A small protein encoded by lncRNA PCBP1-AS1 promotes the replication of influenza virus via regulating the expression of proviral effectors (Ribo-Seq)
Many annotated long noncoding RNAs (lncRNAs) contain small open reading frames (sORFs), some of which have been demonstrated to encode small proteins or micropeptides with fundamental biological importance. While the small proteins or micropeptides hidden in lncRNA are gradually being revealed, their functions in influenza virus infection remain largely unexplored. Here, we identified and characterized a small 110-amino acid protein named PAESP that is encoded by the putative lncRNA PCBP1-AS1. We found that both PCBP1-AS1 and PAESP were upregulated by influenza virus infection as well as type I interferon treatment. Overexpression of PCBP1-AS1 or PAESP enhanced influenza virus replication. Conversely, knockdown of PCBP1-AS1 or knockout of PAESP inhibited viral production. In addition, loss-of-function experiment demonstrated that PAESP is essential for PCBP1-AS1 to facilitate influenza virus replication. More importantly, the overexpression of PAESP increases the mRNA level of several genes such as IFIT2 and IFIT3, which have been proved to be retasked by influenza virus from canonical antiviral factors into proviral effectors. Interestingly, when IFIT2 or IFIT3 expression was knocked down in PAESP-overexpressed cells, the virus titers significantly decreased compared to control cells. These findings reveal a novel lncRNA-derived small protein that is exploited by influenza virus and provide new insights into the virus-host regulatory network. Overall design: To identify putative lncRNAs that can encode functional proteins/peptides during the pathogenesis of  influenza virus infection, we infected A549 cells with or without PR8 influenza virus for 12h, and performed Ribo-seq to find lncRNAs bound by the ribosome.