Calcium-dependent dynamics of cadherin interactions at cell-cell junctions

Cadherins play a key role in the dynamics of cell-cell contact formation and remodeling of junctions and tissues. Cadherin-cadherin interactions are gated by extracellular Ca²⁺, which serves to rigidify the cadherin extracellular domains and promote trans junctional interactions. Here we describe the direct visualization and quantification of spatiotemporal dynamics of N-cadherin interactions across intercellular junctions in living cells using a genetically encodable FRET reporter system. Direct measurements of transjunctional cadherin interactions revealed a sudden, but partial, loss of homophilic interactions (τ = 1.17 ± 0.06 s^-1) upon chelation of extracellular Ca²⁺. A cadherin mutant with reduced adhesive activity (W2A) exhibited a faster, more substantial loss of homophilic interactions (τ = 0.86 ± 0.02 s^-1), suggesting two types of native cadherin interactions - one that is rapidly modulated by changes in extracellular Ca²⁺ and another with relatively stable adhesive activity that is Ca²⁺ independent. The Ca²⁺-sensitive dynamics of cadherin interactions were transmitted to the cell interior where β-catenin translocated to N-cadherin at the junction in both cells. These data indicate that cadherins can rapidly convey dynamic information about the extracellular environment to both cells that comprise a junction.