Picornavirus 2A protease regulates stress granule formation to facilitate viral translation.

Xiaodan Yang,Mingzhou Chen,Shanshan Fan,Yi Zhong,Qiang Zhang,Yali Qin,Dong Guo,Zhulong Hu,Peter Sarnow

doi:10.1371/journal.ppat.1006901

Abstract

Stress granules (SGs) contain stalled messenger ribonucleoprotein complexes and are related to the regulation of mRNA translation. Picornavirus infection can interfere with the formation of SGs. However, the detailed molecular mechanisms and functions of picornavirus-mediated regulation of SG formation are not clear. Here, we found that the 2A protease of a picornavirus, EV71, induced atypical stress granule (aSG), but not typical stress granule (tSG), formation via cleavage of eIF4GI. Furthermore, 2A was required and sufficient to inhibit tSGs induced by EV71 infection, sodium arsenite, or heat shock. Infection of 2A protease activity-inactivated recombinant EV71 (EV71-2AC110S) failed to induce aSG formation and only induced tSG formation, which is PKR and eIF2α phosphorylation-dependent. By using a Renilla luciferase mRNA reporter system and RNA fluorescence in situ hybridization assay, we found that EV71-induced aSGs were beneficial to viral translation through sequestering only cellular mRNAs, but not viral mRNAs. In addition, we found that the 2A protease of other picornaviruses such as poliovirus and coxsackievirus also induced aSG formation and blocked tSG formation. Taken together, our results demonstrate that, on one hand, EV71 infection induces tSG formation via the PKR-eIF2α pathway, and on the other hand, 2A, but not 3C, blocks tSG formation. Instead, 2A induces aSG formation by cleaving eIF4GI to sequester cellular mRNA but release viral mRNA, thereby facilitating viral translation.

Highlights

Stress granules (SGs) form in response to a variety of stresses such as oxidative stress, heat shock (HS), hypoxia, nutrient deprivation, and viral infection [1]
We demonstrate that the 2A protease of Enterovirus 71 (EV71) blocks tSG formation but induces atypical stress granule formation to facilitate viral translation
Representative images of fluorescence intensities observed in foci at indicated times during fluorescence recovery after photobleaching (FRAP) assays are shown in pseudo-colors in the top panels. (D) Effects of eIF2α phosphorylation on T-cell-restricted intracellular antigen 1 (TIA-1) foci

Summary

Introduction

Stress granules (SGs) form in response to a variety of stresses such as oxidative stress, heat shock (HS), hypoxia, nutrient deprivation, and viral infection [1]. During SG formation, messenger RNA (mRNA) translation initiation is inhibited, and polysomes are disassembled. SGs in general are considered to be transient and dynamic Compounds such as cycloheximide (CHX) stabilize mRNAs on polysomes and inhibit SG formation and foster their disassembly [4,5]. The phosphorylation of eIF2α interferes with the formation of the eIF2-GTP-tRNAiMet ternary complex and thereby stalls translation initiation [1,6,7,8]. EIF2α-independent SG formation exists and includes eIF4A inhibition by either pateamine A or hippuristanol and inhibition of eIF4G-eIF4E interactions during hydrogen peroxide-induced oxidative stress [9,10,11,12]

Methods

Results

Discussion

Conclusion