Endocrine Abstracts

VEGF exerts its effects by binding to two tyrosine kinase receptors, KDR and VEGFR1. KDR is critical for transmitting signals for proliferation and migration of endothelial cells but is also expressed in several non-endothelial cells, and is elevated in some human tumour cells. We investigated KDR expression in human thyroid epithelial cells in vitro and thyroid cancers compared with normal thyroid samples examined ex vivo. Expression of KDR was demonstrated using Taqman RT-PCR and Western blotting in a human follicular thyroid cancer line (FTC133) and primary thyroid epithelial cells. KDR expression in these cells demonstrated VEGF-specific and dose-dependent activation of KDR-dependent downstream MAPK signalling and KDR-dependent mitogenesis. KDR mRNA expression was elevated in thyroid cancers (2.5 fold, n=38, P<0.001), and immunohistochemistry demonstrated stronger phosphorylated-KDR staining in thyroid cancer cells compared with normal thyroid cells. Further, we showed that PTTG, a multifunctional protein known to promote angiogenesis, up-regulates KDR (2.2 fold, n=7, P=0.006) and VEGF (2.4 fold, n=4, P<0.001) expression in primary thyroid cells. Next, we examined expression of Inhibitor of DNA binding-3 (ID3), known to be important in VEGF-dependent angiogenesis, and VEGF mRNA expression in a series of thyroid cancers. We observed a strong positive correlation between expression of these genes (R²=0.62, n=38, P<0.001). Stimulation of FTC133 cells with exogenous VEGF increased ID3 expression (2.1 fold, n=6, P<0.001) compared with control, an effect abrogated by a KDR-specific inhibitor, suggesting VEGF regulation of ID3 is KDR-dependent. We suggest the presence of a VEGF-KDR-ID3 dependent autocrine pathway in thyroid cells. By up-regulating both VEGF and KDR expression, we propose that PTTG may promote this autocrine proliferative pathway which may in turn be critical to thyroid cancer progression.