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Pinto MC, Botelho HM, Silva IAL, Railean V, Neumann B, Pepperkok R, Schreiber R, Kunzelmann K, Amaral MD. Systems Approaches to Unravel Molecular Function: High-content siRNA Screen Identifies TMEM16A Traffic Regulators as Potential Drug Targets for Cystic Fibrosis. J Mol Biol 2022; 434:167436. [PMID: 34990652 DOI: 10.1016/j.jmb.2021.167436] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 12/28/2021] [Accepted: 12/28/2021] [Indexed: 11/25/2022]
Abstract
An attractive approach to treat people with Cystic Fibrosis (CF), a life-shortening disease caused by mutant CFTR, is to compensate for the absence of this chloride/bicarbonate channel by activating alternative (non-CFTR) chloride channels. One obvious target for such "mutation-agnostic" therapeutic approach is TMEM16A (anoctamin-1/ANO1), a calcium-activated chloride channel (CaCC) which is also expressed in the airways of people with CF, albeit at low levels. To find novel TMEM16A regulators of both traffic and function, with the main goal of identifying candidate CF drug targets, we performed a fluorescence cell-based high-throughput siRNA microscopy screen for TMEM16A trafficking using a double-tagged construct expressed in human airway cells. About 700 genes were screened (2 siRNAs per gene) of which 262 were identified as candidate TMEM16A modulators (179 siRNAs enhanced and 83 decreased TMEM16A traffic), being G-protein coupled receptors (GPCRs) enriched on the primary hit list. Among the 179 TMEM16A traffic enhancer siRNAs subjected to secondary screening 20 were functionally validated. Further hit validation revealed that siRNAs targeting two GPCRs - ADRA2C and CXCR3 - increased TMEM16A-mediated chloride secretion in human airway cells, while their overexpression strongly diminished calcium-activated chloride currents in the same cell model. The knockdown, and likely also the inhibition, of these two TMEM16A modulators is therefore an attractive potential therapeutic strategy to increase chloride secretion in CF.
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Affiliation(s)
- Madalena C Pinto
- BioISI - Biosystems & Integrative Sciences Institute, Faculty of Sciences, University of Lisboa, Campo Grande, C8, 1749-016 Lisboa, Portugal. https://twitter.com/madalenacfpinto
| | - Hugo M Botelho
- BioISI - Biosystems & Integrative Sciences Institute, Faculty of Sciences, University of Lisboa, Campo Grande, C8, 1749-016 Lisboa, Portugal
| | - Iris A L Silva
- BioISI - Biosystems & Integrative Sciences Institute, Faculty of Sciences, University of Lisboa, Campo Grande, C8, 1749-016 Lisboa, Portugal
| | - Violeta Railean
- BioISI - Biosystems & Integrative Sciences Institute, Faculty of Sciences, University of Lisboa, Campo Grande, C8, 1749-016 Lisboa, Portugal
| | - Beate Neumann
- Cell Biology/Biophysics Unit, and ALMF, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Rainer Pepperkok
- Cell Biology/Biophysics Unit, and ALMF, European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Rainer Schreiber
- Institut für Physiologie, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Karl Kunzelmann
- Institut für Physiologie, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany
| | - Margarida D Amaral
- BioISI - Biosystems & Integrative Sciences Institute, Faculty of Sciences, University of Lisboa, Campo Grande, C8, 1749-016 Lisboa, Portugal.
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Huhtinen A, Hongisto V, Laiho A, Löyttyniemi E, Pijnenburg D, Scheinin M. Gene expression profiles and signaling mechanisms in α 2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells. BMC SYSTEMS BIOLOGY 2017; 11:65. [PMID: 28659168 PMCID: PMC5490158 DOI: 10.1186/s12918-017-0439-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Accepted: 06/09/2017] [Indexed: 12/31/2022]
Abstract
BACKGROUND α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation. RESULTS The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase. CONCLUSIONS α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.
