Identification of microRNAs that mediate thyroid cell growth induced by TSH

Thyroglobulin regulates the expression and localization of the novel iodide transporter solute carrier family 26 member 7 (SLC26A7) in thyrocytes

Solute carrier family 26 member 7 (SLC26A7), identified as a causative gene for congenital hypothyroidism, was found to be a novel iodide transporter expressed on the apical side of the follicular epithelium of the thyroid. We recently showed that TSH suppressed the expression of SLC26A7 and induces its localization to the plasma membrane, where it functions. We also showed that the ability of TSH to induce thyroid hormone synthesis is completely reversed by an autocrine negative-feedback action of thyroglobulin (Tg) stored in the follicular lumen. In the present study, we investigated the potential effect of follicular Tg on SLC26A7 expression and found that follicular Tg significantly suppressed the promoter activity, mRNA level, and protein level of SLC26A7 in rat thyroid FRTL-5 cells. In addition, follicular Tg inhibited the ability of TSH to induce the membrane localization of SLC26A7. In rat thyroid sections, the expression of SLC26A7 was weaker in follicles with a higher concentration of Tg, as evidenced by immunofluorescence staining. These results indicate that Tg stored in the follicular lumen is a feedback suppressor of the expression and membrane localization of SLC26A7, thereby downregulating the transport of iodide into the follicular lumen.

Regulation of solute carrier family 26 member 7 (Slc26a7) by thyroid stimulating hormone in thyrocytes

Iodine transportation is an important step in thyroid hormone biosynthesis. Uptake of iodine into the thyroid follicle is mediated mainly by the basolateral sodium-iodide symporter (NIS or solute carrier family 5 member 5: SLC5A5), and iodine efflux across the apical membrane into the follicular lumen is mediated by pendrin (SLC26A4). In addition to these transporters, SLC26A7, which has recently been identified as a causative gene for congenital hypothyroidism, was found to encode a novel apical iodine transporter in the thyroid. Although SLC5A5 and SLC26A4 have been well-characterized, little is known about SLC26A7, including its regulation by TSH, the central hormone regulator of thyroid function. Using rat thyroid FRTL-5 cells, we showed that the mRNA levels of Slc26a7 and Slc26a4, two apical iodine transporters responsible for iodine efflux, were suppressed by TSH, whereas the mRNA level of Slc5a5 was induced. Forskolin and dibutyryl cAMP (dbcAMP) had the same effect as that of TSH on the mRNA levels of these transporters. TSH, forskolin and dbcAMP also had suppressive effects on SLC26A7 promoter activity, as assessed by luciferase reporter gene assays, and protein levels, as determined by Western blot analysis. TSH, forskolin and dbcAMP also induced strong localization of Slc26a7 to the cell membrane according to immunofluorescence staining and confocal laser scanning microscopy. Together, these results suggest that TSH suppresses the expression level of Slc26a7 but induces its accumulation at the cell membrane, where it functions as an iodine transporter.

LncRNA LIPE-AS1 Predicts Poor Survival of Cervical Cancer and Promotes Its Proliferation and Migration via Modulating miR-195-5p/MAPK Pathway

