Exon-Intron Circular RNA circRNF217 Promotes Innate Immunity and Antibacterial Activity in Teleost Fish by Reducing miR-130-3p Function.

Circular RNA (circRNA) is produced by splicing head to tail and is widely distributed in multicellular organisms, and circRNA reportedly can participate in various cell biological processes. In this study, we discovered a novel exon-intron circRNA derived from probable E3 ubiquitin-protein ligase RNF217 () gene, namely, circRNF217, which was related to the antibacterial responses in teleost fish. Results indicated that circRNF217 played essential roles in host antibacterial immunity and inhibited the invasion into cells. Our study also found a microRNA miR-130-3p, which could inhibit antibacterial immune response and promote invasion into cells by targeting NOD1. Moreover, we also found that the antibacterial effect inhibited by miR-130-3p could be reversed with circRNF217. In mechanism, our data revealed that circRNF217 was a competing endogenous RNA of NOD1 by sponging miR-130-3p, leading to activation of the NF-κB pathway and then enhancing the innate antibacterial responses. In addition, we also found that circRNF217 can promote the antiviral response caused by rhabdovirus through targeting NOD1. Our study provides new insights for understanding the impact of circRNA on host-pathogen interactions and formulating fish disease prevention to resist the severely harmful infection.