The accessory protein ORF3 of porcine epidemic diarrhea virus inhibits cellular interleukin-6 and interleukin-8 productions by blocking the nuclear factor-κB p65 activation.

Porcine epidemic diarrhea virus (PEDV) is an enveloped, single-stranded positive-sense RNA virus that belongs to a porcine entero-pathogenic alphacoronavirus, causing lethal watery diarrhea in piglets. Despite existing study reports the sole accessory protein ORF3 identified as NF-κB antagonist, the contribution of PEDV ORF3 to production of the pro-inflammatory cytokines mediated by NF-κB signaling remains largely unknown. Thus in this present study, we showed that PEDV ORF3 protein significantly inhibited the productions of pro-inflammatory cytokines interleukin-6 (IL-6) and IL-8. The phosphorylation of IκBα was inhibited by ORF3 protein, but no degradation of IκBα was induced in ORF3-expressing cells. Furthermore, PEDV ORF3 inhibited NF-κB activation through preventing nuclear factor p65 phosphorylation and down-regulating p65 expression level, as well as interfering nuclear translocation of p65, eventually resulting into the inhibition of IL-6 and IL-8 production. Our study definitely links PEDV ORF3 to inhibition of pro-inflammatory cytokines production, which will provide new insight into the molecular mechanisms of NF-κB activity inhibited by PEDV proteins to facilitate virus evasion of host innate immune.