RNF122 targets STING for ubiquitination at residues K95, K117, K155 to regulate antiviral response in a teleost fish

Ring finger protein 122 (RNF122) serves as an E3 ubiquitin ligase, modulating antiviral immune response activity in mammals by ubiquitinating two proteins: retinoic acid-inducible gene 1 and melanoma differentiation-associated gene 5. However, knowledge of RNF122's role in teleost fish remains limited, especially concerning the identification of its specific regulatory sites on substrates. In this study, we investigated the regulatory function of RNF122 from the mandarin fish <i>Siniperca chuatsi</i>, termed <i>sc</i>RNF122, in the stimulator of interferon genes (STING)-mediated antiviral immune response, and identified the specific regulatory sites on<i> sc</i>STING. Our results showed that <i>sc</i>RNF122 expression patterns in virus-infected cells responded to mandarin fish ranavirus (MRV) infection. Overexpression of <i>sc</i>RNF122 suppressed <i>sc</i>STING-mediated interferon (IFN) production and facilitated MRV replication. Co-immunoprecipitation assays confirmed an interaction between <i>sc</i>RNF122 and <i>sc</i>STING. Further experiments demonstrated that <i>sc</i>RNF122 exerted its inhibitory effect by promoting the degradation of <i>sc</i>STING, a process that was impeded by MG132 treatment. Ubiquitination assays using various scSTING mutants revealed that <i>sc</i>RNF122 catalyzed the ubiquitination of <i>sc</i>STING at K95, K117, and K155 residues. Moreover, we presented evidence that <i>sc</i>RNF122 significantly impaired<i> sc</i>STING-dependent antiviral immunity by engaging negative regulators within the <i>sc</i>STING signaling cascade. This study emphasized that RNF122 negatively modulated STING-mediated IFN signaling in mandarin fish, attenuated STING's antiviral function, and promoted STING degradation through the ubiquitin-proteasome pathway at three identified lysine residues (K95, K117, and K155). Our finding contributes valuable insights into the regulatory mechanisms governing STING-mediated antiviral innate immunity in teleost fish, laying the groundwork for future research endeavors.