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Wawrzkiewicz-Jałowiecka A, Lalik A, Lukasiak A, Richter-Laskowska M, Trybek P, Ejfler M, Opałka M, Wardejn S, Delfino DV. Potassium Channels, Glucose Metabolism and Glycosylation in Cancer Cells. Int J Mol Sci 2023; 24:ijms24097942. [PMID: 37175655 PMCID: PMC10178682 DOI: 10.3390/ijms24097942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Revised: 04/24/2023] [Accepted: 04/25/2023] [Indexed: 05/15/2023] Open
Abstract
Potassium channels emerge as one of the crucial groups of proteins that shape the biology of cancer cells. Their involvement in processes like cell growth, migration, or electric signaling, seems obvious. However, the relationship between the function of K+ channels, glucose metabolism, and cancer glycome appears much more intriguing. Among the typical hallmarks of cancer, one can mention the switch to aerobic glycolysis as the most favorable mechanism for glucose metabolism and glycome alterations. This review outlines the interconnections between the expression and activity of potassium channels, carbohydrate metabolism, and altered glycosylation in cancer cells, which have not been broadly discussed in the literature hitherto. Moreover, we propose the potential mediators for the described relations (e.g., enzymes, microRNAs) and the novel promising directions (e.g., glycans-orinented drugs) for further research.
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Affiliation(s)
- Agata Wawrzkiewicz-Jałowiecka
- Department of Physical Chemistry and Technology of Polymers, Silesian University of Technology, 44-100 Gliwice, Poland
| | - Anna Lalik
- Department of Systems Biology and Engineering, Silesian University of Technology, 44-100 Gliwice, Poland
- Biotechnology Center, Silesian University of Technology, 44-100 Gliwice, Poland
| | - Agnieszka Lukasiak
- Department of Physics and Biophysics, Institute of Biology, Warsaw University of Life Sciences, 02-776 Warsaw, Poland
| | - Monika Richter-Laskowska
- The Centre for Biomedical Engineering, Łukasiewicz Research Network-Krakow Institute of Technology, 30-418 Krakow, Poland
| | - Paulina Trybek
- Institute of Physics, University of Silesia in Katowice, 41-500 Chorzów, Poland
| | - Maciej Ejfler
- Faculty of Automatic Control, Electronics and Computer Science, Silesian University of Technology, 44-100 Gliwice, Poland
| | - Maciej Opałka
- Faculty of Automatic Control, Electronics and Computer Science, Silesian University of Technology, 44-100 Gliwice, Poland
| | - Sonia Wardejn
- Faculty of Automatic Control, Electronics and Computer Science, Silesian University of Technology, 44-100 Gliwice, Poland
| | - Domenico V Delfino
- Section of Pharmacology, Department of Medicine and Surgery, University of Perugia, 06129 Perugia, Italy
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2
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Zhang L, Zhang M, Bellve K, Fogarty KE, Castro MA, Brauchi S, Kobertz WR. Wheat germ agglutinin-conjugated fluorescent pH sensors for visualizing proton fluxes. J Gen Physiol 2020; 152:133652. [PMID: 31978216 PMCID: PMC7266149 DOI: 10.1085/jgp.201912498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 01/03/2020] [Indexed: 12/04/2022] Open
Abstract
Small-molecule fluorescent wheat germ agglutinin (WGA) conjugates are routinely used to demarcate mammalian plasma membranes, because they bind to the cell’s glycocalyx. Here, we describe the derivatization of WGA with a pH-sensitive rhodamine fluorophore (pHRho; pKa = 7) to detect proton channel fluxes and extracellular proton accumulation and depletion from primary cells. We found that WGA-pHRho labeling was uniform and did not appreciably alter the voltage gating of glycosylated ion channels, and the extracellular changes in pH correlated with proton channel activity. Using single-plane illumination techniques, WGA-pHRho was used to detect spatiotemporal differences in proton accumulation and depletion over the extracellular surface of cardiomyocytes, astrocytes, and neurons. Because WGA can be derivatized with any small-molecule fluorescent ion sensor, WGA conjugates should prove useful to visualize most electrogenic and nonelectrogenic events on the extracellular side of the plasma membrane.
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Affiliation(s)
- Lejie Zhang
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA
| | - Mei Zhang
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA
| | - Karl Bellve
- Biomedical Imaging Group, Molecular Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Kevin E Fogarty
- Biomedical Imaging Group, Molecular Medicine, University of Massachusetts Medical School, Worcester, MA
| | - Maite A Castro
- Department of Biochemistry and Microbiology, Universidad Austral de Chile, Campus Isla Teja, Los Rios, Chile.,Center for the Interdisciplinary Studies on Nervous System, Universidad Austral de Chile, Campus Isla Teja, Los Rios, Chile.,Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA
| | - Sebastian Brauchi
- Department of Physiology, Universidad Austral de Chile, Campus Isla Teja, Los Rios, Chile.,Center for the Interdisciplinary Studies on Nervous System, Universidad Austral de Chile, Campus Isla Teja, Los Rios, Chile.,Universidad Austral de Chile, Campus Isla Teja, Los Rios, Chile.,Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA
| | - William R Kobertz
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA.,Programs in Neuroscience and Chemical Biology, University of Massachusetts Medical School, Worcester, MA
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3
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Kranaster P, Karreman C, Dold JEGA, Krebs A, Funke M, Holzer AK, Klima S, Nyffeler J, Helfrich S, Wittmann V, Leist M. Time and space-resolved quantification of plasma membrane sialylation for measurements of cell function and neurotoxicity. Arch Toxicol 2019; 94:449-467. [PMID: 31828357 DOI: 10.1007/s00204-019-02642-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 12/02/2019] [Indexed: 12/28/2022]
Abstract
While there are many methods to quantify the synthesis, localization, and pool sizes of proteins and DNA during physiological responses and toxicological stress, only few approaches allow following the fate of carbohydrates. One of them is metabolic glycoengineering (MGE), which makes use of chemically modified sugars (CMS) that enter the cellular biosynthesis pathways leading to glycoproteins and glycolipids. The CMS can subsequently be coupled (via bio-orthogonal chemical reactions) to tags that are quantifiable by microscopic imaging. We asked here, whether MGE can be used in a quantitative and time-resolved way to study neuronal glycoprotein synthesis and its impairment. We focused on the detection of sialic acid (Sia), by feeding human neurons the biosynthetic precursor N-acetyl-mannosamine, modified by an azide tag. Using this system, we identified non-toxic conditions that allowed live cell labeling with high spatial and temporal resolution, as well as the quantification of cell surface Sia. Using combinations of immunostaining, chromatography, and western blotting, we quantified the percentage of cellular label incorporation and effects on glycoproteins such as polysialylated neural cell adhesion molecule. A specific imaging algorithm was used to quantify Sia incorporation into neuronal projections, as potential measure of complex cell function in toxicological studies. When various toxicants were studied, we identified a subgroup (mitochondrial respiration inhibitors) that affected neurite glycan levels several hours before any other viability parameter was affected. The MGE-based neurotoxicity assay, thus allowed the identification of subtle impairments of neurochemical function with very high sensitivity.
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Affiliation(s)
- Petra Kranaster
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany.,Konstanz Research School Chemical Biology (KoRS-CB), University of Konstanz, 78457, Konstanz, Germany
| | - Christiaan Karreman
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany
| | - Jeremias E G A Dold
- Konstanz Research School Chemical Biology (KoRS-CB), University of Konstanz, 78457, Konstanz, Germany.,Department of Chemistry, University of Konstanz, 78457, Konstanz, Germany
| | - Alice Krebs
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany.,Konstanz Research School Chemical Biology (KoRS-CB), University of Konstanz, 78457, Konstanz, Germany
| | - Melina Funke
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany
| | - Anna-Katharina Holzer
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany
| | - Stefanie Klima
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany.,Kooperatives Promotionskolleg (KPK) InViTe, University of Konstanz, 78457, Konstanz, Germany
| | - Johanna Nyffeler
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany.,Environmental Protection Agency, Durham, NC, USA
| | - Stefan Helfrich
- The Bioimaging Center, University of Konstanz, 78457, Konstanz, Germany.,KNIME GmbH, 78467, Konstanz, Germany
| | - Valentin Wittmann
- Konstanz Research School Chemical Biology (KoRS-CB), University of Konstanz, 78457, Konstanz, Germany.,Department of Chemistry, University of Konstanz, 78457, Konstanz, Germany
| | - Marcel Leist
- In Vitro Toxicology and Biomedicine, Dept Inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, 78457, Konstanz, Germany. .,Konstanz Research School Chemical Biology (KoRS-CB), University of Konstanz, 78457, Konstanz, Germany.
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4
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Ranjan R, Logette E, Marani M, Herzog M, Tâche V, Scantamburlo E, Buchillier V, Markram H. A Kinetic Map of the Homomeric Voltage-Gated Potassium Channel (Kv) Family. Front Cell Neurosci 2019; 13:358. [PMID: 31481875 PMCID: PMC6710402 DOI: 10.3389/fncel.2019.00358] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 07/19/2019] [Indexed: 11/13/2022] Open
Abstract
The voltage-gated potassium (Kv) channels, encoded by 40 genes, repolarize all electrically excitable cells, including plant, cardiac, and neuronal cells. Although these genes were fully sequenced decades ago, a comprehensive kinetic characterization of all Kv channels is still missing, especially near physiological temperature. Here, we present a standardized kinetic map of the 40 homomeric Kv channels systematically characterized at 15, 25, and 35°C. Importantly, the Kv kinetics at 35°C differ significantly from commonly reported kinetics, usually performed at room temperature. We observed voltage-dependent Q10 for all active Kv channels and inherent heterogeneity in kinetics for some of them. Kinetic properties are consistent across different host cell lines and conserved across mouse, rat, and human. All electrophysiology data from all Kv channels are made available through a public website (Channelpedia). This dataset provides a solid foundation for exploring kinetics of heteromeric channels, roles of auxiliary subunits, kinetic modulation, and for building accurate Kv models.
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Affiliation(s)
- Rajnish Ranjan
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Emmanuelle Logette
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland.,Laboratory of Neural Microcircuitry, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Michela Marani
- Laboratory of Neural Microcircuitry, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Mirjia Herzog
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland.,Laboratory of Neural Microcircuitry, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Valérie Tâche
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Enrico Scantamburlo
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Valérie Buchillier
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland
| | - Henry Markram
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Geneva, Switzerland.,Laboratory of Neural Microcircuitry, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
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5
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Reduced hybrid/complex N-glycosylation disrupts cardiac electrical signaling and calcium handling in a model of dilated cardiomyopathy. J Mol Cell Cardiol 2019; 132:13-23. [PMID: 31071333 DOI: 10.1016/j.yjmcc.2019.05.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 04/12/2019] [Accepted: 05/01/2019] [Indexed: 12/19/2022]
Abstract
Dilated cardiomyopathy (DCM) is the third most common cause of heart failure, with ~70% of DCM cases considered idiopathic. We showed recently, through genetic ablation of the MGAT1 gene, which encodes an essential glycosyltransferase (GlcNAcT1), that prevention of cardiomyocyte hybrid/complex N-glycosylation was sufficient to cause DCM that led to heart failure and early death. Our findings are consistent with increasing evidence suggesting a link between aberrant glycosylation and heart diseases of acquired and congenital etiologies. However, the mechanisms by which changes in glycosylation contribute to disease onset and progression remain largely unknown. Activity and gating of voltage-gated Na+ and K+ channels (Nav and Kv respectively) play pivotal roles in the initiation, shaping and conduction of cardiomyocyte action potentials (APs) and aberrant channel activity was shown to contribute to cardiac disease. We and others showed that glycosylation can impact Nav and Kv function; therefore, here, we investigated the effects of reduced cardiomyocyte hybrid/complex N-glycosylation on channel activity to investigate whether chronic aberrant channel function can contribute to DCM. Ventricular cardiomyocytes from MGAT1 deficient (MGAT1KO) mice display prolonged APs and pacing-induced aberrant early re-activation that can be attributed to, at least in part, a significant reduction in Kv expression and activity that worsens over time suggesting heart disease-related remodeling. MGAT1KO Nav demonstrate no change in expression or maximal conductance but show depolarizing shifts in voltage-dependent gating. Together, the changes in MGAT1KO Nav and Kv function likely contribute to observed anomalous electrocardiograms and Ca2+ handling. These findings provide insight into mechanisms by which altered glycosylation contributes to DCM through changes in Nav and Kv activity that impact conduction, Ca2+ handling and contraction. The MGAT1KO can also serve as a useful model to study the effects of aberrant electrical signaling on cardiac function and the remodeling events that can occur with heart disease progression.
