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

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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
Externally publishedYes

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Apolipoprotein E3
Heparan Sulfate Proteoglycans
Apolipoproteins E
Metabolism
Lipoproteins
Chylomicron Remnants
Heparin Lyase
Electron microscopy
Rats
Association reactions
Hepatocytes
Electron Microscopy
Suramin
VLDL Lipoproteins
Multivesicular Bodies
Liquid chromatography

ASJC Scopus subject areas

  • Biochemistry

Cite this

Secretion-capture role for apolipoprotein E in remnant lipoprotein metabolism involving cell surface heparan sulfate proteoglycans. / Ji, Zhong Sheng; Fazio, Sergio; Lee, Ya Li; Mahley, Robert W.

In: Journal of Biological Chemistry, Vol. 269, No. 4, 28.01.1994, p. 2764-2772.

Research output: Contribution to journalArticle

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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.",
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AU - Fazio, Sergio

AU - Lee, Ya Li

AU - Mahley, Robert W.

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N2 - 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.

AB - 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.

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