Glypican-1 Is Frequently Overexpressed in Human Gliomas and Enhances FGF-2 Signaling in Glioma Cells

Signaling by fibroblast growth factor 2 (FGF-2), an autocrine stimulator of glioma growth, is regulated by heparan sulfate proteoglycans (HSPGs) via a ternary complex with FGF-2 and the FGF receptor (FGFR). To characterize glioma growth signaling, we examined whether altered HSPGs contribute to loss of growth control in gliomas. In a screen of five human glioma cell lines, U118 and U251 cell HSPGs activated FGF-2 signaling via FGFR1c. The direct comparison of U251 glioma cells with normal astrocyte HSPGs demonstrated that the glioma HSPGs had a significantly elevated ability to promote FGF-2-dependent mitogenic signaling via FGFR1c. This enhanced activity correlated with a higher level of overall sulfation, specifically the abundance of 2S- and 6S-containing disaccharides. Glioma cell expression of the cell-surface HSPG glypican-1 closely mirrored the FGF-2 coactivator activity. Furthermore, forced expression of glypican-1 in (glypican-1-deficient) U87 glioma cells enhanced their FGF-2 response. Immunohistochemical analysis revealed a highly significant overexpression of glypican-1 in human astrocytoma and oligodendroglioma samples compared with nonneoplastic gliosis. In summary, these observations suggest that altered HSPGs contribute to enhanced signaling of FGF-2 via FGFR1c in gliomas with glypican-1 playing a significant role in this mitogenic pathway.