Black carp RNF5 inhibits STING/IFN signaling through promoting K48-linked ubiquitination and degradation of STING.

ABSTRACT

Ubiquitination is one of the important post-translational modifications (PTMs) of proteins that plays a vital role in regulating substrate degradation to ensure cellular homeostasis. Ring finger protein 5 (RNF5) is an essential E3 ubiquitin ligase for inhibiting STING-mediated interferon (IFN) signaling in mammals. Nevertheless, the function of RNF5 in STING/IFN pathway remains obscure in teleost. Here, we reported that over-expression of black carp RNF5 (bcRNF5) inhibited STING-mediated transcription activity of bcIFNa, DrIFNφ1, NF-κB and ISRE promoters and antiviral activity against SVCV. Moreover, knockdown of bcRNF5 increased the expression of host genes, including bcIFNa, bcIFNb, bcILß, bcMX1 and bcViperin, and also enhanced the antiviral capability of host cells. Immunofluorescence (IF) and Co-immunoprecipitation (Co-IP) assay confirmed that bcRNF5 was mainly localized in the cytoplasm and interacted with bcSTING. The expression level of bcSTING protein was attenuated by co-expressed bcRNF5 and MG132 treatment rescued this attenuating effect, suggesting that bcRNF5-mediated bcSTING degradation was dependent on the proteasome pathway. Subsequent, Co-IP and immunoblot (IB) experiments identified that bcRNF5 triggered the K48-linked but not K63-linked ubiquitination of bcSTING. Altogether, above results conclude that RNF5 suppresses STING/IFN signaling by enhancing K48-linked ubiquitination and protease degradation of STING in black carp.