Abstract 1285: The effects of the HK5-ferritin interaction and iron on tumor angiogenesis

Angiogenesis, or the development of new blood vessels from existing blood vessels, is a process essential to wound healing, reproduction, and tumor growth. Tumor angiogenesis is an important factor in the growth and spread of cancer. In order for tumors to grow beyond 2mm^3, vasculature is necessary to provide oxygen and nutrients and remove waste products. The imperfect blood vessels built within tumors also allow tumor cells to travel through the bloodstream and metastasize. Endogenous inhibitors of angiogenesis are known to form from plasma proteins. For example, angiostatin is derived from plasmin. A newly described angiogenesis inhibitor derived from high molecular weight kininogen (HK) is domain 5 of HK (HK5). HK5 has been shown to inhibit endothelial cell proliferation, migration and tube formation. HK5 binds to the endothelial cell surface receptors uPAR, cytokeratin-1, gC1qR and tropomyosin to disrupt angiogenic signaling. Our laboratory has shown that the iron storage protein ferritin binds to HK5, inhibiting its antiangiogenic effects and thereby allowing endothelial cells to migrate and proliferate. We have begun to investigate the physical interaction of ferritin with the HK5 protein with the long-term goal of developing inhibitors of the HK5-ferritin interaction. Human recombinant HK5 and ferritin H were purified and their interaction studied using fluorescence anisotropy. The two proteins were found to bind with a Kd of 1.36μM. The influence of metals on the interaction was also evaluated. We found that in the presence of iron the interaction between ferritin and HK5 was maximal, while in the presence of zinc, the interaction was minimal. EDTA pretreatment of the two proteins further improved binding. The results suggest that iron is essential to the optimal binding interaction of HK5 and ferritin. Future studies will be directed at the identification of specific amino acid residues involved in this interaction. (supported by NIH R01 DK071892) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1285.