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Mol Biol Cell. 2013 Sep;24(18):2861-75. doi: 10.1091/mbc.E12-12-0857. Epub 2013 Jul 24.

Arp2/3 complex is essential for actin network treadmilling as well as for targeting of capping protein and cofilin.

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  • 1Institute of Genetics, University of Bonn, D-53115 Bonn, Germany Institute of Molecular Biotechnology, Austrian Academy of Sciences, A-1030 Vienna, Austria Johann Radon Institute for Computational and Applied Mathematics, Austrian Academy of Sciences, A-1030 Vienna, Austria Institute for Biophysical Chemistry, Hannover Medical School, D-30625 Hannover, Germany Helmholtz Centre for Infection Research, D-38124 Braunschweig, Germany Institute for Molecular Cell Biology, University of Münster, D-48149 Münster, Germany Oncology Research Unit, School of Medical Sciences, University of New South Wales, Sydney 2052, Australia Faculty of Mathematics, University of Vienna, A-1090 Vienna, Austria.

Abstract

Lamellipodia are sheet-like protrusions formed during migration or phagocytosis and comprise a network of actin filaments. Filament formation in this network is initiated by nucleation/branching through the actin-related protein 2/3 (Arp2/3) complex downstream of its activator, suppressor of cAMP receptor/WASP-family verprolin homologous (Scar/WAVE), but the relative relevance of Arp2/3-mediated branching versus actin filament elongation is unknown. Here we use instantaneous interference with Arp2/3 complex function in live fibroblasts with established lamellipodia. This allows direct examination of both the fate of elongating filaments upon instantaneous suppression of Arp2/3 complex activity and the consequences of this treatment on the dynamics of other lamellipodial regulators. We show that Arp2/3 complex is an essential organizer of treadmilling actin filament arrays but has little effect on the net rate of actin filament turnover at the cell periphery. In addition, Arp2/3 complex serves as key upstream factor for the recruitment of modulators of lamellipodia formation such as capping protein or cofilin. Arp2/3 complex is thus decisive for filament organization and geometry within the network not only by generating branches and novel filament ends, but also by directing capping or severing activities to the lamellipodium. Arp2/3 complex is also crucial to lamellipodia-based migration of keratocytes.

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