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Xie D, Deng T, Zhai Z, Sun T, Xu Y. The cellular model for Alzheimer's disease research: PC12 cells. Front Mol Neurosci 2023; 15:1016559. [PMID: 36683856 PMCID: PMC9846650 DOI: 10.3389/fnmol.2022.1016559] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 12/08/2022] [Indexed: 01/06/2023] Open
Abstract
Alzheimer's disease (AD) is a common age-related neurodegenerative disease characterized by progressive cognitive decline and irreversible memory impairment. Currently, several studies have failed to fully elucidate AD's cellular and molecular mechanisms. For this purpose, research on related cellular models may propose potential predictive models for the drug development of AD. Therefore, many cells characterized by neuronal properties are widely used to mimic the pathological process of AD, such as PC12, SH-SY5Y, and N2a, especially the PC12 pheochromocytoma cell line. Thus, this review covers the most systematic essay that used PC12 cells to study AD. We depict the cellular source, culture condition, differentiation methods, transfection methods, drugs inducing AD, general approaches (evaluation methods and metrics), and in vitro cellular models used in parallel with PC12 cells.
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Affiliation(s)
- Danni Xie
- State Key Laboratory of Southwestern Chinese Medicine Resources, School of Pharmacy, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Ting Deng
- State Key Laboratory of Southwestern Chinese Medicine Resources, School of Pharmacy, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Zhenwei Zhai
- School of Medical Information Engineering, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Tao Sun
- State Key Laboratory of Southwestern Chinese Medicine Resources, School of Pharmacy, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- School of Medical Information Engineering, Chengdu University of Traditional Chinese Medicine, Chengdu, China
| | - Ying Xu
- TCM Regulating Metabolic Diseases Key Laboratory of Sichuan Province, Hospital of Chengdu University of Traditional Chinese Medicine, Chengdu, China
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Kato S, Nishizawa K, Kobayashi K. Thalamostriatal System Controls the Acquisition, Performance, and Flexibility of Learning Behavior. Front Syst Neurosci 2021; 15:729389. [PMID: 34733142 PMCID: PMC8558393 DOI: 10.3389/fnsys.2021.729389] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Accepted: 09/29/2021] [Indexed: 11/16/2022] Open
Abstract
The dorsal striatum (DS) is a key structure of the basal ganglia circuitry, which regulates various types of learning processes and flexible switching of behavior. Intralaminar thalamic nuclei (ILNs) provide the main source of thalamostriatal inputs to the DS and constitute multiple nuclear groups, each of which innervates specific subdivisions of the striatum. Although the anatomical and electrophysiological properties of thalamostriatal neurons have been previously characterized, the behavioral and physiological functions of these neurons remain unclarified. Two representative thalamostriatal cell groups in the parafascicular nucleus (PF) and the central lateral nucleus (CL) are located in the caudal and rostral regions of the ILNs in rodents. Recently, the behavioral roles of these thalamostriatal cell groups have been investigated by the use of genetic and pharmacological manipulation techniques. In the current review, we summarize behavioral studies on thalamostriatal neurons, showing the key roles of these neurons in different learning processes, such as the acquisition, performance, and flexibility of behavior.
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Affiliation(s)
- Shigeki Kato
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima, Japan
| | - Kayo Nishizawa
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima, Japan
| | - Kazuto Kobayashi
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima, Japan
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Kato S, Fukabori R, Nishizawa K, Okada K, Yoshioka N, Sugawara M, Maejima Y, Shimomura K, Okamoto M, Eifuku S, Kobayashi K. Action Selection and Flexible Switching Controlled by the Intralaminar Thalamic Neurons. Cell Rep 2019; 22:2370-2382. [PMID: 29490273 DOI: 10.1016/j.celrep.2018.02.016] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Revised: 09/19/2017] [Accepted: 02/02/2018] [Indexed: 01/01/2023] Open
Abstract
Learning processes contributing to appropriate selection and flexible switching of behaviors are mediated through the dorsal striatum, a key structure of the basal ganglia circuit. The major inputs to striatal subdivisions are provided from the intralaminar thalamic nuclei, including the central lateral nucleus (CL) and parafascicular nucleus (PF). Thalamostriatal neurons in the PF modulate the acquisition and performance of stimulus-response learning. Here, we address the roles of the CL thalamostriatal neurons in learning processes by using a selective neural pathway targeting technique. We show that the CL neurons are essential for the performance of stimulus-response learning and for behavioral flexibility, including reversal and attentional set-shifting of learned responses. In addition, chemogenetic suppression of neural activity supports the requirements of these neurons for behavioral flexibility. Our results suggest that the main contribution of the CL thalamostriatal neurons is functional control of the basal ganglia circuit linked to the prefrontal cortex.
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Affiliation(s)
- Shigeki Kato
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Ryoji Fukabori
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Kayo Nishizawa
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Kana Okada
- Department of Neurophysiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan
| | - Nozomu Yoshioka
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Masateru Sugawara
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Yuko Maejima
- Department of Pharmacology, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Kenju Shimomura
- Department of Pharmacology, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Masahiro Okamoto
- Department of Systems Neuroscience, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Satoshi Eifuku
- Department of Systems Neuroscience, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
| | - Kazuto Kobayashi
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.
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Selective Membrane Redistribution and Depletion of Gαq-Protein by Pasteurella multocida Toxin. Toxins (Basel) 2016; 8:toxins8080233. [PMID: 27490568 PMCID: PMC4999849 DOI: 10.3390/toxins8080233] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 07/22/2016] [Accepted: 07/25/2016] [Indexed: 02/03/2023] Open
Abstract
Pasteurella multocida toxin (PMT), the major virulence factor responsible for zoonotic atrophic rhinitis, is a protein deamidase that activates the alpha subunit of heterotrimeric G proteins. Initial activation of G alpha-q-coupled phospholipase C-beta-1 signaling by PMT is followed by uncoupling of G alpha-q-dependent signaling, causing downregulation of downstream calcium and mitogenic signaling pathways. Here, we show that PMT decreases endogenous and exogenously expressed G alpha-q protein content in host cell plasma membranes and in detergent resistant membrane (DRM) fractions. This membrane depletion of G alpha-q protein was dependent upon the catalytic activity of PMT. Results indicate that PMT-modified G alpha-q redistributes within the host cell membrane from the DRM fraction into the soluble membrane and cytosolic fractions. In contrast, PMT had no affect on G alpha-s or G beta protein levels, which are not substrate targets of PMT. PMT also had no affect on G alpha-11 levels, even though G alpha-11 can serve as a substrate for deamidation by PMT, suggesting that membrane depletion of PMT-modified G-alpha-q has specificity.
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Carruthers SP, Gurvich CT, Rossell SL. The muscarinic system, cognition and schizophrenia. Neurosci Biobehav Rev 2015; 55:393-402. [PMID: 26003527 DOI: 10.1016/j.neubiorev.2015.05.011] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 04/21/2015] [Accepted: 05/12/2015] [Indexed: 12/26/2022]
Abstract
An increasing body of evidence has implicated the central muscarinic system as contributing to a number of symptoms of schizophrenia and serving as a potential target for pharmaceutical interventions. A theoretical review is presented that focuses on the central muscarinic system's contribution to the cognitive symptoms of schizophrenia. The aim is to bridge the void between pertinent neuropsychological and neurobiological research to provide an explanatory account of the role that the central muscarinic system plays in the symptoms of schizophrenia. First, there will be a brief overview of the relevant neuropsychological schizophrenia literature, followed by a concise introduction to the central muscarinic system. Subsequently, we will draw from animal, neuropsychological and pharmacological literature, and discuss the findings in relation to cognition, schizophrenia and the muscarinic system. Whilst unifying the multiple domains of research into a concise review will act as a useful line of enquiry into the central muscarinic systems contribution to the symptoms of schizophrenia, it will be made apparent that more research is needed in this field.
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Affiliation(s)
- Sean P Carruthers
- Brain and Psychological Sciences Research Centre (BPsyC), Faculty of Health, Arts, Design, Swinburne University of Technology, Melbourne 3122, VIC, Australia; Monash Alfred Psychiatry Research Centre (MAPrc), Monash University Central Clinical School and The Alfred Hospital, Melbourne 3004, VIC, Australia.
| | - Caroline T Gurvich
- Monash Alfred Psychiatry Research Centre (MAPrc), Monash University Central Clinical School and The Alfred Hospital, Melbourne 3004, VIC, Australia
| | - Susan L Rossell
- Brain and Psychological Sciences Research Centre (BPsyC), Faculty of Health, Arts, Design, Swinburne University of Technology, Melbourne 3122, VIC, Australia; Monash Alfred Psychiatry Research Centre (MAPrc), Monash University Central Clinical School and The Alfred Hospital, Melbourne 3004, VIC, Australia; Psychiatry, St Vincent's Hospital, Melbourne 3065, VIC, Australia
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Hammond GRV, Fischer MJ, Anderson KE, Holdich J, Koteci A, Balla T, Irvine RF. PI4P and PI(4,5)P2 are essential but independent lipid determinants of membrane identity. Science 2012; 337:727-30. [PMID: 22722250 PMCID: PMC3646512 DOI: 10.1126/science.1222483] [Citation(s) in RCA: 354] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The quantitatively minor phospholipid phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P(2)] fulfills many cellular functions in the plasma membrane (PM), whereas its synthetic precursor, phosphatidylinositol 4-phosphate (PI4P), has no assigned PM roles apart from PI(4,5)P(2) synthesis. We used a combination of pharmacological and chemical genetic approaches to probe the function of PM PI4P, most of which was not required for the synthesis or functions of PI(4,5)P(2). However, depletion of both lipids was required to prevent PM targeting of proteins that interact with acidic lipids or activation of the transient receptor potential vanilloid 1 cation channel. Therefore, PI4P contributes to the pool of polyanionic lipids that define plasma membrane identity and to some functions previously attributed specifically to PI(4,5)P(2), which may be fulfilled by a more general polyanionic lipid requirement.
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Affiliation(s)
- Gerald R. V. Hammond
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, U.K
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, NICHD, National Institutes of Health, Bethesda, MD 20892, USA
| | - Michael J Fischer
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, U.K
| | - Karen E Anderson
- Inositide Laboratory, Babraham Institute, Babraham Research Campus, Cambridge, CB22 3AT, UK
| | - Jon Holdich
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, U.K
| | - Ardita Koteci
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, U.K
| | - Tamas Balla
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, NICHD, National Institutes of Health, Bethesda, MD 20892, USA
| | - Robin F. Irvine
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, U.K
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Telezhkin V, Brown DA, Gibb AJ. Distinct subunit contributions to the activation of M-type potassium channels by PI(4,5)P2. ACTA ACUST UNITED AC 2012; 140:41-53. [PMID: 22689829 PMCID: PMC3382723 DOI: 10.1085/jgp.201210796] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Low-threshold voltage-gated M-type potassium channels (M channels) are tetraheteromers, commonly of two Kv7.2 and two Kv7.3 subunits. Though gated by voltage, the channels have an absolute requirement for binding of the membrane phospholipid phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)) to open. We have investigated the quantitative relation between the concentration of a water-soluble PI(4,5)P(2) analog, dioctanoyl-PI(4,5)P(2) (DiC(8)-PI(4,5)P(2)), and channel open probability (P(open)) by fast application of increasing concentrations of DiC(8)-PI(4,5)P(2) to the inside face of membrane patches excised from Chinese hamster ovary cells expressing M channels as heteromeric Kv7.2/7.3 subunits. The rationale for the experiments is that this will mimic the effect of changes in membrane PI(4,5)P(2) concentration. Single-channel conductances from channel current-voltage relations in cell-attached mode were 9.2 ± 0.1 pS with a 2.5-mM pipette [K(+)]. Plots of P(open) against DiC(8)-PI(4,5)P(2) concentration were best fitted using a two-component concentration-P(open) relationship with high and low affinity, half-maximal effective concentration (EC(50)) values of 1.3 ± 0.14 and 75.5 ± 2.5 µM, respectively, and Hill slopes of 1.4 ± 0.06. In contrast, homomeric channels from cells expressing only Kv7.2 or Kv7.3 constructs yielded single-component curves with EC(50) values of 76.2 ± 19.9 or 3.6 ± 1.0 µM, respectively. When wild-type (WT) Kv7.2 was coexpressed with a mutated Kv7.3 subunit with >100-fold reduced sensitivity to PI(4,5)P(2), the high-affinity component of the activation curve was lost. Fitting the data for WT and mutant channels to an activation mechanism with independent PI(4,5)P(2) binding to two Kv7.2 and two Kv7.3 subunits suggests that the two components of the M-channel activation curve correspond to the interaction of PI(4,5)P(2) with the Kv7.3 and Kv7.2 subunits, respectively, that channels can open when only the two Kv7.3 subunits have bound DiC(8)-PI(4,5)P(2), and that maximum channel opening requires binding to all four subunits.
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Affiliation(s)
- Vsevolod Telezhkin
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London, WC1E 6BT, England, UK
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Ujcikova H, Dlouha K, Roubalova L, Vosahlikova M, Kagan D, Svoboda P. Up-regulation of adenylylcyclases I and II induced by long-term adaptation of rats to morphine fades away 20days after morphine withdrawal. Biochim Biophys Acta Gen Subj 2011; 1810:1220-9. [DOI: 10.1016/j.bbagen.2011.09.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 09/12/2011] [Accepted: 09/27/2011] [Indexed: 02/04/2023]
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Estes AM, McAllen K, Parker MS, Sah R, Sweatman T, Park EA, Balasubramaniam A, Sallee FR, Walker MW, Parker SL. Maintenance of Y receptor dimers in epithelial cells depends on interaction with G-protein heterotrimers. Amino Acids 2010; 40:371-80. [DOI: 10.1007/s00726-010-0642-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Accepted: 05/25/2010] [Indexed: 12/01/2022]
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Newell KA, Zavitsanou K, Huang XF. Opposing short- and long-term effects on muscarinic M1/4 receptor binding following chronic phencyclidine treatment. J Neurosci Res 2007; 85:1358-63. [PMID: 17342780 DOI: 10.1002/jnr.21247] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Phencyclidine (PCP) is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. Several studies have demonstrated that chronic NMDA receptor antagonist treatment in humans and animals can cause long-term behavioral changes that are reminiscent of negative and cognitive schizophrenia-like symptoms. The muscarinic cholinergic system, which is associated with cognitive functions, has been hypothesized to contribute to PCP's mechanism of action. No study, however, has examined the status of M1/4 receptors in the PCP model of schizophrenia. The aim of the present study was to investigate the effects of chronic (14 day) PCP treatment on mouse brain M1/4 receptors in the short term (1 hr and 24 hr) and long term (14 days) after last PCP administration. [(3)H]pirenzepine was used to target M1/4 receptors. In the short term following chronic PCP treatment, M1/4 binding was significantly increased in regions of the limbic system, caudate-putamen, cortex, and thalamus (ranging from 56% to 368%), compared with saline-treated mice. There were no differences in binding between mice treated with PCP for 14 days and sacrificed 1 hr or 24 hr after the final PCP treatment. In the long term following chronic PCP treatment, M1/4 binding was significantly decreased in all of the above-mentioned brain regions (ranging from 31% to 72%), except in the thalamus, which showed no change. These findings in the long-term group are similar to those reported in post-mortem studies of patients suffering from schizophrenia.
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Affiliation(s)
- Kelly A Newell
- School of Health Sciences, University of Wollongong, Wollongong, New South Wales, Australia.
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Moravcová Z, Rudajev V, Stöhr J, Novotný J, Cerný J, Parenti M, Milligan G, Svoboda P. Long-term agonist stimulation of IP prostanoid receptor depletes the cognate G(s)alpha protein in membrane domains but does not change the receptor level. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1691:51-65. [PMID: 15053924 DOI: 10.1016/j.bbamcr.2003.12.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2003] [Revised: 11/06/2003] [Accepted: 12/15/2003] [Indexed: 11/21/2022]
Abstract
Iloprost (IP) stimulation (1 microM, 2 h) of Flag-epitope-tagged human IP prostanoid receptor (FhIPR) expressed in HEK293 cells resulted in specific decrease of endogenous G(s)alpha protein in detergent-insensitive, caveolin-enriched, membrane domains (DIMs). Receptor protein FhIPR, caveolin, G(i)alpha and GPI-linked, domain markers CD55 and CD59 were unchanged. The same result was obtained in HEK293 cells expressing FhIPR-G(s)alpha fusion protein. The endogenous G(s)alpha decreased, but the level of Flag-hIPR-G(s)alpha protein did not change. The specific depletion of domain-bound pool of G(s)alpha as consequence of iloprost stimulation was also demonstrated in membrane domains prepared according to alkaline treatment plus sonication protocol (detergent-free procedure of Song et al.). Our data further indicated that in control, quiescent cells only a very small amount of IP prostanoid receptor was present in DIMs together with large amount of its cognate G(s)alpha protein. Expressed in quantitative terms, DIMs contained 30-40% of the total cellular amount of G proteins whereas the content of IP prostanoid receptors was 1-3%. The dominant portion (>95%) of FhIPR as well as FhIPR-G(s)alpha was localised in high-density area of the gradient containing detergent-solubilised proteins. FhIPR and FhIPR-G(s)alpha distribution was similar to that of transmembrane plasma membrane (PM) markers (CD147, MHCI, CD29, Tapa1, the alpha subunit of Na,K-ATPase, transmembrane form of CD58 and CD44). All these proteins are known to be fully solubilised by detergent and thus unable to float in density gradient. Our data indicate that (i) long-term agonist stimulation of IP prostanoid receptor is associated with preferential decrease of its cognate G protein G(s)alpha from membrane domains; receptor level is unchanged. (ii) Very small fraction (1-3%) of total cellular amount of receptors is recovered in DIMs together with roughly 40% of G proteins. These data suggest a "supra-stoichiometric" arrangement of G proteins and corresponding receptors in DIMs.
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Affiliation(s)
- Zuzana Moravcová
- Department of Physiology, Faculty of Natural Sciences, Charles University, Vinicna 7, 12000 Prague 2, Czech Republic
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Qian L, Wang Y, Xie J, Rose CM, Yang T, Nakamura T, Sandberg M, Zeng H, Schechter JE, Chow RH, Hamm-Alvarez SF, Mircheff AK. Biochemical changes contributing to functional quiescence in lacrimal gland acinar cells after chronic ex vivo exposure to a muscarinic agonist. Scand J Immunol 2003; 58:550-65. [PMID: 14629627 DOI: 10.1046/j.1365-3083.2003.01343.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Profound secretory dysfunction can be associated with relatively modest lymphocytic infiltration of the lacrimal and salivary glands of Sjögren's syndrome (SjS) patients. SjS patients' sera contain autoantibodies to M3 muscarinic acetylcholine receptors (MAChR) that have variously been reported to have agonistic and antagonistic effects. We sought to identify consequences of chronic agonist stimulation by maintaining acinar cells from rabbit lacrimal glands for 20 h in the presence or absence of 10 microM carbachol (CCh). Exposure to CCh diminished the cells' ability to elevate cytosolic Ca2+ and secrete beta-hexosaminidase in response to acute stimulation with 100 microM CCh, but it enhanced their secretory responses to phenylephrine and ionomycin. Secretory vesicles appeared normal by electron microscopy, but confocal fluorescence microscopy revealed depletion of the secretory vesicle membrane marker, rab3D, and decreased ability to recruit secretory transport vesicles in response to acute 100 microM CCh. Additionally, the apical cortical actin cytoskeleton was disrupted and diminished compared to the basal-lateral cortical network. Subcellular fractionation analyses revealed that total membrane phase protein content was increased. The contents of beta-hexosaminidase and MAChR relative to total protein were not significantly altered, and MAChR abundance in the plasma membrane fraction was increased as the result of redistribution from endomembrane pools. However, relative cellular contents of the heterotrimeric guanosine triphosphate (GTP)-binding proteins, Gq and G11, were decreased. Additional biochemical changes included decreased contents of 47 kDa Gs and Gi3, protein kinase Calpha and rab3D and polymeric immunoglobulin (Ig) receptors; internalization of Na,K-ATPase from the plasma membranes to endomembrane compartments and decreased content of beta-hexosaminidase in the lysosomes. The observations demonstrate that chronic exposure to a MAChR agonist induces refractoriness to optimal stimulation, without causing receptor downregulation, by downregulating postreceptor-signalling mediators and effectors. The cells' secretory mechanisms for IgA and electrolytes also appear to be impaired, as does their ability to properly sort proteins to the lysosomes.
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Affiliation(s)
- L Qian
- Department of Physiology and Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
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Abstract
Multiple mechanisms regulate the signaling of the five members of the family of the guanine nucleotide binding protein (G protein)-coupled muscarinic acetylcholine (ACh) receptors (mAChRs). Following activation by classical or allosteric agonists, mAChRs can be phosphorylated by a variety of receptor kinases and second messenger-regulated kinases. The phosphorylated mAChR subtypes can interact with beta-arrestin and presumably other adaptor proteins as well. As a result, the various mAChR signaling pathways may be differentially altered, leading to short-term or long-term desensitization of a particular signaling pathway, receptor-mediated activation of the mitogen-activated protein kinase pathway downstream of mAChR phosphorylation, as well as long-term potentiation of mAChR-mediated phospholipase C stimulation. Agonist activation of mAChRs may also induce receptor internalization and down-regulation, which proceed in a highly regulated manner, depending on receptor subtype and cell type. In this review, our current understanding of the complex regulatory processes that underlie signaling of mAChR is summarized.
