MECHANISM OF QUERCETIN-INDUCED SUPPRESSION AND DELAY OF HEAT-SHOCK GENE-EXPRESSION AND THERMOTOLERANCE DEVELOPMENT IN HT-29 CELLS

Previous studies have shown that a combination of low pH and quercetin (QCT) treatment following heat shock markedly suppresses and delays t he expression of heat shock protein genes, particularly the HSP70 gene (Lee et al., Biochem, Biophys, Res. Commun., 186:1121-1128, 1992). Th e possible mechanism for alteration of gene expression by treatment wi th QCT at low pH was investigated in human colon carcinoma cells. Cell s were heated at 45 degrees C for 15 min and then incubated at 37 degr ees C for various times (0-12 h) with QCT (0.05-0.2 mM) at pH 7.4 or 6 .5. Gel mobility-shift analysis of whole cell extracts from heated cel ls showed the formation of the heat shock transcription factor (HSF)-h eat shock element (HSE) complex. Dissociation of HSF from the HSE of t he human HSP70 promotor occurred within 4 h under both pH conditions. The kinetics of recovery were not affected by treatment with 0.1% dime thyl sulfoxide (DMSO). However, the dissociation of HSF-HSE complex wa s markedly delayed during treatment with a combination of low pH and Q CT. In addition, in vitro transcription assays showed a suppression of initiation and elongation of HSP70 mRNA. These results may explain wh y the combination of low pH and QCT treatment suppresses and delays th e HSP70 gene expression as well as thermotolerance development.