Esterification of exogenously derived free cholesterol by cultured fibroblasts.

The incorporation and esterification by cultured human fibroblasts of vesicle- or low density lipoprotein-derived free [3H]cholesterol was examined. The rate of the cellular uptake of free [3H]cholesterol from lipid vesicles was similar in both LDL-receptor positive lung fibroblasts and in LDL-receptor negative fibroblasts. When human LDL was used as the carrier of free [3H]cholesterol, however, the LDL-receptor positive lung fibroblasts incorporated significantly more [3H]cholesterol than did the LDL-receptor negative cells. The exchangeable free [3H]cholesterol was available for intracellular esterification. The formation of [3H]cholesteryl esters was markedly inhibited by lysosomotropic drugs, either indicating a partly lysosomal esterification reaction, or implying that free [3H]cholesterol moves through the lysosomal compartment on its way to intracellular esterification sites. Either way, the lysosomes appear to have a metabolic role in the metabolism of exchangeable free [3H]cholesterol.