title: Insulin activation of Rheb, a mediator of mTOR/S6K/4E-BP signaling, is inhibited by TSC1 and 2.
abstract: Tumor suppressor genes evolved as negative effectors of mitogen and nutrient signaling pathways, such that mutations in these genes can lead to pathological states of growth. Tuberous sclerosis (TSC) is a potentially devastating disease associated with mutations in two tumor suppressor genes, TSC1 and 2, that function as a complex to suppress signaling in the mTOR/S6K/4E-BP pathway. However, the inhibitory target of TSC1/2 and the mechanism by which it acts are unknown. Here we provide evidence that TSC1/2 is a GAP for the small GTPase Rheb and that insulin-mediated Rheb activation is PI3K dependent. Moreover, Rheb overexpression induces S6K1 phosphorylation and inhibits PKB phosphorylation, as do loss-of-function mutations in TSC1/2, but contrary to earlier reports Rheb has no effect on MAPK phosphorylation. Finally, coexpression of a human TSC2 cDNA harboring a disease-associated point mutation in the GAP domain, failed to stimulate Rheb GTPase activity or block Rheb activation of S6K1.
authors.affiliation: Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058 Basel, Switzerland.
authors.forename: Attila
authors.initials: A
authors.lastname: Garami
authors.forename: Fried J T
authors.initials: FJ
authors.lastname: Zwartkruis
authors.forename: Takahiro
authors.initials: T
authors.lastname: Nobukuni
authors.forename: Manel
authors.initials: M
authors.lastname: Joaquin
authors.forename: Marta
authors.initials: M
authors.lastname: Roccio
authors.forename: Hugo
authors.initials: H
authors.lastname: Stocker
authors.forename: Sara C
authors.initials: SC
authors.lastname: Kozma
authors.forename: Ernst
authors.initials: E
authors.lastname: Hafen
authors.forename: Johannes L
authors.initials: JL
authors.lastname: Bos
authors.forename: George
authors.initials: G
authors.lastname: Thomas
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002460:Cell Line; D002522:Chlorocebus aethiops; D016147:Genes, Tumor Suppressor; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D017354:Point Mutation; D011494:Protein Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D000076205:Ras Homolog Enriched in Brain Protein; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D007328:Insulin; D020559:Monomeric GTP-Binding Proteins; D009479:Neuropeptides; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D011506:Proteins; D000076205:Ras Homolog Enriched in Brain Protein; D012097:Repressor Proteins; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C087000:EIF4EBP1 protein, human; C490211:RHEB protein, human; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; C546842:MTOR protein, human