Molecular structure and immune-stimulated transcriptional modulation of the first teleostean IFP35 counterpart from rockfish (Sebastes schlegelii)

Interferons (IFNs) and IFN-inducible proteins play numerous physiological roles, particularly in antiviral defense mechanisms of the innate immune response with the presence of pathogens. IFN-induced protein-35 kDa (IFP35) is induced by Type II IFN (IFN-γ); it is a cytoplasmic protein that can be translocated to the nucleus via the stimulation of IFN. In this study, we report the complete molecular characterization of the IFP35 cDNA sequence from the black rockfish in an effort to understand its role in the immune response. The coding sequence of RfIFP35 encoded a putative peptide of 371 amino acids containing two characteristic Nmi/IFP 35 domains (NIDs), which are highly conserved among its counterparts. The protein showed a molecular mass of 42.2 kDa with a theoretical pI of 5.05 and was predicted to be unstable because of its high instability index (49.37). Therefore, the protein-protein interaction is essential for its stability, which may be facilitated by the intrinsically disordered regions in this protein. According to cellular location prediction, the RfIFP35 protein is cytosolic. Phylogenetic analysis showed that RfIFP35 was cladded within the fish counterparts. Tissue distribution profiling revealed a ubiquitous presence of the protein in all examined tissues, with highest expression in the blood followed by the spleen tissues. The expression of RfIFP35 during immune challenge with poly I:C and lipopolysaccharide treatments affirms its putative importance in the first-line host defense system. RfIFN-γ mRNA was significantly expressed at 6 h p.i. in blood and 3 h p.i. in the spleen following treatment with different immune stimulants, and its expression was higher compared to that of RfIFP35 mRNA. Therefore, the modulation patterns of both RfIFP35 and RfIFN-γ suggest that RfIFP35 may be induced by RfIFN-γ.