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Cullum SA, Platt S, Dale N, Isaac OC, Wragg ES, Soave M, Veprintsev DB, Woolard J, Kilpatrick LE, Hill SJ. Mechano-sensitivity of β2-adrenoceptors enhances constitutive activation of cAMP generation that is inhibited by inverse agonists. Commun Biol 2024; 7:417. [PMID: 38580813 PMCID: PMC10997663 DOI: 10.1038/s42003-024-06128-2] [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: 09/27/2023] [Accepted: 03/29/2024] [Indexed: 04/07/2024] Open
Abstract
The concept of agonist-independent signalling that can be attenuated by inverse agonists is a fundamental element of the cubic ternary complex model of G protein-coupled receptor (GPCR) activation. This model shows how a GPCR can exist in two conformational states in the absence of ligands; an inactive R state and an active R* state that differ in their affinities for agonists, inverse agonists, and G-protein alpha subunits. The proportion of R* receptors that exist in the absence of agonists determines the level of constitutive receptor activity. In this study we demonstrate that mechanical stimulation can induce β2-adrenoceptor agonist-independent Gs-mediated cAMP signalling that is sensitive to inhibition by inverse agonists such as ICI-118551 and propranolol. The size of the mechano-sensitive response is dependent on the cell surface receptor expression level in HEK293G cells, is still observed in a ligand-binding deficient D113A mutant β2-adrenoceptor and can be attenuated by site-directed mutagenesis of the extracellular N-glycosylation sites on the N-terminus and second extracellular loop of the β2-adrenoceptor. Similar mechano-sensitive agonist-independent responses are observed in HEK293G cells overexpressing the A2A-adenosine receptor. These data provide new insights into how agonist-independent constitutive receptor activity can be enhanced by mechanical stimulation and regulated by inverse agonists.
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Affiliation(s)
- Sean A Cullum
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Simon Platt
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Natasha Dale
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Oliver C Isaac
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Edward S Wragg
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Mark Soave
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Dmitry B Veprintsev
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Jeanette Woolard
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
| | - Laura E Kilpatrick
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK
- Division of Bimolecular Science and Medicinal Chemistry, School of Pharmacy, Biodiscovery Institute, University of Nottingham, Nottingham, NG7 2RD, UK
| | - Stephen J Hill
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK.
- Centre of Membrane Proteins and Receptors, University of Nottingham, Nottingham, NG7 2UH, UK.
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Cullum SA, Veprintsev DB, Hill SJ. Kinetic analysis of endogenous β 2 -adrenoceptor-mediated cAMP GloSensor™ responses in HEK293 cells. Br J Pharmacol 2023; 180:1304-1315. [PMID: 36495270 PMCID: PMC10952559 DOI: 10.1111/bph.16008] [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: 08/01/2022] [Revised: 11/01/2022] [Accepted: 12/02/2022] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND AND AIM Standard pharmacological analysis of agonist activity utilises measurements of receptor-mediated responses at a set time-point, or at the peak response level, to characterise ligands. However, the occurrence of non-equilibrium conditions may dramatically impact the properties of the response being measured. Here we have analysed the initial kinetic phases of cAMP responses to β2 -adrenoceptor agonists in HEK293 cells expressing the endogenous β2 -adrenoceptor at extremely low levels. EXPERIMENTAL APPROACH The kinetics of β2 -adrenoceptor agonist-stimulated cAMP responses were monitored in real-time, in the presence and absence of antagonists, in HEK293 cells expressing the cAMP GloSensor™ biosensor. Potency (EC50 ) and efficacy (Emax ) values were determined at the peak of the agonist GloSensor™ response and compared to kinetic parameters L50 and IRmax values derived from initial response rates. KEY RESULTS The partial agonists salbutamol and salmeterol displayed reduced relative IRmax values (with respect to isoprenaline) when compared with their Emax values. Except for the fast dissociating bisoprolol, preincubation with β2 -adrenoceptor antagonists produced a large reduction in the isoprenaline peak response due to a state of hemi-equilibrium in this low receptor reserve system. This effect was exacerbated when IRmax parameters were measured. Furthermore, bisoprolol produced a large reduction in isoprenaline IRmax consistent with its short residence time. CONCLUSIONS AND IMPLICATIONS Kinetic analysis of real-time signalling data can provide valuable insights into the hemi-equilibria that can occur in low receptor reserve systems with agonist-antagonist interactions, due to incomplete dissociation of antagonist whilst the peak agonist response is developing.
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Affiliation(s)
- Sean A. Cullum
- Division of Physiology, Pharmacology and Neuroscience, School of Life SciencesUniversity of NottinghamNottinghamUK
- Centre of Membrane Proteins and ReceptorsUniversity of Birmingham and NottinghamNottinghamUK
| | - Dmitry B. Veprintsev
- Division of Physiology, Pharmacology and Neuroscience, School of Life SciencesUniversity of NottinghamNottinghamUK
- Centre of Membrane Proteins and ReceptorsUniversity of Birmingham and NottinghamNottinghamUK
| | - Stephen J. Hill
- Division of Physiology, Pharmacology and Neuroscience, School of Life SciencesUniversity of NottinghamNottinghamUK
- Centre of Membrane Proteins and ReceptorsUniversity of Birmingham and NottinghamNottinghamUK
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Fluorescence Spectroscopy of Low-Level Endogenous β-adrenergic Receptor Expression at the Plasma Membrane of Differentiating Human iPSC-Derived Cardiomyocytes. Int J Mol Sci 2022; 23:ijms231810405. [PMID: 36142320 PMCID: PMC9499492 DOI: 10.3390/ijms231810405] [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: 07/24/2022] [Revised: 09/02/2022] [Accepted: 09/06/2022] [Indexed: 11/17/2022] Open
Abstract
The potential of human-induced pluripotent stem cells (hiPSCs) to be differentiated into cardiomyocytes (CMs) mimicking adult CMs functional morphology, marker genes and signaling characteristics has been investigated since over a decade. The evolution of the membrane localization of CM-specific G protein-coupled receptors throughout differentiation has received, however, only limited attention to date. We employ here advanced fluorescent spectroscopy, namely linescan Fluorescence Correlation Spectroscopy (FCS), to observe how the plasma membrane abundance of the β1- and β2-adrenergic receptors (β1/2-ARs), labelled using a bright and photostable fluorescent antagonist, evolves during the long-term monolayer culture of hiPSC-derived CMs. We compare it to the kinetics of observed mRNA levels in wildtype (WT) hiPSCs and in two CRISPR/Cas9 knock-in clones. We conduct these observations against the backdrop of our recent report of cell-to-cell expression variability, as well as of the subcellular localization heterogeneity of β-ARs in adult CMs.
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The use of fluorescence correlation spectroscopy to characterise the molecular mobility of G protein-coupled receptors in membrane microdomains: an update. Biochem Soc Trans 2021; 49:1547-1554. [PMID: 34436556 DOI: 10.1042/bst20201001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 07/26/2021] [Accepted: 07/28/2021] [Indexed: 12/24/2022]
Abstract
It has become increasingly apparent that some G protein-coupled receptors (GPCRs) are not homogeneously expressed within the plasma membrane but may instead be organised within distinct signalling microdomains. These microdomains localise GPCRs in close proximity with other membrane proteins and intracellular signalling partners and could have profound implications for the spatial and temporal control of downstream signalling. In order to probe the molecular mechanisms that govern GPCR pharmacology within these domains, fluorescence techniques with effective single receptor sensitivity are required. Of these, fluorescence correlation spectroscopy (FCS) is a technique that meets this sensitivity threshold. This short review will provide an update of the recent uses of FCS based techniques in conjunction with GPCR subtype selective fluorescent ligands to characterise dynamic ligand-receptor interactions in whole cells and using purified GPCRs.
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Goulding J, Mistry SJ, Soave M, Woolard J, Briddon SJ, White CW, Kellam B, Hill SJ. Subtype selective fluorescent ligands based on ICI 118,551 to study the human β2-adrenoceptor in CRISPR/Cas9 genome-edited HEK293T cells at low expression levels. Pharmacol Res Perspect 2021; 9:e00779. [PMID: 34003582 PMCID: PMC8130569 DOI: 10.1002/prp2.779] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2021] [Revised: 03/30/2021] [Accepted: 03/31/2021] [Indexed: 12/18/2022] Open
Abstract
Fluorescent ligand technologies have proved to be powerful tools to improve our understanding of ligand‐receptor interactions. Here we have characterized a small focused library of nine fluorescent ligands based on the highly selective β2‐adrenoceptor (β2AR) antagonist ICI 118,551. The majority of fluorescent ICI 118,551 analogs had good affinity for the β2AR (pKD >7.0) with good selectivity over the β1AR (pKD <6.0). The most potent and selective ligands being 8c (ICI 118,551‐Gly‐Ala‐BODIPY‐FL‐X; β2AR pKD 7.48), 9c (ICI 118,551‐βAla‐βAla‐BODIPY‐FL‐X; β2AR pKD 7.48), 12a (ICI 118,551‐PEG‐BODIPY‐X‐630/650; β2AR pKD 7.56), and 12b (ICI 118,551‐PEG‐BODIPY‐FL; β2AR pKD 7.42). 9a (ICI 118,551‐βAla‐βAla‐BODIPY‐X‐630/650) had the highest affinity at recombinant β2ARs (pKD 7.57), but also exhibited significant binding affinity to the β1AR (pKD 6.69). Nevertheless, among the red fluorescent ligands, 9a had the best imaging characteristics in recombinant HEK293 T cells and labeling was mostly confined to the cell surface. In contrast, 12a showed the highest propensity to label intracellular β2ARs in HEK293 T cell expressing exogenous β2ARs. This suggests that a combination of the polyethylene glycol (PEG) linker and the BODIPY‐X‐630/650 makes this ICI 118,551 derivative particularly susceptible to crossing the cell membrane to access the intracellular β2ARs. We have also used these ligands in combination with CRISPR/Cas9 genome‐edited HEK293 T cells to undertake for the first time real‐time ligand binding to native HEK293 T β2ARs at low native receptor expression levels. These studies provided quantitative data on ligand‐binding characteristics but also allowed real‐time visualization of the ligand‐binding interactions in genome‐edited cells using NanoBRET luminescence imaging.
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Affiliation(s)
- Joëlle Goulding
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, UK.,Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
| | - Sarah J Mistry
- Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK.,School of Pharmacy, University of Nottingham, Nottingham, UK
| | - Mark Soave
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, UK.,Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
| | - Jeanette Woolard
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, UK.,Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
| | - Stephen J Briddon
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, UK.,Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
| | - Carl W White
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, UK.,Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK.,Harry Perkins Institute of Medical Research and Centre for Medical Research, University of Western Australia, QEII Medical Centre, Nedlands, Western Australia, Australia.,Australian Research Council Centre for Personalised Therapeutics Technologies, Australia
| | - Barrie Kellam
- Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK.,School of Pharmacy, University of Nottingham, Nottingham, UK
| | - Stephen J Hill
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, University of Nottingham, Nottingham, UK.,Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
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