A-rich function for the Zika virus 3' untranslated region

About This Grant

PROJECT SUMMARY Zika virus (ZIKV) is a re-emerging mosquito-borne flavivirus of significant public health concern. To date there are no effective licensed antiviral treatments or a vaccine. Therefore, elucidating the molecular biology of these viruses and the interactions with the host cell are foundational to identifying and developing effective treatment options. The single-stranded positive-sense RNA genome of ZIKV mimics a cellular mRNA. Specifically, the viral RNA encodes a single open reading frame, has structured untranslated regions (UTRs) adjacent to the open reading frame, and contains a N5’-methyl guanosine cap. Unlike mRNAs however, flaviviruses lack a poly(A) tail. From a multiple sequence alignment of all mosquito-borne flaviviruses we identified conserved regions containing 3-6 tandem adenosines in the 3’ UTR. These A-rich regions are localized in single-stranded regions within and between the XRN-1 resistant pseudoknots (xrRNA), dumbbell and 3’ stem loop (3’SL) RNA structures. In preliminary experiments we investigated the role of the A-rich region between xrRNA2 and the pseudo- dumbbell RNA structure (pre-pseudo/Y-dumbbell). Specifically, we generated three different mutations in a ZIKV Renilla luciferase reporter replicon and infectious clone. These mutants revealed that the pre-YDB A-rich region had a role in translation in both mammalian and mosquito cell lines. Different mass spectrometry studies have shown that the cellular poly(A) binding protein (PABP) interacts with the ZIKV 3’ UTR. Additionally, PABP was previously shown to interact with a region in the dengue virus 3’ UTR that harbors an A-rich motif. In preliminary studies we find that depletion of PABP1 decreased ZIKV, but not cellular, protein levels and viral titers without affecting cell viability. We therefore hypothesize that A-rich regions in the ZIKV 3’ UTR function to recruit cellular RNA binding proteins such as PABP1 to promote distinct steps in the virus infectious cycle. In Aim 1 we will mutate the A-rich regions in the infectious clone and a subgenomic luciferase reporter replicon to investigate the function of select A-rich regions on translation, replication, and viral fitness in mammalian and mosquito cells. In Aim 2, we will investigate the role of PABP1 on ZIKV gene expression and determine if PABP1 and other cellular RNA binding proteins bind A-rich regions in the ZIKV 3’ UTR. Overall, this study will advance our understanding of how flavivirus 3’ UTRs interact with the host to promote distinct steps in the infectious cycle in two vastly different hosts. Understanding how specific sequences in RNA genome function could lead to the therapeutic advancement namely the development of an attenuated vaccine ZIKV strain. Moreover, defining similar and unique RNA-protein interactions between mammalian and mosquito hosts could inform future vector control strategies.