Lack of correlation for sodium iodide symporter mRNA and protein expression and analysis of sodium iodide symporter promoter methylation in benign cold thyroid nodules

Correlation of DNA methylation and lymph node metastasis in papillary thyroid carcinoma

BACKGROUND

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer with a primarily good prognosis, and its 10-year survival rate is over 90%. However, PTC is prone to early lymph node metastasis.

METHODS

Thyroid cancer tissues from PTC patients with lymphatic metastasis and normal tissues were collected for DNA methylation analysis. Different methylation sites, different methylation regions, gene-enriched pathways, and protein-protein interactions (PPIs) were analyzed.

RESULTS

There were 1004 differentially methylated sites in the PTC group versus the control group; these involved 479 hypermethylated sites in 415 related genes, 525 hypomethylated sites in 482 related genes, 64 differentially methylated regions located in the CpG island region, 34 differentially methylated genes closely related to thyroid cancer, and 17 genes with differentially methylated genes in the DNA promoter region.

CONCLUSION

NDRG4 hypermethylation and FOXO3, ZEB2, and CDK6 hypomethylation were associated with PTC lymph node metastasis.

CpG island status as an epigenetic alteration for NIS promoter in thyroid neoplasms; a cross-sectional study with a systematic review

BACKGROUND

Gene silence via methylation of the CpG islands is cancer's most common epigenetic modification. Given the highly significant role of NIS in thyroid cancer (TC) differentiation, this cross-sectional study aimed to investigate the DNA methylation pattern in seven CpG islands (CpG1-7 including +846, +918, +929, +947, +953, +955, and +963, respectively) of the NIS promoter in patients diagnosed with papillary (PTC), follicular (FTC), and multinodular goiter (MNG). Additionally, a systematic review of the literature was conducted to compare our results with studies concerning methylation of the NIS gene promoter.

METHODS

Thyroid specimens from 64 patients met the eligibility criteria, consisting of 28 PTC, 9 FTC, and 27 benign MNG cases. The mRNA of NIS was tested by qRT-PCR. The bisulfite sequencing PCR (BSP) technique was performed to evaluate the promoter methylation pattern of the NIS gene. Sequencing results were received in chromatograph, FASTA, SEQ, and pdf formats and were analyzed using Chromas. The methylation percentage at each position and for each sample was calculated by mC/(mC+C) formula for all examined CpGs; following that, the methylation percentage was also calculated at each CpG site. Besides, a literature search was conducted without restricting publication dates. Nine studies met the eligibility criteria after removing duplicates, unrelated articles, and reviews.

RESULTS

NIS mRNA levels decreased in tumoral tissues of PTC (P = 0.04) and FTC (P = 0.03) patients compared to their matched non-tumoral ones. The methylation of NIS promoter was not common in PTC samples, but it was frequent in FTC (P < 0.05). Significant differences were observed in the methylation levels in the 4th(+ 947), 6th(+ 955), and 7th(+ 963) CpGs sites in the forward strand of NIS promoter between FTC and MNG tissues (76.34 ± 3.12 vs 40.43 ± 8.42, P = 0.004, 69.63 ± 3.03 vs 23.29 ± 6.84, P = 0.001 and 50.33 ± 5.65 vs 24 ± 6.89, P = 0.030, respectively). There was no significant correlation between the expression and methylation status of NIS in PTC and FTC tissues.

CONCLUSION

Perturbation in NIS promoter's methylation individually may have a potential utility in differentiating MNG and FTC tissues. The absence of a distinct methylation pattern implies the importance of other epigenetic processes, which may alter the production of NIS mRNA. In addition, according to the reversibility of DNA methylation, it is anticipated that the design of particular targeted demethylation medicines will lead to a novel cancer therapeutic strategy.

Preliminary Study on the Sequencing of Whole Genomic Methylation and Transcriptome-Related Genes in Thyroid Carcinoma

Simple Summary

Epigenetic alterations are critical for tumor onset and development. DNA methylation is one of the most studied pathways concerning various types of cancer. A promising and exciting avenue of research is the discovery of biomarkers of early-stage malignancies for disease prevention and prognostic indicators following cancer treatment by examining the DNA methylation modification of relevant genes implicated in cancer development. We have made significant advances in the study of DNA methylation and thyroid cancer. This study is novel in that it distinguished methylation changes that occurred primarily in the gene body region of the aforementioned hypermethylated or hypomethylated thyroid cancer genes. Our findings imply that exposing whole-genome DNA methylation patterns and gene expression profiles in thyroid cancer provides new insight into the carcinogenesis of thyroid cancer, demonstrating that gene expression mediated by DNA methylation modifications may play a significant role in tumor growth.

Abstract

Thyroid carcinoma is the most prevalent endocrine cancer globally and the primary cause of cancer-related mortality. Epigenetic modifications are progressively being linked to metastasis. This study aimed to examine whole-genome DNA methylation patterns and the gene expression profiles in thyroid cancer tissue samples using a MethylationEPIC BeadChip (850K), RNA sequencing, and a targeted bisulfite sequencing assay. The results of the Illumina Infinium human methylation kit (850K) analyses identified differentially methylated CpG locations (DMPs) and differentially methylated CpG regions (DMRs) encompassing nearly the entire genome with high resolution and depth. Gene ontology and KEGG pathway analyses revealed that the genes associated with DMRs belonged to various domain-specific ontologies, including cell adhesion, molecule binding, and proliferation. The RNA-Seq study found 1627 differentially expressed genes, 1174 of which that were up-regulated and 453 of which that were down-regulated. The targeted bisulfite sequencing assay revealed that CHST2, DPP4, DUSP6, ITGA2, SLC1A5, TIAM1, TNIK, and ABTB2 methylation levels were dramatically lowered in thyroid cancer patients when compared to the controls, but GALNTL6, HTR7, SPOCD1, and GRM5 methylation levels were significantly raised. Our study revealed that the whole-genome DNA methylation patterns and gene expression profiles in thyroid cancer shed new light on the tumorigenesis of thyroid cancer.

