Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.2.2.7 (heparinase)
 1,270 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lipoprotein lipase (LPL) and apolipoprotein E (apo E) independently enhance binding and uptake of lipoproteins to cells. A coordinate effect of LPL and apo E has been previously described in human hepatozytes where simultaneous addition of both proteins resulted in an additive increase of chylomicron binding and uptake. The role of lipoprotein receptors and proteoglycans in this coordinate effect was now analysed using various cell types and heparinase treatment. To investigate a pathophysiological relevance, the effect of LPL and normal apo E-3 was compared to LPL and four apo E variants, associated with type III hyperlipoproteinemia (HLP). Apo E-3 and LPL increased the binding and uptake of chylomicrons and beta-very low density lipoproteins (VLDL) in an additive way in all cell types analysed, except proteoglycan deficient Chinese hamster ovary (CHO)-cells. Heparinase treatment almost completely abolished the effect of apo E and LPL. Addition of LPL to the apo E variants resulted in significant compensation of their defective function in mediating beta-VLDL binding to low density lipoprotein (LDL)-receptor defective fibroblasts. These findings indicate that the coordinate effect of apo E and LPL is mediated by proteoglycans and lipoprotein receptors, independent of the LDL receptor. LPL may compensate for the defective function of apo E variants by enhancing lipoprotein binding to these receptors. Defects in this mechanism may explain how mutations in the LPL molecule contribute to the manifestation of type III HLP in addition to the presence of a defective apo E.
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PMID:Lipoprotein lipase compensates for the defective function of apo E variants in vitro by interacting with proteoglycans and lipoprotein receptors. 1042 96

Ovarian androgen production is rate limiting for follicular maturation and can induce follicular atresia. Thus, it is important to define the actions of the intraovarian agents, such as apolipoprotein (apo) E, that modulate theca cell androgen production. Theca cell androgen production is stimulated at low concentrations and inhibited at higher concentrations of native apo E. The apo E peptide, acetyl-Y(LRKLRKRLLRDADDL)(2)C or acetyl-Y(141-155)(2)C, has low density lipoprotein (LDL) receptor and LDL receptor-related protein-binding activity, and it mimics the activity of native apo E in the theca-interstitial cell system. To define the role of members of the LDL receptor superfamily in the apo E peptide-mediated responses, we found that receptor-associated protein prevented the stimulation without altering the inhibition of androstenedione production. The apo E peptide (129-162), which has no LDL receptor-binding activity, did not stimulate androstenedione production. The apo E peptide acetyl-Y(141-155)(2)C did not stimulate androstenedione production when cell surface heparan sulfate proteoglycans were degraded with heparinase. The apo E peptide acetyl-Y(141-155)(2)C bound to heparin, a property of LDL receptor ligands, and in this complex the peptide had no effect on androstenedione production. These observations support the conclusion that apo E-mediated stimulation, but not inhibition, of ovarian theca cell androstenedione production was mediated by members of the LDL receptor superfamily.
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PMID:Apolipoprotein E peptide stimulation of rat ovarian theca cell androgen synthesis is mediated by members of the low density lipoprotein receptor superfamily. 1045 43

