Fig. 6. Kinetics of caspase-8 activation, Bid cleavage, cytochrome c release, and caspase-3 activation in response to CDDO. U-937 cells were treated with 5 µM CDDO and harvested at the indicated times. A, cell lysates were assayed for caspase-8 activity. Results are expressed as the fold increase (means; bars, SD) for two independent experiments each performed in duplicate. B, cell lysates were subjected to immunoblot analysis with anti-Bid (upper panel), anti-cytochrome c (middle panel), or anti-caspase-3 (lower panel).