Canstatin acts on endothelial and tumor cells via mitochondrial damage initiated through interaction with αvβ3 and αvβ3 integrins

Canstatin, the noncollagenous domain of collagen type IV alpha-chains, belongs to a series of collagen-derived angiogenic inhibitors. We have elucidated the functional receptors and intracellular signaling induced by canstatin that explain its strong antitumor efficacy in vivo. For this purpose, we generated a canstatin-human serum albumin (CanHSA) fusion protein, employing the HSA moiety as an expression tag. We show that CanHSA triggers a crucial mitochondrial apoptotic mechanism through procaspase-9 cleavage in both endothelial and tumor cells, which is mediated through cross-talk between alpha,beta(3)- and alpha(v)beta(5)-integrin receptors. As a point of reference, we employed the first three kringle domains of angiostatin (Kl-3), fused with HSA, which, in contrast to CanHSA, act only on endothelial cells through alpha(v)beta(3)-integrin receptor-mediated activation of caspase-8 alone, without ensuing mitochondrial damage. Taken together, these results provide insights into how canstatin might exert its strong anticancer effect.