title: Scrib controls Cdc42 localization and activity to promote cell polarization during astrocyte migration.
abstract: BACKGROUND
  Mammalian Scribble (Scrib) plays a conserved role in polarization of epithelial and neuronal cells. Polarization is essential for migration of a variety of cell types; however, the function of Scrib in this context remains unclear. Scrib has been shown to interact with betaPIX, a guanine nucleotide exchange factor for the small GTPases Rac and Cdc42. Cdc42 controls cell polarity from yeast to mammals during asymmetric cell division and epithelial cell polarization, as well as during cell migration. Cdc42 is, in particular, required for polarization and orientation of astrocytes in a scratch-induced polarized migration assay. Using this assay, we characterized Scrib function during polarized cell migration.
  
  
  RESULTS
  Depletion of Scrib by siRNA or expression of dominant-negative constructs inhibits astrocyte polarization. Like Cdc42, Scrib controls protrusion formation, cytoskeleton polarization, and centrosome and Golgi reorientation. Scrib interacts and colocalizes with betaPIX at the front edge of polarizing astrocytes. Perturbation of Scrib localization or of Scrib-betaPIX interaction inhibits betaPIX polarized recruitment. We further show that betaPIX is required for astrocyte polarization and that both the Scrib-binding motif and the GEF activity of betaPIX are essential for its function. Scrib and betaPIX control Cdc42 activation and localization during astrocyte polarization. Thereby, Scrib regulates Cdc42-dependent APC and Dlg1 recruitment to the leading edge to promote cell orientation.
  
  
  CONCLUSIONS
  We conclude that Scrib plays a key role in the establishment of cell polarity during migration. By interacting with betaPIX, Scrib controls localization and activation of the small GTPase Cdc42 and regulates Cdc42-dependent polarization pathways.
authors.affiliation: Cell Polarity and Migration Group, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris cedex 15, France.
authors.forename: Naël
authors.initials: N
authors.lastname: Osmani
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vitale
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Borg
authors.forename: Sandrine
authors.initials: S
authors.lastname: Etienne-Manneville
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000502:physiology; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D051381:Rats; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D034741:RNA, Small Interfering; D064067:Rho Guanine Nucleotide Exchange Factors; D020764:cdc42 GTP-Binding Protein