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

Laboratory of genetics and physiology 2 (LGP2), a member of retinoic acid-inducible gene (RIG)-I-like receptors (RLRs), has been reported to play different roles in IFN signaling in both mammals and teleost fish. In our previous study, black carp (Mylopharyngodon piceus) LGP2 (bcLGP2) has been characterized to positively regulate melanoma differentiation-associated gene 5 (MDA5). In this study, knockdown of bcLGP2 decreased the expression of host genes, including bcIFNb, bcPKR, bcMx1, and bcViperin, and also attenuated the antiviral capability of host cells. The relationship between bcLGP2 and black carp RIG-Ib (bcRIG-Ib) has been explored. Dual-luciferase reporter assay and qRT-PCR assay indicated that bcLGP2 dampened bcRIG-Ib induced transcription of type I interferons (IFNs) and interferon-stimulated genes (ISGs), including PKR, ISG15, and Viperin. Consistently, the plaque assay identified that bcLGP2 attenuated bcRIG-Ib mediated antiviral ability against spring viremia of carp virus (SVCV). Co-immunoprecipitation assay identified the interaction between bcLGP2 and bcRIG-Ib, as well as bcLGP2 and bcRIG-Ib-CARD. And bcRIG-Ib-CARD mediated antiviral ability was also attenuated by bcLGP2. Truncation mutation analysis showed DExD/H-box Helicase domain of bcLGP2 possessed a similar inhibitory effect on bcRIG-Ib to that of bcLGP2, while the C-terminus repressor domain (CTD) presented little impact on bcRIG-Ib. Furthermore, bcLGP2 enhanced the K48-linked ubiquitination of bcRIG-Ib, promoting proteasome-dependent degradation of bcRIG-Ib. Thus, our data supported the conclusion that bcLGP2 interacted with and induced degradation of bcRIG-Ib through proteasome, leading to the dampened antiviral signaling mediated by bcRIG-Ib.