Fig. 1: IAV PB2 protein inhibits IFN signaling pathway.

a, b Luciferase activity in HEK293T cells transfected with IFNβ promoter, ISRE or NF-κB luciferase reporter, Renilla luciferase plasmid, and PB2 plasmids (including NS1-PR8 and empty vector [Vec] were chosen as positive and negative controls, respectively) and treated with SeV (a) or poly(I:C) (b) (n = 3 biologically independent samples). c, d Luciferase activity in HEK293T cells transfected with ISRE or STAT1 promoter-luciferase reporter plasmid, Renilla luciferase plasmid, and PB2 plasmids and treated with IFNβ (c) or IFNα (d) (n = 3 biologically independent samples). e, f qPCR analysis of IFIT1 and ISG15 mRNA in A549 cells transfected with PB2 plasmids and treated with IFNβ (e) or IFNα (f); mRNA results are presented relative to those of untreated cells transfected with a control plasmid (n = 3 biologically independent samples). g HEK293T cells were transfected with PB2 or NS1 plasmid and infected with SeV. The supernatants were inactivated by ultraviolet radiation and collected to treat fresh HEK293T cells for 24 h, followed by infection for 12 h with VSV-GFP. The cells were observed under microscopy and then assessed by flow cytometry. Scale bars, 200 μm. h, i Immunoblot analysis of phosphorylated and total STAT1 or STAT2 in HEK293T cells transfected with PB2 plasmids and treated with IFNβ (h) or IFNα (i) (upper). Densitometry analysis of phosphorylated STAT/total STAT ratio (lower). Data are presented as the mean ± SD and are one representative of three independent experiments. Statistical significance in a–f, h, i was determined by unpaired two-tailed Student’s t test.