Opulence of HDAC4 selectively impairs the production of type I interferon. (A and B) HEK293T cells were transfected with an IFN-β firefly luciferase reporter, along with control vector or gradient concentrations of HDAC4 (0.2, 0.5, and 1 μg), and then left uninfected or infected for another 8 h with SeV. (A) ELISA of IFN-β. (B) Luciferase assay analysis of IFNB1 promoter activity. (C) Quantitative RT-PCR analysis of ISG15, ISG54, and ISG56 mRNA in HEK293T cells with control vector or HDAC4 (500 ng). (D and E) Luciferase assay of IFNB1 promoter activity (D) and quantitative RT-PCR analysis of IFNB1 mRNA (E) in HEK293T cells transfected for 36 h with control vector or HDAC4 (500 ng) and then treated for 8 h with inducers. NS, not significant (P > 0.05), *P < 0.05, **P < 0.01, and ***P < 0.001 (unpaired t-test). Data are representative of three independent experiments with similar results (mean ± SD).