Aims: A growing number of studies have unveiled that long non-coding RNA (lncRNA) is conductive to cervical cancer (CC) development. However, the effect of LIPE-AS1 is remained to be studied in CC. Main Methods: Reverse transcription-polymerase chain reaction (RT-PCR) was employed to measure LIPE-AS1 expression in CC tissues and the adjacent normal tissues. Additionally, we conducted gain- and loss-of functional experiments of LIPE-AS1 and adopted CCK8 assay, BrdU assay, and in vivo tumor formation experiment to test the proliferation of CC cells (HCC94 and HeLa). Besides, the apoptosis, invasion, and epithelial-mesenchymal transformation (EMT) of CC cells were estimated using flow cytometry, transwell assay, and western blot, respectively. Further, LIPE-AS1 downstream targets were analyzed through bioinformatics, and the binding relationships between LIPE-AS1 and miR-195-5p were verified via dual-luciferase activity experiment and RNA Protein Immunoprecipitation (RIP) assay. Moreover, rescue experiments were conducted to confirm the effects of LIPE-AS1 and miR-195-5p in regulating CC development and the expressions of MAPK signaling pathway related proteins were detected by RT-PCR, western blot, and immunofluorescence. Key Findings: LIPE-AS1 was over-expressed in CC tissues (compared to normal adjacent tissues) and was notably related to tumor volume, distant metastasis. Overexpressing LIPE-AS1 accelerated CC cell proliferation, migration and EMT, inhibited apoptosis; while LIPE-AS1 knockdown had the opposite effects. The mechanism studies confirmed that LIPE-AS1 sponges miR-195-5p as a competitive endogenous RNA (ceRNA), which targets the 3'-untranslated region (3'-UTR) of MAP3K8. LIPE-AS1 promoted the expression of MAP3K8 and enhanced ERK1/2 phosphorylation, which were reversed by miR-195-5p. Significance: LIPE-AS1 regulates CC progression through the miR-195-5p/MAPK signaling pathway, providing new hope for CC diagnosis and treatment.

Regulatory effect of miR-195 in the placental dysfunction of preeclampsia

Purpose: Preeclampsia (PE) is a pregnancy specific disease soon after 20 weeks of gestation where major symptoms are hypertension and proteinuria. The underlying pathology is believed to be abnormal placentation. Epigenetic and genetic factors have significant roles in abnormal placental development. MicroRNA's (miRNAs), being one of the most important epigenetic regulators, take part in abnormal placentation. Hsa-miR-195 is a molecule associated with abnormal placental growth mechanisms such as impaired cellular proliferation, inadequate trophoblastic invasion causing defective spiral artery remodeling, and apoptosis. We aimed to evaluate miRNA functions, namely miR-195 expression profile, in order to divulge PE pathogenesis.Methods: In this study, we extracted circulating miRNAs from maternal plasma and placenta from 20 PE patients and 20 normotensive pregnant women. miR-195 was quantified using quantitative real time reverse transcriptase PCR (qRT-PCR). The target genes of miR-195 were predicted by Diana Tools-mirPath, TargetScan, and miRDB databases.Results: We found that miR-195 levels were downregulated (3.83-fold decrease, p < .05) in preeclamptic placenta samples, however miR-195 were undetected in preeclamptic and normotensive plasma samples. The steep down-regulation of miR-195 points to its importance of PE pathogenesis.Conclusion: miR-195 is suggested to regulate PE via its target genes manipulating biological processes such as placental proliferation, apoptosis, and angiogenesis. We propose that detection of decreased miR-195 levels in preeclamptic placentas could be used to enlighten the pathophysiology of PE.

Information theoretic sub-network mining characterizes breast cancer subtypes in terms of cancer core mechanisms

A breast cancer subtype classification scheme, PAM50, based on genetic information is widely accepted for clinical applications. On the other hands, experimental cancer biology studies have been successful in revealing the mechanisms of breast cancer and now the hallmarks of cancer have been determined to explain the core mechanisms of tumorigenesis. Thus, it is important to understand how the breast cancer subtypes are related to the cancer core mechanisms, but multiple studies are yet to address the hallmarks of breast cancer subtypes. Therefore, a new approach that can explain the differences among breast cancer subtypes in terms of cancer hallmarks is needed.

We developed an information theoretic sub-network mining algorithm, differentially expressed sub-network and pathway analysis (DeSPA), that retrieves tumor-related genes by mining a gene regulatory network (GRN) of transcription factors and miRNAs. With extensive experiments of the cancer genome atlas (TCGA) breast cancer sequencing data, we showed that our approach was able to select genes that belong to cancer core pathways such as DNA replication, cell cycle, p53 pathways while keeping the accuracy of breast cancer subtype classification comparable to that of PAM50. In addition, our method produces a regulatory network of TF, miRNA, and their target genes that distinguish breast cancer subtypes, which is confirmed by experimental studies in the literature.

