Identification and expression analysis of nascent polypeptide-associated complex alpha gene in response to immune challenges in Japanese flounder Paralichthys olivaceus

• Paralichthys olivaceus nascent polypeptide-associated complex alpha gene (poNACA) was cloned.
• Constitutively expressed poNACA shows the highest expression in hepatopancreas and gonad tissues.
• poNACA gene expression was significantly up-regulated by PAMPs and bacterial challenges.
• NACA may play important roles in regulation of fish innate immunity.

Nascent polypeptide-associated complex (NAC) is a conserved heterodimeric protein consisting of alpha and beta subunits. In addition to acting as a protein translation chaperone by forming a heterodimer with the beta subunit, NAC alpha (NACA) also shows important immune significance independent of NAC beta in mammalian cells. In lower vertebrates, however, the immunological relevance of NACA has not been revealed yet. In the present study, we identified and characterized a NACA gene (termed poNACA) involved in innate immune response in Japanese flounder Paralichthys olivaceus. poNACA encodes a 215-amino-acid protein, with an apparent molecular weight of 23.5 kDa and an isoelectric point of 4.51. Tissue distribution analysis revealed that poNACA gene was constitutively expressed in all examined tissues and showed dominant expression in hepatopancreas and gonad tissues. In enriched Japanese flounder head kidney macrophages and peripheral blood leucocytes, the expression of poNACA mRNA transcript was significantly induced by LPS, Poly(I:C) and zymosan stimulations. In vivo experiments further revealed that poNACA gene expression was up-regulated in head kidney, gill and spleen tissues in response to Edwardsiella tarda challenges. Furthermore, overexpression of poNACA in Japanese flounder FG-9307 cells resulted in increased gene expression of IL-1beta, IL-11 and TNF-alpha, and myxovirus resistance (Mx). Taken together, our findings indicate that an immune response gene, poNACA, involved in innate immune regulation in P. olivaceus has been identified.