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Affiliation(s)
- Chris J van Koppen
- Institut für Pharmakologie, Universitätsklinikum Essen, Hufelandstrasse 55, D-45122, Essen, Germany.
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Novotny J, Hrbasová M, Kolár F, Svoboda P. Cardiomegaly induced by pressure overload in newborn rats is accompanied by altered expression of the long isoform of G(s)alpha protein and deranged signaling of adenylyl cyclase. Mol Cell Biochem 2003; 245:157-66. [PMID: 12708755 DOI: 10.1023/a:1022828430565] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
G proteins-coupled signaling pathways appear to play a role in the development of cardiac hypertrophy and its progression to heart failure. The present study aimed to investigate trimeric G proteins and adenylyl cyclase signaling in immature as well as in adult rat myocardium during this process caused by pressure overload. Pressure overload was induced in newborn (2-day-old) rats by abdominal aortic banding and myocardial preparations from left ventricular myocardium of immature (10-day-old) and adult (90-day-old) animals were analyzed for the relative content of different G protein subunits and adenylyl cyclase (AC) by immunoblotting with specific antibodies. A functional status of the AC signaling system was also evaluated. Normal maturation of rat heart was accompanied by increased expression of AC type V/VI and VII and of the long isoform (G(s)alphaL) of G(s)alpha protein. In parallel, the amounts of myocardial G(i)alpha/G(o)alpha proteins tended to decrease, and G(q)alpha/G(11)alpha and Gbeta did not change. Interestingly, whereas fluoride-stimulated AC activity increased in the course of maturation, activity of AC measured under other experimental conditions (stimulation by Mn2+, forskolin or isoproterenol) was lower in adult than in young rat myocardium. Pressure overload did not influence distribution of G proteins in immature myocardium, but considerably decreased the content of G(s)alphaL and increased G(o)alpha proteins in hearts of 90-day-old rats. These hearts exhibited worsened functional reserve as compared to age-matched controls and activity of AC was also markedly lower. A considerable reduction in Mn(2+)-stimulated AC activity together with similar decrease in AC activity determined under other stimulation conditions suggests that it is a function of AC catalytic subunit that is primarily impaired in this model of pressure overload.
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Affiliation(s)
- Jiri Novotny
- Department of Physiology and Developmental Biology, Faculty of Natural Sciences, Charles University, Prague, Czech Republic.
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15
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Novotny J, Bourová L, Kolár F, Svoboda P. Membrane-Bound and cytosolic forms of heterotrimeric G proteins in young and adult rat myocardium: influence of neonatal hypo- and hyperthyroidism. J Cell Biochem 2002; 82:215-24. [PMID: 11527147 DOI: 10.1002/jcb.1157] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Membrane and cytosolic fractions prepared from ventricular myocardium of young (21-day-old) hypo- or hyperthyroid rats and adult (84-day-old) previously hypo- or hyperthyroid rats were analyzed by immunoblotting with specific anti-G-protein antibodies for the relative content of Gs alpha, Gi alpha/Go alpha, Gq alpha/G11 alpha, and G beta. All tested G protein subunits were present not only in myocardial membranes but were at least partially distributed in the cytosol, except for Go alpha2, and G11 alpha. Cytosolic forms of the individual G proteins represented about 5-60% of total cellular amounts of these proteins. The long (Gs alpha-L) isoform of Gs alpha prevailed over the short (Gs alpha-S) isoform in both crude myocardial membranes and cytosol. The Gs alpha-L/Gs alpha-S ratio in membranes as well as in cytosol increased during maturation due to a substantial increase in Gs alpha-L. Interestingly, whereas the amount of membrane-bound Gi alpha/Go alpha and Gq alpha/G11 alpha proteins tend to lower during postnatal development, cytosolic forms of these G proteins mostly rise. Neonatal hypothyroidism reduced the amount of myocardial Gs alpha and increased that of Gi alpha/Go alpha proteins. By contrast, neonatal hyperthyroidism increased expression of Gs alpha and decreased that of Gi alpha and G11 alpha in young myocardium. Changes in G protein content induced by neonatal hypo- and hyperthyroidism in young rat myocardium were restored in adulthood. Alterations in the membrane-cytosol balance of G protein subunits associated with maturation or induced by altered thyroid status indicate physiological importance of cytosolic forms of these proteins in the rat myocardium.
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Affiliation(s)
- J Novotny
- Institute of Physiology, Academy of Sciences of the Czech Republic, Prague
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16
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Ihnatovych I, Novotny J, Haugvicova R, Bourova L, Mares P, Svoboda P. Opposing changes of trimeric G protein levels during ontogenetic development of rat brain. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2002; 133:57-67. [PMID: 11850064 DOI: 10.1016/s0165-3806(01)00322-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Developmental changes in the distribution of guanine nucleotide-binding regulatory proteins (G proteins) were investigated in the rat brain during postnatal development. Using a standard or high-resolution urea-SDS-PAGE and specific polyclonal antipeptide antibodies oriented against G(i)alpha1/G(i)alpha2, G(i)alpha3, G(s)alpha, G(o)alpha1/G(o)alpha2, G(q)alpha/G(11)alpha and Gbeta subunit, all these proteins were determined by quantitative immunoblotting in homogenates prepared from cortex, thalamus, hippocampus and pituitary of 1-, 7-, 12-, 18-, 25- and 90-day-old animals. The levels of the majority of G protein alpha subunits, namely G(i)alpha1, G(i)alpha2, G(i)alpha3, G(o)alpha1, G(o)alpha2, G(q)alpha, G(11)alpha and Gbeta, were high already at birth. Whereas the short variant of G(s)alpha, G(s)alphaS, rose sharply in all tested brain regions between postnatal day (PD) 1 and 90, the long variant of G(s)alpha, G(s)alphaL, was unchanged in cortex and thalamus and slightly increased in hippocampus. An increase was observed also in expression of G(i)alpha1/G(i)alpha2 and G(o)alpha1 protein, while G(o)alpha2 remained constant. Minority protein G(o)alpha* dramatically increased in cortex and thalamus, was unchanged in hippocampus and not detectable in pituitary. By contrast, the highest levels of G(i)alpha3 and G(q)alpha/G(11)alpha were detected as early as at PD 1. During the next 90 days, the immunological signal of G(i)alpha3 almost disappeared and G(q)alpha/G(11)alpha continuously declined to the levels corresponding to 50% of the levels determined at birth. Expression of Gbeta subunit was basically unchanged during postnatal development. Our present analysis indicates that G(s)alpha, G(i)alpha/G(o)alpha and G(q)alpha/G(11)alpha proteins are differently expressed in the course of brain development. Differential expression of the individual alpha subunits of trimeric G proteins during postnatal development suggests their different roles in maturation of the brain tissue.
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Affiliation(s)
- Ivanna Ihnatovych
- Department of Developmental Epileptology, Institute of Physiology, Academy of Sciences, Videnska 1083, 142 20 Prague 4, Czech Republic
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17
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Activation of expressed KCNQ potassium currents and native neuronal M-type potassium currents by the anti-convulsant drug retigabine. J Neurosci 2001. [PMID: 11466425 DOI: 10.1523/jneurosci.21-15-05535.2001] [Citation(s) in RCA: 309] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Retigabine [D-23129; N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester] is a novel anticonvulsant compound that is now in clinical phase II development. It has previously been shown to enhance currents generated by KCNQ2/3 K(+) channels when expressed in Chinese hamster ovary (CHO) cells (Main et al., 2000; Wickenden et al., 2000). In the present study, we have compared the actions of retigabine on KCNQ2/3 currents with those on currents generated by other members of the KCNQ family (homomeric KCNQ1, KCNQ2, KCNQ3, and KCNQ4 channels) expressed in CHO cells and on the native M current in rat sympathetic neurons [thought to be generated by KCNQ2/3 channels (Wang et al., 1998)]. Retigabine produced a hyperpolarizing shift of the activation curves for KCNQ2/3, KCNQ2, KCNQ3, and KCNQ4 currents with differential potencies in the following order: KCNQ3 > KCNQ2/3 > KCNQ2 > KCNQ4, as measured either by the maximum hyperpolarizing shift in the activation curves or by the EC(50) values. In contrast, retigabine did not enhance cardiac KCNQ1 currents. Retigabine also produced a hyperpolarizing shift in the activation curve for native M channels in rat sympathetic neurons. The retigabine-induced current was inhibited by muscarinic receptor stimulation, with similar agonist potency but 25% reduced maximum effect. In unclamped neurons, retigabine produced a hyperpolarization and reduced the number of action potentials produced by depolarizing current injections, without change in action potential configuration.
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18
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Tatulian L, Delmas P, Abogadie FC, Brown DA. Activation of expressed KCNQ potassium currents and native neuronal M-type potassium currents by the anti-convulsant drug retigabine. J Neurosci 2001; 21:5535-45. [PMID: 11466425 PMCID: PMC6762632] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2001] [Revised: 05/11/2001] [Accepted: 05/14/2001] [Indexed: 02/20/2023] Open
Abstract
Retigabine [D-23129; N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester] is a novel anticonvulsant compound that is now in clinical phase II development. It has previously been shown to enhance currents generated by KCNQ2/3 K(+) channels when expressed in Chinese hamster ovary (CHO) cells (Main et al., 2000; Wickenden et al., 2000). In the present study, we have compared the actions of retigabine on KCNQ2/3 currents with those on currents generated by other members of the KCNQ family (homomeric KCNQ1, KCNQ2, KCNQ3, and KCNQ4 channels) expressed in CHO cells and on the native M current in rat sympathetic neurons [thought to be generated by KCNQ2/3 channels (Wang et al., 1998)]. Retigabine produced a hyperpolarizing shift of the activation curves for KCNQ2/3, KCNQ2, KCNQ3, and KCNQ4 currents with differential potencies in the following order: KCNQ3 > KCNQ2/3 > KCNQ2 > KCNQ4, as measured either by the maximum hyperpolarizing shift in the activation curves or by the EC(50) values. In contrast, retigabine did not enhance cardiac KCNQ1 currents. Retigabine also produced a hyperpolarizing shift in the activation curve for native M channels in rat sympathetic neurons. The retigabine-induced current was inhibited by muscarinic receptor stimulation, with similar agonist potency but 25% reduced maximum effect. In unclamped neurons, retigabine produced a hyperpolarization and reduced the number of action potentials produced by depolarizing current injections, without change in action potential configuration.
