ABSTRACT
Natural killer enhancing factor (NKEF)-A/B is a member of Peroxiredoxin (Prxs) family, which is named for the function of enhancing NK cells activity. NKEF also plays essential roles in multiple physiology/pathology processes including inflammation regulation, cancer development and redox reactions. However, the regulatory effects of fish NKEF on immune cells remain largely unknown. In this study, the full-length cDNA of NKEF-A (Accession No. MK584553, designated as On-NKEF-A) was identified from Nile tilapia (Oreochromis niloticus). On-NKEF-A encoded a 198 amino acid peptide with molecular mass of 22.085 kDa. On-NKEF-A protein contained a typical 2-Cys family domain, two active sites (51aa and 172aa) that were conserved in mammals, birds, amphibians and fish. Phylogenetic analysis showed that On-NKEF-A had the closest relationship with Zebra mbuna (Maylandia zebra) NKEF. The On-NKEF-A transcription was present in all examined tissues or organs. And the relative high expression levels of On-NKEF-A was found in head kidney leucocytes and nonspecific cytotoxic cells (NCC). After Streptococcus agalactiae stimulation, On-NKEF-A was significantly up-regulated in head kidney, spleen, gill and skin. Also, On-NKEF-A was markedly induced post S. agalactiae, LPS and poly I:C stimulation in head kidney-derived NCC. Moreover, On-NKEF-A was mainly distributed in cytoplasm of fathead minnow cells (FHM cells). The further in vitro analysis found that the recombinant protein of On-NKEF-A (rOn-NKEF-A) could induce the expression of various molecular markers of B cells, macrophages and NCC, enhanced the cytotoxicity of NCC via increasing the effectors expression. The present data collectively indicate that On-NKEF-A participates in anti-bacterial immune response via regulating NCC activity, which will provide new ideas to further explore the defense mechanism of fish against bacteria.
Subject(s)
Cichlids/immunology , Fish Proteins/metabolism , Killer Cells, Natural/immunology , Peroxiredoxins/metabolism , Streptococcus agalactiae/immunology , Amino Acid Sequence , Animals , Cichlids/microbiology , Fish Diseases/immunology , Fish Diseases/microbiology , Fish Proteins/genetics , Fish Proteins/pharmacokinetics , Gills/metabolism , Head Kidney/metabolism , Immunity, Innate/genetics , Immunity, Innate/immunology , Peroxiredoxins/genetics , Peroxiredoxins/pharmacokinetics , Protein Domains/genetics , Skin/metabolism , Spleen/metabolism , Streptococcal Infections/immunologyABSTRACT
Peroxiredoxins catalytically reduce peroxynitrite to nitrite. The peroxidatic cysteine of peroxiredoxins reacts rapidly with peroxynitrite. The rate constant of that reaction can be measured using a stopped flow spectrophotometer either directly by following peroxynitrite disappearance in the region of 300 to 310 nm using an initial rate approach or steady-state measurements or by competition with a reaction of known rate constant. The reactions used to compete with peroxiredoxins include the oxidation of Mn(III)porphyrins and horseradish peroxidase by peroxynitrite. Additionally, a method is described in which a hydroperoxide competes with peroxynitrite for the oxidation of peroxiredoxin. Moreover, a fluorescent technique for determining the kinetics of thioredoxin-mediated peroxiredoxin reduction, closing the catalytic cycle, is also described. All methods reviewed provide reliable values of rate constants and a combination of them can be used to provide further reassurance; applicability and advantages of the different methodologies are discussed.
