Slingshot to the lamellipod

The actin cytoskeleton at the front of migrating cells is an ever-changing species. Although actin is polymerized in the lamellipod, the filaments that are built remain dynamic. Their turnover is mediated by cofilin, which stimulates filament disassembly at or near the pointed ends, thus providing monomers for further polymerization. On page 465, Nagata-Ohashi et al. show that actin filaments take care of their own dynamic behavior via Slingshot-1L (SSH1L), a phosphatase that activates cofilin.

In vitro, F-actin activated SSH1L 10-fold. Migrating epithelial cells accumulated SSH1L (and thus dephosphorylated and active cofilin) in the lamellipod, and this depended on an intact actin assembly.

To bind to F-actin and activate cofilin, SSH1L must first be released from an interaction with 14–3-3 proteins, which sequester SSH1L in the cytoplasm. SSH1L escaped this interaction when...