Evidence of RedOX Imbalance during Zika Virus Infection Promoting the Formation of Disulfide-Bond-Dependent Oligomers of the Envelope Protein.

Flaviviruses replicate in membrane factories associated with the endoplasmic reticulum (ER). Significant levels of flavivirus viral protein accumulation contribute to ER stress. As a consequence, the host cell exhibits an Unfolded Protein Response (UPR), subsequently stimulating appropriate cellular responses such as adaptation, autophagy or apoptosis. The correct redox conditions of this compartment are essential to forming native disulfide bonds in proteins. Zika virus (ZIKV) has the ability to induce persistent ER stress leading to the activation of UPR pathways. In this study, we wondered whether ZIKV affects the redox balance and consequently the oxidative protein folding in the ER. We found that ZIKV replication influences the redox state, leading to the aggregation of the viral envelope protein as amyloid-like structures in the infected cells.

Zika virus subversion of chaperone GRP78/BiP expression in A549 cells during UPR activation.

Flaviviruses replicate in membranous factories associated with the endoplasmic reticulum (ER). Significant levels of flavivirus polyprotein integration contribute to ER stress and the host cell may exhibit an Unfolded Protein Response (UPR) to this protein accumulation, stimulating appropriate cellular responses such as adaptation, autophagy or cell death. These different stress responses support other antiviral strategies initiated by infected cells and can help to overcome viral infection. In epithelial A549 cells, a model currently used to study the flavivirus infection cycle and the host cell responses, all three pathways leading to UPR are activated during infection by Dengue virus (DENV), Yellow Fever virus (YFV) or West Nile virus (WNV). In the present study, we investigated the capacity of ZIKA virus (ZIKV) to induce ER stress in A549 cells. We observed that the cells respond to ZIKV infection by implementing an UPR through activation of the IRE1 and PERK pathway without activation of the ATF6 branch. By modulating the ER stress response, we found that UPR inducers significantly inhibit ZIKV replication. Interestingly, our findings provide evidence that ZIKV could manipulate the UPR to escape this host cell defence system by downregulating GRP78/BiP expression. This subversion of GRP78 expression could lead to unresolved and persistent ER stress which can be a benefit for virus growth.

Subversion of the Heme Oxygenase-1 Antiviral Activity by Zika Virus.

Heme oxygenase-1 (HO-1), a rate-limiting enzyme involved in the degradation of heme, is induced in response to a wide range of stress conditions. HO-1 exerts antiviral activity against a broad range of viruses, including the Hepatitis C virus, the human immunodeficiency virus, and the dengue virus by inhibiting viral growth. It has been reported that HO-1 displays antiviral activity against the Zika virus (ZIKV) but the mechanisms of viral inhibition remain largely unknown. Using a ZIKV RNA replicon with the Green Fluorescent Protein (GFP) as a reporter protein, we were able to show that HO-1 expression resulted in the inhibition of viral RNA replication. Conversely, we observed a decrease in HO-1 expression in cells replicating the ZIKV RNA replicon. The study of human cells infected with ZIKV showed that the HO-1 expression level was significantly lower once viral replication was established, thereby limiting the antiviral effect of HO-1. Our work highlights the capacity of ZIKV to thwart the anti-replicative activity of HO-1 in human cells. Therefore, the modulation of HO-1 as a novel therapeutic strategy against ZIKV infection may display limited effect.

ClearColi BL21(DE3)-based expression of Zika virus antigens illustrates a rapid method of antibody production against emerging pathogens.

Available rapid, simple and accurate methods for detection and diagnosis of emerging viral diseases are required. Recently, there was an urgent need for specific antibodies against mosquito-borne Zika virus (ZIKV), which is an emerging zoonotic disease of medical concern in different regions of the world. Here, we showed that overexpression of ZIKV antigens in ClearColi BL21(DE3), a bacteria strain expressing a non-endotoxic form of LPS, is suitable for the production of specific ZIKV antisera. Two major ZIKV antigenic domains, the domain III from envelope E glycoprotein, which brings the virus-specific epitopes, and the N-terminal region of nonstructural NS1 glycoprotein, which is responsible for pathophysiological conditions, were overexpressed in ClearColi BL21(DE3). Immunization of adult rat with insoluble recombinant ZIKV antigens in inclusion bodies resulted in the production of specific antibodies in a few weeks. Anti-E and anti-NS1 antibodies are efficient as biological tools for ZIKV detection by indirect ELISA and immunoblot assay. This method could successfully be applied to any emerging viruses.