1
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Inan T, Flinko R, Lewis GK, MacKerell AD, Kurkcuoglu O. Identifying and Assessing Putative Allosteric Sites and Modulators for CXCR4 Predicted through Network Modeling and Site Identification by Ligand Competitive Saturation. J Phys Chem B 2024; 128:5157-5174. [PMID: 38647430 PMCID: PMC11139592 DOI: 10.1021/acs.jpcb.4c00925] [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: 02/12/2024] [Revised: 04/04/2024] [Accepted: 04/08/2024] [Indexed: 04/25/2024]
Abstract
The chemokine receptor CXCR4 is a critical target for the treatment of several cancer types and HIV-1 infections. While orthosteric and allosteric modulators have been developed targeting its extracellular or transmembrane regions, the intramembrane region of CXCR4 may also include allosteric binding sites suitable for the development of allosteric drugs. To investigate this, we apply the Gaussian Network Model (GNM) to the monomeric and dimeric forms of CXCR4 to identify residues essential for its local and global motions located in the hinge regions of the protein. Residue interaction network (RIN) analysis suggests hub residues that participate in allosteric communication throughout the receptor. Mutual residues from the network models reside in regions with a high capacity to alter receptor dynamics upon ligand binding. We then investigate the druggability of these potential allosteric regions using the site identification by ligand competitive saturation (SILCS) approach, revealing two putative allosteric sites on the monomer and three on the homodimer. Two screening campaigns with Glide and SILCS-Monte Carlo docking using FDA-approved drugs suggest 20 putative hit compounds including antifungal drugs, anticancer agents, HIV protease inhibitors, and antimalarial drugs. In vitro assays considering mAB 12G5 and CXCL12 demonstrate both positive and negative allosteric activities of these compounds, supporting our computational approach. However, in vivo functional assays based on the recruitment of β-arrestin to CXCR4 do not show significant agonism and antagonism at a single compound concentration. The present computational pipeline brings a new perspective to computer-aided drug design by combining conformational dynamics based on network analysis and cosolvent analysis based on the SILCS technology to identify putative allosteric binding sites using CXCR4 as a showcase.
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Affiliation(s)
- Tugce Inan
- Department
of Chemical Engineering, Istanbul Technical
University, Istanbul 34469, Turkey
| | - Robin Flinko
- Institute
of Human Virology, University of Maryland
School of Medicine, Baltimore, Maryland 21201, United States
| | - George K. Lewis
- Institute
of Human Virology, University of Maryland
School of Medicine, Baltimore, Maryland 21201, United States
| | - Alexander D. MacKerell
- University
of Maryland Computer-Aided Drug Design Center, Department of Pharmaceutical
Sciences, School of Pharmacy, University
of Maryland, Baltimore, Maryland 21201, United States
| | - Ozge Kurkcuoglu
- Department
of Chemical Engineering, Istanbul Technical
University, Istanbul 34469, Turkey
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2
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White CW, Platt S, Kilpatrick LE, Dale N, Abhayawardana RS, Dekkers S, Kindon ND, Kellam B, Stocks MJ, Pfleger KDG, Hill SJ. CXCL17 is an allosteric inhibitor of CXCR4 through a mechanism of action involving glycosaminoglycans. Sci Signal 2024; 17:eabl3758. [PMID: 38502733 PMCID: PMC7615768 DOI: 10.1126/scisignal.abl3758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 02/29/2024] [Indexed: 03/21/2024]
Abstract
CXCL17 is a chemokine principally expressed by mucosal tissues, where it facilitates chemotaxis of monocytes, dendritic cells, and macrophages and has antimicrobial properties. CXCL17 is also implicated in the pathology of inflammatory disorders and progression of several cancers, and its expression is increased during viral infections of the lung. However, the exact role of CXCL17 in health and disease requires further investigation, and there is a need for confirmed molecular targets mediating CXCL17 functional responses. Using a range of bioluminescence resonance energy transfer (BRET)-based assays, here we demonstrated that CXCL17 inhibited CXCR4-mediated signaling and ligand binding. Moreover, CXCL17 interacted with neuropillin-1, a VEGFR2 coreceptor. In addition, we found that CXCL17 only inhibited CXCR4 ligand binding in intact cells and demonstrated that this effect was mimicked by known glycosaminoglycan binders, surfen and protamine sulfate. Disruption of putative GAG binding domains in CXCL17 prevented CXCR4 binding. This indicated that CXCL17 inhibited CXCR4 by a mechanism of action that potentially required the presence of a glycosaminoglycan-containing accessory protein. Together, our results revealed that CXCL17 is an endogenous inhibitor of CXCR4 and represents the next step in our understanding of the function of CXCL17 and regulation of CXCR4 signaling.
