HDAC3 is essential for IFN-γ-induced PI3K-IRF3 activation and galectin-9 expression. A and B, PI3K is crucial for IFN-γ-induced galectin-9 expression and IRF3 activation. HUVECs were pretreated with PI3K inhibitor LY294002 (5 μmol/liter) for 1 h, then treated with 10 ng/ml IFN-γ for 16 h in the presence of LY294002, followed by immunofluorescent staining (A: green, galectin-9; blue, DAPI; Scale bar, 5 μm) and Western blot assay (B). The same amount of dimethyl sulfoxide was included as vehicle control. p-IRF3 indicates phosphorylation of IRF3 at Ser-386. C–E, HDAC3 is crucial for basal level expression of PI3K and IRF3 and IFN-γ-induced IRF3 activation. HUVECs were infected with NTsh or HD3sh RNA for 48 h, then treated with 10 ng/ml IFN-γ for 16 h, followed by Western blot analysis (C, representative image; D, quantitative analysis) and quantitative RT-PCR assays (E). *, p < 0.05; **, p < 0.01. F, IRF3 phosphorylation is essential for galectin-9 expression. HUVECs were transfected with pcDNA3 (vector), pcDNA3-IRF3 (WT), or pcDNA3-IRF3S386A (S386A) plasmids for 48 h, followed by Western blot analysis of IRF3 phosphorylation and galectin-9 expression. Data presented are representative or average ± S.E. (error bars) of three independent experiments.