Figure 2. Hypoxia inhibits TRAIL-induced apoptosis human colon carcinoma cells.

HCT116 cells were pre-exposed to normoxia or hypoxia for 24 h and further incubated with recombinant TRAIL (0–200 ng/ml) for an additional 4 h under the same conditions. (A) Treated cells were photographed with a light microscope (× 200). (B, C) Viable cells were stained with crystal violet. Viability of control cells was set at 100%, and viability relative to the control was estimated. These results are representative of three independent experiments. (D) HCT8 cells were photographed with a light microscope (× 200). (G, H) Viable cells were stained with crystal violet. Viability of control cells was set at 100%, and viability relative to the control was estimated. These results are representative of two independent experiments. Bar graph indicates the number of total cells and percent of apoptotic cells. *p < 0.05 or **p < 0.01 significant differences between control and each treatment group. In (I and J) HCT-116 and HeLa cells were exposed to hypoxia 12 hr after then treated with 100 ng/ml TRAIL for indicated time periods, respectively. Cell viability was measured by the Annexin V assay.