Optogenetic-based Localization of Talin to the Plasma Membrane Promotes Activation of β3 Integrins.
Abstract:
Interaction of talin with the cytoplasmic tails of integrin β triggers integrin activation, leading to an increase of integrin affinity/avidity for extracellular ligands. In talin knockout mice, loss of talin interaction with platelet integrin αIIbβ3 causes a severe hemostatic defect, and loss of talin interaction with endothelial cell integrin αVβ3 affects angiogenesis. In normal cells, talin is auto-inhibited and localized in the cytoplasm. Here we employed an optogenetic platform to assess whether recruitment of full-length talin to the plasma membrane was sufficient to induce integrin activation. A dimerization module (CRY2 fused to the N-terminus of talin; CIBN-CAAX) responsive to 450 nm (blue) light was inserted into CHO cells and endothelial cells also expressing αIIbβ3 or αVβ3, respectively. Thus, exposure of the cells to blue light caused a rapid and reversible recruitment of CRY2-talin to the CIBN-CAAX-decorated plasma membrane. This resulted in β3 integrin activation in both cell types, as well as increasing migration of the endothelial cells. However, membrane recruitment of talin was not sufficient for integrin activation, as membrane-associated Rap1-GTP was also required. Moreover, talin mutations that interfered with its direct binding to Rap1 abrogated β3 integrin activation. Altogether, these results define a role for the plasma membrane recruitment of talin in β3 integrin activation, and they suggest a nuanced sequence of events thereafter involving Rap1-GTP.
