C-terminal Modification of Osteopontin Inhibits Interaction with the αVβ3-Integrin

• Published in: The Journal of biological chemistry 2012-02, Vol.287 (6), p.3788-3797
• Main Authors: Christensen, Brian, Kläning, Eva, Nielsen, Mette S., Andersen, Mikkel H., Sørensen, Esben S.
• Format: Article
• Language: English
• Subjects: Cell Adhesion; Cell Line; Humans; Integrin alphaVbeta3 - genetics; Integrin alphaVbeta3 - metabolism; Integrins; Osteopontin; Osteopontin - genetics; Osteopontin - metabolism; Phosphorylation; Protein Binding; Protein Phosphorylation; Protein Processing, Post-Translational - physiology; Protein Structure; Protein Structure and Folding; Protein Structure, Tertiary; Recombinant Protein Expression
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.277996

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 αVβ3-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 αVβ3-integrin. It is demonstrated that highly phosphorylated OPN has a much reduced capability to promote cell adhesion via the αVβ3-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 αVβ3-integrin, whereas modification of the N terminus does not influence the binding. The inhibited binding of the αVβ3-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 αVβ3-integrin by modification of the highly conserved C-terminal region of the protein.