Novel stress granule-like structures are induced via a paracrine mechanism during viral infection

To rapidly adapt to stresses such as infections, cells have evolved several mechanisms, which include the activation of stress response pathways and the innate immune response. These stress responses result in the rapid inhibition of translation and condensation of stalled mRNAs with RNA-binding proteins and signalling components into cytoplasmic biocondensates called stress granules (SGs). Increasing evidence suggests that SGs contribute to antiviral defence, and thus viruses need to evade these responses to propagate. We previously showed that feline calicivirus (FCV) impairs SG assembly by cleaving the scaffolding protein G3BP1. We also observed that uninfected bystander cells assembled G3BP1-positive granules, suggesting a paracrine response triggered by infection. We now present evidence that virus-free supernatant generated from infected cells can induce the formation of SG-like foci, which we name paracrine granules. They are linked to antiviral activity and exhibit specific kinetics of assembly-disassembly, and protein and RNA composition that are different from canonical SGs. We propose that this paracrine induction reflects a novel cellular defence mechanism to limit viral propagation and promote stress responses in bystander cells.

Automated summary

To adapt to stress conditions like infections, cells have developed stress response pathways and innate immune responses, which result in the formation of stress granules (SGs). SGs play a role in antiviral defense, and viruses need to avoid these responses to continue propagating. This study shows that feline calicivirus (FCV) impairs SG assembly by cleaving the protein G3BP1. Additionally, virus-free supernatant from infected cells can induce the formation of SG-like foci, called paracrine granules, which are linked to antiviral activity.