DAAM1 formin and Ena/VASP proteins assemble functionally distinct actin filaments for focal adhesions

Abstract

Eukaryotic cells contain multiple biochemically distinct actin filament networks, which enable versatile functions of actin in a range of cellular processes. Yet, the mechanisms by which specific actin filament networks are assembled in a common cytoplasm remain elusive. Here, we investigated how functionally distinct actin nanoscale layers, specified by α-actinin and tropomyosin isoforms, Tpm1.6 and Tpm3.2, are assembled at focal adhesions. By combining genetic perturbations with mitochondrial-targeting of actin polymerases, we discovered that DAAM1 formin assembles Tpm3.2-actin filaments, whereas Ena/VASP family proteins polymerize α-actinin cross-linked actin filament bundles at focal adhesions. Consequently, loss of DAAM1 dampened Tpm3.2 protein levels and impaired focal adhesion disassembly, thus phenocopying Tpm3.2-deficient cells. In contrast, Ena/VASP depletion led to defective focal adhesion maturation and loss of α-actinin from focal adhesions. More broadly, our study highlights specific roles for formin and Ena/VASP family proteins in assembling biochemically and functionally distinct linear actin filament arrays in cells.