Effect of GM-CSF on procaspase protein levels, caspase 3 activation, and induction of apoptosis. (A) Growth factor–deprived OCIM2 cells were incubated for 1 hour in the absence of GM-CSF and in the presence of increasing concentrations of GM-CSF. Changes in the protein levels of procaspase 2, 3, 8, 9, and 10 were determined by Western immunoblotting. A band of β-actin, demonstrating equal protein loading, is presented as a loading control. (B) Growth factor–deprived OCIM2 cells were incubated in the absence of GM-CSF and in the presence of increasing concentrations of GM-CSF. The levels of procaspase 3, activated caspase 3, PARP, and cleaved PARP were analyzed by Western immunoblotting. (C) Growth factor–deprived cells were incubated for 6 hours in the absence of GM-CSF and in the presence of increasing concentrations of GM-CSF. The percentage of cells undergoing apoptotic cell death was quantitatively determined by flow cytometry, using annexin V–FITC. The percentage of cells undergoing apoptotic cell death is shown at the lower right of each box. Representative data from 3 different experiments are shown.