Co‐degradation of interferon signaling factor DDX3 by PB1‐F2 as a basis for high virulence of 1918 pandemic influenza

Abstract

The multifunctional influenza virus protein PB1-F2 plays several roles in deregulation of host innate immune responses and is a known immunopathology enhancer of the 1918 influenza pandemic. Here, we show that the 1918 PB1-F2 protein not only interferes with the mitochondria-dependent pathway of type I interferon (IFN) signaling, but also acquired a novel IFN antagonist function by targeting the DEAD-box helicase DDX3, a key downstream mediator in antiviral interferon signaling, toward proteasome-dependent degradation. Interactome analysis revealed that 1918 PB1-F2, but not PR8 PB1-F2, binds to DDX3 and causes its co-degradation. Consistent with intrinsic protein instability as basis for this gain-of-function, internal structural disorder is associated with the unique cytotoxic sequences of the 1918 PB1-F2 protein. Infusing mice with recombinant DDX3 protein completely rescued them from lethal infection with the 1918 PB1-F2-producing virus. Alongside NS1 protein, 1918 PB1-F2 therefore constitutes a potent IFN antagonist causative for the severe pathogenicity of the 1918 influenza strain. Our identification of molecular determinants of pathogenesis should be useful for the future design of new antiviral strategies against influenza pandemics.

Murine cytomegaloviruses m139 targets DDX3 to curtail interferon production and promote viral replication

“…TLR9, for instance, is expressed predominantly by antigen presenting cells such as macrophages and dendritic cells [51]. Only a few viral antagonists of DDX3-mediated IFN signaling have been described: The influenza virus protein PB1-F2 inhibits DDX3 by inducing its proteasomal degradation, while VACV protein K7 and hepatitis B virus polymerase block the interaction of DDX3 with IKKε [42,52,53]. This study describes the first DDX3 antagonist encoded by a herpesvirus, which inhibits IFN production in a similar fashion as VACV K7 (Figure 9A).…”

Influenza A virus PB1-F2 protein: An ambivalent innate immune modulator and virulence factor

“…Mechanistically, 1918 PB1‐F2 but not PR8 PB1‐F2 specifically binds to DDX3, which is a substrate and coactivator of TBK1, 94 and facilitates DDX3 degradation 93 . The unstable 1918 PB1‐F2 adapts DDX3 and UPS to TBK1 93 . Ectopic administration of DDX3 recombinant protein rescued lethal infection of mice with 1918 H1N1 by resupplying sufficient amount of type I IFN, 93 suggesting that 1918 PB1‐F2 affects the outcome of IAV infection by targeting DDX3 for degradation.…”

“…The unstable 1918 PB1‐F2 adapts DDX3 and UPS to TBK1 93 . Ectopic administration of DDX3 recombinant protein rescued lethal infection of mice with 1918 H1N1 by resupplying sufficient amount of type I IFN, 93 suggesting that 1918 PB1‐F2 affects the outcome of IAV infection by targeting DDX3 for degradation.…”

Host–Virus Interaction: How Host Cells Defend against Influenza A Virus Infection

“…Phosphorylation of NS1 is crucial for its function of antagonizing IFN-β expression, since dephosphorylation at position 73 and 83 of the protein induced a high level of IFN-β [91]. Non-structural protein PB1-F2, identified from a+1 open reading frame (ORF) of PB1 gene segment [164], is multifunctional in deregulation of type I interferon [165,166]. It counteracted RLR-mediated activation of IFN pathway not only by targeting mitochondrial MAVS [115,165,167], but also by binding to the DEAD-box helicase DDX3 to induce proteasome-dependent degradation [166].…”