Endothelial cell surface F 1 -F O ATP synthase is active in ATP synthesis and is inhibited by angiostatin

Abstract

Angiostatin blocks tumor angiogenesis in vivo , almost certainly through its demonstrated ability to block endothelial cell migration and proliferation. Although the mechanism of angiostatin action remains unknown, identification of F 1 -F O ATP synthase as the major angiostatin-binding site on the endothelial cell surface suggests that ATP metabolism may play a role in the angiostatin response. Previous studies noting the presence of F 1 ATP synthase subunits on endothelial cells and certain cancer cells did not determine whether this enzyme was functional in ATP synthesis. We now demonstrate that all components of the F 1 ATP synthase catalytic core are present on the endothelial cell surface, where they colocalize into discrete punctate structures. The surface-associated enzyme is active in ATP synthesis as shown by dual-label TLC and bioluminescence assays. Both ATP synthase and ATPase activities of the enzyme are inhibited by angiostatin as well as by antibodies directed against the α- and β-subunits of ATP synthase in cell-based and biochemical assays. Our data suggest that angiostatin inhibits vascularization by suppression of endothelial-surface ATP metabolism, which, in turn, may regulate vascular physiology by established mechanisms. We now have shown that antibodies directed against subunits of ATP synthase exhibit endothelial cell-inhibitory activities comparable to that of angiostatin, indicating that these antibodies function as angiostatin mimetics.