A. Cell viability tests in various lung cancer cell lines. Several lung cancer cell lines (A549, H1299, H460, and SK-MES1 cells) were treated with TRAIL (20 ng/ml) for the indicated times, and cell viability was measured by a CCK-8 assay. B. SK-MES-1, A549, H1299, and H460 cells were transiently transfected with scrambled negative siRNA (Sc) or NEK4 siRNA (siNEK4), and the cells were treated 3 days later with TRAIL (20 ng/ml) for 4 h. Cell death was determined by Annexin V/PI staining. C. A549 cells transiently transfected with Sc or NEK4 siRNAs (si#1 and si#2) were further treated with TRAIL (20 ng/ml) for 4 h. The cells were harvested and subjected to Western blotting with the indicated antibodies. D. DLD1, RKO, and HeLa cells transiently transfected with Sc or siNEK4 were additionally treated with TRAIL (20 ng/ml) for 4h, and cell death was determined.