Human apolipoprotein E (apo E) consists of two distinct domains, the lipid-associating domain (residues 192-299) and the globular domain (residues 1-191) which contains the LDL receptor (LDLR) binding site (residues 129-169). To test the hypothesis that an arginine-rich apo E receptor binding domain (residues 141-150) is sufficient to enhance low-density lipoprotein (LDL) uptake and clearance when covalently linked to a class A amphipathic helix, a peptide in which the receptor binding domain of human apo E, LRKLRKRLLR (hApoE[141-150]), is linked to 18A, a well-characterized high-affinity lipid-associating peptide (DWLKAFYDKVAEKLKEAF), we synthesized the peptide hApoE[141-150]-18A (hE18A) and its end-protected analogue, Ac-hE18A-NH(2). The importance of positively charged residues and the role of the hydrophobic residues in the receptor binding domain were also studied using four analogues. Ac-LRRLRRRLLR-18A-NH(2) [Ac-hE(R)18A-NH(2)] and Ac-LRKMRKRLMR-18A-NH(2) (Ac-mE18A-NH(2)) contained an extended hydrophobic face, including the receptor binding region. Control peptides, Ac-LRLLRKLKRR-18A-NH(2) [Ac-hE(Sc)18A-NH(2)], had the amino acid residues of the apo E receptor binding domain scrambled to disrupt the extended hydrophobic face, and Ac-RRRRRRRRRR-18A-NH(2) (Ac-R(10)18A-NH(2)) had only positively charged Arg residues as the receptor binding domain. The effect of the dual-domain peptides on the uptake and degradation of human LDL by fibroblasts was determined in murine embryonic fibroblasts (MEF1). LDL internalization was enhanced 3-, 5-, and 7-fold by Ac-mE18A-NH(2), Ac-hE18A-NH(2), and Ac-hE(R)18A-NH(2), respectively, whereas the control peptides had no significant biological activity. All three active peptides increased the level of degradation of LDL by 100%. The LDL binding and internalization to MEF1 cells in the presence of these peptides was not saturable over the LDL concentration range that was studied (1-10 microgram/mL). Furthermore, a similar enhancement of LDL internalization was observed independent of the presence of the LDL receptor-related protein (LRP), LDLR, or both. Pretreatment of cells with heparinase and heparitinase abolished more than 80% of the enhanced peptide-mediated LDL uptake and degradation by cells. We conclude that the dual-domain peptides enhanced LDL uptake and degradation by fibroblasts via a heparan sulfate proteoglycan (HSPG)-mediated pathway.
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PMID:The receptor binding domain of apolipoprotein E, linked to a model class A amphipathic helix, enhances internalization and degradation of LDL by fibroblasts. 1062 96

We investigated the mechanism of beta-very low density lipoprotein (beta-VLDL)-induced foam cell formation derived from peritoneal macrophages from control mice and low density lipoprotein (LDL) receptor-deficient mice to elucidate the role of the LDL receptor in this process. The LDL receptor appeared to be of major importance for beta-VLDL metabolism. Consequently, the accumulation of cholesteryl esters in LDL receptor(-)(/)- macrophages is 2.5-fold lower than in LDL receptor(+)(/)(+) macrophages. In the absence of the LDL receptor, however, beta-VLDL was still able to induce cholesteryl ester accumulation and subsequently we characterized the properties of this residual beta-VLDL recognition site(s) of LDL receptor(-)(/)- macrophages. Although the LDL receptor-related protein is expressed on LDL receptor(-)(/)- macrophages, the cell association of beta-VLDL is not influenced by the receptor-associated protein, and treatment of the macrophages with heparinase and chondroitinase was also ineffective. In contrast, both oxidized LDL (OxLDL) and anionic liposomes were able to inhibit the cell association of (125)I-labeled beta-VLDL in LDL receptor(-)(/)- macrophages by 65%. These properties suggest a role for scavenger receptor class B (SR-B), and indeed, in the LDL receptor(-)(/)- macrophages the selective uptake of cholesteryl esters from beta-VLDL was 2.2-fold higher than that of apolipoproteins, a process that could be inhibited by OxLDL, high density lipoprotein (HDL), and beta-VLDL. In conclusion, the LDL receptor on peritoneal macrophages is directly involved in the metabolism of beta-VLDL and the subsequent foam cell formation. When the LDL receptor is absent, SR-B appears to mediate the remaining metabolism of cholesteryl esters from beta-VLDL.
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PMID:Relative importance of the LDL receptor and scavenger receptor class B in the beta-VLDL-induced uptake and accumulation of cholesteryl esters by peritoneal macrophages. 1088 99

