Effect of wild-type Tax and various Tax mutant proteins on NF-κB and MAPK signaling pathways. (A) HEK293T cells were transfected with 100 ng of wt pCMV4-Tax or pCMV-Tax mutants and NF-κB-luciferase reporter. Thirty-six hours after transfection, cells were harvested and lysed with Passive Lysis Buffer (Promega). Luciferase activity was measured on a FLUOstar Optima (BMG). pCMV5-ΔMEKK1 was used as a positive control in this assay. (B) The assay was similarly performed for the MAPK pathway using SRE-luciferase reporter. pCMV5-myc-RasV12 was used as the positive control. Error bars represent mean ± SE of triplicates; results shown are representative of 5 or 6 independent assays.