IκBα-DN mutant restores p53 transcriptional activity in C81 cells. (A) The HTLV-I–transformed cell line C81 was cotransfected (Transfast; Promega) with 2 μg reporter (lanes 1-2, PG13-Luc; lanes 3-4, 4 × NF-κB–Luc; lanes 5-6, HTLV-I–LTR-Luc) and either control (lanes 1, 3, and 5) or 2 μg IκBα-DN (lanes 2, 4, and 6) DNA. Cells were harvested 24 hours after transfection, and luciferase activity was measured. Luciferase values were adjusted for transfection efficiency by using RSV-βgalactosidase. The values represent luciferase activity from 3 independent experiments. Error bars indicate SD. (B) Transfections were performed as for panel A, but the reporter construct CMV-βgalactosidase was used (CMV-βgal). Error bars indicate SD. (C) Western blot analysis for p53 and Tax levels from transfected cells using Ab6 (Oncogene Research Product) and Tab172, respectively, were performed.