Further biochemical investigations on the hemidesmosome-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 genodermatosis 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-beta-N-acetylglucosaminidases and
neuraminidase hydrolysis, as well as
concanavalin A binding experiments were performed on the GB3 radioimmunoprecipitated
polypeptides 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(-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
glycoproteins in cell-cell and cell-substratum attachment. Furthermore, the ability to modulate this
antigen may be relevant for the understanding of the molecular defect involved in
lethal junctional epidermolysis bullosa.