A constitutive transmembrane glycoprotein of Mr 165,000 (desmoglein) in epidermal and non-epidermal desmosomes. II. Immunolocalization and microinjection studies.

Using two monoclonal antibodies described in the preceding paper we determined by immunofluorescence microscopy the distribution of an integral membrane protein of the desmosomal domain, the major glycopolypeptide of Mr 165,000 (bovine muzzle epidermal desmosome band 3; desmoglein) in various normal tissues, tumors and cultured cell lines from several mammalian species. This protein was detected in dotted or streak-like arrays along cell boundary structures which were known to contain non-membrane-integrated desmosomal plaque proteins such as desmoplakins. This is true for epithelial, i.e. cytokeratin-expressing cell types, for the desmin-producing myocardiac and Purkinje fiber cells of the heart, and for certain vimentin-containing cells such as arachnoidal and meningiomal cells and dendritic follicular cells of lymph nodes. However, on the basis of both immunoblot and immunocytochemical reactions, the protein is absent from non-desmosomal adhering junctions, including those devoid of desmoplakin but containing another plaque protein, plakoglobin ("band 5 protein"). We have used these antibodies to localize their epitopes with respect to the cell membrane. By immunoelectron microscopy we found that both epitopes are located in the desmosomal plaques, and this was confirmed by microinjection of purified antibodies into living cultured cells which resulted in labelling of the plaques. From these findings, taken together with previous analyses and localizations of the carbohydrate moieties of this glycoprotein, we conclude that desmoglein is a transmembrane glycoprotein which projects into--and contributes to--the desmosomal plaque structure. This glycoprotein represents a general component of true desmosomes and it is coexpressed with obligatory desmosome-specific plaque proteins such as desmoplakin I. The potential value of this glycoprotein as a desmosomal and cell type marker in histology and tumor diagnosis is discussed.