Effects of Sized Heparin Oligosaccharide on the Interactions of Chinese Hamster Ovary Cell with Thrombospondin

Abstract

Binding and degradation of TSP by CHO cells and adhesion of CHO cells to substrate-adsorbed TSP are mediated by cell surface PGs and inhibitable by heparin. In order to learn how these three processes are related, we studied the effects of defined heparin oligosaccharides up to 18-mer produced by nitrous acid digestion. There was a complex correlation among oligosaccharide chain length, affinity of oligosaccharide for TSP in a solid phase binding assay, and potencies of oligosaccharide in inhibition of the three cellular processes. Inhibition of degradation was more sensitive to shorter oligosaccharides than inhibition of binding. For instance, the 10-mer inhibited binding of TSP to cells by 10% and degradation by 70%. Punctate immunofluorescence of cell surface bound TSP was replaced by a diffuse pattern after incubation in the presence of the 10-mer. These results suggest that the clustering of TSP on the cell surface may trigger endocytosis and degradation. Inhibition of binding of TSP to cells, in turn, was more sensitive to midsized oligosaccharides than inhibition of cell adhesion to adsorbed TSP. Inhibition of adhesion correlated with the ability of oligosaccharides to block binding of 125I-heparin to adsorbed TSP.

Platelet factor 4 modulates the mitogenic activity of basic fibroblast growth factor.

“…Our laboratory has previously examined the binding of thrombospondin to cell-surface heparan sulfate proteoglycans (19, 31,32) and has shown, using competitive binding assays, that PF 4 and /l-thromboglobulin compete for thrombospondin binding to cell-surface heparan sulfate proteoglycans (19). One consequence of this competition is blockage of the internalization of thrombospondin (19).…”

Endogenously Produced Endothelial Lipase Enhances Binding and Cellular Processing of Plasma Lipoproteins via Heparan Sulfate Proteoglycan-mediated Pathway

“…ticipation of HSPGs. Endocytosis via HSPGs depends on their clustering by large, multimeric ligands (40,52,53). Thus, relatively larger LDL particles that also have higher affinity toward EL could be able to trigger clustering of HSPGs more efficiently than HDL.…”

The syndecan family of proteoglycans. Novel receptors mediating internalization of atherogenic lipoproteins in vitro.

“…2 indicates that TSP and LpL-lipoprotein complexes share cell-surface binding sites and a catabolic pathway. This is of particular interest, because the mechanism of TSP internalization is known to involve clustering of its cell-surface HSPG binding sites (94). Notice that TSP (95) and LpL-lipoprotein complexes are both large, multimeric ligands, which would be expected to provoke receptor clustering.…”