Exchange of catenins in cadherin-catenin complex.

beta-Catenin is an intracellular multifunctional protein. In complex with the transmembrane adhesive receptor E-cadherin, it becomes plasma membrane-associated and mediates intercellular adhesion. A cytosolic pool of beta-catenin interacts with DNA-binding proteins and participates in signal transduction. To reveal the possible cross-talk between these two pools, we studied whether beta-catenin is exchanged between its free and cadherin-bound states. We found that pulse-labeled beta-catenin replaces the beta-catenin bound to the cell surface prebiotinylated E-cadherin immediately after synthesis. Approximately 25% of all pulse-labeled beta-catenin destined for E-cadherin associates with this protein via this mechanism. The rest of the newly synthesized beta-catenin arrives at the plasma membrane in a complex with the E-cadherin precursor. Immediately after arrival, this beta-catenin pool is transferred to the prebiotinylated E-cadherin. beta-Catenin released from E-cadherin may participate in new exchange cycles. This beta-catenin exchange is strongly affected in cells that contain mutations in the tumor suppressor gene APC. This process may contribute significantly to both cell-cell adhesion and beta-catenin-dependent signaling.