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Affiliation(s)
- L Tatulian
- Department of Pharmacology and Wellcome Laboratory for Molecular Pharmacology, University College London, London WC1E 6BT, United Kingdom
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19
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Pan Z, Selyanko AA, Hadley JK, Brown DA, Dixon JE, McKinnon D. Alternative splicing of KCNQ2 potassium channel transcripts contributes to the functional diversity of M-currents. J Physiol 2001; 531:347-58. [PMID: 11230508 PMCID: PMC2278468 DOI: 10.1111/j.1469-7793.2001.0347i.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The region of alternative splicing in the KCNQ2 potassium channel gene was determined by RNase protection analysis of KCNQ2 mRNA transcripts. Systematic analysis of KCNQ2 alternative splice variant expression in rat superior cervical ganglia revealed multiple variant isoforms. One class of KCNQ2 splice variants, those that contained exon 15a, was found to have significantly different kinetics to those of the other isoforms. These transcripts encoded channel subunits that, when co-expressed with the KCNQ3 subunit, activated and deactivated approximately 2.5 times more slowly than other isoforms. Deletion of exon 15a in these isoforms produced a reversion to the faster kinetics. Comparison of the kinetic properties of the cloned channel splice variants with those of the native M-current suggests that alternative splicing of the KCNQ2 gene may contribute to the variation in M-current kinetics seen in vivo.
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Affiliation(s)
- Z Pan
- Department of Neurobiology and Behavior and Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
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20
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Steingart RA, Silverman WF, Barron S, Slotkin TA, Awad Y, Yanai J. Neural grafting reverses prenatal drug-induced alterations in hippocampal PKC and related behavioral deficits. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2000; 125:9-19. [PMID: 11154756 DOI: 10.1016/s0165-3806(00)00123-1] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Administration of heroin or phenobarbital to pregnant mice evokes neurochemical and behavioral deficits consequent to disruption of septohippocampal cholinergic innervation. The present study evaluates the relationship between the drug-induced biochemical changes and the behavioral deficits, applying two different approaches: neural grafting and within-individual correlations of biochemistry and behavior. Mice were exposed transplacentally to phenobarbital or heroin on gestational days 9-18 and tested in adulthood. Drug-exposed mice displayed impaired radial arm maze performance, increases in presynaptic choline transporter sites (monitored with [(3)H]hemicholinium-3 binding), upregulation of membrane-associated protein kinase C (PKC) activity, and desensitization of the PKC response to a cholinergic agonist, carbachol. Grafting of cholinergic cells to the impaired hippocampus reversed the behavioral deficits nearly completely and restored basal PKC activity and the PKC response to carbachol to normal; the drug effects on hemicholinium-3 binding were also slightly obtunded by neural grafting, but nevertheless remained significantly elevated. There were significant correlations between the performance in the eight-arm maze and both basal PKC activity and PKC desensitization, and to a lesser extent, between behavioral performance and hemicholinium-3 binding. Taken together, these findings indicate an inextricable link between the biochemical effects of prenatal drug exposure on the PKC signaling cascade and adverse behavioral outcomes. The ability of neural grafting to reverse both the drug-induced changes in PKC and behaviors linked to septohippocampal cholinergic function suggest a mechanistic link between this signaling pathway and neurobehavioral teratology caused by heroin or phenobarbital.
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Affiliation(s)
- R A Steingart
- The Ross Laboratory for Studies in Neural Birth Defects, Department of Anatomy and Cell Biology, The Hebrew University-Hadassah Medical School, Box 12272, 91010, Jerusalem, Israel
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21
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Bourová L, Pesanová Z, Novotný J, Bengtsson T, Svoboda P. Differentiation of cultured brown adipocytes is associated with a selective increase in the short variant of g(s)alpha protein. Evidence for higher functional activity of g(s)alphaS. Mol Cell Endocrinol 2000; 167:23-31. [PMID: 11000517 DOI: 10.1016/s0303-7207(00)00303-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In order to examine whether the differentiation process in brown adipocytes cultivated in primary culture is associated with substantial alterations in the complement of G proteins, the levels of these proteins were investigated with immuno-electrophoretic techniques in membrane preparations from proliferating and differentiated cultured mouse brown adipocytes. We observed that differentiation was associated with a dramatic (more than threefold) increase in the short variant of G(s)alpha protein (G(s)alphaS). The long variant of G(s)alpha (G(s)alphaL), as well as G(i)1alpha, G(i)2alpha, G(q)alpha, G(11)alpha and Gbeta subunit proteins remained unchanged whereas G(i)3alpha protein was decreased. These changes were accompanied by marked increase in isoprenaline-, forskolin- as well as manganese-stimulated adenylyl cyclase. Thus, the marked increase in beta-adrenergic responsiveness of fully differentiated confluent brown adipocytes (day 8-9), as compared with that of proliferating undifferentiated cells of 'fibroblast phenotype' (day 3-4), is associated with a significant increase in the relative proportion between the short and long variants of G(s)alpha (the G(s)alphaS/G(s)alphaL ratio) along with a decrease in G(i)3alpha protein. These data also suggest that the short variant of G(s)alpha exhibits higher functional activity than the long variant of this G protein.
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Affiliation(s)
- L Bourová
- Institute of Physiology, Czech Academy of Sciences, Videánská 1083, 142 20 4, Prague, Czech Republic
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22
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Steingart RA, Abu-Roumi M, Newman ME, Silverman WF, Slotkin TA, Yanai J. Neurobehavioral damage to cholinergic systems caused by prenatal exposure to heroin or phenobarbital: cellular mechanisms and the reversal of deficits by neural grafts. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2000; 122:125-33. [PMID: 10960681 DOI: 10.1016/s0165-3806(00)00063-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Despite the basic differences in their underlying biological targets, prenatal exposure to heroin or phenobarbital produces similar syndromes of neurobehavioral deficits, involving defects in septohippocampal cholinergic innervation-related behaviors. At the cellular level, these deficits are associated with cholinergic hyperactivity, characterized by increased concentrations of muscarinic receptors and enhanced second messenger activity linked to the receptors. In the present study, we determined whether the cellular changes are mechanistically linked to altered behavior, using two different approaches: neural grafting and correlations between behavior and biochemistry within the same individual animals. Mice were exposed transplacentally to phenobarbital or heroin on gestation days 9-18 and, as adults, received fetal cholinergic grafts or were sham-operated. Prenatal drug exposure resulted in deficits in behavioral performance tested in the eight-arm radial maze, accompanied by increases in hippocampal M(1)-muscarinic receptor expression and muscarinic receptor-mediated IP formation. Neural grafting reversed both the behavioral deficits and the muscarinic hyperactivity. In the drug-exposed offspring, there was a significant correlation between maze performance and carbachol-induced inositol phosphate (IP) formation. These studies indicate that deficits of cholinergic function underlie the neurobehavioral deficits seen in the hippocampus of animals exposed prenatally to heroin or phenobarbital, and consequently that the observed cholinergic hyperactivity is an unsuccessful attempt to compensate for the loss of cholinergic function. The fact that the damage can be reversed by neural grafting opens up novel approaches to the restoration of brain function after prenatal insults.
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Affiliation(s)
- R A Steingart
- The Ross Laboratory for Studies in Neural Birth Defects, Department of Anatomy and Cell Biology, The Hebrew University-Hadassah Medical School, Box 12272, 91120 Jerusalem, Israel
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23
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Hadley JK, Noda M, Selyanko AA, Wood IC, Abogadie FC, Brown DA. Differential tetraethylammonium sensitivity of KCNQ1-4 potassium channels. Br J Pharmacol 2000; 129:413-5. [PMID: 10711337 PMCID: PMC1571869 DOI: 10.1038/sj.bjp.0703086] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
In Shaker-group potassium channels the presence of a tyrosine residue, just downstream of the pore signature sequence GYG, determines sensitivity to tetraethylammonium (TEA). The KCNQ family of channels has a variety of amino acid residues in the equivalent position. We studied the effect of TEA on currents generated by KCNQ homomers and heteromers expressed in CHO cells. We used wild-type KCNQ1-4 channels and heteromeric KCNQ2/3 channels incorporating either wild-type KCNQ3 subunits or a mutated KCNQ3 in which tyrosine replaced threonine at position 323 (mutant T323Y). IC50 values were (mM): KCNQ1, 5.0; KCNQ2, 0.3; KCNQ3, > 30; KCNQ4, 3.0; KCNQ2 + KCNQ3, 3.8; and KCNQ2 + KCNQ3(T323Y), 0.5. While the high TEA sensitivity of KCNQ2 may be conferred by a tyrosine residue lacking in the other channels, the intermediate TEA sensitivity of KCNQ1 and KCNQ4 implies that other residues are also important in determining TEA block of the KCNQ channels.
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Affiliation(s)
- J K Hadley
- Department of Pharmacology, University College London.
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24
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Selyanko AA, Hadley JK, Wood IC, Abogadie FC, Jentsch TJ, Brown DA. Inhibition of KCNQ1-4 potassium channels expressed in mammalian cells via M1 muscarinic acetylcholine receptors. J Physiol 2000; 522 Pt 3:349-55. [PMID: 10713961 PMCID: PMC2269765 DOI: 10.1111/j.1469-7793.2000.t01-2-00349.x] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. KCNQ1-4 potassium channels were expressed in mammalian Chinese hamster ovary (CHO) cells stably transfected with M1 muscarinic acetylcholine receptors and currents were recorded using the whole-cell perforated patch technique and cell-attached patch recording. 2. Stimulation of M1 receptors by 10 microM oxotremorine-M (Oxo-M) strongly reduced (to 0-10%) currents produced by KCNQ1-4 subunits expressed individually and also those produced by KCNQ2 + KCNQ3 and KCNQ1 + KCNE1 heteromers, which are thought to generate neuronal M-currents (IK,M) and cardiac slow delayed rectifier currents (IK,s), respectively. 3. The activity of KCNQ2 + KCNQ3, KCNQ2 and KCNQ3 channels recorded with cell-attached pipettes was strongly and reversibly reduced by Oxo-M applied to the extra-patch membrane. 4. It is concluded that M1 receptors couple to all known KCNQ subunits and that inhibition of KCNQ2 + KCNQ3 channels, like that of native M-channels, requires a diffusible second messenger.
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Affiliation(s)
- A A Selyanko
- Department of Pharmacology, University College London, UK.
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25
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Two types of K(+) channel subunit, Erg1 and KCNQ2/3, contribute to the M-like current in a mammalian neuronal cell. J Neurosci 1999. [PMID: 10479678 DOI: 10.1523/jneurosci.19-18-07742.1999] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The potassium M current was originally identified in sympathetic ganglion cells, and analogous currents have been reported in some central neurons and also in some neural cell lines. It has recently been suggested that the M channel in sympathetic neurons comprises a heteromultimer of KCNQ2 and KCNQ3 (Wang et al., 1998) but it is unclear whether all other M-like currents are generated by these channels. Here we report that the M-like current previously described in NG108-15 mouse neuroblastoma x rat glioma cells has two components, "fast" and "slow", that may be differentiated kinetically and pharmacologically. We provide evidence from PCR analysis and expression studies to indicate that these two components are mediated by two distinct molecular species of K(+) channel: the fast component resembles that in sympathetic ganglia and is probably carried by KCNQ2/3 channels, whereas the slow component appears to be carried by merg1a channels. Thus, the channels generating M-like currents in different cells may be heterogeneous in molecular composition.
