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.

Paracingulin Regulates the Activity of Rac1 and RhoA GTPases by Recruiting Tiam1 and GEF-H1 to Epithelial Junctions

“…However, our immunoblot analysis showed that levels of Par3 were unaffected in CGNL1(-) cells, ruling out this possibility. Although Tiam1 has been reported to interact with several proteins, most of these proteins have been identified in fibroblasts/neurons, and not epithelial cell model systems (Mertens et al, 2003;Ten Klooster et al, 2006). Our results provide the first evidence that depletion of a Tiam1-interacting protein results in decreased accumulation of Tiam1 at epithelial junctions, and increased Tiam1 solubility.…”

Non-canonical Interaction of Phosphoinositides with Pleckstrin Homology Domains of Tiam1 and ArhGAP9

“…S1A). As previously reported (27,38), deletion of the entire PHn domain (⌬PH) of Tiam1 resulted in diffuse cytoplasmic staining with greatly reduced actin-rich protrusions ( Fig. 4B and supplemental Fig.…”

Tiam1-deficiency impairs mammary tumor formation in MMTV-c-neu but not in MMTV-c-myc mice

“…Tiam1 also associates with activated Rap1 and in conjunction with the Par polarity complex controls chemokineinduced T-cell polarization (Gerard et al 2007). The association of Tiam1 with IRSp53 and p21Arc provides a direct link between Tiam1-mediated Rac activation and Arp2/3 complex-controlled actin polarization, which is required for cytoskeletal dynamics during cell migration and cell polarization ten Klooster et al 2006). In receptor signaling, activated Ras may activate Rac by direct binding to Tiam1 (Lambert et al 2002) or indirectly by activation of phosphoinositide 3-kinase (PI3-kinase) that may recruit and activate Tiam1 and thereby Rac downstream of Ras (Fleming et al 2000;Zondag et al 2000).…”