heritable channelopathies, such as long QT syndrome (LQTS), are particularly difficult to interpret given the risk of sudden cardiac death associated with pathologic mutations. OBJECTIVE The purpose of this study was to determine whether variants in LQTS-associated genes from whole exome sequencing (WES) represent disease-associated biomarkers or background genetic "noise." METHODS WES variants from Baylor Genetics Laboratories were obtained for 17 LQTS-associated genes. Rare variants from healthy controls were obtained from the GnomAD database. LQTS case variants were extracted from the literature. Amino acid-level mapping and signal-to-noise calculations were conducted. Clinical history and diagnostic studies were analyzed for WES subjects evaluated at our institution. RESULTS Variants in LQTS case-associated genes were present in 38.3% of 7244 WES probands. There was a similar frequency of variants in the WES and healthy cohorts for LQTS1-3 (11.2% and 12.9%, respectively) and LQTS4-17 (27.1% and 38.4%, respectively). WES variants preferentially localized to amino acids altered in control individuals compared to cases. Based on amino acid-level analysis, WES-identified variants are indistinguishable from healthy background variation, whereas LQTS1 and 2 case-identified variants localized to clear pathologic "hotspots." No individuals who underwent clinical evaluation had clinical suspicion for LQTS. CONCLUSION The prevalence of incidentally identified LQTS-associated variants is ∼38% among WES tests. These variants most likely represent benign healthy background genetic variation rather than disease-associated mutations.
Collapse
Affiliation(s)
- Andrew P Landstrom
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas.
| | - Ernesto Fernandez
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas
| | | | - Yaping Yang
- Baylor Miraca Genetic Laboratories, Houston, Texas
| | - Andrew L Dailey-Schwartz
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas
| | - Christina Y Miyake
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas
| | - Hugh D Allen
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas
| | - Daniel J Penny
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas
| | - Jeffrey J Kim
- Department of Pediatrics, Section of Pediatric Cardiology, Baylor College of Medicine, Houston, Texas
| |
Collapse
|
16
|
Cserne Szappanos H, Muralidharan P, Ingley E, Petereit J, Millar AH, Hool LC. Identification of a novel cAMP dependent protein kinase A phosphorylation site on the human cardiac calcium channel. Sci Rep 2017; 7:15118. [PMID: 29123182 PMCID: PMC5680263 DOI: 10.1038/s41598-017-15087-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 10/19/2017] [Indexed: 11/09/2022] Open
Abstract
The "Fight or Flight" response is elicited by extrinsic stress and is necessary in many species for survival. The response involves activation of the β-adrenergic signalling pathway. Surprisingly the mechanisms have remained unresolved. Calcium influx through the cardiac L-type Ca2+ channel (Cav1.2) is absolutely required. Here we identify the functionally relevant site for PKA phosphorylation on the human cardiac L-type Ca2+ channel pore forming α1 subunit using a novel approach. We used a cell free system where we could assess direct effects of PKA on human purified channel protein function reconstituted in proteoliposomes. In addition to assessing open probability of channel protein we used semi-quantitative fluorescent phosphoprotein detection and MS/MS mass spectrometry analysis to demonstrate the PKA specificity of the site. Robust increases in frequency of channel openings were recorded after phosphorylation of the long and short N terminal isoforms and the channel protein with C terminus truncated at aa1504. A protein kinase A anchoring protein (AKAP) was not required. We find the novel PKA phosphorylation site at Ser1458 is in close proximity to the Repeat IV S6 region and induces a conformational change in the channel protein that is necessary and sufficient for increased calcium influx through the channel.
