DEAD-box RNA helicase DDX3X maintains the homeostasis of the Zika virus translation-replication cycle

ABSTRACT DDX3X is a cellular DEAD-box ATP-dependent RNA helicase known to play pivotal roles during the replication cycle of different viruses including some flaviviruses. Whether DDX3X plays a role during replication of Zika virus (ZIKV), a mosquito-borne flavivirus with a broad tissue tropism, has not been explored in detail. Here, we show that DDX3X is required for efficient ZIKV replication in a human microglia cell line but no other cell lines. Mechanistically, we provide evidence showing that DDX3X is recruited to the viral replication compartments where it binds to the 5’UTR of the ZIKV RNA and promotes viral protein synthesis in an ATP-dependent manner. We also show that DDX3X binds to the viral RNA-dependent RNA polymerase NS5 and interferes with viral RNA synthesis in an ATP-independent manner. Such an effect was not observed during replication of Dengue 2 virus in human microglia, revealing specific roles for DDX3X in the regulation of the translation-replication cycle of ZIKV in human microglia. IMPORTANCE Zika virus emerged as a major threat to humans due to its pandemic potential and its association with birth defects and neurological complications. The lack of available vaccines or specific treatments makes the understanding of Zika virus-host interactions a priority. Here, we demonstrate a mechanism by which DDX3X, a cellular ATP-dependent RNA helicase, promotes Zika virus replication by regulating the translation-replication cycle in a human microglia cell line. Considering the threat of this virus to the human population and the wide range of RNA viruses that usurp this host protein to accomplish the replication cycle, DDX3X continuously rises as a potential and valuable target for pharmacological intervention. LIST OF ABBREVIATIONS - CCR1 - Capsid coding region 1 - cHP - Capsid hairpin - CLIP - Cross-linking immunoprecipitation - CNS - Central nervous system - DENV - Dengue virus - DMEM - Dulbecco modified eagle medium - EMSA - electrophoretic mobility shift assay - ER - Endoplasmic reticulum - FISH - Fluorescent in situ hybridization - FTSC - Fluorescein-5-thiosemicarbazide - IFN-β - Interferon beta - ISG15 - Interferon stimulated gene 15 - MFI - Mean fluorescence 7intensity - MOI - Multiplicity of infection - MST - Microscale thermophoresis - NS - Nonstructural protein (1 to 5) - RIPA - Radioimmunoprecipitation buffer assay - RMSD - Root mean square deviation - RMSF - Root mean square fluctuation - RRL - Rabbit reticulocyte lysate - SEM - Standard error median - SL - Stem loop - UTR - Untranslated region - VRC - Viral replication compartment - vRNA - Viral RNA - WHO - World Health Organization - ZIKV - Zika virus