Rheb Inhibits C-Raf Activity and B-Raf/C-Raf Heterodimerization

• Published in: The Journal of biological chemistry Vol. 281; no. 35; pp. 25447 - 25456
• Main Authors: Karbowniczek, Magdalena, Robertson, Gavin P., Henske, Elizabeth Petri
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-09-2006; American Society for Biochemistry and Molecular Biology
• Subjects: Cell Line; Dimerization; Gene Expression Regulation; Humans; Monomeric GTP-Binding Proteins - physiology; Neuropeptides - physiology; Phosphorylation; Protein Structure, Tertiary; Proto-Oncogene Proteins B-raf - chemistry; Proto-Oncogene Proteins B-raf - metabolism; Proto-Oncogene Proteins c-raf - antagonists & inhibitors; Proto-Oncogene Proteins c-raf - chemistry; Proto-Oncogene Proteins c-raf - metabolism; Ras Homolog Enriched in Brain Protein; Serine - chemistry; Signal Transduction; Sirolimus - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M605273200

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.