Tiam1 is recruited to β1-integrin complexes by 14-3-3ζ where it mediates integrin-induced Rac1 activation and motility

Authors

  • Timothy E. O'Toole,

    1. Department of Molecular Cardiology, Joseph J. Jacobs Center for Thrombosis and Vascular Biology, The Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio
    Current affiliation:
    1. Departments of Cardiology and Anatomical Sciences and Neurobiology, respectively, University of Louisville, 580 S. Preston, Louisville, KY 40202.
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  • Katarzyna Bialkowska,

    1. Department of Molecular Cardiology, Joseph J. Jacobs Center for Thrombosis and Vascular Biology, The Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio
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  • Xiaohong Li,

    1. Department of Molecular Cardiology, Joseph J. Jacobs Center for Thrombosis and Vascular Biology, The Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio
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  • Joan E.B. Fox

    Corresponding author
    1. Department of Molecular Cardiology, Joseph J. Jacobs Center for Thrombosis and Vascular Biology, The Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio
    2. Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio
    • Department of Molecular Cardiology, NB50, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Ave., Cleveland, OH 44195.
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Abstract

14-3-3 is an adaptor protein that localizes to the leading edge of spreading cells, returning to the cytoplasm as spreading ceases. Previously, we showed that integrin-induced Rac1 activation and spreading were inhibited by sequestration of 14-3-3ζ and restored by its overexpression. Here, we determined whether 14-3-3 mediates integrin signaling by localizing a guanine nucleotide exchange factor (GEF) to Rac1-activating integrin complexes. We showed that GST-14-3-3ζ recruited the Rac1-GEF, Tiam1, from cell lysates through Tiam1 residues 1–182 (N1–182 Tiam1). The physiological relevance of this interaction was examined in serum-starved Hela cells plated on fibronectin. Both Tiam1 and N1–182 Tiam1 were recruited to 14-3-3-containing β1-integrin complexes, as shown by co-localization and co-immunoprecipitation. Integrin-induced Rac1 activation was inhibited when Tiam1 was depleted with siRNA or by overexpression of catalytically inactive N1–182 Tiam1, which was incorporated into 14-3-3/β1-integrin complexes and inhibited spreading in a manner that was overcome by constitutively active Rac1. Integrin-induced Rac1 activation, spreading, and migration were also inhibited by overexpression of 14-3-3ζ S58D, which was unable to recruit Tiam1 from lysates, co-immunoprecipitate with Tiam1, or mediate its incorporation into β1-integrin complexes. Taken together, these findings suggest a previously unrecognized mechanism of integrin-induced Rac1 activation in which 14-3-3 dimers localize Tiam1 to integrin complexes, where it mediates integrin-dependent Rac1 activation, thus initiating motility-inducing pathways. Moreover, since Tiam1 is recruited to other sites of localized Rac1 activation through its PH-CC-EX domain, the present findings show that a mechanism involving its N-terminal 182 residues is utilized to recruit Tiam1 to motility-inducing integrin complexes. J. Cell. Physiol. 226: 2965–2978, 2011. © 2011 Wiley-Liss, Inc.

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