Ritonavir inhibits NF-κB transcriptional activation and expression of apoptosis- and cell-cycle-associated proteins. (A) Ritonavir inhibits Tax-induced NF-κB transcriptional activation. κB-LUC was transfected into Jurkat cells with Tax-expressing plasmid (▪) or empty vector (□). After transfection, cells were treated with increasing concentrations of ritonavir. Luciferase activity is expressed relative to the basal level measured in cells transfected with the reporter plasmid and Tax-expressing plasmid without further treatment, which was defined as 100. Data represent the mean + SD from 3 independent experiments. (B) Ritonavir inhibits constitutive active NF-κB transcriptional activity in HUT-102 cells. κB-LUC and AP-1-LUC were transfected into HUT-102 cells. After transfection, cells were treated as in panel A. Luciferase activity was normalized, based on the Renilla luciferase activity from phRL-TK. Relative luciferase activity is expressed relative to the basal level measured in cells transfected with the reporter plasmid without further treatment, which was defined as 100. (C-D) Western blot analyses. HUT-102 cells (C) and primary acute-type ATL cells (D) were cultured with the indicated concentration of ritonavir for 24 to 72 hours (HUT-102 cells) and 24 hours (ATL cells). Cells were harvested and subjected to Western blot analysis. The polyvinylidene fluoride membrane was sequentially probed with indicated antibodies.