Interaction between Tiam1 and the Arp2/3 complex links activation of Rac to actin polymerization.
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.
Ten Klooster
Jean Paul
JP
The Netherlands Cancer Institute, Division of Cell Biology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Evers
Eva E
EE
Janssen
Lennert
L
Machesky
Laura M
LM
Michiels
Frits
F
Hordijk
Peter
P
Collard
John G
JG
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
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