FIG 7.

PEDV infection-induced STAT3 activation negatively regulates ISGs. (A and B) Infection with PEDV leads to STAT3 phosphorylation. IPEC-J2 (A) and HEK293 (B) cells were incubated with PEDV at an MOI of 1 for 2 h at 4°C. Unbound viruses were removed, and the cells were further incubated for different periods, as indicated. The cell lysates were blotted with the MAbs against phospho-STAT3 (pSTAT3), STAT3, and β-actin. The mock-infected cells were used as a control. (C and D) Inhibition of STAT3 function enhances antiviral responses. IPEC-J2 (C) and HEK293 (D) cells were treated with the STAT3-specific inhibitor S3I-201 (40 μM) for 24 h. The RNA levels of ISGs, MxA, ISG15, and IFN-β, were determined by quantitative RT-PCR. (E) Effect of STAT3 inhibitor on cell viability. IPEC-J2 and HEK293 cells were treated with S3I-201 at the indicated concentrations or with the carrier control DMSO for 72 h. Cell cytotoxicity was analyzed with the CCK-8 system as described in Materials and Methods. The results are representative of three independent experiments (means and SD). *, P < 0.05. The P value was calculated using Student's t test.