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Maaliki D, Jaffa AA, Nasser S, Sahebkar A, Eid AH. Adrenoceptor Desensitization: Current Understanding of Mechanisms. Pharmacol Rev 2024; 76:358-387. [PMID: 38697858 DOI: 10.1124/pharmrev.123.000831] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 01/15/2024] [Accepted: 01/18/2024] [Indexed: 05/05/2024] Open
Abstract
G-protein coupled receptors (GPCRs) transduce a wide range of extracellular signals. They are key players in the majority of biologic functions including vision, olfaction, chemotaxis, and immunity. However, as essential as most of them are to body function and homeostasis, overactivation of GPCRs has been implicated in many pathologic diseases such as cancer, asthma, and heart failure (HF). Therefore, an important feature of G protein signaling systems is the ability to control GPCR responsiveness, and one key process to control overstimulation involves initiating receptor desensitization. A number of steps are appreciated in the desensitization process, including cell surface receptor phosphorylation, internalization, and downregulation. Rapid or short-term desensitization occurs within minutes and involves receptor phosphorylation via the action of intracellular protein kinases, the binding of β-arrestins, and the consequent uncoupling of GPCRs from their cognate heterotrimeric G proteins. On the other hand, long-term desensitization occurs over hours to days and involves receptor downregulation or a decrease in cell surface receptor protein level. Of the proteins involved in this biologic phenomenon, β-arrestins play a particularly significant role in both short- and long-term desensitization mechanisms. In addition, β-arrestins are involved in the phenomenon of biased agonism, where the biased ligand preferentially activates one of several downstream signaling pathways, leading to altered cellular responses. In this context, this review discusses the different patterns of desensitization of the α 1-, α 2- and the β adrenoceptors and highlights the role of β-arrestins in regulating physiologic responsiveness through desensitization and biased agonism. SIGNIFICANCE STATEMENT: A sophisticated network of proteins orchestrates the molecular regulation of GPCR activity. Adrenoceptors are GPCRs that play vast roles in many physiological processes. Without tightly controlled desensitization of these receptors, homeostatic imbalance may ensue, thus precipitating various diseases. Here, we critically appraise the mechanisms implicated in adrenoceptor desensitization. A better understanding of these mechanisms helps identify new druggable targets within the GPCR desensitization machinery and opens exciting therapeutic fronts in the treatment of several pathologies.
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Affiliation(s)
- Dina Maaliki
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Aneese A Jaffa
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Suzanne Nasser
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Amirhossein Sahebkar
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
| | - Ali H Eid
- Department of Pharmacology and Toxicology, American University of Beirut, Beirut, Lebanon (D.M.); School of Medicine, University of South Carolina, Columbia, South Carolina (A.A.J.); Keele University, Staffordshire, United Kingdom (S.N.); Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran (A.S.); and Department of Basic Medical Sciences, College of Medicine, QU Health, Qatar University, Doha, Qatar (A.H.E.)
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Bahouth SW, Nooh MM, Mancarella S. Involvement of SAP97 anchored multiprotein complexes in regulating cardiorenal signaling and trafficking networks. Biochem Pharmacol 2023; 208:115406. [PMID: 36596415 DOI: 10.1016/j.bcp.2022.115406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 12/26/2022] [Accepted: 12/28/2022] [Indexed: 01/02/2023]
Abstract
SAP97 is a member of the MAGUK family of proteins, but unlike other MAGUK proteins that are selectively expressed in the CNS, SAP97 is also expressed in peripheral organs, like the heart and kidneys. SAP97 has several protein binding cassettes, and this review will describe their involvement in creating SAP97-anchored multiprotein networks. SAP97-anchored networks localized at the inner leaflet of the cell membrane play a major role in trafficking and targeting of membrane G protein-coupled receptors (GPCR), channels, and structural proteins. SAP97 plays a major role in compartmentalizing voltage gated sodium and potassium channels to specific cellular compartments of heart cells. SAP97 undergoes extensive alternative splicing. These splice variants give rise to different SAP97 isoforms that alter its cellular localization, networking, signaling and trafficking effects. Regarding GPCR, SAP97 binds to the β1-adrenergic receptor and recruits AKAP5/PKA and PDE4D8 to create a multiprotein complex that regulates trafficking and signaling of cardiac β1-AR. In the kidneys, SAP97 anchored networks played a role in trafficking of aquaporin-2 water channels. Cardiac specific ablation of SAP97 (SAP97-cKO) resulted in cardiac hypertrophy and failure in aging mice. Similarly, instituting transverse aortic constriction (TAC) in young SAP97 c-KO mice exacerbated TAC-induced cardiac remodeling and dysfunction. These findings highlight a critical role for SAP97 in the pathophysiology of a number of cardiac and renal diseases, suggesting that SAP97 is a relevant target for drug discovery.
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Affiliation(s)
- Suleiman W Bahouth
- Department of Pharmacology, Addiction Science and Toxicology, The University of Tennessee-Health Sciences Center, Memphis, TN, United States.
| | - Mohammed M Nooh
- Department of Biochemistry, Faculty of Pharmacy Cairo University, Cairo, Egypt and Biochemistry Department, Faculty of Pharmacy, October 6 University, Giza, Egypt
| | - Salvatore Mancarella
- Department of Physiology, The University of Tennessee-Health Sciences Center, Memphis, TN, United States
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3
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Gonçalves Antunes M, Sanial M, Contremoulins V, Carvalho S, Plessis A, Becam I. High hedgehog signaling is transduced by a multikinase-dependent switch controlling the apico-basal distribution of the GPCR smoothened. eLife 2022; 11:79843. [PMID: 36083801 PMCID: PMC9462849 DOI: 10.7554/elife.79843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 08/22/2022] [Indexed: 11/13/2022] Open
Abstract
The oncogenic G-protein-coupled receptor (GPCR) Smoothened (SMO) is a key transducer of the hedgehog (HH) morphogen, which plays an essential role in the patterning of epithelial structures. Here, we examine how HH controls SMO subcellular localization and activity in a polarized epithelium using the Drosophila wing imaginal disc as a model. We provide evidence that HH promotes the stabilization of SMO by switching its fate after endocytosis toward recycling. This effect involves the sequential and additive action of protein kinase A, casein kinase I, and the Fused (FU) kinase. Moreover, in the presence of very high levels of HH, the second effect of FU leads to the local enrichment of SMO in the most basal domain of the cell membrane. Together, these results link the morphogenetic effects of HH to the apico-basal distribution of SMO and provide a novel mechanism for the regulation of a GPCR.
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Affiliation(s)
| | | | | | | | - Anne Plessis
- Université Paris Cité, CNRS, Institut Jacques Monod
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Zhai R, Snyder J, Montgomery S, Sato PY. Double life: How GRK2 and β-arrestin signaling participate in diseases. Cell Signal 2022; 94:110333. [PMID: 35430346 PMCID: PMC9929935 DOI: 10.1016/j.cellsig.2022.110333] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 04/09/2022] [Accepted: 04/11/2022] [Indexed: 11/03/2022]
Abstract
G-protein coupled receptor (GPCR) kinases (GRKs) and β-arrestins play key roles in GPCR and non-GPCR cellular responses. In fact, GRKs and arrestins are involved in a plethora of pathways vital for physiological maintenance of inter- and intracellular communication. Here we review decades of research literature spanning from the discovery, identification of key structural elements, and findings supporting the diverse roles of these proteins in GPCR-mediated pathways. We then describe how GRK2 and β-arrestins partake in non-GPCR signaling and briefly summarize their involvement in various pathologies. We conclude by presenting gaps in knowledge and our prospective on the promising pharmacological potential in targeting these proteins and/or downstream signaling. Future research is warranted and paramount for untangling these novel and promising roles for GRK2 and arrestins in metabolism and disease progression.
