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 on 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 ˜∼SVK₁₄ > SCC-12F2 > SCC-15 > SCC-12B2 > 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: (a) The combination of normal keratinocytes, SVK14 and the various SCC Unes provides an attractive model system to study differentiation in vitro; (b) EGF-receptor expression is related to the state of differentiation, both phenomena being sensitive to the external Ca²⁺ concentration; and (c) EGF-receptor expression is related to the capability of cells to differentiate.