Evaluating local thyroid cytopathology practices by molecular quality metrics: A multi-institutional study on 4651 FNAs with a focus on the role of the interventional cytopathologist.

BACKGROUND: The diagnostic accuracy of thyroid fine-needle aspiration (FNA) can be highly influenced by the technical skills of the operator performing the procedure and by interobserver variability in microscopic interpretation. This is particularly true for the indeterminate categories. Recently, molecular testing has been proposed as an ancillary tool for monitoring the performance of different thyroid cytopathology practices. The objective of this multicenter study was to evaluate the quality of different local cytopathology practices by assessing the impact of interventional cytopathologists on FNA adequacy for molecular testing and the variations in mutation rates across different health care centers operating in the Campania region. METHODS: The study included 4651 thyroid FNA samples diagnosed in different Southern Italian clinical laboratories belonging to the TIRNET (the Tiroide Network). FNA samples were collected by different proceduralists and were classified by local cytopathologists according to The Bethesda System for Reporting Thyroid Cytopathology. FNAs classified as atypia of undetermined significance, follicular neoplasm, suspicious for malignancy, and malignant were centralized for a real-time polymerase chain reaction-based, seven-gene test at the authors' institution. RESULTS: Centers that employed interventional cytopathologists obtained fewer unsatisfactory FNA samples for molecular testing (11.3%) than centers that employed noncytopathologists (16.7%; p < .05). Furthermore, a significant variation in the mutation rate was observed in FNAs diagnosed by different local cytopathologists; indeterminate categories had the highest percentage of mutation rate variability among centers. CONCLUSIONS: Interventional cytopathologists obtained higher yields of diagnostic material for molecular testing. Finally, the current results suggest that the variability in mutation rates among different centers may highlight the low reproducibility of microscopic criteria among cytopathologists, particularly for indeterminate cases.

Type 2 deiodinase is expressed in anaplastic thyroid carcinoma and its inhibition causes cell senescence.

Anaplastic thyroid cancer (ATC) is a rare thyroid tumor that frequently originates from the dedifferentiation of a well-differentiated papillary or follicular thyroid cancer. Type 2 deiodinase (D2), responsible for the activation of the thyroid hormone thyroxine into tri-iodothyronine (T3), is expressed in normal thyroid cells and its expression is strongly downregulated in papillary thyroid cancer. In skin cancer, D2 has been associated with cancer progression, dedifferentiation, and epithelial-mesenchymal transition. Here, we show that D2 is highly expressed in anaplastic compared to papillary thyroid cancer cell lines and that D2-derived T3 is required for ATC cell proliferation. D2 inhibition is associated with G1 growth arrest and induction of cell senescence, together with reduced cell migration and invasive potential. Finally, we found that mutated p5372R(R248W), frequently found in ATC, is able to induce D2 expression in transfected papillary thyroid cancer cells. Our results show that the action of D2 is crucial for ATC proliferation and invasiveness, providing a potential new therapeutic target for the treatment of ATC.

Vandetanib downregulates type 2 deiodinase in fibro/adipogenic progenitors.

Treatment with tyrosine kinase inhibitors (TKIs) has been associated with alterations in circulating thyroid hormone levels, possibly related to perturbations in peripheral thyroid hormone metabolism. In this study, we evaluated the effect of the multi-kinase inhibitor vandetanib on the expression of the three deiodinase selenoenzymes, responsible for the thyroid hormone activation (type 1 and type 2 deiodinases) or for its inactivation (type 3 deiodinase). Here, we show that the multi-kinase inhibitor vandetanib determines a strong cell-specific downregulation of type 2 deiodinase (D2) expression and a significant reduction in D2 enzymatic activity. This occurs in the diffused population of fibro/adipogenic progenitors, which reside in different tissues - including the muscles - and normally express D2. Given the widespread diffusion of mesenchymal cells within the body, our results may explain at least partially the alterations in thyroid hormone levels that occur in vandetanib-treated patients. Our findings represent a step forward into the understanding of the mechanisms by which TKIs induce hypothyroidism and identify a resident cell population in which such an effect takes place.

Type 2 Deiodinase Thr92Ala Polymorphism and Aging Are Associated with a Decreased Pituitary Sensitivity to Thyroid Hormone.

Background: The DIO2 Thr92Ala polymorphism (rs225014), which occurs in about 15-30% of Caucasian people, determines a less efficient type 2 deiodinase (D2) enzyme. The aim of this study was to determine the impact of DIO2 Thr92Ala polymorphism on the serum thyrotropin (TSH) levels in thyroidectomized patients with hypothyroidism and to evaluate whether TSH levels and aging could be related, at pituitary level, to D2 activity. Methods: This prospective study was performed on 145 thyroid cancer patients, treated with total thyroidectomy, and undergoing radioiodine treatment after 3 weeks of levothyroxine (LT4) withdrawal. A mouse model has been used to determine D2 protein and mRNA levels in pituitary during aging. Results: Genetic analysis identified DIO2 Thr92Ala polymorphism in 56% of participants: 64/145 (44%) patients were homozygous wild type (WT) (Thr/Thr), 64 (44%) heterozygous (Thr/Ala), and 17 (12%) homozygous mutant (Ala/Ala). A significant negative relationship was observed between aging and the rise in serum TSH levels during LT4 withdrawal. However, this negative correlation found in WT was reduced in heterozygous and lost in mutant homozygous patients (Thr/Thr r = -0.45, p = 0.0002, 95% confidence interval [CI] -0.63 to -0.23; Ala/Thr r = -0.39, p = 0.0012, CI -0.60 to -0.67; and Ala/Ala r = -0.30, p = 0.2347; CI -0.70 to 0.20). Accordingly, when we compared the TSH measured in each patient to its theoretical value predicted from age, the TSH did not reach its putative target in 47% of WT patients, in 70% of Ala/Thr, and 76% of Ala/Ala carrying patients (p = 0.0036). This difference was lost in individuals older than 60 years, suggesting a decline of D2 associated with aging. The hypothesis that the pituitary D2 decreases with age was confirmed by the evidence that D2 mRNA and protein levels were lower in pituitary from old versus young mice. Conclusion: An age-related decline in TSH production in response to hypothyroidism was correlated with decreased D2 levels in pituitary. The presence of DIO2 homozygous Ala/Ala polymorphism was associated with a reduced level of TSH secretion in response to hypothyroidism, indicating a decreased pituitary sensitivity to serum thyroxine variation (Institutional Research Ethics board approval number no. 433/21).

Predictive molecular pathology in metastatic thyroid cancer: the role of RET fusions.

BACKGROUND: Rearranged during transfection (RET) gene fusions are detected in 10-20% of thyroid cancer patients. Recently, RET fusion-positive metastatic thyroid cancers have attracted much attention owing to the FDA approval of two highly selective anti-RET tyrosine kinase inhibitors, namely, selpercatinib, and pralsetinib. AREAS COVERED: This review summarizes the available evidence on the biological and predictive role of RET gene fusions in thyroid carcinoma patients and the latest screening assays currently used to detect these genomic alterations in histological and cytological specimens. EXPERT OPINION: Management of advanced thyroid carcinoma has significantly evolved over the last decade thanks to the approval of three multikinase inhibitors, i.e. sorafenib, lenvatinib, cabozantinib, and of two selective RET-tyrosine inhibitors, i.e. selpercatinib and pralsetinib. In this setting, the detection of RET-fusions in advanced thyroid cancer specimens through the use of next-generation sequencing has become a commonly used strategy in clinical practice to select the best treatment options.

Inactivation of Type 3 Deiodinase Results in Life-long Changes in the Brown Adipose Tissue Transcriptome in the Male Mouse.

