MAPK and SHH pathways modulate type 3 deiodinase expression in papillary thyroid carcinoma

Abstract

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 metast atic 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 (BRAF V600E ) and, at lower levels, in TPC-1 (RET/PTC1) cells (P!0.007 and PZ0.02 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 mM), MEK (U0126, 10-20 mM) or p38 (SB203580, 10-20 mM) 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 mM) 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.

Role of thyroid hormones in the neoplastic process: an overview

“…The crosstalk between the SHH and MAPK pathways for D3 upregulation has also been demonstrated in human PTC cell lines (Romitti et al 2012(Romitti et al , 2016. Similarly, D3 depletion reduces cell proliferation and decreases cyclin D1 levels (Romitti et al 2016). Taken together, these data support the link between D3 overexpression and SHH/ Gli2 pathway reactivation, suggesting that decreased intracellular levels of THs may be a critical factor for tumor growth, at least in some types of cancer.…”

“…In an opposite manner, miR21 positively regulates D3 expression in BCC through grainyhead-like 24:11 transcription factor 3 (GRHL3) (Di Girolamo et al 2016). The crosstalk between the SHH and MAPK pathways for D3 upregulation has also been demonstrated in human PTC cell lines (Romitti et al 2012(Romitti et al , 2016. Similarly, D3 depletion reduces cell proliferation and decreases cyclin D1 levels (Romitti et al 2016).…”

“…Remarkably, D3 levels were positively associated with increased tumor size and increased rates of local and distant metastasis at diagnosis (Romitti et al 2012). Most interesting, D3 upregulation in PTC samples is modulated by crosstalk between the MAPK and SHH pathways and varies according to the genetic alterations in this tumor type (Romitti et al 2016). Increased DIO3 expression was also observed in FTC but not in medullary or anaplastic thyroid carcinoma samples (Romitti et al 2012).…”

“…Tumoral D3 activity is markedly elevated in vascular tumors, including infantile hemangioma and hemangioendothelioma in adults (Huang et al 2000, Luongo et al 2013, even to the extent of inducing clinical hypothyroidism (consumptive hypothyroidism). Opposing regulation of DIO3 or DIO1/ DIO2 expression has been reported in various human neoplasias, such as PTC, TSH tumors, BCC and colon cancer (de Souza Meyer et al 2005, Dentice et al 2007, 2012, Luongo et al 2013, Romitti et al 2016. Studies performed using 105 pituitary tumors demonstrated that D2 and D3 mRNA levels were significantly augmented in pituitary tumors compared with normal pituitary tissue.…”

Papillary Thyroid Carcinoma: A Malignant Tumor with Increased Antioxidant Defense Capacity

“…The extent of thyroid metabolic function is reflected in the levels of circulating T3 and thyroglobulin, upon which the intrathyroid redox status is dependent. Romitti et al (2016) demonstrated that the increase in circulating T3 is caused by higher deiodinase activity in PTC. Larger goiters that have a tendency to grow and to acquire retrosternal position are characterized by increased oxidants production, whereas the negative correlation between TAS and goiter size reveals the importance of appropriate antioxidant capacity in the prevention of goiter growth.…”