Zika virus is an emerging mosquito-borne pathogen that is associated with Guillain-Barré syndrome in adults and microcephaly and other neurological defects in newborns. Despite being declared an international emergency by the World Health Organization, comparatively little is known about its biology. Here, we investigate the strategies employed by the virus to suppress the host antiviral response. We observe that once established, Zika virus infection is impervious to interferon treatment suggesting that the virus deploys effective countermeasures to host cell defences. This is confirmed by experiments showing that Zika virus infection impairs the induction of type-I interferon as well as downstream interferon-stimulated genes. Multiple viral proteins affect these processes. Virus-mediated degradation of STAT2 acts to reduce type-I and type-III interferon-mediated signaling. Further, the NS5 of Zika virus binds to STAT2, and its expression is correlated with STAT2 degradation by the proteasome. Together, our findings provide key insights into how Zika virus blocks cellular defense systems. This in turn is important for understanding pathogenesis and may aid in designing antiviral therapies.

Zika virus (ZIKV), a member of the Flaviviridae family, has recently emerged as an important human pathogen with increasing economic and health impact worldwide. Because of its teratogenic nature and association with the serious neurological condition Guillain-Barré syndrome, a tremendous amount of effort has focused on understanding ZIKV pathogenesis. To gain further insights into ZIKV interaction with host cells, we investigated how this pathogen affects stress response pathways. While ZIKV infection induces stress signaling that leads to phosphorylation of eIF2␣ and cellular translational arrest, stress granule (SG) formation was inhibited. Further analysis revealed that the viral proteins NS3 and NS4A are linked to translational repression, whereas expression of the capsid protein, NS3/NS2B-3, and NS4A interfered with SG formation. Some, but not all, flavivirus capsid proteins also blocked SG assembly, indicating differential interactions between flaviviruses and SG biogenesis pathways. Depletion of the SG components G3BP1, TIAR, and Caprin-1, but not TIA-1, reduced ZIKV replication. Both G3BP1 and Caprin-1 formed complexes with capsid, whereas viral genomic RNA stably interacted with G3BP1 during ZIKV infection. Taken together, these results are consistent with a scenario in which ZIKV uses multiple viral components to hijack key SG proteins to benefit viral replication.IMPORTANCE There is a pressing need to understand ZIKV pathogenesis in order to advance the development of vaccines and therapeutics. The cellular stress response constitutes one of the first lines of defense against viral infection; therefore, understanding how ZIKV evades this antiviral system will provide key insights into ZIKV biology and potentially pathogenesis. Here, we show that ZIKV induces the stress response through activation of the UPR (unfolded protein response) and PKR (protein kinase R), leading to host translational arrest, a process likely mediated by the viral proteins NS3 and NS4A. Despite the activation of translational shutoff, formation of SG is strongly inhibited by the virus. Specifically, ZIKV hijacks the core SG proteins G3BP1, TIAR, and Caprin-1 to facilitate viral replication, resulting in impaired SG assembly. This process is potentially facilitated by the interactions of the viral RNA with G3BP1 as well as the viral capsid protein with G3BP1 and Caprin-1. Interestingly, expression of capsid proteins from several other flaviviruses also inhibited SG formation. Taken together, the present study provides novel insights into how ZIKV modulates cellular stress response pathways during replication.

Zika virus is a teratogenic mosquito-transmitted flavivirus that is associated with birth defects in newborns and Guillain–Barré syndrome in adults. The virus can also be sexually transmitted, but currently, very little is known about the cell types supporting virus replication and persistence in human testes. Using primary cell cultures, we observed that Sertoli but not Leydig cells are highly susceptible to Zika virus infection, a process that is dependent on the TAM family receptor Axl. In cell culture, Sertoli cells could be productively infected with Zika virus for at least 6-weeks. Infection of Sertoli cells resulted in dramatic changes to the transcriptional profile of these cells. The most upregulated mRNA in infected cells was basic fibroblast growth factor (FGF2), a cytokine that was found to enhance Zika virus replication and support viral persistence. Together these findings provide key insights into understanding how Zika virus persists in the male reproductive tract and in turn may aid in developing antiviral therapies or strategies to minimize sexual transmission of this pathogen.

Flaviviruses are significant human pathogens that have an enormous impact on the global health burden. Currently, there are very few vaccines against or therapeutic treatments for flaviviruses, and our understanding of how these viruses cause disease is limited. Evidence suggests that the capsid proteins of flaviviruses play critical nonstructural roles during infection, and therefore, elucidating how these viral proteins affect cellular signaling pathways could lead to novel targets for antiviral therapy. We used affinity purification to identify host cell proteins that interact with the capsid proteins of West Nile and dengue viruses. One of the cellular proteins that formed a stable complex with flavivirus capsid proteins is the peroxisome biogenesis factor Pex19. Intriguingly, flavivirus infection resulted in a significant loss of peroxisomes, an effect that may be due in part to capsid expression. We posited that capsid protein-mediated sequestration and/or degradation of Pex19 results in loss of peroxisomes, a situation that could result in reduced early antiviral signaling. In support of this hypothesis, we observed that induction of the lambda interferon mRNA in response to a viral RNA mimic was reduced by more than 80%. Together, our findings indicate that inhibition of peroxisome biogenesis may be a novel mechanism by which flaviviruses evade the innate immune system during early stages of infection. IMPORTANCERNA viruses infect hundreds of millions of people each year, causing significant morbidity and mortality. Chief among these pathogens are the flaviviruses, which include dengue virus and West Nile virus. Despite their medical importance, there are very few prophylactic or therapeutic treatments for these viruses. Moreover, the manner in which they subvert the innate immune response in order to establish infection in mammalian cells is not well understood. Recently, peroxisomes were reported to function in early antiviral signaling, but very little is known regarding if or how pathogenic viruses affect these organelles. We report for the first time that flavivirus infection results in significant loss of peroxisomes in mammalian cells, which may indicate that targeting of peroxisomes is a key strategy used by viruses to subvert early antiviral defenses. Flaviviruses are arthropod-transmitted pathogens that infect hundreds of millions of people each year. Dengue virus (DENV) is the etiological agent of the most common mosquitoborne disease in the world, dengue fever (reviewed in reference 1). The related flavivirus West Nile virus (WNV) is the most important vector-transmitted pathogen in North America. Despite their medical significance, there are no DENV/WNV-specific vaccines or antiviral therapies that are approved for use in humans. Understanding how these viruses take advantage of and manipulate host cells may provide the foundation for therapies that target virushost interactions.Recent studies identified flavivirus capsid proteins as critical components of the virus-host interface. T...

Zika virus (ZIKV) infection and persistence during pregnancy can lead to microcephaly and other fetal neurological disorders collectively known as Congenital Zika Syndrome. The immunological and virological events that contribute to the establishment of persistent ZIKV infection in humans are unclear though. Here we show that human fetal astrocytes (HFAs), the most abundant cell type in the central nervous system, become persistently infected with ZIKV resulting in continuous viral shedding for at least one month; a process that is facilitated by TIM/TAM receptors. HFAs are relatively resistant to ZIKV-induced apoptosis, a factor that may be important for chronic infection of these cells. Once infection was established, interferon treatment did not reduce virus replication. Moreover, the fact that the innate immune system was highly activated in persistently infected HFAs indicates that the virus can thrive in the presence of a sustained antiviral response. RNAseq analyses of persistently infected cells revealed that ZIKV alters host gene expression in a manner that could affect developmental processes. Conversely, data from sequencing of ZIKV genomes in persistently infected HFAs suggest that adaptive mutations were not required for establishing chronic infection. Based on these results, we postulate that HFAs are reservoirs for ZIKV in the fetal brain and that moderate apoptosis combined with inefficient antiviral response from these cells may contribute to the establishment of chronic brain infection associated with the ZIKV neurodevelopmental abnormalities.