Cell aggregation assays.

Invasion of carcinoma cells is the result of a disequilibrium between invasion promoter and invasion suppressor gene products (Mareel and Van Roy, Anticancer Res 6:419-435, 1986). The E-cadherin/catenin complex is the most potent invasion suppressor at the cell membrane of epithelioid cells (Duffy et al., J Pathol 214:283-293, 2008). This complex consists of E-cadherin, a transmembrane glycoprotein of 120 kDa, which is linked to the actin cytoskeleton via the catenins (Behrens et al., J Cell Biol 108:2435-2447, 1989). Downregulation of the complex is a common feature in invasive carcinoma cells, and has been recognized at several levels, ranging from genomic mutations to functional deficiencies of an apparently intact complex (Ozawa et al., Proc Natl Acad Sci USA 87:4246-4250, 1990). Cell aggregation assays have been set up to test the functionality of the complex in epithelioid tumor cells. Functional integrity of the complex is a prerequisite for cell-cell adhesion between epithelial cells, and measuring cell aggregation in vitro has thus become another elegant tool to study differences between invasive and noninvasive cell types.