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Tuluc P, Theiner T, Jacobo-Piqueras N, Geisler SM. Role of High Voltage-Gated Ca 2+ Channel Subunits in Pancreatic β-Cell Insulin Release. From Structure to Function. Cells 2021; 10:2004. [PMID: 34440773 PMCID: PMC8393260 DOI: 10.3390/cells10082004] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 07/27/2021] [Accepted: 08/03/2021] [Indexed: 02/07/2023] Open
Abstract
The pancreatic islets of Langerhans secrete several hormones critical for glucose homeostasis. The β-cells, the major cellular component of the pancreatic islets, secrete insulin, the only hormone capable of lowering the plasma glucose concentration. The counter-regulatory hormone glucagon is secreted by the α-cells while δ-cells secrete somatostatin that via paracrine mechanisms regulates the α- and β-cell activity. These three peptide hormones are packed into secretory granules that are released through exocytosis following a local increase in intracellular Ca2+ concentration. The high voltage-gated Ca2+ channels (HVCCs) occupy a central role in pancreatic hormone release both as a source of Ca2+ required for excitation-secretion coupling as well as a scaffold for the release machinery. HVCCs are multi-protein complexes composed of the main pore-forming transmembrane α1 and the auxiliary intracellular β, extracellular α2δ, and transmembrane γ subunits. Here, we review the current understanding regarding the role of all HVCC subunits expressed in pancreatic β-cell on electrical activity, excitation-secretion coupling, and β-cell mass. The evidence we review was obtained from many seminal studies employing pharmacological approaches as well as genetically modified mouse models. The significance for diabetes in humans is discussed in the context of genetic variations in the genes encoding for the HVCC subunits.
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Affiliation(s)
- Petronel Tuluc
- Centre for Molecular Biosciences, Department of Pharmacology and Toxicology, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria; (T.T.); (N.J.-P.); (S.M.G.)
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2
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Luan C, Ye Y, Singh T, Barghouth M, Eliasson L, Artner I, Zhang E, Renström E. The calcium channel subunit gamma-4 is regulated by MafA and necessary for pancreatic beta-cell specification. Commun Biol 2019; 2:106. [PMID: 30911681 PMCID: PMC6420573 DOI: 10.1038/s42003-019-0351-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Accepted: 02/08/2019] [Indexed: 12/22/2022] Open
Abstract
Voltage-gated Ca2+ (CaV) channels trigger glucose-induced insulin secretion in pancreatic beta-cell and their dysfunction increases diabetes risk. These heteromeric complexes include the main subunit alpha1, and the accessory ones, including subunit gamma that remains unexplored. Here, we demonstrate that CaV gamma subunit 4 (CaVγ4) is downregulated in islets from human donors with diabetes, diabetic Goto-Kakizaki (GK) rats, as well as under conditions of gluco-/lipotoxic stress. Reduction of CaVγ4 expression results in decreased expression of L-type CaV1.2 and CaV1.3, thereby suppressing voltage-gated Ca2+ entry and glucose stimulated insulin exocytosis. The most important finding is that CaVγ4 expression is controlled by the transcription factor responsible for beta-cell specification, MafA, as verified by chromatin immunoprecipitation and experiments in beta-cell specific MafA knockout mice (MafA Δβcell ). Taken together, these findings suggest that CaVγ4 is necessary for maintaining a functional differentiated beta-cell phenotype. Treatment aiming at restoring CaVγ4 may help to restore beta-cell function in diabetes.
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Affiliation(s)
- Cheng Luan
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
| | - Yingying Ye
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
| | - Tania Singh
- Stem Cell Center, Department of Laboratory Medicine, Lund University, 221 85 Lund, Sweden
| | - Mohammad Barghouth
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
| | - Lena Eliasson
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
| | - Isabella Artner
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
- Stem Cell Center, Department of Laboratory Medicine, Lund University, 221 85 Lund, Sweden
| | - Enming Zhang
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
| | - Erik Renström
- Lund University Diabetes Center, Department of Clinical Sciences Malmö, Lund University, 202 13 Malmö, Sweden
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Neuronal calcium channel α1 subunit interacts with AMPA receptor, increasing its cell surface localisation. Biochem Biophys Res Commun 2018; 498:402-408. [DOI: 10.1016/j.bbrc.2018.02.107] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 02/11/2018] [Indexed: 02/07/2023]
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Simms BA, Zamponi GW. Neuronal voltage-gated calcium channels: structure, function, and dysfunction. Neuron 2014; 82:24-45. [PMID: 24698266 DOI: 10.1016/j.neuron.2014.03.016] [Citation(s) in RCA: 413] [Impact Index Per Article: 41.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Voltage-gated calcium channels are the primary mediators of depolarization-induced calcium entry into neurons. There is great diversity of calcium channel subtypes due to multiple genes that encode calcium channel α1 subunits, coassembly with a variety of ancillary calcium channel subunits, and alternative splicing. This allows these channels to fulfill highly specialized roles in specific neuronal subtypes and at particular subcellular loci. While calcium channels are of critical importance to brain function, their inappropriate expression or dysfunction gives rise to a variety of neurological disorders, including, pain, epilepsy, migraine, and ataxia. This Review discusses salient aspects of voltage-gated calcium channel function, physiology, and pathophysiology.
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Affiliation(s)
- Brett A Simms
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB T2N 4N1, Canada
| | - Gerald W Zamponi
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB T2N 4N1, Canada.
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5
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Ca2+ channel and Na+/Ca2+ exchange localization in cardiac myocytes. J Mol Cell Cardiol 2013; 58:22-31. [DOI: 10.1016/j.yjmcc.2012.11.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Revised: 11/20/2012] [Accepted: 11/28/2012] [Indexed: 01/01/2023]
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Inamori KI, Hara Y, Willer T, Anderson ME, Zhu Z, Yoshida-Moriguchi T, Campbell KP. Xylosyl- and glucuronyltransferase functions of LARGE in α-dystroglycan modification are conserved in LARGE2. Glycobiology 2012; 23:295-302. [PMID: 23125099 PMCID: PMC3555503 DOI: 10.1093/glycob/cws152] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
LARGE-dependent modification enables α-dystroglycan (α-DG) to bind to its extracellular matrix ligands. Mutations in the LARGE gene and several others involved in O-mannosyl glycan synthesis have been identified in congenital and limb-girdle muscular dystrophies that are characterized by perturbed glycosylation and reduced ligand-binding affinity of α-DG. LARGE is a bifunctional glycosyltransferase that alternately transfers xylose and glucuronic acid, thereby generating the heteropolysaccharides on α-DG that confer its ligand binding. Although the LARGE paralog LARGE2 (also referred to as GYLTL1B) has likewise been shown to enhance the functional modification of α-DG in cultured cells, its enzymatic activities have not been identified. Here, we report that LARGE2 is also a bifunctional glycosyltransferase and compare its properties with those of LARGE. By means of a high-performance liquid chromatography-based enzymatic assay, we demonstrate that like LARGE, LARGE2 has xylosyltransferase (Xyl-T) and glucuronyltransferase (GlcA-T) activities, as well as polymerizing activity. Notably, however, the pH optima of the Xyl-T and GlcA-T of LARGE2 are distinct from one another and also from those of LARGE. Our results suggest that LARGE and LARGE2 catalyze the same glycosylation reactions for the functional modification of α-DG, but that they have different biochemical properties.
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Affiliation(s)
- Kei-ichiro Inamori
- Howard Hughes Medical Institute, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242-1101, USA
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Willer T, Lee H, Lommel M, Yoshida-Moriguchi T, de Bernabe DBV, Venzke D, Cirak S, Schachter H, Vajsar J, Voit T, Muntoni F, Loder AS, Dobyns WB, Winder TL, Strahl S, Mathews KD, Nelson SF, Moore SA, Campbell KP. ISPD loss-of-function mutations disrupt dystroglycan O-mannosylation and cause Walker-Warburg syndrome. Nat Genet 2012; 44:575-80. [PMID: 22522420 PMCID: PMC3371168 DOI: 10.1038/ng.2252] [Citation(s) in RCA: 174] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Accepted: 03/21/2012] [Indexed: 12/17/2022]
Abstract
Walker-Warburg syndrome (WWS) is clinically defined as congenital muscular dystrophy accompanied by a variety of brain and eye malformations. It represents the most severe clinical phenotype in a spectrum of alpha-dystroglycan posttranslational processing abnormalities, which share a defect in laminin binding glycan synthesis1. Although six WWS causing genes have been described, only half of all patients can currently be diagnosed genetically2. A cell fusion complementation assay using fibroblasts from undiagnosed WWS individuals identified five novel complementation groups. Further evaluation of one group by linkage analysis and targeted sequencing identified recessive mutations in the isoprenoid synthase domain containing (ISPD) gene. Confirmation of the pathogenicity of the identified ISPD mutations was demonstrated by complementation of fibroblasts with wild-type ISPD. Finally, we show that recessive mutations in ISPD abolish the initial step in laminin binding glycan synthesis by disrupting dystroglycan O-mannosylation. This establishes a novel mechanism for WWS pathophysiology.
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Affiliation(s)
- Tobias Willer
- Department of Molecular Physiology and Biophysics, University of Iowa Roy J and Lucille A Carver College of Medicine, Iowa City, Iowa, USA
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Yang L, Katchman A, Morrow JP, Doshi D, Marx SO. Cardiac L-type calcium channel (Cav1.2) associates with gamma subunits. FASEB J 2010; 25:928-36. [PMID: 21127204 DOI: 10.1096/fj.10-172353] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The cardiac voltage-gated Ca(2+) channel, Ca(v)1.2, mediates excitation-contraction coupling in the heart. The molecular composition of the channel includes the pore-forming α1 subunit and auxiliary α2/δ-1 and β subunits. Ca(2+) channel γ subunits, of which there are 8 isoforms, consist of 4 transmembrane domains with intracellular N- and C-terminal ends. The γ1 subunit was initially detected in the skeletal muscle Ca(v)1.1 channel complex, modulating current amplitude and activation and inactivation properties. The γ1 subunit also shifts the steady-state inactivation to more negative membrane potentials, accelerates current inactivation, and increases peak currents, when coexpressed with the cardiac α1c subunit in Xenopus oocytes and human embryonic kidney (HEK) 293 cells. The γ1 subunit is not expressed, however, in cardiac muscle. We sought to determine whether γ subunits that are expressed in cardiac tissue physically associate with and modulate Ca(v)1.2 function. We now demonstrate that γ4, γ6, γ7, and γ8 subunits physically interact with the Ca(v)1.2 complex. The γ subunits differentially modulate Ca(2+) channel function when coexpressed with the β1b and α2/δ-1 subunits in HEK cells, altering both activation and inactivation properties. The effects of γ on Ca(v)1.2 function are dependent on the subtype of β subunit. Our results identify new members of the cardiac Ca(v)1.2 macromolecular complex and identify a mechanism by which to increase the functional diversity of Ca(v)1.2 channels.
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Affiliation(s)
- Lin Yang
- Division of Cardiology, Department of Medicine, Columbia University, College of Physicians and Surgeons, 622 W. 168th St., New York, NY 10032, USA
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Prins KW, Lowe DA, Ervasti JM. Skeletal muscle-specific ablation of gamma(cyto)-actin does not exacerbate the mdx phenotype. PLoS One 2008; 3:e2419. [PMID: 18545671 PMCID: PMC2409075 DOI: 10.1371/journal.pone.0002419] [Citation(s) in RCA: 24] [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: 04/07/2008] [Accepted: 05/08/2008] [Indexed: 11/29/2022] Open
Abstract
We previously documented a ten-fold increase in γcyto-actin expression in dystrophin-deficient skeletal muscle and hypothesized that increased γcyto-actin expression may participate in an adaptive cytoskeletal remodeling response. To explore whether increased γcyto-actin fortifies the cortical cytoskeleton in dystrophic skeletal muscle, we generated double knockout mice lacking both dystrophin and γcyto-actin specifically in skeletal muscle (ms-DKO). Surprisingly, dystrophin-deficient mdx and ms-DKO mice presented with comparable levels of myofiber necrosis, membrane instability, and deficits in muscle function. The lack of an exacerbated phenotype in ms-DKO mice suggests γcyto-actin and dystrophin function in a common pathway. Finally, because both mdx and ms-DKO skeletal muscle showed similar levels of utrophin expression and presented with identical dystrophies, we conclude utrophin can partially compensate for the loss of dystrophin independent of a γcyto-actin-utrophin interaction.
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Affiliation(s)
- Kurt W. Prins
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Dawn A. Lowe
- Department of Physical Medicine and Rehabilitation, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - James M. Ervasti
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
- * E-mail:
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Kang MG, Chen CC, Wakamori M, Hara Y, Mori Y, Campbell KP. A functional AMPA receptor-calcium channel complex in the postsynaptic membrane. Proc Natl Acad Sci U S A 2006; 103:5561-6. [PMID: 16567654 PMCID: PMC1459393 DOI: 10.1073/pnas.0601289103] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ca(2+) channels play critical roles in the regulation of synaptic activity. In contrast to the well established function of voltage-activated Ca(2+) channels in the presynaptic membrane for neurotransmitter release, some studies are just beginning to elucidate the functions of the Ca(2+) channels in the postsynaptic membrane. In this study, we demonstrated the functional association of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors with the neuronal Ca(2+) channels. A series of biochemical studies showed the specific association of Ca(v)2.1 (alpha(1A)-class) and Ca(v)2.2 (alpha(1B)-class) with AMPA receptors in the postsynaptic membrane. Our electrophysiological and Ca(2+) imaging analyses of recombinant Ca(v)2.1 and AMPA receptors also showed functional coupling of the two channels. Considering the critical roles of postsynaptic intracellular concentration of Ca(2+) ([Ca(2+)](i)) increase and AMPA receptor trafficking for long-term potentiation (LTP) and long-term depression (LTD), the functional association of Ca(2+) channels with the AMPA receptors may provide new insights into the mechanism of synaptic plasticity.
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Affiliation(s)
- Myoung-Goo Kang
- *Howard Hughes Medical Institute and Departments of Physiology and Biophysics, Internal Medicine, and Neurology, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242; and
| | - Chien-Chang Chen
- *Howard Hughes Medical Institute and Departments of Physiology and Biophysics, Internal Medicine, and Neurology, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242; and
| | - Minoru Wakamori
- Laboratory of Molecular Biology, Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Yuji Hara
- Laboratory of Molecular Biology, Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Yasuo Mori
- Laboratory of Molecular Biology, Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
| | - Kevin P. Campbell
- *Howard Hughes Medical Institute and Departments of Physiology and Biophysics, Internal Medicine, and Neurology, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242; and
- To whom correspondence should be addressed. E-mail:
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Affiliation(s)
- H Glossmann
- Institut für Biochemische Pharmakologie der Leopold-Franzens-Universität Innsbruck, Austria
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12
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Abstract
The heart is a rhythmic electromechanical pump, the functioning of which depends on action potential generation and propagation, followed by relaxation and a period of refractoriness until the next impulse is generated. Myocardial action potentials reflect the sequential activation and inactivation of inward (Na(+) and Ca(2+)) and outward (K(+)) current carrying ion channels. In different regions of the heart, action potential waveforms are distinct, owing to differences in Na(+), Ca(2+), and K(+) channel expression, and these differences contribute to the normal, unidirectional propagation of activity and to the generation of normal cardiac rhythms. Changes in channel functioning, resulting from inherited or acquired disease, affect action potential repolarization and can lead to the generation of life-threatening arrhythmias. There is, therefore, considerable interest in understanding the mechanisms that control cardiac repolarization and rhythm generation. Electrophysiological studies have detailed the properties of the Na(+), Ca(2+), and K(+) currents that generate cardiac action potentials, and molecular cloning has revealed a large number of pore forming (alpha) and accessory (beta, delta, and gamma) subunits thought to contribute to the formation of these channels. Considerable progress has been made in defining the functional roles of the various channels and in identifying the alpha-subunits encoding these channels. Much less is known, however, about the functioning of channel accessory subunits and/or posttranslational processing of the channel proteins. It has also become clear that cardiac ion channels function as components of macromolecular complexes, comprising the alpha-subunits, one or more accessory subunit, and a variety of other regulatory proteins. In addition, these macromolecular channel protein complexes appear to interact with the actin cytoskeleton and/or the extracellular matrix, suggesting important functional links between channel complexes, as well as between cardiac structure and electrical functioning. Important areas of future research will be the identification of (all of) the molecular components of functional cardiac ion channels and delineation of the molecular mechanisms involved in regulating the expression and the functioning of these channels in the normal and the diseased myocardium.
