Tyrosine Phosphorylation of the Integrin β3 Subunit Regulates β3 Cleavage by Calpain

Xiaodong Xi,Panagiotis Flevaris,Aleksandra Stojanovic,Athar Chishti,David R Phillips,Stephen C.T Lam,Xiaoping Du

doi:10.1074/jbc.c600039200

Abstract

Outside-in signaling of beta(3) integrins induces and requires phosphorylation at tyrosine 747 (Tyr(747)) and tyrosine 759 (Tyr(759)) of the beta(3) subunit, but the mechanism for this requirement is unclear. On the other hand, a key consequence of integrin signaling, cell spreading, is inhibited by calpain cleavage of beta(3) cytoplasmic domain. Here we show that beta(3) tyrosine phosphorylation inhibits calpain cleavage. Mutating both tyrosines to phenylalanine sensitizes beta(3) to calpain cleavage. Furthermore, phosphorylation at Tyr(747) and Tyr(759) of beta(3) in the focal adhesion sites and the leading edge of spreading platelets was differentially regulated. Selective dephosphorylation of Tyr(759) is associated with calpain cleavage at Tyr(759). Thus, one mechanism by which tyrosine phosphorylation promotes integrin signaling and cell spreading is its inhibition of calpain cleavage of the beta(3) cytoplasmic domain.

Highlights

Integrins mediate cell adhesion and transduce signals that are critical in the dynamic regulation of cell adhesion, spreading, migration, and proliferation [1, 2]
In studying the relationship between these two seemingly unrelated ␤3 modifications that regulate the function of the cytoplasmic domain of ␤3, we found that tyrosine phosphorylation in ␤3 cytoplasmic domain inhibits cleavage of ␤3 by calpain
Since calpain cleavage negatively regulates outside-in signaling-mediated cell spreading, our finding provides a mechanism by which tyrosine phosphorylation of ␤3 promotes integrin outside-in signaling

Summary

Introduction

Integrins mediate cell adhesion and transduce signals that are critical in the dynamic regulation of cell adhesion, spreading, migration, and proliferation [1, 2]. A key consequence of integrin signaling, cell spreading, is inhibited by calpain cleavage of ␤3 cytoplasmic domain. One mechanism by which tyrosine phosphorylation promotes integrin signaling and cell spreading is its inhibition of calpain cleavage of the ␤3 cytoplasmic domain.

Results

Conclusion