title: C-terminal modification of osteopontin inhibits interaction with the αVβ3-integrin.
abstract: Osteopontin (OPN) is a multifunctional phosphorylated protein containing the integrin binding sequence Arg-Gly-Asp through which it interacts with several integrin receptors, such as the α(V)β(3)-integrin. OPN exists in many different isoforms differing in phosphorylation status that are likely to interact differently with integrins. The C-terminal region of OPN is particularly well conserved among mammalian species, which suggests an important functional role of this region. In this study, we show that modification of the extreme C terminus of OPN plays an important regulatory role for the interaction with the α(V)β(3)-integrin. It is demonstrated that highly phosphorylated OPN has a much reduced capability to promote cell adhesion via the α(V)β(3)-integrin compared with lesser phosphorylated forms. The cell attachment promoted by highly phosphorylated OPN could be greatly increased by both dephosphorylation and proteolytic removal of the C terminus. Using recombinantly expressed OPN containing a tag in the N or C terminus, it is shown that a modification in the C-terminal part significantly reduces the adhesion of cells to OPN via the α(V)β(3)-integrin, whereas modification of the N terminus does not influence the binding. The inhibited binding of the α(V)β(3)-integrin to OPN could be restored by proteolytic removal of the C terminus by thrombin and plasmin. These data illustrate a novel mechanism regulating the interaction of OPN and the α(V)β(3)-integrin by modification of the highly conserved C-terminal region of the protein.
authors.affiliation: Protein Chemistry Laboratory, Department of Molecular Biology and Genetics, Aarhus University, DK-8000 Aarhus, Denmark.
authors.forename: Brian
authors.initials: B
authors.lastname: Christensen
authors.forename: Eva
authors.initials: E
authors.lastname: Kläning
authors.forename: Mette S
authors.initials: MS
authors.lastname: Nielsen
authors.forename: Mikkel H
authors.initials: MH
authors.lastname: Andersen
authors.forename: Esben S
authors.initials: ES
authors.lastname: Sørensen
mesh_terms: D002460:Cell Line; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000235:genetics / Q000378:metabolism*; D053495:Osteopontin / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D017434:Protein Structure, Tertiary
chemical_list: D039302:Integrin alphaVbeta3; D053495:Osteopontin