Coronin 1B Coordinates Arp2/3 Complex and Cofilin Activities at the Leading Edge

Actin filament nucleation and turnover are interdependent processes in migrating cells, but the mechanisms coordinating these events are unknown. Coronin 1B influences motility, lamellipodial dynamics and actin filament architecture at the leading edge of Rat2 cells in a manner consistent with a role in coordinating filament formation and turnover. Coronin 1B interacts simultaneously with both Arp2/3 complex and Slingshot (SSH1L) phosphatase, two regulators of actin filament formation and turnover, respectively. Coronin 1B inhibits filament nucleation by Arp2/3 complex and this inhibition is attenuated by phosphorylation of Coronin 1B on Serine 2, a site targeted by SSH1L. Coronin 1B directs SSH1L to lamellipodia where it likely regulates Cofilin. Accordingly, depleting Coronin 1B increases phospho-Cofilin levels and expressing activated Cofilin partially suppresses the effects on lamellipodia dynamics of Coronin 1B depletion. Thus, Coronin 1B coordinates filament nucleation via Arp2/3 complex and turnover by Cofilin at the leading edge of migrating cells