Identification and characterization of host proteins bound to dengue virus 3^' UTR reveal an antiviral role for quaking proteins

The four dengue viruses (DENV1-4) are rapidly reemerging infectious RNA viruses. These positive-strand viral genomes contain structured 3^'' untranslated regions (UTRs) that interact with various host RNA binding proteins (RBPs). These RBPs are functionally important in viral replication, pathogenesis, and defense against host immune mechanisms. Here, we combined RNA chromatography and quantitative mass spectrometry to identify proteins interacting with DENV1-4 3^'' UTRs. As expected, RBPs displayed distinct binding specificity. Among them, we focused on quaking (QKI) because of its preference for the DENV4 3^'' UTR (DENV-4/SG/06K2270DK1/2005). RNA immunoprecipitation experiments demonstrated that QKI interacted with DENV4 genomes in infected cells. Moreover, QKI depletion enhanced infectious particle production of DENV4. On the contrary, QKI did not interact with DENV2 3^'' UTR, and DENV2 replication was not affected consistently by QKI depletion. Next, we mapped the QKI interaction site and identified a QKI response element (QRE) in DENV4 3^'' UTR. Interestingly, removal of QRE from DENV4 3^'' UTR abolished this interaction and increased DENV4 viral particle production. Introduction of the QRE to DENV2 3^'' UTR led to QKI binding and reduced DENV2 infectious particle production. Finally, reporter assays suggest that QKI reduced translation efficiency of viral RNA. Our work describes a novel function of QKI in restricting viral replication.