Thyroid hormone receptors are tumor suppressors in a mouse model of metastatic follicular thyroid carcinoma

A novel APA-based prognostic signature may predict the prognosis of lung adenocarcinoma in an East Asian population

The role of alternative polyadenylation (APA) in tumor development is becoming increasingly evident, but the impact of APA events on the prognosis of LUAD patients is unclear. Therefore, in the present study, we aimed to analyze specific APA events in LUAD to identify novel prognostic biomarkers for LUAD. We first identified prognostic candidate genes for LUAD associated with APA events and validated them in both the East Asian and the USA cohorts, finding that five genes (DCUN1D5, PSMC4, TFAM, THRA, and TMEM100) were of prognostic significance in both populations. Based on this, an APA-based prognostic signature was constructed for the East Asian population. The predictive accuracy of the prognostic signature was further evaluated by the time-dependent ROC, with 1-, 2-, and 3-year AUCs of 0.86, 0.81, and 0.71, respectively. This study may provide new markers for individualized diagnosis and prognostic assessment of LUAD and potential targets for precision treatment.

Pathogenesis of cancers derived from thyroid follicular cells

The genomic simplicity of differentiated cancers derived from thyroid follicular cells offers unique insights into how oncogenic drivers impact tumour phenotype. Essentially, the main oncoproteins in thyroid cancer activate nodes in the receptor tyrosine kinase-RAS-BRAF pathway, which constitutively induces MAPK signalling to varying degrees consistent with their specific biochemical mechanisms of action. The magnitude of the flux through the MAPK signalling pathway determines key elements of thyroid cancer biology, including differentiation state, invasive properties and the cellular composition of the tumour microenvironment. Progression of disease results from genomic lesions that drive immortalization, disrupt chromatin accessibility and cause cell cycle checkpoint dysfunction, in conjunction with a tumour microenvironment characterized by progressive immunosuppression. This Review charts the genomic trajectories of these common endocrine tumours, while connecting them to the biological states that they confer.

High prevalence of parvovirus B19 infection in patients with thyroid nodules: A case-control study

BACKGROUND

The incidence of thyroid nodules has increased dramatically in recent decades. Although this increase has been attributed to improved imaging modalities, the question arises as to whether other environmental factors, such as infectious agents are influential.

METHODS

Adult patients with newly diagnosed papillary thyroid carcinoma, benign thyroid nodules, and healthy euthyroid controls without nodules; were recruited. Various clinical and biochemical parameters including thyroid function tests and serum Parvovirus B19 Ab (IgG) were assessed and compared between groups.

RESULTS

In this study, data from 364 patients with papillary thyroid carcinoma, 370 patients with benign thyroid nodules, and 360 healthy euthyroid individuals without nodules were analyzed as a control group. The prevalence of parvovirus B19 infection in papillary thyroid carcinoma patients was 58.8% that was significantly higher than the two groups of benign thyroid nodules (49.2%) and the control group (45.0%). In the papillary thyroid carcinoma group, a significant positive correlation was found between tumor size and TSH (r = 0.129, p = 0.014), and between tumor size and B19-Ab (r = 0.176, p = 0.001).

CONCLUSION

The rate of parvovirus B19 infection was higher in patients with papillary thyroid carcinoma and benign thyroid nodules than in the control group. Also, patients with papillary thyroid carcinoma had significantly higher rates of B19 infection than those with benign thyroid nodules.

Targeting transcriptional regulators for treatment of anaplastic thyroid cancer

Dysregulation of genes perpetuates cancer progression. During carcinogenesis, cancer cells acquire dependency of aberrant transcriptional programs (known as “transcription addiction”) to meet the high demands for uncontrolled proliferation. The needs for particular transcription programs for cancer growth could be cancer-type-selective. The dependencies of certain transcription regulators could be exploited for therapeutic benefits. Anaplastic thyroid cancer (ATC) is an extremely aggressive human cancer for which new treatment modalities are urgently needed. Its resistance to conventional treatments and the lack of therapeutic options for improving survival might have been attributed to extensive genetic heterogeneity due to subsequent evolving genetic alterations and clonal selections during carcinogenesis. Despite this genetic complexity, mounting evidence has revealed a characteristic transcriptional addiction of ATC cells resulting in evolving diverse oncogenic signaling for cancer cell survival. The transcriptional addiction has presented a huge challenge for effective targeting as shown by the failure of previous targeted therapies. However, an emerging notion is that many different oncogenic signaling pathways activated by multiple upstream driver mutations might ultimately converge on the transcriptional responses, which would provide an opportunity to target transcriptional regulators for treatment of ATC. Here, we review the current understanding of how genetic alterations in cancer distorted the transcription program, leading to acquisition of transcriptional addiction. We also highlight recent findings from studies aiming to exploit the opportunity for targeting transcription regulators as potential therapeutics for ATC.

Common tumor-suppressive signaling of thyroid hormone receptor beta in breast and thyroid cancer cells

The thyroid hormone receptor beta (TRβ) is a tumor suppressor in multiple types of solid tumors, most prominently in breast and thyroid cancer. An increased understanding of the molecular mechanisms by which TRβ abrogates tumorigenesis will aid in understanding the core tumor-suppressive functions of TRβ. Here, we restored TRβ expression in the MDA-MB-468 basal-like breast cancer cell line and perform RNA-sequencing to determine the TRβ-mediated changes in gene expression and associated signaling pathways. The TRβ expressing MDA-MB-468 cells exhibit a more epithelial character as determined by principle component analysis-based iterative PAM50 subtyping score and through reduced expression of mesenchymal cytokeratins. The epithelial to mesenchymal transition pathway is also significantly reduced. The MDA-MB-468 data set was further compared with RNA sequencing results from TRβ expressing thyroid cancer cell line SW1736 to determine which genes are TRβ correspondingly regulated across both cell types. Several pathways including lipid metabolism and chromatin remodeling processes were observed to be altered in the shared gene set. These data provide novel insights into the molecular mechanisms by which TRβ suppresses breast tumorigenesis.

Thyroid Hormone Receptor Beta as Tumor Suppressor: Untapped Potential in Treatment and Diagnostics in Solid Tumors

There is compelling evidence that the nuclear receptor TRβ, a member of the thyroid hormone receptor (TR) family, is a tumor suppressor in thyroid, breast, and other solid tumors. Cell-based and animal studies reveal that the liganded TRβ induces apoptosis, reduces an aggressive phenotype, decreases stem cell populations, and slows tumor growth through modulation of a complex interplay of transcriptional networks. TRβ-driven tumor suppressive transcriptomic signatures include repression of known drivers of proliferation such as PI3K/Akt pathway, activation of novel signaling such as JAK1/STAT1, and metabolic reprogramming in both thyroid and breast cancers. The presence of TRβ is also correlated with a positive prognosis and response to therapeutics in BRCA+ and triple-negative breast cancers, respectively. Ligand activation of TRβ enhances sensitivity to chemotherapeutics. TRβ co-regulators and bromodomain-containing chromatin remodeling proteins are emergent therapeutic targets. This review considers TRβ as a potential biomolecular diagnostic and therapeutic target.

Thyroid hormone and thyroid hormone nuclear receptors: History and present state of art

The present review traces the road leading to discovery of L-thyroxine, thyroid hormone (3,5,3´-triiodo-L-thyronine, T₃) and its cognate nuclear receptors. Thyroid hormone is a pleio-tropic regulator of growth, differentiation, and tissue homeostasis in higher organisms. The major site of the thyroid hormone action is predominantly a cell nucleus. T₃ specific binding sites in the cell nuclei have opened a new era in the field of the thyroid hormone receptors (TRs) discovery. T₃ actions are mediated by high affinity nuclear TRs, TRalpha and TRbeta, which function as T₃-activated transcription factors playing an essential role as transcription-modulating proteins affecting the transcriptional responses in target genes. Discovery and characterization of nuclear retinoid X receptors (RXRs), which form with TRs a heterodimer RXR/TR, positioned RXRs at the epicenter of molecular endocrinology. Transcriptional control via nuclear RXR/TR heterodimer represents a direct action of thyroid hormone. T₃ plays a crucial role in the development of brain, it exerts significant effects on the cardiovascular system, skeletal muscle contractile function, bone development and growth, both female and male reproductive systems, and skin. It plays an important role in maintaining the hepatic, kidney and intestine homeostasis and in pancreas, it stimulates the beta-cell proliferation and survival. The TRs cross-talk with other signaling pathways intensifies the T₃ action at cellular level. The role of thyroid hormone in human cancers, acting via its cognate nuclear receptors, has not been fully elucidated yet. This review is aimed to describe the history of T₃ receptors, starting from discovery of T3 binding sites in the cell nuclei to revelation of T₃ receptors as T₃-inducible transcription factors in relation to T₃ action at cellular level. It also focuses on milestones of investigation, comprising RXR/TR dimerization, cross-talk between T₃ receptors, and other regulatory pathways within the cell and mainly on genomic action of T₃. This review also focuses on novel directions of investigation on relationships between T₃ receptors and cancer. Based on the update of available literature and the author's experimental experience, it is devoted to clinicians and medical students.

Nuclear receptors: Lipid and hormone sensors with essential roles in the control of cancer development

Nuclear receptors (NRs) are a superfamily of ligand-activated transcription factors that act as biological sensors and use a combination of mechanisms to modulate positively and negatively gene expression in a spatial and temporal manner. The highly orchestrated biological actions of several NRs influence the proliferation, differentiation, and apoptosis of many different cell types. Synthetic ligands for several NRs have been the focus of extensive drug discovery efforts for cancer intervention. This review summarizes the roles in tumour growth and metastasis of several relevant NR family members, namely androgen receptor (AR), estrogen receptor (ER), glucocorticoid receptor (GR), thyroid hormone receptor (TR), retinoic acid receptors (RARs), retinoid X receptors (RXRs), peroxisome proliferator-activated receptors (PPARs), and liver X receptors (LXRs). These studies are key to develop improved therapeutic agents based on novel modes of action with reduced side effects and overcoming resistance.

Overexpression of modified human TRβ1 suppresses the growth of hepatocarcinoma SK-hep1 cells in vitro and in xenograft models

Association studies suggest that TRβ1 functions as a tumor suppressor. Thyroid hormone receptors (TRs) mediate transcriptional responses through a highly conserved DNA-binding domain (DBD). We previously constructed an artificially modified human TRβ1 (m-TRβ1) via the introduction of a 108-bp exon sequence into the corresponding position of the wild-type human TRβ1 (TRβ1) DBD. Studies confirmed that m-TRβ1 was functional and could inhibit the proliferation of breast cancer MDA-MB-468 cells in vitro. To understand the role of m-TRβ1 in liver tumor development, we adopted a gain-of-function approach by stably expressing TRβ (m-TRβ1 and TRβ1) genes in a human hepatocarcinoma cell line, SK-hep1 (without endogenous TRβ), and then evaluated the effects of the expressed TRβ on cancer cell proliferation, migration, and tumor growth in cell-based studies and xenograft models. In the presence of 3,5,3-l-triiodothyronine (T3), the expression of TRβ in SK-hep1 cells inhibited cancer cell proliferation and impeded tumor cell migration through the up-regulation of 4-1BB, Caspase-3, and Bak gene expression; down-regulation of Bcl-2 gene expression; and activation of the Caspase-3 protein. TRβ expression in SK-hep1 led to less tumor growth in xenograft models. Additionally, the anti-tumor effect of m-TRβ1 was stronger than that of TRβ1. These data indicate that m-TRβ1 can act as a tumor suppressor in hepatocarcinoma and its role was significantly better than that of TRβ1.

Role of thyroid hormones in the neoplastic process: an overview

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.

Natural Killer Cell (NK-92MI)-Based Therapy for Pulmonary Metastasis of Anaplastic Thyroid Cancer in a Nude Mouse Model

Objective

Natural killer (NK) cells represent the third largest population of lymphocytes, and they play an important role in immune surveillance against tumors. The lungs are a common metastatic site for anaplastic thyroid cancer (ATC), and metastasis is one of the most frequent causes of mortality in this type of cancer. In the current study, we evaluated the effects of NK cell-based immunotherapy for pulmonary metastasis of ATC and determined how it affects the effector molecules of NK cells.

Methods

Human NK cells (NK-92MI) were retrovirally transduced to express the effluc gene. Human ATC cells (CAL-62) were transduced with the effluc and Rluc genes. The cytotoxicity of NK cells against CAL-62 cells was assessed using the CytoTox 96^® Non-Radioactive Cytotoxicity Assay system. Pulmonary metastases of ATC were developed by i.v. injection of CAL-62, and metastasis growth was monitored using bioluminescence imaging (BLI). To treat the metastases, five million NK-92MI cells were injected twice into the caudal vein of nude mice. To assess the targetability of NK cells to ATC tumors, NK-92MI cells expressing the effluc gene (NK/F) were administered through the tail vein of nude mice with a pulmonary metastasis or tumor xenograft. BLI was subsequently performed at 1, 3, 24, and 48 h.

Results

NK/F and CAL-62 cells expressing the effluc or Rluc gene (CAL-62/F, CAL-62/R) were successfully established. Expression of the effluc and Rluc genes in NK/F, CAL-62/F, and CAL-62/R cells was verified by RT-polymerase chain reaction, western blotting, and luciferase assay. After coculture of NK-92MI and CAL-62/F cells for 24 h, the BLI signal intensity of CAL-62/F cells proportionally decreased with the number of cocultured NK cells. An ATC pulmonary metastasis mouse model was successfully generated, and NK cells significantly inhibited the growth of the metastasis (p < 0.01). The NK/F cells exhibited targetability to the pulmonary metastasis and tumor xenograft in the mouse model.

Conclusion

The results of present study suggest that NK cells are able to target ATC tumors and that NK cell-based immunotherapy may serve as an effective therapeutic approach for pulmonary metastases of ATC.

Preliminary results of a non-invasive method to measure tumor size and distribution in vivo

Molecular imaging of reporter gene expression in cancer cells can provide rapid, sensitive and non-invasive monitoring of tumor behavior. The aim of the present study was to establish a non-invasive method to measure tumor size and distribution in vivo. Briefly, H-Ras-transformed cells were stably transfected with a plasmid containing the luciferase gene (Luc), designated as Ras/Luc. Ras/Luc cells were injected into the back or tail vein of nude BALB/cAnN-Foxn1nu/CrlNarl mice (age, 6-8 weeks). Mice were subsequently administered D-luciferin via intra-peritoneal injection, prior to image acquisition. Photons emitted from the mice were detected via an imaging system. Tumor size and distribution in vivo were quantified as photons/second. Andrographolide has demonstrated radiosensitization in previous in vitro and in vivo studies. In the present study, the potential effects of andrographolide cancer metastasis were investigated further, using an imaging system. Preliminary results of andrographolide combined with radiation indicated the inhibition of cancer metastasis. The present mechanistic study of andrographolide-mediated effects demonstrated that activated extracellular signal regulated kinase protein and H₂O₂ production levels were significantly increased by andrographolide. In summary, the present study established a non-invasive method to measure tumor size and distribution in vivo and indicated that andrographolide may be a potential therapeutic strategy in cancer therapy.

Thyroid hormone suppresses expression of stathmin and associated tumor growth in hepatocellular carcinoma

Stathmin (STMN1), a recognized oncoprotein upregulated in various solid tumors, promotes microtubule disassembly and modulates tumor growth and migration activity. However, the mechanisms underlying the genetic regulation of STMN1 have yet to be elucidated. In the current study, we report that thyroid hormone receptor (THR) expression is negatively correlated with STMN1 expression in a subset of clinical hepatocellular carcinoma (HCC) specimens. We further identified the STMN1 gene as a target of thyroid hormone (T₃) in the HepG2 hepatoma cell line. An analysis of STMN1 expression profile and mechanism of transcriptional regulation revealed that T₃ significantly suppressed STMN1 mRNA and protein expression, and further showed that THR directly targeted the STMN1 upstream element to regulate STMN1 transcriptional activity. Specific knockdown of STMN1 suppressed cell proliferation and xenograft tumor growth in mice. In addition, T₃ regulation of cell growth arrest and cell cycle distribution were attenuated by overexpression of STMN1. Our results suggest that the oncogene STMN1 is transcriptionally downregulated by T₃ in the liver. This T₃-mediated suppression of STMN1 supports the theory that T₃ plays an inhibitory role in HCC tumor growth, and suggests that the lack of normal THR function leads to elevated STMN1 expression and malignant growth.

T3/TRs axis in hepatocellular carcinoma: new concepts for an old pair

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and its burden is expected to further increase in the next years. Chronic inflammation, induced by multiple viruses or metabolic alterations, and epigenetic and genetic modifications, cooperate in cancer development via a combination of common and distinct aetiology-specific pathways. In spite of the advances of classical therapies, the prognosis of this neoplasm has not considerably improved over the past few years. The advent of targeted therapies and the approval of the systemic treatment of advanced HCC with the kinase inhibitor sorafenib have provided some hope for the future. However, the benefits obtained from this treatment are still disappointing, as it extends the median life expectancy of patients by only few months. It is thus mandatory to find alternative effective treatments. Although the role played by thyroid hormones (THs) and their nuclear receptors (TRs) in human cancer is still unclear, mounting evidence indicates that they behave as oncosuppressors in HCC. However, the molecular mechanisms by which they exert this effect and the consequence of their activation following ligand binding on HCC progression remain elusive. In this review, we re-evaluate the existing evidence of the role of TH/TRs in HCC development; we will also discuss how TR alterations could affect fundamental biological processes, such as hepatocyte proliferation and differentiation, and consequently HCC progression. Finally, we will discuss if and how TRs can be foreseen as therapeutic targets in HCC and whether selective TR modulation by TH analogues may hold promise for HCC treatment.

Thyroid hormone receptor β1 suppresses proliferation and migration by inhibiting PI3K/Akt signaling in human colorectal cancer cells

Thyroid hormone receptor β1 (TRβ1) is a ligand‑dependent transcription factor that belongs to the superfamily of nuclear receptors. TRβ1 has been found to act as a tumor suppressor in many solid tumors including breast cancer and hepatocellular carcinoma, but its role in the progression of human colorectal cancer (CRC) remains unclear. In this study, microarray data analysis revealed that TRβ1 mRNA was downregulated in CRC tumors compared with that in the normal counterparts in both The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets. Using a CRC tissue microarray (TMA), we confirmed that the expression of TRβ1 was decreased in human CRC tumor tissues in contrast to normal colorectal mucosal tissues. Notably, the TRβ1 expression was strongly correlated with tumor size (p=0.045). Furthermore, we found that CRC cell proliferation and migration were significantly inhibited by TRβ1 overexpression in vitro. Mechanistic studies indicated that activated phosphorylated Akt was clearly suppressed by TRβ1 in the CRC tissues and cells. In conclusion, this study provides evidence that TRβ1 plays a critical role in the progression of CRC via the PI3K/Akt pathway, and the TRβ1 gene may represent a novel target for CRC therapeutics.

