Unregulated LDL cholesterol uptake is detrimental to breast cancer cells

Abstract

Tumor uptake of exogenous cholesterol has been associated with the proliferation of various cancers. Previously, we and others have shown that hypercholesterolemia promotes tumor growth and silencing of the LDL receptor (LDLR) in high LDLR-expressing tumors reduces growth. To advance understanding of how LDL uptake promotes tumor growth, LDLR expression was amplified in breast cancer cell lines with endogenously low LDLR expression. Murine (Mvt1) and human (MDA-MB-468) breast cancer cell lines were transduced to overexpress human LDLR (LDLROE). Successful transduction was confirmed by RNA and protein analysis. Fluorescence-labeled LDL uptake was increased in both Mvt1 and MDA-MD-468 LDLROE cells. The expression of the cholesterol-metabolizing genes, ABCA1 and ABCG1, was increased, while HMGCR was decreased in the MDA-MB-468 LDLROE cells. In contrast, Mvt1 LDLROE cells showed no differences in Abca1 and Abcg1 expression and increased Hmgcr expression. Using a Seahorse analyzer, Mvt1 LDLROE cells showed increased respiration (ATP-linked and maximal) relative to controls, while no statistically significant changes in respiration in MDA-MB-468 LDLROE cells were observed. Growth of LDLROE cells was reduced in culture and in hypercholesterolemic mice by two-fold. However, the expression of proliferation-associated markers (Ki67, PCNA and BrdU-label incorporation) was not decreased in the Mvt1 LDLROE tumors and cells. Caspase-3 cleavage, which is associated with apoptosis, was increased in both the Mvt1 and MDA-MB-468 LDLROE cells relative to controls, with the Mvt1 LDLROE cells also showing decreased phosphorylation of p44/42MAPK. Taken together, our work suggests that while additional LDL can promote tumor growth, unregulated and prolonged LDL uptake is detrimental.