Tax, but not PMA or TNF-α, induction of NF-κB inhibits p53 activity. (A) Jurkat lymphocytes were transfected by using Superfect reagent (Qiagen) with 4 × NF-κB–Luc reporter plasmid and pcTax (2 μg) or control plasmid (pcDNA3, 2 μg). (B) p53 activity was measured by cotransfection of Jurkat cells with the p53-responsive MDM2-Luc reporter construct and p53 (0.4 μg) in the absence or presence of pcTax (2 μg). TNF-α (10 ng/mL) or PMA (10 nM) was added to cells 1 hour prior to transfection. Cells were harvested 24 hours after transfection, and luciferase activity was measured. Activity is represented as relative percentages from at least 3 independent experiments. Values in panel A are expressed as percentage of activity in which Tax activity is set at 100%. Measurements in panel B are expressed as percentage of repression whereby the control is set at 1. Error bars indicate SD.