PTEN deficiency accelerates tumour progression in a mouse model of thyroid cancer

Thyroid Hormone Receptors as Tumor Suppressors in Cancer

Accumulated research has revealed the multifaceted roles of thyroid hormone receptors (TRs) as potent tumor suppressors across various cancer types. This review explores the intricate mechanisms underlying TR-mediated tumor suppression, drawing insights from preclinical mouse models and cancer biology. This review examines the tumor-suppressive functions of TRs, particularly TRβ, in various cancers using preclinical models, revealing their ability to inhibit tumor initiation, progression, and metastasis. Molecular mechanisms underlying TR-mediated tumor suppression are discussed, including interactions with oncogenic signaling pathways like PI3K-AKT, JAK-STAT, and transforming growth factor β. Additionally, this paper examines TRs' effect on cancer stem cell activity and differentiation, showcasing their modulation of key cellular processes associated with tumor progression and therapeutic resistance. Insights from preclinical studies underscore the therapeutic potential of targeting TRs to impede cancer stemness and promote cancer cell differentiation, paving the way for precision medicine in cancer treatment and emphasizing the potential of TR-targeted therapies as promising approaches for treating cancers and improving patient outcomes.

Mouse Models to Examine Differentiated Thyroid Cancer Pathogenesis: Recent Updates

Although the overall prognosis of differentiated thyroid cancer (DTC), the most common endocrine malignancy, is favorable, a subset of patients exhibits aggressive features. Therefore, preclinical models that can be utilized to investigate DTC pathogenesis and novel treatments are necessary. Various mouse models have been developed based on advances in thyroid cancer genetics. This review focuses on recent progress in mouse models that have been developed to elucidate the molecular pathogenesis of DTC.

E-cadherin on epithelial-mesenchymal transition in thyroid cancer

Thyroid carcinoma is a common malignant tumor of endocrine system and head and neck. Recurrence, metastasis and high malignant expression after routine treatment are serious clinical problems, so it is of great significance to explore its mechanism and find action targets. Epithelial-mesenchymal transition (EMT) is associated with tumor malignancy and invasion. One key change in tumour EMT is low expression of E-cadherin. Therefore, this article reviews the expression of E-cadherin in thyroid cancers (TC), discuss the potential mechanisms involved, and outline opportunities to exploit E-cadherin on regulating the occurrence of EMT as a critical factor in cancer therapeutics.

The Role of the MCTS1 and DENR Proteins in Regulating the Mechanisms Associated with Malignant Cell Transformation

The mutations associated with malignant cell transformation are believed to disrupt the expression of a significant number of normal, non-mutant genes. The proteins encoded by these genes are involved in the regulation of many signaling pathways that are responsible for differentiation and proliferation, as well as sensitivity to apoptotic signals, growth factors, and cytokines. Abnormalities in the balance of signaling pathways can lead to the transformation of a normal cell, which results in tumor formation. Detection of the target genes and the proteins they encode and that are involved in the malignant transformation is one of the major evolutions in anti-cancer biomedicine. Currently, there is an accumulation of data that shed light on the role of the MCTS1 and DENR proteins in oncogenesis.

Comparative hematopoiesis and signal transduction in model organisms

Hematopoiesis is a continuous phenomenon involving the formation of hematopoietic stem cells (HSCs) giving rise to diverse functional blood cells. This developmental process of hematopoiesis is evolutionarily conserved, yet comparably different in various model organisms. Vertebrate HSCs give rise to all types of mature cells of both the myeloid and the lymphoid lineages sequentially colonizing in different anatomical tissues. Signal transduction in HSCs facilitates their potency and specifies branching of lineages. Understanding the hematopoietic signaling pathways is crucial to gain insights into their deregulation in several blood-related disorders. The focus of the review is on hematopoiesis corresponding to different model organisms and pivotal role of indispensable hematopoietic pathways. We summarize and discuss the fundamentals of blood formation in both invertebrate and vertebrates, examining the requirement of key signaling nexus in hematopoiesis. Knowledge obtained from such comparative studies associated with developmental dynamics of hematopoiesis is beneficial to explore the therapeutic options for hematopoietic diseases.

Transcription Factor Profiling Identifies Spatially Heterogenous Mediators of Follicular Thyroid Cancer Invasion

While minimally invasive follicular thyroid cancer (miFTC) generally has low risk of recurrence or death, encapsulated angioinvasive (eaFTC) or widely invasive (wiFTC) histological subtypes display significantly worse prognosis. Drivers of invasion are incompletely understood. Therefore, tissue samples including miFTC, eaFTC, and wiFTC tumors, as well as histologically normal thyroid adjacent to benign follicular adenomas, were selected from a cohort (n = 21) of thyroid tumor patients, and the gene expression of selected transcription factors was characterized with quantitative PCR. Invasion-relevant spatial expression patterns of selected transcription factors were subsequently characterized with immunohistochemistry. E2F1 was over-expressed in all 3 subtypes (p<0.01). SP1 was differentially expressed in eaFTC and wiFTC compared with normal (p=0.01 and 0.04, respectively). TCF7L2 was significantly upregulated in wiFTC specifically (p<0.05). While these findings were mRNA specific, immunohistochemistry of additional cancer-associated transcription factors revealed differential expression along the tumor invasive front relative to the central tumor, and histone acetylation modulators emerged as putative invasion markers. These findings may have significant implications for the interpretation of bulk gene expression analysis of thyroid tumor samples or for the development of targeted therapeutics for this rare but aggressive thyroid cancer variant.

Recommendations on Surveillance for Differentiated Thyroid Carcinoma in Children with PTEN Hamartoma Tumor Syndrome

BACKGROUND

PTEN hamartoma tumor syndrome (PHTS) represents a group of syndromes caused by a mutation in the PTEN gene. Children with a germline PTEN mutation have an increased risk of developing differentiated thyroid carcinoma (DTC). Several guidelines have focused on thyroid surveillance in these children, but studies substantiating these recommendations are lacking.

OBJECTIVE

The present study intends to provide the available evidence for a thyroid carcinoma surveillance program in children with PHTS.

METHODS

An extensive literature search was performed to identify all studies on DTC in pediatric PHTS patients. Two pediatric cases are presented to illustrate the pros and cons of thyroid carcinoma surveillance. Recommendations for other patient groups at risk for DTC were evaluated. Consensus within the study team on recommendations for children with PHTS was reached by balancing the incidence and behavior of DTC with the pros and cons of thyroid surveillance, and the different surveillance methods.

RESULTS

In 5 cohort studies the incidence of DTC in childhood ranged from 4 to 12%. In total 57 cases of DTC and/or benign nodular disease in pediatric PHTS patients were identified, of which 27 had proven DTC, with a median age of 12 years (range 4-17). Follicular thyroid carcinoma (FTC) was diagnosed in 52% of the pediatric DTC patients. No evidence was found for a different clinical behavior of DTC in PHTS patients compared to sporadic DTC.

CONCLUSIONS

Children with PHTS are at increased risk for developing DTC, with 4 years being the youngest age reported at presentation and FTC being overrepresented. DTC in pediatric PHTS patients does not seem to be more aggressive than sporadic DTC.

RECOMMENDATIONS

Surveillance for DTC in pediatric PHTS patients seems justified, as early diagnosis may decrease morbidity. Consensus within the study team was reached to recommend surveillance from the age of 10 years onwards, since at that age the incidence of DTC seems to reach 5%. Surveillance for DTC should consist of yearly neck palpation and triennial thyroid ultrasound. Surveillance in children with PHTS should be performed in a center of excellence for pediatric thyroid disease or PHTS.

Novel Targeted Therapies for Metastatic Thyroid Cancer-A Comprehensive Review

The knowledge on thyroid cancer biology has grown over the past decade. Thus, diagnostic and therapeutic strategies to manage thyroid cancer are rapidly evolving. With new insights into tumor biology and cancer genetics, several novel therapies have been approved for the treatment of thyroid cancer. Tyrosine kinase inhibitors (TKIs), such as lenvatinib and sorafenib, have been successfully utilized for the treatment of radioactive iodine (RAI)-refractory metastatic differentiated thyroid cancer (DTC). In addition, pretreatment with mitogen-activated protein kinase (MAPK) inhibitors (trametinib and selumetinib) has been shown to restore RAI avidity in previously RAI-refractory DTCs. Local therapies, such as external beam radiation and radiofrequency/ethanol ablation, have also been employed for treatment of DTC. Vandetanib and cabozantinib are the two TKIs currently approved by the Food and Drug Administration (FDA) for the treatment of medullary thyroid cancer (MTC). Other novel therapies, such as peptide receptor radionuclide therapy and carcinoembryonic antigen (CEA) vaccine, have also been utilized in treating MTC. Ongoing trials on selective rearranged-during-transfection (RET) protooncogene inhibitors, such as LOXO-292 and BLU-667, have demonstrated promising results in the treatment of metastatic MTC resistant to non-selective TKIs. The FDA-approved BRAF/MEK inhibitor combination of dabrafenib and trametinib has revolutionized treatment of BRAFV600E mutation positive anaplastic thyroid cancer. Several other emerging classes of medications, such as gene fusion inhibitors and immune checkpoint inhibitors, are being actively investigated in several clinical trials. In this review, we describe the molecular landscape of thyroid cancer and novel targeted therapies and treatment combinations available for the treatment of metastatic thyroid cancer.

Inflammation suppression prevents tumor cell proliferation in a mouse model of thyroid cancer

The incidence of thyroid cancer, the most frequent endocrine neoplasia, is rapidly increasing. Significant progress has recently been made in the identification of genetic lesions in thyroid cancer; however, whether inflammation contributes to thyroid cancer progression remains unknown. Using a mouse model of aggressive follicular thyroid cancer (FTC; Thrb^PV/PVPten^+/- mice), we aimed to elucidate a cause-effect relationship at the molecular level. The Thrb^PV/PVPten^+/- mouse expresses a dominantly negative thyroid hormone receptor β (denoted as PV) and a deletion of a single allele of the Pten gene. These two oncogenic signaling pathways synergistically activate PI3K-AKT signaling to drive cancer progression as in human FTC. At the age of 5-7 weeks, thyroids of Thrb^PV/PVPten^+/- mice exhibited extensive hyperplasia accompanied by 77.5-fold infiltration of inflammatory monocytes as compared with normal thyroids. Global gene expression profiling identified altered expression of 2387 genes, among which 1353 were upregulated and 1034 were down-regulated. Further analysis identified markedly elevated expression of inflammation mediators and cytokines such as, Csf1r, Csf1, SPP1, Aif1, IL6, Ccl9, Ccl3, Ccl12, and Ccr2 genes and decreased expression of Kit, Ephx2, Cd163, IL15, Ccl11, and Cxcl13 genes. These changes elicited the inflammatory responses in the hyperplastic thyroid of Thrb^PV/PVPten^+/- mice, reflecting early events in thyroid carcinogenesis. We next tested whether attenuating the inflammatory responses could mitigate thyroid cancer progression. We treated the mice with an inhibitor of colony-stimulating factor 1 receptor (CSF1R), pexidartinib (PLX-3397; PLX). CSF1R mediates the activity of the cytokine, colony stimulating factor 1 (CSF1), in the production, differentiation, and functions of monocytes and macrophages. Treatment with PLX decreased 94% and 62% of inflammatory monocytes in the thyroid and bone marrow, respectively, versus controls. Further, PLX suppressed the expression of critical cytokine and inflammation-regulating genes such as Csf1r, SPP1 (OPN), Aif1, IL6, Ccl9, Ccl3, Ccl12, and Ccr2 (25%-80%), resulting in inhibition of 89% tumor cell proliferation, evidenced by Ki-67 immunostaining. These preclinical findings suggest that inflammation occurs in the early stage of thyroid carcinogenesis and plays a critical in cancer progression. Importantly, attenuation of inflammation by inhibitors such as PLX would be beneficial in preventing thyroid cancer.

Steroid receptor coactivator-3 as a target for anaplastic thyroid cancer

Anaplastic thyroid carcinoma (ATC) is an aggressive malignancy without effective therapeutic options to improve survival. Steroid receptor coactivator-3 (SRC-3) is a transcriptional coactivator whose amplification and/or overexpression has been identified in many cancers. In this study, we explored the expression of SRC-3 in ATCs and the effects of a new class of SRC-3 inhibitor-2 (SI-2) in human ATC cells (THJ-11T and THJ-16T cells) and mouse xenograft models to assess therapeutic potential of SI-2 for the treatment of ATC. SRC-3 protein abundance was significantly higher in human ATC tissue samples and ATC cells than in differentiated thyroid carcinomas or normal controls. SI-2 treatment effectively reduced the SRC-3 expression in both ATC cells and ATC xenograft tumors induced by these cells. Cancer cell survival in ATC cells and tumor growth in xenograft tumors were significantly reduced by SI-2 treatment through induction of cancer cell apoptosis and cell cycle arrest. SI-2 also reduced cancer stem-like cells as shown by an inhibition of tumorsphere formation, ALDH activity, and expression of stem cell markers in ATC. These findings indicate that SRC-3 is a potential therapeutic target for treatment of ATC patients and that SI-2 is a potent and promising candidate for a new therapeutic agent.

Triple-high expression of phosphatase and tensin homolog (PTEN), estrogen receptor (ER) and progesterone receptor (PR) may predict favorable prognosis for patients with Type I endometrial carcinoma

Endometrial carcinoma (EC) is the most common malignant tumors in female derived from the endometrial epithelium. Several previous studies have described estrogen receptors (ER), progesterone Receptor (PR) and phosphatase and tensin homolog (PTEN) are associated with clinicopathological factors and prognosis in EC patients. However, during EC patients follow-up, we found that some EC patients with down-regulation of PTEN, but up-regulation of ER or PR , and some EC patients with down-regulation of ER or PR, but up-regulation of PTEN also had a poor prognosis. Therefore, to reveal the prognosis of EC patients with different phenotypes based on PTEN, ER and PR expression, 120 cases formalin-fixed paraffin-embedded EC tissues and 543 cases uterine corpus endometrial carcinoma (UCEC) patients from the cancer genome atlas (TCGA) UCEC datasets were analyzed. Results showed that EC tissues can be classified to PTEN^LER^LPR^L, PTEN^HER^LPR^L, PTEN^HER^HPR^H, PTEN^LER^HPR^H, PTEN^HER^HPR^L, PTEN^HER^LPR^H, and PTEN^LER^HPR^L phenotypes basing on IHC analysis. Additionally, EC patients with PTEN^LER^LPR^L showed high malignancy, while patients with PTEN^HER^HPR^H showed low malignancy. Therefore, combined detection of PTEN, ER, PR may help identify a small subset of EC with more aggressive behavior and may aid in risk stratification.

Multi-omics Signatures and Translational Potential to Improve Thyroid Cancer Patient Outcome

Recent advances in high-throughput molecular and multi-omics technologies have improved our understanding of the molecular changes associated with thyroid cancer initiation and progression. The translation into clinical use based on molecular profiling of thyroid tumors has allowed a significant improvement in patient risk stratification and in the identification of targeted therapies, and thereby better personalized disease management and outcome. This review compiles the following: (1) the major molecular alterations of the genome, epigenome, transcriptome, proteome, and metabolome found in all subtypes of thyroid cancer, thus demonstrating the complexity of these tumors and (2) the great translational potential of multi-omics studies to improve patient outcome.

Whole-genome sequencing of synchronous thyroid carcinomas identifies aberrant DNA repair in thyroid cancer dedifferentiation

The genetics underlying thyroid cancer dedifferentiation is only partly understood and has not yet been characterised using comprehensive pan-genomic analyses. We investigated a unique case with synchronous follicular thyroid carcinoma (FTC), poorly differentiated thyroid carcinoma (PDTC), and anaplastic thyroid carcinoma (ATC), as well as regional lymph node metastases from the PDTC and ATC from a single patient using whole-genome sequencing (WGS). The FTC displayed mutations in CALR, RB1, and MSH2, and the PDTC exhibited mutations in TP53, DROSHA, APC, TERT, and additional DNA repair genes - associated with an immense increase in sub-clonal somatic mutations. All components displayed an overrepresentation of C>T transitions with associated microsatellite instability (MSI) in the PDTC and ATC, with borderline MSI in the FTC. Clonality analyses pinpointed a shared ancestral clone enriched for mutations in TP53-associated regulation of DNA repair and identified important sub-clones for each tumour component already present in the corresponding preceding lesion. This genomic characterisation of the natural progression of thyroid cancer reveals several novel genes of interest for future studies. Moreover, the findings support the theory of a stepwise dedifferentiation process and suggest that defects in DNA repair could play an important role in the clonal evolution of thyroid cancer. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Monocyte recruitment and activated inflammation are associated with thyroid carcinogenesis in a mouse model

Thyroid cancer is the most common endocrine malignancy. Although an association between inflammation and thyroid cancer has long been recognized, a cause-effect relationship at the molecular level has yet to be elucidated. We explored how inflammation could contribute to thyroid carcinogenesis in Thrb^PV/PVPten^+/- mice. The Thrb^PV/PVPten^+/- mouse expresses a dominantly negative thyroid hormone receptor β (denoted as PV) and a deletion of one single allele of the Pten gene. This mutant mouse exhibits aggressive follicular thyroid cancer similarly as in patients. We found significantly increased infiltration of inflammatory monocytes in thyroid tumors of Thrb^PV/PVPten^+/- mice, while no apparent changes in monocyte homeostasis in the bone marrow and blood of tumor-bearing mice. Using global gene expression profiling, we found altered expression of inflammation mediators in that the expression of Ptgs1, Sphk1, OPN, Chil1, Tnfrsf18, IL6, and Ccl12 genes was significantly increased and expression of Kit, Ly96, Ephx2, CD163, IL15, and Ccr2 was significantly decreased. Subsequent validation of the gene expression by mRNA analysis prompted us to further delineate the inflammatory role of osteopontin (OPN) in thyroid carcinogenesis because of its critical role in monocyte/macrophage functions and proinflammatory responses. We found that the protein abundance of OPN and its receptor, integrin β1, was highly increased and, concurrently, the downstream effectors AKT and NF-κB were significantly elevated to drive thyroid tumor progression of Thrb^PV/PVPten^+/- mice. These results demonstrated that increased inflammation driven by elevated expression of immune-related genes and cytokines promoted thyroid cancer progression. Importantly, we uncovered OPN as a novel regulator in inflammatory response during thyroid carcinogenesis. These preclinical findings suggested that OPN can be a potential target for thyroid cancer therapy via modulation of inflammatory signaling.

Targeting autophagy in thyroid cancers

Thyroid cancer is one of the most common endocrine malignancies. Although the prognosis for the majority of thyroid cancers is relatively good, patients with metastatic, radioiodine-refractory or anaplastic thyroid cancers have an unfavorable outcome. With the gradual understanding of the oncogenic events in thyroid cancers, molecularly targeted therapy using tyrosine kinase inhibitors (TKIs) is greatly changing the therapeutic landscape of radioiodine-refractory differentiated thyroid cancers (RR-DTCs), but intrinsic and acquired drug resistance, as well as adverse effects, may limit their clinical efficacy and use. In this setting, development of synergistic treatment options is of clinical significance, which may enhance the therapeutic effect of current TKIs and further overcome the resultant drug resistance. Autophagy is a critical cellular process involved not only in protecting cells and organisms from stressors but also in the maintenance and development of various kinds of cancers. Substantial studies have explored the complex role of autophagy in thyroid cancers. Specifically, autophagy plays important roles in mediating the drug resistance of small-molecular therapeutics, in regulating the dedifferentiation process of thyroid cancers and also in affecting the treatment outcome of radioiodine therapy. Exploring how autophagy intertwines in the development and dedifferentiation process of thyroid cancers is essential, which will enable a more profound understanding of the physiopathology of thyroid cancers. More importantly, these advances may fuel future development of autophagy-targeted therapeutic strategies for patients with thyroid cancers. Herein, we summarize the most recent evidence uncovering the role of autophagy in thyroid cancers and highlight future research perspectives in this regard.

Coding Molecular Determinants of Thyroid Cancer Development and Progression

Thyroid cancer is the most common endocrine malignancy. Its incidence and mortality rates have increased for patients with advanced-stage papillary thyroid cancer. The characterization of the molecular pathways essential in thyroid cancer initiation and progression has made huge progress, underlining the role of intracellular signaling to promote clonal evolution, dedifferentiation, metastasis, and drug resistance. The discovery of genetic alterations that include mutations (BRAF, hTERT), translocations, deletions (eg, 9p), and copy-number gain (eg, 1q) has provided new biological insights with clinical applications. Understanding how molecular pathways interplay is one of the key strategies to develop new therapeutic treatments and improve prognosis.

Metformin and JQ1 synergistically inhibit obesity-activated thyroid cancer

Compelling epidemiological evidence shows a strong positive correlation of obesity with thyroid cancer. In vivo studies have provided molecular evidence that high-fat-diet-induced obesity promotes thyroid cancer progression by aberrantly activating leptin-JAK2-STAT3 signaling in a mouse model of thyroid cancer (Thrb^PV/PVPten^+/- mice). The Thrb^PV/PVPten^+/- mouse expresses a dominantly negative thyroid hormone receptor β (denoted as PV) and a deletion of one single allele of the Pten gene. The Thrb^PV/PVPten^+/- mouse spontaneously develops follicular thyroid cancer, which allows its use as a preclinical mouse model to test potential therapeutics. We recently showed that inhibition of STAT3 activity by a specific inhibitor markedly delays thyroid cancer progression in high-fat-diet-induced obese Thrb^PV/PVPten^+/- mice (HFD-Thrb^PV/PVPten^+/- mice). Further, metformin, a widely used antidiabetic drug, blocks invasion and metastasis, but not thyroid tumor growth in HFD-Thrb^PV/PVPten^+/- mice. To improve efficacy in reducing thyroid tumor growth, we treated HFD-Thrb^PV/PVPten^+/- with JQ1, a potent inhibitor of the activity of bromodomain and extraterminal domain (BET) and with metformin. We found that the combined treatment synergistically suppressed thyroid tumor growth by attenuating STAT3 and ERK signaling, resulting in decreased anti-apoptotic key regulators such as Mcl-1, Bcl-2 and survivin and increased pro-apoptotic regulators such as Bim, BAD and cleave caspase 3. Furthermore, combined treatment of JQ1 and metformin reduced cMyc protein levels to suppress vascular invasion, anaplasia and lung metastasis. These findings indicate that combined treatment is more effective than metformin alone and suggest a novel treatment modality for obesity-activated thyroid cancer.

MicroRNA-146b promotes PI3K/AKT pathway hyperactivation and thyroid cancer progression by targeting PTEN

Recent studies have shown that miR-146b is the most upregulated microRNA in thyroid cancer and has a central role in cancer progression through mechanisms that remain largely unidentified. As phosphoinositide 3-kinase/protein kinase-B (PI3K/AKT) signaling is a fundamental oncogenic driver in many thyroid cancers, we explored a potential role for miR-146b and its target genes in PI3K/AKT activation. Among the predicted target genes of miR-146b, we found the tumor-suppressor phosphatase and tensin homolog (PTEN). Constitutive overexpression of miR-146b in thyroid epithelial cell lines significantly decreased PTEN mRNA and protein levels by direct binding to its 3'-UTR. This was accompanied by PI3K/AKT hyperactivation, leading to the exclusion of FOXO1 and p27 from the nucleus and a corresponding increase in cellular proliferation. Moreover, miR-146b overexpression led to protection from apoptosis and an increased migration and invasion potential, regulating genes involved in epithelial-mesenchymal transition. Notably, with the single exception of E-cadherin expression, all of these outcomes could be reversed by PTEN coexpression. Further analysis showed that miR-146b directly inhibits E-cadherin expression through binding to its 3'-UTR. Interestingly, miR-146b inhibition in human thyroid tumor xenografts, using a synthetic and clinically amenable molecule, blocked tumor growth when delivered intratumorally. Importantly, this inhibition increased PTEN protein levels. In conclusion, our data define a novel mechanism of PI3K/AKT hyperactivation and outline a regulatory role for miR-146b in suppressing PTEN expression, a frequent observation in thyroid cancer. Both events are related to a more aggressive tumoral phenotype. Targeting miR-146b therefore represents a promising therapeutic strategy for the treatment of this disease.

