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Maaliki D, Jaffa AA, Nasser S, Sahebkar A, Eid AH. Adrenoceptor Desensitization: Current Understanding of Mechanisms. Pharmacol Rev 2024; 76:358-387. [PMID: 38697858 DOI: 10.1124/pharmrev.123.000831] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 01/15/2024] [Accepted: 01/18/2024] [Indexed: 05/05/2024] Open
Abstract
G-protein coupled receptors (GPCRs) transduce a wide range of extracellular signals. They are key players in the majority of biologic functions including vision, olfaction, chemotaxis, and immunity. However, as essential as most of them are to body function and homeostasis, overactivation of GPCRs has been implicated in many pathologic diseases such as cancer, asthma, and heart failure (HF). Therefore, an important feature of G protein signaling systems is the ability to control GPCR responsiveness, and one key process to control overstimulation involves initiating receptor desensitization. A number of steps are appreciated in the desensitization process, including cell surface receptor phosphorylation, internalization, and downregulation. Rapid or short-term desensitization occurs within minutes and involves receptor phosphorylation via the action of intracellular protein kinases, the binding of β-arrestins, and the consequent uncoupling of GPCRs from their cognate heterotrimeric G proteins. On the other hand, long-term desensitization occurs over hours to days and involves receptor downregulation or a decrease in cell surface receptor protein level. Of the proteins involved in this biologic phenomenon, β-arrestins play a particularly significant role in both short- and long-term desensitization mechanisms. In addition, β-arrestins are involved in the phenomenon of biased agonism, where the biased ligand preferentially activates one of several downstream signaling pathways, leading to altered cellular responses. In this context, this review discusses the different patterns of desensitization of the α 1-, α 2- and the β adrenoceptors and highlights the role of β-arrestins in regulating physiologic responsiveness through desensitization and biased agonism. SIGNIFICANCE STATEMENT: A sophisticated network of proteins orchestrates the molecular regulation of GPCR activity. Adrenoceptors are GPCRs that play vast roles in many physiological processes. Without tightly controlled desensitization of these receptors, homeostatic imbalance may ensue, thus precipitating various diseases. Here, we critically appraise the mechanisms implicated in adrenoceptor desensitization. A better understanding of these mechanisms helps identify new druggable targets within the GPCR desensitization machinery and opens exciting therapeutic fronts in the treatment of several pathologies.
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Affiliation(s)
- Dina Maaliki
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Aneese A Jaffa
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Suzanne Nasser
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Amirhossein Sahebkar
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Ali H Eid
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
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Hernández-Espinosa DA, Alcántara-Hernández R, Solís KH, García-Sáinz JA. Roles of the α 1B-Adrenergic Receptor Phosphorylation Domains in Signaling and Internalization. Int J Mol Sci 2023; 24:16963. [PMID: 38069285 PMCID: PMC10707169 DOI: 10.3390/ijms242316963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Revised: 11/14/2023] [Accepted: 11/20/2023] [Indexed: 12/18/2023] Open
Abstract
The function of the α1B-adrenergic receptor phosphorylation sites previously detected by mass spectrometry was evaluated by employing mutants, substituting them with non-phosphorylatable amino acids. Substitution of the intracellular loop 3 (IL3) sites did not alter baseline or stimulated receptor phosphorylation, whereas substitution of phosphorylation sites in the carboxyl terminus (Ctail) or both domains (IL3/Ctail) markedly decreased receptor phosphorylation. Cells expressing the IL3 or Ctail receptor mutants exhibited a noradrenaline-induced calcium-maximal response similar to those expressing the wild-type receptor, and a shift to the left in the concentration-response curve to noradrenaline was also noticed. Cells expressing the IL3/Ctail mutant exhibited higher apparent potency and increased maximal response to noradrenaline than those expressing the wild-type receptor. Phorbol ester-induced desensitization of the calcium response to noradrenaline was reduced in cells expressing the IL3 mutant and abolished in cells in which the Ctail or the IL3/Ctail were modified. In contrast, desensitization in response to preincubation with noradrenaline was unaffected in cells expressing the distinct receptor mutants. Noradrenaline-induced ERK phosphorylation was surprisingly increased in cells expressing IL3-modified receptors but not in those expressing receptors with the Ctail or IL3/Ctail substitutions. Our data indicate that phosphorylation sites in the IL3 and Ctail domains mediate and regulate α1B-adrenergic receptor function. Phorbol ester-induced desensitization seems to be closely associated with receptor phosphorylation, whereas noradrenaline-induced desensitization likely involves other elements.
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Affiliation(s)
| | | | | | - J. Adolfo García-Sáinz
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México 04510, Mexico; (D.A.H.-E.); (R.A.-H.); (K.H.S.)
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3
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Renkhold L, Kollmann R, Inderwiedenstraße L, Kienitz MC. PKC-isoform specific regulation of receptor desensitization and KCNQ1/KCNE1 K + channel activity by mutant α 1B-adrenergic receptors. Cell Signal 2021; 91:110228. [PMID: 34958868 DOI: 10.1016/j.cellsig.2021.110228] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 12/20/2021] [Accepted: 12/21/2021] [Indexed: 11/25/2022]
Abstract
Activation of a specific protein kinase C (PKC) isoform during stimulation of Gq protein-coupled receptors (GqPCRs) is determined by homologous receptor desensitization that controls the spatiotemporal formation of downstream Gq signalling molecules. Furthermore, GqPCR-activated PKC isoforms specifically regulate receptor activity via a negative feedback mechanism. In the present study, we investigated the contribution of several phosphorylation sites in the α1B-adrenergic receptor (α1B-AR) for PKC and G protein coupled receptor kinase 2 (GRK2) to homologous receptor desensitization and effector modulation. We analyzed signalling events downstream to human wildtype α1B-ARs and α1B-ARs lacking PKC or GRK2 phosphorylation sites (Δ391-401, α1B-ΔPKC-AR and Δ402-520, α1B-ΔGRK-AR) by means of FRET-based biosensors in HEK293 that served as online-assays of receptor activity. K+ currents through KCNQ1/KCNE1 channels (IKs), which are regulated by both phosphatidylinositol 4,5-bisphosphate (PIP2)-depletion and/or phosphorylation by PKC, were measured as a functional readout of wildtype and mutant α1B-AR receptor activity. As a novel finding, we provide evidence that deletion of PKC and GRK2 phosphorylation sites in α1B-ARs abrogates the contribution of PKCα to homologous receptor desensitization. Instead, the time course of mutant receptor activity was specifically modulated by PKCβ. Mutant α1B-ARs displayed pronounced homologous receptor desensitization that was abolished by PKCβ-specific pharmacological inhibitors. IKs modulation during stimulation of wildtype and mutant α1B-ARs displayed transient inhibition and current facilitation after agonist withdrawal with reduced capability of mutant α1B-ARs to induce IKs inhibition. Pharmacological inhibition of the PKCβ isoform did not augment IKs reduction by mutant α1B-ARs, but shifted IKs modulation towards current facilitation. Coexpression of an inactive (dominant-negative) PKCδ isoform (DN-PKCδ) abolished IKs facilitation in α1B-ΔGRK-AR-expressing cells, but not in α1B-ΔPKC-AR-expressing cells. The data indicate that the differential modulation of IKs activity by α1B-ΔGRK- and α1B-ΔPKC-receptors is attributed to the activation of entirely distinct novel PKC isoforms. To summarize, specific phosphorylation sites within the wildtype and mutant α1B-adrenergic receptors are targeted by different PKC isoforms, resulting in differential regulation of receptor desensitization and effector function.
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Affiliation(s)
- Lina Renkhold
- Klinik für Hautkrankheiten, Universitätsklinikum Münster, Von-Esmarch-Str. 58, D-48149 Münster, Deutschland, Germany
| | - Rike Kollmann
- Department of Cellular Physiology, Institute of Physiology, Ruhr University Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany
| | - Leonie Inderwiedenstraße
- Department of Cellular Physiology, Institute of Physiology, Ruhr University Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany
| | - Marie-Cecile Kienitz
- Department of Cellular Physiology, Institute of Physiology, Ruhr University Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany.
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Liu Y, Shao YT, Ward R, Ma L, Gui HX, Hao Q, Mu X, Yang Y, An S, Guo XX, Xu TR. The C-terminal of the α1b-adreneroceptor is a key determinant for its structure integrity and biological functions. Biosci Biotechnol Biochem 2021; 85:1128-1139. [PMID: 33693487 DOI: 10.1093/bbb/zbab034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 02/19/2021] [Indexed: 12/13/2022]
Abstract
The C-terminal of G protein-coupled receptors is now recognized as being important for G protein activation and signaling function. To detect the role of C-terminal tail in receptor activation, we used the α1b-AR, which has a long C-terminal of 164 amino acids. We constructed the intramolecular FRET sensors, in which the C-terminal was truncated to 10 (∆C-10), 20 (∆C-20), 30 (∆C-30), 50 (∆C-50), 70 (∆C-70), or 90 (∆C-90). The truncated mutants of ∆C-10, ∆C-20, or ∆C-30 cannot induce FRET signal changes and downstream ERK1/2 phosphorylation. However, the truncated mutants of ∆C-50, ∆C-70, or ∆C-90 induce significant FRET signal changes and downstream ERK1/2 phosphorylation, especially ∆C-90. This is particularly true in the case of the ∆C-90, ∆C-70, or ∆C-50 which retained the potential phosphorylation sites (Ser401, Ser404, Ser408, or Ser410). The ∆C-90 showed an increase in agonist-induced FRET signal changes and ERK1/2 phosphorylation in PKC- or endocytosis-dependent and EGFR-, src-, or β-arrestin2-independent.
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Affiliation(s)
- Ying Liu
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China.,Institute of Life Sciences, Jinzhou Medical University, Jinzhou, Liaoning, China
| | - Yu-Ting Shao
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Richard Ward
- Centre for Translational Pharmacology, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Li Ma
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Hao-Xin Gui
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Qian Hao
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Xi Mu
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Yang Yang
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Su An
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Xiao-Xi Guo
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
| | - Tian-Rui Xu
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming, Yunnan, China
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Ye L, Orynbayev M, Zhu X, Lim EY, Dereddi RR, Agarwal A, Bergles DE, Bhat MA, Paukert M. Ethanol abolishes vigilance-dependent astroglia network activation in mice by inhibiting norepinephrine release. Nat Commun 2020; 11:6157. [PMID: 33268792 PMCID: PMC7710743 DOI: 10.1038/s41467-020-19475-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Accepted: 10/16/2020] [Indexed: 12/17/2022] Open
Abstract
Norepinephrine adjusts sensory processing in cortical networks and gates plasticity enabling adaptive behavior. The actions of norepinephrine are profoundly altered by recreational drugs like ethanol, but the consequences of these changes on distinct targets such as astrocytes, which exhibit norepinephrine-dependent Ca2+ elevations during vigilance, are not well understood. Using in vivo two-photon imaging, we show that locomotion-induced Ca2+ elevations in mouse astroglia are profoundly inhibited by ethanol, an effect that can be reversed by enhancing norepinephrine release. Vigilance-dependent astroglial activation is abolished by deletion of α1A-adrenergic receptor from astroglia, indicating that norepinephrine acts directly on these ubiquitous glial cells. Ethanol reduces vigilance-dependent Ca2+ transients in noradrenergic terminals, but has little effect on astroglial responsiveness to norepinephrine, suggesting that ethanol suppresses their activation by inhibiting norepinephrine release. Since abolition of astroglia Ca2+ activation does not affect motor coordination, global suppression of astroglial networks may contribute to the cognitive effects of alcohol intoxication. The effects of norepinephrine on sensory processing in cortical networks are altered by recreational drugs like ethanol. The authors show that ethanol suppresses the activation of astrocytes by inhibiting norepinephrine release which may contribute to the cognitive effects of alcohol intoxication.
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Affiliation(s)
- Liang Ye
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Murat Orynbayev
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Xiangyu Zhu
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.,Xiangya School of Medicine, Central South University, Changsha, Hunan, China
| | - Eunice Y Lim
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.,Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Ram R Dereddi
- The Chica and Heinz Schaller Research Group, Institute for Anatomy and Cell Biology, Heidelberg University, Heidelberg, Germany
| | - Amit Agarwal
- The Chica and Heinz Schaller Research Group, Institute for Anatomy and Cell Biology, Heidelberg University, Heidelberg, Germany.,Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Dwight E Bergles
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Johns Hopkins Kavli Neuroscience Discovery Institute, Baltimore, MD, USA
| | - Manzoor A Bhat
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.,Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Martin Paukert
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA. .,Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA.
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6
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Roles of the G protein-coupled receptor kinase 2 and Rab5 in α 1B-adrenergic receptor function and internalization. Eur J Pharmacol 2020; 867:172846. [PMID: 31811856 DOI: 10.1016/j.ejphar.2019.172846] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 11/21/2019] [Accepted: 12/03/2019] [Indexed: 11/23/2022]
Abstract
Cells expressing eGFP-tagged Rab5 (wild-type or the GDP-Rab5 mutant) and the DsRed-tagged α1B-adrenergic receptors were employed and the roles of GRK2 were studied utilizing paroxetine and the dominant-negative mutant of GRK2 (DN-GRK2). The following parameters were studied: a) FRET (as an index of α1B-adrenergic receptor-Rab5 interaction): b) intracellular accumulation of DsRed fluorescence (receptor internalization); c) α1B-adrenergic receptor phosphorylation, and d) noradrenaline-induced increase in intracellular calcium concentration. Noradrenaline increased α1B-adrenergic receptor-Rab5 interaction, which was blocked by paroxetine and by expression of the dominant-negative GRK2 mutant. Similarly, paroxetine and expression of the DN-GRK2 or the GDP-Rab5 mutants markedly decreased receptor internalization, α1B-adrenergic receptor phosphorylation, and attenuated the ability of the adrenergic agonist to induce homologous desensitization (calcium signaling). The S406, 410,412A α1B-adrenergic receptor mutant did not reproduce the actions of GRK2 inhibition. The data indicate that GRK2 and Rab5 play key roles in α1B-adrenergic receptor phosphorylation, internalization, and desensitization. The possibility that Rab5 might form part of a signaling complex is suggested, as well as that GDP-Rab5 might interfere with the ability of GRK2 to catalyze α1B-adrenergic receptor phosphorylation.
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Hernández-Espinosa DA, Carmona-Rosas G, Alfonzo-Méndez MA, Alcántara-Hernández R, García-Sáinz JA. Sites phosphorylated in human α 1B-adrenoceptors in response to noradrenaline and phorbol myristate acetate. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1866:1509-1519. [PMID: 31325464 DOI: 10.1016/j.bbamcr.2019.07.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Revised: 06/27/2019] [Accepted: 07/14/2019] [Indexed: 01/11/2023]
Abstract
Phosphorylation of the human α1B-adrenergic receptor (fused with the green fluorescent protein) was studied employing the inducible Flp-ln HEK293 T-Rex system for expression. Serine/alanine substitutions were performed in five sites corresponding to those previously identified as phosphorylation targets in the hamster ortholog. Desensitization was decreased in these mutants but receptor phosphorylation was still clearly detected. The protein phosphorylation of the wild-type receptor (fused to the green fluorescent protein) was studied, using mass spectrometry, under baseline and stimulated conditions (noradrenaline or phorbol myristate acetate). Basal phosphorylation was detected at sites located at the intracellular loop 3 and carboxyl terminus, and the number of sites detected increased under agonist activation and stimulation of protein kinase C. The phosphorylation patterns differed under the distinct conditions. Three of the phosphorylation sites detected in this work corresponded to those observed in the hamster receptor. The phosphorylation sites detected included the following: a) at the intracellular loop 3: serines 246, 248, 257, 267, and 277; and threonines 252, 264, and 268, and b) at the carboxyl terminus: serines 396, 400, 402, 406, 423, 425, 427, 455, and 470, and threonines 387, 392, 420, and 475. Our data indicate that complex phosphorylation patterns exist and suggest the possibility that such differences could be relevant in receptor function and subcellular localization.
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Affiliation(s)
- David A Hernández-Espinosa
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - Gabriel Carmona-Rosas
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - Marco A Alfonzo-Méndez
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - Rocío Alcántara-Hernández
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - J Adolfo García-Sáinz
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico.
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Perkovska S, Méjean C, Ayoub MA, Li J, Hemery F, Corbani M, Laguette N, Ventura MA, Orcel H, Durroux T, Mouillac B, Mendre C. V 1b vasopressin receptor trafficking and signaling: Role of arrestins, G proteins and Src kinase. Traffic 2018; 19:58-82. [PMID: 29044966 DOI: 10.1111/tra.12535] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 10/13/2017] [Accepted: 10/13/2017] [Indexed: 11/29/2022]
Abstract
The signaling pathway of G protein-coupled receptors is strongly linked to their trafficking profile. Little is known about the molecular mechanisms involved in the vasopressin receptor V1b subtype (V1b R) trafficking and its impact on receptor signaling and regulation. For this purpose, we investigated the role of β-arrestins in receptor desensitization, internalization and recycling and attempted to dissect the V1b R-mediated MAP kinase pathway. Using MEF cells Knocked-out for β-arrestins 1 and 2, we demonstrated that both β-arrestins 1 and 2 play a fundamental role in internalization and recycling of V1b R with a rapid and transient V1b R-β-arrestin interaction in contrast to a slow and long-lasting β-arrestin recruitment of the V2 vasopressin receptor subtype (V2 R). Using V1b R-V2 R chimeras and V1b R C-terminus truncations, we demonstrated the critical role of the V1b R C-terminus in its interaction with β-arrestins thereby regulating the receptor internalization and recycling kinetics in a phosphorylation-independent manner. In parallel, V1b R MAP kinase activation was dependent on arrestins and Src-kinase but independent on G proteins. Interestingly, Src interacted with hV1b R at basal state and dissociated when receptor internalization occurred. Altogether, our data describe for the first time the trafficking profile and MAP kinase pathway of V1b R involving both arrestins and Src kinase family.
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Affiliation(s)
- Sanja Perkovska
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Catherine Méjean
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Mohammed Akli Ayoub
- Biology Department, College of Science, United Arab Emirates University, Al Ain, United Arab Emirates
| | - Juan Li
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Floriane Hemery
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Maithé Corbani
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Nadine Laguette
- INSERM, U1016, Institut Cochin, Paris, France.,CNRS, UMR 8104, Paris, France.,Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Maria-Angeles Ventura
- INSERM, U1016, Institut Cochin, Paris, France.,CNRS, UMR 8104, Paris, France.,Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Hélène Orcel
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Thierry Durroux
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Bernard Mouillac
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
| | - Christiane Mendre
- Centre National de la Recherche Scientifique (CNRS), Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle (IGF), Montpellier, France.,Institut National de la Santé et de la Recherche Médicale (INSERM), U1191, Montpellier, France.,Université de Montpellier, Montpellier, France
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Alfonzo-Méndez MA, Carmona-Rosas G, Hernández-Espinosa DA, Romero-Ávila MT, García-Sáinz JA. Different phosphorylation patterns regulate α 1D-adrenoceptor signaling and desensitization. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2018; 1865:842-854. [PMID: 29551601 DOI: 10.1016/j.bbamcr.2018.03.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 03/02/2018] [Accepted: 03/13/2018] [Indexed: 12/14/2022]
Abstract
Human α1D-adrenoceptors (α1D-ARs) are a group of the seven transmembrane-spanning proteins that mediate many of the physiological and pathophysiological actions of adrenaline and noradrenaline. Although it is known that α1D-ARs are phosphoproteins, their specific phosphorylation sites and the kinases involved in their phosphorylation remain largely unknown. Using a combination of in silico analysis, mass spectrometry and site directed mutagenesis, we identified distinct α1D-AR phosphorylation patterns during noradrenaline- or phorbol ester-mediated desensitizations. We found that the G protein coupled receptor kinase, GRK2, and conventional protein kinases C isoforms α/β, phosphorylate α1D-AR during these processes. Furthermore, we showed that the phosphorylated residues are located in the receptor's third intracellular loop (S300, S323, T328, S331, S332, S334) and carboxyl region (S441, T442, T477, S486, S492, T507, S515, S516, S518, S543) and are conserved among orthologues but are not conserved among the other human α1-adrenoceptor subtypes. Additionally, we found that phosphorylation in either the third intracellular loop or carboxyl tail was sufficient to regulate calcium signaling desensitization. By contrast, mutations in either of these two domains significantly altered mitogen activated protein kinase (ERK) pathway and receptor internalization, suggesting that they have differential regulatory mechanisms. Our data provide new insights into the functional repercussions of these posttranslational modifications in signaling outcomes and desensitization.
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Affiliation(s)
- Marco A Alfonzo-Méndez
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - Gabriel Carmona-Rosas
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - David A Hernández-Espinosa
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - M Teresa Romero-Ávila
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico
| | - J Adolfo García-Sáinz
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70-248, Ciudad de México CP 04510, Mexico.
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Noradrenaline, oxymetazoline and phorbol myristate acetate induce distinct functional actions and phosphorylation patterns of α 1A-adrenergic receptors. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:2378-2388. [PMID: 28888989 DOI: 10.1016/j.bbamcr.2017.09.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 08/31/2017] [Accepted: 09/04/2017] [Indexed: 01/04/2023]
Abstract
In LNCaP cells that stably express α1A-adrenergic receptors, oxymetazoline increased intracellular calcium and receptor phosphorylation, however, this agonist was a weak partial agonist, as compared to noradrenaline, for calcium signaling. Interestingly, oxymetazoline-induced receptor internalization and desensitization displayed greater effects than those induced by noradrenaline. Phorbol myristate acetate induced modest receptor internalization and minimal desensitization. α1A-Adrenergic receptor interaction with β-arrestins (colocalization/coimmunoprecipitation) was induced by noradrenaline and oxymetazoline and, to a lesser extent, by phorbol myristate acetate. Oxymetazoline was more potent and effective than noradrenaline in inducing ERK 1/2 phosphorylation. Mass spectrometric analysis of immunopurified α1A-adrenergic receptors from cells treated with adrenergic agonists and the phorbol ester clearly showed that phosphorylated residues were present both at the third intracellular loop and at the carboxyl tail. Distinct phosphorylation patterns were observed under the different conditions. The phosphorylated residues were: a) Baseline and all treatments: T233; b) noradrenaline: S220, S227, S229, S246, S250, S389; c) oxymetazoline: S227, S246, S381, T384, S389; and d) phorbol myristate acetate: S246, S250, S258, S351, S352, S401, S402, S407, T411, S413, T451. Our novel data, describing the α1A-AR phosphorylation sites, suggest that the observed different phosphorylation patterns may participate in defining adrenoceptor localization and action, under the different conditions examined.
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Alfonzo-Méndez MA, Alcántara-Hernández R, García-Sáinz JA. Novel Structural Approaches to Study GPCR Regulation. Int J Mol Sci 2016; 18:E27. [PMID: 28025563 PMCID: PMC5297662 DOI: 10.3390/ijms18010027] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Revised: 12/15/2016] [Accepted: 12/21/2016] [Indexed: 01/21/2023] Open
Abstract
BACKGROUND Upon natural agonist or pharmacological stimulation, G protein-coupled receptors (GPCRs) are subjected to posttranslational modifications, such as phosphorylation and ubiquitination. These posttranslational modifications allow protein-protein interactions that turn off and/or switch receptor signaling as well as trigger receptor internalization, recycling or degradation, among other responses. Characterization of these processes is essential to unravel the function and regulation of GPCR. METHODS In silico analysis and methods such as mass spectrometry have emerged as novel powerful tools. Both approaches have allowed proteomic studies to detect not only GPCR posttranslational modifications and receptor association with other signaling macromolecules but also to assess receptor conformational dynamics after ligand (agonist/antagonist) association. RESULTS this review aims to provide insights into some of these methodologies and to highlight how their use is enhancing our comprehension of GPCR function. We present an overview using data from different laboratories (including our own), particularly focusing on free fatty acid receptor 4 (FFA4) (previously known as GPR120) and α1A- and α1D-adrenergic receptors. From our perspective, these studies contribute to the understanding of GPCR regulation and will help to design better therapeutic agents.
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Affiliation(s)
- Marco A Alfonzo-Méndez
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México 04510, Mexico.
| | - Rocío Alcántara-Hernández
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México 04510, Mexico.
| | - J Adolfo García-Sáinz
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México 04510, Mexico.
