Bmi-1 promotes the survival of HL cells. (A) Knockdown of Bmi-1 expression in L591 cells (top) and in L428 cells (bottom). mRNA and protein are shown in the left and right panels, respectively. (B) Knockdown of Bmi-1 led to a marked reduction in the viability of L591 cells (upper) at 24 hours and at 48 hours after transfection compared with control cells (GFP-only vector). Knockdown of Bmi-1 in L428 cells had a significant but less marked effect on cell viability (bottom). Error bars represent the standard error of the mean.