Acyl-CoA cholesterol acyltransferase in cultured glioblastoma cells

We investigated the incorporation of radioactive precursors into cholesteryl ester in cultured glioblastoma cells. It was found that polar cholesterol derivatives and exogenous cholesterol contained in lipoprotein complexes greatly enhanced intracellular cholesteryl ester formation. The direct transfer of the acyl moiety from acyl-CoA to free cholesterol was demonstrated in broken cell preparations. Further evidence of the existence of the acyl-CoA:cholesterol acyltransferase (ACAT) in glioblastoma cells came from the conversion of radioactive cholesterol to cholesteryl ester by glial cell homogenates. The characteristics of the enzymic assay were studied in detail. This enzymic activity was greatly enhanced in homogenates prepared from 7-ketocholesterol-treated cells. Thus, cells more active in cholesterol esterification possessed a higher ACAT activity. Progesterone inhibited cholesterol esterification in cell-free preparations. The marked inhibition of intracellular cholesteryl ester formation in intact cells by progesterone is a strong argument for the exclusive role of ACAT in glioblastoma cells. Similar properties of cholesteryl ester biosynthesis have been observed in neuroblastoma cells and primary brain cell cultures. In conclusion, the same enzyme is involved in cholesteryl ester biosynthesis in all neural cells. Neural and nonneural cells share many fundamental characteristics of cholesteryl ester formation.