(a) Raf-1 activation inhibits caspase-9 cleavage upon serum withdrawal. CCL39-Raf-1:ER cells treated with or without 4-HT were deprived of serum for the indicated time periods. The cell lysates were analyzed by immunoblotting for caspase-9, phospho-MAPK1,3, and total MAPK1. (b) Raf-1 activation inhibits caspase activity CCL39-Raf-1:ER-cells treated or not with 4-HT were deprived of serum for 14 hours as indicated. sts: the effect of 0.3 mM staurosporin is shown as a comparison. Caspase 9 activity was measured using the peptide LEHD-pNA as a substrate and caspase 3 activity using DEVD-pNA. The mean values ± SEM were calculated from at least two separate experiments performed in triplicate.