Fig. 2

Synergistic effect of shikonin and TRAIL on apoptosis induction in TRAIL-resistant A549 cells. a A549 cells were pretreated with shikonin (4 μM) for 12 h and then exposed to TRAIL (50 ng/ml) for another 12 h. Cells were harvested to quantify the induction of apoptosis by annexin V/PI staining and flow cytometry. The data in each plot indicated the percentage of apoptotic cells. b Cell morphology was analyzed under an inverted microscope (magnification × 100) after cells were treated as described in (a). c Whole cell lysates were prepared after cells were treated as described above and were analyzed by Western blotting using antibodies specific to caspase-3, − 8, − 9 and cleaved caspase-3, − 8, − 9. β-Actin was used as the loading control. d-e The data are presented as the means ± SDs of at least three independent experiments, and significant differences between the control group and the other groups in each experiment are shown as*p < 0.05, ** p < 0.01 and ***p < 0.001. S + T: Shikonin + TRAIL