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Recent Advances in Protein Caging Tools for Protein Photoactivation. APPLIED SCIENCES-BASEL 2022. [DOI: 10.3390/app12083750] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In biosciences and biotechnologies, it is recently critical to promote research regarding the regulation of the dynamic functions of proteins of interest. Light-induced control of protein activity is a strong tool for a wide variety of applications because light can be spatiotemporally irradiated in high resolutions. Therefore, synthetic, semi-synthetic, and genetic engineering techniques for photoactivation of proteins have been actively developed. In this review, the conventional approaches will be outlined. As a solution for overcoming barriers in conventional ones, our recent approaches in which proteins were chemically modified with biotinylated caging reagents are introduced to photo-activate a variety of proteins without genetic engineering and elaborate optimization. This review mainly focuses on protein caging and describes the concepts underlying the development of reported approaches that can contribute to the emergence of both novel protein photo-regulating methods and their killer applications.
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Li E, Loen V, van Ham WB, Kool W, van der Heyden MAG, Takanari H. Quantitative Analysis of the Cytoskeleton's Role in Inward Rectifier K IR 2.1 Forward and Backward Trafficking. Front Physiol 2022; 12:812572. [PMID: 35145427 PMCID: PMC8821923 DOI: 10.3389/fphys.2021.812572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Accepted: 12/23/2021] [Indexed: 11/13/2022] Open
Abstract
Alteration of the inward rectifier current IK1, carried by KIR2.1 channels, affects action potential duration, impacts resting membrane stability and associates with cardiac arrhythmias. Congenital and acquired KIR2.1 malfunction frequently associates with aberrant ion channel trafficking. Cellular processes underlying trafficking are intertwined with cytoskeletal function. The extent to which the cytoskeleton is involved in KIR2.1 trafficking processes is unknown. We aimed to quantify the dependence of KIR2.1 trafficking on cytoskeleton function. GFP or photoconvertible Dendra2 tagged KIR2.1 constructs were transfected in HEK293 or HeLa cells. Photoconversion of the Dendra2 probe at the plasma membrane and subsequent live imaging of trafficking processes was performed by confocal laser-scanning microscopy. Time constant of green fluorescent recovery (τg,s) represented recruitment of new KIR2.1 at the plasma membrane. Red fluorescent decay (τr,s) represented internalization of photoconverted KIR2.1. Patch clamp electrophysiology was used to quantify IKIR2.1. Biochemical methods were used for cytoskeleton isolation and detection of KIR2.1-cytoskeleton interactions. Cytochalasin B (20 μM), Nocodazole (30 μM) and Dyngo-4a (10 nM) were used to modify the cytoskeleton. Chloroquine (10 μM, 24 h) was used to impair KIR2.1 breakdown. Cytochalasin B and Nocodazole, inhibitors of actin and tubulin filament formation respectively, strongly inhibited the recovery of green fluorescence at the plasma membrane suggestive for inhibition of KIR2.1 forward trafficking [τg,s 13 ± 2 vs. 131 ± 31* and 160 ± 40* min, for control, Cytochalasin B and Nocodazole, respectively (*p < 0.05 vs. control)]. Dyngo-4a, an inhibitor of dynamin motor proteins, strongly slowed the rate of photoconverted channel internalization, whereas Nocodazole and Cytochalasin B had less effect [τr,s 20 ± 2 vs. 87 ± 14*, 60 ± 16 and 64 ± 20 min (*p < 0.05 vs. control)]. Cytochalasin B treatment (20 μM, 24 h) inhibited IKIR2.1. Chloroquine treatment (10 μM, 24 h) induced intracellular aggregation of KIR2.1 channels and enhanced interaction with the actin/intermediate filament system (103 ± 90 fold; p < 0.05 vs. control). Functional actin and tubulin cytoskeleton systems are essential for forward trafficking of KIR2.1 channels, whereas initial backward trafficking relies on a functional dynamin system. Chronic disturbance of the actin system inhibits KIR2.1 currents. Internalized KIR2.1 channels become recruited to the cytoskeleton, presumably in lysosomes.
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Affiliation(s)
- Encan Li
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Vera Loen
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Willem B van Ham
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Willy Kool
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Marcel A G van der Heyden
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Hiroki Takanari
- Department of Interdisciplinary Researches for Medicine and Photonics, Institute of Post-LED Photonics, University of Tokushima, Tokushima, Japan
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Hager NA, McAtee CK, Lesko MA, O’Donnell AF. Inwardly Rectifying Potassium Channel Kir2.1 and its "Kir-ious" Regulation by Protein Trafficking and Roles in Development and Disease. Front Cell Dev Biol 2022; 9:796136. [PMID: 35223865 PMCID: PMC8864065 DOI: 10.3389/fcell.2021.796136] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2021] [Accepted: 12/15/2021] [Indexed: 11/13/2022] Open
Abstract
Potassium (K+) homeostasis is tightly regulated for optimal cell and organismal health. Failure to control potassium balance results in disease, including cardiac arrythmias and developmental disorders. A family of inwardly rectifying potassium (Kir) channels helps cells maintain K+ levels. Encoded by KCNJ genes, Kir channels are comprised of a tetramer of Kir subunits, each of which contains two-transmembrane domains. The assembled Kir channel generates an ion selectivity filter for K+ at the monomer interface, which allows for K+ transit. Kir channels are found in many cell types and influence K+ homeostasis across the organism, impacting muscle, nerve and immune function. Kir2.1 is one of the best studied family members with well-defined roles in regulating heart rhythm, muscle contraction and bone development. Due to their expansive roles, it is not surprising that Kir mutations lead to disease, including cardiomyopathies, and neurological and metabolic disorders. Kir malfunction is linked to developmental defects, including underdeveloped skeletal systems and cerebellar abnormalities. Mutations in Kir2.1 cause the periodic paralysis, cardiac arrythmia, and developmental deficits associated with Andersen-Tawil Syndrome. Here we review the roles of Kir family member Kir2.1 in maintaining K+ balance with a specific focus on our understanding of Kir2.1 channel trafficking and emerging roles in development and disease. We provide a synopsis of the vital work focused on understanding the trafficking of Kir2.1 and its role in development.
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Affiliation(s)
| | | | | | - Allyson F. O’Donnell
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, United States
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Grant SN, Lester HA. Regulation of epithelial sodium channel activity by SARS-CoV-1 and SARS-CoV-2 proteins. Biophys J 2021; 120:2805-2813. [PMID: 34197807 PMCID: PMC8238646 DOI: 10.1016/j.bpj.2021.06.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 04/21/2021] [Accepted: 06/03/2021] [Indexed: 01/06/2023] Open
Abstract
Severe acute respiratory syndrome (SARS) coronavirus (CoV) 2 (SARS-CoV-2), which causes the coronavirus disease 2019, encodes several proteins whose roles are poorly understood. We tested their ability either to directly form plasma membrane ion channels or to change functions of two mammalian plasma membrane ion channels, the epithelial sodium channel (ENaC) and the α3β4 nicotinic acetylcholine receptor. In mRNA-injected Xenopus oocytes, none of nine SARS-CoV-2 proteins or two SARS-CoV-1 proteins produced conductances, nor did co-injection of several combinations. Immunoblots for ORF8, spike (S), and envelope (E) proteins revealed that the proteins are expressed at appropriate molecular weights. In experiments on coexpression with ENaC, three tested SARS proteins (SARS-CoV-1 E, SARS-CoV-2 E, and SARS-CoV-2 S) markedly decrease ENaC currents. SARS-CoV-1 S protein decreases ENaC currents modestly. Coexpressing the E proteins but not the S proteins with α3β4 nicotinic acetylcholine receptors significantly reduces acetylcholine-induced currents. ENaC inhibition does not occur if the SARS-CoV protein mRNAs are injected 24 h after the ENaC mRNAs, suggesting that SARS-CoV proteins affect early step(s) in functional expression of channel proteins. Consistent with the hypothesis that the SARS-CoV-2 S protein-induced ENaC inhibition involves competition for available protease, mutating the furin cleavage site in SARS-CoV-2 S protein partially relieves inhibition of ENaC currents. Extending previous suggestions that SARS proteins affect ENaC currents via protein kinase C (PKC) activation, PKC activation via phorbol 12-myristate 13-acetate decreases ENaC and α3β4 activity. Phorbol 12-myristate 13-acetate application reduced membrane capacitance ∼5%, presumably via increased endocytosis, but this decrease is much smaller than the SARS proteins' effects on conductances. Also, incubating oocytes in Gö-6976, a PKCα and PKCβ inhibitor, did not alter E or S protein-induced channel inhibition. We conclude that SARS-CoV-1 and SARS-CoV-2 proteins alter the function of human plasma membrane channels, via incompletely understood mechanisms. These interactions may play a role in the coronavirus 2019 pathophysiology.
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Affiliation(s)
- Stephen N Grant
- Division of Chemistry and Chemical Engineering, Pasadena, California
| | - Henry A Lester
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California.
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Engram Cell Excitability State Determines the Efficacy of Memory Retrieval. Neuron 2019; 101:274-284.e5. [DOI: 10.1016/j.neuron.2018.11.029] [Citation(s) in RCA: 106] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 10/12/2018] [Accepted: 11/15/2018] [Indexed: 12/21/2022]
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Chen Y, Lu L, Ye S. Genetic Code Expansion and Optoproteomics. THE YALE JOURNAL OF BIOLOGY AND MEDICINE 2017; 90:599-610. [PMID: 29259524 PMCID: PMC5733852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Nature has invented photoreceptor proteins that are involved in sensing and response to light in living organisms. Genetic code expansion (GCE) technology has provided new tools to transform light insensitive proteins into novel photoreceptor proteins. It is achieved by the site-specific incorporation of unnatural amino acids (Uaas) that carry light sensitive moieties serving as "pigments" that react to light via photo-decaging, cross-linking, or isomerization. Over the last two decades, various proteins including ion channels, GPCRs, transporters, and kinases have been successfully rendered light responsive owing to the functionalities of Uaas. Very recently, Cas9 protein has been engineered to enable light activation of genomic editing by CRISPR. Those novel proteins have not only led to discoveries of dynamic protein conformational changes with implications in diseases, but also facilitated the screening of ligand-protein and protein-protein interactions of pharmacological significance. This review covers the genetic editing principles for genetic code expansion and design concepts that guide the engineering of light-sensitive proteins. The applications have brought up a new concept of "optoproteomics" that, in contrast to "optogenetics," aims to combine optical methods and site-specific proteomics for investigating and intervening in biological functions.
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Affiliation(s)
- Yuting Chen
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University (ECNU), Shanghai, China
| | - Linjie Lu
- Université Pierre-et-Marie-Curie, Laboratory of Computational and Quantitative Biology (LCQB), Institute of Biology Paris-Seine, Paris, France
| | - Shixin Ye
- Université Pierre-et-Marie-Curie, Laboratory of Computational and Quantitative Biology (LCQB), Institute of Biology Paris-Seine, Paris, France,Institut National de la Santé et de la Recherche Médicale, Paris, France,Centre National de la Recherche Scientifique, Paris, France,To whom all correspondence should be addressed: Shixin Ye-Lehmann, Laboratory of Computational and Quantitative Biology, Institute of Biology Paris-Seine, University of Pierre and Marie Curie, Bldg. C, 3rd floor, Room 311a, 4 Place Jussieu, 75006 Paris, France, Tel: 33.(0)1.44.27.60.57, .
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Utrilla RG, Nieto-Marín P, Alfayate S, Tinaquero D, Matamoros M, Pérez-Hernández M, Sacristán S, Ondo L, de Andrés R, Díez-Guerra FJ, Tamargo J, Delpón E, Caballero R. Kir2.1-Nav1.5 Channel Complexes Are Differently Regulated than Kir2.1 and Nav1.5 Channels Alone. Front Physiol 2017; 8:903. [PMID: 29184507 PMCID: PMC5694551 DOI: 10.3389/fphys.2017.00903] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Accepted: 10/25/2017] [Indexed: 12/27/2022] Open
Abstract
Cardiac Kir2.1 and Nav1.5 channels generate the inward rectifier K+ (IK1) and the Na+ (INa) currents, respectively. There is a mutual interplay between the ventricular INa and IK1 densities, because Nav1.5 and Kir2.1 channels exhibit positive reciprocal modulation. Here we compared some of the biological properties of Nav1.5 and Kir2.1 channels when they are expressed together or separately to get further insights regarding their putative interaction. First we demonstrated by proximity ligation assays (PLAs) that in the membrane of ventricular myocytes Nav1.5 and Kir2.1 proteins are in close proximity to each other (<40 nm apart). Furthermore, intracellular dialysis with anti-Nav1.5 and anti-Kir2.1 antibodies suggested that these channels form complexes. Patch-clamp experiments in heterologous transfection systems demonstrated that the inhibition of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) decreased the INa and the IK1 generated by Nav1.5 and Kir2.1 channels when they were coexpressed, but not the IK1 generated by Kir2.1 channels alone, suggesting that complexes, but not Kir2.1 channels, are a substrate of CaMKII. Furthermore, inhibition of CaMKII precluded the interaction between Nav1.5 and Kir2.1 channels. Inhibition of 14-3-3 proteins did not modify the INa and IK1 densities generated by each channel separately, whereas it decreased the INa and IK1 generated when they were coexpressed. However, inhibition of 14-3-3 proteins did not abolish the Nav1.5-Kir2.1 interaction. Inhibition of dynamin-dependent endocytosis reduced the internalization of Kir2.1 but not of Nav1.5 or Kir2.1-Nav1.5 complexes. Inhibition of cytoskeleton-dependent vesicular trafficking via the dynein/dynactin motor increased the IK1, but reduced the INa, thus suggesting that the dynein/dynactin motor is preferentially involved in the backward and forward traffic of Kir2.1 and Nav1.5, respectively. Conversely, the dynein/dynactin motor participated in the forward movement of Kir2.1-Nav1.5 complexes. Ubiquitination by Nedd4-2 ubiquitin-protein ligase promoted the Nav1.5 degradation by the proteasome, but not that of Kir2.1 channels. Importantly, the Kir2.1-Nav1.5 complexes were degraded following this route as demonstrated by the overexpression of Nedd4-2 and the inhibition of the proteasome with MG132. These results suggested that Kir2.1 and Nav1.5 channels closely interact with each other leading to the formation of a pool of complexed channels whose biology is similar to that of the Nav1.5 channels.
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Affiliation(s)
- Raquel G Utrilla
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Paloma Nieto-Marín
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Silvia Alfayate
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - David Tinaquero
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Marcos Matamoros
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Marta Pérez-Hernández
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | | | - Lorena Ondo
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Raquel de Andrés
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa" (UAM-CSIC), Universidad Autónoma de Madrid, Madrid, Spain
| | - F Javier Díez-Guerra
- Departamento de Biología Molecular and Centro de Biología Molecular "Severo Ochoa" (UAM-CSIC), Universidad Autónoma de Madrid, Madrid, Spain
| | - Juan Tamargo
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Eva Delpón
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
| | - Ricardo Caballero
- Department of Pharmacology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense, Madrid, Spain.,CIBERCV, Madrid, Spain
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Leem YE, Jeong HJ, Kim HJ, Koh J, Kang K, Bae GU, Cho H, Kang JS. Cdo Regulates Surface Expression of Kir2.1 K+ Channel in Myoblast Differentiation. PLoS One 2016; 11:e0158707. [PMID: 27380411 PMCID: PMC4933383 DOI: 10.1371/journal.pone.0158707] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 06/21/2016] [Indexed: 01/28/2023] Open
Abstract
A potassium channel Kir2.1-associated membrane hyperpolarization is required for myogenic differentiation. However the molecular regulatory mechanisms modulating Kir2.1 channel activities in early stage of myogenesis are largely unknown. A cell surface protein, Cdo functions as a component of multiprotein cell surface complexes to promote myogenesis. In this study, we report that Cdo forms a complex with Kir2.1 during myogenic differentiation, and is required for the channel activity by enhancing the surface expression of Kir2.1 in the early stage of differentiation. The expression of a constitutively active form of the upstream kinase for p38MAPK, MKK6(EE) can restore Kir2.1 activities in Cdo-depleted C2C12 cells, while the treatment with a p38MAPK inhibitor, SB203580 exhibits a similar effect of Cdo depletion on Kir2.1 surface expression. Furthermore, Cdo-/- primary myoblasts, which display a defective differentiation program, exhibit a defective Kir2.1 activity. Taken together, our results suggest that a promyogenic Cdo signaling is critical for Kir2.1 activities in the induction of myogenic differentiation.
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Affiliation(s)
- Young-Eun Leem
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
| | - Hyeon-Ju Jeong
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
| | - Hyun-Ji Kim
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
| | - Jewoo Koh
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
| | - KyeongJin Kang
- Department of Anatomy, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
| | - Gyu-Un Bae
- Research Center for Cell Fate Control, Sookmyung Women’s University, Seoul, Republic of Korea
| | - Hana Cho
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
- * E-mail: (JSK); (HC)
| | - Jong-Sun Kang
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea
- Samsung Biomedical Research Institute, Suwon, Republic of Korea
- * E-mail: (JSK); (HC)
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Kang JY, Kawaguchi D, Wang L. Optical Control of a Neuronal Protein Using a Genetically Encoded Unnatural Amino Acid in Neurons. J Vis Exp 2016:e53818. [PMID: 27078635 DOI: 10.3791/53818] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Photostimulation is a noninvasive way to control biological events with excellent spatial and temporal resolution. New methods are desired to photo-regulate endogenous proteins expressed in their native environment. Here, we present an approach to optically control the function of a neuronal protein directly in neurons using a genetically encoded unnatural amino acid (Uaa). By using an orthogonal tRNA/aminoacyl-tRNA synthetase pair to suppress the amber codon, a photo-reactive Uaa 4,5-dimethoxy-2-nitrobenzyl-cysteine (Cmn) is site-specifically incorporated in the pore of a neuronal protein Kir2.1, an inwardly rectifying potassium channel. The bulky Cmn physically blocks the channel pore, rendering Kir2.1 non-conducting. Light illumination instantaneously converts Cmn into a smaller natural amino acid Cys, activating Kir2.1 channel function. We express these photo-inducible inwardly rectifying potassium (PIRK) channels in rat hippocampal primary neurons, and demonstrate that light-activation of PIRK ceases the neuronal firing due to the outflux of K(+) current through the activated Kir2.1 channels. Using in utero electroporation, we also express PIRK in the embryonic mouse neocortex in vivo, showing the light-activation of PIRK in neocortical neurons. Genetically encoding Uaa imposes no restrictions on target protein type or cellular location, and a family of photoreactive Uaas is available for modulating different natural amino acid residues. This technique thus has the potential to be generally applied to many neuronal proteins to achieve optical regulation of different processes in brains. The current protocol presents an accessible procedure for intricate Uaa incorporation in neurons in vitro and in vivo to achieve photo control of neuronal protein activity on the molecular level.
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Affiliation(s)
- Ji-Yong Kang
- Department of Neuroscience, School of Medicine, Tufts University
| | - Daichi Kawaguchi
- Molecular Neurobiology Laboratory, The Salk Institute for Biological Studies
| | - Lei Wang
- Department of Pharmaceutical Chemistry and the Cardiovascular Research Institute, University of California, San Francisco;
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Baronas VA, Kurata HT. Inward rectifiers and their regulation by endogenous polyamines. Front Physiol 2014; 5:325. [PMID: 25221519 PMCID: PMC4145359 DOI: 10.3389/fphys.2014.00325] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2014] [Accepted: 08/06/2014] [Indexed: 12/02/2022] Open
Abstract
Inwardly-rectifying potassium (Kir) channels contribute to maintenance of the resting membrane potential and regulation of electrical excitation in many cell types. Strongly rectifying Kir channels exhibit a very steep voltage dependence resulting in silencing of their activity at depolarized membrane voltages. The mechanism underlying this steep voltage dependence is blockade by endogenous polyamines. These small multifunctional, polyvalent metabolites enter the long Kir channel pore from the intracellular side, displacing multiple occupant ions as they migrate to a stable binding site in the transmembrane region of the channel. Numerous structure-function studies have revealed structural elements of Kir channels that determine their susceptibility to polyamine block, and enable the steep voltage dependence of this process. In addition, various channelopathies have been described that result from alteration of the polyamine sensitivity or activity of strongly rectifying channels. The primary focus of this article is to summarize current knowledge of the molecular mechanisms of polyamine block, and provide some perspective on lingering uncertainties related to this physiologically important mechanism of ion channel blockade. We also briefly review some of the important and well understood physiological roles of polyamine sensitive, strongly rectifying Kir channels, primarily of the Kir2 family.
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Affiliation(s)
- Victoria A Baronas
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia Vancouver, BC, Canada
| | - Harley T Kurata
- Department of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia Vancouver, BC, Canada
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Dougherty DA, Van Arnam EB. In vivo incorporation of non-canonical amino acids by using the chemical aminoacylation strategy: a broadly applicable mechanistic tool. Chembiochem 2014; 15:1710-20. [PMID: 24990307 DOI: 10.1002/cbic.201402080] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Indexed: 01/05/2023]
Abstract
We describe a strategy for incorporating non-canonical amino acids site-specifically into proteins expressed in living cells, involving organic synthesis to chemically aminoacylate a suppressor tRNA, protein expression in Xenopus oocytes, and monitoring protein function, primarily by electrophysiology. With this protocol, a very wide range of non-canonical amino acids can be employed, allowing both systematic structure-function studies and the incorporation of reactive functionalities. Here, we present an overview of the methodology and examples meant to illustrate the versatility and power of the method as a tool for investigating protein structure and function.
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Affiliation(s)
- Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (USA).
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12
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Equalizing excitation-inhibition ratios across visual cortical neurons. Nature 2014; 511:596-600. [PMID: 25043046 PMCID: PMC4117808 DOI: 10.1038/nature13321] [Citation(s) in RCA: 463] [Impact Index Per Article: 46.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Accepted: 04/08/2014] [Indexed: 11/26/2022]
Abstract
The relationship between synaptic excitation and inhibition (E/I ratio), two opposing forces in the mammalian cerebral cortex, affects many cortical functions like feature selectivity and gain1,2. Individual pyramidal cells show stable E/I ratios in time despite fluctuating cortical activity levels because when excitation increases, inhibition increases proportionally through the increased recruitment of inhibitory neurons, a phenomenon referred to as excitation-inhibition balance3–9. However, little is known about the distribution of E/I ratios across pyramidal cells. Through their highly divergent axons inhibitory neurons indiscriminately contact most neighboring pyramidal cells10,11. Is inhibition homogeneously distributed or is it individually matched to the different amounts of excitation received by distinct pyramidal cells? Here we discover that pyramidal cells in layer 2/3 of mouse primary visual cortex (V1) each receive inhibition in a similar proportion to their excitation. As a consequence E/I ratios are equalized across pyramidal cells. This matched inhibition is mediated by parvalbumin-expressing (PV) but not somatostatin-expressing (SOM) inhibitory neurons and results from the independent adjustment of synapses originating from the same PV cell but targeting different pyramidal cells. Furthermore, this match is activity-dependent as it is disrupted by perturbing pyramidal cell activity. Thus, the equalization of E/I ratios across pyramidal cells reveals an unexpected degree of order in the spatial distribution of synaptic strengths and indicates that the relationship between cortex’s two opposing forces is stabilized not only in time but also in space.
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Almassy J, Yule DI. Photolysis of caged compounds: studying Ca(2+) signaling and activation of Ca(2+)-dependent ion channels. Cold Spring Harb Protoc 2013; 2013:2013/1/pdb.top066076. [PMID: 23282631 DOI: 10.1101/pdb.top066076] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
A wide variety of signaling molecules have been chemically modified by conjugation to a photolabile chromophore to render the substance temporarily biologically inert. Subsequent exposure to ultraviolet (UV) light can release the active moiety from the "caged" precursor in an experimentally controlled manner. This allows the concentration of active molecule to be precisely manipulated in both time and space. These techniques are particularly useful in experimental protocols designed to investigate the mechanisms underlying Ca(2+) signaling and the activation of Ca(2+)-dependent effectors.
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Affiliation(s)
- Janos Almassy
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
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Inhibiting the clathrin-mediated endocytosis pathway rescues KIR2.1 downregulation by pentamidine. Pflugers Arch 2012. [DOI: 10.1007/s00424-012-1189-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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15
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Butterfield S, Hejjaoui M, Fauvet B, Awad L, Lashuel HA. Chemical strategies for controlling protein folding and elucidating the molecular mechanisms of amyloid formation and toxicity. J Mol Biol 2012; 421:204-36. [PMID: 22342932 DOI: 10.1016/j.jmb.2012.01.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Revised: 01/30/2012] [Accepted: 01/31/2012] [Indexed: 12/12/2022]
Abstract
It has been more than a century since the first evidence linking the process of amyloid formation to the pathogenesis of Alzheimer's disease. During the last three decades in particular, increasing evidence from various sources (pathology, genetics, cell culture studies, biochemistry, and biophysics) continues to point to a central role for the pathogenesis of several incurable neurodegenerative and systemic diseases. This is in part driven by our improved understanding of the molecular mechanisms of protein misfolding and aggregation and the structural properties of the different aggregates in the amyloid pathway and the emergence of new tools and experimental approaches that permit better characterization of amyloid formation in vivo. Despite these advances, detailed mechanistic understanding of protein aggregation and amyloid formation in vitro and in vivo presents several challenges that remain to be addressed and several fundamental questions about the molecular and structural determinants of amyloid formation and toxicity and the mechanisms of amyloid-induced toxicity remain unanswered. To address this knowledge gap and technical challenges, there is a critical need for developing novel tools and experimental approaches that will not only permit the detection and monitoring of molecular events that underlie this process but also allow for the manipulation of these events in a spatial and temporal fashion both in and out of the cell. This review is primarily dedicated in highlighting recent results that illustrate how advances in chemistry and chemical biology have been and can be used to address some of the questions and technical challenges mentioned above. We believe that combining recent advances in the development of new fluorescent probes, imaging tools that enabled the visualization and tracking of molecular events with advances in organic synthesis, and novel approaches for protein synthesis and engineering provide unique opportunities to gain a molecular-level understanding of the process of amyloid formation. We hope that this review will stimulate further research in this area and catalyze increased collaboration at the interface of chemistry and biology to decipher the mechanisms and roles of protein folding, misfolding, and aggregation in health and disease.
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Affiliation(s)
- Sara Butterfield
- Laboratory of Molecular and Chemical Biology of Neurodegeneration, Brain Mind Institute, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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Russell AG, Sadler MJ, Laidlaw HJ, Gutiérrez-Loriente A, Wharton CW, Carteau D, Bassani DM, Snaith JS. Photorelease of tyrosine from α-carboxy-6-nitroveratryl (αCNV) derivatives. Photochem Photobiol Sci 2012; 11:556-63. [PMID: 22249211 DOI: 10.1039/c2pp05320a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The synthesis of photolabile tyrosine derivatives protected on the phenolic oxygen by the α-carboxy-6-nitroveratryl (αCNV) protecting group is described. The compounds undergo rapid photolysis at wavelengths longer than 300 nm to liberate the corresponding phenol in excellent yield (quantum yield for the deprotection of tyrosine = 0.19). Further protection of caged tyrosine is possible, yielding N-Fmoc protected derivatives suitable for direct incorporation of caged tyrosine in solid-phase peptide synthesis.
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Zhang DY, Zhang YH, Sun HY, Lau CP, Li GR. Epidermal growth factor receptor tyrosine kinase regulates the human inward rectifier potassium K(IR)2.3 channel, stably expressed in HEK 293 cells. Br J Pharmacol 2011; 164:1469-78. [PMID: 21486282 PMCID: PMC3221101 DOI: 10.1111/j.1476-5381.2011.01424.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 03/05/2011] [Accepted: 04/04/2011] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE The detailed molecular modulation of inward rectifier potassium channels (including the K(IR) 2.3 channel) is not fully understood. The present study was designed to determine whether human K(IR) 2.3 (K(IR) 2.3) channels were regulated by protein tyrosine kinases (PTKs). EXPERIMENTAL APPROACH Whole-cell patch voltage-clamp, immunoprecipitation, Western blot analysis and site-directed mutagenesis were employed to determine the potential PTK phosphorylation of Kir2.3 current in HEK 293 cells stably expressing Kir2.3 gene. KEY RESULTS The broad-spectrum PTK inhibitor genistein (10 µM) and the selective epidermal growth factor (EGF) kinase inhibitor AG556 (10 µM) reversibly decreased K(IR) 2.3 current and the effect was reversed by the protein tyrosine phosphatase inhibitor, orthovanadate (1 mM). Although EGF (100 ng·mL(-1) ) and orthovanadate enhanced K(IR) 2.3 current, this effect was antagonized by AG556. However, the Src-family tyrosine kinase inhibitor PP2 (10 µM) did not inhibit K(IR) 2.3 current. Tyrosine phosphorylation of K(IR) 2.3 channels was decreased by genistein or AG556, and was increased by EGF or orthovanadate. The decrease of tyrosine phosphorylation of K(IR) 2.3 channels by genistein or AG556 was reversed by orthovanadate or EGF. Interestingly, the response of K(IR) 2.3 channels to EGF or AG556 was lost in the K(IR) 2.3 Y234A mutant channel. CONCLUSION AND IMPLICATIONS These results demonstrate that the EGF receptor tyrosine kinase up-regulates the K(IR) 2.3 channel via phosphorylation of the Y234 residue of the WT protein. This effect may be involved in the endogenous regulation of cellular electrical activity.
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Affiliation(s)
- De-Yong Zhang
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong SAR, China
| | - Yan-Hui Zhang
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong SAR, China
| | - Hai-Ying Sun
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong SAR, China
| | - Chu-Pak Lau
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong SAR, China
| | - Gui-Rong Li
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong SAR, China
- Department of Physiology, Li Ka Shing Faculty of Medicine, The University of Hong KongPokfulam, Hong Kong SAR, China
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Inhibition of lysosomal degradation rescues pentamidine-mediated decreases of KIR2.1 ion channel expression but not that of Kv11.1. Eur J Pharmacol 2011; 652:96-103. [DOI: 10.1016/j.ejphar.2010.10.093] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Revised: 10/13/2010] [Accepted: 10/29/2010] [Indexed: 11/19/2022]
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19
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Pantoja R, Rodriguez EA, Dibas MI, Dougherty DA, Lester HA. Single-molecule imaging of a fluorescent unnatural amino acid incorporated into nicotinic receptors. Biophys J 2010; 96:226-37. [PMID: 19134478 DOI: 10.1016/j.bpj.2008.09.034] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2008] [Accepted: 09/29/2008] [Indexed: 10/21/2022] Open
Abstract
We report on the first, to our knowledge, successful detection of a fluorescent unnatural amino acid (fUAA), Lys(BODIPYFL), incorporated into a membrane protein (the muscle nicotinic acetylcholine receptor, nAChR) in a living cell. Xenopus oocytes were injected with a frameshift-suppressor tRNA, amino-acylated with Lys(BODIPYFL) and nAChR (alpha/beta19'GGGU/gamma/delta) mRNAs. We measured fluorescence from oocytes expressing nAChR beta19'Lys(BODIPYFL), using time-resolved total internal reflection fluorescence microscopy. Under conditions of relatively low receptor density (<0.1 receptors/microm(2)), we observed puncta with diffraction-limited profiles that were consistent with the point-spread function of our microscope. Furthermore, diffraction-limited puncta displayed step decreases in fluorescence intensity, consistent with single-molecule photobleaching. The puncta densities agreed with macroscopic ACh-induced current densities, showing that the fUAA was incorporated, and that receptors were functional. Dose-response relations for the nAChR beta19'Lys(BODIPYFL) receptors were similar to those for wild-type receptors. We also studied nAChR beta19'Lys(BODIPYFL) receptors labeled with alpha-bungarotoxin monoconjugated with Alexa488 (alphaBtxAlexa488). The nAChR has two alphaBtx binding sites, and puncta containing the Lys(BODIPYFL) labeled with alphaBtxAlexa488 yielded the expected three discrete photobleaching steps. We also performed positive control experiments with a nAChR containing enhanced green fluorescent protein in the gamma-subunit M3-M4 loop, which confirmed our nAChR beta19'Lys(BODIPYFL) measurements. Thus, we report on the cell-based single-molecule detection of nAChR beta19'Lys(BODIPYFL).
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Affiliation(s)
- Rigo Pantoja
- Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
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20
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Li GR, Dong MQ. Pharmacology of Cardiac Potassium Channels. CARDIOVASCULAR PHARMACOLOGY - HEART AND CIRCULATION 2010; 59:93-134. [DOI: 10.1016/s1054-3589(10)59004-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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21
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Lee HM, Larson DR, Lawrence DS. Illuminating the chemistry of life: design, synthesis, and applications of "caged" and related photoresponsive compounds. ACS Chem Biol 2009; 4:409-27. [PMID: 19298086 DOI: 10.1021/cb900036s] [Citation(s) in RCA: 369] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Biological systems are characterized by a level of spatial and temporal organization that often lies beyond the grasp of present day methods. Light-modulated bioreagents, including analogs of low molecular weight compounds, peptides, proteins, and nucleic acids, represent a compelling strategy to probe, perturb, or sample biological phenomena with the requisite control to address many of these organizational complexities. Although this technology has created considerable excitement in the chemical community, its application to biological questions has been relatively limited. We describe the challenges associated with the design, synthesis, and use of light-responsive bioreagents; the scope and limitations associated with the instrumentation required for their application; and recent chemical and biological advances in this field.
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Affiliation(s)
- Hsien-Ming Lee
- Departments of Chemistry, Medicinal Chemistry & Natural Products, and Pharmacology, The University of North Carolina, Chapel Hill, North Carolina 27599-3290
| | - Daniel R. Larson
- Department of Anatomy and Structural Biology, The Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461
| | - David S. Lawrence
- Departments of Chemistry, Medicinal Chemistry & Natural Products, and Pharmacology, The University of North Carolina, Chapel Hill, North Carolina 27599-3290
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22
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Kilman VL, Zhang L, Meissner RA, Burg E, Allada R. Perturbing dynamin reveals potent effects on the Drosophila circadian clock. PLoS One 2009; 4:e5235. [PMID: 19384421 PMCID: PMC2668759 DOI: 10.1371/journal.pone.0005235] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2009] [Accepted: 03/19/2009] [Indexed: 01/09/2023] Open
Abstract
Background Transcriptional feedback loops are central to circadian clock function. However, the role of neural activity and membrane events in molecular rhythms in the fruit fly Drosophila is unclear. To address this question, we expressed a temperature-sensitive, dominant negative allele of the fly homolog of dynamin called shibirets1 (shits1), an active component in membrane vesicle scission. Principal Findings Broad expression in clock cells resulted in unexpectedly long, robust periods (>28 hours) comparable to perturbation of core clock components, suggesting an unappreciated role of membrane dynamics in setting period. Expression in the pacemaker lateral ventral neurons (LNv) was necessary and sufficient for this effect. Manipulation of other endocytic components exacerbated shits1's behavioral effects, suggesting its mechanism is specific to endocytic regulation. PKA overexpression rescued period effects suggesting shits1 may downregulate PKA pathways. Levels of the clock component PERIOD were reduced in the shits1-expressing pacemaker small LNv of flies held at a fully restrictive temperature (29°C). Less restrictive conditions (25°C) delayed cycling proportional to observed behavioral changes. Levels of the neuropeptide PIGMENT-DISPERSING FACTOR (PDF), the only known LNv neurotransmitter, were also reduced, but PERIOD cycling was still delayed in flies lacking PDF, implicating a PDF-independent process. Further, shits1 expression in the eye also results in reduced PER protein and per and vri transcript levels, suggesting that shibire-dependent signaling extends to peripheral clocks. The level of nuclear CLK, transcriptional activator of many core clock genes, is also reduced in shits1 flies, and Clk overexpression suppresses the period-altering effects of shits1. Conclusions We propose that membrane protein turnover through endocytic regulation of PKA pathways modulates the core clock by altering CLK levels and/or activity. These results suggest an important role for membrane scission in setting circadian period.
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Affiliation(s)
- Valerie L. Kilman
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
- Center for Sleep and Circadian Biology, Northwestern University, Evanston, Illinois, United States of America
| | - Luoying Zhang
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
| | - Rose-Anne Meissner
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
| | - Elyssa Burg
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
| | - Ravi Allada
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
- Center for Sleep and Circadian Biology, Northwestern University, Evanston, Illinois, United States of America
- * E-mail:
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Boyer SB, Slesinger PA, Jones SVP. Regulation of Kir2.1 channels by the Rho-GTPase, Rac1. J Cell Physiol 2008; 218:385-93. [PMID: 18932198 DOI: 10.1002/jcp.21610] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Mutations in Kir2.1 inwardly rectifying potassium channels are associated with Andersen syndrome, a disease characterized by potentially fatal cardiac arrhythmias. While several Andersen-associated mutations affect membrane expression, the cytoplasmic signals that regulate Kir2.1 trafficking are poorly understood. Here, we investigated whether the Rho-family of small GTPases regulates trafficking of Kir2.1 channels expressed in HEK-293 cells. Treatment with Clostridium difficile toxin B, an inhibitor of Rho-family GTPases, or co-expression of the dominant-negative mutant of Rac1 (Rac1(DN)) increased Kir2.1 channels approximately 2-fold. However, the dominant-negative forms of other Rho-family GTPases, RhoA or Cdc42, did not alter Kir2.1 currents, suggesting a selective effect of Rac1 on Kir2.1 channels. Single-channel properties (gamma, tau(o), tau(c)) and total protein levels of Kir2.1 were unchanged with co-expression of Rac1(DN); however, studies using TIRF microscopy and CFP-tagged Kir2.1 revealed increased channel surface expression. Immunohistochemical detection of extracellularly tagged HA-Kir2.1 channels showed that Rac1(DN) reduced channel internalization when co-expressed. Finally, the dominant-negative mutant of dynamin, which interferes with endocytosis, occluded the Rac1(DN)-induced potentiation of Kir2.1 currents. These data suggest that inhibition of Rac1 increases Kir2.1 surface expression by interfering with endocytosis, likely via a dynamin-dependent pathway. Surprisingly, Rac1(DN) did not alter Kir2.2 current density or internalization, suggesting subunit specific modulation of Kir2.1 channels. Consistent with this, construction of Kir2.1/2.2 chimeras implicated the C-terminal domain of Kir2.1 in mediating the potentiating effect of Rac1(DN). This novel pathway for regulating surface expression of cardiac Kir2.1 channels could have implications for normal and diseased cardiac states.
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Affiliation(s)
- Stephanie B Boyer
- Peptide Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California, USA.
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24
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Gorostiza P, Isacoff EY. Optical switches for remote and noninvasive control of cell signaling. Science 2008; 322:395-9. [PMID: 18927384 DOI: 10.1126/science.1166022] [Citation(s) in RCA: 272] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Although the identity and interactions of signaling proteins have been studied in great detail, the complexity of signaling networks cannot be fully understood without elucidating the timing and location of activity of individual proteins. To do this, one needs a means for detecting and controlling specific signaling events. An attractive approach is to use light, both to report on and control signaling proteins in cells, because light can probe cells in real time with minimal damage. Although optical detection of signaling events has been successful for some time, the development of the means for optical control has accelerated only recently. Of particular interest is the development of chemically engineered proteins that are directly sensitive to light.
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Affiliation(s)
- Pau Gorostiza
- Institució Catalana de Recerca i Estudis Avançats and Institut de Bioenginyeria de Catalunya, Parc Científic de Barcelona, Edifici Hèlix. C/Baldiri Reixac 15, Barcelona 08028, Spain
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25
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Huang LY, Umanah G, Hauser M, Son C, Arshava B, Naider F, Becker JM. Unnatural Amino Acid Replacement in a Yeast G Protein-Coupled Receptor in Its Native Environment. Biochemistry 2008; 47:5638-48. [DOI: 10.1021/bi701866e] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Li-Yin Huang
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - George Umanah
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Melinda Hauser
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Cagdas Son
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Boris Arshava
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Fred Naider
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
| | - Jeffrey M. Becker
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, City University of New York (CUNY), New York City, New York 10314, and Graduate School and University Center, City University of New York (CUNY), New York City, New York 10314
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Effects on membrane capacitance of steroids with antagonist properties at GABAA receptors. Biophys J 2008; 95:176-85. [PMID: 18339741 DOI: 10.1529/biophysj.107.124768] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We investigated the electrophysiological signature of neuroactive steroid interactions with the plasma membrane. We found that charged, sulfated neuroactive steroids, those that exhibit noncompetitive antagonism of GABA(A) receptors, altered capacitive charge movement in response to voltage pulses in cells lacking GABA receptors. Uncharged steroids, some of which are potent enhancers of GABA(A) receptor activity, produced no alteration in membrane capacitance. We hypothesized that the charge movements might result from physical translocation of the charged steroid through the transmembrane voltage, as has been observed previously with several hydrophobic anions. However, the charge movements and relaxation time constants of capacitive currents did not exhibit the Boltzmann-type voltage dependence predicted by a single barrier model. Further, a fluorescently tagged analog of a sulfated neurosteroid altered membrane capacitance similar to the parent compound but produced no voltage-dependent fluorescence change, a result inconsistent with a strong change in the polar environment of the fluorophore during depolarization. These findings suggest that negatively charged sulfated steroids alter the plasma membrane capacitance without physical movement of the molecule through the electric field.
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Lysosome mediated Kir2.1 breakdown directly influences inward rectifier current density. Biochem Biophys Res Commun 2008; 367:687-92. [DOI: 10.1016/j.bbrc.2007.12.168] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2007] [Accepted: 12/21/2007] [Indexed: 01/23/2023]
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Hinard V, Belin D, Konig S, Bader CR, Bernheim L. Initiation of human myoblast differentiation via dephosphorylation of Kir2.1 K+ channels at tyrosine 242. Development 2008; 135:859-67. [PMID: 18216177 DOI: 10.1242/dev.011387] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Myoblast differentiation is essential to skeletal muscle formation and repair. The earliest detectable event leading to human myoblast differentiation is an upregulation of Kir2.1 channel activity, which causes a negative shift (hyperpolarization) of the resting potential of myoblasts. After exploring various mechanisms, we found that this upregulation of Kir2.1 was due to dephosphorylation of the channel itself. Application of genistein, a tyrosine kinase inhibitor, increased Kir2.1 activity and triggered the differentiation process, whereas application of bpV(Phen), a tyrosine phosphatase inhibitor, had the opposite effects. We could show that increased Kir2.1 activity requires dephosphorylation of tyrosine 242; replacing this tyrosine in Kir2.1 by a phenylalanine abolished inhibition by bpV(Phen). Finally, we found that the level of tyrosine phosphorylation in endogenous Kir2.1 channels is considerably reduced during differentiation when compared with proliferation. We propose that Kir2.1 channels are already present at the membrane of proliferating, undifferentiated human myoblasts but in a silent state, and that Kir2.1 tyrosine 242 dephosphorylation triggers differentiation.
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Affiliation(s)
- Valérie Hinard
- Département de Neurosciences Fondamentales, University of Geneva, Centre Médical Universitaire, Geneva 4, Switzerland
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Mason AK, Jacobs BE, Welling PA. AP-2-dependent internalization of potassium channel Kir2.3 is driven by a novel di-hydrophobic signal. J Biol Chem 2008; 283:5973-84. [PMID: 18180291 DOI: 10.1074/jbc.m709756200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The localization and density of Kir2.3 channels are influenced by the balance between PDZ protein interaction at the cell surface and routing into the endocytic pathway. Here, we explore mechanisms by which the Kir2.3 channel is directed into the endocytic pathway. We found that Kir2.3 channels are constitutively internalized from the cell surface in a dynamin-dependent manner, indicative of vesicle-mediated endocytosis. The rate of Kir2.3 endocytosis was dramatically attenuated following RNA interference-mediated knockdown of either alpha adaptin (AP-2 clathrin adaptor) or clathrin heavy chain, revealing that Kir2.3 is internalized by an AP-2 clathrin-dependent mechanism. Structure-rationalized mutagenesis studies of a number of different potential AP-2 interaction motifs indicate that internalization of Kir2.3 is largely dependent on a non-canonical di-isoleucine motif (II413) embedded within the C terminus. Internalization assays using CD4-Kir2.3 chimeras demonstrate that the di-isoleucine signal acts in an autonomous and transplantable manner. Kir2.3 co-immunoprecipitates with alpha adaptin, and disruption of the di-isoleucine motif decreased interaction of the channel with AP-2. Replacement of the di-isoleucine motif with a canonical di-leucine internalization signal actually blocked Kir2.3 endocytosis. Moreover, in yeast three-hybrid studies, the Kir2.3 di-isoleucine motif does not bind the AP-2 alphaC-sigma2 hemicomplex in the way that has been recently observed for canonical di-leucine signals. Altogether, the results indicate that Kir2.3 channels are marked for clathrin-dependent internalization from the plasma membrane by a novel AP-2-dependent signal.
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Affiliation(s)
- Amanda K Mason
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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Li CH, Zhang Q, Teng B, Mustafa SJ, Huang JY, Yu HG. Src tyrosine kinase alters gating of hyperpolarization-activated HCN4 pacemaker channel through Tyr531. Am J Physiol Cell Physiol 2008; 294:C355-62. [PMID: 17977941 PMCID: PMC2784909 DOI: 10.1152/ajpcell.00236.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
We recently discovered that the constitutively active Src tyrosine kinase can enhance hyperpolarization-activated, cyclic nucleotide-gated (HCN) 4 channel activity by binding to the channel protein. To investigate the mechanism of modulation by Src of HCN channels, we studied the effects of a selective inhibitor of Src tyrosine kinase, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), on HCN4 and its mutant channels expressed in HEK 293 cells by using a whole cell patch-clamp technique. We found that PP2 can inhibit HCN4 currents by negatively shifting the voltage dependence of channel activation, decreasing the whole cell channel conductance, and slowing activation and deactivation kinetics. Screening putative tyrosine residues subject to phosphorylation yielded two candidates: Tyr(531) and Tyr(554). Substituting HCN4-Tyr(531) with phenylalanine largely abolished the effects of PP2 on HCN4 channels. Replacing HCN4-Tyr(554) with phenylalanine did not abolish the effects of PP2 on voltage-dependent activation but did eliminate PP2-induced slowing of channel kinetics. The inhibitory effects of HCN channels associated with reduced Src tyrosine activity is confirmed in HL-1 cardiomyocytes. Finally, we found that PP2 can decrease the heart rate in a mouse model. These results demonstrate that Src tyrosine kinase enhances HCN4 currents by shifting their activation to more positive potentials and increasing the whole cell channel conductance as well as speeding the channel kinetics. The tyrosine residue that mediates most of Src's actions on HCN4 channels is Tyr(531).
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Affiliation(s)
- Chen-Hong Li
- Department of Physiology and Pharmacology, Center for Interdisciplinary Research in Cardiovascular Sciences, West Virginia University School of Medicine, Morgantown, WV 26506, USA
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Zitron E, Günth M, Scherer D, Kiesecker C, Kulzer M, Bloehs R, Scholz EP, Thomas D, Weidenhammer C, Kathöfer S, Bauer A, Katus HA, Karle CA. Kir2.x inward rectifier potassium channels are differentially regulated by adrenergic α1A receptors. J Mol Cell Cardiol 2008; 44:84-94. [DOI: 10.1016/j.yjmcc.2007.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2007] [Revised: 09/21/2007] [Accepted: 10/01/2007] [Indexed: 11/30/2022]
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32
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Gorostiza P, Isacoff E. Optical switches and triggers for the manipulation of ion channels and pores. MOLECULAR BIOSYSTEMS 2007; 3:686-704. [PMID: 17882331 DOI: 10.1039/b710287a] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Like fluorescence sensing techniques, methods to manipulate proteins with light have produced great advances in recent years. Ion channels have been one of the principal protein targets of photoswitched manipulation. In combination with fluorescence detection of cell signaling, this has enabled non-invasive, all-optical experiments on cell and tissue function, both in vitro and in vivo. Optical manipulation of channels has also provided insights into the mechanism of channel function. Optical control elements can be classified according to their molecular reversibility as non-reversible phototriggers where light breaks a chemical bond (e.g. caged ligands) and as photoswitches that reversibly photoisomerize. Synthetic photoswitches constitute nanoscale actuators that can alter channel function using three different strategies. These include (1) nanotoggles, which are tethered photoswitchable ligands that either activate channels (agonists) or inhibit them (blockers or antagonists), (2) nanokeys, which are untethered (freely diffusing) photoswitchable ligands, and (3) nanotweezers, which are photoswitchable crosslinkers. The properties of such photoswitches are discussed here, with a focus on tethered photoswitchable ligands. The recent literature on optical manipulation of ion channels is reviewed for the different channel families, with special emphasis on the understanding of ligand binding and gating processes, applications in nanobiotechnology, and with attention to future prospects in the field.
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Affiliation(s)
- Pau Gorostiza
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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33
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Abstract
Biologically active compounds which are light-responsive offer experimental possibilities which are otherwise very difficult to achieve. Since light can be manipulated very precisely, for example, with lasers and microscopes rapid jumps in concentration of the active form of molecules are possible with exact control of the area, time, and dosage. The development of such strategies started in the 1970s. This review summarizes new developments of the last five years and deals with "small molecules", proteins, and nucleic acids which can either be irreversibly activated with light (these compounds are referred to as "caged compounds") or reversibly switched between an active and an inactive state.