Collapse
Affiliation(s)
| | - Padmapriya Muralidharan
- School of Human Sciences, University of Western Australia, Crawley, Western Australia, Australia
| | - Evan Ingley
- Harry Perkins Institute of Medical Research and Centre for Medical Research, University of Western Australia, Nedlands, Western Australia, Australia.,School of Veterinary and Life Sciences, Murdoch University, Murdoch, Western Australia, Australia
| | - Jakob Petereit
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia, Australia
| | - A Harvey Millar
- ARC Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia, Australia
| | - Livia C Hool
- School of Human Sciences, University of Western Australia, Crawley, Western Australia, Australia. .,Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia.
| |
Collapse
|
17
|
Muralidharan P, Cserne Szappanos H, Ingley E, Hool LC. The cardiac L-type calcium channel alpha subunit is a target for direct redox modification during oxidative stress-the role of cysteine residues in the alpha interacting domain. Clin Exp Pharmacol Physiol 2017; 44 Suppl 1:46-54. [PMID: 28306174 DOI: 10.1111/1440-1681.12750] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 02/16/2017] [Accepted: 03/07/2017] [Indexed: 01/21/2023]
Abstract
Cardiovascular disease is the leading cause of death in the Western world. The incidence of cardiovascular disease is predicted to further rise with the increase in obesity and diabetes and with the aging population. Even though the survival rate from ischaemic heart disease has improved over the past 30 years, many patients progress to a chronic pathological condition, known as cardiac hypertrophy that is associated with an increase in morbidity and mortality. Reactive oxygen species (ROS) and calcium play an essential role in mediating cardiac hypertrophy. The L-type calcium channel is the main route for calcium influx into cardiac myocytes. There is now good evidence for a direct role for the L-type calcium channel in the development of cardiac hypertrophy. Cysteines on the channel are targets for redox modification and glutathionylation of the channel can modulate the function of the channel protein leading to the onset of pathology. The cysteine responsible for modification of L-type calcium channel function has now been identified. Detailed understanding of the role of cysteines as possible targets during oxidative stress may assist in designing therapy to prevent the development of hypertrophy and heart failure.
Collapse
Affiliation(s)
- Padmapriya Muralidharan
- School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, WA, Australia
| | - Henrietta Cserne Szappanos
- School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, WA, Australia
| | - Evan Ingley
- Harry Perkins Institute of Medical Research and Centre for Medical Research, University of Western Australia, Perth, WA, Australia.,School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, Australia
| | - Livia C Hool
- School of Anatomy, Physiology and Human Biology, University of Western Australia, Crawley, WA, Australia.,Victor Chang Cardiac Research Institute, Sydney, NSW, Australia
| |
Collapse
|
18
|
Phan K, Ng CA, David E, Shishmarev D, Kuchel PW, Vandenberg JI, Perry MD. The S1 helix critically regulates the finely tuned gating of Kv11.1 channels. J Biol Chem 2017; 292:7688-7705. [PMID: 28280240 DOI: 10.1074/jbc.m117.779298] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 02/26/2017] [Indexed: 11/06/2022] Open
Abstract
Congenital mutations in the cardiac Kv11.1 channel can cause long QT syndrome type 2 (LQTS2), a heart rhythm disorder associated with sudden cardiac death. Mutations act either by reducing protein expression at the membrane and/or by perturbing the intricate gating properties of Kv11.1 channels. A number of clinical LQTS2-associated mutations have been reported in the first transmembrane segment (S1) of Kv11.1 channels, but the role of this region of the channel is largely unexplored. In part, this is due to problems defining the extent of the S1 helix, as a consequence of its low sequence homology with other Kv family members. Here, we used NMR spectroscopy and electrophysiological characterization to show that the S1 of Kv11.1 channels extends seven helical turns, from Pro-405 to Phe-431, and is flanked by unstructured loops. Functional analysis suggests that pre-S1 loop residues His-402 and Tyr-403 play an important role in regulating the kinetics and voltage dependence of channel activation and deactivation. Multiple residues within the S1 helix also play an important role in fine-tuning the voltage dependence of activation, regulating slow deactivation, and modulating C-type inactivation of Kv11.1 channels. Analyses of LQTS2-associated mutations in the pre-S1 loop or S1 helix of Kv11.1 channels demonstrate perturbations to both protein expression and most gating transitions. Thus, S1 region mutations would reduce both the action potential repolarizing current passed by Kv11.1 channels in cardiac myocytes, as well as the current passed in response to premature depolarizations that normally helps protect against the formation of ectopic beats.
