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Mancinelli R, Ceci L, Kennedy L, Francis H, Meadows V, Chen L, Carpino G, Kyritsi K, Wu N, Zhou T, Sato K, Pannarale L, Glaser S, Chakraborty S, Alpini G, Gaudio E, Onori P, Franchitto A. The Effects of Taurocholic Acid on Biliary Damage and Liver Fibrosis Are Mediated by Calcitonin-Gene-Related Peptide Signaling. Cells 2022; 11:1591. [PMID: 35563897 PMCID: PMC9104610 DOI: 10.3390/cells11091591] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 04/07/2022] [Accepted: 05/04/2022] [Indexed: 12/05/2022] Open
Abstract
BACKGROUND & AIMS Cholangiocytes are the target cells of liver diseases that are characterized by biliary senescence (evidenced by enhanced levels of senescence-associated secretory phenotype, SASP, e.g., TGF-β1), and liver inflammation and fibrosis accompanied by altered bile acid (BA) homeostasis. Taurocholic acid (TC) stimulates biliary hyperplasia by activation of 3',5'-cyclic cyclic adenosine monophosphate (cAMP) signaling, thereby preventing biliary damage (caused by cholinergic/adrenergic denervation) through enhanced liver angiogenesis. Also: (i) α-calcitonin gene-related peptide (α-CGRP, which activates the calcitonin receptor-like receptor, CRLR), stimulates biliary proliferation/senescence and liver fibrosis by enhanced biliary secretion of SASPs; and (ii) knock-out of α-CGRP reduces these phenotypes by decreased cAMP levels in cholestatic models. We aimed to demonstrate that TC effects on liver phenotypes are dependent on changes in the α-CGRP/CALCRL/cAMP/PKA/ERK1/2/TGF-β1/VEGF axis. METHODS Wild-type and α-CGRP-/- mice were fed with a control (BAC) or TC diet for 1 or 2 wk. We measured: (i) CGRP levels by both ELISA kits in serum and by qPCR in isolated cholangiocytes (CALCA gene for α-CGRP); (ii) CALCRL immunoreactivity by immunohistochemistry (IHC) in liver sections; (iii) liver histology, intrahepatic biliary mass, biliary senescence (by β-GAL staining and double immunofluorescence (IF) for p16/CK19), and liver fibrosis (by Red Sirius staining and double IF for collagen/CK19 in liver sections), as well as by qPCR for senescence markers in isolated cholangiocytes; and (iv) phosphorylation of PKA/ERK1/2, immunoreactivity of TGF-β1/TGF- βRI and angiogenic factors by IHC/immunofluorescence in liver sections and qPCR in isolated cholangiocytes. We measured changes in BA composition in total liver by liquid chromatography/mass spectrometry. RESULTS TC feeding increased CALCA expression, biliary damage, and liver inflammation and fibrosis, as well as phenotypes that were associated with enhanced immunoreactivity of the PKA/ERK1/2/TGF-β1/TGF-βRI/VEGF axis compared to BAC-fed mice and phenotypes that were reversed in α-CGRP-/- mice fed TC coupled with changes in hepatic BA composition. CONCLUSION Modulation of the TC/ α-CGRP/CALCRL/PKA/ERK1/2/TGF-β1/VEGF axis may be important in the management of cholangiopathies characterized by BA accumulation.
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Affiliation(s)
- Romina Mancinelli
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, 00161 Rome, Italy; (R.M.); (L.P.); (E.G.); (P.O.)
| | - Ludovica Ceci
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Lindsey Kennedy
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
- Richard L. Roudebush VA Medical Center, Indianapolis, IN 46202, USA
| | - Heather Francis
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
- Richard L. Roudebush VA Medical Center, Indianapolis, IN 46202, USA
| | - Vik Meadows
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Lixian Chen
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Guido Carpino
- Department of Movement, Human and Health Sciences, University of Rome “Foro Italico”, 00135 Rome, Italy;
| | - Konstantina Kyritsi
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Nan Wu
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Tianhao Zhou
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Keisaku Sato
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
| | - Luigi Pannarale
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, 00161 Rome, Italy; (R.M.); (L.P.); (E.G.); (P.O.)
| | - Shannon Glaser
- Department of Medical Physiology, Texas A&M University, Bryan, TX 77807, USA; (S.G.); (S.C.)
| | - Sanjukta Chakraborty
- Department of Medical Physiology, Texas A&M University, Bryan, TX 77807, USA; (S.G.); (S.C.)
| | - Gianfranco Alpini
- Division of Gastroenterology and Hepatology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (L.C.); (L.K.); (H.F.); (V.M.); (L.C.); (K.K.); (N.W.); (T.Z.); (K.S.); (G.A.)
