RESUMO
DCC (deleted in colorectal carcinoma) is a broadly expressed cell-surface receptor. Netrin-1 was recently identified as a DCC ligand in brain, but the possibility of other DCC ligands was suggested by the finding that an anti-DCC antibody (clone AF5) neutralized netrin-1-dependent commissural axon outgrowth without blocking DCC/netrin-1 interactions. Here we have searched for alternative cell-surface DCC ligands. A DCC-Ig fusion protein bound to neural and epithelial derived cell lines, indicating that these lines express ligand(s) for DCC. The cell-surface binding activity was mediated by the loop between beta-strands F and G of the fifth fibronectin type III repeat FNIII-D5. The loop included the sequence KNRR, which resembles heparin-binding motifs in other proteins. Heparinase and heparitinase treatment of cells reduced binding of DCC-Ig, suggesting that heparan sulfate proteoglycans are cell-surface DCC ligand(s). This was further supported by heparin blocking experiments and by binding of DCC-Ig to immobilized heparan sulfate. The interaction between DCC-Ig and heparan sulfate/heparin, both on the surface of cells and immobilized on plastic, was blocked by the same anti-DCC antibody that blocks netrin-1-dependent commissural axon outgrowth. Taken together, these findings suggest that the DCC-Ig/heparin interaction may contribute to the biological activity of DCC.
