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)

The endothelial cell surface receptor thrombomodulin (TM) displays various anticoagulant functions: it acts as a cofactor for the activation of protein C (PC) by thrombin, prevents the activation of fibrinogen, platelets and Factor V by thrombin. TM was also shown to accelerate the inhibition of thrombin by its physiological inhibitor antithrombin III (ATIII). The studies performed on rabbit lung TM were undertaken in order to provide better understanding, along with the identification and the characterization of functional domains, to the mechanism of action of TM. On the basis of the physical and chemical properties of TM, which were compatible with those of a proteoglycan, the presence of a sulfated polysaccharide chain covalently bound to TM, constituting an acidic domain independent of the protein C activation cofactor site, was suggested. Further enzymatic and chemical characterization showed that rabbit TM was in fact a chondroitin sulfate proteoglycan. Monoclonal antibodies raised against rabbit TM and proteins known for their ability to neutralize the activity of heparin, as well as TM submitted to chondroitinase digestion were used in order to identify the role of the different structural domains of TM. Binding of thrombin to TM at a primary site on the protein part is a prerequisite for all the biological activities of TM. However, while this binding is sufficient for TM to promote the activation of PC by thrombin, the inhibition by TM of thrombin-induced fibrinogen clotting and factor V activation requires the interaction of thrombin at a secondary site with the polysaccharide chain of TM. This interaction with the polysaccharide chain (which carries a highly sulfated trisaccharide at the non-reducing terminus) leads to the inhibition of the procoagulant functions of TM-bound thrombin towards fibrinogen and factor V as well as an increased reactivity of the enzyme with ATIII. These results were rationalized in the functional model proposed for the rabbit TM-proteoglycan. An original aspect of the TM-proteoglycan resides in the fact that the chondroitin sulfate side chain brings new anticoagulant activities, in addition to the PC activation cofactor activity, to the molecule. TM is a new type of proteoglycan with important regulatory function in hemostasis, which anticoagulant properties depend on both the protein core and the polysaccharide chain.
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PMID:[Thrombomodulin: a new proteoglycan. Structure-function relation]. 165 16

CD44 is a major cell surface receptor for the extracellular matrix glycosaminoglycan hyaluronan (HA). However, the ability of CD44 to bind ligand is strictly regulated. Three activation states of CD44 have been demonstrated: (a) inactive; (b) inducible (by certain CD44-specific mAb); and (c) constitutively active. Starting with two parental cell lines expressing CD44 in the inactive state, a pre-B cell (RAW 253) and a fibroblast (L cells), we used fluorescence-activated cell sorting with fluorescein-conjugated hyaluronan in the presence of inducing mAb to derive variant cell lines with CD44 in the inducible state. Constitutively active derivatives were isolated from the inducible variants by a further round of fluorescence-activated cell sorting in the absence of inducing antibody. However, constitutively active variants could not be isolated directly from parental cells expressing CD44 in the inactive state. These results suggest that two genetic events must occur to obtain an active CD44-HA receptor from an inactive receptor. Variant and parental cell-derived CD44 molecules exhibited differences in migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis that were partly attributable to differences in N-linked glycosylation. Furthermore, culture in tunicamycin for 2-3 d converted parental and inducible cell lines into cells showing constitutive CD44-mediated HA binding. Also, removal of cell surface glycosaminoglycan chains by culture of cells in p-nitrophenyl beta-D-xylopyranoside or treatment with chondroitinase ABC resulted in conversion of cells with an inactive CD44 receptor to an inducible state. These results indicate that carbohydrate side chains of CD44 and/or other molecules on the cell surface that interact with CD44 are potentially involved in regulating the HA-binding function of CD44 on the cell surface.
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PMID:Variant cell lines selected for alterations in the function of the hyaluronan receptor CD44 show differences in glycosylation. 754 38

Angiomodulin (AGM/TAF/mac25) is a 30-kDa glycoprotein that was identified as an integrin-independent cell adhesion protein secreted by human bladder carcinoma cells. AGM is highly accumulated in small blood vessels of tumor tissues. In the present study, we attempted to identify the cell surface receptor and the cell-binding site of AGM using ECV-304 human vascular endothelial cells and BALB/c3T3 mouse fibroblasts. Heparin, heparan sulfate, and dextran sulfate, but not chondroitin sulfate, inhibited both adhesion of the two cell lines to AGM-coated plates and binding of AGM to these cells. Treatment of cells with heparinase, but not chondroitinase, inhibited both cell adhesion to AGM and AGM binding to cells. These results strongly suggested that heparan sulfates are the major receptor for AGM. Furthermore, we determined a 20-amino acid sequence within AGM molecule as its major cell-binding site. The synthetic peptide for the cell-binding sequence showed cell adhesion activity comparable to that of AGM, and the activity was inhibited by heparin and heparan sulfate. The peptide competitively inhibited cell adhesion to AGM and the binding of AGM to cells. These results indicated that AGM binds to cells through interaction of the identified cell-binding sequence with heparan sulfates on cell surface. It was also found that the heparan sulfate-binding peptide inhibited the formation of capillary tube-like structures of vascular endothelial cells in culture.
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PMID:Identification of cell-binding site of angiomodulin (AGM/TAF/Mac25) that interacts with heparan sulfates on cell surface. 1050 91

Midkine (MK), a retinoic acid-inducible heparin-binding protein, is a mitogen which initiates a cascade of intracellular protein tyrosine phosphorylation mediated by the JAK/STAT pathway after binding to its high affinity p200(+)/MKR cell surface receptor in the G401 cell line [Ratovitski, E. A. (1998) J. Biol. Chem. 273, 3654-3660]. In this study, we determined the biophysical characteristics of purified recombinant murine MK and analyzed the requirements for ligand multimerization and cell surface proteoglycan binding for the G401 cell mitogenic activity of MK. Our studies indicate that the secreted form of MK (M = 13 kDa) exists in solution as an asymmetric monomer with a frictional coefficient of 1. 48 and a Stokes radius of 23.7 A. By constructing bead models of MK using the program AtoB and the program HYDRO to predict the hydrodynamic properties of each model, our data suggest that MK has a dumb-bell shape in solution composed of independent N- and C-terminal domains separated by an extended linker. This asymmetric MK monomer is a biologically active ligand with mitogenic activity on G401 cells in vitro. Neither heparin-induced formation of noncovalent MK multimers nor tissue transglutaminase II covalent multimerization of MK enhanced MK mitogenic activity in this system. Since neither heparin competition nor cell treatment with chondroitinase ABC or heparinase III abolished the mitogenic effects of MK on G401 cells, cell-surface proteoglycan binding by MK does not appear to be a requirement for its observed mitogenic effects. These results provide strong evidence that the MK-specific p200(+)/MKR has distinctive biochemical properties which distinguish it from the receptor tyrosine phosphatase cell-surface proteoglycan PTPzeta/RPTPbeta and support the hypothesis that the diverse biological effects of MK are mediated by multiple cell-specific signal transduction receptors.
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PMID:Monomeric midkine induces tumor cell proliferation in the absence of cell-surface proteoglycan binding. 1082 69

Exposure to AG73, a synthetic peptide (LQVQLSIR) from the COOH-terminal region of the laminin alpha1 chain, induces a malignant phenotype in B16F10 melanoma cells. Coinjection of this peptide with the cells results in an increase of lung tumors and also the formation of liver tumors in approximately 50% of the mice (W. H. Kim et al., Int. J. Cancer, 77: 632-639, 1998). Here we have characterized the cell surface receptor and its functional groups on B16F10 cells. Peptide affinity chromatography identified a cell surface protein eluting with 1 M NaCl, which ran in SDS gels as a broad band of M(r) approximately 150,000-200,000. Digestion with heparitinase and chondroitinase produced a core protein of lower molecular weight (M(r) approximately 90,000). Involvement of the glycosaminoglycan (GAG) side chains was demonstrated by inhibition of cell binding to the peptide by heparin, heparan sulfate, and chondroitin sulfate B, but not by chondroitin sulfates A or C, or hyaluronic acid. The IC(50) for heparin was the lowest, followed by heparan sulfate, then chondroitin sulfate B, suggesting that the overall sulfation of the GAG side chain is critical. This was confirmed by inhibition of attachment with chemically modified heparin and heparan sulfate, which also showed that N or O linkages were not important for function. Using sized heparin fragments to inhibit cell binding to the peptide demonstrated that 16-mer is the minimum length required. B16F10 cells form a network when grown on Matrigel, and this is prevented by addition of the AG73 peptide. The GAGs alone did not affect network formation, but heparin, heparan sulfate, and chondroitin sulfate B reversed the inhibitory effect of the peptide, whereas other GAGs were inactive. Furthermore, removal of cell surface GAGs inhibited cell attachment to the peptide. Cells treated with glycosidases and coinjected with the peptide formed liver tumors equal to the control group receiving no peptide, suggesting that the GAGs play an early role in peptide-mediated tumor metastasis. These data indicate that the B16F10 cell receptor for a laminin metastasis-promoting sequence is a heparan sulfate/chondroitin sulfate-containing proteoglycan, and these GAG side chains are functionally important in the cell-peptide interaction.
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PMID:The B16F10 cell receptor for a metastasis-promoting site on laminin-1 is a heparan sulfate/chondroitin sulfate-containing proteoglycan. 1206 3

Prions replicate in the host cell by the self-propagating refolding of the normal cell surface protein, PrP(C), into a beta-sheet-rich conformer, PrP(Sc). Exposure of cells to prion-infected material and subsequent endocytosis can sometimes result in the establishment of an infected culture. However, the relevant cell surface receptors have remained unknown. We have previously shown that cellular heparan sulfates (HS) are involved in the ongoing formation of scrapie prion protein (PrP(Sc)) in chronically infected cells. Here we studied the initial steps in the internalization of prions and in the infection of cells. Purified prion "rods" are arguably the purest prion preparation available. The only proteinaceous component of rods is PrP(Sc). Mouse neuroblastoma N2a, hypothalamus GT1-1, and Chinese hamster ovary cells efficiently bound both hamster and mouse prion rods (at 4 degrees C) and internalized them (at 37 degrees C). Treating cells with bacterial heparinase III or chlorate (a general inhibitor of sulfation) strongly reduced both binding and uptake of rods, whereas chondroitinase ABC was inactive. These results suggested that the cell surface receptor of prion rods involves sulfated HS chains. Sulfated glycans inhibited both binding and uptake of rods, probably by competing with the binding of rods to cellular HS. Treatments that prevented endocytosis of rods also prevented the de novo infection of GT1-1 cells when applied during their initial exposure to prions. These results indicate that HS are an essential part of the cellular receptor used both for prion uptake and for cell infection. Cellular HS thus play a dual role in prion propagation, both as a cofactor for PrP(Sc) synthesis and as a receptor for productive prion uptake.
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PMID:Heparan sulfate is a cellular receptor for purified infectious prions. 1566 47