FIG 4.

VP23 inhibits IFN-β activation by targeting IRF7. (A to C) The IFN-β-luc (A), IRF7-luc (B), or NF-κB-luc (C) reporter was cotransfected with the cGAS and STING constructs as well as the VP23-Flag plasmid or the empty vector into DF-1 cells. Twenty-four hours later, cells were harvested and analyzed by the dual-luciferase reporter assay. (D to H) DF-1 cells were transfected with plasmids expressing chicken STING (D), TBK1 (E), IRF7 (F), TLR3 (G), or MDA5 (H), together with the IRF7-luc or IFN-β-luc reporter and the VP23-Flag or an empty vector plasmid. The dual-luciferase reporter assay was performed at 24 h posttransfection. All cells were transfected with pRL-TK as an internal control to normalize the transfection efficiency, and the fold change relative to the value for the mock-transfected controls was determined. Data are presented as the mean ± SD from three independent experiments. Statistical analysis was performed by using Student's t test (**, P < 0.01).