Amino Acid Residues Involved in Inhibition of Host Gene Expression by Influenza A/Brevig Mission/1/1918 PA-X

Abstract

The influenza A virus (IAV) PA-X protein is a virulence factor that selectively degrades host mRNAs leading to protein shutoff. This function modulates host inflammation, antiviral responses, cell apoptosis, and pathogenesis. In this work we describe a novel approach based on the use of bacteria and plasmid encoding of the PA-X gene under the control of the bacteriophage T7 promoter to identify amino acid residues important for A/Brevig Mission/1/1918 H1N1 PA-X’s shutoff activity. Using this system, we have identified PA-X mutants encoding single or double amino acid changes, which diminish its host shutoff activity, as well as its ability to counteract interferon responses upon viral infection. This novel bacteria-based approach could be used for the identification of viral proteins that inhibit host gene expression as well as the amino acid residues responsible for inhibition of host gene expression.

Natural Selection of H5N1 Avian Influenza A Viruses with Increased PA-X and NS1 Shutoff Activity

“…Importantly, these results demonstrate an evolution in the abilities of NS1 and PA-X proteins to induce host shutoff and show how this is beneficial for IAV. In addition, several in vitro studies have shown that multiple amino acids in PA-X can affect PA-X´s shutoff activity, and that differences between IAV strains or subtypes can occur [ 36 , 38 , 39 , 56 , 62 , 63 ].…”

“…The NS1 and PA-X genes fused to an N-terminal HA epitope tag were cloned into the pCAGGS HA-NH 2 plasmid [ 38 , 39 ] using SphI and NheI restriction sites. The amino acid sequences were as follows: for PA-X OR , A/Hong Kong/483/1997, H5N1 strain, Pubmed protein ID: AAF74340.1; for PA-X CIR , A/mallard/Italy/3401/2005, H5N1 strain, Pubmed protein ID: AGJ72962.1; for NS1 OR, A/Hong Kong/156/97, H5N1 strain, Pubmed protein ID: O56264.1; and for NS1 CIR, A/duck/Bangladesh/27820/2015, H5N1 strain, Pubmed protein ID: AQY17641.1.…”

Antiviral responses versus virus-induced cellular shutoff: a game of thrones between influenza A virus NS1 and SARS-CoV-2 Nsp1

“…IAV NS1 modulates the inhibition of IFN production through variable interventions ( Baker et al., 2015 ; Cheng et al., 2015 ; Nogales et al., 2017a ; Nogales et al., 2017b ; Nogales et al., 2017c ; Hilimire et al., 2020 ; Martinez-Sobrido et al., 2020 ; Chiem et al., 2022 ; Nogales et al., 2022 ). However, other IAV proteins, including PA-X ( Chiem et al., 2021 ), PB1-F2 ( Varga and Palese, 2011 ; Varga et al., 2012 ), or PB2 have also been shown to be involved in inhibition of host antiviral responses during IAV infection ( Forero et al., 2015 ; Yang et al., 2022 ). Following IAV infection, two major cellular pathways are activated to initiate the antiviral innate immune response: Toll-like receptors (TLRs) and RIG-I-like receptors (RLRs) ( Iwasaki and Pillai, 2014 ) ( Figure 5 ).…”