Zika Virus Subverts Stress Granules to Promote and Restrict Viral Gene Expression

Abstract

Introduction: 37 Zika virus (ZIKV) is an enveloped, single-stranded positive-sense RNA virus belonging to the 38 Flaviviridae family, which includes Dengue virus (DENV), Yellow fever virus (YFV), and West Nile 39 virus (WNV) (1). While ZIKV was discovered in Uganda in 1947 (2) , the virus garnered renewed 40 interest during the 2015-2016 outbreak in the Americas (3), in particular because of intrauterine 41 infections and resulting developmental abnormalities such as severe microcephaly, decreased 42 brain tissue, macular scarring, congenital contractures, and hypertonia (4-9). Additionally, adults 43 infected with ZIKV were reported to develop Guillain-Barré syndrome, a debilitating disorder 44 affecting the peripheral nerves (10-13). Similar to other flaviviruses, ZIKV is transmitted by the 45 Aedes aegypti and Aedes albopictus mosquitoes, although recent evidence has shown ZIKV is 46 also capable of sexual and vertical transmission (14-17). While half a century has passed since 47 65 particular, the presence of double-stranded RNA (dsRNA) during viral infection activates protein 66 kinase R (PKR) (19); the accumulation of unfolded proteins in the endoplasmic reticulum (ER) 67 and resulting stress activates PKR-like endoplasmic reticulum kinase (PERK) (20); amino acid 68 starvation activates general control non-repressed 2 (GCN2) (21); and oxidative stress activates 69 5 heme-regulated inhibitor kinase (HRI) (22). Phosphorylation of the a subunit of eIF2 by one of 70 the four stress response kinases results in the stalling of translation initiation, and disassembly of 71 polysomes. Stalled translation initiation complexes bound to mRNA are recognized by several 72 RNA binding proteins, which aggregate to form RNA-protein macromolecular complexes called 73 stress granules (SGs) (23). Once the stressor is abated, eIF2a is dephosphorylated by protein 74 phosphatase 1 (PPI) and the PPI cofactor growth arrest and DNA-damage-inducible 34 75 (GADD34), allowing for the return of sequestered mRNA transcripts to active translation (23). 76 77 SGs are dynamic nonmembrane-bound cytoplasmic structures that can rapidly assemble in 78 response to stress and disassemble once the stress has been alleviated (23). SGs typically 79 contain mRNAs, stalled translation initiation complexes, and numerous RNA binding proteins. 80 Indeed, SGs may contain upwards of 260 different proteins (24), and ~50% of these are proposed 81 to be RNA-binding proteins (25). Of these Ras-GTPase activating binding protein 1 (or GAP SH3 82 domain binding protein 1 [G3BP1]), Caprin1, T-cell internal antigen 1 (TIA-1) and TIA-1 related 83 protein (TIAR) are proposed to be key nucleators of SG assembly (26-29). In addition to 84 translation repression and mRNA sorting, SGs also amplify the innate immune response by 85 aggregating critical antiviral factors (23). Because translation is a critical first step in the flavivirus 86 life cycle, the formation of SGs presents an immediate obstacle to infection. Notably, however, 87 during infection w...