Loss of Desmoglein Binding Is Not Sufficient for Keratinocyte Dissociation in Pemphigus

Pemphigus vulgaris (PV) is a severe autoimmune disease in which autoantibodies against the desmosomal cell adhesion molecules desmoglein (Dsg) 1 and Dsg3 cause intraepidermal blister formation. Mechanistically, the fundamental question is still unresolved whether loss of cell cohesion is a result of (1) direct inhibition of Dsg interaction by autoantibodies or (2) intracellular signaling events, which are altered in response to antibody binding and finally cause desmosome destabilization. We used atomic force microscopy (AFM) to perform Dsg3 adhesion measurements on living keratinocytes to investigate the contributions of direct inhibition and signaling to loss of cell cohesion after autoantibody treatment. Dsg3 binding was rapidly blocked following antibody exposure under conditions where no depletion of surface Dsg3 was detectable, demonstrating direct inhibition of Dsg3 interaction. Inhibition of p38MAPK, a central signaling molecule in PV pathogenesis, abrogated loss of cell cohesion, but had a minor effect on loss of Dsg3 binding. Similarly, the cholesterol-depleting agent methyl-beta-cyclodextrin (beta-MCD) fully blocked cell dissociation, but did not restore Dsg3 interactions or prevent the activation of p38MAPK. These results demonstrate that inhibition of Dsg3 binding is not sufficient to cause loss of cell cohesion, but rather alters signaling events which, in lipid raft-dependent manner, induce cell dissociation.