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Affiliation(s)
- Anna Huhtinen
- Department of Pharmacology, Drug Development and Therapeutics, Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, FI-20520 Turku, Finland
- Unit of Clinical Pharmacology, Turku University Hospital, Turku, Finland
| | - Vesa Hongisto
- Toxicology Division, Misvik Biology Oy, Turku, Finland
| | - Asta Laiho
- Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku, Finland
| | - Eliisa Löyttyniemi
- Department of Biostatistics, Department of Clinical Medicine, University of Turku, Turku, Finland
| | - Dirk Pijnenburg
- PamGene International BV, Wolvenhoek 10, 5211HH s’Hertogenbosch, The Netherlands
| | - Mika Scheinin
- Department of Pharmacology, Drug Development and Therapeutics, Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, FI-20520 Turku, Finland
- Unit of Clinical Pharmacology, Turku University Hospital, Turku, Finland
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Che P, Chen Y, Lu R, Peng N, Gannon M, Wyss JM, Jiao K, Wang Q. Spinophilin Is Indispensable for the α2B Adrenergic Receptor-Elicited Hypertensive Response. PLoS One 2015; 10:e0135030. [PMID: 26244553 PMCID: PMC4526467 DOI: 10.1371/journal.pone.0135030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 07/16/2015] [Indexed: 12/05/2022] Open
Abstract
The α2 adrenergic receptor (AR) subtypes are important for blood pressure control. When activated, the α2A subtype elicits a hypotensive response whereas the α2B subtype mediates a hypertensive effect that counteracts the hypotensive response by the α2A subtype. We have previously shown that spinophilin attenuates the α2AAR-dependent hypotensive response; in spinophilin null mice, this response is highly potentiated. In this study, we demonstrate that spinophilin impedes arrestin-dependent phosphorylation and desensitization of the α2BAR subtype by competing against arrestin binding to this receptor subtype. The Del301-303 α2BAR, a human variation that shows impaired phosphorylation and desensitization and is linked to hypertension in certain populations, exhibits preferential interaction with spinophilin over arrestin. Furthermore, Del301-303 α2BAR-induced ERK signaling is quickly desensitized in cells without spinophilin expression, showing a profile similar to that induced by the wild type receptor in these cells. Together, these data suggest a critical role of spinophilin in sustaining α2BAR signaling. Consistent with this notion, our in vivo study reveals that the α2BAR-elicited hypertensive response is diminished in spinophilin deficient mice. In arrestin 3 deficient mice, where the receptor has a stronger binding to spinophilin, the same hypertensive response is enhanced. These data suggest that interaction with spinophilin is indispensable for the α2BAR to elicit the hypertensive response. This is opposite of the negative role of spinophilin in regulating α2AAR-mediated hypotensive response, suggesting that spinophilin regulation of these closely related receptor subtypes can result in distinct functional outcomes in vivo. Thus, spinophilin may represent a useful therapeutic target for treatment of hypertension.
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Affiliation(s)
- Pulin Che
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, United States of America
| | - Yunjia Chen
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, United States of America
| | - Roujian Lu
- the National Institute for Viral Disease Control and Prevention, China CDC, Beijing, China
| | - Ning Peng
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, United States of America
| | - Mary Gannon
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, United States of America
| | - J. Michael Wyss
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, United States of America
| | - Kai Jiao
- Department of Genetics, University of Alabama at Birmingham, 720 20 Street South, Birmingham, AL 35294, United States of America
| | - Qin Wang
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, Birmingham, AL 35294, United States of America
- * E-mail:
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Lehto J, Hirvonen MM, Johansson J, Kemppainen J, Luoto P, Naukkarinen T, Oikonen V, Arponen E, Rouru J, Sallinen J, Scheinin H, Vuorilehto L, Finnema SJ, Halldin C, Rinne JO, Scheinin M. Validation of [(11) C]ORM-13070 as a PET tracer for alpha2c -adrenoceptors in the human brain. Synapse 2015; 69:172-81. [PMID: 25530024 DOI: 10.1002/syn.21798] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/03/2014] [Accepted: 12/10/2014] [Indexed: 12/24/2022]
Abstract
This study explored the use of the α2C -adrenoceptor PET tracer [(11) C]ORM-13070 to monitor α2C -AR occupancy in the human brain. The subtype-nonselective α2 -AR antagonist atipamezole was administered to eight healthy volunteer subjects to determine its efficacy and potency (Emax and EC50 ) at inhibiting tracer uptake. We also explored whether the tracer could reveal changes in the synaptic concentrations of endogenous noradrenaline in the brain, in response to several pharmacological and sensory challenge conditions. We assessed occupancy from the bound-to-free ratio measured during 5-30 min post injection. Based on extrapolation of one-site binding, the maximal extent of inhibition of striatal [(11) C]ORM-13070 uptake (Emax ) achievable by atipamezole was 78% (95% CI 69-87%) in the caudate nucleus and 65% (53-77%) in the putamen. The EC50 estimates of atipamezole (1.6 and 2.5 ng/ml, respectively) were in agreement with the drug's affinity to α2C -ARs. These findings represent clear support for the use of [(11) C]ORM-13070 for monitoring drug occupancy of α2C -ARs in the living human brain. Three of the employed noradrenaline challenges were associated with small, approximately 10-16% average reductions in tracer uptake in the dorsal striatum (atomoxetine, ketamine, and the cold pressor test; P < 0.05 for all), but insulin-induced hypoglycemia did not affect tracer uptake. The tracer is suitable for studying central nervous system receptor occupancy by α2C -AR ligands in human subjects. [(11) C]ORM-13070 also holds potential as a tool for in vivo monitoring of synaptic concentrations of noradrenaline, but this remains to be further evaluated in future studies.
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Affiliation(s)
- Jussi Lehto
- Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland; Clinical Research Services Turku CRST, Turku, Finland; Unit of Clinical Pharmacology, Turku University Hospital, Turku, Finland
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Cai J, Li J, Liu W, Han Y, Wang H. Alpha2-adrenergic receptors in spiral ganglion neurons may mediate protective effects of brimonidine and yohimbine against glutamate and hydrogen peroxide toxicity. Neuroscience 2013; 228:23-35. [DOI: 10.1016/j.neuroscience.2012.10.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 09/29/2012] [Accepted: 10/01/2012] [Indexed: 10/27/2022]
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Björk K, Svenningsson P. Modulation of monoamine receptors by adaptor proteins and lipid rafts: role in some effects of centrally acting drugs and therapeutic agents. Annu Rev Pharmacol Toxicol 2011; 51:211-42. [PMID: 20887195 DOI: 10.1146/annurev-pharmtox-010510-100520] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The monoamines and their cognate receptors are widespread in the central nervous system and are vital for normal brain function. Dysfunction in these systems underlies several psychiatric and neurological disease states, and consequently monoamines are targets of a host of pharmacotherapies. This review provides an overview on how monoamine receptors are regulated by adaptor proteins and lipid rafts with emphasis on interactions in nerve cells. Monoamine receptors have prominent intracellular loops that provide binding sites for adaptor proteins. Receptor function is further modulated by cholesterol and submembranous microdomains termed lipid rafts. These interactions determine several facets of G protein-coupled receptor (GPCR) function including trafficking, localization, and signaling. Possible roles of adaptor proteins and lipid rafts in disease states and in mediating actions of drugs and therapeutic agents are also discussed.
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Affiliation(s)
- Karl Björk
- Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden
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7
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Salim S, Desai AN, Taneja M, Eikenburg DC. Chronic adrenaline treatment fails to down-regulate the Del301-303-alpha2B-adrenoceptor in neuronal cells. Br J Pharmacol 2010; 158:314-27. [PMID: 19719784 DOI: 10.1111/j.1476-5381.2009.00294.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE A polymorphism of the human alpha(2B)-adrenoceptor (Del(301-303)-alpha(2B)-adrenoceptor) has been described, and this receptor exhibits reduced G-protein-coupled receptor kinase (GRK) phosphorylation and impaired short-term desensitization. Expression of the Del(301-303)-alpha(2B)-adrenoceptor also is associated with an increased risk for myocardial infarction in humans. Recent evidence from our laboratory suggests a quantitative relationship between cellular GRK3 expression levels and the sensitivity of the alpha(2B)-adrenoceptor to agonist-induced down-regulation. Therefore, the present study was undertaken to study agonist-induced down-regulation of the wild-type (WT)- and Del(301-303)-alpha(2B)-adrenoceptor in a neuronal cell model. EXPERIMENTAL APPROACH Haemagglutinin (HA) epitope-tagged WT- and Del(301-303)-alpha(2B)-adrenoceptor containing plasmids were constructed and the receptors were stably or transiently transfected in neuroblastoma/glioma hybrid NG108 cells. The expression levels in stable transfects were approximately 50 fmol x mg(-1). These cells were used to examine agonist-induced down-regulation and phosphorylation of the WT- and Del(301-303)-alpha(2B)-adrenoceptor. KEY RESULTS The Del(301-303)-alpha(2B)-adrenoceptor, compared with the WT-alpha(2B-)adrenoceptor, displayed reduced adrenaline-stimulated (20 microM) phosphorylation and did not down-regulate in response to adrenaline (20-1000 microM). Using immunofluorescence labelling, we observed that transiently transfected WT-alpha(2B)-adrenoceptors internalized upon adrenaline treatment whereas the Del(301-303)-alpha(2B)-adrenoceptor did not. Finally, we determined the effect of adrenaline on the Del(301-303)-alpha(2B)-adrenoceptor in cells stably over-expressing GRK3 3-fold. In spite of the GRK3 over-expression, 20-1000 microM ADR failed to down-regulate or to increase phosphorylation of the Del(301-303)-alpha(2B)-adrenoceptor in these cells. CONCLUSIONS AND IMPLICATIONS The results suggest that the 301-303 deletion mutation of the alpha(2B)-adrenoceptor eliminates agonist-induced down-regulation, an effect that cannot be overcome by increasing agonist concentration or by modest GRK3 over-expression.
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Affiliation(s)
- S Salim
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204-5037, USA
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8
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Heusler P, Rauly-Lestienne I, Tourette A, Tardif S, Ailhaud MC, Croville G, Cussac D. Actions of the prototypical 5-HT1A receptor agonist 8-OH-DPAT at human alpha2-adrenoceptors: (+)8-OH-DPAT, but not (-)8-OH-DPAT is an alpha2B subtype preferential agonist. Eur J Pharmacol 2010; 640:8-14. [PMID: 20450907 DOI: 10.1016/j.ejphar.2010.04.034] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Revised: 03/22/2010] [Accepted: 04/19/2010] [Indexed: 11/18/2022]
Abstract
8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] is the prototypical agonist at serotonin 5-HT1A receptors; however, activity at other targets contributes to the functional effects of the compound as well. We examined the properties of 8-OH-DPAT and its enantiomers at recombinant human (h)alpha2-adrenoceptor subtypes, using a panel of radioligand binding and functional tests. In competition binding experiments using [3H]-RX821002, about 10-fold selectivity of (+)8-OH-DPAT for the halpha2B subtype (pKi about 7) over halpha2A- and halpha2C-adrenoceptors was observed. In contrast, the S(-) enantiomer of 8-OH-DPAT showed similar weak affinities for the three receptor subtypes (pKis<6). The binding affinity of (+)8-OH-DPAT at the halpha2B- and the halpha2A-adrenoceptor was found sensitive to GTPgammaS, a receptor/G protein-uncoupling agent, indicating agonist properties of the drug. Furthermore, using [35S]GTPgammaS binding determination at CHO-halpha2B or CHO-halpha2A cell membranes and G protein coupled inwardly rectifying potassium (GIRK) current recordings in Xenopus oocytes expressing halpha2B, partial agonist activity of (+)8-OH-DPAT at the respective receptors was confirmed in these two different functional assays. Potency of (+)8-OH-DPAT for stimulation of [35S]GTPgammaS incorporation was lower at the halpha2A- than at the halpha2B-adrenoceptor, consistent with binding affinities. Thus, (+)8-OH-DPAT and, as a consequence, racemic (+/-)8-OH-DPAT are partial agonists at halpha2-adrenoceptors with selectivity for the halpha2B subtype, a property that might contribute to the effects of the compound described in native systems.
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Affiliation(s)
- Peter Heusler
- Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, 17, avenue Jean Moulin, F-81106 Castres Cedex, France.
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9
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Davis CN, Bradley SR, Schiffer HH, Friberg M, Koch K, Tolf BR, Bonhaus DW, Lameh J. Differential regulation of muscarinic M1 receptors by orthosteric and allosteric ligands. BMC Pharmacol 2009; 9:14. [PMID: 19951444 PMCID: PMC2794843 DOI: 10.1186/1471-2210-9-14] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2009] [Accepted: 12/02/2009] [Indexed: 11/13/2022] Open
Abstract
Background Activation of muscarinic M1 receptors is mediated via interaction of orthosteric agonists with the acetylcholine binding site or via interaction of allosteric agonists with different site(s) on the receptor. The focus of the present study was to determine if M1 receptors activated by allosteric agonists undergo the same regulatory fate as M1 receptors activated by orthosteric agonists. Results The orthosteric agonists carbachol, oxotremorine-M and pilocarpine were compared to the allosteric agonists AC-42, AC-260584, N-desmethylclozapine and xanomeline. All ligands activated M1 receptors and stimulated interaction of the receptors with β-arrestin-1. All ligands reduced cell surface binding and induced the loss of total receptor binding. Receptor internalization was blocked by treatment with hypertonic sucrose indicating that all ligands induced formation of clathrin coated vesicles. However, internalized receptors recycled to the cell surface following removal of orthosteric, but not allosteric agonists. Whereas all ligands induced loss of cell surface receptor binding, no intracellular vesicles could be observed after treatment with AC-260584 or xanomeline. Brief stimulation of M1 receptors with AC-260584 or xanomeline resulted in persistent activation of M1 receptors, suggesting that continual receptor signaling might impede or delay receptor endocytosis into intracellular vesicles. Conclusion These results indicate that allosteric agonists differ from orthosteric ligands and among each other in their ability to induce different regulatory pathways. Thus, signaling and regulatory pathways induced by different allosteric ligands are ligand specific.
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Affiliation(s)
- Christopher N Davis
- ACADIA Pharmaceuticals Inc, 3911 Sorrento Valley Blvd, San Diego, CA 92121, USA.
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10
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Lu R, Li Y, Zhang Y, Chen Y, Shields AD, Winder DG, Angelotti T, Jiao K, Limbird LE, Zhou Y, Wang Q. Epitope-tagged receptor knock-in mice reveal that differential desensitization of alpha2-adrenergic responses is because of ligand-selective internalization. J Biol Chem 2009; 284:13233-43. [PMID: 19276088 DOI: 10.1074/jbc.m807535200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although ligand-selective regulation of G protein-coupled receptor-mediated signaling and trafficking are well documented, little is known about whether ligand-selective effects occur on endogenous receptors or whether such effects modify the signaling response in physiologically relevant cells. Using a gene targeting approach, we generated a knock-in mouse line, in which N-terminal hemagglutinin epitope-tagged alpha(2A)-adrenergic receptor (AR) expression was driven by the endogenous mouse alpha(2A)AR gene locus. Exploiting this mouse line, we evaluated alpha(2A)AR trafficking and alpha(2A)AR-mediated inhibition of Ca(2+) currents in native sympathetic neurons in response to clonidine and guanfacine, two drugs used for treatment of hypertension, attention deficit and hyperactivity disorder, and enhancement of analgesia through actions on the alpha(2A)AR subtype. We discovered a more rapid desensitization of Ca(2+) current suppression by clonidine than guanfacine, which paralleled a more marked receptor phosphorylation and endocytosis of alpha(2A)AR evoked by clonidine than by guanfacine. Clonidine-induced alpha(2A)AR desensitization, but not receptor phosphorylation, was attenuated by blockade of endocytosis with concanavalin A, indicating a critical role for internalization of alpha(2A)AR in desensitization to this ligand. Our data on endogenous receptor-mediated signaling and trafficking in native cells reveal not only differential regulation of G protein-coupled receptor endocytosis by different ligands, but also a differential contribution of receptor endocytosis to signaling desensitization. Taken together, our data suggest that these HA-alpha(2A)AR knock-in mice will serve as an important model in developing ligands to favor endocytosis or nonendocytosis of receptors, depending on the target cell and pathophysiology being addressed.
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Affiliation(s)
- Roujian Lu
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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11
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Huhtinen A, Scheinin M. Expression and characterization of the human alpha 2B-adrenoceptor in a vascular smooth muscle cell line. Eur J Pharmacol 2008; 587:48-56. [PMID: 18456256 DOI: 10.1016/j.ejphar.2008.03.049] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2007] [Revised: 02/29/2008] [Accepted: 03/14/2008] [Indexed: 01/14/2023]
Abstract
A vascular smooth muscle cell line stably expressing the human alpha 2B-adrenoceptor at a density of 1.5 pmol/mg membrane protein was generated by transfection of rat A7r5 cells. [35S]GTPgammaS binding experiments and [3H]thymidine incorporation experiments indicated that the expressed receptors were functional, had the expected pharmacological characteristics and efficiently stimulated smooth muscle cell proliferation. Confocal fluorescence microscopy was used to visualize alpha2B-adrenoceptors in A7r5-alpha 2B cells and indicated that the receptors were mainly localized in the plasma membrane. The expression of the smooth muscle-specific marker alpha-actin was similar in transfected A7r5-alpha 2B cells and in non-transfected A7r5 wild-type cells. The generated A7r5-alpha 2B cell line will be a useful tool for studying the function and regulation of alpha 2B-adrenoceptors in vascular smooth muscle cells.
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Affiliation(s)
- Anna Huhtinen
- Department of Pharmacology, Drug Development and Therapeutics, University of Turku, FI-20520 Turku, Finland.
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12
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Hein L. Adrenoceptors and signal transduction in neurons. Cell Tissue Res 2006; 326:541-51. [PMID: 16896948 DOI: 10.1007/s00441-006-0285-2] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Accepted: 06/13/2006] [Indexed: 10/24/2022]
Abstract
The adrenergic system is an essential regulator of neuronal, endocrine, cardiovascular, vegetative, and metabolic functions. The endogenous catecholamines epinephrine and norepinephrine activate G-protein-coupled receptors to transmit their signal across the plasma membrane. These adrenoceptors can be divided into three different groups: the alpha(1)-receptors (alpha(1A), alpha(1B), alpha(1D)), alpha(2)-receptors (alpha(2A), alpha(2B), alpha(2C)), and beta-receptors (beta(1), beta(2), beta(3)). This review summarizes recent findings in the field of adrenoceptor signaling in neurons and includes a discussion of receptor-associated proteins, receptor dimerization, subcellular trafficking, and fluorescence optical methods for studying the kinetics of adrenergic signaling. Spatio-temporal imaging may become an important future tool for identifying the physiological significance of these complex signaling mechanisms in vivo. Gene-targeted mouse models carrying deletions in alpha(2)-adrenoceptor have provided detailed insights into specific neuronal functions of the three alpha(2)-receptor subtypes.
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Affiliation(s)
- Lutz Hein
- Institut für Exp. und Klin. Pharmakologie und Toxikologie, Universität Freiburg, Albertstrasse 25, 79104 Freiburg im Breisgau, Germany.
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Desai AN, Salim S, Standifer KM, Eikenburg DC. Involvement of G protein-coupled receptor kinase (GRK) 3 and GRK2 in down-regulation of the alpha2B-adrenoceptor. J Pharmacol Exp Ther 2006; 317:1027-35. [PMID: 16533872 DOI: 10.1124/jpet.105.098996] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Increasing the cellular levels of G protein-coupled receptor kinase (GRK) 2 or GRK3 renders the alpha2B-adrenoceptor (AR) more sensitive to agonist-induced down-regulation (J Pharmacol Exp Ther 312:767-773, 2005). However, an absolute requirement of GRK3 and GRK2 for alpha2B-AR down-regulation is controversial. In this study, using NG108 cells (endogenous alpha2B-AR), we provide strong evidence for a critical role of both GRK3 and GRK2 in down-regulation of the alpha2B-AR. Pretreatment of NG108 cells with 20 microM epinephrine (EPI) begins down-regulating the alpha2B-AR by 2 h. The translocation of GRK3 and GRK2 to the membrane peaks at 30 min, decreasing by 1 h. Although these results may implicate GRK3 and GRK2 in alpha2B-AR down-regulation, significant receptor down-regulation is not observed until 2 h, after GRK3 and GRK2 translocation has peaked and is declining. To more directly establish a role for GRK3 and GRK2 in alpha2B-AR down-regulation, NG108 cells were transfected to express GRK3ct, which binds to liberated Gbetagamma subunits, preventing GRK3 and GRK2 translocation to the membrane. Overexpression of GRK3ct prevented not only the translocation of GRK3 and GRK2 but also the down-regulation of the alpha2B-AR caused by 24-h pretreatment with 20 microM EPI. Taken together, these data provide direct evidence for a role of GRK3 and GRK2 in the down-regulation of the alpha2B-AR and contribute significantly to the increasing evidence in the literature for a pivotal role of GRKs in modulating the agonist-induced down-regulation of the alpha2-AR.
