p120ctn Acts as an Inhibitory Regulator of Cadherin Function in Colon Carcinoma Cells

p120ctn binds to the cytoplasmic domain of cadherins but its role is poorly understood. Colo 205 cells grow as dispersed cells despite their normal expression of E-cadherin and catenins. However, in these cells we can induce typical E-cadherin–dependent aggregation by treatment with staurosporine or trypsin. These treatments concomitantly induce an electrophoretic mobility shift of p120ctn to a faster position. To investigate whether p120ctn plays a role in this cadherin reactivation process, we transfected Colo 205 cells with a series of p120ctn deletion constructs. Notably, expression of NH2-terminally deleted p120ctn induced aggregation. Similar effects were observed when these constructs were introduced into HT-29 cells. When a mutant N-cadherin lacking the p120ctn-binding site was introduced into Colo 205 cells, this molecule also induced cell aggregation, indicating that cadherins can function normally if they do not bind to p120ctn. These findings suggest that in Colo 205 cells, a signaling mechanism exists to modify a biochemical state of p120ctn and the modified p120ctn blocks the cadherin system. The NH2 terminus–deleted p120ctn appears to compete with the endogenous p120ctn to abolish the adhesion-blocking action.