Biomedical subjects

John T Gallagher

Publications and source records attributed to John T Gallagher.

8 recordsLinked to original sources

PubMed2003

Binding of endostatin to endothelial heparan sulphate shows a differential requirement for specific sulphates.

Endostatin is a naturally occurring proteolytic fragment of the C-terminal domain of collagen XVIII. It inhibits angiogenesis by a mechanism that appears to involve binding to HS (heparan sulphate). We have examined the molecular interaction between endostatin and HS from micro- and macrovessel endothelial cells. Two discrete panels of oligosaccharides were prepared from metabolically radiolabelled HS, using digestion with either heparinase I or III, and then examined for their endostatin affinity using a sensitive filter-binding assay. Two types of endostatin-binding regions were identified: one comprising sulphated domains of five or more disaccharides in length, enriched in 6-O-sulphate groups, and the other contained long heparinase I-resistant fragments. In the latter case, evidence from the present study suggests that the binding region encompasses a sulphated domain fragment and a transition zone of intermediate sulphation. The contribution to binding of specific O-sulphate groups was determined using selectively desulphated HS species, namely HS from Hs2st-/- mutant cells, and by comparing the compositions of endostatin-binding and non-binding oligosaccharides. The results indicate that 6-O-sulphates play a dominant role in site selectivity and 2-O-sulphates are not strictly essential.

Binding Sites↗

PubMed2003

Syndecan-1 and -4 synthesized simultaneously by mouse mammary gland epithelial cells bear heparan sulfate chains that are apparently structurally indistinguishable.

Many of the biological functions attributed to cell surface heparan sulfate (HS) proteoglycans, including the Syndecan family, are elicited through the interaction of their HS chains with soluble extracellular molecules. Tightly controlled, cell-specific sulfation and epimerization of HS precursors endows these chains with highly sulfated, iduronate-rich regions, which are major determinants of cytokine and matrix-protein binding and which are interspersed by N-acetylated, poorly sulfated regions. Until this study, there have been no comprehensive structural comparisons made on HS chains decorating simultaneously expressed, but different, syndecan core proteins. In this paper we demonstrate that the HS chains on affinity-purified syndecan-1 and -4 from murine mammary gland cells are essentially identical by a number of parameters. Size determination, disaccharide analyses, enzymatic and chemical scission methods, and affinity co-electrophoresis all failed to reveal any significant differences in fine structure, domain organization, or ligand-binding properties of these HS species. These findings lead us to suggest that the imposition of the fine structure onto HS occurs independently of the core protein to which it is attached and that these core proteins, in addition to the HS chains, may play a pivotal role in the various biological functions ascribed to these macromolecules.

Animals↗

PubMed2002

Heparin sequencing.

Heparin is a highly sulfated glycosaminoglycan widely used as an anticoagulant. Modifications in its relatively uniform structure appear to be key to its recognition and modulation of serine proteases, growth factors, chemokines, and extracellular proteins, as has been most clearly demonstrated in the antithrombin binding site. We sequenced the major oligosaccharides released from mastocytoma heparin by partial nitrous acid using a highly sensitive technique tailored for sequencing of metabolically radiolabeled heparin. It utilizes partial nitrous acid cleavage to allow simultaneous sequencing of the internal components of the oligosaccharide under investigation by specific lysosomal exoenzymes. Sequencing revealed that although the majority of the heparin disaccharides are N-, 2-O-, and 6-O-sulfated, the less sulfated disaccharides (lacking 2-O- or 6-O-sulfates) seem to be spaced out along the chain. The technique may be particularly useful for characterizing heparin from novel sources, such as the glial progenitor cells and Ascidia, as well as for sequencing protein binding sites.

Animals↗

PubMed2002

Characterization of the binding site on heparan sulfate for macrophage inflammatory protein 1alpha.

The CC chemokine macrophage inflammatory protein 1alpha (MIP1alpha) is a key regulator of the proliferation and differentiation of hematopoietic progenitor cells. The activity of MIP1alpha appears to be modulated by its binding to heparan sulfate (HS) proteoglycans, ubiquitous components of the mammalian cell surface and extracellular matrix. In this study we show that HS has highest affinity for the dimeric form of MIP1alpha. The predominantly dimeric BB10010 MIP1alpha interacts with an 8.3-kDa sequence in the HS polysaccharide chain, which it protects from degradation by heparinase enzymes. The major structural motif of this HS fragment appears to consist of 2 sulfate-rich S-domains separated by a short central N-acetylated region. The optimum lengths of these S-domains seem to be 12 to 14 saccharides. We propose that this binding fragment may wrap around the MIP1alpha dimer in a horseshoe shape, facilitating the interaction of the S-domains with the heparin-binding domains on each monomer. Molecular modeling suggests that these S-domains are likely to interact with basic residues Arg 17, Arg 45, and Arg 47 and possibly with Lys 44 on MIP1alpha and that the interconnecting N-acetylated region is of sufficient length to allow the 2 S-domains to bind to these sites on opposite faces of the dimer. Elucidation of the structure of the HS-binding site for MIP1alpha may enable us to devise ways of enhancing its myeloprotective or peripheral blood stem cell mobilization properties, which can be used to improve cancer chemotherapy treatments.

