The p35 and z-VAD-fmk prevent TPA-induced differentiation of U937 cells.

(A-C) Empty vector (pTarget)– or p35-transfected U937 cells were treated with 20 nM TPA for 24 (A) or 48 hours (B,C). (D-F) U937 cells were left untreated or treated with either 20 nM TPA or 100 μM z-VAD-fmk or a TPA/z-VAD-fmk combination for 12 hours (D) or 48 hours (E,F). (A,D) DEVD-AMC peptide cleavage activity shown as mean ± SD of 3 experiments in triplicates. (B,E) Adhesion of TPA-treated cells to the culture flasks shown as mean ± SD of 3 experiments in triplicates. (C,F) CD11b-expressing cells on the plasma membrane. White curves indicate untreated; gray curves, exposed to TPA for 48 hours. Shown is 1 representative of 3 independent experiments (C,F).