Cytokines mainly signal through the JAK/STAT pathway and trigger far-reaching immune responses.. PIAS

“protein inhibitors of activated STAT” (PIAS) control the STAT- and NF-κB-dependant immune signalling in human. The genome of rainbow trout contains eight pias genes, which encode at least 14 different pias transcripts. These transcript variants are differentially expressed in a tissue- and cell-specific manner. Pias1a2 was the most strongly expressed variant among the analysed pias genes in most tissues and in CHSE-214 cells, while pias4a1 variants were commonly low or ab-sent. The knock-out of Pias factors in a CHSE cells using CRISPR/Cas9 technology failed, indicat-ing the vital importance of the trout Pias factors. Due to their significant structural differences, three Pias protein variants were selected for overexpression studies in CHSE-214 cells. All three factors quenched the basal activity of an NF-κB promoter in a dose-dependent fashion, while the activity of an Mx promoter remained unaffected. Nevertheless, all three overexpressed Pias vari-ants from trout strongly reduced the transcript level of the antiviral Stat-dependant mx gene in ifnγ-expressing CHSE-214 cells. Unlike mx, the overexpressed Pias factors modulated the tran-script levels of NF-κB-dependant immune genes (mainly il6, il10, ifna3, and stat4) in ifnγ-expressing CHSE-214 cells in different ways. This dissimilar modulation of expression may result from the physical cooperation of the Pias proteins from trout with differential sets of inter-acting factors bound to distinct nuclear structures, which was reflected by the differential nuclear localization of trout Pias factors. In conclusion, this study provides evidence for the multiplica-tion of pias genes and their subfunctionalisation during salmonid evolution.