The expression of keratin genes in epidermis and cultured epidermal cells

Cultured human epidermal cells and human stratum corneum (callus) contain a number of keratins of different molecular size, but the size distribution is not the same in the two cases. To characterize these keratins in more detail, we compared them by amino acid analysis, immunological reactivity and one-dimensional peptide mapping (Cleveland et al., 1977). No differences in amino acid compositon could be detected among keratins of stratum corneum differing in molecular size by as much as 50%, suggesting that some repeating structure may be present in these molecules. Examination of polypeptide fragments produced by partial enzymatic hydrolysis showed strong similarities among all the keratins of stratum corneum and of cultured epidermal cells, even extending to the keratins of rodents; but the keratins of similar size, whether of stratum corneum or cultured cells, were more closely related than keratins of different size. This conclusion was supported by studies of the immunological reactivity of the keratins. How the epidermal cell generates a family of keratins is a problem of considerable interest. The differences in size and structure between the keratins of stratum corneum and cultured epidermal cells suggest that the epidermal cell can modify the expression its keratin genes.