Abstract
In mammalian cells, low density lipoprotein (LDL) is bound, internalized, and delivered to lysosomes where LDL-cholesteryl esters are hydrolyzed to unesterified cholesterol. The mechanisms of intracellular transport of LDL-cholesterol from lysosomes to other cellular sites and LDL-mediated regulation of cellular cholesterol metabolism are unknown. We have identified a pharmacological agent, U18666A (3-beta-[2-diethyl-amino)ethoxy]androst-5-en-17-one), which impairs the intracellular transport of LDL-derived cholesterol in cultured Chinese hamster ovary (CHO) cells. U18666A blocks the ability of LDL-derived cholesterol to stimulate cholesterol esterification, and to suppress 3-hydroxy-3-methylglutaryl-coenzyme A reductase and LDL receptor activities. However, U18666A does not impair 25-hydroxycholesterol-mediated regulation of these processes. In addition, U18666A impedes the ability of LDL-derived cholesterol to support the growth of CHO cells. However, U18666A has only moderate effects on growth supported by non-lipoprotein cholesterol. LDL binding, internalization, and lysosomal hydrolysis of LDL-cholesteryl esters are not affected by the presence of U18666A. Analysis of intracellular cholesterol transport reveals that LDL-derived cholesterol accumulates in the lysosomes of U18666A-treated CHO cells which results in impaired movement of LDL-derived cholesterol to other cell membranes.
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