FTRCA1, a Species-Specific Member of finTRIM Family, Negatively Regulates Fish IFN Response through Autophage-Lysosomal Degradation of TBK1

Abstract

In mammals, tripartite motif (TRIM) proteins have emerged as pivotal players endowed with, directly, antiviral effects and, indirectly, modulatory capacity of the innate immune response. An unprecedented expansion of TRIM family has occurred in fish; however, the functional role of fish TRIM family members remains largely unknown. In this study, we identify a species-specific TRIM gene from crucian carp Carassius auratus, named FTRCA1, phylogenetically similar to the members of finTRIM, a subfamily of TRIM exclusively in teleost fish. FTRCA1 is induced by IFN and IFN stimuli as a typical IFN-stimulated gene. Overexpression of FTRCA1 negatively regulates IFN antiviral response by inhibition of IRF3 phosphorylation; consistently, knockdown of FTRCA1 results in enhanced levels of IRF3 phosphorylation and also IFN expression following poly(I:C) transfection. Whereas FTRCA1 is associated with several pivotal signaling molecules of RIG-I–like receptor pathway, its association with TBK1 results in autophage-lysosomal degradation of TBK1, thus abrogating the downstream IFN induction. Interestingly, FTRCA1 is phosphorylated by TBK1, but this phosphorylation is not required for downregulation of TBK1 protein. Transfection assays indicate that FTRCA1 is likely an E3 ligase with the requirement of RING finger domain, and deletion of N-terminal RING domain or mutation of seven conservative sites abolishes the negative regulatory function of FTRCA1. Collectively, these results illuminate a novel finTRIM-mediated innate immune modulatory pathway, thus providing insights into species-specific regulation of fish IFN response.

A Novel Transcript Isoform of TBK1 Negatively Regulates Type I IFN Production by Promoting Proteasomal Degradation of TBK1 and Lysosomal Degradation of IRF3

“…First, grass carp SARM1 inhibited GCRV-triggered IFN-I response by affecting the expressions of TRIF, MyD88, IPS-1, TRAF6, TBK1, IRF3, and IRF7 in TRIF-, MyD88-, and IPS-1-dependent pathways ( 29 ). In addition, zebrafish STAT6, FGFR3, MVP, NDRG1a, RPZ5, and FTRCA1 suppressed IFN production by attenuating the kinase activity of TBK1 ( 30 , 31 ), degrading TBK1 ( 32 , 33 ) and phosphorylated IRF7 ( 34 , 35 ), or attenuating IRF7 transcription ( 36 ). Using the luciferase reporter assay system, our previous study ( 18 ) and the present study revealed that TBK1 isoforms, TBK1_tv1–TBK1_tv3, had the same function in inhibiting RLR-mediated type I IFN production with or without SVCV infection.…”

“…However, several deubiquitinases such as CYLD disrupt K63-linked polyubiquitination to terminate TBK1-mediated signaling transduction ( 41 ). Recently, zebrafish MVP and FTRCA1 were found to mediate the lysosome-dependent degradation of TBK1 ( 32 , 33 ). Here, we show that zebrafish TBK1_tv3 is a key kinase that mediates K48-linked ubiquitination at Lys251, Lys256, and Lys271 of TBK1 and promotes TBK1 proteasomal degradation, thus functioning as a negative regulator of type I IFN production.…”

Integrative Transcriptomic Analysis Reveals the Immune Mechanism for A CyHV-3-Resistant Common Carp Strain

“…In the survivors from the resistant strain, the higher PI3K also suggests higher autophagy, since the PI3K/AKT/mTOR pathway enhances this process [28]. Fish TRIM may inhibit the activation of IFN and attenuate IFN regulatory factor (IRF) (41,42). In addition, in carp, nuclear factor, interleukin 3 regulated (NFIL3) stimulated both proinflammatory (e.g., NF-kappa B [NF-κB]) and anti-inflammatory factors (e.g., IL10) (43).…”

Dynamic and Differential Expression of Duplicated Cxcr4/Cxcl12 Genes Facilitates Antiviral Response in Hexaploid Gibel Carp

“…CAB cells were seeded overnight in 6-well plates and transfected with Cg Cxcr4s-pCS2+ and Cg Cxcl12s-pCS2+ respectively using FuGENE HD Transfection Reagent (Promega, Madison, USA) ( 40 , 43 ). After 24 h transfection, 1 μg/ml polyinosinic:polycytidylic acid (poly(I:C)), was transfected to induce the expression of immune genes ( 44 , 45 ). The cells were collected in TRIzol reagent (Invitrogen, Carlsbad, USA) after 24 h stimulation.…”