title: Interaction between Tiam1 and the Arp2/3 complex links activation of Rac to actin polymerization.
abstract: The Rac-specific GEF (guanine-nucleotide exchange factor) Tiam1 (T-lymphoma invasion and metastasis 1) regulates migration, cell-matrix and cell-cell adhesion by modulating the actin cytoskeleton through the GTPase, Rac1. Using yeast two-hybrid screening and biochemical assays, we found that Tiam1 interacts with the p21-Arc [Arp (actin-related protein) complex] subunit of the Arp2/3 complex. Association occurred through the N-terminal pleckstrin homology domain and the adjacent coiled-coil region of Tiam1. As a result, Tiam1 co-localizes with the Arp2/3 complex at sites of actin polymerization, such as epithelial cell-cell contacts and membrane ruffles. Deletion of the p21-Arc-binding domain in Tiam1 impairs its subcellular localization and capacity to activate Rac1, suggesting that binding to the Arp2/3 complex is important for the function of Tiam1. Indeed, blocking Arp2/3 activation with a WASP (Wiskott-Aldrich syndrome protein) inhibitor leads to subcellular relocalization of Tiam1 and decreased Rac activation. Conversely, functionally active Tiam1, but not a GEF-deficient mutant, promotes activation of the Arp2/3 complex and its association with cytoskeletal components, indicating that Tiam1 and Arp2/3 are mutually dependent for their correct localization and signalling. Our data suggests a model in which the Arp2/3 complex acts as a scaffold to localize Tiam1, and thereby Rac activity, which are both required for activation of the Arp2/3 complex and further Arp2/3 recruitment. This 'self-amplifying' signalling module involving Tiam1, Rac and the Arp2/3 complex could thus drive actin polymerization at specific sites in cells that are required for dynamic morphological changes.
authors.affiliation: The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
authors.forename: Jean Paul
authors.initials: JP
authors.lastname: Ten Klooster
authors.forename: Eva E
authors.initials: EE
authors.lastname: Evers
authors.forename: Lennert
authors.initials: L
authors.lastname: Janssen
authors.forename: Laura M
authors.initials: LM
authors.lastname: Machesky
authors.forename: Frits
authors.initials: F
authors.lastname: Michiels
authors.forename: Peter
authors.initials: P
authors.lastname: Hordijk
authors.forename: John G
authors.initials: JG
authors.lastname: Collard
mesh_terms: D008841:Actin Cytoskeleton; D051376:Actin-Related Protein 2-3 Complex / Q000737:chemistry / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002846:Chromatography, Affinity; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D009479:Neuropeptides / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D020798:Two-Hybrid System Techniques; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D003598:Cytoskeletal Proteins; D020662:Guanine Nucleotide Exchange Factors; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; C092069:activity regulated cytoskeletal-associated protein; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein