The F-actin side binding activity of the Arp2/3 complex is essential for actin nucleation and lamellipod extension

Maryse Bailly, Ilia Ichetovkin, Wayne Grant, Noureddine Zebda, Laura M. Machesky, Jeffrey E. Segall, John Condeelis

Research output: Contribution to journalArticlepeer-review

107 Scopus citations

Abstract

Most eukaryotic cells rely on localized actin polymerization to generate and sustain the protrusion activity necessary for cell movement [1, 2]. Such protrusions are often in the form of a flat lamellipod with a leading edge composed of a dense network of actin filaments [3, 4]. The Arp2/3 complex localizes within that network in vivo [3, 4] and nucleates actin polymerization and generates a branched network of actin filaments in vitro [5-7]. The complex has thus been proposed to generate the actin network at the leading edge of crawling cells in vivo [3, 4, 8]. However, the relative contributions of nucleation and branching to protrusive force are still unknown. We prepared antibodies to the p34 subunit of the Arp2/3 complex that selectively inhibit side binding of the complex to F-actin. We demonstrate that side binding is required for efficient nucleation and branching by the Arp2/3 complex in vitro. However, microinjection of these antibodies into cells specifically inhibits lamellipod extension without affecting the EGF-stimulated appearance of free barbed ends in situ. These results indicate that while the side binding activity of the Arp2/3 complex is required for nucleation in vitro and for protrusive force in vivo, it is not required for EGF-stimulated increases in free barbed ends in vivo. This suggests that the branching activity of the Arp2/3 complex is essential for lamellipod extension, while the generation of nucleation sites for actin polymerization is not sufficient.

Original languageEnglish (US)
Pages (from-to)620-625
Number of pages6
JournalCurrent Biology
Volume11
Issue number8
DOIs
StatePublished - Apr 17 2001

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

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