Identification of a small protein encoded by PCBP1-AS1 that promotes replication of influenza virus via inducing enhancement of autophagy

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. However, the small proteins or micropeptides encoded by lncRNAs and their functions in viral infection remain largely unexplored. Here, we identified and characterized a small 110-amino acid protein named ORF6 encoded by the putative lncRNA PCBP1-AS1. Interestingly, both PCBP1-AS1 and ORF6 were significantly upregulated by influenza virus infection. Furthermore, we observed that they were markedly induced by type I interferon treatment. Overexpression of PCBP1-AS1 or ORF6 enhanced influenza virus replication. Conversely, knockdown of PCBP1-AS1 or knockout of ORF6 inhibited the viral production. In addition, loss-of-function experiment demonstrated that ORF6 is essential for PCBP1-AS1 to facilitate influenza virus replication. Importantly, the overexpression of ORF6 induced enhancement of autophagy by increasing the expression of ATG7, a gene encoding an essential effector enzyme for canonical autophagy. These findings reveal a lncRNA-derived small protein that is exploited by influenza virus, and provide new insights into the virus-host regulatory network. Overall design: To explore how ORF6 functions in regulating influenza virus infection, we infected A549 cells overexpressing ORF6 or control cells with PR8 influenza virus for 12h, and performed RNA-seq to find differently expressed mRNA.