Cytoskeletal protein radixin activates integrin αMβ2 by binding to its cytoplasmic tail

Talin binding of integrins, via its band 4.1, ezrin, radixin, and moesin (FERM)-homologous domain, directly activates the integrin receptor. However, it is not known whether other FERM-containing proteins also possess such an integrin activating capability. We report here that radixin, one of the original FERM-domain proteins, binds to the membrane-proximal region of the integrin β2 but not αM cytoplasmic tail. Importantly, we show that radixin binding significantly enhances the adhesive activity of integrin αMβ2. Given the distinct biological activities of radixin and talin, radixin may represent a novel talin-independent pathway for integrin activation under specific settings.