Low density lipoprotein receptor-related protein mediates endocytosis of monoclonal antibodies in cultured cells and rabbit liver

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Abstract

Monoclonal antibodies that bound to the external domain of the rabbit low density lipoprotein receptor-related protein (LRP) were taken into rabbit fibroblasts by receptor-mediated endocytosis. Uptake occurred in fibroblasts from Watanabe-heritable hyperlipidemic rabbits, which lack low density lipoprotein receptors, as well as in normal rabbit fibroblasts. The fate of the internalized antibodies differed, depending on the domain of LRP that was recognized. LRP is synthesized as a single polypeptide chain that is cleaved to form a heterodimer of two noncovalently bound proteins, 1) a 515-kDa subunit that contains the binding domain, and 2) an 85-kDa subunit that contains the membrane-spanning region and cytoplasmic tail. A monoclonal antibody directed against the 515-kDa subunit (anti-LRP 515) rapidly dissociated from LRP at pH 5.2. After uptake by cells this antibody dissociated from the receptor and was degraded in lysosomes. A second antibody directed against the external portion of the 85-kDa subunit (anti-LRP 85) failed to dissociate at acid pH. After uptake by cells this antibody was not degraded, but instead was released from the cells in an acid-precipitable form. When administered intravenously to rabbits, both 125I-labeled antibodies were rapidly cleared from the circulation, 75-95% of the uptake occurring in the liver. The anti-LRP 515 antibody was degraded and acid-soluble products appeared in the plasma. No significant acid-soluble products appeared when the anti-LRP-85 antibody was infused. We conclude that LRP can carry out receptor-mediated endocytosis and that its ligand-binding domain, like the similar domain of the low density lipoprotein receptor, undergoes an acid-dependent conformational change that ejects ligands within the endosome. We also conclude that in the body this endocytotic function is expressed primarily in the liver. Both of these conclusions lend support to the hypothesis that LRP may function in humans and animals as a receptor for apolipoprotein E-enriched lipoproteins, such as chylomicron remnants.

Original languageEnglish (US)
Pages (from-to)21355-21362
Number of pages8
JournalJournal of Biological Chemistry
Volume265
Issue number34
StatePublished - Dec 5 1990

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LDL-Receptor Related Proteins
Lipoprotein Receptors
LDL Receptors
Endocytosis
Liver
Cultured Cells
Monoclonal Antibodies
Cells
Rabbits
Antibodies
Proteins
Acids
Fibroblasts
Chylomicron Remnants
Low Density Lipoprotein Receptor-Related Protein-1
Ligands
Endosomes
Lysosomes
Lipoproteins
Tail

ASJC Scopus subject areas

  • Biochemistry

Cite this

@article{fd6e64d541e94da68b4f088366cee162,
title = "Low density lipoprotein receptor-related protein mediates endocytosis of monoclonal antibodies in cultured cells and rabbit liver",
abstract = "Monoclonal antibodies that bound to the external domain of the rabbit low density lipoprotein receptor-related protein (LRP) were taken into rabbit fibroblasts by receptor-mediated endocytosis. Uptake occurred in fibroblasts from Watanabe-heritable hyperlipidemic rabbits, which lack low density lipoprotein receptors, as well as in normal rabbit fibroblasts. The fate of the internalized antibodies differed, depending on the domain of LRP that was recognized. LRP is synthesized as a single polypeptide chain that is cleaved to form a heterodimer of two noncovalently bound proteins, 1) a 515-kDa subunit that contains the binding domain, and 2) an 85-kDa subunit that contains the membrane-spanning region and cytoplasmic tail. A monoclonal antibody directed against the 515-kDa subunit (anti-LRP 515) rapidly dissociated from LRP at pH 5.2. After uptake by cells this antibody dissociated from the receptor and was degraded in lysosomes. A second antibody directed against the external portion of the 85-kDa subunit (anti-LRP 85) failed to dissociate at acid pH. After uptake by cells this antibody was not degraded, but instead was released from the cells in an acid-precipitable form. When administered intravenously to rabbits, both 125I-labeled antibodies were rapidly cleared from the circulation, 75-95{\%} of the uptake occurring in the liver. The anti-LRP 515 antibody was degraded and acid-soluble products appeared in the plasma. No significant acid-soluble products appeared when the anti-LRP-85 antibody was infused. We conclude that LRP can carry out receptor-mediated endocytosis and that its ligand-binding domain, like the similar domain of the low density lipoprotein receptor, undergoes an acid-dependent conformational change that ejects ligands within the endosome. We also conclude that in the body this endocytotic function is expressed primarily in the liver. Both of these conclusions lend support to the hypothesis that LRP may function in humans and animals as a receptor for apolipoprotein E-enriched lipoproteins, such as chylomicron remnants.",
author = "Joachim Herz and Kowal, {Robert C.} and Ho, {Y. K.} and Brown, {Michael S.} and Goldstein, {Joseph L.}",
year = "1990",
month = "12",
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language = "English (US)",
volume = "265",
pages = "21355--21362",
journal = "Journal of Biological Chemistry",
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T1 - Low density lipoprotein receptor-related protein mediates endocytosis of monoclonal antibodies in cultured cells and rabbit liver

AU - Herz, Joachim

AU - Kowal, Robert C.

AU - Ho, Y. K.

AU - Brown, Michael S.

AU - Goldstein, Joseph L.

PY - 1990/12/5

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N2 - Monoclonal antibodies that bound to the external domain of the rabbit low density lipoprotein receptor-related protein (LRP) were taken into rabbit fibroblasts by receptor-mediated endocytosis. Uptake occurred in fibroblasts from Watanabe-heritable hyperlipidemic rabbits, which lack low density lipoprotein receptors, as well as in normal rabbit fibroblasts. The fate of the internalized antibodies differed, depending on the domain of LRP that was recognized. LRP is synthesized as a single polypeptide chain that is cleaved to form a heterodimer of two noncovalently bound proteins, 1) a 515-kDa subunit that contains the binding domain, and 2) an 85-kDa subunit that contains the membrane-spanning region and cytoplasmic tail. A monoclonal antibody directed against the 515-kDa subunit (anti-LRP 515) rapidly dissociated from LRP at pH 5.2. After uptake by cells this antibody dissociated from the receptor and was degraded in lysosomes. A second antibody directed against the external portion of the 85-kDa subunit (anti-LRP 85) failed to dissociate at acid pH. After uptake by cells this antibody was not degraded, but instead was released from the cells in an acid-precipitable form. When administered intravenously to rabbits, both 125I-labeled antibodies were rapidly cleared from the circulation, 75-95% of the uptake occurring in the liver. The anti-LRP 515 antibody was degraded and acid-soluble products appeared in the plasma. No significant acid-soluble products appeared when the anti-LRP-85 antibody was infused. We conclude that LRP can carry out receptor-mediated endocytosis and that its ligand-binding domain, like the similar domain of the low density lipoprotein receptor, undergoes an acid-dependent conformational change that ejects ligands within the endosome. We also conclude that in the body this endocytotic function is expressed primarily in the liver. Both of these conclusions lend support to the hypothesis that LRP may function in humans and animals as a receptor for apolipoprotein E-enriched lipoproteins, such as chylomicron remnants.

AB - Monoclonal antibodies that bound to the external domain of the rabbit low density lipoprotein receptor-related protein (LRP) were taken into rabbit fibroblasts by receptor-mediated endocytosis. Uptake occurred in fibroblasts from Watanabe-heritable hyperlipidemic rabbits, which lack low density lipoprotein receptors, as well as in normal rabbit fibroblasts. The fate of the internalized antibodies differed, depending on the domain of LRP that was recognized. LRP is synthesized as a single polypeptide chain that is cleaved to form a heterodimer of two noncovalently bound proteins, 1) a 515-kDa subunit that contains the binding domain, and 2) an 85-kDa subunit that contains the membrane-spanning region and cytoplasmic tail. A monoclonal antibody directed against the 515-kDa subunit (anti-LRP 515) rapidly dissociated from LRP at pH 5.2. After uptake by cells this antibody dissociated from the receptor and was degraded in lysosomes. A second antibody directed against the external portion of the 85-kDa subunit (anti-LRP 85) failed to dissociate at acid pH. After uptake by cells this antibody was not degraded, but instead was released from the cells in an acid-precipitable form. When administered intravenously to rabbits, both 125I-labeled antibodies were rapidly cleared from the circulation, 75-95% of the uptake occurring in the liver. The anti-LRP 515 antibody was degraded and acid-soluble products appeared in the plasma. No significant acid-soluble products appeared when the anti-LRP-85 antibody was infused. We conclude that LRP can carry out receptor-mediated endocytosis and that its ligand-binding domain, like the similar domain of the low density lipoprotein receptor, undergoes an acid-dependent conformational change that ejects ligands within the endosome. We also conclude that in the body this endocytotic function is expressed primarily in the liver. Both of these conclusions lend support to the hypothesis that LRP may function in humans and animals as a receptor for apolipoprotein E-enriched lipoproteins, such as chylomicron remnants.

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