Fibrotic microenvironment promotes the metastatic seeding of tumor cells via activating the fibronectin 1/secreted phosphoprotein 1-integrin signaling

The seeding of tumor cells is a critical step in the process of metastasis, but whether and how the microenvironment of target organs affects metastatic seeding remain largely unknown. Based on cell and mouse models, we found that the metastatic seeding and outgrowth of tumor cells were significantly enhanced in fibrotic lungs. The conditioned medium from both fibrotic lungs and the fibrotic lung-derived fibroblasts (CM-FLF) had a strong activity to chemoattract tumor cells and to inhibit the apoptosis of tumor cells. Subsequent investigations revealed that the levels of fibronectin 1 (FN1) and secreted phosphoprotein 1 (SPP1) were significantly increased in fibrotic lungs. Silencing of FN1 in the fibrotic lung-derived fibroblasts dramatically decreased the chemoattracting activity of CM-FLF, while silencing of FN1 or SPP1 in fibroblasts attenuated the anti-apoptosis activity of CM-FLF. Moreover, the CM-FLF-induced apoptosis resistance or chemotaxis of tumor cells was attenuated when ITGAV, the common receptor of FN1 and SPP1, was silenced by RNA interference or blocked by GRGDS treatment in tumor cells. Consistently, ITGAV silencing or GRGDS treatment significantly inhibited the seeding and outgrowth of tumor cells in fibrotic lungs in vivo. Collectively, we suggest that fibrotic microenvironment may enhance the metastatic seeding of tumor cells in the lung by chemoattracting tumor cells and inhibiting their apoptosis via activating the FN1/SPP1-ITGAV signaling. These findings give a novel insight into the regulatory mechanisms of cancer metastasis and provide a potential target for anti-metastasis therapy.

THE ASSOCIATION BETWEEN LYMPH NODE METASTASIS AND MOLECULAR MARKERS IN DIFFERENTIATED THYROID CANCER

Context

There is no consensus regarding routine usage and benefits of molecular markers for prediction of prognosis and assessment of risk groups in differentiated thyroid cancer (DTC).

Objective

We aimed to investigate NIS, Galectin-3, PTEN, P53 and Ki67 expressions in tumor tissue and metastatic lymph nodes in PTC and their association with lymph node metastasis and prognosis.

Material and Methods

Ninety two papillary thyroid cancer patients who underwent total thyroidectomy and central lymph node dissection were included in this study. NIS, Galectin-3, PTEN, P53 and Ki67 immunohistochemical stainings were performed for all surgical tumor tissues and metastatic lymph nodes of the 38 patients. Age, gender, tumor size, multifocality, capsular invasion, extrathyroidal extension and lymphocytic thyroiditis were assessed retrospectively.

Results

Seventy three females (79.3%) and nineteen males (20.7%) were included in this study. Risk of lymph node metastasis was higher in tumors with capsular invasion and extrathyroidal extension (p=0.03 and p < 0.001). NIS, PTEN and Galectin-3 protein expressions in tumor tissue were not associated with gender, tumor size, multifocality, extrathyroidal extension, capsular invasion, lymph node metastasis and tumor recurrence. Mean Ki 67 proliferation index was 2.08±0.95%. Ki 67 proliferation index was associated with tumor size (p=0.012). Intensity and expression of NIS and PTEN in tumor tissue were concordant with intensity and expression in metastatic lymph nodes (p<0.001). Ki 67 proliferation index in tumor was concordant with metastatic lymph nodes (p=0.02).

Conclusions

NIS, PTEN, Galectin-3, Ki67 and P53 expressions were not associated with the risk of lymph node metastasis in PTC patients. Routine analysis of these markers does not seem to be favorable. Further studies with new markers are necessary to determine prognostic predictors.

The Role of the Transcription Factor Nuclear Factor-kappa B in Thyroid Autoimmunity and Cancer

Nuclear factor-kappa B (NF-κB) is a ubiquitous transcription factor that is involved in inflammatory and immune responses, as well as in regulation of expression of many other genes related to cell survival, proliferation, and differentiation. In mammals, NF-κB comprises five subunits that can bind to promoter regions of target genes as homodimers or heterodimers. The most common dimer is the p50/p65 heterodimer. The several combinations of dimers that can be formed contribute to the heterogeneous regulation of NF-κB target genes, and this heterogeneity is further increased by interactions of the NF-κB dimers with other transcription factors, such as steroid hormone receptors, activator protein-1 (AP-1), and cAMP response element binding protein (CREB). In the thyroid, several studies have demonstrated the involvement of NF-κB in thyroid autoimmunity, thyroid cancer, and thyroid-specific gene regulation. The role of NF-κB in thyroid autoimmunity was hypothesized more than 20 years ago, after the finding that the binding of distinct NF-κB heterodimers to the major histocompatibility complex class I gene is hormonally regulated. Further studies have shown increased activity of NF-κB in thyroid autoimmune diseases and in thyroid orbitopathy. Increased activity of NF-κB has also been observed in thyroid cancer, where it correlates with a more aggressive pattern. Of particular interest, mutation of some oncogenes or tumor suppressor genes involved in thyroid carcinogenesis results in constitutive activation of the NF-κB pathway. More recently, it has been shown that NF-κB also has a role in thyroid physiology, as it is fundamental for the expression of the main thyroid-specific genes, such as sodium iodide symporter, thyroid peroxidase, thyroglobulin, Pax8, and TTF-1 (NKX2-1).

Metformin blocks progression of obesity-activated thyroid cancer in a mouse model

Compelling epidemiologic evidence indicates that obesity is associated with a high risk of human malignancies, including thyroid cancer. We previously demonstrated that a high fat diet (HFD) effectively induces the obese phenotype in a mouse model of aggressive follicular thyroid cancer (Thrb^PV/PVPten^+/−mice). We showed that HFD promotes cancer progression through aberrant activation of the leptin-JAK2-STAT3 signaling pathway. HFD-promoted thyroid cancer progression allowed us to test other molecular targets for therapeutic opportunity for obesity-induced thyroid cancer. Metformin is a widely used drug to treat patients with type II diabetes. It has been shown to reduce incidences of neoplastic diseases and cancer mortality in type II diabetes patients. The present study aimed to test whether metformin could be a therapeutic for obesity-activated thyroid cancer. Thrb^PV/PVPten^+/−mice were fed HFD together with metformin or vehicle-only, as controls, for 20 weeks. While HFD-Thrb^PV/PVPten^+/−mice had shorter survival than LFD-treated mice, metformin had no effects on the survival of HFD-Thrb^PV/PVPten^+/−mice. Remarkably, metformin markedly decreased occurrence of capsular invasion and completely blocked vascular invasion and anaplasia in HFD-Thrb^PV/PVPten^+/−mice without affecting thyroid tumor growth. The impeded cancer progression was due to the inhibitory effect of metformin on STAT3-ERK-vimentin and fibronectin-integrin signaling to decrease tumor cell invasion and de-differentiation. The present studies provide additional molecular evidence to support the link between obesity and thyroid cancer risk. Importantly, our findings suggest that metformin could be used as an adjuvant in combination with antiproliferative modalities to improve the outcome of patients with obesity-activated thyroid cancer.

