Molecular characterization and expressional affirmation of the beta proteasome subunit cluster in rock bream immune defense

Immunoproteasomes are primarily induced upon infection and formed by replacing constitutive beta subunits with inducible beta subunits which possess specific cleavage properties that aid in the release of peptides necessary for MHC class I antigen presentation. In this study, we report the molecular characterization and expression analysis of the inducible immunosubunits PSMB8, PSMB9, PSMB9-L, and PSMB10 from rock bream, Oplegnathus fasciatus. The three subunits shared common active site residues and were placed in close proximity to fish homologues in the reconstructed phylogenetic tree, in which the mammalian homologues formed separate clades, indicating a common ancestral origin. The rock bream immunosubunits possessed higher identity and similarity with the fish homologues. RbPSMB8, RbPSMB9, RbPSMB9-L, and RbPSMB10 were multi-exonic genes with 6, 6, 7 and 8 exons, respectively. These four genes were constitutively expressed in all the examined tissues. Immunostimulants such as lipopolysaccharide and poly I:C induced RbPSMB8, RbPSMB9, RbPSMB9-L, and RbPSMB10 in liver and head kidney, suggesting their possible involvement in immune defense in rock bream.