title: Mechanistic target of rapamycin complex 1 (mTORC1)-mediated phosphorylation is governed by competition between substrates for interaction with raptor.
abstract: In this study, the interaction of mTORC1 with its downstream targets p70S6K1 and 4E-BP1 was evaluated in both mouse liver and mouse embryonic fibroblasts following combined disruption of the genes encoding 4E-BP1 and 4E-BP2. Phosphorylation of p70S6K1 was dramatically elevated in the livers of mice lacking 4E-BP1 and 4E-BP2 following feeding-induced activation of mTORC1. Immunoprecipitation of mTORC1 suggested that elevated phosphorylation was the result of enhanced interaction of p70S6K1 with raptor. These findings were extended to a cell culture system wherein loss of 4E-BP1 and 4E-BP2 resulted in elevated interaction of p70S6K1 with IGF1-induced activation of mTORC1 in conjunction with an enhanced rate of p70S6K1 phosphorylation at Thr-389. Furthermore, cotransfecting HA-p70S6K1 with 4E-BP1, but not 4E-BP1(F114A), reduced recovery of mTORC1 in HA-p70S6K1 immunoprecipitates. Together, these findings support the conclusion that, in the absence of 4E-BP proteins, mTORC1-mediated phosphorylation of p70S6K1 is elevated by a reduction in competition between the two substrates for interaction with raptor.
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Dennis
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Jefferson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D039642:Eukaryotic Initiation Factors / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D047468:Immunoprecipitation; D008099:Liver / Q000378:metabolism; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism*; D000076223:Regulatory-Associated Protein of mTOR; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014162:Transfection
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; C491255:Eif4ebp2 protein, mouse; D039642:Eukaryotic Initiation Factors; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011506:Proteins; D000076223:Regulatory-Associated Protein of mTOR; C540162:Rptor protein, mouse; D000076222:Mechanistic Target of Rapamycin Complex 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases