Angiogenesis plays a primary role in tumor growth and metastasis. Angiostatin, a proteolytic fragment containing the first four kringle domains of human plasminogen, can inhibit angiogenesis. The anti-angiogenic activities of kringle 1-5 (K1-5) and kringle 5 fragments of plasminogen are greater than angiostatin in inhibiting angiogenesis and angiogenesis-dependent tumor growth. To further optimize kringle fragment anti-angiogenic activities, mutations were created at the potential glycosylation sites Asn-289 and Thr-346 and the Lys binding site, Leu-532, at kringle 5, including K1-5N289A (replacing Asn by Ala at residue 289), K1-5T346A, K 1-5L532R, K1-5N289A/T346A, K1-5T346A/L532R, K1-5N289A/L532R, and K1-5N289A/T346A/L532R. Wild-type and mutant K1-5 proteins were expressed successfully by the Pichia pastoris expression system. Native K1-5 from proteolytic cleavage and wild-type K1-5 have similar activity in inhibiting basic fibroblast growth factor-induced endothelial cell proliferation. Among these mutated proteins, K1-5N289A/T346A/L532R exhibited the greatest effect in inhibiting endothelial cell proliferation and in inducing endothelial cell apoptosis. Integrin αvβ3-mediated adhesion of K1-5N289A/T346A/L532R to endothelial cells was more greatly enhanced when compared to wild type K1-5. Furthermore, K1-5N289A/ T346A/L532R was most potent in inhibiting basic fibroblast growth factor-induced angiogenesis in Matrigel assay in vivo. Angiogenesis-dependent tumor growth was inhibited by systemically injected K1-5N289A/T346A/L532R into mice. These results demonstrate that alteration of glycosylation and Lys binding properties could increase the anti-angiogenic action of K1-5, possibly via enhanced interaction with integrin αvβ 3 in endothelial cells.
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