Selective Uncoupling of P120ctn from E-Cadherin Disrupts Strong Adhesion

TLDR

p120ctn binds the juxtamembrane domain of classical cadherins and is implicated in cadherin clustering, cell motility, and neuronal outgrowth. The authors created minimal mutations in the juxtamembrane domain that selectively disrupt E‑cadherin–p120 binding while preserving other catenin interactions. Loss of p120 binding to E‑cadherin prevents the transition from weak to strong adhesion, causing cells to form only transient aggregates, fail to recruit actin into junctions, and cannot establish continuous circumferential rings.

Abstract

p120ctn is a catenin whose direct binding to the juxtamembrane domain of classical cadherins suggests a role in regulating cell–cell adhesion. The juxtamembrane domain has been implicated in a variety of roles including cadherin clustering, cell motility, and neuronal outgrowth, raising the possibility that p120 mediates these activities. We have generated minimal mutations in this region that uncouple the E-cadherin–p120 interaction, but do not affect interactions with other catenins. By stable transfection into E-cadherin–deficient cell lines, we show that cadherins are both necessary and sufficient for recruitment of p120 to junctions. Detergent-free subcellular fractionation studies indicated that, in contrast to previous reports, the stoichiometry of the interaction is extremely high. Unlike α- and β-catenins, p120 was metabolically stable in cadherin-deficient cells, and was present at high levels in the cytoplasm. Analysis of cells expressing E-cadherin mutant constructs indicated that p120 is required for the E-cadherin–mediated transition from weak to strong adhesion. In aggregation assays, cells expressing p120-uncoupled E-cadherin formed only weak cell aggregates, which immediately dispersed into single cells upon pipetting. As an apparent consequence, the actin cytoskeleton failed to insert properly into peripheral E-cadherin plaques, resulting in the inability to form a continuous circumferential ring around cell colonies. Our data suggest that p120 directly or indirectly regulates the E-cadherin–mediated transition to tight cell–cell adhesion, possibly blocking subsequent events necessary for reorganization of the actin cytoskeleton and compaction.