title: Raf-1 activation prevents caspase 9 processing downstream of apoptosome formation.
abstract: In many cell types, growth factor removal induces the release of cytochrome-c from mitochondria that leads to activation of caspase-9 in the apoptosome complex. Here, we show that sustained stimulation of the Raf-1/MAPK1,3 pathway prevents caspase-9 activation induced by serum depletion in CCL39/ΔRaf-1:ER fibroblasts. The protective effect mediated by Raf-1 is sensitive to MEK inhibition that is sufficient to induce caspase-9 cleavage in exponentially growing cells. Raf-1 activation does not inhibit the release of cytochrome-c from mitochondria while preventing caspase-9 activation. Gel filtration chromatography analysis of apoptosome formation in cells shows that Raf-1/MAPK1,3 activation does not interfere with APAF-1 oligomerization and recruitment of caspase 9. Raf-1-mediated caspase-9 inhibition is sensitive to emetine, indicating that the protective mechanism requires protein synthesis. However, the Raf/MAPK1,3 pathway does not regulate XIAP. Taken together, these results indicate that the Raf-1/MAPK1,3 pathway controls an apoptosis regulator that prevents caspase-9 activation in the apoptosome complex.
authors.affiliation: Institute of Developmental Biology and Cancer, CNRS UMR6543, A. Lacassagne Center, University of Nice Sophia-Antipolis, 33 Avenue Valombrose, 06189 Nice, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Cagnol
authors.forename: Anna
authors.initials: A
authors.lastname: Mansour
authors.forename: Ellen
authors.initials: E
authors.lastname: Van Obberghen-Schilling
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Chambard