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PA-X 122V broadly determines the #host shutoff #activity of #influenza A viruses

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By G.M.

 


ABSTRACT

Multiple genes are involved in the pathogenicity of influenza A virus. Our previous study reported two naturally occurring amino acid mutations in the polymerase acidic (PA) protein as crucial determinants of the virulence of Eurasian avian-like H1N1 (EA H1N1) influenza viruses. PA-X, an accessory protein encoded by the PA gene, is thought to play a role in viral pathogenicity and regulation of host immune response, but its specific function remains unclear. In this study, we found that two genetically similar EA H1N1 influenza viruses, A/swine/Liaoning/FX38/2017 (FX38) and A/swine/Liaoning/SY72/2018 (SY72), induced significantly different suppression levels of host protein synthesis. The difference in host shutoff activity induced by PA-X protein was the key factor affecting the inhibition of host gene expression. Loss of PA-X expression significantly reduced its host shutoff activity, thereby enhancing host antiviral immune response. PA-X deficiency had no apparent effect on polymerase activity or replication capacity. We pinpointed a single residue 122V involved in the ability of PA-X to inhibit host gene expression and thereby modulate the host antiviral response. Notably, PA-X 122V was highly conserved among multiple subtypes of influenza A viruses and vital for maintaining the inhibitory effects on the host protein synthesis. Together, these findings demonstrate that the PA-X protein plays a major role in the suppression of host protein synthesis during influenza virus infection and elucidate the molecular mechanism by which the amino acid residue 122V in PA-X facilitates its suppression effects on host innate immune responses.

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Link: https://journals.asm.org/doi/full/10.1128/mbio.03433-25?af=R

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