Multiple Poliovirus Proteins Repress Cytoplasmic RNA Granules

We have previously shown that poliovirus (PV) infection induces stress granule (SG) formation early in infection and then inhibits the formation of SG and disperses processing bodies (PBs) by the mid-phase of infection. Loss of SG was linked to cleavage of G3BP1 by viral 3C proteinase (3C(pro)), however dispersal of PBs was not strongly linked to cleavage of specific factors by viral proteinases, suggesting other viral proteins may play roles in inhibition of SG or PB formation. Here we have screened all viral proteins for roles in inducing or inhibiting the formation of RNA granules by creating fusions with mCherry and expressing them individually in cells. Expression of viral proteins separately revealed that the capsid region P1, 2A(pro), 3A, 3C(pro), the protease precursor 3CD and 3D polymerase all affect RNA granules to varying extents, whereas 2BC does not. 2A(pro), which cleaves eIF4GI, induced SGs as expected, and entered novel foci containing the SG nucleating protein G3BP1. Of the two forms of G3BP, only G3BP1 is cleaved by a virus proteinase, 3C(pro), whereas G3BP2 is not cleaved by 3C(pro) or 2A(pro). Surprisingly, 3CD, which contains proteinase activity, differentially repressed PBs but not SGs. Further, both 2A(pro) and 3C(pro) expression dispersed PBs, however molecular targets were different since PB dispersal due to 2A(pro) and heat shock protein (Hsp)90 inhibition but not 3C(pro), could be rescued by application of oxidative stress to cells. The data indicate that PV repression of SGs and PBs is multifactorial, though protease function is dominant.