title: Akt regulates growth by directly phosphorylating Tsc2.
abstract: The direct mechanism by which the serine/threonine kinase Akt (also known as protein kinase B (PKB)) regulates cell growth is unknown. Here, we report that Drosophila melanogaster Akt/PKB stimulates growth by phosphorylating the tuberous sclerosis complex 2 (Tsc2) tumour suppressor and inhibiting formation of a Tsc1-Tsc2 complex. We show that Akt/PKB directly phosphorylates Drosophila Tsc2 in vitro at the conserved residues, Ser 924 and Thr 1518. Mutation of these sites renders Tsc2 insensitive to Akt/PKB signalling, increasing the stability of the Tsc1-Tsc2 complex within the cell. Stimulating Akt/PKB signalling in vivo markedly increases cell growth/size, disrupts the Tsc1-Tsc2 complex and disturbs the distinct subcellular localization of Tsc1 and Tsc2. Furthermore, all Akt/PKB growth signals are blocked by expression of a Tsc2 mutant lacking Akt phosphorylation sites. Thus, Tsc2 seems to be the critical target of Akt in mediating growth signals for the insulin signalling pathway.
authors.affiliation: Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536-0812, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Potter
authors.forename: Laura G
authors.initials: LG
authors.lastname: Pedraza
authors.forename: Tian
authors.initials: T
authors.lastname: Xu
mesh_terms: D000818:Animals; D001665:Binding Sites; D002455:Cell Division; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D005123:Eye / Q000254:growth & development; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
chemical_list: D029721:Drosophila Proteins; D007328:Insulin; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C494918:AKT1 protein, human; C494917:Akt1 protein, Drosophila; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt