IWS1 phosphorylation by AKT3 controls nuclear export of type I IFN mRNAs and sensitivity to viral infection, by regulating the alternative RNA splicing of U2AF2.
We have previously shown that loss of IWS1 phosphorylation promotes the alternative RNA splicing of U2 Associated-Factor 2 (U2AF2), resulting in transcripts lacking exon 2. This exon encodes part of the Serine-Rich (SR) domain of U2AF65, which is responsible for its binding with pre-mRNA Processing Factor 19 (Prp19). Here, we show that whereas both U2AF65 isoforms bind cytoplasmic accumulation response elements (CAR-E) of intronless mRNAs, the loading of Prp19 occurs only in exon 2-containing U2AF65, in cells expressing phosphorylated IWS1, promoting their nucleocytoplasmic export. Furthermore, this Prp19 loading is RNA Pol II dependent. Given that IFNA1 and IFNB1 are among the target genes, the expression of IFNα and IFNβ was decreased in cells deficient in IWS1 phosphorylation, and their sensitivity to the oncolytic VSV, Reovirus and Sendai virus infection was increased accordingly. More importantly, treatment of the lung adenocarcinoma cells with the pan-AKT inhibitor, MK2206 phenocopied the loss of IWS1 phosphorylation and showed increased sensitivity to oncolytic viral infection. These data identify a novel mechanism by which the AKT/p-IWS1 axis, via the epigenetic regulation of alternative RNA splicing, contribute to the sensitivity to oncolytic viruses.