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

Osteoblast-like cells secrete insulin-like growth factor (IGF) binding protein-5 (IGFBP-5), which may act to enhance IGF-stimulated osteoblast function. We recently demonstrated that carboxyl-truncated IGFBP-5 (IGFBP-5(1-169)) binds to the osteoblast surface and stimulates mitogenesis by a pathway that is independent of IGF action. The present study was conducted to determine the mechanism of osteoblast binding of IGFBP-5, beginning with the assumption that cell surface glycosaminoglycans may mediate the binding of this heparin binding protein. Intact 125I-IGFBP-5 and 125I-IGFBP-5(1-169) exhibited one-site binding to mouse osteoblast monolayers with dissociation constants of 28 and 6 nM for intact 125I-IGFBP-5 and 125I-IGFBP-5(1-169), respectively. Osteoblast binding of intact 125I-IGFBP-5 was inhibited by low heparin concentrations, while 125I-IGFBP-5(1-169) binding was stimulated by heparin. Treatment of cells with heparinase or chlorate to decrease surface glycosaminoglycan density failed to reduce the binding of either form of IGFBP-5. In contrast, pretreatment of cells with IGFBP-5 caused down-regulation of 125I-IGFBP-5 binding. Cross-linking studies revealed that both intact 125I-IGFBP-5 and 125I-IGFBP-5(1-169) bind to proteins in Triton extracts of osteoblast membranes, which were absent in osteoblast-derived matrix. Purification of membrane extracts by IGFBP-5 affinity chromatography revealed a 420-kDa band on reduced SDS-polyacrylamide gels. While the membrane protein internalized both forms of IGFBP-5, heparin treatment inhibited the internalization of intact 125I-IGFBP-5 but stimulated 125I-IGFBP-5(1-169) internalization. These data indicate that IGFBP-5 binds to and is internalized by an osteoblast membrane protein, which does not appear to be a proteoglycan. Glycosaminoglycans, however, modulate the binding and internalization of IGFBP-5 in a way that may preferentially favor the intracellular accumulation of the carboxyl-truncated form.
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PMID:Heparin modulates the binding of insulin-like growth factor (IGF) binding protein-5 to a membrane protein in osteoblastic cells. 749 27

The activities of insulin-like growth factor (IGF)-I and -II are regulated by IGF-binding proteins (IGFBPs). Cleavage of IGFBP-4 by the metalloproteinase pregnancy-associated plasma protein-A (PAPP-A) causes release of bound IGF and has been established in several biological systems including the human reproductive system. Using flow cytometry, we first demonstrate that PAPP-A reversibly binds to the cell surface of several cell types analyzed. Heparin and heparan sulfate, but not dermatan or chondroitin sulfate, effectively compete for PAPP-A surface binding, and because incubation of cells with heparinase abrogated PAPP-A adhesion, binding is probably mediated by a cell surface heparan sulfate proteoglycan. Furthermore, the proteolytic activity of PAPP-A is preserved while bound to cells, suggesting that adhesion functions to target its activity to the vicinity of the IGF receptor, decreasing the probability that released IGF is captured by another IGFBP molecule before receptor binding. This mechanism potentially functions in both autocrine and paracrine regulation, as PAPP-A need not be synthesized in a cell to which it adheres. A truncated PAPP-A variant without the five short consensus repeats in the C-terminal third of the 1547-residue PAPP-A subunit, lacked surface binding. We also show that PAPP-A2, a recently discovered IGFBP-5 proteinase with homology to PAPP-A, does not bind cells. This finding allowed further mapping of the PAPP-A adhesion site to short consensus repeat modules 3 and 4 by the expression and analysis of nine PAPP-A/PAPP-A2 chimeras. Interestingly, the proteolytically inactive, disulfide-bound complex of PAPP-A and the proform of eosinophil major basic protein (proMBP), PAPP-A.proMBP, shows only weak surface binding, probably because the adhesion site of PAPP-A is occupied by heparan sulfate, known to be covalently bound to proMBP. This hypothesis was further substantiated by demonstrating that heparinase treatment of PAPP-A.proMBP restores surface binding. We finally propose a model in which IGF bioactivity is regulated by reversible cell surface binding of PAPP-A, which in turn is regulated by proMBP.
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PMID:Cell surface targeting of pregnancy-associated plasma protein A proteolytic activity. Reversible adhesion is mediated by two neighboring short consensus repeats. 1237 Jan 76

Many growth factors and cytokines are immobilized on the extracellular matrix (ECM) by binding to glycosaminoglycans and are stored in an inactive form in the cellular microenvironment. However, the mechanisms of ECM-bound growth factor or cytokine activation have not been well documented. We showed that the insulin-like growth factor type-1 receptor (IGF-1R) was rapidly phosphorylated after the addition of matrix metalloproteinase (MMP)-7 to a serum-starved human colon cancer cell line (HT29) and that phosphorylation was completely inhibited by an IGF-II neutralizing antibody. In the ECM of this cell line, IGF-II and IGF binding protein (BP)-2 coexisted, but IGFBP-2 disappeared from the ECM fraction after treatment with MMP-7 or heparinase III. On the other hand, in a cell line in which IGF-1R was overexpressed, IGF-1R was phosphorylated by supernatant from the MMP-7-treated ECM fraction of HT29 but not by that from a heparinase-III-treated ECM fraction. We also demonstrated that MMP-7 degrades IGFBP-2 in vitro at three cleavage sites (peptide bonds E(151)-L(152), G(175)-L(176) and K(181)-L(182)), which have not been documented previously. Taken together, these results demonstrate that MMP-7 generates bioactive IGF-II by degrading the IGF-II/IGFBP-2 complex binding to heparan sulfate proteoglycan in the ECM, resulting in IGF-II-induced signal transduction. This evidence indicates that some ECM-associated growth factors enhance their ability to bind to their receptors by some proteases in the tumor microenvironment. This mechanism of action ('protease-triggered matricrine') represents an attractive model for understanding ECM-tumor interactions.
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PMID:Matrix metalloproteinase-7 triggers the matricrine action of insulin-like growth factor-II via proteinase activity on insulin-like growth factor binding protein 2 in the extracellular matrix. 1735 88