1
|
Heusler P, Tardif S, Cussac D. Agonist stimulation at human μ opioid receptors in a [(35)S]GTPγS incorporation assay: observation of "bell-shaped" concentration-response relationships under conditions of strong receptor G protein coupling. J Recept Signal Transduct Res 2015; 36:158-66. [PMID: 26466637 DOI: 10.3109/10799893.2015.1069845] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
CONTEXT The appearance of "bell"- (or "inverted U"-) shaped agonist concentration-response curves (CRCs) in in vitro pharmacological experiments is a frequently observed but poorly communicated phenomenon. In the context of G protein coupled receptor research, it is commonly attributed to the recruitment of secondary targets or to desensitization or feedback processes, but the concrete background of these observations often remains intriguing. OBJECTIVE Here, we addressed the subject of bell-shaped agonist CRCs at the µ opioid receptor (µOR) by testing the impact of experimental conditions favoring G protein coupling. METHODS G protein activation by recombinant human µORs heterologously expressed in CHO cells was assessed in [(35)S]GTPγS binding assays using the opioid ligands DAMGO, morphine, fentanyl and naloxone. Experimental conditions were varied by changing the NaCl (10-300 mM) and the GDP concentration (0.3-30 µM). RESULTS Both the sodium and the GDP concentration were inversely related to G protein coupling, as evident by an increase in basal [(35)S]GTPγS incorporation at low sodium and low GDP levels and by the concomitant appearance of the partial agonist activity of the µOR antagonist, naloxone. Bell-shaped CRCs were observed for the efficacious agonists DAMGO, fentanyl and morphine, and this phenomenon was promoted by low sodium as well as by low GDP concentrations. CONCLUSION µOR agonist CRCs show a non-monotonic behavior with a decline of maximal stimulation under conditions of strong receptor-G protein coupling, and this behavior is visible at the level of G protein activation itself.
Collapse
Affiliation(s)
- Peter Heusler
- a Department of Cellular and Molecular Biology , Pierre Fabre Research Center , Castres Cedex , France
| | - Stéphanie Tardif
- a Department of Cellular and Molecular Biology , Pierre Fabre Research Center , Castres Cedex , France
| | - Didier Cussac
- a Department of Cellular and Molecular Biology , Pierre Fabre Research Center , Castres Cedex , France
| |
Collapse
|
2
|
Kienitz MC, Mintert-Jancke E, Hertel F, Pott L. Differential effects of genetically-encoded Gβγ scavengers on receptor-activated and basal Kir3.1/Kir3.4 channel current in rat atrial myocytes. Cell Signal 2014; 26:1182-92. [PMID: 24576551 DOI: 10.1016/j.cellsig.2014.02.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Revised: 01/23/2014] [Accepted: 02/13/2014] [Indexed: 12/23/2022]
Abstract
Opening of G-protein-activated inward-rectifying K(+) (GIRK, Kir3) channels is regulated by interaction with βγ-subunits of Pertussis-toxin-sensitive G proteins upon activation of appropriate GPCRs. In atrial and neuronal cells agonist-independent activity (I(basal)) contributes to the background K(+) conductance, important for stabilizing resting potential. Data obtained from the Kir3 signaling pathway reconstituted in Xenopus oocytes suggest that I(basal) requires free G(βγ). In cells with intrinsic expression of Kir3 channels this issue has been scarcely addressed experimentally. Two G(βγ)-binding proteins (myristoylated phosducin - mPhos - and G(αi1)) were expressed in atrial myocytes using adenoviral gene transfer, to interrupt G(βγ)-signaling. Agonist-induced and basal currents were recorded using whole cell voltage-clamp. Expression of mPhos and G(αi1) reduced activation of Kir3 current via muscarinic M(2) receptors (IK(ACh)). Inhibition of IK(ACh) by mPhos consisted of an irreversible component and an agonist-dependent reversible component. Reduction in density of IK(ACh) by overexpressed Gαi1, in contrast to mPhos, was paralleled by substantial slowing of activation, suggesting a reduction in density of functional M2 receptors, rather than G(βγ)-scavenging as underlying mechanism. In line with this notion, current density and activation kinetics were rescued by fusing the αi1-subunit to an Adenosine A(1) receptor. Neither mPhos nor G(αi1) had a significant effect on I(basal), defined by the inhibitory peptide tertiapin-Q. These data demonstrate that basal Kir3 current in a native environment is unrelated to G-protein signaling or agonist-independent free G(βγ). Moreover, our results illustrate the importance of physiological expression levels of the signaling components in shaping key parameters of the response to an agonist.
Collapse
Affiliation(s)
| | | | - Fabian Hertel
- Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany
| | - Lutz Pott
- Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany
| |
Collapse
|
3
|
Suga H, Haga T. Ligand screening system using fusion proteins of G protein-coupled receptors with G protein alpha subunits. Neurochem Int 2007; 51:140-64. [PMID: 17659814 DOI: 10.1016/j.neuint.2007.06.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2007] [Revised: 06/07/2007] [Accepted: 06/08/2007] [Indexed: 01/04/2023]
Abstract
G protein-coupled receptors (GPCRs) constitute one of the largest families of genes in the human genome, and are the largest targets for drug development. Although a large number of GPCR genes have recently been identified, ligands have not yet been identified for many of them. Various assay systems have been employed to identify ligands for orphan GPCRs, but there is still no simple and general method to screen for ligands of such GPCRs, particularly of G(i)-coupled receptors. We have examined whether fusion proteins of GPCRs with G protein alpha subunit (Galpha) could be utilized for ligand screening and showed that the fusion proteins provide an effective method for the purpose. This article focuses on the followings: (1) characterization of GPCR genes and GPCRs, (2) identification of ligands for orphan GPCRs, (3) characterization of GPCR-Galpha fusion proteins, and (4) identification of ligands for orphan GPCRs using GPCR-Galpha fusion proteins.
Collapse
Affiliation(s)
- Hinako Suga
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| | | |
Collapse
|
4
|
Brown SL, Jala VR, Raghuwanshi SK, Nasser MW, Haribabu B, Richardson RM. Activation and regulation of platelet-activating factor receptor: role of G(i) and G(q) in receptor-mediated chemotactic, cytotoxic, and cross-regulatory signals. THE JOURNAL OF IMMUNOLOGY 2006; 177:3242-9. [PMID: 16920964 DOI: 10.4049/jimmunol.177.5.3242] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycerolphosphocholine; PAF) induces leukocyte accumulation and activation at sites of inflammation via the activation of a specific cell surface receptor (PAFR). PAFR couples to both pertussis toxin-sensitive and pertussis toxin-insensitive G proteins to activate leukocytes. To define the role(s) of G(i) and G(q) in PAF-induced leukocyte responses, two G-protein-linked receptors were generated by fusing G alpha(i3) (PAFR-G alpha(i3)) or G alpha(q) (PAFR-G alpha(q)) at the C terminus of PAFR. Rat basophilic leukemia cell line (RBL-2H3) stably expressing wild-type PAFR, PAFR-G alpha(i3), or PAFR-G alpha(q) was generated and characterized. All receptor variants bound PAF with similar affinities to mediate G-protein activation, intracellular Ca2+ mobilization, phosphoinositide (PI) hydrolysis, and secretion of beta-hexosaminidase. PAFR-G alpha(i3) and PAFR-G alpha(q) mediated greater GTPase activity in isolated membranes than PAFR but lower PI hydrolysis and secretion in whole cells. PAFR and PAFR-G alpha(i3), but not PAFR-G alpha(q), mediated chemotaxis to PAF. All three receptors underwent phosphorylation and desensitization upon exposure to PAF but only PAFR translocated beta arrestin to the cell membrane and internalized. In RBL-2H3 cells coexpressing the PAFRs along with CXCR1, IL-8 (CXCL8) cross-desensitized Ca2+ mobilization to PAF by all the receptors but only PAFR-G alpha(i3) activation cross-inhibited the response of CXCR1 to CXCL8. Altogether, the data indicate that G(i) exclusively mediates chemotactic and cross-regulatory signals of the PAFR, but both G(i) and G(q) activate PI hydrolysis and exocytosis by this receptor. Because chemotaxis and cross-desensitization are exclusively mediated by G(i), the data suggest that differential activation of both G(i) and G(q) by PAFR likely mediate specific as well as redundant signaling pathways.
Collapse
Affiliation(s)
- Stephan L Brown
- Department of Biochemistry, Meharry Medical College, Nashville, TN 37208, USA
| | | | | | | | | | | |
Collapse
|
5
|
Klaasse E, de Ligt RAF, Roerink SF, Lorenzen A, Milligan G, Leurs R, IJzerman AP. Allosteric modulation and constitutive activity of fusion proteins between the adenosine A1 receptor and different 351Cys-mutated Gi alpha-subunits. Eur J Pharmacol 2005; 499:91-8. [PMID: 15363955 DOI: 10.1016/j.ejphar.2004.07.108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2004] [Accepted: 07/26/2004] [Indexed: 11/24/2022]
Abstract
We studied fusion proteins between the human adenosine A1 receptor and different 351Cys-mutated G(i1) alpha-subunits (A1-Gialpha) with respect to two important concepts in receptor pharmacology, i.e. allosteric modulation and constitutive activity/inverse agonism. The aim of our study was twofold. We first analysed whether such fusion products are still subject to allosteric modulation, and, secondly, we investigated the potential utility of the fusion proteins to study constitutive receptor activity. We determined the pharmacological profile of nine different A1-Gialpha fusion proteins in radioligand binding studies. In addition, we performed [35S]GTPgammaS binding experiments to study receptor and G protein activation of selected A1-Gialpha fusion proteins. Compared to unfused adenosine A1 receptors, the affinity of N6-cyclopentyladenosine (CPA) at wild-type A1-Gialpha fusion proteins (351Cys) increased more than eightfold, while the affinity of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) did not change significantly. Furthermore, we showed that the allosteric enhancer of agonist binding, PD81,723 (2-amino-4,5-dimethyl-3-thienyl-[3-(trifluoromethyl)-phenyl]methanone), elicited similar effects on ligand binding; i.e. CPA binding to the A1-Gialpha fusion proteins was enhanced, whereas the affinity of DPCPX was hardly affected. Moreover, sodium ions were unable to decrease agonist binding to the majority of the A1-Gialpha fusion proteins, presumably because they exhibit their effect through uncoupling of the R-G complex. From [35S]GTPgammaS binding experiments, we learned that all the A1-Gialpha fusion proteins tested had a higher basal receptor activity than the unfused adenosine A1 receptor, thereby providing improved conditions to observe inverse agonism. Moreover, the maximal CPA-induced stimulation of basal [35S]GTPgammaS binding was increased for the five A1-Gialpha fusion proteins tested, whereas the inhibition induced by 8-cyclopentyltheophylline (CPT) was more pronounced at 351Cys, 351Ile, and 351Val A1-Gialpha fusion proteins. Thus, the maximal receptor (de)activation depended on the amino acid at position 351 of the Gi alpha-subunit. In conclusion, A1-Gialpha fusion proteins, especially with 351Cys and 351Ile, can be used as research tools to investigate inverse agonism, due to their increased readout window in [35S]GTPgammaS binding experiments.
Collapse
Affiliation(s)
- Elisabeth Klaasse
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
| | | | | | | | | | | | | |
Collapse
|
6
|
Simons PC, Shi M, Foutz T, Cimino DF, Lewis J, Buranda T, Lim WK, Neubig RR, McIntire WE, Garrison J, Prossnitz E, Sklar LA. Ligand-receptor-G-protein molecular assemblies on beads for mechanistic studies and screening by flow cytometry. Mol Pharmacol 2003; 64:1227-38. [PMID: 14573773 DOI: 10.1124/mol.64.5.1227] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
G protein-coupled receptors form a ternary complex of ligand, receptor, and G protein heterotrimer (LRG) during signal transduction from the outside to the inside of a cell. Our goal was to develop a homogeneous, small-volume, bead-based approach compatible with high-throughput flow cytometry that would allow evaluation of G protein coupled receptor molecular assemblies. Dextran beads were derivatized to carry chelated nickel to bind hexahistidine-tagged green fluorescent protein (GFP) and hexahistidine-tagged G proteins. Ternary complexes were assembled on these beads using fluorescent ligand with wild-type receptor or a receptor-Gialpha2 fusion protein, and with a nonfluorescent ligand and receptor-GFP fusion protein. Streptavidin-coated polystyrene beads used biotinylated anti-FLAG antibodies to bind FLAG-tagged G proteins for ternary complex assembly. Validation was achieved by showing time and concentration dependence of ternary complex formation. Affinity measurements of ligand for receptor on particles, of the ligand-receptor complex for G protein on the particles, and receptor-Gialpha2 fusion protein for Gbetagamma, were consistent with comparable assemblies in detergent suspension. Performance was assessed in applications representing the potential of these assemblies for ternary complex mechanisms. We showed the relationship for a family of ligands between LR and LRG affinity and characterized the affinity of both the wild-type and GFP fusion receptors with G protein. We also showed the potential of kinetic measurements to allow observation of individual steps of GTP-induced ternary complex disassembly and discriminated a fast step caused by RG disassembly compared with the slower step of Galphabetagamma disassembly.
Collapse
Affiliation(s)
- Peter C Simons
- Department of Pathology and Cancer Center, University of New Mexico HSC, Albuquerque, NM 87131, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Lynge J, Schulte G, Nordsborg N, Fredholm BB, Hellsten Y. Adenosine A 2B receptors modulate cAMP levels and induce CREB but not ERK1/2 and p38 phosphorylation in rat skeletal muscle cells. Biochem Biophys Res Commun 2003; 307:180-7. [PMID: 12849998 DOI: 10.1016/s0006-291x(03)01125-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The present study examined the existence of the adenosine A(1),A(2A), and A(2B) receptors and the effect of receptor activation on cAMP accumulation and protein phosphorylation in primary rat skeletal muscle cells. Presence of mRNA and protein for all three receptors was demonstrated in both cultured and adult rat skeletal muscle. NECA (10(-9)-10(-4)M) increased the cAMP concentration in cultured muscle cells with an EC(50) of (95% confidence interval)=15 (5.9-25.1) micro M, whereas CGS 21680 (10(-9)-10(-4)M) had no effect on cAMP accumulation. Concentrations of [R]-PIA below 10(-6)M had no effect on cAMP accumulation induced by either isoproterenol or forskolin. NECA resulted in phosphorylation of CREB with an EC(50) of (95% confidence interval)=1.7 (0.40-7.02) micro M, whereas ERK1/2 and p38 phosphorylation was unchanged. The results show that, although the A(1),A(2A), and A(2B) receptors are all present in skeletal muscle cells, the effect of adenosine on adenylyl cyclase activation and phosphorylation of CREB is mainly mediated via the adenosine A(2B) receptor.
Collapse
Affiliation(s)
- Jan Lynge
- Copenhagen Muscle Research Centre, Department of Human Physiology, Institute of Exercise and Sports Sciences, August Krogh Institute, Copenhagen University, Universitetsparken 13, Copenhagen Ø, DK-2100, Denmark
| | | | | | | | | |
Collapse
|
8
|
Hermans E. Biochemical and pharmacological control of the multiplicity of coupling at G-protein-coupled receptors. Pharmacol Ther 2003; 99:25-44. [PMID: 12804697 DOI: 10.1016/s0163-7258(03)00051-2] [Citation(s) in RCA: 221] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
For decades, it has been generally proposed that a given receptor always interacts with a particular GTP-binding protein (G-protein) or with multiple G-proteins within one family. However, for several G-protein-coupled receptors (GPCR), it now becomes generally accepted that simultaneous functional coupling with distinct unrelated G-proteins can be observed, leading to the activation of multiple intracellular effectors with distinct efficacies and/or potencies. Multiplicity in G-protein coupling is frequently observed in artificial expression systems where high densities of receptors are obtained, raising the question of whether such complex signalling reveals artefactual promiscuous coupling or is a genuine property of GPCRs. Multiple biochemical and pharmacological evidence in favour of an intrinsic property of GPCRs were obtained in recent studies. Thus, there are now many examples showing that the coupling to multiple signalling pathways is dependent on the agonist used (agonist trafficking of receptor signals). In addition, the different couplings were demonstrated to involve distinct molecular determinants of the receptor and to show distinct desensitisation kinetics. Such multiplicity of signalling at the level of G-protein coupling leads to a further complexity in the functional response to agonist stimulation of one of the most elaborate cellular transmission systems. Indeed, the physiological relevance of such versatility in signalling associated with a single receptor requires the existence of critical mechanisms of dynamic regulation of the expression, the compartmentalisation, and the activity of the signalling partners. This review aims at summarising the different studies that support the concept of multiplicity of G-protein coupling. The physiological and pharmacological relevance of this coupling promiscuity will be discussed.
Collapse
Affiliation(s)
- Emmanuel Hermans
- Laboratoire de Pharmacologie Expérimentale, Université Catholique de Louvain, FARL 54.10, Avenue Hippocrate 54, B-1200 Brussels, Belgium.
| |
Collapse
|
9
|
Shi M, Bennett TA, Cimino DF, Maestas DC, Foutz TD, Gurevich VV, Sklar LA, Prossnitz ER. Functional capabilities of an N-formyl peptide receptor-G(alpha)(i)(2) fusion protein: assemblies with G proteins and arrestins. Biochemistry 2003; 42:7283-93. [PMID: 12809484 DOI: 10.1021/bi0341657] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
G protein-coupled receptors (GPCRs) must constantly compete for interactions with G proteins, kinases, and arrestins. To evaluate the interactions of these proteins with GPCRs in greater detail, we generated a fusion protein between the N-formyl peptide receptor and the G(alpha)(i2) protein. The functional capabilities of this chimeric protein were determined both in vivo, in stably transfected U937 cells, and in vitro, using a novel reconstitution system of solubilized components. The chimeric protein exhibited a cellular ligand binding affinity indistinguishable from that of the wild-type receptor and existed as a complex, when solubilized, containing betagamma subunits, as demonstrated by sucrose density sedimentation. The chimeric protein mobilized intracellular calcium and desensitized normally in response to agonist. Furthermore, the chimeric receptor was internalized and recycled at rates similar to those of the wild-type FPR. Confocal fluorescence microscopy revealed that internalized chimeric receptors, as identified with fluorescent ligand, colocalized with arrestin, as well as G protein, unlike wild-type receptors. Soluble reconstitution experiments demonstrated that the chimeric receptor, even in the phosphorylated state, existed as a high ligand affinity G protein complex, in the absence of exogenous G protein. This interaction was only partially prevented through the addition of arrestins. Furthermore, our results demonstrate that the GTP-bound state of the G protein alpha subunit displays no detectable affinity for the receptor. Together, these results indicate that complex interactions exist between GPCRs, in their unphosphorylated and phosphorylated states, G proteins, and arrestins, which result in the highly regulated control of GPCR function.
Collapse
MESH Headings
- Animals
- Arrestin/metabolism
- Arrestin/pharmacology
- Calcium/chemistry
- Calcium/metabolism
- GTP-Binding Protein alpha Subunit, Gi2
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Proteins/metabolism
- Heterotrimeric GTP-Binding Proteins/metabolism
- Humans
- Leukemia, Myeloid/metabolism
- Mice
- Microscopy, Confocal/methods
- N-Formylmethionine Leucyl-Phenylalanine/metabolism
- Phosphorylation
- Protein Subunits
- Proto-Oncogene Proteins/genetics
- Proto-Oncogene Proteins/metabolism
- Receptors, Formyl Peptide
- Receptors, Immunologic/genetics
- Receptors, Immunologic/metabolism
- Receptors, Peptide/genetics
- Receptors, Peptide/metabolism
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Transfection
- Tumor Cells, Cultured
- U937 Cells
- Ultracentrifugation/methods
Collapse
Affiliation(s)
- Mei Shi
- Department of Pathology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131, USA
| | | | | | | | | | | | | | | |
Collapse
|
10
|
Gazi L, Wurch T, Lopéz-Giménez JF, Pauwels PJ, Strange PG. Pharmacological analysis of a dopamine D(2Short):G(alphao) fusion protein expressed in Sf9 cells. FEBS Lett 2003; 545:155-60. [PMID: 12804767 DOI: 10.1016/s0014-5793(03)00520-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A dopamine D(2Short) receptor:G(alphao) fusion protein was expressed in Sf9 cells using the baculovirus expression system. [(3)H]Spiperone bound to D(2Short):G(alphao) with a pK(d) approximately 10. Dopamine stimulated the binding of [(35)S]guanosine-5'-O-(3-thio)triphosphate (GTPgammaS) to D(2Short):G(alphao) expressed with Gbeta(1)gamma(2) (E(max)>460%; pEC(50) 5.43+/-0.06). Most of the putative D(2) antagonists behaved as inverse agonists (suppressing basal [(35)S]GTPgammaS binding) at D(2Short):G(alphao)/Gbeta(1)gamma(2) although (-)-sulpiride and ziprasidone were neutral antagonists. Competition of [(3)H]spiperone binding by dopamine and 10,11-dihydroxy-N-n-propylnorapomorphine revealed two binding sites of different affinities, even in the presence of GTP (100 micro M). The D(2Short):G(alphao) fusion protein is therefore a good model for characterising D(2) receptors.
Collapse
Affiliation(s)
- Lucien Gazi
- School of Animal and Microbial Sciences, University of Reading, Whiteknights, RG6 6AJ, Reading, UK
| | | | | | | | | |
Collapse
|
11
|
Bürgi S, Baltensperger K, Honegger UE. Antidepressant-induced switch of beta 1-adrenoceptor trafficking as a mechanism for drug action. J Biol Chem 2003; 278:1044-52. [PMID: 12393876 DOI: 10.1074/jbc.m209972200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Reduction in surface beta(1)-adrenoceptor (beta1AR) density is thought to play a critical role in mediating the therapeutic long term effects of antidepressants. Since antidepressants are neither agonists nor antagonists for G protein-coupled receptors, receptor density must be regulated through processes independent of direct receptor activation. Endocytosis and recycling of the beta1AR fused to green fluorescent protein at its carboxyl-terminus (beta1AR-GFP) were analyzed by confocal fluorescence microscopy of live cells and complementary ligand binding studies. In stably transfected C6 glioblastoma cells, beta1AR-GFP displayed identical ligand-binding isotherms and adenylyl cyclase activation as native beta1AR. Upon exposure to isoproterenol, a fraction of beta1AR-GFP (10-15%) internalized rapidly and colocalized with endocytosed transferrin receptors in an early endosomal compartment in the perinuclear region. Chronic treatment with the tricyclic antidepressant desipramine (DMI) did not affect internalization characteristics of beta1AR-GFP when challenged with isoproterenol. However, internalized receptors were not able to recycle back to the cell surface in DMI-treated cells, whereas recycling of transferrin receptors was not affected. Endocytosed receptors were absent from structures that stained with fluorescently labeled dextran, and inhibition of lysosomal protease activity did not restore receptor recycling, indicating that beta1AR-GFP did not immediately enter the lysosomal compartment. The data suggest a new mode of drug action causing a "switch" of receptor fate from a fast recycling pathway to a slowly exchanging perinuclear compartment. Antidepressant-induced reduction of receptor surface expression may thus be caused by modulation of receptor trafficking routes.
