Paramyxovirus V Proteins Interact with the RIG-I/TRIM25 Regulatory Complex and Inhibit RIG-I Signaling

Abstract

Paramyxovirus V proteins are known antagonists of the RIG-I-like receptor (RLR)-mediated interferon induction pathway, interacting with and inhibiting the RLR MDA5. We report interactions between the Nipah virus V protein and both RIG-I regulatory protein TRIM25 and RIG-I. We also observed interactions between these host proteins and the V proteins of measles virus, Sendai virus, and parainfluenza virus. These interactions are mediated by the conserved C-terminal domain of the V protein, which binds to the tandem caspase activation and recruitment domains (CARDs) of RIG-I (the region of TRIM25 ubiquitination) and to the SPRY domain of TRIM25, which mediates TRIM25 interaction with the RIG-I CARDs. Furthermore, we show that V interaction with TRIM25 and RIG-I prevents TRIM25-mediated ubiquitination of RIG-I and disrupts downstream RIG-I signaling to the mitochondrial antiviral signaling protein. This is a novel mechanism for innate immune inhibition by paramyxovirus V proteins, distinct from other known V protein functions such as MDA5 and STAT1 antagonism. The host RIG-I signaling pathway is a key early obstacle to paramyxovirus infection, as it results in rapid induction of an antiviral response. This study shows that paramyxovirus V proteins interact with and inhibit the activation of RIG-I, thereby interrupting the antiviral signaling pathway and facilitating virus replication.

RIPLET, and not TRIM25, is required for endogenous RIG‐I‐dependent antiviral responses

“…TRIM25 is widely accepted as a positive regulator of RIG‐I signaling, with numerous studies, including our own, describing its regulation of RIG‐I response to viral infection and/or its interaction with RIG‐I . The data presented here clearly show that in two human epithelial cell lines and in primary mouse fibroblasts, TRIM25 is not required for a physiological RIG‐I‐mediated immune response to influenza virus infection.…”

“…TRIM25 is widely accepted as a positive regulator of RIG-I signaling, with numerous studies, including our own, describing its regulation of RIG-I response to viral infection and/or its interaction with RIG-I. 14,[31][32][33][34][35][36] The data presented here clearly show that in two human epithelial cell lines and in primary mouse fibroblasts, TRIM25 is not required for a physiological RIG-Imediated immune response to influenza virus infection. The comprehensive nature of our results further indicates that these observations are not simply a consequence of intrinsic differences between mouse and human cells, or differences between cell types.…”

To TRIM or not to TRIM: the balance of host–virus interactions mediated by the ubiquitin system

“…To date, most studies have implicated TRIM25 as a critical mediator of innate immune signalling through ubiquitination of RIG-I [2,11,[101][102][103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118], while only a handful of studies have proposed RIG-I-independent mechanisms [46,119]. Recent years have brought both exciting discoveries and rousing controversies regarding how ubiquitin and E3 ligases precisely function to activate RIG-I for antiviral signalling, with some groups suggesting a single factor operates as the critical component while others have put forth a cooperative model based on trends gleaned from numerous studies.…”

“…For example, a full in vitro reconstitution of the RIG-I pathway utilizing TRIM25 as the E3 ligase is known to potently activate RIG-I signalling through unanchored K63-linked polyubiquitin chains [21]. In addition, viral products have been found to directly antagonize TRIM25, consequently reducing RIG-I ubiquitination and downstream signalling, including paramyxoviruses V protein, the papillomavirus E6 oncoprotein, the severe acute respiratory syndrome-related coronavirus (SARS-CoV) N protein, the NSs protein of severe fever with thrombocytopenia syndrome virus (SFTSV), the nucleocapsid protein (N) of porcine reproductive and respiratory syndrome virus (PRRSV) and potentially DENV subgenomic RNA [106,107,111,113,115,135]. Specifically, the IAV NS1 protein inhibits both TRIM25 and Riplet, and this occurs in a species-specific manner [104].…”

“…As mentioned above, since its identification as a critical component for induction of RIG-I-mediated innate immunity, TRIM25 has received much attention not only for its importance in antiviral defence, but also for how a diverse range of pathogens have zeroed in and neutralized its function [101,102,104,106,107,109,[111][112][113]115]. Besides TRIM25, other TRIMs have been found to be targeted by viruses.…”