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Kienitz MC, Vladimirova D, Müller C, Pott L, Rinne A. Receptor Species-dependent Desensitization Controls KCNQ1/KCNE1 K+ Channels as Downstream Effectors of Gq Protein-coupled Receptors. J Biol Chem 2016; 291:26410-26426. [PMID: 27834678 DOI: 10.1074/jbc.m116.746974] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 11/09/2016] [Indexed: 12/17/2022] Open
Abstract
Activation of Gq protein-coupled receptors (GqPCRs) might induce divergent cellular responses, related to receptor-specific activation of different branches of the Gq signaling pathway. Receptor-specific desensitization provides a mechanism of effector modulation by restricting the spatiotemporal activation of signaling components downstream of Gq We quantified signaling events downstream of GqPCR activation with FRET-based biosensors in CHO and HEK 293 cells. KCNQ1/KCNE1 channels (IKs) were measured as a functional readout of receptor-specific activation. Activation of muscarinic M1 receptors (M1-Rs) caused robust and reversible inhibition of IKs. In contrast, activation of α1B-adrenergic receptors (α1B-ARs) induced transient inhibition of IKs, which turned into delayed facilitation after agonist withdrawal. As a novel finding, we demonstrate that GqPCR-specific kinetics of IKs modulation are determined by receptor-specific desensitization, evident at the level of Gαq activation, phosphatidylinositol 4,5-bisphosphate (PIP2) depletion, and diacylglycerol production. Sustained IKs inhibition during M1-R stimulation is attributed to robust membrane PIP2 depletion, whereas the rapid desensitization of α1B-AR delimits PIP2 reduction and augments current activation by protein kinase C (PKC). Overexpression of Ca2+-independent PKCδ did not affect the time course of α1B-AR-induced diacylglycerol formation, excluding a contribution of PKCδ to α1B-AR desensitization. Pharmacological inhibition of Ca2+-dependent PKC isoforms abolished fast α1B receptor desensitization and augmented IKs reduction, but did not affect IKs facilitation. These data indicate a contribution of Ca2+-dependent PKCs to α1B-AR desensitization, whereas IKs facilitation is induced by Ca2+-independent PKC isoforms. In contrast, neither inhibition of Ca2+-dependent/Ca2+-independent isoforms nor overexpression of PKCδ induced M1 receptor desensitization, excluding a contribution of PKC to M1-R-induced IKs modulation.
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Affiliation(s)
- Marie-Cécile Kienitz
- From the Institute of Physiology, Ruhr-University Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany
| | - Dilyana Vladimirova
- From the Institute of Physiology, Ruhr-University Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany
| | - Christian Müller
- From the Institute of Physiology, Ruhr-University Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany
| | - Lutz Pott
- From the Institute of Physiology, Ruhr-University Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany
| | - Andreas Rinne
- From the Institute of Physiology, Ruhr-University Bochum, Universitätsstrasse 150, D-44780 Bochum, Germany
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Carboxyl terminus-truncated α1D-adrenoceptors inhibit the ERK pathway. Naunyn Schmiedebergs Arch Pharmacol 2016; 389:911-20. [PMID: 27146292 DOI: 10.1007/s00210-016-1254-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 04/25/2016] [Indexed: 01/06/2023]
Abstract
Human α1D-adrenoceptors are G protein-coupled receptors that mediate adrenaline/noradrenaline actions. There is a growing interest in identifying regulatory domains in these receptors and determining how they function. In this work, we show that the absence of the human α1D-adrenoceptor carboxyl tail results in altered ERK (extracellular signal-regulated kinase) and p38 phosphorylation states. Amino terminus-truncated and both amino and carboxyl termini-truncated α1D-adrenoceptors were transfected into Rat-1, HEK293, and B103 cells, and changes in the phosphorylation state of extracellular signal-regulated kinase was assessed using biochemical and biophysical approaches. The phosphorylation state of other protein kinases (p38, MEK1, and Raf-1) was also studied. Noradrenaline-induced ERK phosphorylation in Rat-1 fibroblasts expressing amino termini-truncated α1D-adrenoceptors. However, in cells expressing receptors with both amino and carboxyl termini truncations, noradrenaline-induced activation was abrogated. Interestingly, ERK phosphorylation that normally occurs through activation of endogenous G protein-coupled receptors, EGF receptors, and protein kinase C, was also decreased, suggesting that downstream steps in the mitogen-activated protein kinase pathway were affected. A similar effect was observed in B103 cells but not in HEK 293 cells. Phosphorylation of Raf-1 and MEK1 was also diminished in Rat-1 fibroblasts expressing amino- and carboxyl-truncated α1D-adrenoceptors. Our data indicate that expression of carboxyl terminus-truncated α1D-adrenoceptors alters ERK and p38 phosphorylation state.
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Castillo-Badillo JA, Sánchez-Reyes OB, Alfonzo-Méndez MA, Romero-Ávila MT, Reyes-Cruz G, García-Sáinz JA. α1B-adrenergic receptors differentially associate with Rab proteins during homologous and heterologous desensitization. PLoS One 2015; 10:e0121165. [PMID: 25799564 PMCID: PMC4370394 DOI: 10.1371/journal.pone.0121165] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Accepted: 01/28/2015] [Indexed: 11/24/2022] Open
Abstract
Internalization of G protein-coupled receptors can be triggered by agonists or by other stimuli. The process begins within seconds of cell activation and contributes to receptor desensitization. The Rab GTPase family controls endocytosis, vesicular trafficking, and endosomal fusion. Among their remarkable properties is the differential distribution of its members on the surface of various organelles. In the endocytic pathway, Rab 5 controls traffic from the plasma membrane to early endosomes, whereas Rab 4 and Rab 11 regulate rapid and slow recycling from early endosomes to the plasma membrane, respectively. Moreover, Rab 7 and Rab 9 regulate the traffic from late endosomes to lysosomes and recycling to the trans-Golgi. We explore the possibility that α1B-adrenergic receptor internalization induced by agonists (homologous) and by unrelated stimuli (heterologous) could involve different Rab proteins. This possibility was explored by Fluorescence Resonance Energy Transfer (FRET) using cells coexpressing α1B-adrenergic receptors tagged with the red fluorescent protein, DsRed, and different Rab proteins tagged with the green fluorescent protein. It was observed that when α1B-adrenergic receptors were stimulated with noradrenaline, the receptors interacted with proteins present in early endosomes, such as the early endosomes antigen 1, Rab 5, Rab 4, and Rab 11 but not with late endosome markers, such as Rab 9 and Rab 7. In contrast, sphingosine 1-phosphate stimulation induced rapid and transient α1B-adrenergic receptor interaction of relatively small magnitude with Rab 5 and a more pronounced and sustained one with Rab 9; interaction was also observed with Rab 7. Moreover, the GTPase activity of the Rab proteins appears to be required because no FRET was observed when dominant-negative Rab mutants were employed. These data indicate that α1B-adrenergic receptors are directed to different endocytic vesicles depending on the desensitization type (homologous vs. heterologous).
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Affiliation(s)
- Jean A. Castillo-Badillo
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70–248, México D.F. 04510, Mexico
| | - Omar B. Sánchez-Reyes
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70–248, México D.F. 04510, Mexico
| | - Marco A. Alfonzo-Méndez
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70–248, México D.F. 04510, Mexico
| | - M. Teresa Romero-Ávila
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70–248, México D.F. 04510, Mexico
| | - Guadalupe Reyes-Cruz
- Departamento de Biología Celular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional-CINVESTAV, Av. Instituto Politécnico Nacional No. 2508, Col. San Pedro Zacatenco, CP 07360, México, D.F., Mexico
| | - J. Adolfo García-Sáinz
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ap. Postal 70–248, México D.F. 04510, Mexico
- * E-mail:
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Burns RN, Singh M, Senatorov IS, Moniri NH. Mechanisms of homologous and heterologous phosphorylation of FFA receptor 4 (GPR120): GRK6 and PKC mediate phosphorylation of Thr³⁴⁷, Ser³⁵⁰, and Ser³⁵⁷ in the C-terminal tail. Biochem Pharmacol 2014; 87:650-9. [PMID: 24412271 DOI: 10.1016/j.bcp.2013.12.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 12/26/2013] [Accepted: 12/27/2013] [Indexed: 01/26/2023]
Abstract
Free fatty acid receptor 4 (FFA4), previously known as GPR120, is a G protein-coupled receptor that promotes numerous anti-inflammatory and antidiabetic effects upon its agonism by long chained unsaturated fatty acids. We have previously demonstrated that agonism of FFA4 with docosahexaenoic acid (DHA) and alpha-linoleic acid (ALA) facilitates rapid and transient phosphorylation of FFA4 expressed ectopically on the surface of HEK293 cells. However, the precise mechanisms that promote FFA4 phosphorylation remain elusive. In the current study, we examined the mechanisms behind both heterologous and homologous phosphorylation of FFA4 and set out to identify the foci of FFA4 phosphorylation. Our results demonstrate that basal and heterologous phosphorylation of FFA4 are mediated by protein kinase C (PKC), while G protein-coupled receptor kinase 6 (GRK6) plays the predominant role in DHA-mediated phosphorylation of FFA4. Furthermore, we identify Thr(347), Ser(350), and Ser(357) in the C-terminal tail as major sites of FFA4 phosphorylation. Concurrent mutation of these three sites leads to a FFA4 receptor that seemingly affects Gαq/11 signaling in a positive manner as demonstrated by heightened intracellular Ca(2+) responses following agonism with DHA. Importantly, this phosphodefective FFA4 mutant lacked the ability to promote β-arrestin-2 recruitment to the cell membrane. Since many of the functionally beneficial physiological effects of FFA4 are noted to be β-arrestin mediated, these findings could provide insight into the structural requirements for FFA4 function.
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Affiliation(s)
- Rebecca N Burns
- Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA 30341, USA
| | - Monalisa Singh
- Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA 30341, USA
| | - Ilya S Senatorov
- Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA 30341, USA
| | - Nader H Moniri
- Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA 30341, USA.
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Segura V, Pérez-Aso M, Montó F, Carceller E, Noguera MA, Pediani J, Milligan G, McGrath IC, D’Ocon P. Differences in the signaling pathways of α(1A)- and α(1B)-adrenoceptors are related to different endosomal targeting. PLoS One 2013; 8:e64996. [PMID: 23717684 PMCID: PMC3663791 DOI: 10.1371/journal.pone.0064996] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Accepted: 04/20/2013] [Indexed: 01/14/2023] Open
Abstract
AIMS To compare the constitutive and agonist-dependent endosomal trafficking of α(1A)- and α(1B)-adrenoceptors (ARs) and to establish if the internalization pattern determines the signaling pathways of each subtype. METHODS Using CypHer5 technology and VSV-G epitope tagged α(1A)- and α(1B)-ARs stably and transiently expressed in HEK 293 cells, we analyzed by confocal microscopy the constitutive and agonist-induced internalization of each subtype, and the temporal relationship between agonist induced internalization and the increase in intracellular calcium (determined by FLUO-3 flouorescence), or the phosphorylation of ERK1/2 and p38 MAP kinases (determined by Western blot). RESULTS AND CONCLUSIONS Constitutive as well as agonist-induced trafficking of α(1A) and α(1B) ARs maintain two different endosomal pools of receptors: one located close to the plasma membrane and the other deeper into the cytosol. Each subtype exhibited specific characteristics of internalization and distribution between these pools that determines their signaling pathways: α(1A)-ARs, when located in the plasma membrane, signal through calcium and ERK1/2 pathways but, when translocated to deeper endosomes, through a mechanism sensitive to β-arrestin and concanavalin A, continue signaling through ERK1/2 and also activate the p38 pathway. α(1B)-ARs signal through calcium and ERK1/2 only when located in the membrane and the signals disappear after endocytosis and by disruption of the membrane lipid rafts by methyl-β-cyclodextrin.
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Affiliation(s)
- Vanessa Segura
- Departamento de Farmacología, Facultad de Farmacia, Universitat de València, Valencia, Spain
| | - Miguel Pérez-Aso
- Departamento de Farmacología, Facultad de Farmacia, Universitat de València, Valencia, Spain
| | - Fermí Montó
- Departamento de Farmacología, Facultad de Farmacia, Universitat de València, Valencia, Spain
| | - Elena Carceller
- Departamento de Farmacología, Facultad de Farmacia, Universitat de València, Valencia, Spain
| | - María Antonia Noguera
- Departamento de Farmacología, Facultad de Farmacia, Universitat de València, Valencia, Spain
| | - John Pediani
- Molecular Pharmacology Group, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences. University of Glasgow, Glasgow, United Kingdom
- Autonomic Physiology Unit, School of Life Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Graeme Milligan
- Molecular Pharmacology Group, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences. University of Glasgow, Glasgow, United Kingdom
| | - Ian Christie McGrath
- Autonomic Physiology Unit, School of Life Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Pilar D’Ocon
- Departamento de Farmacología, Facultad de Farmacia, Universitat de València, Valencia, Spain
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Roles of phosphoinositide-dependent kinase-1 in α1B-adrenoceptor phosphorylation and desensitization. Eur J Pharmacol 2012; 674:179-87. [DOI: 10.1016/j.ejphar.2011.11.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 09/30/2011] [Accepted: 11/10/2011] [Indexed: 11/19/2022]
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García-Sáinz JA, Romero-Ávila MT, Alcántara-Hernández R. Mechanisms involved in α1B-adrenoceptor desensitization. IUBMB Life 2011; 63:811-5. [PMID: 21815242 DOI: 10.1002/iub.519] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Accepted: 05/22/2011] [Indexed: 12/12/2022]
Abstract
α(1B)-Adrenergic receptors mediate many of the actions of the natural catecholamines, adrenaline and noradrenaline. They belong to the seven transmembrane domains G protein-coupled receptor superfamily and exert their actions mainly through activation of Gq proteins and phosphoinositide turnover/calcium signaling. Many hormones and neurotransmitters are capable of inducing α(1B)-adrenergic receptor phosphorylation and desensitization; among them: adrenaline and noradrenaline, phorbol esters, endothelin-I, bradykinin, lysophosphatidic acid, insulin, EGF, PDGF, IGF-I, TGF-β, and estrogens. Key protein kinases for these effects are G protein coupled receptor kinases and protein kinase C. The lipid/protein kinase, phosphoinositide-3 kinase also appears to play a key role, acting upstream of protein kinase C. In addition to the agents employed for cells stimulation, we observed that paracrine/autocrine mediators also participate; these processes include EGF transactivation and sphingosine-1-phosphate production and action. The complex regulation of these receptors unlocks opportunities for therapeutic intervention.
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Affiliation(s)
- J Adolfo García-Sáinz
- Departamento de Biología Celular y Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México. Ap. Postal 70-248, México, Distrito Federal.
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Cabrera-Wrooman A, Romero-Ávila MT, García-Sáinz JA. Roles of the α1A-adrenergic receptor carboxyl tail in protein kinase C-induced phosphorylation and desensitization. Naunyn Schmiedebergs Arch Pharmacol 2010; 382:499-510. [PMID: 20922361 DOI: 10.1007/s00210-010-0569-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Accepted: 09/23/2010] [Indexed: 12/01/2022]
Abstract
Noradrenaline- and tetradecanoyl phorbol acetate (TPA)-induced phosphorylation and functional desensitization of the following receptors were studied: (1) wild-type bovine α(1A)- and hamster α(1B)-adrenergic receptors (ARs), (2) chimeric ARs in which the carboxyl terminus tails were exchanged (α(1AB)- and α(1BA)-ARs), and (3) carboxyl terminus-truncated α(1A)-ARs fussed to enhanced green fluorescent protein. Noradrenaline and TPA pronouncedly increased α(1B)-AR phosphorylation while TPA markedly desensitized these receptors. In contrast, TPA-induced desensitization and TPA- and noradrenaline-induced phosphorylation of α(1A)-ARs were clearly of lesser magnitude. Chimeric ARs with exchanged carboxyl terminus tails showed that the extent of phosphorylation reflected the carboxyl domain rather than the receptor core. Surprisingly, there was no correlation between phosphorylation and functional desensitization, i.e., activation of protein kinase C clearly desensitized both chimeric receptors to a similar extent. Interestingly, TPA and noradrenaline increased carboxyl terminus-truncated α(1A)-AR phosphorylation and TPA also induced receptor desensitization. We were unable to detect carboxyl terminus-truncated α(1A)-AR internalization after 5-min stimulations with noradrenaline or TPA. Our results suggest the following: (a) the α(1A)-AR carboxyl terminus tail was not essential for signaling or desensitization; (b) carboxyl terminus tail exchange "transplanted" the phosphorylation pattern of the receptors, but the functional consequences of such a transplant were very limited; (c) α(1A)-AR desensitization was not associated to receptor internalization.
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Affiliation(s)
- Alejandro Cabrera-Wrooman
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-248, México, 04510, Mexico
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Cotecchia S. Constitutive activity and inverse agonism at the α(₁a) and α(₁b) adrenergic receptor subtypes. Methods Enzymol 2010; 485:123-38. [PMID: 21050914 DOI: 10.1016/b978-0-12-381296-4.00007-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The α(1b)-adrenergic receptor (AR) was, after rhodopsin, the first G protein-coupled receptor (GPCR) in which point mutations were shown to trigger constitutive (agonist-independent) activity. Constitutively activating mutations have been found in other AR subtypes as well as in several GPCRs. This chapter briefly summarizes the main findings on constitutively active mutants of the α(1a)- and α(1b)-AR subtypes and the methods used to predict activating mutations, to measure constitutive activity of Gq-coupled receptors and to investigate inverse agonism. In addition, it highlights the implications of studies on constitutively active AR mutants on elucidating the molecular mechanisms of receptor activation and drug action.
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Affiliation(s)
- Susanna Cotecchia
- Department of General and Environmental Physiology, University of Bari, Italy
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Signaling properties of human alpha(1D)-adrenoceptors lacking the carboxyl terminus: intrinsic activity, agonist-mediated activation, and desensitization. Naunyn Schmiedebergs Arch Pharmacol 2009; 380:99-107. [PMID: 19458937 DOI: 10.1007/s00210-009-0428-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2009] [Accepted: 05/07/2009] [Indexed: 10/20/2022]
Abstract
alpha(1)-Adrenoceptors are differentially regulated by protein kinase C-mediated phosphorylation. The most sensitive member of this family is the alpha(1D)-subtype, which is also characterized by a constitutive activity and a reduced expression at the plasma membrane controlled by the amino terminus. Information on the structural domains that determine the function and regulation of this receptor subtype is scarce. Therefore, the function and phosphorylation of amino terminus-truncated (Delta1-79, (DeltaN)) alpha(1D)-adrenoceptors were studied and compared with those of alpha(1D)-adrenoceptors truncated both at the amino and carboxyl termini (Delta1-79 and Delta441-572, (DeltaN-DeltaC)). These receptors were stably expressed in rat-1 fibroblast, at relatively high density ( approximately 2 pmol/mg of membrane protein), and showed intrinsic activity that was markedly increased by noradrenaline. Interestingly, activation of protein kinase C markedly attenuated (desensitized) the function of both DeltaN and DeltaN-DeltaC alpha(1D)-adrenoceptors. These receptors were photolabeled and immunoprecitated with an antibody directed against an influenza hemagglutinin epitope inserted at the amino termini. Metabolic labeling with radioactive phosphate and receptor immunoprecipitation studies indicated that these receptors are phosphoproteins whose phosphorylation state is increased by noradrenaline and by activation of protein kinase C. Our data indicate that carboxyl terminus-truncated alpha(1D)-adrenoceptors are fully functional and subjected to regulation by phosphorylation. The roles of the carboxyl termini differ among alpha(1)-adrenoceptor subtypes.
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23
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The antagonistic effect of antipsychotic drugs on a HEK293 cell line stably expressing human α1A1-adrenoceptors. Eur J Pharmacol 2008; 596:32-40. [DOI: 10.1016/j.ejphar.2008.08.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 07/21/2008] [Accepted: 08/16/2008] [Indexed: 11/15/2022]
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24
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Tawfeek HAW, Abou-Samra AB. Negative regulation of parathyroid hormone (PTH)-activated phospholipase C by PTH/PTH-related peptide receptor phosphorylation and protein kinase A. Endocrinology 2008; 149:4016-23. [PMID: 18450967 PMCID: PMC2488210 DOI: 10.1210/en.2007-1375] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
PTH binding to the PTH/PTHrP receptor activates adenylate cyclase/protein kinase A (PKA) and phospholipase C (PLC) pathways and increases receptor phosphorylation. The mechanisms regulating PTH activation of PLC signaling are poorly understood. In the current study, we explored the role of PTH/PTHrP receptor phosphorylation and PKA in PTH activation of PLC. When treated with PTH, LLCPK-1 cells stably expressing a green fluorescent protein (GFP)-tagged wild-type (WT) PTH/PTHrP receptor show a small dose-dependent increase in PLC signaling as measured by inositol trisphosphate accumulation assay. In contrast, PTH treatment of LLCPK-1 cells stably expressing a GFP-tagged receptor mutated in its carboxyl-terminal tail so that it cannot be phosphorylated (PD-GFP) results in significantly higher PLC activation (P<0.001). The effects of PTH on PLC activation are dose dependent and reach maximum at the 100 nm PTH dose. When WT receptor-expressing cells are pretreated with H89, a specific inhibitor of PKA, PTH activation of PLC signaling is enhanced in a dose-dependent manner. H89 pretreatment in PD-GFP cells causes a further increase in PLC activation in response to PTH treatment. Interestingly, PTH and forskolin (adenylate cyclase/PKA pathway activator) treatment causes an increase in PLCbeta3 phosphorylation at the Ser1105 inhibitory site and that increase is blocked by the PKA inhibitor, H89. Expression of a mutant PLCbeta3 in which Ser1105 was mutated to alanine (PLCbeta3-SA), in WT or PD cells increases PTH stimulation of inositol 1,4,5-trisphosphate formation. Altogether, these data suggest that PTH signaling to PLC is negatively regulated by PTH/PTHrP receptor phosphorylation and PKA. Furthermore, phosphorylation at Ser1105 is demonstrated as a regulatory mechanism of PLCbeta3 by PKA.
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Affiliation(s)
- Hesham A W Tawfeek
- Endocrine Unit, Massachusetts General Hospital, 55 Fruit Street, Thier 1051, Boston, Massachusetts 02114, USA.
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25
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Mitselos A, Peeters TL, Depoortere I. Desensitization and internalization of the human motilin receptor is independent of the C-terminal tail. Peptides 2008; 29:1167-75. [PMID: 18420306 DOI: 10.1016/j.peptides.2008.02.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2008] [Revised: 02/25/2008] [Accepted: 02/26/2008] [Indexed: 10/22/2022]
Abstract
The motilin receptor (MTLR) is an important therapeutic target for the treatment of hypomotility disorders but desensitization may limit its clinical utility. The aim of this study was to investigate the role of the C-terminal tail of the MTLR in the desensitization, phosphorylation and internalization process. Three MTLR mutants, C-terminally truncated from amino acid 412 till 384 (MTLRDelta385), 374 (MTLRDelta375) or 368 (MTLRDelta369), were constructed and C-terminally tagged with an EGFP and stably expressed in CHO cells co-expressing the Ca(2+) indicator apoaequorin. Activity and desensitization were studied by measuring changes in motilin-induced luminescent Ca(2+) rises. Receptor phosphorylation was investigated by immunoprecipitation and MTLR-EGFP internalization was visualized by fluorescence microscopy. Truncation only reduced MTLR affinity and the efficacy to induce Ca(2+) luminescent responses of the MTLRDelta375-EGFP mutant. Furthermore, the region between amino acid 375 and 368 seems to be important for proper cell surface expression of the MTLR since receptors of the MTLRDelta369-EGFP mutant but not of the other mutants were found intracellularly in vesicles. Truncation of the receptor till amino acid 384 or 374 did neither affect desensitization nor internalization. In contrast phosphorylation of the MTLRDelta385-EGFP mutant was reduced by 80% but was not affected in the MTLRDelta375-EGFP mutant. In conclusion, MTLR desensitization and internalization is not dependent on the presence of the C-terminal tail. Truncation favors internalization via either phosphorylation-independent pathways or via phosphorylation of alternative sites in the receptor.
