mRNA 3’UTR lengthening by alternative polyadenylation attenuates inflammatory responses and correlates with virulence of Influenza A virus

Alternative polyadenylation (APA) leading to changes of mRNA 3’UTRs has been associated to numerous pathologies but its molecular origin and functional consequences often remain enigmatic. We show that all Influenza A virus (IAV) strains cause APA of host transcripts and mapped the effect to a drug-targetable glycine residue (G184) in the viral non-structural protein 1 (NS1) that is required for its interaction with CPSF4. Unexpectedly, this interaction is also conserved in IAVs not causing virus-induced transcriptional shutoff and introduction of G184R in NS1 alleviates APA. Functionally, a recombinant PR8 (NS1-G184R) virus elicited increased secretion of inflammatory cytokines as compared to the parental wild-type in vitro and in vivo, and had a strongly attenuated phenotype in vivo. Finally, we show that many pathogens induce APA, which is potentially used towards similar immunomodulatory effects.