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Lack of beta-arrestin signaling in the absence of active G proteins

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      Abstract

      G protein-independent, arrestin-dependent signaling is a paradigm that broadens the signaling scope of G protein-coupled receptors (GPCRs) beyond G proteins for numerous biological processes. However, arrestin signaling in the collective absence of functional G proteins has never been demonstrated. Here we achieve a state of “zero functional G” at the cellular level using HEK293 cells depleted by CRISPR/Cas9 technology of the Gs/q/12 families of Gα proteins, along with pertussis toxin-mediated inactivation of Gi/o. Together with HEK293 cells lacking β-arrestins (“zero arrestin”), we systematically dissect G protein- from arrestin-driven signaling outcomes for a broad set of GPCRs. We use biochemical, biophysical, label-free whole-cell biosensing and ERK phosphorylation to identify four salient features for all receptors at “zero functional G”: arrestin recruitment and internalization, but—unexpectedly—complete failure to activate ERK and whole-cell responses. These findings change our understanding of how GPCRs function and in particular of how they activate ERK1/2.

      Abstract

      Arrestins terminate signaling from GPCRs, but several lines of evidence suggest that they are also able to transduce signals independently of G proteins. Here, the authors systematically ablate G proteins in cell lines, and show that arrestins are unable to act as genuine signal initiators.

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      Most cited references 68

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      Evolving the lock to fit the key to create a family of G protein-coupled receptors potently activated by an inert ligand.

      We evolved muscarinic receptors in yeast to generate a family of G protein-coupled receptors (GPCRs) that are activated solely by a pharmacologically inert drug-like and bioavailable compound (clozapine-N-oxide). Subsequent screening in human cell lines facilitated the creation of a family of muscarinic acetylcholine GPCRs suitable for in vitro and in situ studies. We subsequently created lines of telomerase-immortalized human pulmonary artery smooth muscle cells stably expressing all five family members and found that each one faithfully recapitulated the signaling phenotype of the parent receptor. We also expressed a G(i)-coupled designer receptor in hippocampal neurons (hM(4)D) and demonstrated its ability to induce membrane hyperpolarization and neuronal silencing. We have thus devised a facile approach for designing families of GPCRs with engineered ligand specificities. Such reverse-engineered GPCRs will prove to be powerful tools for selectively modulating signal-transduction pathways in vitro and in vivo.
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        The Orphan G protein-coupled receptors GPR41 and GPR43 are activated by propionate and other short chain carboxylic acids.

        GPR41 and GPR43 are related members of a homologous family of orphan G protein-coupled receptors that are tandemly encoded at a single chromosomal locus in both humans and mice. We identified the acetate anion as an agonist of human GPR43 during routine ligand bank screening in yeast. This activity was confirmed after transient transfection of GPR43 into mammalian cells using Ca(2+) mobilization and [(35)S]guanosine 5'-O-(3-thiotriphosphate) binding assays and by coexpression with GIRK G protein-regulated potassium channels in Xenopus laevis oocytes. Other short chain carboxylic acid anions such as formate, propionate, butyrate, and pentanoate also had agonist activity. GPR41 is related to GPR43 (52% similarity; 43% identity) and was activated by similar ligands but with differing specificity for carbon chain length, with pentanoate being the most potent agonist. A third family member, GPR42, is most likely a recent gene duplication of GPR41 and may be a pseudogene. GPR41 was expressed primarily in adipose tissue, whereas the highest levels of GPR43 were found in immune cells. The identity of the cognate physiological ligands for these receptors is not clear, although propionate is known to occur in vivo at high concentrations under certain pathophysiological conditions.
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          Structural diversity of G protein-coupled receptors and significance for drug discovery.

          G protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and also the targets of many drugs. Understanding of the functional significance of the wide structural diversity of GPCRs has been aided considerably in recent years by the sequencing of the human genome and by structural studies, and has important implications for the future therapeutic potential of targeting this receptor family. This article aims to provide a comprehensive overview of the five main human GPCR families--Rhodopsin, Secretin, Adhesion, Glutamate and Frizzled/Taste2--with a focus on gene repertoire, general ligand preference, common and unique structural features, and the potential for future drug discovery.
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            Author and article information

            Affiliations
            [1 ]ISNI 0000 0001 2240 3300, GRID grid.10388.32, Molecular, Cellular and Pharmacobiology Section, Institute for Pharmaceutical Biology, University of Bonn, ; Nussallee 6, 53115 Bonn, Germany
            [2 ]ISNI 0000 0001 2248 6943, GRID grid.69566.3a, Graduate School of Pharmaceutical Science, , Tohoku University, ; Sendai, 980-8578 Japan
            [3 ]ISNI 0000 0004 1754 9200, GRID grid.419082.6, PRESTO, Japan Science and Technology Agency (JST), ; 4-1-8, Honcho, Kawaguchi, 332-0012 Japan
            [4 ]ISNI 0000 0000 8517 6224, GRID grid.275559.9, Institute for Molecular Cell Biology, CMB-Center for Molecular Biomedicine, , University Hospital Jena, ; Hans-Knöll-Strasse2, 07745 Jena, Germany
            [5 ]ISNI 0000 0001 1958 8658, GRID grid.8379.5, Bio-Imaging-Center/Rudolf-Virchow-Center, Institute of Pharmacology, , University of Wuerzburg, ; Versbacher Str. 9, 97078 Würzburg, Germany
            [6 ]ISNI 0000 0001 2240 3300, GRID grid.10388.32, Institute for Pharmaceutical Biology, , University of Bonn, ; Nussallee 6, 53115 Bonn, Germany
            [7 ]ISNI 0000 0001 2240 3300, GRID grid.10388.32, Pharmaceutical Biochemistry and Bioanalytics, Institute of Pharmacy, , University of Bonn, ; An der Immenburg 4, 53121 Bonn, Germany
            [8 ]ISNI 0000 0004 5373 4593, GRID grid.480536.c, AMED-CREST, , Japan Agency for Medical Research and Development, ; 1-7-1 Otemachi, Tokyo, 100-0004 Japan
            [9 ]ISNI 0000 0001 2203 7304, GRID grid.419635.c, Molecular Signaling Section, , Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), ; Bethesda, MD 20892 USA
            Contributors
            kostenis@uni-bonn.de
            Journal
            Nat Commun
            Nat Commun
            Nature Communications
            Nature Publishing Group UK (London )
            2041-1723
            23 January 2018
            23 January 2018
            2018
            : 9
            29362459 5780443 2661 10.1038/s41467-017-02661-3
            © The Author(s) 2018

            Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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