EXTRACELLULAR DOMAIN OF PEMPHIGUS-VULGARIS ANTIGEN (DESMOGLEIN-3) MEDIATES WEAK HEMOPHILIC ADHESION

Pemphigus vulgaris antigen is in the cadherin supergene family. We hyp othesized that the extracellular domain of pemphigus vulgaris antigen might mediate hemophilic cell adhesion because 1) the originally descr ibed cadherins (e.g., E-cadherin) mediate this type of adhesion, 2) pe mphigus vulgaris antigen is localized in desmosomes that are cell adhe sion junctions, and 3) autoantibodies in pemphigus vulgaris patients c ause loss of cell adhesion. To test this hypothesis we used a system d eveloped for E-cadherin that, when transfected into L cells (mouse fib roblasts), has been shown to cause aggregation. Because this aggregati on requires the cytoplasmic domain of E-cadherin to bind to catenins, we made a chimeric cDNA construct that encodes the extracellular domai n of pemphigus vulgaris antigen and the cytoplasmic domain of E-cadher in. Analysis by immunofluorescence and flow cytometry with pemphigus v ulgaris sera indicated that the pemphigus vulgaris antigen extracellul ar domain of this chimeric molecule (PVEC) was expressed on the cell s urface of transiently transfected cells and permanently transfected L- cell clones. Immunoprecipitation of the chimeric molecule from extract s of these clones showed that the E-cadherin cytoplasmic domain bound catenins. Surprisingly, these L-cell clones displayed only slight aggr egation compared to an L-cell clone transfected with E-cadherin. This weak aggregation was, however, specific and hemophilic, as determined by cell sorting of only PVEC transfectants into aggregates from mixtur es of PVEC and neomycin resistance gene transfectants, one of which wa s labeled with a fluorescent dye. We conclude that the extracellular d omain of pemphigus vulgaris antigen mediates weak hemophilic adhesion and is not interchangeable in function with the extracellular domain o f E-cadherin.