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Iuri Martin Goemann, Mirian Romitti, Erika L Souza Meyer, Simone Magagnin Wajner and Ana Luiza Maia

Thyroid hormones (TH) are critical regulators of several physiological processes, which include development, differentiation and growth in virtually all tissues. In past decades, several studies have shown that changes in TH levels caused by thyroid dysfunction, disruption of deiodinases and/or thyroid hormone receptor (TR) expression in tumor cells, influence cell proliferation, differentiation, survival and invasion in a variety of neoplasms in a cell type-specific manner. The function of THs and TRs in neoplastic cell proliferation involves complex mechanisms that seem to be cell specific, exerting effects via genomic and nongenomic pathways, repressing or stimulating transcription factors, influencing angiogenesis and promoting invasiveness. Taken together, these observations indicate an important role of TH status in the pathogenesis and/or development of human neoplasia. Here, we aim to present an updated and comprehensive picture of the accumulated knowledge and the current understanding of the potential role of TH status on the different hallmarks of the neoplastic process.

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Iuri Martin Goemann, Vicente Rodrigues Marczyk, Mirian Romitti, Simone Magagnin Wajner and Ana Luiza Maia

Thyroid hormones (THs) are essential for the regulation of several metabolic processes and the energy consumption of the organism. Their action is exerted primarily through interaction with nuclear receptors controlling the transcription of thyroid hormone-responsive genes. Proper regulation of TH levels in different tissues is extremely important for the equilibrium between normal cellular proliferation and differentiation. The iodothyronine deiodinases types 1, 2 and 3 are key enzymes that perform activation and inactivation of THs, thus controlling TH homeostasis in a cell-specific manner. As THs seem to exert their effects in all hallmarks of the neoplastic process, dysregulation of deiodinases in the tumoral context can be critical to the neoplastic development. Here, we aim at reviewing the deiodinases expression in different neoplasias and exploit the mechanisms by which they play an essential role in human carcinogenesis. TH modulation by deiodinases and other classical pathways may represent important targets with the potential to oppose the neoplastic process.

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Débora R Siqueira, Mírian Romitti, Andreia P da Rocha, Lucieli Ceolin, Camila Meotti, Aline Estivalet, Marcia K Puñales and Ana Luiza Maia

The possible role of RET variants in modifying the natural course of medullary thyroid carcinoma (MTC) is still a matter of debate. Here, we investigate whether the RET variants L769L, S836S, and G691S/S904S influence disease presentation in hereditary or sporadic MTC patients. One hundred and two patients with hereditary MTC and 81 patients with sporadic MTC attending our institution were evaluated. The frequencies of RET polymorphisms in hereditary MTC were as follows: L769L, 17.3%; S836S, 7.95%; and S904S/G691S, 18.2%. No associations were observed between these polymorphisms and pheochromocytoma, hyperparathyroidism, lymph node, or distant metastasis. However, patients harboring the S836S variant were younger than those without this allele (17±8.2 vs 28.6±14.4 years, P=0.01), suggesting that these patients had metastases at a young age. Accordingly, the cumulative frequency of local and/or distant metastases as estimated by Kaplan–Meier curves showed that lymph node and distant metastases occurred earlier in patients harboring the S836S variant (P=0.003 and P=0.026 respectively). The S836S allele frequency was higher in sporadic MTC patients than in controls (10.5 vs 3.1%, P=0.01). Individuals harboring the S836S variant were younger (38.6±13.3 vs 48.5±16.7 years, P=0.02) and showed a higher percentage of lymph node and distant metastases (P=0.02 and P=0.04 respectively). Kaplan–Meier estimates of lymph node and distant metastases yielded distinct curves for patients with or without the S836S allele (P=0.002 and P=0.001 respectively). Additional analyses using a COX regression model showed that the S836S variant was independently associated with metastatic disease (hazard ratio 2.82 (95% confidence interval 1.51–5.26), P=0.001). In conclusion, the RET S836S variant is associated with early onset and increased risk for metastatic disease in patients with hereditary or sporadic MTC.

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Mírian Romitti, Simone Magagnin Wajner, Lucieli Ceolin, Carla Vaz Ferreira, Rafaela Vanin Pinto Ribeiro, Helena Cecin Rohenkohl, Shana de Souto Weber, Patrícia Luciana da Costa Lopez, Cesar Seigi Fuziwara, Edna Teruko Kimura and Ana Luiza Maia

Type 3 deiodinase (DIO3, D3) is reactivated in human neoplasias. Increased D3 levels in papillary thyroid carcinoma (PTC) have been associated with tumor size and metastatic disease. The objective of this study is to investigate the signaling pathways involved in DIO3 upregulation in PTC. Experiments were performed in human PTC cell lines (K1 and TPC-1 cells) or tumor samples. DIO3 mRNA and activity were evaluated by real-time PCR and ion-exchange column chromatography respectively. Western blot analysis was used to determine the levels of D3 protein. DIO3 gene silencing was performed via siRNA transfection. DIO3 mRNA levels and activity were readily detected in K1 (BRAFV6 0 0E) and, at lower levels, in TPC-1 (RET/PTC1) cells (P<0.007 and P=0.02 respectively). Similarly, DIO3 mRNA levels were higher in PTC samples harboring the BRAF V600E mutation as compared with those with RET/PTC1 rearrangement or negative for these mutations (P<0.001). Specific inhibition of BRAF oncogene (PLX4032, 3 μM), MEK (U0126, 10–20 μM) or p38 (SB203580, 10–20 μM) signaling was associated with decreases in DIO3 expression in K1 and TPC-1 cells. Additionally, the blockage of the sonic hedgehog (SHH) pathway by cyclopamine (10 μM) resulted in markedly decreases in DIO3 mRNA levels. Interestingly, siRNA-mediated DIO3 silencing induced decreases on cyclin D1 expression and partial G1 phase cell cycle arrest, thereby downregulating cell proliferation. In conclusion, sustained activation of the MAPK and SHH pathways modulate the levels of DIO3 expression in PTC. Importantly, DIO3 silencing was associated with decreases in cell proliferation, thus suggesting a D3 role in tumor growth and aggressiveness.