This paper describes a study concerning the expression of angiogenesis-related genes in cortisol secreting adrenocortical tumors in dogs. The aim of this study was to determine which angiogenesis-related genes are significantly up- or down-regulated in these tumors, when compared to normal adrenal tissue. Six genes, known to be involved in both normal and tumor angiogenesis, were chosen to evaluate: Angiopoietin 1 and 2, their receptor Tie-2, vascular endothelial growth factor (VEGF) and its receptors VEGFR 1 and -2. For quantification of gene expression on messenger RNA level, a quantitative RT-PCR was performed on material of 31 adrenocortical tumors and 9 normal, healthy adrenals. \ud In addition to determining the expression levels of these genes, the presence of Ang-2443, a splice variant of Angiopoietin 2, was also investigated. In dogs this splice variant had not yet been described; therefore the aim was to investigate whether or not this variant was present in dogs, and if so, whether an association with cortisol secreting adrenocortical tumors could be proven. To achieve this, regular PCR and quantitative RT-PCR were performed.\ud To investigate whether the differences in the expression of Ang-2, detected on messenger RNA level, were also present on protein level, a Western blot experiment was performed.\ud \ud Q-PCR results showed no significant differences in expression levels of Angiopoietin 1, Tie-2 and VEGFR 2, and only minor changes in the expression levels of VEGF and VEGFR 1. However, for Angiopoietin 2, expression analysis showed a significant up-regulation in the tumor group when compared to normal adrenals. This up-regulation was confirmed on the protein level by means of Western blot. The presence of Ang-2443 was demonstrated in both normal adrenals and adrenocortical tumors. As for the full length Ang-2, expression analysis showed that this splice variant was significantly up-regulated in the tumor group. Additionally, a difference in expression levels between adenomas and carcinomas was shown for Ang-2443¬, with higher levels of up-regulation in the malignant tumors. Western blot results confirmed these findings on protein level.\ud \ud The results of this study therefore strongly indicate a role of Angiopoietin 2 in the pathogenesis of canine adrenocortical tumors, whereas for the other genes in this study such a role is not implicated by the results. More research is needed to determine the nature of the role of Ang-2 and its splice variant Ang-2443 in the pathogenesis of canine adrenocortical tumors
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