Expression of keratins K6 and K16 in regenerating mouse epidermis is less restricted by cell replication than the expression of K1 and K10.

Biosynthesis of the hyperproliferation-associated keratins K6 and K16 was studied in mouse epidermis following a single topical application of the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). An epidermal cell cohort was followed by pulse-labelling with the thymidine analogue 5-bromodeoxyuridine (BrdUrd). Mice were injected intraperitoneally with BrdUrd 1 h before a single topical application of TPA. TPA induced regenerative epidermal hyperplasia with hyperproliferation and shortened suprabasal transit time. The BrdUrd-labelled cell cohort was followed for 96 h after TPA-treatment by two-colour immunofluorescence staining with antibodies to BrdUrd, keratin K6 and K16. In control animals, K6 and K16 were found only in the hair follicles. K6 expression was immediately induced in all epidermal cell layers of TPA-treated epidermis, including actively replicating cells and it was expressed during the whole observation period. K16 was only present in post-mitotic cells and was transiently expressed 8-72 h after TPA treatment. Our results suggest that the expression of K6 and K16 is less restricted by cellular replication than the normally occurring K1 and K10 keratins.