title: Sub-picomolar relaxin signalling by a pre-assembled RXFP1, AKAP79, AC2, beta-arrestin 2, PDE4D3 complex.
abstract: Biochemical studies suggest that G-protein-coupled receptors (GPCRs) achieve exquisite signalling specificity by forming selective complexes, termed signalosomes. Here, using cAMP biosensors in single cells, we uncover a pre-assembled, constitutively active GPCR signalosome, that couples the relaxin receptor, relaxin family peptide receptor 1 (RXFP1), to cAMP following receptor stimulation with sub-picomolar concentrations of peptide. The physiological effects of relaxin, a pleiotropic hormone with therapeutic potential in cancer metastasis and heart failure, are generally attributed to local production of the peptide, that occur in response to sub-micromolar concentrations. The highly sensitive signalosome identified here provides a regulatory mechanism for the extremely low levels of relaxin that circulate. The signalosome includes requisite Galpha(s), Gbetagamma and adenylyl cyclase 2 (AC2); AC2 is functionally coupled to RXFP1 through AKAP79 binding to helix 8 of the receptor; activation of AC2 is tonically opposed by protein kinase A (PKA)-activated PDE4D3, scaffolded through a beta-arrestin 2 interaction with Ser(704) of the receptor C-terminus. This elaborate, pre-assembled, ligand-independent GPCR signalosome represents a new paradigm in GPCR signalling and provides a mechanism for the distal actions of low circulating levels of relaxin.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge, UK.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Halls
authors.forename: Dermot M F
authors.initials: DM
authors.lastname: Cooper
mesh_terms: D054758:A Kinase Anchor Proteins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4 / Q000378:metabolism; D006801:Humans; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*; D012065:Relaxin / Q000378:metabolism*; D015398:Signal Transduction; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
chemical_list: D054758:A Kinase Anchor Proteins; C487775:AKAP5 protein, human; C000605254:ARRB2 protein, human; D048868:Adaptor Proteins, Signal Transducing; C000605257:Arrb2 protein, rat; D019390:Arrestins; C417543:RXFP1 protein, human; D043562:Receptors, G-Protein-Coupled; D018000:Receptors, Peptide; C504789:Rxfp1 protein, rat; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; C033395:relaxin receptors; D012065:Relaxin; D000242:Cyclic AMP; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D000262:Adenylyl Cyclases; C100622:adenylyl cyclase 2