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6
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Capera J, Serrano-Novillo C, Navarro-Pérez M, Cassinelli S, Felipe A. The Potassium Channel Odyssey: Mechanisms of Traffic and Membrane Arrangement. Int J Mol Sci 2019; 20:ijms20030734. [PMID: 30744118 PMCID: PMC6386995 DOI: 10.3390/ijms20030734] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 02/06/2019] [Accepted: 02/08/2019] [Indexed: 12/29/2022] Open
Abstract
Ion channels are transmembrane proteins that conduct specific ions across biological membranes. Ion channels are present at the onset of many cellular processes, and their malfunction triggers severe pathologies. Potassium channels (KChs) share a highly conserved signature that is necessary to conduct K⁺ through the pore region. To be functional, KChs require an exquisite regulation of their subcellular location and abundance. A wide repertoire of signatures facilitates the proper targeting of the channel, fine-tuning the balance that determines traffic and location. These signature motifs can be part of the secondary or tertiary structure of the protein and are spread throughout the entire sequence. Furthermore, the association of the pore-forming subunits with different ancillary proteins forms functional complexes. These partners can modulate traffic and activity by adding their own signatures as well as by exposing or masking the existing ones. Post-translational modifications (PTMs) add a further dimension to traffic regulation. Therefore, the fate of a KCh is not fully dependent on a gene sequence but on the balance of many other factors regulating traffic. In this review, we assemble recent evidence contributing to our understanding of the spatial expression of KChs in mammalian cells. We compile specific signatures, PTMs, and associations that govern the destination of a functional channel.
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Affiliation(s)
- Jesusa Capera
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain.
| | - Clara Serrano-Novillo
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain.
| | - María Navarro-Pérez
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain.
| | - Silvia Cassinelli
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain.
| | - Antonio Felipe
- Molecular Physiology Laboratory, Departament de Bioquímica i Biomedicina Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona, Avda. Diagonal 643, 08028 Barcelona, Spain.
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7
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Scott H, Panin VM. The role of protein N-glycosylation in neural transmission. Glycobiology 2014; 24:407-17. [PMID: 24643084 DOI: 10.1093/glycob/cwu015] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Recent studies have explored the function of N-linked glycosylation in the nervous system, demonstrating essential roles of carbohydrate structures in neural development. The function of N-glycans in neural physiology remains less understood; however, increasing evidence indicates that N-glycans can play specific modulatory roles controlling neural transmission and excitability of neural circuits. These roles are mediated via effects on synaptic proteins involved in neurotransmitter release, transporters that regulate nerotransmitter concentrations, neurotransmitter receptors, as well as via regulation of proteins that control excitability and response to milieu stimuli, such as voltage-gated ion channels and transient receptor potential channels, respectively. Sialylated N-glycan structures are among the most potent modulators of cell excitability, exerting prominent effects on voltage gated Na(+) and K(+) channels. This modulation appears to be underlain by complex molecular mechanisms involving electrostatic effects, as well as interaction modes based on more specific steric effects and interactions with lectins and other molecules. Data also indicate that particular features of N-glycans, such as their location on a protein and structural characteristics, can be specifically associated with the effect of glycosylation. These features and their functional implications can vary between different cell types, which highlight the importance of in vivo analyses of glycan functions. Experimental challenges are associated with the overwhelming complexity of the nervous system and glycosylation pathways in vertebrates, and thus model organisms like Drosophila should help elucidate evolutionarily conserved mechanisms underlying glycan functions. Recent studies supported this notion and shed light on functions of several glycosylation genes involved in the regulation of the nervous system.
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Affiliation(s)
- Hilary Scott
- Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843, USA
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8
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Klöckner U, Rueckschloss U, Grossmann C, Matzat S, Schumann K, Ebelt H, Müller-Werdan U, Loppnow H, Werdan K, Gekle M. Inhibition of cardiac pacemaker channel hHCN2 depends on intercalation of lipopolysaccharide into channel-containing membrane microdomains. J Physiol 2013; 592:1199-211. [PMID: 24366264 DOI: 10.1113/jphysiol.2013.268540] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Depressed heart rate variability in severe inflammatory diseases can be partially explained by the lipopolysaccharide (LPS)-dependent modulation of cardiac pacemaker channels. Recently, we showed that LPS inhibits pacemaker current in sinoatrial node cells and in HEK293 cells expressing cloned pacemaker channels, respectively. The present study was designed to verify whether this inhibition involves LPS-dependent intracellular signalling and to identify structures of LPS responsible for pacemaker current modulation. We examined the effect of LPS on the activity of human hyperpolarization-activated cyclic nucleotide-gated channel 2 (hHCN2) stably expressed in HEK293 cells. In whole-cell recordings, bath application of LPS decreased pacemaker current (IhHCN2) amplitude. The same protocol had no effect on channel activity in cell-attached patch recordings, in which channels are protected from the LPS-containing bath solution. This demonstrates that LPS must interact directly with or close to the channel protein. After cleavage of LPS into lipid A and the polysaccharide chain, neither of them alone impaired IhHCN2, which suggests that modulation of channel activity critically depends on the integrity of the entire LPS molecule. We furthermore showed that β-cyclodextrin interfered with LPS-dependent channel modulation predominantly via scavenging of lipid A, thereby abrogating the capability of LPS to intercalate into target cell membranes. We conclude that LPS impairs IhHCN2 by a local mechanism that is restricted to the vicinity of the channels. Furthermore, intercalation of lipid A into target cell membranes is a prerequisite for the inhibition that is suggested to depend on the direct interaction of the LPS polysaccharide chain with cardiac pacemaker channels.
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Affiliation(s)
- Udo Klöckner
- Julius Bernstein Institut für Physiologie, Martin Luther Universität Halle-Wittenberg, Magdeburger Strasse 6, 06112 Halle (Saale), Germany.
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9
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Abstract
Control and modulation of electrical signaling is vital to normal physiology, particularly in neurons, cardiac myocytes, and skeletal muscle. The orchestrated activities of variable sets of ion channels and transporters, including voltage-gated ion channels (VGICs), are responsible for initiation, conduction, and termination of the action potential (AP) in excitable cells. Slight changes in VGIC activity can lead to severe pathologies including arrhythmias, epilepsies, and paralyses, while normal excitability depends on the precise tuning of the AP waveform. VGICs are heavily posttranslationally modified, with upward of 30% of the mature channel mass consisting of N- and O-glycans. These glycans are terminated typically by negatively charged sialic acid residues that modulate voltage-dependent channel gating directly. The data indicate that sialic acids alter VGIC activity in isoform-specific manners, dependent in part, on the number/location of channel sialic acids attached to the pore-forming alpha and/or auxiliary subunits that often act through saturating electrostatic mechanisms. Additionally, cell-specific regulation of sialylation can affect VGIC gating distinctly. Thus, channel sialylation is likely regulated through two mechanisms that together contribute to a dynamic spectrum of possible gating motifs: a subunit-specific mechanism and regulated (aberrant) changes in the ability of the cell to glycosylate. Recent studies showed that neuronal and cardiac excitability is modulated through regulated changes in voltage-gated Na(+) channel sialylation, suggesting that both mechanisms of differential VGIC sialylation contribute to electrical signaling in the brain and heart. Together, the data provide insight into an important and novel paradigm involved in the control and modulation of electrical signaling.
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Affiliation(s)
- Andrew R Ednie
- Programs in Cardiovascular Research and Neuroscience, Department of Molecular Pharmacology & Physiology, College of Medicine, University of South Florida, Tampa, Florida, USA
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10
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The role of Drosophila cytidine monophosphate-sialic acid synthetase in the nervous system. J Neurosci 2013; 33:12306-15. [PMID: 23884937 DOI: 10.1523/jneurosci.5220-12.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
While sialylation plays important functions in the nervous system, the complexity of glycosylation pathways and limitations of genetic approaches preclude the efficient analysis of these functions in mammalian organisms. Drosophila has recently emerged as a promising model for studying neural sialylation. Drosophila sialyltransferase, DSiaT, was shown to be involved in the regulation of neural transmission. However, the sialylation pathway was not investigated in Drosophila beyond the DSiaT-mediated step. Here we focused on the function of Drosophila cytidine monophosphate-sialic acid synthetase (CSAS), the enzyme providing a sugar donor for DSiaT. Our results revealed that the expression of CSAS is tightly regulated and restricted to the CNS throughout development and in adult flies. We generated CSAS mutants and analyzed their phenotypes using behavioral and physiological approaches. Our experiments demonstrated that mutant phenotypes of CSAS are similar to those of DSiaT, including decreased longevity, temperature-induced paralysis, locomotor abnormalities, and defects of neural transmission at neuromuscular junctions. Genetic interactions between CSAS, DSiaT, and voltage-gated channel genes paralytic and seizure were consistent with the hypothesis that CSAS and DSiaT function within the same pathway regulating neural excitability. Intriguingly, these interactions also suggested that CSAS and DSiaT have some additional, independent functions. Moreover, unlike its mammalian counterparts that work in the nucleus, Drosophila CSAS was found to be a glycoprotein-bearing N-glycans and predominantly localized in vivo to the Golgi compartment. Our work provides the first systematic analysis of in vivo functions of a eukaryotic CSAS gene and sheds light on evolutionary relationships among metazoan CSAS proteins.
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11
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Social networking among voltage-activated potassium channels. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 117:269-302. [PMID: 23663972 DOI: 10.1016/b978-0-12-386931-9.00010-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Voltage-activated potassium channels (Kv channels) are ubiquitously expressed proteins that subserve a wide range of cellular functions. From their birth in the endoplasmic reticulum, Kv channels assemble from multiple subunits in complex ways that determine where they live in the cell, their biophysical characteristics, and their role in enabling different kinds of cells to respond to specific environmental signals to generate appropriate functional responses. This chapter describes the types of protein-protein interactions among pore-forming channel subunits and their auxiliary protein partners, as well as posttranslational protein modifications that occur in various cell types. This complex oligomerization of channel subunits establishes precise cell type-specific Kv channel localization and function, which in turn drives a diverse range of cellular signal transduction mechanisms uniquely suited to the physiological contexts in which they are found.
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12
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Abstract
Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent intracellular Ca(2+)-mobilising messenger. Much evidence indicates that NAADP targets novel Ca(2+) channels located on acidic organelles but the identity of these channels has remained obscure. Recent studies have converged on a novel class of ion channels, the two-pore channels (TPCs) as likely molecular targets. The location of these channels to the endo-lysosomal system and their sensitivity to NAADP match closely those of endogenous NAADP-sensitive channels in both mammalian cells and sea urchin eggs, where the effects of NAADP were discovered. Moreover, the functional coupling of TPCs to archetypal endoplasmic reticulum (ER) Ca(2+) channels is also matched. Biophysical analysis in conjunction with site-directed mutagenesis demonstrates that TPCs are pore-forming subunits of NAADP-gated ion channels. TPCs have a unique two-repeat structure, are regulated by N-linked glycosylation and harbor an endo-lysosomal targeting motif in their N-terminus. Knockdown studies have shown TPCs to regulate smooth muscle contraction, differentiation and endothelial cell activation consistent with previous studies implicating NAADP in these processes. Thus multiple lines of evidence indicate that TPCs are the likely long sought targets for NAADP.
