LMP1 induction of Bmi-1 is NF-κB dependent. (A) L591 cells transfected with a plasmid expressing an IκBκ mutant that inhibits NF-κB activation. Expression of the IκBκ mutant resulted in the down-regulation of Bmi-1 expression compared with cells transfected with control vector. (B) L428 cells transfected with control plasmid (empty vector), wild-type (wt) LMP1, or a mutant LMP1 incapable of inducing NFκB (AxAxA378stop). WtLMP1, but not AxAxA378stopLMP1, induced Bmi-1 expression.