Epigenetic dysregulation in thyroid neoplasia

Epigenomics in Hurthle Cell Neoplasms: Filling in the Gaps Towards Clinical Application

It has been widely described that cancer genomes have frequent alterations to the epigenome, including epigenetic silencing of various tumor suppressor genes with functions in almost all cancer-relevant signalling pathways, such as apoptosis, cell proliferation, cell migration and DNA repair. Epigenetic alterations comprise DNA methylation, histone modification, and microRNAs dysregulated expression and they play a significant role in the differentiation and proliferation properties of TC. In this review, our group assessed the published evidence on the tumorigenic role of epigenomics in Hurthle cell neoplasms (HCN), highlighting the yet limited, heteregeneous and non-validated data preventing its current use in clinical practice, despite the well developed assessment techniques available. The identified evidence gaps call for a joint endeavour by the medical community towards a deeper and more systematic study of HCN, aiming at defining epigenetic markers in early diagnose, allowing for accurate stratification of maligancy and disease risk and for effective systemic treatment.

HOPX homeobox methylation in differentiated thyroid cancer and its clinical relevance

BACKGROUND

The inactivation of the tumor-suppressor homeodomain-only protein X (HOPX) usually involves promoter methylation in several cancer types. This study aimed to investigate the HOPX-β mRNA expression and promoter methylation and their clinical relevance in differentiated thyroid cancer (DTC).

PATIENTS AND METHODS

Clinicopathological data and paraffin-embedded thyroid tumor tissues from 21 patients with DTC and 6 with benign tumors (T) and their non-tumor parenchyma (NT) were investigated. Tumor cell lines (FTC238, FTC236 and WRO) were treated with demethylating agent. HOPX-β mRNA expression was assessed by qRT-PCR and methylation status by Q-MSP. Thyroid cancer data from Cancer Genome Atlas (TCGA) was also collected.

RESULTS

HOPX-β mRNA re-expression in two cell lines treated with demethylating agent was observed concomitantly with reduced promoter methylation. Reduced mRNA expression in T group compared to their NT was observed, and reduced protein expression in T compared to NT was observed in three cases. Low mRNA expression with high methylation status was detected in 6/14 DTC samples. High methylation status was associated with older age at diagnosis, recurrent or progressive disease and with the presence of new neoplasm event post initial therapy while hyper-methylation correlated with worse overall survival, worse disease-free status and older age.

CONCLUSION

A moderate coupling of downregulation of HOPX-β mRNA expression in DTC followed by high HOPX-β promoter methylation was observed however; high HOPX promoter methylation status was associated with the worse prognosis of DTC patients.

HORMAD2 methylation-mediated epigenetic regulation of gene expression in thyroid cancer

This study is aimed to investigate the methylation level of candidate genes and its impact on thyroid carcinoma (THCA) development. Infinium Human Methylation 450 BeadChip Arrays by Illumina (Illumina HM450K) was the most popular CpG microarray platform widely used in biological and medical research. The methylation level of differentially expressed genes and their corresponding CpG sites were analysed by R programme. The expression of HORMAD2 was evaluated by qRT-PCR and Western blot, while the methylation level was examined via methylation-specific PCR. Cell viability, metastasis, cell cycle and apoptosis were detected by MTT assay, transwell and wound healing assay and flow cytometry, respectively, after treatment with 5-aza-2'-deoxycytidine (5-Aza). Tumour formation assay was used to analyse thyroid tumour growth in nude mice in vivo. The methylation levels of all 116 differentially expressed genes were analysed. HORMAD2 was significantly hypermethylated and its mRNA expression was inhibited in THCA cells. After treatment with 5-Aza, HORMAD2 expression was up-regulated in THCA cells and its overexpression can suppress thyroid cancer cell viability, mobility and invasiveness remarkably. Up-regulation of HORMAD2 in THCA cells could prolong G0/G1 phase and shorten S phase to impede cell mitosis as well as promote thyroid cancer cells apoptosis. Furthermore, tumour formation assay showed that increased HORMAD2 level impeded tumour growth in vivo. Hypermethylation of HORMAD2 could induce THCA progression, while hypomethylation of HORMAD2 retard cell growth and mobility and facilitate apoptosis through increasing its mRNA expression.

