Transactivation of the 4-1BB promoter by HTLV-1 Tax via a single NF-κB site. (A) Schematic representation of the 4-1BB promoter sequence cloned into pGL3basic. Luc represents the open reading frame for the firely luciferase gene, +1 indicates the transcriptional start site. (B) To determine promoter activity, Jurkat T cells were cotransfected with pGL3basic:4-1BBprom (wt) and plasmids as indicated. Luciferase assays were performed 48 hours after transfection. At least 3 independent experiments were performed. Values were normalized to protein content and are given as mean plus or minus standard error. M7, M22, M47: Tax mutants; IκBDN: dominant active inhibitor of NF-κB (IκB); LMP-1: latent membrane protein of the Epstein-Barr virus (NF-κB activator). (C) The responsiveness of the 4-1BB NF-κB–deleted promoter to Tax was analyzed as described in panel B and compared with the 4-1BB wt promoter.