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Affiliation(s)
- Aarti N Desai
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX 77204, USA
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14
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Björk S, Vainio M, Scheinin M. Uneven cellular expression of recombinant α2A-adrenoceptors in transfected CHO cells results in loss of response in adenylyl cyclase inhibition. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1744:38-46. [PMID: 15878396 DOI: 10.1016/j.bbamcr.2004.11.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2004] [Revised: 10/25/2004] [Accepted: 11/05/2004] [Indexed: 11/30/2022]
Abstract
Two populations of Chinese hamster ovary (CHO) cells expressing similar numbers of recombinant human alpha2A-adrenergic receptors (alpha2A-AR) showed different capacity to inhibit adenylyl cyclase (AC) activity. Cells transfected with an integrating vector exhibited agonist-dependent inhibition of forskolin-stimulated AC, whereas cells transfected with a non-integrating episomal vector showed no inhibition. Fluorescent microscopy and flow cytometry revealed a very uneven receptor distribution in the episomally transfected cell population. Monoclonal cell populations were expanded from this parent population. Most clones lacked significant amounts of receptors, while a few expressed receptors at high density; these exhibited efficient agonist-dependent inhibition of forskolin-stimulated AC activity. Thus, dense receptor expression in only a few cells is not sufficient to evoke a significant inhibitory response in a functional assay where AC is stimulated in all cells. Consequently, a false negative result was produced. Furthermore, the cell population transfected with an integrating vector showed loss of homogeneity with increasing passage number.
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Affiliation(s)
- Susann Björk
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Itäinen Pitkäkatu 4, FI-20520 Turku, Finland.
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15
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Olli-Lähdesmäki T, Tiger M, Vainio M, Scheinin M, Kallio J. Ligand-induced α2-adrenoceptor endocytosis: relationship to Gi protein activation. Biochem Biophys Res Commun 2004; 321:226-33. [PMID: 15358239 DOI: 10.1016/j.bbrc.2004.06.131] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2004] [Indexed: 10/26/2022]
Abstract
Most G protein-coupled receptors are desensitized by a uniform two-step mechanism: phosphorylation followed by arrestin binding and internalization. In this study we explored the time-, ligand-, and concentration dependence of alpha2-adrenoceptor internalization in human embryonal kidney (HEK-293) cells expressing alpha2A- and alpha2B-adrenoceptors. We also explored the relationship between ligand-induced receptor internalization and agonist efficacy, determined with a [35S]GTPgammaS binding assay. The results showed rapid dose-dependent internalization of both alpha2A- and alpha2B-receptors; the extent of internalization was directly proportional to agonist efficacy. The agonist UK 14,304 had a subtype-specific high efficacy at alpha2A-AR and dexmedetomidine at alpha2B-AR. Agonist-induced [35S]GTPgammaS binding was totally blocked by pretreatment with pertussis toxin (PTX) for both receptor subtypes, while only about 50% of the internalization was blocked by PTX. The results indicate that the extent of internalization of alpha2A-AR and alpha2B-AR is proportional to agonist efficacy, but only partly dependent on Gi protein coupling.