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Affiliation(s)
- Jeanne M Nerbonne
- Dept. of Molecular Biology and Pharmacology, Washington University Medical School, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
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Affiliation(s)
- Myoung-Goo Kang
- Howard Hughes Medical Institute, Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA 52242, USA
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Arikkath J, Chen CC, Ahern C, Allamand V, Flanagan JD, Coronado R, Gregg RG, Campbell KP. Gamma 1 subunit interactions within the skeletal muscle L-type voltage-gated calcium channels. J Biol Chem 2003; 278:1212-9. [PMID: 12409298 DOI: 10.1074/jbc.m208689200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated calcium channels mediate excitationcontraction coupling in the skeletal muscle. Their molecular composition, similar to neuronal channels, includes the pore-forming alpha(1) and auxiliary alpha(2)delta, beta, and gamma subunits. The gamma subunits are the least characterized, and their subunit interactions are unclear. The physiological importance of the neuronal gamma is emphasized by epileptic stargazer mice that lack gamma(2). In this study, we examined the molecular basis of interaction between skeletal gamma(1) and the calcium channel. Our data show that the alpha(1)1.1, beta(1a), and alpha(2)delta subunits are still associated in gamma(1) null mice. Reexpression of gamma(1) and gamma(2) showed that gamma(1), but not gamma(2), incorporates into gamma(1) null channels. By using chimeric constructs, we demonstrate that the first half of the gamma(1) subunit, including the first two transmembrane domains, is important for subunit interaction. Interestingly, this chimera also restores calcium conductance in gamma(1) null myotubes, indicating that the domain mediates both subunit interaction and current modulation. To determine the subunit of the channel that interacts with gamma(1), we examined the channel in muscular dysgenesis mice. Cosedimentation experiments showed that gamma(1) and alpha(2)delta are not associated. Moreover, alpha(1)1.1 and gamma(1) subunits form a complex in transiently transfected cells, indicating direct interaction between the gamma(1) and alpha(1)1.1 subunits. Our data demonstrate that the first half of gamma(1) subunit is required for association with the channel through alpha(1)1.1. Because subunit interactions are conserved, these studies have broad implications for gamma heterogeneity, function and subunit association with voltage-gated calcium channels.
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Affiliation(s)
- Jyothi Arikkath
- Howard Hughes Medical Institute, Department of Physiology, University of Iowa, Iowa City 52242, USA
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Kang MG, Felix R, Campbell KP. Long-term regulation of voltage-gated Ca(2+) channels by gabapentin. FEBS Lett 2002; 528:177-82. [PMID: 12297300 DOI: 10.1016/s0014-5793(02)03295-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Gabapentin (GBP) is a gamma-aminobutyric acid analog effective in the treatment of seizures. A high-affinity interaction between GBP and the alpha(2)delta subunit of the voltage-gated Ca(2+) channels has been documented. In this report, we examined the effects of the chronic treatment with GBP on neuronal recombinant P/Q-type Ca(2+) channels expressed in Xenopus oocytes. GBP did not affect significantly the amplitude or the voltage dependence of the currents. Exposure to the drug did, however, slow down the kinetics of inactivation in a dose-dependent fashion. In addition, biochemical analysis showed that the integrity of Ca(2+) channel complex is not apparently affected by GBP binding, suggesting that chronic treatment with the drug might cause the channel kinetic modification through subtle conformational changes of the protein complex.
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Affiliation(s)
- Myoung-Goo Kang
- Howard Hughes Medical Institute, Department of Physiology and Biophysics, The University of Iowa College of Medicine, 400 Eckstein Medical Research Building, Iowa City 52242, USA
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Schwartz L, Diamant S, Barhanin J, Atlas D. Tunicamycin Dissociates Depolarization-induced Calcium Entry From Transmitter Release. Involvement of Glycosylated Protein(s) in the Process of Neurosecretion in PC-12 Cells. Eur J Neurosci 2002; 4:1249-1256. [PMID: 12106388 DOI: 10.1111/j.1460-9568.1992.tb00150.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The process of regulated secretion in PC-12 cells is tightly coupled to calcium entry, which is absolutely dependent on extracellular Ca2+([Ca2+]ex). Tunicamycin treatment of the cells dissociated depolarization-triggered Ca2+ influx from depolarization (high K+)-induced transmitter release into two distinct and independent phases. Deplarization-evoked Ca2+ influx was not affected by tunicamycin treatment (1 microg/ml, 72 h), whereas depolarization-evoked transmitter release was strongly inhibited (> 60%), suggesting at least a two-step process, and the participation of glycosylated protein(s) in the actual fusion/secretion step. Similarly, bradykinin-mediated transmitter release was linearly related to and absolutely dependent on Ca2+ entry, and was inhibited by tunicamycin treatment (> 80%), whereas bradykinin-evoked Ca2+ entry was not impaired, indicating that glycosylated protein(s) are essential for bradykinin-evoked release at a step subsequent to Ca2+ influx. The heavily glycosylated alpha2 subunit of the dihydropyridine-sensitive channel, which was used to monitor tunicamycin inhibition of glycosylation, was not expressed in the tunicamycin-treated cells, as shown by Western blot analysis. This observation allowed us to conclude that the alpha1 subunit of the heteromeric dihydropyridine voltage-sensitive Ca2+ channel, which is responsible for Ca2+ entry, is also fully functional when not assembled with its corresponding alpha2 subunit. The molecular properties of the alpha2 subunit, whose role in the complex structure of the channel is not yet understood, are shown for the first time for the L-type Ca2+ channel of PC-12 cells. Similar to cardiac and skeletal muscle cells, the alpha2 subunit appears to be a glycosylated polypeptide of molecular weight 170 kD and to display a characteristic mobility shift to 140 kD under reducing conditions.
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Affiliation(s)
- Lydia Schwartz
- Department of Biological Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel 91904
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Burgess DL, Gefrides LA, Foreman PJ, Noebels JL. A cluster of three novel Ca2+ channel gamma subunit genes on chromosome 19q13.4: evolution and expression profile of the gamma subunit gene family. Genomics 2001; 71:339-50. [PMID: 11170751 DOI: 10.1006/geno.2000.6440] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The CACNG1 gene on chromosome 17q24 encodes an integral membrane protein that was originally isolated as the regulatory gamma subunit of voltage-dependent Ca2+ channels from skeletal muscle. The existence of an extended family of gamma subunits was subsequently demonstrated upon identification of CACNG2 (22q13), CACNG3 (16p12-p13), and CACNG4 and CACNG5 (17q24). In this study, we describe a cluster of three novel gamma subunit genes, CACNG6, CACNG7, and CACNG8, located in a tandem array on 19q13.4. Phylogenetic analysis indicates that this array is paralogous to the cluster containing CACNG1, CACNG5, and CACNG4, respectively, on chromosome 17q24. We developed sensitive RT-PCR assays and examined the expression profile of each member of the gamma subunit gene family, CACNG1-CACNG8. Analysis of 24 human tissues plus 3 dissected brain regions revealed that CACNG1 through CACNG8 are all coexpressed in fetal and adult brain and differentially transcribed among a wide variety of other tissues. The expression of distinct complements of gamma subunit isoforms in different cell types may be an important mechanism for regulating Ca2+ channel function.
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Affiliation(s)
- D L Burgess
- Department of Neurology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
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Metzler DE, Metzler CM, Sauke DJ. Chemical Communication Between Cells. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50033-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Gao B, Sekido Y, Maximov A, Saad M, Forgacs E, Latif F, Wei MH, Lerman M, Lee JH, Perez-Reyes E, Bezprozvanny I, Minna JD. Functional properties of a new voltage-dependent calcium channel alpha(2)delta auxiliary subunit gene (CACNA2D2). J Biol Chem 2000; 275:12237-42. [PMID: 10766861 PMCID: PMC3484885 DOI: 10.1074/jbc.275.16.12237] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have positionally cloned and characterized a new calcium channel auxiliary subunit, alpha(2)delta-2 (CACNA2D2), which shares 56% amino acid identity with the known alpha(2)delta-1 subunit. The gene maps to the critical human tumor suppressor gene region in chromosome 3p21.3, showing very frequent allele loss and occasional homozygous deletions in lung, breast, and other cancers. The tissue distribution of alpha(2)delta-2 expression is different from alpha(2)delta-1, and alpha(2)delta-2 mRNA is most abundantly expressed in lung and testis and well expressed in brain, heart, and pancreas. In contrast, alpha(2)delta-1 is expressed predominantly in brain, heart, and skeletal muscle. When co-expressed (via cRNA injections) with alpha(1B) and beta(3) subunits in Xenopus oocytes, alpha(2)delta-2 increased peak size of the N-type Ca(2+) currents 9-fold, and when co-expressed with alpha(1C) or alpha(1G) subunits in Xenopus oocytes increased peak size of L-type channels 2-fold and T-type channels 1.8-fold, respectively. Anti-peptide antibodies detect the expression of a 129-kDa alpha(2)delta-2 polypeptide in some but not all lung tumor cells. We conclude that the alpha(2)delta-2 gene encodes a functional auxiliary subunit of voltage-gated Ca(2+) channels. Because of its chromosomal location and expression patterns, CACNA2D2 needs to be explored as a potential tumor suppressor gene linking Ca(2+) signaling and lung, breast, and other cancer pathogenesis. The homologous location on mouse chromosome 9 is also the site of the mouse neurologic mutant ducky (du), and thus, CACNA2D2 is also a candidate gene for this inherited idiopathic generalized epilepsy syndrome.
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Affiliation(s)
- Boning Gao
- Hamon Center for Therapeutic Oncology Research, Department of Internal Medicine, Pharmacology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
| | - Yoshitaka Sekido
- Hamon Center for Therapeutic Oncology Research, Department of Internal Medicine, Pharmacology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
| | - Anton Maximov
- Department of Physiology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
| | - Mohamad Saad
- Hamon Center for Therapeutic Oncology Research, Department of Internal Medicine, Pharmacology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
| | - Eva Forgacs
- Hamon Center for Therapeutic Oncology Research, Department of Internal Medicine, Pharmacology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
| | - Farida Latif
- University of Birmingham, Birmingham B15 2TT, United Kingdom
| | - Ming H. Wei
- Laboratory of Immunobiology, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702
| | - Michael Lerman
- Laboratory of Immunobiology, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702
| | - Jung-Ha Lee
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
| | - Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
| | - Ilya Bezprozvanny
- Department of Physiology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
| | - John D. Minna
- Hamon Center for Therapeutic Oncology Research, Department of Internal Medicine, Pharmacology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390
- To whom correspondence should be addressed: Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8593. Tel.: 214-648-4900; Fax: 214-648-4940;
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20
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Visser NA, de Koning MH, Lammi MJ, Häkkinen T, Tammi M, van Kampen GP. Increase of decorin content in articular cartilage following running. Connect Tissue Res 1998; 37:295-302. [PMID: 9862228 DOI: 10.3109/03008209809002446] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The effect of long distance running exercise (40 km/day for 15 weeks, five days a week) on the decorin content of articular cartilage from the knee joint was studied in female beagle dogs. Samples from load bearing sites on the lateral plateau of the tibia (TL), and pooled material from two minimum load bearing sites on the posterior section of lateral (FLP) and medial (FMP) femoral condyles were analyzed. The running exercise protocol did not lead to significant changes in the overall glycosaminoglycan content of the cartilage. However, the amount of decorin significantly increased in the TL samples, and also in the FMP pool. These results support earlier in vitro observations that decorin synthesis is stimulated by loading, independent of the synthesis of aggrecan.
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Affiliation(s)
- N A Visser
- Jan van Breemen Institute, Amsterdam, The Netherlands
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21
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Letts VA, Felix R, Biddlecome GH, Arikkath J, Mahaffey CL, Valenzuela A, Bartlett FS, Mori Y, Campbell KP, Frankel WN. The mouse stargazer gene encodes a neuronal Ca2+-channel gamma subunit. Nat Genet 1998; 19:340-7. [PMID: 9697694 DOI: 10.1038/1228] [Citation(s) in RCA: 409] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Stargazer mice have spike-wave seizures characteristic of absence epilepsy, with accompanying defects in the cerebellum and inner ear. We describe here a novel gene, Cacng2, whose expression is disrupted in two stargazer alleles. It encodes a 36-kD protein (stargazin) with structural similarity to the gamma subunit of skeletal muscle voltage-gated calcium (Ca2+) channels. Stargazin is brain-specific and, like other neuronal Ca2+-channel subunits, is enriched in synaptic plasma membranes. In vitro, stargazin increases steady-state inactivation of alpha1 class A Ca2+ channels. The anticipated effect in stargazer mutants, inappropriate Ca2+ entry, may contribute to their more pronounced seizure phenotype compared with other mouse absence models with Ca2+-channel defects. The discovery that the stargazer gene encodes a gamma subunit completes the identification of the major subunit types for neuronal Ca2+ channels, namely alpha1, alpha2delta, beta and gamma, providing a new opportunity to understand how these channels function in the mammalian brain and how they may be targeted in the treatment of neuroexcitability disorders.
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Affiliation(s)
- V A Letts
- The Jackson Laboratory, Bar Harbor, Maine 04609, USA.
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22
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Taylor CP, Gee NS, Su TZ, Kocsis JD, Welty DF, Brown JP, Dooley DJ, Boden P, Singh L. A summary of mechanistic hypotheses of gabapentin pharmacology. Epilepsy Res 1998; 29:233-49. [PMID: 9551785 DOI: 10.1016/s0920-1211(97)00084-3] [Citation(s) in RCA: 464] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Although the cellular mechanisms of pharmacological actions of gabapentin (Neurontin) remain incompletely described, several hypotheses have been proposed. It is possible that different mechanisms account for anticonvulsant, antinociceptive, anxiolytic and neuroprotective activity in animal models. Gabapentin is an amino acid, with a mechanism that differs from those of other anticonvulsant drugs such as phenytoin, carbamazepine or valproate. Radiotracer studies with [14C]gabapentin suggest that gabapentin is rapidly accessible to brain cell cytosol. Several hypotheses of cellular mechanisms have been proposed to explain the pharmacology of gabapentin: 1. Gabapentin crosses several membrane barriers in the body via a specific amino acid transporter (system L) and competes with leucine, isoleucine, valine and phenylalanine for transport. 2. Gabapentin increases the concentration and probably the rate of synthesis of GABA in brain, which may enhance non-vesicular GABA release during seizures. 3. Gabapentin binds with high affinity to a novel binding site in brain tissues that is associated with an auxiliary subunit of voltage-sensitive Ca2+ channels. Recent electrophysiology results suggest that gabapentin may modulate certain types of Ca2+ current. 4. Gabapentin reduces the release of several monoamine neurotransmitters. 5. Electrophysiology suggests that gabapentin inhibits voltage-activated Na+ channels, but other results contradict these findings. 6. Gabapentin increases serotonin concentrations in human whole blood, which may be relevant to neurobehavioral actions. 7. Gabapentin prevents neuronal death in several models including those designed to mimic amyotrophic lateral sclerosis (ALS). This may occur by inhibition of glutamate synthesis by branched-chain amino acid aminotransferase (BCAA-t).
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Affiliation(s)
- C P Taylor
- Department of Neuroscience Therapeutics, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert Co., Ann Arbor, MI 48105, USA
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23
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Brown JP, Dissanayake VU, Briggs AR, Milic MR, Gee NS. Isolation of the [3H]gabapentin-binding protein/alpha 2 delta Ca2+ channel subunit from porcine brain: development of a radioligand binding assay for alpha 2 delta subunits using [3H]leucine. Anal Biochem 1998; 255:236-43. [PMID: 9451509 DOI: 10.1006/abio.1997.2447] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The novel antiepileptic agent gabapentin (Neurontin) binds with high affinity to the alpha 2 delta subunit of a voltage-dependent Ca2+ channel. We report here a simple purification scheme for detergent-solubilized alpha 2 delta subunits from porcine brain. This involves sequential chromatography on Q-Sepharose, Cu(2+)-charged iminodiacetic acid-Sepharose, wheat germ lectin-agarose, and Mono Q. The purified protein was essentially homogeneous by SDS-polyacrylamide gel electrophoresis with a subunit Mr of 145,000. Using [3H] gabapentin as the radiolabeled tracer and (S)-3-isobutyl gamma-aminobutyric acid to define nonspecific binding, the overall purification factor was 2760-fold and the apparent yield 26.6%. We also developed and validated a novel binding assay for alpha 2 delta Ca2+ channel subunits using the ligand pair L-[3H]leucine/L-isoleucine. Even in binding assays of crude brain membrane fractions, [3H]leucine proved to be remarkably stable and specific for the alpha 2 delta Ca2+ channel subunit. [3H]Leucine offers several advantages over custom-labeled [3H]gabapentin: it has a higher specific activity, is relatively inexpensive, and is available from commercial sources.
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Affiliation(s)
- J P Brown
- Parke-Davis Neuroscience Research Centre, Cambridge University Forvie Site, Cambridge, United Kingdom
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24
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Saito F, Yamada H, Sunada Y, Hori H, Shimizu T, Matsumura K. Characterization of a 30-kDa peripheral nerve glycoprotein that binds laminin and heparin. J Biol Chem 1997; 272:26708-13. [PMID: 9334255 DOI: 10.1074/jbc.272.42.26708] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We have shown previously that a bovine peripheral nerve protein with a molecular mass of about 30 kDa binds laminin in blot overlay assay. In this paper, we have characterized this 30-kDa laminin-binding protein (LBP30). LBP30 was extracted from the crude bovine peripheral nerve membranes at pH 12 or by 0.5 M NaCl but not by 2% Triton X-100. LBP30 bound to heparin-Sepharose in the presence of 0.5 M NaCl. The results of lectin staining indicated that LBP30 contained both terminally sialylated and nonsialylated Ser/Thr-linked oligosaccharides. LBP30 bound laminin-2 as well as laminin-1 but not fibronectin or collagen type IV. When immobilized LBP30 was incubated with the crude peripheral nerve membrane extracts, all of the endogenous peripheral nerve laminin chain isoforms, the alpha1, alpha2, beta1, beta2, and gamma1 chains, were detected bound to LBP30. The binding of LBP30 to laminin was inhibited by heparin, heparan sulfate, dextran sulfate, or NaCl but was not affected significantly by chondroitin sulfate, dextran, or EDTA. Although LBP30 bound to laminin-1 denatured with SDS in a nonreducing condition, the binding was reduced drastically when laminin-1 was denatured with SDS in a reducing condition, suggesting that the binding of LBP30 is somewhat dependent on the high order structure of laminin-1. Immunohistochemical analysis demonstrated the broad distribution of LBP30 in the perineurium and endoneurium of bovine peripheral nerve. These results indicate that LBP30 is a laminin- and heparin-binding glycoprotein localized in the perineurium and endoneurium of bovine peripheral nerve.
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Affiliation(s)
- F Saito
- Department of Neurology and Neuroscience, Teikyo University School of Medicine, Tokyo 173, Japan
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25
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Ibraghimov-Beskrovnaya O, Dackowski WR, Foggensteiner L, Coleman N, Thiru S, Petry LR, Burn TC, Connors TD, Van Raay T, Bradley J, Qian F, Onuchic LF, Watnick TJ, Piontek K, Hakim RM, Landes GM, Germino GG, Sandford R, Klinger KW. Polycystin: in vitro synthesis, in vivo tissue expression, and subcellular localization identifies a large membrane-associated protein. Proc Natl Acad Sci U S A 1997; 94:6397-402. [PMID: 9177229 PMCID: PMC21061 DOI: 10.1073/pnas.94.12.6397] [Citation(s) in RCA: 132] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The primary structure of polycystin predicts a large integral membrane protein with multiple cell recognition motifs, but its function remains unknown. Insight into polycystin's normal function and its role in the development of autosomal dominant polycystic kidney disease (PKD1) requires the assembly of an extensive collection of molecular reagents to examine its expression and create model systems for functional studies. Development of these crucial reagents has been complicated due to the presence of transcriptionally active homologous loci. We have assembled the authentic full-length PKD1 cDNA and demonstrated expression of polycystin in vitro. Polyclonal antibodies directed against distinct extra- and intracellular domains specifically immunoprecipitated in vitro translated polycystin. The panel of antibodies was used to determine localization of polycystin in renal epithelial and endothelial cell lines and tissues of fetal, adult, and cystic origins. In normal adult kidney and maturing fetal nephrons, polycystin expression was confined to epithelial cells of the distal nephron and vascular endothelial cells. Expression in the proximal nephron was only observed after injury-induced cell proliferation. Polycystin expression was confined to ductal epithelium in liver, pancreas, and breast, and restricted to astrocytes in normal brain. We report clear evidence for the membrane localization of polycystin by both tissue sections and by confocal microscopy in cultured renal and endothelial cells. Interestingly, when cultured cells made cell-cell contact, polycystin was localized to the lateral membranes of cells in contact. These data suggest that polycystin is likely to have a widespread role in epithelial cell differentiation and maturation and in cell-cell interactions.
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26
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Gee NS, Brown JP, Dissanayake VU, Offord J, Thurlow R, Woodruff GN. The novel anticonvulsant drug, gabapentin (Neurontin), binds to the alpha2delta subunit of a calcium channel. J Biol Chem 1996; 271:5768-76. [PMID: 8621444 DOI: 10.1074/jbc.271.10.5768] [Citation(s) in RCA: 843] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Gabapentin (1-(aminomethyl)cyclohexane acetic acid; Neurontin) is a novel anticonvulsant drug, with a mechanism of action apparently dissimilar to that of other antiepileptic agents. We report here the isolation and characterization of a [3H]gabapentin-binding protein from pig cerebral cortex membranes. The detergent-solubilized binding protein was purified 1022-fold, in a six-step column-chromatographic procedure, with a yield of 3.9%. The purified protein had an apparent subunit Mr of 130,000, and was heavily glycosylated. The partial N-terminal amino acid sequence of the Mr 130,000 polypeptide, EPFPSAVTIK, was identical to that reported for the alpha2delta subunit of the L-type Ca2+ channel from rabbit skeletal muscle (Hamilton, S. L., Hawkes, M. J., Brush, K., Cook, R., Chang, R. J., and Smilowitz, H. M. (1989) Biochemistry 28, 7820-7828). High levels of [3H]gabapentin binding sites were found in membranes prepared from rat brain, heart and skeletal muscle. Binding of [3H]gabapentin to COS-7 cells transfected with alpha2delta cDNA was elevated >10-fold over controls, consistent with the expression of alpha2 delta protein, as measured by Western blotting. Finally, purified L-type Ca2+ channel complexes were fractionated, under dissociating conditions, on an ion-exchange column; [3H]gabapentin binding activity closely followed the elution of the alpha2 delta subunit. [3H]Gabapentin is the first pharmacological agent described that interacts with an alpha2delta subunit of a voltage-dependent Ca2+ channel.
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Affiliation(s)
- N S Gee
- Parke-Davis Neuroscience Research Centre, Cambridge University Forvie Site, Robinson Way, Cambridge CB2 2QB, United Kingdom
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27
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De Waard M, Gurnett CA, Campbell KP. Structural and functional diversity of voltage-activated calcium channels. ION CHANNELS 1996; 4:41-87. [PMID: 8744206 DOI: 10.1007/978-1-4899-1775-1_2] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Data gathered from the expression of cDNAs that encode the subunits of voltage-dependent Ca2+ channels have demonstrated important structural and functional similarities among these channels. Despite these convergences, there are also significant differences in the nature and functional importance of subunit-subunit and protein-Ca2+ channel interactions. There is evidence demonstrating that the functional differences between Ca2+ channel subtypes is due to several factors, including the expression of distinct alpha 1 subunit proteins, the selective association of structural subunits and modulatory proteins, and differences in posttranslational processing and cell regulation. We summarize several avenues of research that should provide significant clues about the structural features involved in the biophysical and functional diversity of voltage-dependent Ca2+ channels.
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Affiliation(s)
- M De Waard
- Howard Hughes Medical Institute, Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City 52242, USA
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28
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Witcher DR, De Waard M, Liu H, Pragnell M, Campbell KP. Association of native Ca2+ channel beta subunits with the alpha 1 subunit interaction domain. J Biol Chem 1995; 270:18088-93. [PMID: 7629119 DOI: 10.1074/jbc.270.30.18088] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
beta Subunits of voltage-dependent Ca2+ channels play an important role in regulating Ca2+ channel function. The sites of alpha 1-beta subunit interaction have been localized recently to cytoplasmic domains of both subunits. The alpha 1 subunit interaction domain (AID) is an 18-amino-acid conserved motif located between repeats I and II on all alpha 1 subunits which is essential for the binding of beta subunits. In order to further study the interaction of beta subunits with AID, we have expressed a 50-amino-acid glutathione S-transferase (GST) fusion protein from the alpha 1A subunit that contains the AID. Mutant GST fusion proteins that contain a single amino acid change (Y392S, Y392F, and Y392W) in the AIDA along with control GST were coupled to glutathione-Sepharose beads to form affinity beads. Binding assays using these affinity beads with in vitro synthesized 35S-labeled beta 2 and beta 3 subunits demonstrate that the hydroxyl group on tyrosine 392 of AIDA is critical for binding to beta subunits. The affinity bead assay was also used to identify and characterize native beta subunits from detergent extracts of different tissues. The AIDA affinity beads, but not the control or Y392S beads, specifically bind beta subunits from detergent extracts of skeletal muscle, cardiac muscle, and brain. Immunoblot analyses demonstrate the presence of beta 1a in skeletal muscle, beta 2 and beta 3 in cardiac muscle, and beta 1b, beta 3, and beta 4 in brain. The assays also demonstrate the AIDA beads bind to beta subunits from tissue homogenates extracted with low salt and no detergent suggesting the existence of a pool of beta subunits which is not always associated with alpha 1 subunits. Also, beta subunits from solubilized skeletal muscle triads can be affinity-purified using AIDA CNBr-Sepharose. Our data demonstrate that the AID binds to native beta subunits from detergent and non-detergent tissue extracts illustrating that this domain on the alpha 1 subunit is the major anchoring site for the beta subunit.
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Affiliation(s)
- D R Witcher
- Howard Hughes Medical Institute, Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City 52242, USA
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29
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Adelman JP. Proteins that interact with the pore-forming subunits of voltage-gated ion channels. Curr Opin Neurobiol 1995; 5:286-95. [PMID: 7580150 DOI: 10.1016/0959-4388(95)80040-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Voltage-gated ion channels are composed of pore-forming subunits, as well as auxiliary subunits that modify the functions of these channels. In addition, the channels interact with other modulatory proteins in a more transient manner, although with significant effects on channel activity. Even though many second-messenger systems influence the voltage-gated ion channels, only in a few cases has clear evidence for direct protein-protein interactions been demonstrated. Recent biochemical and genetic studies have helped to elucidate the scope of the interactions between these ion channels and various modulatory proteins by determining the structures and functions of nonpore-forming subunits.
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Affiliation(s)
- J P Adelman
- Vollum Institute, Oregon Health Sciences University, Portland, USA
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30
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Parys JB, de Smedt H, Missiaen L, Bootman MD, Sienaert I, Casteels R. Rat basophilic leukemia cells as model system for inositol 1,4,5-trisphosphate receptor IV, a receptor of the type II family: functional comparison and immunological detection. Cell Calcium 1995; 17:239-49. [PMID: 7664312 DOI: 10.1016/0143-4160(95)90070-5] [Citation(s) in RCA: 112] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This study concerns the detection and analysis of the highly homologous type II-like inositol 1,4,5-trisphosphate (InsP3) receptors (InsP3R-II, -IV and -V). We have particularly investigated RBL-2H3 cells, which at the mRNA level predominantly expressed InsP3R-IV [De Smedt H. Missiaen L. Parys JB. et al. (1994) Determination of relative amounts of inositol trisphosphate receptor mRNA isoforms by ratio polymerase chain reaction. J. Biol. Chem., 269, 21691-21698]. When measured in identical experimental conditions, microsomes from RBL-2H3 cells were characterized by a much higher InsP3 binding affinity (Kd 3.8 +/- 0.8 nM, Bmax 0.40 +/- 0.08 pmol/mg protein) than microsomes from A7r5 cells (Kd 65 +/- 7 nM, Bmax 0.65 +/- 0.08 pmol/mg protein) or from cerebellum (Kd 135 +/- 14 nM, Bmax 7.35 +/- 1.13 pmol/mg protein). An affinity-purified antibody against the C-terminus of type II-like InsP3Rs detected, after SDS-PAGE and immunoblotting, a 250 kD protein in RBL-2H3 and C3H10T1/2 cells, but not in other cell types. An isoform-specific antibody against the C-terminus of InsP3R-I was used to determine the presence of the various InsP3R-I splice isoforms at the protein level. The 273 kD (brain), 261 kD (peripheral tissues) and 256 kD (Xenopus oocytes) isoforms were recognized. Expression of InsP3R-I in RBL-2H3 cells was very low. Taken together, our results support the hypothesis that InsP3R isoforms may differ to a large extent in their affinity for InsP3 and suggest that RBL-2H3 cells are a useful model for the study of InsP3R-IV.
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MESH Headings
- Amino Acid Sequence
- Animals
- Calcium/metabolism
- Calcium Channels/analysis
- Calcium Channels/classification
- Calcium Channels/drug effects
- Calcium Channels/immunology
- Calcium Channels/physiology
- Inositol 1,4,5-Trisphosphate/metabolism
- Inositol 1,4,5-Trisphosphate Receptors
- Leukemia, Basophilic, Acute/pathology
- Leukemia-Lymphoma, Adult T-Cell/pathology
- Mice
- Mice, Inbred C3H
- Microsomes
- Molecular Sequence Data
- Polymerase Chain Reaction
- RNA, Messenger/biosynthesis
- RNA, Neoplasm/biosynthesis
- Rats
- Receptors, Cytoplasmic and Nuclear/analysis
- Receptors, Cytoplasmic and Nuclear/classification
- Receptors, Cytoplasmic and Nuclear/drug effects
- Receptors, Cytoplasmic and Nuclear/immunology
- Receptors, Cytoplasmic and Nuclear/physiology
- Tumor Cells, Cultured/drug effects
- Tumor Cells, Cultured/metabolism
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Affiliation(s)
- J B Parys
- Laboratorium voor Fysiologie, KU Leuven, Belgium
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31
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Primary structure and muscle-specific expression of the 50-kDa dystrophin-associated glycoprotein (adhalin). J Biol Chem 1993. [DOI: 10.1016/s0021-9258(20)80440-2] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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32
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Woscholski R, Marmé D. Dihydropyridine binding of the calcium channel complex from skeletal muscle is modulated by subunit interaction. Cell Signal 1992; 4:209-18. [PMID: 1319724 DOI: 10.1016/0898-6568(92)90084-l] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The dihydropyridine-binding subunit alpha 1 of the calcium channel complex from rabbit skeletal muscle can be partially depleted from the alpha 2 delta beta-complex using wheat germ agglutinin-affinity chromatography. This depletion of the alpha 1 from the other subunits leads to a loss of dihydropyridine-binding, which can be fully reconstituted by repletion of the alpha 1 with the other subunits. Reassembly of these subunits results in an increase in the Kd and Bmax of the dihydropyridine-binding indicating that the non-dihydropyridine-binding subunits influence dihydropyridine-binding. The affinity of the alpha 1 subunit for the other subunits was determined to be approximately 35 nM. Since the free alpha 1 subunit will not bind to the beta subunit alone, there is evidence, given the selective partitioning of the beta subunit to the lectin-bound subunit pool, that either beta binds with higher affinity to the alpha 2 delta-complex than to the free alpha 1 subunit or that the bound alpha 1 creates or modulates beta-binding. This indicates a functional high affinity interaction between the dihydropyridine-binding alpha 1 subunit and the alpha 2 delta beta-complex.
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Affiliation(s)
- R Woscholski
- University of Freiburg, Institute of Molecular Cell Biology, Germany
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33
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34
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Ohlendieck K, Briggs FN, Lee KF, Wechsler AW, Campbell KP. Analysis of excitation-contraction-coupling components in chronically stimulated canine skeletal muscle. EUROPEAN JOURNAL OF BIOCHEMISTRY 1991; 202:739-47. [PMID: 1662614 DOI: 10.1111/j.1432-1033.1991.tb16428.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The chronic stimulation of predominantly fast-twitch mammalian skeletal muscle causes a transformation to physiological characteristics of slow-twitch skeletal muscle. Here, we report the effects of chronic stimulation on the protein components of the sarcoplasmic reticulum and transverse tubular membranes which are directly involved in excitation-contraction coupling. Comparison of protein composition of microsomal fractions from control and chronically stimulated muscle was performed by immunoblot analysis and also by staining with Coomassie blue or the cationic carbocyanine dye Stains-all. Consistent with previous experiments, a greatly reduced density was observed for the fast-twitch isozyme of Ca(2+)-ATPase, while the expression of the slow-twitch Ca(2+)-ATPase was found to be greatly enhanced. Components of the sarcolemma (Na+/K(+)-ATPase, dystrophin-glycoprotein complex) and the free sarcoplasmic reticulum (Ca(2+)-binding protein sarcalumenin and a 53-kDa glycoprotein) were not affected by chronic stimulation. The relative abundance of calsequestrin was slightly reduced in transformed skeletal muscle. However, the expression of the ryanodine receptor/Ca(Ca2+)-release channel from junctional sarcoplasmic reticulum and the transverse tubular dihydropyridine-sensitive Ca2+ channel, as well as two junctional sarcoplasmic reticulum proteins of 90 kDa and 94 kDa, was greatly suppressed in transformed muscle. Thus, the expression of the major protein components of the triad junction involved in excitation-contraction coupling is suppressed, while the expression of other muscle membrane proteins is not affected in chronically stimulated muscle.
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Affiliation(s)
- K Ohlendieck
- Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City
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35
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Heterologous regulation of the cardiac Ca2+ channel alpha 1 subunit by skeletal muscle beta and gamma subunits. Implications for the structure of cardiac L-type Ca2+ channels. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54728-1] [Citation(s) in RCA: 162] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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36
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Pragnell M, Sakamoto J, Jay SD, Campbell KP. Cloning and tissue-specific expression of the brain calcium channel beta-subunit. FEBS Lett 1991; 291:253-8. [PMID: 1657644 DOI: 10.1016/0014-5793(91)81296-k] [Citation(s) in RCA: 164] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
A cDNA clone encoding a protein with high homology to the beta-subunit of the rabbit skeletal muscle dihydropyridine-sensitive calcium channel was isolated from a rat brain cDNA library. This rat brain beta-subunit cDNA hybridizes to a 3.4 kb message that is expressed in high levels in the cerebral hemispheres and hippocampus but is significantly reduced in cerebellum. The open reading frame encodes 597 amino acids with a predicted mass of 65 679 Da which is 82% homologous with the skeletal muscle beta-subunit. The brain cDNA encodes a unique 153 amino acid C-terminus and predicts the absence of a muscle-specific 50 amino acid internal segment. It also encodes numerous consensus phosphorylation sites suggesting a role in calcium channel regulation. The corresponding human beta-subunit gene was localized to chromosome 17. Hence the encoded brain beta-subunit, which has a primary structure highly similar to its isoform in skeletal muscle, may have a comparable role as an integral regulatory component of a neuronal calcium channel.
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Affiliation(s)
- M Pragnell
- Howard Hughes Medical Institute, Program in Neuroscience, University of Iowa College of Medicine, Iowa City 52242
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37
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Sakamoto J, Campbell K. A monoclonal antibody to the beta subunit of the skeletal muscle dihydropyridine receptor immunoprecipitates the brain omega-conotoxin GVIA receptor. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55150-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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38
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Affiliation(s)
- W A Catterall
- Department of Pharmacology, University of Washington, Seattle 98195
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39
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Abstract
The stoichiometry, cellular location, glycosylation, and hydrophobic properties of the components in the dystrophin-glycoprotein complex were examined. The 156, 59, 50, 43, and 35 kd dystrophin-associated proteins each possess unique antigenic determinants, enrich quantitatively with dystrophin, and were localized to the skeletal muscle sarcolemma. The 156, 50, 43, and 35 kd dystrophin-associated proteins contained Asn-linked oligosaccharides. The 156 kd dystrophin-associated glycoprotein contained terminally sialylated Ser/Thr-linked oligosaccharides. Dystrophin, the 156 kd, and the 59 kd dystrophin-associated proteins were found to be peripheral membrane proteins, while the 50 kd, 43 kd, and 35 kd dystrophin-associated glycoproteins and the 25 kd dystrophin-associated protein were confirmed as integral membrane proteins. These results demonstrate that dystrophin and its 59 kd associated protein are cytoskeletal elements that are tightly linked to a 156 kd extracellular glycoprotein by way of a complex of transmembrane proteins.
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Affiliation(s)
- J M Ervasti
- Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City 52242
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40
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Ohlendieck K, Ervasti JM, Matsumura K, Kahl SD, Leveille CJ, Campbell KP. Dystrophin-related protein is localized to neuromuscular junctions of adult skeletal muscle. Neuron 1991; 7:499-508. [PMID: 1654951 DOI: 10.1016/0896-6273(91)90301-f] [Citation(s) in RCA: 302] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Dystrophin-related protein (DRP) is an autosomal gene product with high homology to dystrophin. We have used highly specific antibodies to the unique C-terminal peptide sequences of DRP and dystrophin to examine the subcellular localization and biochemical properties of DRP in adult skeletal muscle. DRP is enriched in isolated sarcolemma from control and mdx mouse muscle, but is much less abundant than dystrophin. Immunofluorescence microscopy localized DRP almost exclusively to the neuromuscular junction region in rabbit and mouse skeletal muscle, as well as mdx mouse muscle and denervated mouse muscle. DRP is also present in normal size and abundance and localizes to the neuromuscular junction region in muscle from the dystrophic mouse model dy/dy. Thus, DRP is a junction-specific membrane cytoskeletal protein that may play an important role in the organization of the postsynaptic membrane of the neuromuscular junction.
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Affiliation(s)
- K Ohlendieck
- Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City 52242
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41
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Jay SD, Sharp AH, Kahl SD, Vedvick TS, Harpold MM, Campbell KP. Structural characterization of the dihydropyridine-sensitive calcium channel alpha 2-subunit and the associated delta peptides. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)49986-3] [Citation(s) in RCA: 189] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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42
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Chapter 4. Diversity of Neuronal Calcium Channels. ANNUAL REPORTS IN MEDICINAL CHEMISTRY 1991. [DOI: 10.1016/s0065-7743(08)61191-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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43
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McPherson PS, Campbell KP. Solubilization and biochemical characterization of the high affinity [3H]ryanodine receptor from rabbit brain membranes. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(17)44774-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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44
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De Jongh K, Warner C, Catterall W. Subunits of purified calcium channels. Alpha 2 and delta are encoded by the same gene. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)77174-3] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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45
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Bosse E, Regulla S, Biel M, Ruth P, Meyer HE, Flockerzi V, Hofmann F. The cDNA and deduced amino acid sequence of the gamma subunit of the L-type calcium channel from rabbit skeletal muscle. FEBS Lett 1990; 267:153-6. [PMID: 2163895 DOI: 10.1016/0014-5793(90)80312-7] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Complementary DNAs for the gamma subunit of the calcium channel of rabbit skeletal muscle were isolated on the basis of peptide sequences derived from the purified protein. The deduced primary structure is without homology to other known protein sequences and is consistent with the gamma subunit being an integral membrane protein.
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Affiliation(s)
- E Bosse
- Medizinische Biochemie, Universität des Saarlandes, Homburg/Saar, FRG
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46
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Boess FG, Balasubramanian MK, Brammer MJ, Campbell IC. Stimulation of muscarinic acetylcholine receptors increases synaptosomal free calcium concentration by protein kinase-dependent opening of L-type calcium channels. J Neurochem 1990; 55:230-6. [PMID: 2162377 DOI: 10.1111/j.1471-4159.1990.tb08843.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In synaptosomes prepared from rat cerebral cortex, free cytosolic calcium concentration ([Ca2+]i) was measured using the fluorescent dye fura-2. Incubation of fura-2-loaded synaptosomes with carbachol increased [Ca2+]i in a dose-dependent manner (1-1,000 microM), with a maximum response of 22 +/- 2% at approximately 100 microM and an EC50 (calculated concentration producing 50% of the maximum response) of 30 microM. The effect of carbachol (100 microM) on [Ca2+]i was antagonised by atropine, but not by hexamethonium (10 microM). The calculated concentration of atropine needed for 50% inhibition (IC50) was 260 nM. The rise in [Ca2+]i produced by carbachol was reduced in the absence of extrasynaptosomal Ca2+ and effectively blocked by the L-type calcium channel blocker nifedipine (with an IC50 of 29 nM). The response to carbachol was reduced if the synaptosomes were preincubated with the protein kinase inhibitors H7 [1-(5-isoquinolinylsulfonyl)-2- methylpiperazine] (from 17% in the solvent control to 4%) and staurosporine (from 20% in the solvent control to 3%). These results show that stimulation of muscarinic acetylcholine receptors in synaptosomes increases [Ca2+]i by protein kinase-dependent activation of 1,4-dihydropyridine-sensitive calcium channels.
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Affiliation(s)
- F G Boess
- Department of Neuroscience, Institute of Psychiatry, DeCrespigny Park, London, England
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47
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Kim HS, Wei XY, Ruth P, Perez-Reyes E, Flockerzi V, Hofmann F, Birnbaumer L. Studies on the structural requirements for the activity of the skeletal muscle dihydropyridine receptor/slow Ca2+ channel. Allosteric regulation of dihydropyridine binding in the absence of alpha 2 and beta components of the purified protein complex. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38478-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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48
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Ahlijanian MK, Westenbroek RE, Catterall WA. Subunit structure and localization of dihydropyridine-sensitive calcium channels in mammalian brain, spinal cord, and retina. Neuron 1990; 4:819-32. [PMID: 2163262 DOI: 10.1016/0896-6273(90)90135-3] [Citation(s) in RCA: 232] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Monoclonal antibodies that recognize the alpha 2 delta subunits of calcium channels from skeletal muscle immunoprecipitate a complex of alpha 1, alpha 2 delta, beta, and gamma subunits. They also immunoprecipitate 64% of rabbit brain dihydropyridine-sensitive calcium channels. Iodination of partially purified brain calcium channels followed by immunoprecipitation reveals alpha 1-, alpha 2 delta-, and beta-like subunits that have apparent molecular masses of 175, 142, and 57 kd, respectively. A polypeptide of 100 kd is also specifically immunoprecipitated. Immunocytochemical studies identify dihydropyridine-sensitive calcium channels in neuronal somata and proximal dendrites in rat brain, spinal cord, and retina. Staining of many neuronal somata is uneven, revealing relatively high densities of dihydropyridine-sensitive calcium channels at the base of major dendrites. L-type calcium channels in this location may serve to mediate long-lasting increases in intracellular calcium in the cell body in response to excitatory inputs to the dendrites.
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Affiliation(s)
- M K Ahlijanian
- Department of Pharmacology, School of Medicine, University of Washington, Seattle 98195
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49
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Ervasti JM, Ohlendieck K, Kahl SD, Gaver MG, Campbell KP. Deficiency of a glycoprotein component of the dystrophin complex in dystrophic muscle. Nature 1990; 345:315-9. [PMID: 2188135 DOI: 10.1038/345315a0] [Citation(s) in RCA: 739] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Dystrophin, the protein encoded by the Duchenne muscular dystrophy (DMD) gene, exists in a large oligomeric complex. We show here that four glycoproteins are integral components of the dystrophin complex and that the concentration of one of these is greatly reduced in DMD patients. Thus, the absence of dystrophin may lead to the loss of a dystrophin-associated glycoprotein, and the reduction in this glycoprotein may be one of the first stages of the molecular pathogenesis of muscular dystrophy.
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Affiliation(s)
- J M Ervasti
- Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City 52242
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50
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Jay SD, Ellis SB, McCue AF, Williams ME, Vedvick TS, Harpold MM, Campbell KP. Primary structure of the gamma subunit of the DHP-sensitive calcium channel from skeletal muscle. Science 1990; 248:490-2. [PMID: 2158672 DOI: 10.1126/science.2158672] [Citation(s) in RCA: 219] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Affinity-purified, polyclonal antibodies to the gamma subunit of the dihydropyridine (DHP)-sensitive, voltage-dependent calcium channel have been used to isolate complementary DNAs to the rabbit skeletal muscle protein from an expression library. The deduced primary structure indicates that the gamma subunit is a 25,058-dalton protein that contains four transmembrane domains and two N-linked glycosylation sites, consistent with biochemical analyses showing that the gamma subunit is a glycosylated hydrophobic protein. Nucleic acid hybridization studies indicate that there is a 1200-nucleotide transcript in skeletal muscle but not in brain or heart. The gamma subunit may play a role in assembly, modulation, or the structure of the skeletal muscle calcium channel.
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Affiliation(s)
- S D Jay
- Howard Hughes Medical Institute, University of Iowa College of Medicine, Iowa City 52242
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