Analysis of NIS Plasma Membrane Interactors Discloses Key Regulation by a SRC/RAC1/PAK1/PIP5K/EZRIN Pathway with Potential Implications for Radioiodine Re-Sensitization Therapy in Thyroid Cancer

The functional expression of the sodium-iodide symporter (NIS) at the membrane of differentiated thyroid cancer (DTC) cells is the cornerstone for the use of radioiodine (RAI) therapy in these malignancies. However, NIS gene expression is frequently downregulated in malignant thyroid tissue, and 30% to 50% of metastatic DTCs become refractory to RAI treatment, which dramatically decreases patient survival. Several strategies have been attempted to increase the NIS mRNA levels in refractory DTC cells, so as to re-sensitize refractory tumors to RAI. However, there are many RAI-refractory DTCs in which the NIS mRNA and protein levels are relatively abundant but only reduced levels of iodide uptake are detected, suggesting a posttranslational failure in the delivery of NIS to the plasma membrane (PM), or an impaired residency at the PM. Because little is known about the molecules and pathways regulating NIS delivery to, and residency at, the PM of thyroid cells, we here employed an intact-cell labeling/immunoprecipitation methodology to selectively purify NIS-containing macromolecular complexes from the PM. Using mass spectrometry, we characterized and compared the composition of NIS PM complexes to that of NIS complexes isolated from whole cell (WC) lysates. Applying gene ontology analysis to the obtained MS data, we found that while both the PM-NIS and WC-NIS datasets had in common a considerable number of proteins involved in vesicle transport and protein trafficking, the NIS PM complexes were particularly enriched in proteins associated with the regulation of the actin cytoskeleton. Through a systematic validation of the detected interactions by co-immunoprecipitation and Western blot, followed by the biochemical and functional characterization of the contribution of each interactor to NIS PM residency and iodide uptake, we were able to identify a pathway by which the PM localization and function of NIS depends on its binding to SRC kinase, which leads to the recruitment and activation of the small GTPase RAC1. RAC1 signals through PAK1 and PIP5K to promote ARP2/3-mediated actin polymerization, and the recruitment and binding of the actin anchoring protein EZRIN to NIS, promoting its residency and function at the PM of normal and TC cells. Besides providing novel insights into the regulation of NIS localization and function at the PM of TC cells, our results open new venues for therapeutic intervention in TC, namely the possibility of modulating abnormal SRC signaling in refractory TC from a proliferative/invasive effect to the re-sensitization of these tumors to RAI therapy by inducing NIS retention at the PM.

Translational Potential of Epigenetic-Based Markers on Fine-Needle Aspiration Thyroid Specimens

The awareness of epigenetic alterations leading to neoplasia attracted the attention of researchers toward its potential use in the management of cancer, from diagnosis to prognosis and prediction of response to therapies. Our group has focused its attention on the epigenomics of thyroid neoplasms. Although most of the epigenetic studies have been applied on histological samples, the fact is that cytology, through fine-needle aspiration, is a primary diagnostic method for many pathologies, of which thyroid nodules are one of the most paradigmatic examples. This has led to an increasing literature report of epigenetic studies using these biological samples over the past decade. In this review, our group aimed to document recent research of epigenetic alterations and its associated assessment techniques, based on cytology material. Our review covers the main epigenetic categories—DNA methylation, histone modification, and RNA-silencing—whose evidence in thyroid cytology samples may represent solid soil for future prospectively designed studies aiming at validating patterns of epigenetic alterations and their potential use in the clinical management of thyroid neoplasms.

DNA methylation in thyroid cancer

In recent years, cancer genomics has provided new insights into genetic alterations and signaling pathways involved in thyroid cancer. However, the picture of the molecular landscape is not yet complete. DNA methylation, the most widely studied epigenetic mechanism, is altered in thyroid cancer. Recent technological advances have allowed the identification of novel differentially methylated regions, methylation signatures and potential biomarkers. However, despite recent progress in cataloging methylation alterations in thyroid cancer, many questions remain unanswered. The aim of this review is to comprehensively examine the current knowledge on DNA methylation in thyroid cancer and discuss its potential clinical applications. After providing a general overview of DNA methylation and its dysregulation in cancer, we carefully describe the aberrant methylation changes in thyroid cancer and relate them to methylation patterns, global hypomethylation and gene-specific alterations. We hope this review helps to accelerate the use of the diagnostic, prognostic and therapeutic potential of DNA methylation for the benefit of thyroid cancer patients.

DNA methylation alterations as therapeutic prospects in thyroid cancer

BACKGROUND

Thyroid cancer is one of the most common endocrine malignancies. Although the 10-year survival rate of differentiated thyroid cancer (DTC) is about 90% after conventional treatments, a small proportion of patients still suffer from tumor recurrence or drug resistance.

OBJECTIVE

This review article summarizes recent researches and clinical trials related to target drugs that reduce mortality in thyroid cancer.

METHODS

This is a review of the recent literature and clinical trials on the three main aspects including methylation genes in thyroid cancers, the relationship between BRAF mutation and gene methylation, target and dehypermethylation drugs in clinical trials.

RESULTS

We propose new approaches to treating malignant thyroid cancer, based on advances in understanding the relationship between genetic and epigenetic changes in thyroid cancer. Although the effect of traditional treatment for thyroid cancer is relatively good, a small proportion of patients still suffer from tumor recurrence or drug resistance. Molecular targeted drugs and dehypermethylation drugs have more promising outcomes in aggressive thyroid cancer compared with conventional treatments.

CONCLUSION

Based on what was discussed in this review, we suggest that integration of epigenetic and targeted therapies into conventional treatments will reduce the occurrence of refractory radioiodine differentiated thyroid cancer and improve the outcomes in aggressive thyroid cancer patients.

A Carboxy-Terminal Monoleucine-Based Motif Participates in the Basolateral Targeting of the Na+/I- Symporter

The Na+/iodide (I-) symporter (NIS), a glycoprotein expressed at the basolateral plasma membrane of thyroid follicular cells, mediates I- accumulation for thyroid hormonogenesis and radioiodide therapy for differentiated thyroid carcinoma. However, differentiated thyroid tumors often exhibit lower I- transport than normal thyroid tissue (or even undetectable I- transport). Paradoxically, the majority of differentiated thyroid cancers show intracellular NIS expression, suggesting abnormal targeting to the plasma membrane. Therefore, a thorough understanding of the mechanisms that regulate NIS plasma membrane transport would have multiple implications for radioiodide therapy. In this study, we show that the intracellularly facing carboxy-terminus of NIS is required for the transport of the protein to the plasma membrane. Moreover, the carboxy-terminus contains dominant basolateral information. Using internal deletions and site-directed mutagenesis at the carboxy-terminus, we identified a highly conserved monoleucine-based sorting motif that determines NIS basolateral expression. Furthermore, in clathrin adaptor protein (AP)-1B-deficient cells, NIS sorting to the basolateral plasma membrane is compromised, causing the protein to also be expressed at the apical plasma membrane. Computer simulations suggest that the AP-1B subunit σ1 recognizes the monoleucine-based sorting motif in NIS carboxy-terminus. Although the mechanisms by which NIS is intracellularly retained in thyroid cancer remain elusive, our findings may open up avenues for identifying molecular targets that can be used to treat radioiodide-refractory thyroid tumors that express NIS intracellularly.

Implications of Na+/I- Symporter Transport to the Plasma Membrane for Thyroid Hormonogenesis and Radioiodide Therapy

Iodine is a crucial component of thyroid hormones; therefore, a key requirement for thyroid hormone biosynthesis is that iodide (I⁻) be actively accumulated in the thyroid follicular cell. The ability of the thyroid epithelia to concentrate I⁻ is ultimately dependent on functional Na⁺/ I⁻ symporter (NIS) expression at the plasma membrane. Underscoring the significance of NIS for thyroid physiology, loss-of-function mutations in the NIS-coding SLC5A5 gene cause an I⁻ transport defect, resulting in dyshormonogenic congenital hypothyroidism. Moreover, I⁻ accumulation in the thyroid cell constitutes the cornerstone for radioiodide ablation therapy for differentiated thyroid carcinoma. However, differentiated thyroid tumors often exhibit reduced (or even undetectable) I⁻ transport compared with normal thyroid tissue, and they are diagnosed as cold nodules on thyroid scintigraphy. Paradoxically, immunohistochemistry analysis revealed that cold thyroid nodules do not express NIS or express normal, or even higher NIS levels compared with adjacent normal tissue, but NIS is frequently intracellularly retained, suggesting the presence of posttranslational abnormalities in the transport of the protein to the plasma membrane. Ultimately, a thorough comprehension of the mechanisms that regulate NIS transport to the plasma membrane would have multiple implications for radioiodide therapy, opening the possibility to identify new molecular targets to treat radioiodide-refractory thyroid tumors. Therefore, in this review, we discuss the current knowledge regarding posttranslational mechanisms that regulate NIS transport to the plasma membrane under physiological and pathological conditions affecting the thyroid follicular cell, a topic of great interest in the thyroid cancer field.

Positive radionuclide imaging of miRNA expression using RILES and the human sodium iodide symporter as reporter gene is feasible and supports a protective role of miRNA-23a in response to muscular atrophy

MicroRNAs (miRNAs) are key players in many biological processes and are considered as an emerging class of pharmacology drugs for diagnosis and therapy. However to fully exploit the therapeutic potential of miRNAs, it is becoming crucial to monitor their expression pattern using medical imaging modalities. Recently, we developed a method called RILES, for RNAi-Inducible Luciferase Expression System that relies on an engineered regulatable expression system to switch-ON the expression of the luciferase gene when a miRNA of interest is expressed in cells. Here we investigated whether replacing the luciferase reporter gene with the human sodium iodide symporter (hNIS) reporter gene will be also suited to monitor the expression of miRNAs in a clinical setting context. We provide evidence that radionuclide imaging of miRNA expression using hNIS is feasible although it is not as robust as when the luciferase reporter gene is used. However, under appropriate conditions, we monitored the expression of several miRNAs in cells, in the liver and in the tibialis anterior muscle of mice undergoing muscular atrophy. We demonstrated that radiotracer accumulation in transfected cells correlated with the induction of hNIS and with the expression of miRNAs detected by real time PCR. We established the kinetic of miRNA-23a expression in mice and demonstrated that this miRNA follows a biphasic expression pattern characterized by a loss of expression at a late time point of muscular atrophy. At autopsy, we found an opposite expression pattern between miRNA-23a and one of the main transcriptional target of this miRNA, APAF-1, and as downstream target, Caspase 9. Our results report the first positive monitoring of endogenously expressed miRNAs in a nuclear medicine imaging context and support the development of additional work to establish the potential therapeutic value of miRNA-23 to prevent the damaging effects of muscular atrophy.

Hypermethylation of a New Distal Sodium/Iodide Symporter (NIS) enhancer (NDE) is associated with reduced NIS expression in thyroid tumors

CONTEXT

In thyroid tumors, reduced radioiodine uptake is associated with worse patient outcome concomitantly with low sodium/iodide symporter (NIS) mRNA expression. Previous studies showed that CpG-island methylation in the NIS proximal promoter does not correlate with mRNA expression.

OBJECTIVES

The aim of the study was to identify new CpG-islands within the NIS 5'region and investigate the involvement of their methylation in NIS expression.

DESIGN

DNA was obtained from 30 pairs of thyroid samples: tumor (T) and surrounding nontumor (NT) samples. All T samples had reduced NIS mRNA expression compared to NT samples.

MAIN OUTCOME MEASURES

Methylation degree was quantified by bisulfite sequencing, and NIS expression by real-time PCR and Western blot. Reporter gene assays were performed to determine CpG-island functionality. Tumor cell cultures were treated with 5-Aza demethylating agent to determine NIS expression, methylation status, and (125)I uptake.

RESULTS

We identified a new CpG-island2 with 14 CpG sites, located -2152/-1887 relative to ATG site. CpG-island2 was hypermethylated in T compared to NT samples, in both benign and malignant tumor groups. There was a significant inverse correlation between NIS mRNA expression and degree of CpG-island2 methylation in NT and T samples. This sequence increased the expression of a reporter gene; thus, it was considered a new enhancer. Cell culture treatments with 5-Aza reduced CpG-island2 methylation levels concomitantly with restoration of NIS mRNA and protein expression and (125)I uptake.

CONCLUSIONS

We identified a new distal enhancer, NIS distal enhancer, that regulates gene expression through DNA methylation. This enhancer is hypermethylated in T compared to NT samples and is associated with decreased NIS expression in tumors. This epigenetic deregulation may be an early event in tumorigenesis.

Genetic mutations, molecular markers and future directions in research

Recent molecular studies have described a number of abnormalities associated with the pathogenesis of thyroid carcinoma. These distinct molecular events are often associated with specific stages of tumor development and may serve as prognostic factors and therapeutic targets. A better understanding of the mechanisms involved in thyroid cancer pathogenesis, will hopefully help translate these discoveries to improved patient care.

Serum 8-OHdG and HIF-1α levels: do they affect the development of malignancy in patients with hypoactive thyroid nodules?

Aim of the study

This study aimed to evaluate 8-OHdG and hypoxia-inducible factor 1 (HIF-1α) levels in patients with hypoactive thyroid nodules (toxic multi-nodular goiter, Graves’ disease, and Hashimoto's thyroiditis), as these parameters may be related to oxidative stress and the pathogenesis of cancer.

Material and methods

The study included patients diagnosed with Graves’ disease (n = 20), toxic multinodular goiter (n = 20), and Hashimoto thyroiditis (n = 20), and 20 healthy controls. HIF-1α levels were measured in blood samples and 8-OHdG levels were measured in urine – both via ELISA.

Results

HIF-1α and 8-OHdG levels were significantly higher in the patient groups than in the control group (p < 0.05). In the Hashimoto's thyroiditis patients a correlation was observed between 8-OHdG and thyroglobulin antibodies (p = 0.03). A significant relation was found between 8-OHdG and HIF-1α in the patient group (p < 0.01). Carcinoma was detected in 7 of 43 female patients, but not in any of the male patients. No difference was observed in 8-OHdG or HIF-1α levels between the patients with and without papillary carcinoma (p > 0.05). There was no significant difference in 8-OHdG or HIF-1α levels between the patients with biopsy results that were benign, malignant, and non-diagnostic (p > 0.05).

Conclusions

Serum HIF-1α and urine 8-OHdG levels were significantly higher in the patients with thyroid diseases; however, a relationship with cancer was not observed.

5-aza-2'-deoxycytidine has minor effects on differentiation in human thyroid cancer cell lines, but modulates genes that are involved in adaptation in vitro

BACKGROUND

In thyroid cancer, the lack of response to specific treatment, for example, radioactive iodine, can be caused by a loss of differentiation characteristics of tumor cells. It is hypothesized that this loss is due to epigenetic modifications. Therefore, drugs releasing epigenetic repression have been proposed to reverse this silencing.

METHODS

We investigated which genes were reinduced in dedifferentiated human thyroid cancer cell lines when treated with the demethylating agent 5-aza-2'-deoxycytidine (5-AzadC) and the histone deacetylase inhibitors trichostatin A (TSA) and suberoylanilide hydroxamic acid, by using reverse transcriptase-polymerase chain reaction and microarrays. These results were compared to the expression patterns in in vitro human differentiated thyrocytes and in in vivo dedifferentiated thyroid cancers. In addition, the effects of 5-AzadC on DNA quantities and cell viability were investigated.

RESULTS

Among the canonical thyroid differentiation markers, most were not, or only to a minor extent, re-expressed by 5-AzadC, whether or not combined with TSA or forskolin, an inducer of differentiation in normal thyrocytes. Furthermore, 5-AzadC-modulated overall mRNA expression profiles showed only few commonly regulated genes compared to differentiated cultured primary thyrocytes. In addition, most of the commonly strongly 5-AzadC-induced genes in cell lines were either not regulated or upregulated in anaplastic thyroid carcinomas. Further analysis of which genes were induced by 5-AzadC showed that they were involved in pathways such as apoptosis, antigen presentation, defense response, and cell migration. A number of these genes had similar expression responses in 5-AzadC-treated nonthyroid cell lines.

CONCLUSIONS

Our results suggest that 5-AzadC is not a strong inducer of differentiation in thyroid cancer cell lines. Under the studied conditions and with the model used, 5-AzadC treatment does not appear to be a potential redifferentiation treatment for dedifferentiated thyroid cancer. However, this may reflect primarily the inadequacy of the model rather than that of the treatment. Moreover, the observation that 5-AzadC negatively affected cell viability in cell lines could still suggest a therapeutic opportunity. Some of the genes that were modulated by 5-AzadC were also induced in nonthyroid cancer cell lines, which might be explained by an epigenetic modification resulting in the adaptation of the cell lines to their culture conditions.

Methylation levels of sodium-iodide symporter (NIS) promoter in benign and malignant thyroid tumors with reduced NIS expression

DNA methylation regulates gene expression. Aberrant methylation plays an important role in human tumorigenesis. We have previously detected reduced NIS mRNA expression in thyroid tumors as compared to non-tumor tissues. Thus, in this study we investigated whether the methylation of the CpG-island located in the NIS gene promoter was associated with reduced mRNA expression in thyroid tumors. Methylation levels of 30 pairs of samples from 10 benign and 20 malignant thyroid tumors (T) along with matched non-tumor (NT) areas were determined by semiquantitative methylation specific-PCR. NIS methylation was detected in all samples. Methylation levels and frequencies did not differ between the groups and were not associated with BRAF mutational status. Highest methylation levels and frequencies were detected in the 5' region of the CpG-island decreasing toward the 3' end. Intraindividual analysis (T versus NT) showed high tumor methylation levels in 40 % of the samples in the benign group and 30 % in the malignant group, associated with low NIS mRNA expression. No quantitative correlation was detected between methylation levels and mRNA expression in any the groups. The results of this study showed that methylation of NIS promoter is a very frequent event in both benign and malignant tumors as well as in their surrounding tissues, and characterized a non-homogeneous methylation pattern along the CpG island. Therefore, further investigations involving other sites that may be implicated in methylation regulation of NIS expression are warranted.

Inverse correlation of miRNA and cell cycle-associated genes suggests influence of miRNA on benign thyroid nodule tumorigenesis

CONTEXT

The molecular etiology of cold and benign thyroid nodules (CBTNs) is largely unknown. Increased thyroid epithelial cell proliferation is a hallmark of CBTNs. MicroRNAs (miRNAs) are prominent regulators of cell proliferation.

OBJECTIVE

Our objective was to assess the influence of miRNAs on the increased proliferation and thus the molecular etiology of CBTNs.

