title: Inter-α-inhibitor impairs TSG-6-induced hyaluronan cross-linking.
abstract: Under inflammatory conditions and in the matrix of the cumulus-oocyte complex, the polysaccharide hyaluronan (HA) becomes decorated covalently with heavy chains (HCs) of the serum glycoprotein inter-α-inhibitor (IαI). This alters the functional properties of the HA as well as its structural role within extracellular matrices. The covalent transfer of HCs from IαI to HA is catalyzed by TSG-6 (tumor necrosis factor-stimulated gene-6), but TSG-6 is also known as a HA cross-linker that induces condensation of the HA matrix. Here, we investigate the interplay of these two distinct functions of TSG-6 by studying the ternary interactions of IαI and TSG-6 with well defined films of end-grafted HA chains. We demonstrate that TSG-6-mediated cross-linking of HA films is impaired in the presence of IαI and that this effect suppresses the TSG-6-mediated enhancement of HA binding to CD44-positive cells. Furthermore, we find that the interaction of TSG-6 and IαI in the presence of HA gives rise to two types of complexes that independently promote the covalent transfer of heavy chains to HA. One type of complex interacts very weakly with HA and is likely to correspond to the previously reported covalent HC·TSG-6 complexes. The other type of complex is novel and binds stably but noncovalently to HA. Prolonged incubation with TSG-6 and IαI leads to HA films that contain, in addition to covalently HA-bound HCs, several tightly but noncovalently bound molecular species. These findings have important implications for understanding how the biological activities of TSG-6 are regulated, such that the presence or absence of IαI will dictate its function.
authors.affiliation: From the Biosurfaces Unit, CIC biomaGUNE, 20009 Donostia-San Sebastian, Spain.
authors.forename: Natalia S
authors.initials: NS
authors.lastname: Baranova
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Foulcer
authors.forename: David C
authors.initials: DC
authors.lastname: Briggs
authors.forename: Viranga
authors.initials: V
authors.lastname: Tilakaratna
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Enghild
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Milner
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Day
authors.forename: Ralf P
authors.initials: RP
authors.lastname: Richter
mesh_terms: D000510:Alpha-Globulins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D015153:Blotting, Western; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D003432:Cross-Linking Reagents / Q000737:chemistry; D006801:Humans; D018960:Hyaluronan Receptors / Q000737:chemistry / Q000378:metabolism*; D006820:Hyaluronic Acid / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008857:Microscopy, Interference; D011485:Protein Binding; D020349:Surface Plasmon Resonance
chemical_list: D000510:Alpha-Globulins; D015815:Cell Adhesion Molecules; D003432:Cross-Linking Reagents; D018960:Hyaluronan Receptors; C072273:TNFAIP6 protein, human; C011877:inter-alpha-inhibitor; D006820:Hyaluronic Acid
keywords: Carbohydrate-binding Protein; Extracellular Matrix; Extracellular Matrix Proteins; Glycosaminoglycan; Hyaluronan; Multifunctional Protein; Protein Complexes; Protein Self-assembly; Protein-Protein Interactions; Supramolecular Interactions