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Journal of Lipid Research, Vol 36, 2651-2660, Copyright © 1995 by Lipid Research, Inc.
FJ Field, E Born and SN Mathur
The source for triacylglycerol-rich lipoprotein cholesterol was
investigated in CaCo-2 cells grown on filters separating an upper and a
lower well. Oleic acid, a fatty acid that promotes triacylglycerol-rich
lipoprotein synthesis and secretion in CaCo-2 cells, increased the
vesicular-mediated influx of plasma membrane cholesterol to the endoplasmic
reticulum. Unesterified and esterified cholesterol derived from the plasma
membrane were increased in triacylglycerol-rich lipoproteins secreted by
cells incubated with oleic acid. Fatty acids, which increased the number of
lipoprotein particles secreted (increased apoB secretion), increased plasma
membrane cholesterol influx and secretion. Oleic acid caused a modest
increase in the synthesis of cholesterol and a two-fold increase in
cholesteryl esters. The amount of newly synthesized cholesterol secreted in
lipoproteins of density < 1.006 g/ml represented a small fraction of
that present within the cell; however, oleic acid did increase the amount
of both newly synthesized cholesterol and cholesteryl esters in
triacylglycerol-rich lipoproteins. Oleic acid did not affect the fraction
of newly synthesized cholesterol trafficking to the plasma membrane.
Compared to cholesterol delivered to cells in micelles, plasma membrane
cholesterol was the much preferred substrate for acyl-CoA:cholesterol
acyltransferase. Micellar cholesterol displaced cholesterol from the plasma
membrane causing more of it to influx intracellularly for esterification
and secretion. We propose that plasma membrane cholesterol is the major
source for triacylglycerol-rich lipoprotein cholesterol in CaCo-2 cells.
Micellar cholesterol and newly synthesized cholesterol replenish the plasma
membrane cholesterol that is being used for the transport of lipids.
ARTICLES
Triacylglycerol-rich lipoprotein cholesterol is derived from the plasma membrane in CaCo-2 cells
Department of Internal Medicine, University of Iowa, Iowa City 52242, USA.
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