Bone sialoprotein mediates human endothelial cell attachment and migrationand promotes angiogenesis

Bone sialoprotein (BSP) is a secreted glycoprotein primarily found in sites of biomineralization. Recently, we demonstrated that BSP is strongly upreg ulated in osteotropic cancers and particularly those that exhibit microcalc ifications, BSP contains an Arg-Gly-Asp (RGD) motif found in other adhesive molecules that interact with cellular integrins, In bone, BSP has been sho wn to mediate the attachment of osteoblasts and osteoclasts via alpha(v)bet a(3) integrin receptors. Ligands for alpha(v)beta(3) integrin are considere d to play a central role during angiogenesis. Therefore, we used human umbi lical vein endothelial cells (HUVECs) to study the potential role of BSP in angiogenesis. We found that purified eukaryotic recombinant human BSP (rhB SP) is able to promote both adhesion and chemotactic migration of HUVECs in a dose-dependent manner. These interactions involve HUVEC alpha(v)beta(3) integrin receptors and the RGD domain of BSP. Indeed, HUVECs attach to a re combinant BSP fragment containing the RGD domain, whereas this response is not observed with the same fragment in which RGD has been mutated to Lys-Al a-Glu (KAE), A cyclic RGD BSP peptide inhibits both adhesion and migration of HUVECs to rhBSP, Moreover, anti-alpha(v)beta(3) but not anti-alpha(v)bet a(5) monoclonal antibodies also prevent BSP-mediated adhesion and migration of HUVECs. We observed that both rhBSP and the RGD BSP recombinant fragmen t stimulated ongoing angiogenesis on the chorioallantoic chick membrane ass ay. BSP angiogenic activity was inhibited by anti-alpha(v)beta(3) antibody, and the KAE BSP fragment was inactive. Our findings represent the first re port implicating BSP in angiogenesis. BSP could play a critical role in ang iogenesis associated with bone formation and with tumor growth and metastat ic dissemination.