XAF1 facilitates IRF1-dependent induction of antiviral ISGs. (A–D) The IRF1 plasmid (100 ng) was cotransfected with the pRL-TK-Luc vector (10 ng), and DDX58 (A), MX1 (B), OAS2 (C), or DDX60 (D) promoter-luciferase reporter vector (100 ng each) into HEK293T cells in a 24-well plate. After 24 h, relative luciferase activity was quantified. (E–H) The IRF1 plasmid (100 ng) was cotransfected with the pRL-TK-Luc vector (10 ng) and the control vector (pGL4.17), DDX58, MX1, OAS2, DDX60 promoter-luciferase reporter vector, or mutant vector (100 ng each) into HEK293T cells in a 24-well plate. After 24 h, DDX58 (E), MX1 (F), OAS2 (G), or DDX60 (H) luciferase activity was quantified. (I–L) The XAF1 (100 ng) and IRF1 (0, 10, and 30 ng) plasmids were cotransfected with the pRL-TK-Luc vector (10 ng), and DDX58 (I), MX1 (J), OAS2 (K), or DDX60 (L) promoter-luciferase reporter vector (100 ng each) into HEK293T cells in a 24-well plate. After 24 h, relative luciferase activity was quantified. All data from three independent experiments are presented as mean ± SD; *, P < 0.05 and **, P < 0.01 indicate significant difference by unpaired Student's t test.