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Insights into the dynamics of ligand-induced dimerisation via mathematical modelling and analysis. J Theor Biol 2022; 538:110996. [DOI: 10.1016/j.jtbi.2021.110996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 12/08/2021] [Accepted: 12/20/2021] [Indexed: 11/21/2022]
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2
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Casadó-Anguera V, Moreno E, Mallol J, Ferré S, Canela EI, Cortés A, Casadó V. Reinterpreting anomalous competitive binding experiments within G protein-coupled receptor homodimers using a dimer receptor model. Pharmacol Res 2018; 139:337-347. [PMID: 30472462 DOI: 10.1016/j.phrs.2018.11.032] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Revised: 11/14/2018] [Accepted: 11/21/2018] [Indexed: 12/01/2022]
Abstract
An increasing number of G protein-coupled receptors (GPCRs) have been reported to be expressed in the plasma membrane as dimers. Since most ligand binding data are currently fitted by classical equations developed only for monomeric receptors, the interpretation of data could be misleading in the presence of GPCR dimers. On the other hand, the equations developed from dimer receptor models assuming the existence of two orthosteric binding sites within the dimeric molecule offer the possibility to directly calculate macroscopic equilibrium dissociation constants for the two sites, an index of cooperativity (DC) that reflects the molecular communication within the dimer and, importantly, a constant of radioligand-competitor allosteric interaction (KDAB) in competitive assays. Here, we provide a practical way to fit competitive binding data that allows the interpretation of apparently anomalous results, such as competition curves that could be either bell-shaped, monophasic or biphasic depending on the assay conditions. The consideration of a radioligand-competitor allosteric interaction allows fitting these curve patterns both under simulation conditions and in real radioligand binding experiments, obtaining competitor affinity parameters closer to the actual values. Our approach is the first that, assuming the formation of receptor homodimers, is able to explain several experimental results previously considered erroneous due to their impossibility to be fitted. We also deduce the radioligand concentration responsible for the conversion of biphasic to monophasic or to bell-shaped curves in competitive radioligand binding assays. In conclusion, bell-shaped curves in competitive binding experiments constitute evidence for GPCR homodimerization.
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Affiliation(s)
- Verònica Casadó-Anguera
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Institute of Biomedicine of the University of Barcelona (IBUB), Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
| | - Estefanía Moreno
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Institute of Biomedicine of the University of Barcelona (IBUB), Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
| | - Josefa Mallol
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Institute of Biomedicine of the University of Barcelona (IBUB), Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
| | - Sergi Ferré
- National Institute on Drug Abuse, I.R.P., N.I.H., D.H.H.S., Baltimore, MD, 21224, USA.
| | - Enric I Canela
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Institute of Biomedicine of the University of Barcelona (IBUB), Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
| | - Antoni Cortés
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Institute of Biomedicine of the University of Barcelona (IBUB), Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
| | - Vicent Casadó
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Spain; Institute of Biomedicine of the University of Barcelona (IBUB), Department of Biochemistry and Molecular Biomedicine, Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028, Barcelona, Spain.
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3
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Ligand Binding Dynamics for Pre-dimerised G Protein-Coupled Receptor Homodimers: Linear Models and Analytical Solutions. Bull Math Biol 2018; 81:3542-3574. [PMID: 29349610 PMCID: PMC6722261 DOI: 10.1007/s11538-017-0387-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 12/21/2017] [Indexed: 11/25/2022]
Abstract
Evidence suggests that many G protein-coupled receptors (GPCRs) are bound together forming dimers. The implications of dimerisation for cellular signalling outcomes, and ultimately drug discovery and therapeutics, remain unclear. Consideration of ligand binding and signalling via receptor dimers is therefore required as an addition to classical receptor theory, which is largely built on assumptions of monomeric receptors. A key factor in developing theoretical models of dimer signalling is cooperativity across the dimer, whereby binding of a ligand to one protomer affects the binding of a ligand to the other protomer. Here, we present and analyse linear models for one-ligand and two-ligand binding dynamics at homodimerised receptors, as an essential building block in the development of dimerised receptor theory. For systems at equilibrium, we compute analytical solutions for total bound labelled ligand and derive conditions on the cooperativity factors under which multiphasic log dose–response curves are expected. This could help explain data extracted from pharmacological experiments that do not fit to the standard Hill curves that are often used in this type of analysis. For the time-dependent problems, we also obtain analytical solutions. For the single-ligand case, the construction of the analytical solution is straightforward; it is bi-exponential in time, sharing a similar structure to the well-known monomeric competition dynamics of Motulsky–Mahan. We suggest that this model is therefore practically usable by the pharmacologist towards developing insights into the potential dynamics and consequences of dimerised receptors.
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4
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Franco R, Martínez-Pinilla E, Lanciego JL, Navarro G. Basic Pharmacological and Structural Evidence for Class A G-Protein-Coupled Receptor Heteromerization. Front Pharmacol 2016; 7:76. [PMID: 27065866 PMCID: PMC4815248 DOI: 10.3389/fphar.2016.00076] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 03/11/2016] [Indexed: 12/25/2022] Open
Abstract
Cell membrane receptors rarely work on isolation, often they form oligomeric complexes with other receptor molecules and they may directly interact with different proteins of the signal transduction machinery. For a variety of reasons, rhodopsin-like class A G-protein-coupled receptors (GPCRs) seem an exception to the general rule of receptor-receptor direct interaction. In fact, controversy surrounds their potential to form homo- hetero-dimers/oligomers with other class A GPCRs; in a sense, the field is going backward instead of forward. This review focuses on the convergent, complementary and telling evidence showing that homo- and heteromers of class A GPCRs exist in transfected cells and, more importantly, in natural sources. It is time to decide between questioning the occurrence of heteromers or, alternatively, facing the vast scientific and technical challenges that class A receptor-dimer/oligomer existence pose to Pharmacology and to Drug Discovery.
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Affiliation(s)
- Rafael Franco
- Departament de Bioquímica i Biomedicina Molecular, Facultat de Biología, Universitat de BarcelonaBarcelona, Spain; Centro de Investigación Biomédica en Red: Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos IIIMadrid, Spain; Institute of Biomedicine, University of BarcelonaBarcelona, Spain
| | - Eva Martínez-Pinilla
- Instituto de Neurociencias del Principado de Asturias, Departamento de Morfología y Biología Celular, Facultad de Medicina, Universidad de OviedoAsturias, Spain; Neurosciences Division, Centre for Applied Medical Research, University of NavarraPamplona, Spain; Instituto de Investigaciones Sanitarias de NavarraPamplona, Spain
| | - José L Lanciego
- Centro de Investigación Biomédica en Red: Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos IIIMadrid, Spain; Neurosciences Division, Centre for Applied Medical Research, University of NavarraPamplona, Spain; Instituto de Investigaciones Sanitarias de NavarraPamplona, Spain
| | - Gemma Navarro
- Departament de Bioquímica i Biomedicina Molecular, Facultat de Biología, Universitat de BarcelonaBarcelona, Spain; Centro de Investigación Biomédica en Red: Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos IIIMadrid, Spain
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5
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Cortés A, Gracia E, Moreno E, Mallol J, Lluís C, Canela EI, Casadó V. Moonlighting Adenosine Deaminase: A Target Protein for Drug Development. Med Res Rev 2014; 35:85-125. [DOI: 10.1002/med.21324] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Antoni Cortés
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
| | - Eduard Gracia
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
| | - Estefania Moreno
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
| | - Josefa Mallol
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
| | - Carme Lluís
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
| | - Enric I. Canela
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
| | - Vicent Casadó
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED); Institute of Biomedicine of the University of Barcelona (IBUB); Department of Biochemistry and Molecular Biology; Faculty of Biology; University of Barcelona; Barcelona Spain
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6
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Franco N, Franco R. Understanding the added value of g-protein-coupled receptor heteromers. SCIENTIFICA 2014; 2014:362937. [PMID: 24864225 PMCID: PMC4017843 DOI: 10.1155/2014/362937] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Accepted: 03/10/2014] [Indexed: 06/03/2023]
Abstract
G-protein-coupled receptors (GPCRs) constitute the most populated family of proteins within the human genome. Since the early sixties work on GPCRs and on GPCR-mediated signaling has led to a number of awards, the most recent being the Nobel Prize in Chemistry for 2012. The future of GPCRs research is surely based on their capacity for heteromerization. Receptor heteromers offer a series of challenges that will help in providing success in academic/basic research and translation into more effective and safer drugs.
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Affiliation(s)
- Nuria Franco
- Department Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Prevosti Building, Diagonal 645, 08028 Barcelona, Spain
| | - Rafael Franco
- Department Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Prevosti Building, Diagonal 645, 08028 Barcelona, Spain
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7
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Moreno E, Moreno-Delgado D, Navarro G, Hoffmann HM, Fuentes S, Rosell-Vilar S, Gasperini P, Rodríguez-Ruiz M, Medrano M, Mallol J, Cortés A, Casadó V, Lluís C, Ferré S, Ortiz J, Canela E, McCormick PJ. Cocaine disrupts histamine H3 receptor modulation of dopamine D1 receptor signaling: σ1-D1-H3 receptor complexes as key targets for reducing cocaine's effects. J Neurosci 2014; 34:3545-58. [PMID: 24599455 PMCID: PMC3942573 DOI: 10.1523/jneurosci.4147-13.2014] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Revised: 01/16/2014] [Accepted: 01/27/2014] [Indexed: 01/19/2023] Open
Abstract
The general effects of cocaine are not well understood at the molecular level. What is known is that the dopamine D1 receptor plays an important role. Here we show that a key mechanism may be cocaine's blockade of the histamine H3 receptor-mediated inhibition of D1 receptor function. This blockade requires the σ1 receptor and occurs upon cocaine binding to σ1-D1-H3 receptor complexes. The cocaine-mediated disruption leaves an uninhibited D1 receptor that activates Gs, freely recruits β-arrestin, increases p-ERK 1/2 levels, and induces cell death when over activated. Using in vitro assays with transfected cells and in ex vivo experiments using both rats acutely treated or self-administered with cocaine along with mice depleted of σ1 receptor, we show that blockade of σ1 receptor by an antagonist restores the protective H3 receptor-mediated brake on D1 receptor signaling and prevents the cell death from elevated D1 receptor signaling. These findings suggest that a combination therapy of σ1R antagonists with H3 receptor agonists could serve to reduce some effects of cocaine.
