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Kayastha K, Zhou Y, Brünle S. Structural perspectives on chemokine receptors. Biochem Soc Trans 2024:BST20230358. [PMID: 38856028 DOI: 10.1042/bst20230358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 05/02/2024] [Accepted: 05/07/2024] [Indexed: 06/11/2024]
Abstract
Chemokine receptors are integral to the immune system and prime targets in drug discovery that have undergone extensive structural elucidation in recent years. We outline a timeline of these structural achievements, discuss the intracellular negative allosteric modulation of chemokine receptors, analyze the mechanisms of orthosteric receptor activation, and report on the emerging concept of biased signaling. Additionally, we highlight differences of G-protein binding among chemokine receptors. Intracellular allosteric modulators in chemokine receptors interact with a conserved motif within transmembrane helix 7 and helix 8 and exhibit a two-fold inactivation mechanism that can be harnessed for drug-discovery efforts. Chemokine recognition is a multi-step process traditionally explained by a two-site model within chemokine recognition site 1 (CRS1) and CRS2. Recent structural studies have extended our understanding of this complex mechanism with the identification of CRS1.5 and CRS3. CRS3 is implicated in determining ligand specificity and surrounds the chemokine by almost 180°. Within CRS3 we identified the extracellular loop 2 residue 45.51 as a key interaction mediator for chemokine binding. Y2917.43 on the other hand was shown in CCR1 to be a key determinant of signaling bias which, along with specific chemokine-dependent phosphorylation ensembles at the G-protein coupled receptors (GPCR's) C-terminus, seems to play a pivotal role in determining the direction of signal bias in GPCRs.
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Affiliation(s)
- Kanwal Kayastha
- Leiden Institute of Chemistry, Faculty of Science, Leiden University, Einsteinweg 55, Leiden 2333 CC, The Netherlands
| | - Yangli Zhou
- Leiden Institute of Chemistry, Faculty of Science, Leiden University, Einsteinweg 55, Leiden 2333 CC, The Netherlands
| | - Steffen Brünle
- Leiden Institute of Chemistry, Faculty of Science, Leiden University, Einsteinweg 55, Leiden 2333 CC, The Netherlands
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2
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Smith JS, Hilibrand AS, Skiba MA, Dates AN, Calvillo-Miranda VG, Kruse AC. The M3 Muscarinic Acetylcholine Receptor Can Signal through Multiple G Protein Families. Mol Pharmacol 2024; 105:386-394. [PMID: 38641412 PMCID: PMC11114115 DOI: 10.1124/molpharm.123.000818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 04/01/2024] [Accepted: 04/08/2024] [Indexed: 04/21/2024] Open
Abstract
The M3 muscarinic acetylcholine receptor (M3R) is a G protein-coupled receptor (GPCR) that regulates important physiologic processes, including vascular tone, bronchoconstriction, and insulin secretion. It is expressed on a wide variety of cell types, including pancreatic beta, smooth muscle, neuronal, and immune cells. Agonist binding to the M3R is thought to initiate intracellular signaling events primarily through the heterotrimeric G protein Gq. However, reports differ on the ability of M3R to couple to other G proteins beyond Gq. Using members from the four primary G protein families (Gq, Gi, Gs, and G13) in radioligand binding, GTP turnover experiments, and cellular signaling assays, including live cell G protein dissociation and second messenger assessment of cAMP and inositol trisphosphate, we show that other G protein families, particularly Gi and Gs, can also interact with the human M3R. We further show that these interactions are productive as assessed by amplification of classic second messenger signaling events. Our findings demonstrate that the M3R is more promiscuous with respect to G protein interactions than previously appreciated. SIGNIFICANCE STATEMENT: The study reveals that the human M3 muscarinic acetylcholine receptor (M3R), known for its pivotal roles in diverse physiological processes, not only activates intracellular signaling via Gq as previously known but also functionally interacts with other G protein families such as Gi and Gs, expanding our understanding of its versatility in mediating cellular responses. These findings signify a broader and more complex regulatory network governed by M3R and have implications for therapeutic targeting.
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Affiliation(s)
- Jeffrey S Smith
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts (J.S.S., A.S.H., M.A.S., A.N.D., V.G.C.-M., A.C.K.) and Brigham and Women's Hospital, Boston, Massachusetts (J.S.S.)
| | - Ari S Hilibrand
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts (J.S.S., A.S.H., M.A.S., A.N.D., V.G.C.-M., A.C.K.) and Brigham and Women's Hospital, Boston, Massachusetts (J.S.S.)
| | - Meredith A Skiba
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts (J.S.S., A.S.H., M.A.S., A.N.D., V.G.C.-M., A.C.K.) and Brigham and Women's Hospital, Boston, Massachusetts (J.S.S.)
| | - Andrew N Dates
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts (J.S.S., A.S.H., M.A.S., A.N.D., V.G.C.-M., A.C.K.) and Brigham and Women's Hospital, Boston, Massachusetts (J.S.S.)
| | - Victor G Calvillo-Miranda
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts (J.S.S., A.S.H., M.A.S., A.N.D., V.G.C.-M., A.C.K.) and Brigham and Women's Hospital, Boston, Massachusetts (J.S.S.)
| | - Andrew C Kruse
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts (J.S.S., A.S.H., M.A.S., A.N.D., V.G.C.-M., A.C.K.) and Brigham and Women's Hospital, Boston, Massachusetts (J.S.S.)
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3
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Gardner J, Eiger DS, Hicks C, Choi I, Pham U, Chundi A, Namjoshi O, Rajagopal S. GPCR kinases differentially modulate biased signaling downstream of CXCR3 depending on their subcellular localization. Sci Signal 2024; 17:eadd9139. [PMID: 38349966 PMCID: PMC10927030 DOI: 10.1126/scisignal.add9139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2022] [Accepted: 01/22/2024] [Indexed: 02/15/2024]
Abstract
Some G protein-coupled receptors (GPCRs) demonstrate biased signaling such that ligands of the same receptor exclusively or preferentially activate certain downstream signaling pathways over others. This phenomenon may result from ligand-specific receptor phosphorylation by GPCR kinases (GRKs). GPCR signaling can also exhibit location bias because GPCRs traffic to and signal from subcellular compartments in addition to the plasma membrane. Here, we investigated whether GRKs contributed to location bias in GPCR signaling. GRKs translocated to endosomes after stimulation of the chemokine receptor CXCR3 or other GPCRs in cultured cells. GRK2, GRK3, GRK5, and GRK6 showed distinct patterns of recruitment to the plasma membrane and to endosomes depending on the identity of the biased ligand used to activate CXCR3. Analysis of engineered forms of GRKs that localized to either the plasma membrane or endosomes demonstrated that biased CXCR3 ligands elicited different signaling profiles that depended on the subcellular location of the GRK. Each GRK exerted a distinct effect on the regulation of CXCR3 engagement of β-arrestin, internalization, and activation of the downstream effector kinase ERK. Our work highlights a role for GRKs in location-biased GPCR signaling and demonstrates the complex interactions between ligands, GRKs, and cellular location that contribute to biased signaling.
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Affiliation(s)
- Julia Gardner
- Trinity College, Duke University, Durham, NC, 27710, USA
| | | | - Chloe Hicks
- Trinity College, Duke University, Durham, NC, 27710, USA
| | - Issac Choi
- Department of Medicine, Duke University, Durham, NC, 27710, USA
| | - Uyen Pham
- Department of Biochemistry, Duke University, Durham, NC, 27710, USA
| | - Anand Chundi
- Pratt School of Engineering, Duke University, Durham, NC, 27710, USA
| | - Ojas Namjoshi
- Center for Drug Discovery RTI International, Research Triangle Park, NC, 27709, USA
- Present address: Engine Biosciences, 733 Industrial Rd., San Carlos, CA, 94070, USA
| | - Sudarshan Rajagopal
- Department of Biochemistry, Duke University, Durham, NC, 27710, USA
- Department of Medicine, Duke University, Durham, NC, 27710, USA
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4
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Hicks C, Gardner J, Eiger DS, Camarda ND, Pham U, Dhar S, Rodriguez H, Chundi A, Rajagopal S. ACKR3 Proximity Labeling Identifies Novel G protein- and β-arrestin-independent GPCR Interacting Proteins. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.27.577545. [PMID: 38410489 PMCID: PMC10896341 DOI: 10.1101/2024.01.27.577545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
The canonical paradigm of GPCR signaling recognizes G proteins and β-arrestins as the two primary transducers that promote GPCR signaling. Recent evidence suggests the atypical chemokine receptor 3 (ACKR3) does not couple to G proteins, and β-arrestins are dispensable for some of its functions. Here, we employed proximity labeling to identify proteins that interact with ACKR3 in cells devoid of β-arrestin. We identified proteins involved in the endocytic machinery and evaluated a subset of proteins conserved across several GPCR-based proximity labeling experiments. We discovered that the bone morphogenic protein 2-inducible kinase (BMP2K) interacts with many different GPCRs with varying dependency on β-arrestin. Together, our work highlights the existence of modulators that can act independently of G proteins and β-arrestins to regulate GPCR signaling and provides important evidence for other targets that may regulate GPCR signaling.
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Affiliation(s)
- Chloe Hicks
- National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Julia Gardner
- Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Dylan Scott Eiger
- Department of Medicine, Brigham and Women’s Hospital, Boston, MA, 02215, USA
- Harvard Medical School, Boston, MA, 02215, USA
| | - Nicholas D. Camarda
- Genetics, Molecular, and Cellular Biology Program, Tufts Graduate School of Biomedical Sciences, Boston, MA, 02111, USA
| | - Uyen Pham
- Department of Biochemistry, Duke University, Durham, NC, 27710, USA
| | - Saisha Dhar
- Trinity College, Duke University, Durham, NC, 27710, USA
| | | | - Anand Chundi
- Pratt School of Engineering, Duke University, Durham, NC, 27710, USA
| | - Sudarshan Rajagopal
- Department of Biochemistry, Duke University, Durham, NC, 27710, USA
- Department of Medicine, Duke University, Durham, NC, 27710, USA
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Barki N, Jenkins L, Marsango S, Dedeo D, Bolognini D, Dwomoh L, Abdelmalik AM, Nilsen M, Stoffels M, Nagel F, Schulz S, Tobin AB, Milligan G. Phosphorylation bar-coding of free fatty acid receptor 2 is generated in a tissue-specific manner. eLife 2023; 12:RP91861. [PMID: 38085667 PMCID: PMC10715726 DOI: 10.7554/elife.91861] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2023] Open
Abstract
Free fatty acid receptor 2 (FFAR2) is activated by short-chain fatty acids and expressed widely, including in white adipocytes and various immune and enteroendocrine cells. Using both wild-type human FFAR2 and a designer receptor exclusively activated by designer drug (DREADD) variant we explored the activation and phosphorylation profile of the receptor, both in heterologous cell lines and in tissues from transgenic knock-in mouse lines expressing either human FFAR2 or the FFAR2-DREADD. FFAR2 phospho-site-specific antisera targeting either pSer296/pSer297 or pThr306/pThr310 provided sensitive biomarkers of both constitutive and agonist-mediated phosphorylation as well as an effective means to visualise agonist-activated receptors in situ. In white adipose tissue, phosphorylation of residues Ser296/Ser297 was enhanced upon agonist activation whilst Thr306/Thr310 did not become phosphorylated. By contrast, in immune cells from Peyer's patches Thr306/Thr310 become phosphorylated in a strictly agonist-dependent fashion whilst in enteroendocrine cells of the colon both Ser296/Ser297 and Thr306/Thr310 were poorly phosphorylated. The concept of phosphorylation bar-coding has centred to date on the potential for different agonists to promote distinct receptor phosphorylation patterns. Here, we demonstrate that this occurs for the same agonist-receptor pairing in different patho-physiologically relevant target tissues. This may underpin why a single G protein-coupled receptor can generate different functional outcomes in a tissue-specific manner.
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Affiliation(s)
- Natasja Barki
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Laura Jenkins
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Sara Marsango
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Domonkos Dedeo
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Daniele Bolognini
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Louis Dwomoh
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Aisha M Abdelmalik
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Margaret Nilsen
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Manon Stoffels
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | | | - Stefan Schulz
- 7TM Antibodies GmbHJenaGermany
- Institute of Pharmacology and Toxicology, University Hospital JenaJenaGermany
| | - Andrew B Tobin
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
| | - Graeme Milligan
- Centre for Translational Pharmacology, School of Molecular Biosciences, College of Medical, Veterinary and Life Sciences, University of GlasgowGlasgowUnited Kingdom
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Ridley AJL, Ou Y, Karlsson R, Pun N, Birchenough HL, Mulholland IZ, Birch ML, MacDonald AS, Jowitt TA, Lawless C, Miller RL, Dyer DP. Chemokines form complex signals during inflammation and disease that can be decoded by extracellular matrix proteoglycans. Sci Signal 2023; 16:eadf2537. [PMID: 37934811 DOI: 10.1126/scisignal.adf2537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Accepted: 10/20/2023] [Indexed: 11/09/2023]
Abstract
Chemokine-driven leukocyte recruitment is a key component of the immune response and of various diseases. Therapeutically targeting the chemokine system in inflammatory disease has been unsuccessful, which has been attributed to redundancy. We investigated why chemokines instead have specific, specialized functions, as demonstrated by multiple studies. We analyzed the expression of genes encoding chemokines and their receptors across species, tissues, and diseases. This analysis revealed complex expression patterns such that genes encoding multiple chemokines that mediated recruitment of the same leukocyte type were expressed in the same context, such as the genes encoding the CXCR3 ligands CXCL9, CXCL10, and CXCL11. Through biophysical approaches, we showed that these chemokines differentially interacted with extracellular matrix glycosaminoglycans (ECM GAGs), which was enhanced by sulfation of specific GAGs. Last, in vivo approaches demonstrated that GAG binding was critical for the CXCL9-dependent recruitment of specific T cell subsets but not of others, irrespective of CXCR3 expression. Our data demonstrate that interactions with ECM GAGs regulated whether chemokines were presented on cell surfaces or remained more soluble, thereby affecting chemokine availability and ensuring specificity of chemokine action. Our findings provide a mechanistic understanding of chemokine-mediated immune cell recruitment and identify strategies to target specific chemokines during inflammatory disease.
