Human Bocavirus VP2 Upregulates IFN-β Pathway by Inhibiting Ring Finger Protein 125–Mediated Ubiquitination of Retinoic Acid–Inducible Gene-I

Abstract

Precise regulation of innate immunity is crucial for maintaining optimal immune responses against infections. Whereas positive regulation of IFN signaling elicits rapid type I IFNs, negative regulation is equally important in preventing the production of superfluous IFNs that can be hazardous to the host. The positive regulators of IFN pathway are known to be the main targets of viruses to antagonize the innate immune system. Whether viruses target the negative regulators of IFN pathway remains to be fully investigated. In this study, we report that the structural protein VP2 of human Bocavirus modulates IFN pathway by targeting the ring finger protein 125 (RNF125), a negative regulator of type I IFN signaling, which conjugates Lys48-linked ubiquitination to retinoic acid–inducible gene-I (RIG-I) and subsequently leads to the proteasome-dependent degradation of RIG-I. VP2 not only upregulated Sendai virus (SeV)–induced IFNB promoter activity, but also enhanced SeV-induced IFN-β production at both mRNA and protein levels. In agreement, the level of Ser396-phosphorylated IFN regulatory factor 3 stimulated by SeV was enhanced in the presence of VP2. Furthermore, VP2 was demonstrated to physically interact with RNF125, resulting in the reduction of RNF125-mediated ubiquitination and proteasome-dependent degradation of RIG-I. Additional study indicated that endogenous RIG-I degradation was decreased in VP2-expressing cells. Our study delineates a unique phenomenon for aberrant activation of IFN regulatory factor 3 pathway and may represent a new mechanism underlying viral manipulation of the host immune system.

Long noncoding RNAs in viral infections

“…More complex is the ubiquitin-regulation of RIG-I. RIG-I can be ubiquitinated and degraded by RNF125 (Ring Finger Protein 125) and deubiquitinated and stabilized by USP4 (Wang et al, 2013; Luo et al, 2013). Further, RIG-I can be ubiquitinated and activated by TRIM25, which, in turn, can be ubiquitinated and degraded by LUBAC (linear ubiquitin chain assembly complex) and deubiquitinated and stabilized by USP15 (Davis and Gack, 2015) (Fig.…”

SUMO Modification Stabilizes Enterovirus 71 Polymerase 3D To Facilitate Viral Replication

“…Flag-SUMO-1, -2, and -3 were created by amplifying and inserting their coding sequences into pCAGGS. HA-K48-Ub and HA-K63-Ub were mutants of HA-Ub with all the lysine residues except K48 and K63 mutated into arginines (52). HA-UB-KO (knockout) was a mutant of ubiquitin created by the replacement of lysine residue 63 (Lys63) of HA-K63-Ub with arginine.…”

“…According to the protocol, 10 g of corresponding antibody was incubated with 50 l of protein G Dynabeads for 20 min before incubation with the supernatants from the cell lysis for 25 min. Following several washes with PBST (PBS with 0.02% Tween 20), the complexes were boiled with electrophoresis sample buffer, followed by immunoblot (IB) analysis with the indicated antibodies as previously described (45,52).…”

Regulation of cellular innate antiviral signaling by ubiquitin modification

“…The ORF1 of hepatitis E virus contains the papain-like cysteine protease domain and deubiquitinates RIG-I to inhibit poly(I:C)-induced activation of IRF3 [89]. On the contrary, human bocavirus VP2 deubiquitinates RNF125-mediated K48-linked ubiquitination of RIG-I, promotes the stability of RIG-I and upregulates IFNβ induction [90]. However, these in vitro studies have been performed in an over-expression system or with purified proteins.…”