Secretion-capture role for apolipoprotein E in remnant lipoprotein metabolism involving cell surface heparan sulfate proteoglycans

Zhong Sheng Ji, Sergio Fazio, Ya Li Lee, Robert W. Mahley

    Research output: Contribution to journalArticle

    180 Scopus citations

    Abstract

    To determine the impact of enhanced apolipoprotein (apo) E secretion on the mechanism of remnant lipoprotein uptake, rat hepatoma cells (McA-RH7777) were stably transfected with normal human apoE3 or receptor binding-defective apoE-Leiden. After a 2-h incubation, the human apoE secreted from the transfected hepatocytes was 10-12 times greater than the endogenous rat apoE. The apoE3-transfected cells bound and internalized rabbit β-very low density lipoproteins (β-VLDL) to a much greater degree than did apoE-Leiden- transfected cells and nontransfected cells. The apoE3-secreting cells displayed a 2-3.5-fold enhancement of cell-associated β-VLDL compared to either the apoE-Leiden-transfected or nontransfected cells. Fluorescently labeled β-VLDL were observed to concentrate within intracellular granules of the apoE3-transfected cells, presumably within endosomes and lysosomes. Furthermore, electron microscopy revealed that the apoE3-secreting cells displayed abundant β-VLDL and chylomicron remnants on their cell surfaces and microvilli, in contrast to nontransfected or apoE-Leiden-secreting cells. Electron microscopy also revealed an abundance of chylomicron remnants within intracellular vesicles and multivesicular bodies of apoE3-transfected hepatocytes. Heparinase treatment (3 units/ml) completely abolished the increased association of β-VLDL with apoE3-transfected cells but did not affect the limited association of β-VLDL with apoE-Leiden-transfected or nontransfected cells. We established that the apoE3-enriched β-VLDL were bound to cell surface heparan sulfate proteoglycans, as was the newly synthesized and secreted apoE3 (~12% of the total secreted apoE3 was released by heparinase and suramin; 4% by heparin). In addition, reisolation of β-VLDL by fast performance liquid chromatography after their incubation with exogenous apoE3, with medium from apoE3-secreting cells, or with the apoE3-secreting cells themselves revealed that the particles were enriched in apoE3 and displayed enhanced binding. These results suggest a secretion- capture role for apoE and indicate an important role for heparan sulfate proteoglycans on the cell surface for remnant lipoprotein metabolism.

    Original languageEnglish (US)
    Pages (from-to)2764-2772
    Number of pages9
    JournalJournal of Biological Chemistry
    Volume269
    Issue number4
    StatePublished - Jan 28 1994

    ASJC Scopus subject areas

    • Biochemistry
    • Molecular Biology
    • Cell Biology

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