The glypicans (GPC) constitute a family of glycosylphosphatidylinositol (GPI)-anchored, heparan sulfate proteoglycans. Six members of this family have been identified in mammals (GPC1-GPC6). All glypican core proteins contain an N-terminal signal peptide, a large globular cysteine-rich domain (CRD) with 14 invariant cysteine residues, a stalk-like region containing the heparan sulfate attachment sites, and a C-terminal GPI attachment site.
Mutations in Glypican 3 cause a rare disorder in humans, Simpson-Golabi-Behmel Syndrome, which is characterized by pre- and postnatal overgrowth of multiple tissues and organs and an increased risk for developing embryonic tumors. These features are also present in the mouse knock-out of Glypican 3 indicating that Glypican 3 regulates cell survival and inhibits cell proliferation during development. Glypican 3 has been implicated in regulating many different signaling pathways including: IGF, FGF, BMP and Wnt. An endoproteolytic processing of Glypican 3 by proprotein convertases is required for the modulation of Wnt signaling. Direct interaction of Glypican 3 with FGF-basic has been observed and is mediated by the heparan sulfate chains.