Collapse
Affiliation(s)
- Sibylle Bürgi
- Department of Pharmacology, University of Bern, Switzerland
| | | | | |
Collapse
|
12
|
Leaney JL, Benians A, Graves FM, Tinker A. A novel strategy to engineer functional fluorescent inhibitory G-protein alpha subunits. J Biol Chem 2002; 277:28803-9. [PMID: 12048213 DOI: 10.1074/jbc.m204683200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Signaling studies in living cells would be greatly facilitated by the development of functional fluorescently tagged G-protein alpha subunits. We have designed G(i/o)alpha subunits fused to the cyan fluorescent protein and assayed their function by studying the following two signal transduction pathways: the regulation of G-protein-gated inwardly rectifying K(+) channels (Kir3.0 family) and adenylate cyclase. Palmitoylation and myristoylation consensus sites were removed from G(i/o) alpha subunits (G(i1)alpha, G(i2)alpha, G(i3)alpha, and G(oA)alpha) and a mutation introduced at Cys(-4) rendering the subunit resistant to pertussis toxin. This construct was fused in-frame with cyan fluorescent protein containing a short peptide motif from GAP43 that directs palmitoylation and thus membrane targeting. Western blotting confirmed G(i/o)alpha protein expression. Confocal microscopy and biochemical fractionation studies revealed membrane localization. Each mutant G(i/o) alpha subunit significantly reduced basal current density when transiently expressed in a stable cell line expressing Kir3.1 and Kir3.2A, consistent with the sequestration of the Gbetagamma dimer by the mutant Galpha subunit. Moreover, each subunit was able to support A1-mediated and D2S-mediated channel activation when transiently expressed in pertussis toxin-treated cells. Overexpression of tagged G(i3)alpha and G(oA)alpha alpha subunits reduced receptor-mediated and forskolin-induced cAMP mobilization.
Collapse
Affiliation(s)
- Joanne L Leaney
- BHF Laboratories, Room 420, 4th Floor, and Centre for Clinical Pharmacology, Department of Medicine, University College London, 5 University Street, London WC1E 6JJ, United Kingdom
| | | | | | | |
Collapse
|
13
|
Milligan G. Construction and analysis of function of G protein-coupled receptor-G protein fusion proteins. Methods Enzymol 2002; 343:260-73. [PMID: 11665572 DOI: 10.1016/s0076-6879(02)43141-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Graeme Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
| |
Collapse
|
14
|
Wurch T, Pauwels PJ. Analytical pharmacology of G protein-coupled receptors by stoichiometric expression of the receptor and G(alpha) protein subunits. J Pharmacol Toxicol Methods 2001; 45:3-16. [PMID: 11489661 DOI: 10.1016/s1056-8719(01)00126-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The description of a new family of recombinant proteins, which are constructed by the covalent fusion of the cDNA encoding a G protein-coupled receptor with that of a G(alpha) protein subunit, has recently been introduced as an original strategy to explore receptor pharmacology under defined experimental conditions. As such, a controlled 1:1 stoichiometry of receptor and G(alpha) protein expression can be achieved, as well as a forced spatial proximity to each other. Fusion proteins have been revealed as active at the receptor ligand binding level and functional at the G(alpha) protein and effector level. Insights on analytical pharmacological data are discussed for wild-type and mutant receptors interacting with a given G(alpha) protein subunit and different subtypes of either wild-type or mutant G(alpha) proteins activated by a single receptor subtype. A possible alteration of the receptor:G(alpha) protein selectivity may occur due either to the spatial proximity of both protein partners or to a constraint receptor state unable to accommodate to different G(alpha) protein states. Coactivation of endogenous G(alpha) proteins in host cells expressing a fusion protein has also been observed, but depends mainly on the coupling efficiency of the receptor and G(alpha) protein engaged in the fusion process. The ligand's apparent intrinsic activity has been shown to be either enhanced, attenuated, or unmodified when the functional responses of a fusion protein are compared to the coexpression of both fusion protein partners.
Collapse
Affiliation(s)
- T Wurch
- Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, 17, Avenue Jean Moulin, 81106 Castres Cédex, France
| | | |
Collapse
|
15
|
Schulte G, Fredholm BB. Human Adenosine A1, A2A, A2B, and A3 Receptors Expressed in Chinese Hamster Ovary Cells All Mediate the Phosphorylation of Extracellular-Regulated Kinase 1/2. Mol Pharmacol 2000. [DOI: 10.1124/mol.58.3.477] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
|