Untitled

172

128

A comparative analysis was carried out of heparan sulfate (HS) and chondroitin sulfate (CS) chains of the ectodomains of hybrid type transmembrane proteoglycans, syndecan-1 and -4, synthesized simultaneously by normal murine mammary gland epithelial cells. Although the HS chains were structurally indistinguishable, intriguingly the CS chains were structurally and functionally distinct, probably reflecting the differential regulation of sulfotransferases involved in the synthesis of HS and CS. The CS chains of the two syndecans comprised nonsulfated, 4-O-, 6-O-, and 4,6-O-disulfated N-acetylgalactosamine-containing disaccharide units and were significantly different, with a higher degree of sulfation for syndecan-4. Functional analysis using a BIAcore system showed that basic fibroblast growth factor (bFGF) specifically bound only to the HS chains of both syndecans, whereas midkine (MK) and pleiotrophin (PTN) bound not only to the HS but also to the CS chains. Stronger binding of MK and PTN to the CS chains of syndecan-4 than those of syndecan-1 was revealed, supporting the structural and functional differences. Intriguingly, removal of the CS chains decreased the association and dissociation rate constants of MK, PTN, and bFGF for both syndecans, suggesting the simultaneous binding of these growth factors to both types of chains, producing a ternary complex that transfers the growth factors to the corresponding cell surface receptors more efficiently compared with the HS chains alone. The involvement of the core protein was also shown in the binding of MK and PTN to syndecan-1, suggesting the possibility of cooperation with the HS and/or CS chains in the binding of these growth factors and their delivery to the cell surface receptors. Proteoglycans (PG) 1 bear glycosaminoglycans (GAGs) such as heparan sulfate (HS) and chondroitin sulfate (CS). The repeating disaccharide unit in the HS and CS backbones isGlcUA/IdceA-GlcNAc and GlcUA-GalNAc, respectively, onto which are superimposed specific modification patterns, most notably the addition of sulfate groups by a variety of sulfotransferases (1). PGs are distributed ubiquitously in extracellular matrices and at cell surfaces (2). Syndecans are the major cell surface PGs expressed by virtually all epithelial cells. Four kinds of syndecans form a gene family, the transmembrane and cytoplasmic domain being conserved among all of the members (3-7). These syndecans are expressed with different cell-, tissue-, and developmental stage-specific patterns (8, 9), suggesting distinct functions for each family member (10), although some shared activities have been observed, for example, for syndecan-1 and -4 (3, 5, 11, 12).The majority of GAG chains added to the core proteins of syndecans are of the HS type, although syndecan-1 (13) and syndecan-4 (14) are modified by CS chains as well. The HS chains bind collagen types I, III, and V (15), fibronectin (16), tenascin (17), thrombospondin (18) and basic fibroblast growth factor (bFGF) (19,20), and other components of the cellula...

Section: Discussionmentioning

confidence: 73%

“…Various FGFs including FGF-1, -2, -7, and -8 are produced by cells of the mammary gland at different stages of development (49). bFGF stimulates branching morphogenesis during mammary gland development (64) and also acts as a survival factor for mammary epithelial cells (65).…”

Section: Discussionmentioning

confidence: 99%

Chondroitin Sulfate Chains on Syndecan-1 and Syndecan-4 from Normal Murine Mammary Gland Epithelial Cells Are Structurally and Functionally Distinct and Cooperate with Heparan Sulfate Chains to Bind Growth Factors

Deepa

Yamada

Zako

et al. 2004

172

128

“…The majority of cytokines, chemokines, morphogens, and growth factors bind heparin/HS, and the activity of many of these regulatory proteins is dependent on or is modulated by the polysaccharide (56). Therefore, Npn-1 and perhaps other members of the neuropilin family (1) may have a far wider spectrum of activity than currently appreciated.…”

Section: Discussionmentioning

confidence: 99%

Interactions of Multiple Heparin Binding Growth Factors with Neuropilin-1 and Potentiation of the Activity of Fibroblast Growth Factor-2

West

Rees

Duchesne

et al. 2005

Self Cite

155

148

The hypothesis that neuropilin-1 (Npn-1) may interact with heparin-binding proteins other than vascular endothelial growth factor has been tested using an optical biosensor-based binding assay. The results show that fibroblast growth factor ( ). These results suggest that Npn-1 possesses a "heparin" mimetic site that is able to interact at least in part through ionic bonding with the heparin binding site on many of the proteins studied. Npn-1 was also found to potentiate the growth stimulatory activity of FGF-2 on human umbilical vein endothelial cells, indicating that Npn-1 may not just bind but also regulate the activity of heparin-binding proteins.

