Fig. 5. Activation of caspase-8 and cleavage of Bid in response to CDDO. A, U-937, HL-60, and U-937/Bcl-xL cells were treated with 5 µM CDDO and harvested at the indicated times. U-937 cells were also treated with 10 µM ara-C and harvested at 2 h. Total cell lysates were assayed for caspase-8 activity. The results are expressed as fold-increase in caspase-8 activity compared with control (means of two independent experiments, each performed in duplicate; bars, SD). B, U-937 or HL-60 cells were treated with 5 µM CDDO and harvested at the indicated times. Total cell lysates were analyzed by immunoblotting with anti-Bid antibody. IB, immunoblot; FL, full length; CF, cleaved fragment.