Functional characterization of duck TBK1 in IFN-β induction

TRAF family member-associated NF-κB activator (TANK)-binding kinase 1 (TBK1) serves as hub molecule at the crossroad of multiple signaling pathways of type I interferon (IFN) induction. The importance of TBK1 in innate immunity has been demonstrated in mammalian, however the characterization and function of TBK1 in avian remains largely unknown. In this study, we cloned duck TBK1 (duTBK1) from duck embryo fibroblasts (DEFs) for the first time, which encoded 729 amino acids and had a high amino acid identity with goose and cormorant TBK1s. The duTBK1 showed a diffuse cytoplasmic localization in DEFs and was extensively expressed in all tested tissues. Overexpression of duTBK1 induced IFN-β production through the activation of IRF1 and NF-κB in DEFs. The N-terminal kinase domain and the ubiquitin-like domain in middle of duTBK1 played pivotal roles in IFN-β induction as well as in IRF1 and NF-κB activation. Furthermore, knockdown of duTBK1 by small interfering RNA significantly decreased poly(I:C)- or Sendai virus (SeV)-induced IFN-β expression. In addition, duTBK1 expression dramatically reduced the replication of both duck reovirus (DRV) and duck Tembusu virus (DTMUV) in DEFs. These results suggested that the duTBK1 played a pivotal role in mediating duck antiviral innate immunity.