CONCENTRATION-DEPENDENT DIFFERENTIAL-EFFECTS OF N-ACETYL-L-CYSTEINE ON THE EXPRESSION OF HSP70 AND METALLOTHIONEIN GENES INDUCED BY CADMIUMIN HUMAN AMNIOTIC CELLS

Cadmium induces the expression of the 70 kDa heat shock: protein (HSP7 0) and metallothionein (MT), both of which are considered to be associ ated with intracellular glutathione (GSH) metabolism in the cellular p rotection mechanism against cadmium-induced cellular injury. We determ ined the effects of N-acetyl-L-cysteine (NAG), which increases the int racellular GSH levels, on the induction of HSP70 and MT gene expressio n in a cultured cell line of human amniotic cells (WISH) exposed to Cd Cl2,. The mRNA level of MT-II, a major isoform of MT genes, was more p rominently increased than that of HSP70 when WISH cells were exposed t o CdCl2 (5-15 mu M, for 6h). The treatment of WISH cells with 1.5 and 30mM NAC for 2h increased the intracellular GSH levels by 1.4- and 3.1 -fold, respectively. Pretreatment of cells with 30mM NAC significantly reduced both HSP70 and MT-II mRNA levels in the cells exposed to 50 m u M CdCl2,. This concentration of NAC also efficiently suppressed the cadmium-induced lethality. On the contrary, pretreatment with 1.5mM NA C suppressed only the induction of HSP70 gene expression in the 50 mu M CdCl2-treated cells, and did not inhibit the metal toxicity. However , this low concentration of NAC efficiently suppressed lipid peroxidat ion which was increased by 50 mu M CdCl2,. Furthermore, this low conce ntration of NAG: also decreased the CdCl2-induced gene expression of H SP32 which represents a general response to oxidative stress. Taken to gether, NAC seems to have at least two concentration-dependent functio ns in WISH cells exposed to CdCl2,; the low concentration of NRC can s uppress the induction of HSP70 gene expression as well as the increase of lipid peroxidation via an antioxidant pathway, while the high conc entration of NAC can suppress the induction of MT-II mRNA as well as c admium-induced cell death. Our present data suggest that changes in in tracellular redox status, as reflected by GSH concentration, have more important effects on the induction of HSP70 mRNA rather than that of MT-II mRNA in human amniotic cells exposed to cadmium. (C) 1998 Elsevi er Science B.V.