Investigating the effects of Chromosome 21 genes on pathological angiogenesis
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Patients with trisomy of chromosome 21, known as Down’s syndrome (DS), have a lower incidence of solid tumours than unaffected age-matched individuals. However, the cellular and molecular basis for this observation is not well understood. We hypothesised that a direct link between Down’s syndrome and angiogenesis exists, whereby the overexpression of human chromosome 21 (Hsa21) genes causes the repression of angiogenesis (gene dosage effects) resulting in the inhibition of solid tumour growth. In this project we investigated the angiogenic phenotype of an animal model of Down’s syndrome, the Tc1 mouse, which contains a large freely segregating fragment of Hsa21 containing over 200 human genes. We found that the growth of both B16F0 melanoma and Lewis Lung Carcinoma cells was impaired in Tc1 mice. Tumour vascularity also was reduced. This is supportive of the epidemiological data from the human DS population and supports the hypothesis that Hsa21 contains anti-angiogenic genes. Candidate genes were selected due to their endothelial specificity or likelihood to function in angiogenesis based on functional data or similarity to other proteins. Ex vivo RNAi assays were used to examine their roles in angiogenesis. We have found that reducing the expression of human Adamts1, Erg, Jamb or Pttg1ip in Tc1 tissue can restore its angiogenic potential, suggesting that the dosage of these genes (i.e. 3 copies instead of 2) can inhibit angiogenesis. Following from this study we also examined the role of selected adhesion related genes found on chromosome 21 in angiogenesis. Cldn14 encodes the tight junction molecule Claudin14 but its role in angiogenesis was unknown. We found that partial, but not complete, depletion of Cldn14 can increase the proportion of non-lumenated tumour blood vessels; decrease supporting cell association with tumour vessels; and increase endothelial cell proliferation in vivo, ex vivo and in vitro. Taken together this series of experiments has identified novel regulators of angiogenesis and has demonstrated the gene dosage effects of a subset of Hsa21 genes on angiogenic processes.
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