title: Cdc42, Par6, and aPKC regulate Arp2/3-mediated endocytosis to control local adherens junction stability.
abstract: BACKGROUND
  By acting as a dynamic link between adjacent cells in a monolayer, adherens junctions (AJs) maintain the integrity of epithelial tissues while allowing for neighbor exchange. Although it is not currently understood how this combination of AJ stability and plasticity is achieved, junctionally associated actin filaments are likely to play a role, because actin-based structures have been implicated in AJ organization and in the regulation of junctional turnover.
  
  
  RESULTS
  Here, through exploring the role of actin cytoskeletal regulators in the developing Drosophila notum, we have identified a critical role for Cdc42-aPKC-Par6 in the maintenance of AJ organization. In this system, the loss or inhibition of Cdc42-aPKC-Par6 leads to junctional discontinuities, the formation of ectopic junctional structures, and defects in apical actin cytoskeletal organization. Affected cells also undergo progressive apical constriction and, frequently, delamination. Surprisingly, this Cdc42-aPKC-Par6-dependent regulation of junctional stability was found to be independent of several well-known targets of Cdc42-aPKC-Par6: Baz, Lgl, Rac, and SCAR. However, similar AJ defects are observed in wasp, arp2/3, and dynamin mutant cells, suggesting a requirement for actin-mediated endocytosis in the maintenance of junctional stability downstream of Cdc42. This was confirmed in endocytosis assays, which revealed a requirement for Cdc42, Arp2/3, and Dynamin for normal rates of E-cadherin internalization.
  
  
  CONCLUSIONS
  By focusing on the molecular mechanisms required to maintain an epithelium, this analysis reveals a novel role for the epithelial polarity machinery, Cdc42-Par6-aPKC, in local AJ remodeling through the control of Arp2/3-dependent endocytosis.
authors.affiliation: MRC Laboratory for Molecular Cell Biology, Division of Life Sciences, University College London, Gower Street, London WC1E 6BT, UK.
authors.forename: Marios
authors.initials: M
authors.lastname: Georgiou
authors.forename: Eliana
authors.initials: E
authors.lastname: Marinari
authors.forename: Jemima
authors.initials: J
authors.lastname: Burden
authors.forename: Buzz
authors.initials: B
authors.lastname: Baum
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D022005:Adherens Junctions / Q000378:metabolism*; D000818:Animals; D015820:Cadherins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D004330:Drosophila / Q000166:cytology*; D029721:Drosophila Proteins / Q000378:metabolism*; D034281:Dynamins / Q000378:metabolism; D004705:Endocytosis; D011493:Protein Kinase C / Q000378:metabolism*; D011679:Pupa / Q000166:cytology; D051316:Wiskott-Aldrich Syndrome Protein / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D015820:Cadherins; D029721:Drosophila Proteins; C477859:WASp protein, Drosophila; D051316:Wiskott-Aldrich Syndrome Protein; C115015:PKC-3 protein; C532584:Par-6 protein, Drosophila; D011493:Protein Kinase C; D020764:cdc42 GTP-Binding Protein; D034281:Dynamins