title: Heparan sulfate proteoglycans are receptors for the cell-surface trafficking and biological activity of transglutaminase-2.
abstract: Transglutaminase type 2 (TG2) is both a protein cross-linking enzyme and a cell adhesion molecule with an elusive unconventional secretion pathway. In normal conditions, TG2-mediated modification of the extracellular matrix modulates cell motility, proliferation and tissue repair, but under continuous cell insult, higher expression and elevated extracellular trafficking of TG2 contribute to the pathogenesis of tissue scarring. In search of TG2 ligands that could contribute to its regulation, we characterized the affinity of TG2 for heparan sulfate (HS) and heparin, an analogue of the chains of HS proteoglycans (HSPGs). By using heparin/HS solid-binding assays and surface plasmon resonance we showed that purified TG2 has high affinity for heparin/HS, comparable to that for fibronectin, and that cell-surface TG2 interacts with heparin/HS. We demonstrated that cell-surface TG2 directly associates with the HS chains of syndecan-4 without the mediation of fibronectin, which has affinity for both syndecan-4 and TG2. Functional inhibition of the cell-surface HS chains of wild-type and syndecan-4-null fibroblasts revealed that the extracellular cross-linking activity of TG2 depends on the HS of HSPG and that syndecan-4 plays a major but not exclusive role. We found that heparin binding did not alter TG2 activity per se. Conversely, fibroblasts deprived of syndecan-4 were unable to effectively externalize TG2, resulting in its cytosolic accumulation. We propose that the membrane trafficking of TG2, and hence its extracellular activity, is linked to TG2 binding to cell-surface HSPG.
authors.affiliation: School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Scarpellini
authors.forename: Renée
authors.initials: R
authors.lastname: Germack
authors.forename: Hugues
authors.initials: H
authors.lastname: Lortat-Jacob
authors.forename: Takashi
authors.initials: T
authors.lastname: Muramatsu
authors.forename: Ellen
authors.initials: E
authors.lastname: Billett
authors.forename: Timothy
authors.initials: T
authors.lastname: Johnson
authors.forename: Elisabetta A M
authors.initials: EA
authors.lastname: Verderio
mesh_terms: D000818:Animals; D020405:Dermis / Q000166:cytology; D005110:Extracellular Space / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism*; D006493:Heparin / Q000378:metabolism; D006497:Heparan Sulfate / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D021381:Protein Transport / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D053671:Syndecan-4 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D011503:Transglutaminases / Q000378:metabolism*
chemical_list: D019204:GTP-Binding Proteins; D019812:Heparan Sulfate Proteoglycans; D006493:Heparin; D006497:Heparan Sulfate; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011956:Receptors, Cell Surface; D053671:Syndecan-4; D011503:Transglutaminases; C508306:Sdc4 protein, mouse