Quantitative assessment of preoperative serum thyrotropin level and thyroid cancer

Thyroid stimulating hormone (TSH) is the major growth factor for thyrocytes, but the pathogenic role of serum TSH in thyroid cancer (TC) is unknown. The association between TSH level and the development of thyroid cancer has been widely evaluated recently. However, the results remain conflicting. To develop an understanding of the relationship between TSH exposure and thyroid cancer, a meta-analysis of 56 studies involving 20227 thyroid cancer cases and 50003 controls with benign thyroid nodule was performed. Overall, significantly increased TSH level was observed in thyroid cancer patients compared with controls (RoM: 1.44, 95% CI: 1.32-1.56, P < 10-5). The pooled analyses also revealed that higher serum TSH level were significantly associated with the size of TC nodule and malignancy as well as lymph node metastasis. Furthermore, significantly increased THS levels were observed preferentially for papillary thyroid cancer when stratified by histological type of tumors. However, the diagnostic value of TSH level for TC might be limited. These results suggest that higher serum TSH concentration is associated with an increased risk of thyroid cancer.

2-Iodohexadecanal inhibits thyroid cell growth in part through the induction of let-7f microRNA

It is well known that pituitary TSH exerts the major task in the regulation of thyroid function. However, this gland is capable of certain degree of autonomy, independently of TSH control. Iodine plays an important role in thyroid physiology and biochemistry. The thyroid is capable of producing different iodolipids such as 2-iodohexadecanal (2-IHDA). It was shown that this iodolipid mimic some of the inhibitory effects of excess iodide on several thyroid parameters.

OBJECTIVES

To identify the miRNAs regulated by 2-IHDA in rat thyroid cells and likely characterize their role in thyroid cell proliferation and function.

RESULTS

FRTL-5 cells were grown in the presence of TSH and treated with 2-IHDA. Among the miRNAs up-regulated by 2-IHDA we focused on miR-let-7f and miR-138. When we transfected the miRNAs, miR-let-7f but not miR-138 overexpression inhibited proliferation of FRTL 5 cells, while miR-let-7f inhibition restored cell growth in 2-IHDA treated cultures. Analysis of cell cycle by flow cytometric DNA analysis revealed that miR-let-7f inhibition reduced the percentage of 2-IHDA treated cells in G1 phase and an increased of the percentage of cells in S phase was observed upon anti-let-7f transfection. The expresion of Cyclin D1 and Cyclin D3 were reduced after the transfection of miR-let-7f and miR-138, respectively. In in vivo studies we observed that miR-let-7f and miR-138 were up regulated by 2-IHDA during goiter involution.

CONCLUSION

These results suggest that the inhibitory effects of 2-IHDA on FRTL-5 thyroid cell proliferation are mediated in part through the induction of let-7f microRNA.

microRNA expression in autonomous thyroid adenomas: Correlation with mRNA regulation

The objective of the study was to identify the deregulated miRNA in autonomous adenoma and to correlate the data with mRNA regulation. Seven autonomous adenoma with adjacent healthy thyroid tissues were investigated. Twelve miRNAs were downregulated and one was upregulated in the tumors. Combining bioinformatic mRNA target prediction and microarray data on mRNA regulations allowed to identify mRNA targets of our deregulated miRNAs. A large enrichment in mRNA encoding proteins involved in extracellular matrix organization and different phosphodiesterases were identified among these putative targets. The direct interaction between miR-101-3p and miR-144-3p and PDE4D mRNA was experimentally validated. The global miRNA profiles were not greatly modified, confirming the definition of these tumors as minimal deviation tumors. These results support a role for miRNA in the regulation of extracellular matrix proteins and tissue remodeling occurring during tumor development, and in the important negative feedback of the cAMP pathway, which limits the consequences of its constitutive activation in these tumors.

microRNA-339-5p modulates Na+/I- symporter-mediated radioiodide uptake

Na(+)/I(-) symporter (NIS)-mediated radioiodide uptake (RAIU) serves as the basis for targeted ablation of thyroid cancer remnants. However, many patients with thyroid cancer have reduced NIS expression/function and hence do not benefit from radioiodine therapy. microRNA (miR) has emerged as a promising therapeutic target in many diseases; yet, the role of miRs in NIS-mediated RAIU has not been investigated. In silico analysis was used to identify miRs that may bind to the 3'UTR of human NIS (hNIS). The top candidate miR-339-5p directly bound to the 3'UTR of hNIS. miR-339-5p overexpression decreased NIS-mediated RAIU in HEK293 cells expressing exogenous hNIS, decreased the levels of NIS mRNA, and RAIU in transretinoic acid/hydrocortisone (tRA/H)-treated MCF-7 human breast cancer cells as well as thyrotropin-stimulated PCCl3 rat thyroid cells. Nanostring nCounter rat miR expression assay was conducted to identify miRs deregulated by TGFβ, Akti-1/2, or 17-AAG known to modulate RAIU in PCCl3 cells. Among 38 miRs identified, 18 were conserved in humans. One of the 18 miRs, miR-195, was predicted to bind to the 3'UTR of hNIS and its overexpression decreased RAIU in tRA/H-treated MCF-7 cells. miR-339-5p was modestly increased in most papillary thyroid carcinomas (PTCs), yet miR-195 was significantly decreased in PTCs. Interestingly, the expression profiles of 18 miRs could be used to distinguish most PTCs from nonmalignant thyroid tissues. This is the first report, to our knowledge, demonstrating that hNIS-mediated RAIU can be modulated by miRs, and that the same miRs may also play roles in the development or maintenance of thyroid malignancy. Accordingly, miRs may serve as emerging targets to halt the progression of thyroid cancer and to enhance the efficacy of radioiodine therapy.

MiRNA expression may account for chronic but not for acute regulation of mRNA expression in human thyroid tumor models

Background

For thyroid tumorigenesis, two main human in vitro models are available: primary cultures of human thyrocytes treated with TSH or EGF/serum as models for autonomous adenomas (AA) or papillary thyroid carcinomas (PTC) respectively, and human thyroid tumor derived cell lines. Previous works of our group have assessed properties of those models, with a special emphasis on mRNA regulations. It is often assumed that miRNA may be one of the primary events inducing these mRNA regulations.

Methods

The purpose of this study was to investigate the representativity of those models to study microRNA regulations and their relation with mRNA expression. To achieve this aim, the miRNA expressions profiles of primary cultures treated with TSH or EGF/serum and of 6 thyroid cancer cell lines were compared to the expression profiles of 35 tumor tissues obtained by microarrays.

Results

Our data on primary cultures have shown that the TSH or EGF/serum treatment did not greatly modify the microRNA expression profiles, which is contrary to what is observed for mRNA expression profiles, although they still evolved differently according to the treatment. The analysis of miRNA and mRNA expressions profiles in the cell lines has shown that they have evolved into a common, dedifferentiated phenotype, closer to ATC than to the tumors they are derived from.

Conclusions

Long-terms TSH or EGF/serum treatments do not mimic AA or PTC respectively in terms of miRNA expression as they do for mRNA, suggesting that the regulations of mRNA expression induced by these physiological agents occur independently of miRNA. The general patterns of miRNA expression in the cell lines suggest that they represent a useful model for undifferentiated thyroid cancer. Mirna probably do not mediate the rapid changes in gene expression in rapid cell biology regulation.

