Black carp LGP2 suppresses RIG-I mediated IFN signaling during the antiviral innate immunity

HSC70 functions as a negatively regulator in IFN signaling pathway via suppressing K63-linked ubiquitination of RIG-I in black carp

Heat shock cognate 70 (HSC70), a highly conserved molecular chaperone in the heat shock protein 70 (HSP70) family, plays an essential role in maintaining the homeostasis of the cellular environment. Furthermore, although previous studies have investigated potential function of HSC70 in innate antiviral immunity, further research is still required to fully elucidate its role. In this study, we cloned and characterized the HSC70 homolog gene from black carp (Mylopharyngodon piceus), which consists of 1950 nucleotides encoding 650 amino acids, migrates at approximately 71 kDa on SDS-PAGE, and is distributed in the cytoplasm. In response to different stimuli (SVCV, poly (I:C) and LPS), the transcription level of black carp HSC70 (bcHSC70) all increased to a certain extent. Luciferase reporter assay demonstrated that co-transfected bcHSC70 obviously reduced activity of interferon (IFN) promoters mediated by most factors in the RLRs pathway, and further qRT-PCR and plaque assay indicated that co-transfection of bcHSC70 with bcRIG-I decreased the bcRIG-I-mediated IFN transcription and antiviral ability resisting spring viremia of carp virus (SVCV), whereas knockdown of bcHSC70 improves the host cellular antiviral activity. Noteworthily, co-immunoprecipitation (co-IP) assay and immunofluorescence (IF) assay confirmed bcHSC70 interacts with bcRIG-I, and weaken K63-linked polyubiquitination of bcRIG-I. In summary, our study revealed that HSC70 negatively regulates IFN signaling pathway through impairing K63-linked ubiquitination of RIG-I in black carp, which provides an important basis for exploring innate immune regulatory mechanisms in teleost fish.

STAT2 negatively regulates RIG-I in the antiviral innate immunity of black carp

The signal transducer and activator of transcription 2 (STAT2), a downstream factor of type I interferons (IFNs), is a key component of the cellular antiviral immunity response. However, the role of STAT2 in the upstream of IFN signaling, such as the regulation of pattern recognition receptors (PRRs), remains unknown. In this study, STAT2 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized. The open reading frame (ORF) of bcSTAT2 comprises 2523 nucleotides and encodes 841 amino acids, which presents the conserved structure to that of mammalian STAT2. The dual-luciferase reporter assay and the plaque assay showed that bcSTAT2 possessed certain IFN-inducing ability and antiviral ability against both spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV). Interestingly, we detected the association between bcSTAT2 and bcRIG-I through co-immunoprecipitation (co-IP) assay. Moreover, when bcSTAT2 was co-expressed with bcRIG-I, bcSTAT2 obviously suppressed bcRIG-I-induced IFN expression and antiviral activity. The subsequent co-IP assay and immunoblotting (IB) assay further demonstrated that bcSTAT2 inhibited K63-linked polyubiquitination but not K48-linked polyubiquitination of bcRIG-I, however, did not affect the oligomerization of bcRIG-I. Thus, our data conclude that black carp STAT2 negatively regulates RIG-I through attenuates its K63-linked ubiquitination, which sheds a new light on the regulation of the antiviral innate immunity cascade in vertebrates.

IFI16 plays a critical role in avian reovirus induced cellular immunosuppression and suppresses virus replication

Avian reovirus (ARV), which commonly induces viral arthritis or tenosynovitis and immunosuppression in chickens, is associated with the nonstructural protein p17 that plays a crucial role in viral replication and regulates cellular signaling pathways through its interaction with cellular proteins. In our previous study, we identified the host protein IFN-γ-inducible protein-16 (IFI16) as an interacting partner of ARV p17 through yeast two-hybrid screening. In the current study, we further confirmed the interaction between IFI16 and p17 protein using coimmunoprecipitation, glutathione S-transferase (GST)-pulldown assay, and laser confocal microscopy techniques. Additionally, we found that the amino acid of p1761-119 is responsible for mediating the interaction with the HINa and HINb domains of IFI16. Interestingly, we observed a significant increase in IFI16 expression upon ARV infection or p17 protein exposure. Moreover, the replication of ARV was found to be largely influenced by the quantity of IFI16 protein. Overexpression of IFI16 led to a significant decrease in ARV replication, while knockdown of the IFI16 expression led to the contrary result. Additionally, our findings demonstrate that IFI16 plays a crucial role in the induction of inflammatory cytokines IFN-β and IL-1β during ARV infection as confirmed by qRT-PCR and ELISA analyses. In conclusion, our study provides novel insights into the functional role of p17 protein and the pathogenic mechanism underlying ARV infection, particularly its association with inflammatory response. Furthermore, it offers new perspectives for identifying potential therapeutic targets against ARV infection.