Abstract
In this study, we investigate cadmium-and zinc-induced metallothionein(MT) gene expression with energy depletion by metabolic inhibitors. When cadmium-resistant Chinese hamster ovary (CdR) cells exposed to cadmium in the present of sodium azide, enhanced MT gene expression was observed by Northern analysis. However the position of probe / mRNA complex shifted significantly. To further confirm whether MT really induced by metabolic inhibitor, we analyzed MT expression by quantitative real-time polymerase chain reaction. Notably, metabolic inhibitors did not affect cadmium-induced MT gene expression. We also analyzed whether cadmium influx is energy dependent. Analysis of cadmium content in cells after giving metabolic inhibitor showed that cadmium transport does not require energy supply. Zinc is also a transition metal that induces MT gene expression. However, zinc-induced MT gene expression was blocked in the presence of metabolic inhibitors. This finding co-relate with the reduction of zinc uptake after giving metabolic inhibitor. This result indicates that zinc transport is energy dependent in CdR cells. We also investigated the relationship between AMPK activity and zinc uptake. When cells exposed to zinc in the present of AMPK activator (AICA riboside), MT induction was inhibited by AICA riboside. AICA riboside blocked zinc uptake but not affect ATP level. AMPK was phosphorylated when cells exposed to zinc at the present of metabolic inhibitors. We therefore hypothesized that ATP depletion blocked zinc uptake through AMPK activation. Our results indicate that cadmium and zinc differentially regulate MT gene expression in CdR cells in the present of metabolic inhibitor.