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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1995;15:593-600.)
© 1995 American Heart Association, Inc.

Articles

The Enhanced Association of Apolipoprotein E With Apolipoprotein B–Containing Lipoproteins in Serum-Stimulated Hepatocytes Occurs Intracellularly

Sergio Fazio; Zemin Yao

From the Gladstone Institute of Cardiovascular Disease (S.F.), Cardiovascular Research Institute, University of California, San Francisco, and the Lipid and Lipoprotein Research Group and Department of Biochemistry (Z.Y.), University of Alberta, Edmonton, Canada.

Correspondence to Sergio Fazio, MD, PhD, Division of Endocrinology, Vanderbilt University, School of Medicine, Medical Center North, AA 4206, Nashville, TN 37232-2250. E-mail fazios@ctrvax.vanderbilt.edu.

Abstract Synthesis and secretion of VLDL in HepG2 cells are stimulated by several lipogenic factors, including serum. We previously found that the amount of apolipoprotein (apo) E associated with large lipoproteins such as VLDL increased under conditions of stimulated lipogenesis. The present study was designed to determine if the increased apoE association with VLDL occurs intracellularly or after secretion. In addition to HepG2, we studied rat hepatoma McA-RH7777 cells for production of endogenous rat apoE and transfected human apoE3. In both hepatoma cell lines stimulation of lipogenesis and production of large apoB-containing lipoproteins by serum resulted in increased apoE association with these particles and in decreased apoE association with HDL without affecting the total apoE output. Although evidence of apoE redistribution was seen among lipoproteins in the media, the apoE newly secreted under conditions of stimulated lipogenesis mainly associated with apoB-containing lipoproteins at the expense of its association with HDL. However, this effect was not attributable to reduced HDL lipid and apoA-I mass. Finally, redistribution of apoE from HDL to apoB-containing lipoproteins was also observed intracellularly in both HepG2 and transfected McA-RH7777 cells expressing human apoE3. These data suggest that the redistribution of apoE from HDL to apoB-containing lipoproteins upon activated lipogenesis in hepatoma cells occurs intracellularly and is not attributable to a decrease in HDL production.

Key Words: apoE • HepG2 • rat hepatoma • apoB • lipoprotein secretion

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