Figure 3

TRAIL induces c-Abl activation and cleavage in colon and prostate cancer cells. HCT116 (A), LNCaP, and PC3 (B) cells were treated with TRAIL (50 ng/ml) and/or STI571 (0.3 μM) for different time periods; then protein levels of c-Abl, caspase 8, and β-actin were determined. In (C), HCT116 cells were treated with STI571 (S, 0.3 μM), zVAD (Z, 20 μM), and/or TRAIL (T, 50 ng/ml) for 4 h. Then protein levels of both the total and Tyr412 phosphorylated forms of c-Abl were determined. Traces were representative of three separate experiments with similar results. The extent of Tyr412 phosphorylation as an index of kinase activation was quantified by standardizing the total non-cleaved c-Abl level and presented in parentheses. (D) After treating HCT116 cells with STI571 (S, 0.3 μM) and/or TRAIL (T, 50 ng/ml) for 3 h, c-Abl kinase activity was determined by in vitro kinase assay using GST-CRK as substrate.