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26
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Selyanko AA, Hadley JK, Wood IC, Abogadie FC, Delmas P, Buckley NJ, London B, Brown DA. Two types of K(+) channel subunit, Erg1 and KCNQ2/3, contribute to the M-like current in a mammalian neuronal cell. J Neurosci 1999; 19:7742-56. [PMID: 10479678 PMCID: PMC6782456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/1999] [Revised: 06/28/1999] [Accepted: 07/02/1999] [Indexed: 02/13/2023] Open
Abstract
The potassium M current was originally identified in sympathetic ganglion cells, and analogous currents have been reported in some central neurons and also in some neural cell lines. It has recently been suggested that the M channel in sympathetic neurons comprises a heteromultimer of KCNQ2 and KCNQ3 (Wang et al., 1998) but it is unclear whether all other M-like currents are generated by these channels. Here we report that the M-like current previously described in NG108-15 mouse neuroblastoma x rat glioma cells has two components, "fast" and "slow", that may be differentiated kinetically and pharmacologically. We provide evidence from PCR analysis and expression studies to indicate that these two components are mediated by two distinct molecular species of K(+) channel: the fast component resembles that in sympathetic ganglia and is probably carried by KCNQ2/3 channels, whereas the slow component appears to be carried by merg1a channels. Thus, the channels generating M-like currents in different cells may be heterogeneous in molecular composition.
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Affiliation(s)
- A A Selyanko
- Department of Pharmacology, University College London, London, WC1E 6BT, United Kingdom
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27
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Cunningham ML, Filtz TM, Harden TK. Protein kinase C-promoted inhibition of Galpha(11)-stimulated phospholipase C-beta activity. Mol Pharmacol 1999; 56:265-71. [PMID: 10419544 DOI: 10.1124/mol.56.2.265] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The effects of protein kinase C (PKC) activation on inositol lipid signaling were examined. Using the turkey erythrocyte model of receptor-regulated phosphoinositide hydrolysis, we developed a membrane reconstitution assay to study directly the effects of activation of PKC on the activities of Galpha(11), independent of potential effects on the receptor or on PLC-beta. Membranes isolated from erythrocytes pretreated with 4beta-phorbol-12beta-myristate-13alpha-acetate (PMA) exhibited a decreased capacity for Galpha(11)-mediated activation of purified, reconstituted PLC-beta1. This inhibitory effect was dependent on both the time and concentration of PMA incubation and occurred as a decrease in the efficacy of GTPgammaS for activation of PLC-beta1, both in the presence and absence of agonist; no change in the apparent affinity for the guanine nucleotide occurred. Similar inhibitory effects were observed after treatment with the PKC activator phorbol-12,13-dibutyrate but not after treatment with an inactive phorbol ester. The inhibitory effects of PMA were prevented by coaddition of the PKC inhibitor bisindolylmaleimide. Although the effects of PKC could be localized to the membrane, no phosphorylation of Galpha(11) occurred either in vitro in the presence of purified PKC or in intact erythrocytes after PMA treatment. These results support the hypothesis that a signaling protein other than Galpha(11) is the target for PKC and that PKC-promoted phosphorylation of this protein results in a phosphorylation-dependent suppression of Galpha(11)-mediated PLC-beta1 activation.
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Affiliation(s)
- M L Cunningham
- University of North Carolina School of Medicine, Department of Pharmacology, Chapel Hill, North Carolina, USA.
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28
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Jewell-Motz EA, Donnelly ET, Eason MG, Liggett SB. Agonist-mediated downregulation of G alpha i via the alpha 2-adrenergic receptor is targeted by receptor-Gi interaction and is independent of receptor signaling and regulation. Biochemistry 1998; 37:15720-5. [PMID: 9843377 DOI: 10.1021/bi980999r] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
One mechanism of long-term agonist-promoted desensitization of alpha2AR function is downregulation of the cellular levels of the alpha subunit of the inhibitory G protein, Gi. In transfected CHO cells expressing the human alpha2AAR, a 40.1 +/- 3.3% downregulation of Galphai2 protein occurred after 24 h of exposure of the cells to epinephrine, which was not accompanied by a decrease in Galphai2 mRNA. The essential step that targets Gi for degradation by agonist occupancy of the receptor was explored using mutated alpha2AAR lacking specific structural or functional elements. These consisted of 5HT1A receptor and beta2AR sequences substituted at residues 113-149 of the second intracellular loop and 218-235 and 355-371 of the N- and C-terminal regions of the third intracellular loop (altered Gi and Gs coupling), deletion of Ser296-299 (absent GRK phosphorylation), and substitution of Cys442 (absent palmitoylation and receptor downregulation). Of these mutants, only those with diminished Gi coupling displayed a loss of agonist-promoted Gi downregulation, thus excluding Gs coupling and receptor downregulation, palmitoylation, and phosphorylation as necessary events. Furthermore, coupling-impaired receptors consisting of mutations in the second or third loops ablated Gi downregulation, suggesting that a discreet structural motif of the receptor is unlikely to represent a key element in the process. While pertussis toxin ablated Gi downregulation, blocking downstream intracellular consequences of alpha2AAR activation or mimicking these pathways by heterologous means failed to implicate cAMP/adenylyl cyclase, phospholipase C, phospholipase D, or MAP kinase pathways in alpha2AAR-mediated Gi downregulation. Taken together, agonist-promoted Gi downregulation requires physical alpha2AAR-Gi interaction which targets Gi for degradation in a manner that is independent of alpha2AAR trafficking, regulation, or second messengers.
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MESH Headings
- Animals
- CHO Cells
- Cricetinae
- Down-Regulation/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/agonists
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Humans
- Mutagenesis, Insertional
- Mutagenesis, Site-Directed
- Phosphorylation
- Receptors, Adrenergic, alpha-2/genetics
- Receptors, Adrenergic, alpha-2/metabolism
- Receptors, Adrenergic, alpha-2/physiology
- Recombinant Fusion Proteins/chemical synthesis
- Recombinant Fusion Proteins/genetics
- Signal Transduction/genetics
- Transfection
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Affiliation(s)
- E A Jewell-Motz
- Department of Medicine, University of Cincinnati College of Medicine, Ohio 45267-0564, USA
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29
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Jasper JR. Stepping back and looking forward: downregulation of G proteins as a mechanism of desensitization in tissues. Focus on "Carbachol-induced desensitization of PLC-beta pathway in rat myometrium: downregulation of Gqalpha/G11alpha". THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C634-5. [PMID: 9730945 DOI: 10.1152/ajpcell.1998.275.3.c634] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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30
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Lajat S, Harbon S, Tanfin Z. Carbachol-induced desensitization of PLC-beta pathway in rat myometrium: downregulation of Gqalpha/G11alpha. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C636-45. [PMID: 9730946 DOI: 10.1152/ajpcell.1998.275.3.c636] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the estrogen-treated rat myometrium, carbachol increased the generation of inositol phosphates by stimulating the muscarinic receptor-Gq/G11-phospholipase C-beta3 (PLC-beta3) cascade. Exposure to carbachol resulted in a rapid and specific (homologous) attenuation of the subsequent muscarinic responses in terms of inositol phosphate production, PLC-beta3 translocation to membrane, and contraction. Refractoriness was accompanied by a reduction of membrane muscarinic binding sites and an uncoupled state of residual receptors. Protein kinase C (PKC) altered the functionality of muscarinic receptors and contributed to the initial period of desensitization. A delayed phase of the muscarinic refractoriness was PKC independent and was associated with a downregulation of Gqalpha/G11alpha. Atropine failed to induce desensitization as well as Gqalpha/G11alpha downregulation, indicating that both events involve active occupancy of the receptor. Prolonged exposure to AlF-4 reduced subsequent AlF-4 as well as carbachol-mediated inositol phosphate responses and similarly induced downregulation of Gqalpha/G11alpha. Data suggest that a decrease in the level of Gqalpha/G11alpha is subsequent to its activation and may account for heterologous desensitization.
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Affiliation(s)
- S Lajat
- Signalisation et Régulations Cellulaires, Centre National de la Recherche Scientifique, EP1088, Université Paris-Sud, 91405 Orsay Cedex, France
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31
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Magni P, Maggi R, Pimpinelli F, Motta M. Cholinergic muscarinic mechanisms regulate neuropeptide Y gene expression via protein kinase C in human neuroblastoma cells. Brain Res 1998; 798:75-82. [PMID: 9666082 DOI: 10.1016/s0006-8993(98)00471-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Neuropeptide Y (NPY) participates in the control of several functions in the nervous system. NPYergic neurons present in brain areas involved in cognitive processes are linked to ascending projections of the cholinergic system, a finding that suggests a role for acetylcholine in the control of these cells. In the present study, the effect of the activation of cholinergic muscarinic receptors on the expression of the human NPY gene was assessed. The SH-SY5Y neuroblastoma cell line was used as an in vitro model of human neurons; NPY mRNA levels were evaluated by Northern blot analysis. The results indicate that: (a) the expression of the human NPY gene in SH-SY5Y cells is stimulated by the cholinergic muscarinic agonist, carbachol; (b) this effect is mediated by the M3 muscarinic receptor subtype, as indicated by the inhibitory effect of the M3 antagonist 4-DAMP; (c) protein kinase C (PKC) activation plays an important role in the induction of NPY gene expression in this system, as suggested by experiments with the PKC activator, TPA, and the PKC inhibitor, GF 109203X; (d) the stimulation of NPY mRNA levels by TPA and by carbachol in SH-SY5Y cells requires de novo synthesis of RNA and protein. In conclusion, the present study shows that the activation of PKC-coupled muscarinic receptors as the M3 subtype positively modulates the expression of the human NPY gene in SH-SY5Y neuroblastoma cells, via PKC-related mechanisms.
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Affiliation(s)
- P Magni
- Center for Endocrinological Oncology, Institute of Endocrinology, University of Milan, via G. Balzaretti, 9, 20133 Milan, Italy.
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Steingart RA, Barg J, Maslaton J, Nesher M, Yanai J. Pre- and postsynaptic alterations in the septohippocampal cholinergic innervations after prenatal exposure to drugs. Brain Res Bull 1998; 46:203-9. [PMID: 9667813 DOI: 10.1016/s0361-9230(97)00454-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The present study was designed to evaluate possible presynaptic and postsynaptic alterations in the hippocampal cholinergic innervations that account for the hippocampus-related behavioral deficits found after prenatal drug exposure. Mice were prenatally exposed to either phenobarbital or heroin. On postnatal day 50, the hippocampi were removed and protein kinase C (PkC) activity, the amounts of Gi, Go, and Gq guanosine 5'-triphosphate binding proteins (G-proteins), and choline transports were determined. Basal PkC activity was higher than control levels in both phenobarbital and heroin treated mice, by 41% and 35%, respectively. The increase of PkC activity in response to carbachol was impaired in both treatment groups: in control mice, membrane PkC activity in hippocampal slices increased by 40%-50%, while no such response, or even slight reduction in PkC activity, was observed in the drug-exposed offspring. A significant increase was found in Gi and Gq G-proteins (18%-21%) in mice exposed to phenobarbital or to heroin compared with control levels. The amount of choline transporters, determined by hemicholinium binding, increased by 70% compared with the control level in mice prenatally exposed to heroin, and increased by 71% in mice prenatally exposed to phenobarbital. The alterations in basal and carbachol-stimulated hippocampal PkC activity after prenatal drug exposure may be related to an impairment in long-term potentiation (LTP); which plays an important role in hippocampal related behavioral abilities, changes in which are caused by prenatal drug exposure.
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Affiliation(s)
- R A Steingart
- Department of Anatomy and Embryology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel
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33
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Lajat S, Tanfin Z, Guillon G, Harbon S. Modulation of phospholipase C pathway and level of Gq alpha/G11 alpha in rat myometrium during gestation. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:C895-904. [PMID: 8843720 DOI: 10.1152/ajpcell.1996.271.3.c895] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The regulation of the receptor-G protein-phospholipase C (PLC) cascade was investigated in rat myometrium at midgestation (day 12) and at term (day 21) comparatively to the estrogen-treated tissue (day 0). Carbachol-mediated generation of [3H]inositol phosphates was insensitive to pertussis toxin and was enhanced at days 12 and 21 two- and threefold, respectively, with no alteration of muscarinic sites (M3 subtype). A similar increase could be detected in the production of inositol 1,4,5-trisphosphate, indicating the stimulation of a PLC degrading phosphatidylinositol 4,5-bisphosphate. AlF4- also enhanced PLC activation during gestation, suggesting pregnancy-related regulations that bypass receptor activation. Immunoreactive G proteins, Gq alpha and G11 alpha, and PLC-beta 3 were detected in all myometrial preparations. The amount of PLC-beta 3 was similar in day 0 and day 21 myometrium, although decreasing by 75% at midgestation. Of significance was the increased amount of Gq alpha in day 12 and day 21 myometrium (3- and 2-fold, respectively) which coincided with the enhanced phosphoinositide breakdown. The upregulation of Gq alpha may contribute to the enhanced PLC activity during pregnancy and at term.
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Affiliation(s)
- S Lajat
- Centre National de la Recherche Scientifique Unité de Recherche Associée 1131, Université Paris Sud, Orsay, France
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34
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Bünemann M, Brandts B, Pott L. Downregulation of muscarinic M2 receptors linked to K+ current in cultured guinea-pig atrial myocytes. J Physiol 1996; 494 ( Pt 2):351-62. [PMID: 8841996 PMCID: PMC1160639 DOI: 10.1113/jphysiol.1996.sp021497] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. Desensitization of muscarinic K+ current (IK(ACh)) was studied in cultured atrial myocytes from guinea-pig hearts using whole-cell voltage clamp. 2. Three different types of desensitization could be identified. A fast component which upon rapid superfusion with ACh resulted in a partial relaxation of IK(ACh) within a few seconds to a plateau which was maintained in the presence of ACh. Recovery from this type of desensitization paralleled the decay of IK(ACh) after washout of the agonist. A second type of desensitization was observed within minutes. This was reversed around 10 min after washout of ACh. Both types were heterologous with regard to the A1 receptor and the novel phospholipid (Pl) receptor, both of which activate IK(ACh) via the same signalling pathway. 3. A third type of desensitization (downregulation) occurred upon exposure of the cultures for 24-48 h to the muscarinic agonist carbachol (CCh). The level of downregulation depended on the concentration of CCh (0.1 microM < or = [CCh] < or = 10 microM). No recovery was observed within 5 h after washout of CCh. Thereafter sensitivity to ACh slowly returned (half-time (t1/2), approximately 20 h). 4. Downregulation by CCh (0.1-5 microM) was characterized by an increase in EC50 for ACh with no reduction in maximum IK(ACh). With 5 microM CCh, EC50 was increased from 0.1 to 3.7 microM. At 10 microM CCh EC50 was increased to 15 microM and maximal current that could be evoked by ACh was reduced to 15%. 5. Downregulation by CCh was homologous with regard to A1 and Pl receptors. Maximum IK(ACh), assayed by a saturating concentration of Pl, was not reduced in downregulated cells, suggesting a mechanism localized at the M2 receptor. 6. The changes in the concentration-response curves can be accounted for by assuming an excess of M2 receptors relative to the subsequent component of the signalling pathway. 7. As the intact heart is under tonic vagal control, downregulation is likely to contribute to controlling the sensitivity of the heart to vagal activity in situ.
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Affiliation(s)
- M Bünemann
- Institut für Physiologie, Ruhr Universität Bochum, Germany
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35
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Willars GB, Challiss RA, Stuart JA, Nahorski SR. Contrasting effects of phorbol ester and agonist-mediated activation of protein kinase C on phosphoinositide and Ca2+ signalling in a human neuroblastoma. Biochem J 1996; 316 ( Pt 3):905-13. [PMID: 8670170 PMCID: PMC1217436 DOI: 10.1042/bj3160905] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effects of protein kinase C (PKC) activation on muscarinic receptor-mediated phosphoinositide and Ca2+ signalling were examined in the human neuroblastoma, SH-SY5Y. Carbachol evoked rapid transient elevations of Ins(1,4,5)P3 and intracellular [Ca2+] followed by lower sustained elevations. Phorbol 12,13-dibutyrate (PDBu) preferentially attenuated transient phases. Removal of the transplasmalemmal Ca2+ gradient coupled with depletion of intracellular Ca2+ stores with thapsigargin also reduced carbachol-mediated Ins(1,4,5)P3 accumulation. Under these conditions, PDBu virtually abolished Ins(1,4,5)P3 responses to carbachol thereby implicating both Ca(2+)- and PKC-sensitive components. PDBu also reduced agonist-mediated accumulation of inositol phosphates and depletion of lipids, thereby eliminating an effect of PKC on Ins(1,4,5)P3 metabolism or phosphoinositide synthesis. In electroporated cells, PDBu inhibited Ins(1,4,5)P3 accumulation mediated by carbachol or guanosine 5'-[gamma-thio]-triphosphate, the latter indicating that some PDBu-sensitive elements were downstream of the receptor. The PKC inhibitor, Ro-318220, protected against PDBu but did not enhance responses to maximal concentrations of carbachol, indicating no feedback inhibition by agonist-activated PKC. Muscarinic antagonist activity of Ro-318220 complicated such assessment at low agonist concentrations. Carbachol or PDBu induced cytosol to membrane translocation of PKC alpha. This was faster and possibly greater with PDBu, which may explain the lack of feedback by agonist-activated PKC. These results indicate that, in SH-SY5Y cells, PDBu activation of PKC preferentially inhibits rapid muscarinic receptor-mediated phosphoinositide and Ca2+ responses via suppression of PtdIns(4,5)P2 hydrolysis. This is at least partially through inhibition of Gq-protein/phosphoinositidase C coupling. However, at least at high agonist concentrations, a major agonist-mediated PKC feedback is not present in these cells.
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Affiliation(s)
- G B Willars
- Department of Cell Physiology and Pharmacology, University of Leicester, U.K
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36
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Myslivecek J, Trojan S, Tucek S. Biphasic changes in the density of muscarinic and beta-adrenergic receptors in cardiac atria of rats treated with diisopropylfluorophosphate. Life Sci 1996; 58:2423-30. [PMID: 8691987 DOI: 10.1016/0024-3205(96)00246-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Chronic treatment with organophosphate inhibitors of cholinesterases is known to bring about down-regulation of muscarinic acetylcholine receptors in the heart while its effect on the functionally antagonistic beta-adrenergic receptors is not known. We describe experiments in which rats were exposed to daily injections of diisopropylflurophosphate (DFP) and the density of muscarinic and beta-adrenergic binding sites in their cardiac atria was measured according to the binding of (3H)quinuclidinyl benzilate ((3H)QNB) and (-)-4-(3-tert-butylamino-2-hydroxy)-propoxy-(5,7-3H) benzimidazol-2-one ((3H)CGP 12177) as subtype non-specific muscarinic and beta-adrenergic ligands, respectively. Biphasic course of changes was discovered with both ligands. With the dosage scheme applied, the density of beta-adrenoceptors was augmented 24 h after the first dose of DFP and decreased to about one half of control values after 5 days of treatment with DFP. The density of muscarinic receptors was augmented after two days of treatment with DFP and decreased to about one half of control values after 5 days of treatment. Comparatively small changes in the heart rate were observed during the treatment, they reflected changes in the muscarinic and beta-adrenergic receptor density. The finding of DFP-induced changes in the binding of (3H)CGP 12177 suggests that the mechanisms responsible for the control of the density of muscarinic and beta-adrenergic receptors in the heart cells are interconnected but potential roles of other factors involved in in vivo experiments deserve further analysis. The transient increase in the density of muscarinic receptors after two days of DFP treatment appears related to published data on transient stimulation by cholinergic agonists of the transcription of mRNAs for muscarinic receptors.