Tumor suppressive actions of the nuclear receptor corepressor 1

Nuclear Receptor Corepressor 1 (NCoR) is an important transcriptional regulator that interacts with nuclear receptors and other transcription factors. Recent results have shown the presence of inactivating mutations or deletions of the NCoR gene in human tumors. NCoR has a strong tumor suppressor activity, inhibiting invasion, metastasis formation and tumor growth in xenograft mouse models. These changes are associated to transcriptional inhibition of genes linked to bad prognosis and increased metastasis in cancer patients. NCoR loss causes a long-term repression of NCoR gene transcription, suggesting that NCoR deficiency in the cancer cell could be propagated playing a role in tumor progression in the absence of NCoR gene mutations. The thyroid hormone receptor TRβ increases NCoR expression and this induction is essential in mediating the anti-metastatic and tumor suppressive actions of the receptor. Since metastasis is the main cause of cancer-related deaths, these results define NCoR as a potential target for cancer therapy.

Reduced expression of THRβ in papillary thyroid carcinomas: relationship with BRAF mutation, aggressiveness and miR expression

PURPOSE

Down-regulation of thyroid hormone receptor beta (THRβ) gene has been described in several human malignancies, including thyroid cancer. In this study, we analyzed THRβ mRNA expression in surgical specimens from a series of human papillary thyroid carcinomas (PTCs), characterized by their genotypic and clinical-biological features.

METHODS

Thirty-six PTCs were divided into two groups according to the 2009 American Thyroid Association risk classification (17 low, 19 intermediate), and each group was divided into subgroups based on the presence or absence of the BRAFV600E mutation (21 BRAF mutated, 15 BRAF wild type). Gene expression was analyzed using fluidic cards containing probes and primers specific for the THRβ gene, as well as for genes of thyroperoxidase (TPO), sodium/iodide symporter (NIS), thyroglobulin (Tg) and thyroid stimulating hormone receptor (TSH-R) and for some miRNAs involved in thyroid neoplasia and targeting THRβ. The mRNA levels of each tumor tissue were compared with their correspondent normal counterpart.

RESULTS

THRβ transcript was down-regulated in all PTCs examined. No significant differences were found between intermediate- vs low-risk PTCs patients, and BRAF-mutated vs BRAF wild-type groups. THRβ expression was directly correlated with NIS, TPO, Tg and TSH-R, and inversely correlated to miR-21, -146a, -181a and -221 expression.

CONCLUSIONS

Our results demonstrate that down-regulation of THRβ is a common feature of PTCs. While it is not associated with a more aggressive phenotype of PTC, it correlates with the reduction of all the markers of differentiation and is associated with overexpression of some miRNAs supposed to play a role in thyroid tumorigenesis.

Hepatic FOXO1 Target Genes Are Co-regulated by Thyroid Hormone via RICTOR Protein Deacetylation and MTORC2-AKT Protein Inhibition

MTORC2-AKT is a key regulator of carbohydrate metabolism and insulin signaling due to its effects on FOXO1 phosphorylation. Interestingly, both FOXO1 and thyroid hormone (TH) have similar effects on carbohydrate and energy metabolism as well as overlapping transcriptional regulation of many target genes. Currently, little is known about the regulation of MTORC2-AKT or FOXO1 by TH. Accordingly, we performed hepatic transcriptome profiling in mice after FOXO1 knockdown in the absence or presence of TH, and we compared these results with hepatic FOXO1 and THRB1 (TRβ1) ChIP-Seq data. We identified a subset of TH-stimulated FOXO1 target genes that required co-regulation by FOXO1 and TH. TH activation of FOXO1 was directly linked to an increase in SIRT1-MTORC2 interaction and RICTOR deacetylation. This, in turn, led to decreased AKT and FOXO1 phosphorylation. Moreover, TH increased FOXO1 nuclear localization, DNA binding, and target gene transcription by reducing AKT-dependent FOXO1 phosphorylation in a THRB1-dependent manner. These events were associated with TH-mediated oxidative phosphorylation and NAD(+) production and suggested that downstream metabolic effects by TH can post-translationally activate other transcription factors. Our results showed that RICTOR/MTORC2-AKT can integrate convergent hormonal and metabolic signals to provide coordinated and sensitive regulation of hepatic FOXO1-target gene expression.

Local hypothyroidism favors the progression of preneoplastic lesions to hepatocellular carcinoma in rats

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that mediate most of the effects elicited by the thyroid hormone, 3,5,3'-L-triiodothyronine (T3). TRs have been implicated in tumorigenesis, although it is unclear whether they act as oncogenes or tumor suppressors, and at which stage of tumorigenesis their dysregulation occurs. Using the resistant-hepatocyte rat model (R-H model), we found down-regulation of TRβ1 and TRα1 and their target genes in early preneoplastic lesions and hepatocellular carcinoma (HCCs), suggesting that a hypothyroid status favors the onset and progression of preneoplastic lesions to HCC. Notably, TRβ1 and, to a lesser extent, TRα1 down-regulation was observed only in preneoplastic lesions positive for the progenitor cell marker, cytokeratin-19 (Krt-19) and characterized by a higher proliferative activity, compared to the Krt-19 negative ones. TRβ1 down-regulation was observed also in the vast majority of the analyzed human HCCs, compared to the matched peritumorous liver or to normal liver. Hyperthyroidism induced by T3 treatment caused up-regulation of TRβ1 and of its target genes in Krt-19(+) preneoplastic rat lesions and was associated with nodule regression. In HCC, TRβ1 down-regulation was not the result of hypermethylation of its promoter, but was associated with an increased expression of TRβ1-targeting microRNAs ([miR]-27a, -181a, and -204). An inverse correlation between TRβ1 and miR-181a was also found in human cirrhotic peritumoral tissue, compared to normal liver.

CONCLUSION

Down-regulation of TRs, especially TRβ1, is an early and relevant event in liver cancer development and is species and etiology independent. The results also suggest that a hypothyroid status of preneoplastic lesions may contribute to their progression to HCC and that the reversion of this condition may represent a possible therapeutic goal to interfere with the development of this tumor.

Nuclear receptor expression in human differentiated thyroid tumors

BACKGROUND

Nuclear receptors (NRs) play a key role in endocrine signaling and metabolism and are important therapeutic targets in a number of hormone-dependent malignancies. Studies on the role of NRs in thyroid cancer are limited.

OBJECTIVE

The objective of the study was to examine systematically the expression of the 48 human NRs in a series of benign and malignant thyroid tissues. Within the papillary carcinoma cohort, we sought to determine if NR expression differed significantly by BRAF mutation status.

