Effect of depsipeptide on activation of caspases 3, 8, and 9 and on processing of caspases 8 and 9. (A) Depsipeptide induces activation of caspases 3 and 8 but not caspase 9. Human CLL cells were exposed to depsipeptide (0.38 μM) for 4 hours and compared with media control at 24 hours. Changes in caspase 3, caspase 8, and caspase 9 activities were determined by a colorimetric reaction assay. Error bars represent 95% confidence intervals (CI). (B) Depsipeptide induces processing of the caspase 8 but not the caspase 9 pro-form. To confirm the findings of selective caspase 8 activation in CLL cells, protein lysates were prepared, and 50 μg protein per lane was separated on a 14% SDS-PAGE gel. Loading equivalence was confirmed by blotting with an antibody for constitutively expressed protein GAPDH. The unprocessed form of caspase 8 and caspase 9 was detected with the use of appropriate antibodies.