Effect of Bmi-1 knockdown on 5-FU-induced apoptosis. Flow cytometry was performed to measure apoptotic rates. Percentages of apoptotic cells were identified in (A) untreated SK-siNS, (B) SK-siNS cells treated with 10 mg/l 5-FU for 72 h, (C) untreated SK-siBmi1 and (D) SK-siBmi1 cells treated with 10 mg/l 5-FU for 72 h. 5-FU, 5-fluorouracil; FITC, fluorescein isothiocyanate; siNS, negative control siRNA oligonucleotides; siBmi1, Bmi-1 targeted siRNA oligonucleotide; Bmi-1, B-cell-specific Moloney murine leukemia virus insertion site 1.