MEK kinase activity is not necessary for Raf-1 function
Martin Hüser,
Jeni Luckett,
Antonio Chiloeches1,
Kathryn Mercer,
Mabel Iwobi,
Susan Giblett,
Xiao-Ming Sun2,
Jane Brown3,
Richard Marais1, and
Catrin Pritchard4
Department of Biochemistry, 2MRC Toxicology Unit and 3Division of Biomedical Services, University of Leicester, University Road, Leicester LE1 7RH and 1Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK 4Corresponding author e-mail: cap8{at}le.ac.ukM.Hüser, J.Luckett and A.Chiloeches contributed equally to this work
Abstract:
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-1FF/FF mice has no detectable activity towards MEK in vitro, and yet raf-1FF/FF mice survive to adulthood, are fertile and have an apparently normal phenotype. In cells derived from both the raf-1–/– and raf-1FF/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.
Key Words: Keywords: apoptosis/knockout/MEK kinase/Raf-1/tyrosine phosphorylation