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Affiliation(s)
- Günter Mayer
- Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany.
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34
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Tikku S, Epshtein Y, Collins H, Travis AJ, Rothblat GH, Levitan I. Relationship between Kir2.1/Kir2.3 activity and their distributions between cholesterol-rich and cholesterol-poor membrane domains. Am J Physiol Cell Physiol 2007; 293:C440-50. [PMID: 17459945 DOI: 10.1152/ajpcell.00492.2006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Our earlier studies have shown that Kir2.x channels are suppressed by an increase in the level of cellular cholesterol, whereas cholesterol depletion enhances the activity of the channels. In this study, we show that Kir2.1 and Kir2.3 channels have double-peak distributions between cholesterol-rich (raft) and cholesterol-poor (non-raft) membrane fractions, indicating that the channels exist in two different types of lipid environment. We also show that whereas methyl-beta-cyclodextrin-induced cholesterol depletion removes cholesterol from both raft and non-raft membrane fractions, cholesterol enrichment results in cholesterol increase exclusively in the raft fractions. Kinetics of both depletion-induced Kir2.1 enhancement and enrichment-induced Kir2.1 suppression correlate with the changes in the level of raft cholesterol. Furthermore, we show not only that cholesterol depletion shifts the distribution of the channels from cholesterol-rich to cholesterol-poor membrane fractions but also that cholesterol enrichment has the opposite effect. These observations suggest that change in the level of raft cholesterol alone is sufficient to suppress Kir2 activity and to facilitate partitioning of the channels to cholesterol-rich domains. Therefore, we suggest that partitioning to membrane rafts plays an important role in the sensitivity of Kir2 channels to cholesterol.
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Affiliation(s)
- Saloni Tikku
- Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, USA
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35
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Colley BS, Biju KC, Visegrady A, Campbell S, Fadool DA. Neurotrophin B receptor kinase increases Kv subfamily member 1.3 (Kv1.3) ion channel half-life and surface expression. Neuroscience 2006; 144:531-46. [PMID: 17101229 PMCID: PMC1884406 DOI: 10.1016/j.neuroscience.2006.09.055] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2006] [Revised: 09/21/2006] [Accepted: 09/22/2006] [Indexed: 01/29/2023]
Abstract
Kv subfamily member 1.3 (Kv1.3), a member of the Shaker family of potassium channels, has been found to play diverse roles in immunity, metabolism, insulin resistance, sensory discrimination, and axonal targeting in addition to its traditional role in the stabilization of the resting potential. We demonstrate that the neurotrophin B receptor (TrkB) causes an upregulation of Kv1.3 ion channel protein expression in the absence of the preferred ligand for the receptor (brain-derived neurotrophic factor; BDNF) and oppositely downregulates levels of Kv subfamily member 1.5. Although the effect occurs in the absence of the ligand, Kv1.3 upregulation by TrkB is dependent upon the catalytic domain of the TrkB kinase as well as tyrosine (Y) residues in the N and C terminus of the Kv1.3 channel. Using pulse-chase experiments we find that TrkB alters the half-life residence of the channel by approximately 2x and allows it to sustain activity as reflected in an increased current magnitude without alteration of kinetic properties. TrkB and Kv1.3 co-immunoprecipitate from tissue preparations of the mouse olfactory bulb and olfactory cortex, and by immunocytochemical approaches, are found to be co-localized in the glomerular, mitral cell, and internal plexiform layers of the olfactory bulb. These data suggest that Kv1.3 is not only modulated by direct phosphorylation in the presence of BDNF-activated TrkB kinase, but also may be fine tuned via regulation of surface expression while in the proximity of neurotrophic factor receptors. Given the variability of TrkB expression during development, regeneration, or neuronal activation, modulation of surface expression and turnover of Kv channels could significantly impact neuronal excitability, distinct from that of tyrosine kinase phosphorylation.
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Affiliation(s)
- B S Colley
- Department of Biological Science, Programs in Neuroscience and Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
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36
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Santarius M, Lee C, Anderson R. Supervised membrane swimming: small G-protein lifeguards regulate PIPK signalling and monitor intracellular PtdIns(4,5)P2 pools. Biochem J 2006; 398:1-13. [PMID: 16856876 PMCID: PMC1525017 DOI: 10.1042/bj20060565] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Regulation of PIPK (phosphatidylinositol phosphate kinase) and PtdIns(4,5)P2 signalling by small G-proteins and their effectors is key to many biological functions. Through selective recruitment and activation of different PIPK isoforms, small G-proteins such as Rho, Rac and Cdc42 modulate actin dynamics and cytoskeleton-dependent cellular events in response to extracellular signalling. These activities affect a number of processes, including endocytosis, bacterial penetration into host cells and cytolytic granule-mediated targeted cell killing. Small G-proteins and their modulators are also regulated by phosphoinositides through translocation and conformational changes. Arf family small G-proteins act at multiple sites as regulators of membrane trafficking and actin cytoskeletal remodelling, and regulate a feedback loop comprising phospholipase D, phosphatidic acid, PIPKs and PtdIns(4,5)P2, contributing to enhancement of PtdIns(4,5)P2-mediated cellular events and receptor signalling. Na+, Kir (inwardly rectifying K+), Ca2+ and TRP (transient receptor potential) ion channels are regulated by small G-proteins and membrane pools of PtdIns(4,5)P2. Yeast phosphatidylinositol 4-phosphate 5-kinases Mss4 and Its3 are involved in resistance against disturbance of sphingolipid biosynthesis and maintenance of cell integrity through the synthesis of PtdIns(4,5)P2 and downstream signalling through the Rom2/Rho2 and Rgf1/Rho pathways. Here, we review models for regulated intracellular targeting of PIPKs by small G-proteins and other modulators in response to extracellular signalling. We also describe the spatial and temporal cross-regulation of PIPKs and small G-proteins that is critical for a number of cellular functions.
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Affiliation(s)
- Megan Santarius
- *Program in Molecular and Cellular Pharmacology, University of Wisconsin-Madison, 1300 University Avenue, Madison, WI 53706, U.S.A
| | - Chang Ho Lee
- †Department of Pharmacology, College of Medicine, Hanyang University, 17 Hengdang-dong, Seongdong-ku, Seoul, 133-791, South Korea
- To whom correspondence should be addressed (email )
| | - Richard A. Anderson
- *Program in Molecular and Cellular Pharmacology, University of Wisconsin-Madison, 1300 University Avenue, Madison, WI 53706, U.S.A
- ‡Department of Pharmacology, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, U.S.A
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37
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38
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Arinsburg SS, Cohen IS, Yu HG. Constitutively active Src tyrosine kinase changes gating of HCN4 channels through direct binding to the channel proteins. J Cardiovasc Pharmacol 2006; 47:578-86. [PMID: 16680072 PMCID: PMC1693968 DOI: 10.1097/01.fjc.0000211740.47960.8b] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Cardiac pacemaker current, if, is generated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Our previous studies demonstrated that altered tyrosine phosphorylation can modulate the properties of both if and HCN channels. To assess a hypothesis that the intracellular tyrosine kinase Src may play a role in modulation by tyrosine phosphorylation of if, we cotransfected HEK293 cells with HCN4 and Src proteins. When HCN4 was cotransfected with a constitutively activated Src protein (Src529), the resultant voltage-dependent HCN4 activation was positively shifted (HCN4: V1/2 = -93 mV; Src529: V1/2 = -80 mV). The activation kinetics were accelerated at some potentials but not over the entire voltage range tested (eg, at -95 mV, tau_act(HCN4) = 3,243 ms; tau_act(Src529) = 1,113 ms). When HCN4 was cotransfected with a dominant negative Src protein (Src296), the HCN4 activation was shifted more negative to a smaller degree (HCN4: V1/2 = -93 mV; Src296: V1/2 = -98 mV; statistically insignificant) and the activation kinetics were slowed at most test potentials (eg, at -95 mV, tau_act(Src296) = 7,396 ms). Neither Src529 nor Src296 significantly altered HCN4 current density. Coimmunoprecipitation experiments revealed that Src forms a complex with HCN4 in HEK293 cells and in rat ventricular myocytes. Our data provide a novel mechanism of if regulation by Src tyrosine phosphorylation.
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Affiliation(s)
- Suzanne S. Arinsburg
- From the New York College of Osteopathic Medicine of the New York Institute of Technology, NY
| | - Ira S. Cohen
- From the Institute of Molecular Cardiology and Department of Physiology & Biophysics, State University of New York at Stony Brook, Stony Brook, NY
| | - Han-Gang Yu
- From the New York College of Osteopathic Medicine of the New York Institute of Technology, NY
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39
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Xiu X, Hanek AP, Wang J, Lester HA, Dougherty DA. A Unified View of the Role of Electrostatic Interactions in Modulating the Gating of Cys Loop Receptors. J Biol Chem 2005; 280:41655-66. [PMID: 16216879 DOI: 10.1074/jbc.m508635200] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the Cys loop superfamily of ligand-gated ion channels, a global conformational change, initiated by agonist binding, results in channel opening and the passage of ions across the cell membrane. The detailed mechanism of channel gating is a subject that has lent itself to both structural and electrophysiological studies. Here we defined a gating interface that incorporates elements from the ligand binding domain and transmembrane domain previously reported as integral to proper channel gating. An overall analysis of charged residues within the gating interface across the entire superfamily showed a conserved charging pattern, although no specific interacting ion pairs were conserved. We utilized a combination of conventional mutagenesis and the high precision methodology of unnatural amino acid incorporation to study extensively the gating interface of the mouse muscle nicotinic acetylcholine receptor. We found that charge reversal, charge neutralization, and charge introduction at the gating interface are often well tolerated. Furthermore, based on our data and a reexamination of previously reported data on gamma-aminobutyric acid, type A, and glycine receptors, we concluded that the overall charging pattern of the gating interface, and not any specific pairwise electrostatic interactions, controls the gating process in the Cys loop superfamily.
