Specific kinase inhibitors prevent CSF-1–induced caspase activation. Enriched human monocytes were exposed for indicated times (days) to 100 ng/mL CSF-1. (A left) Flow cytometry analysis of FAM-IETD and FAM-DEVD cleavage activities. (A right) Indicated cell-surface marker expression (percentages indicate double-positive cells). One representative of 5 independent experiments is shown. (B) Monocytes were exposed for 0 to 4 days to 100 ng/mL CSF-1 alone or in association with U0126 (U0, 10 μmol/L), or LY294002 (LY, 10 μmol/L), added 30 minutes before CSF-1 treatment, and the expression of indicated proteins was analyzed by immunoblot. HSC70 indicates loading control. *Cleavage fragments. (C) Monocytes were exposed to 100 ng/mL CSF-1 alone or in association with PP2 (10 μmol/L), U0126 (U0, 10 μmol/L), LY294002 (LY, 10 μmol/L), SB202190 (SB, 5 μmol/L), GF109203X (GFX, 5 μmol/L), or Q-VD-OPH (QVD, 50 μmol/L) added to the culture medium 30 minutes before CSF-1, and differentiation was studied by morphologic examination and FACS analysis at day 2. (D) Monocytes were exposed for 4 days (d4) as in panel C, and the expression of indicated proteins was analyzed by immunoblot. HSC70 indicates loading control. Molecular weight (MW) is given in kilodaltons. *Cleavage fragments. A vertical line has been inserted to indicate a repositioned gel lane. One representative blot is shown, and the ratio of NPM* to the HSC70 protein level was measured by the analysis of 3 independent experiments with ImageJ software. ^#P < .01, ^##P < .001, ^###P < .001 (vs d4). Results obtained with wortmaninn were similar to those obtained with LY294002 (not shown). The vertical line indicates repositioned gel lanes caused by the removal of an irrelevant control.