REUL Is a Novel E3 Ubiquitin Ligase and Stimulator of Retinoic-Acid-Inducible Gene-I

Abstract

RIG-I and MDA5 are cytoplasmic sensors that recognize different species of viral RNAs, leads to activation of the transcription factors IRF3 and NF-κB, which collaborate to induce type I interferons. In this study, we identified REUL, a RING-finger protein, as a specific RIG-I-interacting protein. REUL was associated with RIG-I, but not MDA5, through its PRY and SPRY domains. Overexpression of REUL potently potentiated RIG-I-, but not MDA5-mediated downstream signalling and antiviral activity. In contrast, the RING domain deletion mutant of REUL suppressed Sendai virus (SV)-induced, but not cytoplasmic polyI:C-induced activation of IFN-β promoter. Knockdown of endogenous REUL by RNAi inhibited SV-triggered IFN-β expression, and also increased VSV replication. Full-length RIG-I, but not the CARD domain deletion mutant of RIG-I, underwent ubiquitination induced by REUL. The Lys 154, 164, and 172 residues of the RIG-I CARD domain were critical for efficient REUL-mediated ubiquitination, as well as the ability of RIG-I to induce activation of IFN-β promoter. These findings suggest that REUL is an E3 ubiquitin ligase of RIG-I and specifically stimulates RIG-I-mediated innate antiviral activity.

Mechanism of inhibiting type I interferon induction by hepatitis B virus X protein

“…However, in comparison with RIG I-2CARD, the K172R mutation, causing the former's marked loss of ubiquitination and poorly binding to CARDIF (Gack et al, 2007), did not reduce the amount of HBx precipitated (data not shown). A study has described that E3 ubiquitin ligase REUL-mediated attachment of Lys63-linked polyubiquitin chains to 2CARD domain at residues K154 and K164 is also necessary for eliciting RIG I signaling (Gao et al, 2009). Therefore, further experiments using RIG I-2CARD mutant, in which three ubiquitination sites are replaced, would help clarify whether ubiquitin chains influence HBx's binding to RIG I-2CARD.…”

The ubiquitin-specific protease 17 is involved in virus-triggered type I IFN signaling

“…For example, two ubiquitin E3 enzymes, TRIM25 and REUL (also called RNF135 and Riplet), have been demonstrated to catalyze K63-linked polyubiquitinations of RIG-I, which are critical for activation of RIG-I and signaling to downstream components [30][31][32]. Two DUBs, A20 and CYLD, have been demonstrated to remove the K63-linked polyubiquitin chains from RIG-I and thereby negatively regulate virus-induced type I IFN signaling [36,37].…”

“…Several ubiquitin ligase enzymes have been identified to regulate these processes [28][29][30][31][32][33][34][35]. However, only a few DUBs are known to regulate these pathways: A20 was shown to negatively regulate the RIG-I-induced antiviral state [36], DUBA was identified to be required for efficient deubiquitination of TRAF3 and to function as a negative regulator of innate immune responses [25], and CYLD, known as a tumor suppressor, was recently reported to negatively regulate the activation of TBK1/ IKKε [37].…”

Regulation of Virus-triggered Signaling by OTUB1- and OTUB2-mediated Deubiquitination of TRAF3 and TRAF6

“…It has been shown that the E3 ubiquitin ligase TRIM25 catalyzes Lys 63 -linked ubiquitination of RIG-I, and this ubiquitination is essential for the interaction of RIG-I with VISA as well as for its ability to signal (22). The Riplet/REUL E3 ubiquitin ligase also targets RIG-I for ubiquitination, which positively regulates RIG-I-mediated signaling (23). In contrast, the E3 ubiquitin ligase RNF125 catalyzes Lys 48 -linked ubiquitination of RIG-I and negatively regulates RIG-I-mediated signaling (24).…”