Quercetin suppresses heat shock response by down regulation of HSF1.

A bioflavonoid quercetin suppressed the stress response in heat-shocked cells and we have investigated the inhibitory mechanism in this report. After treatment of cells with nonlethal concentrations of quercetin, the binding of heat shock factor (HSF) to the heat shock element (HSE) was inhibited as detected by gel shift assay. We examined whether quercetin inhibits heat shock response by inhibiting HSF trimer-formation and found it was not the case. Instead, pretreatment of the cells with quercetin caused a decrease in the level of HSF1, especially of the constitutively phosphorylated form. This decrease was more prominent in heat-shocked cells than in control cells. These data suggest that (1) quercetin does not affect the trimer formation of HSF1, and (2) the decline of the HSF1-HSE complex might be linked to the decrease of HSF1 levels caused by quercetin.