Abstract
ABSTRACT It has been reported that metallothionein (MT) may be associated with energy metabolism. In this work, we used a metabolic inhibitor to treat cells, and investigated the effect of sodium azide (NaN3) on the regulation of MT gene expression. When cadmium-resistant Chinese hamster ovary (CdR) cells exposed to mentals at the presence of NaN3 or other kinds of metabolic inhibitor (ie. rotenone, antimycin A, oligomycin), a differential regulation of MT gene expression was observed. NaN3 enhanced MT gene expression for cadmium-treated cells, but inhibited the expression for zinc-treated cells. We further use GH3 cells to investigate wheaher the differential regulation of MT genes is cell type specific. In GH3 cells, either MT gene expression induced by cadmium or zinc was inhibited by NaN3. MTI and MTII mRNAs were coordinately expressed when cells were stimulated by Cd and NaN3. However, the enhanced MT mRNA accumulation by NaN3 for cadmium-treated cells was not due to the increase of MT mRNA. NaN3 did not affect cadmium accumulation in CdR cells, but markedly reduced cellular zinc content in either cadmium- or zinc-treated cells. The DNA binding activity of MT transcriptional factor (MTF-1) increased after the co-treatment of NaN3 and metals as demonstrated by electrophoretic mobility shift assay. Notably, MTF-1 concentration was not affected by any of the treatments. We also found that the specific chelator of free intracellular Ca2+, BAPTA-AM, consistently attenuaed the induction of MT gene. In addition, the Ca2+ ionophor A23187 subtantially enhanced cadmium induced MT gene expression, indicating that elevation of intracellular Ca2+ was essential for this response. Results of our study indicate that MT gene expression in CdR cells is differentially regulated by NaN3 at the presence of metals.