S-1P inhibits cyt c and Smac/DIABLO release and caspase-3 activation induced by serum deprivation in HL-60 cells.

(A) Cytosolic extracts from HL-60 cells left untreated in the presence or absence of 5 μM S-1P for 8 hours were subjected to 15% SDS-PAGE and immunoblotted with anti-cyt c, anti-Smac/DIABLO, and anti-COX II, as described in Figure 1. (B) Proteins from duplicate extracts were analyzed by immunoblotting with anti–caspase-3 antibody. The mobilities of 32-kd precursor (p32) and proteolytically processed forms (p20 and p17) are indicated. Similar results were obtained in 3 independent experiments. (C) HL-60 cells were treated as described above. Loss of viability was assessed by the MTT assay. Samples were made in quadruplicate. Mean values with standard deviation are shown.