High molecular weight kininogen (HK) is an abundant plasma protein and member of the contact phase of coagulation that is involved in a number of important biological processes. We have previously reported that kallikrein-cleaved HK (HKa) induces rapid apoptosis of proliferating endothelial cells and inhibits angiogenesis. We have recently produced a kininogen deficient mouse by deleting the murine gene for kininogen that is expressed in liver, mKng1. These mice lack detectable kininogen, despite persistent expression of mRNA from the mKng2 gene, primarily expressed in kidney. To further determine the importance of kininogen in the regulation of angiogenesis, we assessed angiogenesis in mKng1−/− mice. These mice demonstrated increased angiogenesis in subcutaneously-implanted Matrigel plugs containing vascular endothelial cell growth factor (VEGF) or basic fibroblast growth factor (bFGF), compared to wild-type littermates. We also assessed the growth of B16F10 melanoma cells and Lewis lung carcinomas planted subcutaneously in mKng1−/− mice. In both cases, in particular with the B16F10 implants, tumor growth occurred substantially faster in the setting of kininogen deficiency (mean tumor volume of mKng1−/− mice 4820 ± 728 mm3 vs 1990 ± 412 mm3 in wild type mice; P = 0.003). Differences in growth rates were apparent approximately 8 days after tumor implantation, and were associated with increases in tumor microvascular density. Several reports suggest that the urokinase receptor (uPAR), which binds HKa, mediates its antiangiogenic activity. However, using Matrigel plug assays we observed that HKa inhibited angiogenesis equally well in wild type and uPAR−/− mice. These studies demonstrate that kininogen serves as an endogenous regulator of angiogenesis. Current studies are focused on better defining the mechanisms of this activity.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.