Altered glycosylation of glycolipids, glycoproteins, or proteoglycans are frequently observed in tumor tissues and cultured cancer cell lines. These changes have diagnostic use but also can contribute to the ability of tumor cells to grow, induce neovascularization, metastasize, and avoid host immune surveillance. We are primarily studying sulfated glycoconjugates and their interaction with extracellular matrix and cell surface adhesion molecules, including thrombospondin-1, laminin, and apolipoprotein E. Human small cell lung carcinoma cell lines are used to examine expression and function of novel sulfated glycolipids. These glycolipids interact with thrombospondin-1 and contribute to adhesion of SCLC cells on a thrombospondin-1 matrix. Endothelial cell heparan sulfate proteoglycans are used to examine the specificity of thrombospondin-1 for binding to proteoglycans required for signaling by angiogenic growth factors. Heparin oligosaccharides are being used to define the molecular basis for interactions of heparin and heparan sulfate proteoglycans with two binding motifs on the thrombospondin-1 molecule. Inhibitors of these interactions are being tested for effects on angiogenesis and tumor growth.Interactions of heparin with intact human thrombospondin-1 (TSP1) and two heparin-binding fragments of TSP1 were characterized using chemically modified heparins, a vascular heparan sulfate proteoglycan, and a series of heparin oligosaccharides prepared by partial deaminative cleavage. The avidity of TSP1 binding increased with oligosaccharide size, with plateaus at 4 to 6 and at 8 to 10 monosaccharide units. The dependence on oligosaccharide size for binding to the recombinant amino-terminal heparin-binding domain of TSP1 was the same as that of the intact TSP1 molecule but differed from that of a synthetic heparin-binding peptide from the type 1 repeats, suggesting that the interaction between intact TSP1 and heparin is primarily mediated by the amino-terminal domain. Based on activities of chemically modified heparins, binding to TSP1 depended primarily on 2-N- and 6-O-sulfation of glucosamine and to a lesser degree on 2,3-O-sulfation and the carboxyl residues of the uronic acids. In contrast, all of these modifications were required for binding of heparin to the type 1 repeat peptides. Affinity purification of heparin octasaccharides on immobilized TSP1 type 1 repeat peptides revealed a preference for oligosaccharides containing the disaccharide sequence IdoA(2-OSO3)alpha1-4-GlcNS(6-OSO3). Binding of these oligosaccharides to the peptide required the Trp residues. These data demonstrate that the heparin-binding specificities of intact TSP1 and peptides from the type 1 repeats overlap with that of basic fibroblast growth factor (FGF2) and are consistent with the ability of these TSP1-derived molecules to inhibit FGF2-stimulated angiogenesis.
Showing the most recent 10 out of 18 publications