DESIGN

By using microarrays, we defined the molecular pattern of increased proliferation of CBTNs as a differential expression of cell-cycle-associated genes and miRNAs. In silico integration of differentially expressed miRNAs and mRNAs showed an inverse correlation between the expression of 59 miRNAs and 133 mRNAs. Inverse correlations between cell-cycle-associated genes such as CDKN1C and miR-221, CCND1 and miR-31, GADD45A and miR-130b, or CDKN1A and let-7f suggest a modulation of proliferation in CBTNs by miRNAs. Their expression was validated using quantitative RT-PCR and functionally characterized in cell line models.

RESULTS

Comparative quantitative RT-PCR of 20 samples of CBTNs and their surrounding tissue revealed an 11-fold down-regulation of miR-31 with a 2.6-fold up-regulation of CCND1, and a 2.6-fold up-regulation of miR-130b with a 2.3-fold down-regulation of its target GADD45A. Using HTori and FTC-133 cell lines, we analyzed proliferation, cell cycle, and apoptosis after transfection of miRNA-31 and miRNA-130b mimic and inhibitors. Overexpression of miR-31 and the resultant down-regulation of CCND1 led to an arrest in the cell cycle phase G1. Overexpression of miR-130b led to an increase of apoptosis and necrosis within 72 h.

CONCLUSION

miR-31 and miR-130b may have an effect on tumorigenesis of CBTNs by regulating proliferation and apoptosis and the cell cycle through cyclin D1.

Global analysis of viral infection in an archaeal model system

The origin and evolutionary relationship of viruses is poorly understood. This makes archaeal virus-host systems of particular interest because the hosts generally root near the base of phylogenetic trees, while some of the viruses have clear structural similarities to those that infect prokaryotic and eukaryotic cells. Despite the advantageous position for use in evolutionary studies, little is known about archaeal viruses or how they interact with their hosts, compared to viruses of bacteria and eukaryotes. In addition, many archaeal viruses have been isolated from extreme environments and present a unique opportunity for elucidating factors that are important for existence at the extremes. In this article we focus on virus-host interactions using a proteomics approach to study Sulfolobus Turreted Icosahedral Virus (STIV) infection of Sulfolobus solfataricus P2. Using cultures grown from the ATCC cell stock, a single cycle of STIV infection was sampled six times over a 72 h period. More than 700 proteins were identified throughout the course of the experiments. Seventy one host proteins were found to change their concentration by nearly twofold (p < 0.05) with 40 becoming more abundant and 31 less abundant. The modulated proteins represent 30 different cell pathways and 14 clusters of orthologous groups. 2D gel analysis showed that changes in post-translational modifications were a common feature of the affected proteins. The results from these studies showed that the prokaryotic antiviral adaptive immune system CRISPR-associated proteins (CAS proteins) were regulated in response to the virus infection. It was found that regulated proteins come from mRNAs with a shorter than average half-life. In addition, activity-based protein profiling (ABPP) profiling on 2D-gels showed caspase, hydrolase, and tyrosine phosphatase enzyme activity labeling at the protein isoform level. Together, this data provides a more detailed global view of archaeal cellular responses to viral infection, demonstrates the power of quantitative two-dimensional differential gel electrophoresis and ABPP using 2D gel compatible fluorescent dyes.

Use of sodium iodide symporter expression in differentiated thyroid carcinomas

OBJECTIVE

We aimed to investigate the use of NIS mRNA and protein expression as a diagnostic and/or prognostic marker in patients with differentiated thyroid cancer (DTC).

DESIGN

This is a case-control study.

PATIENTS

We studied 397 thyroid nodules tissue samples, including 224 papillary thyroid carcinomas (PTCs), 41 follicular carcinomas, 58 nodular goiters, 56 follicular adenomas and 18 normal tissues assembled in a tissue microarray.

MEASUREMENTS

NIS protein was identified using a monoclonal antibody that labelled only the follicular cell basolateral membrane of all 397 tissue samples. In addition, NIS mRNA was quantified in 145 DTC patients and 85 PTC cases were screened for BRAF(V600E) mutation.

RESULTS

We found low NIS mRNA expression and low or negative NIS protein expression in most DTC. NIS expression was lower in DTC patients over 45 years old and in tumours larger than 2 cm. There was a tendency for lower NIS expression in advanced stages and patients presenting recurrences. All 13 DTC patients who succumbed to the disease were NIS negative at immunohistochemistry and had very low mRNA expression. NIS expression was lower in PTC presenting BRAF(V600E) mutation. However, neither NIS immunohistochemical analysis nor NIS mRNA quantified expression could identify individuals with poor prognosis.

CONCLUSIONS

Our data suggest that NIS expression may help characterize patients' risk and individuals with a poor response to therapy, but is not useful as a diagnostic or prognostic marker, reinforcing the current concept that an appropriate management of DTC patient is the most important and modifiable prognostic factor.

Muc-1 expression may help characterize thyroid nodules but does not predict patients' outcome

Our purpose was to evaluate MUC1 clinical utility in the diagnosis and prognosis of thyroid cancer patients. We studied the protein expression of MUC1 in 289 thyroid carcinomas and 121 noncancerous thyroid nodules. There were 41 follicular carcinomas (FC) and 248 papillary thyroid carcinomas (PTC) including 149 classic (CPTC), 20 tall cell (TCPTC) and 79 follicular variants (FVPTC). In addition, we used a quantitative real-time PCR (q-PCR) method to measure MUC1 mRNA expression levels in 108 carcinomas, 23 hyperplasias, and 19 FA. According to their serum Tg levels and other evidences of recurrence/metastasis, the patients were classified as free-of-disease (185 cases) or bad outcome (56 cases, 10 deaths). MUC1 protein was identified in 80.2% PTC; 48.8% FC; 68.3% FVPTC; 70% TCPTC; 21.8% FA; 30% hyperplasias and 6% normal thyroid tissues. MUC1 distinguished benign from malignant thyroid tissues (sensitivity = 89%; specificity = 53%). MUC1 also differentiated FC from FA (p = 0.0083). q-PCR mRNA expression of MUC1 also distinguished malignant from benign nodules (Mann-Whitney test, p < 0.0001). However, neither IHC nor mRNA MUC1 expression was associated with any clinical or pathological feature of aggressiveness or outcome. We suggest that MUC1 expression may help differentiate follicular patterned thyroid lesions.

