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Lohr C. Role of P2Y receptors in astrocyte physiology and pathophysiology. Neuropharmacology 2023; 223:109311. [PMID: 36328064 DOI: 10.1016/j.neuropharm.2022.109311] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Revised: 10/24/2022] [Accepted: 10/27/2022] [Indexed: 11/07/2022]
Abstract
Astrocytes are active constituents of the brain that manage ion homeostasis and metabolic support of neurons and directly tune synaptic transmission and plasticity. Astrocytes express all known P2Y receptors. These regulate a multitude of physiological functions such as cell proliferation, Ca2+ signalling, gliotransmitter release and neurovascular coupling. In addition, P2Y receptors are fundamental in the transition of astrocytes into reactive astrocytes, as occurring in many brain disorders such as neurodegenerative diseases, neuroinflammation and epilepsy. This review summarizes the current literature addressing the function of P2Y receptors in astrocytes in the healthy brain as well as in brain diseases.
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Affiliation(s)
- Christian Lohr
- Institute of Cell and Systems Biology of Animals, University of Hamburg, Germany.
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Khouchlaa A, El Menyiy N, Guaouguaou FE, El Baaboua A, Charfi S, Lakhdar F, El Omari N, Taha D, Shariati MA, Rebezov M, El-Shazly M, Bouyahya A. Ethnomedicinal use, phytochemistry, pharmacology, and toxicology of Daphne gnidium: A review. JOURNAL OF ETHNOPHARMACOLOGY 2021; 275:114124. [PMID: 33865924 DOI: 10.1016/j.jep.2021.114124] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/18/2021] [Accepted: 04/10/2021] [Indexed: 06/12/2023]
Abstract
ETHNOPHARMACOLOGICAL RELEVANCE Daphne gnidium L., (Lazaz or Metnan) is a perennial plant that grows around the Mediterranean basin, in Southern Europe, North Africa and the Middle East. It is used in different countries for hair care and to treat several diseases including skin cancer, diabetes, nervous breakdowns, sinusitis, poisoning, rheumatic disorders, odontalgia, muscular pain, and gastrointestinal infections. It is also used as anti-inflammatory, insecticide, and anti-parasitic remedy. AIM OF THE REVIEW In this review, previous studies on D. gnidium including its botanical description, taxonomy, geographical distribution, medicinal use, phytochemistry, and pharmacological properties were critically highlighted and discussed for suggesting the exploration of this specie and its bioactive compounds in medical applications. MATERIALS AND METHODS Data on D. gnidium were gathered from Scientific search engines including PubMed, ScienceDirect, SpringerLink, Web of Science, Scopus, Wiley Online, SciFinder, and Google Scholar. Reports on D. gnidium written in English published before September 2020 were summarized. RESULTS In traditional medicine, D. gnidium is used to treat diabetes, gastrointestinal infections, skin cancer, nervous breakdowns, and sinusitis. The extracts and essential oil of D. gnidium exhibited several biological properties such as antibacterial, antifungal, antiviral, antigenotoxic, hemolytic, anti-inflammatory, immunomodulatory, neuroprotective, allelopathic, and insecticidal effects. Phytochemical investigations identified several chemical classes of secondary metabolites in D. gnidium essential oil and extracts including terpenoids, coumarins, flavonoids, fatty acids, and alkanes. CONCLUSIONS The findings presented in this study showed a link between the traditional medicinal use and scientific biological results about D. gnidium. However, further investigations should be carried out to support medical and cosmetic applications of this species. Indeed, D. gnidium and its main compounds should be confirmed concerning their safety and their bioavailability. Moreover, pharmacodynamic studies should be conducted to support their efficacy in medical applications.
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Affiliation(s)
- Aya Khouchlaa
- Laboratory of Human Pathologies Biology, Department of Biology, Faculty of Sciences, Genomic Center of Human Pathologies, Faculty of Medicine and Pharmacy, Mohammed V University in Rabat, Morocco.
| | - Naoual El Menyiy
- Laboratory of Natural Substances, Pharmacology, Environment, Modeling, Health and Quality of Life (SNAMOPEQ), Faculty of Sciences Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, Fez, Morocco.
| | - Fatima-Ezzahrae Guaouguaou
- Mohammed V University in Rabat, LPCMIO, Materials Science Center (MSC), Ecole Normale Supérieure, Rabat, Morocco
| | - Aicha El Baaboua
- Biology and Health Laboratory, Department of Biology, Faculty of Science, Abdelmalek-Essaadi University, Tetouan, Morocco
| | - Saoulajan Charfi
- Laboratory of Human Pathologies Biology, Department of Biology, Faculty of Sciences, Genomic Center of Human Pathologies, Faculty of Medicine and Pharmacy, Mohammed V University in Rabat, Morocco.
| | - Fatima Lakhdar
- Department of Biology, Laboratory of Marine Biotechnology and Environment, Faculty of Sciences, Chouaib Doukkali University, BP 20, El Jadida 24000, Morocco.
| | - Nasreddine El Omari
- Laboratory of Histology, Embryology, and Cytogenetic, Faculty of Medicine and Pharmacy, Mohammed V University in Rabat, Morocco.
| | - Douae Taha
- Laboratoire de Spectroscopie, Modélisation Moléculaire, Matériaux, Nanomatériaux, Eau et Environnement, CERNE2D, Faculté des Sciences, Université Mohammed V, Rabat, Morocco.
| | - Mohammad Ali Shariati
- Department of Technology of Food Production, K.G. Razumoysky Moscow State University of Technologies and Management (the First Cossack University) 109004, Moscow, Russian Federation.
| | - Maksim Rebezov
- V. M. Gorbatov Federal Research Center for Food Systems of Russian, Academy of Sciences, 109029, Moscow, Russian Federation.
| | - Mohamed El-Shazly
- Department of Pharmacognosy, Faculty of Pharmacy, Ain-Shams University, Cairo, 11566, Egypt; Department of Pharmaceutical Biology, Faculty of Pharmacy and Biotechnology, German University in Cairo, Cairo, 11835, Egypt.
| | - Abdelhakim Bouyahya
- Laboratory of Human Pathologies Biology, Department of Biology, Faculty of Sciences, Genomic Center of Human Pathologies, Faculty of Medicine and Pharmacy, Mohammed V University in Rabat, Morocco.
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Paniagua-Herranz L, Gil-Redondo JC, Queipo MJ, González-Ramos S, Boscá L, Pérez-Sen R, Miras-Portugal MT, Delicado EG. Prostaglandin E 2 Impairs P2Y 2/P2Y 4 Receptor Signaling in Cerebellar Astrocytes via EP3 Receptors. Front Pharmacol 2017; 8:937. [PMID: 29311938 PMCID: PMC5743739 DOI: 10.3389/fphar.2017.00937] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Accepted: 12/11/2017] [Indexed: 02/05/2023] Open
Abstract
Prostaglandin E2 (PGE2) is an important bioactive lipid that accumulates after tissue damage or inflammation due to the rapid expression of cyclooxygenase 2. PGE2 activates specific G-protein coupled EP receptors and it mediates pro- or anti-inflammatory actions depending on the cell-context. Nucleotides can also be released in these situations and they even contribute to PGE2 production. We previously described the selective impairment of P2Y nucleotide signaling by PGE2 in macrophages and fibroblasts, an effect independent of prostaglandin receptors but that involved protein kinase C (PKC) and protein kinase D (PKD) activation. Considering that macrophages and fibroblasts influence inflammatory responses and tissue remodeling, a similar mechanism involving P2Y signaling could occur in astrocytes in response to neuroinflammation and brain repair. We analyzed here the modulation of cellular responses involving P2Y2/P2Y4 receptors by PGE2 in rat cerebellar astrocytes. We demonstrate that PGE2 inhibits intracellular calcium responses elicited by UTP in individual cells and that inhibiting this P2Y signaling impairs the astrocyte migration elicited by this nucleotide. Activation of EP3 receptors by PGE2 not only impairs the calcium responses but also, the extracellular regulated kinases (ERK) and Akt phosphorylation induced by UTP. However, PGE2 requires epidermal growth factor receptor (EGFR) transactivation in order to dampen P2Y signaling. In addition, these effects of PGE2 also occur in a pro-inflammatory context, as evident in astrocytes stimulated with bacterial lipopolysaccharide (LPS). While we continue to investigate the intracellular mechanisms responsible for the inhibition of UTP responses, the involvement of novel PKC and PKD in cerebellar astrocytes cannot be excluded, kinases that could promote the internalization of P2Y receptors in fibroblasts.
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Verkhratsky A, Burnstock G. Purinergic and glutamatergic receptors on astroglia. ADVANCES IN NEUROBIOLOGY 2014; 11:55-79. [PMID: 25236724 DOI: 10.1007/978-3-319-08894-5_4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Astroglial cells express many neurotransmitter receptors; the receptors to glutamate and ATP being the most abundant. Here, we provide a concise overview on the expression and main properties of astroglial glutamate receptors (ionotropic receptors represented by AMPA and NMDA subtypes) and metabotropic (mainly mGluR5 and mGluR3 subtypes) and purinoceptors (adenosine receptors of A1, A2A, A2B, and A3 types, ionotropic P2X1/5 and P2X7 subtypes, and metabotropic P2Y purinoceptors). We also discuss the role of these receptors in glial physiology and pathophysiology.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Life Sciences, School of Biological Sciences, The University of Manchester, 1.124 Stopford Building, Oxford Road, Manchester, M13 9PT, UK,
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Burnstock G, Fredholm BB, North RA, Verkhratsky A. The birth and postnatal development of purinergic signalling. Acta Physiol (Oxf) 2010; 199:93-147. [PMID: 20345419 DOI: 10.1111/j.1748-1716.2010.02114.x] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.
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Affiliation(s)
- G Burnstock
- Autonomic Neuroscience Centre, Royal Free and University College Medical School, London, UK.
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Verkhrasky A, Krishtal OA, Burnstock G. Purinoceptors on Neuroglia. Mol Neurobiol 2009; 39:190-208. [DOI: 10.1007/s12035-009-8063-2] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2009] [Accepted: 02/24/2009] [Indexed: 02/06/2023]
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Delicado EG, Jiménez AI, Carrasquero LMG, Castro E, Miras-Portugal MT. Cross-talk among epidermal growth factor, Ap(5)A, and nucleotide receptors causing enhanced ATP Ca(2+) signaling involves extracellular kinase activation in cerebellar astrocytes. J Neurosci Res 2005; 81:789-96. [PMID: 16052566 DOI: 10.1002/jnr.20609] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In previous papers, we reported that ATP calcium responses in cerebellar astrocytes were strongly potentiated by preincubation with nanomolar concentrations of the diadenosine pentaphosphate Ap(5)A. However, the intracellular signaling pathway mediating this effect was not defined. We also showed that stimulation of astrocytes with the dinucleotide led to the activation of extracellular regulated kinases (ERKs). Here, we examined whether ERKs are involved in the potentiating mechanism and intracellular mechanism leading to their activation. Epidermal growth factor (EGF) exactly reproduced the potentiation displayed by the dinucleotide. Moreover, the potentiation of ATP responses by Ap(5)A and EGF was completely abolished by the MAP kinase (MEK) inhibitor U-0126, indicating that ERK activation is a required step for the potentiation event. Our data also indicated that ERK activation and the potentiation of ATP calcium responses were sensitive to the src-like kinase inhibitor herbimycin A, p21(ras) farnesyltransferase inhibitor peptide, and some PKC inhibitors. Taken together, our findings reveal that Ap(5)A triggers the potentiation of ATP calcium responses through an intracellular mechanism that is insensitive to pertussis toxin and that this potentiation requires src protein-mediated ERK activation and the participation of an atypical protein kinase C isoform activated downstream from ERK.
