Beta3 integrin activation improves alphavbeta3-mediated retraction of fibrin matrices

Integrins are heterodimeric transmembrane glycoproteins that mediate cell interactions with the extracellular matrix. In vivo, integrin affinity can be modulated by intracellular signaling events. This can be simulated by a point mutation (D723R) in the cytoplasmic tail of the beta3 integrin subunit which results in constitutive activation. The effects of beta3 integrin activation on the function of alphavbeta3, an integrin which is important to the adhesive events of multiple cell types, were addressed using Chinese hamster ovary cells expressing either the wild-type alphavbeta3 integrin or the mutant alphavbeta3(D723R). The interactions of these cell lines with fibrin matrices were compared.

Receptor expression levels were confirmed by FACS analyses using a monoclonal anti-alphavbeta3 antibody. Cell attachment to fibrin-coated dishes was determined after 1 h by fixation and crystal violet staining followed by elution of the dye and OD measurement. Fibrin clot retraction was measured by culturing cells in fibrin clots for 24 h. The clots were detached from the dish and the surface area was calculated at individual time points.

CHO alphavbeta3(D723R) cells displayed a greater than twofold increase in attachment to fibrinogen or to fibrin matrices when compared to wild-type transfectants. Further, CHO alphavbeta3(D723R) cell retraction of fibrin matrices was significantly greater at nearly all time points.

Activation of the beta3 integrin subunit significantly improves the interaction of alphavbeta3 with fibrin and may play a role in the integrin-mediated signaling events which occur following vascular injury.