PT  - JOURNAL ARTICLE
AU  - Markku Hakala
AU  - Hugo Wioland
AU  - Mari Tolonen
AU  - Antoine Jegou
AU  - Guillaume Romet-Lemonne
AU  - Pekka Lappalainen
TI  - Twinfilin uncaps filament barbed ends to promote turnover of lamellipodial actin networks
AID  - 10.1101/864769
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 864769
4099  - http://biorxiv.org/content/early/2019/12/04/864769.short
4100  - http://biorxiv.org/content/early/2019/12/04/864769.full
AB  - Coordinated polymerization of actin filaments provides force for cell migration, morphogenesis, and endocytosis. Capping Protein (CP) is central regulator of actin dynamics in all eukaryotes. It binds actin filament (F-actin) barbed ends with high affinity and slow dissociation kinetics to prevent filament polymerization and depolymerization. In cells, however, CP displays remarkably rapid dynamics within F-actin networks, but the underlying mechanism has remained enigmatic. We report that a conserved cytoskeletal regulator, twinfilin, is responsible for CP’s rapid dynamics and specific localization in cells. Depletion of twinfilin led to stable association of CP with cellular F-actin arrays and its treadmilling throughout leading-edge lamellipodium. These were accompanied by diminished F-actin disassembly rates. In vitro single filament imaging approaches revealed that twinfilin directly promotes dissociation of CP from filament barbed ends, while allowing subsequent filament depolymerization. These results uncover an evolutionary conserved bipartite mechanism that controls how actin cytoskeleton-mediated forces are generated in cells.