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J. Biol. Chem., Vol. 275, Issue 47, 36852-36861, November 24, 2000
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From the Although sterol carrier protein-2 (SCP-2)
participates in the uptake and intracellular trafficking of
cholesterol, its effect on "reverse cholesterol transport" has not
been explored. As shown herein, SCP-2 expression inhibited high
density lipoprotein (HDL)-mediated efflux of
[3H]cholesterol and fluorescent
22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3b-ol (NBD-cholesterol) up to 61 and 157%, respectively. Confocal
microscopy of living cells allowed kinetic analysis of two
intracellular pools of HDL-mediated NBD-cholesterol efflux: the highly
fluorescent lipid droplet pool and the less fluorescent pool outside
the lipid droplets, designated the cytoplasmic compartment. Both the
whole cell and the cytoplasmic compartment exhibited two similar
kinetic pools, the half-times of which were consistent with protein
(tb1/2 near 1 min) and vesicular
(td1/2 = 10-20 min) mediated sterol transfer. Although SCP-2 expression did not alter cytoplasmic sterol
pool sizes, the rapid tb1/2 decreased
36%, while the slower td1/2 increased
113%. Lipid droplets also exhibited two kinetic pools of
NBD-cholesterol efflux but with half-times over 200% shorter than
those of the cytoplasmic compartment. The lipid droplet slower
effluxing pool size and td1/2 were
increased 48% and 115%, respectively, in SCP-2-expressing cells.
Concomitantly, the level of the lipid droplet-specific adipose
differentiation-related protein decreased 70%. Overall,
HDL-mediated sterol efflux from L-cell fibroblasts reflected that of
the cytoplasmic rather than lipid droplet compartment. SCP-2
differentially modulated sterol efflux from the two cytoplasmic pools.
However, net efflux was determined primarily by inhibition of the
slowly effluxing pool rather than by acceleration of the rapid
protein-mediated pool. Finally, SCP-2 expression also inhibited sterol
efflux from lipid droplets, an effect related to decreased adipose
differentiation-related protein, a lipid droplet surface protein that
binds cholesterol with high affinity.
Sterol Carrier Protein-2 Alters High Density
Lipoprotein-mediated Cholesterol Efflux*
,
,
,
¶
Department of Physiology and Pharmacology
and the § Department of Pathobiology, Texas A & M
University, College Station, Texas 77843-4466
*
This work was supported in part by Grant GM31651 from the
National Institutes of Health.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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