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Circular RNA circDtx1 regulates IRF3-mediated antiviral immune responses through suppression of miR-15a-5p-dependent TRIF downregulation in teleost fish.

ABSTRACT: Circular RNAs (circRNAs) represent a class of widespread and diverse covalently closed circular endogenous RNAs that exert crucial functions in regulating gene expression in mammals. However, the function and regulation mechanism of circRNAs in lower vertebrates are still unknown. Here, we discovered a novel circRNA derived from Deltex E3 ubiquitin ligase 1 (Dtx1) gene, namely, circDtx1, which was related to the antiviral responses in teleost fish. Results indicated that circDtx1 played essential roles in host antiviral immunity and inhibition of SCRV replication. Our study also found a microRNA miR-15a-5p, which could inhibit antiviral immune response and promote viral replication by targeting TRIF. Moreover, we also found that the antiviral effect inhibited by miR-15a-5p could be reversed with the circDtx1. In mechanism, our data revealed that circDtx1 was a competing endogenous RNA (ceRNA) of TRIF by sponging miR-15a-5p, leading to activation of the NF-κB/IRF3 pathway, and then enhancing the innate antiviral responses. Our results indicated that circRNAs played a regulatory role in immune responses in teleost fish.

SUBMITTER: Zheng W

PROVIDER: S-EPMC8009406 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Ubiquitination, as one of the most prevalent posttranslational modifications of proteins, enables a tight control of host immune responses. Many viruses hijack the host ubiquitin system to regulate host antiviral responses for their survival. Here, we found that the fish pathogen nervous necrosis virus (NNV) recruited Lateolabrax japonicus E3 ubiquitin ligase ring finger protein 34 (LjRNF34) to inhibit the RIG-I-like receptor (RLR)-mediated interferon (IFN) response via ubiquitinating Lateolabrax japonicus TANK-binding kinase 1 (LjTBK1) and interferon regulatory factor 3 (LjIRF3). Ectopic expression of LjRNF34 greatly enhanced NNV replication and prevented IFN production, while deficiency of LjRNF34 led to the opposite effect. Furthermore, LjRNF34 targeted LjTBK1 and LjIRF3 via its RING domain. Of note, the interactions between LjRNF34 and LjTBK1 or LjIRF3 were conserved in different cellular models derived from fish. Mechanically, LjRNF34 promoted K27- and K48-linked ubiquitination and degradation of LjTBK1 and LjIRF3, which in turn diminished LjTBK1-induced translocation of LjIRF3 from the cytoplasm to the nucleus. Ultimately, NNV capsid protein (CP) was found to bind with LjRNF34, CP induced LjTBK1 and LjIRF3 degradation, and IFN suppression depended on LjRNF34. Our finding demonstrates a novel mechanism by which NNV CP evaded host innate immunity via LjRNF34 and provides a potential drug target for the control of NNV infection. IMPORTANCE Ubiquitination plays an essential role in the regulation of innate immune responses to pathogens. NNV, a type of RNA virus, is the causal agent of a highly destructive disease in a variety of marine and freshwater fish. A previous study reported NNV could hijack the ubiquitin system to manipulate the host's immune responses; however, how NNV utilizes ubiquitination to facilitate its own replication is not well understood. Here, we identified a novel distinct role of E3 ubiquitin ligase LjRNF34 as an IFN antagonist to promote NNV infection. NNV capsid protein utilized LjRNF34 to target LjTBK1 and LjIRF3 for K27- and K48-linked ubiquitination and degradation. Importantly, the interactions between LjRNF34 and CP, LjTBK1, or LjIRF3 are conserved in different cellular models derived from fish, suggesting it is a general immune evasion strategy exploited by NNV to target the IFN response via RNF34.

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Circular RNA circDtx1 regulates IRF3-mediated antiviral immune responses through suppression of miR-15a-5p-dependent TRIF downregulation in teleost fish.

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