title: Rheb binds tuberous sclerosis complex 2 (TSC2) and promotes S6 kinase activation in a rapamycin- and farnesylation-dependent manner.
abstract: Recently the tuberous sclerosis complex 2 (TSC2) tumor suppressor gene product has been identified as a negative regulator of protein synthesis upstream of the mTOR and ribosomal S6 kinases. Because of the homology of TSC2 with GTPase-activating proteins for Rap1, we examined whether a Ras/Rap-related GTPase might be involved in this process. TSC2 was found to bind to Rheb-GTP in vitro and to reduce Rheb GTP levels in vivo. Over-expression of Rheb but not Rap1 promoted the activation of S6 kinase in a rapamycin-dependent manner, suggesting that Rheb acts upstream of mTOR. The ability of Rheb to induce S6 phosphorylation was also inhibited by a farnesyl transferase inhibitor, suggesting that Rheb may be responsible for the Ras-independent anti-neoplastic properties of this drug.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine and Walther Cancer Institute, Indianapolis, Indiana 46202, USA. acastro@iupui.edu
authors.forename: Ariel F
authors.initials: AF
authors.lastname: Castro
authors.forename: John F
authors.initials: JF
authors.lastname: Rebhun
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Clark
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Quilliam
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D002460:Cell Line; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D015151:Immunoblotting; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017368:Protein Prenylation; D000076205:Ras Homolog Enriched in Brain Protein; D012097:Repressor Proteins / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
chemical_list: D000970:Antineoplastic Agents; D009479:Neuropeptides; C490211:RHEB protein, human; D000076205:Ras Homolog Enriched in Brain Protein; D012097:Repressor Proteins; C000624653:TSC2 protein, human; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C546842:MTOR protein, human; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020123:Sirolimus