Bmi-1 and LMP1 down-regulate expression of the ATM tumor suppressor in HL cells. (A) Knockdown of Bmi-1 expression in L428 cells resulted in the up-regulation of ATM expression. (left) Changes in mRNA. (right) Changes in protein. Knockdown of Bmi-1 in the KM-H2 cell line produced similar effects on ATM expression (data not shown). (B) ATM expression was higher in EBV-negative L591 cells than in EBV-positive L591 cells (left). Knockdown of LMP1 in EBV-positive L591 cells led to the up-regulation of ATM transcription (right). These data show that ATM expression is suppressed by LMP1 in EBV-positive HL cells. (C) Inhibition of NF-κB in L428 and cells up-regulated ATM expression. Similar effects were also observed in KM-H2 cells (data not shown).