title: Dissociation of raptor from mTOR is a mechanism of rapamycin-induced inhibition of mTOR function.
abstract: The mammalian target of rapamycin (mTOR) is a Ser/Thr protein kinase that plays a crucial role in a nutrient-sensitive signalling pathway that regulates cell growth. TOR signalling is potently inhibited by rapamycin, through the direct binding of a FK506-binding protein 12 (FKBP12)/rapamycin complex to the TOR FRB domain, a segment amino terminal to the kinase catalytic domain. The molecular basis for the inhibitory action of FKBP12/rapamycin remains uncertain. Raptor (regulatory associated protein of mTOR) is a recently identified mTOR binding partner that is essential for mTOR signalling in vivo, and whose binding to mTOR is critical for mTOR-catalysed substrate phosphorylation in vitro. Here we investigated the stability of endogenous mTOR/raptor complex in response to rapamycin in vivo, and to the direct addition of a FKBP12/rapamycin complex in vitro. Rapamycin diminished the recovery of endogenous raptor with endogenous or recombinant mTOR in vivo; this inhibition required the ability of mTOR to bind the FKBP12/rapamycin complex, but was independent of mTOR kinase activity. Rapamycin, in the presence of FKBP12, inhibited the association of raptor with mTOR directly in vitro, and concomitantly reduced the mTOR-catalysed phosphorylation of raptor-dependent, but not raptor-independent substrates; mTOR autophosphorylation was unaltered. These observations indicate that rapamycin inhibits mTOR function, at least in part, by inhibiting the interaction of raptor with mTOR; this action uncouples mTOR from its substrates, and inhibits mTOR signalling without altering mTOR's intrinsic catalytic activity.
authors.affiliation: Biosignal Research Center, Kobe University, Kobe 657-8501, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Oshiro
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Yoshino
authors.forename: Sujuti
authors.initials: S
authors.lastname: Hidayat
authors.forename: Chiharu
authors.initials: C
authors.lastname: Tokunaga
authors.forename: Kenta
authors.initials: K
authors.lastname: Hara
authors.forename: Satoshi
authors.initials: S
authors.lastname: Eguchi
authors.forename: Joseph
authors.initials: J
authors.lastname: Avruch
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Yonezawa
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D004305:Dose-Response Relationship, Drug; D006801:Humans; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D000076223:Regulatory-Associated Protein of mTOR; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D020123:Sirolimus / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases; D022061:Tacrolimus Binding Protein 1A / Q000037:antagonists & inhibitors
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D011506:Proteins; C463659:RPTOR protein, human; D000076223:Regulatory-Associated Protein of mTOR; D011494:Protein Kinases; C546842:MTOR protein, human; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D022061:Tacrolimus Binding Protein 1A; D020123:Sirolimus