Revised Manuscript Received January 26, 1994· abstract: The expression of apoE mRNA in the adrenal gland is inversely correlated to steroidogenesis and directly correlated to the level of cholesteryl ester stores. To further investigate the relationship between apoE and cellular cholesterolhomeostasis, several parameters of cholesterol metabolism in the murine Y1 adrenal cell line engineered to constitutively express human apoE (Yl-E cells) have been studied. It is reported here that Yl-E cells have increased cellular cholesterolcontent and markedly reduced efflux of free cholesterol as compared to control Y1 cells that do not express apoE. Yl-E cells have increases in both free and esterified cholesterol. However, Y1 and Yl-E cells incorporate [14C] oleate into cholesteryl ester at similar rates and have similar levels of maximal ACAT activity in isolated microsomes. Turnover of cholesteryl ester stores prelabeled with [14C] oleate occurred at similar rates in Yl-E and control Y1cells, suggesting that increased cholesteryl ester stores in Yl-E cells do not resultfrom reduced cholesteryl ester hydrolysis. Yl-E cells showed reduced cholesterol efflux as compared to control Y1 cells with eithernative high-density lipoprotein or cholesterol-free reconstituted particles as extracellular acceptors. Cholesterol efflux was not altered by inhibition of ACAT, suggesting that cholesterol esterification in Yl-E cells is not inhibiting efflux. These results suggest that reduced cholesterol efflux is responsible, at least in part, for the cholesterol accumulation in Yl-E cells. In comparison to the rat adrenal gland in vivo, Yl-E cells resemble adrenocortical cells under conditions where steroidogenesis is suppressed and apoE expression and cholesteryl ester storage are increased. Thus, apoE expression in Y1 cells alters cholesterol metabolism to promote cholesteryl ester storage with reduced cholesterol utilization for either steroidogenesis or efflux from the cell.