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Affiliation(s)
- Tuire Olli-Lähdesmäki
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Turku, Finland
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16
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Antov Y, Barbul A, Korenstein R. Electroendocytosis: stimulation of adsorptive and fluid-phase uptake by pulsed low electric fields. Exp Cell Res 2004; 297:348-62. [PMID: 15212939 DOI: 10.1016/j.yexcr.2004.03.027] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2003] [Revised: 02/19/2004] [Indexed: 11/21/2022]
Abstract
We present a novel approach for stimulating uptake via endocytic pathways by exposing cells to a train of pulsed low electric fields (LEF) in the range of 2.5-20 V/cm. Electric field treatment of COS 5-7 and HaCaT cells in the presence of BSA-FITC augments the adsorption of the probe to plasma membranes with subsequent enhanced internalization. The uptake of BSA-FITC is maximal when the cells are exposed to LEF in the presence of the probe while uptake of a fluid-phase marker, propidium iodide (PI), is more effective when the probe is added immediately after termination of a 1-min exposure. LEF-stimulated uptake decays with a half-life of about 3 and 1 min for and BSA-FITC and PI, respectively. The uptake is inefficient at 4 degrees C but increases with temperature. The uptake proceeds via cell membrane vesiculation, showing a high extent of colocalization of BSA-FITC with plasma membrane vesicles labeled with a phospholipid fluorescent analogue. Unlike constitutive endocytosis where the BSA-FITC is exposed to acidic pH, in LEF-induced uptake the probe is exposed to the more alkaline pH of the cytosol. The staining kinetics of nuclear targets by PI reflects the release of the probe from the LEF-induced vesicles into the cytosol 1-3 h after exposure. The LEF-induced adsorptive pathway was approximately 2.5 more effective than the LEF-induced fluid-phase one. The observed 5- to 6-fold increase of BSA-FITC uptake induced by LEF may be partially attributed to a clathrin-dependent route (up to 25%), whereas the rest of the uptake may be assigned to macropinocytotic and clathrin/caveolin independent pathways or to a novel, yet unidentified, route driven by LEF. This study provides a basis for a general approach towards the efficient incorporation of a variety of molecules such as antibodies, enzymes or genes into cells.
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Affiliation(s)
- Yulia Antov
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel-Aviv, Israel
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Estall JL, Yusta B, Drucker DJ. Lipid raft-dependent glucagon-like peptide-2 receptor trafficking occurs independently of agonist-induced desensitization. Mol Biol Cell 2004; 15:3673-87. [PMID: 15169869 PMCID: PMC491827 DOI: 10.1091/mbc.e03-11-0825] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The intestinotrophic and cytoprotective actions of glucagon-like peptide-2 (GLP-2) are mediated by the GLP-2 receptor (GLP-2R), a member of the class II glucagon-secretin G protein-coupled receptor superfamily. Although native GLP-2 exhibits a short circulating half-life, long-acting degradation-resistant GLP-2 analogues are being evaluated for therapeutic use in human subjects. Accordingly, we examined the mechanisms regulating signaling, internalization, and trafficking of the GLP-2R to identify determinants of receptor activation and desensitization. Heterologous cells expressing the transfected rat or human GLP-2R exhibited a rapid, dose-dependent, and prolonged desensitization of the GLP-2-stimulated cAMP response and a sustained GLP-2-induced decrease in levels of cell surface receptor. Surprisingly, inhibitors of clathrin-dependent endocytosis failed to significantly decrease GLP-2R internalization, whereas cholesterol sequestration inhibited ligand-induced receptor internalization and potentiated homologous desensitization. The hGLP-2R localized to both Triton X-100-soluble and -insoluble (lipid raft) cellular fractions and colocalized transiently with the lipid raft marker caveolin-1. Although GLP-2R endocytosis was dependent on lipid raft integrity, the receptor transiently associated with green fluorescent protein tagged-early endosome antigen 1-positive vesicles and inhibitors of endosomal acidification attenuated the reappearance of the GLP-2R on the cell surface. Our data demonstrate that GLP-2R desensitization and raft-dependent trafficking represent distinct and independent cellular mechanisms and provide new evidence implicating the importance of a clathrin- and dynamin-independent, lipid raft-dependent pathway for homologous G protein-coupled receptor internalization.
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Affiliation(s)
- Jennifer L Estall
- Department of Laboratory Medicine and Pathobiology, University of Toronto, The Banting and Best Diabetes Centre, Toronto General Hospital, Toronto, Canada M5G 2C4
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