α-Catenin-mediated cadherin clustering couples cadherin and actin dynamics

The function of the actin-binding domain of a-catenin, alpha ABD, including its possible role in the direct anchorage of the cadherin catenin complex to the actin cytoskeleton, has remained uncertain. We identified two point mutations on the alpha ABD surface that interfere with alpha ABD binding to actin and used them to probe the role of a-catenin actin interactions in adherens junctions. We found that the junctions directly bound to actin via alpha ABD were more dynamic than the junctions bound to actin indirectly through vinculin and that recombinant alpha ABD interacted with cortical actin but not with actin bundles. This interaction resulted in the formation of numerous short-lived cortex-bound alpha ABD clusters. Our data suggest that alpha ABD clustering drives the continuous assembly of transient, actin-associated cadherin catenin clusters whose disassembly is maintained by actin depolymerization. It appears then that such actin-dependent alpha ABD clustering is a unique molecular mechanism mediating both integrity and reassembly of the cell cell adhesive interface formed through weak cis- and trans-intercadherin interactions.