THE UNFOLDED PROTEIN RESPONSE IN ZIKA VIRUS INFECTION

Abstract

Zika virus (ZIKV) is an emerging arbovirus that belongs to the Flaviviridae family. It is known to cause severe illnesses, such as neonatal microcephaly and the development of Guillain-Barre syndrome. However, the exact mechanism of ZIKV-linked complications remains indistinct. Emerging studies implicate ZIKV in taking advantage of the host's unfolded protein response (UPR) to replicate and cause infection. Therefore, this kinetic study aims to investigate the individual contributions of the three UPR pathways, namely, inositol-requiring enzyme 1 alpha (IRE1 alpha), activating transcription factor 6 (ATF6), and protein kinase R-like endoplasmic reticulum kinase (PERK) during ZIKV infection to examine whether dysregulation of the arms UPR would disrupt ZIKV replication and/or the cellular response to infection. We report that ZIKV induces ER stress in A549 human lung epithelial cells, leading to sustained activation of the tripartite UPR pathways (IRE1 alpha, PERK, and ATF6) and transient induction of the downstream effectors, including X-box-binding protein 1 (XBP1), activating transcription factor 4 (ATF4), CCAAT enhancer-binding protein-homologous protein (CHOP), and growth arrest and DNA damage-inducible protein 34 (GADD34). We show that ZIKV causes continued phosphorylation of the eukaryotic translation initiation factor 2 alpha (eIF2 alpha) and ribosomal RNA degradation, leading to host translational shutdown and cell death. We found that the binding immunoglobulin protein (BiP) that acts as a UPR regulator is suppressed by ZIKV, indicating that ZIKV suppresses BiP to keep the UPR sustained and facilitate its replication. We observed that ZIKV replication is hindered when cells are treated with ER-stress inducers before infection but not after infection, implying that ZIKV can bypass and manipulate the UPR for its benefit. We use specific and selective pharmacologic inhibitors to demonstrate that suppression of PERK activation has no effect, whereas inhibition of ATF6 activation inhibits late-stage ZIKV replication. Notably, PERK and ATF6 suppression influenced ZIKV replication in the early and late stages of infection. We found that a pharmacological ER-stress inhibitor diminishes ZIKV replication by inhibiting the PERK and ATF6 arms of the UPR while enhancing the activation of the IRE1 alpha arm. This shows that distinct UPR arms regulate ZIKV in different ways and at different times.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Ford (Supervisor) & Shiu-Wan Chan (Supervisor)