The cadherin-catenin cell-cell adhesion complex is essential for tissue development and homeostasis. While the requirement of each component to intercellular adhesion has been long established, we know much less about the structural and chemical modifications that regulate this complex. One barrier to understanding cadherin/catenin adhesion regulation is the lack of a well-defined system for analysis. A second barrier is that catenins serve functions outside of the cadherin-catenin complex, confounding loss of function analyses. Cells dividing within an epithelium undergo stereotypic shape changes to separate the genome while also maintaining the adhesive barrier, but how the cadherin-catenin complex might be regulated to accommodate this essential process is unknown. We have generated a variant of ?-catenin that shows enhanced binding F- actin in vitro. CRISPR/Cas9-generated ?-catenin knockout cells restored with this variant show a prominent mitotic defect, particularly during cytokinesis. This shows that persistent coupling between ?-catenin and F- actin blocks cell division, and suggests that the ?-catenin/F-actin interaction may be regulated during mitosis (Aim 1). We've identified an evolutionarily conserved phosphorylation scheme in ?-catenin that lies within a linker region that joins the actin-binding and mechano-sensitive regions of ?-catenin, each of which are essential for ?-catenin adhesive function in mammalian cells and flies. As this phosphorylation is upregulated during mitosis, we hypothesize that ?-catenin phosphorylation regulates cell division by altering the actin- binding and/or mechanosensing property of ?-catenin (Aim 2). Lastly, we've found that a form of ?-catenin that functions outside of the cadherin complex can bind phosphatidylinositol-3,4,5-trisphosphate (PIP3)-enriched membranes and direct cortical actin organizations that might be relevant to mitotic division (Aim 3). Altogether, this proposal incorporates skills from a multi-disciplinary team of collaborative investigators, using cell lines, Drosophila, mechanical and biochemical approaches to address the fundamental question of how ?-catenin is structurally modified during mitosis, which will have broad implications for adhesion regulation across diverse cell types.
A barrier to understanding cadherin/catenin adhesion regulation is the lack of a well-defined system for analysis. We hypothesize that cells dividing in an epithelium undergo chemical and mechanical modification of their cadherin-catenin adhesions to accommodate the stereotypic membrane shape changes required for reliable mitotic division.