Epidermal growth factor receptor expression related to differentiation capacity in normal and transformed keratinocytes

Abstract

Epidermal growth factor (EGF) and Ca2+ have been indicated to play a major role in skin development. We have used normal keratinocytes, SV40-transformed keratinocytes (SVK14) and various squamous carcinoma cell (SCC) lines as in vitro model system to study the effect of the extracellular Ca2+ concentration of EGF-receptor expression in relation to the capability of cells to differentiate. The cell lines used exhibit a decreasing capacity to differentiate in the order of keratinocytes approximately SVK14 greater than SCC-12F2 greater than SCC-15 greater than SCC-12B2 greater than SCC-4, as judged from Ca2+-ionophore-induced cornified envelope formation. Under normal Ca2+ conditions, all cell lines (except for SCC-15) exhibited two classes of EGF-binding sites. The number of low-affinity binding sites increased considerably as cells were less able to differentiate, while the apparent dissociation constant (kd) was similar in all cell lines. In contrast, the properties of high-affinity EGF binding varied in the various cell lines without a clear relationship to the degree of differentiation capacity. Lowering the extracellular Ca2+ concentration to 0.06 mM resulted in a decrease of Ca2+ ionophore-induced cornified envelope formation, demonstrating the decreased ability to differentiate under these conditions. The decreased ability to differentiate was accompanied by a marked increase in the number of EGF-binding sites, but without a change of the kd. Furthermore, no high-affinity EGF-binding sites were detectable under these conditions. Finally, addition of Ca2+ to low Ca2+-cultured cells caused a rapid decrease of EGF binding in all cell lines, most prominently in normal keratinocytes and SCC-12F2 cells. The data presented demonstrate: The combination of normal keratinocytes, SVK14 and the various SCC lines provides an attractive model system to study differentiation in vitro; EGF-receptor expression is related to the state of differentiation, both phenomena being sensitive to the external Ca2+ concentration; and EGF-receptor expression is related to the capability of cells to differentiate.