- Richard L. Roudebush VA Medical Center, Indianapolis, IN 46202, USA
| | - Eugenio Gaudio
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, 00161 Rome, Italy; (R.M.); (L.P.); (E.G.); (P.O.)
| | - Paolo Onori
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, 00161 Rome, Italy; (R.M.); (L.P.); (E.G.); (P.O.)
| | - Antonio Franchitto
- Department of Anatomical, Histological, Forensic Medicine and Orthopedics Sciences, Sapienza University of Rome, 00161 Rome, Italy; (R.M.); (L.P.); (E.G.); (P.O.)
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2
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Liang YL, Belousoff MJ, Zhao P, Koole C, Fletcher MM, Truong TT, Julita V, Christopoulos G, Xu HE, Zhang Y, Khoshouei M, Christopoulos A, Danev R, Sexton PM, Wootten D. Toward a Structural Understanding of Class B GPCR Peptide Binding and Activation. Mol Cell 2020; 77:656-668.e5. [PMID: 32004469 DOI: 10.1016/j.molcel.2020.01.012] [Citation(s) in RCA: 71] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Revised: 10/03/2019] [Accepted: 01/07/2020] [Indexed: 12/14/2022]
Abstract
Class B G protein-coupled receptors (GPCRs) are important therapeutic targets for major diseases. Here, we present structures of peptide and Gs-bound pituitary adenylate cyclase-activating peptide, PAC1 receptor, and corticotropin-releasing factor (CRF), (CRF1) receptor. Together with recently solved structures, these provide coverage of the major class B GPCR subfamilies. Diverse orientations of the extracellular domain to the receptor core in different receptors are at least partially dependent on evolutionary conservation in the structure and nature of peptide interactions. Differences in peptide interactions to the receptor core also influence the interlinked TM2-TM1-TM6/ECL3/TM7 domain, and this is likely important in their diverse signaling. However, common conformational reorganization of ECL2, linked to reorganization of ICL2, modulates G protein contacts. Comparison between receptors reveals ICL2 as a key domain forming dynamic G protein interactions in a receptor- and ligand-specific manner. This work advances our understanding of class B GPCR activation and Gs coupling.
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Affiliation(s)
- Yi-Lynn Liang
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Matthew J Belousoff
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Peishen Zhao
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Cassandra Koole
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Madeleine M Fletcher
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Tin T Truong
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Villy Julita
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - George Christopoulos
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - H Eric Xu
- The CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China; Center for Cancer and Cell Biology, Innovation and Integration Program, Van Andel Research Institute, Grand Rapids, MI, USA
| | - Yan Zhang
- Departments of Biophysics and Pathology of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310058, China
| | - Maryam Khoshouei
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Arthur Christopoulos
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia
| | - Radostin Danev
- Graduate School of Medicine, University of Tokyo, S402, 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan.
| | - Patrick M Sexton
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia; School of Pharmacy, Fudan University, Shanghai 201203, China.
| | - Denise Wootten
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, VIC, Australia; School of Pharmacy, Fudan University, Shanghai 201203, China.
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3
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Liang YL, Khoshouei M, Deganutti G, Glukhova A, Koole C, Peat TS, Radjainia M, Plitzko JM, Baumeister W, Miller LJ, Hay DL, Christopoulos A, Reynolds CA, Wootten D, Sexton PM. Cryo-EM structure of the active, G s-protein complexed, human CGRP receptor. Nature 2018; 561:492-497. [PMID: 30209400 PMCID: PMC6166790 DOI: 10.1038/s41586-018-0535-y] [Citation(s) in RCA: 165] [Impact Index Per Article: 27.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 06/26/2018] [Indexed: 12/29/2022]
Abstract
Calcitonin gene-related peptide (CGRP) is a widely expressed neuropeptide that has a major role in sensory neurotransmission. The CGRP receptor is a heterodimer of the calcitonin receptor-like receptor (CLR) class B G-protein-coupled receptor and a type 1 transmembrane domain protein, receptor activity-modifying protein 1 (RAMP1). Here we report the structure of the human CGRP receptor in complex with CGRP and the Gs-protein heterotrimer at 3.3 Å global resolution, determined by Volta phase-plate cryo-electron microscopy. The receptor activity-modifying protein transmembrane domain sits at the interface between transmembrane domains 3, 4 and 5 of CLR, and stabilizes CLR extracellular loop 2. RAMP1 makes only limited direct contact with CGRP, consistent with its function in allosteric modulation of CLR. Molecular dynamics simulations indicate that RAMP1 provides stability to the receptor complex, particularly in the positioning of the extracellular domain of CLR. This work provides insights into the control of G-protein-coupled receptor function.
