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.