1. Uncoupling Raf1 from MEK1/2 Impairs Only a Subset of Cellular Responses to Raf Activation
- Author
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Ron Bumeister, Michael A. White, Gray W. Pearson, Melanie H. Cobb, and Dale O. Henry
- Subjects
MAPK/ERK pathway ,Neurite ,MAP Kinase Kinase 2 ,Cell ,MAP Kinase Kinase 1 ,Protein Serine-Threonine Kinases ,Biology ,PC12 Cells ,Biochemistry ,Serine ,Mice ,Gene expression ,Neurites ,medicine ,Animals ,c-Raf ,Molecular Biology ,Mitogen-Activated Protein Kinase Kinases ,Effector ,Kinase ,3T3 Cells ,Cell Biology ,Protein-Tyrosine Kinases ,Recombinant Proteins ,Rats ,Cell biology ,Enzyme Activation ,Proto-Oncogene Proteins c-raf ,medicine.anatomical_structure - Abstract
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.
- Published
- 2000