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Ras recruits Raf‐1 to the plasma membrane for activation by tyrosine phosphorylation.
Author(s) -
Marais R.,
Light Y.,
Paterson H.F.,
Marshall C.J.
Publication year - 1995
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1995.tb07316.x
Subject(s) - proto oncogene tyrosine protein kinase src , receptor tyrosine kinase , tyrosine phosphorylation , biology , phosphorylation , sh3 domain , tyrosine kinase , microbiology and biotechnology , sh2 domain , phosphorylation cascade , grb2 , signal transduction , tyrosine , biochemistry , protein kinase a , protein phosphorylation
A central feature of signal transduction downstream of both receptor and oncogenic tyrosine kinases is the Ras‐dependent activation of a protein kinase cascade consisting of Raf‐1, Mek (MAP kinase kinase) and ERKs (MAP kinases). To study the role of tyrosine kinase activity in the activation of Raf‐1, we have examined the properties of p74Raf‐1 and oncogenic Src that are necessary for activation of p74Raf‐1. We show that in mammalian cells activation of p74Raf‐1 by oncogenic Src requires pp60Src to be myristoylated and the ability of p74Raf‐1 to interact with p21Ras‐GTP. The Ras/Raf interaction is required for p21Ras‐GTP to bring p74Raf‐1 to the plasma membrane for phosphorylation at tyrosine 340 or 341, probably by membrane‐bound pp60Src. When oncogenic Src is expressed with Raf‐1, p74Raf‐1 is activated 5‐fold; however, when co‐expressed with oncogenic Ras and Src, Raf‐1 is activated 25‐fold and this is associated with a further 3‐fold increase in tyrosine phosphorylation. Thus, p21Ras‐GTP is the limiting component in bringing p74Raf‐1 to the plasma membrane for tyrosine phosphorylation. Using mutants of Raf‐1 at Tyr340/341, we show that in addition to tyrosine phosphorylation at these sites, there is an additional activation step resulting from p21Ras‐GTP recruiting p74Raf‐1 to the plasma membrane. Thus, the role of Ras in Raf‐1 activation is to bring p74Raf‐1 to the plasma membrane for at least two different activation steps.