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Affiliation(s)
- Estefanía Moreno
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - David Moreno-Delgado
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Gemma Navarro
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Hanne M. Hoffmann
- Neuroscience Institute and Department of Biochemistry and Molecular Biology, Faculty of Medicine, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
| | - Silvia Fuentes
- Neuroscience Institute and Department of Biochemistry and Molecular Biology, Faculty of Medicine, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
| | - Santi Rosell-Vilar
- Neuroscience Institute and Department of Biochemistry and Molecular Biology, Faculty of Medicine, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
| | - Paola Gasperini
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Mar Rodríguez-Ruiz
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Mireia Medrano
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Josefa Mallol
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Antoni Cortés
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Vicent Casadó
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Carme Lluís
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Sergi Ferré
- National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland 21224, and
| | - Jordi Ortiz
- Neuroscience Institute and Department of Biochemistry and Molecular Biology, Faculty of Medicine, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
| | - Enric Canela
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
| | - Peter J. McCormick
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED)
- Institute of Biomedicine of the University of Barcelona (IBUB) and
- Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Barcelona, 08028 Spain
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, United Kingdom NR4 7TJ
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8
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Ferré S, Casadó V, Devi LA, Filizola M, Jockers R, Lohse MJ, Milligan G, Pin JP, Guitart X. G protein-coupled receptor oligomerization revisited: functional and pharmacological perspectives. Pharmacol Rev 2014; 66:413-34. [PMID: 24515647 DOI: 10.1124/pr.113.008052] [Citation(s) in RCA: 431] [Impact Index Per Article: 43.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Most evidence indicates that, as for family C G protein-coupled receptors (GPCRs), family A GPCRs form homo- and heteromers. Homodimers seem to be a predominant species, with potential dynamic formation of higher-order oligomers, particularly tetramers. Although monomeric GPCRs can activate G proteins, the pentameric structure constituted by one GPCR homodimer and one heterotrimeric G protein may provide a main functional unit, and oligomeric entities can be viewed as multiples of dimers. It still needs to be resolved if GPCR heteromers are preferentially heterodimers or if they are mostly constituted by heteromers of homodimers. Allosteric mechanisms determine a multiplicity of possible unique pharmacological properties of GPCR homomers and heteromers. Some general mechanisms seem to apply, particularly at the level of ligand-binding properties. In the frame of the dimer-cooperativity model, the two-state dimer model provides the most practical method to analyze ligand-GPCR interactions when considering receptor homomers. In addition to ligand-binding properties, unique properties for each GPCR oligomer emerge in relation to different intrinsic efficacy of ligands for different signaling pathways (functional selectivity). This gives a rationale for the use of GPCR oligomers, and particularly heteromers, as novel targets for drug development. Herein, we review the functional and pharmacological properties of GPCR oligomers and provide some guidelines for the application of discrete direct screening and high-throughput screening approaches to the discovery of receptor-heteromer selective compounds.
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Affiliation(s)
- Sergi Ferré
- Integrative Neurobiology Section, National Institute on Drug Abuse, Intramural Research Program, National Institutes on Drug Abuse, Department of Health and Human Services, 333 Cassell Drive, Baltimore, Maryland 21224.
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9
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Roche D, Gil D, Giraldo J. Mathematical modeling of G protein-coupled receptor function: what can we learn from empirical and mechanistic models? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 796:159-81. [PMID: 24158805 DOI: 10.1007/978-94-007-7423-0_8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Empirical and mechanistic models differ in their approaches to the analysis of pharmacological effect. Whereas the parameters of the former are not physical constants those of the latter embody the nature, often complex, of biology. Empirical models are exclusively used for curve fitting, merely to characterize the shape of the E/[A] curves. Mechanistic models, on the contrary, enable the examination of mechanistic hypotheses by parameter simulation. Regretfully, the many parameters that mechanistic models may include can represent a great difficulty for curve fitting, representing, thus, a challenge for computational method development. In the present study some empirical and mechanistic models are shown and the connections, which may appear in a number of cases between them, are analyzed from the curves they yield. It may be concluded that systematic and careful curve shape analysis can be extremely useful for the understanding of receptor function, ligand classification and drug discovery, thus providing a common language for the communication between pharmacologists and medicinal chemists.
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Affiliation(s)
- David Roche
- Laboratory of Systems Pharmacology and Bioinformatics, Institut de Neurociències and Unitat de Bioestadística, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain
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10
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Gracia E, Moreno E, Cortés A, Lluís C, Mallol J, McCormick PJ, Canela EI, Casadó V. Homodimerization of adenosine A₁ receptors in brain cortex explains the biphasic effects of caffeine. Neuropharmacology 2013; 71:56-69. [PMID: 23523559 DOI: 10.1016/j.neuropharm.2013.03.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2012] [Revised: 02/27/2013] [Accepted: 03/12/2013] [Indexed: 11/30/2022]
Abstract
Using bioluminescence resonance energy transfer and proximity ligation assays, we obtained the first direct evidence that adenosine A₁ receptors (A₁Rs) form homomers not only in cell cultures but also in brain cortex. By radioligand binding experiments in the absence or in the presence of the A₁Rs allosteric modulator, adenosine deaminase, and by using the two-state dimer receptor model to fit binding data, we demonstrated that the protomer-protomer interactions in the A₁R homomers account for some of the pharmacological characteristics of agonist and antagonist binding to A₁Rs. These pharmacological properties include the appearance of cooperativity in agonist binding, the change from a biphasic saturation curve to a monophasic curve in self-competition experiments and the molecular cross-talk detected when two different specific molecules bind to the receptor. In this last case, we discovered that caffeine binding to one protomer increases the agonist affinity for the other protomer in the A₁R homomer, a pharmacological characteristic that correlates with the low caffeine concentrations-induced activation of agonist-promoted A₁R signaling. This pharmacological property can explain the biphasic effects reported at low and high concentration of caffeine on locomotor activity.
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Affiliation(s)
- Eduard Gracia
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Faculty of Biology, University of Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain.
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11
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Franco R, Martínez-Pinilla E, Ricobaraza A, McCormick PJ. Challenges in the development of heteromer-GPCR-based drugs. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 117:143-62. [PMID: 23663968 DOI: 10.1016/b978-0-12-386931-9.00006-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
G-protein-coupled receptors are targets of a variety of diseases. Drug screening has been classically performed assuming the occurrence of monomeric receptors. As more and more receptor heteromers are identified, the challenge is now to develop screening assays to select heteromer-specific drugs. These drugs may, for instance, be able to interact preferentially with prerather than with postsynaptic receptors. Heteromer-based drug discovery opens new perspectives in both Academic pursuits and for the Pharmaceutical industry.
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Affiliation(s)
- Rafael Franco
- Applied Medical Research Center (CIMA), University of Navarra, Pamplona, Spain
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12
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Giraldo J. Modeling cooperativity effects in dimeric G protein-coupled receptors. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 115:349-73. [PMID: 23415098 DOI: 10.1016/b978-0-12-394587-7.00008-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
G protein-coupled receptors organize into oligomeric arrangements to exert their function. In this chapter, three models of dimeric receptors, the two-state dimer receptor model, the metabotropic glutamate receptor model, and the asymmetric/symmetric three-state dimer receptor model are revisited focusing on the cooperative effects between their binding sites and the subunits they are composed of. The mathematical analysis reveals the complexity of the intra-receptor interactions providing insights on the mechanistic aspects of receptor function.
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Affiliation(s)
- Jesús Giraldo
- Laboratory of Systems Pharmacology and Bioinformatics, Institut de Neurociències and Unitat de Bioestadística, Universitat Autònoma de Barcelona, Bellaterra, Spain
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13
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Koshimizu TA, Nakamura K, Egashira N, Hiroyama M, Nonoguchi H, Tanoue A. Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems. Physiol Rev 2012; 92:1813-64. [DOI: 10.1152/physrev.00035.2011] [Citation(s) in RCA: 250] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.
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Affiliation(s)
- Taka-aki Koshimizu
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical University, Tochigi, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan; Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan; and Department of Internal Medicine, Kitasato University, Kitasato Institute Medical Center Hospital, Saitama, Japan
| | - Kazuaki Nakamura
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical University, Tochigi, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan; Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan; and Department of Internal Medicine, Kitasato University, Kitasato Institute Medical Center Hospital, Saitama, Japan
| | - Nobuaki Egashira
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical University, Tochigi, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan; Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan; and Department of Internal Medicine, Kitasato University, Kitasato Institute Medical Center Hospital, Saitama, Japan
| | - Masami Hiroyama
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical University, Tochigi, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan; Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan; and Department of Internal Medicine, Kitasato University, Kitasato Institute Medical Center Hospital, Saitama, Japan
| | - Hiroshi Nonoguchi
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical University, Tochigi, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan; Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan; and Department of Internal Medicine, Kitasato University, Kitasato Institute Medical Center Hospital, Saitama, Japan
| | - Akito Tanoue
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical University, Tochigi, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Tokyo, Japan; Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan; and Department of Internal Medicine, Kitasato University, Kitasato Institute Medical Center Hospital, Saitama, Japan
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Singh S, Zhang M, Bertheleme N, Kara E, Strange PG, Byrne B. Radioligand binding analysis as a tool for quality control of GPCR production for structural characterization: adenosine A(2a)R as a template for study. CURRENT PROTOCOLS IN PROTEIN SCIENCE 2012; Chapter 29:29.3.1-29.3.22. [PMID: 22294328 DOI: 10.1002/0471140864.ps2903s67] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Functional characterization of G protein-coupled receptors is essential to ascertain the suitability of a protein target for downstream studies and to help develop optimal expression and isolation procedures. Radioligand binding analysis is a well-established technique, which allows direct measurement of the amount of functional receptor in a sample. It can be readily applied to both membrane-bound and soluble receptor samples and is an ideal method for monitoring the amount of functional protein at each stage in the expression and isolation process. This unit presents protocols for the radioligand binding analysis of the human adenosine A(2a) receptor and provides examples of how these assays can be used at several stages to help optimize expression, solubilization, and isolation procedures.
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Affiliation(s)
- Shweta Singh
- Membrane Protein Crystallography Group, Division of Molecular Biosciences, Imperial College London, London, UK
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15
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May LT, Bridge LJ, Stoddart LA, Briddon SJ, Hill SJ. Allosteric interactions across native adenosine-A3 receptor homodimers: quantification using single-cell ligand-binding kinetics. FASEB J 2011; 25:3465-76. [PMID: 21715680 PMCID: PMC3177574 DOI: 10.1096/fj.11-186296] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
A growing awareness indicates that many G-protein-coupled receptors (GPCRs) exist as homodimers, but the extent of the cooperativity across the dimer interface has been largely unexplored. Here, measurement of the dissociation kinetics of a fluorescent agonist (ABA-X-BY630) from the human A1 or A3 adenosine receptors expressed in CHO-K1 cells has provided evidence for highly cooperative interactions between protomers of the A3-receptor dimer in single living cells. In the absence of competitive ligands, the dissociation rate constants of ABA-X-BY630 from A1 and A3 receptors were 1.45 ± 0.05 and 0.57 ± 0.07 min−1, respectively. At the A3 receptor, this could be markedly increased by both orthosteric agonists and antagonists [15-, 9-, and 19-fold for xanthine amine congener (XAC), 5′-(N-ethyl carboxamido)adenosine (NECA), and adenosine, respectively] and reduced by coexpression of a nonbinding (N250A) A3-receptor mutant. The changes in ABA-X-BY630 dissociation were much lower at the A1 receptor (1.5-, 1.4-, and 1.5-fold). Analysis of the pEC50 values of XAC, NECA, and adenosine for the ABA-X-BY630-occupied A3-receptor dimer yielded values of 6.0 ± 0.1, 5.9 ± 0.1, and 5.2 ± 0.1, respectively. This study provides new insight into the spatial and temporal specificity of drug action that can be provided by allosteric modulation across a GPCR homodimeric interface.—May, L. T., Bridge, L. J., Stoddart, L. A., Briddon, S. J., Hill, S. J. Allosteric interactions across native adenosine-A3 receptor homodimers: quantification using single-cell ligand-binding kinetics.
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Affiliation(s)
- Lauren T May
- Institute of Cell Signalling, School of Biomedical Sciences, The University of Nottingham, Nottingham, UK, NG7 2UH
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16
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A2A adenosine receptor ligand binding and signalling is allosterically modulated by adenosine deaminase. Biochem J 2011; 435:701-9. [DOI: 10.1042/bj20101749] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A2ARs (adenosine A2A receptors) are highly enriched in the striatum, which is the main motor control CNS (central nervous system) area. BRET (bioluminescence resonance energy transfer) assays showed that A2AR homomers may act as cell-surface ADA (adenosine deaminase; EC 3.5.4.4)-binding proteins. ADA binding affected the quaternary structure of A2ARs present on the cell surface. ADA binding to adenosine A2ARs increased both agonist and antagonist affinity on ligand binding to striatal membranes where these proteins are co-expressed. ADA also increased receptor-mediated ERK1/2 (extracellular-signal-regulated kinase 1/2) phosphorylation. Collectively, the results of the present study show that ADA, apart from regulating the concentration of extracellular adenosine, may behave as an allosteric modulator that markedly enhances ligand affinity and receptor function. This powerful regulation may have implications for the physiology and pharmacology of neuronal A2ARs.
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Vendrell M, Molero A, González S, Pérez-Capote K, Lluis C, McCormick PJ, Franco R, Cortés A, Casadó V, Albericio F, Royo M. Biotin Ergopeptide Probes for Dopamine Receptors. J Med Chem 2011; 54:1080-90. [DOI: 10.1021/jm101566d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Marc Vendrell
- Combinatorial Chemistry Unit, Barcelona Science Park, University of Barcelona, 08028 Barcelona, Spain
| | - Anabel Molero
- Combinatorial Chemistry Unit, Barcelona Science Park, University of Barcelona, 08028 Barcelona, Spain
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials, and Nanomedicine, Barcelona Science Park, 08028 Barcelona, Spain
| | - Sergio González
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Kamil Pérez-Capote
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Carme Lluis
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Peter J. McCormick
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Rafael Franco
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Antoni Cortés
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Vicent Casadó
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain
| | - Fernando Albericio
- CIBER-BBN, Networking Centre on Bioengineering, Biomaterials, and Nanomedicine, Barcelona Science Park, 08028 Barcelona, Spain
- Institute for Research in Biomedicine, 08028 Barcelona, Spain
| | - Miriam Royo
- Combinatorial Chemistry Unit, Barcelona Science Park, University of Barcelona, 08028 Barcelona, Spain
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Moreno JL, Holloway T, Albizu L, Sealfon SC, González-Maeso J. Metabotropic glutamate mGlu2 receptor is necessary for the pharmacological and behavioral effects induced by hallucinogenic 5-HT2A receptor agonists. Neurosci Lett 2011; 493:76-9. [PMID: 21276828 DOI: 10.1016/j.neulet.2011.01.046] [Citation(s) in RCA: 169] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Revised: 01/11/2011] [Accepted: 01/20/2011] [Indexed: 01/18/2023]
Abstract
Hallucinogenic drugs, including mescaline, psilocybin and lysergic acid diethylamide (LSD), act at serotonin 5-HT2A receptors (5-HT2ARs). Metabotropic glutamate receptor 2/3 (mGluR2/3) ligands show efficacy in modulating the responses induced by activation of 5-HT2ARs. The formation of a 5-HT2AR-mGluR2 complex suggests a functional interaction that affects the hallucinogen-regulated cellular signaling pathways. Here, we tested the cellular and behavioral effects of hallucinogenic 5-HT2AR agonists in mGluR2 knockout (mGluR2-KO) mice. Mice were intraperitoneally injected with the hallucinogens DOI (2 mg/kg) and LSD (0.24 mg/kg), or vehicle. Head-twitch behavioral response, expression of c-fos, which is induced by all 5-HT2AR agonists, and expression of egr-2, which is hallucinogen-specific, were determined in wild type and mGluR2-KO mice. [(3)H]Ketanserin binding displacement curves by DOI were performed in mouse frontal cortex membrane preparations. Head twitch behavior was abolished in mGluR2-KO mice. The high-affinity binding site of DOI was undetected in mGluR2-KO mice. The hallucinogen DOI induced c-fos in both wild type and mGluR2-KO mice. However, the induction of egr-2 by DOI was eliminated in mGlu2-KO mice. These findings suggest that the 5-HT2AR-mGluR2 complex is necessary for the neuropsychological responses induced by hallucinogens.
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Affiliation(s)
- José L Moreno
- Department of Psychiatry, Mount Sinai School of Medicine, 1425 Madison Avenue, Box 1229, New York, NY 10029, United States
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19
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Striatal pre- and postsynaptic profile of adenosine A(2A) receptor antagonists. PLoS One 2011; 6:e16088. [PMID: 21264319 PMCID: PMC3019225 DOI: 10.1371/journal.pone.0016088] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Accepted: 12/04/2010] [Indexed: 11/19/2022] Open
Abstract
Striatal adenosine A(2A) receptors (A(2A)Rs) are highly expressed in medium spiny neurons (MSNs) of the indirect efferent pathway, where they heteromerize with dopamine D(2) receptors (D(2)Rs). A(2A)Rs are also localized presynaptically in cortico-striatal glutamatergic terminals contacting MSNs of the direct efferent pathway, where they heteromerize with adenosine A(1) receptors (A(1)Rs). It has been hypothesized that postsynaptic A(2A)R antagonists should be useful in Parkinson's disease, while presynaptic A(2A)R antagonists could be beneficial in dyskinetic disorders, such as Huntington's disease, obsessive-compulsive disorders and drug addiction. The aim or this work was to determine whether selective A(2A)R antagonists may be subdivided according to a preferential pre- versus postsynaptic mechanism of action. The potency at blocking the motor output and striatal glutamate release induced by cortical electrical stimulation and the potency at inducing locomotor activation were used as in vivo measures of pre- and postsynaptic activities, respectively. SCH-442416 and KW-6002 showed a significant preferential pre- and postsynaptic profile, respectively, while the other tested compounds (MSX-2, SCH-420814, ZM-241385 and SCH-58261) showed no clear preference. Radioligand-binding experiments were performed in cells expressing A(2A)R-D(2)R and A(1)R-A(2A)R heteromers to determine possible differences in the affinity of these compounds for different A(2A)R heteromers. Heteromerization played a key role in the presynaptic profile of SCH-442416, since it bound with much less affinity to A(2A)R when co-expressed with D(2)R than with A(1)R. KW-6002 showed the best relative affinity for A(2A)R co-expressed with D(2)R than co-expressed with A(1)R, which can at least partially explain the postsynaptic profile of this compound. Also, the in vitro pharmacological profile of MSX-2, SCH-420814, ZM-241385 and SCH-58261 was is in accordance with their mixed pre- and postsynaptic profile. On the basis of their preferential pre- versus postsynaptic actions, SCH-442416 and KW-6002 may be used as lead compounds to obtain more effective antidyskinetic and antiparkinsonian compounds, respectively.