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Affiliation(s)
- Amanda J L Ridley
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Yaqing Ou
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Richard Karlsson
- Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Nabina Pun
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Holly L Birchenough
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Iashia Z Mulholland
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Mary L Birch
- Biological Services Facility, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PT, UK
| | - Andrew S MacDonald
- Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Thomas A Jowitt
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Craig Lawless
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
| | - Rebecca L Miller
- Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Douglas P Dyer
- Wellcome Centre for Cell-Matrix Research, Lydia Becker Institute of Immunology and Inflammation, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester M13 9PT, UK
- Geoffrey Jefferson Brain Research Centre, Manchester Academic Health Science Centre, Northern Care Alliance NHS Group, University of Manchester, Manchester M6 8HD, UK
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Eiger DS, Hicks C, Gardner J, Pham U, Rajagopal S. Location bias: A "Hidden Variable" in GPCR pharmacology. Bioessays 2023; 45:e2300123. [PMID: 37625014 DOI: 10.1002/bies.202300123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/09/2023] [Accepted: 08/16/2023] [Indexed: 08/27/2023]
Abstract
G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors and primarily signal through two main effector proteins: G proteins and β-arrestins. Many agonists of GPCRs promote "biased" responses, in which different cellular signaling pathways are activated with varying efficacies. The mechanisms underlying biased signaling have not been fully elucidated, with many potential "hidden variables" that regulate this behavior. One contributor is "location bias," which refers to the generation of unique signaling cascades from a given GPCR depending upon the cellular location at which the receptor is signaling. Here, we review evidence that GPCRs are expressed at and traffic to various subcellular locations and discuss how location bias can impact the pharmacologic properties and characterization of GPCR agonists. We also evaluate how differences in subcellular environments can modulate GPCR signaling, highlight the physiological significance of subcellular GPCR signaling, and discuss the therapeutic potential of exploiting GPCR location bias.
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Affiliation(s)
- Dylan Scott Eiger
- Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, USA
- Harvard Medical School, Boston, Massachusetts, USA
| | - Chloe Hicks
- Trinity College, Duke University, Durham, North Carolina, USA
| | - Julia Gardner
- Trinity College, Duke University, Durham, North Carolina, USA
| | - Uyen Pham
- Department of Biochemistry, Duke University, Durham, North Carolina, USA
| | - Sudarshan Rajagopal
- Department of Biochemistry, Duke University, Durham, North Carolina, USA
- Department of Medicine, Duke University, Durham, North Carolina, USA
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8
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Sánchez-Soto M, Boldizsar NM, Schardien KA, Madaras NS, Willette BKA, Inbody LR, Dasaro C, Moritz AE, Drube J, Haider RS, Free RB, Hoffman C, Sibley DR. G Protein-Coupled Receptor Kinase 2 Selectively Enhances β-Arrestin Recruitment to the D 2 Dopamine Receptor through Mechanisms That Are Independent of Receptor Phosphorylation. Biomolecules 2023; 13:1552. [PMID: 37892234 PMCID: PMC10605370 DOI: 10.3390/biom13101552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 10/16/2023] [Accepted: 10/18/2023] [Indexed: 10/29/2023] Open
Abstract
The D2 dopamine receptor (D2R) signals through both G proteins and β-arrestins to regulate important physiological processes, such as movement, reward circuitry, emotion, and cognition. β-arrestins are believed to interact with G protein-coupled receptors (GPCRs) at the phosphorylated C-terminal tail or intracellular loops. GPCR kinases (GRKs) are the primary drivers of GPCR phosphorylation, and for many receptors, receptor phosphorylation is indispensable for β-arrestin recruitment. However, GRK-mediated receptor phosphorylation is not required for β-arrestin recruitment to the D2R, and the role of GRKs in D2R-β-arrestin interactions remains largely unexplored. In this study, we used GRK knockout cells engineered using CRISPR-Cas9 technology to determine the extent to which β-arrestin recruitment to the D2R is GRK-dependent. Genetic elimination of all GRK expression decreased, but did not eliminate, agonist-stimulated β-arrestin recruitment to the D2R or its subsequent internalization. However, these processes were rescued upon the re-introduction of various GRK isoforms in the cells with GRK2/3 also enhancing dopamine potency. Further, treatment with compound 101, a pharmacological inhibitor of GRK2/3 isoforms, decreased β-arrestin recruitment and receptor internalization, highlighting the importance of this GRK subfamily for D2R-β-arrestin interactions. These results were recapitulated using a phosphorylation-deficient D2R mutant, emphasizing that GRKs can enhance β-arrestin recruitment and activation independently of receptor phosphorylation.
