Evidence for a differential functional regulation of the two β3-integrins αVβ3 and αIIbβ3

Abstract The functional regulation of integrins is a major determinant of cell adhesion, migration and tissue maintenance. The binding of cytoskeletal proteins to various sites of integrin cytoplasmic domains is a key mechanism of this functional regulation. Expression of recombinant integrin α IIb β 3 and α M β 2 lacking the GFFKR-region in CHO cells results in constitutively activated integrins. In contrast, CHO cells stably expressing either a GFFKR-deleted α V(del) β 3 or a FF to AA-substituted α V(AA) β 3 do not reveal a constitutively activated integrin. Adhesion to immobilized fibrinogen is strongly impaired in α V(del) β 3 or α V(AA) β 3 -expressing cells, whereas it is not impaired in α IIb β 3 and α M β 2 , both lacking the GFFKR-region. In a parallel plate flow chamber assay, α V β 3 -expressing cells adhere firmly to fibrinogen and spread even at shear rates of 15 to 20 dyn/cm 2 , whereas α V(del) β 3 or α V(AA) β 3 cells are detached at 15 dyn/cm 2 . Actin stress fiber formation and focal adhesion plaques containing α V β 3 are observed in α V β 3 cells but not in α V(del) β 3 or α V(AA) β 3 -expressing cells. As an additional manifestation of impaired outside–in signaling, phosphorylation of pp125 FAK was reduced in these cells. In summary, we report that the GFFKR-region of the α V -cytoplasmic domain and in particular two phenylalanines are essential for integrin α V β 3 function, especially for outside–in signaling. Our results suggest that the two β 3 -integrins α IIb β 3 and α V β 3 are differentially regulated via their GFFKR-region.