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20
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Franco R, Seeman P, Barrera C, Aymerich MS. Cocaine self-administration markedly increases dopamine D2receptor negative cooperativity for dopamine binding: A receptor dimer-based analysis. Synapse 2010; 64:566-9. [DOI: 10.1002/syn.20775] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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21
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Casadó V, Barrondo S, Spasic M, Callado LF, Mallol J, Canela E, Lluís C, Meana J, Cortés A, Sallés J, Franco R. Gi protein coupling to adenosine A1-A2A receptor heteromers in human brain caudate nucleus. J Neurochem 2010; 114:972-80. [PMID: 20477947 DOI: 10.1111/j.1471-4159.2010.06810.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Pharmacological characterization of adenosine A(1) and A(2A) receptors in human brain caudate nucleus membranes led to non-cooperative binding of radiolabelled ligands. In human caudate nucleus but not in cortex, the agonist binding to A(1) receptors was modulated by the agonist binding to A(2A) receptors indicating a functional negative cross-talk. Accordingly, the A(1) receptor-activation-mediated G(i)-dependent guanosine 5'-o-(3-[(35)S]thio-triphosphate) binding was modulated by agonist binding to A(2A) receptors. A(2A) receptors occupation led to a decrease in the potency of A(1) receptor agonists. These results indicate that A(1) but not A(2A) receptors activation, likely occurring at low adenosine concentrations, engages a G(i)-mediated signaling; however, when both receptors are occupied by adenosine, there is an A(2A) receptor-mediated impairment of G(i)-operated transducing units. These findings are relevant to get insight into the complex relationships derived from co-expression of multiple neurotransmitter/neuromodulator receptors subtypes that individually are coupled to different G proteins. A further finding was the demonstration that the A(2A) receptor agonist, CGS 21680, at high concentrations able to significantly bind to the A(1) receptor, behaved as a partial agonist of the later receptor. This fact might be taken into account when characterizing CGS 21680 actions in human cells expressing A(1) receptors when the compound is used at micromolar concentrations.
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Affiliation(s)
- Vicent Casadó
- Biochemistry and Molecular Biology Department, University of Barcelona, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, CIBERNED, Barcelona, Spain
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22
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Kenakin T, Miller LJ. Seven transmembrane receptors as shapeshifting proteins: the impact of allosteric modulation and functional selectivity on new drug discovery. Pharmacol Rev 2010; 62:265-304. [PMID: 20392808 DOI: 10.1124/pr.108.000992] [Citation(s) in RCA: 458] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
It is useful to consider seven transmembrane receptors (7TMRs) as disordered proteins able to allosterically respond to a number of binding partners. Considering 7TMRs as allosteric systems, affinity and efficacy can be thought of in terms of energy flow between a modulator, conduit (the receptor protein), and a number of guests. These guests can be other molecules, receptors, membrane-bound proteins, or signaling proteins in the cytosol. These vectorial flows of energy can yield standard canonical guest allostery (allosteric modification of drug effect), effects along the plane of the cell membrane (receptor oligomerization), or effects directed into the cytosol (differential signaling as functional selectivity). This review discusses these apparently diverse pharmacological effects in terms of molecular dynamics and protein ensemble theory, which tends to unify 7TMR behavior toward cells. Special consideration will be given to functional selectivity (biased agonism and biased antagonism) in terms of mechanism of action and potential therapeutic application. The explosion of technology that has enabled observation of diverse 7TMR behavior has also shown how drugs can have multiple (pluridimensional) efficacies and how this can cause paradoxical drug classification and nomenclatures.
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Affiliation(s)
- Terry Kenakin
- GlaxoSmithKline, 5 Moore Drive, Mailtstop V-287, Research Triangle Park, NC 27709, USA.
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23
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Franco R, Canela EI, Casado V, Ferre S. Platforms for the identification of GPCR targets, and of orthosteric and allosteric modulators. Expert Opin Drug Discov 2010; 5:391-403. [DOI: 10.1517/17460441003653163] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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24
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The asymmetric/symmetric activation of GPCR dimers as a possible mechanistic rationale for multiple signalling pathways. Trends Pharmacol Sci 2010; 31:15-21. [DOI: 10.1016/j.tips.2009.10.008] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2009] [Revised: 10/23/2009] [Accepted: 10/26/2009] [Indexed: 11/16/2022]
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25
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Soriano A, Vendrell M, Gonzalez S, Mallol J, Albericio F, Royo M, Lluís C, Canela EI, Franco R, Cortés A, Casadó V. A hybrid indoloquinolizidine peptide as allosteric modulator of dopamine D1 receptors. J Pharmacol Exp Ther 2009; 332:876-85. [PMID: 20026675 DOI: 10.1124/jpet.109.158824] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The indoloquinolizidine-peptide 28 [(3S,12bR)-N-((S)-1-((S)-1-((S)-2-carbamoylpyrrolidin-1-yl)-3-(4-fluorophenyl)-1-oxopropan-2-ylamino)-4-cyclohexyl-1-oxobutan-2-yl)-1,2,3,4,6,7,12, 12b-octahydroindolo[2,3-a]quinolizine-3-carboxamide], a trans-indoloquinolizidine-peptide hybrid obtained by a combinatorial approach, behaved as an orthosteric ligand of all dopamine D(2)-like receptors (D(2), D(3), and D(4)) and dopamine D(5) receptors, but as a negative allosteric modulator of agonist and antagonist binding to striatal dopamine D(1) receptors. Indoloquinolizidine-peptide 28 induced a concentration-dependent hyperbolic increase in the antagonist apparent equilibrium dissociation constant values and altered the dissociation kinetics of dopamine D(1) receptor antagonists. The negative allosteric modulation was also found when agonist binding to D(1) receptors was assayed. Indoloquinolizidine-peptide 28 was a weak ago-allosteric modulator but markedly led to a decreased potency without decreasing the maximum partial/full agonist-mediated effect on cAMP levels. Compounds able to decrease the potency while preserving the efficacy of D(1) receptor agonists are promising for exploration in psychotic pathologies.
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Affiliation(s)
- Aroa Soriano
- Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona, Spain
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Soriano A, Ventura R, Molero A, Hoen R, Casadó V, Cortés A, Fanelli F, Albericio F, Lluís C, Franco R, Royo M. Adenosine A2A receptor-antagonist/dopamine D2 receptor-agonist bivalent ligands as pharmacological tools to detect A2A-D2 receptor heteromers. J Med Chem 2009; 52:5590-602. [PMID: 19711895 DOI: 10.1021/jm900298c] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Adenosine A(2A) (A(2A)R) and dopamine D(2) (D(2)R) receptors mediate the antagonism between adenosinergic and dopaminergic transmission in striatopallidal GABAergic neurons and are pharmacological targets for the treatment of Parkinson's disease. Here, a family of heterobivalent ligands containing a D(2)R agonist and an A(2A)R antagonist linked through a spacer of variable size was designed and synthesized to study A(2A)R-D(2)R heteromers. Bivalent ligands with shorter linkers bound to D(2)R or A(2A)R with higher affinity than the corresponding monovalent controls in membranes from brain striatum and from cells coexpressing both receptors. In contrast, no differences in affinity of bivalent versus monovalent ligands were detected in experiments using membranes from cells expressing only one receptor. These findings indicate the existence of A(2A)R-D(2)R heteromers and of a simultaneous interaction of heterobivalent ligands with both receptors. The cooperative effect derived from the simultaneous interaction suggests the occurrence of A(2A)R-D(2)R heteromers in cotransfected cells and in brain striatum. The dopamine/adenosine bivalent action could constitute a novel concept in Parkinson's disease pharmacotherapy.
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Affiliation(s)
- Aroa Soriano
- Institut d'Investigacions Biomediques August Pi i Sunyer (IDIBAPS), Centro de Investigacion Biomedica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), and Department of Biochemistry and Molecular Biology, University of Barcelona, Avenida Diagonal 645, E-08028 Barcelona, Spain
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Casadó V, Cortés A, Mallol J, Pérez-Capote K, Ferré S, Lluis C, Franco R, Canela EI. GPCR homomers and heteromers: a better choice as targets for drug development than GPCR monomers? Pharmacol Ther 2009; 124:248-57. [PMID: 19664655 DOI: 10.1016/j.pharmthera.2009.07.005] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Accepted: 07/21/2009] [Indexed: 10/20/2022]
Abstract
G protein-coupled receptors (GPCR) are targeted by many therapeutic drugs marketed to fight against a variety of diseases. Selection of novel lead compounds are based on pharmacological parameters obtained assuming that GPCR are monomers. However, many GPCR are expressed as dimers/oligomers. Therefore, drug development may consider GPCR as homo- and hetero-oligomers. A two-state dimer receptor model is now available to understand GPCR operation and to interpret data obtained from drugs interacting with dimers, and even from mixtures of monomers and dimers. Heteromers are distinct entities and therefore a given drug is expected to have different affinities and different efficacies depending on the heteromer. All these concepts would lead to broaden the therapeutic potential of drugs targeting GPCRs, including receptor heteromer-selective drugs with a lower incidence of side effects, or to identify novel pharmacological profiles using cell models expressing receptor heteromers.