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Affiliation(s)
- Carl W. White
- Cell Signalling and Pharmacology Research Group, Division of Physiology, Pharmacology & Neuroscience, School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, United Kingdom
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Australian Research Council Centre for Personalised Therapeutics Technologies, Australia
- Dimerix Limited, Melbourne, Australia
| | - Simon Platt
- Cell Signalling and Pharmacology Research Group, Division of Physiology, Pharmacology & Neuroscience, School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, United Kingdom
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
| | - Laura E. Kilpatrick
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
- School of Pharmacy, Biodiscovery Institute, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Natasha Dale
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Australian Research Council Centre for Personalised Therapeutics Technologies, Australia
| | - Rekhati S. Abhayawardana
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Australian Research Council Centre for Personalised Therapeutics Technologies, Australia
| | - Sebastian Dekkers
- Cell Signalling and Pharmacology Research Group, Division of Physiology, Pharmacology & Neuroscience, School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, United Kingdom
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
- School of Pharmacy, Biodiscovery Institute, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Nicholas D Kindon
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
- School of Pharmacy, Biodiscovery Institute, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Barrie Kellam
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
- School of Pharmacy, Biodiscovery Institute, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Michael J Stocks
- School of Pharmacy, Biodiscovery Institute, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Kevin D. G. Pfleger
- Harry Perkins Institute of Medical Research and Centre for Medical Research, The University of Western Australia, QEII Medical Centre, Nedlands, Western Australia 6009, Australia
- Australian Research Council Centre for Personalised Therapeutics Technologies, Australia
- Dimerix Limited, Melbourne, Australia
| | - Stephen J. Hill
- Cell Signalling and Pharmacology Research Group, Division of Physiology, Pharmacology & Neuroscience, School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, United Kingdom
- Centre of Membrane Proteins and Receptors, University of Birmingham and University of Nottingham, The Midlands, UK
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3
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Klaver D, Gander H, Frena B, Amato M, Thurnher M. Crosstalk between purinergic receptor P2Y 11 and chemokine receptor CXCR7 is regulated by CXCR4 in human macrophages. Cell Mol Life Sci 2024; 81:132. [PMID: 38472446 DOI: 10.1007/s00018-024-05158-7] [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: 11/03/2023] [Revised: 01/22/2024] [Accepted: 02/05/2024] [Indexed: 03/14/2024]
Abstract
P2Y11 is a G protein-coupled ATP receptor that activates IL-1 receptor (IL-1R) in a cyclic AMP dependent manner. In human macrophages, P2Y11/IL-1R crosstalk with CCL20 as a prime target is controlled by phosphodiesterase 4 (PDE4), which mediates breakdown of cyclic AMP. Here, we used gene expression analysis to identify activation of CXCR4 and CXCR7 as a hallmark of P2Y11 signaling. We found that PDE4 inhibition with rolipram boosts P2Y11/IL-1R-induced upregulation of CXCR7 expression and CCL20 production in an epidermal growth factor receptor dependent manner. Using an astrocytoma cell line, naturally expressing CXCR7 but lacking CXCR4, P2Y11/IL-1R activation effectively induced and CXCR7 agonist TC14012 enhanced CCL20 production even in the absence of PDE4 inhibition. Moreover, CXCR7 depletion by RNA interference suppressed CCL20 production. In macrophages, the simultaneous activation of P2Y11 and CXCR7 by their respective agonists was sufficient to induce CCL20 production with no need of PDE4 inhibition, as CXCR7 activation increased its own and eliminated CXCR4 expression. Finally, analysis of multiple CCL chemokines in the macrophage secretome revealed that CXCR4 inactivation and CXCR7 activation selectively enhanced P2Y11/IL-1R-mediated secretion of CCL20. Altogether, our data establish CXCR7 as an integral component of the P2Y11/IL-1R-initiated signaling cascade and CXCR4-associated PDE4 as a regulatory checkpoint.
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Affiliation(s)
- Dominik Klaver
- Immunotherapy Unit, Department of Urology, Medical University of Innsbruck, Innrain 66a, Innsbruck, 6020, Austria
| | - Hubert Gander
- Immunotherapy Unit, Department of Urology, Medical University of Innsbruck, Innrain 66a, Innsbruck, 6020, Austria
| | - Beatrice Frena
- Immunotherapy Unit, Department of Urology, Medical University of Innsbruck, Innrain 66a, Innsbruck, 6020, Austria
| | - Marco Amato
- Central Institute for Blood Transfusion & Department of Immunology (ZIB), Tirol Kliniken GmbH, Innsbruck, Austria
| | - Martin Thurnher
- Immunotherapy Unit, Department of Urology, Medical University of Innsbruck, Innrain 66a, Innsbruck, 6020, Austria.
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4
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Di Marino D, Conflitti P, Motta S, Limongelli V. Structural basis of dimerization of chemokine receptors CCR5 and CXCR4. Nat Commun 2023; 14:6439. [PMID: 37833254 PMCID: PMC10575954 DOI: 10.1038/s41467-023-42082-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2021] [Accepted: 09/28/2023] [Indexed: 10/15/2023] Open
Abstract
G protein-coupled receptors (GPCRs) are prominent drug targets responsible for extracellular-to-intracellular signal transduction. GPCRs can form functional dimers that have been poorly characterized so far. Here, we show the dimerization mechanism of the chemokine receptors CCR5 and CXCR4 by means of an advanced free-energy technique named coarse-grained metadynamics. Our results reproduce binding events between the GPCRs occurring in the minute timescale, revealing a symmetric and an asymmetric dimeric structure for each of the three investigated systems, CCR5/CCR5, CXCR4/CXCR4, and CCR5/CXCR4. The transmembrane helices TM4-TM5 and TM6-TM7 are the preferred binding interfaces for CCR5 and CXCR4, respectively. The identified dimeric states differ in the access to the binding sites of the ligand and G protein, indicating that dimerization may represent a fine allosteric mechanism to regulate receptor activity. Our study offers structural basis for the design of ligands able to modulate the formation of CCR5 and CXCR4 dimers and in turn their activity, with therapeutic potential against HIV, cancer, and immune-inflammatory diseases.
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Affiliation(s)
- Daniele Di Marino
- Department of Life and Environmental Sciences - New York-Marche Structural Biology Centre (NY-MaSBiC), Polytechnic University of Marche, Via Brecce Bianche, 60131, Ancona, Italy
- Neuronal Death and Neuroprotection Unit, Department of Neuroscience, Mario Negri Institute for Pharmacological Research-IRCCS, Via Mario Negri 2, 20156, Milan, Italy
- National Biodiversity Future Center (NBFC), Palermo, Italy
| | - Paolo Conflitti
- Università della Svizzera italiana (USI), Faculty of Biomedical Sciences, Euler Institute, Via G. Buffi 13, CH-6900, Lugano, Switzerland
| | - Stefano Motta
- Department of Earth and Environmental Sciences, University of Milano-Bicocca, Piazza della Scienza 1, 20126, Milan, Italy
| | - Vittorio Limongelli
- Università della Svizzera italiana (USI), Faculty of Biomedical Sciences, Euler Institute, Via G. Buffi 13, CH-6900, Lugano, Switzerland.
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5
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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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6
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Stoneman MR, Raicu V. Fluorescence-Based Detection of Proteins and Their Interactions in Live Cells. J Phys Chem B 2023. [PMID: 37205844 DOI: 10.1021/acs.jpcb.3c01419] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Recent advances in fluorescence-based microscopy techniques, such as single molecule fluorescence, Förster resonance energy transfer (FRET), fluorescence intensity fluctuations analysis, and super-resolution microscopy have expanded our ability to study proteins in greater detail within their native cellular environment and to investigate the roles that protein interactions play in biological functions, such as inter- and intracellular signaling and cargo transport. In this Perspective, we provide an up-to-date overview of the current state of the art in fluorescence-based detection of proteins and their interactions in living cells with an emphasis on recent developments that have facilitated the characterization of the spatial and temporal organization of proteins into oligomeric complexes in the presence and absence of natural and artificial ligands. Further advancements in this field will only deepen our understanding of the underlying mechanisms of biological processes and help develop new therapeutic targets.