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Affiliation(s)
- Yi-Lynn Liang
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Maryam Khoshouei
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
- Novartis Institutes for Biomedical Research, Novartis Pharma, Basel, Switzerland
| | | | - Alisa Glukhova
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Cassandra Koole
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Thomas S Peat
- CSIRO Biomedical Manufacturing, Melbourne, Victoria, Australia
| | - Mazdak Radjainia
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
- Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Jürgen M Plitzko
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Wolfgang Baumeister
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Laurence J Miller
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Scottsdale, AZ, USA
| | - Deborah L Hay
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand
| | - Arthur Christopoulos
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | | | - Denise Wootten
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.
- School of Pharmacy, Fudan University, Shanghai, China.
| | - Patrick M Sexton
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.
- School of Pharmacy, Fudan University, Shanghai, China.
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4
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Bower RL, Yule L, Rees TA, Deganutti G, Hendrikse ER, Harris PWR, Kowalczyk R, Ridgway Z, Wong AG, Swierkula K, Raleigh DP, Pioszak AA, Brimble MA, Reynolds CA, Walker CS, Hay DL. Molecular Signature for Receptor Engagement in the Metabolic Peptide Hormone Amylin. ACS Pharmacol Transl Sci 2018; 1:32-49. [PMID: 32219203 DOI: 10.1021/acsptsci.8b00002] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Indexed: 11/30/2022]
Abstract
The pancreatic peptide hormone, amylin, plays a critical role in the control of appetite, and synergizes with other key metabolic hormones such as glucagon-like peptide 1 (GLP-1). There is opportunity to develop potent and long-acting analogues of amylin or hybrids between these and GLP-1 mimetics for treating obesity. To achieve this, interrogation of how the 37 amino acid amylin peptide engages with its complex receptor system is required. We synthesized an extensive library of peptides to profile the human amylin sequence, determining the role of its disulfide loop, amidated C-terminus and receptor "capture" and "activation" regions in receptor signaling. We profiled four signaling pathways with different ligands at multiple receptor subtypes, in addition to exploring selectivity determinants between related receptors. Distinct roles for peptide subregions in receptor binding and activation were identified, resulting in peptides with greater activity than the native sequence. Enhanced peptide activity was preserved in the brainstem, the major biological target for amylin. Interpretation of our data using full-length active receptor models supported by molecular dynamics, metadynamics, and supervised molecular dynamics simulations guided the synthesis of a potent dual agonist of GLP-1 and amylin receptors. The data offer new insights into the function of peptide amidation, how allostery drives peptide-receptor interactions, and provide a valuable resource for the development of novel amylin agonists for treating diabetes and obesity.
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Affiliation(s)
- Rebekah L Bower
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Lauren Yule
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Tayla A Rees
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Giuseppe Deganutti
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, U.K
| | - Erica R Hendrikse
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Paul W R Harris
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Renata Kowalczyk
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Zachary Ridgway
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
| | - Amy G Wong
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
| | - Katarzyna Swierkula
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, U.K
| | - Daniel P Raleigh
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States.,Department of Structural and Molecular Biology, University College London, London WC1E 6BT, U.K
| | - Augen A Pioszak
- Department of Biochemistry and Molecular Biology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, United States
| | - Margaret A Brimble
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Christopher A Reynolds
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, U.K
| | - Christopher S Walker
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
| | - Debbie L Hay
- School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand.,School of Biological Sciences, School of Chemical Sciences, and Maurice Wilkins Centre, The University of Auckland, Auckland, 1010, New Zealand
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5
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Woolley MJ, Reynolds CA, Simms J, Walker CS, Mobarec JC, Garelja ML, Conner AC, Poyner DR, Hay DL. Receptor activity-modifying protein dependent and independent activation mechanisms in the coupling of calcitonin gene-related peptide and adrenomedullin receptors to Gs. Biochem Pharmacol 2017; 142:96-110. [PMID: 28705698 PMCID: PMC5609567 DOI: 10.1016/j.bcp.2017.07.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 07/06/2017] [Indexed: 12/23/2022]
Abstract
Calcitonin gene-related peptide (CGRP) or adrenomedullin (AM) receptors are heteromers of the calcitonin receptor-like receptor (CLR), a class B G protein-coupled receptor, and one of three receptor activity-modifying proteins (RAMPs). How CGRP and AM activate CLR and how this process is modulated by RAMPs is unclear. We have defined how CGRP and AM induce Gs-coupling in CLR-RAMP heteromers by measuring the effect of targeted mutagenesis in the CLR transmembrane domain on cAMP production, modeling the active state conformations of CGRP and AM receptors in complex with the Gs C-terminus and conducting molecular dynamics simulations in an explicitly hydrated lipidic bilayer. The largest effects on receptor signaling were seen with H295A5.40b, I298A5.43b, L302A5.47b, N305A5.50b, L345A6.49b and E348A6.52b, F349A6.53b and H374A7.47b (class B numbering in superscript). Many of these residues are likely to form part of a group in close proximity to the peptide binding site and link to a network of hydrophilic and hydrophobic residues, which undergo rearrangements to facilitate Gs binding. Residues closer to the extracellular loops displayed more pronounced RAMP or ligand-dependent effects. Mutation of H3747.47b to alanine increased AM potency 100-fold in the CGRP receptor. The molecular dynamics simulation showed that TM5 and TM6 pivoted around TM3. The data suggest that hydrophobic interactions are more important for CLR activation than other class B GPCRs, providing new insights into the mechanisms of activation of this class of receptor. Furthermore the data may aid in the understanding of how RAMPs modulate the signaling of other class B GPCRs.
