FMDV leader protease cleaves G3BP1 and G3BP2 and inhibits stress granule formation

Like other viruses, the picornavirus foot-and-mouth disease virus (FMDV, genus aphthovirus), one of the most notorious pathogens in global livestock industry, needs to navigate antivirals host responses to establish an infection. There is substantial insight into how FMDV suppresses the type I IFN response, but it is largely unknown whether and how FMDV modulates the integrated stress response. Here, we show that the stress response is suppressed during FMDV infection. Using a chimeric recombinant encephalomyocarditis virus (EMCV), in which we functionally replaced the endogenous stress response antagonist by FMDV Lpro or 3Cpro, we demonstrate an essential role for Lpro in suppressing stress granule (SG) formation. Consistently, infection with a recombinant FMDV lacking Lpro resulted in SG formation. Additionally, we show that Lpro cleaves the known SG scaffold proteins G3BP1 and G3BP2, but not TIA-1. We demonstrate that the closely related equine rhinitis A virus (ERAV) Lpro also cleaves G3BP1 and G3BP2 and also suppresses SG formation, indicating that these abilities are conserved amongst aphthoviruses. Neither FMDV or ERAV Lpro interfered with phosphorylation of PKR or eIF2α, indicating that Lpro does not affect SG formation by inhibiting the PKR-triggered signaling cascade. Taken together, our data suggest that aphthoviruses actively target scaffolding proteins G3BP1 and G3BP2 and antagonize SG formation to modulate the integrated stress response.IMPORTANCE The picornavirus foot and mouth disease virus (FMDV) is a notorious animal pathogen that puts a major economic burden on global life stock industry. Outbreaks have significant consequences for animal health and product safety. Like many other viruses, FMDV must manipulate antiviral host responses to establish infection. Upon infection, viral dsRNA is detected which results in activation of the PKR-mediated stress response, leading to a stop in cellular and viral translation and the formation of stress granules (SG), which are thought to have antiviral properties. Here we show that FMDV can suppress SG formation via its leader protease (Lpro). Simultaneously we observed that Lpro can cleave the SG scaffolding proteins G3BP1 and G3BP2. Understanding the molecular mechanisms of FMDV's antiviral host response evasion strategies may help to develop countermeasures to control FMDV infections in the future.