Metallothionein 4 (MT4)

The deduced 62-amino acid MT4 protein is 94% identical to mouse Mt4 and approximately 60% identical to other human MTs. MT4 has an insertion at position 5 relative to MT1A and MT2A. Promoter and reporter analysis determined that zinc treatment, but not treatment with other metals, glucocorticoids, or mitogens, results in a 2-fold upregulation of MT4 expression. Solution hybridization analysis revealed that Mt4 expression is restricted to mouse tongue epithelium. In situ hybridization analysis demonstrated enhanced Mt4 expression in the stratum spinosum of mouse tongue, esophagus, and upper stomach, whereas Mt1 expression is confined to the basal cell layer of tongue epithelium. Biochemical fractionation analyses indicated that Mt4 is the predominant metallothionein in normal tongue and contains primarily zinc and copper but not cadmium.