Protein synthesis inhibitors, in synergy with 5-azacytidine, restore sodium/iodide symporter gene expression in human thyroid adenoma cell line, KAK-1, suggesting trans-active transcriptional repressor

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.

B-RafV600E inhibits sodium iodide symporter expression via regulation of DNA methyltransferase 1

B-RafV600E mutant is found in 40-70% of papillary thyroid carcinoma (PTC) and has an important role in the pathogenesis of PTC. The sodium iodide symporter (NIS) is an integral plasma membrane glycoprotein that mediates active iodide transport into the thyroid follicular cells, and B-RafV600E has been known to be associated with the loss of NIS expression. In this study, we found that B-RafV600E inhibited NIS expression by the upregulation of its promoter methylation, and that specific regions of CpG islands of NIS promoter in B-RafV600E harboring PTC were highly methylated compared with surrounding normal tissue. Although DNA methyltransferase 3a and 3b (DNMT3a,3b) were not increased by B-RafV600E, DNMT1 expression was markedly upregulated in PTC and B-RafV600E expressing thyrocytes. Furthermore, DNMT1 expression was upregulated by B-RafV600E induced NF-κB activation. These results led us to conclude that NIS promoter methylation, which was induced by B-RafV600E, is one of the possible mechanisms involved in NIS downregulation in PTC.

The PARP inhibitor PJ34 modifies proliferation, NIS expression and epigenetic marks in thyroid cancer cell lines

Since PARP-1 is supposed to be part of a multimeric repressor of sodium iodide symporter (NIS) expression, in this study the effect of the PARP inhibitor PJ34 on several properties of thyroid cancer cell lines was investigated. In TPC1, BCPAP, FRO, WRO cell lines PJ34 induced a strong increase in NIS mRNA levels. In BCPAP and TPC1 cells also significant increase of radio-iodine uptake was induced. Accordingly, in transfection experiments performed in TPC1 cells, treatment with PJ34 increased NIS promoter activity without affecting PARP-1 binding to the promoter sequence. We also investigated the epigenetic status of NIS promoter after PJ34 treatment in TPC1 cell line: in addition to an increase of histone modification activation marks (H3K9K14ac, H3K4me3), surprisingly we observed also an increase of H3K27me3, a classical repressive mark. Our data demonstrate that in various thyroid cancer cell lines PARP inhibition increases NIS gene expression through a particular modulation of transcriptional regulatory mechanisms. Therefore, we suggest that PARP inhibitors may deserve future investigations as tools for medical treatment of thyroid cancer.

Induction of sodium/iodide symporter (NIS) expression and radioiodine uptake in non-thyroid cancer cells

BACKGROUND

This study was designed to explore the therapeutic potential of suppressing MAP kinase and PI3K/Akt pathways and histone deacetylase (HDAC) to induce the expression of sodium/iodide symporter (NIS) and radioiodine uptake in non-thyroid cancer cells.

METHODS

We tested the effects of the MEK inhibitor RDEA119, the Akt inhibitor perifosine, and the HDAC inhibitor SAHA on NIS expression in thirteen human cancer cell lines derived from melanoma, hepatic carcinoma, gastric carcinoma, colon carcinoma, breast carcinoma, and brain cancers. We also examined radioiodine uptake and histone acetylation at the NIS promoter in selected cells.

RESULTS

Overall, the three inhibitors could induce NIS expression, to various extents, in melanoma and all the epithelial carcinoma-derived cells but not in brain cancer-derived cells. SAHA was most effective and its effect could be significantly enhanced by RDEA119 and perifosine. The expression of NIS, at both mRNA and protein levels, was most robust in the melanoma cell M14, hepatic carcinoma cell HepG2, and the gastric carcinoma cell MKN-7 cell. Radioiodine uptake was correspondingly induced, accompanied by robust increase in histone acetylation at the NIS promoter, in these cells when treated with the three inhibitors.

CONCLUSIONS

This is the first demonstration that simultaneously suppressing the MAP kinase and PI3K/Akt pathways and HDAC could induce robust NIS expression and radioiodine uptake in certain non-thyroid human cancer cells, providing novel therapeutic implications for adjunct radioiodine treatment of these cancers.

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.

Identification of cyclic adenosine 3',5'-monophosphate response element modulator as an activator of the human sodium/iodide symporter upstream enhancer

The lack of Na(+)/I(-) symporter (NIS) gene expression in some thyroid cancer patients has been a major hurdle that limits the efficacy of standard radioactive iodide therapy. The molecular mechanism that contributes to low NIS expression is not well understood. Activated NIS gene expression is stimulated by thyroid-stimulating hormone-mediated cAMP/protein kinase A signaling through a NIS upstream enhancer (NUE). The cAMP pathway is also stimulated by forskolin. In the current work, we studied the mechanism of transcriptional activation of NIS in normal thyroid cells and thyroid cancer cells. We identified the cAMP response element modulator (CREM) activator as a new component of the transcription complex that is important for NIS gene expression. The CREM complex is seen in the normal thyroid cells and BRAF (V600E) thyroid cancer cells (BHP 17-10) but is missing in rearranged in transformation/papillary thyroid carcinoma-1 rearrangement thyroid cancer cells (BHP 2-7). This complex is believed to be responsible for the loss of NUE activity and reduced NIS expression in the BHP 2-7 cell line. In BHP 2-7 cells, forskolin stimulated the thyroid-specific transcription factor Pax 8, but CREM activator mRNA did not increase, and this produced a small increase in NUE activity. Ectopic expression of CREM activator enhanced activity of the NUE, indicating that CREM is an essential regulator of NIS gene expression.

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.