Thyroid stem cells and cancer

Effects of selenium and iodine on Kashin-Beck disease: an updated review

Kashin-Beck disease (KBD) is an endochondral osteogenesis disorder characterised by epiphysis damage and secondary deformable arthropathy induced by multiple external factors, among which selenium (Se) and iodine deficiency are important influencing factors. Iodine deficiency is usually accompanied by a low Se content in the soil in the KBD areas of China. Se can reverse oxidative damage to chondrocytes. In addition, Se is related to the bone conversion rate and bone mineral density. Low Se will hinder growth and change bone metabolism, resulting in a decrease in the bone conversion rate and bone mineral density. Thyroid hormone imbalance caused by thyroid dysfunction caused by iodine deficiency can damage bone homeostasis. Compared with Se deficiency alone, Se combined with iodine deficiency can reduce the activity of glutathione peroxidase more effectively, which increases the vulnerability of chondrocytes and other target cells to oxidative stress, resulting in chondrocyte death. Clinical studies have shown that supplementation with Se and iodine is helpful for the prevention and treatment of KBD.

The Haematopoietically-expressed homeobox transcription factor: roles in development, physiology and disease

The Haematopoietically expressed homeobox transcription factor (Hhex) is a transcriptional repressor that is of fundamental importance across species, as evident by its evolutionary conservation spanning fish, amphibians, birds, mice and humans. Indeed, Hhex maintains its vital functions throughout the lifespan of the organism, beginning in the oocyte, through fundamental stages of embryogenesis in the foregut endoderm. The endodermal development driven by Hhex gives rise to endocrine organs such as the pancreas in a process which is likely linked to its role as a risk factor in diabetes and pancreatic disorders. Hhex is also required for the normal development of the bile duct and liver, the latter also importantly being the initial site of haematopoiesis. These haematopoietic origins are governed by Hhex, leading to its crucial later roles in definitive haematopoietic stem cell (HSC) self-renewal, lymphopoiesis and haematological malignancy. Hhex is also necessary for the developing forebrain and thyroid gland, with this reliance on Hhex evident in its role in endocrine disorders later in life including a potential role in Alzheimer's disease. Thus, the roles of Hhex in embryological development throughout evolution appear to be linked to its later roles in a variety of disease processes.

Endocrine Regulation on Bone by Thyroid

BACKGROUND

As an endocrine organ, the thyroid acts on the entire body by secreting a series of hormones, and bone is one of the main target organs of the thyroid.

SUMMARY

This review highlights the roles of thyroid hormones and thyroid diseases in bone homeostasis.

CONCLUSION

Thyroid hormones play significant roles in the growth and development of bone, and imbalance of thyroid hormones can impair bone homeostasis.

Adult mouse and human organoids derived from thyroid follicular cells and modeling of Graves' hyperthyroidism

The thyroid is essential for maintaining systemic homeostasis by regulating thyroid hormone concentrations in the bloodstream. This study describes an organoid-based model system to study mouse and human thyroid biology. Moreover, the study explores the potential of human organoids for modeling autoimmune disease, the anti-TSH receptor (TSHR) antibody-driven Graves’ hyperthyroidism.

The thyroid maintains systemic homeostasis by regulating serum thyroid hormone concentrations. Here we report the establishment of three-dimensional (3D) organoids from adult thyroid tissue representing murine and human thyroid follicular cells (TFCs). The TFC organoids (TFCOs) harbor the complete machinery of hormone production as visualized by the presence of colloid in the lumen and by the presence of essential transporters and enzymes in the polarized epithelial cells that surround a central lumen. Both the established murine as human thyroid organoids express canonical thyroid markers PAX8 and NKX2.1, while the thyroid hormone precursor thyroglobulin is expressed at comparable levels to tissue. Single-cell RNA sequencing and transmission electron microscopy confirm that TFCOs phenocopy primary thyroid tissue. Thyroid hormones are readily detectable in conditioned medium of human TFCOs. We show clinically relevant responses (increased proliferation and hormone secretion) of human TFCOs toward a panel of Graves’ disease patient sera, demonstrating that organoids can model human autoimmune disease.

The Possible Role of Cancer Stem Cells in the Resistance to Kinase Inhibitors of Advanced Thyroid Cancer

Target therapy with various kinase inhibitors (KIs) has been extended to patients with advanced thyroid cancer, but only a subset of these compounds has displayed efficacy in clinical use. However, after an initial response to KIs, dramatic disease progression occurs in most cases. With the discovery of cancer stem cells (CSCs), it is possible to postulate that thyroid cancer resistance to KI therapies, both intrinsic and acquired, may be sustained by this cell subtype. Indeed, CSCs have been considered as the main drivers of metastatic activity and therapeutic resistance, because of their ability to generate heterogeneous secondary cell populations and survive treatment by remaining in a quiescent state. Hence, despite the impressive progress in understanding of the molecular basis of thyroid tumorigenesis, drug resistance is still the major challenge in advanced thyroid cancer management. In this view, definition of the role of CSCs in thyroid cancer resistance may be crucial to identifying new therapeutic targets and preventing resistance to anti-cancer treatments and tumor relapse. The aim of this review is to elucidate the possible role of CSCs in the development of resistance of advanced thyroid cancer to current anti-cancer therapies and their potential implications in the management of these patients.

Functions of stem cells of thyroid glands in health and disease

Thyroid gland has been implicated in the regulation of many functions using endocrine, paracrine and autocrine signals. Functional thyroid follicular cells derived from stem cells attracted a great interest from researchers as a strategy for thyroid's regenerative therapy. Thyroid has a very low rate of turnover; however, studies showed that the regenerative ability is enhanced following diseases or thyroidectomy, which promotes the role of stem cell. The objective of this review is to summarize the morphological characterization and the expression of stem cell genes/markers in the thyroid. Also, to highlight the mechanisms of tumor formation in thyroid via its stem cells. The most important thyroid stem cell's markers are: stem cell antigen 1 (SCA-1), octamer-binding transcription 4 (OCT-4), p63, CD34+ CD45-, paired box gene 8 (PAX-8), thyroid transcription factor 1 (TTF-1), thyroid transcription factor 2 (TTF-2), hematopoietically expressed homeobox protein HHEX, the transcription factor GATA-4, hepatocyte nuclear factor 4-α (HNF-4-α) and homeobox transcription factor Nanog (hNanog). This review highlights the functional characterization describing the mechanisms of stem cell's differentiation into functional thyroid follicle and proposing mechanisms involving in cancer formation through one of these cell types: fetal cell, thyroblasts, prothyrocytes, certain genetic mutation in the mature thyroid cells or presence of a special type of cells (cancer stem cell) which are responsible for different types of cancer formation. Understanding the mechanisms of thyroid's stem cell in cancer formation and the expression of the biomarkers in normal and abnormal thyroid status are promising physiological tools in promoting thyroid regeneration and in provision management for thyroid cancer.

Gene master regulators of papillary and anaplastic thyroid cancers

We hypothesize that distinct cell phenotypes are governed by different sets of gene master regulators (GMRs) whose strongly protected (by the homeostatic mechanisms) abundance modulates most cell processes by coordinating the expression of numerous genes from the corresponding functional pathways. Gene Commanding Height (GCH), a composite measure of gene expression control and coordination, is introduced to establish the gene hierarchy in each phenotype. If the hypothesis is true, than one can selectively destroy cancer nodules from a heterogeneous tissue by altering the expression of genes whose GCHs are high in cancer but low in normal cell phenotype. Here, we test the hypothesis and show its utility for the thyroid cancer (TC) gene therapy. First, we prove that malignant and cancer free surrounding areas of a surgically removed papillary TC (PTC) tumor are governed by different GMRs. Second, we show that stable transfection of a gene induces larger transcriptomic alterations in the cells where it has higher GCH than in other cells. For this, we profiled the transcriptomes of the papillary BCPAP and anaplastic 8505C TC cell lines before and after stable transfection with NEMP1, DDX19B, PANK2 or UBALD1. The four genes were selected to have similar expression levels but significantly different GCH scores in the two cell lines before transfection. Indeed, each of the four genes triggered larger alterations in the cells where they had larger GCH. Our results prove the feasibility of a personalized gene therapy approach that selectively targets the cancer cells from a tissue.

Upregulation of RSPO2-GPR48/LGR4 signaling in papillary thyroid carcinoma contributes to tumor progression

The signaling pathway involving the R-spondins and its cognate receptor, GPR48/LGR4, is crucial in development and carcinogenesis. However, the functional implications of the R-spondin-GPR48/LGR4 pathway in thyroid remain to be identified. The aim of this study was to investigate the role of R-spondin-GPR48/LGR4 signaling in papillary thyroid carcinomas. We retrospectively reviewed a total of 214 patients who underwent total thyroidectomy and cervical lymph node dissection for papillary thyroid carcinoma. The role of GPR48/LGR4 in proliferation and migration was examined in thyroid cancer cell lines. R-spondin 2, and GPR48/LGR4 were expressed at significantly higher levels in thyroid cancer than in normal controls. Elevated GPR48/LGR4 expression was significantly associated with tumor size (P=0.049), lymph node metastasis (P=0.004), recurrence (P=0.037), and the BRAFV600E mutation (P=0.003). Moreover, high GPR48/LGR4 expression was an independent risk factor for lymph node metastasis (P=0.027) and the BRAFV600E mutation (P=0.009). in vitro assays demonstrated that elevated expression of GPR48/LGR4 promoted proliferation and migration of thyroid cancer cells, whereas downregulation of GPR48/LGR4 decreased proliferation and migration by inhibition of the β-catenin pathway. Moreover, treatment of thyroid cancer cells with exogenous R-spondin 2 induced activation of the β-catenin pathway through GPR48/LGR4. The R-spondin 2-GPR48/LGR4 signaling axis also induced the phosphorylation of ERK, as well as phosphorylation of LRP6 and serine 9 of GSK3β. Our findings demonstrate that upregulation of the R-spondin 2-GPR48/LGR4 pathway contributes to tumor aggressiveness in papillary thyroid carcinoma by promoting ERK phosphorylation, suggesting that this pathway represents a novel therapeutic target for treatment of differentiated thyroid cancer.

Pathological processes and therapeutic advances in radioiodide refractory thyroid cancer

While in most patients with non-medullary thyroid cancer (TC), disease remission is achieved by thyroidectomy and ablation of tumor remnants by radioactive iodide (RAI), a substantial subgroup of patients with metastatic disease present tumor lesions that have acquired RAI resistance as a result of dedifferentiation. Although oncogenic mutations in BRAF, TERT promoter and TP53 are associated with an increased propensity for induction of dedifferentiation, the role of genetic and epigenetic aberrations and their effects on important intracellular signaling pathways is not yet fully elucidated. Also immune, metabolic, stemness and microRNA pathways have emerged as important determinants of TC dedifferentiation and RAI resistance. These signaling pathways have major clinical implications since their targeting could inhibit TC progression and could enable redifferentiation to restore RAI sensitivity. In this review, we discuss the current insights into the pathological processes conferring dedifferentiation and RAI resistance in TC and elaborate on novel advances in diagnostics and therapy to improve the clinical outcome of RAI-refractory TC patients.

Sonic Hedgehog Signaling in Thyroid Cancer

Thyroid cancer is the most common malignancy of the endocrine system. The initiation of thyroid cancer is often triggered by a genetic mutation in the phosphortidylinositol-3 kinase (PI3K) or mitogen-activated protein kinase (MAPK) pathway, such as RAS and BRAF, or by the rearrangement of growth factor receptor tyrosine kinase genes such as RET/PTC. The sonic hedgehog (Shh) pathway is evolutionarily conserved and plays an important role in the embryonic development of normal tissues and organs. Gene mutations in the Shh pathway are involved in basal cell carcinomas (BCC). Activation of the Shh pathway due to overexpression of the genes encoding the components of this pathway stimulates the growth and spread of a wide range of cancer types. The Shh pathway also plays an important role in cancer stem cell (CSC) self-renewal. GDC-0449 and LDE-225, two inhibitors of this pathway, have been approved for treating BCC and are being tested as a single agent or in combination with other drugs for treating various other cancers. Here, we review the recent findings on activation of the Shh pathway in thyroid cancer and its role in maintaining thyroid CSC self-renewal. We also summarize the recent developments on crosstalk of the Shh pathway with the MAPK and PI3K oncogenic pathways, and its implications for combination therapy.

Cancer stem cells as a potential therapeutic target in thyroid carcinoma

A number of studies have indicated that tumor growth and proliferation is dependent on a small subset of cells, defined as cancer stem cells (CSCs). CSCs have the capability to self-renew, and are involved with cancer propagation, relapse and metastatic dissemination. CSCs have been isolated from numerous tissues, including normal and cancerous thyroid tissue. A regulatory network of signaling pathways and microRNAs (miRNAs) control the properties of CSCs. Differentiated thyroid carcinoma is the most common type of endocrine cancer, with an increasing incidence. Anaplastic thyroid carcinoma is the most rare type of endocrine cancer; however, it also exhibits the highest mortality rate among thyroid malignancies, with an extremely short survival time. Thyroid CSCs are invasive and highly resistant to conventional therapies, including radiotherapy and chemotherapy, which results in disease relapse even when the primary lesion has been eradicated. Therefore, targeting thyroid CSCs may represent an effective treatment strategy against aggressive neoplasms, including recurrent and radioresistant tumors. The present review summarizes the current literature regarding thyroid CSCs and discusses therapeutic strategies that target these cells, with a focus on the function of self-renewal pathways and miRNAs. Elucidation of the mechanisms that regulate CSC growth and survival may improve novel therapeutic approaches for treatment-resistant thyroid cancers.

1,25 dihydroxyvitamin D3 inhibits the proliferation of thyroid cancer stem-like cells via cell cycle arrest

BACKGROUND

An anti-proliferative effect of vitamin D has been reported in different carcinomas, including thyroid cancer. Cancer stem cells (CSCs), a very small fraction of cancer cells, are widely believed to be responsible for cancer initiation, relapse and metastasis.

OBJECTIVES

We addressed the question as to whether CSCs derived from the anaplastic thyroid carcinoma cell lines SW1736, C643, HTh74 and its doxorubicin- resistant subline HTh74R are also a target of vitamin D action.

METHODS

The effect of calcitriol on growth of HTh74, HTh74R, SW1736 and C643 cell lines was investigated by cell viability assays. In stem-enriched cells derived from thyro-spheres cell cycle analysis and apoptotic assays were performed. Furthermore, the role of calcitriol in the formation of cancer thyro-spheres and its putative differentiation-inducing effect were analysed.

RESULTS

CSCs isolated as thyro-spheres from all the four anaplastic thyroid carcinoma cells expressed vitamin D receptors as did their parental cells. Calcitriol inhibited proliferation of anaplastic thyroid carcinoma cells with a more pronounced effect on doxorubicin-resistant HTh74R cells, and it significantly reduced the capacity to form stem cell-derived spheres and decreased the size of these spheres that consist of CSCs and their progenitor cells. As revealed by cell cycle analysis, calcitriol induced G2/M phase arrest in thyro-sphere cells derived cells from HTh74, HTh74R and C643 but did not affect apoptosis. Finally, calcitriol altered morphology of CSCs.

CONCLUSION

Calcitriol inhibited the growth of CSCs derived from anaplastic thyroid cancer cells. It may also exert a pro-differentiation effect in thyroid CSCs.