MicroRNA in teleost fish

MicroRNAs (miRNAs) are transcriptional and posttranscriptional regulators involved in nearly all known biological processes in distant eukaryotic clades. Their discovery and functional characterization have broadened our understanding of biological regulatory mechanisms in animals and plants. They show both evolutionary conserved and unique features across Metazoa. Here, we present the current status of the knowledge about the role of miRNA in development, growth, and physiology of teleost fishes, in comparison to other vertebrates. Infraclass Teleostei is the most abundant group among vertebrate lineage. Fish are an important component of aquatic ecosystems and human life, being the prolific source of animal proteins worldwide and a vertebrate model for biomedical research. We review miRNA biogenesis, regulation, modifications, and mechanisms of action. Specific sections are devoted to the role of miRNA in teleost development, organogenesis, tissue differentiation, growth, regeneration, reproduction, endocrine system, and responses to environmental stimuli. Each section discusses gaps in the current knowledge and pinpoints the future directions of research on miRNA in teleosts.

ZNF367 inhibits cancer progression and is targeted by miR-195

Background

Several members of the zinc finger protein family have been recently shown to have a role in cancer initiation and progression. Zinc finger protein 367 (ZNF367) is a member of the zinc finger protein family and is expressed in embryonic or fetal erythroid tissue but is absent in normal adult tissue.

Methodology/Principal Findings

We show that ZNF367 is overexpressed in adrenocortical carcinoma, malignant pheochromocytoma/paraganglioma and thyroid cancer as compared to normal tissue and benign tumors. Using both functional knockdown and ectopic overexpression in multiple cell lines, we show that ZNF367 inhibits cellular proliferation, invasion, migration, and adhesion to extracellular proteins in vitro and in vivo. Integrated gene and microRNA expression analyses showed an inverse correlation between ZNF367 and miR-195 expression. Luciferase assays demonstrated that miR-195 directly regulates ZNF367 expression and that miR-195 regulates cellular invasion. Moreover, integrin alpha 3 (ITGA3) expression was regulated by ZNF367.

Conclusions/Significance

Our findings taken together suggest that ZNF367 regulates cancer progression.

Thyroglobulin suppresses thyroid-specific gene expression in cultures of normal but not neoplastic human thyroid follicular cells

CONTEXT

It was shown in the rat thyroid that thyroglobulin (Tg) stored in the follicular lumen is a potent regulator of thyroid-specific gene expression to maintain the function of individual follicles. However, the actions of Tg as a regulatory molecule in human thyroid have not been studied.

OBJECTIVE

Our objective was to determine the effect of Tg on gene expression in normal and diseased human thyroid and to examine whether the proposed model of negative-feedback autocrine regulation of thyroid function by Tg is applicable in the human as well as the rat.

DESIGN

Primary cultures of human thyrocytes were established from normal thyroid, Graves' disease thyroid, adenomatous goiter, follicular adenoma, and papillary carcinoma tissues obtained during surgery. Cells were stimulated with physiologic (ie, follicular) concentrations of Tg, and mRNA and protein expression of genes involved in thyroid hormonogenesis were evaluated. The effects of Tg on thyroid-specific gene expression were also assessed in 2 human papillary carcinoma cell lines.

RESULTS

Transcript levels of genes participating in thyroid hormone biosynthesis were significantly reduced by Tg in thyrocyte cultures derived from normal and Graves' thyroid, but not in cultures derived from thyroid neoplasms and adenomatous goiter.

CONCLUSION

It was confirmed that Tg acts as a negative-feedback regulator of gene expression in human thyrocytes, suggesting that Tg signaling may constitute a common mechanism for maintaining thyroid homeostasis in species with follicular thyroid morphology. However, certain diseases of intrinsic thyroid overgrowth appear to be associated with an escape from the regulatory mechanism of Tg.