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Affiliation(s)
| | | | | | - Priscila Y. Sato
- Corresponding author at: Drexel University College of Medicine, Department of Pharmacology and Physiology, 245 N 15th Street, NCB 8152, Philadelphia, PA 19102, USA. (P.Y. Sato)
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Nooh MM, Mancarella S, Bahouth SW. Novel Paradigms Governing β1-Adrenergic Receptor Trafficking in Primary Adult Rat Cardiac Myocytes. Mol Pharmacol 2018; 94:862-875. [PMID: 29848777 DOI: 10.1124/mol.118.112045] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Accepted: 05/23/2018] [Indexed: 12/11/2022] Open
Abstract
The β1-adrenergic receptor (β1-AR) is a major cardiac G protein-coupled receptor, which mediates cardiac actions of catecholamines and is involved in genesis and treatment of numerous cardiovascular disorders. In mammalian cells, catecholamines induce the internalization of the β1-AR into endosomes and their removal promotes the recycling of the endosomal β1-AR back to the plasma membrane; however, whether these redistributive processes occur in terminally differentiated cells is unknown. Compartmentalization of the β1-AR in response to β-agonists and antagonists was determined by confocal microscopy in primary adult rat ventricular myocytes (ARVMs), which are terminally differentiated myocytes with unique structures such as transverse tubules (T-tubules) and contractile sarcomeres. In unstimulated ARVMs, the fluorescently labeled β1-AR was expressed on the external membrane (the sarcolemma) of cardiomyocytes. Exposing ARVMs to isoproterenol redistributed surface β1-ARs into small (∼225-250 nm) regularly spaced internal punctate structures that overlapped with puncta stained by Di-8 ANEPPS, a membrane-impermeant T-tubule-specific dye. Replacing the β-agonist with the β-blocker alprenolol, induced the translocation of the wild-type β1-AR from these punctate structures back to the plasma membrane. This step was dependent on two barcodes, namely, the type-1 PDZ binding motif and serine at position 312 of the β1-AR, which is phosphorylated by a pool of cAMP-dependent protein kinases anchored at the type-1 PDZ of the β1-AR. These data show that redistribution of the β1-AR in ARVMs from internal structures back to the plasma membrane was mediated by a novel sorting mechanism, which might explain unique aspects of cardiac β1-AR signaling under normal or pathologic conditions.
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Affiliation(s)
- Mohammed M Nooh
- Departments of Pharmacology (M.M.N., S.W.B.) and Physiology (S.M.), The University of Tennessee Health Sciences Center, Memphis, Tennessee; and Department of Biochemistry, Faculty of Pharmacy Cairo University, Cairo, Egypt (M.M.N.)
| | - Salvatore Mancarella
- Departments of Pharmacology (M.M.N., S.W.B.) and Physiology (S.M.), The University of Tennessee Health Sciences Center, Memphis, Tennessee; and Department of Biochemistry, Faculty of Pharmacy Cairo University, Cairo, Egypt (M.M.N.)
| | - Suleiman W Bahouth
- Departments of Pharmacology (M.M.N., S.W.B.) and Physiology (S.M.), The University of Tennessee Health Sciences Center, Memphis, Tennessee; and Department of Biochemistry, Faculty of Pharmacy Cairo University, Cairo, Egypt (M.M.N.)
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Gupta MK, Mohan ML, Naga Prasad SV. G Protein-Coupled Receptor Resensitization Paradigms. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2018; 339:63-91. [PMID: 29776605 DOI: 10.1016/bs.ircmb.2018.03.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cellular responses to extracellular milieu/environment are driven by cell surface receptors that transmit the signal into the cells resulting in a synchronized and measured response. The ability to provide such exquisite responses to changes in external environment is mediated by the tight and yet, deliberate regulation of cell surface receptor function. In this regard, the seven transmembrane G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors that regulate responses like cardiac contractility, vision, and olfaction including platelet activation. GPCRs regulate these plethora of events through GPCR-activation, -desensitization, and -resensitization. External stimuli (ligands or agonists) activate GPCR initiating downstream signals. The activated GPCR undergoes inactivation or desensitization by phosphorylation and binding of β-arrestin resulting in diminution of downstream signals. The desensitized GPCRs are internalized into endosomes, wherein they undergo dephosphorylation or resensitization by protein phosphatase to be recycled back to the cell membrane as naïve GPCR ready for the next wave of stimuli. Despite the knowledge that activation, desensitization, and resensitization shoulder an equal role in maintaining GPCR function, major advances have been made in understanding activation and desensitization compared to resensitization. However, increasing evidence shows that resensitization is exquisitely regulated process, thereby contributing to the dynamic regulation of GPCR function. In recognition of these observations, in this chapter we discuss the key advances on the mechanistic underpinning that drive and regulate GPCR function with a focus on resensitization.
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Affiliation(s)
- Manveen K Gupta
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Maradumane L Mohan
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
| | - Sathyamangla V Naga Prasad
- Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States.
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Bahouth SW, Nooh MM. Barcoding of GPCR trafficking and signaling through the various trafficking roadmaps by compartmentalized signaling networks. Cell Signal 2017; 36:42-55. [PMID: 28449947 PMCID: PMC5512170 DOI: 10.1016/j.cellsig.2017.04.015] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 04/21/2017] [Accepted: 04/22/2017] [Indexed: 01/08/2023]
Abstract
Proper signaling by G protein coupled receptors (GPCR) is dependent on the specific repertoire of transducing, enzymatic and regulatory kinases and phosphatases that shape its signaling output. Activation and signaling of the GPCR through its cognate G protein is impacted by G protein-coupled receptor kinase (GRK)-imprinted "barcodes" that recruit β-arrestins to regulate subsequent desensitization, biased signaling and endocytosis of the GPCR. The outcome of agonist-internalized GPCR in endosomes is also regulated by sequence motifs or "barcodes" within the GPCR that mediate its recycling to the plasma membrane or retention and eventual degradation as well as its subsequent signaling in endosomes. Given the vast number of diverse sequences in GPCR, several trafficking mechanisms for endosomal GPCR have been described. The majority of recycling GPCR, are sorted out of endosomes in a "sequence-dependent pathway" anchored around a type-1 PDZ-binding module found in their C-tails. For a subset of these GPCR, a second "barcode" imprinted onto specific GPCR serine/threonine residues by compartmentalized kinase networks was required for their efficient recycling through the "sequence-dependent pathway". Mutating the serine/threonine residues involved, produced dramatic effects on GPCR trafficking, indicating that they played a major role in setting the trafficking itinerary of these GPCR. While endosomal SNX27, retromer/WASH complexes and actin were required for efficient sorting and budding of all these GPCR, additional proteins were required for GPCR sorting via the second "barcode". Here we will review recent developments in GPCR trafficking in general and the human β1-adrenergic receptor in particular across the various trafficking roadmaps. In addition, we will discuss the role of GPCR trafficking in regulating endosomal GPCR signaling, which promote biochemical and physiological effects that are distinct from those generated by the GPCR signal transduction pathway in membranes.
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Affiliation(s)
- Suleiman W Bahouth
- Department of Pharmacology, The University of Tennessee Health Sciences Center, 71 S. Manassas, Memphis, TN 38103, USA.
| | - Mohammed M Nooh
- Department of Biochemistry, Faculty of Pharmacy Cairo University, Kasr El-Aini St., Cairo 11562, Egypt
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Hayashi K, Gotou M, Matsui T, Imahashi K, Nishimoto T, Kobayashi H. Identification of phosphorylation sites on β1-adrenergic receptor in the mouse heart. Biochem Biophys Res Commun 2017; 488:362-367. [PMID: 28501616 DOI: 10.1016/j.bbrc.2017.05.054] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 05/08/2017] [Indexed: 11/17/2022]
Abstract
β1-adrenergic receptor (Adrb1) belongs to the superfamily of G-protein-coupled receptors (GPCRs) and plays a critical role in the regulation of heart rate and myocardial contraction force. GPCRs are phosphorylated at multiple sites to regulate distinct signal transduction pathways in different tissues. However, little is known about the location and function of distinct phosphorylation sites of Adrb1 in vivo. To clarify the mechanisms underlying functional regulation associated with Adrb1 phosphorylation in vivo, we aimed to identify Adrb1 phosphorylation sites in the mouse heart using phosphoproteomics techniques with nano-flow liquid chromatography/tandem mass spectrometry (LC-MS/MS). We revealed the phosphorylation residues of Adrb1 to be Ser274 and Ser280 in the third intracellular loop and Ser412, Ser417, Ser450, Ser451, and Ser462 at the C-terminus. We also found that phosphorylation at Ser274, Ser280, and Ser462 was enhanced in response to stimulation with an Adrb1 agonist. This is the first study to identify Adrb1 phosphorylation sites in vivo. These findings will provide novel insights into the regulatory mechanisms mediated by Adrb1 phosphorylation.
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Affiliation(s)
- Kozo Hayashi
- Integrated Technology Research Laboratories, Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Japan.
| | - Masamitsu Gotou
- Integrated Technology Research Laboratories, Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Japan.
| | - Toshikatsu Matsui
- Cardiovascular and Metabolic Drug Discovery Unit, Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Japan.
| | - Kenichi Imahashi
- Cardiovascular and Metabolic Drug Discovery Unit, Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Japan.
| | - Tomoyuki Nishimoto
- Cardiovascular and Metabolic Drug Discovery Unit, Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Japan.
| | - Hiroyuki Kobayashi
- Integrated Technology Research Laboratories, Pharmaceutical Research Division, Takeda Pharmaceutical Company Limited, Fujisawa, Japan.
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Hinz L, Ahles A, Ruprecht B, Küster B, Engelhardt S. Two serines in the distal C-terminus of the human ß1-adrenoceptor determine ß-arrestin2 recruitment. PLoS One 2017; 12:e0176450. [PMID: 28472170 PMCID: PMC5417508 DOI: 10.1371/journal.pone.0176450] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 04/11/2017] [Indexed: 01/14/2023] Open
Abstract
G protein-coupled receptors (GPCRs) undergo phosphorylation at several intracellular residues by G protein-coupled receptor kinases. The resulting phosphorylation pattern triggers arrestin recruitment and receptor desensitization. The exact sites of phosphorylation and their function remained largely unknown for the human β1-adrenoceptor (ADRB1), a key GPCR in adrenergic signal transduction and the target of widely used drugs such as β-blockers. The present study aimed to identify the intracellular phosphorylation sites in the ADRB1 and to delineate their function. The human ADRB1 was expressed in HEK293 cells and its phosphorylation pattern was determined by mass spectrometric analysis before and after stimulation with a receptor agonist. We identified a total of eight phosphorylation sites in the receptor's third intracellular loop and C-terminus. Analyzing the functional relevance of individual sites using phosphosite-deficient receptor mutants we found phosphorylation of the ADRB1 at Ser461/Ser462 in the distal part of the C-terminus to determine β-arrestin2 recruitment and receptor internalization. Our data reveal the phosphorylation pattern of the human ADRB1 and the site that mediates recruitment of β-arrestin2.
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Affiliation(s)
- Laura Hinz
- Institute of Pharmacology and Toxicology, Technical University of Munich, Munich, Germany
| | - Andrea Ahles
- Institute of Pharmacology and Toxicology, Technical University of Munich, Munich, Germany
- * E-mail: (AA); (SE)
| | - Benjamin Ruprecht
- Chair of Proteomics and Bioanalytics, Technical University of Munich, Freising, Germany
- Center for Protein Science Munich (CIPSM), Freising, Germany
| | - Bernhard Küster
- Chair of Proteomics and Bioanalytics, Technical University of Munich, Freising, Germany
- Center for Protein Science Munich (CIPSM), Freising, Germany
- German Cancer Consortium (DKTK), Heidelberg, Germany
- German Cancer Research Center (DKFZ), Heidelberg, Germany
- Bavarian Biomolecular Mass Spectrometry Center, Technical University of Munich, Freising, Germany
| | - Stefan Engelhardt
- Institute of Pharmacology and Toxicology, Technical University of Munich, Munich, Germany
- German Center for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Munich, Germany
- * E-mail: (AA); (SE)
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Two barcodes encoded by the type-1 PDZ and by phospho-Ser312 regulate retromer/WASH-mediated sorting of the ß1-adrenergic receptor from endosomes to the plasma membrane. Cell Signal 2017; 29:192-208. [DOI: 10.1016/j.cellsig.2016.10.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 10/31/2016] [Accepted: 10/31/2016] [Indexed: 01/23/2023]
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Shin SY, Nguyen LK. Dissecting Cell-Fate Determination Through Integrated Mathematical Modeling of the ERK/MAPK Signaling Pathway. Methods Mol Biol 2017; 1487:409-432. [PMID: 27924583 DOI: 10.1007/978-1-4939-6424-6_29] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The past three decades have witnessed an enormous progress in the elucidation of the ERK/MAPK signaling pathway and its involvement in various cellular processes. Because of its importance and complex wiring, the ERK pathway has been an intensive subject for mathematical modeling, which facilitates the unraveling of key dynamic properties and behaviors of the pathway. Recently, however, it became evident that the pathway does not act in isolation but closely interacts with many other pathways to coordinate various cellular outcomes under different pathophysiological contexts. This has led to an increasing number of integrated, large-scale models that link the ERK pathway to other functionally important pathways. In this chapter, we first discuss the essential steps in model development and notable models of the ERK pathway. We then use three examples of integrated, multipathway models to investigate how crosstalk of ERK signaling with other pathways regulates cell-fate decision-making in various physiological and disease contexts. Specifically, we focus on ERK interactions with the phosphoinositide-3 kinase (PI3K), c-Jun N-terminal kinase (JNK), and β-adrenergic receptor (β-AR) signaling pathways. We conclude that integrated modeling in combination with wet-lab experimentation have been and will be instrumental in gaining an in-depth understanding of ERK signaling in multiple biological contexts.
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Affiliation(s)
- Sung-Young Shin
- Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, VIC, 3800, Australia.,Biomedicine Discovery Institute, Monash University, Clayton, VIC, 3800, Australia
| | - Lan K Nguyen
- Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton, VIC, 3800, Australia. .,Biomedicine Discovery Institute, Monash University, Clayton, VIC, 3800, Australia.
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Nooh MM, Mancarella S, Bahouth SW. Identification of novel transplantable GPCR recycling motif for drug discovery. Biochem Pharmacol 2016; 120:22-32. [PMID: 27645110 DOI: 10.1016/j.bcp.2016.09.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 09/14/2016] [Indexed: 12/12/2022]
Abstract
β1-Adrenergic receptor (β1-AR) agonists and antagonists are widely used in the treatment of major cardiovascular diseases such as heart failure and hypertension. The β1-AR like other G protein-coupled receptors (GPCRs) are endocytosed in response to intense agonist activation. Recycling of the agonist-internalized β1-AR is dependent on its carboxy-terminal type-1 PSD-95/DLG/ZO1 (PDZ) and on phospho-serine312 in the third intracellular loop of the β1-AR. Progressive elongation of the β1-AR at its C-tail inactivated the PDZ-biding domain and inhibited the recycling of the β1-AR. However, fusing a twenty amino acid peptide derived from the multiple cloning region of the mammalian expression vector pCDNA3 to the C-tail of the β1-AR (β1-AR[+20]) produced a chimeric β1-AR that recycled rapidly and efficiently. The β1-AR[+20] recycled in a type-1 PDZ and phospho-Ser312-independent manner, indicating that this peptide provided a general GPCR recycling signal. Fusing the enhanced yellow fluorescent protein (EYFP) down-stream of β1-AR[+20] generated a β1-AR-EYFP chimera that was expressed on the membrane and recycled efficiently after agonist-induced internalization. This construct trafficked in a PDZ-SNX27/retromer-independent manner. We also fused EYFP to the N-terminus of the β1-AR to created EYFP-WT β1-AR. This construct recycled in PDZ and SNX27/retromer dependent manner. These β1-AR-EYFP constructs would be useful for high throughput screening (HTS) programs to identify new entities that would interfere with the recycling of agonist internalized GPCR that traffic in PDZ-dependent vs. PDZ-independent roadmaps.
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Affiliation(s)
- Mohammed M Nooh
- Department of Pharmacology, The University of Tennessee Health Sciences Center, 71 S. Manassas, Memphis, TN 38103, USA; Department of Biochemistry, Faculty of Pharmacy Cairo University, Kasr El-Aini St., Cairo 11562, Egypt
| | - Salvatore Mancarella
- Department of Physiology, The University of Tennessee Health Sciences Center, 71 S. Manassas, Memphis, TN 38103, USA
| | - Suleiman W Bahouth
- Department of Pharmacology, The University of Tennessee Health Sciences Center, 71 S. Manassas, Memphis, TN 38103, USA.
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Prostaglandin E2-stimulated prostanoid EP4 receptors induce prolonged de novo prostaglandin E2 synthesis through biphasic phosphorylation of extracellular signal-regulated kinases mediated by activation of protein kinase A in HCA-7 human colon cancer cells. Eur J Pharmacol 2015; 768:149-59. [PMID: 26518053 DOI: 10.1016/j.ejphar.2015.10.044] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 10/21/2015] [Accepted: 10/26/2015] [Indexed: 02/03/2023]
Abstract
Approximately two decades have passed since E-type prostanoid 4 (EP4) receptors were cloned, and the signaling pathways mediated by these receptors have since been implicated in cancer development through the alliance of Gαi-protein/phosphatidylinositol 3-kinase (PI3K)/extracellular signal-regulated kinases (ERKs) activation. Although prostanoid EP4 receptors were initially identified as Gαs-coupled receptors, the specific/distinctive role(s) of prostanoid EP4 receptor-induced cAMP/protein kinase A (PKA) pathways in cancer development have not yet been elucidated in detail. We previously reported using HCA-7 human colon cancer cells that prostaglandin E2 (PGE2)-stimulated prostanoid EP4 receptors induced cyclooxygenase-2 (COX-2) as an initiating event in development of colon cancer. Moreover, this induction of COX-2 was mediated by transactivation of epidermal growth factor (EGF) receptors. However, direct activation of EGF receptors by EGF also induced similar amounts of COX-2 in this cell line. Thus, the emergence of unique role(s) for prostanoid EP4 receptors is expected by clarifying the different signaling mechanisms between PGE2-stimulated prostanoid EP4 receptors and EGF-stimulated EGF receptors to induce COX-2 and produce PGE2. We here demonstrated that prostanoid EP4 receptor activation by PGE2 in HCA-7 cells led to PKA-dependent re-activation of ERKs, which resulted in prolonged de novo synthesis of PGE2. Although EGF-stimulated EGF receptors in cells also induced COX-2 and the de novo synthesis of PGE2, the activation of this pathway was transient and not mediated by PKA. Therefore, the novel mechanism underlying prolonged de novo synthesis of PGE2 has provided an insight into the importance of prostanoid EP4 receptor-mediated Gαs-protein/cAMP/PKA pathway in development of colon cancer.
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Gilbert CE, Zuckerman DM, Currier PL, Machamer CE. Three basic residues of intracellular loop 3 of the beta-1 adrenergic receptor are required for golgin-160-dependent trafficking. Int J Mol Sci 2014; 15:2929-45. [PMID: 24566136 PMCID: PMC3958891 DOI: 10.3390/ijms15022929] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 01/24/2014] [Accepted: 02/12/2014] [Indexed: 12/14/2022] Open
Abstract
Golgin-160 is a member of the golgin family of proteins, which have been implicated in the maintenance of Golgi structure and in vesicle tethering. Golgin-160 is atypical; it promotes post-Golgi trafficking of specific cargo proteins, including the β-1 adrenergic receptor (β1AR), a G protein-coupled receptor. Here we show that golgin-160 binds directly to the third intracellular loop of β1AR and that this binding depends on three basic residues in this loop. Mutation of the basic residues does not affect trafficking of β1AR from the endoplasmic reticulum through the Golgi complex, but results in reduced steady-state levels at the plasma membrane. We hypothesize that golgin-160 promotes incorporation of β1AR into specific transport carriers at the trans-Golgi network to ensure efficient delivery to the cell surface. These results add to our understanding of the biogenesis of β1AR, and suggest a novel point of regulation for its delivery to the plasma membrane.
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Affiliation(s)
- Catherine E Gilbert
- Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA.
| | - David M Zuckerman
- Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe St., Baltimore, MD 21205, USA.
| | - Pamela L Currier
- Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA.
| | - Carolyn E Machamer
- Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA.
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15
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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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Li X, Nooh MM, Bahouth SW. Role of AKAP79/150 protein in β1-adrenergic receptor trafficking and signaling in mammalian cells. J Biol Chem 2013; 288:33797-33812. [PMID: 24121510 DOI: 10.1074/jbc.m113.470559] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein kinase A-anchoring proteins (AKAPs) participate in the formation of macromolecular signaling complexes that include protein kinases, ion channels, effector enzymes, and G-protein-coupled receptors. We examined the role of AKAP79/150 (AKAP5) in trafficking and signaling of the β1-adrenergic receptor (β1-AR). shRNA-mediated down-regulation of AKAP5 in HEK-293 cells inhibited the recycling of the β1-AR. Recycling of the β1-AR in AKAP5 knockdown cells was rescued by shRNA-resistant AKAP5. However, truncated mutants of AKAP5 with deletions in the domains involved in membrane targeting or in binding to calcineurin or PKA failed to restore the recycling of the β1-AR, indicating that full-length AKAP5 was required. Furthermore, recycling of the β1-AR in rat neonatal cardiac myocytes was dependent on targeting the AKAP5-PKA complex to the C-terminal tail of the β1-AR. To analyze the role of AKAP5 more directly, recycling of the β1-AR was determined in ventricular myocytes from AKAP5(-/-) mice. In AKAP5(-/-) myocytes, the agonist-internalized β1-AR did not recycle, except when full-length AKAP5 was reintroduced. These data indicate that AKAP5 exerted specific and profound effects on β1-AR recycling in mammalian cells. Biochemical or real time FRET-based imaging of cyclic AMP revealed that deletion of AKAP5 sensitized the cardiac β1-AR signaling pathway to isoproterenol. Moreover, isoproterenol-mediated increase in contraction rate, surface area, or expression of β-myosin heavy chains was significantly greater in AKAP5(-/-) myocytes than in AKAP5(+/+) myocytes. These results indicate a significant role for the AKAP5 scaffold in signaling and trafficking of the β1-AR in cardiac myocytes and mammalian cells.
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Affiliation(s)
- Xin Li
- Department of Pharmacology, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - Mohammed M Nooh
- Department of Pharmacology, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - Suleiman W Bahouth
- Department of Pharmacology, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163.
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Reprogramming of G protein-coupled receptor recycling and signaling by a kinase switch. Proc Natl Acad Sci U S A 2013; 110:15289-94. [PMID: 24003153 DOI: 10.1073/pnas.1306340110] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The postendocytic recycling of signaling receptors is subject to multiple requirements. Why this is so, considering that many other proteins can recycle without apparent requirements, is a fundamental question. Here we show that cells can leverage these requirements to switch the recycling of the beta-2 adrenergic receptor (B2AR), a prototypic signaling receptor, between sequence-dependent and bulk recycling pathways, based on extracellular signals. This switch is determined by protein kinase A-mediated phosphorylation of B2AR on the cytoplasmic tail. The phosphorylation state of B2AR dictates its partitioning into spatially and functionally distinct endosomal microdomains mediating bulk and sequence-dependent recycling, and also regulates the rate of B2AR recycling and resensitization. Our results demonstrate that G protein-coupled receptor recycling is not always restricted to the sequence-dependent pathway, but may be reprogrammed as needed by physiological signals. Such flexible reprogramming might provide a versatile method for rapidly modulating cellular responses to extracellular signaling.