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Affiliation(s)
- Esmerilda G Delicado
- Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense de Madrid, Madrid, Spain.
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Burnstock G, Knight GE. Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 240:31-304. [PMID: 15548415 DOI: 10.1016/s0074-7696(04)40002-3] [Citation(s) in RCA: 573] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Institute, Royal Free and University College Medical School, London NW3 2PF, United Kingdom
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Jiménez AI, Castro E, Delicado EG, Miras-Portugal MT. Specific diadenosine pentaphosphate receptor coupled to extracellular regulated kinases in cerebellar astrocytes. J Neurochem 2002; 83:299-308. [PMID: 12423240 DOI: 10.1046/j.1471-4159.2002.01111.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In this study, we show specific intracellular responses evoked by the stimulation of astrocytes with the P1,P5-di(adenosine-5')pentaphosphate, Ap5A. The stimulation of astrocytes with micromolar concentrations of the dinucleotide elicited rapid increases in intracellular calcium concentration ([Ca2+]i), showing an EC50 value of 15.27 +/- 0.61 micro m. Moreover, the stimulation of cells with nanomolar concentrations of Ap5A, unable to induce calcium responses, increased the phosphorylated forms of extracellular-signal regulated kinase 1/2 (ERK) with an EC50 value of 9.8 +/- 2.4 nm. The maximal activation was observed at 100 nm Ap5A, which was similar to that produced by epidermal growth factor (EGF) under the same experimental conditions. The present data reported here indicate that Ap5A mediated these effects by interacting with a specific receptor, not yet identified, which was different from the P2Y1 and P2Y2/P2Y4 receptors present in all individual astrocytes.
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Affiliation(s)
- Ana I Jiménez
- Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain
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James G, Butt AM. P2Y and P2X purinoceptor mediated Ca2+ signalling in glial cell pathology in the central nervous system. Eur J Pharmacol 2002; 447:247-60. [PMID: 12151016 DOI: 10.1016/s0014-2999(02)01756-9] [Citation(s) in RCA: 189] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Activation of purinoceptors by extracellular ATP is an important component of the glial response to injury in the central nervous system (CNS). ATP has been shown to evoke raised cytosolic [Ca(2+)] in astrocytes, oligodendrocytes, and microglia, the three major glial cell types in the CNS. Glial cells express a heterogenous collection of metabotropic P2Y and ionotropic P2X purinoceptors, which respectively mobilise Ca(2+) from intracellular stores and trigger Ca(2+) influx across the plasmalemma. It is likely that different receptors have distinct roles in glial cell physiology and pathology. Our studies on optic nerve glia in situ indicate that P2Y(1) and P2Y(2/4) receptors are activated at low ATP concentrations, suggesting they are the predominant purinoceptors mediating physiological Ca(2+) signalling. Glia also express P2X(1) and P2X(3) purinoceptors, which mediate fast, rapidly desensitising current and may also be important in signalling. At high concentrations, such as occur in CNS injury, ATP induces large and prolonged increases in glial [Ca(2+)](i) with a primary role for P2Y purinoceptors and inositol trisphosphate (IP(3))-dependent release of Ca(2+) from intracellular stores. In addition, we found that high concentrations of ATP activated a significant P2X component that did not desensitise or saturate and was dependent on extracellular Ca(2+). These are characteristic properties of the P2X(7) subtype, and we provide in situ evidence that application of the P2X(7) receptor agonist benzoyl-benzoyl ATP (BzATP) evokes raised [Ca(2+)](i) in optic nerve glia, and that the dye YO-PRO-1, which passes through pore-forming P2X(7) receptors, is taken up by astrocytes, oligodendrocytes and microglia. Glia also express P2X(2) and P2X(4) receptors that are also pore-forming in the presence of sustained high ATP concentrations and which may also be important in the glial injury response. There is evidence that activation of P2 purinoceptors is a key step in triggering reactive changes in glial cells, including expression of immediate early genes, induction of extracellular signal regulated kinase and cyclooxygenase-2, synthesis of phospholipase A(2), release of arachidonic acid, production of prostaglandins and release of interleukins. We show that the ATP-mediated increase in glial [Ca(2+)](i) is potentiated by arachidonic acid and reduced by the inhibition of phospholipase A(2) inhibition. Together, the results implicate ATP as a primary signalling molecule in glial cells and indicate specific roles for P2Y and P2X purinoceptors in glial cell pathology.