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Affiliation(s)
- Michael J Woolley
- Institute of Clinical Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Christopher A Reynolds
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK
| | - John Simms
- School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, UK
| | | | - Juan Carlos Mobarec
- School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK
| | - Michael L Garelja
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Alex C Conner
- Institute of Clinical Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - David R Poyner
- School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, UK.
| | - Debbie L Hay
- School of Biological Sciences, University of Auckland, Auckland, New Zealand.
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6
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Singh Y, Gupta G, Shrivastava B, Dahiya R, Tiwari J, Ashwathanarayana M, Sharma RK, Agrawal M, Mishra A, Dua K. Calcitonin gene-related peptide (CGRP): A novel target for Alzheimer's disease. CNS Neurosci Ther 2017; 23:457-461. [PMID: 28417590 PMCID: PMC6492742 DOI: 10.1111/cns.12696] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 03/11/2017] [Accepted: 03/17/2017] [Indexed: 12/22/2022] Open
Abstract
Alzheimer's disease (AD) is leading cause of death among older characterized by neurofibrillary tangles, oxidative stress, progressive neuronal deficits, and increased levels of amyloid-β (Aβ) peptides. Cholinergic treatment could be the best suitable physiological therapy for AD. Calcitonin gene-related peptide (CGRP) is a thirty-seven-amino acid regulatory neuropeptide resulting from different merging of the CGRP gene, which also includes adrenomedullin, amylin, calcitonin, intermedin, and calcitonin receptor-stimulating peptide. It is a proof for a CGRP receptor within nucleus accumbens of brain that is different from either the CGRP1 or CGRP2 receptor in which it demonstrates similar high-affinity binding for salmon calcitonin, CGRP, and amylin, a possession which is not shared by any extra CGRP receptors. Binding of CGRP to its receptor increases activated cAMP-dependent pkA and PI3 kinase, resulting in N-terminal fragments that are shown to exert complex inhibitory as well facilitator actions on nAChRs. Fragments such as CGRP1-4, CGRP1-5, and CGRP1-6 rapidly as well as reversibly improve agonist sensitivity of nAChRs without straight stimulating those receptors and produce the Ca2+ -induced intracellular Ca2+ mobilization. Renin-angiotensin-aldosterone system (RAAS)-activated angiotensin-type (AT4) receptor is also beneficial in AD. It has been suggested that exogenous administration of CGRP inhibits infiltration of macrophages and expression of various inflammatory mediators such as NFkB, IL-1b, TNF-α, iNOS, matrix metalloproteinase (MMP)-9, and cell adhesion molecules like intercellular adhesion molecule (ICAM)-1 which attenuates consequence of inflammation in AD. Donepezil, a ChEI, inhibits acetylcholinesterase and produces angiogenesis and neurogenesis, in the dentate gyrus of the hippocampus of WT mice after donepezil administration. However, none of the results discovered in CGRP-knockout mice and WT mice exposed to practical denervation. Therefore, selective agonists of CGRP receptors may become the potential candidates for treatment of AD.
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Affiliation(s)
- Yogendra Singh
- School of PharmacyJaipur National UniversityJagatpuraJaipurIndia
| | - Gaurav Gupta
- School of PharmacyJaipur National UniversityJagatpuraJaipurIndia
- School of Medicine and Public HealthUniversity of NewcastleNewcastleNSWAustralia
| | | | - Rajiv Dahiya
- Laboratory of Peptide Research and DevelopmentSchool of Pharmacy, The University of the West IndiesSt. Augustine, Trinidad & TobagoWest Indies
| | - Juhi Tiwari
- School of PharmacyJaipur National UniversityJagatpuraJaipurIndia
| | | | | | - Mohit Agrawal
- School of pharmacySuresh Gyan Vihar UniversityJaipurIndia
| | - Anurag Mishra
- School of pharmacySuresh Gyan Vihar UniversityJaipurIndia
| | - Kamal Dua
- Discipline of PharmacyGraduate School of HealthUniversity of Technology SydneySydneyNSWAustralia
- School of Biomedical Sciences and PharmacyUniversity of NewcastleNewcastleNSWAustralia
- School of Pharmaceutical SciencesShoolini UniversitySolanHimachal PradeshIndia
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7
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Abstract
It is now recognized that G protein-coupled receptors (GPCRs), once considered largely independent functional units, have a far more diverse molecular architecture. Receptor activity-modifying proteins (RAMPs) provide an important example of proteins that interact with GPCRs to modify their function. RAMPs are able to act as pharmacological switches and chaperones, and they can regulate signaling and/or trafficking in a receptor-dependent manner. This review covers recent discoveries in the RAMP field and summarizes the known GPCR partners and functions of RAMPs. We also discuss the first peptide-bound structures of RAMP-GPCR complexes, which give insight into the molecular mechanisms that enable RAMPs to alter the pharmacology and signaling of GPCRs.
