title: Regulated shedding of syndecan-1 and -4 ectodomains by thrombin and growth factor receptor activation.
abstract: The syndecan family of transmembrane heparan sulfate proteoglycans is abundant on the surface of all adherent mammalian cells. Syndecans bind and modify the action of various growth factors/cytokines, proteases/antiproteases, cell adhesion molecules, and extracellular matrix components. Syndecan expression is highly regulated during wound repair, a process orchestrated by many of these effectors. Each syndecan ectodomain is shed constitutively by cultured cells, but the mechanism and significance of this shedding are not understood. Therefore, we examined (i) whether physiological agents active during wound repair influence syndecan shedding, and (ii) whether wound fluids contain shed syndecan ectodomains. Using SVEC4-10 endothelial cells we find that certain proteases and growth factors accelerate shedding of the syndecan-1 and -4 ectodomains. Protease-accelerated shedding is completely inhibited by serum-containing media. Thrombin activity is duplicated by the 14-amino acid thrombin receptor agonist peptide that directly activates the thrombin receptor and is not inhibited by serum. Epidermal growth factor family members accelerate shedding but FGF-2, platelet-derived growth factor-AB, transforming growth factor-beta, tumor necrosis factor-alpha, and vascular endothelial cell growth factor 165 do not. Shed ectodomains are soluble, stable in the conditioned medium, have the same size core proteins regardless whether shed at a basal rate, or accelerated by thrombin or epidermal growth factor-family members and are found in acute human dermal wound fluids. Thus, shedding is accelerated by activation of at least two distinct receptor classes, G protein-coupled (thrombin) and protein tyrosine kinase (epidermal growth factor). Proteases and growth factors active during wound repair can accelerate syndecan shedding from cell surfaces. Regulated shedding of syndecans suggests physiological roles for the soluble proteoglycan ectodomains.
authors.affiliation: Joint Program in Neonatology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: S V
authors.initials: SV
authors.lastname: Subramanian
authors.forename: M L
authors.initials: ML
authors.lastname: Fitzgerald
authors.forename: M
authors.initials: M
authors.lastname: Bernfield
mesh_terms: D000595:Amino Acid Sequence; D066258:Amphiregulin; D000906:Antibodies; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D066255:EGF Family of Proteins; D016228:Endothelial Growth Factors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000502:physiology*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D000939:Epitopes; D066246:ErbB Receptors / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006023:Glycoproteins / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology*; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011509:Proteoglycans / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000502:physiology*; D018179:Receptors, Thrombin / Q000502:physiology*; D011994:Recombinant Proteins / Q000494:pharmacology; D012867:Skin / Q000293:injuries; D053668:Syndecan-1; D053671:Syndecan-4; D053667:Syndecans; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D016211:Transforming Growth Factor alpha / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D014947:Wounds and Injuries / Q000503:physiopathology
chemical_list: C587848:AREG protein, human; D066258:Amphiregulin; D000906:Antibodies; D066255:EGF Family of Proteins; D016228:Endothelial Growth Factors; D000939:Epitopes; D006023:Glycoproteins; D006133:Growth Substances; C587883:HBEGF protein, human; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D010982:Platelet-Derived Growth Factor; D011509:Proteoglycans; D017978:Receptors, Growth Factor; D018179:Receptors, Thrombin; D011994:Recombinant Proteins; C508241:SDC1 protein, human; C508304:SDC4 protein, human; D053668:Syndecan-1; D053671:Syndecan-4; D053667:Syndecans; D016211:Transforming Growth Factor alpha; D014409:Tumor Necrosis Factor-alpha; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D013917:Thrombin; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate