Urokinase-type plasminogen-activator and normal thyroid cell adhesion to the extracellular matrix

Emerging molecular markers for the prognosis of differentiated thyroid cancer patients

Epithelial thyroid cancers are represented by the differentiated papillary and follicular thyroid carcinomas which, following dedifferentiation, are thought to give rise to the highly aggressive and incurable anaplastic thyroid carcinomas. Although derived from the same cell type, the different thyroid tumors show specific histological features, biological behavior and degree of differentiation as a consequence of different genetic alterations. Over the last few years, our knowledge regarding the molecular alterations underlying thyroid cell malignant transformation and cancer progression has considerably increased; however, the prognosis of differentiated thyroid cancer patients still relies on high-risk clinic-pathological variables. In particular, the actual staging systems provides only a rough prediction for cancer mortality and risk of recurrences, including in each risk group patients with highly different tumor-specific progression, disease-free interval and survival time. In order to improve DTC patient's risk stratification, both the European and the American Thyroid Associations proposed practical guidelines to integrate the actual staging systems with additional clinical features such as the tumor histological variant, the results of post-ablative whole body scan and the serum thyroglobulin levels. Despite that, patients within the same risk group still show a very heterogeneous behavior in terms of disease-free interval. As a consequence, the identification of new prognostic molecular biomarkers able to testify tumor aggressiveness is highly required. Here we'll review recently characterized new molecular markers potentially able to ameliorate the prognosis in DTC patients.

Regulation of human thyroid follicular cell function by inhibition of vascular endothelial growth factor receptor signalling

The potential autocrine role of human thyroid vascular endothelial growth factors (VEGFs) was examined using the VEGF receptor (VEGFR) inhibitor, ZM306416HCl. ZM306416HCl reduced VEGFR2 phosphorylation and inhibited endogenous, steady-state levels of p42/44 MAPK phosphorylation. It potently inhibited the secretion of plasminogen activators (PA) and increased (125)I uptake. Cell survival was compromised but rescued with insulin and TSH. Although the EGF receptor remained responsive to challenge by EGF in p42/44 MAPK assays, stimulatory effects of EGF on PA production were prevented by ZM306416HCl and those of protein kinase C stimulator, TPA reduced. In assays of (125)I uptake, ZM306416HCl prevented the inhibitory effects of EGF but not those of TPA. We conclude that autocrine VEGF may modulate thyroid function and that VEGFR inhibition increases iodide uptake and decreases PA production through regulation of p42/44 MAPK phosphorylation. VEGFR inhibition may have effects on thyroid function which may contribute to "off target" effects in clinical trials.

Regulation of plasminogen activators in human thyroid follicular cells and their relationship to differentiated function

Human thyroid cells in culture take up and organify (125)I when cultured in TSH (acting through cAMP) and insulin. They also secrete urokinase (uPA) and tissue-type (tPA) plasminogen activators (5-100 IU/10(6)cells/day). TSH and insulin both decreased secreted PA activity (PAA), uPA and tPA protein and their mRNAs. Autocrine fibroblast growth factor increased secreted PAA and inhibited thyroid cell (125)I uptake. Epidermal growth factor (EGF) and the protein kinase C (PKC) activator, TPA significantly increased PAA and inhibited thyroid differentiated function, (TPA > EGF). For TPA, effects were rapid, increased PAA secretion and decreased (125)I uptake being seen at 4 h whereas for EGF, a 24 h incubation was required. qRT-PCR showed significantly increased mRNA expression of uPA with lesser effects on tPA. Aprotinin, which inhibits PAA, increased (125)I uptake but did not abrogate the effects of TPA and EGF. The MEKK inhibitor, PD98059 partially reversed the effects of EGF and TPA on PAA, and largely reversed the effects of EGF but not TPA on differentiated function. PKC inhibitors bisindoylmaleimide 1, and the specific PKCbeta inhibitor, LY379196 completely reversed the effects of TPA on (125)I uptake and PAA whereas EGF effects were unaffected. TPA inhibited follicle formation and this effect was blocked by LY379196 but not PD98059. We conclude that in thyroid cells, MAPK activation inversely correlates with (125)I uptake and directly correlates with PA expression, in contrast to the effects of cAMP. TPA effects on iodide metabolism, dissolution of follicles and uPA synthesis are mediated predominantly through PKCbeta whereas EGF exerts its effects through MAPK but not PKCbeta.

Differential expression of the components of the plasminogen activating system in human thyroid tumour derived cell lines and papillary carcinomas

We characterised the expression of the plasminogen activators (uPA and tPA), the uPA receptor (uPAR) and the PAs inhibitors (PAI-1 and PAI-2) in human thyroid cell lines derived from normal thyroid, follicular adenoma, follicular, papillary and anaplastic carcinomas. Urokinase PA activity was detected in the supernatant of normal thyrocytes and augmented in those of all tumour cells. Quantitative RT-PCR analysis showed that uPA, uPAR and PAI-1 mRNAs increased in all carcinoma cells. Similar results were found in 13 papillary thyroid carcinoma (PTC) tissues which were mirrored in Western blot experiments. A correlation was found between tumour size and uPA mRNA increase, and higher levels of uPA and uPAR mRNAs were found in metastatic PTC. In conclusion, thyroid carcinoma cell lines and PTC overexpress uPA, uPAR and PAI-1 and the correlation of uPA and its cognate receptor with tumour size and metastasis may suggest their potential prognostic relevance in thyroid cancer.

Urokinase-type plasminogen activator up-regulates the expression of its cellular receptor

The expression of the receptor for the urokinase-type plasminogen activator (uPAR) can be regulated by several hormones, cytokines, tumor promoters, etc. Recently, it has been reported that uPAR is capable of transducing signals, even though it is lacking a transmembrane domain and a cytoplasmatic tail. We now report that uPAR cell surface expression can be positively regulated by its ligand, uPA, in thyroid cells. The effect of uPA is independent of its proteolytic activity, since inactivated uPA or its aminoterminal fragment have the same effects of the active enzyme. The increase of uPAR on the cell surface correlates with an increase of specific uPAR mRNA. Finally, uPA up-regulates uPAR expression also in other cell lines of different type and origin, thus suggesting that the regulatory role of uPA on uPAR expression is not restricted to thyroid cells, but it occurs in different tissues, both normal and tumoral.