Catch and Release of Cytokines Mediated by Tumor Phosphatidylserine Converts Transient Exposure into Long-Lived Inflammation

Immune cells constantly survey the host for pathogens or tumors and secrete cytokines to alert surrounding cells of these threats. In vivo, activated immune cells secrete cytokines for several hours, yet an acute immune reaction occurs over days. Given these divergent timescales, we addressed how cytokine-responsive cells translate brief cytokine exposure into phenotypic changes that persist over long timescales. We studied melanoma cell responses to transient exposure to the cytokine interferon γ (IFNγ) by combining a systems-scale analysis of gene expression dynamics with computational modeling and experiments. We discovered that IFNγ is captured by phosphatidylserine (PS) on the surface of viable cells both in vitro and in vivo then slowly released to drive long-term transcription of cytokine-response genes. This mechanism introduces an additional function for PS in dynamically regulating inflammation across diverse cancer and primary cell types and has potential to usher in new immunotherapies targeting PS and inflammatory pathways.

Inhibition of STAT3 signaling blocks obesity-induced mammary hyperplasia in a mouse model

Compelling epidemiologic evidence indicates that obesity is a risk factor for human cancers, including breast. However, molecular mechanisms by which obesity could contribute to the development of breast cancer remain unclear. To understand the impact of obesity on breast cancer development, we used a mutant mouse that expresses a mutated thyroid hormone receptor β (denoted as PV) with haplodeficiency of the Pten gene (Thrb^PV/PVPten^+/- mice). We previously showed that adult nulliparous female Thrb^PV/PVPten^+/- mice developed extensive mammary hyperplasia and breast tumors. In this study, we induced obesity in Thrb^PV/PVPten^+/- mice by feeding them a high fat diet (HFD). We found HFD exacerbated the extent of mammary hyperplasia in Thrb^PV/PVPten^+/- mice. HFD elevated serum leptin levels but had no effect on the levels of serum thyroid stimulating hormone, thyroid hormones, and estrogens. Molecular analysis showed that the obesity-induced hyperplasia was mediated by the leptin/leptin receptor-JAK1-STAT3 pathway to increase key cell cycle regulators to stimulate mammary epithelial cell proliferation. Activated STAT3 signaling led to altered expression in the key regulators of epithelial-mesenchymal-transition (EMT) to augment invasiveness and migration of mammary proliferating epithelial cells. Moreover, treatment of HFD-Thrb^PV/PVPten^+/- mice with a STAT3 inhibitor, S3I-201, markedly reversed the obesity-induced mammary hyperplasia and reduced EMT signals to lessen cell invasiveness and migration. Our studies not only elucidated how obesity could contribute to mammary hyperplasia at the molecular level, but also, importantly, demonstrated that inhibition of the STAT3 activity could be a novel treatment strategy for obesity-induced breast cancer progression.

PI3K/AKT Pathway and Its Mediators in Thyroid Carcinomas

Thyroid malignancies are the most common endocrine system carcinomas, with four histopathological forms. The phosphoinositide 3-kinase-protein kinase B/AKT (PI3K-PKB/AKT) pathway is one of the most critical molecular signaling pathways implicated in key cellular processes. Its continuous activation by several aberrant receptor tyrosine kinases (RTKs) and genetic mutations in its downstream effectors result in high cell proliferation in a broad number of cancers, including thyroid carcinomas. In this review article, the role of different signaling pathways of PI3K/AKT in thyroid cancers, with the emphasis on the PI3K/AKT/mammalian target of rapamycin (mTOR), PI3K/AKT/forkhead box O (FOXO) and PI3K/AKT/phosphatase and tensin homolog deleted on chromosome ten (PTEN) pathways, and various therapeutic strategies targeting these pathways have been summarized. In most of the in vitro studies, agents inhibiting mTOR in monotherapy or in combination with chemotherapy for thyroid malignancies have been introduced as promising anticancer therapies. FOXOs and PTEN are two outstanding downstream targets of the PI3K/AKT pathway. At the present time, no study has been undertaken to consider thyroid cancer treatment via FOXOs and PTEN targeting. According to the critical role of these proteins in cell cycle arrest, it seems that a treatment strategy based on the combination of FOXOs or PTEN activity induction with PI3K/AKT downstream mediators (e.g., mTOR) inhibition will be beneficial and promising in thyroid cancer 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.

SAHA-induced loss of tumor suppressor Pten gene promotes thyroid carcinogenesis in a mouse model

Thyroid cancer is on the rise. Novel approaches are needed to improve the outcome of patients with recurrent and advanced metastatic thyroid cancers. FDA approval of suberoylanilide hydroxamic acid (SAHA; vorinostat), an inhibitor of histone deacetylase, for the treatment of hematological malignancies led to the clinical trials of vorinostat for advanced thyroid cancer. However, patients were resistant to vorinostat treatment. To understand the molecular basis of resistance, we tested the efficacy of SAHA in two mouse models of metastatic follicular thyroid cancer: Thrb(PV/PV) and Thrb(PV/PV)Pten(+/-) mice. In both, thyroid cancer is driven by overactivation of PI3K-AKT signaling. However, the latter exhibit more aggressive cancer progression due to haplodeficiency of the tumor suppressor, the Pten gene. SAHA had no effects on thyroid cancer progression in Thrb(PV/PV) mice, indicative of resistance to SAHA. Unexpectedly, thyroid cancer progressed in SAHA-treated Thrb(PV/PV)Pten(+/-) mice with accelerated occurrence of vascular invasion, anaplastic foci, and lung metastasis. Molecular analyses showed further activated PI3K-AKT in thyroid tumors of SAHA-treated Thrb(PV/PV)Pten(+/-) mice, resulting in the activated effectors, p-Rb, CDK6, p21(Cip1), p-cSrc, ezrin, and matrix metalloproteinases, to increase proliferation and invasion of tumor cells. Single-molecule DNA analysis indicated that the wild-type allele of the Pten gene was progressively lost, whereas carcinogenesis progressed in SAHA-treated Thrb(PV/PV)Pten(+/-) mice. Thus, this study has uncovered a novel mechanism by which SAHA-induced loss of the tumor suppressor Pten gene to promote thyroid cancer progression. Effectors downstream of the Pten loss-induced signaling may be potential targets to overcome resistance of thyroid cancer to SAHA.

Loss of tyrosine phosphorylation at Y406 abrogates the tumor suppressor functions of the thyroid hormone receptor β

We have recently identified that phosphorylation at tyrosine (Y)406 is critical for the tumor suppressor functions of the thyroid hormone receptor β1 (TRβ) in a breast cancer line. However, still unclear is whether the critical tumor suppressor role of phosphorylated Y406 of TRβ is limited to only breast cancer cells or could be extended to other cell types. In the present studies, we addressed this question by stably expressing TRβ, a mutated TRβ oncogene (PV), or a TRβ mutated at Y406 (TRβY406F) in rat PCCL3 thyroid follicular cells and evaluated their tumor characteristics in athymic mice with elevated thyroid stimulating hormone. PCCL3 cells stably expressing PV (PCCL3-PV), TRβY406F (PCCL3-TRβY406F), or vector only (PCCL3-Neo) developed tumors with sizes in the rank order of TRβY406F>PV = Neo, whereas PCCL3 cells expressing TRβ (PCCL3-TRβ) barely developed tumors. As evidenced by markedly elevated Ki67, cyclin D1, and p-Rb protein abundance, proliferative activity was high in PV and TRβY406F tumors, but low in TRβ tumors. These results indicate that TRβ acted as a tumor suppressor in PCCL3 cells, whereas TRβY406F and PV had lost tumor suppressor activity. Interestingly, TRβY406F tumors had very low necrotic areas with decreased TNFα-NFκB signaling to lower apoptotic activity. In contrast, PV tumors had prominent large necrotic areas, with no apparent changes in TNFα-NFκB signaling, indicating distinct oncogenic activities of mutant PV and TRβY406F. Thus, the present studies uncovered a novel mechanism by which TRβ could function as a tumor suppressor through modulation of the TNFα-NFκB signaling. © 2016 Wiley Periodicals, Inc.

