title: Mammalian target of rapamycin complex I (mTORC1) activity in ras homologue enriched in brain (Rheb)-deficient mouse embryonic fibroblasts.
abstract: The Ras-like GTPase Rheb has been identified as a crucial activator of mTORC1. Activation most likely requires a direct interaction between Rheb and mTOR, but the exact mechanism remains unclear. Using a panel of Rheb-deficient mouse embryonic fibroblasts (MEFs), we show that Rheb is indeed essential for the rapid increase of mTORC1 activity following stimulation with insulin or amino acids. However, mTORC1 activity is less severely reduced in Rheb-deficient MEFs in the continuous presence of serum or upon stimulation with serum. This remaining mTORC1 activity is blocked by depleting the cells for amino acids or imposing energy stress. In addition, MEK inhibitors and the RSK-inhibitor BI-D1870 interfere in mTORC1 activity, suggesting that RSK acts as a bypass for Rheb in activating mTORC1. Finally, we show that this rapamycin-sensitive, Rheb-independent mTORC1 activity is important for cell cycle progression. In conclusion, whereas rapid adaptation in mTORC1 activity requires Rheb, a second Rheb-independent activation mechanism exists that contributes to cell cycle progression.
authors.affiliation: Molecular Cancer Research, Centre for Biomedical Genetics and Cancer Genomics Centre, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Marlous J
authors.initials: MJ
authors.lastname: Groenewoud
authors.forename: Susan M I
authors.initials: SM
authors.lastname: Goorden
authors.forename: Jorien
authors.initials: J
authors.lastname: Kassies
authors.forename: Wendy
authors.initials: W
authors.lastname: Pellis-van Berkel
authors.forename: Richard F
authors.initials: RF
authors.lastname: Lamb
authors.forename: Ype
authors.initials: Y
authors.lastname: Elgersma
authors.forename: Fried J T
authors.initials: FJ
authors.lastname: Zwartkruis
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D015870:Gene Expression; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D018345:Mice, Knockout; D020559:Monomeric GTP-Binding Proteins / Q000172:deficiency* / Q000235:genetics; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009479:Neuropeptides / Q000172:deficiency* / Q000235:genetics; D011247:Pregnancy; D034622:RNA Interference; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D046912:Multiprotein Complexes; D009479:Neuropeptides; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; C490213:Rheb protein, mouse; C540162:Rptor protein, mouse; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020123:Sirolimus