Thyroglobulin increases thyroid cell proliferation via the suppression of specific microRNAs

Thyroglobulin (Tg), stored in the follicular lumen, has also been shown recently to perform two unexpected roles: as an autocrine negative-feedback suppressor of thyroid function in the presence of TSH and as a potent inducer of thyroid cell growth in the absence of TSH. However, the underlying molecular mechanism(s) remain unclear. To elucidate a molecular pathway linking Tg to increased cell proliferation, we examined the regulation of microRNAs (miRNAs) by Tg using an miRNA microarray. We identified 21 miRNAs whose expression was significantly suppressed by Tg in rat thyroid FRTL-5 cells. Using specific miRNA analogs, we determined that miR-16, miR-24, and miR-195 mediate the induction of thyroid cell growth by Tg. The expression of miR-16 and miR-195 target genes, Mapk8, Ccne1, and Cdc6, which were previously shown to be essential for TSH-stimulated thyroid cell growth, were also induced by Tg. Moreover, the Tg-induced expression of these genes was reduced by overexpression of miR-16 and miR-195. Similarly, the induction of c-Myc by Tg was reduced by miR-24 overexpression. These results suggest that Tg could alter thyroid cell proliferation by increasing the expression of cell division-related genes such as Mapk8, Ccne1, Cdc6, and c-Myc through its suppression of specific microRNAs (miR-16, miR-24, and miR-195). In addition, we identified phosphatidylinositol 3-kinase as a key signaling pathway, linking Tg with cell proliferation. The present data support an important role for miRNAs as effectors for the effect of Tg on cell proliferation and perhaps other functions of Tg in the thyroid cell.

Multiplicity of hormone-secreting tumors: common themes about cause, expression, and management

CONTEXT

Multiplicity of hormone-secreting tumors occurs in a substantial portion of hormone-excess states. Multiplicity increases the difficulty of management and drives the selection of special strategies.

EVIDENCE ACQUISITION

This is a synthesis from publications about tumor development and expression, and also about types of clinical strategy for hormone-secreting tumors.

EVIDENCE SYNTHESIS

Comparisons were made between patient groups with solitary tumors vs those with multiple tumors. Major themes with clinical relevance emerged. Usually, tumor multiplicity develops from a genetic susceptibility in all cells of a tissue. This applies to hormone-secreting tumors that begin as either polyclonal (such as in the parathyroids of familial hypocalciuric hypercalcemia) or monoclonal tumors (such as in the parathyroids of multiple endocrine neoplasia type 1 [MEN1]). High penetrance of a hereditary tumor frequently results in bilaterality and in several other types of multiplicity. Managements are better for the hormone excess than for the associated cancers. Management strategies can be categorized broadly as ablation that is total, subtotal, or zero. Examples are discussed for each category, and 1 example of each category is named here: 1) total ablation of the entire tissue with effort to replace ablated functions (for example, in C-cell neoplasia of multiple endocrine neoplasia type 2); 2) subtotal ablation with increased likelihood of persistent disease or recurrent disease (for example, in the parathyroid tumors of MEN1); or 3) no ablation of tissue with or without the use of pharmacotherapy (for example, with blockers for secretion of stomach acid in gastrinomas of MEN1).

CONCLUSIONS

Tumor multiplicity usually arises from defects in all cells of the precursor tissue. Even the optimized managements involve compromises. Still, an understanding of pathophysiology and of therapeutic options should guide optimized management.

Differential expression profiling and functional analysis of microRNAs through stage I-III papillary thyroid carcinoma

OBJECTIVE

To elucidate the mechanisms undergoing the pathogenesis of PTC, this study try to find stage specific microRNAs (miRNAs) using microarray chip in stage I, II and III papillary thyroid carcinoma (PTC) tissues as well predict miRNAs binding target genes and their molecular functions.

METHODS

PTC specimens of stage I, II, and III and their paired adjacent non-tumor tissue (one patient for each stage) were collected. The expressions of miRNAs were examined using miRNA microarray chip. The most significant changed miRNAs from microarray were verified by using quantitative RT-PCR. The Potential miRNAs regulating target genes and their preliminary biological functions were forecasted with variety function prediction software.

RESULTS

Ten miRNAs exhibited sequential up regulation expression profiles and five miRNAs performed sequential down regulation throughout stage I to III (p<0.05). After normalization, Fifteen miRNAs showed significant different compared to adjacent non-tumor tissues (p<0.05). Among of them, the most significant up regulation and down regulation miRNAs were miR-146b-5p and miR-335, respectively. Both of them were verified with qRT-PCR. 34 target genes for miR-146-5p and 36 target genes for miR-335 was predicted.

