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BRET-Based Biosensors to Measure Agonist Efficacies in Histamine H 1 Receptor-Mediated G Protein Activation, Signaling and Interactions with GRKs and β-Arrestins. Int J Mol Sci 2022; 23:ijms23063184. [PMID: 35328605 PMCID: PMC8953162 DOI: 10.3390/ijms23063184] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 03/10/2022] [Accepted: 03/11/2022] [Indexed: 02/04/2023] Open
Abstract
The histamine H1 receptor (H1R) is a G protein-coupled receptor (GPCR) and plays a key role in allergic reactions upon activation by histamine which is locally released from mast cells and basophils. Consequently, H1R is a well-established therapeutic target for antihistamines that relieve allergy symptoms. H1R signals via heterotrimeric Gq proteins and is phosphorylated by GPCR kinase (GRK) subtypes 2, 5, and 6, consequently facilitating the subsequent recruitment of β-arrestin1 and/or 2. Stimulation of a GPCR with structurally different agonists can result in preferential engagement of one or more of these intracellular signaling molecules. To evaluate this so-called biased agonism for H1R, bioluminescence resonance energy transfer (BRET)-based biosensors were applied to measure H1R signaling through heterotrimeric Gq proteins, second messengers (inositol 1,4,5-triphosphate and Ca2+), and receptor-protein interactions (GRKs and β-arrestins) in response to histamine, 2-phenylhistamines, and histaprodifens in a similar cellular background. Although differences in efficacy were observed for these agonists between some functional readouts as compared to reference agonist histamine, subsequent data analysis using an operational model of agonism revealed only signaling bias of the agonist Br-phHA-HA in recruiting β-arrestin2 to H1R over Gq biosensor activation.
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Rodriguez BA, Bhan A, Beswick A, Elwood PC, Niiranen TJ, Salomaa V, Trégouët DA, Morange PE, Civelek M, Ben-Shlomo Y, Schlaeger T, Chen MH, Johnson AD, Johnson AD. A Platelet Function Modulator of Thrombin Activation Is Causally Linked to Cardiovascular Disease and Affects PAR4 Receptor Signaling. Am J Hum Genet 2020; 107:211-221. [PMID: 32649856 DOI: 10.1016/j.ajhg.2020.06.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Accepted: 06/03/2020] [Indexed: 12/17/2022] Open
Abstract
Dual antiplatelet therapy reduces ischemic events in cardiovascular disease, but it increases bleeding risk. Thrombin receptors PAR1 and PAR4 are drug targets, but the role of thrombin in platelet aggregation remains largely unexplored in large populations. We performed a genome-wide association study (GWAS) of platelet aggregation in response to full-length thrombin, followed by clinical association analyses, Mendelian randomization, and functional characterization including iPSC-derived megakaryocyte and platelet experiments. We identified a single sentinel variant in the GRK5 locus (rs10886430-G, p = 3.0 × 10-42) associated with increased thrombin-induced platelet aggregation (β = 0.70, SE = 0.05). We show that disruption of platelet GRK5 expression by rs10886430-G is associated with enhanced platelet reactivity. The proposed mechanism of a GATA1-driven megakaryocyte enhancer is confirmed in allele-specific experiments. Utilizing further data, we demonstrate that the allelic effect is highly platelet- and thrombin-specific and not likely due to effects on thrombin levels. The variant is associated with increased risk of cardiovascular disease outcomes in UK BioBank, most strongly with pulmonary embolism. The variant associates with increased risk of stroke in the MEGASTROKE, UK BioBank, and FinnGen studies. Mendelian randomization analyses in independent samples support a causal role for rs10886430-G in increasing risk for stroke, pulmonary embolism, and venous thromboembolism through its effect on thrombin-induced platelet reactivity. We demonstrate that G protein-coupled receptor kinase 5 (GRK5) promotes platelet activation specifically via PAR4 receptor signaling. GRK5 inhibitors in development for the treatment of heart failure and cancer could have platelet off-target deleterious effects. Common variants in GRK5 may modify clinical outcomes with PAR4 inhibitors, and upregulation of GRK5 activity or signaling in platelets may have therapeutic benefits.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | - Andrew D Johnson
- National Heart, Lung, and Blood Institute, Division of Intramural Research, Population Sciences Branch, The Framingham Heart Study, Framingham, MA 01702, USA.
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Verweij EWE, Al Araaj B, Prabhata WR, Prihandoko R, Nijmeijer S, Tobin AB, Leurs R, Vischer HF. Differential Role of Serines and Threonines in Intracellular Loop 3 and C-Terminal Tail of the Histamine H 4 Receptor in β-Arrestin and G Protein-Coupled Receptor Kinase Interaction, Internalization, and Signaling. ACS Pharmacol Transl Sci 2020; 3:321-333. [PMID: 32296771 PMCID: PMC7155198 DOI: 10.1021/acsptsci.0c00008] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Indexed: 12/24/2022]
Abstract
The histamine H4 receptor (H4R) activates Gαi-mediated signaling and recruits β-arrestin2 upon stimulation with histamine. β-Arrestins play a regulatory role in G protein-coupled receptor (GPCR) signaling by interacting with phosphorylated serine and threonine residues in the GPCR C-terminal tail and intracellular loop 3, resulting in receptor desensitization and internalization. Using bioluminescence resonance energy transfer (BRET)-based biosensors, we show that G protein-coupled receptor kinases (GRK) 2 and 3 are more quickly recruited to the H4R than β-arrestin1 and 2 upon agonist stimulation, whereas receptor internalization dynamics toward early endosomes was slower. Alanine-substitution revealed that a serine cluster at the distal end of the H4R C-terminal tail is essential for the recruitment of β-arrestin1/2, and consequently, receptor internalization and desensitization of G protein-driven extracellular-signal-regulated kinase (ERK)1/2 phosphorylation and label-free cellular impedance. In contrast, alanine substitution of serines and threonines in the intracellular loop 3 of the H4R did not affect β-arrestin2 recruitment and receptor desensitization, but reduced β-arrestin1 recruitment and internalization. Hence, β-arrestin recruitment to H4R requires the putative phosphorylated serine cluster in the H4R C-terminal tail, whereas putative phosphosites in the intracellular loop 3 have different effects on β-arrestin1 versus β-arrestin2. Mutation of these putative phosphosites in either intracellular loop 3 or the C-terminal tail did not affect the histamine-induced recruitment of GRK2 and GRK3 but does change the interaction of H4R with GRK5 and GRK6, respectively. Identification of H4R interactions with these proteins is a first step in the understanding how this receptor might be dysregulated in pathophysiological conditions.
