Quercetin-induced apoptosis in the monoblastoid cell line U937 in vitro and the regulation of heat shock proteins expression

Quercetin, a widely distributed plant flavonoid, inhibits the growth of tum or cells and the expression of heat shock proteins. In this study we examin ed quercetin - induced apoptosis of U937 cells in vitro and the regulation of heat shock proteins expression. The quercetin - induced apoptosis was de monstrated to be dose- and time- dependent. Flow cytometry analysis reveale d that sub - G(1) peak appeared at 12 hours, 24 hours and 48 hours respecti vely when treated with 50mM of quercetin and at 6 hours, 12 hours, 24 hours and 48 hours with 100mM of quercetin. Agarose gel electrophoresis demonstr ated a typical ladder-like pattern of DNA fragments in the same time interv als with 50mM of quercetin and at 6 hours only with 100mM of quercetin. The distribution of DNA contents showed that U937 cells were accumulated mainl y at G(2)/M phase when incubated with 50mM of quercetin for 24 hours and 48 hours. There was no specific effect on cell cycle distribution at 100mM of quercetin. On exposure to 100mM of quercetin, the inhibition of hsp27 and hsp70 expression was observed from 12 hours to 48 hours and 6 hours to 48 h ours respectively. The inhibition of hsp90 expression was not found eiyher at 50mM or 100mM of quercetin exposure. When incubated with 50mM of quercet in, there was no inhibitiory effect on hsp27, hsp70 and hsp90 expression by the Western blot analysis. These results suggested that it is dependent on the dose and exposure time of quercetin to induce apoptosis of U937 cells in vitro, to affect the cell cycle distribution and to regulate the express ion of hsp27 and hsp70.