MEK kinase activity is not necessary for Raf-1 function

EMBO J. 2001 Apr 17;20(8):1940-51. doi: 10.1093/emboj/20.8.1940.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Cell Division
  • Embryo, Mammalian / pathology
  • Genes, Essential
  • Genotype
  • Heterozygote
  • Homozygote
  • MAP Kinase Kinase Kinase 1*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mutation
  • Phenotype
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins c-raf / genetics
  • Proto-Oncogene Proteins c-raf / metabolism*
  • Signal Transduction
  • Yolk Sac / blood supply
  • Yolk Sac / pathology


  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • MAP Kinase Kinase Kinase 1
  • Map3k1 protein, mouse