Figure 3.

IFN-γ-induced transcriptional activation by Stat1α is enhanced by CBP and repressed by E1A. (A) IFN-γ induces reporter activity in cells expressing endogenous Stat1α. (B) Overexpression of CBP enhances IFN-γ-induced transcription. (C) E1A inhibits IFN-γ-induced Stat1α transactivation by competing for CBP/p300-binding. U2-OS cells were transfected with 0.5 μg of luciferase reporter, 0.3 μg of CMVβgal, and various amounts of RSVCBP, CMVE1A12S, and CMVE1A(Δ64-68) as indicated. Twenty-four hours after transfection, cells were treated with 5 ng of IFN-γ per ml for 6 hr and harvested for luciferase assay and β-gal assay. All transfections were done in triplicates. Results shown are the mean ± SD of two to four experiments. Results from only the IFN-γ-treated samples are presented in B and C as reporter activities from untreated cells did not change significantly.