Endocrine Abstracts

Anaplastic thyroid carcinomas (ATC) are characterised by a poor prognosis, due to a highly proliferative, metastatic and undifferentiated state. Follicular thyroid cells undergo epithelial to mesenchymal transition (EMT) by the upregulation of TGFβ pathway. Interestingly, in many epithelial cancer types a correlation between high levels of SIX1 expression and TGFβ signaling has been described.

Objective: Study the role of SIX1 homeoprotein in thyroid cancer, as a potential marker of TGFβ pathway and EMT.

Methods: Analysis of SIX1 expression in thyroid cancer cells by qPCR and western-blot. Evaluation of the effect of multiple ligands and inhibitors of TGFβ and PI3K pathway in the SIX1 levels. Generation of stable cells that overexpress SIX1 or SIX1 shRNAs by lentiviral particles. Quantification of cell proliferation, migration and invasion by BrDU, cell cycle, wound-healing and matrigel invasion assays. Luciferase assays for analyzing TGFβ activation.

Results: We show ATC cells present higher mRNA and protein levels of SIX1 comparing to the control cell line NThyOri and papillary thyroid cancer cells. Overexpression of SIX1 produces an increase of EMT markers, cell proliferation, migration, invasion, and amplifies TGFβ pathway. Opposite results were found by loss-of-function experiments. TGFβ1 treatment has a dual effect over SIX1 expression whereas the inhibition of the PI3K pathway, mediated by the overexpression of PTEN or by using the AKTi inhibitor, reduces SIX1 expression in ATC cell lines.

Conclusions: Given that SIX1 participates in the epithelial dedifferentiation and malignant behaviour of ATC cells, we described it as a potential therapeutic marker in ATC.