Adaptive thermogenesis in small mammals and infants takes place in brown adipose tissue (BAT). Heat is produced via uncoupling protein 1 (UCP1)-mediated uncoupling between oxidation of energy substrates and adenosine 5'-triphosphate synthesis. Thyroid hormone (TH) signaling plays a role in this process. The deiodinases activate thyroxine (T4) to 3,5,3'-triiodothyronine (T3) (D2) or inactivate T4 and T3 to 3,3,5'-triiodothyronine and T2 (D3), respectively. Using a mouse model with selective inactivation of Dio3 in BAT (flox-Dio3 × UCP1-cre = BAT-D3KO), we now show that knocking out D3 resulted in premature exposure of developing brown adipocytes (embryonic days 16.5-18.5) to T3 signaling, leading to an earlier expression of key BAT genes, including Cidea, Cox8b, Dio2, Ucp1, and Pgc1α. Adult BAT-D3KO mice exhibited increased expression of 1591 genes as assessed by RNA sequencing, including 19 gene sets related to mitochondria, 8 related to fat, and 8 related to glucose homeostasis. The expression of 243 genes was changed by more than 1.5-fold, 36 of which play a role in metabolic/thermogenic processes. BAT-D3KO mice weigh less and exhibit smaller white adipocyte area, but maintain normal energy expenditure at room temperature (22 °C) and in the cold (4 °C). They also defend their core temperature more effectively and do not lose as much body weight when exposed to cold. We conclude that the coordinated actions of Dio3 in the embryonic BAT define the timing and intensity of T3 signaling during brown adipogenesis. Enhanced T3 signaling during BAT embryogenesis (Dio3 inactivation) results in selective life-long modifications in the BAT transcriptome.

Combination of Lenvatinib and Pembrolizumab as Salvage Treatment for Paucicellular Variant of Anaplastic Thyroid Cancer: A Case Report.

Anaplastic thyroid cancer (ATC) is a rare but aggressive thyroid cancer, responsible for about 50% of all thyroid cancer-related deaths. During the last two decades, the development of a multimodal personalized approach resulted in an increased survival. Here, we present an unusual case of a 54-year old woman with a paucicellular metastatic ATC, a rare variant of ATC, who was treated with a combination of surgery, radiation therapy and cytotoxic chemotherapy. More than two years later, when the disease was rapidly growing, a combination of lenvatinib and pembrolizumab induced a partial tumor response of lung metastasis that persisted over 18 months. Paucicellular ATC may initially show a less aggressive behavior compared to other histological ATC variants. However, over the time, its clinical course can rapidly progress like common ATC. The combination of lenvatinib and pembrolizumab was effective as a salvage therapy for a long period of time.

Thyroid Hormone Action in Muscle Atrophy.

Skeletal muscle atrophy is a condition associated with various physiological and pathophysiological conditions, such as denervation, cachexia, and fasting. It is characterized by an altered protein turnover in which the rate of protein degradation exceeds the rate of protein synthesis, leading to substantial muscle mass loss and weakness. Muscle protein breakdown reflects the activation of multiple proteolytic mechanisms, including lysosomal degradation, apoptosis, and ubiquitin-proteasome. Thyroid hormone (TH) plays a key role in these conditions. Indeed, skeletal muscle is among the principal TH target tissue, where TH regulates proliferation, metabolism, differentiation, homeostasis, and growth. In physiological conditions, TH stimulates both protein synthesis and degradation, and an alteration in TH levels is often responsible for a specific myopathy. Intracellular TH concentrations are modulated in skeletal muscle by a family of enzymes named deiodinases; in particular, in muscle, deiodinases type 2 (D2) and type 3 (D3) are both present. D2 activates the prohormone T4 into the active form triiodothyronine (T3), whereas D3 inactivates both T4 and T3 by the removal of an inner ring iodine. Here we will review the present knowledge of TH action in skeletal muscle atrophy, in particular, on the molecular mechanisms presiding over the control of intracellular T3 concentration in wasting muscle conditions. Finally, we will discuss the possibility of exploiting the modulation of deiodinases as a possible therapeutic approach to treat muscle atrophy.

Long-term management of lenvatinib-treated thyroid cancer patients: a real-life experience at a single institution.

PURPOSE: The efficacy of lenvatinib for advanced and progressive radioactive iodine refractory differentiated thyroid cancer is well established. Herein, we retrospectively evaluated the long-term safety and efficacy of lenvatinib in 23 patients treated at a single Institution. METHODS: Clinical data of all patients treated for a differentiated thyroid cancer with lenvatinib from April 2015 to September 2020 were retrospectively analyzed. RESULTS: A total of 23 patients were included. In all, 21 patients received lenvatinib as first-line systemic therapy. Median age at initiation of lenvatinib treatment was 68 (44-90) years. Median duration of the study from initiation of lenvatinib to study end was 23 (2-65) months. The indication for lenvatinib treatment was documented progression of distant metastases in 20 patients and of locally advanced disease in the other 3 and median duration of lenvatinib therapy was 15 (2-64) months. Best treatment responses were: partial response in 6 patients, stable disease in 14, progressive disease in 1, and not evaluable in 2. Median progression-free survival was 25 months (95% CI: 12-40) and median overall survival was 46 months (95% CI: 28-65). Three patients had to discontinue lenvatinib treatment due to serious adverse events and no drug-related death was observed. Ten patients continued lenvatinib for more than 24 months and the only newly registered adverse event after this period of time was one case of G2 proteinuria. Six patients continued lenvatinib treatment beyond documented tumor progression due to oligoprogression or slowly progressive disease (median time 18.5 months, 8-42 months). A total of 14 patients were alive at the end of the study: 11 showed partial response/stable disease on lenvatinib, including 3 who had a stable disease after local ablative therapy for oligoprogressive metastases; 3 had to change treatment, including 2 for lenvatinib-related serious adverse events and 1 for progressive disease. CONCLUSIONS: Long-term lenvatinib treatment is safe and some patients may experience persistent long-term control of the disease. Late treatment-related AEs rarely occurred. Oligoprogressive and slowly progressive disease can be managed without treatment withdrawal as long as there are some clinical benefits.

A Type 2 Deiodinase-Dependent Increase in Vegfa Mediates Myoblast-Endothelial Cell Crosstalk During Skeletal Muscle Regeneration.

Background: The type 2 deiodinase (DIO2) converts thyroxine to 3,3',5-triiodothyronine (T3), modulating intracellular T3. An increase in DIO2 within muscle stem cells during skeletal muscle regeneration leads to T3-dependent potentiation of differentiation. The muscle stem cell niche comprises numerous cell types, which coordinate the regeneration process. For example, muscle stem cells provide secretory signals stimulating endothelial cell-mediated vascular repair, and, in turn, endothelial cells promote muscle stem differentiation. We hypothesized that Dio2 loss in muscle stem cells directly impairs muscle stem cell-endothelial cell communication, leading to downstream disruption of endothelial cell function. Methods: We assessed the production of proangiogenic factors in differentiated C2C12 cells and in a C2C12 cell line without Dio2 (D2KO C2C12) by real-time quantitative-polymerase chain reaction and enzyme-linked immunosorbent assay. Conditioned medium (CM) was collected daily in parallel to evaluate its effects on human umbilical vein endothelial cell (HUVEC) proliferation, migration and chemotaxis, and vascular network formation. The effects of T3-treatment on vascular endothelial growth factor (Vegfa) mRNA expression in C2C12 cells and mouse muscle were assessed. Chromatin immunoprecipitation (ChIP) identified thyroid hormone receptor (TR) binding to the Vegfa gene. Using mice with a targeted disruption of Dio2 (D2KO mice), we determined endothelial cell number by immunohistochemistry/flow cytometry and evaluated related gene expression in both uninjured and injured skeletal muscle. Results: In differentiated D2KO C2C12 cells, Vegfa expression was 46% of wildtype (WT) C2C12 cells, while secreted VEGF was 45%. D2KO C2C12 CM exhibited significantly less proangiogenic effects on HUVECs. In vitro and in vivo T3 treatment of C2C12 cells and WT mice, and ChIP using antibodies against TRα, indicated that Vegfa is a direct genomic T3 target. In uninjured D2KO soleus muscle, Vegfa expression was decreased by 28% compared with WT mice, while endothelial cell numbers were decreased by 48%. Seven days after skeletal muscle injury, D2KO mice had 36% fewer endothelial cells, coinciding with an 83% decrease in Vegfa expression in fluorescence-activated cell sorting purified muscle stem cells. Conclusion:Dio2 loss in the muscle stem cell impairs muscle stem cell-endothelial cell crosstalk via changes in the T3-responsive gene Vegfa, leading to downstream impairment of endothelial cell function both in vitro and in vivo.

