Angiomodulin (AGM/TAF/mac25) is a 30-kDa
glycoprotein that was identified as an
integrin-independent cell adhesion
protein secreted by human bladder
carcinoma cells. AGM is highly accumulated in small blood vessels of
tumor tissues. In the present study, we attempted to identify the
cell surface receptor and the cell-binding site of AGM using ECV-304 human vascular endothelial cells and BALB/c3T3 mouse fibroblasts.
Heparin,
heparan sulfate, and
dextran sulfate, but not
chondroitin sulfate, inhibited both adhesion of the two cell lines to AGM-coated plates and binding of AGM to these cells. Treatment of cells with
heparinase, but not
chondroitinase, inhibited both cell adhesion to AGM and AGM binding to cells. These results strongly suggested that heparan
sulfates are the major receptor for AGM. Furthermore, we determined a 20-amino
acid sequence within AGM molecule as its major cell-binding site. The synthetic
peptide for the cell-binding sequence showed cell adhesion activity comparable to that of AGM, and the activity was inhibited by
heparin and
heparan sulfate. The
peptide competitively inhibited cell adhesion to AGM and the binding of AGM to cells. These results indicated that AGM binds to cells through interaction of the identified cell-binding sequence with heparan
sulfates on cell surface. It was also found that the
heparan sulfate-binding
peptide inhibited the formation of capillary tube-like structures of vascular endothelial cells in culture.