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Affiliation(s)
- Marta Sánchez-Soto
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Noelia M. Boldizsar
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Kayla A. Schardien
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Nora S. Madaras
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Blair K. A. Willette
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Laura R. Inbody
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Christopher Dasaro
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Amy E. Moritz
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Julia Drube
- Institut für Molekulare Zellbiologie, CMB-Center for Molecular Biomedicine, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Hans-Knöll-Straße 2, D-07745 Jena, Germany (R.S.H.); (C.H.)
| | - Raphael S. Haider
- Institut für Molekulare Zellbiologie, CMB-Center for Molecular Biomedicine, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Hans-Knöll-Straße 2, D-07745 Jena, Germany (R.S.H.); (C.H.)
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, Queen’s Medical Centre, University of Nottingham, Nottingham NG7 2UH, UK
- Centre of Membrane Protein and Receptors, Universities of Birmingham and Nottingham, Birmingham B15 2TT, UK
| | - R. Benjamin Free
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
| | - Carsten Hoffman
- Institut für Molekulare Zellbiologie, CMB-Center for Molecular Biomedicine, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Hans-Knöll-Straße 2, D-07745 Jena, Germany (R.S.H.); (C.H.)
| | - David R. Sibley
- Molecular Neuropharmacology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 35 Convent Drive, Bethesda, MD 20892, USA (R.B.F.)
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9
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Sadee W. Ligand-Free Signaling of G-Protein-Coupled Receptors: Physiology, Pharmacology, and Genetics. Molecules 2023; 28:6375. [PMID: 37687205 PMCID: PMC10489045 DOI: 10.3390/molecules28176375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/28/2023] [Accepted: 08/30/2023] [Indexed: 09/10/2023] Open
Abstract
G-protein-coupled receptors (GPCRs) are ubiquitous sensors and regulators of cellular functions. Each GPCR exists in complex aggregates with multiple resting and active conformations. Designed to detect weak stimuli, GPCRs can also activate spontaneously, resulting in basal ligand-free signaling. Agonists trigger a cascade of events leading to an activated agonist-receptor G-protein complex with high agonist affinity. However, the ensuing signaling process can further remodel the receptor complex to reduce agonist affinity, causing rapid ligand dissociation. The acutely activated ligand-free receptor can continue signaling, as proposed for rhodopsin and μ opioid receptors, resulting in robust receptor activation at low agonist occupancy with enhanced agonist potency. Continued receptor stimulation can further modify the receptor complex, regulating sustained ligand-free signaling-proposed to play a role in opioid dependence. Basal, acutely agonist-triggered, and sustained elevated ligand-free signaling could each have distinct functions, reflecting multi-state conformations of GPCRs. This review addresses basal and stimulus-activated ligand-free signaling, its regulation, genetic factors, and pharmacological implications, focusing on opioid and serotonin receptors, and the growth hormone secretagogue receptor (GHSR). The hypothesis is proposed that ligand-free signaling of 5-HT2A receptors mediate therapeutic effects of psychedelic drugs. Research avenues are suggested to close the gaps in our knowledge of ligand-free GPCR signaling.
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Affiliation(s)
- Wolfgang Sadee
- Cancer Biology and Genetics, College of Medicine, The Ohio State University, Columbus, OH 43210, USA;
- Bioengineering and Therapeutic Sciences, University of California, San Francisco, CA 94158, USA
- Aether Therapeutics Inc., Austin, TX 78756, USA
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