Oncogenic mutations of thyroid hormone receptor β

The C-terminal frame-shift mutant of the thyroid hormone receptor TRβ1, PV, functions as an oncogene. An important question is whether the oncogenic activity of mutated TRβ1 is uniquely dependent on the PV mutated sequence. Using four C-terminal frame-shift mutants—PV, Mkar, Mdbs, and AM—we examined that region in the oncogenic actions of TRβ1 mutants. Remarkably, these C-terminal mutants induced similar growth of tumors in mouse xenograft models. Molecular analyses showed that they physically interacted with the p85α regulatory subunit of PI3K similarly in cells. In vitro GST-binding assay showed that they bound to the C-terminal Src-homology 2 (CSH2) of p85α with markedly higher avidity. The sustained association of mutants with p85α led to activation of the common PI3K-AKT-ERK/STAT3 signaling to promote cell proliferation and invasion and to inhibit apoptosis. Thus, these results argue against the oncogenic activity of PV being uniquely dependent on the PV mutated sequence. Rather, these four mutants could favor a C-terminal conformation that interacted with the CSH2 domain of p85α to initiate activation of PI3K to relay downstream signaling to promote tumorigenesis. Thus, we propose that the mutated C-terminal region of TRβ1 could function as an “onco-domain” and TRβ1 is a potential therapeutic target.

Signaling Pathways in Thyroid Cancer and Their Therapeutic Implications

Thyroid cancer is a common malignancy of endocrine system, and has now become the fastest increasing cancer among all the malignancies. The development, progression, invasion, and metastasis are closely associated with multiple signaling pathways and the functions of related molecules, such as Src, Janus kinase (JAK)-signal transducers and activators of transcription (STAT), mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)/Akt, NF-κB, thyroid stimulating hormone receptor (TSHR), Wnt-β-catenin and Notch signaling pathways. Each of the signaling pathways could exert its function singly or through network with other pathways. These pathways could cooperate, promote, antagonize, or interact with each other to form a complex network for the regulation. Dysfunction of this network could increase the development, progression, invasion, and metastasis of thyroid cancer. Inoperable thyroid cancer still has a poor prognosis. However, signaling pathway-related targeted therapies offer the hope of longer quality of meaningful life for this small group of patients. Signaling pathway-related targets provide unprecedented opportunities for further research and clinical development of novel treatment strategies for this cancer. In the present work, the advances in these signaling pathways and targeted treatments of thyroid cancer were reviewed.

Methods to Study Metastasis in Genetically Modified Mice

Metastasis is often modeled by xenotransplantation of cell lines in immunodeficient mice. A wealth of information about tumor cell behavior in the new environment is obtained from these efforts. Yet by design, this approach is "tumor-centric," as it focuses on cell-autonomous determinants of human tumor dissemination in mouse tissues, in effect using the animal body as a sophisticated "Petri dish" providing nutrients and support for tumor growth. Transgenic or gene knockout mouse models of cancer allow the study of tumor spread as a systemic disease and offer a complimentary approach for studying the natural history of cancer. This introduction is aimed at describing the overall methodological approach to studying metastasis in genetically modified mice, with a particular focus on using animals with regulated expression of potent human oncogenes in the breast.

Inhibition of STAT3 activity delays obesity-induced thyroid carcinogenesis in a mouse model

Compelling epidemiologic studies indicate that obesity is a risk factor for many human cancers, including thyroid cancer. In recent decades, the incidence of thyroid cancer has dramatically increased along with a marked rise in obesity prevalence. We previously demonstrated that a high fat diet (HFD) effectively induced the obese phenotype in a mouse model of thyroid cancer (Thrb(PV/PV)Pten(+/-) mice). Moreover, HFD activates the STAT3 signal pathway to promote more aggressive tumor phenotypes. The aim of the present study was to evaluate the effect of S3I-201, a specific inhibitor of STAT3 activity, on HFD-induced aggressive cancer progression in the mouse model of thyroid cancer. WT and Thrb(PV/PV)Pten(+/-) mice were treated with HFD together with S3I-201 or vehicle-only as controls. We assessed the effects of S3I-201 on HFD-induced thyroid cancer progression, the leptin-JAK2-STAT3 signaling pathway, and key regulators of epithelial-mesenchymal transition (EMT). S3I-201 effectively inhibited HFD-induced aberrant activation of STAT3 and its downstream targets to markedly inhibit thyroid tumor growth and to prolong survival. Decreased protein levels of cyclins D1 and B1, cyclin dependent kinase 4 (CDK4), CDK6, and phosphorylated retinoblastoma protein led to the inhibition of tumor cell proliferation in S3I-201-treated Thrb(PV/PV)Pten(+/-) mice. Reduced occurrence of vascular invasion and blocking of anaplasia and lung metastasis in thyroid tumors of S3I-201-treated Thrb(PV/PV)Pten(+/-) mice were mediated via decreased expression of vimentin and matrix metalloproteinases, two key effectors of EMT. The present findings suggest that inhibition of the STAT3 activity would be a novel treatment strategy for obesity-induced thyroid cancer.

Synergistic signaling of KRAS and thyroid hormone receptor β mutants promotes undifferentiated thyroid cancer through MYC up-regulation

Undifferentiated thyroid carcinoma is one of the most aggressive human cancers with frequent RAS mutations. How mutations of the RAS gene contribute to undifferentiated thyroid cancer remains largely unknown. Mice harboring a potent dominant negative mutant thyroid hormone receptor β, TRβPV (Thrb(PV/PV)), spontaneously develop well-differentiated follicular thyroid cancer similar to human cancer. We genetically targeted the Kras(G12D) mutation to thyroid epithelial cells of Thrb(PV/PV) mice to understand how Kras(G12D) mutation could induce undifferentiated thyroid cancer in Thrb(PV/PV)Kras(G12D) mice. Thrb(PV/PV)Kras(G12D) mice exhibited poorer survival due to more aggressive thyroid tumors with capsular invasion, vascular invasion, and distant metastases to the lung occurring at an earlier age and at a higher frequency than Thrb(PV/PV) mice did. Importantly, Thrb(PV/PV)Kras(G12D) mice developed frequent anaplastic foci with complete loss of normal thyroid follicular morphology. Within the anaplastic foci, the thyroid-specific transcription factor paired box gene 8 (PAX8) expression was virtually lost and the loss of PAX8 expression was inversely correlated with elevated MYC expression. Consistently, co-expression of KRAS(G12D) with TRβPV upregulated MYC levels in rat thyroid pccl3 cells, and MYC acted to enhance the TRβPV-mediated repression of the Pax8 promoter activity of a distant upstream enhancer, critical for thyroid-specific Pax8 expression. Our findings indicated that synergistic signaling of KRAS(G12D) and TRβPV led to increased MYC expression. Upregulated MYC contributes to the initiation of undifferentiated thyroid cancer, in part, through enhancing TRβPV-mediated repression of the Pax8 expression. Thus, MYC might serve as a potential target for therapeutic intervention.

HMGB1-Induced Cross Talk between PTEN and miRs 221/222 in Thyroid Cancer

High mobility group box 1 (HMGB1) is an ubiquitous protein that plays different roles in the nucleus, cytoplasm, and extracellular space. It is an important DAMP molecule that allows communication between damaged or tumor cells and the immune system. Tumor cells exploit HMGB1's ability to activate intracellular pathways that lead to cell growth and migration. Papillary thyroid cancer is a well-differentiated tumor and is often used to study relationships between cells and the inflammatory microenvironment as the latter is characterized by high levels of inflammatory cells and cytokines. Anaplastic thyroid cancer is one of the most lethal human cancers in which many microRNAs and tumor suppressor genes are deregulated. Upregulation of microRNAs 221 and 222 has been shown to induce the malignant phenotype in many human cancers via inhibition of PTEN expression. In this study we suggest that extracellular HMGB1 interaction with RAGE enhances expression of oncogenic cluster miR221/222 that in turn inhibits tumor suppressor gene PTEN in two cell lines derived from human thyroid anaplastic and papillary cancers. The newly identified pathway HMGB1/RAGE/miR221/222 may represent an effective way of tumor escape from immune surveillance that could be used to develop new therapeutic strategies against anaplastic tumors.

