MEK kinase activity is not necessary for Raf-1 function

Abstract

contributed equally to this work Raf-1 protein kinase has been identi®ed 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.

c-Jun, at the crossroad of the signaling network

“…Some of the knockout mice, including Raf-1(−/−), Map3k3(−/−) and Map3k4(−/−), die in embryogenesis but of different causes Kuan et al, 1999). The Raf-1(−/−) fetuses show vascular defects in the yolk sac and placenta as well as increased apoptosis of embryonic tissues (Hüser et al, 2001), the Map3k3(−/−) embryos die due to impaired blood vessels development (Yang et al, 2000), while the Map3k4(−/−) mice die from neural tube defects associated with massively elevated apoptosis before and during neural tube closure (Chi et al, 2005). On the other hand, some MAPKKK knockout mice, such as Ask1(−/−), Tpl2(−/−) and Map3k2 (−/−), survive embryonic development and are born alive with no overt developmental defects.…”

Rho kinase in the regulation of cell death and survival

“…Fas activation stimulates the formation of Raf-1-ROCK2 complexes thereby down-regulating ROCK2 activity. This mechanism may contribute to the phenotype of Raf-1 deficient mice such as fetal liver apoptosis, embryonic lethality, and selective hypersensitivity to Fas-induced cell death [52,87].…”

Le rôle des kinasesMek1etMek2dans la formation de la barrière hématoplacentaire chez la souris

“…Réduction de la couche des spongiotrophoblastes et diminution du nombre de vaisseaux embryonnaires du labyrinthe [18] K-Ras G12D Absence de l'invasion de la vascularisation embryonnaire dans la région du labyrinthe [19] …”

“…Le rôle de la voie ERK/MAPK lors du développement placentaire a été largement démontré chez la souris par la caractérisation de mutants pour des gènes associés à l'activation de la voie. Les mutants Erk2, Fgfr2, Gab1 (GRB2-associated-binding protein 1), Mek1, Sos1, b-Raf, Raf-1 et le mutant hypomorphe pour Grb2 décèdent entre les jours 10,5 et 11,5 de la gestation et présentent tous des anomalies de développement placentaire (Tableau I) [7][8][9][10][11][12][13][14][15][16][17][18][19]. Pour l'ensemble de…”