CircYthdc2 and Ythdc2-170aa inhibit host antiviral innate immunity. A and B The schematic diagram of siRNAs (A) and circYthdc2 overexpression plasmid structure (B). C qPCR analysis of circYthdc2 and linear Ythdc2 mRNA in MIC cells treated with siRNAs. qPCR analysis of circYthdc2 and linear Ythdc2 mRNA in MKC cells overexpressing circYthdc2. D and E qPCR assays were performed to determine the expression levels of IFN1, TNF-α, Mx1, ISG15, and Viperin in MIC cells transfected with NC or si-circYthdc2 (D) and transfected in MKC cells with circYthdc2 or pLC5-circ and Linear-FLAG-Ythdc2-170aa or pcDNA3.1-FLAG after SCRV infection (E). F circYthdc2 and Ythdc2-170aa promote SCRV replication. MIC cells transfected with NC or si-circYthdc2 and MKC cells were transfected with pLC5-circ or circYthdc2 and pcDNA3.1-FLAG or Linear-FLAG-Ythdc2-170aa for 24 h, respectively, then infected with SCRV at 24 h. The qPCR analysis was conducted for intracellular and supernatant SCRV RNA expression. G MKC cells seeded in 48-well plates overnight were treated with cultural supernatants at the dose indicated for 48 h. Then, cell monolayers were fixed with 4% paraformaldehyde and stained with 1% crystal violet. MKC cells were transfected with Linear-FLAG-Ythdc2-170aa or pcDNA3.1-FLAG. H Effect of circYthdc2 on cell viability after SCRV infection. MIC cells were transfected with NC or si-circYthdc2 for 24 h and then treated with SCRV for 24 h. Cell viability assay was measured. I Ythdc2-170aa counteracts the negative effect of STING. Relative luciferase activities were detected in MKC after cotransfection with STING, MAVS, TRIF, and TBK1 expression plasmid, pRL-TK Renilla luciferase plasmid, luciferase reporters, pcDNA3.1-FLAG or Linear-FLAG-Ythdc2-170aa. J Relative protein levels of STING in MIC cells after transfected with NC or si-circYthdc2 and in MKC cells with pLC5-circ or circYthdc2 and pcDNA3.1-FLAG or Linear-FLAG-Ythdc2-170aa or Linear-FL-Ythdc2-AG. All data represented the mean ± SE from three independent triplicated experiments. *, p < 0.05; **, p < 0.01