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SAP97 controls the trafficking and resensitization of the beta-1-adrenergic receptor through its PDZ2 and I3 domains. PLoS One 2013; 8:e63379. [PMID: 23696820 PMCID: PMC3656048 DOI: 10.1371/journal.pone.0063379] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2012] [Accepted: 04/03/2013] [Indexed: 01/11/2023] Open
Abstract
Previous studies have determined that the type-1 PDZ sequence at the extreme carboxy-terminus of the ß1-adrenergic receptor (ß1-AR) binds SAP97 and AKAP79 to organize a scaffold involved in trafficking of the ß1-AR. In this study we focused on characterizing the domains in SAP97 that were involved in recycling and resensitization of the ß1-AR in HEK-293 cells. Using a SAP97 knockdown and rescue strategy, we determined that PDZ-deletion mutants of SAP97 containing PDZ2 rescued the recycling and resensitization of the ß1-AR. Among the three PDZs of SAP97, PDZ2 displayed the highest affinity in binding to the ß1-AR. Expression of isolated PDZ2, but not the other PDZs, inhibited the recycling of the ß1-AR by destabilizing the macromolecular complex involved in trafficking and functional resensitization of the ß1-AR. In addition to its PDZs, SAP97 contains other protein interacting domains, such as the I3 sequence in the SRC homology-3 (SH3) domain, which binds to AKAP79. Deletion of I3 from SAP97 (ΔI3-SAP97) did not affect the binding of SAP97 to the ß1-AR. However, ΔI3-SAP97 could not rescue the recycling of the ß1-AR because it failed to incorporate AKAP79/PKA into the SAP97-ß1-AR complex. Therefore, bipartite binding of SAP97 to the ß1-AR and to AKAP79 is necessary for SAP97-mediated effects on recycling, externalization and functional resensitization of the ß1-AR. These data establish a prominent role for PDZ2 and I3 domains of SAP97 in organizing the ß1-adrenergic receptosome involved in connecting the ß1-AR to trafficking and signaling networks.
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Dunn HA, Walther C, Godin CM, Hall RA, Ferguson SSG. Role of SAP97 protein in the regulation of corticotropin-releasing factor receptor 1 endocytosis and extracellular signal-regulated kinase 1/2 signaling. J Biol Chem 2013; 288:15023-34. [PMID: 23576434 DOI: 10.1074/jbc.m113.473660] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The corticotropin-releasing factor (CRF) receptor 1 (CRFR1) is a target for the treatment of psychiatric diseases such as depression, schizophrenia, anxiety disorder, and bipolar disorder. The carboxyl-terminal tail of the CRFR1 terminates in a PDZ-binding motif that provides a potential site for the interaction of PSD-95/Discs Large/Zona Occludens 1 (PDZ) domain-containing proteins. In this study, we found that CRFR1 interacts with synapse-associated protein 97 (SAP97; also known as DLG1) by co-immunoprecipitation in human embryonic 293 (HEK 293) cells and cortical brain lysates and that this interaction is dependent upon an intact PDZ-binding motif at the end of the CRFR1 carboxyl-terminal tail. Similarly, we demonstrated that SAP97 is recruited to the plasma membrane in HEK 293 cells expressing CRFR1 and that mutation of the CRFR1 PDZ-binding motif results in the redistribution of SAP97 into the cytoplasm. Overexpression of SAP97 antagonized agonist-stimulated CRFR1 internalization, whereas single hairpin (shRNA) knockdown of endogenous SAP97 in HEK 293 cells resulted in increased agonist-stimulated CRFR1 endocytosis. CRFR1 was internalized as a complex with SAP97 resulting in the redistribution of SAP97 to endocytic vesicles. Overexpression or shRNA knockdown of SAP97 did not significantly affect CRFR1-mediated cAMP formation, but SAP97 knockdown did significantly attenuate CRFR1-stimulated ERK1/2 phosphorylation in a PDZ interaction-independent manner. Taken together, our studies show that SAP97 interactions with CRFR1 attenuate CRFR1 endocytosis and that SAP97 is involved in coupling G protein-coupled receptors to the activation of the ERK1/2 signaling pathway.
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Affiliation(s)
- Henry A Dunn
- J Allyn Taylor Centre for Cell Biology, Robarts Research Institute, University of Western Ontario, London, Ontario N6A 5K8, Canada
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20
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Mizuno K, Kurokawa K, Shibasaki M, Ohkuma S. β₁-adrenergic receptor up-regulation induced by nadolol is mediated via signal transduction pathway coupled to α₁-adrenergic receptors. Brain Res 2011; 1414:10-21. [PMID: 21871614 DOI: 10.1016/j.brainres.2011.07.057] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2011] [Revised: 06/30/2011] [Accepted: 07/27/2011] [Indexed: 01/05/2023]
Abstract
Although up-regulation of β-adrenergic receptors (β-ARs) occurs after long-term use of their antagonists in various tissues, the available data are little on mechanisms of β-AR up-regulation induced by their continuous blockade. The present study attempted to clarify mechanisms of β-AR up-regulation using mouse cerebral cortical neurons continuously exposed to nadolol (10 nM), a non-selective β-AR antagonist, for 24 h. Nadolol dose-dependently induced both subtypes of β-ARs, β₁- and β₂-ARs, which were not suppressed by protein A kinase inhibition with KT5720. On the other hand, blockade of α₁-ARs, which are immunohistochemically confirmed to be co-localized with β-ARs in the same neurons, significantly inhibited only β₁-AR up-regulation and the expression of β₂-ARs did not alter. In addition, phenylephrine, an agonist specific to α₁-ARs up-regulated β₁-ARs, but not β₂-ARs. Under the conditions with β-AR up-regulation, the level of phosphorylated protein kinase Cα (pPKCα) increased, which is significantly suppressed by prazosin, an α1-AR antagonist. Furthermore, nadolol decreased the degradation of mRNA of β₁-ARs, but not β₂-ARs. These results indicate that the nadolol-induced β₁-AR up-regulation is mediated via PKC-relating pathway via α₁-AR activation with stabilizing β₁-AR mRNA and that the increased expression of β₂-ARs is regulated by pathways different from those for β₁-AR expression.
