Defective low-density lipoprotein metabolism in cultured, normal, transformed, and malignant keratinocytes

To obtain more information on differences in cellular behavior during the differentiation process, a number of types of epithelial cells with and without a defect in cornified envelope formation were compared as to the regulation of intracellular cholesterol synthesis by low-density lipoprotein (LDL) and the uptake and degradation of [125I]LDL. The following cells were cultured: normal skin fibroblasts (F), normal (K) and SV 40 transformed (SVK14) keratinocytes, and a number of squamous carcinoma cell (SCC) lines in which the defective terminal differentiation was found to occur in the following order of intensity: SCC-12F2 less than SCC-25 approximately equal to SCC-15 less than SCC-12B2 less than SCC-4. Compared with normal human fibroblasts, most of the cells under study showed a defective response to changes of the extracellular serum LDL concentration. The degree of inducibility of cholesterol synthesis after the cells were deprived of extracellular sources of cholesterol as well as the degree of the LDL-induced suppression of the intracellular cholesterol synthesis in cells preincubated in medium supplemented with lipoprotein-deficient serum decreased in the following order: F greater than SCC-4 greater than SCC-15 approximately equal to SCC-25 greater than SCC-12B2 congruent to SCC-12F2 greater than SVK14 approximately equal to K. A defect in LDL metabolism was found to be responsible for the partial or complete failure of LDL to regulate the cholesterol metabolism, because when sterol was delivered to all cell types in artificial nonlipoprotein form (i.e., as 25-hydroxycholesterol) a marked suppression of cholesterol synthesis was observed. For all SCC lines tested except SCC-12B2 good correlation was found between the degree of LDL-induced suppression of cholesterol synthesis and the decreasing ability of cells to differentiate into squames or cornified envelope-forming cells. The transformation of keratinocytes by SV 40 virus did not lead to any change in the response of the cells to changes in the extracellular LDL concentration since both the normal and the transformed keratinocytes showed the same response to LDL (i.e., no response).