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MESH Headings
- Acetylcholine/chemistry
- Amino Acid Sequence
- Amino Acids/chemistry
- Animals
- Biochemistry/methods
- Blotting, Western
- Bungarotoxins/chemistry
- Cations
- Cell Membrane/metabolism
- Cysteine/chemistry
- Cystine/chemistry
- Databases, Protein
- Dose-Response Relationship, Drug
- Electrodes
- Electrophysiology
- Glycine/chemistry
- Ions
- Kinetics
- Ligands
- Mice
- Models, Chemical
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis
- Mutation
- Oocytes/metabolism
- Protein Binding
- Protein Conformation
- Protein Structure, Secondary
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- Receptors, Nicotinic/chemistry
- Sequence Homology, Amino Acid
- Static Electricity
- Torpedo
- Xenopus laevis
- gamma-Aminobutyric Acid/chemistry
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Affiliation(s)
- Xinan Xiu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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40
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Ippolito DL, Xu M, Bruchas MR, Wickman K, Chavkin C. Tyrosine phosphorylation of K(ir)3.1 in spinal cord is induced by acute inflammation, chronic neuropathic pain, and behavioral stress. J Biol Chem 2005; 280:41683-93. [PMID: 16223722 PMCID: PMC2392895 DOI: 10.1074/jbc.m507069200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Tyrosine phosphorylation is an important means of regulating ion channel function. Our previous gene expression studies using the Xenopus laevis oocyte system suggested that tyrosine phosphorylation of G-protein-gated inwardly rectifying potassium channels (K(ir)3 or GIRK) suppressed basal channel conductance and accelerated channel deactivation. To assess whether similar mechanisms regulate K(ir)3 function in mammalian cells, we developed and characterized a phosphoselective antibody recognizing K(ir)3.1 phosphorylated at tyrosine 12 in the N-terminal domain and then probed for evidence of K(ir)3.1 phosphorylation in cultured mammalian cells and spinal cord. The antibody was found to discriminate between the phospho-Tyr(12) of K(ir)3.1 and the native state in transfected cell lines and in primary cultures of mouse atria. Following either mouse hindpaw formalin injection or sciatic nerve ligation, pY12-K(ir)3.1 immunoreactivity was enhanced unilaterally in the superficial layers of the spinal cord dorsal horn, regions previously described as expressing K(ir)3.1 channels. Mice lacking K 3.1 following targeted gene disruption did not show specific pY12-K(ir)3.1 immunoreactivity after sciatic nerve ligation. Further, mice exposed to repeatedly forced swim stress showed bilateral enhancement in pY12-K(ir)3.1 in the dorsal horn. This study provides evidence that K(ir)3 tyrosine phosphorylation occurred during acute and chronic inflammatory pain and under behavioral stress. The reduction in K(ir)3 channel activity is predicted to enhance neuronal excitability under physiologically relevant conditions and may mediate a component of the adaptive physiological response.
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Affiliation(s)
| | - Mei Xu
- Department of Pharmacology, University of Washington, Seattle, Washington 98195
| | - Michael R. Bruchas
- Department of Pharmacology, University of Washington, Seattle, Washington 98195
| | - Kevin Wickman
- Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota 55455
| | - Charles Chavkin
- Department of Pharmacology, University of Washington, Seattle, Washington 98195
- To whom correspondence should be addressed: Dept. of Pharmacology, University of Washington, Box 357280, 1959 Pacific Ave. N. E., Seattle, WA 98195-7280. Tel.: 206-543-4266; Fax: 206-685-3822; E-mail:
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41
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Toselli M, Biella G, Taglietti V, Cazzaniga E, Parenti M. Caveolin-1 expression and membrane cholesterol content modulate N-type calcium channel activity in NG108-15 cells. Biophys J 2005; 89:2443-57. [PMID: 16040758 PMCID: PMC1366744 DOI: 10.1529/biophysj.105.065623] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Caveolins are the main structural proteins of glycolipid/cholesterol-rich plasmalemmal invaginations, termed caveolae. In addition, caveolin-1 isoform takes part in membrane remodelling as it binds and transports newly synthesized cholesterol from endoplasmic reticulum to the plasma membrane. Caveolin-1 is expressed in many cell types, including hippocampal neurons, where an abundant SNAP25-caveolin-1 complex is detected after induction of persistent synaptic potentiation. To ascertain whether caveolin-1 influences neuronal voltage-gated Ca2+ channel basal activity, we stably expressed caveolin-1 into transfected neuroblastoma x glioma NG108-15 hybrid cells [cav1(+) clone] that lack endogenous caveolins but express N-type Ca2+ channels upon cAMP-induced neuronal differentiation. Whole-cell patch-clamp recordings of cav1(+) cells demonstrated that N-type current density was reduced in size by approximately 70% without any significant change in the time course of activation and inactivation and voltage dependence. Moreover, the cav1(+) clone exhibited a significantly increased proportion of membrane cholesterol compared to wild-type NG108-15 cells. To gain insight into the mechanism underlying caveolin-1 lowering of N-current density, and more precisely to test whether this was indirectly caused by caveolin-1-induced enhancement of membrane cholesterol, we compared single N-type channel activities in cav1(+) clone and wild-type NG108-15 cells enriched with cholesterol after exposure to a methyl-beta-cyclodextrin-cholesterol complex. A lower Ca2+ channel activity was recorded from cell-attached patches of both cell types, thus supporting the view that the increased proportion of membrane cholesterol is ultimately responsible for the effect. This is due to a reduction in the probability of channel opening caused by a significant decrease of channel mean open time and by an increase of the frequency of null sweeps.
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Affiliation(s)
- M Toselli
- Department of Cellular and Molecular Physiological and Pharmacological Sciences, and INFM (National Institute of Matter Physics), University of Pavia, Pavia, Italy
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42
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Mora SI, Escobar LI. Phosphorylation of a tyrosine at the N-terminus regulates the surface expression of GIRK5 homomultimers. FEBS Lett 2005; 579:3019-23. [PMID: 15896779 DOI: 10.1016/j.febslet.2005.04.056] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Accepted: 04/22/2005] [Indexed: 11/27/2022]
Abstract
The G protein-coupled inwardly rectifying GIRK5 and Delta5GIRK5 splicing variants do not express functional potassium channels. In contrast, Delta25GIRK5 forms functional homomultimers in Xenopus laevis oocytes. A tyrosine is present at the N-term of the non-functional isoforms. We studied the effect of endogenous tyrosine phosphorylation on the GIRK5 surface and functional expression. Unlike wild type channels, GIRK5Y16A and Delta5GIRK5Y16A mutants displayed inwardly rectifying currents and inhibitors of Src tyrosine kinase promoted the traffiking of GIRK5 to the cell surface. This is the first evidence that endogenous phosphorylation of a tyrosine residue in a GIRK channel inhibits its surface expression.
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Affiliation(s)
- S Ivonne Mora
- Departamento de Fisiologia, Facultad de Medicina, Universidad Nacional Autonoma de Mexico, 04510 Mexico, DF
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43
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Romanenko VG, Fang Y, Byfield F, Travis AJ, Vandenberg CA, Rothblat GH, Levitan I. Cholesterol sensitivity and lipid raft targeting of Kir2.1 channels. Biophys J 2004; 87:3850-61. [PMID: 15465867 PMCID: PMC1304896 DOI: 10.1529/biophysj.104.043273] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
This study investigates how changes in the level of cellular cholesterol affect inwardly rectifying K+ channels belonging to a family of strong rectifiers (Kir2). In an earlier study we showed that an increase in cellular cholesterol suppresses endogenous K+ current in vascular endothelial cells, presumably due to effects on underlying Kir2.1 channels. Here we show that, indeed, cholesterol increase strongly suppressed whole-cell Kir2.1 current when the channels were expressed in a null cell line. However, cholesterol level had no effect on the unitary conductance and only little effect on the open probability of the channels. Moreover, no cholesterol effect was observed either on the total level of Kir2.1 protein or on its surface expression. We suggest, therefore, that cholesterol modulates not the total number of Kir2.1 channels in the plasma membrane but rather the transition of the channels between active and silent states. Comparing the effects of cholesterol on members of the Kir2.x family shows that Kir2.1 and Kir2.2 have similar high sensitivity to cholesterol, Kir2.3 is much less sensitive, and Kir2.4 has an intermediate sensitivity. Finally, we show that Kir2.x channels partition virtually exclusively into Triton-insoluble membrane fractions indicating that the channels are targeted into cholesterol-rich lipid rafts.
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Affiliation(s)
- Victor G Romanenko
- Institute for Medicine and Engineering, Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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44
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Correia MJ, Wood TG, Prusak D, Weng T, Rennie KJ, Wang HQ. Molecular characterization of an inward rectifier channel (IKir) found in avian vestibular hair cells: cloning and expression of pKir2.1. Physiol Genomics 2004; 19:155-69. [PMID: 15316115 DOI: 10.1152/physiolgenomics.00096.2004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A fast inwardly rectifying current has been observed in some of the sensory cells (hair cells) of the inner ear of several species. While the current was presumed to be an IKir current, contradictory evidence existed as to whether the cloned channel actually belonged to the Kir2.0 subfamily of potassium inward rectifiers. In this paper, we report for the first time converging evidence from electrophysiological, biochemical, immunohistochemical, and genetic studies that show that the Kir2.1 channel carries the fast inwardly rectifying currents found in pigeon vestibular hair cells. Following cytoplasm extraction from single type II and multiple pigeon vestibular hair cells, mRNA was reverse transcribed, amplified, and sequenced. The open reading frame (ORF), consisting of a 1,284-bp nucleotide sequence, showed 94, 85, and 83% identity with Kir2.1 subunit sequences from chick lens, Kir2 sequences from human heart, and a mouse macrophage cell line, respectively. Phylogenetic analyses revealed that pKir2.1 formed an immediate node with hKir2.1 but not with hKir2.2-2.4. Hair cells (type I and type II) and supporting cells in the sensory epithelium reacted positively with a Kir2.1 antibody. The whole cell current recorded in oocytes and CHO cells, transfected with pigeon hair cell Kir2.1 (pKir2.1), demonstrated blockage by Ba2+ and sensitivity to changing K+ concentration. The mean single-channel linear slope conductance in transfected CHO cells was 29 pS. The open dwell time was long (approximately 300 ms at -100 mV), and the closed dwell time was short (approximately 34 ms at -100 mV). Multistates ranging from 3-6 were noted in some single-channel responses. All of the above features have been described for other Kir2.1 channels. Current clamp studies of native pigeon vestibular hair cells illustrated possible physiological roles of the channel and showed that blockage of the channel by Ba2+ depolarized the resting membrane potential by approximately 30 mV. Negative currents hyperpolarized the membrane approximately 20 mV before block but approximately 60 mV following block. RT-PCR studies revealed that the pKir2.1 channels found in pigeon vestibular hair cells were also present in pigeon vestibular nerve, vestibular ganglion, lens, neck muscle, brain (brain stem, cerebellum and optic tectum), liver, and heart.