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Affiliation(s)
- Eléonore W E Verweij
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Betty Al Araaj
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Wimzy R Prabhata
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Rudi Prihandoko
- Centre for Translational Pharmacology, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Saskia Nijmeijer
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Andrew B Tobin
- Centre for Translational Pharmacology, Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Rob Leurs
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
| | - Henry F Vischer
- Division of Medicinal Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands
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4
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Mangmool S, Parichatikanond W, Kurose H. Therapeutic Targets for Treatment of Heart Failure: Focus on GRKs and β-Arrestins Affecting βAR Signaling. Front Pharmacol 2018; 9:1336. [PMID: 30538631 PMCID: PMC6277550 DOI: 10.3389/fphar.2018.01336] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 10/30/2018] [Indexed: 12/19/2022] Open
Abstract
Heart failure (HF) is a heart disease that is classified into two main types: HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). Both types of HF lead to significant risk of mortality and morbidity. Pharmacological treatment with β-adrenergic receptor (βAR) antagonists (also called β-blockers) has been shown to reduce the overall hospitalization and mortality rates and improve the clinical outcomes in HF patients with HFrEF but not HFpEF. Although, the survival rate of patients suffering from HF continues to drop, the management of HF still faces several limitations and discrepancies highlighting the need to develop new treatment strategies. Overstimulation of the sympathetic nervous system is an adaptive neurohormonal response to acute myocardial injury and heart damage, whereas prolonged exposure to catecholamines causes defects in βAR regulation, including a reduction in the amount of βARs and an increase in βAR desensitization due to the upregulation of G protein-coupled receptor kinases (GRKs) in the heart, contributing in turn to the progression of HF. Several studies show that myocardial GRK2 activity and expression are raised in the failing heart. Furthermore, β-arrestins play a pivotal role in βAR desensitization and, interestingly, can mediate their own signal transduction without any G protein-dependent pathway involved. In this review, we provide new insight into the role of GRKs and β-arrestins on how they affect βAR signaling regarding the molecular and cellular pathophysiology of HF. Additionally, we discuss the therapeutic potential of targeting GRKs and β-arrestins for the treatment of HF.
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Affiliation(s)
- Supachoke Mangmool
- Department of Pharmacology, Faculty of Pharmacy, Mahidol University, Bangkok, Thailand
| | | | - Hitoshi Kurose
- Department of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan
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Shang Z, Han F, Zhou X, Bao Z, Zhu J, Wang T, Lu Q, Du L, Li W, Lv D, Yin X. A variant of GRK5 is associated with the therapeutic efficacy of repaglinide in Chinese Han patients with type 2 diabetes mellitus. Drug Dev Res 2018; 79:129-135. [PMID: 29663513 DOI: 10.1002/ddr.21426] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2017] [Revised: 01/28/2018] [Accepted: 03/13/2018] [Indexed: 12/22/2022]
Abstract
Post-Market Research We aimed to investigate the impact of G protein-coupled receptor kinase 5 (GRK5) rs10886471 polymorphism on repaglinide efficacy in Chinese patients with type 2 diabetes mellitus (T2DM). A total of 300 T2DM patients and 210 healthy controls were genotyped for GRK5 rs10886471 on a three-dimensional polyacrylamide gel-based DNA microarray. Eighty-five patients with the same genotypes of cytochrome P450 (CYP) 2C8*3 139Arg and organic anion-transporting polypeptide 1B1 (OATP1B1) 521TT were randomly selected to orally take repaglinide for eight consecutive weeks. Then, the biochemical indicators and pharmacodynamic parameters were measured before and after repaglinide treatment. The T allelic frequency of GRK5 rs10886471 was higher in T2DM patients than in healthy subjects (p < .01). T2DM patients with genotypes CC and CT at GRK5 rs10886471 had a significant reduction in terms of fasting plasma glucose (FPG) compared with those with genotype TT (p < .01). In addition, the carriers of genotypes CC and CT at GRK5 rs10886471 had higher differential values of postprandial serum insulin (PINS) compared with genotype TT carriers (p < .05). These findings suggest that GRK5 rs10886471 polymorphism may influence the therapeutic efficacy of repaglinide in Chinese Han T2DM patients.
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Affiliation(s)
- Zhenhai Shang
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China.,Department of Pharmacy, the Affiliated Hospital of Xuzhou Medical University, Xuzhou, China
| | - Feifei Han
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China.,Department of Diagnostics, Clinical College, Xuzhou Medical University, Xuzhou, China
| | - Xueyan Zhou
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China
| | - Zejun Bao
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China
| | - Jing Zhu
- Department of Pharmacy, the First Affiliated Hospital of Soochow University, Suzhou, China
| | - Tao Wang
- Department of Pharmacy, the Affiliated Hospital of Xuzhou Medical University, Xuzhou, China
| | - Qian Lu
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China
| | - Lei Du
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China
| | - Wei Li
- Department of Endocrinology, the Affiliated Hospital of Xuzhou Medical University, Xuzhou, China
| | - Dongmei Lv
- Department of Pharmacy, the Affiliated Hospital of Xuzhou Medical University, Xuzhou, China
| | - Xiaoxing Yin
- Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou, China
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“Barcode” and Differential Effects of GPCR Phosphorylation by Different GRKs. METHODS IN PHARMACOLOGY AND TOXICOLOGY 2016. [DOI: 10.1007/978-1-4939-3798-1_5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Homan KT, Waldschmidt HV, Glukhova A, Cannavo A, Song J, Cheung JY, Koch WJ, Larsen SD, Tesmer JJG. Crystal Structure of G Protein-coupled Receptor Kinase 5 in Complex with a Rationally Designed Inhibitor. J Biol Chem 2015; 290:20649-20659. [PMID: 26032411 DOI: 10.1074/jbc.m115.647370] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptor kinases (GRKs) regulate cell signaling by initiating the desensitization of active G protein-coupled receptors. The two most widely expressed GRKs (GRK2 and GRK5) play a role in cardiovascular disease and thus represent important targets for the development of novel therapeutic drugs. In the course of a GRK2 structure-based drug design campaign, one inhibitor (CCG215022) exhibited nanomolar IC50 values against both GRK2 and GRK5 and good selectivity against other closely related kinases such as GRK1 and PKA. Treatment of murine cardiomyocytes with CCG215022 resulted in significantly increased contractility at 20-fold lower concentrations than paroxetine, an inhibitor with more modest selectivity for GRK2. A 2.4 Å crystal structure of the GRK5·CCG215022 complex was determined and revealed that the inhibitor binds in the active site similarly to its parent compound GSK180736A. As designed, its 2-pyridylmethyl amide side chain occupies the hydrophobic subsite of the active site where it forms three additional hydrogen bonds, including one with the catalytic lysine. The overall conformation of the GRK5 kinase domain is similar to that of a previously determined structure of GRK6 in what is proposed to be its active state, but the C-terminal region of the enzyme adopts a distinct conformation. The kinetic properties of site-directed mutants in this region are consistent with the hypothesis that this novel C-terminal structure is representative of the membrane-bound conformation of the enzyme.
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Affiliation(s)
- Kristoff T Homan
- Life Sciences Institute and the Departments of Pharmacology and Biological Sciences, University of Michigan, Ann Arbor, Michigan 48109
| | - Helen V Waldschmidt
- Vahlteich Medicinal Chemistry Core and the Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Alisa Glukhova
- Life Sciences Institute and the Departments of Pharmacology and Biological Sciences, University of Michigan, Ann Arbor, Michigan 48109
| | - Alessandro Cannavo
- Center for Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140
| | - Jianliang Song
- Center for Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140
| | - Joseph Y Cheung
- Center for Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140
| | - Walter J Koch
- Center for Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140
| | - Scott D Larsen
- Vahlteich Medicinal Chemistry Core and the Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - John J G Tesmer
- Life Sciences Institute and the Departments of Pharmacology and Biological Sciences, University of Michigan, Ann Arbor, Michigan 48109.
