Uncoupling Raf1 from MEK1/2 impairs only a subset of cellular responses to Raf activation.
The Raf family of serine/threonine protein kinases is intimately involved in the transmission of cell regulatory signals controlling proliferation and differentiation. The best characterized Raf substrates are MEK1 and MEK2. The activation of MEK1/2 by Raf is required to mediate many of the cellular responses to Raf activation, suggesting that MEK1/2 are the dominant Raf effector proteins. However, accumulating evidence suggests that there are additional Raf substrates and that subsets of Raf-induced regulatory events are mediated independently of Raf activation of MEK1/2. To examine the possibility that there is bifurcation at the level of Raf in activation of MEK1/2-dependent and MEK1/2-independent cell regulatory events, we engineered a kinase-active Raf1 variant (RafBXB(T481A)) with an amino acid substitution that disrupts MEK1 binding. We find that disruption of MEK1/2 association uncouples Raf from activation of ERK1/2, induction of serum-response element-dependent gene expression, and induction of growth and morphological transformation. However, activation of NF-kappaB-dependent gene expression and induction of neurite differentiation were unimpaired. In addition, Raf-dependent activation of p90 ribosomal S6 kinase was only slightly impaired. These results support the hypothesis that Raf kinases utilize multiple downstream effectors to regulate distinct cellular activities.
Pearson
G
G
Departments of Cell Biology and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Bumeister
R
R
Henry
D O
DO
Cobb
M H
MH
White
M A
MA
D016475:3T3 Cells; D000818:Animals; D004789:Enzyme Activation; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D016501:Neurites; D016716:PC12 Cells; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism
D011994:Recombinant Proteins; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases