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The Journal of Lipid Research, Vol. 39, 845-860, April 1998
Copyright © 1998 by Lipid Research, Inc.
Chylomicron remnant uptake is regulated by the expression and function of heparan sulfate proteoglycan in hepatocytes
Bing-Ji Zenga,
Bok-Cheng Mortimera,
Ian J. Martinsa,
Ulrich Seydela, and
Trevor G. Redgravea
a Department of Physiology, The University of Western Australia, Nedlands, WA, 6907, Australia
Correspondence to:
Trevor G. Redgrave.
Chylomicron remnants transport cholesterol from the intestine, and are removed from the circulation principally by the liver. While hepatic receptors, including the low density lipoprotein (LDL) receptor account for endocytosis, heparan sulfate proteoglycans (HSPG) participate in the initial binding of remnants to liver cells. To explore the interactions between HSPG and endocytosis of remnants, in the present study the expression of HSPG was inhibited in HepG2 cells transfected by a synthetic antisense oligodeoxynucleotide SYN5. Immunofluorescent staining by a monoclonal anti-syndecan antibody showed significant reduction in the expression of syndecan in SYN5-treated cells compared with control cells. Remnant binding decreased by about 5070% in SYN5-transfected cells. Monoclonal antibodies to either heparan sulphate or the LDL receptor decreased binding by about 6065%. The glycosylation inhibitor ß-nitrophenyl-xylopyranoside inhibited remnant uptake by 25%, whereas 4-nitrophenyl-ß-D-galactopyranoside had no effect on remnant binding. Heparinase completely abolished binding at appropriate concentrations. Heparitinase was less effective than heparinase in inhibiting remnant binding. Suramin completely abolished the remnant binding. Poly-arginine, poly-lysine, and protamine all reduced remnant uptake by the cells, as did polybrene, a synthetic polycation, suggesting a role of cationanion interactions in remnant binding. Brefeldin A, colchicine, and monensin caused the fluorescence associated with remnants to persist within the cells, confirming that blockers of tubulovesicular processes and Golgi function inhibit the intracellular transport and degradation of the remnants.
Our results show that remnant binding to liver cells depends on the LDL receptor, on the expression of HSPG core proteins, and on the functionality of heparan sulfate in HSPG.Zeng, B-J., B-C. Mortimer, I. J. Martins, U. Seydel, and T. G. Redgrave. Chylomicron remnant uptake is regulated by the expression and function of heparan sulfate proteoglycan in hepatocytes. J. Lipid Res. 1998. 39: 845860.
Supplementary key words:
antisense, antibody, competitor, inhibitor, receptor, blocker, metabolism, lipoprotein, glycosaminoglycan, confocal microscope

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Copyright © 1998 by the American Society for Biochemistry and Molecular Biology.
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