Binding Sites↗

PubMed2002

Fibroblast growth factor-2 binds to small heparin-derived oligosaccharides and stimulates a sustained phosphorylation of p42/44 mitogen-activated protein kinase and proliferation of rat mammary fibroblasts.

We examine the relationship between the chain length of heparin-derived oligosaccharides, fibroblast growth factor (FGF)-2 binding kinetics and the ability of the oligosaccharides to allow FGF-2-induced proliferation of chlorate-treated rat mammary fibroblasts. First, using an optical biosensor, we show that FGF-2 did not bind disaccharides, but definitively bound to tetrasaccharides. As the chain length increased from tetrasaccharide to octasaccharide, there was a substantial increase in k(ass) (564000 M(-1) x s(-1) to 2000000 M(-1) x s(-1), respectively) and affinity (K(d) 77 nM to 11 nM, respectively) for FGF-2. From decasaccharides and longer, the k(ass) and affinity for FGF-2 was reduced substantially (tetradecasaccharide k(ass) 470000 M(-1) x s(-1), K(d) 30 nM). In chlorate-treated, and hence sulphated, glycosaminoglycan-deficient cells, FGF-2 alone or in the presence of disaccharides did not stimulate DNA synthesis and it only elicited an early transient dual phosphorylation of p42/44 mitogen-activated protein kinase (MAPK). In the same cells FGF-2 in the presence of tetrasaccharides and longer oligosaccharides was able to restore DNA synthesis and enable the sustained dual phosphorylation of p42/44(MAPK). However, the oligosaccharides from tetrasaccharides to octasaccharides were less potent in proliferation assays than deca- and longer oligosaccharides. Therefore, there was no correlation between the binding parameters and the potency of the oligosaccharides in DNA synthesis assays. These results demonstrate that tetrasaccharides are able to bind FGF-2 and enable FGF-2 to stimulate cell proliferation, which sets important boundary conditions for models of the FGF-2-heparan sulphate-FGF receptor complex.

Animals↗

PubMed2002

New insights into heparan sulphate biosynthesis from the study of mutant mice.

Heparan sulphate (HS) is an essential co-receptor for a number of growth factors, morphogens and adhesion proteins. The biosynthetic modifications involved in the generation of a mature HS chain may determine the strength and outcome of HS-ligand interactions. These modifications are catalysed by a complex family of enzymes, some of which occur as multiple gene products. Various mutant mice have now been generated, which lack the function of isolated components of the HS biosynthetic pathway. In this discussion, we outline the key findings of these studies, and use them to put into context our own work concerning the structure of the HS generated by the Hs2st -/- mice.

Animals↗

PubMed2001

The mode of action of heparan and dermatan sulfates in the regulation of hepatocyte growth factor/scatter factor.

Hepatocyte growth factor/scatter factor, in addition to binding to its specific signal-transducing receptor, Met, also interacts with both heparan and dermatan sulfates with high affinity. We have investigated the comparative role of these two glycosaminoglycans in the activation of Met by hepatocyte growth factor/scatter factor. Using glycosaminoglycan-deficient CHO pgsA-745 cells we have shown that growth factor activity is critically dependent upon glycosaminoglycans, and that heparan sulfate and dermatan sulfate are equally potent as co-receptors. Cross-linked 1:1 conjugates of growth factor and either heparan or dermatan sulfate do not dimerize under physiological conditions and are biologically active. This implies that a ternary signaling complex with Met forms in vivo. Native Met isolated from CHO pgsA-745 cells shows only very weak intrinsic affinity for heparin in vitro. Also, a heparin-derived hexasaccharide, which is the minimal size for high affinity binding to the growth factor alone, is sufficient to induce biological activity. Together these observations imply that the role of these glycosaminoglycan may be primarily to effect a conformational change in hepatocyte growth factor/scatter factor, rather than to induce a necessary growth factor dimerization, or to stabilize a ternary complex by additionally interacting with Met.

Animals↗

PubMedDate not supplied

Heparan sulfate 2-O-sulfotransferase (Hs2st) and mouse development.

Heparan sulphate 2-O-sulphotransferase (Hs2st) acts at an intermediate stage in the pathway of biosynthesis of heparan sulphate (HS), catalysing the transfer of sulphate from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to the C2-position of selected hexuronic acid residues within the maturing HS chain. It is well established that 2-O-sulphation within HS, particularly of iduronate residues, is essential for HS to participate in a variety of high-affinity ligand-binding interactions. HS plays a central role in embryonic development and cellular function, modulating the activities of an extensive range of growth factors. Interestingly, in contrast to the early failure of embryos entirely lacking HS, Hs2st(-/-) mice survive until birth, but die perinatally due to a complete failure of kidney formation. The phenotype of Hs2st(-/-) mutant kidneys suggests that signalling between two tissues, ureteric bud and metanephric mesenchyme, is disrupted. We discuss candidate signalling molecules that may mediate this interaction. The HS generated by these mice lacks 2-O-sulphate groups but is extensively modified above wild type levels by O-sulphation at C-6 of glucosamine-N-sulfate (GlcNS) residues. We will discuss the potentially altered role of this atypical HS in growth factor signalling.

Animals↗