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8
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Qi Q, Wang X, Strizich G, Wang T. Genetic Determinants of Type 2 Diabetes in Asians. ACTA ACUST UNITED AC 2015; 2015. [PMID: 27583258 DOI: 10.19070/2328-353x-si01001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Type 2 diabetes (T2D) has become a major health problem throughout the world and the epidemic is particularly severe in Asian countries. Compared with European populations, Asians tend to develop diabetes at a younger age and at much higher incidence rates given the same amount of weight gain. Genome-wide association studies (GWAS) have identified over 70 loci associated with T2D. Although the majority of GWAS results were conducted in populations of European ancestry, recent GWAS in Asians have made important contributions to the identification of T2D susceptibility loci. These studies not only confirmed T2D susceptibility loci initially identified in European populations, but also identified novel susceptibility loci that provide new insights into the pathophysiology of diseases. In this article, we review GWAS results of T2D conducted in East and South Asians and compare them to those of European populations. Currently identified T2D genetic variants do not appear to explain the phenomenon that Asians are more susceptible to T2D than European populations, suggesting further studies in Asian populations are needed.
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Affiliation(s)
- Q Qi
- Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - X Wang
- Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Epidemiology and Biostatistics, School of Public Health, Peking University Health Science Center, 38 Xueyuan Road, Haidian District, Beijing 100191, China
| | - G Strizich
- Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - T Wang
- Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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9
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Beautrait A, Michalski KR, Lopez TS, Mannix KM, McDonald DJ, Cutter AR, Medina CB, Hebert AM, Francis CJ, Bouvier M, Tesmer JJG, Sterne-Marr R. Mapping the putative G protein-coupled receptor (GPCR) docking site on GPCR kinase 2: insights from intact cell phosphorylation and recruitment assays. J Biol Chem 2014; 289:25262-75. [PMID: 25049229 PMCID: PMC4155688 DOI: 10.1074/jbc.m114.593178] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
G protein-coupled receptor kinases (GRKs) phosphorylate agonist-occupied receptors initiating the processes of desensitization and β-arrestin-dependent signaling. Interaction of GRKs with activated receptors serves to stimulate their kinase activity. The extreme N-terminal helix (αN), the kinase small lobe, and the active site tether (AST) of the AGC kinase domain have previously been implicated in mediating the allosteric activation. Expanded mutagenesis of the αN and AST allowed us to further assess the role of these two regions in kinase activation and receptor phosphorylation in vitro and in intact cells. We also developed a bioluminescence resonance energy transfer-based assay to monitor the recruitment of GRK2 to activated α2A-adrenergic receptors (α2AARs) in living cells. The bioluminescence resonance energy transfer signal exhibited a biphasic response to norepinephrine concentration, suggesting that GRK2 is recruited to Gβγ and α2AAR with EC50 values of 15 nm and 8 μm, respectively. We show that mutations in αN (L4A, V7E, L8E, V11A, S12A, Y13A, and M17A) and AST (G475I, V477D, and I485A) regions impair or potentiate receptor phosphorylation and/or recruitment. We suggest that a surface of GRK2, including Leu4, Val7, Leu8, Val11, and Ser12, directly interacts with receptors, whereas residues such as Asp10, Tyr13, Ala16, Met17, Gly475, Val477, and Ile485 are more important for kinase domain closure and activation. Taken together with data on GRK1 and GRK6, our data suggest that all three GRK subfamilies make conserved interactions with G protein-coupled receptors, but there may be unique interactions that influence selectivity.
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Affiliation(s)
- Alexandre Beautrait
- From the Department of Biochemistry and the Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | | | | | | | | | | | | | | | | | - Michel Bouvier
- From the Department of Biochemistry and the Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, Québec H3C 3J7, Canada
| | - John J G Tesmer
- the Departments of Pharmacology and Biological Chemistry, Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
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Nooh MM, Chumpia MM, Hamilton TB, Bahouth SW. Sorting of β1-adrenergic receptors is mediated by pathways that are either dependent on or independent of type I PDZ, protein kinase A (PKA), and SAP97. J Biol Chem 2013; 289:2277-94. [PMID: 24324269 DOI: 10.1074/jbc.m113.513481] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The β1-adrenergic receptor (β1-AR) is a target for treatment of major cardiovascular diseases, such as heart failure and hypertension. Recycling of agonist-internalized β1-AR is dependent on type I PSD-95/DLG/ZO1 (PDZ) in the C-tail of the β1-AR and on protein kinase A (PKA) activity (Gardner, L. A., Naren, A. P., and Bahouth, S. W. (2007) J. Biol. Chem. 282, 5085-5099). We explored the effects of point mutations in the PDZ and in the activity of PKA on recycling of the β1-AR and its binding to the PDZ-binding protein SAP97. These studies indicated that β1-AR recycling was inhibited by PKA inhibitors and by mutations in the PDZ that interfered with SAP97 binding. The trafficking effects of short sequences differing in PDZ and SAP97 binding were examined using chimeric mutant β1-AR. β1-AR chimera containing the type I PDZ of the β2-adrenergic receptor that does not bind to SAP97 failed to recycle except when serine 312 was mutated to aspartic acid. β1-AR chimera with type I PDZ sequences from the C-tails of aquaporin-2 or GluR1 recycled in a SAP97- and PKA-dependent manner. Non-PDZ β1-AR chimera derived from μ-opioid, dopamine 1, or GluR2 receptors promoted rapid recycling of chimeric β1-AR in a SAP97- and PKA-independent manner. Moreover, the nature of the residue at position -3 in the PDZ regulated whether the β1-AR was internalized alone or in complex with SAP97. These results indicate that divergent pathways were involved in trafficking the β1-AR and provide a roadmap for its trafficking via type I PDZs versus non-PDZs.
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Affiliation(s)
- Mohammed M Nooh
- From the Department of Pharmacology, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163 and
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11
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Yang P, Glukhova A, Tesmer JJG, Chen Z. Membrane orientation and binding determinants of G protein-coupled receptor kinase 5 as assessed by combined vibrational spectroscopic studies. PLoS One 2013; 8:e82072. [PMID: 24278472 PMCID: PMC3838385 DOI: 10.1371/journal.pone.0082072] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2013] [Accepted: 10/20/2013] [Indexed: 11/18/2022] Open
Abstract
G-protein coupled receptors (GPCRs) are integral membrane proteins involved in a wide variety of biological processes in eukaryotic cells, and are targeted by a large fraction of marketed drugs. GPCR kinases (GRKs) play important roles in feedback regulation of GPCRs, such as of β-adrenergic receptors in the heart, where GRK2 and GRK5 are the major isoforms expressed. Membrane targeting is essential for GRK function in cells. Whereas GRK2 is recruited to the membrane by heterotrimeric Gβγ subunits, the mechanism of membrane binding by GRK5 is not fully understood. It has been proposed that GRK5 is constitutively associated with membranes through elements located at its N-terminus, its C-terminus, or both. The membrane orientation of GRK5 is also a matter of speculation. In this work, we combined sum frequency generation (SFG) vibrational spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) to help determine the membrane orientation of GRK5 and a C-terminally truncated mutant (GRK51-531) on membrane lipid bilayers. It was found that GRK5 and GRK51-531 adopt a similar orientation on model cell membranes in the presence of PIP2 that is similar to that predicted for GRK2 in prior studies. Mutation of the N-terminal membrane binding site of GRK5 did not eliminate membrane binding, but prevented observation of this discrete orientation. The C-terminus of GRK5 does not have substantial impact on either membrane binding or orientation in this model system. Thus, the C-terminus of GRK5 may drive membrane binding in cells via interactions with other proteins at the plasma membrane or bind in an unstructured manner to negatively charged membranes.
