Build actin at the right place, right time

Cells explore their environment by sending out filopodia and lamellipodia. These protrusions encounter extracellular matrix components that encourage adhesion and cell spreading through actin polymerization. On page 881, DeMali et al. show how sites of cell adhesion specifically attract actin-polymerizing proteins, thus linking adhesion to protrusion.

Adhesion and actin polymerization are coordinated by an interaction between proteins essential for both. DeMali et al. identified an association between vinculin, a protein found in focal complexes, and the Arp2/3 actin nucleation and remodeling complex. Induction of lamellipodial formation (e.g., by EGF) or integrin clustering (e.g., by fibronectin) stimulated the binding of vinculin to Arp2/3. The strongest association required signaling effects downstream of PI3K, including Rac1-induced activation of Arp2/3 and a PIP₂-induced conformational change in vinculin.

Binding recruited Arp2/3 to focal complexes at the...