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Affiliation(s)
- J Myslivecek
- Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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37
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Smit MJ, Timmerman H, Hijzelendoorn JC, Fukui H, Leurs R. Regulation of the human histamine H1 receptor stably expressed in Chinese hamster ovary cells. Br J Pharmacol 1996; 117:1071-80. [PMID: 8882599 PMCID: PMC1909783 DOI: 10.1111/j.1476-5381.1996.tb16699.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. The human H1 receptor gene expressed in Chinese hamster ovary cells (CHOhumH1) encodes a classical histamine H1 receptor with a pharmacology similar to that of the H1 receptor found in guinea-pig cerebellum and the endogenously expressed human H1 receptor in 1321N1 astrocytoma cells as determined by [3H]-mepyramine binding studies. 2. In CHOhumH1 cells, histamine induced a concentration-dependent rise in inositol phosphates (EC50 2.23 +/- 0.97 microM) and a rapid increase of [Ca2+]i, followed by a sustained increase of [Ca2+]i upon addition of 100 microM histamine. 3. Short-term exposure of CHOhumH1 cells to histamine (100 microM) resulted in a decrease of subsequent histamine-induced Ca2+ responses. The histamine-induced desensitization appeared to be heterologous as the ATP-induced Ca2+ response was also found to be affected. 4. The process of heterologous histamine-induced desensitization of the Ca2+ response in CHOhumH1 cells can be ascribed to an alteration at the level of the intracellular Ca2+ pool, as the Ca2+ response of caffeine (10 mM), which releases Ca2+ from intracellular Ca2+ stores was also attenuated upon short-term histamine exposure. 5. In CHOhumH1 cells the PKC activator, PMA, was found to inhibit the histamine (100 microM)-induced Ca2+ response concentration-dependently (IC50 0.2 +/- 0.03 microM) as well as the ATP (100 microM)-induced Ca2+ response. However, this inhibition was only partial and less effective than histamine-pretreatment. Moreover, in CHOhumH1 cells PKC downregulation induced by long-term exposure to PMA (1 microM) did not affect the histamine-induced desensitization nor did pretreatment with the specific PKC inhibitor Ro-31-8220 (10 microM), indicating that in CHOhumH1 cells PKC is probably not involved in the heterologous desensitization. 6. Long-term treatment of CHOhumH1 cells with histamine or other H1 agonists resulted in a time- and concentration-dependent decrease in the number of H1 receptor binding sites (maximal reduction: 47 +/- 5%). 7. Long-term exposure of CHOhumH1 cells to ATP or PMA did not affect H1 receptor density. 8. Both histamine (100 microM)- and ATP (100 microM)-induced Ca2+ responses were affected upon long-term exposure of cells to histamine (100 microM), which might be explained by an alteration at a level distant from the receptor. 9. These results show that in CHOhumH1 cells the human histamine H1 receptor is susceptible to short-term and long-term receptor regulation in which PKC does not seem to play a role. The CHOhumH1 cells therefore provide an excellent model system for studying the mechanism(s) of PKC-independent H1 receptor regulation.
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Affiliation(s)
- M J Smit
- Department of Pharmacochemistry, Vrije Universiteit, Amsterdam, Netherlands
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38
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van Biesen T, Hawes BE, Raymond JR, Luttrell LM, Koch WJ, Lefkowitz RJ. G(o)-protein alpha-subunits activate mitogen-activated protein kinase via a novel protein kinase C-dependent mechanism. J Biol Chem 1996; 271:1266-9. [PMID: 8576109 DOI: 10.1074/jbc.271.3.1266] [Citation(s) in RCA: 172] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Mitogen-activated protein kinase (MAPK) is activated in response to both receptor tyrosine kinases and G-protein-coupled receptors. Recently, Gi-coupled receptors, such as the alpha 2A adrenergic receptor, were shown to mediate Ras-dependent MAPK activation via a pathway requiring G-protein beta gamma subunits (G beta gamma) and many of the same intermediates involved in receptor tyrosine kinase signaling. In contrast, Gq-coupled receptors, such as the M1 muscarinic acetylcholine receptor (M1AChR), activate MAPK via a pathway that is Ras-independent but requires the activity of protein kinase C (PKC). Here we show that, in Chinese hamster ovary cells, the M1AChR and platelet-activating factor receptor (PAFR) mediate MAPK activation via the alpha-subunit of the G(o) protein. G(o)-mediated MAPK activation was sensitive to treatment with pertussis toxin but insensitive to inhibition by a G beta gamma-sequestering peptide (beta ARK1ct). M1AChR and PAFR catalyzed G(o) alpha-subunit GTP exchange, and MAPK activation could be partially rescued by a pertussis toxin-insensitive mutant of G(o) alpha but not by similar mutants of Gi. G(o)-mediated MAPK activation was insensitive to inhibition by a dominant negative mutant of Ras (N17Ras) but was completely blocked by cellular depletion of PKC. Thus, M1AChR and PAFR, which have previously been shown to couple to Gq, are also coupled to G(o) to activate a novel PKC-dependent mitogenic signaling pathway.
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Affiliation(s)
- T van Biesen
- Howard Hughes Medical Institute, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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39
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Mullaney I, Caulfield MP, Svoboda P, Milligan G. Activation, cellular redistribution and enhanced degradation of the G proteins Gq and G11 by endogenously expressed and transfected phospholipase C-coupled muscarinic m1 acetylcholine receptors. PROGRESS IN BRAIN RESEARCH 1996; 109:181-7. [PMID: 9009705 DOI: 10.1016/s0079-6123(08)62100-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- I Mullaney
- Division of Biochemistry and Molecular Biology, University of Glasgow, UK
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40
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Detjen K, Yang J, Logsdon CD. Muscarinic acetylcholine receptor down-regulation limits the extent of inhibition of cell cycle progression in Chinese hamster ovary cells. Proc Natl Acad Sci U S A 1995; 92:10929-33. [PMID: 7479912 PMCID: PMC40544 DOI: 10.1073/pnas.92.24.10929] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Cellular desensitization is believed to be important for growth control but direct evidence is lacking. In the current study we compared effects of wild-type and down-regulation-resistant mutant m3 muscarinic receptors on Chinese hamster ovary (CHO-K1) cell desensitization, proliferation, and transformation. We found that down-regulation of m3 muscarinic acetylcholine receptors was the principal mechanism of desensitization of receptor-activated inositol phosphate phospholipid hydrolysis in these cells. Activation of wild-type and mutant receptors inhibited anchorage-independent growth as assayed by colony formation in agar. However, the potency for inhibition of anchorage-independent growth was greater for cells expressing the mutant receptor. Activation of either receptor also initially inhibited anchorage-dependent cell proliferation in randomly growing populations. Rates of DNA synthesis and cell division were profoundly reduced by carbachol in cells expressing either receptor at early time points. Analysis of cell cycle parameters indicated that cell cycle progression was inhibited at transitions from G1 to S and G2/M to G1 phases. However, mutant receptor effects on anchorage-dependent growth were sustained, whereas wild-type receptor effects were transient. Thus, receptor down-regulation restored cell cycle progression. In contrast, activation of either receptor blocked entry into the cell cycle from quiescence, and this response was not reduced by receptor down-regulation. Therefore, activation of m3 muscarinic acetylcholine receptors inhibited CHO cell anchorage-dependent and -independent growth. In anchored cells carbachol inhibited the cell cycle at three distinct points. Inhibitions at two of these points were eliminated by wild-type receptor down-regulation while the other was not. These results directly demonstrate that desensitization mechanisms can act as principal determinants of cellular growth responses.
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Affiliation(s)
- K Detjen
- Department of Physiology, University of Michigan, Ann Arbor 48109-0622, USA
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41
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van de Westerlo E, Yang J, Logsdon C, Williams JA. Down-regulation of the G-proteins Gq alpha and G11 alpha by transfected human M3 muscarinic acetylcholine receptors in Chinese hamster ovary cells is independent of receptor down-regulation. Biochem J 1995; 310 ( Pt 2):559-63. [PMID: 7654194 PMCID: PMC1135931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Chinese hamster ovary cells stably transfected with human M3 muscarinic acetylcholine receptors show a 40-50% reduction in the immunoreactive G-proteins Gq alpha and G11 alpha when stimulated with the cholinergic agonist carbachol. This effect is seen after 9 h, is maximal after 24 h, and occurs over a range of carbachol concentrations that activate phosphoinositide hydrolysis in these cells. The effect is specific for Gq alpha family proteins as Gs alpha was slightly increased after carbachol treatment and G13 alpha was unchanged. Using a urea gel system, we were able to resolve Gq alpha and G11 alpha, both of which were down-regulated by carbachol. An M3 receptor mutant, with C-terminal threonines changed to alanines as described previously, binds ligand and activates phosphoinositide hydrolysis normally but is not down-regulated in response to carbachol. This receptor, however, induces Gq alpha/G11 alpha down-regulation similarly to wild-type M3 receptors, indicating that G-protein down-regulation is not directly coupled to receptor down-regulation. Thus down-regulation of Gq alpha and G11 alpha may contribute to heterologous desensitization particularly at longer times of agonist exposure.
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Affiliation(s)
- E van de Westerlo
- Department of Physiology, University of Michigan, Ann Arbor 48109, USA
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42
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Palmer TM, Gettys TW, Stiles GL. Differential interaction with and regulation of multiple G-proteins by the rat A3 adenosine receptor. J Biol Chem 1995; 270:16895-902. [PMID: 7622506 DOI: 10.1074/jbc.270.28.16895] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Interaction of the rat A3 adenosine receptor (A3AR) with G-proteins has been assessed using a stably transfected Chinese hamster ovary cell system. The non-selective AR agonist 5'-N-ethylcarboxamidoadenosine (NECA) increased the labeling of a 41-kDa membrane protein by 4-azidoanilido-[alpha-32P]guanosine 5'-triphosphate (AA-[32P]GTP), a photolabile GTP analogue. Subsequent immunoprecipitation of Gi alpha-subunits indicated that NECA stimulated incorporation of label into both Gi alpha-2 and Gi alpha-3. Additional experiments revealed an A3AR stimulation of label into Gq and/or G11 alpha-subunits, albeit to a lesser degree than that elicited by endogenous P2U purinergic receptors. No interaction with Gs could be detected. Sustained cellular exposure to NECA induced A3AR desensitization and specific down-regulation of Gi alpha-3 and G-protein beta-subunits without changing levels of Gi alpha-2, Gs alpha, or Gq+11 alpha-subunits. Therefore the A3AR can interact with Gi alpha-2, Gi alpha-3, and, to some extent, Gq-like proteins, but sustained agonist exposure down-regulates only one of the G-proteins with which it interacts. This is the first description of the differing specificities of A3AR/G-protein coupling versus down-regulation in situ and provides a potential mechanism by which the A3AR could elicit the heterologous desensitization of signaling events mediated by Gi3.
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Affiliation(s)
- T M Palmer
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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43
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Shah BH, MacEwan DJ, Milligan G. Gonadotrophin-releasing hormone receptor agonist-mediated down-regulation of Gq alpha/G11 alpha (pertussis toxin-insensitive) G proteins in alpha T3-1 gonadotroph cells reflects increased G protein turnover but not alterations in mRNA levels. Proc Natl Acad Sci U S A 1995; 92:1886-90. [PMID: 7892195 PMCID: PMC42387 DOI: 10.1073/pnas.92.6.1886] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Prolonged exposure of alpha T3-1 pituitary gonadotrophs to a gonadotrophin-releasing hormone receptor agonist results in marked down-regulation of the pertussis toxin-insensitive G proteins Gq alpha and G11 alpha. The turnover of Gq alpha/G11 alpha was substantially accelerated in the presence of agonist. By contrast, the rate of degradation of the G protein Gi2 alpha was unaffected by agonist treatment. Analysis of Gq alpha/G11 alpha mRNA levels by reverse transcription-PCR demonstrated no detectable differences between control and agonist-treated cells. These studies indicate that gonadotrophin-releasing hormone receptor agonist-mediated down-regulation of Gq alpha/G11 alpha is a reflection of enhanced proteolysis of the activated G proteins.
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Affiliation(s)
- B H Shah
- Division of Biochemistry and Molecular Biology, University of Glasgow, Scotland, United Kingdom
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44
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Fisher SK. Homologous and heterologous regulation of receptor-stimulated phosphoinositide hydrolysis. Eur J Pharmacol 1995; 288:231-50. [PMID: 7774668 DOI: 10.1016/0922-4106(95)90035-7] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Signal transduction at a diverse range of pharmacologically distinct receptors is effected by the enhanced turnover of inositol phospholipids, with the attendant formation of inositol 1,4,5-trisphosphate and diacylglycerol. Although considerable progress has been made in recent years towards the identification and characterization of the individual components of this pathway, much less is known of mechanisms that may underlie its regulation. In this review, evidence is presented for the potential regulation of inositol lipid turnover at the level of receptor, phosphoinositide-specific phospholipase C and substrate availability in response to either homologous or heterologous stimuli. Available data indicate that the extent of receptor-stimulated inositol lipid hydrolysis is regulated by multiple mechanisms that operate at different levels of the signal transduction pathway.
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Affiliation(s)
- S K Fisher
- Neuroscience Laboratory, University of Michigan, Ann Arbor 48104-1687, USA
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45
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Kim GD, Milligan G. Receptor availability defines the extent of agonist-mediated G-protein down-regulation in neuroblastoma x glioma hybrid cells transfected to express the beta 2-adrenoceptor. FEBS Lett 1994; 355:166-70. [PMID: 7982493 DOI: 10.1016/0014-5793(94)01169-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Sustained exposure of neuroblastoma x glioma hybrid, NG108-15, cells transfected to express the human beta 2-adrenoceptor (clone beta N22) to isoprenaline or iloprost (an agonist at the endogenously expressed IP prostanoid receptor) resulted in a substantial and selective down-regulation of the alpha subunit of the G-protein Gs. Treatment of these cells with the irreversible beta-adrenoceptor antagonist bromoacetyl alprenolol menthane diminished both the potency and the maximal ability of isoprenaline but not of iloprost to cause Gs alpha down-regulation. These results demonstrate that the extent of agonist-mediated Gs alpha down-regulation is dependent upon the availability of receptor to agonist.
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Affiliation(s)
- G D Kim
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
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46
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Chambers J, Park J, Cronk D, Chapman C, Kennedy FR, Wilson S, Milligan G. Beta 3-adrenoceptor agonist-induced down-regulation of Gs alpha and functional desensitization in a Chinese hamster ovary cell line expressing a beta 3-adrenoceptor refractory to down-regulation. Biochem J 1994; 303 ( Pt 3):973-8. [PMID: 7980470 PMCID: PMC1137641 DOI: 10.1042/bj3030973] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Chinese hamster ovary (CHO) cells transfected to express human beta 2- or beta 3-adrenoceptors (beta 2-CHO and beta 3-CHO cells) were exposed to the beta-adrenoceptor agonist isoprenaline at various concentrations and for differing times. Sustained exposure of the beta 2-CHO but not beta 3-CHO cells to isoprenaline resulted in a time- and concentration-dependent down-regulation of the receptor as measured by a reduction in specific binding of [125I]cyanopindolol. Such maintained exposure of cells expressing either receptor to the agonist produced a marked down-regulation of immunologically detectable levels of the alpha subunit of the stimulatory guanine-nucleotide-binding protein Gs. This effect was specific for Gs because levels of both G12 alpha and Gq alpha/G11 alpha were unaltered by isoprenaline treatment of both beta 2-CHO and beta 3-CHO cells. The effect of isoprenaline on Gs alpha down-regulation was some 30-fold more potent in the beta 2-CHO than in the beta 3-CHO cells. Time courses of isoprenaline-induced down-regulation of Gs alpha were not different, however, in the two cell lines. Isoprenaline treatment of the beta 3-CHO cells produced a desensitization of agonist-mediated regulation of adenylyl cyclase, manifested by a 4-fold reduction in the potency and a 30% reduction in maximal effect of the agonist, whereas desensitization of the beta 2-CHO cells was considerably greater (25-fold reduction in potency and 70% reduction in maximal effect). These results demonstrate that agonist-induced down-regulation of the G-protein which interacts with a receptor can be produced by both beta 2- and beta 3-adrenoceptors. Despite apparent concurrence of down-regulation of receptors and G-proteins in other systems [e.g. Adie, Mullaney, McKenzie and Milligan (1992) Biochem. J. 285, 529-536], agonist-induced receptor down-regulation does not appear to be a prerequisite for down-regulation of the G-protein. Furthermore, the results suggest that agonist-induced down-regulation of a G-protein may be sufficient, in the absence of receptor regulation, to induce some agonist desensitization of effector function.
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Affiliation(s)
- J Chambers
- SB Pharmaceuticals, Pinnacles, Harlow, U.K
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47
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Mullaney I, Milligan G. Equivalent regulation of wild type and an epitope-tagged variant of Gs alpha by the IP prostanoid receptor following expression in neuroblastoma x glioma hybrid, NG108-15, cells. FEBS Lett 1994; 353:231-4. [PMID: 7525345 DOI: 10.1016/0014-5793(94)01043-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
NG108-15 cells were transfected to stably express a haemagglutinin epitope-tagged variant of the long isoform of Gs alpha. Clone BST15 expressed this polypeptide at similar levels to the endogenous long isoform of Gs alpha. Treatment of clone BST15 with the IP prostanoid receptor agonist iloprost resulted in down-regulation of both forms of Gs alpha with both dose-effect curves to iloprost and time courses of loss of the two forms of Gs alpha being indistinguishable. These results demonstrate that the IP prostanoid receptor interacts with and regulates the epitope-tagged variant of Gs alpha in an equivalent manner to the unmodified protein and indicates that the epitope-tagged polypeptide can be used to analyse mechanisms of receptor regulation of cellular G-protein levels.
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Affiliation(s)
- I Mullaney
- Division of Biochemistry and Molecular Biology, University of Glasgow, Scotland, UK
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48
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Svoboda P, Milligan G. Agonist-induced transfer of the alpha subunits of the guanine-nucleotide-binding regulatory proteins Gq and G11 and of muscarinic m1 acetylcholine receptors from plasma membranes to a light-vesicular membrane fraction. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 224:455-62. [PMID: 7925360 DOI: 10.1111/j.1432-1033.1994.00455.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A clone of a Chinese hamster ovary (CHO) cell line expressing high levels of the human muscarinic M1 acetylcholine (Hm1) receptor undergoes a substantial agonist-specific down-regulation of both Hm1 receptors and the alpha subunits of the guanine-nucleotide-binding (G)-proteins Gq and G11 which is accompanied by a desensitization of inositol-phospholipid-specific-phospholipase-C response [Mullaney, I., Dodd, M. W., Buckley, N. J. & Milligan, G. (1993) Biochem. J. 289, 125-131]. To examine early events in this process, the effect of agonist on subcellular distribution of Gq alpha and G11 alpha and of Hm1 receptors was assessed after short-term and long-term treatment with carbachol. Short-term (30 min) incubation with carbachol (1 mM) induced a simultaneous transfer of a proportion of both Gq alpha and G11 alpha and Hm1 receptors from plasma membranes to distinct light vesicular membranes. The total number of receptors and of Gq alpha and G11 alpha in each cell remained unchanged under these conditions. A similar transfer was noted for the G-protein Gs alpha but not for intrinsic plasma membrane markers. The plasma membrane, as well as light vesicular membrane, pool of Gs alpha subunit was unaffected by further sustained incubation with carbachol (16 h), whereas Hm1 receptors and both Gq alpha and G11 alpha proteins were down-regulated to 25% and 40%, respectively, when compared with untreated cells. Such observations support the idea that down-regulation of both the Hm1 receptor and its associated inositol-phospholipid-specific-phospholipase-C-linked G-proteins is produced by two sequential steps. The first is a transfer of signal-transducing polypeptides from the plasma membrane to a non-plasma membrane light vesicle fraction. The second step is represented by an agonist-specific down-regulation pathway. Both the Hm1 receptor and Gq alpha/G11 alpha appear to follow similar sequestration and down-regulation patterns.
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Affiliation(s)
- P Svoboda
- Department of Biochemistry, University of Glasgow, Scotland
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49
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Kim G, Carr I, Anderson L, Zabavnik J, Eidne K, Milligan G. The long isoform of the rat thyrotropin-releasing hormone receptor down-regulates Gq proteins. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32110-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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50
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Williams RJ, Kelly E. Gs alpha-dependent and -independent desensitisation of prostanoid IP receptor-activated adenylyl cyclase in NG108-15 cells. Eur J Pharmacol 1994; 268:177-86. [PMID: 7525317 DOI: 10.1016/0922-4106(94)90187-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
NG108-15 mouse neuroblastoma x rat glioma cells were treated with the prostanoid IP receptor agonist iloprost (1 microM) and the time course of changes in the levels of prostanoid IP receptors, adenylyl cyclase activity, and the alpha-subunit of the stimulatory guanine nucleotide binding regulatory protein, Gs, were measured. Incubation of cells with iloprost produced a biphasic time course of desensitisation of prostanoid IP receptor-activated adenylyl cyclase. Parallel analysis of iloprost-induced loss of membrane Gs alpha, NaF-stimulated adenylyl cyclase and [3H]iloprost binding suggested only monophasic curves, with t0.5 values similar to the initial phase of desensitisation of iloprost-stimulated adenylyl cyclase activity. This suggests that the loss of receptor and Gs alpha occur at the same time and account for the initial period of desensitisation due to iloprost pretreatment. Pretreatment of NG108-15 cells with cholera toxin produced a near complete loss of membrane-associated Gs alpha, but the loss of [3H]iloprost binding due to iloprost treatment was not affected by pretreatment with cholera toxin, suggesting that prostanoid IP receptors can be down-regulated in the absence of any coupling to Gs. The second phase of desensitisation of iloprost-stimulated adenylyl cyclase activity, during which there was no further change in NaF-stimulated adenylyl cyclase or in the membrane levels of Gs alpha, was not due to protein kinase A activation, since elevating intracellular cyclic AMP levels with forskolin did not subsequently decrease iloprost-stimulated adenylyl cyclase activity or [3H]iloprost binding. These results demonstrate that iloprost pretreatment of NG108-15 cells induces two distinct phases of desensitisation; an initial desensitisation due to concurrent loss of prostanoid IP receptors and Gs alpha, and then a further desensitisation by an as yet uncharacterized mechanism during which there is no further loss of Gs alpha.
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Affiliation(s)
- R J Williams
- Department of Pharmacology, School of Medical Sciences, University of Bristol, UK
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