LARP7 in papillary thyroid carcinoma induces NIS expression through suppression of the SHH signaling pathway

The incidence of thyroid cancer has increased the past few decades, the most frequent type has been identified to be the papillary thyroid carcinoma (PTC). Following thyroidectomy, radioiodine ablation treatment on PTC is routinely performed. However, many patients do not benefit from radioiodine therapy. Therefore, novel targeted therapies to suppress tumor growth and improve radioiodine uptake are required. La ribonucleoprotein domain family member (LARP)7 is a member of the LARP family and functions as a potential suppressor of the progression of carcinoma. In the present study, the expression status of LARP7 in PTC tissues and cell lines was investigated, and the cell viability, proliferation and apoptotic rate, radioiodine uptake ability of PTC cells with overexpression of LARP7 in vitro was determined. Expression levels of LARP7 were significantly downregulated in PTC tissues and cell lines. Overexpression of LARP7 inhibited the proliferation and increased the radioiodine uptake ability of PTC cells in vitro and inhibited the tumor growth in vivo. Furthermore, LARP7 overexpression inhibited the sonic hedgehog (SHH) signaling pathway and increased sodium/iodide symporter (NIS) expression. However, treatment with recombinant human SHH partially reduced radioiodine uptake ability and NIS expression induced by LARP7. In conclusion, LARP7 may act as a tumor suppressor in PTC by inhibiting the SHH signaling pathway and may be a promising therapeutic target in patients with PTC.

Retracted Article: Down-regulation of Rab10 inhibits hypoxia-induced invasion and EMT in thyroid cancer cells by targeting HIF-1α through the PI3K/Akt pathway

Rab10, a member of the Rab family, is localized to endocytic compartments and serves as a regulator of intracellular vesicle trafficking. Previous studies mainly paid attention to the role of Rab10 in transport. Recently, Rab10 has been reported to be involved in the progression of various cancers. However, the biological functions of Rab10 in thyroid cancer remain unknown. In this study, we demonstrated that Rab10 was highly expressed in thyroid cancer tissues and cell lines. Down-regulation of Rab10 inhibited hypoxia-induced migration, invasion and epithelial–mesenchymal transition (EMT) of thyroid cancer cells. Moreover, HIF-1α and the PI3K/Akt pathway were involved in the inhibitory effect of Rab10 down-regulation on thyroid cancer cell invasion and EMT induced by hypoxia. Taken together, our study provided further evidence to support the role of Rab10 as a therapeutic target for thyroid cancer.

Rab10, a member of the Rab family, is localized to endocytic compartments and serves as a regulator of intracellular vesicle trafficking.

The relationship between RASSF1A promoter methylation and thyroid carcinoma: A meta-analysis of 14 articles and a bioinformatics of 2 databases (PRISMA)

BACKGROUND

DNA promoter methylation can suppresses gene expression and shows an important role in the biological functions of Ras association domain family 1A (RASSF1A). Many studies have performed to elucidate the role of RASSF1A promoter methylation in thyroid carcinoma, while the results were conflicting and heterogeneous. Here, we analyzed the data of databases to determine the relationship between RASSF1A promoter methylation and thyroid carcinoma.

