Targeted disruption of the c-Myc gene reduced the responsiveness to TRAIL and the expression of DR5 in PC3-MM2 cells. (A) PC3-MM2 cells were transfected with siRNA against c-Myc or scrambled siRNA as a control. After 48 h, the transfectants were treated with TRAIL (2 or 10 ng/ml) for 6 h, and the percentage of apoptotic cells was determined using Annexin V staining and flow cytometry (left). In addition, the transfectants were treated with graded single doses of TRAIL (1~10 ng/ml), and percentage of cell survival was determined after 96 h incubation using the MTT assay (right). Data represent the mean ± SE of triplicate experiments. *p < 0.05, **p < 0.01, ***p < 0.001. (B) The transfected cells incubated with anti-DR5 antibody (1:100), and subsequently labeled with FITC-conjugated secondary antibodies (1:200) to determine the surface expression of DR5. Mouse IgG was also used as an isotype control. The shaded and unshaded peaks correspond to control and specific staining, respectively.