Kinetic regulation of β3 integrin tyrosine phosphorylation

Abstract

Tyrosine phosphorylation of β3 integrins is a permissive stage in the activation of αIIbβ3 and αvβ3 in platelets and leukocytes, respectively. In this study we demonstrated direct phosphorylation of β3 integrins as a result of interaction with soluble monomeric ligand, and we characterized the differential kinetics of β3 phosphorylation as a consequence of α subunit pairing. We found that 133 phosphorylation is initiated by RGD peptide binding in a dose-dependent and saturable fashion with αIIbβ3 becoming phosphorylated and dephosphorylated more rapidly than αvβ3. Site mapping of phosphate incorporation reveals significant phosphorylation at Tyr-747 in both β3 integrin species with incorporation at Tyr-759 found at significant levels only in αIIbβ3. Mutation of cytoplasmic β3 tyrosine residues in a transfection model prevents cell adhesion via these integrins. These data demonstrate that recognition of ligand is sufficient to induce 133 tyrosine phosphorylation and suggests that this event is regulated by the α subunit pairing of β3.