Apolipoprotein E (apoE) is the primary recognition signal on triglyceride-rich lipoproteins responsible for interacting with low density lipoprotein (LDL) receptors and LDL receptor-related protein (LRP). It has been shown that lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) promote receptor-mediated uptake and degradation of very low density lipoproteins (VLDL) and remnant particles, possibly by directly binding to lipoprotein receptors. In this study we have investigated the requirement for apoE in lipase-stimulated VLDL degradation. We compared binding and degradation of normal and apoE-depleted human VLDL and apoE knockout mouse VLDL in human foreskin fibroblasts. Surface binding at 37 degrees C of apoE knockout VLDL was greater than that of normal VLDL by 3- and 40-fold, respectively, in the presence of LPL and HTGL. In spite of the greater stimulation of surface binding, lipase-stimulated degradation of apoE knockout mouse VLDL was significantly lower than that of normal VLDL (30, 30, and 80%, respectively, for control, LPL, and HTGL treatments). In the presence of LPL and HTGL, surface binding of apoE-depleted human VLDL was, respectively, 40 and 200% of normal VLDL whereas degradation was, respectively, 25 and 50% of normal VLDL. LPL and HTGL stimulated degradation of normal VLDL in a dose-dependent manner and by a LDL receptor-mediated pathway. Maximum stimulation (4-fold) was seen in the presence LPL (1 microgram/ml) or HTGL (3 microgram/ml) in lovastatin-treated cells. On the other hand, degradation of apoE-depleted VLDL was not significantly increased by the presence of lipases even in lovastatin-treated cells. Surface binding of apoE-depleted VLDL to metabolically inactive cells at 4 degrees C was higher in control and HTGL-treated cells, but unchanged in the presence of LPL. Degradation of prebound apoE-depleted VLDL was only 35% as efficient as that of normal VLDL. Surface binding of apoE knockout or apoE-depleted VLDL was to heparin sulfate proteoglycans because it was completely abolished by heparinase treatment. However, apoE appears to be a primary determinant for receptor-mediated VLDL degradation. Our studies suggest that overexpression of LPL or HTGL may not protect against lipoprotein accumulation seen in apoE deficiency.
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PMID:Lipoprotein lipase- and hepatic triglyceride lipase- promoted very low density lipoprotein degradation proceeds via an apolipoprotein E-dependent mechanism. 1106 Mar 56

A promising strategy to solve the problems of insufficient membrane penetration of drugs and low target specificity is the localization of targeting and uptake-facilitating ligands on the surface of drug-carrier systems. This study investigated the role of a peptide derived from the LDL receptor (LDLr)-binding domain of apolipoprotein E (apoE) in initiating endocytosis in brain capillary endothelial cells. The highly cationic tandem dimer of apoE residues (141-150) was coupled covalently onto poly(ethylene glycol)-derivatized liposomes. Membrane binding and cellular uptake was monitored qualitatively by confocal-laser-scanning microscopy as well as quantitatively using a fluorescence assay. The peptide mediated an efficient, energy-dependent translocation of liposomes across the membrane of brain capillary endothelial cells. Liposomes without surface-located peptides displayed neither membrane accumulation nor cellular uptake. Low peptide affinity to LDLr and internalization of the complex into fibroblasts with up- and down-regulated receptor expression levels, as well as complex translocation into cells incubated with an antibody against the LDLr, pointed to a dominating role of an LDLr-independent transport route. Enzymatic digestion of heparan sulfate proteoglycan (HSPG) with heparinase I and addition of heparin and poly-l-lysin as competitors of HSPG and HSPG ligands, respectively, resulted in a significant loss in liposome internalization. The results suggested that HSPG played a major role in the apoE-peptide-mediated uptake of liposomes into endothelial cells of brain microvessels.
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PMID:An apolipoprotein E-derived peptide mediates uptake of sterically stabilized liposomes into brain capillary endothelial cells. 1569 27


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