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

J Biol Chem. 1994 Jan 28;269(4):2764-72.


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 beta-very low density lipoproteins (beta-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 beta-VLDL compared to either the apoE-Leiden-transfected or nontransfected cells. Fluorescently labeled beta-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 beta-VLDL and chylomicron remnants on their cell surfaces and microvilli, in contrast to non-transfected 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 beta-VLDL with apoE3-transfected cells but did not affect the limited association of beta-VLDL with apoE-Leiden-transfected or nontransfected cells. We established that the apoE3-enriched beta-VLDL were bound to cell surface heparan sulfate proteoglycans, as was the newly synthesized and secreted apoE3 (approximately 12% of the total secreted apoE3 was released by heparinase and suramin; 4% by heparin). In addition, reisolation of beta-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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apolipoprotein E3
  • Apolipoproteins E / isolation & purification
  • Apolipoproteins E / metabolism*
  • Biological Transport
  • Cell Line
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure
  • Heparan Sulfate Proteoglycans
  • Heparitin Sulfate / metabolism*
  • Humans
  • Kinetics
  • Lipoproteins, VLDL / metabolism*
  • Liver Neoplasms
  • Liver Neoplasms, Experimental
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Microscopy, Electron
  • Models, Biological
  • Models, Structural
  • Proteoglycans / metabolism*
  • Rabbits
  • Rats
  • Receptors, Lipoprotein / biosynthesis
  • Receptors, Lipoprotein / metabolism*
  • Transfection
  • Tumor Cells, Cultured


  • Apolipoprotein E3
  • Apolipoproteins E
  • Heparan Sulfate Proteoglycans
  • Lipoproteins, VLDL
  • Low Density Lipoprotein Receptor-Related Protein-1
  • Proteoglycans
  • Receptors, Lipoprotein
  • apolipoprotein E3 (Leidein)
  • Heparitin Sulfate