CONCLUSION

MicroRNA profile assay successfully detected a branch of differential expression miRNAs between PTC and normal tissue. Some of them also showed stage specific. Biological function analysis showed that target genes were involved in five aspects including cell proliferation, differentiation, apoptosis, cycle, and signaling transduction pathway, suggesting the regulatory role of abnormal expression of critical miRNAs in the pathogenesis of PTC.

MicroRNA expression array identifies novel diagnostic markers for conventional and oncocytic follicular thyroid carcinomas

OBJECTIVE

The most difficult thyroid tumors to be diagnosed by cytology and histology are conventional follicular carcinomas (cFTCs) and oncocytic follicular carcinomas (oFTCs). Several microRNAs (miRNAs) have been previously found to be consistently deregulated in papillary thyroid carcinomas; however, very limited information is available for cFTC and oFTC. The aim of this study was to explore miRNA deregulation and find candidate miRNA markers for follicular carcinomas that can be used diagnostically.

DESIGN

Thirty-eight follicular thyroid carcinomas (21 cFTCs, 17 oFTCs) and 10 normal thyroid tissue samples were studied for expression of 381 miRNAs using human microarray assays. Expression of deregulated miRNAs was confirmed by individual RT-PCR assays in all samples. In addition, 11 follicular adenomas, two hyperplastic nodules (HNs), and 19 fine-needle aspiration samples were studied for expression of novel miRNA markers detected in this study.

RESULTS

The unsupervised hierarchical clustering analysis demonstrated individual clusters for cFTC and oFTC, indicating the difference in miRNA expression between these tumor types. Both cFTCs and oFTCs showed an up-regulation of miR-182/-183/-221/-222/-125a-3p and a down-regulation of miR-542-5p/-574-3p/-455/-199a. Novel miRNA (miR-885-5p) was found to be strongly up-regulated (>40-fold) in oFTCs but not in cFTCs, follicular adenomas, and HNs. The classification and regression tree algorithm applied to fine-needle aspiration samples demonstrated that three dysregulated miRNAs (miR-885-5p/-221/-574-3p) allowed distinguishing follicular thyroid carcinomas from benign HNs with high accuracy.

CONCLUSIONS

In this study we demonstrate that different histopathological types of follicular thyroid carcinomas have distinct miRNA expression profiles. MiR-885-5p is highly up-regulated in oncocytic follicular carcinomas and may serve as a diagnostic marker for these tumors. A small set of deregulated miRNAs allows for an accurate discrimination between follicular carcinomas and hyperplastic nodules and can be used diagnostically in fine-needle aspiration biopsies.

Regulation of dual oxidase expression and H2O2 production by thyroglobulin

BACKGROUND

Thyroglobulin (Tg) is a macromolecular precursor in thyroid hormone synthesis to which iodine is stably bound. Tg, which is stored in the follicular space, is also a potent negative feedback regulator of follicular function, and this is achieved by suppressing mRNA levels of thyroid-specific genes such as the sodium/iodide symporter (Slc5a5), Tg, and thyroid peroxidase. Dual oxidase 1 (DUOX1) and DUOX2, originally identified in the thyroid, are nicotinamide adenine dinucleotide phosphate (NADPH) oxidases that are necessary to produce the H2O2 required for thyroid hormone biosynthesis. Since follicular Tg regulates the expression of genes that are essential for thyroid hormone synthesis, we hypothesized that Tg might also regulate DUOX expression and H2O2 production.

METHODS

Rat thyroid FRTL-5 cells were treated with Tg, and the mRNA expression of Duox1 and Duox2 and their corresponding maturation factors Duoxa1 and Duoxa2 were evaluated by DNA microarray and real-time PCR. Duox2 promoter activity was examined by luciferase reporter gene assay. Protein levels of DUOX2 were also examined by Western blot analysis. Intracellular H2O2 generation was quantified by a fluorescent dye, 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, and acetyl ester (CM-H2DCFDA).

RESULTS

mRNA levels of Duox2 and its activation factor Duoxa2 (but not Duox1 or Duoxa1) were significantly suppressed by Tg in a dose-dependent manner and a time-dependent fashion in rat thyroid FRTL-5 cells. DUOX2 promoter activity was significantly suppressed by Tg in a dose-dependent manner. Protein levels of DUOX2 and H2O2 generation in cells were also reduced by Tg treatment.

CONCLUSIONS

We show that physiological concentrations of Tg suppressed the expression and function of DUOX2 in thyroid cells. These results suggest that Tg is a strong suppressor of the expression and the activity of DUOX2/DUOXA2, thereby regulating iodide organification and hormone synthesis in the thyroid. The evidence supports a reported model in which accumulated Tg in thyroid follicles plays important roles in autoregulating the function of individual follicles, which produces the basis of follicular heterogeneity.

Propylthiouracil increases sodium/iodide symporter gene expression and iodide uptake in rat thyroid cells in the absence of TSH

BACKGROUND

Propylthiouracil (PTU) and methimazole (MMI) are drugs that are widely used to treat Graves' disease. Although both exert an antithyroid effect primarily by blocking thyroid peroxidase activity, their molecular structure and other actions are different. We hypothesized that PTU and MMI may have differential effects on thyroid-specific gene expression and function.

METHODS

The effects of PTU and MMI on thyroid-specific gene expression and function were examined in rat thyroid FRTL-5 cells using DNA microarray, reverse transcriptase (RT)-polymerase chain reaction (PCR), real-time PCR, Western blot, immunohistochemistry, and radioiodine uptake studies.

RESULTS

DNA microarray analysis showed a marked increase in sodium/iodide symporter (NIS) gene expression after PTU treatment, whereas MMI had no effect. RT-PCR and real-time PCR analysis revealed that PTU-induced NIS mRNA levels were comparable to those elicited by thyroid-stimulating hormone (TSH). PTU increased 5'-1880-bp and 5'-1052-bp activity of the rat NIS promoter. While PTU treatment also increased NIS protein levels, the size of the induced protein was smaller than that induced by TSH, and the protein localized predominantly in the cytoplasm rather than the plasma membrane. Accumulation of (125)I in FRTL-5 cells was increased by PTU stimulation, but this effect was weaker than that produced by TSH.

CONCLUSIONS

We found that PTU induces NIS expression and iodide uptake in rat thyroid FRTL-5 cells in the absence of TSH. Although PTU and MMI share similar antithyroid activity, their effects on other thyroid functions appear to be quite different, which could affect their therapeutic effectiveness.

Thyroglobulin (Tg) activates MAPK pathway to induce thyroid cell growth in the absence of TSH, insulin and serum

The growth of thyroid cells is tightly regulated by thyroid stimulating hormone (TSH) through the cyclic adenosine 3', 5'-monophosphate (cAMP) signaling pathway by potentiating the mitogenic activity of insulin and insulin-like growth factors (IGFs). However, we recently reported that thyroglobulin (Tg), a major product of the thyroid, also induces the growth of thyroid cells cultured in 0.2% serum in the absence of TSH and insulin. In this report, we demonstrate that Tg induced phosphorylation of molecules of the c-Raf/MEK/ERK pathway of the mitogen-activated protein kinase (MAPK). The MEK-1/2 inhibitor PD98059 suppressed Tg-induced phosphorylation of ERK1/2 and reduced bromodeoxyuridine (BrdU) incorporation. Tg also induced expression of the essential transcriptional factors c-Myc, c-Fos and c-Jun and phosphorylation of the retinoblastoma (Rb) protein. The present results, together with the previous report, suggest that Tg utilizes multiple signaling cascades to induce thyroid cell growth independent of TSH/cAMP stimulation.