Fig. 4.

Suppression of host immune and non-immune promoter activities and IFN-β protein synthesis by coronavirus nsp1 proteins. (A) 293 cells stably transfected with IFN-β or ISG15 promoter-driven reporters were transfected with nsp1-expressing plasmids or control plasmids. Cells were stimulated with Poly I:C or NDV for 24 h and firefly luciferase activities were measured. (B) Normal 293 cells were co-transfected with nsp1-expressing plasmids and SV40-, HSV-TK- or CMV-promoter-driven reporter plasmids for 24 h, and Renilla luciferase activity measured. (C) Normal 293 cells transfected with nsp1-expressing plasmids or control plasmids, and then stimulated by NDV for 24 h. Titers of IFN-β in cell supernatants were measured by ELISA. Error bars indicate standard errors of triplicate treatments in three individual experiments. Statistical analysis was performed using paired Student's t-test (**, p < 0.01; *, p < 0.05; NS, not significant, p > 0.05).