“…Multiple proteins are known to bind HS, and therefore, individual HS chains are likely to act as "multireceptors" for different proteins (59 ). The dynamics of ternary complex formation and, consequently, the activation of FGF-signaling pathways may, therefore, be determined by the relative rate constants and abundance of competing proteins binding to FGF/FGFR binding sequences within the HS chains.…”

Section: Fgfr1 and -2 Interact Differently With Heparin/hsmentioning

confidence: 99%

Fibroblast Growth Factor Receptors 1 and 2 Interact Differently with Heparin/Heparan Sulfate

Powell¹,

Fernig²,

Turnbull³

2002

Self Cite

Heparan sulfate (HS) regulates the kinetics of fibroblast growth factor 2 (FGF2)-stimulated intracellular signaling and differentially activates cell proliferation of cells expressing different FGF receptors (FGFRs). Evidence suggests that HS interacts with both FGFs andFGFRs to form active ternary signaling complexes. Here we compare the interactions of two FGFRs with HS. We show that the ectodomains of FGFR1 IIIc and FGFR2 IIIc exhibit specific interactions with different characteristics for both heparin and porcine mucosal HS. These glycans are both known to activate FGF signaling via these receptors. FGFR2 interacts with a higher apparent affinity than FGFR1 despite both involving 6-O-, 2-O-, and N-sulfates. FGFR1 and FGFR2 bind heparin with mean association rate constants of 1.9 ؋ 10 5 and 2.1 ؋ 10 6 M ؊1 s ؊1 , respectively, and dissociation rate constants of 1.2 ؋ 10 ؊2 and 2.7 ؋ 10 ؊2 s ؊1 , respectively. These produced calculated affinities of 63 and 13 nM, respectively. Hence, FGFR1 and FGFR2 bind to heparin chains with markedly different kinetics and affinities. We propose a mechanistic model where the kinetic parameters of the HS/FGFR interaction are a key element regulating the formation of ternary complexes and the resulting FGF signaling outcomes. Fibroblast growth factors (FGFs)1 utilize a co-receptor system consisting of tyrosine kinase receptors (FGFRs) and heparan sulfate proteoglycans (HSPGs) (1, 2). The FGFRs belong to a family of five genes (FGFR1-5), from which alternative splicing generates diverse isoforms (3, 4). Heparan sulfate (HS) is a family of linear polysaccharides located at the surface of cells and in the extracellular matrix. HS chains are attached to core proteins, forming a class of glycoproteins called proteoglycans (5). HS consists of a backbone disaccharide repeat of alternating glucosamine and hexuronate monosaccharides on which are superimposed highly variable patterns of N-and O-linked sulfate groups and uronate epimerization; that is, iduronate (IdoUA) or glucuronate residues. This creates diverse molecular motifs, which present unique displays of sulfate, carboxyl, and hydroxyl groups (6). The modifications are clustered, producing the domain structure of HS; that is, stretches of sulfated saccharides (termed NS domains or S domains) separated by N-acetyl-rich saccharides (termed NA domains). The NS domains are rich in IdoUA and the NA domains in glucuronate. Heparin can be regarded as a special class of HS expressed by mast cells and also oligodendrocyte type-2 astrocyte progenitor cells (7). Heparin is highly sulfated, contains a high abundance of IdoUA, and lacks the ordered domain structure seen in HS (8). The sequences within heparin may in many aspects resemble those of highly sulfated NS domains of HS.It has been shown that heparin and HS bind to proteins and modulate their activities via specific sulfated sequences within the chains (commonly within the NS domains) (6,8). This is particularly apparent for FGFs, which recognize different structural motifs in HS...