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Affiliation(s)
- Greg James
- Centre for Neuroscience Research, GKT Guy's Campus, King's College London, Hodgkin Building, SE1 1UL, London, UK
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Delicado EG, Jiménez AI, Castro E, Miras-Portugal MT. Cerebellar astrocytes coexpress different purinoceptors: Cross-talk between several transduction mechanisms. Drug Dev Res 2001. [DOI: 10.1002/ddr.1105] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Bolego C, Centemeri C, Abbracchio MP, Ceruti S, Cattabeni F, Jacobson KA, Puglisi L, Rovati GE, Burnstock G, Nicosia S. Two Distinct P2Y Receptors Are Involved in Purine- and Pyrimidine-Evoked Ca 2+ Elevation in Mammalian Brain Astrocytic Cultures. Drug Dev Res 2001; 52:122-132. [PMID: 38239931 PMCID: PMC10794909 DOI: 10.1002/ddr.1106] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
ATP and 2-methyl-thio-ATP (2-Me-SATP) increase cytosolic calcium concentrations ([Ca2+]i) in rat striatal astrocytes (Centemeri et al. [1997] Br J Pharmacol 121:1700-1706). The aim of the present study was to: (1) characterize pyrimidine-induced [Ca2+]i increases in the same experimental system, and (2) try to identify the multiple P2Y receptor subtypes mediating Ca2+ mobilization. UDP and UTP triggered a concentration-dependent [Ca2+]i elevation (EC50s = 0.58 μM ± 0.4 and 31 μM ± 6, respectively).Pyrimidine-evoked [Ca2+]i elevation was solely due to mobilization from intracellular stores, because: (1) removing calcium from extracellular medium or (2) blocking its influx with Ni2+ did not modify UTP responses; (3) the store-depleting agent thapsigargin completely abolished UTP-evoked [Ca2+]i increments. Guanosine-5'-O-(2-thiodiphosphate) partially inhibited the UTP response, whereas pertussis toxin (PTx) had no effect. The phospholipase C inhibitor U-73122 significantly reduced the UTP-evoked [Ca2+]i rise. Computer-assisted analysis indicated that the UTP and UDP responses are mediated by a single receptor, while ATP and 2-Me-SATP interact with two distinct receptors. The selective P2Y1 receptor antagonist MRS2179 abolished the ATP higher potency component. Sequential challenges with the same nucleotides resulted in almost complete homologous desensitization. Pre-exposure to UTP lowered the subsequent responses to either ATP or 2-Me-SATP. Maximally active concentrations of UTP and ATP were not additive. In conclusion, [Ca2+]i elevation in astrocytes by purines and pyrimidines is mediated by two distinct P2Y receptors, likely the P2Y1 and P2Y6 subtypes.
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Affiliation(s)
- Chiara Bolego
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
| | - Carlo Centemeri
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
| | | | - Stefania Ceruti
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
| | - Flaminio Cattabeni
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
| | - Kenneth A. Jacobson
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, NIDDK, NIH, Bethesda, Maryland
| | - Lina Puglisi
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
| | - Gian Enrico Rovati
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
| | - Geoffrey Burnstock
- Autonomic Neuroscience Institute, Royal Free Hospital, School of Medicine, London, United Kingdom
| | - Simonetta Nicosia
- Department of Pharmacological Sciences, University of Milan, Milan, Italy
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Cho YJ, Lee SY, Kim YS, Lee EJ, Seo MS, Yeon G, Lee KH, Lee KJ, Jo YK, Rha HK. Adenosine triphosphate-induced heterologous desensitization of endothelin-1- and glutamate-evoked calcium increases in cultured rat cortical astrocytes. Neurosci Lett 2000; 286:33-6. [PMID: 10822146 DOI: 10.1016/s0304-3940(00)01073-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In rat cortical astrocytes, we investigated the occurrence of cross-talks between purinoceptor and endothelin (ET) receptor, or glutamate receptor. The treatments of adenosine triphosphate (ATP), ET-1, and glutamate induced the increase of intracellular calcium level in the astrocytes. In repetitive additions of ATP to astrocytes, the second application of ATP exhibited comparable amplitude of calcium response, but the stimulation with ATP completely blocked subsequent ET-1- or glutamate-evoked calcium responses showing complete heterologous desensitization. In contrast, ET-1 and glutamate failed to desensitize the response elicited by ATP. Preincubation with sphingosine, a protein kinase C (PKC) inhibitor, reversed the ATP-induced desensitization of ET-1- and glutamate-evoked calcium responses. Taken together, these results demonstrate the resistance of purinoceptor to homologous desensitization, and unidirectional desensitization between ATP and other receptors such as ET and glutamate receptors, suggesting a dominant role of purinoceptor in modulating calcium signal of astrocytes.
