Cell surface syndecan-1 on distinct cell types differs in fine structure and ligand binding of its heparan sulfate chains.

Abstract

Heparan sulfate (HS) can bind a large variety of biological effectors, including extracellular matrix components, growth factors, chemokines, degradative enzymes, and protease inhibitors. Where studied, HS is known to be structurally heterogeneous and to vary in sulfation pattern between cells and tissues. Because heparan sulfate can represent several distinct proteoglycans, we asked whether the structural variation in the heparan sulfate chains of a single species of cell surface proteoglycan is a reproducible, differentiated characteristic and whether the variation can result in distinct biological functions. We studied the molecular structure and binding affinity for type I collagen and fibroblast growth factor-2 of syndecan-1 purified from the surfaces of NMuMG normal murine mammary gland epithelia, NIH/3T3 fibroblasts, and BALB/3T3 endothelioid cells. Syndecan-1 from these cell types varied in molecular mass largely due to variation in the length of the HS chains. Although the highly sulfated and N-acetylated domains in these HS chains were organized similarly, the number of highly sulfated domains differed. The disaccharide compositions were also similar except for reproducible and consistent differences in the amount of hexuronic acid-N-sulfated-6-O-sulfated glucosamine and 2-O-sulfated hexuronic acid-N-sulfated glucosamine. These differences were confirmed by oligosaccharide mapping, which showed cell type-specific variations in the composition of the highly sulfated domains. These structural variations correlated with cell type-specific differences in the affinity of syndecan-1 and its isolated HS chains for type I collagen. However, no differences in affinity for fibroblast growth factor-2 were detected. The results indicate that the size, fine structure, and ligand affinity of the HS chains on a single proteoglycan species differ in a consistent and reproducible manner between cell types. Thus, the variation in structure and binding ability of HS on syndecan-1 is a differentiated characteristic of the cell type that can enable cells to respond distinctly to the HS-binding effectors in the cellular microenvironment.