title: A new HECT ubiquitin ligase regulating chemotaxis and development in Dictyostelium discoideum.
abstract: Cyclic AMP (cAMP) binding to G-protein-coupled receptors (GPCRs) orchestrates chemotaxis and development in Dictyostelium. By activating the RasC-TORC2-PKB (PKB is also known as AKT in mammals) module, cAMP regulates cell polarization during chemotaxis. TORC2 also mediates GPCR-dependent stimulation of adenylyl cyclase A (ACA), enhancing cAMP relay and developmental gene expression. Thus, mutants defective in the TORC2 Pia subunit (also known as Rictor in mammals) are impaired in chemotaxis and development. Near-saturation mutagenesis of a Pia mutant by random gene disruption led to selection of two suppressor mutants in which spontaneous chemotaxis and development were restored. PKB phosphorylation and chemotactic cell polarization were rescued, whereas Pia-dependent ACA stimulation was not restored but bypassed, leading to cAMP-dependent developmental gene expression. Knocking out the gene encoding the adenylylcyclase B (ACB) in the parental strain showed ACB to be essential for this process. The gene tagged in the suppressor mutants encodes a newly unidentified HECT ubiquitin ligase that is homologous to mammalian HERC1, but harbours a pleckstrin homology domain. Expression of the isolated wild-type HECT domain, but not a mutant HECT C5185S form, from this protein was sufficient to reconstitute the parental phenotype. The new ubiquitin ligase appears to regulate cell sensitivity to cAMP signalling and TORC2-dependent PKB phosphorylation.
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano (TO) 10043, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Pergolizzi
authors.affiliation: Department of Oncology, University of Torino, AOU S. Luigi, Orbassano (TO) 10043, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Bracco
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano (TO) 10043, Italy salvatore.bozzaro@unito.it.
authors.forename: Salvatore
authors.identifier: 0000-0001-6323-6190
authors.initials: S
authors.lastname: Bozzaro
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D016764:Cell Polarity; D002633:Chemotaxis; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics; D019204:GTP-Binding Proteins / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D016153:Genes, Suppressor; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010766:Phosphorylation; D000072417:Protein Domains; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D013379:Substrate Specificity; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; D004247:DNA; D000242:Cyclic AMP; D044767:Ubiquitin-Protein Ligases; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases
keywords: Dictyostelium; HECT ubiquitin ligase; HERC1; Pia; Rictor; TORC2; cAMP signalling