Regulation of the uptake of high-density lipoprotein-originated cholesteryl ester by HepG2 cells: Role of low-density lipoprotein and plasma lipid transfer protein

Abstract

Cholesteryl ester uptake by the human hepatoma cell line HepG2 was studied in vitro by using radiolabeled cholesteryl ester as a tracer. After the cells were incubated in a lipoprotein deficient condition, the rate of radio labeled cholesteryl ester uptake from low-density lipoprotein (LDL) was estimated to be some 25-times higher than that from high-density lipoprotein (HDL). LDL-cholesteryl ester uptake was suppressed by preincubation of the cells with LDL, but pretreatment of the cells with HDL did not show significant effect. HDL-cholesteryl ester uptake was only slightly suppressed by pretreatment of the cells with LDL, and there was no effect with HDL pretreatment. HDL-cholesteryl ester uptake was not affected either by the presence of LDL or human plasma lipid transfer protein alone in the medium under our experimental conditions. Lipid transfer protein enhanced the uptake of radiolabeled cholesteryl ester originating from HDL by the cells only in the presence of LDL. Thus, lipid transfer protein catalyzes a bypass to LDL for the uptake by HepG2 cells of cholesteryl ester molecules which originate in HDL, and this pathway is much more efficient than direct uptake of cholesteryl ester originating in HDL by these cells.