A Desmoplakin Point Mutation with Enhanced Keratin Association Ameliorates Pemphigus Vulgaris Autoantibody-Mediated Loss of Cell Cohesion

Abstract

Desmoplakin (DP) serves to anchor intermediate filaments in desmosomal complexes. Recent data suggest that a specific DP point mutation (S2849G) exhibits increased keratin filament association and fosters Ca(2+) insensitivity of desmosomes in keratinocytes, presumably by rendering DP inaccessible for protein kinase C (PKC) phosphorylation. Previously, we have reported that depletion of the desmosomal adhesion molecule desmoglein (Dsg)3 induced by autoantibodies from patients with the blistering skin disease pemphigus vulgaris (PV) IgG is reduced in maturated desmosomes and dependent on PKC signaling. We investigated the role of DP-S2849G for loss of cell cohesion mediated by PV-IgG. In cell dissociation assays, expression of green fluorescent protein-tagged DP-S2849G (DP-S2849G-GFP) increased cell cohesion in two different human keratinocyte cell lines and ameliorated loss of cell adhesion induced by pemphigus autoantibodies. Depletion of Dsg3 was inhibited by DP-S2849G-GFP in the cytoskeletal (Triton X-100 insoluble) fraction, and keratin filament retraction, a hallmark of PV, was efficiently blocked similar to treatment with the PKC inhibitor Bim-X. We found that DP is phosphorylated after incubation with PV-IgG in a PKC-dependent manner and that DP-S2849G-GFP expression prevents DP phosphorylation and increases association of PKC-α with PKC scaffold receptor for activated C-kinase 1. Taken together, our data indicate that DP phosphorylation at S2849 represents an important mechanism in pemphigus pathogenesis, which, by reversing Ca(2+) insensitivity, promotes Dsg3 depletion.