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Affiliation(s)
- Michael R Stoneman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
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7
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Functional Heterodimerization between the G Protein-Coupled Receptor GPR17 and the Chemokine Receptors 2 and 4: New Evidence. Int J Mol Sci 2022; 24:ijms24010261. [PMID: 36613703 PMCID: PMC9820414 DOI: 10.3390/ijms24010261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 12/16/2022] [Accepted: 12/17/2022] [Indexed: 12/28/2022] Open
Abstract
GPR17, a G protein-coupled receptor, is a pivotal regulator of myelination. Its endogenous ligands trigger receptor desensitization and downregulation allowing oligodendrocyte terminal maturation. In addition to its endogenous agonists, GPR17 could be promiscuously activated by pro-inflammatory oxysterols and chemokines released at demyelinating lesions. Herein, the chemokine receptors CXCR2 and CXCR4 were selected to perform both in silico modelling and in vitro experiments to establish their structural and functional interactions with GPR17. The relative propensity of GPR17 and CXCR2 or CXCR4 to form homo- and hetero-dimers was assessed by homology modelling and molecular dynamics (MD) simulations, and co-immunoprecipitation and immunoenzymatic assay. The interaction between chemokine receptors and GPR17 was investigated by determining receptor-mediated modulation of intracellular cyclic adenosine monophosphate (cAMP). Our data show the GPR17 association with CXCR2 or CXCR4 and the negative regulation of these interactions by CXCR agonists or antagonists. Moreover, GPR17 and CXCR2 heterodimers can functionally influence each other. In contrast, CXCR4 can influence GPR17 functionality, but not vice versa. According to MD simulations, all the dimers reached conformational stability and negative formation energy, confirming the experimental observations. The cross-talk between these receptors could play a role in the development of the neuroinflammatory milieu associated with demyelinating events.
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8
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Zhao R, Liu J, Li Z, Zhang W, Wang F, Zhang B. Recent Advances in CXCL12/CXCR4 Antagonists and Nano-Based Drug Delivery Systems for Cancer Therapy. Pharmaceutics 2022; 14:pharmaceutics14081541. [PMID: 35893797 PMCID: PMC9332179 DOI: 10.3390/pharmaceutics14081541] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 07/15/2022] [Accepted: 07/22/2022] [Indexed: 01/27/2023] Open
Abstract
Chemokines can induce chemotactic cell migration by interacting with G protein-coupled receptors to play a significant regulatory role in the development of cancer. CXC chemokine-12 (CXCL12) can specifically bind to CXC chemokine receptor 4 (CXCR4) and is closely associated with the progression of cancer via multiple signaling pathways. Over recent years, many CXCR4 antagonists have been tested in clinical trials; however, Plerixafor (AMD3100) is the only drug that has been approved for marketing thus far. In this review, we first summarize the mechanisms that mediate the physiological effects of the CXCL12/CXCR4 axis. Then, we describe the use of CXCL12/CXCR4 antagonists. Finally, we discuss the use of nano-based drug delivery systems that exert action on the CXCL12/CXCR4 biological axis.
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Affiliation(s)
| | | | | | | | - Feng Wang
- Correspondence: (F.W.); (B.Z.); Tel.: +86-536-8462490 (B.Z.)
| | - Bo Zhang
- Correspondence: (F.W.); (B.Z.); Tel.: +86-536-8462490 (B.Z.)
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9
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The M 1 muscarinic receptor is present in situ as a ligand-regulated mixture of monomers and oligomeric complexes. Proc Natl Acad Sci U S A 2022; 119:e2201103119. [PMID: 35671422 PMCID: PMC9214538 DOI: 10.1073/pnas.2201103119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Although it is appreciated that members of the large family of rhodopsin-like cell surface receptors can form dimeric or larger protein complexes when expressed at high levels in cultured cells, their organizational state within native cells and tissues of the body is largely unknown. We assessed this in neurons of the central nervous system by replacing the M1 muscarinic acetylcholine receptor in mice with a form of this receptor with an added fluorescent protein. Receptor function was unaltered by this change, and the biophysical approach we used demonstrated that the receptor exists as a mixture of monomers and dimers or oligomers. Drug treatments that target this receptor promote its monomerization, which may have significance for receptor function. The quaternary organization of rhodopsin-like G protein-coupled receptors in native tissues is unknown. To address this we generated mice in which the M1 muscarinic acetylcholine receptor was replaced with a C-terminally monomeric enhanced green fluorescent protein (mEGFP)–linked variant. Fluorescence imaging of brain slices demonstrated appropriate regional distribution, and using both anti-M1 and anti–green fluorescent protein antisera the expressed transgene was detected in both cortex and hippocampus only as the full-length polypeptide. M1-mEGFP was expressed at levels equal to the M1 receptor in wild-type mice and was expressed throughout cell bodies and projections in cultured neurons from these animals. Signaling and behavioral studies demonstrated M1-mEGFP was fully active. Application of fluorescence intensity fluctuation spectrometry to regions of interest within M1-mEGFP–expressing neurons quantified local levels of expression and showed the receptor was present as a mixture of monomers, dimers, and higher-order oligomeric complexes. Treatment with both an agonist and an antagonist ligand promoted monomerization of the M1-mEGFP receptor. The quaternary organization of a class A G protein-coupled receptor in situ was directly quantified in neurons in this study, which answers the much-debated question of the extent and potential ligand-induced regulation of basal quaternary organization of such a receptor in native tissue when present at endogenous expression levels.
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10
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CXCR4 as a novel target in immunology: moving away from typical antagonists. FUTURE DRUG DISCOVERY 2022; 4:FDD77. [PMID: 35875591 PMCID: PMC9298491 DOI: 10.4155/fdd-2022-0007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Accepted: 06/17/2022] [Indexed: 11/17/2022] Open
Abstract
CXCR4 has been a target of interest in drug discovery for numerous years. However, so far, most if not all studies focused on finding antagonists of CXCR4 function. Recent studies demonstrate that targeting a minor allosteric pocket of CXCR4 induces an immunomodulating effect in immune cells expressing CXCR4, connected to the TLR pathway. Compounds binding in this minor pocket seem to be functionally selective with inverse agonistic properties in selected GPCR signaling pathways (Gi activation), but additional signaling pathways are likely to be involved in the immunomodulating effects. In depth research into these CXCR4-targeted immunomodulators could lead to novel treatment options for (auto)-immune diseases.
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11
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Adhikari DP, Biener G, Stoneman MR, Badu DN, Paprocki JD, Eis A, Park PSH, Popa I, Raicu V. Comparative photophysical properties of some widely used fluorescent proteins under two-photon excitation conditions. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021; 262:120133. [PMID: 34243141 DOI: 10.1016/j.saa.2021.120133] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 06/17/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
Understanding the photophysical properties of fluorescent proteins (FPs), such as emission and absorption spectra, molecular brightness, photostability, and photo-switching, is critical to the development of criteria for their selection as tags for fluorescent-based biological applications. While two-photon excitation imaging techniques have steadily gained popularity - due to comparatively deeper penetration depth, reduced out-of-focus photobleaching, and wide separation between emission spectra and two-photon excitation spectra -, most studies reporting on the photophysical properties of FPs tend to remain focused on single-photon excitation. Here, we report our investigation of the photophysical properties of several commonly used fluorescent proteins using two-photon microscopy with spectral resolution in both excitation and emission. Our measurements indicate that not only the excitation (and sometimes emission) spectra of FPs may be markedly different between single-photon and two-photon excitation, but also their relative brightness and their photo-stability. A good understanding of the photophysical properties of FPs under two-photon excitation is essential for choosing the right tag(s) for a desired experiment.
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Affiliation(s)
- Dhruba P Adhikari
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Gabriel Biener
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | | | - Dammar N Badu
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Joel D Paprocki
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Annie Eis
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Paul S-H Park
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ionel Popa
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA; Department of Biological Sciences, University of Wisconsin-Milwaukee, WI 53211, USA.
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12
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Integration and Spatial Organization of Signaling by G Protein-Coupled Receptor Homo- and Heterodimers. Biomolecules 2021; 11:biom11121828. [PMID: 34944469 PMCID: PMC8698773 DOI: 10.3390/biom11121828] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 11/29/2021] [Accepted: 12/01/2021] [Indexed: 01/14/2023] Open
Abstract
Information flow from a source to a receiver becomes informative when the recipient can process the signal into a meaningful form. Information exchange and interpretation is essential in biology and understanding how cells integrate signals from a variety of information-coding molecules into complex orchestrated responses is a major challenge for modern cell biology. In complex organisms, cell to cell communication occurs mostly through neurotransmitters and hormones, and receptors are responsible for signal recognition at the membrane level and information transduction inside the cell. The G protein-coupled receptors (GPCRs) are the largest family of membrane receptors, with nearly 800 genes coding for these proteins. The recognition that GPCRs may physically interact with each other has led to the hypothesis that their dimeric state can provide the framework for temporal coincidence in signaling pathways. Furthermore, the formation of GPCRs higher order oligomers provides the structural basis for organizing distinct cell compartments along the plasma membrane where confined increases in second messengers may be perceived and discriminated. Here, we summarize evidence that supports these conjectures, fostering new ideas about the physiological role played by receptor homo- and hetero-oligomerization in cell biology.
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13
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Joseph MD, Tomas Bort E, Grose RP, McCormick PJ, Simoncelli S. Quantitative Super-Resolution Imaging for the Analysis of GPCR Oligomerization. Biomolecules 2021; 11:biom11101503. [PMID: 34680136 PMCID: PMC8533726 DOI: 10.3390/biom11101503] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 10/06/2021] [Accepted: 10/09/2021] [Indexed: 12/13/2022] Open
Abstract
G-protein coupled receptors (GPCRs) are known to form homo- and hetero- oligomers which are considered critical to modulate their function. However, studying the existence and functional implication of these complexes is not straightforward as controversial results are obtained depending on the method of analysis employed. Here, we use a quantitative single molecule super-resolution imaging technique named qPAINT to quantify complex formation within an example GPCR. qPAINT, based upon DNA-PAINT, takes advantage of the binding kinetics between fluorescently labelled DNA imager strands to complementary DNA docking strands coupled to protein targeting antibodies to quantify the protein copy number in nanoscale dimensions. We demonstrate qPAINT analysis via a novel pipeline to study the oligomerization of the purinergic receptor Y2 (P2Y2), a rhodopsin-like GPCR, highly expressed in the pancreatic cancer cell line AsPC-1, under control, agonistic and antagonistic conditions. Results reveal that whilst the density of P2Y2 receptors remained unchanged, antagonistic conditions displayed reduced percentage of oligomers, and smaller numbers of receptors in complexes. Yet, the oligomeric state of the receptors was not affected by agonist treatment, in line with previous reports. Understanding P2Y2 oligomerization under agonistic and antagonistic conditions will contribute to unravelling P2Y2 mechanistic action and therapeutic targeting.
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Affiliation(s)
- Megan D. Joseph
- London Centre for Nanotechnology, University College London, London WC1H 0AH, UK;
| | - Elena Tomas Bort
- Centre for Tumour Biology, Barts Cancer Institute, Queen Mary University of London, London EC1M 6BQ, UK; (E.T.B.); (R.P.G.)
- Centre for Endocrinology, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London EC1M 6BQ, UK;
| | - Richard P. Grose
- Centre for Tumour Biology, Barts Cancer Institute, Queen Mary University of London, London EC1M 6BQ, UK; (E.T.B.); (R.P.G.)
| | - Peter J. McCormick
- Centre for Endocrinology, William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London EC1M 6BQ, UK;
| | - Sabrina Simoncelli
- London Centre for Nanotechnology, University College London, London WC1H 0AH, UK;
- Department of Chemistry, University College London, London WC1H 0AJ, UK
- Correspondence:
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Biener G, Stoneman MR, Raicu V. Fluorescence intensity fluctuation analysis of receptor oligomerization in membrane domains. Biophys J 2021; 120:3028-3039. [PMID: 34214533 DOI: 10.1016/j.bpj.2021.06.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 06/02/2021] [Accepted: 06/11/2021] [Indexed: 11/26/2022] Open
Abstract
Fluorescence micrographs of the plasma membrane of cells expressing fluorescently labeled G protein-coupled receptors (GPCRs) often exhibit small clusters of pixels (or puncta) with intensities that are higher than those of the surrounding pixels. Although studies of GPCR interactions in uniform membrane areas abound, understanding the details of the GPCR interactions within such puncta as well as the nature of the membrane formations underlying the puncta is hampered by the lack of adequate experimental techniques. Here, we introduce an enhancement of a recently developed method termed fluorescence intensity fluctuation spectrometry, which permits analysis of protein-protein interactions within the puncta in live cell membranes. We applied the novel fluorescence intensity fluctuation data analysis protocol to previously published data from cells expressing human secretin receptors and determined that the oligomer size increases with receptor concentration and duration of treatment with cognate ligand, not only within uniform regions of the membrane (in agreement with previous publications) but also within the puncta. In addition, we found that the number density and fractional area of the puncta increased after treatment with ligand. This method could be applied for probing the evolution in the time of the chain of events that begins with ligand binding and continues with coated pits formation and receptor internalization for other GPCRs and, indeed, other membrane receptors in living cells.
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Affiliation(s)
- Gabriel Biener
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Michael R Stoneman
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Valerică Raicu
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.
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