[A highly sialylated, embryonic form of the neural cell adhesion molecule in Wilms tumor: identification of a cell adhesion molecule as a onco-developmental antigen].

The neural cell adhesion molecule NCAM is a general Ca2+ -independent cell adhesion molecule which exerts important functions during the development of the nervous system. NCAM polypeptides exist in various isoforms all of which have a similar extracellular domain structure containing a homophilic binding site for establishment of cell-cell contacts. A common structural feature of NCAM is the presence of homopolymers of alpha 2,8-linked sialic acid residues, the so-called polysialic acid, which is developmentally regulated. It undergoes a change from a highly less sialylated short chain form from embryonic to adult life. The polysialic acid regulates the homophilic adhesive properties of NCAM. The highly sialylated form of NCAM typically found in developing tissues decreases homophilic NCAM-NCAM interactions and, therefore, cell-cell contacts due to its large excluded volume and electric repulsive forces. We have used a monoclonal antibody against polysialic acid, polyclonal antibodies against NCAM, polysialic acid specific bacteriophage-encoded endoneuraminidases and a NCAM cDNA to investigate this molecule by light and electron microscopic immunolabeling, in situ hybridization and immunochemistry. The highly sialylated form of NCAM was found to be expressed in a developmentally-regulated fashion in embryonic kidney, undetectable in the normal adult kidney and re-expressed in Wilms tumor. In Wilms tumor the blastemal cell masses as well as epithelial differentiations such as tubules and glomeruloid bodies were immunolabeled whereas the stroma did not label for polysialic acid. Combination of immunoprecipitation and immunoblotting using antibodies against polysialic acid and NCAM, respectively, directly demonstrated structural relationship of renal polysialic acid with NCAM polypeptide. By immunoblot analysis two NCAM isoforms of approximately 120 and 140 kD were found in Wilms tumor. Immuno-electron microscopy provided direct morphological evidence for prevention of cell-cell contacts due to the presence of a thick cell surface coat composed of polysialic acid. In nephroblastomatosis complexes only blastemal cells exhibited immunocytochemically detectable polysialic acid. All other investigated kidney tumors, i.e. clear cell sarcoma, malignant rhabdoid tumor, cystic nephroma and renal cell carcinoma, were negative. These data allow the conclusion that the highly sialyated, embryonic form of NCAM is an onco-developmental antigen in human kidney. At the same time this is the first observation that a molecule with a well defined role for controlled cell migration and differentiation during embryonic organ development represents an onco-developmental antigen.