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Affiliation(s)
- Debbie L Hay
- School of Biological Sciences and Maurice Wilkins Center, University of Auckland, Auckland 1142, New Zealand;
| | - Augen A Pioszak
- Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104;
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8
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G-protein coupled receptor solubilization and purification for biophysical analysis and functional studies, in the total absence of detergent. Biosci Rep 2015; 35:BSR20140171. [PMID: 25720391 PMCID: PMC4400634 DOI: 10.1042/bsr20140171] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
G-protein coupled receptors (GPCRs) constitute the largest class of membrane proteins and are a major drug target. A serious obstacle to studying GPCR structure/function characteristics is the requirement to extract the receptors from their native environment in the plasma membrane, coupled with the inherent instability of GPCRs in the detergents required for their solubilization. In the present study, we report the first solubilization and purification of a functional GPCR [human adenosine A2A receptor (A2AR)], in the total absence of detergent at any stage, by exploiting spontaneous encapsulation by styrene maleic acid (SMA) co-polymer direct from the membrane into a nanoscale SMA lipid particle (SMALP). Furthermore, the A2AR–SMALP, generated from yeast (Pichia pastoris) or mammalian cells, exhibited increased thermostability (∼5°C) compared with detergent [DDM (n-dodecyl-β-D-maltopyranoside)]-solubilized A2AR controls. The A2AR–SMALP was also stable when stored for prolonged periods at 4°C and was resistant to multiple freeze-thaw cycles, in marked contrast with the detergent-solubilized receptor. These properties establish the potential for using GPCR–SMALP in receptor-based drug discovery assays. Moreover, in contrast with nanodiscs stabilized by scaffold proteins, the non-proteinaceous nature of the SMA polymer allowed unobscured biophysical characterization of the embedded receptor. Consequently, CD spectroscopy was used to relate changes in secondary structure to loss of ligand binding ([3H]ZM241385) capability. SMALP-solubilization of GPCRs, retaining the annular lipid environment, will enable a wide range of therapeutic targets to be prepared in native-like state to aid drug discovery and understanding of GPCR molecular mechanisms. It is universally acknowledged that exposing cell-surface receptors to detergent is detrimental. We have used a polymer to extract the receptor and surrounding lipid as a nanoparticle that provides a novel solution compatible with purification and receptor-based drug discovery assays.
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9
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Abstract
In mammals, secretin is a 27-amino acid peptide that was first studied in 1902 by Bayliss and Starling from the extracts of the jejunal mucosa for its ability to stimulate pancreatic secretion. To date, secretin has only been identified in tetrapods, with the earliest diverged secretin found in frogs. Despite being the first hormone discovered, secretin's evolutionary origin remains enigmatic, it shows moderate sequence identity in nonmammalian tetrapods but is highly conserved in mammals. Current hypotheses suggest that although secretin has already emerged before the divergence of osteichthyans, it was lost in fish and retained only in land vertebrates. Nevertheless, the cognate receptor of secretin has been identified in both actinopterygian fish (zebrafish) and sarcopterygian fish (lungfish). However, the zebrafish secretin receptor was shown to be nonbioactive. Based on the present information that the earliest diverged bioactive secretin receptor was found in lungfish, and its ability to interact with both vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide potently suggested that secretin receptor was descended from a VPAC-like receptor gene before the Actinopterygii-Sarcopterygii split in the vertebrate lineage. Hence, secretin and secretin receptor have gone through independent evolutionary trajectories despite their concurrent emergence post-2R. A functional secretin-secretin receptor axis has probably emerged in the amphibians. Although the pleiotropic actions of secretin are well documented in the literature, only limited information of its physiological functions in nonmammalian tetrapods have been reported. To decipher the structural and functional divergence of secretin and secretin receptor, functional characterization of the ligand-receptor pair in nonmammals would be the next perspective for investigation.
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Affiliation(s)
- Janice K V Tam
- School of Biological SciencesThe University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
| | - Leo T O Lee
- School of Biological SciencesThe University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
| | - Jun Jin
- School of Biological SciencesThe University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
| | - Billy K C Chow
- School of Biological SciencesThe University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
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10
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Abstract
The CGRP (calcitonin gene-related peptide) receptor is a family B GPCR (G-protein-coupled receptor). It consists of a GPCR, CLR (calcitonin receptor-like receptor) and an accessory protein, RAMP1 (receptor activity modifying protein 1). RAMP1 is needed for CGRP binding and also cell-surface expression of CLR. CLR is an example of a family B GPCR. Unlike family A GPCRs, little is known about how these receptors are activated by their endogenous ligands. This review considers what is known about the activation of family B GPCRs and then considers how this might be applied to CLR, particularly in light of new knowledge of the crystal structures of family A GPCRs.
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11
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Barwell J, Gingell JJ, Watkins HA, Archbold JK, Poyner DR, Hay DL. Calcitonin and calcitonin receptor-like receptors: common themes with family B GPCRs? Br J Pharmacol 2012; 166:51-65. [PMID: 21649645 DOI: 10.1111/j.1476-5381.2011.01525.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The calcitonin receptor (CTR) and calcitonin receptor-like receptor (CLR) are two of the 15 human family B (or Secretin-like) GPCRs. CTR and CLR are of considerable biological interest as their pharmacology is moulded by interactions with receptor activity-modifying proteins. They also have therapeutic relevance for many conditions, such as osteoporosis, diabetes, obesity, lymphatic insufficiency, migraine and cardiovascular disease. In light of recent advances in understanding ligand docking and receptor activation in both the family as a whole and in CLR and CTR specifically, this review reflects how applicable general family B GPCR themes are to these two idiosyncratic receptors. We review the main functional domains of the receptors; the N-terminal extracellular domain, the juxtamembrane domain and ligand interface, the transmembrane domain and the intracellular C-terminal domain. Structural and functional findings from the CLR and CTR along with other family B GPCRs are critically appraised to gain insight into how these domains may function. The ability for CTR and CLR to interact with receptor activity-modifying proteins adds another level of sophistication to these receptor systems but means careful consideration is needed when trying to apply generic GPCR principles. This review encapsulates current thinking in the realm of family B GPCR research by highlighting both conflicting and recurring themes and how such findings relate to two unusual but important receptors, CTR and CLR.
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Affiliation(s)
- James Barwell
- School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham, UK
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12
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Egea SC, Dickerson IM. Direct interactions between calcitonin-like receptor (CLR) and CGRP-receptor component protein (RCP) regulate CGRP receptor signaling. Endocrinology 2012; 153:1850-60. [PMID: 22315449 PMCID: PMC3320266 DOI: 10.1210/en.2011-1459] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Calcitonin gene-related peptide (CGRP) is a neuropeptide with multiple neuroendocrine roles, including vasodilation, migraine, and pain. The receptor for CGRP is a G protein-coupled receptor (GPCR) that requires three proteins for function. CGRP binds to a heterodimer composed of the GPCR calcitonin-like receptor (CLR) and receptor activity-modifying protein (RAMP1), a single transmembrane protein required for pharmacological specificity and trafficking of the CLR/RAMP1 complex to the cell surface. In addition, the CLR/RAMP1 complex requires a third protein named CGRP-receptor component protein (RCP) for signaling. Previous studies have demonstrated that depletion of RCP from cells inhibits CLR signaling, and in vivo studies have demonstrated that expression of RCP correlates with CLR signaling and CGRP efficacy. It is not known whether RCP interacts directly with CLR to exert its effect. The current studies identified a direct interaction between RCP and an intracellular domain of CLR using yeast two-hybrid analysis and coimmunoprecipitation. When this interacting domain of CLR was expressed as a soluble fusion protein, it coimmunoprecipitated with RCP and inhibited signaling from endogenous CLR. Expression of this dominant-negative domain of CLR did not significantly inhibit trafficking of CLR to the cell surface, and thus RCP may not have a chaperone function for CLR. Instead, RCP may regulate CLR signaling in the cell membrane, and direct interaction between RCP and CLR is required for CLR activation. To date, RCP has been found to interact only with CLR and represents a novel neuroendocrine regulatory step in GPCR signaling.
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Affiliation(s)
- Sophie C Egea
- Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33101, USA
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13
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Garcia GL, Dong M, Miller LJ. Differential determinants for coupling of distinct G proteins with the class B secretin receptor. Am J Physiol Cell Physiol 2012; 302:C1202-12. [PMID: 22277758 DOI: 10.1152/ajpcell.00273.2011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The secretin receptor is a prototypic class B G protein-coupled receptor that is activated by binding of its natural peptide ligand. The signaling effects of this receptor are mediated by coupling with Gs, which activates cAMP production, and Gq, which activates intracellular calcium mobilization. We have explored the molecular basis for the coupling of each of these G proteins to this receptor using systematic site-directed mutagenesis of key residues within each of the intracellular loop regions, and studying ligand binding and secretin-stimulated cAMP and calcium responses. Mutation of a conserved histidine in the first intracellular loop (H157A and H157R) markedly reduced cell surface expression, resulting in marked reduction in cAMP and elimination of measurable calcium responses. Mutation of an arginine (R153A) in the first intracellular loop reduced calcium, but not cAMP responses. Mutation of a dibasic motif in the second intracellular loop (R231A/K232A) had no significant effects on any measured responses. Mutations in the third intracellular loop involving adjacent lysine and leucine residues (K302A/L303A) or two arginine residues separated by a leucine and an alanine (R318A/R321A) significantly reduced cAMP responses, while the latter also reduced calcium responses. Additive effects were elicited by combining the effective mutations, while combining all the effective mutations resulted in a construct that continued to bind secretin normally, but that elicited no significant cAMP or calcium responses. These data suggest that, while some receptor determinants are clearly shared, there are also distinct determinants for coupling with each of these G proteins.
