Biomedical subjects

S Guimond

Publications and source records attributed to S Guimond.

7 recordsLinked to original sources

PubMed2003

Heparan sulphate sulphotransferase expression in mice and Caenorhabditis elegans.

Heparan sulphate (HS) acts as a multifunctional cell regulator, with specific sulphated saccharide sequences designed for selective interactions with many proteins. Functionally, these interactions result in regulation of the protein activities, and there is growing evidence that cells can dynamically alter the structure of HS sequences that they display. HS biosynthesis involves the action of a complex set of enzymes with polymerase, epimerase and sulphotransferase (ST) activities. In higher organisms, multiple isoforms of STs decorate the nascent HS chains with specific patterns of sulphation that confer selective biological functions. The study of HSSTs in model organisms provides a valuable opportunity to examine the expression of these enzymes in relation to the structure and activities of the HS produced. Here we describe that, in mice, there are stage-specific combinations of HSST isoenzymes that underlie the synthesis of different HS species at different times in the developing brain. This differential expression of HSSTs results in the synthesis of structurally variant HS species that form functional signalling complexes with specific fibroblast growth factors and their receptors. Regulated synthesis of specific HS species could be a mechanism for the regulation of proliferation and differentiation in the developing brain. We also describe evidence that a Caenorhabditis elegans orthologue of the mammalian 2OST enzyme, called HST-2, is essential for the normal development of this nematode. Together, these studies emphasize the importance of HSSTs in the biosynthesis of functionally variant HS proteoglycans, and demonstrate the importance of these complex regulatory molecules in developmental processes.

Animals↗

PubMed2001

Heparan sulfate: decoding a dynamic multifunctional cell regulator.

The heparan sulfates are a family of cell-surface and matrix polysaccharides with an incredible degree of structural diversity that are distributed widely in virtually all metazoan organisms. Recent genetic, biochemical and cell-biological studies have led to increased understanding of the biosynthetic mechanisms that produce these complex molecules, as well as their functional versatility in regulating protein activities. The dynamic expression of heparan sulfates with differing sugar sequences suggests a new concept in which the repertoire of sequences produced by a particular cell or tissue is designated its 'heparanome'. This review discusses recent developments and surveys emerging experimental strategies that hold promise for revealing the functional specificity and mechanisms of action of heparan sulfates as multifunctional cell regulators.

Animals↗

PubMed2001

Dynamic biosynthesis of heparan sulphate sequences in developing mouse brain: a potential regulatory mechanism during development.

Over recent years our understanding of the functions of the heparan sulphate (HS) family of complex polysaccharides has shifted dramatically. Once seen as simply structural scaffolding in the extracellular matrix, they are now viewed as critical players in the regulatory network of cells. They are strategically located at the cell surface and in the extracellular matrix, and there has been an increasing realization that specific sequences in the HS chains are designed for selective interactions with many proteins. Functionally, these interactions result in regulation of the protein activities. It is becoming clear that HS functions as a new class of multifunctional cell regulator. There is also growing evidence that cells can dynamically alter the structure of HS sequences that they express. Here we review recent developments and describe evidence for regulated changes in the synthesis and structure of HS chains expressed during early mouse brain development. The data suggest a new concept in which dynamic changes in biosynthesis of different HS sequences create distinct cellular HS repertoires, the heparanome. Their expression, in specific spatio-temporal patterns, is likely to endow organisms with novel regulatory mechanisms for controlling the activity of specific HS-binding proteins.

Animals↗

PubMed1998

Detection of protein tyrosine kinase activity using a high-capacity streptavidin-coated membrane and optimized biotinylated peptide substrates.

A protein tyrosine kinase (PTK) assay system is described that uses a series of optimized biotinylated peptide substrates in conjunction with a streptavidin-coated matrix (SAM(2)) biotin capture membrane. The SAM(2) biotin capture membrane provides low backgrounds and high linear binding capacity (up to approximately 3.6 nmol of biotinylated PTK peptide/cm(2)), resulting in high signal-to-noise ratios and greater reproducibility. Capture of the phosphorylated peptide substrates onto the SAM(2) membrane is rapid and occurs independent of the amino acid sequence of the peptide, thereby overcoming difficulties commonly encountered with other methodologies. Two broad-specificity biotinylated PTK peptide substrates were identified with optimum kinetic properties, allowing members from eight distinct classes of enzymes, including transmembrane (epidermal growth factor receptor (EGFR), fibroblast growth factor receptor, insulin receptor, and platelet-derived growth factor receptor) and cytoplasmic (p43(abl), p56(lck), p60(src), and p93(fes)) PTKs, to be analyzed. A third biotinylated peptide substrate, shown to be highly selective for the EGFR, was used to illustrate the versatility of this system for both broad specificity and highly selective detection of PTK activity. The ability to accurately detect activity under optimum conditions and with crude cell extract samples, including kinetic analysis and with enzyme detection limits in the low femtomole range, supports the utility of this assay system for studying PTK enzymes.

