Zasp and talin – working together to activate integrins

Integrins are heterodimeric adhesion receptors that link the extracellular matrix (ECM) to the cytoskeleton; they are activated by the binding of talin to the cytoplasmic tail of β-integrin, which results in a conformational change of the integrin extracellular domains and allows ligand binding. Additional factors regulate integrin activation, and either act through talin or directly on integrins, but the underlying mechanisms are not fully understood. On page 5647, Frieder Schöck, David Calderwood and colleagues investigate the role of Z-band alternatively spliced PDZ-motif-containing protein (Zasp) in the activation of β1-integrins. Zasp is known to localise to integrin adhesion sites, but was thought to function primarily in the assembly and maintenance of the muscle contractile machinery. Here, the authors report that co-expression of Zasp with the talin head domain potentiates α5β1 integrin activation in Chinese hamster ovary (CHO) cells, suggesting that Zasp cooperates with talin to activate integrins. They also show that, in Drosophila, Zasp deficiency leads to detachment of αPS2βPS integrins from the ECM, an indicator of perturbed integrin activation in vivo, without affecting talin localisation. Moreover, they find that Zasp specifically coactivates β1- and not β3-integrins, which are activated by kindlins. Taken together, these data identify Zasp as a new regulator of integrin activation, with a mode of action that is distinct from that of other known integrin coactivators.