Molecular cloning and functional analysis of duck ubiquitin-specific protease 18 (USP18) gene

In mammals, ubiquitin-specific protease 18 (USP18) is an interferon (IFN)-inducible gene and is a negative regulator of Toll-like receptor-mediated nuclear factor kappa B (NF-κB) activation. The role of USP18 in ducks (duUSP18) remains poorly understood. In the present study, we cloned and characterized the full-length coding sequence of duUSP18 from duck embryo fibroblasts (DEFs). In healthy ducks, duUSP18 transcripts were broadly expressed in different tissues, with higher expression levels in the spleen, lung and kidney. Quantitative real-time PCR (qRT-PCR) analysis revealed that duUSP18 could be induced by treatment with Poly(I:C) or LPS. Overexpression of duUSP18 inhibited NF-κB and IFN-β expression. Furthermore, deletion mutant analysis revealed that the duUSP18 region between aa 75 and 304 was essential for inhibiting NF-κB. In addition, overexpression of duUSP18 also suppressed the secretion of NF-κB-dependent proinflammatory cytokines. Taken together, these results suggest that duUSP18 regulates duck innate immune responses.