Functional inactivation of thyroid transcription factor-1 in PCCl3 thyroid cells

Thyroid transcription factor-1 (TTF-1) is a key regulator of thyroid development and function. In order to identify the genes whose expression depends on TTF-1 transcriptional activity within the thyrocyte we analyzed the consequence of the functional inactivation of this factor in PCCl3 cells. The expression of a fusion protein composed of the DNA binding domain of TTF-1 and of the strong repressive domain of the engrailed protein resulted in a dramatic loss of epithelial cell morphology and in proliferation arrest. These changes were reversed when the inhibition of endogenous TTF-1 was relieved. No change was observed when a similar fusion protein containing point mutations abolishing DNA binding activity was produced in the cells. Besides the expected down-regulation of expression of the main genes linked to the differentiated thyroid function, we observed a decreased expression of the transcription factors Hhex, Pax 8 and TTF-2 and of E-cadherin. By contrast, both ThOX-1 and DUOXA-1 genes were up-regulated, as well as the ones encoding vimentin and several proteins involved in cell cycle arrest. Our data thus extend the known roles of TTF-1 in thyroid development and in the expression of differentiated function in the adult organ to the control of epithelial morphology and of cell division in mature thyrocytes.

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► Inhibiting TTF-1 transcriptional activity induces EMT in PCCl3 cells and impairs cell proliferation.
► These effects are reversed when the inhibition of TTF-1 is relieved.
► TTF-1 positively regulates Hhex, TTF-2, Pax 8, DUOXA-2 and E-cadherin expression in PCCl3 cells.
► TTF-1 exerts a negative control on ThOX1/Duox1, DUOXA-1, vimentin and TGFβ expression in the same cells.