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

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.

Essential Role of Enterovirus 2A Protease in Counteracting Stress Granule Formation and the Induction of Type I Interferon

“…Importantly, we did not observe these small SGs upon infection with the other chimeric EMCVs. This is consistent with previous reports that overexpression of 2A pro can induce the formation of some small SGs (31,37,38), most likely through its activity to cleave eIF4G and cause a host mRNA translation shutoff. Intriguingly, as infection with EMCV-2A pro progressed, these small SGs disappeared and we did not observe any SGs at 8 hpi.…”

“…1). Suppression of SG formation was previously reported for PV (34), for CV-B3 (35), and-while this work was in progress-also for EV-A71 (36,37). Here, we provide evidence that CV-A21, another member of the EV-C species, and EV-D68, an EV-D species member, also suppress the formation of SGs.…”

“…Intriguingly, as infection with EMCV-2A pro progressed, these small SGs disappeared and we did not observe any SGs at 8 hpi. A similar pattern of SGs that first appear and subsequently disappear during the course of infection has frequently been reported for enteroviruses (34)(35)(36)(37). Infection with EMCV-2Am did not induce small SGs at 4 hpi, nor did it suppress the formation of larger SGs at 8 hpi.…”

“…Enteroviruses also actively suppress the ISR. Infection of cells with PV, CV-B3, and EV-A71 results in the formation of small SGs early in infection, but these disappear later in infection (34)(35)(36)(37). Again, conflicting observations about the identity of the viral antagonist have been reported.…”

“…3C pro was shown to cleave G3BP1 and suppress SG formation, and overexpression of a cleavage-resistant G3BP1 decreased virus replication, although this decrease was rather modest (34,36,38). Recently, however, evidence was presented that 2A pro from EV-A71, PV, or CV suppresses SG formation induced by infection, as well as that induced by sodium arsenite or heat shock (37).…”