SV 40-transformed (SVK14) and normal keratinocytes: similarity in the expression of low-density lipoprotein, epidermal growth factor, glucocorticoid receptors, and the regulation of lipid metabolism.

ABSTRACT

Transformation of normal keratinocytes by simian virus 40 (SV 40) leads to the establishment of epithelial cell lines that can be cultured in the absence of the feeder layer and do not become senescent in culture. The SVK14 cell line developed by Taylor-Papadimitriou et al can serve as a model for study of the modification of various cellular processes by certain pharmacologic and physiologic agents, because these cells resemble normal keratinocytes with respect to a variety of parameters related to proliferation and differentiation, as follows The SVK14 cells show the same ability to form ionophore-induced cross-linked envelopes that is strongly suppressed when the calcium level in the culture medium is reduced. When cultured in a high-calcium medium, both cell types showed a high rate of de novo cholesterol synthesis that was independent of the extracellular lipoprotein concentration. Cells cultured in a low-calcium medium had a much lower rate of cholesterol synthesis, but this rate increased markedly in cells preincubated in lipoprotein-deficient (LPDS) medium and decreased again with the addition of increasing amounts of low-density lipoprotein (LDL). Both types of cell showed decreased ability to bind epidermal growth factor (EGF) and LDL during calcium-induced differentiation, the expression of LDL and/or EGF receptors being high in low-calcium and low in high-calcium cells. Addition of etretinate (0.05-5.0 microM) suppressed cholesterol synthesis and strongly stimulated triglyceride synthesis in both cell types without significantly affecting the rate of protein synthesis. The addition of small doses of glucocorticoids (10(-9) to 10(-6) M) led to stimulation and higher doses (up to 5 X 10(-5) M) to inhibition of cell proliferation.