Rotavirus NSP1 Inhibits NFκB Activation by Inducing Proteasome-Dependent Degradation of β-TrCP: A Novel Mechanism of IFN Antagonism

Abstract

Mechanisms by which viruses counter innate host defense responses generally involve inhibition of one or more components of the interferon (IFN) system. Multiple steps in the induction and amplification of IFN signaling are targeted for inhibition by viral proteins, and many of the IFN antagonists have direct or indirect effects on activation of latent cytoplasmic transcription factors. Rotavirus nonstructural protein NSP1 blocks transcription of type I IFNα/β by inducing proteasome-dependent degradation of IFN-regulatory factors 3 (IRF3), IRF5, and IRF7. In this study, we show that rotavirus NSP1 also inhibits activation of NFκB and does so by a novel mechanism. Proteasome-mediated degradation of inhibitor of κB (IκBα) is required for NFκB activation. Phosphorylated IκBα is a substrate for polyubiquitination by a multisubunit E3 ubiquitin ligase complex, Skp1/Cul1/F-box, in which the F-box substrate recognition protein is β-transducin repeat containing protein (β-TrCP). The data presented show that phosphorylated IκBα is stable in rotavirus-infected cells because infection induces proteasome-dependent degradation of β-TrCP. NSP1 expressed in isolation in transiently transfected cells is sufficient to induce this effect. Targeted degradation of an F-box protein of an E3 ligase complex with a prominent role in modulation of innate immune signaling and cell proliferation pathways is a unique mechanism of IFN antagonism and defines a second strategy of immune evasion used by rotaviruses.

Enterovirus 71 2C Protein Inhibits TNF-α–Mediated Activation of NF-κB by Suppressing IκB Kinase β Phosphorylation

“…Adenovirus E1A protein inhibits TNF-a-induced NF-kB activation through suppression of IKK activity and IkBa phosphorylation (36). Rotavirus NSP1 inhibits NF-kB activation by inducing proteasomedependent degradation of b-transducin repeat-containing protein (37,38). In the current study, we report that EV71 2C protein can directly interact with IKKb by inhibiting IKKb activation and IkBa phosphorylation/degradation, and thus inhibits TNF-ainduced NF-kB activation.…”

The Early Interferon Response to Rotavirus Is Regulated by PKR and Depends on MAVS/IPS-1, RIG-I, MDA-5, and IRF3

“…The rotavirus gene segment encoding the nonstructural protein 1 (NSP1) is an important determinant of host restriction of viral replication both in vitro (17,53) and in vivo (9). Specifically, we along with others have reported a role for NSP1 in regulating the ability of rotavirus to efficiently cause diarrhea in mice (9), spread from animal to animal (9), replicate in vivo and in vitro (4,(15)(16)(17), and antagonize IFN (4,5,17,24,25,53). Thus, the host innate immune response is an important determinant of rotavirus host range restriction and depends on both the virus strain and host cell or tissue type.…”

“…At least two distinct mechanisms by which rotaviruses inhibit the host IFN response have been reported: (i) NSP1-mediated proteasomal degradation of host transcription factors IRF3 and IRF7, resulting in diminished IFN-␤ gene transcription and antiviral activity (4,5), and (ii) proteasomal degradation of ␤-TrCP, leading to inhibition of NF-B activity and subsequent IFN-␤ gene transcription (24). In contrast to these examples, we reported that the UK bovine rotavirus strain was unable to block IFN-␤ secretion in murine fibroblasts (17), and this correlated with the lack of murine IRF3 degradation by UK NSP1 (53).…”

Rotavirus Disease Mechanisms Diarrhea, Vomiting and Inflammation : How and Why

“…Moreover, NSP1 seems to interact with the cellular transcription factor interferon regulatory factor 3 (IRF3) and targets it for degradation by the proteasome, thus acting to avoid the host antiviral defense by the blocking INF production [14][15][16][17][18] . However, NSP1 seems not to be necessary for rotavirus replication in vitro and its role is not fully clear 19 .…”