A functional insertion/deletion polymorphism in the promoter region of the NFKB1 gene increases the risk of papillary thyroid carcinoma

This study aimed to assess whether an insertion/deletion polymorphic variation rs28362491 in the NFKB1 promoter region was related to the risk of papillary thyroid carcinoma (PTC). Genomic DNA was extracted from the peripheral venous blood of 352 patients with PTC and 459 controls. The NFKB1 rs28362491 polymorphism was genotyped by using a polymerase chain reaction assay. We found that the frequency of the heterozygous genotype ATTG1/ATTG2 was significantly higher in the cases compared to the controls (odds ratios [OR]=1.44, 95% confidence intervals [CI]=1.05-1.96, p=0.02). Moreover, the frequency of ATTG1/ATTG2+ATTG1/ATTG1 genotypes was significantly elevated in the cases compared to the controls (OR=1.38, 95% CI=1.03-1.85, p=0.03). These findings suggest that the -94 insertion/deletion ATTG polymorphism in the NFKB1 promoter might be associated with an increased risk of PTC.

Modeling anaplastic thyroid carcinoma in the mouse

Anaplastic thyroid carcinoma is the least common form of thyroid cancer; however, it accounts for the majority of deaths associated with this family of malignancies. A number of genetically engineered immunocompetent mouse models recapitulating the genetic and histological features of anaplastic thyroid cancer have been very recently generated and represent an invaluable tool to dissect the mechanisms involved in the progression from indolent, well-differentiated tumors to aggressive, undifferentiated carcinomas and to identify novel therapeutic targets. In this review, we focus on the relevant characteristics associated with these models and on what we have learned in terms of anaplastic thyroid cancer biology, genetics, and response to targeted therapy.

Modulation of sodium iodide symporter in thyroid cancer

Radioactive iodine (RAI) is a key therapeutic modality for thyroid cancer. Loss of RAI uptake in thyroid cancer inversely correlates with patient's survival. In this review, we focus on the challenges encountered in delivering sufficient doses of I-131 to eradicate metastatic lesions without increasing the risk of unwanted side effects. Sodium iodide symporter (NIS) mediates iodide influx, and NIS expression and function can be selectively enhanced in thyroid cells by thyroid-stimulating hormone. We summarize our current knowledge of NIS modulation in normal and cancer thyroid cells, and we propose that several reagents evaluated in clinical trials for other diseases can be used to restore or further increase RAI accumulation in thyroid cancer. Once validated in preclinical mouse models and clinical trials, these reagents, mostly small-molecule inhibitors, can be readily translated into clinical practice. We review available genetically engineered mouse models of thyroid cancer in terms of their tumor development and progression as well as their thyroid function. These mice will not only provide important insights into the mechanisms underlying the loss of RAI uptake in thyroid tumors but will also serve as preclinical animal models to evaluate the efficacy of candidate reagents to selectively increase RAI uptake in thyroid cancers. Taken together, we anticipate that the optimal use of RAI in the clinical management of thyroid cancer is yet to come in the near future.

MCT-1 expression and PTEN deficiency synergistically promote neoplastic multinucleation through the Src/p190B signaling activation

Multinucleation is associated with malignant neoplasms; however, the molecular mechanism underlying the nuclear abnormality remains unclear. Loss or mutation of PTEN promotes the development of malignant tumors. We now demonstrate that increased expression of the oncogene MCT-1 (multiple copies in T-cell malignancy 1) antagonizes PTEN gene presentation, PTEN protein stability and PTEN functional activity, thereby further promoting phosphoinositide 3 kinase/AKT signaling, survival rate and malignancies of the PTEN-deficient cells. In the PTEN-null cancer cells, MCT-1 interacts with p190B and Src in vivo, supporting that they are in proximity of the signaling complexes. MCT-1 overexpression and PTEN loss synergistically augments the Src/p190B signaling function that leads to inhibition of RhoA activity. Under such a condition, the incidence of mitotic catastrophes including spindle multipolarity and cytokinesis failure is enhanced, driving an Src/p190B/RhoA-dependent neoplastic multinucleation. Targeting MCT-1 by the short hairpin RNA markedly represses the Src/p190B function, improves nuclear structures and suppresses xenograft tumorigenicity of the PTEN-null breast cancer cells. Consistent with the oncogenic effects in vitro, clinical evidence has confirmed that MCT-1 gene stimulation is correlated with p190B gene promotion and PTEN gene suppression in human breast cancer. Accordingly, MCT-1 gene induction is recognized as a potential biomarker of breast tumor development. Abrogating MCT-1 function may be a promising stratagem for management of breast cancer involving Src hyperactivation and/or PTEN dysfunction.

Genetics and epigenetics of sporadic thyroid cancer

Thyroid carcinoma is the most common endocrine malignancy, and although the disease generally has an excellent prognosis, therapeutic options are limited for patients not cured by surgery and radioiodine. Thyroid carcinomas commonly contain one of a small number of recurrent genetic mutations. The identification and study of these mutations has led to a deeper understanding of the pathophysiology of this disease and is providing new approaches to diagnosis and therapy. Papillary thyroid carcinomas usually contain an activating mutation in the RAS cascade, most commonly in BRAF and less commonly in RAS itself or through gene fusions that activate RET. A chromosomal translocation that results in production of a PAX8-PPARG fusion protein is found in follicular carcinomas. Anaplastic carcinomas may contain some of the above changes as well as additional mutations. Therapies that are targeted to these mutations are being used in patient care and clinical trials.

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.

A model for the epigenetic switch linking inflammation to cell transformation: deterministic and stochastic approaches

Recently, a molecular pathway linking inflammation to cell transformation has been discovered. This molecular pathway rests on a positive inflammatory feedback loop between NF-κB, Lin28, Let-7 microRNA and IL6, which leads to an epigenetic switch allowing cell transformation. A transient activation of an inflammatory signal, mediated by the oncoprotein Src, activates NF-κB, which elicits the expression of Lin28. Lin28 decreases the expression of Let-7 microRNA, which results in higher level of IL6 than achieved directly by NF-κB. In turn, IL6 can promote NF-κB activation. Finally, IL6 also elicits the synthesis of STAT3, which is a crucial activator for cell transformation. Here, we propose a computational model to account for the dynamical behavior of this positive inflammatory feedback loop. By means of a deterministic model, we show that an irreversible bistable switch between a transformed and a non-transformed state of the cell is at the core of the dynamical behavior of the positive feedback loop linking inflammation to cell transformation. The model indicates that inhibitors (tumor suppressors) or activators (oncogenes) of this positive feedback loop regulate the occurrence of the epigenetic switch by modulating the threshold of inflammatory signal (Src) needed to promote cell transformation. Both stochastic simulations and deterministic simulations of a heterogeneous cell population suggest that random fluctuations (due to molecular noise or cell-to-cell variability) are able to trigger cell transformation. Moreover, the model predicts that oncogenes/tumor suppressors respectively decrease/increase the robustness of the non-transformed state of the cell towards random fluctuations. Finally, the model accounts for the potential effect of competing endogenous RNAs, ceRNAs, on the dynamics of the epigenetic switch. Depending on their microRNA targets, the model predicts that ceRNAs could act as oncogenes or tumor suppressors by regulating the occurrence of cell transformation.

An increasing amount of evidence demonstrates a close relation between inflammation and cancer development, which reveals the importance of the tumor microenvironment for the development of cancers. Recently, a molecular pathway linking inflammation to cell transformation, which is a prerequisite to cancer development, has been discovered. This molecular pathway is based on a positive inflammatory feedback loop between NF-κB, Lin28, Let-7 microRNA and IL6, allowing the occurrence of an epigenetic switch leading to cell transformation. Here, we propose a computational model to account for the dynamics of this epigenetic switch. We show that an irreversible bistable switch is at the core of the dynamics of the system. The model further indicates that oncogenes (activators of the switch) and tumor suppressors (inhibitors of the switch) regulate the occurrence of cell transformation by modulating the threshold of inflammatory signal needed to induce the switch. Stochastic simulations of the model suggest that molecular fluctuations are able to trigger cell transformation, highlighting possible links between stochasticity and cancer development. Finally, the model predicts a crucial role of competing endogenous RNAs (ceRNAs) for the dynamics of the epigenetic switch and the occurrence of cell transformation.

