Osteopontin O-glycosylation contributes to its phosphorylation and cell adhesion properties

In this study, we demonstrated that OPN O-glycosylation self-regulates its biological activities and also affects its phosphorylation status. We prepared two recombinant OPNs, wild-type (WT)-OPN and mutant OPN (ΔO-OPN), lacking five O-glycosylation sites at a threonine–proline rich region. O-glycan defects in OPN increased its phosphorylation level, as observed by dephosphorylation assays. Moreover, compared with WT-OPN, ΔO-OPN exhibited enhanced cell spreading and adhesion activities and decreased associations with β1 integrins. This suggested that defects in O-glycans in OPN altered these activities, and that β1 integrins have a less important role in adhesion to ΔO-OPN. Cell adhesion activity of dephosphorylated ΔO-OPN was higher than cell adhesion activities of ΔO-OPN and dephosphorylated WT-OPN. This suggested that some of the phosphorylation in ΔO-OPN caused by O-glycan defects and O-glycans of OPN suppressed OPN cell adhesion activity. Thus, functional activities of OPN can be determined by the combined glycosylation and phosphorylation statuses and not by either status alone.

Source: BJ Signal - July 7, 2014 Category: Biochemistry Authors: Y Kariya, M Kanno, K Matsumoto-Morita, M Konno, Y Yamaguchi, Y Hashimoto Tags: BJ Biomolecules Source Type: research