LMP1 induces Bmi-1 expression in HL cells. (A) Expression of Bmi-1 in EBV-negative HL cell lines L428 and KMH2 and in the EBV-positive (LMP1-positive) L591 HL cell line compared with the EBV-negative variant, L591-SD3. Although Bmi-1 is highly expressed in all parental lines, irrespective of EBV status, loss of the EBV episome from L591 cells resulted in its down-regulation (for all figures, mRNA and protein are shown in upper and lower panels, respectively). (B) Knockdown of LMP1 expression (L591+LMP1 siRNA) down-regulates Bmi-1 expression in EBV-positive L591 cells compared with cells treated with transfection reagent (RiboJuice; Novagen) alone. (C) Ectopic expression of LMP1 in EBV-negative L428 cells up-regulates Bmi-1 expression.