Liver X Receptor LXRα Promotes Grass Carp Reovirus Infection by Attenuating IRF3–CBP Interaction and Inhibiting RLR Antiviral Signaling

Liver X receptors (LXRs) are nuclear receptors involved in metabolism and the immune response. Different from mammalian LXRs, which include two isoforms, LXRα and LXRβ, only a single LXRα gene exists in the piscine genomes. Although a study has suggested that piscine LXR inhibits intracellular bacterial survival, the functions of piscine LXRα in viral infection are unknown. In this study, we show that overexpression of LXRα from grass carp (Ctenopharyngodon idellus), which is named as gcLXRα, increases host susceptibility to grass carp reovirus (GCRV) infection, whereas gcLXRα knockdown in CIK (C. idellus kidney) cells inhibits GCRV infection. Consistent with these functional studies, gcLXRα knockdown promotes the transcription of antiviral genes involved in the RIG-I-like receptor (RLR) antiviral signaling pathway, including IFN regulatory factor (IRF3) and the type I IFN IFN1. Further results show that gcLXRα knockdown induces the expression of CREB-binding protein (CBP), a transcriptional coactivator. In the knockdown of CBP, the inhibitory effect of gcLXRα knockdown in limiting GCRV infection is completely abolished. gcLXRα also interacts with IRF3 and CBP, which impairs the formation of the IRF3/CBP transcription complex. Moreover, gcLXRα heterodimerizes with RXRg, which cooperatively impair the transcription of the RLR antiviral signaling pathway and promote GCRV infection. Taken together, to our knowledge, our findings provide new insight into the functional correlation between nuclear receptor LXRα and the RLR antiviral signaling pathway, and they demonstrate that gcLXRα can impair the RLR antiviral signaling pathway and the production of type I IFN via forming gcLXRα/RXRg complexes and attenuating IRF3/CBP complexes.