Tumor blood vessels have morphogenetic defects that impact tumor pathogenesis, primarily through the initiation of hypoxia-related signaling. Vessels found in tumors are tortuous, dilated and leaky. Limited evidence has indicated that tumor endothelial cells (ECs) have excess centrosomes, which may explain their abnormal phenotype. However, the mechanisms responsible for these cellular alterations are largely undefined. Our group recently demonstrated that excess VEGF signaling increases the frequency of centrosome over-duplication in developing blood vessels and in human ECs. Unequal centrosome numbers (>2) can have deleterious cellular consequences due to disruption of the cells microtubule-organizing center. Propagation and assimilation of defective ECs during angiogenic sprouting may explain, in part, the tortuous, leaky and/or chemoresistant blood vessel phenotype commonly observed in tumor tissue. This proposal aims to test the hypothesis that tumor vessel ECs are abnormal downstream of centrosome number dysregulation, and that this dysregulation contributes to the abnormal structure and function of tumor vessels. Accordingly, we will test this hypothesis in two aims. Aim #1 will determine the mechanisms and consequences of centrosome dysregulation on EC behaviors. Genetic perturbations will be introduced into human primary ECs to cause centrosome over-duplication, independent of pleiotropic proangiogenic signaling. Modified ECs will be challenged in a migratory assay and a 3D-angiogenesis assay in which they will proliferate, sprout and branch in vitro to determine the effects of centrosome dysregulation on angiogenesis. Aim #2 will determine the linkage between tumor progression and centrosome duplication in ECs of tumor vessels. Using a novel transgenic approach to mark EC DNA, I will analyze the endothelial compartment in mouse mammary tumors for centrosome abnormalities to be correlated with tumor stage and invasiveness to determine the effects of dysregulation of centrosome duplication on tumor progression. Additionally, tumor and normal ECs will be isolated and cultured ex vivo and challenged to the same functional assays in aim #1. Information from this investigation will illuminate key early events (dysregulation of centrosome duplication) in tumor blood vessel angiogenesis, and show how these events link to abnormal vessel development and tumor progression.