The transcription factor MTF-1 mediates metal regulation of the mouse ZnT1gene

Metal regulation of the mouse zinc transporter (ZnT)-1 gene was examined in cultured cells and in the developing conceptus. Zinc or cadmium treatment of cell lines rapidly (3 h) and dramatically (about la-fold) induced ZnT1 m RNA levels. In cells incubated in medium supplemented with Chelex-treated f etal bovine serum, to remove metal ions, levels of ZnT1 mRNA were reduced, and induction of this message in response to zinc or cadmium was accentuate d (up to 31-fold induction). Changes in ZnT1 gene expression in these exper iments paralleled those of metallothionein I (MT-I), Inhibition of RNA synt hesis blocked metal induction of ZnT1 and MT-1 mRNAs, whereas inhibition of protein synthesis did not. Metal response element-binding transcription fa ctor (MTF)-1 mediates metal regulation of the metallothionein I gene. In vi tro DNA-binding assays demonstrated that mouse MTF-1 can bind avidly to the two metal-response element sequences found in the ZnT1 promoter. Using mou se embryo fibroblasts with homozygous deletions of the MTF-1 gene, it was s hown that this transcription factor is essential for basal as well as metal (zinc and cadmium) regulation of the ZnT1 gene in these cells. In vivo, Zn T1 mRNA was abundant in the midgestation visceral yolk sac and placenta. Di etary zinc deficiency during pregnancy down-regulated ZnT1 and MT-I mRNA le vels (4-5-fold and >20-fold, respectively) in the visceral yolk sac, but ha d little effect on these mRNAs in the placenta. Homozygous knockout of the MTF-1 gene in transgenic mice also led to a 4-6-fold reduction in ZnT1 mRNA levels and a loss of MT-I mRNA in the visceral yolk sac, These results sug gest that MTF-1 mediates the response to metal ions of both the ZnT1 and th e MT-I genes the visceral yolk sac, Overall, these studies suggest that MTF -1 directly coordinates the regulation of genes involved in zinc homeostasi s and protection against metal toxicity.