Cleavage of Armadillo/beta-catenin by the caspase DrICE in Drosophila apoptotic epithelial cells

<p>Abstract</p> <p>Background</p> <p>During apoptosis cells become profoundly restructured through concerted cleavage of cellular proteins by caspases. In epithelial tissues, apoptotic cells loose their apical/basal polarity and are extruded from the epithelium. We used the <it>Drosophila </it>embryo as a system to investigate the regulation of components of the zonula adherens during apoptosis. Since Armadillo/beta-catenin (Arm) is a major regulator of cadherin-mediated adhesion, we analyzed the mechanisms of Arm proteolysis in apoptosis.</p> <p>Results</p> <p>We define early and late apoptotic stages and find that early in apoptosis <it>D</it>α-catenin remains relatively stable, while Arm and <it>D</it>E-cadherin protein levels are strongly reduced. Arm is cleaved by caspases in embryo extracts and we provide evidence that the caspase-3 homolog drICE cleaves Arm in vitro and in vivo. Cleavage by drICE creates a stable protein fragment that remains associated with the plasma membrane early in apoptosis. To further understand the role of caspase-mediated cleavage of Arm, we examined potential caspase cleavage sites and found that drICE cleaves Arm at a unique DQVD motif in the N-terminal domain of the protein. Mutation of the drICE cleavage site in Arm results in a protein that is not cleaved in vitro and in vivo. Furthermore we provide evidence that cleavage of Arm plays a role in the removal of <it>D</it>E-cadherin from the plasma membrane during apoptosis.</p> <p>Conclusion</p> <p>This study defines the specificity of caspase cleavage of Arm in <it>Drosophila </it>apoptotic cells. Our data suggest that N-terminal truncation of Arm by caspases is evolutionarily conserved and thus might provide a principal mechanism involved in the disassembly of adherens junctions during apoptosis.</p