The balance between cell migration and cell?cell adhesion is crucial during development and is altered in disease states such as metastatic cancers. Cells migrate during development to specific sites when upon contact with other cells; they become stationary and differentiate into tissues. Thus, strong cell?cell adhesion is necessary in maintaining tissue integrity. Changes in cell?cell adhesion reinitiate cell migration during cell turnover or wound healing or allow metastatic cells to scatter to distant organs. The formation and stabilization of cell-cell adhesion complexes (adherens junctions) is essential for metazoan development, organogenesis, and tissue homeostasis, and it also necessary for some pathophysiological conditions, such as wound healing. In contrast, loss of adherens junctions is a hallmark of cancer, leading to unrestricted cell proliferation and metastasis. Cell-cell adherens junctions require the proper assembly of multi-protein complexes at the plasma cell membrane. Here, homotypic interactions between the calcium-binding ectodomains of single transmembrane pass cadherin receptors allow neighboring cells to bind to one another. The interactions of their cytoplasmic tail domains with ?-catenin, which in turn binds to ?-catenin, appear to direct the formation of adherens junctions, by inhibiting the production of lamellopodia. However, without tension, this ternary cadherin/?-catenin/?-catenin complex does not bind directly to the actin network, which is necessary for stabilizing these junctions and for tissue homeostasis. In the first 3 years of funding by GM094483, we determined the crystal structure of dimeric full-length human ?-catenin and of vinculin-bound ?-catenin, and these structures and our biochemical and biological studies defined the roles of the vinculin-?-catenin interaction in the formation and stabilization of adherens junctions. By moving from crystal structures and 3D reconstructions to biochemistry and then to biology, the proposed studies will define how adherens junctions are stabilized and control the organization of the actin cytoskeleton. Collectively, our proposed studies will significantly increase our understanding of ?-catenin monomer-dimer transitions and their effects on membrane dynamics, migration, and cell adhesion. Importantly, our multi-disciplinary studies will also lay the foundation for understanding how these controls are lost during tumor progression and may suggest new avenues for therapeutic intervention.

Public Health Relevance

Program Narrative Metazaon development and homeostasis requires that cells form stable contacts, coined adherens junctions, with their neighbors. Adherens junctions are multi- protein complexes that are directed by homotypic interactions of the extracellular domains of transmembrane cadherin receptors, which bind to ?-catenin via their intracellular tail domains; ?-catenin then binds to ?-catenin and this ternary complex appears to direct the formation of adherens junctions. Our research program will define how these junctions are stabilized and control the actin network.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Macromolecular Structure and Function C Study Section (MSFC)
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Xu, Jianhua
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Scripps Florida
United States
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Rangarajan, Erumbi S; Izard, Tina (2013) Dimer asymmetry defines ?-catenin interactions. Nat Struct Mol Biol 20:188-93
Rangarajan, Erumbi S; Izard, Tina (2012) The cytoskeletal protein *-catenin unfurls upon binding to vinculin. J Biol Chem 287:18492-9