FIG 7.

SARS-CoV-2 NSP1 blocks IFN signaling. (A) HEK 293T cells were transfected with plasmids encoding the indicated viral proteins, ISRE firefly luciferase reporter, and control Renilla luciferase reporter. Twenty-four hours later, cells were induced with 100 U/ml of IFN-α for 16 h. Firefly and Renilla reporter activity was measured by luciferase assay. The ISRE reporter activity was normalized against Renilla reporter values, and the data are presented as fold activity relative to the pcDNA empty vector control. (B) HEK 293T cells were transfected with pcDNA carrying the indicated proteins, ISRE firefly luciferase reporter, and control Renilla reporter. The cells were induced 24 h later with 100 U/ml of IFN-α for 16 h, and then firefly and Renilla luciferase activities were measured. The ISRE reporter activity was normalized against Renilla reporter values, and the data are presented as fold activity relative to the pcDNA empty vector control. (C and D) Huh7 cells were transfected with plasmids encoding the indicated SARS-CoV-2 proteins. Twenty-four hours later, cells were induced with 100 U/ml of IFN-α for 2 h and then processed for indirect immunofluorescence microscopy with antibodies against FLAG and STAT2. The total fluorescent intensity of STAT2 was measured using Volocity software (n = 20). Data are means ± SEM from three independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.