Localization of metallothionein in hair follicles of normal skin and the basal cell layer of hyperplastic epidermis : possible association with cell proliferation

Metallothionein is a low-molecular-weight metal-binding protein. Although it is inducible by a variety of agents and ubiquitously present in many tissues, its physiologic functions are still not clear. The present study was undertaken to determine the possible functions of metallothionein in both the proliferation and differentiation of epidermal keratinocytes. Metallothionein was detected immunohistochemically in hair matrix cells of the bulb and cells of the outer root sheath of anagen hair follicles, but not in dermal papillae in normal skin in the back of mice. In hyperplastic epidermal tissue, induced by either a phorbol ester tumor promoter or cholera toxin, the basal cells of the interfollicular epidermis stained strongly for metallothionein. Elevated expression of mRNA of the metallothionein gene was also demonstrated when the skin was stimulated by agents that induced hyperplasia. Papillomas produced by two-stage carcinogenesis protocols also stained for metallothionein. These observations suggest that metallothionein is involved in the proliferation of epidermal keratinocytes.