A. Luciferase (shLuc) and ING2-knocked down (shING2) cells were exposed to MNNG (10 μM; 1h) and apoptosis (% sub-G1) was assessed at 0, 12, 24, 48 and 72 h after treatment by flow cytometry following propidium iodide staining. Results are mean ± SEM of three independent determinations. *P<0.01 compared with the control group. B. MNNG-treated shLuc and shING2 cell lysates prepared at 0, 24, 48 and 72 h post-treatment were subjected to immunoblotting with caspase-3 (top panel), and caspase-9 (middle panel), PARP and ING2 antibodies. Equal protein content was confirmed by anti-β-tubulin immunoblotting. C. Mock- and MNNG (10 μM; 1 h)-treated cells were dually stained with annexin V and PI, and subsequently analyzed by flow cytometry. % cells showing PI-positive/annexin V-positive (upper right quadrant), PI-negative/annexin V-positive (lower right quadrant), and PI-positive/annexin V-negative (upper left quadrant) staining is indicated.