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Affiliation(s)
- Y J Cho
- Department of Pharmacology, College of Medicine, The Catholic University of Korea, Seoul, South Korea
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Otero M, Garrad RC, Velázquez B, Hernández-Pérez MG, Camden JM, Erb L, Clarke LL, Turner JT, Weisman GA, González FA. Mechanisms of agonist-dependent and -independent desensitization of a recombinant P2Y2 nucleotide receptor. Mol Cell Biochem 2000; 205:115-23. [PMID: 10821429 DOI: 10.1023/a:1007018001735] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
UTP activates P2Y, receptors in both 1321N1 cell transfectants expressing the P2Y2 receptor and human HT-29 epithelial cells expressing endogenous P2Y, receptors with an EC50 of 0.2-1.0 microM. Pretreatment of these cells with UTP diminished the effectiveness of a second dose of UTP (the IC50 for UTP-induced receptor desensitization was 0.3-1.0 microM for both systems). Desensitization and down-regulation of the P2Y2 nucleotide receptor may limit the effectiveness of UTP as a therapeutic agent. The present studies investigated the phenomenon of P2Y2 receptor desensitization in human 1321N1 astrocytoma cells expressing recombinant wild type and C-terminal truncation mutants of the P2Y2 receptor. In these cells, potent P2Y2 receptor desensitization was observed after a 5 min exposure to UTP. Full receptor responsiveness returned 5-10 min after removal of UTP. Thapsigargin, an inhibitor of Ca2+-ATPase in the endoplasmic reticulum, induced an increase in the intracellular free calcium concentration, [Ca2+]i, after addition of desensitizing concentrations of UTP, indicating that P2Y2 receptor desensitization is not due to depletion of calcium from intracellular stores. Single cell measurements of increases in [Ca2+]i induced by UTP in 1321N1 cell transfectants expressing the P2Y2 receptor indicate that time- and UTP concentration-dependent desensitization occurred uniformly across a cell population. Other results suggest that P2Y2 receptor phosphorylation/dephosphorylation regulate receptor desensitization/resensitization. A 5 min preincubation of 1321N1 cell transfectants with the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), reduced the subsequent response to UTP by about 50%, whereas co-incubation of PMA with UTP caused a greater inhibition in the response. The protein phosphatases-1 and -2A inhibitor, okadaic acid, partially blocked resensitization of the receptor. Furthermore, C-terminal truncation mutants of the P2Y2 receptor that eliminated several potential phosphorylation sites including two for PKC were resistant to UTP-, but not phorbol ester-induced desensitization. Down regulation of protein kinase C isoforms prevented phorbol ester-induced desensitization but had no effect on agonist-induced desensitization of wild type or truncation mutant receptors. These results suggest that phosphorylation of the C-terminus of the P2Y2 receptor by protein kinases other than protein kinase C mediates agonist-induced receptor desensitization. A better understanding of the molecular mechanisms of P2Y2 nucleotide receptor desensitization may help optimize a promising cystic fibrosis pharmacotherapy based on the activation of anion secretion in airway epithelial cells by P2Y, receptor agonists.
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Affiliation(s)
- M Otero
- Department of Chemistry, University of Puerto Rico, San Juan 00931-3346, USA
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Rathbone MP, Middlemiss PJ, Gysbers JW, Andrew C, Herman MA, Reed JK, Ciccarelli R, Di Iorio P, Caciagli F. Trophic effects of purines in neurons and glial cells. Prog Neurobiol 1999; 59:663-90. [PMID: 10845757 DOI: 10.1016/s0301-0082(99)00017-9] [Citation(s) in RCA: 314] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In addition to their well known roles within cells, purine nucleotides such as adenosine 5' triphosphate (ATP) and guanosine 5' triphosphate (GTP), nucleosides such as adenosine and guanosine and bases, such as adenine and guanine and their metabolic products xanthine and hypoxanthine are released into the extracellular space where they act as intercellular signaling molecules. In the nervous system they mediate both immediate effects, such as neurotransmission, and trophic effects which induce changes in cell metabolism, structure and function and therefore have a longer time course. Some trophic effects of purines are mediated via purinergic cell surface receptors, whereas others require uptake of purines by the target cells. Purine nucleosides and nucleotides, especially guanosine, ATP and GTP stimulate incorporation of [3H]thymidine into DNA of astrocytes and microglia and concomitant mitosis in vitro. High concentrations of adenosine also induce apoptosis, through both activation of cell-surface A3 receptors and through a mechanism requiring uptake into the cells. Extracellular purines also stimulate the synthesis and release of protein trophic factors by astrocytes, including bFGF (basic fibroblast growth factor), nerve growth factor (NGF), neurotrophin-3, ciliary neurotrophic factor and S-100beta protein. In vivo infusion into brain of adenosine analogs stimulates reactive gliosis. Purine nucleosides and nucleotides also stimulate the differentiation and process outgrowth from various neurons including primary cultures of hippocampal neurons and pheochromocytoma cells. A tonic release of ATP from neurons, its hydrolysis by ecto-nucleotidases and subsequent re-uptake by axons appears crucial for normal axonal growth. Guanosine and GTP, through apparently different mechanisms, are also potent stimulators of axonal growth in vitro. In vivo the extracellular concentration of purines depends on a balance between the release of purines from cells and their re-uptake and extracellular metabolism. Purine nucleosides and nucleotides are released from neurons by exocytosis and from both neurons and glia by non-exocytotic mechanisms. Nucleosides are principally released through the equilibratory nucleoside transmembrane transporters whereas nucleotides may be transported through the ATP binding cassette family of proteins, including the multidrug resistance protein. The extracellular purine nucleotides are rapidly metabolized by ectonucleotidases. Adenosine is deaminated by adenosine deaminase (ADA) and guanosine is converted to guanine and deaminated by guanase. Nucleosides are also removed from the extracellular space into neurons and glia by transporter systems. Large quantities of purines, particularly guanosine and, to a lesser extent adenosine, are released extracellularly following ischemia or trauma. Thus purines are likely to exert trophic effects in vivo following trauma. The extracellular purine nucleotide GTP enhances the tonic release of adenine nucleotides, whereas the nucleoside guanosine stimulates tonic release of adenosine and its metabolic products. The trophic effects of guanosine and GTP may depend on this process. Guanosine is likely to be an important trophic effector in vivo because high concentrations remain extracellularly for up to a week after focal brain injury. Purine derivatives are now in clinical trials in humans as memory-enhancing agents in Alzheimer's disease. Two of these, propentofylline and AIT-082, are trophic effectors in animals, increasing production of neurotrophic factors in brain and spinal cord. Likely more clinical uses for purine derivatives will be found; purines interact at the level of signal-transduction pathways with other transmitters, for example, glutamate. They can beneficially modify the actions of these other transmitters.
