Background
Stress granules (SGs) are granular aggregates in the cytoplasm that are formed under a variety of stress situations including viral infection. Previous studies indicate that poliovirus, a member of Picornaviridae, can induce SG formation. However, the exact mechanism by which the picornaviruses induce SG formation is unknown. Method: The localization of SG markers in cells infected with coxsackievirus B3 (CVB3) or enterovirus 71 (EV71) and in cells expressing each viral protein was determined via immunofluorescence assays or plasmid transfection. Eight plasmids expressing mutants of the 2A protease (2A(pro)) of CVB3 were generated using a site-directed mutagenesis strategy. The cleavage efficiencies of eIF4G by CVB3 2A(pro) and its mutants were determined via western blotting assays.
Conclusion
Both CVB3 and EV71 infections can induce SG formation, and 2A(pro) plays a crucial role in the induction of SG formation during these infections. This finding may help us to better understand how picornaviruses initiate the SG response.
Results
In this study, we found that CVB3 infection induced SG formation, as evidenced by the co-localization of some accepted SG markers in viral infection-induced granules. Furthermore, we identified that 2A(pro) of CVB3 was the key viral component that triggered SG formation. A 2A(pro) mutant with the G122E mutation, which exhibited very low cleavage efficiency toward eIF4G, significantly attenuated its capacity for SG induction, indicating that the protease activity was required for 2A(pro) to initiate SG formation. Finally, we observed that SGs also formed in EV71-infected cells. Expression of EV71 2A(pro) alone was also sufficient to cause SG formation.