Modulation of thyroid-specific gene expression in normal and nodular human thyroid tissues from adults: an in vivo effect of thyrotropin

Targeting the inward rectifier potassium channel 5.1 in thyroid cancer: artificial intelligence-facilitated molecular docking for drug discovery

BACKGROUND

Recurrent and metastatic thyroid cancer is more invasive and can transform to dedifferentiated thyroid cancer, thus leading to a severe decline in the 10-year survival. The thyroid-stimulating hormone receptor (TSHR) plays an important role in differentiation process. We aim to find a therapeutic target in redifferentiation strategies for thyroid cancer.

METHODS

Our study integrated the differentially expressed genes acquired from the Gene Expression Omnibus database by comparing TSHR expression levels in the Cancer Genome Atlas database. We conducted functional enrichment analysis and verified the expression of these genes by RT-PCR in 68 pairs of thyroid tumor and paratumor tissues. Artificial intelligence-enabled virtual screening was combined with the VirtualFlow platform for deep docking.

RESULTS

We identified five genes (KCNJ16, SLC26A4, TG, TPO, and SYT1) as potential cancer treatment targets. TSHR and KCNJ16 were downregulated in the thyroid tumor tissues, compared with paired normal tissues. In addition, KCNJ16 was lower in the vascular/capsular invasion group. Enrichment analyses revealed that KCNJ16 may play a significant role in cell growth and differentiation. The inward rectifier potassium channel 5.1 (Kir5.1, encoded by KCNJ16) emerged as an interesting target in thyroid cancer. Artificial intelligence-facilitated molecular docking identified Z2087256678_2, Z2211139111_1, Z2211139111_2, and PV-000592319198_1 (-7.3 kcal/mol) as the most potent commercially available molecular targeting Kir5.1.

CONCLUSION

This study may provide greater insights into the differentiation features associated with TSHR expression in thyroid cancer, and Kir5.1 may be a potential therapeutic target in the redifferentiation strategies for recurrent and metastatic thyroid cancer.

Levothyroxine suppressive therapy in differentiated thyroid cancer treatment

Levothyroxine therapy in management of diferentiated thyroid carcinoma (DTC) has been common practice for decades. Levothyroxine is being administered to patiens with DTC after total thyreoidectomy (with or without postopreative radioiodine treatment) not only to restore euthyroidism but to suppress the production of thyroid-stimulating hormone (TSH) as well because TSH is considered as a growth factor for thyroid follicular cells. However there has been a downside to this threatment recently. The main concerns are the known risks related to iatrogenic subclinical or even mild but clinicaly overt iatrogenic hyperthyroidism. Therefore individualized treatment approach aiming to balance between the risk of tumor recurence and the risks related to hypertyhroidism in view of pateints age, risk factors and comorbidities is essential. Close folow-up is therefore necessary with frequent dose adjustments according to target TSH values published in American Thyroid Association guidelines.

A Positive Feedback Loop Between DICER1 and Differentiation Transcription Factors Is Important for Thyroid Tumorigenesis

Background: DICER1 plays a central role in microRNA biogenesis and functions as a tumor suppressor in thyroid cancer, which is the most frequent endocrine malignancy with a rapidly increasing incidence. Thyroid cancer progression is associated with loss of cell differentiation and reduced expression of thyroid differentiation genes and response to thyrotropin (TSH). Here we investigated whether a molecular link exists between DICER1 and thyroid differentiation pathways. Methods: We used bioinformatic tools to search for transcription factor binding sites in the DICER1 promoter. DICER1, NKX2-1, PAX8, and CREB expression levels were evaluated by gene and protein expression in vitro and by interrogation of The Cancer Genome Atlas (TCGA) thyroid cancer data. Transcription factor binding and activity were assayed by chromatin immunoprecipitation, band-shift analysis, and promoter-reporter gene activity. Gene-silencing and overexpression approaches were used to elucidate the functional link between DICER1 and differentiation. Results: We identified binding sites for NKX2-1 and CREB within the DICER1 promoter and found that both transcription factors are functional in thyroid cells. TSH induced DICER1 expression in differentiated thyroid cells, at least in part, through the cAMP/PKA/CREB pathway. TCGA analysis revealed a significant positive correlation between CREB and DICER1 expression in human thyroid tumors. NKX2-1 overexpression increased DICER1 promoter activity and expression in vitro, and this was significantly greater in the presence of CREB and/or PAX8. Gain- and loss-of-function assays revealed that DICER1 regulates NKX2-1 expression in thyroid tumor cells and vice versa, thus establishing a positive feedback loop between both proteins. We also found a positive correlation between NKX2-1 and DICER1 expression in human thyroid tumors. DICER1 silencing decreased PAX8 expression and, importantly, the expression and activity of the sodium iodide symporter, which is essential for the diagnostic and therapeutic use of radioiodine in thyroid cancer. Conclusions: The differentiation transcription factors NKX2.1, PAX8, and CREB act in a positive feedback loop with DICER1. As the expression of these transcription factors is markedly diminished in thyroid cancer, our findings suggest that DICER1 downregulation in this cancer is mediated, at least partly, through impairment of its transcription.

Radio-Iodide Treatment: From Molecular Aspects to the Clinical View

Simple Summary

This year marks the 80th commemoration of the first time that radio-iodide treatment (RAI) was used. RAI is one of the most effective targeted internal radiation anticancer therapies ever devised and it has been used for many decades, however, a thorough understanding of the underlying molecular mechanisms involved could greatly improve the success of this therapy. This is an in-depth innovative review focusing on the molecular mechanisms underlying radio-iodide therapy in thyroid cancer and how the alteration of these mechanisms affects the results in the clinic.

Abstract

Thyroid radio-iodide therapy (RAI) is one of the oldest known and used targeted therapies. In thyroid cancer, it has been used for more than eight decades and is still being used to improve thyroid tumor treatment to eliminate remnants after thyroid surgery, and tumor metastases. Knowledge at the molecular level of the genes/proteins involved in the process has led to improvements in therapy, both from the point of view of when, how much, and how to use the therapy according to tumor type. The effectiveness of this therapy has spread into other types of targeted therapies, and this has made sodium/iodide symporter (NIS) one of the favorite theragnostic tools. Here we focus on describing the molecular mechanisms involved in radio-iodide therapy and how the alteration of these mechanisms in thyroid tumor progression affects the diagnosis and results of therapy in the clinic. We analyze basic questions when facing treatment, such as: (1) how the incorporation of radioiodine in normal, tumor, and metastatic thyroid cells occurs and how it is regulated; (2) the pros and cons of thyroid hormonal deprivation vs. recombinant human Thyroid Stimulating Hormone (rhTSH) in radioiodine residence time, treatment efficacy, thyroglobulin levels and organification, and its influence on diagnostic imaging tests and metastasis treatment; and (3) the effect of stunning and the possible causes. We discuss the possible incorporation of massive sequencing data into clinical practice, and we conclude with a socioeconomical and clinical vision of the above aspects.

Novel therapeutic options for radioiodine-refractory thyroid cancer: redifferentiation and beyond

PURPOSE OF REVIEW

Radioiodine-refractory thyroid cancers represent the main cause of thyroid cancer-related death. At present, targeted therapies with multikinase inhibitors represent a unique therapeutic tool, though they have limited benefit on patient survival and severe drug-associated adverse events. This review summarizes current treatment strategies for radioiodine-refractory thyroid cancer and focuses on novel approaches to redifferentiate thyroid cancer cells to restore responsiveness to radioiodine administration.

RECENT FINDINGS

We summarize and discuss recent clinical trial findings and early data from real-life experiences with multikinase-inhibiting drugs. Possible alternative strategies to traditional redifferentiation are also discussed.

SUMMARY

The current review focuses primarily on the major advancements in the knowledge of the pathophysiology of iodine transport and metabolism and the genetic and epigenetic alterations occurring in thyroid neoplasia as described using preclinical models. Results of clinical studies employing new compounds to induce thyroid cancer cell redifferentiation by acting against specific molecular targets are also discussed. Finally, we describe the current scenario emerging from such findings as well as future perspectives.

The Molecular Function and Clinical Role of Thyroid Stimulating Hormone Receptor in Cancer Cells

The thyroid stimulating hormone (TSH) and its cognate receptor (TSHR) are of crucial importance for thyrocytes to proliferate and exert their functions. Although TSHR is predominantly expressed in thyrocytes, several studies have revealed that functional TSHR can also be detected in many extra-thyroid tissues, such as primary ovarian and hepatic tissues as well as their corresponding malignancies. Recent advances in cancer biology further raise the possibility of utilizing TSH and/or TSHR as a therapeutic target or as an informative index to predict treatment responses in cancer patients. The TSH/TSHR cascade has been considered a pivotal modulator for carcinogenesis and/or tumor progression in these cancers. TSHR belongs to a sub-group of family A G-protein-coupled receptors (GPCRs), which activate a bundle of well-defined signaling transduction pathways to enhance cell renewal in response to external stimuli. In this review, recent findings regarding the molecular basis of TSH/TSHR functions in either thyroid or extra-thyroid tissues and the potential of directly targeting TSHR as an anticancer strategy are summarized and discussed.

Management and follow-up of differentiated thyroid cancer not submitted to radioiodine treatment: a systematic review

INTRODUCTION

The treatment of differentiated thyroid cancer (DTC) has been changing. In low (LR) and intermediate (IR) risk DTC, surgery is becoming more conservative and the usefulness of radioiodine (¹³¹I) has been questioned. An increasing number of patients are treated with lobectomy or total thyroidectomy (TTx), but without ¹³¹I. Consequently, the management and the follow-up of these patients need to be revised.

EVIDENCE ACQUISITION

We reviewed the available data about the management of these growing categories of patients. We focused on the emerging roles of the conventional tools in the follow-up [thyroglobulin (Tg), thyroglobulin antibodies (TgAb) and neck ultrasound (US)]. Moreover, we evaluated the changes in the use of levothyroxine (L-T4) therapy, and the role of the ongoing risk re-stratification.

EVIDENCE SYNTHESIS

Tg, TgAb and neck US continue to represent the cornerstone of the follow-up, however, a change in their interpretation is needed. In particular, the absolute value of Tg and TgAb lost their clinical meaning, while their trend over time acquired a greater value. At variance, the diagnostic role of neck US is becoming very relevant for the early identification of the local recurrences. In addition, L-T4 therapy should be personalized according with the type of surgery, the age of patients and their comorbidities.

CONCLUSIONS

Management of DTC treated with lobectomy or TTx but without ¹³¹I is worldwide changing. The evidences suggest that in this setting of patients with LR or IR of recurrences, a relaxed surveillance could represent the most reasonable choice.

Thyrotropin, but Not Thyroid-Stimulating Antibodies, Induces Biphasic Regulation of Gene Expression in Human Thyrocytes

Background: Thyrotropin (TSH) and thyroid-stimulating antibodies (TSAbs) activate TSH receptor (TSHR) signaling by binding to its extracellular domain. TSHR signaling has been studied extensively in animal thyrocytes and in engineered cell lines, and differences in signaling have been observed in different cell systems. We, therefore, decided to characterize and compare TSHR signaling mediated by TSH and monoclonal TSAbs in human thyrocytes in primary culture. Methods: We used quantitative reverse transcription-polymerase chain reaction to measure mRNA levels of thyroid-specific genes thyroglobulin (TG), thyroperoxidase (TPO), iodothyronine deiodinase type 2 (DIO2), sodium-iodide symporter (NIS), and TSHR after stimulation by TSH or two monoclonal TSAbs, KSAb1 and M22. We also compared secreted TG protein after TSHR activation by TSH and TSAbs using an enzyme-linked immunosorbent assay. TSHR cell surface expression was determined using fluorescence activated cell sorting (FACS). Results: We found that TSH at low doses increases and at high doses (>1 mU/mL) decreases levels of gene expression for TSHR, TG, TPO, NIS, and DIO2. The biphasic effect of TSH on signaling was not caused by downregulation of cell surface TSHRs. This bell-shaped biphasic dose-response curve has been termed an inverted U-shaped dose-response curve (IUDRC). An IUDRC was also found for TSH-induced regulation of TG secretion. In contrast, KSAb1- and M22-induced regulation of TSHR, TG, TPO, NIS, and DIO2 gene expression, and secreted TG followed a monotonic dose-response curve that plateaus at high doses of activating antibody. Conclusions: Our data demonstrate that the physiological activation of TSHRs by TSH in primary cultures of human thyrocytes is characterized by a regulatory mechanism that may inhibit thyrocyte overstimulation. In contrast, TSAbs do not exhibit biphasic regulation. Although KSAb1 and M22 may not be representative of all TSAbs found in patients with Graves' disease, we suggest that persistent robust stimulation of TSHRs by TSAbs, unrelieved by a decrease at high TSAb levels, fosters chronic stimulation of thyrocytes in Graves' hyperthyroidism.

Thyroid Hormone Supplementation Therapy for Differentiated Thyroid Cancer After Lobectomy: 5 Years of Follow-Up

Background: Lobectomy with preservation of the contralateral lobe has already become the most preferred surgical method for patients with low-risk thyroid cancer. The incidence of and risk factors for the development of hypothyroidism after lobectomy for thyroid cancer remains unclear. The previous practice of levothyroxine supplementation post-thyroidectomy, to bring about thyroid stimulating hormone (TSH) suppression, had some serious side effects. This study aimed to evaluate the incidence of hypothyroidism and to identify the factors associated with hypothyroidism requiring thyroid hormone replacement. Methods: We retrospectively reviewed the charts of 256 consecutive patients with differentiated thyroid cancer treated with lobectomy at the Gangnam Severance Hospital between April and December 2014 who were followed-up for more than 5 years. Patients were evaluated using a thyroid function test at the time of outpatient visit every 6 months for the 1st year, with an annual follow-up thereafter. Results: After 5 years, 66.0% (169) of the patients needed levothyroxine supplementation to maintain euthyroid status. The incidence of hypothyroidism requiring levothyroxine supplementation increased until 3 years but showed no significant change in the 4 and 5th year. Recurrence showed no difference between the group with and without levothyroxine supplementation. The presence of thyroiditis and preoperative TSH levels were correlated with postoperative levothyroxine supplementation to maintain euthyroid status, in univariate and multivariate analyses. Conclusion: High preoperative TSH levels and/or thyroiditis indicate a significantly increased likelihood of developing hypothyroidism requiring thyroid hormone supplementation after a thyroid lobectomy. Patients with an increased risk of postoperative hypothyroidism must be aware of their risk factors and should undergo more intensive follow-ups.

Thyroid hormone therapy in differentiated thyroid cancer

Surgery-with or without postoperative radioiodine-is the standard of care for most patients with differentiated thyroid carcinoma (DTC). Thyroid hormone replacement therapy is the mainstay of long-term medical management. Patients treated with total thyroidectomy and some who undergo lobectomy alone require thyroid hormone therapy to restore euthyroidism with normal serum thyroid-stimulating hormone (TSH) levels. Because TSH acts as a growth factor for thyroid follicular cells (including those that are neoplastic), it can potentially affect the onset and/or progression of follicular-cell derived thyroid cancer. For this reason, some patients are placed on thyroid hormone therapy at doses that suppress secretion of TSH (suppression therapy). This mini-review looks at the potential benefits and risks of this practice in patients diagnosed with DTC. Aggressive TSH-suppressive therapy is of little or no benefit to the vast majority of patients with DTC. Practice guidelines, therefore, recommend a graded algorithm in which the potential benefits of suppression are weighed against the associated cardiovascular and skeletal risks. Large randomized controlled studies are needed to confirm the presumed oncological benefits of TSH-suppression and its causal role in adverse cardiac, skeletal, and quality of life effects and to assess the efficacy of TSH normalization in reversing or reducing these effects.

Optimal Thyrotropin Suppression Therapy in Low-Risk Thyroid Cancer Patients after Lobectomy

Background: This study aimed to identify the clinical results after thyrotropin suppression therapy (TST) cessation and evaluated clinical factors associated with successful TST cessation. Methods: Patients who underwent lobectomy due to low-risk papillary thyroid carcinoma (PTC) were included in this study. We compared clinical characteristics and outcomes between patients who succeeded to stop TST and failed to stop TST. Results: A total of 363 patients were included in the study. One hundred and ninety-three patients (53.2%, 193/363) succeeded to stop TST. The independent associated factors for successful TST cessation were the preoperative thyroid-stimulating hormone (TSH) level and the maintenance period of TST. Patients with low TSH level showed a higher success rate for levothyroxine (LT4) cessation than patients with high TSH level (1.79 ± 1.08 and 2.76 ± 1.82 mU/L, p < 0.001). Patients who failed to discontinue TST showed a longer maintenance period of TST than patients who succeeded to discontinue TST (54.09 ± 17.44 and 37.58 ± 17.68 months, p < 0.001). Conclusions: Preoperative TSH level and maintenance period of TST are important factors for successful cessation of TST. If TST cessation is planned for patients who are taking LT4 after lobectomy, a higher success rate of TST cessation is expected with low preoperative TSH level and early cessation of LT4.

Association of Thyrotropin Suppression With Survival Outcomes in Patients With Intermediate- and High-Risk Differentiated Thyroid Cancer

IMPORTANCE

Suppression of thyrotropin (often referred to as thyroid-stimulating hormone, or TSH) with levothyroxine used in management of intermediate- and high-risk differentiated thyroid cancer (DTC) to reduce the likelihood of progression and death is based on conflicting evidence.

OBJECTIVE

To examine a cohort of patients with intermediate- and high-risk DTC to assess the association of thyrotropin suppression with progression-free survival (PFS) and overall survival.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used a multicenter database analysis including patients from tertiary referral centers and local clinics followed up for a mean (SD) of 7.2 (5.8) years. Patients with DTC treated uniformly with total thyroidectomy and radioactive iodine between January 1, 1979, and March 1, 2015, were included. Among the 1012 patients, 145 patients were excluded due to the lack of longitudinal thyrotropin measurements.

EXPOSURES

Levothyroxine therapy to target thyrotropin suppression with dose adjustments based on changing thyrotropin goal.

MAIN OUTCOMES AND MEASURES

The primary outcome measures were overall survival and PFS. A Cox proportional hazards model was used to assess the contribution of age, sex, tumor size, histology, and lymph node and distant metastases at landmarks 1.5, 3.0, and 5.0 years. The patients were divided into 3 groups based on mean thyrotropin score before each landmark: (1) suppressed thyrotropin, (2) moderately suppressed or low-normal thyrotropin, and (3) low-normal or elevated thyrotropin.

RESULTS

Among 867 patients (557 [64.2%] female; mean [SD] age, 48.5 [16.5] years) treated with a median (range) cumulative dose of 151 (30-1600) mCi radioactive iodine, disease progression was observed in 293 patients (33.8%), and 34 patients (3.9%) died; thus, the study was underpowered in death events. Thyrotropin suppression was not associated with improved PFS at landmarks 1.5 (P = .41), 3.0 (P = .51), and 5.0 (P = .64) years. At 1.5 and 3.0 years, older age (hazard ratio [HR], 1.06; 95% CI, 1.03-1.08 and HR, 1.05; 95% CI, 1.01-1.08, respectively), lateral neck lymph node metastases (HR, 4.64; 95% CI, 2.00-10.70 and HR, 4.02; 95% CI, 1.56-10.40, respectively), and distant metastases (HR, 7.54; 95% CI, 3.46-16.50 and HR, 7.10; 95% CI, 2.77-18.20, respectively) were independently associated with subsequent time to progression, while at 5.0 years, PFS was shorter for patients with lateral neck lymph node metastases (HR, 3.70; 95% CI, 1.16-11.90) and poorly differentiated histology (HR, 71.80; 95% CI, 9.80-526.00).

CONCLUSIONS AND RELEVANCE

Patients with intermediate- and high-risk DTC might not benefit from thyrotropin suppression. This study provides the justification for a randomized trial.

Differentiated Thyroid Carcinoma in Pediatric Age: Genetic and Clinical Scenario

Introduction: Follicular-derived differentiated thyroid carcinoma (DTC) is the most common endocrine and epithelial malignancy in children. The differences in the clinical and pathological features of pediatric vs. adult DTC could relate to a different genetic profile. Few studies are currently available in this issue, however, and most of them involved a limited number of patients and focused mainly on radiation-exposed populations. Materials and Methods: We considered 59 pediatric patients who underwent surgery for DTC between 2000 and 2017. RET/PTC rearrangement was investigated with fluorescent in situ hybridization and real-time polymerase chain reaction. Sequencing was used to analyze mutations in the BRAF, NRAS, PTEN, PIK3CA genes, and the TERT promoter. The pediatric patients' clinical and molecular features were compared with those of 178 adult patients. Results: In our pediatric sample, male gender and age <15 years coincided with more extensive disease and more frequent lymph node and distant metastases. Compared with adults, the pediatric patients were more likely to have lymph node and distant metastasis, and to need second treatments (p < 0.01). In all, 44% of the pediatric patients were found to carry molecular alterations. RET/PTC rearrangement was confirmed as the most frequent genetic alteration in childhood DTC (24.6%) and correlated with aggressive features. BRAFV600E was only identified in 16% of the pediatric DTCs, while NRASQ61R, NRASQ61K, and TERTC250T mutations were very rare. Conclusions: Pediatric DTC is more aggressive at diagnosis and more likely to recur than its adult counterpart. Unlike the adult disease, point mutations have no key genetic role.

Molecular Profiling of Follicular Variant of Papillary Thyroid Cancer Reveals Low-Risk Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features: A Paradigm Shift to Reduce Aggressive Treatment of Indolent Tumors

INTRODUCTION

Encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) has been reclassified into noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and invasive EFVPTC. NIFTP is considered a low-risk neoplasm. Therefore, follicular variant of papillary thyroid cancer (FVPTC) presently has two distinct histopathological subtypes - invasive EFVPTC and infiltrative/diffuse FVPTC. Molecular characteristics of these groups remain unclear.

METHODOLOGY

Thirty FVPTCs (10 NIFTPs, 12 invasive EFVPTCs, and 8 infiltrative/diffuse variants) were reviewed and screened for BRAF and RAS mutations by restriction fragment length morphism-polymerase chain reaction (PCR) and Sanger sequencing. The mRNA expression levels of iodine-metabolizing genes were analyzed using real-time PCR. The mutations status and mRNA expression levels were correlated with clinicopathological features.

RESULTS

All 10 NIFTPs had predominant follicular pattern. One case showed NRAS mutation, whereas none showed BRAF mutation. All invasive EFVPTC had capsular and/or lymphovascular invasion and 4/12 showed lymph node metastasis. BRAF and NRAS were seen in three cases each of invasive FVPTC. All eight infiltrating/diffuse FVPTCs showed infiltration into adjacent thyroid parenchyma and lymph node metastasis.

CONCLUSION

BRAF mutation was observed in 62.5% of cases; however, no NRAS mutation was found. Sodium iodide symporter (NIS) expressions in NIFTP were similar to that of normal thyroid tissue, whereas it was downregulated in invasive and infiltrative/diffuse FVPTC. Our study supports the argument that NIFTP can be considered as low-risk follicular thyroid neoplasm. Those tumors that harbor BRAF mutations may be offered a complete thyroidectomy because they show decreased expression of NIS gene which confers a tendency to lose radioactive iodine avidity and further recurrence of the tumor.

Aberrant Iodine Autoregulation Induces Hypothyroidism in a Mouse Strain in the Absence of Thyroid Autoimmunity

We investigated factors underlying the varying effects of a high dietary iodide intake on serum T4 levels in a wide spectrum of mouse strains, including thyroiditis-susceptible NOD.H2h4, NOD.H2k, and NOD mice, as well as other strains (BALB/c, C57BL/6, NOD.Lc7, and B10.A4R) not previously investigated. Mice were maintained for up to 8 months on control or iodide-supplemented water (NaI 0.05%). On iodized water, serum T4 was reduced in BALB/c (males and females) in association with colloid goiters but was not significantly changed in mice that developed thyroiditis, namely NOD.H2h4 (males and females) or male NOD.H2k mice. Neither goiters nor decreased T4 developed in C57BL/6, NOD, NOD.Lc7, or B10.A4R female mice. In further studies, we focused on males in the BALB/c and NOD.H2h4 strains that demonstrated a large divergence in the T4 response to excess iodide. Excess iodide ingestion increased serum TSH levels to the same extent in both strains, yet thyroidal sodium iodide symporter (NIS) messenger RNA (mRNA) levels (quantitative polymerase chain reaction) revealed greatly divergent responses. NOD.H2h4 mice that remained euthyroid displayed a physiological NIS iodine autoregulatory response, whereas NIS mRNA was inappropriately elevated in BALB/c mice that became hypothyroid. Thus, autoimmune thyroiditis-prone NOD.H2h4 mice adapted normally to a high iodide intake, presumably by escape from the Wolff-Chaikoff block. In contrast, BALB/c mice that did not spontaneously develop thyroiditis failed to escape from this block and became hypothyroid. These data in mice may provide insight into the mechanism by which iodide-induced hypothyroidism occurs in some humans without an underlying thyroid disorder.

BRAF-Oncogene-Induced Senescence and the Role of Thyroid-Stimulating Hormone Signaling in the Progression of Papillary Thyroid Carcinoma

Oncogene-induced senescence (OIS) explains the phenomenon of cellular senescence triggered by the action of oncogenes. It is a mechanism adopted by a cell to inhibit progression of benign tumors into malignancy, occurs in premalignant lesions, and is almost never present in malignant lesions. BRAF mutations occur in about 40-45% of all papillary thyroid carcinomas (PTCs) and of which 99.7% is the BRAFV600E mutation. A unique phenotype of the BRAFV600E mutation is the upregulation of the thyroid-stimulating hormone receptor (TSHR) on thyrocyte membranes. Despite the overexpression of the receptor, BRAFV600E cells undergo cell cycle arrest leading to OIS via a negative feedback signaling mechanism. A simultaneous increase in serum thyroid-stimulating hormone (TSH) in response to hypothyroidism (common in autoimmune diseases such as Hashimoto's thyroiditis) would cause senescent tumor cells to overcome OIS and proceed towards malignancy, hence showing the importance of TSH/TSHR signaling in the development of PTCs. Increase in TSH/TSHR signaling triggers an increase in levels of downstream enzymes such as manganese superoxide dismutase (MnSOD) and dual-specific phosphatase 6 (DUSP6) which eventually results in the production of oncogenic proteins such as c-Myc. Therefore, the detection of these genetic alterations as effective biomarkers for premalignant lesions of PTC is important in clinical settings and techniques such as polymerase chain reaction-mediated restriction fragment length polymorphism (PCR-RFLP) and real-time PCR can be used to detect the BRAFV600E point mutation and overexpression of TSHR, MnSOD, and DUSP6, respectively.

Temporal Changes in Thyroid Nodule Volume: Lack of Effect on Paranodular Thyroid Tissue Volume

BACKGROUND

The term "nodular goiter" has long been used to refer to a nodular thyroid gland, based on the assumption that nodule growth may be associated with hyperplasia of the surrounding non-nodular tissue. The aim of this prospective, multicenter, observational study was to determine whether nodule growth is accompanied by growth in the non-nodular tissue.

METHODS

Eight Italian thyroid-disease referral centers enrolled 992 consecutive patients with one to four benign nodules. Nodular and non-nodular thyroid tissue volumes were assessed for five years with annual ultrasound examinations.

RESULTS

In participants whose nodules remained stable (n = 839), thyroid volumes did not change (baseline 15.0 mL [confidence interval (CI) 14.5-15.6]; five-year evaluation 15.1 mL [CI 14.5-15.7]). In participants with significant growth of one or more nodule (n = 153), thyroid volumes increased and by year 5 were significantly greater than those of the former group (17.4 mL [CI 16-18.7]). In 76 individuals with unilateral nodules that grew, the mean nodular lobe volume significantly exceeded that of the contralateral lobe (8.6 mL [CI 7.4-9.8] vs. 6.7 mL [CI 6-7.4]). The unaffected lobe volumes remained stable over time, while nodular lobes grew steadily and were significantly greater at the end of follow-up (10.1 mL [CI 8.9-11.3]). Excluding the volume of the largest growing nodule in these cases, the remaining volume of the affected lobe remained virtually unchanged with respect to its baseline value. Furthermore, there was no significant difference in the non-nodular tissue volume between the unaffected lobe and the affected lobe (with the largest growing nodule volume subtracted), both at baseline and at the end of follow-up.

CONCLUSIONS

The growth of thyroid nodules is a local process, not associated with growth of the surrounding non-nodular tissue. Therefore, a normal-sized thyroid containing nodules should be referred to as a "uni- or multinodular thyroid gland" and considered a distinct entity from "uni- or multinodular goiter."

Targeting the TSH receptor in thyroid cancer

Recent advances in the arena of theranostics have necessitated a re-examining of previously established fields. The existing paradigm of therapeutic thyroid-stimulating hormone receptor (TSHR) targeting in the post-surgical management of differentiated thyroid cancer using levothyroxine and recombinant human thyroid-stimulating hormone (TSH) is well understood. However, in an era of personalized medicine, and with an increasing awareness of the risk profile of longstanding pharmacological hyperthyroidism, it is imperative clinicians understand the molecular basis and magnitude of benefit for individual patients. Furthermore, TSHR has been recently re-conceived as a selective target for residual metastatic thyroid cancer, with pilot data demonstrating effective targeting of nanoparticles to thyroid cancers using this receptor as a target. This review examines the evidence for TSHR signaling as an oncogenic pathway and assesses the evidence for ongoing TSHR expression in thyroid cancer metastases. Priorities for further research are highlighted.

Different expression of TSH receptor and NIS genes in thyroid cancer: role of epigenetics

The TSH receptor (TSHR) and sodium/iodide symporter (NIS) are key players in radioiodine-based treatment of differentiated thyroid cancers. While NIS (SLC5AS) expression is diminished/lost in most thyroid tumors, TSHR is usually preserved. To examine the mechanisms that regulate the expression of NIS and TSHR genes in thyroid tumor cells, we analyzed their expression after inhibition of ras-BRAF-MAPK and PI3K-Akt-mTOR pathways and the epigenetic control occurring at the gene promoter level in four human thyroid cancer cell lines. Quantitative real-time PCR was used to measure NIS and TSHR mRNA in thyroid cancer cell lines (TPC-1, BCPAP, WRO, and FTC-133). Western blotting was used to assess the levels of total and phosphorylated ERK and Akt. Chromatin immunoprecipitation was performed for investigating histone post-translational modifications of the TSHR and NIS genes. ERK and Akt inhibitors elicited different responses of the cells in terms of TSHR and NIS mRNA levels. Akt inhibition increased NIS transcript levels and reduced those of TSHR in FTC-133 cells but had no significant effects in BCPAP. ERK inhibition increased the expression of both genes in BCPAP cells but had no effects in FTC-133. Histone post-translational modifications observed in the basal state of the four cell lines as well as in BCPAP treated with ERK inhibitor and FTC-133 treated with Akt inhibitor show cell- and gene-specific differences. In conclusion, our data indicate that in thyroid cancer cells the expression of TSHR and NIS genes is differently controlled by multiple mechanisms, including epigenetic events elicited by major signaling pathways involved in thyroid tumorigenesis.

Nucleophosmin delocalization in thyroid tumour cells

Nucleophosmin (NPM) is a multifunctional nucleolar protein that, depending on the context, can act as oncogene or tumour suppressor. Mutations of the NPM1 gene induce delocalization of NPM in acute myeloid leukaemia. Differently, in solid tumours, only NPM overexpression, but not delocalization, has been so far reported. Here, NPM localization in thyroid tumours was investigated. By using immunohistochemistry, we show increase of NPM cytoplasmic localization in follicular adenomas and papillary carcinomas compared to normal thyroid tissue (p = 0.0125 and <0.0001, respectively). NPM1 mutations commonly found in human leukaemia are not present in thyroid tumours. Immunofluorescence in cultured cell lines was utilized to discriminate between nucleolar and nuclear localization. We show that in thyroid cancer cell lines NPM localizes both in the nucleolus and in nucleus, while in non-tumorigenic thyroid cell lines localizes only in nucleolus. Either presence of the histone deacetylase inhibitor trichostatin A or absence of thyroid-stimulating hormone induces NPM nuclear localization in non-tumorigenic thyroid cell lines.

Transcriptome, methylome and genomic variations analysis of ectopic thyroid glands

Background

Congenital hypothyroidism from thyroid dysgenesis (CHTD) is predominantly a sporadic disease characterized by defects in the differentiation, migration or growth of thyroid tissue. Of these defects, incomplete migration resulting in ectopic thyroid tissue is the most common (up to 80%). Germinal mutations in the thyroid-related transcription factors NKX2.1, FOXE1, PAX-8, and NKX2.5 have been identified in only 3% of patients with sporadic CHTD. Moreover, a survey of monozygotic twins yielded a discordance rate of 92%, suggesting that somatic events, genetic or epigenetic, probably play an important role in the etiology of CHTD.

Methodology/Principal Findings

To assess the role of somatic genetic or epigenetic processes in CHTD, we analyzed gene expression, genome-wide methylation, and structural genome variations in normal versus ectopic thyroid tissue. In total, 1011 genes were more than two-fold induced or repressed. Expression array was validated by quantitative real-time RT-PCR for 100 genes. After correction for differences in thyroid activation state, 19 genes were exclusively associated with thyroid ectopy, among which genes involved in embryonic development (e.g. TXNIP) and in the Wnt pathway (e.g. SFRP2 and FRZB) were observed. None of the thyroid related transcription factors (FOXE1, HHEX, NKX2.1, NKX2.5) showed decreased expression, whereas PAX8 expression was associated with thyroid activation state. Finally, the expression profile was independent of promoter and CpG island methylation and of structural genome variations.

Conclusions/Significance

This is the first integrative molecular analysis of ectopic thyroid tissue. Ectopic thyroids show a differential gene expression compared to that of normal thyroids, although molecular basis could not be defined. Replication of this pilot study on a larger cohort could lead to unraveling the elusive cause of defective thyroid migration during embryogenesis.

Oncogenic ras blocks the cAMP pathway and dedifferentiates thyroid cells via an impairment of pax8 transcriptional activity

A deranged differentiation is often a landmark of transformed cells. We used a thyroid cell line expressing an inducible Ras oncoprotein in order to study the hierarchy of molecular events leading to suppression of thyroid-specific gene expression. We find that, upon Ras activation, there is an immediate global down-regulation of thyroid differentiation, which is associated with an inhibition of the cAMP signaling pathway. We demonstrate that an unusual negative cross talk between Ras oncogene and the cAMP pathway induces inactivation of the transcription factor Pax8 that we propose as a crucial event in Ras-induced dedifferentiation.

Prohibitin is overexpressed in papillary thyroid carcinomas bearing the BRAF(V600E) mutation

BACKGROUND

Prohibitin (PHB) is a multifunctional protein that is localized in different intracellular sites. PHB may exert different roles in tumorigenesis, having either a permissive action on tumor growth or an oncosuppressor role, depending on the cellular context. The objective of this study was to evaluate PHB expression in normal thyroid tissues, thyroid follicular adenomas (FAs), and papillary thyroid carcinomas (PTCs).

METHODS

PHB expression was analyzed by immunohistochemistry, Western blot, and quantitative reverse transcription polymerase chain reaction (RT-PCR). Transfections in the BCPAP and TPC-1 thyroid cancer cell lines were used to evaluate the PHB promoter activity.

RESULTS

In terms of protein and mRNA levels, normal tissues from patients with serum thyrotropin (TSH) values >0.8mU/L had PHB levels that were significantly reduced compared to specimens from patients with serum TSH values <0.5mU/L, suggesting that TSH exerts an inhibitory effect on PHB expression. Consistent with this was the finding that the presence of TSH was associated with low PHB levels in normal FRTL5 thyroid cells. Immunohistochemical analysis showed relatively low and high PHB expression in FAs and PTCs, respectively. PHB mRNA and protein overexpression, as assessed by quantitative RT-PCR and Western blot, was noted only in PTCs bearing the BRAF(V600E) mutation. Notably, cell transfection experiments suggested that presence of the BRAF(V600E) mutation may be associated to increase of the PHB promoter activity.

CONCLUSIONS

PHB is overexpressed in PTCs bearing the BRAF(V600E) mutation. We postulate that the presence of the BRAF(V600E) mutation increases PHB promoter activity and therefore potentially mediates effects of this mutation on the behavior of BRAF(V600E) positive PTCs.

A molecular analysis and long-term follow-up of two siblings with severe congenital hypothyroidism carrying the IVS30+1G>T intronic thyroglobulin mutation

OBJECTIVE: To extend the molecular analysis of the IVS30+1G>T intronic thyroglobulin (TG) mutation, and to report the eleven year follow-up of the affected patients. METHOSD: Two siblings with severe congenital hypothyroidism with fetal and neonatal goiter, harboring the IVS30+1G>T mutation were included. Nodular and non-nodular thyroid tissue specimens were collected. Specific thyroid genes expression was evaluated by real-timePCR and by immunohistochemistry. RESULTS: In non-nodular tissue specific thyroid genes mRNA were reduced when compared to normal thyroid sample. In the nodule, TPO and NIS expression was very low. Microscopic examinations showed very large follicular-lumina and swollen vesicles of endoplasmatic-reticulum. Strong cytoplasmatic and low follicular-lumen TG immunostaining were detected. Intracellular NIS, membrane TPO and TSHR immunostaining had higher positivity in non-nodular sample. Both patients had a long-term adequate developmental outcome, besides one patient have been lately-treated. CONCLUSIONS: IVS30+1G>T mutation not only lead to very enlarge endoplasmatic-reticulum, but also to alterations of specific thyroid genes expression. The clinical evolution of patients harboring these mutations strengthen the concept of the influence of environment, like iodine nutrition, to determine the final phenotypic appearance.

Association of low sodium-iodide symporter messenger ribonucleic acid expression in malignant thyroid nodules with increased intracellular protein staining

CONTEXT

The expression of sodium iodide symporter (NIS) is required for iodide uptake in thyroid cells. Benign and malignant thyroid tumors have low iodide uptake. However, previous studies by RT-PCR or immunohistochemistry have shown divergent results of NIS expression in these nodules.

OBJECTIVE

The objective of the study was to investigate NIS mRNA transcript levels, compare with NIS and TSH receptor proteins expression, and localize the NIS protein in thyroid nodules samples and their surrounding nonnodular tissues (controls).

DESIGN

NIS mRNA levels, quantified by real-time RT-PCR, and NIS and TSH receptor proteins, evaluated by immunohistochemistry, were examined in surgical specimens of 12 benign and 13 malignant nodules and control samples.

RESULTS

When compared with controls, 83.3% of the benign and 100% of the malignant nodules had significantly lower NIS gene expression. Conversely, 66.7% of the benign and 100% of malignant nodules had stronger intracellular NIS immunostaining than controls. Low gene expression associated with strong intracellular immunostaining was most frequently detected in malignant (100%) than benign nodules (50%; P = 0.005). NIS protein was located at the basolateral membrane in 24% of the control samples, 8.3% of the benign, and 15.4% of the malignant nodules. The percentage of benign nodules with strong TSH receptor positivity (41.6%) was higher than malignant (7.7%).

CONCLUSION

We confirmed that reduced NIS mRNA expression in thyroid malignant nodules is associated with strong intracellular protein staining and may be related to the inability of the NIS protein to migrate to the cellular basolateral membrane. These results may explain the low iodide uptake of malignant nodules.

Notch signaling is involved in expression of thyrocyte differentiation markers and is down-regulated in thyroid tumors

CONTEXT

Notch genes encode receptors for a signaling pathway that regulates cell growth and differentiation in various contexts, but the role of Notch signaling in thyroid follicular cells has never been fully published.

OBJECTIVE

The objective of the study was to characterize the expression of Notch pathway components in thyroid follicular cells and Notch signaling activities in normal and transformed thyrocytes. DESIGN/SETTING AND PATIENTS: Expression of Notch pathway components and key markers of thyrocyte differentiation was analyzed in murine and human thyroid tissues (normal and tumoral) by quantitative RT-PCR and immunohistochemistry. The effects of Notch overexpression in human thyroid cancer cells and FTRL-5 cells were explored with analysis of gene expression, proliferation assays, and experiments involving transfection of a luciferase reporter construct containing human NIS promoter regions.

RESULTS

Notch receptors are expressed during the development of murine thyrocytes, and their expression levels parallel those of thyroid differentiation markers. Notch signaling characterized also normal adult thyrocytes and is regulated by TSH. Notch pathway components are variably expressed in human normal thyroid tissue and thyroid tumors, but expression levels are clearly reduced in undifferentiated tumors. Overexpression of Notch-1 in thyroid cancer cells restores differentiation, reduces cell growth rates, and stimulates NIS expression via a direct action on the NIS promoter.

CONCLUSION

Notch signaling is involved in the determination of thyroid cell fate and is a direct regulator of thyroid-specific gene expression. Its deregulation may contribute to the loss of differentiation associated with thyroid tumorigenesis.

Expression of hepatocyte nuclear factor-1alpha mRNA in human anaplastic thyroid cancer cell lines and tumors

BACKGROUND

Hepatocyte nuclear factor (HNF)-1alpha and HNF-1beta are related transcription factors that are mainly expressed in liver cells. Our previous study showed that HNF-1beta was highly expressed in papillary thyroid cancer cell lines and tumors. HNF-1alpha mRNA, however, was not detected in differentiated thyroid cancer cell lines. The objective of this study was to determine whether HNF-1alpha is expressed in dedifferentiated anaplastic thyroid cancer cells.

METHODS

Total RNA isolated from six anaplastic thyroid cancer cell lines and 38 surgical samples was analyzed for HNF-1alpha mRNA by conventional reverse-transcription polymerase chain reaction (RT-PCR) or real-time RT-PCR. HNF-1alpha DNA binding activity was measured by gel retardation assay and HNF-1alpha protein was identified by Western blotting.

RESULTS

HNF-1alpha mRNA was expressed in four of the six anaplastic cell lines. The presence of HNF-1alpha protein and DNA binding activity was detected in three lines with higher HNF-1alpha mRNA level. Three cell lines also expressed HNF-1beta. HNF-1alpha transcripts were also detected in five out of six anaplastic tumors, but not in the papillary tumors except one with weak PCR signal.

CONCLUSION

HNF-1alpha mRNA was detected in high frequency in anaplastic thyroid cancer cell lines and tumors. HNF-1alpha might play a role in the pathogenesis of anaplastic thyroid cancer.

Microarray analysis of thyroid stimulating hormone, insulin-like growth factor-1, and insulin-induced gene expression in FRTL-5 thyroid cells

To determine which genes are regulated by thyroid stimulating hormone (thyrotropin, TSH), insulin and insulin-like growth factor-1 (IGF-1) in the rat thyroid, we used the microarray technology and observed the changes in gene expression. The expressions of genes for bone morphogenetic protein 6, the glucagon receptor, and cyclin D1 were increased by both TSH and IGF-1; for cytochrome P450, 2c37, the expression was decreased by both. Genes for cholecystokinin, glucuronidase, beta, demethyl-Q 7, and cytochrome c oxidase, subunit VIIIa, were up-regulated; the genes for ribosomal protein L37 and ribosomal protein L4 were down-regulated by TSH and insulin. However, there was no gene observed to be regulated by all three: TSH, IGF-1, and insulin molecules studied. These findings suggest that TSH, IGF-1, and insulin stimulate different signal pathways, which can interact with one another to regulate the proliferation of thyrocytes, and thereby provide additional influence on the process of cellular proliferation.

BRAF mutations in papillary thyroid carcinomas inhibit genes involved in iodine metabolism

CONTEXT

BRAF mutations are common in papillary thyroid carcinomas (PTCs). By affecting the expression of genes critically related to the development and differentiation of thyroid cancer, they may influence the prognosis of these tumors.

OBJECTIVE

Our objective was to characterize the expression of thyroid-specific genes associated with BRAF mutation in PTCs. DESIGN/SETTING AND PATIENTS: We examined the expression of key markers of thyrocyte differentiation in 56 PTCs with BRAF mutations (BRAF-mut) and 37 with wild-type BRAF (BRAF-wt). Eight samples of normal thyroid tissue were analyzed as controls. Quantitative PCR was used to measure mRNA levels for the sodium/iodide symporter (NIS), apical iodide transporter (AIT-B), thyroglobulin (Tg), thyroperoxidase (TPO), TSH receptor (TSH-R), the transcription factor PAX8, and glucose transporter type 1 (Glut1). NIS protein expression and localization was also analyzed by immunohistochemistry.

RESULTS

mRNA levels for all thyroid-specific genes were reduced in all PTCs vs. normal thyroid tissues. NIS, AIT-B, Tg, and TPO expression was significantly lower in BRAF-mut tumors than in the BRAF-wt group. Glut-1 transcript levels were increased in all PTCs, and additional increases were noted in BRAF-mut tumors. In both tumor subsets, the NIS protein that was expressed was abnormally retained in the cytoplasm.

CONCLUSION

BRAF V600E mutation in PTCs is associated with reduced expression of key genes involved in iodine metabolism. This effect may alter the effectiveness of diagnostic and/or therapeutic use of radioiodine in BRAF-mut PTCs.

Perspectives and limitations of microarray-based gene expression profiling of thyroid tumors

Microarray technology has become a powerful tool to analyze the gene expression of tens of thousands of genes simultaneously. Microarray-based gene expression profiles are available for malignant thyroid tumors (i.e., follicular thyroid carcinoma, and papillary thyroid carcinoma), and for benign thyroid tumors (such as autonomously functioning thyroid nodules and cold thyroid nodules). In general, the two main foci of microarray investigations are improved understanding of the pathophysiology/molecular etiology of thyroid neoplasia and the detection of genetic markers that could improve the differential diagnosis of thyroid tumors. Their results revealed new features, not known from one-gene studies. Simultaneously, the increasing number of microarray analyses of different thyroid pathologies raises the demand to efficiently compare the data. However, the use of different microarray platforms complicates cross-analysis. In addition, there are other important differences between these studies: 1) some studies use intraindividual comparisons, whereas other studies perform interindividual comparisons; 2) the reference tissue is defined as strictly nonnodular healthy tissue or also contains benign lesions such as goiter, follicular adenoma, and hyperplastic nodules in some studies; and 3) the widely used Affymetrix GeneChip platform comprises several GeneChip generations that are only partially compatible. Moreover, the different studies are characterized by strong differences in data analysis methods, which vary from simple empiric filters to sophisticated statistic algorithms. Therefore, this review summarizes and compares the different published reports in the context of their study design. It also illustrates perspectives and solutions for data set integration and meta-analysis, as well as the possibilities to combine array analysis with other genetic approaches.

Defects in iodide metabolism in thyroid cancer and implications for the follow-up and treatment of patients

The two major steps of iodine metabolism--uptake and organification--are altered in thyroid cancer tissues. Organification defects result in a rapid discharge of radioiodine from thyroid cells, a short effective half-life of iodine, and a low rate of thyroid hormone synthesis. These defects are mainly due to decreased expression of functional genes encoding the sodium-iodide symporter and thyroid peroxidase and could result in a low radiation dose to thyroid cancer cells. TSH stimulation that is achieved with injections of recombinant human TSH, or long-term withdrawal of thyroid hormone treatment increases iodine-131 uptake in two-thirds of patients with metastatic disease and increases thyroglobulin production in all patients with metastases, even in the absence of detectable uptake. Serum thyroglobulin determination obtained following TSH stimulation and neck ultrasonography is the most sensitive combination for the detection of small tumor foci. Radioiodine treatment is effective when a high radiation dose can be delivered (in patients with high uptake and retention of radioiodine) and when tumor foci are sensitive to the effects of radiation therapy (younger patients, with a well-differentiated tumor and/or with small metastases). The other patients rarely respond to radioiodine treatment, and when progression occurs, other treatment modalities should be considered. Novel strategies are currently being explored to restore iodine uptake in cancer cells that are unable to concentrate radioiodine.

Nonsurgical approaches to the management of thyroid nodules

Epidemiologic studies have documented substantial increases in the frequency of nodular thyroid disease. This trend is largely due to the increasing detection of nodules by the routine use of sonography in clinical practice. Only a small percentage of the nodules currently being detected will prove to be malignant. The probability of malignancy is similar in nonpalpable and palpable nodules. Fine-needle aspiration cytology has a central role in identifying malignant nodules, which are generally treated with surgery. Most thyroid nodules are cytologically benign and can be managed nonsurgically. Nodules that are completely asymptomatic require follow-up without treatment. Cosmetic problems and/or compression-related symptoms may be indications for surgery. When surgery is contraindicated or refused, several nonsurgical approaches are available. These include levothyroxine therapy, radioiodine treatment, percutaneous ethanol injections, and the new technique of laser photocoagulation. Levothyroxine therapy is the most widely used approach, but its clinical efficacy and safety are controversial. Levothyroxine might, nonetheless, be appropriate in selected cases characterized by low risk for adverse effects and nodule characteristics associated with response to this type of therapy. Radioiodine is the therapy of choice for toxic nodules or for symptomatic nodular goiters when surgery is not possible. Percutaneous ethanol injection should be used, in our opinion, as the first-line therapy only for recurrent symptomatic cystic nodules. Laser therapy should be reserved for selected patients treated in experienced centers only. With these options, clinicians can personalize the management of nodular thyroid disease according to a careful cost-benefit analysis.