CHARACTERIZATION OF A 50-KDA COMPONENT OF EPITHELIAL BASEMENT-MEMBRANES USING GDA-J F3 MONOCLONAL-ANTIBODY/

Using the monoclonal antibody GDA-J/F3, a 50-kDa noncollagenous compon ent of human skin basement membrane zone was identified. Immunofluores cence stainings of normal human skin with the GDA-J/F3 antibody showed a linear fluorescence decorating the basement membrane zone. With imm unoelectron microscopy, the epitope was localized to the insertion poi nts of the anchoring fibrils into the lamina densa The antigen is dist inct from collagen VII, from the main structural protein of the anchor ing fibrils, and from several other structural molecules of the baseme nt membrane zone, because the GDA-J/F3 antibody did not react with pur ified basement membrane components in vitro. In serum-free cultures, t he antigen was synthesized and secreted by normal and transformed huma n keratinocytes and to a lesser extent by normal human skin fibroblast s. Immunoprecipitation of radiolabeled epithelial cell-conditioned med ium with the GDA-J/F3 antibody yielded two polypeptides that migrated on SDS-polyacrylamide gel electrophoresis with apparent molecular mass es of 46 and 50 kDa under nonreducing conditions. Using reducing gels, only the 50-kDa polypeptide was observed. The antigen was resistant t o digestion with bacterial collagenase but sensitive to trypsin and pe psin. It also bound to heparin and DEAE cellulose at low ionic strengt h and alkaline pH. These findings indicate that the GDA-J/F3 antigen i s a small globular disulphide-bonded protein with a potential to inter act with basement membrane proteoglycans. Integration of the GDA-J/F3 antigen into the histoarchitecture of the dermo-epidermal junction is dependent on the presence of collagen VII, because the GDA-J/F3 epitop e was missing in several patients with a genetic blistering disorder o f the skin, epidermolysis bullosa dystrophica, who lacked collagen VII and anchoring fibrils.