The biology of the sodium iodide symporter and its potential for targeted gene delivery

The sodium iodide symporter (NIS) is responsible for thyroidal, salivary, gastric, intestinal and mammary iodide uptake. It was first cloned from the rat in 1996 and shortly thereafter from human and mouse tissue. In the intervening years, we have learned a great deal about the biology of NIS. Detailed knowledge of its genomic structure, transcriptional and post-transcriptional regulation and pharmacological modulation has underpinned the selection of NIS as an exciting approach for targeted gene delivery. A number of in vitro and in vivo studies have demonstrated the potential of using NIS gene therapy as a means of delivering highly conformal radiation doses selectively to tumours. This strategy is particularly attractive because it can be used with both diagnostic (99mTc, 125I, 124I)) and therapeutic (131I, 186Re, 188Re, 211At) radioisotopes and it lends itself to incorporation with standard treatment modalities, such as radiotherapy or chemoradiotherapy. In this article, we review the biology of NIS and discuss its development for gene therapy.

Potential utility and limitations of thyroid cancer cell lines as models for studying thyroid cancer

BACKGROUND

Tumor-derived cell lines are widely used to study the mechanisms involved in thyroid carcinogenesis but recent studies have reported redundancy among thyroid cancer cell lines and identification of some "thyroid cell lines" that are likely not of thyroid origin.

SUMMARY

In this review, we have summarized the uses, the limitations, and the existing problems associated with the available follicular cell-derived thyroid cancer cell lines. There are some limitations to the use of cell lines as a model to "mimic" in vivo tumors. Based on the gene expression profiles of thyroid cell lines originating from tumors of different types it has become apparent that some of the cell lines are closely related to each other and to those of undifferentiated carcinomas. Further, many cell lines have lost the expression of thyroid-specific genes and have altered karyotypes, while they exhibit activation of several oncogenes (BRAF, v-raf murine sarcoma viral oncogene homolog B1; RAS, rat sarcoma; and RET/PTC, rearranged in transformation/papillary thyroid carcinoma) and inactivation of tumor suppressor gene (TP53) which is known to be important for thyroid tumorigenesis.

CONCLUSIONS

A careful selection of thyroid cancer cell lines that reflect the major characteristics of a particular type of thyroid cancer being investigated could be used as a good model system to analyze the signaling pathways that may be important in thyroid carcinogenesis. Further, the review of literature also suggests that some of the limitations can be overcome by using multiple cell lines derived from the same type of tumor.

Epigenetic silencing of TTF-1/NKX2-1 through DNA hypermethylation and histone H3 modulation in thyroid carcinomas

Thyroid transcription factor-1 (TTF-1), also known as NKX2-1, is a homeodomain containing transcriptional factor identified in thyroid, lung and central nervous system. In the thyroid, TTF-1 is essential for thyroid organogenesis and governs thyroid functions by regulating various thyroid-specific genes. We previously demonstrated that most differentiated thyroid neoplasms, including follicular adenomas/carcinomas and papillary carcinomas, express TTF-1 at both protein and mRNA levels. However, certain subtypes of thyroid cancers have shown low or negative expression of TTF-1. The aim of our study was to investigate the function of epigenetic modification in dysregulation of TTF-1 in thyroid carcinoma cells. We evaluated the expression of TTF-1 in primary thyroid tissues (normal thyroid, papillary carcinoma and undifferentiated carcinoma) and in thyroid carcinoma cell lines using immunohistochemistry and RT-PCR. Methylation-specific PCR targeting CpG islands of TTF-1 and chromatin immunoprecipitation (ChIP) for histone H3 lysine 9 (H3-lys9) were applied to clarify the correlation of the TTF-1 expression profile and epigenetic status. We also explored whether epigenetic modifiers, including 5-aza-deoxycytidine, could restore TTF-1 expression in thyroid carcinoma cells. In our current study, immunohistochemistry and RT-PCR showed positive expression of TTF-1 in normal thyroids and papillary carcinomas. Meanwhile, most of the undifferentiated carcinomas and the cell lines lost TTF-1 expression. No methylation in the CpG of TTF-1 promoter was detected in normal thyroids or papillary carcinomas. In contrast, DNA methylation was identified in 60% of the undifferentiated carcinomas (6/10) and 50% of the cell lines (4/8). ChIP assay demonstrated that acetylation of H3-lys9 was positively correlated with TTF-1 expression in thyroid carcinoma cells. Finally, DNA demethylating agents could restore TTF-1 gene expression in the thyroid carcinoma cell lines. Our data suggest that epigenetics is involved with inactivation of TTF-1 in thyroid carcinomas, and provide a possible means of using TTF-1 as a target for differentiation-inducing therapy through epigenetic modification.

Influence of signal transducer and activator of transcription-1 signaling on thyroid morphology and function

Interferon (IFN)-gamma has been involved in the pathogenesis of Hashimoto thyroiditis. It is a cytokine released by infiltrating mononuclear cells that mediates its actions mainly through signal transducer and activator of transcription-1 (STAT1) but also through other transcription factors. To dissect the effect of IFN gamma on thyroid morphology and function, we crossed transgenic mice that express IFN gamma specifically in the thyroid gland to mice deficient in STAT1. Lack of STAT1 ameliorated the abnormal thyroid morphology and the primary hypothyroidism typical of IFN gamma transgenic mice but not the suppressed iodine accumulation. Interestingly, lack of STAT1 alone decreased iodine accumulation, seemingly through expression of TGFbeta. These results indicate that STAT1 is required to mediate some but not all of the phenotypic changes induced by IFN gamma and that it also regulates iodine accumulation via TGFbeta signaling.

Perspectives for improved and more accurate classification of thyroid epithelial tumors

CONTEXT

Histologic examination of thyroid nodules is the current standard to distinguish benign from malignant thyroid epithelial tumors and to classify histologic subtypes. This review analyzes the problems in histological differential diagnosis as well as contradictions between histology and molecular data and describes possibilities to combine histology with molecular data in an effort to more accurately classify thyroid epithelial tumors.

EVIDENCE ACQUISITION

Published literature, addressing the current recommendations for thyroid tumor classification, as well as literature on the application of histology and molecular studies on the etiology of thyroid tumors is analyzed.

EVIDENCE SYNTHESIS

The current histologic criteria to classify thyroid tumors, especially follicular-patterned tumors, are hampered by considerable interobserver variability. The detection of somatic mutations via genotyping and the definition of potentially informative gene expression signatures by microarray analyses, which can distinguish cancer subtypes as well as low- and high-risk cohorts, have recently demonstrated significant diagnostic potential. Moreover, in a routine diagnostic setting, micro-RNA profiling appears most promising due to their relative stability and the high accuracy of their expression profiles.