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Affiliation(s)
- Gene L Garcia
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Scottsdale, AZ 85259, USA
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14
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Conner M, Hicks MR, Dafforn T, Knowles TJ, Ludwig C, Staddon S, Overduin M, Günther UL, Thome J, Wheatley M, Poyner DR, Conner AC. Functional and biophysical analysis of the C-terminus of the CGRP-receptor; a family B GPCR. Biochemistry 2008; 47:8434-44. [PMID: 18636754 DOI: 10.1021/bi8004126] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
G-protein coupled receptors (GPCRs) typically have a functionally important C-terminus which, in the largest subfamily (family A), includes a membrane-parallel eighth helix. Mutations of this region are associated with several diseases. There are few C-terminal studies on the family B GPCRs and no data supporting the existence of a similar eighth helix in this second major subfamily, which has little or no sequence homology to family A GPCRs. Here we show that the C-terminus of a family B GPCR (CLR) has a disparate region from N400 to C436 required for CGRP-mediated internalization, and a proximal region of twelve residues (from G388 to W399), in a similar position to the family A eighth helix, required for receptor localization at the cell surface. A combination of circular and linear dichroism, fluorescence and modified waterLOGSY NMR spectroscopy (SALMON) demonstrated that a peptide mimetic of this domain readily forms a membrane-parallel helix anchored to the liposome by an interfacial tryptophan residue. The study reveals two key functions held within the C-terminus of a family B GPCR and presents support for an eighth helical region with striking topological similarity to the nonhomologous family A receptor. This helix structure appears to be found in most other family B GPCRs.
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15
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Glaser SS, Ueno Y, DeMorrow S, Chiasson VL, Katki KA, Venter J, Francis HL, Dickerson IM, DiPette DJ, Supowit SC, Alpini GD. Knockout of alpha-calcitonin gene-related peptide reduces cholangiocyte proliferation in bile duct ligated mice. J Transl Med 2007; 87:914-26. [PMID: 17618297 DOI: 10.1038/labinvest.3700602] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The role of sensory innervation in the regulation of liver physiology and the pathogenesis of cholestatic liver disease are undefined. Biliary proliferation has been shown to be coordinately controlled by parasympathetic and sympathetic innervation of the liver. The aim of our study was to address the role of the sensory neuropeptide calcitonin gene-related peptide (alpha-CGRP) in the regulation of cholangiocyte proliferation during cholestasis induced by extrahepatic bile duct obstruction (BDL). Our study utilized a knockout (KO) mouse model, which lacks the sensory neuropeptide alpha-CGRP. Wild-type (WT) and alpha-CGRP KO mice were subjected to sham surgery or BDL for 3 and 7 days. In addition, immediately after BDL, WT and KO mice were administered the CGRP receptor antagonist (CGRP(8-37)) for 3 and 7 days by osmotic minipumps. Liver sections and isolated cholangiocytes were evaluated for proliferation markers. Isolated WT BDL (3 days) cholangiocytes were stimulated with alpha- and beta-CGRP and evaluated for proliferation and cAMP-mediated signaling. Lack of alpha-CGRP inhibits cholangiocyte proliferation induced by BDL at both 3 and 7 days. BDL-induced cholangiocyte proliferation in WT mice was associated with increases of circulating alpha-CGRP levels. In vitro, alpha- and beta-CGRP stimulated proliferation in purified BDL cholangiocytes, induced elevation of cAMP levels, and stimulated the activation of cAMP-dependent protein kinase A and cAMP response element binding protein DNA binding. In conclusion, sensory innervation of the liver and biliary expression of alpha-CGRP play an important role in the regulation of cholangiocyte proliferation during cholestasis.
