Influenza Virus Non-Structural Protein 1 (NS1) Disrupts Interferon Signaling

Abstract

Type I interferons (IFNs) function as the first line of defense against viral infections by modulating cell growth, establishing an antiviral state and influencing the activation of various immune cells. Viruses such as influenza have developed mechanisms to evade this defense mechanism and during infection with influenza A viruses, the non-structural protein 1 (NS1) encoded by the virus genome suppresses induction of IFNs-α/β. Here we show that expression of avian H5N1 NS1 in HeLa cells leads to a block in IFN signaling. H5N1 NS1 reduces IFN-inducible tyrosine phosphorylation of STAT1, STAT2 and STAT3 and inhibits the nuclear translocation of phospho-STAT2 and the formation of IFN-inducible STAT1:1-, STAT1:3- and STAT3:3- DNA complexes. Inhibition of IFN-inducible STAT signaling by NS1 in HeLa cells is, in part, a consequence of NS1-mediated inhibition of expression of the IFN receptor subunit, IFNAR1. In support of this NS1-mediated inhibition, we observed a reduction in expression of ifnar1 in ex vivo human non-tumor lung tissues infected with H5N1 and H1N1 viruses. Moreover, H1N1 and H5N1 virus infection of human monocyte-derived macrophages led to inhibition of both ifnar1 and ifnar2 expression. In addition, NS1 expression induces up-regulation of the JAK/STAT inhibitors, SOCS1 and SOCS3. By contrast, treatment of ex vivo human lung tissues with IFN-α results in the up-regulation of a number of IFN-stimulated genes and inhibits both H5N1 and H1N1 virus replication. The data suggest that NS1 can directly interfere with IFN signaling to enhance viral replication, but that treatment with IFN can nevertheless override these inhibitory effects to block H5N1 and H1N1 virus infections.

Inhibition of Reactive Oxygen Species Production Ameliorates Inflammation Induced by Influenza A Viruses via Upregulation of SOCS1 and SOCS3

“…The elevation of SOCS1 and SOCS3 expression following influenza virus infection, as shown in the present studies (Fig. 5E) and in other literature (27,28,37), is likely to reflect the combined effect of a dynamic interaction between the host and the pathogen, resulting in the modulation of multiple signaling pathways infected with influenza viruses as indicated in the presence of 1% DMSO control or 1 mM apocynin for 24 h. Uninfected cells cultured in medium containing 1% DMSO were used as negative controls. ROS production (red) was detected by immunofluorescence with CellROX Deep Red reagent, and the total nuclei were shown with DAPI staining (blue).…”

“…SOCS1 and SOCS3 are the key negative regulators of cytokine signaling. Previous research suggests that influenza viruses manipulate SOCS expression and function to modulate antiviral cytokine production to promote virus replication and survival (27,28). In A549 cells, SOCS1 (Fig.…”

Influenza virus-induced lung injury: pathogenesis and implications for treatment

“…The sialic acid specificity of different viruses has been suggested to explain why some viruses appear to be more lethal than others [5, 73,75]. [41,42] It also induces the downregulation of the IFN-α receptor [43] and upregulates inhibitors of JAK/STAT signalling (SOCS1 and SOCS3) [43,44] During infection, non-structural protein-1 also blocks pro-apoptotic signalling by protein kinase R [45,46] and prevents the activation of NF-κB [47] Nonstructural protein-2 Expressed during replication, not part of the mature virion…”

Interferons as Biomarkers and Effectors: Lessons Learned from Animal Models

“…However, the NS1 from reconstructed strains of influenza H1N1 that caused the Spanish flu pandemic, which killed approximately 50 million people, inhibited expression of additional ISGs and allowed virus replication in the presence of IFN. IFN−α treatment has been shown to restore inhibitory effects of NS1 from both H5N1 and H1N1 virus infections [63]. Recent focus has been directed towards the development of NS1-truncated A/Viet Nam/1203/04 strains of influenza H5N1, made by reverse genetics, to be used as live−attenuated vaccines against H5N1 highly pathogenic avian influenza [64].…”