METHODS

We used the data from 14 cancer-normal studies and Gene Expression Omnibus (GEO) database to analyze RASSF1A promoter methylation in thyroid carcinoma susceptibility. The data from the Cancer Genome Atlas project (TCGA) database was used to analyze the relationship between RASSF1A promoter methylation and thyroid carcinoma susceptibility, clinical characteristics, prognosis. Odds ratios were estimated for thyroid carcinoma susceptibility and hazard ratios were estimated for thyroid carcinoma prognosis. The heterogeneity between studies of meta-analysis was explored using H, I values, and meta-regression. We adopted quality criteria to classify the studies of meta-analysis. Subgroup analyses were done for thyroid carcinoma susceptibility according to ethnicity, methods, and primers.

RESULTS

Result of meta-analysis indicated that RASSF1A promoter methylation is associated with higher susceptibility to thyroid carcinoma with small heterogeneity. Similarly, the result from GEO database also showed that a significant association between RASSF1A gene promoter methylation and thyroid carcinoma susceptibility. For the results of TCGA database, we found that RASSF1A promoter methylation is associated with susceptibility and poor disease-free survival (DFS) of thyroid carcinoma. In addition, we also found a close association between RASSF1A promoter methylation and patient tumor stage and age, but not in patients of different genders.

CONCLUSIONS

The methylation status of RASSF1A promoter is strongly associated with thyroid carcinoma susceptibility and DFS. The RASSF1A promoter methylation test can be applied in the clinical diagnosis of thyroid carcinoma.

Inhibition of BRD4 suppresses tumor growth and enhances iodine uptake in thyroid cancer

Thyroid cancer is a common malignancy of the endocrine system. Although radioiodine (131)I treatment on differentiated thyroid cancer is widely used, many patients still fail to benefit from (131)I therapy. Therefore, exploration of novel targeted therapies to suppress tumor growth and improve radioiodine uptake remains necessary. Bromodomain-containing protein 4 (BRD4) is an important member of the bromodomain and extra terminal domain family that influences transcription of downstream genes by binding to acetylated histones. In the present study, we found that BRD4 was up-regulated in thyroid cancer tissues and cell lines. Inhibition of BRD4 in thyroid cancer cells by JQ1 resulted in cell cycle arrest at G0/G1 phase and enhanced (131)I uptake in vitro and suppressed tumor growth in vivo. Moreover, JQ1 treatment suppressed C-MYC but enhanced NIS expression. We further demonstrated that BRD4 was enriched in the promoter region of C-MYC, which could be markedly blocked by JQ1 treatment. In conclusion, our findings revealed that the aberrant expression of BRD4 in thyroid cancer is possibly involved in tumor progression, and JQ1 is potentially an effective chemotherapeutic agent against human thyroid cancer.

Synergy between HDAC and PARP Inhibitors on Proliferation of a Human Anaplastic Thyroid Cancer-Derived Cell Line

Anaplastic thyroid carcinoma (ATC) is a very aggressive human malignancy, having a marked degree of invasiveness and no features of thyroid differentiation. It is known that either HDAC inhibitors or PARP inhibitors have antiproliferative effects on thyroid cancer cells. Therefore, in this study the possible synergy between the two types of compounds has been investigated. The ATC-derived cell line SW1736 has been treated with the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) and the PARP inhibitor PJ34, alone or in combination. In terms of cell viability, the combination index value was always lower than 1 at various tested dosages, indicating, therefore, synergy in a wide range of doses for both compounds. Synergy was also observed in induction of apoptosis. In terms of thyroid-specific gene expression, synergy was observed for TSHR mRNA levels but not for NIS, TTF1, TTF2, and PAX8 mRNA levels. Altogether, these data suggest that the combined use of HDAC and PARP inhibitors may be a useful strategy for treatment of ATC.

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.

Clinical significance of histone deacetylase (HDAC)-1, HDAC-2, HDAC-4, and HDAC-6 expression in human malignant and benign thyroid lesions

Histone deacetylases (HDACs) have been associated with human malignant tumor development and progression, and HDAC inhibitors are currently being explored as anticancer agents in clinical trials. The present study aimed to evaluate the clinical significance of HDAC-1, HDAC-2, HDAC-4, and HDAC-6 proteins' expression in human malignant and benign thyroid lesions. HDAC-1, HDAC-2, HDAC-4, and HDAC-6 proteins' expression was assessed immunohistochemically on paraffin-embedded thyroid tissues obtained from 74 patients with benign and malignant thyroid lesions. Enhanced HDAC-2 and HDAC-6 expression was significantly more frequently observed in malignant, compared to benign, thyroid lesions (p = 0.0042 and p = 0.0069, respectively). Enhanced HDAC-2, HDAC-4, and HDAC-6 expression was significantly more frequently observed in cases with papillary carcinoma compared to hyperplastic nodules (p = 0.0065, p = 0.0394, and p = 0.0061, respectively). In malignant thyroid lesions, HDAC-1, HDAC-4, and HDAC-6 expression was significantly associated with tumor size (p = 0.0169, p = 0.0056, and p = 0.0234, respectively); HDAC-2 expression with lymphatic and vascular invasion (p = 0.0299 and p = 0.0391, respectively); and HDAC-4 expression with capsular invasion (p = 0.0464). The cellular pattern of HDAC-1 and HDAC-2 distribution (nuclear vs. nuclear and cytoplasmic) presented a distinct discrimination between malignant and benign thyroid lesions (p = 0.0030 and p = 0.0028, respectively) as well as between papillary carcinoma and hyperplastic nodules (p = 0.0036 and p = 0.0028, respectively). HDAC-1, HDAC-2, HDAC-4, and HDAC-6 may be associated with the malignant thyroid transformation and could be considered as useful biomarkers and possible therapeutic targets in this neoplasia.

Histone deacetylase inhibition affects sodium iodide symporter expression and induces 131I cytotoxicity in anaplastic thyroid cancer cells

BACKGROUND

Anaplastic thyroid cancers (ATCs) represent only 1%-2% of all thyroid tumors, but they account for up to 50% of the mortality. Treatment of differentiated thyroid carcinomas is well standardized and the use of radioiodine represents an essential step; in contrast, there is no standardized therapeutic approach for anaplastic tumors and their prognosis is poor. The resistance of ATC to radioiodine treatment is principally due to the absence of expression of the sodium iodide symporter (NIS), mainly due to epigenetic silencing. The acetylation status of histones is involved in the epigenetic control of gene expression and is usually disrupted in advanced thyroid cancer. Histone deacetylase inhibitors have been demonstrated as potent anticancer drugs with several different effects on cell viability and differentiation.

METHODS

Stabilized ATC cell lines (BHT-101 and CAL-62) and primary cultures from patients who underwent thyroidectomy for ATC were treated with the histone deacetylase inhibitor LBH589. After treatment, we evaluated the expression and function of NIS. Gene expression was evaluated by real-time polymerase chain reaction (RT-PCR), NIS promoter activity was determined with a luciferase reporter assay, and protein expression was assessed through immunofluorescence. We tested the protein function by (125)I uptake and efflux experiments; finally the cytotoxic effect of (131)I was determined with a clonogenic assay.

RESULTS

Our results demonstrate that treatment with LBH589 leads to NIS RNA expression as shown by RT-PCR and luciferase assay, and to protein expression as determined by immunofluorescence in vitro and by immunohistochemistry in xenograft tumors. Moreover, (125)I uptake and efflux experiments show the correct protein function and iodine retention, which translate into cytotoxicity effects, as demonstrated by a clonogenic assay with (131)I.

CONCLUSIONS

This study supplies a new potential strategy for the treatment of ATC by modifying gene expression with the aim of inducing responsiveness towards radioiodine therapy.