Generation of Novel Thyroid Cancer Stem-Like Cell Clones: Effects of Resveratrol and Valproic Acid

Anaplastic thyroid cancer is an aggressive and highly lethal cancer for which conventional therapies have proved ineffective. Cancer stem-like cells (CSCs) represent a small fraction of cells in the cancer that are resistant to chemotherapy and radiation therapy and are responsible for tumor reoccurrence and metastasis. We characterized CSCs in thyroid carcinomas and generated clones of CSC lines. Our study showed that anaplastic thyroid cancers had significantly more CSCs than well-differentiated thyroid cancers. We also showed that Aldefluor-positive cells revealed significantly higher expression of stem cell markers, self-renewal properties, thyrosphere formation, and enhanced tumorigenicity. In vivo passaging of Aldefluor-positive cells resulted in the growth of larger, more aggressive tumors. We isolated and generated two clonal spheroid CSC lines derived from anaplastic thyroid cancer that were even more enriched with stem cell markers and more tumorigenic than the freshly isolated Aldefluor-positive cells. Resveratrol and valproic acid treatment of one of the CSC lines resulted in a significant decrease in stem cell markers, Aldefluor expression, proliferation, and invasiveness, with an increase in apoptosis and thyroid differentiation markers, suggesting that these cell lines may be useful for discovering new adjuvant therapies for aggressive thyroid cancers. For the first time, we have two thyroid CSC lines that will be useful tools for the study of thyroid CSC targeted therapies.

Cancer stem-like cell behavior in anaplastic thyroid cancer: A challenging dilemma

AIMS

Anaplastic thyroid carcinoma (ATC) is an undifferentiated tumor of the thyroid which is characterized with poor prognosis, leading to its aggressive behavior and resistance to conventional therapies. Cancer stem cells (CSCs) are tumor cells that have self-renewal and clonal tumor initiation. Like other cancers, many studies have shown that ATC also has tumor cells with properties like stem cells. To evaluate the concept of cancer stem-like cell theory of ATC, we conducted this study to emphasize both on the concept of cancer stemness origin of these cells and target them for further therapeutic purposes. In the current study, we showed that two ATC cell lines, SW1736 and C643, have subpopulations (SP) that are similar to CSCs.

MATERIALS AND METHODS

Using MACS technique, cells positive for CD133 were isolated and subsequently validated with flow cytometry. For further analysis, expression of some stemness markers was evaluated.

KEY FINDINGS

ABCG2, CD133, and Sox2 were significantly up-regulated, while Nestin was down-regulated in CD133(pos) subpopulation compared to CD133(neg) cells. In contrast to previous reports that over-expression of Nestin was considered as a marker for thyroid CSCs, we noticed that expression of Nestin was declined in stem cell-like tumor cells, derived from ATC cell lines.

SIGNIFICANCE

This study reconfirmed the concept of cancer stem-like cell identity of SW1736 and C643 cells. Indeed, the characterization of CSCs should not be merely based on surface markers. Cell origin and genetic background should be additionally considered on CSCs subpopulation of ATCs for therapeutics.

Normal vs cancer thyroid stem cells: the road to transformation

Recent investigations in thyroid carcinogenesis have led to the isolation and characterisation of a subpopulation of stem-like cells, responsible for tumour initiation, progression and metastasis. Nevertheless, the cellular origin of thyroid cancer stem cells (SCs) remains unknown and it is still necessary to define the process and the target population that sustain malignant transformation of tissue-resident SCs or the reprogramming of a more differentiated cell. Here, we will critically discuss new insights into thyroid SCs as a potential source of cancer formation in light of the available information on the oncogenic role of genetic modifications that occur during thyroid cancer development. Understanding the fine mechanisms that regulate tumour transformation may provide new ground for clinical intervention in terms of prevention, diagnosis and therapy.

Expression of CD133 in differentiated thyroid cancer of young patients

AIMS

CD133 expression in cancer is frequently associated with poor outcome. Thyroid carcinomas are rare in childhood and adolescence and are associated with a higher risk of recurrence and more metastases than the adult tumours. The aim of the study was to assess whether the expression of CD133 in thyroid carcinomas of children, adolescents and young adults was correlated with clinical prognostic factors.

METHODS

Tissue microarrays were constructed with 235 tumours coming from 208 young adults with a median age of 28 years and 27 children with a median age of 13 years. An immunohistochemical study was performed with anti-CD133 antibody. CD133 expression was evaluated, using a semiquantitative score based on the percentage of positive cells. The mutation status of tumours was evaluated by reverse transcriptase PCR. Three cell lines were used to confirm CD133 expression by western blot.

RESULTS

CD133 expression was found in 43% of adult and 37% of child tumours and was confirmed by western blot in cell lines. In young adults, the expression of CD133 was significantly more frequent in patients with tumours >3 cm (p=0.04) and in patients with lymph node metastases (p=0.02). The expression of CD133 was more frequent in patients in whom the tumour presented a BRAF mutation (p=0.03).

CONCLUSIONS

CD133 expression is correlated with tumour size, lymph nodes metastases and BRAF mutations in young adults. The presence of these cancer stem cells could offer new therapeutic alternatives for aggressive thyroid cancers.

An improved protocol for mRNA quantification after fluorescence-activated cell sorting with an increased signal to noise ratio in flow cytometry

We established a method to analyze cells collected by fluorescence-activated cell sorting (FACS) named mRNA quantification after FACS (FACS-mQ), in which cells are labeled with a fluorescent dye in a manner that minimizes RNA degradation, and then cells sorted by FACS are examined by analyzing their gene expression profile. In this study, we established a modified protocol to analyze molecules with a low expression level, such as N-cadherin and thyroid transcription factor, by improving the signal to noise ratio in flow cytometry. Use of a fluorophore-conjugated second antibody and the appropriate choice of a fluorescence dye showed a marked increase in the signal to noise ratio. Use of the Can Get Signal Immunostain in diluting antibodies shortened the reaction time. In real-time reverse transcription-PCR, a significant decrease in the copy number of intracellular mRNAs was not observed after in-tube immunostaining. These results indicated that the present protocol is useful for separating and analyzing cells by FACS-mQ, targeting a molecule with a low expression level.

Bioluminescent human thyrospheres allow noninvasive detection of anaplastic thyroid cancer growth and metastases in vivo

BACKGROUND

We have previously demonstrated that thyrospheres derived from human anaplastic thyroid cancer (ATC) cell lines can reconstitute and sustain tumor growth in vivo. The aim of this study was to use luciferase-expressing thyrospheres to establish a clinically relevant mouse model of ATC that allows noninvasive and sensitive monitoring of tumor progression.

METHODS

Two human ATC cell lines stably transfected with a firefly luciferase gene were used to generate thyrospheres under stem cell culture conditions. Cells were orthotopically implanted into the thyroids of immunodeficient NOD/SCIDIl2rg-/- mice to initiate tumors. Tumor progression and metastasis were evaluated by bioluminescent imaging weekly as well as histologic analysis postmortem.

RESULTS

We show that only 100 thyrosphere cells are needed for tumor development, and that tumors can be monitored with bioluminescent imaging as early as 7-14 days after implantation. Subsequent histologic evaluation of tissue sections confirmed characteristics of high-grade malignant neoplasms.

CONCLUSIONS

This approach offers rapid and highly sensitive noninvasive detection options for the preclinical assessment of novel ATC therapeutics in vivo.

Mechanisms of therapeutic resistance in cancer (stem) cells with emphasis on thyroid cancer cells

The two main reasons for death of cancer patients, tumor recurrence and metastasis, are multi-stage cellular processes that involve increased cell plasticity and coincide with elevated resistance to anti-cancer treatments. Epithelial-to-mesenchymal transition (EMT) is a key contributor to metastasis in many cancer types, including thyroid cancer and is known to confer stem cell-like properties onto cancer cells. This review provides an overview of molecular mechanisms and factors known to contribute to cancer cell plasticity and capable of enhancing cancer cell resistance to radio- and chemotherapy. We elucidate the role of DNA repair mechanisms in contributing to therapeutic resistance, with a special emphasis on thyroid cancer. Next, we explore the emerging roles of autophagy and damage-associated molecular pattern responses in EMT and chemoresistance in tumor cells. Finally, we demonstrate how cancer cells, including thyroid cancer cells, can highjack the oncofetal nucleoprotein high-mobility group A2 to gain increased transformative cell plasticity, prevent apoptosis, and enhance metastasis of chemoresistant tumor cells.

Thyroid tumor-initiating cells: increasing evidence and opportunities for anticancer therapy (review)

Accumulating evidence supports the notion that thyroid cancer is initiated by tumor-initiating cells (TICs) (commonly known as cancer stem cells), which are thought to play a crucial role in malignant progression, therapeutic resistance and recurrence. Thyroid TICs have been isolated and identified using specific biomarkers (such as CD133), the side population, sphere formation and aldehyde dehydrogenase activity assays. Although their characteristics remain largely unknown, TICs provide an attractive cellular mechanism to explain therapeutic refractoriness. Efforts are currently being directed toward the identification of therapeutic strategies that could target these cells. The present review discusses the cellular origins of TICs and the main approaches used to isolate and identify thyroid TICs, with a focus on the remaining challenges and opportunities for anticancer therapy.

Fetal cell carcinogenesis of the thyroid: a modified theory based on recent evidence

Thyroid cancer cells were believed to be generated by multi-step carcinogenesis, in which cancer cells are derived from thyrocytes, via multiple incidences of damage to their genome, especially in oncogenes or anti-oncogenes that accelerate proliferation or foster malignant phenotypes, such as the ability to invade the surrounding tissue or metastasize to distant organs, until a new hypothesis, fetal cell carcinogenesis, was presented. In fetal cell carcinogenesis, thyroid tumor cells are assumed to be derived from three types of fetal thyroid cell which only exist in fetuses or young children, namely, thyroid stem cells (TSCs), thyroblasts and prothyrocytes, by proliferation without differentiation. Genomic alternations, such as RET/PTC and PAX8-PPARγ1 rearrangements and a mutation in the BRAF gene, play an oncogenic role by preventing thyroid fetal cells from differentiating. Fetal cell carcinogenesis effectively explains recent molecular and clinical evidence regarding thyroid cancer, including thyroid cancer initiating cells (TCICs), and it underscores the importance of identifying a stem cells and clarifying the molecular mechanism of organ development in cancer research. It introduces three important concepts, the reverse approach, stem cell crisis and mature and immature cancers. Further, it implies that analysis of a small population of cells in a cancer tissue will be a key technique in establishing future laboratory tests. In the contrary, mass analysis such as gene expression profiling, whole genomic scan, and proteomics analysis may have definite limitations since they can only provide information based on many cells.

Multiple pluripotent stem cell markers in human anaplastic thyroid cancer: the putative upstream role of SOX2

BACKGROUND

Anaplastic thyroid carcinoma (ATC) is a rare and aggressive endocrine tumor with highly undifferentiated morphology. It has been suggested that cancer stem cells (CSCs) might play a central role in ATC. The objectives of this study were (i) to characterize CSCs from ex vivo ATC specimens by investigating the expression of several pluripotent stem cell markers, and (ii) to evaluate in vitro drug resistance modifications after specific CSC transcription factor switch-off.

METHODS

In ex vivo experiments, eight formalin-fixed, paraffin-embedded ATC specimens were analyzed by reverse-transcription and real-time quantitative PCR and immunohistochemistry. In in vitro experiments using ATC SW1736 cells, the expression levels of OCT-4, NANOG, and ABCG2 and the sensitivity to either cisplatin or doxorubicin were evaluated after silencing.

RESULTS

OCT-4, KLF4, and SOX2 transcription factors and C-KIT and THY-1 stem surface antigens showed variable up-regulation in all ATC cases. The SW1736 cell line was characterized by a high percentage of stem population (10.4±2.1% of cells were aldehyde dehydrogenase positive) and high expression of several CSC markers (SOX2, OCT4, NANOG, C-MYC, and SSEA4). SOX2 silencing down-regulated OCT-4, NANOG, and ABCG2. SOX2 silencing sensitized SW1736 cells, causing a significant cell death increase (1.8-fold) in comparison to control cells with 10 μM cisplatin (93.9±3.4% vs. 52.6±9.4%, p<0.01) and 2.7 fold with 0.5 μM doxorubicin (45.8±9.9% vs. 17.1±3.4% p<0.01). ABCG2 silencing caused increased cell death with both cisplatin (74.9±1.4%) and doxorubicin treatment (74.1±0.1%) vs. no-target-treated cells (respectively, 45.8±1.0% and 48.6±1.0%, p<0.001).

CONCLUSIONS

The characterization of CSCs in ATC through the analysis of multiple pluripotent stem cell markers might be useful in identifying cells with a stem-like phenotype capable of resisting conventional chemotherapy. In addition, our data demonstrate that SOX2 switch-off through ABCG2 transporter down-regulation has a major role in overcoming CSC chemotherapy resistance.

Peri-conceptional changes in maternal exposure to sewage sludge chemicals disturbs fetal thyroid gland development in sheep

Ewes were exposed to sewage sludge-fertilized pastures in a study designed investigate pre-conceptual and/or gestational exposure to environmental chemicals. The in utero impact on fetal thyroid morphology and function at day 110 (of 145) of pregnancy was then determined. Pre-conceptual exposure increased the relative thyroid organ weights in male fetuses. The number of thyroid follicles in thyroids of fetuses after pre-conceptual or gestational exposure was reduced. This correlated with an increase in Ki67 positive cells. Pre-conceptual exposure to sewage sludge reduced small blood vessels in fetal thyroids. Thyroid tissues of exposed fetuses contained regions where mature angio-follicular units were reduced exhibiting decreased immunostaining for sodium-iodide symporter (NIS). Fetal plasma levels of fT3 and fT4 in exposed animals, however, were not different from controls suggesting compensatory changes in the thyroid gland to maintain homeostasis in exposed fetuses. The regional aberrations in thyroid morphology may impact on the post-natal life of the exposed offspring.

Stem cells and cancer stem-like cells in endocrine tissues

Cancer stem-like cells are a subpopulation of self-renewing cells that are more resistant to chemotherapy and radiation therapy than the other surrounding cancer cells. The cancer stem cell model predicts that only a subset of cancer cells possess the ability to self-renew and produce progenitor cells that can reconstitute and sustain tumor growth. Evidence supporting the existence of cancer stem-like cells in the thyroid, pituitary, and in other endocrine tissues is rapidly accumulating. These cells have been studied using specific biomarkers including: CD133, CD44, Nestin, Nanog, and aldehyde dehydrogenase enzyme. Putative cancer stem-like cells can be studied in vitro using serum-free media supplemented with basic fibroblast growth factor and epidermal growth factor grown in low attachment plates or in extracellular matrix leading to sphere formation in vitro. Cancer stem-like cells can also be separated by fluorescent cell sorting and used for in vitro or in vivo studies. Injection of enriched populations of cancer stem-like cells (also referred to as tumor initiating cells) into immunodeficient mice results in growth of xenografts which express cancer stem-like biomarkers. Human cancer stem-like cells have been identified in thyroid cancer cell lines, in primary thyroid cancers, in normal pituitary, and in pituitary tumors. Other recent studies suggest the existence of stem cells and cancer stem-like cells in endocrine tumors of the gastrointestinal tract, pancreas, lungs, adrenal, parathyroid, and skin. New discoveries in this field may lead to more effective therapies for highly aggressive and lethal endocrine cancers.

Identifying thyroid stem/progenitor cells: advances and limitations

Continuing advances in stem cell science have prompted researchers to envisage the potential application of stem cells for the management of several debilitating disorders, thus raising the expectations of transplant clinicians. In particular, in order to find a source of adult stem cells alternative to embryonic stem cells (ESCs) for the exploration of novel strategies in regenerative medicine, researchers have attempted to identify and characterise adult stem/progenitor cells resident in compact organs, since these populations appear to be responsible for physiological tissue renewal and regeneration after injury. In particular, recent studies have also reported evidence for the existence of adult stem/progenitor cell populations in both mouse and human thyroids. Here, I provide a review of published findings about ESC lines capable of generating thyroid follicular cells, thyroid somatic stem cells and cancer stem cells within the thyroid. The three subjects are analysed by also considering the criticism recently raised against their existence and potential utility. I comment specifically on the significance of resident thyroid stem cells in the developmental biology of the gland and their putative role in the pathogenesis of thyroid disorders and on the protocols employed for their identification. I finally provide my opinion on whether from basic science results obtained to date it is possible to extrapolate any convincing basic for future treatment of thyroid disorders.

Absence of the BRAF and the GRIM-19 mutations in oncocytic (Hürthle cell) solid cell nests of the thyroid

We report the first case of oncocytic solid cell nests (SCNs), found in the right lobe of the thyroid of a 70-year-old man. Conventional SCNs and 1 papillary microcarcinoma (mPTC) were also found in the left lobe. In the oncocytic SCNs, 80% of the main cells showed oncocytic cytoplasm immunoreactive for porin and proteins of the SDHB and SDHA genes. Positivity for cytokeratin 19, p63, galectin-3, and HBME-1 and negativity for thyroglobulin, thyroperoxidase, vimentin, Oct-4, and α-fetoprotein were found in oncocytic and conventional SCNs. An inverse correlation was found between oncocytic metaplasia and p63. Association with C cells was confirmed at protein and messenger RNA levels in both types of SCNs. No germinal mutation of GRIM-19 was detected. No somatic BRAF mutation was found in any of the SCNs nor in the mPTC. We conclude that SCNs may acquire mitochondrial alterations similar to those seen in follicular and C cells, as well as in their respective tumors.

Thyroid cancer susceptibility polymorphisms: confirmation of loci on chromosomes 9q22 and 14q13, validation of a recessive 8q24 locus and failure to replicate a locus on 5q24

Five single nucleotide polymorphisms (SNPs) associated with thyroid cancer (TC) risk have been reported: rs2910164 (5q24); rs6983267 (8q24); rs965513 and rs1867277 (9q22); and rs944289 (14q13). Most of these associations have not been replicated in independent populations and the combined effects of the SNPs on risk have not been examined. This study genotyped the five TC SNPs in 781 patients recruited through the TCUKIN study. Genotype data from 6122 controls were obtained from the CORGI and Wellcome Trust Case-Control Consortium studies. Significant associations were detected between TC and rs965513A (p=6.35×10(-34)), rs1867277A (p=5.90×10(-24)), rs944289T (p=6.95×10(-7)), and rs6983267G (p=0.016). rs6983267 was most strongly associated under a recessive model (P(GG vs GT + TT)=0.004), in contrast to the association of this SNP with other cancer types. However, no evidence was found of an association between rs2910164 and disease under any risk model (p>0.7). The rs1867277 association remained significant (p=0.008) after accounting for genotypes at the nearby rs965513 (p=2.3×10(-13)) and these SNPs did not tag a single high risk haplotype. The four validated TC SNPs accounted for a relatively large proportion (∼11%) of the sibling relative risk of TC, principally owing to the large effect size of rs965513 (OR 1.74).

Selenium, selenoproteins and the thyroid gland: interactions in health and disease

The trace element selenium is an essential micronutrient that is required for the biosynthesis of selenocysteine-containing selenoproteins. Most of the known selenoproteins are expressed in the thyroid gland, including some with still unknown functions. Among the well-characterized selenoproteins are the iodothyronine deiodinases, glutathione peroxidases and thioredoxin reductases, enzymes involved in thyroid hormone metabolism, regulation of redox state and protection from oxidative damage. Selenium content in selenium-sensitive tissues such as the liver, kidney or muscle and expression of nonessential selenoproteins, such as the glutathione peroxidases GPx1 and GPx3, is controlled by nutritional supply. The thyroid gland is, however, largely independent from dietary selenium intake and thyroid selenoproteins are preferentially expressed. As a consequence, no explicit effects on thyroid hormone profiles are observed in healthy individuals undergoing selenium supplementation. However, low selenium status correlates with risk of goiter and multiple nodules in European women. Some clinical studies have demonstrated that selenium-deficient patients with autoimmune thyroid disease benefit from selenium supplementation, although the data are conflicting and many parameters must still be defined. The baseline selenium status of an individual could constitute the most important parameter modifying the outcome of selenium supplementation, which might primarily disrupt self-amplifying cycles of the endocrine-immune system interface rectifying the interaction of lymphocytes with thyroid autoantigens. Selenium deficiency is likely to constitute a risk factor for a feedforward derangement of the immune system-thyroid interaction, while selenium supplementation appears to dampen the self-amplifying nature of this derailed interaction.

AUF1 and HuR: possible implications of mRNA stability in thyroid function and disorders

Abstract

RNA-binding proteins may regulate every aspect of RNA metabolism, including pre-mRNA splicing, mRNA trafficking, stability and translation of many genes. The dynamic association of these proteins with RNA defines the lifetime, cellular localization, processing and the rate at which a specific mRNA is translated. One of the pathways involved in regulating of mRNA stability is mediated by adenylate uridylate-rich element (ARE) binding proteins. These proteins are involved in processes of apoptosis, tumorigenesis and development. Out of many ARE-binding proteins, two of them AUF1 and HuR were studied most extensively and reported to regulate the mRNA stability in vivo. Our previously published data demonstrate that both proteins are involved in thyroid carcinogenesis. Several other reports postulate that mRNA binding proteins may participate in thyroid hormone actions. However, until now, exacts mechanisms and the possible role of post-transcriptional regulation and especially the role of AUF1 and HuR in those processes remain not fully understood. In this study we shortly review the possible function of both proteins in relation to development and various physiological and pathophysiological processes, including thyroid function and disorders.

