, Volume 122, Issue 3, pp 661-670
Date: 23 Oct 2009

High ACAT1 expression in estrogen receptor negative basal-like breast cancer cells is associated with LDL-induced proliferation

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The specific role of dietary fat in breast cancer progression is unclear, although a low-fat diet was associated with decreased recurrence of estrogen receptor alpha negative (ER) breast cancer. ER basal-like MDA-MB-231 and MDA-MB-436 breast cancer cell lines contained a greater number of cytoplasmic lipid droplets compared to luminal ER+ MCF-7 cells. Therefore, we studied lipid storage functions in these cells. Both triacylglycerol and cholesteryl ester (CE) concentrations were higher in the ER cells, but the ability to synthesize CE distinguished the two types of breast cancer cells. Higher baseline, oleic acid- and LDL-stimulated CE concentrations were found in ER compared to ER+ cells. The differences corresponded to greater mRNA and protein levels of acyl-CoA:cholesterol acyltransferase 1 (ACAT1), higher ACAT activity, higher caveolin-1 protein levels, greater LDL uptake, and lower de novo cholesterol synthesis in ER cells. Human LDL stimulated proliferation of ER MDA-MB-231 cells, but had little effect on proliferation of ER+ MCF-7 cells. The functional significance of these findings was demonstrated by the observation that the ACAT inhibitor CP-113,818 reduced proliferation of breast cancer cells, and specifically reduced LDL-induced proliferation of ER cells. Taken together, our studies show that a greater ability to take up, store and utilize exogenous cholesterol confers a proliferative advantage to basal-like ER breast cancer cells. Differences in lipid uptake and storage capability may at least partially explain the differential effect of a low-fat diet on human breast cancer recurrence.

ACAT1 is the commonly used name for acyl-CoA: cholesterol acyltransferase; the gene symbol is SOAT1.