Biochimica et Biophysica Acta, 942 (1988) 45-56 45 Elsevier BBA 74035 The new basement membrane antigen recognized by the monoclonal antibody GB3 is a large size glycoprotein: modulation of its expression by retinoic acid Patrick Verrando, Anne Pisani and Jean-Paul Ortonne Laboratoire de Recherches Dermatologiques, UER M$decine, Nice (France) (Received 25 November 1987) (Revised manuscript received 6 April 1988) Key words: Basement membrane; Antigen; Glycoprotein; Monoclonal antibody; Retinoic acid; (Human epidermis) Further biochemical investigations on the hemidesmosome-associated epidermal basement membrane com- ponent 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 epidermol- ysis 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-fl-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 -s 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. Introduction Basement membranes are specialized extracell- ular matrices which, by forming a complex scaf- fold, are involved in various biological processes such as spreading, migration, attachment and dif- ferentiation of their overlying cell population [1,2]. Although the total number of components re- Correspondence: J.-P. Ortonne, Laboratoire de Recherches Dermatologiques, UER Mrdecine, avenue de Valombrose, 06034 Nice Cedex, France. quired to form a functional basement membrane is still unknown, some biochemical constituents have been characterized and ultrastructurally localized in mammalian basement membranes, specially in the human epidermal basement mem- brane [2,3]. A comprehensive characterization of the ubiquitous basement membrane proteins and their poorly understood relationships is sought, since the basement membrane is implicated in a variety of diseases, such as diabetes mellitus and polycystic kidney disease, and skin disorders such as epidermolysis bullosa acquisita [2]. 0005-2736/88/$03.50 © 1988 Elsevier Science Publishers B.V. (Biomedical Division)