Abstract
RIG-I-like receptors (RLRs) play important roles in response to virus infection by regulating host innate immune signaling pathways. Meanwhile, the RLR signaling pathway is also tightly regulated by host and virus to achieve the immune homeostasis between antiviral responses and virus survival. Here, we found that zebrafish TRIM25 (zbTRIM25) functioned as a positive regulator of RLR signaling pathway during red spotted grouper nervous necrosis virus (RGNNV) infection. Post-RGNNV infection, zbTRIM25 expression was obviously inhibited and ectopic expression of zbTRIM25 led to enhanced expression of RLR signaling pathway-related genes. Overexpression and knockdown analysis revealed that zbTRIM25 promoted zebrafish RIG-I (zbRIG-I)-mediated IFN signaling and inhibited RGNNV replication. Mechanistically, zbTRIM25 bound to zbRIG-I; in particular, the SPRY domain of zbTRIM25 interacted with the tandem caspase activation and recruitment domains (2CARD) and repressor domain (RD) regions of zbRIG-I. zbTRIM25 promoted the K63 polyubiquitination of 2CARD and RD regions of zbRIG-I. Furthermore, zbTRIM25-mediated zbRIG-I activation of IFN production was enhanced by K63-linked ubiquitin, indicating that zbTRIM25-mediated zbRIG-I polyubiquitination was essential for RIG-I-triggered IFN induction. In conclusion, these findings reveal a novel mechanism that zbTRIM25 positively regulates the innate immune response by targeting and promoting the K63-linked polyubiquitination of zbRIG-I.
Highlights
The innate immune system recognizes pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) as against microbial pathogen invasion [1]
We investigated the expression of zbTRIM25 in RGNNVinfected zebrafish embryos at 24 h, and the results were concordant with ZBE3 cells (Figure 1B)
All these results demonstrate that zbTRIM25 is a positive regulator of Retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs) signaling pathway and functions as an antiviral factor during red spotted grouper nervous necrosis virus (RGNNV) infection in zebrafish
Summary
The innate immune system recognizes pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs) as against microbial pathogen invasion [1]. Retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs), as intracellular PRRs, composed of RIG-I, MDA5, and LGP2, recognize non-self signatures of viral RNAs in the cytosol of cells. It has been revealed that RLRs respond in vivo or in vitro to the stimulation of NNV and possess capacities in the induction of IFNs and ISGs in a variety of fish species. Our previous studies suggested that RLR signaling pathway was activated during red spotted grouper nervous necrosis virus (RGNNV) infection in sea perch and its key components possessed anti-RGNNV activities [5, 6]. RNF122 negatively regulated RLR signaling pathway by targeting RIG-I [7]. TRIM25 E3 ubiquitin ligase induced the K63linked ubiquitination of RIG-I, which activated RLR signaling pathway to elicit host antiviral innate immunity [10]
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