Abstract
UAP56, a member of the DExD/H-box RNA helicase family, is essential for pre-mRNA splicing and mRNA export in eukaryotic cells. In influenza A virus-infected cells, UAP56 mediates viral mRNA nuclear export, facilitates viral ribonucleoprotein complex formation through direct interaction with the viral nucleoprotein, and may indirectly affect antiviral host responses by binding to and/or facilitating the activation of the antiviral host factors MxA and PKR. Here, we demonstrate that UAP56 also co-localizes with the influenza A viral NS1 protein, which counteracts host cell innate immune responses stimulated by virus infection. The UAP56–NS1 association relies on the RNA-binding residues R38 and K41 in NS1 and may be mediated by single-stranded RNA. UAP56 association with NS1 does not affect the NS1-mediated downregulation of cellular innate immune pathways in reporter gene assays, leaving in question the exact biological role and relevance of the UAP56–NS1 association.
Highlights
UAP56, a member of the DExD/H-box RNA helicase family, is highly conserved from yeast to humans and plays a critical role in pre-mRNA splicing and mRNA nuclear export (Luo et al, 2001)
To test the possibility that UAP56–NS1 association is mediated by nucleic acids, we examined the UAP56–NS1 association in cell lysates treated with RNase III, RNase A, and RNase H
UAP56/URH49 facilitates the efficient replication of influenza A viruses through its roles in pre-mRNA splicing, mRNA nuclear export, and the indirect suppression of cellular antiviral responses (Luo et al, 2001); these functions are affected by the viral NS1 protein (Fortes et al, 1994; Qiu and Krug, 1994)
Summary
UAP56, a member of the DExD/H-box RNA helicase family, is highly conserved from yeast to humans and plays a critical role in pre-mRNA splicing and mRNA nuclear export (Luo et al, 2001). UAP56 functions as a component of the transcript export (TREX) complex to efficiently export spliced mRNAs to the cytoplasm (Jensen et al, 2001; MacMorris et al, 2003). Influenza viruses replicate in the nucleus of infected cells and usurp the cellular nuclear export systems for the transport of viral mRNA from the nucleus to the cytoplasm. They rely on host factors such as UAP56/URH49 for efficient replication (Read and Digard, 2010; Wisskirchen et al, 2011b). UAP56/URH49-depletion has been shown to increase the accumulation
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