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MESH Headings
- Aequorin/metabolism
- Amino Acid Sequence
- Animals
- Apoproteins/metabolism
- CHO Cells
- Calcium/metabolism
- Cricetinae
- Cricetulus
- Dose-Response Relationship, Drug
- Gastrointestinal Agents/pharmacology
- Green Fluorescent Proteins/metabolism
- Humans
- Luminescent Measurements
- Microscopy, Fluorescence
- Molecular Sequence Data
- Motilin/pharmacology
- Mutation
- Phosphorylation
- Precipitin Tests
- Protein Structure, Tertiary
- Receptors, Gastrointestinal Hormone/chemistry
- Receptors, Gastrointestinal Hormone/genetics
- Receptors, Gastrointestinal Hormone/metabolism
- Receptors, Neuropeptide/chemistry
- Receptors, Neuropeptide/genetics
- Receptors, Neuropeptide/metabolism
- Recombinant Proteins/metabolism
- Sequence Analysis, Protein
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Affiliation(s)
- Anna Mitselos
- Centre for Gastroenterological Research, Catholic University of Leuven, B-3000 Leuven, Belgium
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26
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Stanasila L, Abuin L, Dey J, Cotecchia S. Different Internalization Properties of the α1a- and α1b-Adrenergic Receptor Subtypes: The Potential Role of Receptor Interaction with β-Arrestins and AP50. Mol Pharmacol 2008; 74:562-73. [DOI: 10.1124/mol.107.043422] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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27
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Molina-Muñoz T, Romero-Avila MT, Avendaño-Vázquez SE, García-Sáinz JA. Phosphorylation, desensitization and internalization of human alpha1B-adrenoceptors induced by insulin-like growth factor-I. Eur J Pharmacol 2007; 578:1-10. [PMID: 17915215 DOI: 10.1016/j.ejphar.2007.08.047] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2007] [Revised: 08/21/2007] [Accepted: 08/24/2007] [Indexed: 10/22/2022]
Abstract
The effect of insulin-like growth factor-I (IGF-I) on human alpha(1B)-adrenoceptor function, phosphorylation state and cellular location was studied. Rat-1 fibroblasts were transfected with a plasmid construction containing enhanced green fluorescent protein joined to the carboxyl terminus of the human alpha(1B)-adrenoceptor. Receptors were identified by radioligand binding and photoaffinity labeling, and were immunoprecipitated with an antiserum generated against the enhanced green fluorescent protein. The receptor was functional, as evidenced by noradrenaline action on intracellular calcium and inositol phosphate production. IGF-I had no significant effect by itself on these parameters but markedly reduced the effects of noradrenaline. IGF-I induced alpha(1B)-adrenoceptor phosphorylation, which was markedly reduced by the following agents: pertussis toxin, a metalloproteinase inhibitor, diphtheria toxin mutant CRM 197, an epidermal growth factor (EGF) receptor intrinsic kinase activity inhibitor, and by phosphoinositide 3-kinase and protein kinase C inhibitors. IGF-I action appears to involve activation of a pertussis toxin-sensitive G protein, shedding of heparin-binding EGF and autocrine activation of EGF receptors. G protein subunits and phosphotyrosine residues stimulate phosphoinositide 3-kinase activity leading to activation of protein kinase C, which in turn phosphorylates alpha(1B)-adrenoceptors. Confocal fluorescent microscopy showed that alpha(1B)-adrenoceptors fussed to the green fluorescent protein were located in plasma membrane and intracellular vesicles in the basal state. IGF-I induced receptor redistribution favoring the intracellular location; this effect was blocked by hypertonic sucrose and concanavalin A. Our data show that IGF-I induces alpha(1B)-adrenoceptor desensitization associated to receptor phosphorylation and internalization.
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Affiliation(s)
- Tzindilú Molina-Muñoz
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-248, México D. F. 04510, Mexico
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28
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Cotecchia S. Constitutive activity and inverse agonism at the α1adrenoceptors. Biochem Pharmacol 2007; 73:1076-83. [PMID: 17125741 DOI: 10.1016/j.bcp.2006.10.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 10/20/2006] [Accepted: 10/24/2006] [Indexed: 10/23/2022]
Abstract
Mutations of G protein-coupled receptors (GPCR) can increase their constitutive (agonist-independent) activity. Some of these mutations have been artificially introduced by site-directed mutagenesis, others occur spontaneously in human diseases. The alpha(1B)adrenoceptor was the first GPCR in which point mutations were shown to trigger receptor activation. This article briefly summarizes some of the findings reported in the last several years on constitutive activity of the alpha(1)adrenoceptor subtypes, the location where mutations have been found in the receptors, the spontaneous activity of native receptors in recombinant as well as physiological systems. In addition, it will highlight how the analysis of the pharmacological and molecular properties of the constitutively active adrenoceptor mutants provided an important contribution to our understanding of the molecular mechanisms underlying the mechanism of receptor activation and inverse agonism.
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Affiliation(s)
- Susanna Cotecchia
- Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, 1005 Lausanne, Switzerland.
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29
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Hori S, Matsuo N, Yamamoto A, Hazui T, Yagi H, Nakano M, Suzuki Y, Miki A, Ohtani H, Sawada Y. Piloerection induced by replacing fluvoxamine with milnacipran. Br J Clin Pharmacol 2007; 63:665-71. [PMID: 17324248 PMCID: PMC2000592 DOI: 10.1111/j.1365-2125.2006.02838.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
AIMS To present a case of piloerection after replacing fluvoxamine maleate with milnacipran hydrochloride, and to analyse this effect based on receptor occupancy theory. METHODS A 40-year-old female with a 3-year history of panic disorder was prescribed fluvoxamine 50 mg day(-1) in addition to clorazepate dipotassium and sulpiride. Depression was not improved and she complained of fatigue, lack of energy and drowsiness. These symptoms worsened within a few days of an increase in the dose of fluvoxamine to 50 mg twice daily. Since an interaction between fluvoxamine and tizanidine, prescribed by another clinic, was suspected, fluvoxamine was replaced with milnacipran 50 mg day(-1). Although her drowsiness improved, she complained of piloerection throughout her body. This symptom gradually abated within a week and when the dosage of milnacipran was increased to 100 mg day(-1) at 2 months, no further piloerection occurred. We calculated the changes in alpha(1)-adrenoceptor occupancy by endogenous norepinephrine during treatment with the usual doses of milnacipran, fluvoxamine and imipramine by using pharmacokinetic and pharmacodynamic parameters obtained from the literature. RESULTS The ratios of alpha(1)-adrenoceptor occupancy by endogenous norepinephrine during the treatment with milnacipran, fluvoxamine and imipramine to that without drug were estimated to be 7.13, 1.00 and 4.12, respectively. The alpha(1)-adrenoceptor occupancy by endogenous norepinephrine was increased in a dose-dependent manner by milnacipran, whereas fluvoxamine had essentially no effect. CONCLUSIONS The piloerection observed after the replacement of fluvoxamine with milnacipran in this patient appears to have been due to an increase in the alpha(1)-adrenoceptor occupancy by endogenous norepinephrine induced by milnacipran.
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Affiliation(s)
- Satoko Hori
- Laboratory of Drug Informatics, Graduate School of Pharmaceutical SciencesTokyo
| | | | | | | | | | | | | | - Akiko Miki
- Laboratory of Drug Informatics, Graduate School of Pharmaceutical SciencesTokyo
| | - Hisakazu Ohtani
- Laboratory of Drug Informatics, Graduate School of Pharmaceutical SciencesTokyo
| | - Yasufumi Sawada
- Laboratory of Drug Informatics, Graduate School of Pharmaceutical SciencesTokyo
- Graduate School of Interdisciplinary Information Studies, The University of TokyoTokyo
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30
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Hein P, Michel MC. Signal transduction and regulation: are all alpha1-adrenergic receptor subtypes created equal? Biochem Pharmacol 2006; 73:1097-106. [PMID: 17141737 DOI: 10.1016/j.bcp.2006.11.001] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2006] [Revised: 10/30/2006] [Accepted: 11/01/2006] [Indexed: 02/06/2023]
Abstract
The current manuscript reviews the evidence whether and how subtypes of alpha(1)-adrenergic receptors, i.e. alpha(1A)-, alpha(1B)- and alpha(1D)-adrenergic receptors, differentially couple to signal transduction pathways and exhibit differential susceptibility to regulation. In both regards studies in tissues or cells natively expressing the subtypes are hampered because the relative expression of the subtypes is poorly controlled and the observed effects may be cell-type specific. An alternative approach, i.e. transfection of multiple subtypes into the same host cell line overcomes this limitation, but it often remains unclear whether results in such artificial systems are representative for the physiological situation. The overall evidence suggests that indeed subtype-intrinsic and cell type-specific factors interact to direct alpha(1)-adrenergic receptor signaling and regulation. This may explain why so many apparently controversial findings have been reported from various tissues and cells. One of the few consistent themes is that alpha(1D)-adrenergic receptors signal less effectively upon agonist stimulation than the other subtypes, most likely because they exhibit spontaneous internalization.
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Affiliation(s)
- Peter Hein
- Department of Pharmacology, University of Würzburg, Würzburg, Germany
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31
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Flores RV, Hernández-Pérez MG, Aquino E, Garrad RC, Weisman GA, Gonzalez FA. Agonist-induced phosphorylation and desensitization of the P2Y2 nucleotide receptor. Mol Cell Biochem 2006; 280:35-45. [PMID: 16311903 PMCID: PMC1633720 DOI: 10.1007/s11010-005-8050-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2004] [Accepted: 05/27/2005] [Indexed: 11/29/2022]
Abstract
Purification of HA-tagged P2Y2 receptors from transfected human 1321N1 astrocytoma cells yielded a protein with a molecular size determined by SDS-PAGE to be in the range of 57-76 kDa, which is typical of membrane glycoproteins with heterogeneous complex glycosylation. The protein phosphatase inhibitor, okadaic acid, attenuated the recovery of receptor activity from the agonist-induced desensitized state, suggesting a role for P2Y2 receptor phosphorylation in desensitization. Isolation of HA-tagged P2Y2 nucleotide receptors from metabolically [32P]-labelled cells indicated a (3.8 +/- 0.2)-fold increase in the [32P]-content of the receptor after 15 min of treatment with 100 microM UTP, as compared to immunoprecipitated receptors from untreated control cells. Receptor sequestration studies indicated that approximately 40% of the surface receptors were internalized after a 15-min stimulation with 100 microM UTP. Point mutation of three potential GRK and PKC phosphorylation sites in the third intracellular loop and C-terminal tail of the P2Y2 receptor (namely, S243A, T344A, and S356A) extinguished agonist-induced receptor phosphorylation, caused a marked reduction in the efficacy of UTP to desensitize P2Y2 receptor signalling to intracellular calcium mobilization, and impaired agonist-induced receptor internalization. Activation of PKC isoforms with phorbol 12-myristate 13-acetate that caused heterologous receptor desensitization did not increase the level of P2Y2 receptor phosphorylation. Our results indicate a role for receptor phosphorylation by phorbol-insensitive protein kinases in agonist-induced desensitization of the P2Y2 nucleotide receptor.
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Affiliation(s)
| | | | - Edna Aquino
- Departments of Chemistry, Río Piedras Campus, and
| | - Richard C. Garrad
- Department of Biomedical Sciences, Southwest Missouri State
University, Springfield, MO; and
| | - Gary A. Weisman
- Department of Biochemistry, University of Missouri-Columbia,
MO
| | - Fernando A. Gonzalez
- Departments of Chemistry, Río Piedras Campus, and
- Biochemistry, Medical Sciences Campus, University of Puerto
Rico, San Juan, PR
- * To whom correspondence should be addressed: Dr.
Fernando A. Gonzalez, Department of Chemistry, University of Puerto Rico,
Río Piedras Campus, P.O. Box 23346, San Juan, PR 00931-3346, Tel
(787) 764-0000 ext 2437, FAX (787) 758-5612, e-mail:
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32
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Stanasila L, Abuin L, Diviani D, Cotecchia S. Ezrin directly interacts with the alpha1b-adrenergic receptor and plays a role in receptor recycling. J Biol Chem 2005; 281:4354-63. [PMID: 16352594 DOI: 10.1074/jbc.m511989200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Using the yeast two-hybrid system, we identified ezrin as a protein interacting with the C-tail of the alpha1b-adrenergic receptor (AR). The interaction was shown to occur in vitro between the receptor C-tail and the N-terminal portion of ezrin, or Four-point-one ERM (FERM) domain. The alpha1b-AR/ezrin interaction occurred inside the cells as shown by the finding that the transfected alpha1b-AR and FERM domain or ezrin could be coimmunoprecipitated from human embryonic kidney 293 cell extracts. Mutational analysis of the alpha1b-AR revealed that the binding site for ezrin involves a stretch of at least four arginines on the receptor C-tail. The results from both receptor biotinylation and immunofluorescence experiments indicated that the FERM domain impaired alpha1b-AR recycling to the plasma membrane without affecting receptor internalization. The dominant negative effect of the FERM domain, which relies on its ability to mask the ezrin binding site for actin, was mimicked by treatment of cells with cytochalasin D, an actin depolymerizing agent. A receptor mutant (DeltaR8) lacking its binding site in the C-tail for ezrin displayed delayed receptor recycling. These findings identify ezrin as a new protein directly interacting with a G protein-coupled receptor and demonstrate the direct implication of ezrin in GPCR trafficking via an actin-dependent mechanism.