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MESH Headings
- Adrenergic Agents/pharmacology
- Adrenergic beta-Antagonists/pharmacology
- Analysis of Variance
- Animals
- Benzophenanthridines/pharmacology
- Carbazoles/pharmacology
- Cells, Cultured
- Cerebral Cortex/cytology
- Dopamine beta-Hydroxylase/metabolism
- Embryo, Mammalian
- Enzyme Inhibitors/pharmacology
- Mice
- Mice, Inbred ICR
- Nadolol/pharmacology
- Neurons/drug effects
- Pyrroles/pharmacology
- Receptors, Adrenergic, alpha-1/genetics
- Receptors, Adrenergic, alpha-1/metabolism
- Receptors, Adrenergic, beta-1/genetics
- Receptors, Adrenergic, beta-1/metabolism
- Signal Transduction/drug effects
- Time Factors
- Up-Regulation/drug effects
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Affiliation(s)
- Koji Mizuno
- Department of Pharmacology, Kawasaki Medical School, Matsushima 577, Kurashiki 701-0192, Japan
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21
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Cheng SB, Quinn JA, Graeber CT, Filardo EJ. Down-modulation of the G-protein-coupled estrogen receptor, GPER, from the cell surface occurs via a trans-Golgi-proteasome pathway. J Biol Chem 2011; 286:22441-55. [PMID: 21540189 PMCID: PMC3121390 DOI: 10.1074/jbc.m111.224071] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Revised: 04/26/2011] [Indexed: 11/06/2022] Open
Abstract
GPER is a G(s)-coupled seven-transmembrane receptor that has been linked to specific estrogen binding and signaling activities that are manifested by plasma membrane-associated enzymes. However, in many cell types, GPER is predominately localized to the endoplasmic reticulum (ER), and only minor amounts of receptor are detectable at the cell surface, an observation that has caused controversy regarding its role as a plasma membrane estrogen receptor. Here, we show that GPER constitutively buds intracellularly into EEA-1+ endosomes from clathrin-coated pits. Nonvisual arrestins-2/-3 do not co-localize with GPER, and expression of arrestin-2 dominant-negative mutants lacking clathrin- or β-adaptin interaction sites fails to block GPER internalization suggesting that arrestins are not involved in GPER endocytosis. Like β1AR, which recycles to the plasma membrane, GPER co-traffics with transferrin+, Rab11+ recycling endosomes. However, endocytosed GPER does not recycle to the cell surface, but instead returns to the trans-Golgi network (TGN) and does not re-enter the ER. GPER is ubiquitinated at the cell surface, exhibits a short half-life (t½;) <1 h), and is protected from degradation by the proteasome inhibitor, MG132. Disruption of the TGN by brefeldin A induces the accumulation of endocytosed GPER in Rab11+ perinuclear endosomes and prevents GPER degradation. Our results provide an explanation as to why GPER is not readily detected on the cell surface in some cell types and further suggest that TGN serves as the checkpoint for degradation of endocytosed GPER.
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Affiliation(s)
- Shi-Bin Cheng
- From the Division of Hematology & Oncology, Rhode Island Hospital and Brown University, Providence, Rhode Island 02903
| | - Jeffrey A. Quinn
- From the Division of Hematology & Oncology, Rhode Island Hospital and Brown University, Providence, Rhode Island 02903
| | - Carl T. Graeber
- From the Division of Hematology & Oncology, Rhode Island Hospital and Brown University, Providence, Rhode Island 02903
| | - Edward J. Filardo
- From the Division of Hematology & Oncology, Rhode Island Hospital and Brown University, Providence, Rhode Island 02903
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22
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Gardner LA, Hajjhussein H, Frederick-Dyer KC, Bahouth SW. Rab11a and its binding partners regulate the recycling of the ß1-adrenergic receptor. Cell Signal 2010; 23:46-57. [PMID: 20727405 DOI: 10.1016/j.cellsig.2010.07.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 07/27/2010] [Accepted: 07/30/2010] [Indexed: 01/12/2023]
Abstract
ß1-adrenergic receptors (ß1-AR) are internalized in response to agonists and then recycle back for another round of signaling. The serine 312 to alanine mutant of the ß1-AR (S312A) is internalized but does not recycle. We determined that WT ß1-AR and S312A were internalized initially to an early sorting compartment because they colocalized by >70% with the early endosomal markers rab5a and early endosomal antigen-1 (EEA1). Subsequently, the WT ß1-AR trafficked via rab4a-expressing sorting endosomes to recycling endosomes. In recycling endosomes WT ß1-AR were colocalized by >70% with the rab11 GTPase. S312A did not colocalize with either rab4a or rab11, instead they exited from early endosomes to late endosomes/lysosomes in which they were degraded. Rab11a played a prominent role in recycling of the WT ß1-AR because dominant negative rab11a inhibited, while constitutively active rab11a accelerated the recycling of the ß1-AR. Next, we determined the effect of each of the rab11-interacting proteins on trafficking of the WT ß1-AR. The recycling of the ß1-AR was markedly inhibited when myosin Vb, FIP2, FIP3 and rabphillin were knocked down. These data indicate that rab11a and a select group of its binding partners play a prominent role in recycling of the human ß1-AR.
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Affiliation(s)
- Lidia A Gardner
- Department of Neurology, University of Tennessee Health Sciences Center, Memphis, TN 38163, USA
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23
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Dai S, Hall DD, Hell JW. Supramolecular assemblies and localized regulation of voltage-gated ion channels. Physiol Rev 2009; 89:411-52. [PMID: 19342611 DOI: 10.1152/physrev.00029.2007] [Citation(s) in RCA: 281] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
This review addresses the localized regulation of voltage-gated ion channels by phosphorylation. Comprehensive data on channel regulation by associated protein kinases, phosphatases, and related regulatory proteins are mainly available for voltage-gated Ca2+ channels, which form the main focus of this review. Other voltage-gated ion channels and especially Kv7.1-3 (KCNQ1-3), the large- and small-conductance Ca2+-activated K+ channels BK and SK2, and the inward-rectifying K+ channels Kir3 have also been studied to quite some extent and will be included. Regulation of the L-type Ca2+ channel Cav1.2 by PKA has been studied most thoroughly as it underlies the cardiac fight-or-flight response. A prototypical Cav1.2 signaling complex containing the beta2 adrenergic receptor, the heterotrimeric G protein Gs, adenylyl cyclase, and PKA has been identified that supports highly localized via cAMP. The type 2 ryanodine receptor as well as AMPA- and NMDA-type glutamate receptors are in close proximity to Cav1.2 in cardiomyocytes and neurons, respectively, yet independently anchor PKA, CaMKII, and the serine/threonine phosphatases PP1, PP2A, and PP2B, as is discussed in detail. Descriptions of the structural and functional aspects of the interactions of PKA, PKC, CaMKII, Src, and various phosphatases with Cav1.2 will include comparisons with analogous interactions with other channels such as the ryanodine receptor or ionotropic glutamate receptors. Regulation of Na+ and K+ channel phosphorylation complexes will be discussed in separate papers. This review is thus intended for readers interested in ion channel regulation or in localization of kinases, phosphatases, and their upstream regulators.
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Affiliation(s)
- Shuiping Dai
- Department of Pharmacology, University of Iowa, Iowa City, IA 52242-1109, USA
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Hoshino T, Namba T, Takehara M, Nakaya T, Sugimoto Y, Araki W, Narumiya S, Suzuki T, Mizushima T. Prostaglandin E2 stimulates the production of amyloid-beta peptides through internalization of the EP4 receptor. J Biol Chem 2009; 284:18493-502. [PMID: 19407341 DOI: 10.1074/jbc.m109.003269] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amyloid-beta (Abeta) peptides, generated by the proteolysis of beta-amyloid precursor protein by beta- and gamma-secretases, play an important role in the pathogenesis of Alzheimer disease. Inflammation is also important. We recently reported that prostaglandin E(2) (PGE(2)), a strong inducer of inflammation, stimulates the production of Abeta through EP(2) and EP(4) receptors, and here we have examined the molecular mechanism. Activation of EP(2) and EP(4) receptors is coupled to an increase in cellular cAMP levels and activation of protein kinase A (PKA). We found that inhibitors of adenylate cyclase and PKA suppress EP(2), but not EP(4), receptor-mediated stimulation of the Abeta production. In contrast, inhibitors of endocytosis suppressed EP(4), but not EP(2), receptor-mediated stimulation. Activation of gamma-secretase was observed with the activation of EP(4) receptors but not EP(2) receptors. PGE(2)-dependent internalization of the EP(4) receptor was observed, and cells expressing a mutant EP(4) receptor lacking the internalization activity did not exhibit PGE(2)-stimulated production of Abeta. A physical interaction between the EP(4) receptor and PS-1, a catalytic subunit of gamma-secretases, was revealed by immunoprecipitation assays. PGE(2)-induced internalization of PS-1 and co-localization of EP(4), PS-1, and Rab7 (a marker of late endosomes and lysosomes) was observed. Co-localization of PS-1 and Rab7 was also observed in the brain of wild-type mice but not of EP(4) receptor null mice. These results suggest that PGE(2)-stimulated production of Abeta involves EP(4) receptor-mediated endocytosis of PS-1 followed by activation of the gamma-secretase, as well as EP(2) receptor-dependent activation of adenylate cyclase and PKA, both of which are important in the inflammation-mediated progression of Alzheimer disease.
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Affiliation(s)
- Tatsuya Hoshino
- Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto 862-0973, Japan
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25
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Zhang X, Wang F, Chen X, Chen Y, Ma L. Post-endocytic fates of -opioid receptor are regulated by GRK2-mediated receptor phosphorylation and distinct -arrestin isoforms. J Neurochem 2008; 106:781-92. [DOI: 10.1111/j.1471-4159.2008.05431.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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26
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Hanyaloglu AC, von Zastrow M. Regulation of GPCRs by endocytic membrane trafficking and its potential implications. Annu Rev Pharmacol Toxicol 2008; 48:537-68. [PMID: 18184106 DOI: 10.1146/annurev.pharmtox.48.113006.094830] [Citation(s) in RCA: 447] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The endocytic pathway tightly controls the activity of G protein-coupled receptors (GPCRs). Ligand-induced endocytosis can drive receptors into divergent lysosomal and recycling pathways, producing essentially opposite effects on the strength and duration of cellular signaling via heterotrimeric G proteins, and may also promote distinct signaling events from intracellular membranes. This chapter reviews recent developments toward understanding the molecular machinery and functional implications of GPCR sorting in the endocytic pathway, focusing on mammalian GPCRs whose ligand-induced endocytosis is mediated primarily by clathrin-coated pits. Lysosomal sorting of a number of GPCRs occurs via a highly conserved mechanism requiring covalent tagging of receptors with ubiquitin. There is increasing evidence that additional, noncovalent mechanisms control the sorting of endocytosed GPCRs to lysosomes in mammalian cells. Recycling of several GPCRs to the plasma membrane is also specifically sorted, via a mechanism requiring both receptor-specific and shared sorting proteins. The current data reveal an unprecedented degree of specificity and plasticity in the cellular regulation of mammalian GPCRs by endocytic membrane trafficking. These developments have fundamental implications for GPCR pharmacology, and suggest new mechanisms that could be exploited in GPCR-directed pharmacotherapy.
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Affiliation(s)
- Aylin C Hanyaloglu
- Institute of Reproductive Biology and Development, Imperial College London, Hammersmith Campus, London, United Kingdom
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Gavi S, Yin D, Shumay E, Wang HY, Malbon CC. Insulin-like growth factor-I provokes functional antagonism and internalization of beta1-adrenergic receptors. Endocrinology 2007; 148:2653-62. [PMID: 17363461 DOI: 10.1210/en.2006-1569] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Hormones that activate receptor tyrosine kinases have been shown to regulate G protein-coupled receptors, and herein we investigate the ability of IGF-I to regulate the beta(1)-adrenergic receptor. Treating Chinese hamster ovary cells in culture with IGF-I is shown to functionally antagonize the ability of expressed beta(1)-adrenergic receptors to accumulate intracellular cAMP in response to stimulation by the beta-adrenergic agonist Iso. The attenuation of beta(1)-adrenergic action was accompanied by internalization of beta(1)-adrenergic receptors in response to IGF-I. Inhibiting either phosphatidylinositol 3-kinase or the serine/threonine protein kinase Akt blocks the ability of IGF-I to antagonize and to internalize beta(1)-adrenergic receptors. Mutation of one potential Akt substrate site Ser412Ala, but not another Ser312Ala, of the beta(1)-adrenergic receptor abolishes the ability of IGF-I to functionally antagonize and to sequester the beta(1)-adrenergic receptor. We also tested the ability of IGF-I to regulate beta(1)-adrenergic receptors and their signaling in adult canine cardiac myocytes. IGF-I attenuates the ability of beta(1)-adrenergic receptors to accumulate intracellular cAMP in response to Iso and promotes internalization of beta(1)-adrenergic receptors in these cardiac myocytes.
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Affiliation(s)
- Shai Gavi
- Department of Pharmacology, Diabetes and Metabolic Diseases Research Center, School of Medicine-HSC, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
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Gardner LA, Naren AP, Bahouth SW. Assembly of an SAP97-AKAP79-cAMP-dependent protein kinase scaffold at the type 1 PSD-95/DLG/ZO1 motif of the human beta(1)-adrenergic receptor generates a receptosome involved in receptor recycling and networking. J Biol Chem 2006; 282:5085-5099. [PMID: 17170109 DOI: 10.1074/jbc.m608871200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Appropriate trafficking of the beta(1)-adrenergic receptor (beta(1)-AR) after agonist-promoted internalization is crucial for the resensitization of its signaling pathway. Efficient recycling of the beta(1)-AR required the binding of the protein kinase A anchoring protein-79 (AKAP79) to the carboxyl terminus of the beta(1)-AR (Gardner, L. A., Tavalin, S. A., Goehring, A., Scott, J. D., and Bahouth, S. W. (2006) J. Biol. Chem. 281, 33537-33553). In this study we show that AKAP79 forms a complex with the type 1 PDZ-binding sequence (ESKV) at the extreme carboxyl terminus of the beta(1)-AR, which is mediated by the membrane-associated guanylate kinase (MAGUK) protein SAP97. Thus, the PDZ and its associated SAP97-AKAP79 complex are involved in targeting the cyclic AMP-dependent protein kinase (PKA) to the beta(1)-AR. The PDZ and its scaffold were required for efficient recycling of the beta(1)-AR and for PKA-mediated phosphorylation of the beta(1)-AR at Ser(312). Overexpression of the catalytic subunit of PKA or mutagenesis of Ser(312) to the phosphoserine mimic aspartic acid both rescued the recycling of the trafficking-defective beta(1)-ARDelta PDZ mutant. Thus, trafficking signals transmitted from the PDZ-associated scaffold in the carboxyl terminus of the beta(1)-AR to Ser(312) in the 3rd intracellular loop (3rd IC) were paramount in setting the trafficking itinerary of the beta(1)-AR. The data presented here show that a novel beta(1)-adrenergic receptosome is organized at the beta(1)-AR PDZ to generate a scaffold essential for trafficking and networking of the beta(1)-AR.
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Affiliation(s)
- Lidia A Gardner
- Departments of Pharmacology and University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - Anjaparavanda P Naren
- Physiology, the University of Tennessee Health Sciences Center, Memphis, Tennessee 38163
| | - Suleiman W Bahouth
- Departments of Pharmacology and University of Tennessee Health Sciences Center, Memphis, Tennessee 38163.
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Hicks SW, Horn TA, McCaffery JM, Zuckerman DM, Machamer CE. Golgin-160 Promotes Cell Surface Expression of the Beta-1 Adrenergic Receptor. Traffic 2006; 7:1666-77. [PMID: 17118120 DOI: 10.1111/j.1600-0854.2006.00504.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Golgin-160 is a ubiquitously expressed peripheral Golgi membrane protein that is important for transduction of certain pro-apoptotic signals at the Golgi complex. However, the role of golgin-160 in normal Golgi structure and function is unknown. Here, we show that depletion of golgin-160 using RNA interference (RNAi) does not affect Golgi morphology or constitutive membrane traffic in HeLa cells. However, depletion of golgin-160 leads to significantly decreased cell surface levels of exogenously expressed beta1-adrenergic receptor (beta1AR), which can be rescued by expression of RNAi-resistant forms of golgin-160. Furthermore, overexpression of golgin-160 leads to higher surface levels of beta1AR. Golgin-160 is localized mostly in the cis and medial regions of the Golgi stack by immunoelectron microscopy, suggesting that it does not directly promote incorporation of beta1AR into transport vesicles at the trans Golgi network. Golgin-160 interacts with beta1AR in vitro, and we mapped the interaction to a region between residues 140 and 257 in the head of golgin-160 and the third intracellular loop of beta1AR. Our results support the idea that golgin-160 may promote efficient surface delivery of a subset of cargo molecules.
