MEK kinase activity is not necessary for Raf-1 function.
Raf-1 protein kinase has been identified as an integral component of the Ras/Raf/MEK/ERK signalling pathway in mammals. Activation of Raf-1 is achieved by RAS:GTP binding and other events at the plasma membrane including tyrosine phosphorylation at residues 340/341. We have used gene targeting to generate a 'knockout' of the raf-1 gene in mice as well as a rafFF mutant version of endogenous Raf-1 with Y340FY341F mutations. Raf-1(-/-) mice die in embryogenesis and show vascular defects in the yolk sac and placenta as well as increased apoptosis of embryonic tissues. Cell proliferation is not affected. Raf-1 from cells derived from raf-1(FF/FF) mice has no detectable activity towards MEK in vitro, and yet raf-1(FF/FF) mice survive to adulthood, are fertile and have an apparently normal phenotype. In cells derived from both the raf-1(-/-) and raf-1(FF/FF) mice, ERK activation is normal. These results strongly argue that MEK kinase activity of Raf-1 is not essential for normal mouse development and that Raf-1 plays a key role in preventing apoptosis.
Hüser
M
M
Department of Biochemistry, MRC Toxicology Unit and Division of Biomedical Services, University of Leicester, University Road, Leicester LE1 7RH, UK.
Luckett
J
J
Chiloeches
A
A
Mercer
K
K
Iwobi
M
M
Giblett
S
S
Sun
X M
XM
Brown
J
J
Marais
R
R
Pritchard
C
C
D000818:Animals; D017209:Apoptosis; D002455:Cell Division; D004622:Embryo, Mammalian / Q000473:pathology; D020043:Genes, Essential; D005838:Genotype; D006579:Heterozygote; D006720:Homozygote; D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D015017:Yolk Sac / Q000098:blood supply / Q000473:pathology
D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048728:MAP Kinase Kinase Kinase 1; C482578:Map3k1 protein, mouse