miR-203 negatively regulates RLR-mediated antiviral immune response via targeting trim25 in rainbow trout (Oncorhynchus mykiss)

MicroRNAs (miRNAs) have been widely demonstrated to be involved in fish immune process as important post-transcriptional regulators. trim25, a key member of the RLR pathway, performs a critical function in antiviral immunity in fish. However, the antiviral immune mechanism of miRNAs and trim25 in rainbow trout (Oncorhynchus mykiss) remains largely unknown. Herein, we detected expression patterns of miR-203 and trim25 after rainbow trout infected with IHNV, and overexpressed and repressed miR-203 and trim25 to investigate their functions in vitro and in vivo. Expression patterns suggested that miR-203 and trim25 are potential regulators in interferon-mediated innate immune responses. In vitro, trim25 was verified as a target of miR-203 by luciferase reporter assay, and overexpression of miR-203 significantly inhibited trim25 expression and resulted in down-regulation of downstream immune genes including rig-I, irf3, irf7, ifn, mx1, and nf-κb, and co-transfection of trim25 diminished this inhibitory effect. miR-203 overexpression significantly enhanced IHNV n gene expression. On the contrary, the expression level of trim25 and downstream genes were markedly increased after inhibition of miR-203. In vivo, agomiR-203 significantly depressed the expression of trim25, and then reduced the expression levels of rig-I, irf3, irf7, ifn, and mx1. Furthermore, overexpression of trim25 significantly reduced IHNV copies. Overexpression of miR-203 inhibited cell proliferation and promoted apoptosis, which was attenuated by the introduction of trim25, while the opposite results were obtained upon miR-203 suppression. This study contributes to the understanding of post-transcriptional regulatory mechanism governing antiviral immunity in rainbow trout and provides a theoretical basis for using miRNAs as target drugs to treat viral diseases.