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Affiliation(s)
- Vicent Casadó
- Departament de Bioquímica i Biologia Molecular, CIBERNED (Centro de Investigación en Red de Enfermedades Neurodegenerativas) and Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS) Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain
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28
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Casadó V, Ferrada C, Bonaventura J, Gracia E, Mallol J, Canela EI, Lluís C, Cortés A, Franco R. Useful pharmacological parameters for G-protein-coupled receptor homodimers obtained from competition experiments. Agonist-antagonist binding modulation. Biochem Pharmacol 2009; 78:1456-63. [PMID: 19643089 DOI: 10.1016/j.bcp.2009.07.012] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2009] [Revised: 07/16/2009] [Accepted: 07/20/2009] [Indexed: 11/26/2022]
Abstract
Many G-protein-coupled receptors (GPCRs) are expressed on the plasma membrane as dimers. Since drug binding data are currently fitted using equations developed for monomeric receptors, the interpretation of the pharmacological data are equivocal in many cases. As reported here, GPCR dimer models account for changes in competition curve shape as a function of the radioligand concentration used, something that cannot be explained by monomeric receptor models. Macroscopic equilibrium dissociation constants for the agonist and homotropic cooperativity index reflecting the intramolecular communication within the dopamine D1 or adenosine A2A receptor homodimer as well as hybrid equilibrium dissociation constant, which reflects the antagonist/agonist modulation may be calculated by fitting binding data from antagonist/agonist competition experiments to equations developed from dimer receptor models. Comparing fitting the data by assuming a classical monomeric receptor model or a dimer model, it is shown that dimer receptor models provide more clues useful in drug discovery than monomer-based models.
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Affiliation(s)
- Vicent Casadó
- Institut d'Investigacions Biomèdiques August Pi i Sunyer, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona, Avda. Diagonal 465, 08028 Barcelona, Spain.
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29
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Ferrada C, Moreno E, Casadó V, Bongers G, Cortés A, Mallol J, Canela EI, Leurs R, Ferré S, Lluís C, Franco R. Marked changes in signal transduction upon heteromerization of dopamine D1 and histamine H3 receptors. Br J Pharmacol 2009; 157:64-75. [PMID: 19413572 DOI: 10.1111/j.1476-5381.2009.00152.x] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND AND PURPOSE Functional interactions between the G protein-coupled dopamine D1 and histamine H3 receptors have been described in the brain. In the present study we investigated the existence of D1-H3 receptor heteromers and their biochemical characteristics. EXPERIMENTAL APPROACH D1-H3 receptor heteromerization was studied in mammalian transfected cells with Bioluminescence Resonance Energy Transfer and binding assays. Furthermore, signalling through mitogen-activated protein kinase (MAPK) and adenylyl cyclase pathways was studied in co-transfected cells and compared with cells transfected with either D1 or H3 receptors. KEY RESULTS Bioluminescence Resonance Energy Transfer and binding assays confirmed that D1 and H3 receptors can heteromerize. Activation of histamine H3 receptors did not lead to signalling towards the MAPK pathway unless dopamine D1 receptors were co-expressed. Also, dopamine D1 receptors, usually coupled to G(s) proteins and leading to increases in cAMP, did not couple to G(s) but to G(i) in co-transfected cells. Furthermore, signalling via each receptor was blocked not only by a selective antagonist but also by an antagonist of the partner receptor. CONCLUSIONS AND IMPLICATIONS D1-H3 receptor heteromers constitute unique devices that can direct dopaminergic and histaminergic signalling towards the MAPK pathway in a G(s)-independent and G(i)-dependent manner. An antagonist of one of the receptor units in the D1-H3 receptor heteromer can induce conformational changes in the other receptor unit and block specific signals originating in the heteromer. This gives rise to unsuspected therapeutic potentials for G protein-coupled receptor antagonists.
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Affiliation(s)
- Carla Ferrada
- Molecular Neurobiology Unit, IDIBAPS, CIBERNED, Department of Biochemistry and Molecular Biology, School of Biology, University of Barcelona, Barcelona, Spain
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Franco R. G-protein-coupled receptor heteromers or how neurons can display differently flavoured patterns in response to the same neurotransmitter. Br J Pharmacol 2009; 158:23-31. [PMID: 19422387 DOI: 10.1111/j.1476-5381.2009.00181.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
It is becoming accepted that G-protein-coupled receptors (GPCRs) arrange in the neuronal membrane into homo- and hetero-oligomers and, therefore, these complexes mediate neurotransmission. New models are then needed to understand GPCR operation and predict the consequences of GPCR homo- or hetero-oligomerization. Although there is not any unifying theory addressing how hetero-oligomerization occurs, recent models have been devised to understand the thermodynamics of binding of neurotransmitters to GPCRs and the allosteric protomer-protomer interactions involved in neurotransmitter-mediated activation of GPCRs. Although a model to predict how signalling is produced via homo- or hetero-oligomerization is lacking, functional data show that receptor oligomers exist to produce a variety of effects in neurons in response to a single neurotransmitter.
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Affiliation(s)
- Rafael Franco
- Molecular Neurobiology Unit, Institut d'Investigacions Biomèdiques August Pi i Sunyer, Departament de Bioquímica i Biología Molecular, School of Biology, University of Barcelona, Spain.
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31
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Brain receptor mosaics and their intramembrane receptor-receptor interactions: molecular integration in transmission and novel targets for drug development. J Acupunct Meridian Stud 2009; 2:1-25. [PMID: 20633470 DOI: 10.1016/s2005-2901(09)60011-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Accepted: 01/06/2009] [Indexed: 11/21/2022] Open
Abstract
The concept of intramembrane receptor-receptor interactions and evidence for their existence was introduced by Agnati and Fuxe in 1980/81 suggesting the existence of heteromerization of receptors. In 1982, they proposed the existence of aggregates of multiple receptors in the plasma membrane and coined the term receptor mosaics (RM). In this way, cell signaling becomes a branched process beginning at the level of receptor recognition at the plasma membrane where receptors can directly modify the ligand recognition and signaling capacity of the receptors within a RM. Receptor-receptor interactions in RM are classified as operating either with classical cooperativity, when consisting of homomers or heteromers of similar receptor subtypes having the same transmitter, or non-classical cooperativity, when consisting of heteromers. It has been shown that information processing within a RM depends not only on its receptor composition, but also on the topology and the order of receptor activation determined by the concentrations of the ligands and the receptor properties. The general function of RM has also been demonstrated to depend on allosteric regulators (e.g., homocysteine) of the receptor subtypes present. RM as integrative nodes for receptor-receptor interactions in conjunction with membrane associated proteins may form horizontal molecular networks in the plasma membrane coordinating the activity of multiple effector systems modulating the excitability and gene expression of the cells. The key role of electrostatic epitope-epitope interactions will be discussed for the formation of the RM. These interactions probably represent a general molecular mechanism for receptor-receptor interactions and, without a doubt, indicate a role for phosphorylation-dephosphorylation events in these interactions. The novel therapeutic aspects given by the RMs will be discussed in the frame of molecular neurology and psychiatry and combined drug therapy appears as the future way to go.
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Abstract
Receptor heteromers constitute a new area of research that is reshaping our thinking about biochemistry, cell biology, pharmacology and drug discovery. In this commentary, we recommend clear definitions that should facilitate both information exchange and research on this growing class of transmembrane signal transduction units and their complex properties. We also consider research questions underlying the proposed nomenclature, with recommendations for receptor heteromer identification in native tissues and their use as targets for drug development.
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Brea J, Castro M, Giraldo J, López-Giménez JF, Padín JF, Quintián F, Cadavid MI, Vilaró MT, Mengod G, Berg KA, Clarke WP, Vilardaga JP, Milligan G, Loza MI. Evidence for distinct antagonist-revealed functional states of 5-hydroxytryptamine(2A) receptor homodimers. Mol Pharmacol 2009; 75:1380-91. [PMID: 19279328 DOI: 10.1124/mol.108.054395] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The serotonin (5-hydroxytryptamine; 5-HT) 2A receptor is a cell surface class A G protein-coupled receptor that regulates a multitude of physiological functions of the body and is a target for antipsychotic drugs. Here we found by means of fluorescence resonance energy transfer and immunoprecipitation studies that the 5-HT(2A)-receptor homodimerized in live cells, which we linked with its antagonist-dependent fingerprint in both binding and receptor signaling. Some antagonists, like the atypical antipsychotics clozapine and risperidone, differentiate themselves from others, like the typical antipsychotic haloperidol, antagonizing these 5-HT(2A) receptor-mediated functions in a pathway-specific manner, explained here by a new model of multiple active interconvertible conformations at dimeric receptors.
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Affiliation(s)
- José Brea
- Departamento de Farmacología, Instituto de Farmacia Industrial, Universidad de Santiago de Compostela, Spain
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34
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Neurotransmitter receptor heteromers in neurodegenerative diseases and neural plasticity. J Neural Transm (Vienna) 2008; 116:983-7. [PMID: 19002553 DOI: 10.1007/s00702-008-0148-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2008] [Accepted: 10/20/2008] [Indexed: 10/21/2022]
Abstract
Metabotropic receptors for neurotransmitters on the plasma membrane of neurons are forming homo- hetero- dimers and even homo- or hetero-oligomers. Neurotransmission has been studied assuming that these G-protein-coupled receptors were monomers. Then, on considering receptor dimers, we are entering a new era for the understanding how neurotransmitter receptors decode signals originating at the nervous system. At the moment it is becoming clear that receptor homo and hetero-oligomers provide signaling diversity, help to understand synaptic plasticity and open new therapeutic potential as targets for neurodegenerative and neuropsychiatric diseases.
