Changes in basal cell subpopulations and tissue differentiation in human epidermal cultures treated with epidermal...

Cell kinetic studies on cultured human epidermal cells have indicated that cycling basal cells may be divided into at least two subpopulations that seem to differ with respect to the rate of DNA replication. The present study was undertaken in order to elucidate the biological significance of these subpopulations. The proliferation characteristics of cultured basal cells were changed by the addition of epidermal growth factor (EGF) and cholera toxin to the culture medium. It was shown that EGF and cholera toxin stimulated the growth of human epidermal cells in culture. Simultaneously, the terminal differentiation of the cells was inhibited resulting in a reduced multilayering and a reduced formation of the cornified envelope. However, only minor differences in the protein synthesis pattern were observed between cultures maintained in the presence or absence of the growth stimulators. The effect of EGF and cholera toxin on the basal cell subpopulations was investigated after 3H-thymidine labelling followed by cell sorting and autoradiography. In the presence of EGF and cholera toxin dramatic changes were induced in the labelling pattern of sorted S-phase cells indicating significant alterations in the balance between the subpopulations of cycling basal cells. Our results with these substances are in accord with the hypothesis that the observed cell kinetic subpopulations may be related to regeneration or early events in the differentiation process of the keratinocyte.