Two-chain high molecular weight kininogen induces endothelial cell apoptosis and inhibits angiogenesis: partial activity within domain 5

We previously reported that the binding of two-chain high molecular weight kininogen (HKa) to endothelial cells may occur through interactions with en dothelial urokinase receptors. Since the binding of urokinase to urokinase receptors activates signaling responses and may stimulate mitogenesis, we a ssessed the effect of HKa binding on endothelial cell proliferation. Unexpe ctedly, HKa inhibited proliferation in response to several growth factors, with 50% inhibition caused by similar to 10 nM HKa. This activity was Zn2dependent and not shared by either single-chain high molecular weight kinin ogen (HK) or low molecular weight kininogen. HKa selectively inhibited the proliferation of human umbilical vein and dermal microvascular endothelial cells, but did not affect that of umbilical vein or human aortic smooth mus cle cells, trophoblasts, fibroblasts, or carcinoma cells. Inhibition of end othelial proliferation by HKa was associated with endothelial cell apoptosi s and unaffected by antibodies that block the binding of HK or HKa to any o f their known endothelial receptors. Recombinant HK domain 5 displayed acti vity similar to that of HKa. In vivo, HKa inhibited neovascularization of s ubcutaneously implanted Matrigel plugs, as well as rat corneal angiogenesis . These results demonstrate that HKa is a novel inhibitor of angiogenesis, whose activity is dependent on the unique conformation of the two-chain mol ecule.