Amino Acid Sequence↗

PubMed1996

Two hierarchies of FGF-2 signaling in heparin: mitogenic stimulation and high-affinity binding/receptor transphosphorylation.

FGF-2 activates multiple signaling pathways by a cell surface signaling complex assembled with FGF, its receptor tyrosine kinase, and heparan sulfate proteoglycan. Heparan sulfate binds to a site on the receptor and at least one site on the growth factor. Several models propose an important role for heparan sulfate not only in facilitating FGF-2 binding to its receptor tyrosine kinase but also in promoting signaling via formation of receptor dimers. Such dimers are capable of transphosphorylation of the cytoplasmic domain of the receptor, leading to the generation of phosphotyrosines that are important initiators of intracellular signaling pathways. To explore the participation of heparan sulfates in the formation of a signaling complex that activates these pathways, the binding and activity of FGF-2 on Swiss 3T3 fibroblasts and F32 lymphoid cells is examined with either native or modified forms of heparin. As shown previously, fibroblasts treated with chlorate, which inhibits the sulfation of heparan sulfate and its subsequent binding to FGF-2, display a dramatically reduced response to picomolar concentrations of FGF-2, but binding to receptors and a mitogenic response is restored by heparin. However, the restoration of high-affinity binding is seen only at an optimal concentration of heparin. Excess heparin competes for binding sites within the signaling complex such that high-affinity binding and receptor transphosphorylation are reduced. Despite this, mitogenic signaling is not diminished. A similar result is observed using heparin fragments that promote mitogenesis but not high-affinity binding. These results suggest that the high-affinity signaling complex that is necessary for stable receptor transphosphorylation differs from the signaling complex sufficient for triggering mitogenesis. We speculate that heparan sulfate in vivo participates in two hierarchies of receptor activation. In one, heparan sulfate participates in FGF-2 binding to its receptor tyrosine kinase and activation of mitogenic signaling, perhaps through monomeric receptors or the transient formation of receptor dimers. In the second hierarchy, heparan sulfate participates in the stabilization of a signaling complex that is likely to be comprised of receptor multimers that carry out effective receptor transphosphorylation. A further description of this mechanism may lead to an understanding of how heparan sulfate or its homologues can regulate specific signaling pathways within the cell.

3T3 Cells↗

PubMed1994

Regulation by heparan sulfate in fibroblast growth factor signaling.

The integral role of heparan sulfate proteoglycans in FGF signaling provides a potential means of regulating FGF activity. This regulation may be used by the cell, where the modification of heparan sulfate glycosaminoglycans during their synthesis in the Golgi can produce cell type- and potentially ligand-specific sulfation sequences. The description of these sequences will not only provide information on how this regulation is achieved, perhaps lending insight into other heparan sulfate-ligand interactions, but may also discern sulfated mimetics that can be used to disrupt or alter FGF signaling. These mimetics may be useful in the treatment disrupt or alter FGF signaling. These mimetics may be useful in the treatment of disease, or in understanding how FGF signaling via discrete pathways within the cell leads to specific cellular responses, such as activation of mitogenic signaling pathways, calcium fluxes, and cellular differentiation.

Aggrecans↗

PubMed1993

Activating and inhibitory heparin sequences for FGF-2 (basic FGF). Distinct requirements for FGF-1, FGF-2, and FGF-4.

Chlorate-treated Swiss 3T3 fibroblasts, with impaired synthesis of heparan sulfate proteoglycan, were used as target cells in assessing the ability of exogenous heparin-derived saccharides to promote the mitogenic activity of basic fibroblast growth factor 2 (FGF-2). Full-size native heparin (carrying iduronosyl 2-O-sulfate and glucosaminyl 6-O-sulfate groups), as well as a dodecasaccharide fraction isolated after limited deaminative cleavage of heparin, were efficient promoters, whereas the corresponding decasaccharides, or smaller oligosaccharides, were inactive. Neither selectively 2-O-desulfated nor preferentially 6-O-desulfated heparin were active. However, the latter derivative competed with native heparin for binding to FGF-2 and thus blocked the ability of native heparin to promote the mitogenic activity of FGF-2. The 6-O-desulfated heparin also prevented the ability of FGF-2 to suppress myogenic differentiation in MM14 mouse myoblasts. The binding region for FGF-2 has been identified as a pentasaccharide sequence containing a single essential O-sulfate group, at C2 of iduronic acid (1). It is proposed that the dodecasaccharide sequence required to promote receptor signaling by FGF-2 encompasses this pentasaccharide region, which binds the growth factor, and a site interacting with the receptor that contains essential 2-O- and 6-O-sulfate groups. Similar studies involving the related growth factors, FGF-1 and FGF-4, revealed differential effects of saccharides. The mitogenic effect induced by FGF-1 thus was not blocked by either the 2-O- or the 6-O-desulfated heparins. However, both of these derivatives, at high concentrations, promote mitogenic activity of FGF-4. It is concluded that specific saccharide sequences within heparan sulfate glycosaminoglycan chains favor the signaling by distinct members of the FGF family.

3T3 Cells↗