Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.1.1.34 (lipoprotein lipase)
7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Various aspects of lipoprotein lipase (LPL) metabolism, including cell surface binding, degradation, and enzymatic activity, were compared between Chinese hamster ovary (CHO) cells and two distinct proteoglycan-deficient CHO cell lines. The contribution of low density lipoprotein receptor-related protein in binding LPL was also analyzed by the use of a 39-kDa receptor-associated protein expressed as a glutathione S-transferase fusion protein (GST-RAP). Equilibrium binding data with 125I-LPL revealed the presence of a class of high affinity binding sites with a KD of 7.8 nM in CHO cells, whereas no high affinity binding was observed for proteoglycan-deficient cells. The high affinity binding of LPL in CHO cells appeared to be concentrated in cell surface projections and was not effectively inhibited by GST-RAP. Moreover, degradation of endogenous and exogenous LPL was significantly greater in control CHO cells than in proteoglycan-deficient cells. Degradation of LPL in CHO cells was not affected by GST-RAP, suggesting that proteoglycans and not low density lipoprotein receptor-related protein are responsible for the majority of binding and degradation of LPL in these cells. Our data also show that proteoglycan binding is not essential for the assembly of active LPL homodimers, although proteoglycan binding controls the distribution of LPL activity. Furthermore, LPL produced by CHO cells was more stable than LPL produced by proteoglycan-deficient cells.
...
PMID:Heparan sulfate proteoglycans are primarily responsible for the maintenance of enzyme activity, binding, and degradation of lipoprotein lipase in Chinese hamster ovary cells. 759 70

Cell surface proteoglycans participate in molecular events that regulate cell adhesion, migration, and proliferation. To investigate the organization of these molecules at the cell surface, the distribution of two well-known proteoglycan ligands has been studied. These ligands, lipoprotein lipase and basic fibroblast growth factor, showed a characteristic binding pattern consisting of highly organized parallel arrays that crossed the upper surface of human skin fibroblasts. The proteoglycan nature of the binding sites was evident from their susceptibility to heparinases, and from ligand displacement by heparin. Parallel localization of the ligands and actin, and treatment of the cells with cytochalasin, showed that the binding proteoglycans are organized by the actin cytoskeleton. The ligands induced a different behaviour of the binding sites on incubation of the cells at 37 degrees C. Lipoprotein lipase produced a movement of the binding proteoglycans along the actin filaments towards the cell center. In contrast, after binding of basic fibroblast growth factor the binding proteoglycans remained spread over the cell surface and actin depolymerization was induced. Since an increasing number of ligands appear to depend on proteoglycans for their interactions with their high affinity receptors, distribution and movement of proteoglycans at the cell surface that is organized by the actin cytoskeleton could direct and enhance the encounters between the ligands and their specific receptors.
...
PMID:Actin cytoskeleton of fibroblasts organizes surface proteoglycans that bind basic fibroblast growth factor and lipoprotein lipase. 760 10

Hepatic lipase (HL) and lipoprotein lipase (LpL) are structurally related lipolytic enzymes that have distinct functions in lipoprotein catabolism. In addition to its lipolytic activity, LpL binds to very low density lipoproteins and promotes their interaction with the low density lipoprotein receptor-related protein (LRP) (Chappell, D. A., Fry, G. L., Waknitz, M. A., Muhonen, L. E., Pladet M. W., Iverius, P. H., and Strickland, D. K. (1993) J. Biol. Chem. 268, 14168-14175). In vitro binding assays revealed that HL also binds to purified LRP with a KD of 52 nM. Its binding to LRP is inhibited by the 39-kDa receptor-associated protein (RAP), a known LRP antagonist, and by heparin. 125I-Labeled HL is rapidly internalized and degraded by HepG2 cell lines, and approximately 70% of the cellular internalization and degradation is blocked by either exogenously added RAP or anti-LRP IgG. Mouse fibroblasts that lack LRP display a greatly diminished capacity to internalize and degrade HL when compared to control fibroblasts. These data indicate that LRP-mediated cellular uptake of HL accounts for a substantial portion of the internalization of this molecule. Proteoglycans have been shown to participate in the clearance of LpL, and consequently a role for proteoglycans in HL clearance pathway was also investigated. Chinese hamster ovary cell lines that are deficient in proteoglycan biosynthesis were unable to internalize or degrade 125I-HL despite the fact that these cells express LRP. Thus, the initial binding of HL to cell surface proteoglycans is an obligatory step for the delivery of the enzyme to LRP for endocytosis. A small, but significant, amount of 125I-HL was internalized in LRP deficient cells indicating that an LRP-independent pathway for HL internalization does exist. This pathway could involve cell surface proteoglycans, the LDL receptor, or some other unidentified surface protein.
...
PMID:The cellular internalization and degradation of hepatic lipase is mediated by low density lipoprotein receptor-related protein and requires cell surface proteoglycans. 772 52

It has previously been shown that lipoprotein lipase can mediate uptake of remnant lipoprotein particles via binding to the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP). Binding of lipoprotein lipase, and of triglyceride-rich lipoproteins associated with the lipase, to LRP depends on an intact carboxyl-terminal folding domain of the lipase (Nykjaer, A., Bengtsson-Olivecrona, G., Lookene, A., Moestrup, S. K., Petersen, C. M., Weber, W., Beisiegel, W., and Gliemann, J. (1993) J. Biol. Chem. 268, 15048-15055). Here we show that the site for binding to the receptor is within residues 380-425 of the bovine and residues 378-423 of the human lipoprotein lipase. We demonstrate that a carboxyl-terminal fragment of human lipoprotein lipase (residues 378-448), expressed as fusion protein in Escherichia coli, binds to purified and cellular LRP but not to lipoproteins. Binding of the fragment to purified LRP was blocked by heparin. In addition, the fragment inhibited the binding of lipase and the lipase-mediated binding of lipoproteins to the purified receptor. The fragment exhibited reduced binding to proteoglycan-deficient cells. Moreover, the fragment inhibited the uptake of lipoproteins in cells mediated by the lipase via binding to heparan sulfate proteoglycans and LRP. We conclude that the fragment contains the site for binding to LRP and a candidate site for interaction with heparan sulfate proteoglycans, whereas binding to lipoproteins is inefficient. The fragment can therefore inhibit the lipase-mediated lipoprotein uptake, a process that may promote the development of atherosclerosis when occurring in cells of the arterial wall.
...
PMID:A carboxyl-terminal fragment of lipoprotein lipase binds to the low density lipoprotein receptor-related protein and inhibits lipase-mediated uptake of lipoprotein in cells. 798 48

The association of plasma low density lipoproteins (LDL) with arterial proteoglycans (PG) is of key importance in LDL retention and modification in the artery wall. Lipoprotein lipase (LpL), the rate-limiting enzyme for hydrolysis of lipoprotein triglyceride, is known to bind both LDL and arterial PG. In the presence of LpL, cellular internalization and degradation of LDL is enhanced by a pathway initiated by interaction of LDL with a cell surface heparan sulfate proteoglycan. To determine whether LpL enhances the binding of LDL to arterial chondroitin sulfate (CS)PG and dermatan sulfate (DS)PG, the major extracellular PG of the artery wall, a microtiter plate assay was used to study LpL-PG-LDL interactions. Binding of LDL to both CSPG and DSPG was increased in the presence of LpL but differential effects were seen for the two PG. LpL enhanced the binding of LDL to CSPG a maximum of 20% and to DSPG a maximum of 40%. Heparin displacement of PG binding suggested a greater binding strength for DSPG-LpL-LDL with 0.25 micrograms heparin required to displace 50% of DSPG compared to 0.01 micrograms to displace 50% of CSPG. The greater enhancement of DSPG-LDL interaction by LpL is of particular interest since increases in DSPG correlate with the accumulation of aortic cholesterol. These data suggest that lipoprotein lipase may enhance the interaction of plasma low density lipoprotein with arterial chondroitin sulfate proteoglycan and dermatan sulfate proteoglycan and thus facilitate low density lipoprotein retention in the artery wall.
...
PMID:Lipoprotein lipase enhances the interaction of low density lipoproteins with artery-derived extracellular matrix proteoglycans. 837 Oct 63

It has been suggested previously that lipoprotein lipase may act as a ligand to enhance binding and uptake of lipoprotein particles. In the present study we have examined the capacity of bovine milk lipoprotein lipase to induce intracellular accumulation of triglyceride and cholesterol ester by VLDL (Sr 60-400) isolated from Type IV hypertriglyceridemic subject (HTg-VLDL) in HepG2 cells, independent of its lipolytic activity. We have also attempted to elucidate the cellular receptor mechanisms responsible for these effects. HTg-VLDL-mediated increases in intracellular triglyceride and cholesterol ester were dependent on the presence of an active lipase. Bovine milk lipoprotein lipase (LPL) increases triglyceride mass by 301% +/- 28% (P < 0.0005) and cholesterol ester mass by 176% +/- 12% (P < 0.0005). These HTg-VLDL-mediated increases in intracellular triglyceride and cholesterol ester did not occur when heat-inactivated lipase was used. Rhizopus lipase could replace LPL and cause equivalent increases in intracellular triglyceride and cholesterol ester (472% +/- 61%(P < 0.005) and 202% +/- 25% (P < 0.025) respectively vs. control). HTg-VLDL treated with LPL and reisolated also caused equivalent increases (274% +/- 18%(P < 0.01) and 177% +/- 12% (P < 0.005) for triglyceride and cholesterol ester). LDL also caused increases in intracellular cholesterol ester (189% +/- 20%(P < 0.005)), although three times more LDL cholesterol had to be added to achieve the same effect. These LDL-induced increases were effectively blocked by monoclonal antibodies directed against the B,E receptor binding domains of apo B (-97% +/- 13% (P < 0.0005) with anti-apo B 5E11 and -68% +/- 13% (P < 0.05) for anti-apo B B1B3) or by anti-B,E receptor antibodies (-77% +/- 7% (P < 0.01) antibody C7). These same antibodies had little effect on the HTg-VLDL+LPL-induced increases in cholesterol ester (+21%, +15% and -22% for 5E11, B1B3 and C7, respectively). Monoclonal anti-apo E antibodies also had no effect on LDL-mediated increases in intracellular cholesterol ester, but had a small and significant effect on VLDL-mediated increases in cholesterol ester. However, heparin, which interferes with cell surface proteoglycan interaction, was very effective at blocking HTg-VLDL-mediated increases in cholesterol ester in the presence of LPL (-86% +/- 8% P < 0.0005). Heparin was also effective in the presence of Rhizopus lipase (-79%) or lipolyzed re-isolated HTg-VLDL (-95%). These results suggest that lipoprotein lipase may enhance the uptake process beyond its role in lipolytic remodelling but does not appear to be an absolute requirement. In contrast, heparin had no effect on LDL-mediated cholesterol ester accumulation. Lactoferrin, which inhibits interaction with the low density lipoprotein receptor-related protein (LRP), was also very effective at inhibiting HTg-VLDL increases in intracellular cholesterol ester (-95% +/- 6%, P < 0.01). However, there was no effect of either heparin or lactoferrin on HTg-VLDL-mediated triglyceride accumulation. Thus cell surface heparin sulphate may facilitate intracellular lipid acquisition by providing a stabilizing bridge with the lipoproteins and enhance uptake through receptor-mediated processes such as LRP.
...
PMID:Inhibition of lipoprotein lipase induced cholesterol ester accumulation in human hepatoma HepG2 cells. 864 51

Previous studies (Sivaram, P., Choi, S. Y., Curtiss, L. K., and Goldberg, I. J.(1994) J. Biol. Chem. 269, 9409-9412) from this laboratory showed that the NH2-terminal region of apoB (NTAB) has binding domains for lipoprotein lipase (LPL). LPL binding to endothelial cells, we hypothesize, involves interaction both with heparan sulfate proteoglycans and with a protein that has homology to NTAB. To test whether cell-surface NTAB would increase the amount and affinity of LPL binding to cells, we produced stable Chinese hamster ovary cell lines that have NTAB anchored to the cell surface. A cDNA encoding the amino-terminal 17% of apoB (apoB17) was fused to a cDNA coding for the last 37 amino acids of decay-accelerating factor (DAF), which contains the signal for glycosylphosphatidylinositol anchor attachment. The fused construct was sequence-verified and cloned into expression vector pCMV5. The pCMV5-apoB17-DAF plasmid was cotransfected with a neomycin resistance gene into wild-type (WT) cells and mutant heparan sulfate proteoglycan-deficient Chinese hamster ovary cells (745 cells), and stable cell lines were established. Expression of apoB17 on the cell surface was confirmed by the release of apoB17 by phosphatidylinositol-specific phospholipase C. LPL binding to WT and apoB17-DAF-transfected cells was determined. Using 0.8-6 microg of LPL, 1.3-2.2-fold more LPL associated with apoB17-DAF WT cells compared with WT cells; apoB17-DAF also increased LPL binding to 745 cells. After heparinase treatment, LPL binding to apoB17-DAF cells was still greater than to treated WT cells. This increased binding to apoB17-DAF cells was almost abolished by treatment of cells with phosphatidylinositol-specific phospholipase C or anti-apoB monoclonal antibody. LPL dissociated from WT cells with k-1 = 2.55 x 10(-2) min-1, whereas LPL dissociated more slowly from apoB17-DAF-containing cells with k-1 = 1.08 x 10(-2) min-1. Furthermore, almost 95% of the LPL on WT cells was dissociated by 1 M NaCl, while only 65% of the LPL dissociated from apoB17-DAF cells at the same high salt concentration. Similarly, in high salt, more LPL remained associated with apoB17-DAF cells than with nontransfected 745 cells. These data show that NTAB on cell surfaces can function as a LPL-binding protein. Moreover, they demonstrate that LPL association with cells can be increased by simultaneously binding to both proteoglycan and non-proteoglycan binding sites.
...
PMID:Cell-surface expression of an amino-terminal fragment of apolipoprotein B increases lipoprotein lipase binding to cells. 870 44