CONCLUSIONS

It is very likely that molecular definitions of thyroid tumors mentioned in the current World Health Organization classification will be further developed, leading to future progress in defining thyroid tumor types by an integrated histologic and molecular approach. These integrated classifications need to be evaluated for their specific impact on thyroid tumor diagnosis and prognosis.

Epigenetic dysregulation in thyroid neoplasia

Gain-of-function mutations in oncogenes have aided our understanding of the molecular mechanisms of thyroid carcinogenesis. Mutations or deletions cause inactivation of tumor suppressor genes in thyroid carcinomas. However, recent advances have disclosed the significance of epigenetic events in the development and progression of human tumorigenesis. Indeed, various tumor-suppressor genes and thyroid hormone-related genes are epigenetically silenced in thyroid tumors. This article reviews the evidence for epigenetic gene dysregulation in follicular cell-derived thyroid carcinomas including papillary thyroid carcinoma, follicular thyroid carcinoma, and undifferentiated thyroid carcinoma. The authors also discuss future applications of epigenetics as ancillary diagnostic tools and in the design of targeted therapies for thyroid cancer.

Increased iodine uptake in thyroid carcinoma after treatment with sodium butyrate and decitabine (5-Aza-dC)

OBJECTIVE

To determine if epigenetic-modifying drugs can increase iodine uptake in thyroid carcinoma cell lines.

STUDY DESIGN

Human thyroid carcinoma cell lines were tested for iodine uptake before and after treatment with epigenetic-modifying agents.

RESULTS

Thyroid carcinoma cell lines DRO and 2-7 had high levels of DNA methylation (74% and 80%) compared with normal thyroid tissue (6%) (P < 0.05). This finding correlated with low levels of sodium iodide symporter (NIS) expression in the untreated thyroid carcinoma cell line. Combination treatment with the epigenetic-modifying agents 5-aza-2'-deoxycytidine and sodium butyrate resulted in increases in NIS messenger RNA levels, global histone acetylation, and 9- and 8-fold increases in I(125) uptake for the DRO and 2-7 cells, respectively.

CONCLUSIONS

Epigenetic-modifier drugs represent a novel adjuvant treatment for those patients with radioablation-resistant thyroid cancer.

SIGNIFICANCE

Epigenetic-modifying agents show potential for treatment of radioablation-resistant thyroid cancer.

Insights from molecular pathways: potential pharmacologic targets of benign thyroid nodules

PURPOSE OF REVIEW

To describe molecular pathways that might be of relevance for a potential pharmacologic therapy of benign thyroid nodules.

RECENT FINDINGS

Constitutively activating thyrotropin receptor mutations have been found in about 60% of hot nodules. Its predominant role for signaling in hot nodules has been confirmed by in-vitro mutagenesis studies, thyrotropin receptor modeling and microarray studies. In contrast, the basic molecular cause of cold thyroid nodules is so far largely unknown. Defective sodium/iodide symporter trafficking, accumulation of T4-deficient, insufficiently iodinated thyroglobulin, increased oxidative stress and differential expression of several Gqalpha-protein kinase C pathway-associated genes have, however, recently been identified in cold thyroid nodules.

SUMMARY

As disturbed thyrotropin receptor signaling plays a central role in hot thyroid nodules, the identification of effective low-molecular-weight thyrotropin receptor ligands, such as thyrotropin receptor agonists, inverse agonists and antagonists has a pharmacologic potential in the diagnosis and treatment of thyroid cancer, Graves' disease and hot thyroid nodules, respectively. Further studies have to clarify the pharmacologic potential of the enhancement of antioxidative mechanisms and the inhibition of Gqalpha-protein kinase C signaling in cold thyroid nodules.

Proteomic profiling of cold thyroid nodules

Cold thyroid nodules (CTNs) represent a frequent endocrine disorder accounting for up to 85% of thyroid nodules in a population living in an iodine-deficient area. Benign CTNs need to be distinguished from thyroid cancer, which is relatively rare. The molecular etiology of benign CTNs is unresolved. To obtain novel insights into their pathogenesis, protein expression profiling was performed in a series of 27 solitary CTNs (10 follicular adenoma and 20 adenomatous nodules) and surrounding normal thyroid tissues using two-dimensional gel electrophoresis combined with mass spectrometry analysis, Western blotting, and immunohistochemistry. The proteome analysis revealed a specific fingerprint of CTNs with up-regulation of three functional systems: 1) thyroid cell proliferation, 2) turnover of thyroglobulin, and 3) H2O2 detoxification. Western blot analysis and immunohistochemistry confirmed the proteome data and showed that CTNs exhibit significant up-regulation of proteins involved in thyroid hormone synthesis yet are deficient in T4-containing thyroglobulin. This is consequential to intranodular iodide deficiency, mainly due to cytoplasmic sodium iodide symporter localization, and portrays the CTN as an activated proliferating lesion with an intranodular hypothyroid milieu. Furthermore, we provide preliminary evidence that up-regulation of H2O2 generation in CTNs could override the antioxidative system resulting in oxidative stress, which is suggested by the finding of raised 8-oxo-guanidine DNA adduct formation in CTNs.

Gene methylation in thyroid tumorigenesis

Aberrant gene methylation plays an important role in human tumorigenesis, including thyroid tumorigenesis. Many tumor suppressor genes are aberrantly methylated in thyroid cancer, and some even in benign thyroid tumors, suggesting a role of this epigenetic event in early thyroid tumorigenesis. Methylation of some of these genes tends to occur in certain types of thyroid cancer and is related to specific signaling pathways. For example, methylation of PTEN and RASSF1A genes occurs mostly in follicular thyroid cancer, and its tumorigenic role may be related to the phosphatidylinositol 3-kinase/Akt signaling pathway, whereas methylation of genes for tissue inhibitor of metalloproteinase-3, SLC5A8, and death-associated protein kinase occurs in papillary thyroid cancer and is related to the BRAF/MAPK kinase/MAPK pathway. Methylation of thyroid-specific genes, such as those for sodium/iodide symporter and thyroid-stimulating hormone receptor, is also common in thyroid cancer. Although its tumorigenic role is not clear, methylation, and hence silencing, of these thyroid-specific genes is a cause for the failure of clinical radioiodine treatment of thyroid cancer. Unlike gene methylation, histone modifications have been relatively poorly investigated in thyroid tumors. Future studies need to emphasize the mechanistic aspects of these two types of epigenetic alterations to uncover new molecular mechanisms in thyroid tumorigenesis and to provide novel therapeutic targets for thyroid cancer.

