In vitro human thyroid follicular cells have been shown to secrete vascular endothelial growth factors (VEGFs). VEGFs transduce their effects by binding to their receptors, VEGFRs, leading to receptor phosphorylation and recruitment of downstream signalling molecules. Using RT-PCR we found that normal human thyroid follicular cells in culture express VEGFR-1, VEGFR-2 and VEGFR-3. Western blotting using antisera specific for phosphotyrosine at 1214 of the GRB2 SH2 binding site of VEGFR-21, revealed the expression of single band of phosphorylated VEGFR-2 of mol wt ~210,000 in these cells. Using antisera for unphosphorylated VEGFR-2, immunoreactivty of a band of identical size was found as well as lower mol wt bands. Immunoreactive proteins of similar size were labelled in the rat thyroid FRTL5 cell line with these antisera. Immunohistochemical staining of human thyroid tissue sections showed phosphorylated and unphosphorylated VEGFR-2 expression in follicular cells which varied with disease state. The functional significance of VEGFR expression on human thyroid cells was studied using specific inhibitors. Following 72h treatment, a dose-dependent increase in thyroid function, measured by 125I uptake, was found (5 fold increase at 10-6M VEGFRi, p<0.01) and a dose-dependent decrease in secreted plasminogen activator activity (PAA) was found (reduced by 98% at 10-6M VEGFRi, p<0.01). Chronic treatment with VEGFRi completely inhibited phosphorylation of p42/44 MAPK although expression of this kinase was not inhibited. Inhibition of phosphorylation of p42/44MAPK with PD98059 also increased 125I uptake and inhibited PAA. We conclude that VEGFR expression is not restricted to endothelial cells but is found in normal thyroid follicular cells. This VEGFR-2 is activated as shown by its phosphorylation at Y1214. Endogenous production of VEGFs may result in decreased thyroid function and increased PAA which both may play a role in goitrogenesis.
1.Stewart et al. Histopathology 2003, 43:33-39. A kind gift of K C Gatter
04 - 06 Apr 2005
British Endocrine Societies