Stimulation of Fibroblast Growth Factor Receptor-1 Occupancy and Signaling by Cell Surface-Associated Syndecans and Glypican

• Published in: The Journal of cell biology 1996-04, Vol.133 (2), p.405-416
• Main Authors: Steinfeld, Robert, Van Den Berghe, Herman, David, Guido
• Format: Article
• Language: English
• Subjects: Base Sequence; Cell Differentiation; Cell growth; Cells; Cross-Linking Reagents; Fibroblast Growth Factor 2 - genetics; Fibroblast Growth Factor 2 - metabolism; Fibroblast Growth Factor 2 - pharmacology; Fibroblast growth factor receptors; Fibroblast growth factors; Fibroblasts; Glycophorin - analysis; Glycosaminoglycans - analysis; Glypicans; Hematopoietic Stem Cells - cytology; Heparan Sulfate Proteoglycans; Heparin; Heparin - pharmacology; Heparitin Sulfate - analysis; Heparitin Sulfate - genetics; Heparitin Sulfate - metabolism; Heparitin Sulfate - physiology; Humans; K562 cells; Lipopolysaccharide Receptors - analysis; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Membrane Glycoproteins - physiology; Molecular Sequence Data; Protein Binding; Proteoglycans - genetics; Proteoglycans - metabolism; Proteoglycans - physiology; Receptor Protein-Tyrosine Kinases; Receptor, Fibroblast Growth Factor, Type 1; Receptors; Receptors, Fibroblast Growth Factor - genetics; Receptors, Fibroblast Growth Factor - metabolism; Recombinant Fusion Proteins - isolation & purification; Recombinant Fusion Proteins - metabolism; Signal Transduction - physiology; Transfection; Tumor Cells, Cultured
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.133.2.405

The formation of distinctive basic FGF-heparan sulfate complexes is essential for the binding of bFGF to its cognate receptor. In previous experiments, cell-surface heparan sulfate proteoglycans extracted from human lung fibroblasts could not be shown to promote high affinity binding of bFGF when added to heparan sulfate-deficient cells that express FGF receptor-1 (FGFR1). In alternative tests to establish whether cell-surface proteoglycans can support the formation of the required complexes, K562 cells were first transfected with the IIIc splice variant of FGFR1 and then transfected with constructs coding for either syndecan-1, syndecan-2, syndecan-4 or glypican, or with an antisense syndecan-4 construct. Cells cotransfected with receptor and proteoglycan showed a two- to three-fold increase in neutral salt-resistant specific125I-bFGF binding in comparison to cells transfected with only receptor or cells cotransfected with receptor and anti-syndecan-4. Exogenous heparin enhanced the specific binding and affinity cross-linking of125I-bFGF to FGFR1 in receptor transfectants that were not cotransfected with proteoglycan, but had no effect on this binding and decreased the yield of bFGFR cross-links in cells that were cotransfected with proteoglycan. Receptor-transfectant cells showed a decrease in glycophorin A expression when exposed to bFGF. This suppression was dose-dependent and obtained at significantly lower concentrations of bFGF in proteoglycan-cotransfected cells. Finally, complementary cell-free binding assays indicated that the affinity of125I-bFGF for an immobilized FGFR1 ectodomain was increased threefold when the syndecan-4 ectodomain was coimmobilized with receptor. Equimolar amounts of soluble syndecan-4 ectodomain, in contrast, had no effect on this binding. We conclude that, at least in K562 cells, syndecans and glypican can support bFGF-FGFR1 interactions and signaling, and that cell-surface association may augment their effectiveness.