Regulation of Angiogenesis

Abstract: Angiogenesis is the formation of new blood vessels from pre-existing ones. New blood vessel formation is fundamental in processes such as reproduction, embryonic development and wound healing. Growth of neoplasms is accompanied by increased angiogenesis. This thesis describes cellular and molecular mechanisms of importance for angiogenesis. The effects of a number of different anti-angiogenic substances on tumor growth were investigated. Fibroblast growth factor-2 (FGF-2) is involved in different processes in angiogenesis. We have shown that Crk, an adaptor protein, participates in signaling downstream of FGF receptor-1, via the juxtamembrane tyrosine residue 463. Signal transduction through FGF receptor-1 and Crk regulates endothelial cell proliferation. Anti-angiogenic effects of endostatin, latent antithrombin and prelatent antithrombin were evaluated. We found that FGF-2- and vascular endothelial growth factor (VEGF)- induced angiogenesis in the chick chorioallantoic membrane assay is inhibited by these anti-angiogenic substances, which also efficiently reduce tumor growth in mice. Molecular mechanisms underlying the anti-angiogenic effects were investigated and endostatin was found to mediate its activity through induction of a 125 kDa kinase, leading to apoptosis. Endostatin was shown to be dependent on heparin/heparan sulfate binding for angiogenesis inhibition only in FGF-2- stimulated vessels, and not in those stimulated with VEGF. A peptide encompassing residues 180-199 in endostatin, capable of mimicking the effects of endostatin on endothelial cells was identified. Latent antithrombin and prelatent antithrornbin were found to exert their anti-angiogenic effects through negative regulation of focal adhesion kinase and focal adhesion formation.