Specific Interaction of Angiostatin with Integrin α _vβ₃ in Endothelial Cells

Angiostatin, the N-terminal four kringles (K1-4) of plasminogen, blocks tumor-mediated angiogenesis and has great therapeutic potential. However, angiostatin's mechanism of anti-angiogenic action is unclear. We found that bovine arterial endothelial (BAE) cells adhere to angiostatin in an integrin-dependent manner and that integrins α_vβ ₃, α₉β₁, and to a lesser extent α₄β₁, specifically bind to angiostatin. α_vβ₃ is a predominant receptor for angiostatin on BAE cells, since a function-blocking antibody to α_vβ ₃ effectively blocks adhesion of BAE cells to angiostatin, but an antibody to α₉β₁ does not. ε-Aminocaproic acid, a Lys analogue, effectively blocks angiostatin binding to BAE cells, indicating that an unoccupied Lys-binding site of the kringles may be required for integrin binding. It is known that other plasminogen fragments containing three or five kringles (K1-3 or K1-5) have an anti-angiogenic effect, but plasminogen itself does not. We found that K1-3 and K1-5 bind to α _vβ₃, but plasminogen does not. These results suggest that the anti-angiogenic action of angiostatin may be mediated via interaction with α_vβ₃. Angiostatin binding to α _vβ₃ does not strongly induce stress-fiber formation, suggesting that angiostatin may prevent angiogenesis by perturbing the α_vβ₃-mediated signal transduction that may be necessary for angiogenesis.