Adducin is required for desmosomal cohesion in keratinocytes

Adducin is a protein organizing the cortical actin cytoskeleton and a target of RhoA and PKC signaling. However, the role for intercellular cohesion is unknown. We found that adducin silencing induced disruption of the actin cytoskeleton, reduced intercellular adhesion of human keratinocytes, and decreased the levels of the desmosomal adhesion molecule desmoglein (Dsg)3 by reducing its membrane incorporation. Because loss of cell cohesion and Dsg3 depletion is observed in the autoantibody-mediated blistering skin disease pemphigus vulgaris (PV), we applied antibody fractions of PV patients. A rapid phosphorylation of adducin at serine 726 was detected in response to these autoantibodies. To mechanistically link autoantibody binding and adducin phosphorylation, we evaluated the role of several disease-relevant signaling molecules. Adducin phosphorylation at serine 726 was dependent on Ca(2+) influx and PKC but occurred independent of p38 MAPK and PKA. Adducin phosphorylation is protective, because phosphorylation-deficient mutants resulted in loss of cell cohesion and Dsg3 fragmentation. Thus, PKC elicits both positive and negative effects on cell adhesion, since its contribution to cell dissociation in pemphigus is well established. We additionally evaluated the effect of RhoA on adducin phosphorylation because RhoA activation was shown to block pemphigus autoantibody-induced cell dissociation. Our data demonstrate that the protective effect of RhoA activation was dependent on the presence of adducin and its phosphorylation at serine 726. These experiments provide novel mechanisms for regulation of desmosomal adhesion by RhoA- and PKC-mediated adducin phosphorylation in keratinocytes.