title: Relieving autophagy and 4EBP1 from rapamycin resistance.
abstract: The mammalian target of rapamycin complex 1 (mTORC1) is a multiprotein signaling complex regulated by oncogenes and tumor suppressors. Outputs downstream of mTORC1 include ribosomal protein S6 kinase 1 (S6K1), eukaryotic translation initiation factor 4E (eIF4E), and autophagy, and their modulation leads to changes in cell growth, proliferation, and metabolism. Rapamycin, an allosteric mTORC1 inhibitor, does not antagonize equally these outputs, but the reason for this is unknown. Here, we show that the ability of rapamycin to activate autophagy in different cell lines correlates with mTORC1 stability. Rapamycin exposure destabilizes mTORC1, but in cell lines where autophagy is drug insensitive, higher levels of mTOR-bound raptor are detected than in cells where rapamycin stimulates autophagy. Using small interfering RNA (siRNA), we find that knockdown of raptor relieves autophagy and the eIF4E effector pathway from rapamycin resistance. Importantly, nonefficacious concentrations of an ATP-competitive mTOR inhibitor can be combined with rapamycin to synergistically inhibit mTORC1 and activate autophagy but leave mTORC2 signaling intact. These data suggest that partial inhibition of mTORC1 by rapamycin can be overcome using combination strategies and offer a therapeutic avenue to achieve complete and selective inhibition of mTORC1.
authors.affiliation: Developmental and Molecular Pathways, Novartis Institutes for BioMedical Research, 250 Massachusetts Avenue, Cambridge,Massachusetts 02139, USA.
authors.forename: Beat
authors.initials: B
authors.lastname: Nyfeler
authors.forename: Philip
authors.initials: P
authors.lastname: Bergman
authors.forename: Ellen
authors.initials: E
authors.lastname: Triantafellow
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Wilson
authors.forename: Yanyi
authors.initials: Y
authors.lastname: Zhu
authors.forename: Branko
authors.initials: B
authors.lastname: Radetich
authors.forename: Peter M
authors.initials: PM
authors.lastname: Finan
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Klionsky
authors.forename: Leon O
authors.initials: LO
authors.lastname: Murphy
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects*; D018797:Cell Cycle Proteins; D002460:Cell Line; D004351:Drug Resistance / Q000502:physiology*; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010750:Phosphoproteins / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D000076223:Regulatory-Associated Protein of mTOR; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D005456:Fluorescent Dyes; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011506:Proteins; D034741:RNA, Small Interfering; C463659:RPTOR protein, human; D000076223:Regulatory-Associated Protein of mTOR; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus