Molecular cloning, functional characterization and antiviral activity of porcine DDX3X

Human DDX3X is a newly discovered DEAD-box RNA helicase. In addition to involvement of eukaryotic gene expression regulation, human DDX3X has recently been demonstrated to be a critical molecule in innate immune signaling pathways and to contribute to type I interferon (IFN) induction. In the present study, porcine DDX3X was cloned by RT-PCR from PK-15 cells and its function in regulating IFN-β was characterized. The putative porcine DDX3X ORF encodes 662 amino acids possessing several conserved motifs. Sequence alignments indicated that porcine DDX3X has high identity at the amino acid level to those of horse (96.7%), mouse (97.6%), cattle (98.5%), dog (98.6%) and human (98.9%). Ectopic expression of porcine DDX3X significantly activated IFN-β expression, whereas knockdown of porcine DDX3X inhibited dsRNA- or Sendai virus (SeV)-induced IFN-β. Furthermore, porcine DDX3X co-localized with IPS-1, TBK1 and IKKε, and enhanced IFN-β promoter activation induced by these molecules. We also investigated the role of porcine DDX3X during porcine reproductive and respiratory syndrome virus (PRRSV) infection and found that overexpression of DDX3X significantly inhibited PRRSV replication, indicating that DDX3X is a potential antiviral agent.