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Affiliation(s)
- Stuart W Hicks
- Department of Cell Biology, Johns Hopkins University School of Medicine, 725 Wolfe Street, Baltimore, MD 21205, USA
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30
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Gardner LA, Tavalin SJ, Goehring AS, Scott JD, Bahouth SW. AKAP79-mediated targeting of the cyclic AMP-dependent protein kinase to the beta1-adrenergic receptor promotes recycling and functional resensitization of the receptor. J Biol Chem 2006; 281:33537-53. [PMID: 16940053 DOI: 10.1074/jbc.m601809200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Resensitization of G protein-coupled receptors (GPCR) following prolonged agonist exposure is critical for restoring the responsiveness of the receptor to subsequent challenges by agonist. The 3'-5' cyclic AMP-dependent protein kinase (PKA) and serine 312 in the third intracellular loop of the human beta(1)-adrenergic receptor (beta(1)-AR) were both necessary for efficient recycling and resensitization of the agonist-internalized beta(1)-AR (Gardner, L. A., Delos Santos, N. M., Matta, S. G., Whitt, M. A., and Bahouth, S. W. (2004) J. Biol. Chem. 279, 21135-21143). Because PKA is compartmentalized near target substrates by interacting with protein kinase A anchoring proteins (AKAPs), the present study was undertaken to identify the AKAP involved in PKA-mediated phosphorylation of the beta(1)-AR and in its recycling and resensitization. Here, we report that Ht-31 peptide-mediated disruption of PKA/AKAP interactions prevented the recycling and functional resensitization of heterologously expressed beta(1)-AR in HEK-293 cells and endogenously expressed beta(1)-AR in SK-N-MC cells and neonatal rat cortical neurons. Whereas several endogenous AKAPs were identified in HEK-293 cells, small interfering RNA-mediated down-regulation of AKAP79 prevented the recycling of the beta(1)-AR in this cell line. Co-immunoprecipitations and fluorescence resonance energy transfer (FRET) microscopy experiments in HEK-293 cells revealed that the beta(1)-AR, AKAP79, and PKA form a ternary complex at the carboxyl terminus of the beta(1)-AR. This complex was involved in PKA-mediated phosphorylation of the third intracellular loop of the beta(1)-AR because disruption of PKA/AKAP interactions or small interfering RNA-mediated down-regulation of AKAP79 both inhibited this response. Thus, AKAP79 provides PKA to phosphorylate the beta(1)-AR and thereby dictate the recycling and resensitization itineraries of the beta(1)-AR.
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Affiliation(s)
- Lidia A Gardner
- Department of Pharmacology, University of Tennessee Health Sciences Center, Memphis, Tennessee 38163, USA
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31
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Zeitoun O, Santos NMD, Gardner LA, White SW, Bahouth SW. Mutagenesis within Helix 6 of the Human β1-Adrenergic Receptor Identifies Lysine324as a Residue Involved in Imparting the High-Affinity Binding State of Agonists. Mol Pharmacol 2006; 70:838-50. [PMID: 16760361 DOI: 10.1124/mol.106.025346] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Competition binding isotherms for agonists to G protein-coupled receptors (GPCR) display high and low binding affinities. Mutagenesis of lysine at position 324 in helix 6 of the wild-type (WT) human beta1-adrenergic receptor (beta1-AR) generated mutant receptors that had GTP-insensitive single low-affinity binding sites for agonists and reduced potencies of full or partial agonists in stimulating adenylyl cyclase. Unlike the WT beta1-AR, intrinsic activities of full and partial agonists in activating the Lys324-->Ala beta1-AR (K324A) mutant were correlated with their binding affinities to the K324A mutant. In assays, such as agonist-mediated phosphorylation and recycling, the K324A mutant and the WT beta1-AR behaved similarly. However, in fluorescence resonance energy transfer assays that determined the proximity between the WT beta1-AR or the K324A mutant to G(s)alpha, there were significant differences. The conceptual framework of the ternary complex model could not adequately account for the behavior of the K324A mutant except under assumptions of low receptor-G protein binding affinities. The single low-affinity binding site of the K324A mutant to isoproterenol was converted by the C-terminal 11-amino-acid peptide of G(s)alpha, which acts a GDP-bound G(s)alpha mimic, to high- and low-affinity sites. Based upon the three-dimensional architecture of the human beta1-AR, the distance between Lys324 and the Asp/Glu-Arg-Tyr motif in helix 3 was the shortest among the various amino acids in helix 6. These findings indicate that Lys324 lies in a groove between helices 3 and 6, and its mutagenesis generates a mutant receptor with very low binding affinity for the GDP-bound isoform of G(s).
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MESH Headings
- Adenylyl Cyclases/metabolism
- Adrenergic Agonists/chemistry
- Amino Acid Sequence
- Cells, Cultured
- Enzyme Activation/drug effects
- GTP-Binding Protein alpha Subunits, Gs/metabolism
- Humans
- Isoproterenol/pharmacology
- Lysine/metabolism
- Microscopy, Confocal
- Models, Molecular
- Molecular Sequence Data
- Multiprotein Complexes/metabolism
- Mutagenesis, Site-Directed
- Mutant Proteins/chemistry
- Mutant Proteins/genetics
- Mutation/drug effects
- Phosphorylation/drug effects
- Protein Binding
- Protein Structure, Secondary
- Protein Transport/drug effects
- Receptors, Adrenergic, beta-1/chemistry
- Receptors, Adrenergic, beta-1/genetics
- Reproducibility of Results
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Affiliation(s)
- Omeima Zeitoun
- Department of Pharmacology, The University of Tennessee Health Sciences center, 874 Union Avenue, Memphis, TN 38163, USA
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32
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Delos Santos NM, Gardner LA, White SW, Bahouth SW. Characterization of the residues in helix 8 of the human beta1-adrenergic receptor that are involved in coupling the receptor to G proteins. J Biol Chem 2006; 281:12896-907. [PMID: 16500896 DOI: 10.1074/jbc.m508500200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Several key amino acids within amphipathic helix 8 of the human beta1-adrenergic receptor (beta1-AR) were mutagenized to characterize their role in signaling by G protein-coupled receptors. Mutagenesis of phenylalanine at position 383 in the hydrophobic interface to histidine (F383H) prevented the biosynthesis of the receptor, indicating that the orientation of helix 8 is important for receptor biosynthesis. Mutagenesis of aspartic acid at position 382 in the hydrophilic interface to leucine (D382L) reduced the binding and uncoupled the receptor from G protein activation. Mutagenesis of the basic arginine residue at position 384 to glutamine (R384Q) or to glutamic acid (R384E) increased basal and agonist-stimulated adenylyl cyclase activities. R384Q and R384E displayed features associated with constitutively active receptors because inverse agonists markedly reduced their elevated basal adenylyl cyclase activities. Isoproterenol increased the phosphorylation and promoted the desensitization of the Gly389 or Arg389 allelic variants of the wild type beta1-AR but failed to produce these effects in R384Q and R384E, because these receptors were maximally phosphorylated and desensitized under basal conditions. In contrast to the membranous distribution of the wild type beta1-AR, R384Q and R384E were localized mostly within intracellular punctate structures. Inverse agonists restored the membranous distribution of R384Q and R384E, indicating that they recycled normally when their constitutive internalization was blocked by inverse agonists. These data combined with computer modeling of the putative three-dimensional organization of helix 8 indicated that the amphipathic character of helix 8 and side chain projections of Asp382 and Arg384 within the hydrophilic interface might serve as a tethering site for the G protein.
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Affiliation(s)
- Noel M Delos Santos
- Department of Pediatrics, Division of Pediatric Nephrology, the University of Tennessee Health Sciences Center, Memphis, Tennessee 38163, USA
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