Regulation of hsp70 synthesis induced by cupric sulfate and zinc sulfate in thermotolerant HeLa cells.

Upon exposure to the heavy metals copper and zinc, a large amount of 70,000-Da heat shock protein (hsp70) was synthesized in normal, non-thermotolerant (NT) HeLa cells, whereas only a little increase of hsp70 synthesis was observed in thermotolerant (TT) cells. To determine the inhibition mechanism of hsp70 induction in the TT cells, we first analyzed the hsp70 mRNA of these cells. Hsp70 mRNA in the NT cells increased immediately after exposure to these metals. In TT cells, however, the increase of hsp70 mRNA was delayed, even though it eventually increased to a similar or slightly lower level compared with NT cells. Further analysis of the activation of heat shock transcription factor (HSF) showed that a significant activation of HSF was observed immediately after exposure to these metals in the NT cells, whereas the activation of HSF was initially repressed in the TT cells. Thus, the decreased induction of hsp70 synthesis observed in the TT cells seemed to be due to the reduced translation of hsp70 mRNA and also in part to the reduced activation of HSF. Furthermore, by the gel mobility shift assay using anti-hsp70 antibody, the association of copper- and zinc-activated HSF with hsp70 was observed in both NT and TT cells. The amount of HSF-hsp70 complex was prominent in TT cells, in which the hsp70 content was 5 to 10 times higher than that in the NT cells. These findings strongly suggest that the activity of HSF is negatively regulated by hsp70 in the TT cells.