α-Actinin-4/FSGS1 is required for Arp2/3-dependent actin assembly at the adherens junction

J Cell Biol. 2012 Jan 9;196(1):115-30. doi: 10.1083/jcb.201103116.

Abstract

We have developed an in vitro assay to study actin assembly at cadherin-enriched cell junctions. Using this assay, we demonstrate that cadherin-enriched junctions can polymerize new actin filaments but cannot capture preexisting filaments, suggesting a mechanism involving de novo synthesis. In agreement with this hypothesis, inhibition of Arp2/3-dependent nucleation abolished actin assembly at cell-cell junctions. Reconstitution biochemistry using the in vitro actin assembly assay identified α-actinin-4/focal segmental glomerulosclerosis 1 (FSGS1) as an essential factor. α-Actinin-4 specifically localized to sites of actin incorporation on purified membranes and at apical junctions in Madin-Darby canine kidney cells. Knockdown of α-actinin-4 decreased total junctional actin and inhibited actin assembly at the apical junction. Furthermore, a point mutation of α-actinin-4 (K255E) associated with FSGS failed to support actin assembly and acted as a dominant negative to disrupt actin dynamics at junctional complexes. These findings demonstrate that α-actinin-4 plays an important role in coupling actin nucleation to assembly at cadherin-based cell-cell adhesive contacts.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism*
  • Actin-Related Protein 2-3 Complex / physiology*
  • Actinin / genetics
  • Actinin / physiology*
  • Actins / analysis
  • Adherens Junctions / metabolism*
  • Animals
  • Cadherins / metabolism
  • Cell Adhesion / genetics
  • Cell Line
  • Dogs
  • Point Mutation
  • Polymerization

Substances

  • Actin-Related Protein 2-3 Complex
  • Actins
  • Cadherins
  • Actinin