EGFR signaling to p120-catenin through phosphorylation at Y228

Epidermal growth factor receptor (EGFR) signals to p120(ctn) (p120), implying a role for EGFR in modulating cell-cell adhesion in epithelial tissues. p120 controls cadherin turnover, and may have other roles that modulate cadherin adhesiveness. To clarify the role for EGFR and other tyrosine kinases in regulating p120 function, we have generated and characterized a new phosphospecific antibody to p120 Y228, as well as a novel siRNA-based reconstitution system for analyzing roles of individual p120 phosphorylation events. In A431 cells, epidermal growth factor induced striking p120 phosphorylation at Y228. Y228-phosphorylated p120 localized to adherens junctions and lamellipodia, and was significantly enhanced in cells around the colony periphery. A screen of carcinoma cell lines revealed that some contain unusually high steady state levels of Y228 phosphorylation, suggesting that disregulated kinase activity in tumors may affect adhesion by constitutive cross talk to cadherin complexes. Despite these observations, mutation of Y228 and other prominent Src-associated p120 phosphorylation sites did not noticeably reduce the ability of E-cadherin to assemble junctions and induce compaction of cultured cells. Although A431 cells display significant activation of both EGFR and Src kinases, our data suggest that these account for only a fraction of the steady state activity that targets p120 Y228, and that Src family kinases are not necessary intermediates for epidermal growth factor-induced signaling to p120 Y228.