Title
Apolipoprotein E is resistant to intracellular degradation in vitro and in vivo. Evidence for retroendocytosis
Author
Gaubius instituut TNO
Rensen, P.C.N.
Jong, M.C.
van Vark, L.C.
van der Boom, H.
Hendriks, W.L.
van Berkel, T.J.C.
Biessen, E.A.L.
Havekes, L.M.
Publication year
2000
Abstract
Apolipoprotein E (apoE) is an important determinant for the uptake of triglyceride-rich lipoproteins and emulsions by the liver, but the intracellular pathway of apoE following particle internalization is poorly defined. In the present study, we investigated whether retroendocytosis is a unique feature of apoE as compared with apoB by studying the intracellular fate of very low density lipoprotein-sized apoE-containing triglyceride-rich emulsion particles and LDL after LDLr-mediated uptake. Incubation of HepG2 cells with [3H]cholesteryl oleate-labeled particles at 37 °C led to a rapid release of [3H]cholesterol within 30 min for both LDL and emulsion particles. In contrast, emulsion-derived 125I-apoE was more resistant to degradation (≥120 min) than LDL-derived 125I-apoB (30 min). Incubation at 18 °C, which allows endosomal uptake but prevents lysosomal degradation, with subsequent incubation at 37 °C resulted in a time-dependent release of intact apoE from the cells (up to 14% of the endocytosed apoE at 4 h). The release of apoE was accelerated by the presence of protein-free emulsion (20%) or high density lipoprotein (26%). Retroendocytosis of intact particles could be excluded since little intact [3H]cholesteryl oleate was released (
Subject
Animals
Apolipoproteins B
Apolipoproteins E
Biological Transport
Blood
Cells, Cultured
Cholesterol Esters
Emulsions
Endocytosis
Lipoproteins
Lipoproteins, LDL
Lipoproteins, VLDL
Liver
Lysosomes
Male
Mice
Mice, Inbred C57BL
Protein Processing, Post-Translational
Animalia
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DOI
https://doi.org/10.1074/jbc.275.12.8564
TNO identifier
235497
ISSN
0021-9258
Source
Journal of Biological Chemistry, 275 (275), 8564-8571
Document type
article