Activation of IRE1 Endonuclease Activity Regulates Zika Virus Replication and Antiviral Response During Infection in Human Microglia

Zika virus (ZIKV) can infect and replicate in the endoplasmic reticulum (ER) of different human cell types, including neural progenitor cells, radial glial cells, astrocytes, and microglia in the brain. ZIKV infection of microglia is expected to trigger both ER stress and the induction of an antiviral response through production of type-I interferons and pro-inflammatory cytokines, contributing to neuroinflammation during infection. Despite their critical role in ZIKV pathogenesis, the interplay between ER stress and the antiviral response during infection has not been fully characterized in human microglia. In this work, we show that infection of a human microglia cell line with ZIKV triggers the induction of an antiviral response and the activation of the endonuclease activity of the unfolded protein response sensor IRE1. Interestingly, we observed that both IRE1 and XBP1 were sequestered to the viral replication sites during infection. Moreover, pharmacological inhibition or hyperactivation of the endonuclease activity of IRE1 resulted in reduced viral titers. As such, while inhibition of IRE1 resulted in an increased type-I interferon response, hyperactivation led to a decrease in ZIKV RNA levels and the appearance of ER-derived cytoplasmic structures containing NS3, IRE1, and XBP1. Together, our data indicate that regulation of the endonuclease activity of IRE1 is critical for both ZIKV replication and immune activation, highlighting the potential of the ER stress sensor as a target for the development of antivirals to treat ZIKV infections.