Low density lipoprotein receptor internalizes low density and very low density lipoproteins that are bound to heparan sulfate proteoglycans via lipoprotein lipase

Low density lipoprotein receptor internalizes low density and very low density lipoproteins that are bound to heparan sulfate proteoglycans via lipoprotein lipase

Gaubius Instituut TNO
Mulder, M.
Lombardi, P.
Jansen, H.
van Berkel, T.J.C.
Frants, R.R.
Havekes, L.M.

1993

It has previously been shown that lipoprotein lipase (LPL) enhances the binding of low density lipoproteins (LDL) and very low density lipoproteins (VLDL) to HepG2 cells and fibroblasts, up to 80-fold. This increase in binding is LDL receptor-independent and is due to a bridging of LPL between extracellular heparan sulfate proteoglycans (HSPG) and the lipoproteins. In the present paper, we show that preincubation of the cells with LPL, followed by washing prior to the binding experiment, increased binding to the same extent as occurs when the binding is performed in the presence of LPL. This indicates that the formation of a complex of LPL with the lipoproteins is not a prerequisite of binding. Binding curves and Scatchard analyses reveal that both the number of binding sites and the affinity of the binding are increased 20-30-fold by the addition of 3.4 ug/ml LPL. The addition of LPL also resulted in an enhanced uptake and subsequent lysosomal degradation of both LDL and VLDL when compared with binding, although to a lesser extent (up to 25-fold when measured after 5 h at 37 °C). Strikingly, enhanced uptake did not occur in LDL receptor-negative fibroblasts. In addition, down- regulation of the LDL receptor activity by preincubation of the cells for 48 h with either LDL or beta-VLDL resulted in a parallel decrease in the uptake of LPL-mediated HSPG-bound LDL, whereas the LPL-mediated binding itself was not diminished. These observations indicate that the uptake of LPL-mediated HSPG- bound LDL and VLDL mainly proceeds via the LDL receptor. Binding of labeled LDL to the cells at 4 °C for 2 h followed by a chase period at 37 °C revealed that in absolute terms, the initial rate of internalization of HSPG- bound LDL is comparable with that of LDL receptor-bound LDL (0.58 and 0.44 ng/min/mg of cell protein, respectively). We conclude that in LDL receptor- positive cells, the LPL-mediated binding of LDL and VLDL to HSPG is followed by internalization of the lipoproteins mainly through the rapid process of the classical LDL receptor recycling system, whereas only a minor portion is internalized via the much slower process of HSPG uptake. Chemicals/CAS: lipoprotein lipase, 83137-80-8, 9004-02-8; Heparan Sulfate Proteoglycan; Heparin Lyase, EC 4.2.2.7; Heparitin Sulfate, 9050-30-0; Lipoprotein Lipase, EC 3.1.1.34; Lipoproteins, LDL; Lipoproteins, VLDL; Polysaccharide-Lyases, EC 4.2.2.; Proteoglycans; Receptors, LDL

Animal
Biological Transport
Carcinoma, Hepatocellular
Cattle
Female
Fibroblasts
Heparan Sulfate Proteoglycan
Heparin Lyase
Heparitin Sulfate
Human
Kinetics
Lipoprotein Lipase
Lipoproteins, LDL
Lipoproteins, VLDL
Liver Neoplasms
Milk
Models, Biological
Polysaccharide-Lyases
Protein Binding
Proteoglycans
Receptors, LDL
Support, Non-U.S. Gov't
Tumor Cells, Cultured

http://resolver.tudelft.nl/uuid:8d9647dd-64ab-4226-9dfe-443e92cb3e69

232126

0021-9258

Journal of Biological Chemistry, 268 (268), 9369-9375

article