Activation of the Small GTPase Rac Is Sufficient to Disrupt Cadherin-dependent Cell-Cell Adhesion in Normal Human Keratinocytes

Medical Research Council Laboratory for Molecular Cell Biology and the Department of Biochemistry and Molecular Biology, University College London, London WC1E 6BT, United Kingdom.
Molecular Biology of the Cell (Impact Factor: 4.47). 12/2000; 11(11):3703-21. DOI: 10.1091/mbc.11.11.3703
Source: PubMed


To achieve strong adhesion to their neighbors and sustain stress and tension, epithelial cells develop many different specialized adhesive structures. Breakdown of these structures occurs during tumor progression, with the development of a fibroblastic morphology characteristic of metastatic cells. During Ras transformation, Rac-signaling pathways participate in the disruption of cadherin-dependent adhesion. We show that sustained Rac activation per se is sufficient to disassemble cadherin-mediated contacts in keratinocytes, in a concentration- and time-dependent manner. Cadherin receptors are removed from junctions before integrin receptors, suggesting that pathways activated by Rac can specifically interfere with cadherin function. We mapped an important region for disruption of junctions to the putative second effector domain of the Rac protein. Interestingly, although this region overlaps the domain necessary to induce lamellipodia, we demonstrate that the disassembly of cadherin complexes is a new Rac activity, distinct from Rac-dependent lamellipodia formation. Because Rac activity is also necessary for migration, Rac is a good candidate to coordinately regulate cell-cell and cell-substratum adhesion during tumorigenesis.

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Available from: Vania Braga
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    • "While much is known about how adherens junctions are formed, less is known about the signaling events and molecular interactions that lead to junctional dissociation. Activation of Rac1 and Cdc42 can abolish the multi-cellular organization of breast carcinoma cells in a 3D matrix [20] and disrupts cell–cell adhesions in human keratinocytes [4] and pancreatic carcinoma cells [13]. Moreover, Rac1 and Cdc42 are both known to interact with isoform 1 of the IQ motif containing GTPase activating protein (IQGAP) family of proteins [21], and a Rac-1–IQGAP1 interaction is thought to mediate the dissociation of β-catenin from E-cadherin downstream of HGF in MDCK cells [10]. "
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    ABSTRACT: p-21 activated 6 (PAK6), first identified as interacting with the androgen receptor (AR), is over-expressed in multiple cancer tissues and has been linked to the progression of prostate cancer, however little is known about PAK6 function in the absence of AR signaling. We report here that PAK6 is specifically required for carcinoma cell–cell dissociation downstream of hepatocyte growth factor (HGF) for both DU145 prostate cancer and HT29 colon cancer cells. Moreover, PAK6 overexpression can drive cells to escape from adhesive colonies in the absence of stimulation. We have localized PAK6 to cell–cell junctions and have detected a direct interaction between the kinase domain of PAK6 and the junctional protein IQGAP1. Co-expression of IQGAP1 and PAK6 increases cell colony escape and leads to elevated PAK6 activation. Further studies have identified a PAK6/E-cadherin/IQGAP1 complex downstream of HGF. Moreover, we find that β-catenin is also localized with PAK6 in cell–cell junctions and is a novel PAK6 substrate. We propose a unique role for PAK6, independent of AR signaling, where PAK6 drives junction disassembly during HGF-driven cell–cell dissociation via an IQGAP1/E-cadherin complex that leads to the phosphorylation of β-catenin and the disruption of cell–cell adhesions. Electronic supplementary material The online version of this article (doi:10.1007/s00018-013-1528-5) contains supplementary material, which is available to authorized users.
    Full-text · Article · Dec 2013 · Cellular and Molecular Life Sciences CMLS
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    • "Cadherins link adherens junctions to the actin cytoskeleton [2]. The small GTPase Rac1 is a key regulator of the epithelial actin cytoskeleton, which influences dynamics of cell-cell contacts [3], [4], [5], [6], [7]. Rac1 is activated upon E-cadherin clustering during de novo cell junction formation and activity decreases as junctions mature [4], [7], [8]. "
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    ABSTRACT: Cell-cell junctions are an integral part of epithelia and are often disrupted in cancer cells during epithelial-to-mesenchymal transition (EMT), which is a main driver of metastatic spread. We show here that Metastasis suppressor-1 (Mtss1; Missing in Metastasis, MIM), a member of the IMD-family of proteins, inhibits cell-cell junction disassembly in wound healing or HGF-induced scatter assays by enhancing cell-cell junction strength. Mtss1 not only makes cells more resistant to cell-cell junction disassembly, but also accelerates the kinetics of adherens junction assembly. Mtss1 drives enhanced junction formation specifically by elevating Rac-GTP. Lastly, we show that Mtss1 depletion reduces recruitment of F-actin at cell-cell junctions. We thus propose that Mtss1 promotes Rac1 activation and actin recruitment driving junction maintenance. We suggest that the observed loss of Mtss1 in cancers may compromise junction stability and thus promote EMT and metastasis.
    Full-text · Article · Mar 2012 · PLoS ONE
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    • "Major players functionally connecting classical cadherins to the actin cytoskeleton are the Rho GTPases. Studies using dominant-active and dominant-negative Rho-GTPase mutants demonstrate that aberrant Rho-GTPase signaling in general disrupts cell–cell adhesion, presumably through misregulation of the cytoskeletal organization (Braga et al., 1997, 2000). Conversely, cadherin activity has been shown to affect Rho-GTPase function, with one example being activation of Rac1 by forced cadherin clustering, for which a number of mechanisms have been proposed (Betson et al., 2002; Goodwin et al., 2003; Fukuyama et al., 2006). "
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    ABSTRACT: The dynamic functional linkage of cadherins with the underlying actin cytoskeleton is tightly regulated to achieve proper cell-cell adhesion. p120-catenin (p120) regulates both cadherin stability and actin dynamics, but the relationship between these two functions remains unclear. Using a novel proteomic approach called reversible cross-link immunoprecipitation, or ReCLIP, we previously identified a physical interaction between p120 and Rho-associated protein kinase 1 (ROCK1), a major effector of RhoA. In this paper, we show that a discrete fraction of cellular ROCK1 coimmunoprecipitates with p120 and precisely colocalizes to adherens junctions (AJs). Manipulation of AJs using a calcium-switch assay and cadherin-blocking antibodies indicates direct recruitment of ROCK1 to newly forming junctions. Importantly, we find that p120 links ROCK1 to the cadherin complex, as ROCK1 coimmunoprecipitates with wild-type but not p120-uncoupled E-cadherin. Moreover, depletion of ROCK1 using short-hairpin RNA results in dramatic mislocalization of the cadherin complex and junctional actin. These data are consistent with a model in which p120 dynamically regulates Rho-GTPase activity at the cadherin complex through transient interaction with several of its up- and downstream effectors, including ROCK1.
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