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35
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Gracia E, Cortés A, Meana JJ, García-Sevilla J, Herhsfield MS, Canela EI, Mallol J, Lluís C, Franco R, Casadó V. Human adenosine deaminase as an allosteric modulator of human A(1) adenosine receptor: abolishment of negative cooperativity for [H](R)-pia binding to the caudate nucleus. J Neurochem 2008; 107:161-70. [PMID: 18680557 DOI: 10.1111/j.1471-4159.2008.05602.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It has been shown that adenosine deaminase (ADA; EC 3.5.4.4) behaves as an ecto-enzyme anchored to membrane proteins, among them A(1) adenosine receptors (A(1)Rs). Bovine ADA interacts with A(1)Rs from many species and regulates agonists binding to receptors in an activity-independent form. However, it was not known whether human ADA exerted any effect on the agonist binding to human A(1)Rs, because of both technical difficulties in obtaining pure human ADA and tissues containing human A(1)Rs. In this study, human ADA was purified to homogeneity. Taking in consideration that A(1)Rs form homodimers and taking advantage of a new procedure to fit binding data to receptors dimers, which allows to calculate ligand dissociation constants and the degree of cooperativity between the two subunits in the dimer, here it is demonstrated that human ADA markedly enhances the agonist and antagonist affinity and abolishes the negative cooperativity on agonist binding to human striatal A(1)Rs. ADA also increases the ability of the agonist to decrease the forskolin-induced cAMP levels. The results show that human ADA, apart from reducing the adenosine concentration and thus preventing A(1)R desensitization, binds to A(1)R behaving as an allosteric effector that markedly enhances agonist affinity and increases receptor functionality. The physiological role of the interaction is to make receptors more sensitive to adenosine. This powerful regulation has important implications for the physiology and pharmacology of neuronal A(1)Rs.
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Affiliation(s)
- Eduard Gracia
- Institut d'Investigacions Biomèdiques August Pi i Sunyer, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), University of Barcelona, Spain.
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36
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Fuxe K, Marcellino D, Rivera A, Diaz-Cabiale Z, Filip M, Gago B, Roberts D, Langel U, Genedani S, Ferraro L, de la Calle A, Narvaez J, Tanganelli S, Woods A, Agnati L. Receptor–receptor interactions within receptor mosaics. Impact on neuropsychopharmacology. ACTA ACUST UNITED AC 2008; 58:415-52. [DOI: 10.1016/j.brainresrev.2007.11.007] [Citation(s) in RCA: 167] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2007] [Revised: 11/26/2007] [Accepted: 11/29/2007] [Indexed: 01/01/2023]
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Franco R, Casadó V, Cortés A, Pérez-Capote K, Mallol J, Canela E, Ferré S, Lluis C. Novel pharmacological targets based on receptor heteromers. ACTA ACUST UNITED AC 2008; 58:475-82. [PMID: 18620000 DOI: 10.1016/j.brainresrev.2008.06.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2008] [Revised: 06/11/2008] [Accepted: 06/12/2008] [Indexed: 12/24/2022]
Abstract
Studies performed in the last 10 years have provided solid evidence indicating that G-protein-coupled receptors are expressed on the plasma membrane as homo and heterodimers. The first consequence of this fact is that homo and heterodimers are the true targets of natural (hormones, neurotransmitters) and synthetic drugs. Furthermore a given receptor in a heteromer may display a different functional and/or pharmacological profile than the same receptor characterized as monomer or as homodimer. Recent evidence indicates that receptor heteromers are sensors that lead to a fine-tuning in neurotransmission or hormone regulation; mainly this is achieved by a modification of the signaling pathways activated via a given receptor when it is forming a given heteromer. Quite often antagonists display variable affinities when a given receptor is expressed with different heteromeric partners. This fact should be taken into account in the development of new drugs. Finally it should be pointed out that radioligand binding data has to be analyzed by a model that considers receptors as dimers and not as monomers. This model provides a novel approach to characterize drugs interacting with the orthosteric center (agonists/antagonists) or with allosteric centers (allosteric regulators).
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Affiliation(s)
- Rafael Franco
- Institut d'Investigació Biomèdica August Pi i Sunyer (IDIBAPS), Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona, Spain.
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38
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Giraldo J. On the fitting of binding data when receptor dimerization is suspected. Br J Pharmacol 2008; 155:17-23. [PMID: 18536745 DOI: 10.1038/bjp.2008.234] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Mechanistic and empirical modelling are compared in context of dimeric receptors. In particular, the supposed advantages of the two-state dimer model for fitting of binding data with respect to classical approaches such as the two-independent sites model are investigated. The two models are revisited from both the mechanistic and empirical point of views. The problem of overparameterized models and the benefits of the concurrent use of mechanistic and empirical models for mechanism analysis are discussed. The pros and cons of mathematical models are examined with special emphasis given to the interpretation of the connection between the shapes of the curves and receptor cooperativity. It is shown that a given pharmacological phenotype (curve shape) can be obtained from different receptor genotypes (as, for instance, non-interconvertible monomeric receptor species, receptor-G protein interactions and dimeric receptors), though values of the Hill coefficient greater than one are indicative of receptor oligomerization. The existence of a relationship between the recently defined dimer cooperativity index and the more familiar Hill coefficient is proven.
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Affiliation(s)
- J Giraldo
- Grup Biomatemàtic de Recerca, Institut de Neurociències and Unitat de Bioestadística, Universitat Autònoma de Barcelona, Bellaterra, Spain.
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39
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Conformational cross-talk between alpha2A-adrenergic and mu-opioid receptors controls cell signaling. Nat Chem Biol 2008; 4:126-31. [PMID: 18193048 DOI: 10.1038/nchembio.64] [Citation(s) in RCA: 203] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Accepted: 11/27/2007] [Indexed: 12/22/2022]
Abstract
Morphine, a powerful analgesic, and norepinephrine, the principal neurotransmitter of sympathetic nerves, exert major inhibitory effects on both peripheral and brain neurons by activating distinct cell-surface G protein-coupled receptors-the mu-opioid receptor (MOR) and alpha2A-adrenergic receptor (alpha2A-AR), respectively. These receptors, either singly or as a heterodimer, activate common signal transduction pathways mediated through the inhibitory G proteins (G(i) and G(o)). Using fluorescence resonance energy transfer microscopy, we show that in the heterodimer, the MOR and alpha2A-AR communicate with each other through a cross-conformational switch that permits direct inhibition of one receptor by the other with subsecond kinetics. We discovered that morphine binding to the MOR triggers a conformational change in the norepinephrine-occupied alpha2A-AR that inhibits its signaling to G(i) and the downstream MAP kinase cascade. These data highlight a new mechanism in signal transduction whereby a G protein-coupled receptor heterodimer mediates conformational changes that propagate from one receptor to the other and cause the second receptor's rapid inactivation.
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40
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Casadó V, Cortés A, Ciruela F, Mallol J, Ferré S, Lluis C, Canela EI, Franco R. Old and new ways to calculate the affinity of agonists and antagonists interacting with G-protein-coupled monomeric and dimeric receptors: The receptor–dimer cooperativity index. Pharmacol Ther 2007; 116:343-54. [DOI: 10.1016/j.pharmthera.2007.05.010] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2007] [Accepted: 05/18/2007] [Indexed: 10/23/2022]
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41
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Franco R, Casadó V, Cortés A, Mallol J, Ciruela F, Ferré S, Lluis C, Canela EI. G-protein-coupled receptor heteromers: function and ligand pharmacology. Br J Pharmacol 2007; 153 Suppl 1:S90-8. [PMID: 18037920 DOI: 10.1038/sj.bjp.0707571] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Almost all existing models for G-protein-coupled receptors (GPCRs) are based on the occurrence of monomers. Recent studies show that many GPCRs are dimers. Therefore for some receptors dimers and not monomers are the main species interacting with hormones/neurotransmitters/drugs. There are reasons for equivocal interpretations of the data fitting to receptor dimers assuming they are monomers. Fitting data using a dimer-based model gives not only the equilibrium dissociation constants for high and low affinity binding to receptor dimers but also a 'cooperativity index' that reflects the molecular communication between monomers within the dimer. The dimer cooperativity index (D(C)) is a valuable tool that enables to interpret and quantify, for instance, the effect of allosteric regulators. For different receptors heteromerization confers a specific functional property for the receptor heteromer that can be considered as a 'dimer fingerprint'. The occurrence of heteromers with different pharmacological and signalling properties opens a complete new field to search for novel drug targets useful to combat a variety of diseases and potentially with fewer side effects. Antagonists, which are quite common marketed drugs targeting GPCRs, display variable affinities when a given receptor is expressed with different heteromeric partners. This fact should be taken into account in the development of new drugs.
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Affiliation(s)
- R Franco
- Departament de Bioquímica i Biologia Molecular, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, Institut d'Investigació Biomèdica August Pi i Sunyer (IDIBAPS), Universitat de Barcelona, Barcelona, Spain.
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42
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Milligan G, Smith NJ. Allosteric modulation of heterodimeric G-protein-coupled receptors. Trends Pharmacol Sci 2007; 28:615-20. [PMID: 18022255 DOI: 10.1016/j.tips.2007.11.001] [Citation(s) in RCA: 137] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Revised: 08/30/2007] [Accepted: 11/02/2007] [Indexed: 11/25/2022]
Abstract
G-protein-coupled receptors (GPCRs) are, and will probably remain, the most tractable class of targets for the development of small-molecule therapeutic medicines. Currently, all approved GPCR-directed medicines are agonists or antagonists at orthosteric binding sites - except for the calcimimetic cinacalcet, which is a positive allosteric modulator of Ca(2+)-sensing receptors, and maraviroc, an allosteric inhibitor of CC-chemokine receptor (CCR) 5. It is now widely accepted that GPCRs exist and might function as dimers, and there is growing evidence for the physiological presence and relevance of GPCR heterodimers. Molecules that can regulate a GPCR within a heterodimer, through allosteric effects between the two protomers of the dimer or between a protomer or protomers and the associated G protein, offer the potential to function in a highly selective and tissue-specific way. Despite the conceptual attraction of such allosteric regulators of GPCR heterodimers as drugs, they cannot be identified by screening approaches that routinely use a 'one GPCR target at a time' strategy. In our opinion, this will require the development of new approaches for screening and a return to the use of physiologically relevant cell systems at an early stage in compound identification.
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Affiliation(s)
- Graeme Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland, UK.
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43
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Carriba P, Ortiz O, Patkar K, Justinova Z, Stroik J, Themann A, Müller C, Woods AS, Hope BT, Ciruela F, Casadó V, Canela EI, Lluis C, Goldberg SR, Moratalla R, Franco R, Ferré S. Striatal adenosine A2A and cannabinoid CB1 receptors form functional heteromeric complexes that mediate the motor effects of cannabinoids. Neuropsychopharmacology 2007; 32:2249-59. [PMID: 17356572 DOI: 10.1038/sj.npp.1301375] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The mechanism of action responsible for the motor depressant effects of cannabinoids, which operate through centrally expressed cannabinoid CB1 receptors, is still a matter of debate. In the present study, we report that CB1 and adenosine A2A receptors form heteromeric complexes in co-transfected HEK-293T cells and rat striatum, where they colocalize in fibrilar structures. In a human neuroblastoma cell line, CB1 receptor signaling was found to be completely dependent on A2A receptor activation. Accordingly, blockade of A2A receptors counteracted the motor depressant effects produced by the intrastriatal administration of a cannabinoid CB1 receptor agonist. These biochemical and behavioral findings demonstrate that the profound motor effects of cannabinoids depend on physical and functional interactions between striatal A2A and CB1 receptors.
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MESH Headings
- Adenosine A2 Receptor Agonists
- Analysis of Variance
- Animals
- Arachidonic Acids/pharmacology
- Behavior, Animal
- Cannabinoids/agonists
- Cannabinoids/antagonists & inhibitors
- Cannabinoids/pharmacology
- Cell Line, Transformed
- Corpus Striatum/drug effects
- Corpus Striatum/metabolism
- Cyclic AMP/metabolism
- Drug Interactions
- Humans
- Luminescent Proteins/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Motor Activity/drug effects
- Protein Binding/drug effects
- Rats
- Rats, Wistar
- Receptor, Adenosine A2A/deficiency
- Receptor, Adenosine A2A/physiology
- Receptor, Cannabinoid, CB1/agonists
- Receptor, Cannabinoid, CB1/deficiency
- Receptor, Cannabinoid, CB1/physiology
- Transfection
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Affiliation(s)
- Paulina Carriba
- Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona, Spain
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44
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Ferré S, Agnati LF, Ciruela F, Lluis C, Woods AS, Fuxe K, Franco R. Neurotransmitter receptor heteromers and their integrative role in 'local modules': the striatal spine module. BRAIN RESEARCH REVIEWS 2007; 55:55-67. [PMID: 17408563 PMCID: PMC2039920 DOI: 10.1016/j.brainresrev.2007.01.007] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 01/17/2007] [Accepted: 01/18/2007] [Indexed: 12/01/2022]
Abstract
'Local module' is a fundamental functional unit of the central nervous system that can be defined as the minimal portion of one or more neurons and/or one or more glial cells that operates as an independent integrative unit. This review focuses on the importance of neurotransmitter receptor heteromers for the operation of local modules. To illustrate this, we use the striatal spine module (SSM), comprised of the dendritic spine of the medium spiny neuron (MSN), its glutamatergic and dopaminergic terminals and astroglial processes. The SSM is found in the striatum, and although aspects such as neurotransmitters and receptors will be specific to the SSM, some general principles should apply to any local module in the brain. The analysis of some of the receptor heteromers in the SSM shows that receptor heteromerization is associated with particular elaborated functions in this local module. Adenosine A(2A) receptor-dopamine D(2) receptor-glutamate metabotropic mGlu(5) receptor heteromers are located adjacent to the glutamatergic synapse of the dendritic spine of the enkephalin MSN, and their cross-talk within the receptor heteromers helps to modulate postsynaptic plastic changes at the glutamatergic synapse. A(1) receptor-A(2A) receptor heteromers are found in the glutamatergic terminals and the molecular cross-talk between the two receptors in the heteromer helps to modulate glutamate release. Finally, dopamine D(2) receptor-non-alpha(7) nicotinic acetylcholine receptor heteromers, which are located in dopaminergic terminals, introduce the new concept of autoreceptor heteromer.
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Affiliation(s)
- Sergi Ferré
- Behavioral Neuroscience Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Department of Health and Human Services, Nathan Shock Drive, Baltimore, MD 21224, USA.
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45
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Fredholm BB, Chern Y, Franco R, Sitkovsky M. Aspects of the general biology of adenosine A2A signaling. Prog Neurobiol 2007; 83:263-76. [PMID: 17804147 DOI: 10.1016/j.pneurobio.2007.07.005] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2007] [Revised: 04/05/2007] [Accepted: 07/19/2007] [Indexed: 01/10/2023]
Abstract
Many of our current hopes of finding better ways to treat Parkinson's disease or to stop its progression rely on studies of adenosine A2A receptors in the brain. Yet any drug targeting central receptors will also potentially affect receptors in other sites. Furthermore, several fundamental aspects of adenosine receptor biology must be taken into account. For these reasons the "Targeting adenosine A2A receptors in Parkinson's disease and other CNS disorders" meeting in Boston included selected aspects of the general biology of adenosine A2A receptor signaling. Some of the presentations from this part of the meeting are summarized in this first chapter. As will be apparent to the reader, these different parts do not form an integrated whole, but they do indicate areas the organizers felt might illuminate remaining questions regarding the roles of adenosine A2A receptors. The contributors to this part of the meeting have summarized some of the key questions below.
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MESH Headings
- Adenosine/metabolism
- Animals
- Dimerization
- Encephalitis/genetics
- Encephalitis/immunology
- Encephalitis/metabolism
- Humans
- Hypoxia, Brain/genetics
- Hypoxia, Brain/immunology
- Hypoxia, Brain/metabolism
- Hypoxia-Inducible Factor 1, alpha Subunit/genetics
- Hypoxia-Inducible Factor 1, alpha Subunit/immunology
- Hypoxia-Inducible Factor 1, alpha Subunit/metabolism
- Parkinson Disease/genetics
- Parkinson Disease/immunology
- Parkinson Disease/metabolism
- Receptor, Adenosine A2A/genetics
- Receptor, Adenosine A2A/metabolism
- Receptors, G-Protein-Coupled/genetics
- Receptors, G-Protein-Coupled/metabolism
- Signal Transduction/genetics
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Affiliation(s)
- Bertil B Fredholm
- Department of Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden.
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46
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Michel AD, Chambers LJ, Clay WC, Condreay JP, Walter DS, Chessell IP. Direct labelling of the human P2X7 receptor and identification of positive and negative cooperativity of binding. Br J Pharmacol 2007; 151:103-14. [PMID: 17339830 PMCID: PMC2012979 DOI: 10.1038/sj.bjp.0707196] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE The P2X(7) receptor exhibits complex pharmacological properties. In this study, binding of a [(3)H]-labelled P2X(7) receptor antagonist to human P2X(7) receptors has been examined to further understand ligand interactions with this receptor. EXPERIMENTAL APPROACH The P2X(7) receptor antagonist, N-[2-({2-[(2-hydroxyethyl)amino]ethyl}amino)-5-quinolinyl]-2-tricyclo[3.3.1.1(3,7)]dec-1-ylacetamide (compound-17), was radiolabelled with tritium and binding studies were performed using membranes prepared from U-2 OS or HEK293 cells expressing human recombinant P2X(7) receptors. KEY RESULTS Binding of [(3)H]-compound-17 was higher in membranes prepared from cells expressing P2X(7) receptors than from control cells and was inhibited by ATP suggesting labelled sites represented human P2X(7) receptors. Binding was reversible, saturable and modulated by P2X(7) receptor ligands (Brilliant Blue G, KN62, ATP, decavanadate). Furthermore, ATP potency was reduced in the presence of divalent cations or NaCl. Radioligand binding exhibited both positive and negative cooperativity. Positive cooperativity was evident from bell shaped Scatchard plots, reduction in radioligand dissociation rate by unlabelled compound-17 and enhancement of radioligand binding by KN62 and unlabelled compound-17. ATP and decavanadate inhibited binding in a negative cooperative manner as they enhanced radioligand dissociation. CONCLUSIONS These data demonstrate that human P2X(7) receptors can be directly labelled and provide novel insights into receptor function. The positive cooperativity observed suggests that binding of compound-17 to one subunit in the P2X(7) receptor complex enhances subsequent binding to other P2X(7) subunits in the same complex. The negative cooperative effects of ATP suggest that ATP and compound-17 bind at separate, interacting, sites on the P2X(7) receptor.
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Affiliation(s)
- A D Michel
- Neurology & GI Centre of Excellence for Drug Discovery, GlaxoSmithKline Research and Development Limited, Harlow, Essex, UK.
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47
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Marcellino D, Roberts DCS, Navarro G, Filip M, Agnati L, Lluís C, Franco R, Fuxe K. Increase in A2A receptors in the nucleus accumbens after extended cocaine self-administration and its disappearance after cocaine withdrawal. Brain Res 2007; 1143:208-20. [PMID: 17320828 DOI: 10.1016/j.brainres.2007.01.079] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Revised: 01/16/2007] [Accepted: 01/18/2007] [Indexed: 10/23/2022]
Abstract
Effects of extended cocaine self-administration and its withdrawal have been studied on A(2A) and D(2) receptor binding characteristics and expression in the nucleus accumbens and the anterior and posterior dorsal striatum of the rat (Rattus norvegicus). Biochemical binding techniques have been used with the D(2)-like receptor antagonist radioligand [(3)H]-Raclopride and the A(2A) receptor antagonist radioligand [(3)H]-ZM 241385 and immunoblots to study their expression. A substantial and significant increase in functional A(2A), but not in functional D(2) receptors, was observed in the nucleus accumbens immediately following 10 days of cocaine self-administration which returned to normal levels after 7 days of drug withdrawal. In contrast, in the posterior dorsal striatum significant reductions in A(2A) expression were observed immediately after cocaine self-administration which was associated with a trend for a reduction of the A(2A) receptor antagonist binding sites. In cocaine withdrawal groups, significant increases in the density and K(d) value of D(2)-like antagonist binding sites were observed in the nucleus accumbens in the absence of changes in D(2) expression, suggesting an up-regulation of D(3) receptors in this region after cocaine withdrawal. A(2A) receptor increases in the nucleus accumbens induced by cocaine may represent a compensatory up-regulation to counteract cocaine-induced increases in D(2) signaling and D(3) signaling which is in line with its disappearance in the 7-day withdrawal group displaying increased reinforcing efficacy of cocaine. A(2A) agonists may therefore represent cocaine antagonist drugs to be used in treatment of cocaine addiction acting inter alia by antagonizing signaling in accumbens A(2A)/D(2) and A(2A)/D(3) heteromers.
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Affiliation(s)
- Daniel Marcellino
- Department of Neuroscience, Karolinska Institutet, 17177 Stockholm, Sweden.
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48
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Giménez-Llort L, Schiffmann SN, Shmidt T, Canela L, Camón L, Wassholm M, Canals M, Terasmaa A, Fernández-Teruel A, Tobeña A, Popova E, Ferré S, Agnati L, Ciruela F, Martínez E, Scheel-Kruger J, Lluis C, Franco R, Fuxe K, Bader M. Working memory deficits in transgenic rats overexpressing human adenosine A2A receptors in the brain. Neurobiol Learn Mem 2007; 87:42-56. [PMID: 16824773 DOI: 10.1016/j.nlm.2006.05.004] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2006] [Revised: 05/23/2006] [Accepted: 05/25/2006] [Indexed: 11/25/2022]
Abstract
Adenosine receptors in the central nervous system have been implicated in the modulation of different behavioural patterns and cognitive functions although the specific role of A(2A) receptor (A(2A)R) subtype in learning and memory is still unclear. In the present work we establish a novel transgenic rat strain, TGR(NSEhA2A), overexpressing adenosine A(2A)Rs mainly in the cerebral cortex, the hippocampal formation, and the cerebellum. Thereafter, we explore the relevance of this A(2A)Rs overexpression for learning and memory function. Animals were behaviourally assessed in several learning and memory tasks (6-arms radial tunnel maze, T-maze, object recognition, and several Morris water maze paradigms) and other tests for spontaneous motor activity (open field, hexagonal tunnel maze) and anxiety (plus maze) as modification of these behaviours may interfere with the assessment of cognitive function. Neither motor performance and emotional/anxious-like behaviours were altered by overexpression of A(2A)Rs. TGR(NSEhA2A) showed normal hippocampal-dependent learning of spatial reference memory. However, they presented working memory deficits as detected by performance of constant errors in the blind arms of the 6 arm radial tunnel maze, reduced recognition of a novel object and a lack of learning improvement over four trials on the same day which was not observed over consecutive days in a repeated acquisition paradigm in the Morris water maze. Given the interdependence between adenosinic and dopaminergic function, the present results render the novel TGR(NSEhA2A) as a putative animal model for the working memory deficits and cognitive disruptions related to overstimulation of cortical A(2A)Rs or to dopaminergic prefrontal dysfunction as seen in schizophrenic or Parkinson's disease patients.
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MESH Headings
- Analysis of Variance
- Animals
- Animals, Genetically Modified
- Anxiety/metabolism
- Cerebellum/metabolism
- Cerebral Cortex/metabolism
- Exploratory Behavior/physiology
- Genetic Engineering/methods
- Hippocampus/metabolism
- Humans
- Male
- Maze Learning/physiology
- Memory Disorders/genetics
- Memory Disorders/metabolism
- Memory, Short-Term/physiology
- Models, Animal
- Motor Activity/physiology
- Rats
- Rats, Sprague-Dawley
- Receptor, Adenosine A2A/genetics
- Receptor, Adenosine A2A/metabolism
- Receptor, Metabotropic Glutamate 5
- Receptors, Dopamine D2/metabolism
- Receptors, Metabotropic Glutamate/metabolism
- Statistics, Nonparametric
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Affiliation(s)
- Lydia Giménez-Llort
- Medical Psychology Unit, Department of Psychiatry and Forensic Medicine, School of Medicine, Institute of Neuroscience, Autonomous University of Barcelona, Barcelona, Spain
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49
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Fuxe K, Canals M, Torvinen M, Marcellino D, Terasmaa A, Genedani S, Leo G, Guidolin D, Diaz-Cabiale Z, Rivera A, Lundstrom L, Langel U, Narvaez J, Tanganelli S, Lluis C, Ferré S, Woods A, Franco R, Agnati LF. Intramembrane receptor–receptor interactions: a novel principle in molecular medicine. J Neural Transm (Vienna) 2006; 114:49-75. [PMID: 17066251 DOI: 10.1007/s00702-006-0589-0] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2006] [Accepted: 10/04/2006] [Indexed: 10/24/2022]
Abstract
In 1980/81 Agnati and Fuxe introduced the concept of intramembrane receptor-receptor interactions and presented the first experimental observations for their existence in crude membrane preparations. The second step was their introduction of the receptor mosaic hypothesis of the engram in 1982. The third step was their proposal that the existence of intramembrane receptor-receptor interactions made possible the integration of synaptic (WT) and extrasynaptic (VT) signals. With the discovery of the intramembrane receptor-receptor interactions with the likely formation of receptor aggregates of multiple receptors, so called receptor mosaics, the entire decoding process becomes a branched process already at the receptor level in the surface membrane. Recent developments indicate the relevance of cooperativity in intramembrane receptor-receptor interactions namely the presence of regulated cooperativity via receptor-receptor interactions in receptor mosaics (RM) built up of the same type of receptor (homo-oligomers) or of subtypes of the same receptor (RM type1). The receptor-receptor interactions will to a large extent determine the various conformational states of the receptors and their operation will be dependent on the receptor composition (stoichiometry), the spatial organization (topography) and order of receptor activation in the RM. The biochemical and functional integrative implications of the receptor-receptor interactions are outlined and long-lived heteromeric receptor complexes with frozen RM in various nerve cell systems may play an essential role in learning, memory and retrieval processes. Intramembrane receptor-receptor interactions in the brain have given rise to novel strategies for treatment of Parkinson's disease (A2A and mGluR5 receptor antagonists), schizophrenia (A2A and mGluR5 agonists) and depression (galanin receptor antagonists). The A2A/D2, A2A/D3 and A2A/mGluR5 heteromers and heteromeric complexes with their possible participation in different types of RM are described in detail, especially in the cortico-striatal glutamate synapse and its extrasynaptic components, together with a postulated existence of A2A/D4 heteromers. Finally, the impact of intramembrane receptor-receptor interactions in molecular medicine is discussed outside the brain with focus on the endocrine, the cardiovascular and the immune systems.
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Affiliation(s)
- K Fuxe
- Department of Neuroscience, Division of Cellular and Molecular Neurochemistry, Karolinska Institutet, Stockholm, Sweden.
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50
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Franco R, Lluis C, Canela EI, Mallol J, Agnati L, Casadó V, Ciruela F, Ferré S, Fuxe K. Receptor-receptor interactions involving adenosine A1 or dopamine D1 receptors and accessory proteins. J Neural Transm (Vienna) 2006; 114:93-104. [PMID: 17024327 DOI: 10.1007/s00702-006-0566-7] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2006] [Accepted: 07/13/2006] [Indexed: 11/24/2022]
Abstract
The molecular basis for the known intramembrane receptor-receptor interactions among heptahelical receptors (G protein coupled receptors, GPCR) was postulated to be heteromerization based on receptor subtype specific interactions between different types of homomers of GPCR. Adenosine and dopamine receptors in the basal ganglia have been fundamental to demonstrate the existence of receptor heteromers and the functional consequences of such molecular interactions. The heterodimer is only one type of heteromeric complex and the evidence is equally compatible with the existence of higher order heteromeric complexes, where also adapter proteins such as homer proteins and scaffolding proteins can exist, assisting in the process of linking the GPCR and ion channel receptors together in a receptor mosaic that may have special integrative value and may constitute the molecular basis for learning and memory. Heteromerization of D(2) dopamine and A(2A) adenosine receptors is reviewed by Fuxe in another article in this special issue. Here, heteromerization between D(1) dopamine and A(1) adenosine receptors is reviewed. Heteromers formed by dopamine D(1) and D(2) receptors and by adenosine A(1) and A(2A) receptors also occur in striatal cells and open new perspectives to understand why two receptors with apparently opposite effects are expressed in the same neuron and in the nerve terminals. The role of accessory proteins also capable of interacting with receptor-receptor heteromers in regulating the traffic and the molecular physiology of these receptors is also discussed. Overall, the knowledge of the reason why such complex networks of receptor-receptor and receptor-protein interactions occur in striatal cells is crucial to develop new strategies to combat neurological and neuropsychiatric diseases.
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Affiliation(s)
- R Franco
- Molecular Neurobiology Unit, Department of Biochemistry and Molecular Biology, IDIBAPS (Institut d'Investigacions Biomèdiques August Pi i Sunyer), Universitat de Barcelona, Barcelona, Spain.
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