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Affiliation(s)
- M P Rathbone
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada
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Xue D, Xu J, McGuire SO, Devitre D, Sun GY. Studies on the cytosolic phospholipase A2 in immortalized astrocytes (DITNC) revealed new properties of the calcium ionophore, A23187. Neurochem Res 1999; 24:1285-91. [PMID: 10492524 DOI: 10.1023/a:1020981224876] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Besides playing an important role in the maintenance of cell membrane phospholipids, phospholipases A2 (PLA2) are responsible for the release of arachidonic acid (AA) which is a precursor for prostaglandin biosynthesis. The cytosolic PLA2 has been the focus of recent studies, probably due to its ability to respond to protein kinases and changes in intracellular calcium levels. In this study, we examined agents for stimulation of the cytosolic phospholipase A2 in immortalized astrocytes (DITNC). Incubation of DITNC cells with [14C]arachidonic acid (AA) resulted in a time-dependent uptake of the label into phospholipids (PL) and neutral glycerides. In prelabeled cells, release of labeled AA could be stimulated by calcium mobilizing agents such as calcium ionophore A23187 (4-20 microM) and thimerosal (100 microM), and by phorbol myristate acetate (PMA, 100 nM), an agent for activation of protein kinase C. The release of AA could also be stimulated by ATP (200 microM), probably through activation of the purinergic receptor but not by glutamate (1 mM). The stimulated release of AA was dependent on extracellular Ca2+ and was inhibited by mepacrine (50 microM), a non-specific PLA2 inhibitor. Western blot analysis further confirmed the presence of an 85 kDa cPLA2 in both membrane and cytosol fractions of these cells and stimulation by A23187 resulted in translocation of this protein to the membrane fraction. Besides labeled fatty acids, A23187 also stimulated the concomitant release of labeled PL into the culture medium and this event was accompanied by the increased release in lactate dehydrogenase (LDH). Results thus revealed that besides activation of cPLA2, the calcium ionophore A23187 is capable of perturbating cell membrane integrity.
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Affiliation(s)
- D Xue
- Biochemistry Department and Nutritional Sciences Program, University of Missouri, Columbia 65212, USA
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19
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Abstract
Cellular distribution and activation by phorbol myristate acetate (PMA) of classical (alpha, betaI, betaII,gamma), novel (delta, epsilon, theta, eta), and atypical (zeta, iota) protein kinase C (PKC) isoforms were studied in cultured rat neonatal microglial and astroglial cells by Western blot analysis. Among the classical isoforms, only betaII was expressed in microglia and astrocytes in the same abundance. The expression of betaI in microglia was less abundant, while PKCalpha was not detectable in this cell type. PKCgamma was absent in both cell populations. A different pattern of expression was also found for novel and atypical isoenzymes: Both cell types expressed delta, theta, eta, zeta, and iota isoforms, but PKCepsilon was absent in microglia and the expression of PKCzeta and PKCiota in these cells was low compared to astrocytes. The pattern of PKC distribution in cytosolic and particulate fractions as well as activation by short (10 min) and prolonged (4 hr) PMA treatment in both cell types were similar. On the whole, in comparison with astrocytes, PKC in microglial cells was less expressed, both in terms of number of isoforms and level of expression. The microglial profile of PKC isoforms differed from that of rat peritoneal macrophages, which did express PKCalpha. Preliminary evidence suggests that the ability of PMA to enhance cyclic AMP responses in astrocytes, but not in microglia, is related to the different pattern of expression of PKCalpha and PKCepsilon in the two cell types.
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Affiliation(s)
- N Slepko
- Laboratory of Pathophysiology, Istituto Superiore di Sanità, Rome, Italy
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Jim�nez AI, Castro E, Mirabet M, Franco R, Delicado EG, Miras-Portugal MT. Potentiation of ATP calcium responses by A2B receptor stimulation and other signals coupled to Gs proteins in type-1 cerebellar astrocytes. Glia 1999. [DOI: 10.1002/(sici)1098-1136(199904)26:2<119::aid-glia3>3.0.co;2-d] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Abstract
Calcium waves represent a widespread form of intercellular communication. Although they have been thought for a long time to require gap junctions, we recently demonstrated that mouse cortical astrocytes use an extracellular messenger for calcium wave propagation. The present experiments identify ATP as a major extracellular messenger in this system. Medium collected from astrocyte cultures during (but not before) calcium wave stimulation contains ATP. The excitatory effects of medium samples and of ATP are blocked by purinergic receptor antagonists and by pretreatment with apyrase; these same purinergic receptor antagonists block propagation of electrically evoked calcium waves. ATP, applied at the concentration measured in medium samples, evokes responses that are qualitatively and quantitatively similar to those evoked by those medium samples. These data implicate ATP as an important transmitter between CNS astrocytes.
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Langley D, Pearce B. Pyrimidine nucleotide-stimulated thromboxane A2 release from cultured glia. Cell Mol Neurobiol 1998; 18:477-86. [PMID: 9777248 DOI: 10.1023/a:1026323208437] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
1. Uridine triphosphate (UTP), uridine diphosphate (UDP), cytidine triphosphate (CTP), and deoxythymidine triphosphate (TTP) caused concentration-dependent increases in the release of thromboxane A2 (TXA2) from cultured glia prepared from the newborn rat cerebral cortex. Although each of the pyrimidine nucleotides displayed similar potencies, CTP and TTP were considerably less effective than either UTP or UDP. The purine nucleotide ATP was equally as potent as the pyrimidine nucleotides but was marginally less effective than either UTP or UDP. 2. The ability of UTP, UDP, TTP, and CTP to promote TXA2 release from cultured glia was inhibited in a concentration-dependent manner by suramin and was markedly reduced when incubations were performed either in Ca(2+)-free medium or on cultures which had been maintained in serum-free growth medium for 4 days prior to experimentation. 3. Challenges with UTP and UDP in combination were found to elicit a response which was no different from the effects of these nucleotides alone; in addition, their effects were reversed by the phospholipase A2 inhibitor ONO-RS-082. A slight reduction in UTP- and UDP-stimulated TXA2 release was observed in cultures grown in the presence of leucine methyl ester, a treatment reported to limit microglial survival. 4. These results suggest that glia are targets for extracellular pyrimidine nucleotides and that their ability to release eicosanoids from these cells may be important in the brain's response to damage.
