Targeting Ser78 phosphorylation of Hsp27 achieves potent antiviral effects against enterovirus A71 infection

A positive-sense (+) single-stranded RNA (ssRNA) virus (e.g. enterovirus A71, EV-A71) depends on viral polypeptide translation for initiation of virus replication after entry. We reported that EV-A71 hijacks Hsp27 to induce hnRNP A1 cytosol redistribution to initiate viral protein translation, but the underlying mechanism is still elusive. Here, we show that phosphorylation-deficient Hsp27-3A (Hsp27^S15/78/82A) and Hsp27^S78A fail to translocate into the nucleus and induce hnRNP A1 cytosol redistribution, while Hsp27^S15A and Hsp27^S82A display similar effects to the wild type Hsp27. Furthermore, we demonstrate that the viral 2A protease (2A^pro) activity is a key factor in regulating Hsp27/hnRNP A1 relocalization. Hsp27^S78A dramatically decreases the IRES activity and viral replication, which are partially reduced by Hsp27^S82A. However, Hsp27^S15A displays the same activity as the wild-type Hsp27. Peptide S78 potently suppresses EV-A71 protein translation and reproduction through blockage of EV-A71-induced Hsp27 phosphorylation and Hsp27/hnRNP A1 relocalization. A point mutation (S78A) on S78 impairs its inhibitory functions on Hsp27/hnRNP A1 relocalization and viral replication. Taken together, we demonstrate the importance of Ser78 phosphorylation of Hsp27 regulated by virus infection in nuclear translocation, hnRNP A1 cytosol relocation, and viral replication, suggesting a new path (such as peptide S78) for target-based antiviral strategy.