Kinetics of caspase cleavage during MK differentiation.

Bone marrow CD34⁺ cells were cultured as in Figure 1. Western blot analyses were performed with anti–human caspase-9 (A) and anti–human caspase-3 (B) Abs. Equal loading was checked by stripping the membranes and reprobing with antiactin mAb (C). Positions of molecular mass markers are indicated at the right. Note that the 10-kd subunit of caspase-9 and the 17-kd active subunit of caspase-3 are not found in MKs lysed at day 8 (lane 1), detected when MKs are shedding platelets at day 12 of culture (lane 2). This cleavage is inhibited by z-VAD.fmk (lane 3), is increased by STS treatment (lane 4), and is also found later in culture, at day 13 (lane 5). Experiments were repeated twice and yielded similar results.