Specific alterations in keratin biosynthesis in mouse epidermis in vivo and in explant culture following a single exposure to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate

Abstract

Treatment of mouse skin with a single dose of the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) causes dramatic alterations in the biosynthesis of specific epidermal keratins. TPA was applied either topically to the skin of mice or added to the culture medium of skin explants maintained in vitro. Twenty-four h after exposure, skin samples were pulse labeled with [35S]methionine, and epidermal proteins were extracted and resolved by two-dimensional gel electrophoresis. In whole animals, TPA caused a marked decrease in the biosynthesis of the Mr 67,000 (basic) and 59,000 (acidic) keratins, specific markers for suprabasal differentiation in the epidermis. In addition, the synthesis of an acidic keratin of Mr 48,000 and a basic keratin of Mr 62,000 was also decreased. Concomitantly, TPA caused an increase in the synthesis of a basic keratin of Mr 60,000 and acidic keratins of Mr 52,000 and 49,000, markers for proliferating cells and primary epidermal cell cultures. The normal pattern of keratin synthesis observed in explants from normal skin was similar to that observed in skin samples from animals treated with TPA, except that synthesis of the Mr 67,000 basic keratin subunit was maintained. The addition of TPA to culture medium containing the skin explants resulted in a dose-dependent decrease in the synthesis of this keratin. Furthermore, resulting patterns of keratinization were identical to epidermis treated with TPA in vivo. These results suggest that a single acute exposure to TPA alters normal differentiation of mouse epidermal cells in vivo while causing a pronounced basal cell hyperproliferation. This response can be reproduced following TPA exposure to skin explants in culture, suggesting that the changes in keratinization observed are independent of the animal. Specific keratins modulated during TPA-induced hyperplasia may serve as marker proteins for aberrant epidermal cell growth and differentiation leading to the development of neoplasia.