Differences in Regulation ofDrosophilaand Vertebrate Integrin Affinity by Talin

Abstract

Integrin-mediated cell adhesion is essential for development of multicellular organisms. In worms, flies, and vertebrates, talin forms a physical link between integrin cytoplasmic domains and the actin cytoskeleton. Loss of either integrins or talin leads to similar phenotypes. In vertebrates, talin is also a key regulator of integrin affinity. We used a ligand-mimetic Fab fragment, TWOW-1, to assess talin's role in regulating Drosophila αPS2βPS affinity. Depletion of cellular metabolic energy reduced TWOW-1 binding, suggesting αPS2βPS affinity is an active process as it is for vertebrate integrins. In contrast to vertebrate integrins, neither talin knockdown by RNA interference nor talin head overexpression had a significant effect on TWOW-1 binding. Furthermore, replacement of the transmembrane or talin-binding cytoplasmic domains of αPS2βPS with those of human αIIbβ3 failed to enable talin regulation of TWOW-1 binding. However, substitution of the extracellular and transmembrane domains of αPS2βPS with those of αIIbβ3 resulted in a constitutively active integrin whose affinity was reduced by talin knockdown. Furthermore, wild-type αIIbβ3 was activated by overexpression of Drosophila talin head domain. Thus, despite evolutionary conservation of talin's integrin/cytoskeleton linkage function, talin is not sufficient to regulate Drosophila αPS2βPS affinity because of structural features inherent in the αPS2βPS extracellular and/or transmembrane domains.