Specific Interaction of DDX6 with an RNA Hairpin in the 3´-UTR of the Dengue Genome Mediates G1 Phase Arrest

The extent to which viral genomic RNAs interact with host factors and contribute to host response and disease pathogenesis is not well known. Here, we report that the human RNA helicase DDX6 specifically binds to the viral most conserved RNA hairpin in the A3 element in the dengue 3´-UTR, with nanomolar affinities. DDX6 CLIP confirmed the interaction in HuH-7 cells infected by dengue virus serotype 2. This interaction requires three conserved residues, Lys307, Lys367, and Arg369, as well as the unstructured extension in the C-terminal domain of DDX6. Interestingly, alanine substitution of these three basic residues resulted in RNA-independent ATPase activity, suggesting a mechanism by which RNA-binding and ATPase activities are coupled in DEAD-box helicases. Furthermore, we applied a cross-omics gene enrichment approach to suggest that DDX6 is functionally related to cell cycle regulation and viral pathogenicity. Indeed, infected cells exhibited cell cycle arrest in G1 phase and a decrease in the early S phase. Exogeneous expression of intact DDX6, but not A3-binding-deficient mutants, alleviated these effects by rescue of the DNA pre-initiation complex expression. Disruption of the DDX6-binding site was found in dengue and Zika live-attenuated vaccine strains. Our results suggested that dengue virus has evolved an RNA aptamer against DDX6 to alter host cell states, and defined DDX6 as a new regulator of G1/S transition. Overall design: Next generation sequencing of DDX6 CLIP-seq of DENV-2 (16681) infected and uninfected HuH-7 cells, in triplicate, using Illumina HiSeq4000