STING induction is regulated by STAT1/2 and RELA. (A) A549 cells were transfected with control siRNA, siRNA targeting IFN-α/βR, and/or siRNA targeting TNFR. After 48 h, cells were transfected with 5′pppRNA or treated with TNF-α and IFN-α for 24 h. Whole-cell extracts were analyzed by SDS-PAGE and subjected to immunoblotting. (B to D) Stat1+/+ MEFs and Stat1−/− MEFs (B) and A549 cells transfected with control siRNA or siRNA targeting STAT2 (siSTAT2) or RELA (siRELA) (C, D) were treated with 5′pppRNA at 48 h after transfection. STING, STAT1, pY701STAT1 (pSTAT1), STAT2, RELA, RIG-I, A20, and actin protein levels were analyzed by Western blotting. Statistical analysis was performed by Student's test (*, P < 0.05; **, P < 0.01; ***, P < 0.001).