PATIENTS AND METHODS

RNA was isolated from multinodular goiter (MNG; n=6), papillary carcinoma (PTC, n=14), follicular carcinoma (FC; n=5), and Hürthle cell carcinoma (HCC; n=7). The 48 human NRs were profiled in this panel by quantitative real time polymerase chain reaction. Protein expression for selected NRs (Rev-erbα and LXR-β) was examined by immunohistochemistry (IHC) on tissue microarrays comprising benign and malignant thyroid tissues.

RESULTS

Across all groups of benign and malignant thyroid tissue, there was prominent expression of LXR-β and ROR-γ. Key findings in PTC were marked overexpression of RXR-γ and Rev-erbα compared to MNG. Within the PTC cohort, when BRAF(V600E) tumors were compared with wild type BRAF, there was relative upregulation of RXR-γ and Rev-erbα and downregulation of AR, ERR-γ, and ROR-γ. In FC, EAR-2 was overexpressed, while PPAR-α and PPAR-δ were underexpressed compared to MNG. The NR expression profile of HCC was distinct, characterized by significant downregulation of a wide range of NRs. IHC for Rev-erbα and LXR-β localized protein expression to the tumor cells. Moderate to strong Rev-erbα immunostaining was seen in 22 out of 23 PTC, and, overall, staining was stronger than in the benign group.

CONCLUSIONS

These results represent the first systematic examination of NR expression in thyroid cancer. Our finding of tumor-specific patterns of NR expression, as well as significant differences in NR expression between BRAF(V600E) and wild type BRAF PTC, provides a basis for further mechanistic studies and highlights potential novel therapeutic targets for this malignancy.

An in vivo mouse model of metastatic human thyroid cancer

BACKGROUND

Mouse models of metastatic human cancers are important tools in preclinical studies for testing new systematic therapies and studying effectors of cancer metastasis. The major drawbacks of current mouse models for metastatic thyroid cancer are that they have low metastasis rates and do not allow in vivo tumor detection. Here, we report and characterize an in vivo detectable metastasis mouse model of human thyroid cancer using multiple thyroid cancer cell lines.

METHODS

Human anaplastic thyroid cancer cell lines 8505C, C-643, SW-1736, and THJ-16T; follicular thyroid cancer cell lines FTC-133, FTC-236, and FTC-238; and Hürthle cell carcinoma cell line XTC-1 were transfected with a linearized pGL4.51[luc2/CMV/Neo] vector or transduced with lentivirus containing Luc2-eGFP reporter genes. The stably transfected cells were injected intravenously into NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ mice. Tumors were detected with an in vivo imaging system-Xenogen IVIS. Vemurafenib, a BRAF inhibitor, was used to treat lung metastases generated from 8505C-Luc2 cells with a BRAF(V600E) mutation to test the accuracy of the model to evaluate response to therapy.

RESULTS

Intravenous injection of as few as 30,000 8505C-Luc2 cells produced lung metastases in 100% of the injected mice, and many of these mice also developed bone metastases at a later stage of the disease. Similarly, metastatic tumors also developed in all mice injected with C-643-Luc2, THJ-16T-Luc2, FTC-133-Luc2, FTC-236-Luc2, FTC-238-Luc2, and XTC-1-Luc2 cells. The metastases were easily detectable in vivo, and tumor progression could be dynamically and accurately followed and correlated with the actual tumor burden. Furthermore, disease progression could be easily controlled by adjusting the number of injected cells. The in vivo treatment of 8505C xenograft lung metastases with vemurafenib dramatically reduced the growth and signal intensity with good correlation with actual tumor burden.

CONCLUSIONS

Herein we report an in vivo detectable mouse model of metastatic human thyroid cancer that is reliable and reproducible. It will serve as a useful tool in the preclinical testing of alternative systematic therapies for metastatic thyroid cancer, and for functional studies of thyroid cancer tumor biology in vivo.

Inhibition of tumorigenesis by the thyroid hormone receptor β in xenograft models

BACKGROUND

Previous studies showed a close association between several types of human cancers and somatic mutations of thyroid hormone receptor β (TRβ) and reduced expression of TRβ due to epigenetic inactivation and/or deletion of the THRB gene. These observations suggest that TRβ could act as a tumor suppressor in carcinogenesis. However, the mechanisms by which TRβ could function to inhibit tumorigenesis are less well understood.

METHODS

We used the human follicular thyroid cancer cell lines (FTC-133 and FTC-236 cells) to elucidate how functional expression of the THRB gene could affect tumorigenesis. We stably expressed the THRB gene in FTC cells and evaluated the effects of the expressed TRβ on cancer cell proliferation, migration, and tumor growth in cell-based studies and xenograft models.

RESULTS

Expression of TRβ in FTC-133 cells, as compared with control FTC cells without TRβ, reduced cancer cell proliferation and impeded migration of tumor cells through inhibition of the AKT-mTOR-p70 S6K pathway. TRβ expression in FTC-133 and FTC-236 led to less tumor growth in xenograft models. Importantly, new vessel formation was significantly suppressed in tumors induced by FTC cells expressing TRβ compared with control FTC cells without TRβ. The decrease in vessel formation was mediated by the downregulation of vascular endothelial growth factor in FTC cells expressing TRβ.

CONCLUSIONS

These findings indicate that TRβ acts as a tumor suppressor through downregulation of the AKT-mTOR-p70 S6K pathway and decreased vascular endothelial growth factor expression in FTC cells. The present results raise the possibility that TRβ could be considered as a potential therapeutic target for thyroid cancer.

Thyroid hormone receptor inhibits hepatoma cell migration through transcriptional activation of Dickkopf 4

Triiodothyronine (T3) is a potent form of thyroid hormone mediates several physiological processes including cellular growth, development, and differentiation via binding to the nuclear thyroid hormone receptor (TR). Recent studies have demonstrated critical roles of T3/TR in tumor progression. Moreover, long-term hypothyroidism appears to be associated with the incidence of human hepatocellular carcinoma (HCC), independent of other major HCC risk factors. Dickkopf (DKK) 4, a secreted protein that antagonizes the canonical Wnt signaling pathway, is induced by T3 at both mRNA and protein levels in HCC cell lines. However, the mechanism underlying T3-mediated regulation of DKK4 remains unknown. In the present study, the 5' promoter region of DKK4 was serially deleted, and the reporter assay performed to localize the T3 response element (TRE). Consequently, we identified an atypical direct repeat TRE between nucleotides -1645 and -1629 conferring T3 responsiveness to the DKK4 gene. This region was further validated using chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assay (EMSA). Stable DKK4 overexpression in SK-Hep-1 cells suppressed cell invasion and metastatic potential, both in vivo andin vitro, via reduction of matrix metalloproteinase-2 (MMP-2) expression. Our findings collectively suggest that DKK4 upregulated by T3/TR antagonizes the Wnt signal pathway to suppress tumor cell progression, thus providing new insights into the molecular mechanism underlying thyroid hormone activity in HCC.