The NANOG Transcription Factor Induces Type 2 Deiodinase Expression and Regulates the Intracellular Activation of Thyroid Hormone in Keratinocyte Carcinomas.

Type 2 deiodinase (D2), the principal activator of thyroid hormone (TH) signaling in target tissues, is expressed in cutaneous squamous cell carcinomas (SCCs) during late tumorigenesis, and its repression attenuates the invasiveness and metastatic spread of SCC. Although D2 plays multiple roles in cancer progression, nothing is known about the mechanisms regulating D2 in cancer. To address this issue, we investigated putative upstream regulators of D2 in keratinocyte carcinomas. We found that the expression of D2 in SCC cells is positively regulated by the NANOG transcription factor, whose expression, besides being causally linked to embryonic stemness, is associated with many human cancers. We also found that NANOG binds to the D2 promoter and enhances D2 transcription. Notably, blockage of D2 activity reduced NANOG-induced cell migration as well as the expression of key genes involved in epithelial-mesenchymal transition in SCC cells. In conclusion, our study reveals a link among endogenous endocrine regulators of cancer, thyroid hormone and its activating enzyme, and the NANOG regulator of cancer biology. These findings could provide the basis for the development of TH inhibitors as context-dependent anti-tumor agents.

Author Correction: Thyroid hormone induces progression and invasiveness of squamous cell carcinomas by promoting a ZEB-1/E-cadherin switch.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Thyroid hormone induces progression and invasiveness of squamous cell carcinomas by promoting a ZEB-1/E-cadherin switch.

Epithelial tumor progression often involves epithelial-mesenchymal transition (EMT). We report that increased intracellular levels of thyroid hormone (TH) promote the EMT and malignant evolution of squamous cell carcinoma (SCC) cells. TH induces the EMT by transcriptionally up-regulating ZEB-1, mesenchymal genes and metalloproteases and suppresses E-cadherin expression. Accordingly, in human SCC, elevated D2 (the T3-producing enzyme) correlates with tumor grade and is associated with an increased risk of postsurgical relapse and shorter disease-free survival. These data provide the first in vivo demonstration that TH and its activating enzyme, D2, play an effective role not only in the EMT but also in the entire neoplastic cascade starting from tumor formation up to metastatic transformation, and supports the concept that TH is an EMT promoter. Our studies indicate that tumor progression relies on precise T3 availability, suggesting that pharmacological inactivation of D2 and TH signaling may suppress the metastatic proclivity of SCC.

Management of one patient with oligoprogressive thyroid cancer during treatment with lenvatinib.

Recent thyroid cancer guidelines found it reasonable to use local therapies during treatment with tyrosine kinase inhibitors (TKIs) in selected patients with oligoprogressive disease, namely, in the presence of a single progressing lesion in an otherwise TKI-responsive metastatic cancer. However, there is a lack of experience in the management of oligoprogressive thyroid cancers. This report illustrates the case of one patient with oligoprogressive thyroid cancer during therapy with lenvatinib. We found that the application of local ablative therapy in oligoprogressive disease prolonged the progression-free survival and thus extended the time to therapy interruption. However, the optimal care for TKI-treated oligoprogressive cancers remains unclear and needs to be investigated in prospective trials.

