A 25-hydroxycholesterol-resistant cell line deficient in acyl-coA:cholesterol acyltransferase

We describe a line of mutant Chinese hamster ovary cells, SRD-4 cells, that lacks acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity and fails to synthesize cholesteryl esters when stimulated with 25-hydroxycholesterol or low density lipoprotein. The cells also have a partial defect in their ability to repress transcription of three sterol-regulated genes, 3-hydroxy-3-methylglutaryl-coenzyme A synthase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, and the low density lipoprotein receptor. The cells were selected by mutagenesis followed by growth in the presence of 25-hydroxycholesterol, which kills the parental cells by cholesterol depletion, owing to an inhibition of cholesterol synthesis and a stimulation of cholesterol esterification. Treatment of parental cells with compound 58-035 (3-(decyldimethylsilyl)-N-[2-(4-methylphenyl)-1-phenylethyl] propanamide), an inhibitor of ACAT, abolished cholesterol esterification but did not reproduce the defect in gene repression seen in the SRD-4 cells, and it only partially reproduced the resistance to the killing effect of 25-hydroxycholesterol. We conclude that the SRD-4 cells most likely have two independent defects, one in ACAT and the other in a factor that mediates sterol-dependent transcriptional repression. The SRD-4 cells thus resemble a line of hamster cells previously isolated (Cadigan, K.M., Heider, J.G., and Chang, T.-Y. (1988) J. Biol. Chem. 263, 274-282), which has similar independent defects. The results raise the possibility that a partial resistance to sterol repression provides a growth advantage to cells that lack ACAT.