Diet-induced obesity increases tumor growth and promotes anaplastic change in thyroid cancer in a mouse model

Recent epidemiological studies provide strong evidence suggesting obesity is a risk factor in several cancers, including thyroid cancer. However, the molecular mechanisms by which obesity increases the risk of thyroid cancer are poorly understood. In this study, we evaluated the effect of diet-induced obesity on thyroid carcinogenesis in a mouse model that spontaneously develops thyroid cancer (Thrb(PV/PV)Pten(+/-) mice). These mice harbor a mutated thyroid hormone receptor-β (denoted as PV) and haplodeficiency of the Pten gene. A high-fat diet (HFD) efficiently induced the obese phenotype in Thrb(PV/PV)Pten(+/-) mice after 15 weeks. Thyroid tumor growth was markedly greater and survival was significantly lower in Thrb(PV/PV)Pten(+/-) mice fed an HFD than in controls fed a low-fat diet (LFD). The HFD increased thyroid tumor cell proliferation by increasing the protein levels of cyclin D1 and phosphorylated retinoblastoma protein to propel cell cycle progression. Histopathological analysis showed that the frequency of anaplasia of thyroid cancer was significantly greater (2.6-fold) in the HFD group than the LFD group. The HFD treatment led to an increase in parametrial/epididymal fat pad and elevated serum leptin levels in Thrb(PV/PV)Pten(+/-) mice. Further molecular analyses indicated that the HFD induced more aggressive pathological changes that were mediated by increased activation of the Janus kinase 2-signaling transducer and activator of transcription 3 (STAT3) signaling pathway and induction of STAT3 target gene expression. Our findings demonstrate that diet-induced obesity exacerbates thyroid cancer progression in Thrb(PV/PV)Pten(+/-) mice and suggest that the STAT3 signaling pathway could be tested as a potential target for the treatment of thyroid cancer.

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.

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

Association studies suggest that thyroid hormone receptor β (TRβ) could function as a tumor suppressor in breast cancer development, but unequivocal evidence is still lacking. To understand the role of TRβ in breast tumor development, we adopted the gain-of-function approach by stably expressing the THRB gene in a human breast cancer cell line, MCF-7 (MCF-7-TRβ). Parental MCF-7 cells express the estrogen receptor, but not TRs. MCF-7 cells, stably expressing only the selectable marker, the Neo gene, were also generated as control for comparison (MCF-7-Neo cells). Cell-based studies indicate that the estrogen (E2)-dependent growth of MCF-7 cells was inhibited by the expression of TRβ in the presence of the thyroid hormone (T3). In a xenograft mouse model, large tumors rapidly developed after inoculation of MCF-7-Neo cells in athymic mice. In contrast, markedly smaller tumors (98% smaller) were found when MCF-7-TRβ cells were inoculated in athymic mice, indicating that TRβ inhibited the E2-dependent tumor growth of MCF-7 cells. Further detailed molecular analysis showed that TRβ acted to activate apoptosis and decrease proliferation of tumor cells, resulting in inhibition of tumor growth. The TRβ-mediated inhibition of tumor growth was elucidated via down-regulation of the JAK-STAT-cyclin D pathways. This in vivo evidence shows that TRβ could act as a tumor suppressor in breast tumorigenesis. The present study provides new insights into the role of TR in breast cancer.

Thyroid hormone, thyroid hormone receptors, and cancer: a clinical perspective

Thyroid hormones (THs) may play a role in diseases other than hyper- and hypothyroidism. Several lines of evidence suggest tumor-promoting effects of TH and TH receptors. They are possibly mediated by phosphatidylinositol-3-kinase and MAPK and involve among others stimulation of angiogenesis via αvβ3. Thus, an increased risk for colon, lung, prostate, and breast cancer with lower TSH has been demonstrated in epidemiological studies, even suggesting a TH dose effect on cancer occurrence. Furthermore, higher TH levels were associated with an advanced clinical stage of breast and prostate cancer. In rodent models, TH stimulated growth and metastasis of tumor transplants, whereas hypothyroidism had opposite effects. In clinical studies of glioblastoma and head and neck cancer, hypothyroid patients showed longer survival than euthyroid patients. Also, patients with renal cell cancer that were treated with the tyrosine kinase inhibitor sunitinib and developed hypothyroidism in due course showed significantly longer survival than patients that remained euthyroid. Development of hypothyroidism was an independent predictor for survival in two studies. Yet, it is still possible that hypothyroidism is only a surrogate marker for treatment efficacy and does not positively influence treatment outcome by itself. Future cancer treatment studies, especially with substances that can induce hypothyroidism, should therefore be designed in a way that allows for an analysis of thyroid function status and its contribution on treatment outcome.

Molecular pathogenesis and mechanisms of thyroid cancer

Thyroid cancer is a common endocrine malignancy. There has been exciting progress in understanding its molecular pathogenesis in recent years, as best exemplified by the elucidation of the fundamental role of several major signalling pathways and related molecular derangements. Central to these mechanisms are the genetic and epigenetic alterations in these pathways, such as mutation, gene copy-number gain and aberrant gene methylation. Many of these molecular alterations represent novel diagnostic and prognostic molecular markers and therapeutic targets for thyroid cancer, which provide unprecedented opportunities for further research and clinical development of novel treatment strategies for this cancer.

FOXO1 controls thyroid cell proliferation in response to TSH and IGF-I and is involved in thyroid tumorigenesis

TSH and insulin/IGF-I synergistically induce the proliferation of thyroid cells mainly through the cAMP and phosphatidylinositol 3-kinase (PI3K) pathways. However, the events involved in this cooperative induction remain unknown, and molecules that are potentially controlled by both TSH and IGF-I are interesting candidates as integrators of both stimuli. The finding that the PI3K pathway is frequently activated in thyroid malignancies has attracted attention to this pathway in the thyroid field. One of the targets of PI3K is Forkhead box O (FoxO)-1, a widely expressed transcription factor involved in a variety of cellular processes such as differentiation, proliferation, and apoptosis. Here we show that FoxO1 is highly expressed in differentiated rat thyroid cells and human thyroid tissue compared with human thyroid tumor-derived cells and surgically removed thyroid tumors, in which its expression is reduced. In differentiated cells, TSH/cAMP treatment decreases FoxO1 mRNA and protein levels through proteasome activation, whereas both TSH and IGF-I control FoxO1 localization by promoting a rapid exclusion from the nucleus in an Akt-dependent manner. FoxO1 can control p27(KIP1) expression in differentiated and tumor cells of the thyroid. Furthermore, FoxO1 reexpression in tumor cells promotes a decrease in their proliferation rate, whereas FoxO1 interference in differentiated cells increases their proliferation. These data point to an important role of FoxO1 in mediating the effects of TSH and IGF-I on thyroid cell proliferation and provide a link between loss of FoxO1 expression and the uncontrolled proliferation of thyroid tumor cells.

Targeting the FOXO1/KLF6 axis regulates EGFR signaling and treatment response

EGFR activation is both a key molecular driver of disease progression and the target of a broad class of molecular agents designed to treat advanced cancer. Nevertheless, resistance develops through several mechanisms, including activation of AKT signaling. Though much is known about the specific molecular lesions conferring resistance to anti-EGFR-based therapies, additional molecular characterization of the downstream mediators of EGFR signaling may lead to the development of new classes of targeted molecular therapies to treat resistant disease. We identified a transcriptional network involving the tumor suppressors Krüppel-like factor 6 (KLF6) and forkhead box O1 (FOXO1) that negatively regulates activated EGFR signaling in both cell culture and in vivo models. Furthermore, the use of the FDA-approved drug trifluoperazine hydrochloride (TFP), which has been shown to inhibit FOXO1 nuclear export, restored sensitivity to AKT-driven erlotinib resistance through modulation of the KLF6/FOXO1 signaling cascade in both cell culture and xenograft models of lung adenocarcinoma. Combined, these findings define a novel transcriptional network regulating oncogenic EGFR signaling and identify a class of FDA-approved drugs as capable of restoring chemosensitivity to anti-EGFR-based therapy for the treatment of metastatic lung adenocarcinoma.