Specific interaction of angiostatin with integrin αvβ3 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 alpha (v)beta (3), alpha (9)beta (1), and to a lesser extent alpha (4)beta (1) specifically bind to angiostatin. alpha (v)beta (3) is a predominant receptor for angiostatin on BAE cells, since a function-blocking antibody to alpha (v)beta (3) effectively blocks adhesion of BAE cells to angiostatin, but an antibody to alpha (9)beta (1) does not. e-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 alpha (v)beta (3), but plasminogen does not. These results suggest that the anti-angiogenic action of angiostatin may be mediated via interaction with alpha (v)beta (3). Angiostatin binding to alpha (v)beta (3) does not strongly induce stress-fiber formation, suggesting that angiostatin may prevent angiogenesis by perturbing the alpha (v)beta (3)-mediated signal transduction that may be necessary for angiogenesis.