Rheb binds and regulates the mTOR kinase.
BACKGROUND
The target of rapamycin (TOR), in complex with the proteins raptor and LST8 (TOR complex 1), phosphorylates the p70S6K and 4E-BP1 to promote mRNA translation. Genetic evidence establishes that TOR complex activity in vivo requires the small GTPase Rheb, and overexpression of Rheb can rescue TOR from inactivation in vivo by amino-acid withdrawal. The Tuberous Sclerosis heterodimer (TSC1/TSC2) functions as a Rheb GTPase activator and inhibits TOR signaling in vivo.


RESULTS
Here, we show that Rheb binds to the TOR complex specifically, independently of its ability to bind TSC2, through separate interactions with the mTOR catalytic domain and with LST8. Rheb binding to the TOR complex in vivo and in vitro does not require Rheb guanyl nucleotide charging but is modulated by GTP and impaired by certain mutations (Ile39Lys) in the switch 1 loop. Nucleotide-deficient Rheb mutants, although capable of binding mTOR in vivo and in vitro, are inhibitory in vivo, and the mTOR polypeptides that associate with nucleotide-deficient Rheb in vivo lack kinase activity in vitro. Reciprocally, mTOR polypeptides bound to Rheb(Gln64Leu), a mutant that is nearly 90% GTP charged, exhibit substantially higher protein kinase specific activity than mTOR bound to wild-type Rheb.


CONCLUSIONS
The TOR complex 1 is a direct target of Rheb-GTP, whose binding enables activation of the TOR kinase.
Long
Xiaomeng
X
Diabetes Unit and Medical Services and Department of Molecular Biology, Massachusetts General Hospital, Boston, 02114, USA.
Lin
Yenshou
Y
Ortiz-Vega
Sara
S
Yonezawa
Kazuyoshi
K
Avruch
Joseph
J
D048868:Adaptor Proteins, Signal Transducing; D002478:Cells, Cultured; D017931:DNA Primers; D004789:Enzyme Activation / Q000502:physiology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000235:genetics; D014176:Protein Biosynthesis / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins; D012333:RNA, Messenger / Q000378:metabolism*; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D012097:Repressor Proteins / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D014162:Transfection; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; D009479:Neuropeptides; D011506:Proteins; C490211:RHEB protein, human; D012333:RNA, Messenger; C463659:RPTOR protein, human; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D012097:Repressor Proteins; C000624653:TSC2 protein, human; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D006160:Guanosine Triphosphate; D011494:Protein Kinases; C546842:MTOR protein, human; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins