Genistein inhibits herbimycin A-induced over-expression of inducible heat shock protein 70 kDa.

It has been shown that expression of heat shock proteins (HSPs) can interfere with the effectiveness of therapeutic cytotoxic drugs. In this study, we investigated the regulation of expression of HSPs in human epidermoid A-431 cells. Two known protein tyrosine kinase inhibitors were studied. Treatment of cells with herbimycin A increased production of inducible HSP 70 kDa (HSP-70i) in a concentration-dependent manner, whereas genistein did not. The increase induced by herbimycin A was observed within 2 h, reached a peak at 6 h, and remained above the basal level 3 days later. Pretreatment with genistein inhibited the herbimycin A-induced increase in HSP-70i. Herbimycin A treatment increased levels of HSP-70i mRNA in cells, suggesting that herbimycin A increases HSP-70i by promoting transcription. Treatment with genistein or genistein combined with herbimycin A did not increase HSP-70i mRNA, suggesting that the inhibitory effect of genistein also occurs at the level of mRNA production. Herbimycin A increased intracellular Ca2+ concentration ([Ca2+]i), but treatment with genistein decreased it. Chelation of [Ca2+]i with BAPTA blocked the herbimycin A-induced increase in HSP-70i mRNA and HSP-70i protein. Herbimycin A induced the phosphorylation of heat shock factor 1 (HSF1), while genistein reduced HSF1 production. The ability of genistein to inhibit the herbimycin A-induced increase in HSP-70i is not associated with genistein's capacity to decrease basal [Ca2+]i, but because it decreases HSFI production. The herbimycin A-induced increase in HSP-70i protected cells from hypoxia injury.