Quercetin counteracts the pro‐viral effect of heat shock response in grass carp cells with its therapeutic potential against aquareovirus

Abstract

We have previously shown that heat shock protein (Hsp70) is significantly up-regulated by grass carp reovirus (GCRV) infection, and Hsp70 plays a positive role in facilitating GCRV infection in vitro through unknown mechanisms. Considering the fact that Hsp70 is the most highly induced heat shock protein in cells undergoing the conserved heat shock response (HSR), we determined here that both aquareovirus infection and heat shock induced expression of Hsp70 in grass carp ctenopharyngodon idella kidney cell line (CIK). The pro-viral function of heat shock response was associated with the involvement of Hsp70 in the replication and transcription complex (RTC) of GCRV104 as shown by co-localization of Hsp70 with viral double-stranded RNA (dsRNA). Furthermore, we evaluated the potential of grass carp Hsp70 as a novel fish antiviral target through its down-regulation by plant-derived quercetin, a major dietary flavonoid and known mammalian transcriptional repressor for heat shock factor 1 (HSF-1). In the presence of 50 µM quercetin, grass carp Hsp70 expression was significantly suppressed in cells stressed with either GCRV-104 infection or heat shock. Reduced viral protein expression and descendent virions correlated with the down-regulation of Hsp70 by quercetin in GCRV104-infected grass carp cells, and the pro-viral effect of heat shock could be counteracted by quercetin, which highlighted the involvement of heat shock response protein Hsp70 as a quercetin-mediated antiviral target. Antiviral effects of quercetin in a dose-dependent manner were also observed for GCRV JX-01, a different genotype of GCRV, which predicted a broad-spectrum nature of quercetin in suppressing aquareovirus replication. Overall, the data here indicated that quercetin acted as a specific suppressor for grass carp Hsp70 expression in cells stressed with either aquareovirus or heat shock, and the suppressing effect of quercetin on aquareovirus infection implied its potential as an environmental-friendly and broad-spectrum antiviral drug through targeting fish heat shock response protein.