Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.6.4 (chondroitinase)
 2,039 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombospondin-1 (TSP1) has potent biological effects on vasculature smooth muscle cells (SMCs) and endothelial cells. The regulation of extracellular accumulation of TSP1 is mediated by a previously obscure process of endocytosis which leads to its lysosomal degradation. Since members of the low density lipoprotein receptor (LDLR) family have been found to mediate endocytosis which leads to degradation of a diverse array of ligands, we evaluated their possible role in the uptake and degradation of TSP1 by vascular SMCs, endothelial-cells and fibroblasts. 125I-TSP1 was found to be internalized and degraded lysosomally by all these cell types. Both the internalization and degradation of 125I-TSP1 could be inhibited by a specific antagonist of the LDLR family, the 39-kD receptor-associated protein (RAP). Antibodies to the LDLR-related protein (LRP) completely blocked the uptake and degradation of 125I-TSP1 in SMCs and fibroblasts but not endothelial cells. Solid-phase binding assays confirmed that LRP bound to TSP1 and that the interaction was of high affinity (Kd = 5 nM). Neither RAP nor LRP antibodies inhibited the binding of 125I-TSP1 to surfaces of SMCs. However, cell surface binding, as well as, endocytosis and degradation could be blocked by heparin or by pre-treatment of the cells with either heparitinase, chondroitinase or beta-D-xyloside. The data indicates that cell surface proteoglycans are involved in the LRP-mediated clearance of TSP1. A model for the clearance of TSP1 by these cells is that TSP1 bound to proteoglycans is presented to LRP for endocytosis. In endothelial cells, however, the internalization of TSP1 was not mediated by LRP but since RAP inhibited TSP1 uptake and degradation, we postulate that another member of the LDLR family is likely to be involved.
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PMID:Identification of the low density lipoprotein receptor-related protein (LRP) as an endocytic receptor for thrombospondin-1. 777 83

Proteoglycans (PGs) have been suggested to work as receptors in lipoprotein uptake mechanisms. An interaction between apolipoprotein E (apoE) and glucosaminoglycans (GAG), polysaccharides linked to proteoglycans, has been proposed in this pathway. At the same time, proteoglycans, apoE as well as lipoprotein receptors have been reported to be constituents of amyloid plaques, one hallmark of Alzheimer's disease. With this study, we are the first to investigate the interaction between beta very low density lipoprotein (beta-VLDL) and a neuronal highly abundant GAG, chondroitin sulphate (CS), comparing hippocampal neurons, expressing high levels of low density lipoprotein receptor related protein (LRP) and U373 astrocytoma cells, highly positive for the low density lipoprotein receptor (LDLR). We were able demonstrate that degradation of chondroitin sulphate proteoglycans (CSPGs) with chondroitinase ABC resulted in reduced (125)I-beta-VLDL uptake. We showed that externally added CSs compete with internalization of beta-VLDL. The effect was found to be dose-dependent, but was influenced neither by cell type, nor receptor type. The position of sulphation of added CSs showed only a slight influence. The data generated suggested an interaction between apolipoproteins and soluble CSs; therefore, 3H-cholesterol linked to apoE was coadministered with CSs to the cells. The results revealed that apoE bound, but no unbound cholesterol, was reduced in cellular internalization, suggesting that CSPGs may be involved in lipoprotein uptake in the intact brain, mediated, at least in part, by apoE.
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PMID:Role of chondroitin sulphate in the uptake of beta-VLDL by brain cells. 1619 Aug 94