Abstract

Further biochemical investigations on the hemidesmosone-associated epidermal basement membrane component recognized by the monoclonal antibody GB3 are presented in this study. We previously found that the expression of this constituent is impaired in a severe genedermatosis termed lethal junctional epidermolysis bullosa. We demonstrate now that this factor is a very large glycoprotein (apparent molecular weight, 600 kDa) made up of polypeptides in the range of 93.5 to 150 kDa, and containing N-linked oligosaccharide chains. Both endo-β-N-acetylglucosaminidases and neuraminidase hydrolysis, as well as concanavalin A binding experiments were performed on the GB3 radioimmunoprecipitated peptides from cultured human keratinocytes. They showed that the antigen subunits probably bear both ‘high-mannose’ and ‘complex’ type glycosidic chains. The chronic exposure of cultured human keratinocytes to retinoic acid (10⁻⁸ to 10⁻⁶ M) resulted in no apparent changes in the overall bulk of these glycosidic chains, but a dose-dependent increase of synthesis and secretion of the antigen was observed. A relative induction factor of 4 was obtained in cultures treated with 10^t-6 M retinoic acid. This induction was also observed morphologically by indirect immunofluorescence at the basement membrane zone from cultured human keratinocytes grown on dead de-epidermized dermis. These results further emphasize the influence of glycoprotiens in cell-cell and cell-substratum attachment. Furthermore, the ability to modulate this antigen must be relevant for the understanding of the molecular defect involved in lethal junctional epidermolysis bullosa.

Keywords: Basement membrane; Antigen; Glucoprotein; Monoclonal antibody; Retinoic acid; (Human epidermis)