title: Stalk-dependent and Stalk-independent Signaling by the Adhesion G Protein-coupled Receptors GPR56 (ADGRG1) and BAI1 (ADGRB1).
abstract: The adhesion G protein-coupled receptors (aGPCRs) are a large yet poorly understood family of seven-transmembrane proteins. A defining characteristic of the aGPCR family is the conserved GAIN domain, which has autoproteolytic activity and can cleave the receptors near the first transmembrane domain. Several aGPCRs, including ADGRB1 (BAI1 or B1) and ADGRG1 (GPR56 or G1), have been found to exhibit significantly increased constitutive activity when truncated to mimic GAIN domain cleavage (ΔNT). Recent reports have suggested that the new N-terminal stalk, which is revealed by GAIN domain cleavage, can directly activate aGPCRs as a tethered agonist. We tested this hypothesis in studies on two distinct aGPCRs, B1 and G1, by engineering mutant receptors lacking the entire NT including the stalk (B1- and G1-SL, with "SL" indicating "stalkless"). These receptors were evaluated in a battery of signaling assays and compared with full-length wild-type and cleavage-mimicking (ΔNT) forms of the two receptors. We found that B1-SL, in multiple assays, exhibited robust signaling activity, suggesting that the membrane-proximal stalk region is not necessary for its activation. For G1, however, the results were mixed, with the SL mutant exhibiting robust activity in several signaling assays (including TGFα shedding, activation of NFAT luciferase, and β-arrestin recruitment) but reduced activity relative to ΔNT in a distinct assay (activation of SRF luciferase). These data support a model in which the activation of certain pathways downstream of aGPCRs is stalk-dependent, whereas signaling to other pathways is stalk-independent.
authors.affiliation: From the Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Ayush
authors.initials: A
authors.lastname: Kishore
authors.affiliation: From the Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Ryan H
authors.initials: RH
authors.lastname: Purcell
authors.affiliation: From the Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Nassiri-Toosi
authors.affiliation: From the Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322 rhall3@emory.edu.
authors.forename: Randy A
authors.identifier: http://orcid.org/0000-0002-8318-8728
authors.initials: RA
authors.lastname: Hall
mesh_terms: D000494:Allosteric Regulation; D019943:Amino Acid Substitution; D042501:Angiogenic Proteins / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019390:Arrestins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D017930:Genes, Reporter; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D050778:NFATC Transcription Factors / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010446:Peptide Fragments / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D059748:Proteolysis; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D016211:Transforming Growth Factor alpha / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination; D000071557:beta-Arrestins
chemical_list: C468226:ADGRB1 protein, human; C118925:ADGRG1 protein, human; D042501:Angiogenic Proteins; D019390:Arrestins; D008024:Ligands; D050778:NFATC Transcription Factors; D010446:Peptide Fragments; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C587886:TGFA protein, human; D016211:Transforming Growth Factor alpha; D000071557:beta-Arrestins
keywords: G protein-coupled receptor (GPCR); arrestin; proteolysis; receptor structure-function; signal transduction; ubiquitylation (ubiquitination)