Cholesterol Metabolism in High Risk Neuroblastoma. Contributions by the SR-B1 Receptor and Cholesterol Ester Accumulation

Background: Cancer cells promote their survival by reprogramming metabolic pathways. Alterations in cholesterol metabolism have been observed as one of these mechanisms, including reduced levels of high-density lipoprotein (HDL) cholesterol in cancer patients. In high-risk neuroblastoma (HRNB), an extra cranial pediatric cancer, activation of genes associated with cholesterol synthesis has been reported. However, it is unclear whether modification in exogenous sources of cholesterol also occur in HRNB. An external source of cholesterol is from lipoproteins via the scavenger receptor class B type 1 (SR-B1) lipoprotein receptor that mediates the selective uptake of cholesteryl esters (CE) into the cell. In neuroblastoma high expression of SR-B1 correlates with poor prognosis. Objective: Our goal was to examine whether the accumulation of cholesteryl ester occurs in HRNB cells and whether this process is correlated with SR-B1 expression. Methods and Results: Human neuroblastoma cell lines expressing wild type p53; SH-SY-5Y, SMS-KCNR, and mutated p53; SK-N-BE (2), and BE (2) C were cultured. Western blot analysis confirmed the presence of the HDL receptor, SR-B1, and the multidrug resistant protein 1 (MDR1). Fluorescence staining of lipid droplets was performed using Nile Red. The neutral lipid content in SH-SY-5Y and SMS-KCNR, was higher at 24 hours than 72 hours suggesting that at 24 hours either increased accumulation or synthesis of neutral lipids occurred. To examine cholesterol esterification, cells were incubated with 14C-oleate. Cells were collected, lipids extracted with cold acetone and neutral lipids separated by thin layer chromatography. The results indicated notable reduction in cholesterol esterification in p53-mutated cells as compared to the wild type cells. However, triglyceride synthesis seems unaffected by p53 mutation when compared with the wild type. Conclusions: We confirm that there is accumulation of cholesteryl esters and high expression of SR-B1 in HRNB. These findings present a more in depth understanding of molecular mechanisms that drive progression of HRNB and may provide unique molecular targets to combat HRNB and other cancers. Future plans will include investigating cholesteryl ester accumulation and SR-B1 expression as a function of cell proliferation in HRNB. Additionally, human neuroblastoma tissue samples will be used to investigate the association between overexpression of SR-B1 and tumor aggressiveness.