Abstract
The human interferon (IFN)-induced MxA protein is a key antiviral host restriction factor exhibiting broad antiviral activity against many RNA viruses, including highly pathogenic avian influenza A viruses (IAV) of the H5N1 and H7N7 subtype. To date the mechanism for how MxA exerts its antiviral activity is unclear, however, additional cellular factors are believed to be essential for this activity. To identify MxA cofactors we performed a genome-wide siRNA-based screen in human airway epithelial cells (A549) constitutively expressing MxA using an H5N1 reporter virus. These data were complemented with a proteomic screen to identify MxA-interacting proteins. The combined data identified SMARCA2, the ATPase subunit of the BAF chromatin remodeling complex, as a crucial factor required for the antiviral activity of MxA against IAV. Intriguingly, our data demonstrate that although SMARCA2 is essential for expression of some IFN-stimulated genes (ISGs), and the establishment of an antiviral state, it is not required for expression of MxA, suggesting an indirect effect on MxA activity. Transcriptome analysis of SMARCA2-depleted A549-MxA cells identified a small set of SMARCA2-regulated factors required for activity of MxA, in particular IFITM2 and IGFBP3. These findings reveal that several virus-inducible factors work in concert to enable MxA restriction of IAV.
Highlights
The human interferon (IFN)-induced MxA protein is a key antiviral host restriction factor exhibiting broad antiviral activity against many RNA viruses, including highly pathogenic avian influenza A viruses (IAV) of the H5N1 and H7N7 subtype
We focused on one particular factor, SMARCA2, which was validated as being required for efficient MxA restriction of both H5N1 and H7N7 IAVs
SMARCA2 is one of two mutually exclusive ATPase subunits of the evolutionary highly conserved BAF chromatin remodeling complex, which has been shown to be involved in regulation of gene expression, cell cycle control and tumorigenesis[35,42,43,44,45,46,47,48,49,50]
Summary
The human interferon (IFN)-induced MxA protein is a key antiviral host restriction factor exhibiting broad antiviral activity against many RNA viruses, including highly pathogenic avian influenza A viruses (IAV) of the H5N1 and H7N7 subtype. The combined data identified SMARCA2, the ATPase subunit of the BAF chromatin remodeling complex, as a crucial factor required for the antiviral activity of MxA against IAV. Transcriptome analysis of SMARCA2-depleted A549-MxA cells identified a small set of SMARCA2-regulated factors required for activity of MxA, in particular IFITM2 and IGFBP3 These findings reveal that several virus-inducible factors work in concert to enable MxA restriction of IAV. After recognition of pathogen-associated molecular patterns, such as viral RNA, the cell responds by secreting type I and III interferons These interferons bind to their respective receptors leading to JAK-STAT signaling and eventually to induction of several hundred interferon-stimulated genes (ISGs), of which some have direct effector activity against particular viruses[7]. The promotor-bound BAF complex facilitates rapid induction and basal level expression and, upon stimulation, induction of ISGs to a higher extent
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