Regulation of Angiogenesis by the Kallikrein-Kinin System

High molecular weight kininogen (HK) is a plasma protein that is cleaved by plasma kallikrein in the clinical settings of sepsis and chronic inflammatory diseases such as rheumatoid arthritis and Crohn's disease. This proteolytic event results in a nonapeptide, bradykinin (BK), and a kinin-free derivative of HK, namely HKa. BK promotes angiogenesis by upregulation of bFGF through the B1 receptor or by stimulation of VEGF formation via the B2 receptor. Kininogen- deficient rats show diminished angiogenesis when neovascularization is stimulated. The formation of HKa results in exposure of domain 5 (D5). HKa or D5 inhibit endothelial cell migration and proliferation, both of which are needed for angiogenesis. In the chicken chorioallantoic membrane assay when neovascularization is stimulated by bFGF or VEGF, HKa or D5 inhibit angiogenesis. Monoclonal antibody C11C1, which prevents binding of HK to endothelial cells, also limits its conversion to BK thus downregulating angiogenesis. In vivo, mAb C11C1 inhibits tumor angiogenesis in mice as well as in experimental inflammatory arthritis and inflammatory bowel disease in Lewis rats. In vitro HKa or D5 inhibits endothelial cell adhesion to vitronectin and fibrinogen, resulting in anokis and apoptosis. The HKa receptor, uPAR, forms a signaling complex containing the integrin αvβ3 or α5β1, caveolin, Src kinase Yes, focal adhesion kinase and paxcillin. HKa physically disrupts the complex by interfering with the binding of vitronectin to uPAR. Both mAb C11C1 and D5 have potential applications for controlling unwanted angiogenesis in inflammation and cancer.