The uptake of triglyceride-rich lipoproteins has been described as being mediated by apolipoprotein E and lipoprotein lipase (LpL). Proteoglycans, the LDL-receptor, and the LDL receptor-related protein (LRP) are the cellular acceptors. In addition to LpL, hepatic lipase (HL) has been shown to bind to LRP. In this study, the role of HL in lipoprotein uptake was investigated. Human chylomicrons and rabbit beta-VLDL were used as ligands for human hepatoma cells, primary human hepalocytes, normal and proteoglycan-deficient Chinese hamster ovary (CHO) cells, and normal and LDL receptor-deficient human fibroblasts. We show that HL induces stimulation of the uptake of chylomicrons and beta-VLDL into the different cell lines. HL is known to bind to heparan sulfate, and experiments on normal and proteoglycan-deficient CHO cells showed that cell surface proteoglycans are essential for HL-mediated uptake of lipoproteins. To exclude LDL receptor-mediated uptake. we performed experiments on LDL receptor-deficient fibroblasts that demonstrated that the LDL receptor was not important for the HL-mediated uptake of lipoproteins. Crosslinking experiments confirmed the binding of HL to LRP on the cell surface. To identify the region of HL involved in the interaction with LRP, we used a C-terminal fragment of LpL, known to inhibit LpL-mediated uptake. HL-mediated lipoprotein uptake was suppressed by this fragment. Our experiments indicate that HL, like LpL, can mediate the uptake of lipoproteins into cells, most probably via a C-terminal binding site. The uptake, initiated by proteoglycan binding, is mediated by LRP.
...
PMID:Hepatic lipase mediates the uptake of chylomicrons and beta-VLDL into cells via the LDL receptor-related protein (LRP). 872 46

The possibility that diabetes reduces functional, heparin-releasable lipoprotein lipase (HR-LPL) activity on the coronary vasculature of perfused hearts by altering endothelial binding sites for the enzyme was examined by measuring the binding and subsequent heparin-induced release of exogenous lipoprotein lipase purified from bovine milk (mLPL). Rat hearts were first perfused with heparin (5 U/mL) for 5 min to displace endogenous HR-LPL into the perfusate. The subsequent perfusion of control hearts with 0.05-2 micrograms/mL mLPL resulted in a progressive increase in bound exogenous enzyme that could be released by a second heparin perfusion. Induction of an acute, insulin-deficient model of diabetes (100 mg/kg streptozotocin 4-5 days prior to heart perfusions) reduced endogenous HR-LPL activity, but the binding and heparin-induced release of mLPL (0.5 microgram/mL) were the same as measured in control hearts. Therefore, diabetes does not alter low-affinity, high-capacity proteoglycan binding sites for mLPL on the endothelium of perfused hearts.
...
PMID:Endothelial binding sites for lipoprotein lipase are not diminished in perfused hearts from diabetic rats. 902 78

An enzyme- linked immunosorbent assay (ELISA) for heparan sulfate proteoglycan (HSPG) was developed based on the high affinity binding profile of HSPG to lipoprotein lipase (LPL). LPL was shown to bind to precoated HSPG in dose dependent manner and was determined spectrophotometrically using specific anti- LPL antibody. This ELISA allowed to evaluate HSPG produced by PC12 cell with clear linearity at range of 10 - 500 ng/ml. Soluble chondroitin sulfate proteoglycan (CSPG) from rat brain, which was not detectable by this method, did not exhibit any inhibitory effects on affinity binding of HSPG to LPL, even if 8 times higher concentrations of CSPG to HSPG was added. The sensitivity of this ELISA was about 100 times higher than that of conventional carbazole reaction method. These findings indicated its potential usefulness of this method for measuring small amounts of HSPG capable of binding to LPL and for studying biological implications of HSPG - LPL interaction.
...
PMID:An enzyme- linked immunosorbent assay for heparan sulfate proteoglycans. 915 Apr 21


<< Previous 1 2 3 4 Next >>

---