Comparison of cytotoxicity, activity of caspases and surface expression of DR5, CD44 and CD133 in SNU-475/TR cells and other HCC cells in the absence and presence of TRAIL. (A) SNU-475/TR cells and the parental SNU-475 cells were treated with various concentrations of TRAIL (0. 1. 10. 100 and 200 ng/ml). Percentage of cell survival was determined after 96 h of incubation using MTT assay. Each bar represents the mean ± SD of triplicate experiments. **P<0.01, ***P<0.001 compared to the SNU-475 cells. (B) SNU-475/TR and SNU-475 cells were treated with TRAIL (1 or 10 ng/ml) for 24 h, and the level of activation by the cleavage (Cl.) of pro-caspase-8 (Casp8), −3 (Casp3), −9 (Casp9) and PARP and the expression of CD44/CD133 were determined by western blot analysis. Tubulin was used as a loading control. (C) Both cell lines were stained with anti-DR5 antibody to determine the surface expression of DR5 by a flow cytometer. (D) Four HCC and SNU-475/TR cell lines were stained with anti-CD133 or anti-CD44 antibody to determine the surface expression of CD44 or CD133 by a flow cytometer. HCC, hepatocellular carcinoma; TRAIL, TNF-related apoptosis inducing ligand; DR4, death receptor TRAIL-R1; PARP, poly(ADP-ribose) polymerase.