STI571-induced cell resistance to TRAIL is dependent on p73. (A) HCT116 cells were transfected with p73 siRNA, and were treated with TRAIL (50 ng/ml) and/or STI571 (0.3 μM) as indicated. Cell viability at 24 h and protein expression of p73 were determined. * p < 0.05, indicating a significant reduction of TRAIL-induced apoptosis by STI571. # p < 0.05, indicating a significant difference of TRAIL-elicited cell death between p73 siRNA and scrambled control cells. In some experiments, caspase 3 (B), JNK and p38 activations (C) were measured by assessing their cleavage form and phosphorylation state. Data of immunoblotting were representative of three separate experiments with similar results.