Negative Regulation of the Serine/Threonine Kinase B-Raf by Akt

• Published in: The Journal of biological chemistry Vol. 275; no. 35; p. 27354
• Main Author: Guan, K.-L.
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 01.09.2000
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M004371200

B-Raf contains multiple Akt consensus sites located within its amino-terminal regulatory domain. One site, Ser 364 , is conserved with c-Raf but two additional sites, Ser 428 and Thr 439 , are unique to B-Raf. We have investigated the role of both the conserved and unique phosphorylation sites in the regulation of B-Raf activity in vitro and in vivo . We show that phosphorylation of B-Raf by Akt occurs at multiple residues within its amino-terminal regulatory domain, at both the conserved and unique phosphorylation sites. The alteration of the serine residues within the Akt consensus sites to alanines results in a progressive increase in enzymatic activity in vitro and in vivo . Furthermore, expression of Akt inhibits epidermal growth factor-induced B-Raf activity and inhibition of Akt with LY294002 up-regulates B-Raf activity, suggesting that Akt negatively regulates B-Raf in vivo . Our results demonstrate that B-Raf activity can be negatively regulated by Akt through phosphorylation in the amino-terminal regulatory domain of B-Raf. This cross-talk between the B-Raf and Akt serine/threonine kinases is likely to play an important role in modulating the signaling specificity of the Ras/Raf pathway and in promoting biological outcome.