Neuropeptide B and W: neurotransmitters in an emerging G-protein-coupled receptor system

Deorphanised G-protein-coupled receptors represent new and expanding targets for drug development. Neuropeptide B (NPB) and W (NPW) have recently been identified as the cognate endogenous ligands for the orphan receptor GPR7, now designated as NPBW(1). NPB and NPW also bound to a second related orphan receptor, GPR8, now designated as NPBW(2) that is present in humans but not rats or mice. In humans, high levels of NPW mRNA have been visualised in the substantia nigra, whereas moderate expression levels have been detected in the amygdala and hippocampus. In peripheral tissues, expression of NPW mRNA has been confirmed in the progenital system, comprising the kidney, testis, uterus, ovary and placenta, and also in stomach homogenates. Immunocytochemical, molecular biological and autoradiography techniques have revealed a discrete CNS distribution for NPBW(1) in human, mouse and rat. Highest expression of NPBW(1) mRNA and protein was identified in the amygdala and hypothalamic nuclei known to regulate feeding behaviour. [(125)I]-NPW bound with a single high affinity to rat amygdala, K(D)=0.44 nM and 150 fmol mg(-1) protein. Physiological studies demonstrate that intracerebroventricular infusion of NPBW(1) ligands modulates feeding behaviour, regulates the release of corticosterone, prolactin and growth hormone while also manipulating pain pathway. Mouse knockout models of the gene encoding either NPB or NPBW(1) have a gender-specific phenotype, with moderate obesity evident in males but not females. Further investigation is required to elucidate the precise physiological role of NPB and NPW as neurotransmitters.

CpG island methylation of tumor-related promoters occurs preferentially in undifferentiated carcinoma

OBJECTIVE

To understand the role of epigenetic inactivation of tumor-related genes in the pathogenesis of thyroid cancer, we investigated the methylation profile of distinct thyroid neoplasms.

DESIGN

We analyzed the methylation pattern of 17 gene promoters in nine thyroid cancer cell lines and in 38 primary thyroid carcinomas (13 papillary thyroid carcinoma [PTC], 10 follicular thyroid carcinoma [FTC], 9 undifferentiated thyroid carcinoma [UTC], 6 medullary thyroid carcinoma [MTC]), 12 goiters, and 10 follicular adenomas (FA) by methylation- specific polymerase chain reaction (PCR). Epigenetic inactivation was validated by expression analysis.

MAIN OUTCOME

Twelve of these genes (RASSF1A, p16(INK4A), TSHR, MGMT, DAPK, ERalpha, ERbeta, RARbeta, PTEN, CD26, SLC5A8, and UCHL1) were frequently methylated in UTC (15%-86%) and thyroid cancer cell lines (25%-100%). In the more aggressive UTC, the mean methylation index (MI = 0.44) was the highest compared to other thyroid alterations PTC (MI = 0.29, p = 0.123), FTC (MI = 0.15, p = 0.005), MTC (MI = 0.13; p = 0.017), FA (MI = 0.27; p = 0.075) and goiters (MI = 0.23; p = 0.024). Methylation of TSHR, MGMT, UCHL1, and p16 occurred preferentially in UTC and this inactivation was reverted by a demethylating agent.

CONCLUSIONS

Our results show that hypermethylation of several tumor-related gene promoters is a frequent event in UTC. The hypermethylation status may be reversed by DNA demethylating agents. Their clinical value remains to be investigated.

Induction of a CXCL8 binding site on endothelial syndecan-3 in rheumatoid synovium

OBJECTIVE

To identify and characterize which endothelial heparan sulfate proteoglycans (HSPGs) bind the chemokine CXCL8 (interleukin-8) in human rheumatoid arthritis (RA) and nonrheumatoid synovia.

METHOD

CXCL8 binding to endothelial HSPGs in RA and nonrheumatoid synovia was determined by heparinase treatment followed by an in situ binding assay and autoradiography. Endothelial HSPGs were characterized by immunohistochemical analysis and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Phosphatidyinositol-specific phospholipase C (PI-PLC) and antibodies to HSPGs were used in in situ binding experiments to identify which HSPGs bound CXCL8.

RESULTS

The expression of heparan sulfate on microvascular endothelial cells was demonstrated in RA and nonrheumatoid synovia. Using antibodies to syndecan-1-4 and glypican-1, -3, and -4, the selective expression of syndecan-3 by endothelial cells was detected in RA and nonrheumatoid synovia. In addition, RT-PCR showed the presence of syndecan-3 messenger RNA in endothelial cells extracted from RA and nonrheumatoid synovia. (125)I-CXCL8 bound to venular endothelial cells; treatment with heparinases I and III significantly reduced this binding in RA but not nonrheumatoid synovia. (125)I-CXCL8 binding was not reduced after treatment with PI-PLC, which cleaves glycosyl phosphatidylinositol linkages, suggesting that CXCL8 did not bind to glypicans. Treatment of synovia with a syndecan-3 antibody reduced CXCL8 binding to RA but not nonrheumatoid endothelial cells; however, no reduction in binding was observed with syndecan-2 or glypican-4 antibodies.

CONCLUSION

Our results show the selective induction of a CXCL8 binding site on endothelial syndecan-3 in RA synovium. This site may be involved in leukocyte trafficking into RA synovial tissue.

Molecular pathogenesis of euthyroid and toxic multinodular goiter

The purpose of this review is to summarize current knowledge of the etiology of euthyroid and toxic multinodular goiter (MNG) with respect to the epidemiology, clinical characteristics, and molecular pathology. In reconstructing the line of events from early thyroid hyperplasia to MNG we will argue the predominant neoplastic character of nodular structures, the nature of known somatic mutations, and the importance of mutagenesis. Furthermore, we outline direct and indirect consequences of these somatic mutations for thyroid pathophysiology and summarize information concerning a possible genetic background of euthyroid goiter. Finally, we discuss uncertainties and open questions in differential diagnosis and therapy of euthyroid and toxic MNG.