Molecular cloning and functional characterization of the NFIL3/E4BP4 transcription factor of grass carp, Ctenopharyngodon idella

NFIL3 (nuclear factor interleukin 3-regulated) is an important bZIP transcription factor in the immune response and immune cells' development. Here, we identified the NFIL3 gene from grass carp (Ctenopharyngodon idella; gcNFIL3). The deduced amino acid sequence of gcNFIL3 is 468 residues with a typical bZIP domain. Phylogenetics demonstrated that gcNFIL3 clustered closely with NFIL3 of zebrafish. Real-time PCR revealed gcNFIL3 is constitutively expressed in all tissues examined. Its expression was significantly upregulated in head kidney and trunk kidney after stimulation by bacteria. Immunofluorescence microscopy revealed that gcNFIL3 is mainly expressed in the nucleus. Overexpression of gcNFIL3 reduces Aeromonas hydrophila invasion and proliferation. In CIK cells, gcNFIL3 could induce the activation of NF-kappa B and upregulates the expression of IL10 and IFN. These results indicated that gcNFIL3 has immunoregulatory properties and might play a role in the immune response of fish.