Transcription factor Runx2 is a regulator of epithelial-mesenchymal transition and invasion in thyroid carcinomas

Runx2/Cbfa1 is a member of the Runt-related transcription factor family and is an essential regulator of osteoblast/chondrocyte differentiation. Recently, aberrant expression of Runx2 and its oncogenic functions have been identified in the progression and metastasis of human cancers. In this study, we investigated the expression profile of Runx family genes in normal thyroid tissue, non-neoplastic but abnormal thyroid tissue, various types of thyroid tumors and representative human thyroid carcinoma cell lines. Using reverse transcriptase-PCR and western blotting, we found that Runx2 was consistently upregulated in papillary carcinomas (PCs) and thyroid carcinoma cell lines compared with normal thyroid tissue. With immunohistochemistry, we observed negative or focal immunoreactivity of Runx2 in the nuclei of normal thyroid follicular cells. None of the non-neoplastic thyroid tissues, including Graves' thyroid and adenomatous goiter, had diffuse positivity of Runx2. Expression of Runx2 in benign follicular adenomas varied from negative to diffusely positive. Meanwhile, all malignant thyroid tumors showed some Runx2 immunopositivity. It was diffuse and intense in 83% (19/23) of PCs, 71% (5/7) of follicular carcinomas (FCs) and 40% (4/10) of undifferentiated carcinomas (UCs). In thyroid carcinoma cell lines, the MEK inhibitor U0126 suppressed Runx2, suggesting an association of the MAPK/ERK pathway with Runx2 regulation. Effective silencing of Runx2 by short interfering RNA (siRNA) demonstrated downregulation of EMT-related molecules (SNAI2, SNAI3 and TWIST1), MMP2 and vasculogenic factors (VEGFA and VEGFC) in thyroid carcinoma cells. We also confirmed that Runx2 silencing suppresses thyroid carcinoma cell invasion in transwell assays. In conclusion, this study provides insight into the potential molecular mechanism of thyroid cancer invasion. Our data suggest that enhanced Runx2 is functionally linked to tumor invasion and metastasis of thyroid carcinoma by regulating EMT-related molecules, matrix metalloproteinases and angiogenic/lymphangiogenic factors.

Rap1 and its regulatory proteins: the tumor suppressor, oncogene, tumor suppressor gene axis in head and neck cancer

Squamous cell carcinoma of the head and neck (SCCHN) is the sixth most common cancer, globally. Previously, we showed that Rap1GAP is a tumor suppressor gene that inhibits tumor growth, but promotes invasion in SCCHN. In this work, we discuss the role of Rap1 and Rap1GAP in SCCHN progression in the context of a microRNA-oncogene-tumor suppressor gene axis, and investigate the role of Rap1GAP in EZH2-mediated invasion. Loss of expression of microRNA-101 in SCCHN leads to upregulation of EZH2, a histone methyltransferase. Overexpression of EZH2 silences Rap1GAP via methylation, thereby promoting activation of its target, Rap1. This microRNA-controlled activation of Rap1, via EZH2-mediated silencing of Rap1GAP, is a novel mechanism of Rap1 regulation. In two independent SCCHN cell lines, downregulation of EZH2 inhibits proliferation and invasion. In both cell lines, stable knockdown of EZH2 (shEZH2) recovers Rap1GAP expression and inhibits proliferation. However, siRNA-mediated knockdown of Rap1GAP in these cells rescues proliferation but not invasion. Thus, EZH2 promotes proliferation and invasion via Rap1GAP-dependent and -independent mechanisms, respectively. Although the studies presented here are in the context of SCCHN, our results may have broader implications, given that Rap1GAP acts as a tumor suppressor in pancreatic cancer, thyroid cancer, and melanoma.

