A Drosophila APC tumour suppressor homologue functions in cellular adhesion

Adenomatous polyposis coli (APC) is an important tumour suppressor in the intestinal epithelium. Its function in reducing nuclear beta-catenin and T-cell factor (TCF)-mediated transcription is conserved from Drosophila to mammals. But APC proteins are also associated with the plasma membrane. Here, we show that mutational inactivation of Drosophila E-APC causes delocalization of Armadillo (the Drosophila beta-catenin) but not DE-cadherin from adhesive plasma membranes. Extensive gaps between these membranes are visible at the ultrastructural level. The oocyte is also mislocalized in E-APC mutant egg chambers, a phenotype that results from a failure of cadherin-based adhesion. These results indicate that Drosophila APC functions in cellular adhesion; these results could have implications for colorectal adenoma formation and tumour progression in humans.