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Thyroid carcinomas encompass a wide spectrum ranging from differentiated thyroid carcinoma (DTC) to poorly differentiated (PDC) and anaplastic thyroid carcinoma (ATC). DTC of both follicular (FTC) and papillary (PTC) types can progress to PDC and AC. The aim of our study was to evaluate if there is differential microRNA (miRNA) expression in various tumor subtypes during this progression. The miRNA profile of differentiated carcinomas (Follicular and Papillary) and ATC were compared with that of PDCs either by itself or in a background of differentiated carcinomas and anaplastic carcinomas. Unsupervised hierarchical clustering analysis revealed that FTC and PDC tend to cluster together in the absence of ATC. Interestingly, in cases with presence of all components i.e. FTC, PDC and ATC, the miRNA profile of poorly differentiated component clusters with that of the Anaplastic carcinoma component. miR-494 and miR-125a-5p were found to be differentially regulated in tumors with an anaplastic component and even the well-differentiated component (FTC) of these tumors were found to be aligned with the anaplastic profile. In addition, we also discovered some differentially regulated miRNAs in follicular variant of papillary thyroid carcinoma as compared to follicular thyroid carcinoma (miR-486-5p and miR-31).
Thyroid transcription factor-1 (TTF-1) is known to play key roles in thyroid organogenesis, in thyroid cell proliferation and in the expression of genes involved in thyroid differentiated function. Many human thyroid cancer cell lines keep producing TTF-1 despite the loss of differentiated gene expression, raising a question about the role of the factor in these cells. In order to investigate this point, we used a chimeric protein acting as a functional antagonist of TTF-1 transcriptional activity that was expressed conditionally in 8505C cells originating from an anaplastic thyroid carcinoma. We observed a growth arrest of 8505C thyroid cancer cells when the endogenous TTF-1 transcriptional activity was inhibited. It correlated with decreased levels of several mRNAs encoding positive effectors of cell proliferation like CDK1 and cyclinB1, and increased levels of various mRNAs encoding negative regulators of cell division like CDKN2B and DUSP6. In conclusion, the persistence of TTF-1 expression observed in the dedifferentiated human thyroid cancer cell line 8505C reflects the need of TTF-1 activity for the proliferation of these tumor cells.