Apoptosis induced by PUMA in p53-deficient human fibroblast-like synoviocytes (FLS). Cultured FLS were transfected with siRNA and then, 3 days later, with 10 μg of PUMA, PUMA-dBH3, or pCEP4. (a) DNA fragmentation as determined by histone release. Histone release was measured by ELISA in samples collected 9 hours after the second transfection. The fold induction of DNA fragmentation in FLS transfected with PUMA plasmids is shown relative to the control value of pCEP4-transfected cells. *p < 0.05, n = 3. (b) Cell viability. Trypan blue exclusion was evaluated at 24 hours after cDNA transfection in 2.5 μg of siRNA-treated FLS. Data are presented as the percentage of non-viable cells. *p < 0.01, **p < 0.001, n = 3. (c) Caspase-3 activation. Caspase-3 levels were determined in control (sc) and p53-deficient (p53) FLS 8 hours after transfection with PUMA. *p < 0.05, n = 3.