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Affiliation(s)
- D Langley
- Department of Pharmacology, School of Pharmacy, London, UK
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Chen CC, Wang JK, Chen WC, Lin SB. Protein kinase C eta mediates lipopolysaccharide-induced nitric-oxide synthase expression in primary astrocytes. J Biol Chem 1998; 273:19424-30. [PMID: 9677361 DOI: 10.1074/jbc.273.31.19424] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The signaling pathway involved in protein kinase C (PKC) activation and role of PKC isoforms in lipopolysaccharide (LPS)-induced nitric oxide (NO) release were studied in primary cerebellar astrocytes. LPS caused a dose- and time-dependent increase in NO release and inducible NO synthase (iNOS) expression. The tyrosine kinase inhibitor, genestein, the phosphatidylcholine-phospholipase C inhibitor, D609, and the phosphatidate phosphodrolase inhibitor, propranolol, attenuated the LPS effects, whereas the PI-PLC inhibitor, U73122, had no effect. The PKC inhibitors (staurosporine, Ro 31-8220, Go 6976, and calphostin C) also inhibited LPS-induced NO release and iNOS expression. However, long term (24 h) pretreatment of cells with 12-O-tetradecanoyl phorbol-13-acetate (TPA) did not affect the LPS response. Previous results have shown that TPA-induced translocation, but not down-regulation, of PKCeta occurs in astrocytes (Chen, C. C., and Chen, W. C. (1996) Glia 17, 63-71), suggesting possible involvement of PKCeta in LPS-mediated effects. Treatment with antisense oligonucleotides for PKCeta or delta, another isoform abundantly expressed in astrocytes, demonstrated the involvement of PKCeta, but not delta, in LPS-mediated effects. Stimulation of cells for 1 h with LPS caused activation of nuclear factor (NF)-kB in the nuclei as detected by the formation of a NF-kB-specific DNA-protein complex; this effect was inhibited by genestein, D609, propranolol, or Ro 31-8220 or by PKCeta antisense oligonucleotides, but not by long term TPA treatment. These data suggest that in astrocytes, LPS might activate phosphatidylcholine-phospholipase C and phosphatidylcholine-phospholipase D through an upstream protein tyrosine kinase to induce PKC activation. Of the PKC isoforms present in these cells, only activation of PKCeta by LPS resulted in the stimulation of NF-kB-specific DNA-protein binding and then initiated the iNOS expression and NO release. This is further evidence demonstrating that different members of the PKC family within a single cell are involved in specific physiological responses.
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Affiliation(s)
- C C Chen
- Institutes of Pharmacology, College of Medicine, National Taiwan University, No.1, Jen-Ai Road, 1st Section, Taipei 10018, Taiwan.
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Meller N, Altman A, Isakov N. New perspectives on PKCtheta, a member of the novel subfamily of protein kinase C. Stem Cells 1998; 16:178-92. [PMID: 9617893 DOI: 10.1002/stem.160178] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Members of the protein kinase C (PKC) family of serine/threonine protein kinases have been implicated in numerous cellular responses in a large variety of cell types. Expression patterns of individual members and differences in their cofactor requirements and potential substrate specificity suggest that each isoenzyme may be involved in specific regulatory processes. The PKCtheta isoenzyme exhibits a relatively restricted expression pattern with high protein levels found predominantly in hematopoietic cells and skeletal muscle. PKCtheta was found to be expressed in T, but not B lymphocytes, and to colocalize with the T-cell antigen receptor (TCR) at the site of contact between the antigen-responding T cell and the antigen-presenting cell (APC). Colocalization of PKCtheta with the TCR was selective for this isoenzyme and occurred only upon antigen-mediated responses leading to T-cell activation and proliferation. PKCtheta was found to be involved in the regulation of transcriptional activation of early-activation genes, predominantly AP-1, and its cellular distribution and activation were found to be regulated by the 14-3-3 protein. Other findings indicated that PKCtheta can associate with the HIV negative factor (Nef) protein, suggesting that altered regulation of PKCtheta by Nef may contribute to the T-cell impairments that are characteristic of infection by HIV. PKCtheta is expressed at relatively high levels in skeletal muscle, where it is suggested to play a role in signal transduction in both the developing and mature neuromuscular junction. In addition, PKCtheta appears to be involved in the insulin-mediated response of intact skeletal muscle, as well as in experimentally induced insulin resistance of skeletal muscle. Further studies suggest that PKCtheta is expressed in endothelial cells and is involved in multiple processes essential for angiogenesis and wound healing, including the regulation of cell cycle progression, formation and maintenance of actin cytoskeleton, and formation of capillary tubes. Here, we review recent progress in the study of PKCtheta and discuss its potential role in various cellular responses.
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Affiliation(s)
- N Meller
- Department of Microbiology and Immunology, Faculty of Health Sciences, and the Cancer Research Center, Ben Gurion University of the Negev, Beer Sheva, Israel
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Abstract
ATP-induced arachidonic acid (AA) release was studied in [3H]AA-prelabeled cultured astrocytes. To characterize the P2 purinoceptor-mediated effect of ATP, the subtype-specific agonists 2-methylthio ATP (2-MeSATP) and UTP were compared. ATP, UTP, or 2-MeSATP induced a dose-dependent increase of [3H]AA release, with EC50 values of 22.7 microM, 29.4 microM, and 1.68 microM, respectively; alpha,beta-methyleneATP and adenosine had no effect. The order of potency was ATP = UTP > or = 2-MeSATP, indicating that ATP interacted with both P2Y1 and P2Y2 receptors to mediate AA release in astrocytes. The effect of ATP, UTP, or 2-MeSATP was markedly inhibited by pretreatment of cells with pertussis toxin. Ca2+ ionophore-A23187 and PKC activator-TPA mimicked the effects of these three agonists to stimulate AA release. ATP, UTP, and 2-MeSATP induced a rapidly initial rise of [Ca2+]i and a sustained [Ca2+]i increase. The AA release was blocked in the external Ca2+ free in condition the sustained [Ca2+]i increase was abolished. Both A23187- and TPA-induced AA release were also blocked in this condition. Furthermore, inorganic Ca2+ channel blocker Co2+ inhibited ATP, UTP, or 2-MeSATP induced AA release as well. Long-term (24 h) treatment of cells with TPA resulted in an attenuation of three agonists, TPA or A23187 response. Similarly, ATP or TPA promoted AA release was inhibited by the mitogen-activated protein kinase (MAPK) cascade inhibitor PD 98059. ATP, TPA, or A23187 induced an increase in the activity and tyrosine phosphorylation of p42 MAPK, as well as a molecular weight shift, consistent with phosphorylation, of cytosolic phospholipase A2 (cPLA2). ATP- and TPA-stimulated activation of p42 MAPK activity and tyrosine phosphorylation were inhibited by long-term TPA treatment, while A23187-stimulated effects were completely blocked. Furthermore, tyrosine phosphorylation and activation of p42 MAPK and mobility shift of cPLA2 induced by A23187 were reversed in the absence of external Ca2+, suggesting the involvement of PKCalpha in MAPK activation and mobility shift of cPLA2. Taken together, ATP-stimulated AA release was secondary to the activation of P2Y1 and P2Y2 receptors/PLC pathway. Ca2+ and PKC interact to regulate this response. Elevation of intracellular Ca2+, the mechanism involving extracellular Ca2+ influx, might act partly through PKCalpha activation and in turn MAPK might be activated, leading to cPLA2 phosphorylation and AA release.
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Affiliation(s)
- W C Chen
- Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei
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Maier R, Glatz A, Mosbacher J, Bilbe G. Cloning of P2Y6 cDNAs and identification of a pseudogene: comparison of P2Y receptor subtype expression in bone and brain tissues. Biochem Biophys Res Commun 1997; 237:297-302. [PMID: 9268704 DOI: 10.1006/bbrc.1997.7135] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Cellular responses to ATP/UTP and analogs are mediated by G-protein coupled P2Y receptors and have been proposed to play a role in the regulation of bone metabolism. Using a degenerate PCR approach on MG-63 cell cDNA we found PCR fragments coding for human P2Y1 and a new receptor, P2Y6. cDNA cloning of the P2Y6 receptor identified three cDNA isoforms. Two contained the same contiguous ORFs but differed in their 5' UTRs and may therefore originate by alternative splicing whereas the third represents a pseudogene. Analysis of P2Y receptor subtype expression in human bone and the osteoblastic cell lines OHS-4 and MG-63 by RT-PCR showed that all known human P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, and P2Y7) were expressed. In contrast, analysis of brain-derived cell lines suggests that a selective expression of P2Y receptor subtypes occurs in brain tissue.
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Affiliation(s)
- R Maier
- Novartis Pharma Inc., Basel, CH-4002, Switzerland
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Chen CC, Wang JK, Chen WC. TPA induces translocation but not down-regulation of new PKC isoform eta in macrophages, MDCK cells and astrocytes. FEBS Lett 1997; 412:30-4. [PMID: 9257683 DOI: 10.1016/s0014-5793(97)00697-2] [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: 02/05/2023]
Abstract
New type protein kinase C (PKC) eta was found to be expressed in RAW 264.7 and J774A.1 macrophages, Madin-Darby canine kidney (MDCK) cells and astrocytes by Western blot analysis. Both cytosol and membrane in macrophages and astrocytes express this isoform, however, the expression in the membrane is more abundant than that in the cytosol. On the other hand, only membrane PKC eta was detected in MDCK cells. Exposure of the cells to 1 microM TPA for 10 min resulted in the translocation of PKC eta from the cytosolic to the membrane fraction. This translocation maintained at a constant level after 1.5, 3, 6 and 24 h TPA treatment. However, another new type PKC delta which expressed in the macrophages and astrocytes was down-regulated after long-term (6 and 24 h) TPA treatment. The immunoreactive band of PKC eta in J774A.1 macrophages was blocked by the control PKC eta antigenic peptide. Incubation of RAW 264.7 macrophages with UTP (1, 10 and 100 microM) resulted in the accumulation of inositol phosphates, indicating the presence of P2 receptor-coupled PLC pathway in these cells. This natural activator UTP also induced translocation of PKC eta from cytosol to the membrane in RAW 264.7 macrophages after 1, 5 or 10 min treatment. Immunofluorescence microscopy revealed that in RAW 264.7 cells, PKC eta is located in the cytoplasm organelle, plasma membrane and nuclear envelope. Stimulation of the cells with TPA resulted in translocation to the plasma membrane. This translocation of PKC eta was still apparent after 24 h treatment with TPA.
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Affiliation(s)
- C C Chen
- Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei.
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