Tax represses TGF-β1–mediated transcriptional responses in a dose-dependent manner.
TGF-β1 responsive HepG2 cells were cotransfected with (A) p15-luc (5 μg) or PAI-luc (2 μg) and an expression vector encoding for Tax (2 μg) or an empty vector (control); (B) HTLV-I LTR Luc (2 μg) and the Tax expression vector (2 μg) (Tax) or an empty vector (control) were cotransfected; (C) 2 μg of an empty vector containing the minimal adenovirus MLP promoter (MLP-luc) or a vector containing 12 copies of the CAGA box upstream from the MLP promoter (CAGA12-luc) and with an expression vector encoding for various levels of Tax construct (0.5, 2, or 5 μg) or a Rex vector expression (pCMV Rex) used as control; (D) the (CAGA)12-Luc (2 μg) and a Tax construct (2 μg) when indicated (+) and increasing amounts of Smad3 construct (0.2, 0.5, and 2 μg). Basal and TGF-β1–induced luciferase activities are indicated. The results are representative of at least 3 independent experiments in which each assay was conducted in triplicate.