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Affiliation(s)
- Laura Stanasila
- Département de Pharmacologie et de Toxicologie, Faculté de Biologie et de Médecine, Lausanne, Switzerland
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33
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Kakar SS, Malik MT, Winters SJ, Mazhawidza W. Gonadotropin-releasing hormone receptors: structure, expression, and signaling transduction. VITAMINS AND HORMONES 2004; 69:151-207. [PMID: 15196882 DOI: 10.1016/s0083-6729(04)69006-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Sham S Kakar
- Department of Medicine, University of Louisville, Louisville, Kentucky 40202, USA
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34
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Toews ML, Prinster SC, Schulte NA. Regulation of alpha-1B adrenergic receptor localization, trafficking, function, and stability. Life Sci 2003; 74:379-89. [PMID: 14607266 DOI: 10.1016/j.lfs.2003.09.024] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The alpha-1 adrenergic receptors (alpha(1)ARs) play important roles in normal physiology and in many disease states, and understanding their signaling pathways and regulatory mechanisms is thus of considerable relevance, in particular for identifying pharmacological targets for therapeutic modulation. The expression, function, localization, trafficking, and stability of these receptors are all subject to complex regulation by diverse molecular mechanisms. This article highlights recent studies from our laboratory and others focused on the localization and trafficking of the alpha-1B adrenergic receptor (alpha(1B)AR) subtype and on changes in its stability that are likely to be involved in regulating receptor expression. The role(s) of protein kinase C in alpha(1B)AR sequestration, endocytosis, and extracellular signal-regulated kinase (ERK) activation are summarized, and evidence for alpha(1B)AR localization in caveolae/rafts is presented. Receptor structural domains involved in the multiple steps and mechanisms of agonist-induced desensitization are described. Finally, aspects of alpha(1B)AR structural stability that appear to control its drug-induced up- and down-regulation are discussed. Our understanding of regulation for the alpha(1B)AR subtype provides a model for studies of the differential regulation of the other alpha(1)AR subtypes and may lead to identification of new molecular targets for therapeutic intervention in a variety of disease states.
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Affiliation(s)
- Myron L Toews
- Department of Pharmacology, University of Nebraska Medical Center, 986260 Nebraska Medical Center, Omaha, NE 68198-6260, USA.
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35
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Young KW, Nash MS, Challiss RAJ, Nahorski SR. Role of Ca2+ feedback on single cell inositol 1,4,5-trisphosphate oscillations mediated by G-protein-coupled receptors. J Biol Chem 2003; 278:20753-60. [PMID: 12670945 DOI: 10.1074/jbc.m211555200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The dynamics of inositol 1,4,5-trisphosphate (Ins (1,4,5)P3) production during periods of G-protein-coupled receptor-mediated Ca2+ oscillations have been investigated using the pleckstrin homology (PH) domain of phospholipase C (PLC) delta1 tagged with enhanced green fluorescent protein (eGFP-PHPLCdelta1). Activation of noradrenergic alpha1B and muscarinic M3 receptors recombinantly expressed in the same Chinese hamster ovary cell indicates that Ca2+ responses to these G-protein-coupled receptors are stimulus strength-dependent. Thus, activation of alpha1B receptors produced transient base-line Ca2+ oscillations, sinusoidal Ca2+ oscillations, and then a steady-state plateau level of Ca2+ as the level of agonist stimulation increased. Activation of M3 receptors, which have a higher coupling efficiency than alpha1B receptors, produced a sustained increase in intracellular Ca2+ even at low levels of agonist stimulation. Confocal imaging of eGFP-PHPLCdelta1 visualized periodic increases in Ins(1,4,5)P3 production underlying the base-line Ca2+ oscillations. Ins(1,4,5)P3 oscillations were blocked by thapsigargin but not by protein kinase C down-regulation. The net effect of increasing intracellular Ca2+ was stimulatory to Ins(1,4,5)P3 production, and dual imaging experiments indicated that receptor-mediated Ins(1,4,5)P3 production was sensitive to changes in intracellular Ca2+ between basal and approximately 200 nM. Together, these data suggest that alpha1B receptor-mediated Ins(1,4,5)P3 oscillations result from a positive feedback effect of Ca2+ onto phospholipase C. The mechanisms underlying alpha1B receptor-mediated Ca2+ responses are therefore different from those for the metabotropic glutamate receptor 5a, where Ins(1,4,5)P3 oscillations are the primary driving force for oscillatory Ca2+ responses (Nash, M. S., Young, K. W., Challiss, R. A. J., and Nahorski, S. R. (2001) Nature 413, 381-382). For alpha1B receptors the Ca2+-dependent Ins(1,4,5)P3 production may serve to augment the existing regenerative Ca2+-induced Ca2+-release process; however, the sensitivity to Ca2+ feedback is such that only transient base-line Ca2+ spikes may be capable of causing Ins(1,4,5)P3 oscillations.
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MESH Headings
- Animals
- CHO Cells
- Calcium Signaling/physiology
- Cricetinae
- Enzyme Inhibitors/pharmacology
- Feedback, Physiological/physiology
- GTP-Binding Proteins/metabolism
- Inositol 1,4,5-Trisphosphate/biosynthesis
- Inositol 1,4,5-Trisphosphate/metabolism
- Norepinephrine/metabolism
- Protein Kinase C/metabolism
- Receptor, Metabotropic Glutamate 5
- Receptor, Muscarinic M3
- Receptors, Adrenergic, alpha-1/metabolism
- Receptors, Metabotropic Glutamate/metabolism
- Receptors, Muscarinic/metabolism
- Staurosporine/pharmacology
- Thapsigargin/pharmacology
- Type C Phospholipases/metabolism
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Affiliation(s)
- Kenneth W Young
- Department of Cell Physiology and Pharmacology, Medical Sciences Building, University of Leicester, University Road, Leicester LE1 9HN, United Kingdom.
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36
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Diviani D, Lattion AL, Abuin L, Staub O, Cotecchia S. The adaptor complex 2 directly interacts with the alpha 1b-adrenergic receptor and plays a role in receptor endocytosis. J Biol Chem 2003; 278:19331-40. [PMID: 12644451 DOI: 10.1074/jbc.m302110200] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Using the yeast two-hybrid system, we identified the mu 2 subunit of the clathrin adaptor complex 2 as a protein interacting with the C-tail of the alpha 1b-adrenergic receptor (AR). Direct association between the alpha 1b-AR and mu 2 was demonstrated using a solid phase overlay assay. The alpha 1b-AR/mu 2 interaction occurred inside the cells, as shown by the finding that the transfected alpha 1b-AR and the endogenous mu 2 could be coimmunoprecipitated from HEK-293 cell extracts. Mutational analysis of the alpha 1b-AR revealed that the binding site for mu 2 does not involve canonical YXX Phi or dileucine motifs but a stretch of eight arginines on the receptor C-tail. The binding domain of mu 2 for the receptor C-tail involves both its N terminus and the subdomain B of its C-terminal portion. The alpha 1b-AR specifically interacted with mu 2, but not with the mu 1, mu 3, or mu 4 subunits belonging to other AP complexes. The deletion of the mu 2 binding site in the C-tail markedly decreased agonist-induced receptor internalization as demonstrated by confocal microscopy as well as by the results of a surface receptor biotinylation assay. The direct association of the adaptor complex 2 with a G protein-coupled receptor has not been reported so far and might represent a common mechanism underlying clathrin-mediated receptor endocytosis.
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Affiliation(s)
- Dario Diviani
- Institut de Pharmacologie et de Toxicologie, Faculté de Médecine, 1005 Lausanne, Switzerland
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Jackson A, Iwasiow RM, Chaar ZY, Nantel MF, Tiberi M. Homologous regulation of the heptahelical D1A receptor responsiveness: specific cytoplasmic tail regions mediate dopamine-induced phosphorylation, desensitization and endocytosis. J Neurochem 2002; 82:683-97. [PMID: 12153492 DOI: 10.1046/j.1471-4159.2002.01001.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
In the present study, we investigate the role of specific cytoplasmic tail (CT) regions of the D1A receptor in mediating dopamine (DA)-induced phosphorylation, desensitization and endocytosis. Results obtained in human embryonic kidney (HEK) cells expressing the wild-type (WT) or truncation forms (Delta425, Delta379 and Delta351) of the D1A receptor show that sequences located downstream of Gly379 regulate DA-mediated phosphorylation-dependent desensitization of D1A receptors. However, the longer truncation mutant Delta351 failed to undergo detectable DA-induced phosphorylation while exhibiting DA-induced desensitization features similar to the shorter truncation mutant Delta379. These data potentially suggest a novel role for a receptor phosphorylation-independent process in the DA-promoted D1A subtype desensitization. Our immunofluorescence data also suggest that sequences located between Cys351 and Gly379 play an important role in DA-mediated receptor endocytosis. Additionally, time-course studies were done in intact cells expressing WT or truncation receptors to measure the observed rate constant for adenylyl cyclase (AC) activation or k(obs), a parameter linked to the receptor-G protein coupling status. In agreement with the desensitization data, Delta425- and Delta379-expressing cells exhibit an increase of kobs in comparison with WT-expressing cells. Nevertheless, Delta351-expressing cells, which harbor similar desensitization features of Delta379-expressing cells, display no change in k(obs) when compared with WT-expressing cells. Our results suggest that a defective DA-induced endocytosis may hamper Delta351 resensitization and concomitant increase in k(obs). Thus, our study showing that specific D1A receptor CT sequences regulate DA-induced phosphorylation, desensitization, and endocytosis highlights the underlying molecular complexity of signaling at dopaminergic synapses.
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Affiliation(s)
- Adele Jackson
- Ottawa Health Research Institute, Department of Medicine/Cellular, University of Ottawa, Ontario, Canada
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Liu S, Carrillo JJ, Pediani JD, Milligan G. Effective information transfer from the alpha 1b-adrenoceptor to Galpha 11 requires both beta/gamma interactions and an aromatic group four amino acids from the C terminus of the G protein. J Biol Chem 2002; 277:25707-14. [PMID: 11994281 DOI: 10.1074/jbc.m201015200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Co-expression of the alpha(1b)-adrenoreceptor and Galpha(11) in cells derived from a Galpha(q)/Galpha(11) knock-out mouse allows agonist-mediated elevation of intracellular Ca(2+) levels that is transduced by beta/gamma released from the G protein alpha subunit. Mutation of Tyr(356) of Galpha(11) to Phe, within a receptor contact domain, had little effect on function but this was reduced greatly by alteration to Ser and virtually eliminated by conversion to Asp. This pattern was replicated following incorporation of each form of Galpha(11) into fusion proteins with the alpha(1b)-adrenoreceptor. Following a [(35)S]guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding assay, immunoprecipitation of the wild type alpha(1b)-adrenoreceptor-Galpha(11) fusion protein indicated that the agonist phenylephrine stimulated guanine nucleotide exchange on Galpha(11) more than 30-fold. Information transfer by agonist was controlled in residue 356 Galpha(11) mutants with rank order Tyr > Phe > Trp > Ile > Ala = Gln = Arg > Ser > Asp, although these alterations did not alter the binding affinity of either phenylephrine or an antagonist ligand. Mutation of a beta/gamma contact interface in the alpha(1b)-adrenoreceptor-Tyr(356) Galpha(11) fusion protein did not alter ligand binding affinity but did reduce greatly beta/gamma binding and phenylephrine stimulation of [(35)S]GTPgammaS binding. It also prevented agonist elevation of intracellular Ca(2+) levels, as did a mutation in Galpha(11) that prevents G protein subunit dissociation. These results indicate that a bulky aromatic group is required four amino acids from the C terminus of Galpha(11) to maximize information transfer from an agonist-occupied receptor and disprove the hypothesis that tyrosine phosphorylation of this residue is required for G protein activation (Umemori, H., Inoue, T., Kume, S., Sekiyama, N., Nagao, M., Itoh, H., Nakanishi, S., Mikoshiba, K., and Yamamoto, T. (1997) Science 276, 1878-1881). This is distinct from Galpha(i1), where hydrophobicity of the amino acid is the key determinant at this location. They also further demonstrate a key role for the beta/gamma complex in enhancing receptor to G protein alpha subunit information transfer.
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Affiliation(s)
- Sen Liu
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, United Kingdom
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Vicentic A, Robeva A, Rogge G, Uberti M, Minneman KP. Biochemistry and pharmacology of epitope-tagged alpha(1)-adrenergic receptor subtypes. J Pharmacol Exp Ther 2002; 302:58-65. [PMID: 12065700 DOI: 10.1124/jpet.302.1.58] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Human alpha(1A)-, alpha(1B)-, and alpha(1D)-adrenergic receptors were tagged at their amino termini with FLAG epitopes and stably expressed in human embryonic kidney (HEK)293 cells. Tagged receptors demonstrated a wild-type pharmacology and mobilization of intracellular Ca(2+). After solubilization and immunoprecipitation, monomers, dimers, and trimers of each subtype were apparent on Western blots. Further denaturation with 6 M urea reduced most oligomers to monomers. Deglycosylation reduced the molecular size of alpha(1A)-, and to a lesser extent alpha(1B)- and alpha(1D)-adrenergic receptors. Radioligand binding site density was highest for alpha(1A)- and much lower for alpha(1B)- and alpha(1D)-adrenergic receptors, but did not correlate with protein expression. Commercial anti-alpha(1)-adrenergic receptor antibodies did not recognize the tagged receptors in Western blots of cell lysates, and substantial cross-reactivity was still observed after solubilization and immunoprecipitation. Surprisingly, only receptor monomers were apparent after photoaffinity labeling with (125)I-arylazidoprazosin, and the intensity of photoaffinity-labeling correlated with the density of radioligand binding sites. We conclude that epitope-tagged alpha(1)-adrenergic receptors exist as both monomers and oligomers in HEK293 cells, but there is substantial discrepancy between protein and binding site expression. Because only monomers are detected by photoaffinity labeling, dimers and trimers observed on Western blots may be pharmacologically inactive.
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Affiliation(s)
- Aleksandra Vicentic
- Department of Pharmacology, 5017 Rollins Research Center, Emory University School of Medicine, 1510 Clifton Road, Atlanta, GA 30322, USA
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40
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Castro-Fernández C, Conn PM. Regulation of the gonadotropin-releasing hormone receptor (GnRHR) by RGS proteins: role of the GnRHR carboxyl-terminus. Mol Cell Endocrinol 2002; 191:149-56. [PMID: 12062898 DOI: 10.1016/s0303-7207(02)00082-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The cytoplasmic carboxyl-terminus of G-protein coupled receptors (GPCRs), absent in the mammalian gonadotropin-releasing hormone receptor (GnRHR), plays an important role in receptor expression, desensitization, internalization and efficiency of coupling to G proteins. Regulators of G protein signaling (RGS) likewise are involved in regulating GPCR-G protein mediated responses and can regulate transcription of other genes. In this study, we evaluate differential expression, ligand binding and effector coupling of the rat GnRHR (rGnRHR) and a chimera of rGnRHR with the pre-mammalian carboxyl domain (rGnRHR-C-tail). Membrane expression of the chimeric receptor and G(q)alpha and G(s)alpha-mediated signaling was increased 2- and 1.5-fold, respectively by RGS10, while RGS3 did not interfere with rGnRHR and rGnRHR-C-tail cell surface expression in spite of negatively regulating GnRH-stimulated G(q)alpha-mediated signaling by both receptors. The rGnRHR and rGnRHR-C-tail showed similar internalization rates in the presence of either RGS protein, indicating that the modification of rGnRHR expression and regulation in the presence of a carboxyl-terminus by RGS10 was not caused by alteration of the internalization rate. The observations in this study implicate the carboxyl domain of the receptor as a site of interaction for RGS10, but not RGS3. This is the first evidence of an altered cell surface expression and regulation of the GnRHR bearing a carboxyl-terminus by RGS proteins.
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Affiliation(s)
- Cecilia Castro-Fernández
- Oregon National Primate Research Center and Department of Physiology and Pharmacology, Oregon Health and Science University, 505 NW 185th Avenue, Beaverton, OR 97006, USA
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41
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Björklöf K, Lundström K, Abuin L, Greasley PJ, Cotecchia S. Co- and posttranslational modification of the alpha(1B)-adrenergic receptor: effects on receptor expression and function. Biochemistry 2002; 41:4281-91. [PMID: 11914074 DOI: 10.1021/bi015790j] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have characterized the maturation, co- and posttranslational modifications, and functional properties of the alpha(1B)-adrenergic receptor (AR) expressed in different mammalian cells transfected using conventional approaches or the Semliki Forest virus system. We found that the alpha(1B)-AR undergoes N-linked glycosylation as demonstrated by its sensitivity to endoglycosidases and by the effect of tunicamycin on receptor maturation. Pulse-chase labeling experiments in BHK-21 cells demonstrate that the alpha(1B)-AR is synthesized as a 70 kDa core glycosylated precursor that is converted to the 90 kDa mature form of the receptor with a half-time of approximately 2 h. N-Linked glycosylation of the alpha(1B)-AR occurs at four asparagines on the N-terminus of the receptor. Mutations of the N-linked glycosylation sites did not have a significant effect on receptor function or expression. Surprisingly, receptor mutants lacking N-linked glycosylation migrated as heterogeneous bands in SDS-PAGE. Our findings demonstrate that N-linked glycosylation and phosphorylation, but not palmitoylation or O-linked glycosylation, contribute to the structural heterogeneity of the alpha(1B)-AR as it is observed in SDS-PAGE. The modifications found are similar in the different mammalian expression systems explored. Our findings indicate that the Semliki Forest virus system can provide large amounts of functional and fully glycosylated alpha(1B)-AR protein suitable for biochemical and structural studies. The results of this study contribute to elucidate the basic steps involved in the processing of G protein-coupled receptors as well as to optimize strategies for their overexpression.
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MESH Headings
- Amino Acid Sequence
- Animals
- Binding Sites
- Blotting, Western
- Cell Line
- Cell Membrane/metabolism
- Cricetinae
- DNA, Complementary/metabolism
- Electrophoresis, Polyacrylamide Gel
- Glycosylation
- Green Fluorescent Proteins
- Inositol Phosphates/metabolism
- Kinetics
- Luminescent Proteins/metabolism
- Microscopy, Fluorescence
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Mutation
- Palmitic Acids/chemistry
- Phosphorylation
- Precipitin Tests
- Protein Binding
- Protein Biosynthesis
- Protein Conformation
- Protein Processing, Post-Translational
- Receptors, Adrenergic, alpha/chemistry
- Receptors, Adrenergic, alpha/metabolism
- Recombinant Fusion Proteins/metabolism
- Semliki forest virus/metabolism
- Sequence Homology, Amino Acid
- Time Factors
- Transfection
- Tunicamycin/pharmacology
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Affiliation(s)
- Katja Björklöf
- Institut de Pharmacologie et Toxicologie, Université de Lausanne, 1005 Lausanne, Switzerland, and F. Hoffmann-La Roche Reasearch Laboratories, 4070 Basel, Switzerland
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42
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Price RR, Morris DP, Biswas G, Smith MP, Schwinn DA. Acute agonist-mediated desensitization of the human alpha 1a-adrenergic receptor is primarily independent of carboxyl terminus regulation: implications for regulation of alpha 1aAR splice variants. J Biol Chem 2002; 277:9570-9. [PMID: 11781325 DOI: 10.1074/jbc.m111762200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Despite important roles in myocardial hypertrophy and benign prostatic hyperplasia, little is known about acute effects of agonist stimulation on alpha(1a)-adrenergic receptor (alpha(1a)AR) signaling and function. Regulatory mechanisms are likely complex since 12 distinct human alpha(1a)AR carboxyl-terminal splice variants have been isolated. After determining the predominance of the alpha(1a-1)AR isoform in human heart and prostate, we stably expressed an epitope-tagged alpha(1a-1)AR cDNA in rat-1 fibroblasts and subsequently examined regulation of signaling, phosphorylation, and internalization of the receptor. Human alpha(1a)AR-mediated inositol phosphate signaling is acutely desensitized in response to both agonist and phorbol 12-myristate 13-acetate (PMA) exposure. Concurrent with desensitization, alpha(1a)ARs in (32)P(i)-labeled cells are rapidly phosphorylated in response to both NE and PMA stimulation. Despite the ability of PKC to desensitize alpha(1a)ARs when directly activated with PMA, inhibitors of PKC have no effect on agonist-mediated desensitization. In contrast, involvement of GRK kinases is suggested by the ability of GRK2 to desensitize alpha(1a)ARs. Internalization of cell surface alpha(1a)ARs also occurs in response to agonist stimulation (but not PKC activation), but is initiated more slowly than receptor desensitization. Significantly, deletion of the alpha(1a)AR carboxyl terminus has no effect on receptor internalization or either agonist-induced or GRK-mediated receptor desensitization. Because mechanisms underlying acute agonist-mediated regulation of human alpha(1a)ARs are primarily independent of the carboxyl terminus, they may be common to all functional alpha(1a)AR isoforms.
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Affiliation(s)
- R Reyn Price
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710, USA
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43
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Grouzmann E, Meyer C, Bürki E, Brunner H. Neuropeptide Y Y2 receptor signalling mechanisms in the human glioblastoma cell line LN319. Peptides 2001; 22:379-86. [PMID: 11287092 DOI: 10.1016/s0196-9781(01)00344-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Neuropeptide Y (NPY) regulates neurotransmitter release through activation of the Y2 receptor subtype. We have recently characterized a human glioblastoma cell line, LN319, that expresses exclusively NPY Y2 receptors and have demonstrated that NPY triggers transient decreases in cAMP and increases in intracellular calcium responses. The present study was designed to further characterize calcium signalling by NPY and bradykinin (BK) in LN319 cells. Both agonists elevated free intracellular calcium ([Ca(2+)](i)) without soliciting calcium influx. NPY appeared to activate two distinct signalling cascades that liberate calcium from thapsigargin- and ryanodine-insensitive compartments. One pathway proceeded through phospholipase C (PLC)-dependent phosphatidylinositol turnover, while the other triggered calcium release through a so far unidentified mediator. Part of the response was sensitive to pertussis toxin (PTX) under conditions where the toxin totally abolished the NPY-mediated effects on cAMP. The calcium release induced by BK on the other hand was largely PTX-insensitive, PLC-dependent, and from both thapsigargin- and ryanodine-sensitive stores. Following stimulation with NPY, subsequent [Ca(2+)](i) responses to NPY were strongly depressed. Partial heterologous desensitization occurred, when BK was used as the first agonist, whereas NPY had no effect on a subsequent stimulation with BK. These data suggest that NPY-induced calcium mobilization in LN319 cells involves two different G proteins and signalling mediators, and a hitherto unidentified calcium compartment. Homologous desensitization of NPY signalling might be explained by receptor-G protein uncoupling, while heterologous desensitization by BK could be the result of either transient depletion or inhibition of a mediator in the calcium signalling cascades activated by NPY.
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Affiliation(s)
- E Grouzmann
- Division of Hypertension, Lausanne University Hospital, 1011, Lausanne, Switzerland.
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44
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Cheng KW, Leung PCK. The expression, regulation and signal transduction pathways of the mammalian gonadotropin-releasing hormone receptor. Can J Physiol Pharmacol 2000. [DOI: 10.1139/y00-096] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Normal mammalian sexual maturation and reproductive functions require the integration and precise coordination of hormones at the hypothalamic, pituitary, and gonadal levels. Hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator in this system; after binding to its receptor (GnRHR), it stimulates de novo synthesis and release of gonadotropins in anterior pituitary gonadotropes. Since the isolation of the GnRHR cDNA, the expression of GnRHR mRNA has been detected not only in the pituitary, but also in extrapituitary tissues, including the ovary and placenta. It has been shown that change in GnRHR mRNA is one of the mechanisms for regulating the expression of the GnRHR. To help understand the molecular mechanism(s) involved in transcriptional regulation of the GnRHR gene, the 5' flanking region of the GnRHR gene has recently been isolated. Initial characterization studies have identified several DNA regions in the GnRHR 5' flanking region which are responsible for both basal expression and GnRH-mediated homologous regulation of this gene in pituitary cells. The mammalian GnRHR lacks a C-terminus and possesses a relatively short third intracellular loop; both features are important in desensitization of many others G-protein coupled receptors (GPCRs), Homologous desensitization of GnRHR has been shown to be regulated by various serine-threonine protein kinases including protein kinase A (PKA) and protein kinase C (PKC), as well as by G-protein coupled receptor kinases (GRKs). Furthermore, GnRHR was demonstrated to couple with multiple G proteins (Gq/11, Gs, and Gi), and to activate cascades that involved the PKC, PKA, and mitogen-activator protein kinases. These results suggest the diversity of GnRHR-G protein coupling and signal transduction systems. The identification of second form of GnRH (GnRH-II) in mammals adds to the complexity of the GnRH-GnRHR system. This review summaries our recent progress in understanding the regulation of GnRHR gene expression and the GnRHR signal transduction pathways.Key words: gonadotropin-releasing hormone receptor, transcriptional regulation, desensitization, signal transduction.
