The reovirus σ3 protein induces proteasomal degradation of IKKβ to modulate the host response to infection

ABSTRACT Reovirus strains differ in their capacity to modulate host antiviral signaling, but the viral determinants underlying these differences have remained unclear. In this study, we identify the outer capsid protein σ3 as the viral determinant responsible for inducing the loss of the NF-κB kinase, IKKβ. We demonstrate that introduction of the σ3 encoding gene segment of strain T3A in the background of strain T3D L recapitulates IKK loss observed during T3A infection. Our results indicate that de novo expression of T3A σ3 during infection is necessary to mediate the loss of IKK. Further, the presence of T3A σ3 alone is sufficient. We show that T3A σ3 interacts with the IKK complex and targets IKKβ for degradation through a Cullin-RING ligase–proteasome dependent mechanism. Loss of IKKβ results in impaired NF-κB activation and reduced IFN-β expression. Consequently, the T3D L /T3A S4 monoreassortant exhibits a replication advantage compared to T3D L . Collectively, these findings uncover a previously uncharacterized mechanism by which reovirus σ3 suppresses innate antiviral signaling through targeted degradation of IKKβ, providing new insight into reovirus mediated immune modulation. IMPORTANCE Successful viral infection and replication requires that the virus suppress host immune defenses, particularly innate immunity, which relies on signaling cascades to produce antiviral cytokines. Many viruses encode proteins to target key signaling molecules, such as those in the NF-κB pathway, but the exact mechanisms of evasion vary across viral families and even between closely related strains. In this study, we uncover a novel function of the reovirus outer capsid protein σ3 to promote IKKβ degradation. Our findings reveal that σ3 associates with a complex of proteins that includes IKKβ, a central kinase in the NF-κB pathway, to mediate its degradation via the proteasomal pathway. σ3 mediated IKKβ loss decreases type I IFN expression during infection and enhances viral replication. Coupled with previous observations that σ3 from other reovirus strains antagonizes NF-κB by altering its transcriptional activity, this work demonstrates that this conserved viral protein adopts strain-specific strategies to subvert host defenses.