The recycling of apolipoprotein E and its amino-terminal 22 kDa fragment: Evidence for multiple redundant pathways

Monica H. Farkas, Karl H. Weisgraber, Virginia L. Shepherd, MacRae F. Linton, Sergio Fazio, Larry L. Swift

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

A portion of apolipoprotein E (apoE) internalized by hepatocytes is spared degradation and is recycled. To investigate the intracellular routing of recycling apoE, primary hepatocyte cultures from LDL receptor-deficient mice and mice deficient in receptor-associated protein [a model of depressed expression of LDL receptor-related protein (LRP)] were incubated with human VLDL containing 125I-labeled human recombinant apoE3. Approximately 30% of the internalized intact apoE was recycled after 4 h. The N-terminal 22 kDa fragment of apoE was also resecreted, demonstrating that this apoE domain contains sufficient sequence to recycle. The 22 kDa fragment has reduced affinity for lipoproteins, suggesting that apoE recycling is linked to the ability of apoE to bind directly to a recycling receptor. Finally, apoE was found to recycle equally well in the presence of brefeldin A, a drug that blocks transport from the endoplasmic reticulum and leads to collapse of the Golgi stacks. Our studies demonstrate that apoE recycling occurs 1) in the absence of the LDL receptor or under conditions of markedly reduced LRP expression; 2) when apoE lacks the carboxyl-terminal domain, which allows binding to the lipoprotein; and 3) in the absence of an intact Golgi apparatus. We conclude that apoE recycling occurs through multiple redundant pathways.

Original languageEnglish (US)
Pages (from-to)1546-1554
Number of pages9
JournalJournal of Lipid Research
Volume45
Issue number8
DOIs
Publication statusPublished - Aug 2004
Externally publishedYes

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Keywords

  • Brefeldin A
  • LDL receptor
  • LDL receptor-related protein
  • Low density lipoprotein
  • Receptor-associated protein
  • Very low density lipoprotein

ASJC Scopus subject areas

  • Endocrinology

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