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Affiliation(s)
- Pei Yang
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Alisa Glukhova
- Departments of Pharmacology and Biological Chemistry, Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
- Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - John J. G. Tesmer
- Departments of Pharmacology and Biological Chemistry, Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail: (ZC); (JJGT)
| | - Zhan Chen
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail: (ZC); (JJGT)
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Biochemical and Cellular Specificity of Peptide Inhibitors of G Protein-Coupled Receptor Kinases. Int J Pept Res Ther 2013; 20:1-12. [PMID: 25530741 DOI: 10.1007/s10989-013-9357-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Identifying novel allosteric inhibitors of G protein-coupled receptor kinases (GRKs) would be of considerable use in limiting both the extent of desensitization of GPCRs as well as downstream positive regulation through GRKs. Several peptides have previously been identified as inhibitors of specific GRKs, but to date there have been few comparisons of the selectivities of these materials on the seven GRKs, modifications to allow cell penetration, or off-target activities. The goal of this study was to determine if a panel of peptides mimicking domains on either GPCRs or GRKs would exhibit selective inhibition of GRKs 2, 5, 6 and 7 phosphorylation of rhodopsin. Peptides included sequences from GRK5; helices 3, 9, and 10 (α3, α9, and α10) in the RH domain, and the N-terminal peptide (N-Ter), as well as the intracellular loop 1 (iL1) of the β2-adrenergic receptor (β2AR), and the Gα transducin C-tail (TCT). While some selectivity for individual GRKs was found, overall selectivity was limited and often not reflective of structural predictions. Off-target effects were probed by determining peptide inhibition of adenylyl cyclase (AC) and PKA, and while peptides had no effect on AC activity, N-Ter, iL1, and α10 were potent inhibitors of PKA. To probe inhibition of GRK activity in intact cells, we synthesized TAT-tagged peptides, and found that TAT-α9-R169A and TAT-TCT inhibited isoproterenol-stimulated GRK phosphorylation of the β2AR; however, the TAT peptides also inhibited isoproterenol and forskolin stimulation of AC activity. Our findings demonstrate potent peptide inhibition of GRK activities in vitro, highlight the differences in the environments of biochemical and cell-based assays, and illustrate the care that must be exercised in interpreting results of either assay alone.
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Li H, Gan W, Lu L, Dong X, Han X, Hu C, Yang Z, Sun L, Bao W, Li P, He M, Sun L, Wang Y, Zhu J, Ning Q, Tang Y, Zhang R, Wen J, Wang D, Zhu X, Guo K, Zuo X, Guo X, Yang H, Zhou X, Zhang X, Qi L, Loos RJ, Hu FB, Wu T, Liu Y, Liu L, Yang Z, Hu R, Jia W, Ji L, Li Y, Lin X. A genome-wide association study identifies GRK5 and RASGRP1 as type 2 diabetes loci in Chinese Hans. Diabetes 2013; 62:291-8. [PMID: 22961080 PMCID: PMC3526061 DOI: 10.2337/db12-0454] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Substantial progress has been made in identification of type 2 diabetes (T2D) risk loci in the past few years, but our understanding of the genetic basis of T2D in ethnically diverse populations remains limited. We performed a genome-wide association study and a replication study in Chinese Hans comprising 8,569 T2D case subjects and 8,923 control subjects in total, from which 10 single nucleotide polymorphisms were selected for further follow-up in a de novo replication sample of 3,410 T2D case and 3,412 control subjects and an in silico replication sample of 6,952 T2D case and 11,865 control subjects. Besides confirming seven established T2D loci (CDKAL1, CDKN2A/B, KCNQ1, CDC123, GLIS3, HNF1B, and DUSP9) at genome-wide significance, we identified two novel T2D loci, including G-protein-coupled receptor kinase 5 (GRK5) (rs10886471: P = 7.1 × 10(-9)) and RASGRP1 (rs7403531: P = 3.9 × 10(-9)), of which the association signal at GRK5 seems to be specific to East Asians. In nondiabetic individuals, the T2D risk-increasing allele of RASGRP1-rs7403531 was also associated with higher HbA(1c) and lower homeostasis model assessment of β-cell function (P = 0.03 and 0.0209, respectively), whereas the T2D risk-increasing allele of GRK5-rs10886471 was also associated with higher fasting insulin (P = 0.0169) but not with fasting glucose. Our findings not only provide new insights into the pathophysiology of T2D, but may also shed light on the ethnic differences in T2D susceptibility.
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Affiliation(s)
- Huaixing Li
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Wei Gan
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Ling Lu
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Xiao Dong
- Key Laboratory of Systems Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Xueyao Han
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Beijing, China
| | - Cheng Hu
- Department of Endocrinology and Metabolism, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Zhen Yang
- Institute of Endocrinology and Diabetology, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Liang Sun
- Key Laboratory of Geriatrics, Beijing Hospital and Beijing Institute of Geriatrics, Ministry of Health, Beijing, China
| | - Wei Bao
- Department of Nutrition and Food Hygiene, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Ministry of Education Key Laboratory for Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Pengtao Li
- State Key Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China
| | - Meian He
- Ministry of Education Key Laboratory for Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
- Institute of Occupational Medicine, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Liangdan Sun
- Institute of Dermatology, No. 1 Hospital, Anhui Medical University, Hefei, Anhui, China
- Department of Dermatology, No. 1 Hospital, Anhui Medical University, Hefei, Anhui, China
- State Key Laboratory Incubation Base of Dermatology, Ministry of National Science and Technology, Hefei, Anhui, China
| | - Yiqin Wang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Jingwen Zhu
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Qianqian Ning
- Key Laboratory of Systems Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
| | - Yong Tang
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Beijing, China
| | - Rong Zhang
- Department of Endocrinology and Metabolism, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Jie Wen
- Institute of Endocrinology and Diabetology, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Di Wang
- Department of Nutrition and Food Hygiene, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Ministry of Education Key Laboratory for Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Xilin Zhu
- State Key Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China
| | - Kunquan Guo
- Ministry of Education Key Laboratory for Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
- Institute of Occupational Medicine, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Xianbo Zuo
- Institute of Dermatology, No. 1 Hospital, Anhui Medical University, Hefei, Anhui, China
- Department of Dermatology, No. 1 Hospital, Anhui Medical University, Hefei, Anhui, China
- State Key Laboratory Incubation Base of Dermatology, Ministry of National Science and Technology, Hefei, Anhui, China
| | - Xiaohui Guo
- Peking University First Hospital, Beijing, China
| | - Handong Yang
- Dongfeng Central Hospital, Dongfeng Motor Corporation and Hubei University of Medicine, Shiyan, Hubei, China
| | - Xianghai Zhou
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Beijing, China
| | | | | | - Xuejun Zhang
- Institute of Dermatology, No. 1 Hospital, Anhui Medical University, Hefei, Anhui, China
- Department of Dermatology, No. 1 Hospital, Anhui Medical University, Hefei, Anhui, China
- State Key Laboratory Incubation Base of Dermatology, Ministry of National Science and Technology, Hefei, Anhui, China
| | - Lu Qi
- Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts
| | - Ruth J.F. Loos
- Department of Preventive Medicine, Charles R. Bronfman Institute of Personalized Medicine, Mount Sinai School of Medicine, New York, New York
- Department of Preventive Medicine, Child Health and Development Institute, Mount Sinai School of Medicine, New York, New York
| | - Frank B. Hu
- Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts
| | - Tangchun Wu
- Ministry of Education Key Laboratory for Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
- Institute of Occupational Medicine, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Ying Liu
- State Key Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China
| | - Liegang Liu
- Department of Nutrition and Food Hygiene, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Ministry of Education Key Laboratory for Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Ze Yang
- Key Laboratory of Geriatrics, Beijing Hospital and Beijing Institute of Geriatrics, Ministry of Health, Beijing, China
| | - Renming Hu
- Institute of Endocrinology and Diabetology, Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, China
| | - Weiping Jia
- Department of Endocrinology and Metabolism, Shanghai Diabetes Institute, Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Clinical Center for Diabetes, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China
| | - Linong Ji
- Department of Endocrinology and Metabolism, Peking University People's Hospital, Beijing, China
- Corresponding author: Xu Lin, , Yixue Li, , or Linong Ji,
| | - Yixue Li
- Key Laboratory of Systems Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
- Shanghai Center for Bioinformation Technology, Shanghai, China
- College of Life Science and Biotechnology, Shanghai Jiaotong University, Shanghai, China
- Corresponding author: Xu Lin, , Yixue Li, , or Linong Ji,
| | - Xu Lin
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Graduate School of the Chinese Academy of Sciences, Shanghai, China
- Corresponding author: Xu Lin, , Yixue Li, , or Linong Ji,
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Raghuwanshi SK, Su Y, Singh V, Haynes K, Richmond A, Richardson RM. The chemokine receptors CXCR1 and CXCR2 couple to distinct G protein-coupled receptor kinases to mediate and regulate leukocyte functions. THE JOURNAL OF IMMUNOLOGY 2012; 189:2824-32. [PMID: 22869904 DOI: 10.4049/jimmunol.1201114] [Citation(s) in RCA: 102] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The chemokine receptors, CXCR1 and CXCR2, couple to Gαi to induce leukocyte recruitment and activation at sites of inflammation. Upon activation by CXCL8, these receptors become phosphorylated, desensitized, and internalized. In this study, we investigated the role of different G protein-coupled receptor kinases (GRKs) in CXCR1- and CXCR2-mediated cellular functions. To that end, short hairpin RNA was used to inhibit GRK2, 3, 5, and 6 in RBL-2H3 cells stably expressing CXCR1 or CXCR2, and CXCL8-mediated receptor activation and regulation were assessed. Inhibition of GRK2 and GRK6 increased CXCR1 and CXCR2 resistance to phosphorylation, desensitization, and internalization, respectively, and enhanced CXCL8-induced phosphoinositide hydrolysis and exocytosis in vitro. GRK2 depletion diminished CXCR1-induced ERK1/2 phosphorylation but had no effect on CXCR2-induced ERK1/2 phosphorylation. GRK6 depletion had no significant effect on CXCR1 function. However, peritoneal neutrophils from mice deficient in GRK6 (GRK6(-/-)) displayed an increase in CXCR2-mediated G protein activation but in vitro exhibited a decrease in chemotaxis, receptor desensitization, and internalization relative to wild-type (GRK6(+/+)) cells. In contrast, neutrophil recruitment in vivo in GRK6(-/-) mice was increased in response to delivery of CXCL1 through the air pouch model. In a wound-closure assay, GRK6(-/-) mice showed enhanced myeloperoxidase activity, suggesting enhanced neutrophil recruitment, and faster wound closure compared with GRK6(+/+) animals. Taken together, the results indicate that CXCR1 and CXCR2 couple to distinct GRK isoforms to mediate and regulate inflammatory responses. CXCR1 predominantly couples to GRK2, whereas CXCR2 interacts with GRK6 to negatively regulate receptor sensitization and trafficking, thus affecting cell signaling and angiogenesis.
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Affiliation(s)
- Sandeep K Raghuwanshi
- Department of Biology, Julius L. Chambers Biomedical/Biotechnology Research Institute, North Carolina Central University, Durham, NC 27707, USA
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15
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Kulahin N, Sanni SJ, Slaaby R, Nøhr J, Gammeltoft S, Hansen JL, Jorgensen R. A BRET assay for monitoring insulin receptor interactions and ligand pharmacology. J Recept Signal Transduct Res 2012; 32:57-64. [PMID: 22272819 DOI: 10.3109/10799893.2011.647351] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The insulin receptor (IR) belongs to the receptor tyrosine kinase super family and plays an important role in glucose homeostasis. The receptor interacts with several large docking proteins that mediate signaling from the receptor, including the insulin receptor substrate (IRS) family and Src homology-2-containing proteins (Src). Here, we applied the bioluminescence resonance energy transfer 2 (BRET2) technique to study the IR signaling pathways. The interaction between the IR and the substrates IRS1, IRS4 and Shc was examined in response to ligands with different signaling properties. The association between IR and the interacting partners could successfully be monitored when co-expressing green fluorescent protein 2 (GFP2) tagged substrates with Renilla reniformis luciferase 8 (Rluc8) tagged IR. Through additional optimization steps, we developed a stable and flexible BRET2 assay for monitoring the interactions between the IR and its substrates. Furthermore, the insulin analogue X10 was characterized in the BRET2 assay and was found to be 10 times more potent with respect to IRS1, IRS4 and Shc recruitment compared to human insulin. This study demonstrates that the BRET2 technique can be applied to study IR signaling pathways, and that this assay can be used as a platform for screening and characterization of IR ligands.
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Affiliation(s)
- Nikolaj Kulahin
- Incretin Biology, Hagedorn Research Institute, Gentofte, Denmark
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16
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Smith SB, Maixner D, Greenspan J, Dubner R, Fillingim R, Ohrbach R, Knott C, Slade G, Bair E, Gibson DG, Zaykin DV, Weir B, Maixner W, Diatchenko L. Potential genetic risk factors for chronic TMD: genetic associations from the OPPERA case control study. THE JOURNAL OF PAIN 2011; 12:T92-101. [PMID: 22074755 PMCID: PMC3268684 DOI: 10.1016/j.jpain.2011.08.005] [Citation(s) in RCA: 125] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Revised: 07/14/2011] [Indexed: 11/17/2022]
Abstract
UNLABELLED Genetic factors play a role in the etiology of persistent pain conditions, putatively by modulating underlying processes such as nociceptive sensitivity, psychological well-being, inflammation, and autonomic response. However, to date, only a few genes have been associated with temporomandibular disorders (TMD). This study evaluated 358 genes involved in pain processes, comparing allelic frequencies between 166 cases with chronic TMD and 1,442 controls enrolled in the OPPERA (Orofacial Pain: Prospective Evaluation and Risk Assessment) study cooperative agreement. To enhance statistical power, 182 TMD cases and 170 controls from a similar study were included in the analysis. Genotyping was performed using the Pain Research Panel, an Affymetrix gene chip representing 3,295 single nucleotide polymorphisms, including ancestry-informative markers that were used to adjust for population stratification. Adjusted associations between genetic markers and TMD case status were evaluated using logistic regression. The OPPERA findings provided evidence supporting previously reported associations between TMD and 2 genes: HTR2A and COMT. Other genes were revealed as potential new genetic risk factors for TMD, including NR3C1, CAMK4, CHRM2, IFRD1, and GRK5. While these findings need to be replicated in independent cohorts, the genes potentially represent important markers of risk for TMD, and they identify potential targets for therapeutic intervention. PERSPECTIVE Genetic risk factors for TMD pain were explored in the case-control component of the OPPERA cooperative agreement, a large population-based prospective cohort study. Over 350 candidate pain genes were assessed using a candidate gene panel, with several genes displaying preliminary evidence for association with TMD status.
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Affiliation(s)
- Shad B. Smith
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Dylan Maixner
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Joel Greenspan
- Department of Neural and Pain Sciences, and Brotman Facial Pain Center, University of Maryland Dental School, Baltimore, MD
| | - Ron Dubner
- Department of Neural and Pain Sciences, and Brotman Facial Pain Center, University of Maryland Dental School, Baltimore, MD
| | - Roger Fillingim
- Department of Community Dentistry and Behavioral Science, University of Florida, Gainesville, FL
| | - Richard Ohrbach
- Department of Oral Diagnostic Services, University at Buffalo, Buffalo, NY
| | | | - Gary Slade
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Dental Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Eric Bair
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Endodontics, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Dustin G. Gibson
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Dmitri V. Zaykin
- National Institute of Environmental Health Sciences, Research Triangle Park, NC
| | - Bruce Weir
- Department of Biostatistics, University of Washington, Seattle, WA
| | - William Maixner
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Endodontics, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Luda Diatchenko
- Center for Neurosensory Disorders, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Department of Endodontics, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Carolina Center for Genome Sciences at Chapel Hill, Chapel Hill, NC
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17
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Nagai H. Recent research and developmental strategy of anti-asthma drugs. Pharmacol Ther 2011; 133:70-8. [PMID: 21924291 DOI: 10.1016/j.pharmthera.2011.09.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 08/09/2011] [Indexed: 01/10/2023]
Abstract
Extensive research over the past decade has provided information about the pharmacotherapy of bronchial asthma (BA). Anti-asthma drugs are classified into two categories: relievers (for the relief of asthma attack symptoms) and controllers (for the prevention of asthma symptoms). This paper aims to review the recent advancements of anti-asthma drugs that are controller medicines. The controllers mainly act on immune and inflammatory responses in BA development. 1) Immunomodulators. Drugs that act on the immune response are classified into two categories: immunosuppressors and immunomodulators, including immunopotentiators. The immunomodulation of the Th1 and Th2 imbalance is the first strategy of the controller because allergic BA is thought to be caused by Th2-polarized immunity. Suplatast is a novel immunomodulator that can adjust the imbalance in the Th1/Th2 immune response and shows clear clinical efficacy against BA. The immunomodulator approach has shifted from a more theoretical and conceptual model to one supported by evidence of clinical efficacy.2) Anti-inflammatory agents. Corticosteroids,mast cell stabilizers and autacoid inhibitors are anti-inflammatory agents for BA. The clinical superiority of the combined therapy of inhaled corticosteroids and long-acting beta2 agonists is evident. This combined therapy shows a potent synergic anti-inflammatory effect compared to the effect by corticosteroids alone. Currently, the anti-inflammatory agents for BA under development are drugs affecting lipid mediators. The prostaglandin (PG) D2 antagonist, PGE2, EP3 agonist and PGI2 agonist are being considered in addition to well-established leukotriene and thromboxane A2 inhibitors. New development strategies and therapeutics for controllers are described in this review.
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Affiliation(s)
- Hiroichi Nagai
- Gifu Junior College of Health Science 2-92 higashi-uzura, Gifu 500-8281, Japan.
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18
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Gurevich EV, Tesmer JJG, Mushegian A, Gurevich VV. G protein-coupled receptor kinases: more than just kinases and not only for GPCRs. Pharmacol Ther 2011; 133:40-69. [PMID: 21903131 DOI: 10.1016/j.pharmthera.2011.08.001] [Citation(s) in RCA: 318] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 08/01/2011] [Indexed: 12/24/2022]
Abstract
G protein-coupled receptor (GPCR) kinases (GRKs) are best known for their role in homologous desensitization of GPCRs. GRKs phosphorylate activated receptors and promote high affinity binding of arrestins, which precludes G protein coupling. GRKs have a multidomain structure, with the kinase domain inserted into a loop of a regulator of G protein signaling homology domain. Unlike many other kinases, GRKs do not need to be phosphorylated in their activation loop to achieve an activated state. Instead, they are directly activated by docking with active GPCRs. In this manner they are able to selectively phosphorylate Ser/Thr residues on only the activated form of the receptor, unlike related kinases such as protein kinase A. GRKs also phosphorylate a variety of non-GPCR substrates and regulate several signaling pathways via direct interactions with other proteins in a phosphorylation-independent manner. Multiple GRK subtypes are present in virtually every animal cell, with the highest expression levels found in neurons, with their extensive and complex signal regulation. Insufficient or excessive GRK activity was implicated in a variety of human disorders, ranging from heart failure to depression to Parkinson's disease. As key regulators of GPCR-dependent and -independent signaling pathways, GRKs are emerging drug targets and promising molecular tools for therapy. Targeted modulation of expression and/or of activity of several GRK isoforms for therapeutic purposes was recently validated in cardiac disorders and Parkinson's disease.
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Affiliation(s)
- Eugenia V Gurevich
- Department of Pharmacology, Vanderbilt University, 2200 Pierce Avenue, Preston Research Building, Rm. 454, Nashville, TN 37232, United States.
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19
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James JR, McColl J, Oliveira MI, Dunne PD, Huang E, Jansson A, Nilsson P, Sleep DL, Gonçalves CM, Morgan SH, Felce JH, Mahen R, Fernandes RA, Carmo AM, Klenerman D, Davis SJ. The T cell receptor triggering apparatus is composed of monovalent or monomeric proteins. J Biol Chem 2011; 286:31993-2001. [PMID: 21757710 PMCID: PMC3173209 DOI: 10.1074/jbc.m111.219212] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Understanding the component stoichiometry of the T cell antigen receptor (TCR) triggering apparatus is essential for building realistic models of signal initiation. Recent studies suggesting that the TCR and other signaling-associated proteins are preclustered on resting T cells relied on measurements of the behavior of membrane proteins at interfaces with functionalized glass surfaces. Using fluorescence recovery after photobleaching, we show that, compared with the apical surface, the mobility of TCRs is significantly reduced at Jurkat T cell/glass interfaces, in a signaling-sensitive manner. Using two biophysical approaches that mitigate these effects, bioluminescence resonance energy transfer and two-color coincidence detection microscopy, we show that, within the uncertainty of the methods, the membrane components of the TCR triggering apparatus, i.e. the TCR complex, MHC molecules, CD4/Lck and CD45, are exclusively monovalent or monomeric in human T cell lines, implying that TCR triggering depends only on the kinetics of TCR/pMHC interactions. These analyses also showed that constraining proteins to two dimensions at the cell surface greatly enhances random interactions versus those between the membrane and the cytoplasm. Simulations of TCR-pMHC complex formation based on these findings suggest how unclustered TCR triggering-associated proteins might nevertheless be capable of generating complex signaling outputs via the differential recruitment of cytosolic effectors to the cell membrane.
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Affiliation(s)
- John R James
- Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom
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20
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Wang D, Yuen EY, Zhou Y, Yan Z, Xiang YK. Amyloid beta peptide-(1-42) induces internalization and degradation of beta2 adrenergic receptors in prefrontal cortical neurons. J Biol Chem 2011; 286:31852-63. [PMID: 21757762 DOI: 10.1074/jbc.m111.244335] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Emerging evidence indicates that amyloid β peptide (Aβ) initially induces subtle alterations in synaptic function in Alzheimer disease. We have recently shown that Aβ binds to β(2) adrenergic receptor (β(2)AR) and activates protein kinase A (PKA) signaling for glutamatergic regulation of synaptic activities. Here we show that in the cerebrums of mice expressing human familial mutant presenilin 1 and amyloid precursor protein genes, the levels of β(2)AR are drastically reduced. Moreover, Aβ induces internalization of transfected human β(2)AR in fibroblasts and endogenous β(2)AR in primary prefrontal cortical neurons. In fibroblasts, Aβ treatment also induces transportation of β(2)AR into lysosome, and prolonged Aβ treatment causes β(2)AR degradation. The Aβ-induced β(2)AR internalization requires the N terminus of the receptor containing the peptide binding sites and phosphorylation of β(2)AR by G protein-coupled receptor kinase, not by PKA. However, the G protein-coupled receptor kinase phosphorylation of β(2)AR and the receptor internalization are much slower than that induced by βAR agonist isoproterenol. The Aβ-induced β(2)AR internalization is also dependent on adaptor protein arrestin 3 and GTPase dynamin, but not arrestin 2. Functionally, pretreatment of primary prefrontal cortical neurons with Aβ induces desensitization of β(2)AR, which leads to attenuated response to subsequent stimulation with isoproterenol, including decreased cAMP levels, PKA activities, PKA phosphorylation of serine 845 on α-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) receptor subunit 1 (GluR1), and AMPA receptor-mediated miniature excitatory postsynaptic currents. This study indicates that Aβ induces β(2)AR internalization and degradation leading to impairment of adrenergic and glutamatergic activities.
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Affiliation(s)
- Dayong Wang
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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21
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Kulahin N, Grunnet LG, Lundh M, Christensen DP, Jorgensen R, Heding A, Billestrup N, Berezin V, Bock E, Mandrup-Poulsen T. Direct demonstration of NCAMcis-dimerization and inhibitory effect of palmitoylation using the BRET2technique. FEBS Lett 2010; 585:58-64. [DOI: 10.1016/j.febslet.2010.11.043] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2010] [Revised: 11/17/2010] [Accepted: 11/19/2010] [Indexed: 10/18/2022]
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22
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Importance of regions outside the cytoplasmic tail of G-protein-coupled receptors for phosphorylation and dephosphorylation. Biochem J 2010; 428:235-45. [PMID: 20345371 DOI: 10.1042/bj20100139] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Two GPCRs (G-protein-coupled receptors), TRHR (thyrotropin-releasing hormone receptor) and beta(2)AR (beta(2)-adrenergic receptor), are regulated in distinct manners. Following agonist binding, TRHR undergoes rapid phosphorylation attributable to GRKs (GPCR kinases); beta(2)AR is phosphorylated by both second messenger-activated PKA (protein kinase A) and GRKs with slower kinetics. TRHR co-internalizes with arrestin, whereas beta(2)AR recruits arrestin, but internalizes without it. Both receptors are dephosphorylated following agonist removal, but TRHR is dephosphorylated much more rapidly while it remains at the plasma membrane. We generated chimaeras swapping the C-terminal domains of these receptors to clarify the role of different receptor regions in phosphorylation, internalization and dephosphorylation. beta(2)AR with a TRHR cytoplasmic tail (beta(2)AR-TRHR) and TRHR with a beta(2)AR tail (TRHR-beta(2)AR) signalled to G-proteins normally. beta(2)AR-TRHR was phosphorylated well at the PKA site in the third intracellular loop, but poorly at GRK sites in the tail, whereas TRHR-beta(2)AR was phosphorylated strongly at GRK sites in the tail (Ser(355)/Ser(356) of the beta(2)AR). Both chimaeric receptors exhibited prolonged, but weak, association with arrestin at the plasma membrane, but high-affinity arrestin interactions and extensive co-internalization of receptor with arrestin required a phosphorylated TRHR tail. In contrast, swapping C-terminal domains did not change the rates of phosphorylation and dephosphorylation or the dependence of TRHR dephosphorylation on the length of agonist exposure. Thus the interactions of GPCRs with GRKs and phosphatases are determined not simply by the amino acid sequences of the substrates, but by regions outside the cytoplasmic tails.
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Vayttaden SJ, Friedman J, Tran TM, Rich TC, Dessauer CW, Clark RB. Quantitative modeling of GRK-mediated beta2AR regulation. PLoS Comput Biol 2010; 6:e1000647. [PMID: 20098494 PMCID: PMC2798957 DOI: 10.1371/journal.pcbi.1000647] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Accepted: 12/15/2009] [Indexed: 11/18/2022] Open
Abstract
We developed a unified model of the GRK-mediated β2 adrenergic receptor (β2AR) regulation that simultaneously accounts for six different biochemical measurements of the system obtained over a wide range of agonist concentrations. Using a single deterministic model we accounted for (1) GRK phosphorylation in response to various full and partial agonists; (2) dephosphorylation of the GRK site on the β2AR; (3) β2AR internalization; (4) recycling of the β2AR post isoproterenol treatment; (5) β2AR desensitization; and (6) β2AR resensitization. Simulations of our model show that plasma membrane dephosphorylation and recycling of the phosphorylated receptor are necessary to adequately account for the measured dephosphorylation kinetics. We further used the model to predict the consequences of (1) modifying rates such as GRK phosphorylation of the receptor, arrestin binding and dissociation from the receptor, and receptor dephosphorylation that should reflect effects of knockdowns and overexpressions of these components; and (2) varying concentration and frequency of agonist stimulation “seen” by the β2AR to better mimic hormonal, neurophysiological and pharmacological stimulations of the β2AR. Exploring the consequences of rapid pulsatile agonist stimulation, we found that although resensitization was rapid, the β2AR system retained the memory of the previous stimuli and desensitized faster and much more strongly in response to subsequent stimuli. The latent memory that we predict is due to slower membrane dephosphorylation, which allows for progressive accumulation of phosphorylated receptor on the surface. This primes the receptor for faster arrestin binding on subsequent agonist activation leading to a greater extent of desensitization. In summary, the model is unique in accounting for the behavior of the β2AR system across multiple types of biochemical measurements using a single set of experimentally constrained parameters. It also provides insight into how the signaling machinery can retain memory of prior stimulation long after near complete resensitization has been achieved. The β2 adrenergic receptor (β2AR) is involved in regulating many cellular processes such as smooth muscle relaxation in the airways and the vasculature. Drugs that activate the β2AR are used in treating asthma and chronic obstructive pulmonary disorder (COPD), and prolonged use of these drugs leads to the loss of their effects. Thus, a dynamic model of how the β2AR responds to different drugs is fundamental to their rational use. In this study a consensus model of G protein coupled receptor kinase (GRK)-mediated receptor regulation was formulated based on quantitative measures of six processes involved in β2AR regulation. This model was then used to simulate the consequences of manipulating key rates associated with the GRK-mediated β2AR regulation, leading to predictions which will provide a useful framework for further tests and elaborations of the model in basic and clinical research.
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Affiliation(s)
- Sharat J Vayttaden
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas, United States of America
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Baameur F, Morgan DH, Yao H, Tran TM, Hammitt RA, Sabui S, McMurray JS, Lichtarge O, Clark RB. Role for the regulator of G-protein signaling homology domain of G protein-coupled receptor kinases 5 and 6 in beta 2-adrenergic receptor and rhodopsin phosphorylation. Mol Pharmacol 2009; 77:405-15. [PMID: 20038610 DOI: 10.1124/mol.109.058115] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phosphorylation of G protein-coupled receptors (GPCRs) by GPCR kinases (GRKs) is a major mechanism of desensitization of these receptors. GPCR activation of GRKs involves an allosteric site on GRKs distinct from the catalytic site. Although recent studies have suggested an important role of the N- and C-termini and domains surrounding the kinase active site in allosteric activation, the nature of that site and the relative roles of the RH domain in particular remain unknown. Based on evolutionary trace analysis of both the RH and kinase domains of the GRK family, we identified an important cluster encompassing helices 3, 9, and 10 in the RH domain in addition to sites in the kinase domain. To define its function, a panel of GRK5 and -6 mutants was generated and screened by intact-cell assay of constitutive GRK phosphorylation of the beta(2)-adrenergic receptor (beta 2AR), in vitro GRK phosphorylation of light-activated rhodopsin, and basal catalytic activity measured by tubulin phosphorylation and autophosphorylation. A number of double mutations within helices 3, 9, and 10 reduced phosphorylation of the beta2AR and rhodopsin by 50 to 90% relative to wild-type GRK, as well as autophosphorylation and tubulin phosphorylation. Based on these results, helix 9 peptide mimetics were designed, and several were found to inhibit rhodopsin phosphorylation by GRK5 with an IC(50) of approximately 30 microM. In summary, our studies have uncovered previously unrecognized functionally important sites in the regulator of G-protein signaling homology domain of GRK5 and -6 and identified a peptide inhibitor with potential for specific blockade of GRK-mediated phosphorylation of receptors.
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Affiliation(s)
- Faiza Baameur
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Medical School, 6431 Fannin St, Houston, TX 77030, USA
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Huang CC, Yoshino-Koh K, Tesmer JJG. A surface of the kinase domain critical for the allosteric activation of G protein-coupled receptor kinases. J Biol Chem 2009; 284:17206-17215. [PMID: 19364770 PMCID: PMC2719358 DOI: 10.1074/jbc.m809544200] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 03/10/2009] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptor (GPCR) kinases (GRKs) phosphorylate activated GPCRs and initiate their desensitization. Many prior studies suggest that activated GPCRs dock to an allosteric site on the GRKs and thereby stimulate kinase activity. The extreme N-terminal region of GRKs is clearly involved in this process, but its role is not understood. Using our recent structure of bovine GRK1 as a guide, we generated mutants of solvent-exposed residues in the GRK1 kinase domain that are conserved among GRKs but not in the extended protein kinase A, G, and C family and evaluated their catalytic activity. Mutation of select residues in strands beta1 and beta3 of the kinase small lobe, alphaD of the kinase large lobe, and the protein kinase A, G, and C kinase C-tail greatly impaired receptor phosphorylation. The most dramatic effect was observed for mutation of an invariant arginine on the beta1-strand (approximately 1000-fold decrease in k(cat)/K(m)). These residues form a continuous surface that is uniquely available in GRKs for protein-protein interactions. Surprisingly, these mutants, as well as a 19-amino acid N-terminal truncation of GRK1, also show decreased catalytic efficiency for peptide substrates, although to a lesser extent than for receptor phosphorylation. Our data suggest that the N-terminal region and the newly identified surface interact and stabilize the closed, active conformation of the kinase domain. Receptor binding is proposed to promote this interaction, thereby enhancing GRK activity.
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Affiliation(s)
- Chih-Chin Huang
- From the Life Sciences Institute, Department of Pharmacology, University of Michigan, Ann Arbor, Michigan 48109-2216
| | - Kae Yoshino-Koh
- From the Life Sciences Institute, Department of Pharmacology, University of Michigan, Ann Arbor, Michigan 48109-2216
| | - John J G Tesmer
- From the Life Sciences Institute, Department of Pharmacology, University of Michigan, Ann Arbor, Michigan 48109-2216.
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A polymorphism of G-protein coupled receptor kinase5 alters agonist-promoted desensitization of beta2-adrenergic receptors. Pharmacogenet Genomics 2008; 18:729-32. [PMID: 18622265 DOI: 10.1097/fpc.0b013e32830967e9] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Beta-agonist treatment of asthma displays substantial interindividual variation, which has prompted polymorphism discovery and characterization of beta2-adrenergic (beta2AR) signaling genes. beta2AR function undergoes desensitization during persistent agonist exposure because of receptor phosphorylation by G-protein coupled receptor kinases (GRKs). GRK5 was found to be highly expressed in airway smooth muscle, the tissue target for beta-agonists. The coding region is polymorphic at codon 41, where Gln can be substituted by Leu (minor allele), but almost exclusively in those of African descent. In transfected cells, GRK5-Leu41 evoked a greater degree of agonist-promoted desensitization of adenylyl cyclase compared with GRK5-Gln41. Consistent with this functional effect, agonist-promoted beta2AR phosphorylation was greater in cells expressing GRK5-Leu41, as was the rate of agonist-promoted receptor internalization. In studies with mutated beta2AR lacking PKA-phosphorylation sites, this phenotype was confirmed as being GRK-specific. So, GRK5-Leu41 represents a gain-of-function polymorphism that evokes enhanced loss-of-function of beta2AR during persistent agonist exposure, and thus may contribute to beta-agonist variability in asthma treatment of African-Americans.
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Xin W, Tran TM, Richter W, Clark RB, Rich TC. Roles of GRK and PDE4 activities in the regulation of beta2 adrenergic signaling. ACTA ACUST UNITED AC 2008; 131:349-64. [PMID: 18347080 PMCID: PMC2279169 DOI: 10.1085/jgp.200709881] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
An important focus in cell biology is understanding how different feedback mechanisms regulate G protein-coupled receptor systems. Toward this end we investigated the regulation of endogenous beta(2) adrenergic receptors (beta2ARs) and phosphodiesterases (PDEs) by measuring cAMP signals in single HEK-293 cells. We monitored cAMP signals using genetically encoded cyclic nucleotide-gated (CNG) channels. This high resolution approach allowed us to make several observations. (a) Exposure of cells to 1 muM isoproterenol triggered transient increases in cAMP levels near the plasma membrane. Pretreatment of cells with 10 muM rolipram, a PDE4 inhibitor, prevented the decline in the isoproterenol-induced cAMP signals. (b) 1 muM isoproterenol triggered a sustained, twofold increase in phosphodiesterase type 4 (PDE4) activity. (c) The decline in isoproterenol-dependent cAMP levels was not significantly altered by including 20 nM PKI, a PKA inhibitor, or 3 muM 59-74E, a GRK inhibitor, in the pipette solution; however, the decline in the cAMP levels was prevented when both PKI and 59-74E were included in the pipette solution. (d) After an initial 5-min stimulation with isoproterenol and a 5-min washout, little or no recovery of the signal was observed during a second 5-min stimulation with isoproterenol. (e) The amplitude of the signal in response to the second isoproterenol stimulation was not altered when PKI was included in the pipette solution, but was significantly increased when 59-74E was included. Taken together, these data indicate that either GRK-mediated desensitization of beta2ARs or PKA-mediated stimulation of PDE4 activity is sufficient to cause declines in cAMP signals. In addition, the data indicate that GRK-mediated desensitization is primarily responsible for a sustained suppression of beta2AR signaling. To better understand the interplay between receptor desensitization and PDE4 activity in controlling cAMP signals, we developed a mathematical model of this system. Simulations of cAMP signals using this model are consistent with the experimental data and demonstrate the importance of receptor levels, receptor desensitization, basal adenylyl cyclase activity, and regulation of PDE activity in controlling cAMP signals, and hence, on the overall sensitivity of the system.
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Affiliation(s)
- Wenkuan Xin
- Department of Pharmacology, College of Medicine and Center for Lung Biology, University of South Alabama, Mobile, AL 36688, USA
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