p38MAPK Signaling but not Direct Inhibition of Desmoglein Binding is Crucial for Loss of Cell Cohesion in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a severe autoimmune disease caused by autoantibodies against the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg3. Both, direct inhibition of Dsg interaction by autoantibody binding and intracellular signaling events are discussed to be essential and sufficient for loss of cell cohesion finally leading to epidermal blister formation. Here we used atomic force microscopy (AFM) to perform Dsg3 adhesion measurements on the surface of living keratinocytes to determine the contribution of direct inhibition and p38MAPK‐ and lipid‐raft‐dependent signaling to loss of cell cohesion after treatment with Dsg3‐specific autoantibodies. Direct inhibition of Dsg3 binding was almost complete after 15 min antibody treatment and did not proceed further up to 120 min under conditions where no reduction of surface Dsg3 was detectable. However, loss of cell cohesion and keratin retraction progressed during this time course. Interestingly, direct inhibition of Dsg3 binding was still profound when loss of cell‐cell‐cohesion was completely abrogated by p38MAPK inhibition. This demonstrates that p38MAPK suppression prevents loss of cell cohesion despite Dsg3 binding still being blocked. Furthermore, signaling is lipid‐raft‐dependent because methyl‐ß‐cyclodextrin (ß‐MCD) also fully prevented loss of cell cohesion, but did not reduce direct inhibition of Dsg3 binding. Taken together, these results demonstrate that inhibition of Dsg3 binding alone is not sufficient to cause loss of cell cohesion but rather alters p38MAPK‐ and lipid‐raft‐dependent signaling events which in turn cause cell dissociation.