title: A new role for the p85-phosphatidylinositol 3-kinase regulatory subunit linking FRAP to p70 S6 kinase activation.
abstract: The serine/threonine kinase p70 S6 kinase (p70S6K) phosphorylates the 40 S ribosomal protein S6, modulating the translation of an mRNA subset that encodes ribosomal proteins and translation elongation factors. p70S6K is activated in response to mitogenic stimuli and is required for progression through the G(1) phase of the cell cycle and for cell growth. Activation of p70S6K is regulated by phosphorylation of seven different residues distributed throughout the protein, a subset of which depends on the activity of p85/p110 phosphatidylinositol 3-kinase (PI3K); in fact, the phosphorylation status of Thr(229) and Thr(389) is intimately linked to PI3K activity. In the full-length enzyme, however, these sites are also acutely sensitive to the action of FKBP 12-rapamycin-associated protein (FRAP). The mechanism by which PI3K and FRAP cooperate to induce p70S6K activation remains unclear. Here we show that the p85 regulatory subunit of PI3K also controls p70S6K activation by mediating formation of a ternary complex with p70S6K and FRAP. The p85 C-terminal SH2 domain is responsible for p85 coupling to p70S6K and FRAP, because deletion of the C-terminal SH2 domain inhibits complex formation and impairs p70S6K activation by PI3K. Formation of this complex is not required for activation of a FRAP-independent form of p70S6K, however, underscoring the role of p85 in regulating FRAP-dependent p70S6K activation. These studies thus show that, in addition to the contribution of PI3K activity, the p85 regulatory subunit plays a critical role in p70S6K activation.
authors.affiliation: Department of Immunology and Oncology, Centro Nacional de Biotecnologia, Consejo Superior de Investigaciones Cientificas, Carretera de Colmenar Km 15, Cantoblanco, Madrid E-28049, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Gonzalez-Garcia
authors.forename: Elia
authors.initials: E
authors.lastname: Garrido
authors.forename: Carmen
authors.initials: C
authors.lastname: Hernandez
authors.forename: Beatriz
authors.initials: B
authors.lastname: Alvarez
authors.forename: Concepcion
authors.initials: C
authors.lastname: Jimenez
authors.forename: Doreen A
authors.initials: DA
authors.lastname: Cantrell
authors.forename: Nicholas
authors.initials: N
authors.lastname: Pullen
authors.forename: Ana C
authors.initials: AC
authors.lastname: Carrera
mesh_terms: D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D020104:Immunophilins / Q000378:metabolism*; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000099221:Protein Kinase C zeta
chemical_list: D020104:Immunophilins; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D000099221:Protein Kinase C zeta