Increased caspase-8- and -3-like activity in mutant osteoblasts. Caspase-1 (A), caspase-8 (B), and caspase-3, -6, and -7 (caspase-like) (C) were determined in Co and Ap cells. Caspase-3, -6, and -7 activity was also determined in the absence or presence of caspase-8 inhibitor (z-IETD-fmk) (D). Ap cells showed increased caspase-8 and caspase-3 activities, and the latter was inhibited by the specific caspase-8 inhibitor. The data are the mean ± SEM of four values. *, P < 0.05 versus Co cells; #, P < 0.05 versus Co or Ap cells untreated with the caspase-8 inhibitor.