Collapse
Affiliation(s)
- Kevin Phan
- From the Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010.,the St. Vincent's Clinical School, University of New South Wales, New South Wales 2052, and
| | - Chai Ann Ng
- From the Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010.,the St. Vincent's Clinical School, University of New South Wales, New South Wales 2052, and
| | - Erikka David
- From the Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010
| | - Dmitry Shishmarev
- the School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Philip W Kuchel
- the School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Jamie I Vandenberg
- From the Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010.,the St. Vincent's Clinical School, University of New South Wales, New South Wales 2052, and
| | - Matthew D Perry
- From the Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010, .,the St. Vincent's Clinical School, University of New South Wales, New South Wales 2052, and
| |
Collapse
|
19
|
Hyltén-Cavallius L, Iepsen EW, Wewer Albrechtsen NJ, Svendstrup M, Lubberding AF, Hartmann B, Jespersen T, Linneberg A, Christiansen M, Vestergaard H, Pedersen O, Holst JJ, Kanters JK, Hansen T, Torekov SS. Patients With Long-QT Syndrome Caused by Impaired hERG-Encoded K v11.1 Potassium Channel Have Exaggerated Endocrine Pancreatic and Incretin Function Associated With Reactive Hypoglycemia. Circulation 2017; 135:1705-1719. [PMID: 28235848 PMCID: PMC5412733 DOI: 10.1161/circulationaha.116.024279] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 02/14/2017] [Indexed: 11/23/2022]
Abstract
Supplemental Digital Content is available in the text. Background: Loss-of-function mutations in hERG (encoding the Kv11.1 voltage-gated potassium channel) cause long-QT syndrome type 2 (LQT2) because of prolonged cardiac repolarization. However, Kv11.1 is also present in pancreatic α and β cells and intestinal L and K cells, secreting glucagon, insulin, and the incretins glucagon-like peptide-1 (GLP-1) and GIP (glucose-dependent insulinotropic polypeptide), respectively. These hormones are crucial for glucose regulation, and long-QT syndrome may cause disturbed glucose regulation. We measured secretion of these hormones and cardiac repolarization in response to glucose ingestion in LQT2 patients with functional mutations in hERG and matched healthy participants, testing the hypothesis that LQT2 patients have increased incretin and β-cell function and decreased α-cell function, and thus lower glucose levels. Methods: Eleven patients with LQT2 and 22 sex-, age-, and body mass index–matched control participants underwent a 6-hour 75-g oral glucose tolerance test with ECG recording and blood sampling for measurements of glucose, insulin, C-peptide, glucagon, GLP-1, and GIP. Results: In comparison with matched control participants, LQT2 patients had 56% to 78% increased serum insulin, serum C-peptide, plasma GLP-1, and plasma GIP responses (P=0.03–0.001) and decreased plasma glucose levels after glucose ingestion (P=0.02) with more symptoms of hypoglycemia (P=0.04). Sixty-three percent of LQT2 patients developed hypoglycemic plasma glucose levels (<70 mg/dL) versus 36% control participants (P=0.16), and 18% patients developed serious hypoglycemia (<50 mg/dL) versus none of the controls. LQT2 patients had defective glucagon responses to low glucose, P=0.008. β-Cell function (Insulin Secretion Sensitivity Index-2) was 2-fold higher in LQT2 patients than in controls (4398 [95% confidence interval, 2259–8562] versus 2156 [1961–3201], P=0.03). Pharmacological Kv11.1 blockade (dofetilide) in rats had similar effect, and small interfering RNA inhibition of hERG in β and L cells increased insulin and GLP-1 secretion up to 50%. Glucose ingestion caused cardiac repolarization disturbances with increased QTc intervals in both patients and controls, but with a 122% greater increase in QTcF interval in LQT2 patients (P=0.004). Conclusions: Besides a prolonged cardiac repolarization phase, LQT2 patients display increased GLP-1, GIP, and insulin secretion and defective glucagon secretion, causing decreased plasma glucose and thus increased risk of hypoglycemia. Furthermore, glucose ingestion increased QT interval and aggravated the cardiac repolarization disturbances in LQT2 patients. Clinical Trial Registration: URL: http://clinicaltrials.gov. Unique identifier: NCT02775513.
Collapse
Affiliation(s)
- Louise Hyltén-Cavallius
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Eva W Iepsen
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Nicolai J Wewer Albrechtsen
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Mathilde Svendstrup
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Anniek F Lubberding
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Bolette Hartmann
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Thomas Jespersen
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Allan Linneberg
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Michael Christiansen
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Henrik Vestergaard
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Oluf Pedersen
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Jens J Holst
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Jørgen K Kanters
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.)
| | - Torben Hansen
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.).
| | - Signe S Torekov
- From Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., A.F.L., B.H., T.J., M.C., J.J.H., J.K.K., S.S.T.); Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (L.H.-C., E.W.I., N.J.W.A., M.S., B.H., H.V., O.P., J.J.H., T.H., S.S.T.); Research Centre for Prevention and Health, the Capital Region of Denmark, Copenhagen (A.L.); Gentofte, Aalborg and Herlev University Hospitals, Denmark (J.K.K.); Faculty of Health Sciences, University of Southern Denmark, Odense (T.H.); Department of Clinical Experimental Research, Rigshospitalet, Denmark (A.L.); Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark (A.L.); Danish Diabetes Academy, Odense, Denmark (E.W.I., M.S.); Department of Clinical Biochemistry, Statens Serum Institut, Copenhagen, Denmark (M.C.); and Steno Diabetes Center Copenhagen, Gentofte, Denmark (H.V.).
| |
Collapse
|
20
|
Li K, Jiang Q, Bai X, Yang YF, Ruan MY, Cai SQ. Tetrameric Assembly of K + Channels Requires ER-Located Chaperone Proteins. Mol Cell 2017; 65:52-65. [DOI: 10.1016/j.molcel.2016.10.027] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Revised: 09/02/2016] [Accepted: 10/20/2016] [Indexed: 10/20/2022]
|
21
|
Perry MD, Ng CA, Phan K, David E, Steer K, Hunter MJ, Mann SA, Imtiaz M, Hill AP, Ke Y, Vandenberg JI. Rescue of protein expression defects may not be enough to abolish the pro-arrhythmic phenotype of long QT type 2 mutations. J Physiol 2016; 594:4031-49. [PMID: 26958806 DOI: 10.1113/jp271805] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Accepted: 02/25/2016] [Indexed: 01/28/2023] Open
Abstract
KEY POINTS Most missense long QT syndrome type 2 (LQTS2) mutations result in Kv11.1 channels that show reduced levels of membrane expression. Pharmacological chaperones that rescue mutant channel expression could have therapeutic potential to reduce the risk of LQTS2-associated arrhythmias and sudden cardiac death, but only if the mutant Kv11.1 channels function normally (i.e. like WT channels) after membrane expression is restored. Fewer than half of mutant channels exhibit relatively normal function after rescue by low temperature. The remaining rescued missense mutant Kv11.1 channels have perturbed gating and/or ion selectivity characteristics. Co-expression of WT subunits with gating defective missense mutations ameliorates but does not eliminate the functional abnormalities observed for most mutant channels. For patients with mutations that affect gating in addition to expression, it may be necessary to use a combination therapy to restore both normal function and normal expression of the channel protein. ABSTRACT In the heart, Kv11.1 channels pass the rapid delayed rectifier current (IKr ) which plays critical roles in repolarization of the cardiac action potential and in the suppression of arrhythmias caused by premature stimuli. Over 500 inherited mutations in Kv11.1 are known to cause long QT syndrome type 2 (LQTS2), a cardiac electrical disorder associated with an increased risk of life threatening arrhythmias. Most missense mutations in Kv11.1 reduce the amount of channel protein expressed at the membrane and, as a consequence, there has been considerable interest in developing pharmacological agents to rescue the expression of these channels. However, pharmacological chaperones will only have clinical utility if the mutant Kv11.1 channels function normally after membrane expression is restored. The aim of this study was to characterize the gating phenotype for a subset of LQTS2 mutations to assess what proportion of mutations may be suitable for rescue. As an initial screen we used reduced temperature to rescue expression defects of mutant channels expressed in Xenopus laevis oocytes. Over half (∼56%) of Kv11.1 mutants exhibited functional gating defects that either dramatically reduced the amount of current contributing to cardiac action potential repolarization and/or reduced the amount of protective current elicited in response to premature depolarizations. Our data demonstrate that if pharmacological rescue of protein expression defects is going to have clinical utility in the treatment of LQTS2 then it will be important to assess the gating phenotype of LQTS2 mutations before attempting rescue.
Collapse
Affiliation(s)
- Matthew D Perry
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,St Vincent's Clinical School, University of New South Wales, NSW, 2052, Australia
| | - Chai Ann Ng
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,St Vincent's Clinical School, University of New South Wales, NSW, 2052, Australia
| | - Kevin Phan
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,St Vincent's Clinical School, University of New South Wales, NSW, 2052, Australia
| | - Erikka David
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia
| | - Kieran Steer
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,Faculty of Science, McGill University, Montreal, Quebec, Canada
| | - Mark J Hunter
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia
| | - Stefan A Mann
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,St Vincent's Clinical School, University of New South Wales, NSW, 2052, Australia
| | - Mohammad Imtiaz
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia
| | - Adam P Hill
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,St Vincent's Clinical School, University of New South Wales, NSW, 2052, Australia
| | - Ying Ke
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, Molecular Cardiology and Biophysics Division, Darlinghurst, NSW, 2010, Australia.,St Vincent's Clinical School, University of New South Wales, NSW, 2052, Australia
| |
Collapse
|
22
|
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.
Collapse
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
| |
Collapse
|
23
|
Foo B, Williamson B, Young JC, Lukacs G, Shrier A. hERG quality control and the long QT syndrome. J Physiol 2016; 594:2469-81. [PMID: 26718903 DOI: 10.1113/jp270531] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 12/07/2015] [Indexed: 11/08/2022] Open
Abstract
Long-QT syndrome type-2 (LQT2) is characterized by reduced functional expression of the human ether-à-go-go related (hERG) gene product, resulting in impaired cardiac repolarization and predisposition to fatal arrhythmia. Previous studies have implicated abnormal trafficking of misfolded hERG as the primary mechanism of LQT2, with misfolding being caused by mutations in the hERG gene (inherited) or drug treatment (acquired). More generally, environmental and metabolic stresses present a constant challenge to the folding of proteins, including hERG, and must be countered by robust protein quality control (QC) systems. Disposal of partially unfolded yet functional plasma membrane (PM) proteins by protein QC contributes to the loss-of-function phenotype in various conformational diseases including cystic fibrosis (CF) and long-QT syndrome type-2 (LQT2). The prevalent view has been that the loss of PM expression of hERG is attributed to biosynthetic block by endoplasmic reticulum (ER) QC pathways. However, there is a growing appreciation for protein QC pathways acting at post-ER cellular compartments, which may contribute to conformational disease pathogenesis. This article will provide a background on the structure and cellular trafficking of hERG as well as inherited and acquired LQT2. We will review previous work on hERG ER QC and introduce the more novel view that there is a significant peripheral QC at the PM and peripheral cellular compartments. Particular attention is drawn to the unique role of the peripheral QC system in acquired LQT2. Understanding the QC process and players may provide targets for therapeutic intervention in dealing with LQT2.
Collapse
Affiliation(s)
- Brian Foo
- Department of Physiology, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Brittany Williamson
- Department of Biochemistry, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Jason C Young
- Department of Biochemistry, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Gergely Lukacs
- Department of Physiology, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Alvin Shrier
- Department of Physiology, McGill University, Montréal, Québec, Canada, H3G 1Y6
| |
Collapse
|
24
|
Perry MD, Ng CA, Mann SA, Sadrieh A, Imtiaz M, Hill AP, Vandenberg JI. Getting to the heart of hERG K(+) channel gating. J Physiol 2015; 593:2575-85. [PMID: 25820318 PMCID: PMC4500344 DOI: 10.1113/jp270095] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 03/13/2015] [Indexed: 12/24/2022] Open
Abstract
Potassium ion channels encoded by the human ether-a-go-go related gene (hERG) form the ion-conducting subunit of the rapid delayed rectifier potassium current (IKr ). Although hERG channels exhibit a widespread tissue distribution they play a particularly important role in the heart. There has been considerable interest in hERG K(+) channels for three main reasons. First, they have very unusual gating kinetics, most notably rapid and voltage-dependent inactivation coupled to slow deactivation, which has led to the suggestion that they may play a specific role in the suppression of arrhythmias. Second, mutations in hERG are the cause of 30-40% of cases of congenital long QT syndrome (LQTS), the commonest inherited primary arrhythmia syndrome. Third, hERG is the molecular target for the vast majority of drugs that cause drug-induced LQTS, the commonest cause of drug-induced arrhythmias and cardiac death. Drug-induced LQTS has now been reported for a large range of both cardiac and non-cardiac drugs, in which this side effect is entirely undesired. In recent years there have been comprehensive reviews published on hERG K(+) channels (Vandenberg et al. 2012) and we will not re-cover this ground. Rather, we focus on more recent work on the structural basis and dynamics of hERG gating with an emphasis on how the latest developments may facilitate translational research in the area of stratifying risk of arrhythmias.
Collapse
Affiliation(s)
- Matthew D Perry
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Chai-Ann Ng
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Stefan A Mann
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Arash Sadrieh
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Mohammad Imtiaz
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Adam P Hill
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| |
Collapse
|
25
|
Large-scale mutational analysis of Kv11.1 reveals molecular insights into type 2 long QT syndrome. Nat Commun 2014; 5:5535. [PMID: 25417810 PMCID: PMC4243539 DOI: 10.1038/ncomms6535] [Citation(s) in RCA: 134] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 10/09/2014] [Indexed: 12/23/2022] Open
Abstract
It has been suggested that deficient protein trafficking to the cell membrane is the dominant mechanism associated with type 2 Long QT syndrome (LQT2) caused by Kv11.1 potassium channel missense mutations, and that for many mutations the trafficking defect can be corrected pharmacologically. However, this inference was based on expression of a small number of Kv11.1 mutations. We performed a comprehensive analysis of 167 LQT2-linked missense mutations in four Kv11.1 structural domains and found that deficient protein trafficking is the dominant mechanism for all domains except for the distal carboxy-terminus. Also, most pore mutations--in contrast to intracellular domain mutations--were found to have severe dominant-negative effects when co-expressed with wild-type subunits. Finally, pharmacological correction of the trafficking defect in homomeric mutant channels was possible for mutations within all structural domains. However, pharmacological correction is dramatically improved for pore mutants when co-expressed with wild-type subunits to form heteromeric channels.