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Affiliation(s)
- Robert Hooper
- Department of Cell and Developmental Biology, University College London, UK.
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13
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Patel S, Ramakrishnan L, Rahman T, Hamdoun A, Marchant JS, Taylor CW, Brailoiu E. The endo-lysosomal system as an NAADP-sensitive acidic Ca(2+) store: role for the two-pore channels. Cell Calcium 2011; 50:157-67. [PMID: 21529939 DOI: 10.1016/j.ceca.2011.03.011] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Accepted: 03/26/2011] [Indexed: 12/22/2022]
Abstract
Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca(2+) that is tapped by the Ca(2+)-mobilizing messenger, NAADP. In this article, we review evidence that NAADP-mediated Ca(2+) release from this acidic Ca(2+) store proceeds through activation of the newly described two-pore channels (TPCs). We discuss recent advances in defining the sub-cellular targeting, topology and biophysics of TPCs. We also discuss physiological roles and the evolution of this ubiquitous ion channel family.
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Affiliation(s)
- Sandip Patel
- Department of Cell and Developmental Biology, University College London, London, UK.
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Hooper R, Churamani D, Brailoiu E, Taylor CW, Patel S. Membrane topology of NAADP-sensitive two-pore channels and their regulation by N-linked glycosylation. J Biol Chem 2011; 286:9141-9. [PMID: 21173144 PMCID: PMC3059026 DOI: 10.1074/jbc.m110.189985] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 12/13/2010] [Indexed: 11/26/2022] Open
Abstract
Two-pore channels (TPCs) localize to the endolysosomal system and have recently emerged as targets for the Ca(2+)-mobilizing messenger, nicotinic acid adenine dinucleotide phosphate (NAADP). However, their membrane topology is unknown. Using fluorescence protease protection assays, we show that human TPC1 and TPC2 possess cytosolic N and C termini and therefore an even number of transmembrane regions. Fluorophores placed at position 225 or 347 in TPC1, or 339 in TPC2 were also cytosolic, whereas a fluorophore at position 628 in TPC1 was luminal. These data together with sequence similarity to voltage-gated Ca(2+) and Na(+) channels, and unbiased in silico predictions are consistent with a topology in which two homologous domains are present, each comprising 6 transmembrane regions and a re-entrant pore loop. Immunocytochemical analysis of selectively permeabilized cells using antipeptide antibodies confirmed that the C-terminal tails of recombinant TPCs are cytosolic and that residues 240-254 of TPC2 prior to putative pore 1 are luminal. Both TPC1 and TPC2 are N-glycosylated with residues 599, 611, and 616 contributing to glycosylation of TPC1. This confirms the luminal position of these residues, which immediately precede the putative pore loop of the second domain. Mutation of all three glycosylation sites in TPC1 enhances NAADP-evoked cytosolic Ca(2+) signals. Our data establish essential features of the topology of two-pore channels.
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Affiliation(s)
- Robert Hooper
- From the Department of Cell and Developmental Biology, University College London, London WC1E 6BT, United Kingdom
| | - Dev Churamani
- From the Department of Cell and Developmental Biology, University College London, London WC1E 6BT, United Kingdom
| | - Eugen Brailoiu
- the Department of Pharmacology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, and
| | - Colin W. Taylor
- the Department of Pharmacology, Cambridge University, Cambridge CB2 1PD, United Kingdom
| | - Sandip Patel
- From the Department of Cell and Developmental Biology, University College London, London WC1E 6BT, United Kingdom
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