Importance of membrane-proximal N-glycosylation on integrin beta 1 in its activation and complex formation

N-Glycosylation of integrin alpha 5 beta 1 plays important roles in cell biologic functions; however, the mechanisms that underlie those roles remain poorly understood. Here, we present evidence that the membrane-proximal N-glycosylation on integrin beta 1 could positively regulate cell migration by promoting beta 1 activation. The S4-6 beta 1 mutant contains only 3 N-glycosylation sites, which are essential for alpha 5 and beta 1 heterodimer formation, and despite only a small difference in expression levels of alpha 5 beta 1 between wild-type and S4-6 mutant, cell spreading and migration of the S4-6 mutant was significantly decreased compared with that of control. Consistent with these phenotypes, beta 1-mediated cellular signaling and its activation were clearly suppressed in the S4-6 mutant. Of note, these developments could be rescued by restoration of N-glycosylation sites in the membrane-proximal domain. Further study on the regulatory mechanisms suggested that membrane-proximal N-glycosylation is critical for intermolecular interactions between integrin beta 1 and other cell membrane proteins, such as syndecan-4 and epidermal growth factor receptor. Moreover, alpha 2,6-sialylation is required for beta 1 activation. These data suggest a novel regulatory mechanism where in N-glycosylation near the cell membraneon beta 1 may serve as a platform that facilitates its complex formation on the cell membrane, thereby affecting integrin-mediated functions.