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Affiliation(s)
- Shannon S Glaser
- Department of Medicine, Scott & White Hospital, The Texas A&M University System Health Science Center, College of Medicine, Temple, TX 76504, USA
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16
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Conner AC, Simms J, Barwell J, Wheatley M, Poyner DR. Ligand binding and activation of the CGRP receptor. Biochem Soc Trans 2007; 35:729-32. [PMID: 17635135 DOI: 10.1042/bst0350729] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The receptor for CGRP (calcitonin gene-related peptide) is a heterodimer between a GPCR (G-protein-coupled receptor), CLR (calcitonin receptor-like receptor) and an accessory protein, RAMP1 (receptor activity-modifying protein 1). Models have been produced of RAMP1 and CLR. It is likely that the C-terminus of CGRP interacts with the extracellular N-termini of CLR and RAMP1; the extreme N-terminus of CLR is particularly important and may interact directly with CGRP and also with RAMP1. The N-terminus of CGRP interacts with the TM (transmembrane) portion of the receptor; the second ECL (extracellular loop) is especially important. Receptor activation is likely to involve the relative movements of TMs 3 and 6 to create a G-protein-binding pocket, as in Family A GPCRs. Pro321 in TM6 appears to act as a pivot. At the base of TMs 2 and 3, Arg151, His155 and Glu211 may form a loose equivalent of the Family A DRY (Asp-Arg-Tyr) motif. Although the details of this proposed activation mechanism clearly do not apply to all Family B GPCRs, the broad outlines may be conserved.
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Affiliation(s)
- A C Conner
- School of Medicine, University of Swansea, Swansea SA2 8PP, UK
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17
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Roy S, Rached M, Gallo-Payet N. Differential regulation of the human adrenocorticotropin receptor [melanocortin-2 receptor (MC2R)] by human MC2R accessory protein isoforms alpha and beta in isogenic human embryonic kidney 293 cells. Mol Endocrinol 2007; 21:1656-69. [PMID: 17456795 DOI: 10.1210/me.2007-0041] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The ACTH receptor [melanocortin-2 receptor (MC2R)] is the smallest known G protein-coupled receptor (GPCR). Herein, human MC2R accessory protein (MRAP) isoforms alpha and beta, cloned from a human fetal adrenal gland, were expressed with c-Myc-tagged MC2R (Myc-MC2R) in 293/Flp recombinase target site cells by homologous recombination. Although insertion of Myc-MC2R at the plasma membrane occurred without MRAP assistance, ACTH stimulation of cAMP production was only detected in cells coexpressing MC2R with either MRAP isoform. On the other hand, a MC2R-green fluorescent protein fusion transfected with either MRAPalpha or MRAPbeta was impaired both in cell membrane localization and signaling. MRAP isoforms were also tagged with either Flag or 6xHis epitopes. In cell populations coexpressing transiently and/or stably Myc-MC2R with MRAPalpha or MRAPbeta, stimulation with ACTH induced production of cAMP with EC(50) values lower in MRAPalpha- than in MRAPbeta-expressing cells. ACTH only bound Myc-MC2R in the presence of MRAP. Higher Myc-MC2R cell surface density was observed in the presence of MRAPbeta comparatively to MRAPalpha, possibly contributing to higher ACTH binding capacity and higher maximal cAMP responses observed in MRAPbeta-expressing cells. Immunofluorescence studies indicated that MRAP isoforms were localized near the plasma membrane and in the vicinity, but not colocalized, with Myc-MC2R. In summary, through the generation of a new all-human experimental model devoid of endogenous MCRs, we present evidence that human MRAP isoforms, although not essential for MC2R localization at the plasma membrane, are essential for ACTH binding and ACTH-induced cAMP production and that they differentially regulate, although modestly, cell membrane density and functional properties of MC2R.
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Affiliation(s)
- Simon Roy
- Service d'Endocrinologie, Département de Médecine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4
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18
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Matsumoto ML, Narzinski K, Kiser PD, Nikiforovich GV, Baranski TJ. A comprehensive structure-function map of the intracellular surface of the human C5a receptor. I. Identification of critical residues. J Biol Chem 2006; 282:3105-21. [PMID: 17135254 DOI: 10.1074/jbc.m607679200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptors are one of the largest protein families in nature; however, the mechanisms by which they activate G proteins are still poorly understood. To identify residues on the intracellular face of the human C5a receptor that are involved in G protein activation, we performed a genetic analysis of each of the three intracellular loops and the carboxyl-terminal tail of the receptor. Amino acid substitutions were randomly incorporated into each loop, and functional receptors were identified in yeast. The third intracellular loop contains the largest number of preserved residues (positions resistant to amino acid substitutions), followed by the second loop, the first loop, and lastly the carboxyl terminus. Surprisingly, complete removal of the carboxyl-terminal tail did not impair C5a receptor signaling. When mapped onto a three-dimensional structural model of the inactive state of the C5a receptor, the preserved residues reside on one half of the intracellular surface of the receptor, creating a potential activation face. Together these data provide one of the most comprehensive functional maps of the intracellular surface of any G protein-coupled receptor to date.
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Affiliation(s)
- Marissa L Matsumoto
- Department of Medicine and Molecular Biology, Washington School of Medicine, Missouri 63110, USA
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