THE DISTRIBUTION OF THE DESMOSOMAL PROTEIN, PLAKOPHILIN 1, IN HUMAN SKIN AND SKIN TUMORS

Desmosomes are predominant among the types of plaque-bearing adhering junctions found in human skin, These structures contain a set of desmo somal cadherins and cytoplasmic plaque proteins, the synthesis of whic h is differentiation dependent, As plakophilin 1, a member of the arma dillo gene family, is an important accessory desmosomal plaque protein , we raised several monoclonal antibodies specific for this protein an d applied immunohistochemical and immunoblotting procedures to study t he distribution of plakophilin I in desmosomes in adult and fetal skin , psoriatic epidermis, various epithelial skin tumors, and keratinocyt e sheets grown in culture. In epidermis, the spinous layers were promi nently immunostained by plakophilin 1 antibodies, whereas the basal ce ll layer was only weakly stained and the stratum corneum was entirely unstained. The staining observed in psoriatic epidermis was somewhat h eterogeneous, In hair follicles, the outer root sheath (ORS) was delin eated in its suprabasal cell layers, with variable staining in its upp er and lower parts. All basal cells of the ORS remained unstained, as did upper inner root sheath (IRS) and matrix cells of lower bulb. In e ccrine sweat glands, the reaction was confined to inner dermal ductal cells, with the acini remaining unstained, The desmosomal immunostaini ng observed in basal cell carcinomas (BCCs) and squamous cell carcinom as (SCCs) was very heterogeneous: In general, junctions in well-differ entiated stratified tumor regions were more intensely stained than sec tions of poorly differentiated and invasively growing BCCs and SCCs. P lakophilin 1 was also prominent in the desmosomes of keratinocyte shee ts grown in culture, The cell type-specific, i.e., differentiation-dep endent, distribution of desmosomal plakophilin 1 is discussed in relat ion both to the stratification of the cutaneous epithelia and to tumor differentiation and growth.