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45
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Doronin S, Lin F, Wang HY, Malbon CC. The full-length, cytoplasmic C-terminus of the beta 2-adrenergic receptor expressed in E. coli acts as a substrate for phosphorylation by protein kinase A, insulin receptor tyrosine kinase, GRK2, but not protein kinase C and suppresses desensitization when expressed in vivo. Protein Expr Purif 2000; 20:451-61. [PMID: 11087685 DOI: 10.1006/prep.2000.1322] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ability of the cytoplasmic, full-length C-terminus of the beta 2-adrenergic receptor (BAC1) expressed in Escherichia coli to act as a functional domain and substrate for protein phosphorylation was tested. BAC1 was expressed at high-levels, purified, and examined in solution as a substrate for protein phosphorylation. The mobility of BAC1 on SDS-PAGE mimics that of the native receptor itself, displaying decreased mobility upon chemical reduction of disulfide bonds. Importantly, the C-terminal, cytoplasmic domain of the receptor expressed in E. coli was determined to be a substrate for phosphorylation by several candidate protein kinases known to regulate G-protein-linked receptors. Mapping was performed by proteolytic degradation and matrix-assisted laser desorption ionization, time-of-flight mass spectrometry. Purified BAC1 is phosphorylated readily by protein kinase A, the phosphorylation occurring within the predicted motif RRSSSK. The kinetic properties of the phosphorylation by protein kinase A displayed cooperative character. The activated insulin receptor tyrosine kinase, which phosphorylates the beta-adrenergic receptor in vivo, phosphorylates BAC1. The Y364 residue of BAC1 was predominantly phosphorylated by the insulin receptor kinase. GRK2 catalyzed modest phosphorylation of BAC1. Phosphorylation of the human analog of BAC1 in which Cys341 and Cys378 were mutated to minimize disulfide bonding constraints, displayed robust phosphorylation following thermal activation, suggesting under standard conditions that the population of BAC1 molecules capable of assuming the "activated" conformer required by GRKs is low. BAC1 was not a substrate for protein kinase C, suggesting that the canonical site in the second cytoplasmic loop of the intact receptor is preferred. The functional nature of BAC1 was tested additionally by expression of BAC1 protein in human epidermoid carcinoma A431 cells. BAC1 was found to act as a dominant-negative, blocking agonist-induced desensitization of the beta-adrenergic receptor when expressed in mammalian cells. Thus, the C-terminal, cytoplasmic tail of this G-protein-linked receptor expressed in E. coli acts as a functional domain, displaying fidelity with regard to protein kinase action in vivo and acting as a dominant-negative with respect to agonist-induced desensitization.
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Affiliation(s)
- S Doronin
- Department of Molecular Pharmacology, University Medical Center, SUNY/Stony Brook, Stony Brook, New York 11794, USA.
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46
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Michelotti GA, Price DT, Schwinn DA. Alpha 1-adrenergic receptor regulation: basic science and clinical implications. Pharmacol Ther 2000; 88:281-309. [PMID: 11337028 DOI: 10.1016/s0163-7258(00)00092-9] [Citation(s) in RCA: 175] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Adrenergic receptors (ARs) are members of the G-protein-coupled receptor family, which includes alpha 1ARs, alpha 2ARs, beta 1ARs, beta 2ARs, beta 3ARs, adenosine, muscarinic, angiotensin, endothelin receptors, and many others that are responsible for a large variety of physiologic effects through G-protein coupling. This review focuses on alpha 1ARs and their regulation at both the mRNA and protein levels. Currently, three alpha 1AR subtypes have been characterized both pharmacologically and at the gene level: alpha 1aAR, alpha 1bAR, and alpha 1dAR. These are expressed in a species- and tissue-dependent manner. Mutagenesis approaches have been extremely valuable in the identification of key residues that govern alpha 1AR ligand binding and signaling. These studies reveal that alpha 1ARs have evolved an exquisitely sensitive regulation of their activity in which any disruption of the native structure has profound effects on subsequent function and effector coupling. Significant advances have also been made in the elucidation of signaling pathway components, resulting in the identification of novel pathways that can lead to pathologic conditions. Specific topics include mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and G-protein-coupled receptor cross-talk pathways. Within this context, recent studies identifying underlying transcriptional mechanisms involved in the regulation of the alpha 1AR subtypes are also discussed. Finally, given the potentially important role of alpha 1ARs in the vasculature, as well as in the pathology of many diseases, such as myocardial hypertrophy and benign prostatic hyperplasia, the clinical relevance of alpha 1AR distribution, pharmacology, and therapeutic intervention is reviewed.
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Affiliation(s)
- G A Michelotti
- Department of Anesthesiology, Duke University Medical Center, Box 3094, Durham, NC 27710, USA
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47
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Backstrom JR, Price RD, Reasoner DT, Sanders-Bush E. Deletion of the serotonin 5-HT2C receptor PDZ recognition motif prevents receptor phosphorylation and delays resensitization of receptor responses. J Biol Chem 2000; 275:23620-6. [PMID: 10816555 DOI: 10.1074/jbc.m000922200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation-deficient serotonin 5-HT(2C) receptors were generated to determine whether phosphorylation promotes desensitization of receptor responses. Phosphorylation of mutant 5-HT(2C) receptors that lack the carboxyl-terminal PDZ recognition motif (Ser(458)-Ser-Val-COOH; DeltaPDZ) was not detectable based on a band-shift phosphorylation assay and incorporation of (32)P. Treatment of cells stably expressing DeltaPDZ or wild-type 5-HT(2C) receptors with serotonin produced identical maximal responses and EC(50) values for eliciting [(3)H]inositol phosphate formation. In calcium imaging studies, treatment of cells expressing DeltaPDZ or wild-type 5-HT(2C) receptors with 100 nm serotonin elicited initial maximal responses and decay rates that were indistinguishable. However, a second application of serotonin 2.5 min after washout caused maximal responses that were approximately 5-fold lower with DeltaPDZ receptors relative to wild-type 5-HT(2C) receptors. After 10 min, responses of DeltaPDZ receptors recovered to wild-type 5-HT(2C) receptor levels. Receptors with single mutations at Ser(458) (S458A) or Ser(459) (S459A) decreased serotonin-mediated phosphorylation to 50% of wild-type receptor levels. Furthermore, subsequent calcium responses of S459A receptors were diminished relative to S458A and wild-type receptors. These results establish that desensitization occurs in the absence of 5-HT(2C) receptor phosphorylation and suggest that receptor phosphorylation at Ser(459) enhances resensitization of 5-HT(2C) receptor responses.
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Affiliation(s)
- J R Backstrom
- Department of Pharmacology and the Center for Molecular Neuroscience, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA.
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48
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Fang X, Gaudette D, Furui T, Mao M, Estrella V, Eder A, Pustilnik T, Sasagawa T, Lapushin R, Yu S, Jaffe RB, Wiener JR, Erickson JR, Mills GB. Lysophospholipid growth factors in the initiation, progression, metastases, and management of ovarian cancer. Ann N Y Acad Sci 2000; 905:188-208. [PMID: 10818454 DOI: 10.1111/j.1749-6632.2000.tb06550.x] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Levels of lysophosphatidic acid (LPA) and lysophosphatidylcholine (LPC) are elevated in the plasma and ascites of ovarian cancer patients, but not in most other tumor types. LPA increases cell proliferation, cell survival, resistance to cisplatin, cell shrinkage, and production of vascular endothelial growth factor, urokinase plasminogen activator, and LPA itself in ovarian cancer cells, but not in normal ovarian surface epithelial cells. PSP24 and members of the endothelial differentiation gene (EDG) family (EDG1, EDG2, EDG4, and EDG7) of G protein-coupled receptors mediate LPA signaling. Ovarian cancer cell lines do not express EDG1 mRNA, have variable EDG2 mRNA and protein levels, and frequently exhibit levels of EDG4 mRNA and protein, suggesting that EDG4 may contribute to the deleterious effects of LPA in ovarian cancer. In contrast, activation of the EDG2 LPA receptor on ovarian cancer cells may lead to apoptosis and counter the effects of other LPA receptors. Thus, the development of agonists and antagonists for the appropriate spectrum of LPA receptors may alter proliferation, apoptosis, or response to therapy of ovarian cancer cells. Indeed, over 60% of all current drugs target the G protein-coupled family of receptors, making the LPA receptor family a "drugable" target. LPC, although not as thoroughly studied, increases cellular proliferation and mediates multiple other functions through unique signaling pathways.
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Affiliation(s)
- X Fang
- Department of Molecular Oncology, University of Texas, MD Anderson Cancer Center, Houston 77030, USA.
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49
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Vázquez-Prado J, Medina LC, Romero-Avila MT, González-Espinosa C, García-Sáinz JA. Norepinephrine- and phorbol ester-induced phosphorylation of alpha(1a)-adrenergic receptors. Functional aspects. J Biol Chem 2000; 275:6553-9. [PMID: 10692461 DOI: 10.1074/jbc.275.9.6553] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Maximal adrenergic responses in Rat-1 fibroblasts expressing alpha(1a)-adrenergic receptors are not blocked by activation of protein kinase C. In contrast, activation of protein kinase C induces the phosphorylation of alpha(1b)-adrenoreceptors and blocks their actions. The effect of norepinephrine and phorbol esters on alpha(1a)-adrenoreceptor phosphorylation and coupling to G proteins were studied. Both stimuli lead to dose-dependent receptor phosphorylation. Interestingly, protein kinase C activation affected to a much lesser extent the actions of alpha(1a)-adrenergic receptors than those of the alpha(1b) subtype (norepinephrine elicited increases in calcium in whole cells and [(35)S]GTPgammaS binding to membranes). Basal phosphorylation of alpha(1a)-adrenergic receptors was much less than that observed with the alpha(1b) subtype. The carboxyl terminus seems to be the main domain for receptor phosphorylation. Therefore, chimeric receptors, where the carboxyl-terminal tails of alpha(1a) and alpha(1b) adrenergic receptors were exchanged, were constructed and expressed. alpha(1a)-Adrenoreceptors wearing the carboxyl tail of the alpha(1b) subtype had a high basal phosphorylation and displayed a strong phosphorylation in response to norepinephrine and phorbol esters. Our results demonstrate that stimulation of alpha(1a)-adrenergic receptor, or activation of protein kinase C, leads to alpha(1a)-adrenergic receptor phosphorylation. alpha(1a)-Adrenoreceptors are affected to a much lesser extent than alpha(1b)-adrenoreceptors by protein kinase C activation.
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Affiliation(s)
- J Vázquez-Prado
- Departamento de Biología Celular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-248, México City 04510, México
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García-Sáinz JA, Vázquez-Prado J, del Carmen Medina L. Alpha 1-adrenoceptors: function and phosphorylation. Eur J Pharmacol 2000; 389:1-12. [PMID: 10686290 DOI: 10.1016/s0014-2999(99)00896-1] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
This review focuses on alpha(1)-adrenoceptor phosphorylation and function. Most of what is currently known is based on studies on the hamster alpha(1B)-adrenoceptor. It is known that agonist stimulation leads to homologous desensitization of these receptors and current evidence indicates that such decrease in receptor activity is associated with receptor phosphorylation. Such receptor phosphorylation seems to involve G protein-receptor kinases and the receptor phosphorylation sites have been located in the carboxyl tail (Ser(404), Ser(408), and Ser(410)). There is also evidence showing that in addition to desensitization, receptor phosphorylation is associated with internalization and roles of beta-arrestins have been observed. Direct activation of protein kinase C leads to receptor desensitization/internalization associated with phosphorylation; the protein-kinase-C-catalyzed receptor phosphorylation sites have been also located in the carboxyl tail (Ser(394) and Ser(400)). Activation of G(q)-coupled receptors, such as the endothelin ET(A) receptor induces alpha(1B)-adrenoceptor phosphorylation and desensitization. Such effect involves protein kinase C and a yet unidentified tyrosine kinase. Activation of G(i)-coupled receptors, such as the lysophosphatidic acid receptor, also induces alpha(1B)-adrenoceptor phosphorylation and desensitization. These effects involve protein kinase C and phosphatidyl inositol 3-kinase. Interestingly, activation of epidermal growth factor receptors also induces alpha(1B)-adrenoceptor phosphorylation and desensitization involving protein kinase C and phosphatidyl inositol 3-kinase. A pivotal role of these kinases in heterologous desensitization is evidenced.
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Affiliation(s)
- J A García-Sáinz
- Departamento de Biología Celular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México. Apartado postal 70-248, México, Mexico.
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