Heat shock protein 70 is associated with CSFV NS5A protein and enhances viral RNA replication.

The non-structural 5A (NS5A) protein of classical swine fever virus (CSFV) is proven to be involved in viral replication and can also modulate cellular signaling via to its ability to interact with various cellular proteins. Here, HSP70/NS5A complex formation is confirmed by coimmunoprecipitation and GST-pulldown studies. Additionally, the N-terminal amino acids (29-240) of NS5A were identified as the interaction region through in vivo deletion analyses, and confocal microscopy showed that NS5A and HSP70 colocalized in the cytoplasm. Overexpression of HSP70 via the eukaryotic expression plasmid pDsRED N1 or lentivirus significantly promoted viral RNA synthesis. Whereas the knockdown of HSP70 by lentivirus-mediated shRNA or inhibition by quercetin markedly decreased the viral load. These data suggest that HSP70 plays a critical role in the viral life cycle, particularly during the virus RNA replication period. The investigation of HSP70 protein functions may be beneficial for developing new strategies to treat CSFV infection.