Reciprocal interplay between thyroid hormone and microRNA-21 regulates hedgehog pathway-driven skin tumorigenesis.

The thyroid hormone-inactivating (TH-inactivating) enzyme type 3 iodothyronine deiodinase (D3) is an oncofetal protein that is rarely expressed in adult life but has been shown to be reactivated in the context of proliferation and neoplasms. D3 terminates TH action within the tumor microenvironment, thereby enhancing cancer cell proliferation. However, the pathological role of D3 and the contribution of TH metabolism in cancer have yet to be fully explored. Here, we describe a reciprocal regulation between TH action and the cancer-associated microRNA-21 (miR21) in basal cell carcinoma (BCC) skin tumors. We found that, besides being negatively regulated by TH at the transcriptional level, miR21 attenuates the TH signal by increasing D3 levels. The ability of miR21 to positively regulate D3 was mediated by the tumor suppressor gene GRHL3, a hitherto unrecognized D3 transcriptional inhibitor. Finally, in a BCC mouse model, keratinocyte-specific D3 depletion markedly reduced tumor growth. Together, our results establish TH action as a critical hub of multiple oncogenic pathways and provide functional and mechanistic evidence of the involvement of TH metabolism in BCC tumorigenesis. Moreover, our results identify a miR21/GRHL3/D3 axis that reduces TH in the tumor microenvironment and has potential to be targeted as a therapeutic approach to BCC.

Activated Thyroid Hormone Promotes Differentiation and Chemotherapeutic Sensitization of Colorectal Cancer Stem Cells by Regulating Wnt and BMP4 Signaling.

Thyroid hormone is a pleiotropic factor that controls many cellular processes in multiple cell types such as cancer stem cells (CSC). Thyroid hormone concentrations in the blood are stable, but the action of the deiodinases (D2-D3) provides cell-specific regulation of thyroid hormone activity. Deregulation of deiodinase function and thyroid hormone status has been implicated in tumorigenesis. Therefore, we investigated the role of thyroid hormone metabolism and signaling in colorectal CSCs (CR-CSC), where deiodinases control cell division and chemosensitivity. We found that increased intracellular thyroid hormone concentration through D3 depletion induced cell differentiation and sharply mitigated tumor formation. Upregulated BMP4 expression and concomitantly attenuated Wnt signaling accompanied these effects. Furthermore, we demonstrate that BMP4 is a direct thyroid hormone target and is involved in a positive autoregulatory feedback loop that modulates thyroid hormone signaling. Collectively, our findings highlight a cell-autonomous metabolic mechanism by which CR-CSCs exploit thyroid hormone signaling to facilitate their self-renewal potential and suggest that drug-induced cell differentiation may represent a promising therapy for preventing CSC expansion and tumor progression.

The selective loss of the type 2 iodothyronine deiodinase in mouse thyrotrophs increases basal TSH but blunts the thyrotropin response to hypothyroidism.

The type 2 iodothyronine deiodinase (D2) is essential for feedback regulation of TSH by T4. We genetically inactivated in vivo D2 in thyrotrophs using a mouse model of Cga-driven cre recombinase. Pituitary D2 activity was reduced 90% in the Cga-cre D2 knockout (KO) mice compared with control Dio2(fl/fl) mice. There was no growth or reproductive phenotype. Basal TSH levels were increased 1.5- to 1.8-fold, but serum T4 and T3 were not different from the controls in adult mice. In hypothyroid adult mice, suppression of TSH by T4, but not T3, was impaired. Despite mild basal TSH elevation, the TSH increase in response to hypothyroidism was 4-fold reduced in the Cga-cre D2KO compared with control mice despite an identical level of pituitary TSH α- and ß-subunit mRNAs. In neonatal Cga-cre D2KO mice, TSH was also 2-fold higher than in the controls, but serum T4 was elevated. Despite a constant TSH, serum T4 increased 2-3-fold between postnatal day (P) 5 and P15 in both genotypes. The pituitary, but not cerebrocortical, D2 activity was markedly elevated in P5 mice decreasing towards adult levels by P17. In conclusion, a congenital severe reduction of thyrotroph D2 causes a major impairment of the TSH response to hypothyroidism. This would be deleterious to the compensatory adaptation of the thyroid gland to iodine deficiency.

Intracellular inactivation of thyroid hormone is a survival mechanism for muscle stem cell proliferation and lineage progression.

Precise control of the thyroid hormone (T3)-dependent transcriptional program is required by multiple cell systems, including muscle stem cells. Deciphering how this is achieved and how the T3 signal is controlled in stem cell niches is essentially unknown. We report that in response to proliferative stimuli such as acute skeletal muscle injury, type 3 deiodinase (D3), the thyroid hormone-inactivating enzyme, is induced in satellite cells where it reduces intracellular thyroid signaling. Satellite cell-specific genetic ablation of dio3 severely impairs skeletal muscle regeneration. This impairment is due to massive satellite cell apoptosis caused by exposure of activated satellite cells to the circulating TH. The execution of this proapoptotic program requires an intact FoxO3/MyoD axis, both genes positively regulated by intracellular TH. Thus, D3 is dynamically exploited in vivo to chronically attenuate TH signaling under basal conditions while also being available to acutely increase gene programs required for satellite cell lineage progression.

The sonic hedgehog-induced type 3 deiodinase facilitates tumorigenesis of basal cell carcinoma by reducing Gli2 inactivation.

Thyroid hormone (TH) is an important regulator of growth, development, and metabolism. Most of the active TH T3 is generated by peripheral TH metabolism mediated by the iodothyronine deiodinases. Type 3 deiodinase (D3) inactivates T3 via specific deiodination reactions. It is an oncofetal protein frequently expressed in neoplastic tissues and is a direct target of the sonic hedgehog (Shh) pathway in basal cell carcinomas (BCCs). However, the molecular mechanisms triggered by T3 in BCC are still mostly unrevealed. Here, we demonstrate that D3 action is critical in the proliferation and survival of BCC cells. D3 depletion or T3 treatment induce apoptosis of BCC cells and attenuate Shh signaling. This is achieved through a direct impairment of Gli2 protein stability by T3. T3 induces protein kinase A, which in turn destabilizes Gli2 protein via its C-terminal degron. Finally, in a mouse model of BCC, T3-topical treatment significantly reduces tumor growth. These results demonstrate the existence of a previously unrecognized cross talk between TH and Gli2 oncogene, providing functional and mechanistic evidence of the involvement of TH metabolism in Shh-induced cancer. TH-mediated Gli2 inactivation would be beneficial for therapeutically purposes, because the inhibition of Shh-Gli2 signaling is an attractive target for several anticancer drugs, currently in clinical trials.

Type 3 deiodinase and consumptive hypothyroidism: a common mechanism for a rare disease.

The major product secreted by the thyroid is thyroxine (T4), whereas most of the biologically active triiodothyronine (T3) derives from the peripheral conversion of T4 into T3. The deiodinase enzymes are involved in activation and inactivation of thyroid hormones (THs). Type 1 and type 2 deiodinase (D1 and D2) convert T4 into T3 whereas D3 degrades T4 and T3 into inactive metabolites and is thus the major physiological TH inactivator. The hypothalamic-pituitary-thyroid axis maintains circulating TH levels constant, while the deiodinases tissue-specifically regulate intracellular thyroid status by controlling TH action in a precise spatio-temporal fashion. Here we review the data related to the recent identification of a paraneoplastic syndrome called "consumptive hypothyroidism," which exemplifies how deiodinases alter substantially the concentration of TH in blood. This syndrome results from the aberrant uncontrolled expression of D3 that can induce a severe form of hypothyroidism by inactivating T4 and T3 in defined tumor tissue. This rare TH insufficiency generally affects patients in the first years of life, and has distinct features in terms of diagnosis, treatment, and prognosis with respect to other forms of hypothyroidism.