Collapse
|
26
|
Pandey D, Yen CF, Lee CL, Wu MP. Electrosurgical technology: Quintessence of the laparoscopic armamentarium. Gynecol Minim Invasive Ther 2014. [DOI: 10.1016/j.gmit.2014.06.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
|
27
|
Ke Y, Hunter MJ, Ng CA, Perry MD, Vandenberg JI. Role of the cytoplasmic N-terminal Cap and Per-Arnt-Sim (PAS) domain in trafficking and stabilization of Kv11.1 channels. J Biol Chem 2014; 289:13782-91. [PMID: 24695734 DOI: 10.1074/jbc.m113.531277] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The N-terminal cytoplasmic region of the Kv11.1a potassium channel contains a Per-Arnt-Sim (PAS) domain that is essential for the unique slow deactivation gating kinetics of the channel. The PAS domain has also been implicated in the assembly and stabilization of the assembled tetrameric channel, with many clinical mutants in the PAS domain resulting in reduced stability of the domain and reduced trafficking. Here, we use quantitative Western blotting to show that the PAS domain is not required for normal channel trafficking nor for subunit-subunit interactions, and it is not necessary for stabilizing assembled channels. However, when the PAS domain is present, the N-Cap amphipathic helix must also be present for channels to traffic to the cell membrane. Serine scan mutagenesis of the N-Cap amphipathic helix identified Leu-15, Ile-18, and Ile-19 as residues critical for the stabilization of full-length proteins when the PAS domain is present. Furthermore, mutant cycle analysis experiments support recent crystallography studies, indicating that the hydrophobic face of the N-Cap amphipathic helix interacts with a surface-exposed hydrophobic patch on the core of the PAS domain to stabilize the structure of this critical gating domain. Our data demonstrate that the N-Cap amphipathic helix is critical for channel stability and trafficking.
Collapse
Affiliation(s)
- Ying Ke
- From the Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, 405 Liverpool Street and St. Vincent's Clinical School, University of New South Wales, Victoria Street, Darlinghurst, New South Wales 2010, Australia
| | - Mark J Hunter
- From the Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, 405 Liverpool Street and
| | - Chai Ann Ng
- From the Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, 405 Liverpool Street and St. Vincent's Clinical School, University of New South Wales, Victoria Street, Darlinghurst, New South Wales 2010, Australia
| | - Matthew D Perry
- From the Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, 405 Liverpool Street and St. Vincent's Clinical School, University of New South Wales, Victoria Street, Darlinghurst, New South Wales 2010, Australia
| | - Jamie I Vandenberg
- From the Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, 405 Liverpool Street and St. Vincent's Clinical School, University of New South Wales, Victoria Street, Darlinghurst, New South Wales 2010, Australia
| |
Collapse
|
28
|
Apaja PM, Foo B, Okiyoneda T, Valinsky WC, Barriere H, Atanasiu R, Ficker E, Lukacs GL, Shrier A. Ubiquitination-dependent quality control of hERG K+ channel with acquired and inherited conformational defect at the plasma membrane. Mol Biol Cell 2013; 24:3787-804. [PMID: 24152733 PMCID: PMC3861077 DOI: 10.1091/mbc.e13-07-0417] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Membrane trafficking in concert with the peripheral quality control machinery plays a critical role in preserving plasma membrane (PM) protein homeostasis. Unfortunately, the peripheral quality control may also dispose of partially or transiently unfolded polypeptides and thereby contribute to the loss-of-expression phenotype of conformational diseases. Defective functional PM expression of the human ether-a-go-go-related gene (hERG) K(+) channel leads to the prolongation of the ventricular action potential that causes long QT syndrome 2 (LQT2), with increased propensity for arrhythmia and sudden cardiac arrest. LQT2 syndrome is attributed to channel biosynthetic processing defects due to mutation, drug-induced misfolding, or direct channel blockade. Here we provide evidence that a peripheral quality control mechanism can contribute to development of the LQT2 syndrome. We show that PM hERG structural and metabolic stability is compromised by the reduction of extracellular or intracellular K(+) concentration. Cardiac glycoside-induced intracellular K(+) depletion conformationally impairs the complex-glycosylated channel, which provokes chaperone- and C-terminal Hsp70-interacting protein-dependent polyubiquitination, accelerated internalization, and endosomal sorting complex required for transport-dependent lysosomal degradation. A similar mechanism contributes to the down-regulation of PM hERG harboring LQT2 missense mutations, with incomplete secretion defect. These results suggest that PM quality control plays a determining role in the loss-of-expression phenotype of hERG in certain hereditary and acquired LTQ2 syndromes.
Collapse
Affiliation(s)
- Pirjo M Apaja
- Department of Physiology and Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montréal, QC H3E 1Y6, Canada
| | | | | | | | | | | | | | | | | |
Collapse
|