INDUCTION OF HEAT-SHOCK-70 MESSENGER-RNA BY CADMIUM IS MEDIATED BY GLUTATHIONE SUPPRESSIVE AND NON-SUPPRESSIVE TRIGGERS

The induction mechanism of heat shock 70 (Hsp70) gene by cadmium was i nvestigated. In human amniotic WISH cells, Hsp 70 was induced by cadmi um in a dose- and time-dependent manner. Cadmium-induced Hsp70 mRNA le vels were enhanced 3- to 4-fold after depletion of intracellular gluta thione (GSH) by either diethylmaleate or buthionine sulfoximine. Under these conditions, hydrogen peroxide might increase in the absence of substrate for glutathione peroxidase. We found that exogenous hydrogen peroxide alone induced Hsp70 which was further enhanced significantly after GSH-depletion by diethylmaleate. On the other hand, treatment o f cells by diethyldithiocarbamate, an inhibitor of superoxide dismutas e, induced Hsp70 2-fold over the level of control. This induction was further stimulated by cadmium even in the presence of GSH. Furthermore , a 4-fold increase of intracellular GSH by the treatment of cells wit h glutathione isopropyl ester did not diminish the cadmium-induced Hsp 70. Gel mobility shift assays of nuclear extracts, from these differen tly treated cells, with oligonucleotide containing a promoter region o f Hsp70 gene revealed that the levels of Hsp70 mRNA observed in the pr esent study corresponded to the changes of transcription. These result s imply that the induction of Hsp70 mRNA by cadmium is mediated at lea st partly via reactive oxygen species and attenuated by cellular GSH a nd that some part of cadmium-induced Hsp70 can not be eliminated by GS H, suggesting that multiple signals are functioning for this induction .