FGFR2 isoforms support epithelial-stromal interactions in thyroid cancer progression

Alternate splicing yields two distinct isoforms of the fibroblast growth factor (FGF) receptor FGFR2-IIIb and FGFR2-IIIc varying their extracellular structure in human thyroid cancer, in which FGFR expression is commonly dysregulated. In this study, we characterized the function of these variants in modulating thyroid cancer behavior. Enforced expression of either FGFR2-IIIb or FGFR2-IIIc in thyroid epithelial cancer cells reduced expression of fibronectin, MAGE-A3 and MMP9, while increasing p21 and enhancing Rb dephosphorylation. Consistent with these tumor-suppressive properties, FGFR2-IIIb and FGFR2-IIIc each diminished invasive behavior in vitro and reduced tumor growth and metastasis in vivo. Notably, these effects contrasted with those produced by expression of these FGFR isoforms in fibroblasts, in which they both stimulated cell growth. Moreover, in xenograft tumors generated by coimplantation of epithelial and fibroblast cells expressing that same isoform, there was no significant effect on tumor progression. Conversely, FGFR2-IIIb expression in epithelial cells yielded higher FGF4/FGF7 expression that, in the presence of FGFR2-IIIc-expressing fibroblasts, enhanced tumor progression. Together, our findings highlight the importance of cellular context in assigning growth properties to growth factor receptor isoforms. More specifically, they show how alternative splicing of FGFR2 yields heteroisoforms critical to the growth-promoting actions of FGFs that exert distinct epithelial-stromal effects in thyroid cancer.

Update on the molecular signature of differentiated thyroid cancer: clinical implications and potential opportunities

With the development and maturation of new technologies, there has been a steady incorporation of powerful new tools into the evaluation and management of thyroid nodules and thyroid cancer. An increasing number of reports on oncogene testing and molecular screening in fine-needle aspiration biopsy samples have been published. However, there remains a paucity of data and consensus on combining both conventional and molecular technologies to determine the diagnosis and/or prognosis of disease. All patients with differentiated thyroid cancer stand to benefit from the identification and incorporation of reliable molecular markers into clinical practice. Identification of reliable markers would allow for stratification of treatment, affording the medical and surgical teams an ability to individually tailor evaluation and treatment, applying aggressive therapy and monitoring only when clinically warranted. For the majority of patients with thyroid cancer, the incorporation of a validated, multifaceted molecular profiling system may not improve survival; however, there is great opportunity for these efforts to decrease the morbidity associated with our current approach.

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.

Targeted therapy of thyroid cancer

Systemic chemotherapies for advanced or metastatic thyroid carcinomas have been of only limited effectiveness. For patients with differentiated or medullary carcinomas unresponsive to conventional treatments, novel therapies are needed to improve disease outcomes. Multiple novel therapies primarily targeting angiogenesis have entered clinical trials for metastatic thyroid carcinoma. Partial response rates up to 30% have been reported in single agent studies, but prolonged disease stabilization is more commonly seen. The most successful agents target the vascular endothelial growth factor receptors, with potential targets including the mutant kinases associated with papillary and medullary oncogenesis. Two drugs approved for other malignancies, sorafenib and sunitinib, have had promising preliminary results reported, and are being used selectively for patients who do not qualify for clinical trials. Additional agents targeting tumor vasculature, nuclear receptors, epigenetic abnormalities, and the immune response to neoplasia have also been investigated. Randomized trials for several agents are underway that may lead to eventual drug approval for thyroid cancer. Treatment for patients with metastatic or advanced thyroid carcinoma now emphasizes clinical trial opportunities for novel agents with considerable promise. Alternative options now exist for use of tyrosine kinase inhibitors that are well tolerated and may prove worthy of regulatory approval for this disease.

Clinical implications of molecular markers in follicular cell-derived thyroid cancer

The increasing use/applications of molecular biology techniques have provided new insights on the genetic changes that underlie carcinogenesis and tumor progression in thyroid cancer. Molecular analysis may improve the histopathologic evaluation of follicular cell-derived thyroid carcinoma, not only elucidating some unresolved problems related to the diagnosis and disease prognosis, but also by improving patient management. Besides increasing our comprehension of cancer biology, either genetic alterations or gene expression profiles implicated in thyroid carcinogenesis shed new light on innovative diagnostic procedures as well as on targeted therapies.

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.