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Affiliation(s)
- Manning J Correia
- Department of Otolaryngology, University of Texas Medical Branch, Galveston, Texas 77555-1063, USA.
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45
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Nguyen A, Rothman DM, Stehn J, Imperiali B, Yaffe MB. Caged phosphopeptides reveal a temporal role for 14-3-3 in G1 arrest and S-phase checkpoint function. Nat Biotechnol 2004; 22:993-1000. [PMID: 15273693 DOI: 10.1038/nbt997] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2004] [Accepted: 05/25/2004] [Indexed: 01/20/2023]
Abstract
Using classical genetics to study modular phosphopeptide-binding domains within a family of proteins that are functionally redundant is difficult when other members of the domain family compensate for the product of the knocked-out gene. Here we describe a chemical genetics approach that overcomes this limitation by using UV-activatable caged phosphopeptides. By incorporating a caged phosphoserine residue within a consensus motif, these reagents simultaneously and synchronously inactivate all phosphoserine/phosphothreonine-binding domain family members in a rapid and temporally regulated manner. We applied this approach to study the global function of 14-3-3 proteins in cell cycle control. Activation of the caged phosphopeptides by UV irradiation displaced endogenous proteins from 14-3-3-binding, causing premature cell cycle entry, release of G1 cells from interphase arrest and loss of the S-phase checkpoint after DNA damage, accompanied by high levels of cell death. This class of reagents will greatly facilitate molecular dissection of kinase-dependent signaling pathways when applied to other phosphopeptide-binding domains including SH2, Polo-box and tandem BRCT domains.
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Affiliation(s)
- Anhco Nguyen
- Center for Cancer Research and Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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46
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Strømgaard A, Jensen AA, Strømgaard K. Site-Specific Incorporation of Unnatural Amino Acids into Proteins. Chembiochem 2004; 5:909-16. [PMID: 15239046 DOI: 10.1002/cbic.200400060] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Anne Strømgaard
- Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, 8000 Aarhus C, Denmark
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47
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Leite JF, Blanton MP, Shahgholi M, Dougherty DA, Lester HA. Conformation-dependent hydrophobic photolabeling of the nicotinic receptor: electrophysiology-coordinated photochemistry and mass spectrometry. Proc Natl Acad Sci U S A 2003; 100:13054-9. [PMID: 14569028 PMCID: PMC240743 DOI: 10.1073/pnas.2133028100] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2003] [Accepted: 08/22/2003] [Indexed: 11/18/2022] Open
Abstract
We characterized the differential accessibility of the nicotinic acetylcholine receptor alpha1 subunit in the open, closed, and desensitized states by using electrophysiology-coordinated photolabeling by several lipophilic probes followed by mass spectrometric analysis. Voltage-clamped oocytes expressing receptors were preincubated with one of the lipophilic probes and were continually exposed to acetylcholine; UV irradiation was applied during 500-ms pulses to + 40 or to -140 mV (which produced closed or approximately 50% open receptors, respectively). In the open state, there was specific probe incorporation within the N-terminal domain at residues that align with the beta8-beta9 loop of the acetylcholine-binding protein. In the closed state, probe incorporation was identified at several sites of the N-terminal domain within the conserved cysteine loop (residues 128-142), the cytoplasmic loop (M3-M4), and M4. The labeling pattern in the M4 region is consistent with previous results, further defining the lipid-exposed face of this transmembrane alpha-helix. These results show regions within the N-terminal domain that are involved in gating-dependent conformational shifts, confirm that the cysteine loop resides at or near the protein-membrane interface, and show that segments of the M3-M4 loop are near to the lipid bilayer.
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Affiliation(s)
- John F Leite
- Divisions of Biology and Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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48
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Jones SVP. Role of the small GTPase Rho in modulation of the inwardly rectifying potassium channel Kir2.1. Mol Pharmacol 2003; 64:987-93. [PMID: 14500755 DOI: 10.1124/mol.64.4.987] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The inwardly rectifying potassium channel Kir2.1 is inhibited by a variety of G-protein-coupled receptors (GPCRs). However, the mechanisms underlying the inhibition have not been fully elucidated. In this study the role of the small GTPase, Rho, in mediating this inhibition was determined. Stimulation of the m1 muscarinic receptor inhibited Kir2.1, when both receptor and channel were coexpressed in tsA201 cells. The inhibition of Kir2.1 by carbachol was reversible and atropine-sensitive. Cotransfection with a dominant-negative mutant of the small GTPase Rho abolished the inhibition of Kir2.1 with current amplitudes remaining at control levels in the presence of carbachol. Conversely, cotransfection with the constitutively activated mutant of Rho resulted in a reduction in basal Kir2.1 current amplitudes, suggesting that Rho inhibits Kir2.1. To further confirm the involvement of Rho in the signal transduction pathway, cotransfection with C3 transferase (EFC3), a selective inhibitor of Rho, abolished the reduction in Kir2.1 currents noted upon application of carbachol under control conditions. Preincubation with the phosphatidylinositol 3-kinase inhibitor wortmannin or the Rho kinase inhibitor (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide, 2 HCl (Y-27632) had no effect on agonist-induced inhibition of Kir2.1, precluding these kinases as downstream effectors of Rho in mediation of the signal. In addition, 2'-amino-3'-methoxyflavone (PD98059), an inhibitor of mitogen-activated protein (MAP) kinase kinase (MEK), had no effect on the m1 receptor-induced inhibition of Kir2.1, suggesting that MAP kinases are not involved in the signaling pathway. In conclusion, these data indicate that the small GTPase, Rho, transduces the m1 muscarinic receptor-induced inhibition of Kir2.1 via an unidentified mechanism.
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Affiliation(s)
- S V Penelope Jones
- Department of Psychiatry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0603, USA.
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49
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Bendahhou S, Donaldson MR, Plaster NM, Tristani-Firouzi M, Fu YH, Ptácek LJ. Defective potassium channel Kir2.1 trafficking underlies Andersen-Tawil syndrome. J Biol Chem 2003; 278:51779-85. [PMID: 14522976 DOI: 10.1074/jbc.m310278200] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Andersen-Tawil syndrome is a skeletal and cardiac muscle disease with developmental features caused by mutations in the inward rectifier K+ channel gene KCNJ2. Patients harboring these mutations exhibit extremely variable expressivities. To explore whether these mutations can be correlated with a specific patient phenotype, we expressed both wild-type (WT) and mutant genes cloned into a bi-cistronic vector. Functional expression in human embryonic kidney 293 cells showed that none of the mutant channels express current when present alone. When co-expressed with WT channels, only construct V302M-WT yields inward current. Confocal microscopy fluorescence revealed three patterns of channel expression in the cell: 1) mutations D71V, N216H, R218Q, and pore mutations co-assemble and co-localize to the membrane with the WT and exert a dominant-negative effect on the WT channels; 2) mutation V302M leads to channels that lose their ability to co-assemble with WT and traffic to the cell surface; 3) deletions Delta 95-98 and Delta 314-315 lead to channels that do not traffic to the membrane but retain their ability to co-assemble with WT channels. These data show that the Andersen-Tawil syndrome phenotype may occur through a dominant-negative effect as well as through haplo-insufficiency and reveal amino acids critical in trafficking and conductance of the inward rectifier K+ channels.
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Affiliation(s)
- Saïd Bendahhou
- Department of Human Molecular Biology and Genetics, University of Utah, Salt Lake City, Utah 84112, USA.
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50
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Monahan SL, Lester HA, Dougherty DA. Site-specific incorporation of unnatural amino acids into receptors expressed in Mammalian cells. CHEMISTRY & BIOLOGY 2003; 10:573-80. [PMID: 12837390 DOI: 10.1016/s1074-5521(03)00124-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We describe an approach to achieve unnatural amino acid incorporation into channels and receptors expressed in mammalian cells. We show that microelectroporation provides a general method to deliver DNA, mRNA, and tRNA simultaneously. In both CHO cells and cultured neurons, microelectroporation efficiently delivers an in vitro transcribed, serine amber suppressor tRNA, leading to nonsense suppression in a mutant EGFP gene. In CHO cells, both natural and unnatural amino acids chemically appended to a suppressor tRNA are site specifically incorporated into the nicotinic acetylcholine receptor (nAChR). Electrophysiology confirms the expected functional consequences of the unnatural residue. The microelectroporation strategy described here is more general, less tedious, and less damaging to mammalian neuronal and nonneuronal cells than previous approaches to nonsense suppression in small cells and provides the first example of unnatural amino acid incorporation in mammalian cells using chemically aminoacylated tRNA.
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MESH Headings
- Acetylcholine/metabolism
- Amino Acids/chemistry
- Amino Acids/genetics
- Animals
- CHO Cells
- Cells, Cultured
- Codon, Nonsense
- Cricetinae
- Electroporation/methods
- Gene Expression
- Genes, Suppressor
- Green Fluorescent Proteins
- Luminescent Proteins/metabolism
- Neurons
- RNA, Transfer, Amino Acyl/metabolism
- Receptors, Cell Surface/biosynthesis
- Receptors, Cell Surface/chemistry
- Receptors, Cell Surface/genetics
- Receptors, Nicotinic/genetics
- Receptors, Nicotinic/metabolism
- Transfection
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Affiliation(s)
- Sarah L Monahan
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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