In the present study we provide evidence for the involvement of N-CAM in the spreading of human
renal cell carcinomas (RCC) through the interaction with the subendothelial matrix. We found that in tumor cell lines derived from human RCC the increase of growth rate and the loss of adhesiveness to inert substrate were accompanied by N-CAM expression and by the appearance of specific binding to endothelial
heparan sulfate. Indeed, the adhesion of
tumor cells to human endothelial cells and
heparan sulfate in vitro was inhibited by
monoclonal antibodies able to bind and inactivate N-CAM and was abrogated by endothelial cell treatment with
heparitinase. Furthermore, when the renal epithelial cell line COS7 was transfected with a
cDNA coding for N-CAM a significant increase in the ability to bind both endothelium and
heparan sulfate in vitro was observed. Of note, HS complexed with epithelial
growth factor could enhance the proliferation of RCC-derived
tumor cells; this effect was also achieved by cross-linking of N-CAM at the surface of
tumor cells, suggesting that N-CAM could transduce an activation signal across the cell membrane. This was also supported by the finding that N-CAM cross-linking induced a strong
calcium mobilization from internal stores and opening of surface
calcium channels in such
tumor cells. N-CAM was detectable in vivo at the
tumor site in the areas of active proliferation, as judged by the coexpression of Ki67
nuclear antigen, and
heparan sulfate was present in the wall of blood vessels in the proximity of the
tumor. These findings would suggest that growing kidney
tumors might use N-CAM to bind the subendothelial matrix and complexed
growth factors during tissue invasion and spreading.