title: Phosphorylation of mammalian target of rapamycin (mTOR) at Ser-2448 is mediated by p70S6 kinase.
abstract: The mammalian target of rapamycin (mTOR) coordinates cell growth with the growth factor and nutrient/energy status of the cell. The phosphatidylinositol 3-kinase-AKT pathway is centrally involved in the transmission of mitogenic signals to mTOR. Previous studies have shown that mTOR is a direct substrate for the AKT kinase and identified Ser-2448 as the AKT target site in mTOR. In this study, we demonstrate that rapamycin, a specific inhibitor of mTOR function, blocks serum-stimulated Ser-2448 phosphorylation and that this drug effect is not explained by the inhibition of AKT. Furthermore, the phosphorylation of Ser-2448 was dependent on mTOR kinase activity, suggesting that mTOR itself or a protein kinase downstream from mTOR was responsible for the modification of Ser-2448. Here we show that p70S6 kinase phosphorylates mTOR at Ser-2448 in vitro and that ectopic expression of rapamycin-resistant p70S6 kinase restores Ser-2448 phosphorylation in rapamycin-treated cells. In addition, we show that cellular amino acid status, which modulates p70S6 kinase (S6K1) activity via the TSC/Rheb pathway, regulates Ser-2448 phosphorylation. Finally, small interfering RNA-mediated depletion of p70S6 kinase reduces Ser-2448 phosphorylation in cells. Taken together, these results suggest that p70S6 kinase is a major effector of mTOR phosphorylation at Ser-2448 in response to both mitogen- and nutrient-derived stimuli.
authors.affiliation: Program in Signal Transduction Research, The Burnham Institute, La Jolla, California 92037, USA. gchiang@burnham.org
authors.forename: Gary G
authors.initials: GG
authors.lastname: Chiang
authors.forename: Robert T
authors.initials: RT
authors.lastname: Abraham
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001798:Blood Proteins / Q000494:pharmacology; D001943:Breast Neoplasms; D004351:Drug Resistance; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney / Q000166:cytology; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism*; D034741:RNA, Small Interfering; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
chemical_list: D000900:Anti-Bacterial Agents; D001798:Blood Proteins; D034741:RNA, Small Interfering; D012694:Serine; D011494:Protein Kinases; C546842:MTOR protein, human; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus