The relationship of polysialic acid and the neural cell adhesion molecule N-CAM in Wilms tumor and their subcellular distributions.

In previous studies we have reported that polysialic acid is an oncodevelopmental antigen in human kidney but its relationship to the neural cell adhesion molecule (N-CAM) remained undefined. In the present study, we showed by the combination of immunoprecipitation and immunoblotting that renal polysialic acid is a structural component of N-CAM polypeptide and that two highly sialylated N-CAM isoforms of approximately 120 kDa and 140 kDa existed in Wilms tumor. The presence of a cell surface coat composed of polysialic acid and N-CAM was revealed by immunoelectron microscopy, and morphological evidence for its involvement in modulating cell-cell adhesion has been provided. Furthermore, highly sialylated N-CAM was detectable extracellularly. N-CAM immunolabeling was present in compartments from the nuclear envelope to the plasma membrane. However, polysialic acid was only detectable at the cell surface suggesting that in Wilms tumor cells sialyl polymer synthesis may occur partially or exclusively at this site.