Grouper DHCR24 Exerts Pro-Viral Activity Through Tollip-mediated Autophagic Degradation of STING and TBK1

Cholesterol metabolism plays a significant role in regulating innate antiviral immunity during viral infection. However, the molecular mechanisms by which enzymes regulate the interferon signaling pathway are not well elucidated. Here, we investigated the potential function of the key enzyme in cholesterol synthesis, 3β-hydroxysteroid-Δ24 reductase (DHCR24), from grouper (EcDHCR24) during Singapore grouper iridovirus (SGIV) infection. Upon incubation with SGIV, the expression level of EcDHCR24 was significantly up-regulated in grouper spleen (GS) cells. Interestingly, EcDHCR24 overexpression significantly enhanced SGIV replication in GS cells, and inhibited the mRNA level of IFN-stimulated genes (ISGs) in vitro. Consistently, EcDHCR24 silencing exerted the ‌opposite effects. EcDHCR24 overexpression also reduced the expression levels of these ISGs expression induced by sting, tbk1, irf3, and irf7. Furthermore, as an endoplasmic reticulum-localized protein, EcDHCR24 was found to interact with STING and TBK1. Mechanistically, EcDHCR24 enhanced the degradation of STING and TBK1 through the autophagy-lysosome pathway in a dose-dependent manner. Furthermore, it was worth noting that EcDHCR24 also interacted with toll-interacting protein (Tollip), and overexpression of EcTollip promoted EcDHCR24-medated degradation of STING and TBK1. Collectively, our findings revealed for the first time that fish DHCR24 negatively regulated interferon activation through Tollip-mediated autophagic degradation of the STING-TBK1 axis, and provided new insights into the mechanism by which DHCR24 regulates viral infection in fish.