Transcriptional activity of the 5'-flanking region of the thyroid transcription factor-1 gene in human thyroid cell lines

Thyroid transcription factor-1 (TTF-1, NKX2-1) is a homeodomain-containing transcriptional factor that binds to and activates the promoters of thyroid and lung-specific genes, such as thyroglobulin, thyroid peroxidase, and thyroid stimulating hormone receptor. TTF-1 is known to play a key role in the development of the thyroid. However, the precise mechanism of TTF-1 gene transcription in human thyroid cells has not been studied. The expression of transcriptional activity in various lengths of the 5'-flanking region of the human TTF -1 gene was studied in TTF-1 positive and negative human thyroid cell lines. Increased transcriptional activity was observed in thyroid cell lines containing plasmids that coded for a sequence proximal to the transcription start site of exon 1 of the TTF-1 gene. However, we did not observe any difference in promoter activity in the region up to -2.6 kb from the proximal transcription start site of the TTF-1 gene between TTF-1 positive and negative cells. These results suggest that the proximal 5'-flanking region of the human TTF -1 gene does not contain sufficient cis-active regulatory information to direct gene expression in thyroid cells, and that other cis- or trans-acting factors participate in the thyroid specific gene expression of TTF-1.

Insulin receptor isoforms and insulin-like growth factor receptor in human follicular cell precursors from papillary thyroid cancer and normal thyroid

CONTEXT

Factors involved in the biology of normal and cancer stem/precursor cells from the thyroid are unknown. Thyroid cancer cells are responsive to insulin and IGF-I and IGF-II and often overexpress the insulin receptor (IR) and the IGF-I receptor (IGF-IR).

OBJECTIVE

We investigated the role of IR isoforms (IR-A and IR-B), IGF-IR, and their ligands in thyroid follicular cell precursors both normal and malignant.

DESIGN

We established cultures of follicular cell precursors as thyrospheres from three papillary thyroid cancers and the corresponding nonaffected tissues. The expression of IR, IGF-IR, and their ligands was evaluated by quantitative RT-PCR and, in one case, also by Western blot. The effects of insulin and IGFs on thyrosphere growth and self-renewal were evaluated.

RESULTS

Thyrospheres were characterized by the expression of stem cell markers and low/absent thyroid specific markers. Thyrospheres from normal tissue, but not from cancer tissue, could be induced to differentiate. Both IR isoforms, IGF-IR, IGF-I and IGF-II, were expressed at high levels in thyrospheres and markedly decreased in differentiating cells. IR-A was the predominant isoform in thyrospheres, especially from cancer, while IR-B was predominant in differentiating cells. Cancer thyrosphere growth was stimulated by insulin and IGFs.

CONCLUSIONS

Our data suggest that IR isoforms and IGF-IR play a role in the biology of follicular thyroid precursors. Cell differentiation is associated with marked changes in the expression of these receptors and cognate ligands. These data may provide insight for future differentiation therapies in thyroid cancer.

Messenger RNA quantification after fluorescence-activated cell sorting using in situ hybridization

Recent studies using stem cells or cancer stem cells have revealed the importance of detecting minor populations of cells in blood or tissue and analyzing their biological characteristics. The only possible method for carrying out such procedures is fluorescence-activated cell sorting (FACS). However, FACS has the following two limitations. First, cells without an appropriate cell surface marker cannot be sorted. Second, some laborious procedures such as rapid sorting or treatment under sterilized conditions may require in order to analyze their biological characteristics. If a specific mRNA in a particular cell type can be stained with a florescent dye and then the cells can be sorted without causing RNA degradation, a more simple and universal method for sorting and analyzing cells with a specific gene expression pattern could be established since the biological characteristics of the sorted cells could then be determined by analyzing their gene expression profile. In this study, we established a basic protocol for messenger RNA quantification after FACS (FACS-mQ) using a cRNA probe. This method could be used for the detection and analysis of stem cells or cancer stem cells in various tissues.

Messenger RNA quantification after fluorescence activated cell sorting using intracellular antigens

Recent studies using stem cells or cancer stem cells have revealed the importance of detecting minor populations of cells in blood or tissue and analyzing their biological characteristics. The only possible method for carrying out such procedures is fluorescence activated cell sorting (FACS). However, FACS has the following limitations. First, cells without an appropriate cell surface marker cannot be sorted. Second, the cells have to be kept alive during the sorting process in order to analyze their biological characteristics. If an intracellular antigen that was specific to a particular cell type could be stained with a florescent dye and then the cells can be sorted without causing RNA degradation, a more simple and universal method for sorting and analyzing cells with a specific gene expression pattern could be established since the biological characteristics of the sorted cells could then be determined by analyzing their gene expression profile. In this study, we established a basic protocol for messenger RNA quantification after FACS (FACS-mQ) targeting intracellular antigens. This method can be used for the detection and analysis of stem cells or cancer stem cells in various tissues.

Cytotoxic chemotherapy for differentiated thyroid carcinoma

For patients with metastatic differentiated thyroid carcinoma that progresses despite standard therapies, systemic cytotoxic chemotherapy has traditionally been a limited option. Historically, phase II studies and small retrospective series have failed to identify highly effective drugs or regimens, in part by failing to recruit sufficient numbers of patients. Doxorubicin remains the single most effective cytotoxic chemotherapy for the treatment of metastatic disease, although complete responses are rare, partial responses limited and toxicity considerable. Newer agents, such as pemetrexed, may be of benefit and potentially better tolerated. Newer approaches to treatment as well as trial design and recruitment, emphasising the role of thyroid cancer patients in early drug trials, may yield advances in patient benefit.