title: Rheb inhibits C-raf activity and B-raf/C-raf heterodimerization.
abstract: The Ras-Raf-MEK signaling cascade is critical for normal development and is activated in many forms of cancer. We have recently shown that B-Raf kinase interacts with and is inhibited by Rheb, the target of the GTPase-activating domain of the tuberous sclerosis complex 2 gene product tuberin. Here, we demonstrate for the first time that activation of Rheb is associated with decreased B-Raf and C-Raf phosphorylation at residues Ser-446 and Ser-338, respectively, concomitant with a decrease in the activities of both kinases and decreased heterodimerization of B-Raf and C-Raf. Importantly, the impact of Rheb on B-Raf/C-Raf heterodimerization and kinase activity are rapamycin-insensitive, indicating that they are independent of Rheb activation of the mammalian target of rapamycin-Raptor complex. In addition, we found that Rheb inhibits the association of B-Raf with H-Ras. Taken together, these results support a central role of Rheb in the regulation of the Ras/B-Raf/C-Raf/MEK signaling network.
authors.affiliation: Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Karbowniczek
authors.forename: Gavin P
authors.initials: GP
authors.lastname: Robertson
authors.forename: Elizabeth Petri
authors.initials: EP
authors.lastname: Henske
mesh_terms: D002460:Cell Line; D019281:Dimerization; D005786:Gene Expression Regulation; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000502:physiology*; D009479:Neuropeptides / Q000502:physiology*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D048493:Proto-Oncogene Proteins B-raf / Q000737:chemistry / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D000076205:Ras Homolog Enriched in Brain Protein; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology
chemical_list: D009479:Neuropeptides; C490211:RHEB protein, human; D000076205:Ras Homolog Enriched in Brain Protein; D012694:Serine; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D020559:Monomeric GTP-Binding Proteins; D020123:Sirolimus