Thyroid hormone receptors and cancer

BACKGROUND

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that mediate the actions of the thyroid hormone (T3) in development, growth, and differentiation. The THRA and THRB genes encode several TR isoforms that express in a tissue- and development-dependent manner. In the past decades, a significant advance has been made in the understanding of TR actions in maintaining normal cellular functions. However, the roles of TRs in human cancer are less well understood. The reduced expression of TRs because of hypermethylation, or deletion of TR genes found in human cancers suggests that TRs could function as tumor suppressors. A close association of somatic mutations of TRs with human cancers further supports the notion that the loss of normal functions of TR could lead to uncontrolled growth and loss of cell differentiation.

SCOPE OF REVIEW

In line with the findings from association studies in human cancers, mice deficient in total functional TRs (Thra1(-/-)Thrb(-/-) mice) or with a targeted homozygous mutation of the Thrb gene (denoted PV; Thrb(PV/PV) mice) spontaneously develop metastatic thyroid carcinoma. This review will examine the evidence learned from these genetically engineered mice that provided strong evidence to support the critical role of TRs in human cancer.

MAJOR CONCLUSIONS

Loss of normal functions of TR by deletion or by mutations could contribute to cancer development, progression and metastasis.

GENERAL SIGNIFICANCE

Novel mechanistic insights are revealed in how aberrant TR activities lead to carcinogenesis. Mouse models of thyroid cancer provide opportunities to identify molecular targets as potential treatment modalities. This article is part of a Special Issue entitled Thyroid hormone signalling.

Thyroid hormone actions in liver cancer

The thyroid hormone 3,3',5-triiodo-L-thyronine (T3) mediates several physiological processes, including embryonic development, cellular differentiation, metabolism, and the regulation of cell proliferation. Thyroid hormone receptors (TRs) generally act as heterodimers with the retinoid X receptor (RXR) to regulate target genes. In addition to their developmental and metabolic functions, TRs have been shown to play a tumor suppressor role, suggesting that their aberrant expression can lead to tumor transformation. Conversely, recent reports have shown an association between overexpression of wild-type TRs and tumor metastasis. Signaling crosstalk between T3/TR and other pathways or specific TR coregulators appear to affect tumor development. Since TR actions are complex as well as cell context-, tissue- and time-specific, aberrant expression of the various TR isoforms has different effects during diverse tumorigenesis. Therefore, elucidation of the T3/TR signaling mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a summary of recent studies focusing on the role of TRs in hepatocellular carcinomas (HCCs).

Biological significance of a thyroid hormone-regulated secretome

The thyroid hormone, 3,3,5-triiodo-L-thyronine (T3), modulates several physiological processes, including cellular growth, differentiation, metabolism and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Several intracellular and extracellular protein candidates are regulated by T3. Moreover, T3-regulated secreted proteins participate in physiological processes or cellular transformation. T3 has been employed as a marker in several disorders, such as cardiovascular disorder in chronic kidney disease, as well as diseases of the liver, immune system, endocrine hormone metabolism and coronary artery. Our group subsequently showed that T3 regulates several tumor-related secretory proteins, leading to cancer progression via alterations in extracellular matrix proteases and tumor-associated signaling pathways in hepatocellular carcinomas. Therefore, elucidation of T3/thyroid hormone receptor-regulated secretory proteins and their underlying mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a detailed summary on the known secretory proteins regulated by T3 and their physiological significance. This article is part of a Special Issue entitled: An Updated Secretome.

Reactivation of the silenced thyroid hormone receptor β gene expression delays thyroid tumor progression

That a knock-in mouse harboring a dominant-negative thyroid hormone receptor (TR)-β (Thrb) mutation develops metastatic thyroid cancer strongly suggests the involvement of TRβ in carcinogenesis. Epigenetic silencing of the THRB gene is common in human cancers. The aim of the present study was to determine how DNA methylation affected the expression of the THRB gene in differentiated thyroid cancer (DTC) and how reexpression of the THRB gene attenuated the cancer phenotypes. We used methylation-specific PCR to examine the expression and promoter methylation of the THRB gene in DTC tissues. Thyroid cancer cells with hypermethylated THRB were treated with the demethylating agents 5'-aza-2'-deoxycytidine (5'-aza-CdR) and zebularine to evaluate their impact on the cancer cell phenotypes. THRB mRNA expression in DTC was 90% lower than in normal controls, and this decrease was associated with a higher tumor/lymph node staging. The promoter methylation level of the THRB gene had a significant negative correlation with the expression level of the THRB gene. Treatment of FTC-236 cells with 5'-aza-CdR or zebularine induced reexpression of the THRB gene and inhibited cell proliferation and migration. FTC-236 cells stably expressing TRβ exhibited lower cell proliferation and migration through inhibition of β-catenin signaling pathways compared with FTC-236 without TRβ. 5'-Aza-CdR also led to suppression of tumor growth in an in vivo xenograft model using FTC-236 cells consistent with the cell-based studies. These finding indicate that TRβ is a tumor suppressor and could be tested as a potential therapeutic target.

Common genetic variants in pituitary-thyroid axis genes and the risk of differentiated thyroid cancer

Thyroid hormone receptors, THRA and THRB, together with the TSH receptor, TSHR, are key regulators of thyroid function. Alterations in the genes of these receptors (THRA, THRB and TSHR) have been related to thyroid diseases, including thyroid cancer. Moreover, there is evidence suggesting that predisposition to differentiated thyroid cancer (DTC) is related to common genetic variants with low penetrance that interact with each other and with environmental factors. In this study, we investigated the association of single nucleotide polymorphisms (SNPs) in the THRA (one SNP), THRB (three SNPs) and TSHR (two SNPs) genes with DTC risk. A case-control association study was conducted with 398 patients with sporadic DTC and 479 healthy controls from a Spanish population. Among the polymorphisms studied, only THRA-rs939348 was found to be associated with an increased risk of DTC (recessive model, odds ratio=1.80, 95% confidence interval=1.03-3.14, P=0.037). Gene-gene interaction analysis using the genotype data of this study together with our previous genotype data on TG and TRHR indicated a combined effect of the pairwises: THRB-TG (P interaction=0.014, THRB-rs3752874 with TG-rs2076740; P interaction=0.099, THRB-rs844107 with TG-rs2076740) and THRB-TRHR (P interaction=0.0024, THRB-rs3752874 with TRHR-rs4129682) for DTC risk in a Spanish population. Our results confirm that THRA is a risk factor for DTC, and we show for the first time the combined effect of THRB and TG or TRHR on DTC susceptibility, supporting the importance of gene-gene interaction in thyroid cancer risk.

Is there a role for inherited TRβ mutation in human carcinogenesis? [corrected]

Resistance to thyroid hormone (RTH) is a rare autosomal dominant inherited disorder characterized by end-organ reduced sensitivity to thyroid hormone. This syndrome is caused by mutations of the thyroid hormone receptor (TR) β gene, and its clinical presentation is quite variable. Goiter is reported to be the most common finding. A close association of TRβ mutations with human cancers has become apparent, but the role of TRβ mutants in the carcinogenesis is still undefined. Moreover, higher TSH levels, described in RTH syndrome, are correlated with increased risk of thyroid malignancy, whereas TSH receptor stimulation is likely to be involved in tumor progression. We report here an illustrative case of a 29 year-old patient with RTH caused by a mutation in exon 9 (A317T) of TRβ gene, who presented multicentric papillary thyroid cancer. We review the literature on this uncommon feature, and discuss the potential role of this mutation on human tumorigenesis, as well as the challenges in patient follow-up.

Role of TSH in the spontaneous development of asymmetrical thyroid carcinoma in mice with a targeted mutation in a single allele of the thyroid hormone-β receptor

Mutations of the thyroid hormone receptor-β gene (THRB) cause resistance to thyroid hormone (RTH). A mouse model of RTH harboring a homozygous thyroid hormone receptor (TR)-β mutation known as PV (Thrb(PV/PV) mouse) spontaneously develops follicular thyroid cancer (FTC). Similar to RTH patients with mutations of two alleles of the THRB gene, the Thrb(PV/PV) mouse exhibits elevated thyroid hormones accompanied by highly nonsuppressible TSH. However, the heterozygous Thrb(PV/+) mouse with mildly elevated TSH (~2-fold) does not develop FTC. The present study examined whether the mutation of a single allele of the Thrb gene is sufficient to induce FTC in Thrb(PV/+) mice under stimulation by high TSH. Thrb(PV/+) mice and wild-type siblings were treated with propylthiouracil (PTU) to elevate serum TSH. Thrb(PV/+)mice treated with PTU (Thrb(PV/+)-PTU) spontaneously developed FTC similar to human thyroid cancer, but wild-type siblings treated with PTU did not. Interestingly, approximately 33% of Thrb(PV/+)-PTU mice developed asymmetrical thyroid tumors, as is frequently observed in human thyroid cancer. Molecular analyses showed activation of the cyclin 1-cyclin-dependent kinase-4-transcription factor E2F1 pathway to increase thyroid tumor cell proliferation of Thrb(PV/+)-PTU mice. Moreover, via extranuclear signaling, the PV also activated the integrin-Src-focal adhesion kinase-AKT-metalloproteinase pathway to increase migration and invasion of tumor cells. Therefore, mutation of a single allele of the Thrb gene is sufficient to drive the TSH-simulated hyperplastic thyroid follicular cells to undergo carcinogenesis. The present study suggests that the Thrb(PV/+)-PTU mouse model potentially could be used to gain insights into the molecular basis underlying the association between thyroid cancer and RTH seen in some affected patients.

Modeling follicular thyroid cancer for future therapies

Therapeutic choices are limited for undifferentiated metastatic thyroid carcinomas. Although implanted subcutaneous thyroid tumors are standard preclinical models to examine the efficacy of new therapeutic agents, these xenograft models frequently fail to predict the outcomes of clinical trials in patients with metastatic thyroid carcinomas. Genetically engineered mouse models with alterations similar to human cancers in their pathological progression and in an immunocompetent environment offer unparalleled opportunities for evaluating novel potential molecular targets. We review recent advances in the modeling of follicular thyroid carcinoma with distant metastasis and in the use of these mouse models in preclinical studies, emphasizing the significance of genetically engineered mouse models in clinical applications.

MiR-224 targets the 3'UTR of type 1 5'-iodothyronine deiodinase possibly contributing to tissue hypothyroidism in renal cancer

Type 1 iodothyronine deiodinase (DIO1) catalyses the conversion of prohormone thyroxine to the active thyroid hormone 3,3′,5-triiodothyronine (T3), important regulator of cell proliferation and differentiation. DIO1 expression is reduced in the most common type of kidney neoplasia, clear cell Renal Cell Carcinoma (ccRCC). MicroRNAs are small, non-coding RNAs that regulate gene expression at posttranscriptional levels. The aim of this study was to analyze the potential regulation of DIO1 expression by microRNAs in ccRCC. Bioinformatic analysis revealed that 3′UTR of the human DIO1 gene transcript contains miR-224 and miR-383 target sites, which are conserved across mammalian species. Semi-quantitative real-time PCR was used to analyze the expression of miR-224 and miR-383 in 32 samples of ccRCC tumors (T) and in 32 matched control (C) samples. We observed statistically significant (p = 0.0002) more than four fold increase in miR-224 expression and nearly two fold increase in miR-383 expression in samples T compared to samples C. Tumor specific changes in expression of miR-224 negatively correlated with changes in DIO1 expression and intracellular T3 concentration. Transfection of HeLa cell line with miR-224 and miR-383 suppressed the activity of a luciferase reporter containing the 3′UTR of DIO1. This was abolished when constructs mutated at the miR-224 and miR-383 target sites were used instead, indicating that miR-224 and miR-383 directly bind to DIO1 3′UTR. Finally, induced expression of miR-224 in Caki-2 cells resulted in significant (p<0.01) reduction of DIO1 mRNA. This study provides a novel miRNA-mediated regulatory mechanism of DIO1 expression in ccRCC.

Thyroid hormone receptor mutations in cancer and resistance to thyroid hormone: perspective and prognosis

Thyroid hormone, operating through its receptors, plays crucial roles in the control of normal human physiology and development; deviations from the norm can give rise to disease. Clinical endocrinologists often must confront and correct the consequences of inappropriately high or low thyroid hormone synthesis. Although more rare, disruptions in thyroid hormone endocrinology due to aberrations in the receptor also have severe medical consequences. This review will focus on the afflictions that are caused by, or are closely associated with, mutated thyroid hormone receptors. These include Resistance to Thyroid Hormone Syndrome, erythroleukemia, hepatocellular carcinoma, renal clear cell carcinoma, and thyroid cancer. We will describe current views on the molecular bases of these diseases, and what distinguishes the neoplastic from the non-neoplastic. We will also touch on studies that implicate alterations in receptor expression, and thyroid hormone levels, in certain oncogenic processes.

Mutant thyroid hormone receptors (TRs) isolated from distinct cancer types display distinct target gene specificities: a unique regulatory repertoire associated with two renal clear cell carcinomas

Thyroid hormone receptors (TRs) are hormone-regulated transcription factors that regulate a diverse array of biological activities, including metabolism, homeostasis, and development. TRs also serve as tumor suppressors, and aberrant TR function (via mutation, deletion, or altered expression) is associated with a spectrum of both neoplastic and endocrine diseases. A particularly high frequency of TR mutations has been reported in renal clear cell carcinoma (RCCC) and in hepatocellular carcinoma (HCC). We have shown that HCC-TR mutants regulate only a fraction of the genes targeted by wild-type TRs but have gained the ability to regulate other, unique, targets. We have suggested that this altered gene recognition may contribute to the neoplastic phenotype. Here, to determine the generality of this phenomenon, we examined a distinct set of TR mutants associated with RCCC. We report that two different TR mutants, isolated from independent RCCC tumors, possess greatly expanded target gene specificities that extensively overlap one another, but only minimally overlap that of the wild-type TRs, or those of two HCC-TR mutants. Many of the genes targeted by either or both RCCC-TR mutants have been previously implicated in RCCC and include a series of metallothioneins, solute carriers, and genes involved in glycolysis and energy metabolism. We propose as a hypothesis that TR mutations from RCCC and HCC may play tissue-specific roles in carcinogenesis, and that the divergent target gene recognition patterns of TR mutants isolated from the two different types of tumors may arise from different selective pressures during development of RCCC vs. HCC.

Recruitment of the oncoprotein v-ErbA to aggresomes

Aggresome formation, a cellular response to misfolded protein aggregates, is linked to cancer and neurodegenerative disorders. Previously we showed that Gag-v-ErbA (v-ErbA), a retroviral variant of the thyroid hormone receptor (TRα1), accumulates in and sequesters TRα1 into cytoplasmic foci. Here, we show that foci represent v-ErbA targeting to aggresomes. v-ErbA colocalizes with aggresomal markers, proteasomes, hsp70, HDAC6, and mitochondria. Foci have hallmark characteristics of aggresomes: formation is microtubule-dependent, accelerated by proteasome inhibitors, and they disrupt intermediate filaments. Proteasome-mediated degradation is critical for clearance of v-ErbA and T(3)-dependent TRα1 clearance. Our studies highlight v-ErbA's complex mode of action: the oncoprotein is highly mobile and trafficks between the nucleus, cytoplasm, and aggresome, carrying out distinct activities within each compartment. Dynamic trafficking to aggresomes contributes to the dominant negative activity of v-ErbA and may be enhanced by the viral Gag sequence. These studies provide insight into novel modes of oncogenesis across multiple cellular compartments.

Global expression profiling reveals gain-of-function oncogenic activity of a mutated thyroid hormone receptor in thyroid carcinogenesis

Thyroid hormone receptors (TRs) are critical in regulating gene expression in normal physiological processes. Decreased expression and/or somatic mutations of TRs have been shown to be associated several types of human cancers including liver, breast, lung, and thyroid. To understand the molecular mechanisms by which mutated TRs promote carcinogenesis, an animal model of follicular thyroid carcinoma (FTC) (Thrb(PV/PV) mice) was used in the present study. The Thrb(PV/PV) mouse harbors a knockin dominant negative PV mutation, identified in a patient with resistance to thyroid hormone. To understand whether oncogenic actions of PV involve not only the loss of normal TR functions but also gain-of-function activities, we compared the gene expression profiles of thyroid lesions in Thrb(PV/PV) mice and Thra1(-/-)Thrb(-/-) mice that also spontaneously develop FTC, but with less severe malignancy. Analysis of the cDNA microarray data derived from microdissected thyroid tumor cells of these two mice showed contrasting global gene expression profiles. With stringent selection using 2.5-fold change (p<0.01) in cDNA microarray analysis, 241 genes with altered gene expression were identified. Nearly half of the genes (n=103: 42.7% of total) with altered gene expression in thyroid tumor cells of Thrb(PV/PV) mice were associated with tumorigenesis and metastasis; some of these genes function as oncogenes in human thyroid cancers. The remaining genes were found to function in transcriptional regulation, RNA processing, cell proliferation, apoptosis, angiogenesis, and cytoskeleton modification. These results indicate that the more aggressive thyroid tumor progression in Thrb(PV/PV) mice was not due simply to the loss of tumor suppressor functions of TR via mutation but also, importantly, to gain-of-function in the oncogenic activities of PV to drive thyroid carcinogenesis. Thus, the present study identifies a novel mechanism by which a mutated TRβ evolves with an oncogenic advantage to promote thyroid carcinogenesis.

Untranslated regions of thyroid hormone receptor beta 1 mRNA are impaired in human clear cell renal cell carcinoma

Thyroid hormone receptor β1 (TRβ1) is a hormone-dependent transcription factor activated by 3,5,3'-l-triiodothyronine (T3). TRβ1 functions as a tumor suppressor and disturbances of the THRB gene are frequent findings in cancer. Translational control mediated by untranslated regions (UTRs) regulates cell proliferation, metabolism and responses to cellular stress, processes that are involved in carcinogenesis. We hypothesized that reduced TRβ1 expression in clear cell renal cell cancer (ccRCC) results from regulatory effects of TRβ1 5' and 3'UTRs on protein translation. We determined TRβ1 expression and alternative splicing of TRβ1 5' and 3'UTRs in ccRCC and control tissue together with expression of the type 1 deiodinase enzyme (coded by DIO1, a TRβ1 target gene). Tissue concentrations of T3 (which are generated in part by D1) and expression of miRNA-204 (an mRNA inhibitor for which a putative interaction site was identified in the TRβ1 3'UTR) were also determined. TRβ1 mRNA and protein levels were reduced by 70% and 91% in ccRCC and accompanied by absent D1 protein, a 58% reduction in tissue T3 concentration and 2-fold increase in miRNA-204. Structural analysis of TRβ1 UTR variants indicated that reduced TRβ1 expression may be maintained in ccRCC by posttranscriptional mechanisms involving 5'UTRs and miRNA-204. The tumor suppressor activity of TRβ1 indicates that reduced TRβ1 expression and tissue hypothyroidism in ccRCC tumors is likely to be involved in the process of carcinogenesis or in maintaining a proliferative advantage to malignant cells.