Abstract
Cell Surface Heparan Sulfate Proteoglycans: Selective Regulators of Ligand-Receptor Encounters
Highlights
From the Division of Newborn Medicine, Department of Pediatrics, Children’s Hospital, Harvard Medical School, Boston, Massachusetts 02115
Cell surface heparan sulfate proteoglycans (HSPGs),1 substantially more abundant than most receptors, modulate encounters of extracellular protein ligands with their receptors by forming HSprotein complexes
Two gene families account for most cell surface HSPGs
Summary
The glypican core proteins contain six invariant disulfide bonds, are likely to be globular, and place HS chains adjacent to the plasma membrane Expression of both the syndecans and glypicans is extensively regulated during mouse embryogenesis and results in discrete adult expression patterns for each HSPG such that every adherent cell exhibits a distinct repertoire of cell surface HSPGs. Binding to HS chains is remarkably widespread among extracellular proteins, especially matrix proteins, proteases and their inhibitors, lipases, lipoproteins, growth factors and their binding proteins, cytokines, chemokines, collectins, and antimicrobial peptides. A recently identified intracellular protein, syndesmos, binds to the cytoplasmic domain of syndecan-4 via the C1 and V subdomains [23] This interaction can regulate cell spreading and actin stress fiber organization. Syndecan-1, the predominant HSPG in mammary epithelial cells, apparently acts as a coreceptor for TABLE I Mutations identified in HS biosynthetic enzyme and proteoglycan core protein genes
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