CRIM1-b-Catenin-Cadherin Interactions in Eye Development and Disease

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Our long-term goal is an understanding of the mechanisms of lens development. In this application, our more restricted goal is to determine how the unusual transmembrane protein CRIM1 mediates epithelial adhesion and morphogenesis in the developing lens. Our preliminary analysis has shown that CRIM1 regulates cell adhesion through interactions with beta-catenin and cadherins. CRIM1 can form a complex with b-catenin which in turn interacts with cadherins. Our central hypothesis is that through complex formation with catenins and cadherins, CRIM1 regulates epithelial cell adhesion and morphogenesis. To investigate the function of CRIM1 in the lens, we propose two specific aims: Aim 1. To determine the mechanism of interaction between CRIM1, beta-catenin and cadherins. With interaction assays that are cell-based or recombinant protein-based we will determine whether CRIM1 binds beta-catenin with any of the known ligand binding mechanisms. This will include an assessment of the role of phosphorylation as this is known to influence binding of other beta-catenin ligands. We will also determine the stoichiometry of CRIM1-beta-catenin/cadherin complexes as this may have important biological implications. Aim 2. To determine whether the CRIM1-beta-catenin interaction regulates cadherin-dependent adhesion in the lens. Using forms of CRIM1 that either cannot or obligatorily interact with beta-catenin we will determine, using rescue of CRIM1 conditionally mutant mice, whether the CRIM1-beta-catenin interaction is important for cadherin dependent adhesion in the developing lens. The study of developmental morphogenesis is interesting in its own right but also has important consequences for our understanding of disease. For example, regulation of cadherin adhesiveness is critical for eye-specific diseases such as secondary cataract formation where there is an epithelial to mesenchymal transition and in the vascular diseases diabetic retinopathy and age-related macular degeneration that require the modulation of VE-cadherin in vascular endothelial cells. The down-regulation of cadherin expression and activity is also know to be a critical step in epithelial tumor progression as it allows tumor cells to leave the epithelium, become invasive and ultimately form metastases.