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 S. Condeelis

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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

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Actin-Related Protein 2-3 Complex
actin
Actins
Nucleation
Polymerization
polymerization
branching
microfilaments
Actin Cytoskeleton
Epidermal Growth Factor
antibodies
Antibodies
Microinjections
Eukaryotic Cells
cell movement
Cell Movement
eukaryotic cells
cells
Cells
In Vitro Techniques

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)

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The F-actin side binding activity of the Arp2/3 complex is essential for actin nucleation and lamellipod extension. / Bailly, Maryse; Ichetovkin, Ilia; Grant, Wayne; Zebda, Noureddine; Machesky, Laura M.; Segall, Jeffrey E.; Condeelis, John S.

In: Current Biology, Vol. 11, No. 8, 17.04.2001, p. 620-625.

Research output: Contribution to journalArticle

Bailly, Maryse ; Ichetovkin, Ilia ; Grant, Wayne ; Zebda, Noureddine ; Machesky, Laura M. ; Segall, Jeffrey E. ; Condeelis, John S. / The F-actin side binding activity of the Arp2/3 complex is essential for actin nucleation and lamellipod extension. In: Current Biology. 2001 ; Vol. 11, No. 8. pp. 620-625.
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