Induction of thyroid gene expression and radioiodine uptake in melanoma cells: novel therapeutic implications

Recognition of Melanocytes in Immuno-Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis

Melanocytes produce melanin to protect the skin from UV-B radiation. Notwithstanding, the spectrum of their functions extends far beyond their well-known role as melanin production factories. Melanocytes have been considered as sensory and computational cells. The neurotransmitters, neuropeptides, and other hormones produced by melanocytes make them part of the skin’s well-orchestrated and complex neuroendocrine network, counteracting environmental stressors. Melanocytes can also actively mediate the epidermal immune response. Melanocytes are equipped with ectopic sensory systems similar to the eye and nose and can sense light and odor. The ubiquitous inner circadian rhythm controls the body’s basic physiological processes. Light not only affects skin photoaging, but also regulates inner circadian rhythms and communicates with the local neuroendocrine system. Do melanocytes “see” light and play a unique role in photoentrainment of the local circadian clock system? Why, then, are melanocytes responsible for so many mysterious functions? Do these complex functional devices work to maintain homeostasis locally and throughout the body? In addition, melanocytes have also been shown to be localized in internal sites such as the inner ear, brain, and heart, locations not stimulated by sunlight. Thus, what can the observation of extracutaneous melanocytes tell us about the “secret identity” of melanocytes? While the answers to some of these intriguing questions remain to be discovered, here we summarize and weave a thread around available data to explore the established and potential roles of melanocytes in the biological communication of skin and systemic homeostasis, and elaborate on important open issues and propose ways forward.

Network analysis reveals essential proteins that regulate sodium-iodide symporter expression in anaplastic thyroid carcinoma

Anaplastic thyroid carcinoma (ATC) is the most rare and lethal form of thyroid cancer and requires effective treatment. Efforts have been made to restore sodium-iodide symporter (NIS) expression in ATC cells where it has been downregulated, yet without complete success. Systems biology approaches have been used to simplify complex biological networks. Here, we attempt to find more suitable targets in order to restore NIS expression in ATC cells. We have built a simplified protein interaction network including transcription factors and proteins involved in MAPK, TGFβ/SMAD, PI3K/AKT, and TSHR signaling pathways which regulate NIS expression, alongside proteins interacting with them. The network was analyzed, and proteins were ranked based on several centrality indices. Our results suggest that the protein interaction network of NIS expression regulation is modular, and distance-based and information-flow-based centrality indices may be better predictors of important proteins in such networks. We propose that the high-ranked proteins found in our analysis are expected to be more promising targets in attempts to restore NIS expression in ATC cells.

Melanoma and Thyroid Carcinoma: Our Current Understanding

Melanoma is listed among the most common cancers in the United States, with new cases increasing steadily.1 Due to the aggressive nature of melanoma and its high risk of metastasis, early detection and treatment is essential. It is noted that the majority of unresectable and metastatic melanomas are BRAF V600-mutated.2 Recently, rates of papillary thyroid carcinoma have also been increasing. Studies have indicated BRAF V600-mutations are common in papillary thyroid carcinoma, second only to melanoma. The BRAF mutation in thyroid carcinoma similarly portends more aggressive behavior. The association between melanoma and thyroid disease was noted in several patients in our clinic and fueled our literature review in an attempt to better understand this clinical observation. A systematic English-language literature review was performed using PubMed Central and ScienceDirect online databases. Search parameters included articles published from January 2000 to July 2018 and key search terms were melanoma and thyroid carcinoma and BRAF mutation and thyroid cancer. The initial search yielded 2,470 and 234 articles in each respective database. Articles that lacked relevant information were excluded. The literature we reviewed supports our theory that thyroid dysfunction is disproportionately noted among patients with a history of melanoma. In order to detect disease early, it is critical for dermatologists, internists, family practitioners, endocrinologists, and oncologists to be aware of the association between these two primary malignancies when proceeding with appropriate screening examinations.

MAPK Inhibitors Enhance HDAC Inhibitor-Induced Redifferentiation in Papillary Thyroid Cancer Cells Harboring BRAF V600E: An In Vitro Study

Clinical efficacy of redifferentiation therapy with histone deacetylase inhibitor (HDACi) for lethal radioiodine-refractory papillary thyroid cancer (RR-PTC) is urgently needed to be improved. Given that the impairment of histone acetylation is a mechanism in BRAF^V600E-mitogen-activated protein kinase (MAPK)-induced aberrant silencing of thyroid iodine-metabolizing genes, dual inhibition of HDAC and MAPK may produce a more favorable effect. In this study, we treated BRAF^V600E-mutant (BCPAP and K1) and BRAF-wild-type (BHP 2-7) cells with HDACi (panobinostat) and MAPK inhibitor (dabrafenib or selumetinib), alone or in combination, and we tested the expression of iodine- and glucose-metabolizing genes, radioiodine uptake and efflux, and toxicity. We found that panobinostat alone increased iodine-metabolizing gene expression, promoted radioiodine uptake and toxicity, and suppressed GLUT1 expression in all the cells. However, MAPKi (dabrafenib or selumetinib) induced these effects only in BRAF^V600E-mutant cells. Combined treatment with panobinostat and MAPKi (dabrafenib or selumetinib) displayed a more robust BRAF^V600E-dependent redifferentiation effect than panobinostat alone via further improving the acetylation level of histone at the sodium-iodide symporter (NIS) promoter. In conclusion, MAPK inhibitors enhance HDACi-induced redifferentiation in PTC cells harboring BRAF^V600E, warranting animal and clinical trials.

Synergistic inhibition of MEK/ERK and BRAF V600E with PD98059 and PLX4032 induces sodium/iodide symporter (NIS) expression and radioiodine uptake in BRAF mutated papillary thyroid cancer cells

Background and Aims

The activating mutation BRAF^V600E is a frequent genetic event in papillary thyroid carcinomas (PTC). Mutation BRAF^V600E is associated with the loss of a sodium/iodine symporter (NIS), and subsequent radioiodide-refractory (RAI) metastatic disease. Use of BRAF V600E inhibitors could partly restore NIS expression and Iodide uptake by inhibition of mitogen-activated protein kinase (MAPK) pathway. Previous study has reported that the BRAF V600E inhibitors could re-activate MAPK signals. In the present study, we investigated whether the combination treatment of BRAF V600E inhibitor and MAPK signal inhibitor could more effectively increase NIS expression and RAI uptake, and explore the mechanisms.

Methods

BCPAP and K1 cells were exposed to increasing concentrations of BRAF V600E inhibitor PLX4032 (0.01 μM, 0.1 μM, 1 μM) or MEK/ERK inhibitor PD98059 (0.01 μM, 0.1 μM, 1 μM) or with their association or/and in the presence of 3 mM perchlorate (ClO⁻ ₄) for 0–72 h. Iodide uptake and expression of BRAF, phosphorylated (p) ERK1/2, NIS were detected.

Results

PLX4032 or PD98059 alone did not induce NIS expression and increase Iodide uptake in BCPAP and K1 cells. But combined treatment of PLX4032 and PD98059 significantly induce NIS expression and increase Iodide uptake in BCPAP and K1 cells. PLX4032 alone inhibited p-ERK expression at early time, and re-activated p-ERK expression at late time. However, combined treatment of PLX4032 and PD98059 completely inhibited p-ERK expression.

Conclusion

Simultaneously suppressing BRAF V600E and p-ERK restored NIS expression and increase Iodide uptake in PTC cells, which was associated the inhibition of p-ERK expression. The results warrants clinical trials to confirm.

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

INTRODUCTION

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

METHODOLOGY

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

RESULTS

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

CONCLUSION

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

Robust Thyroid Gene Expression and Radioiodine Uptake Induced by Simultaneous Suppression of BRAF V600E and Histone Deacetylase in Thyroid Cancer Cells

CONTEXT

Use of BRAF V600E inhibitors to restore thyroid iodide-handling gene expression and radioactive iodine (RAI) avidity is an attractive therapeutic strategy for RAI-refractory thyroid cancer, but recent initial clinical responses were modest. Given histone deacetylation at the sodium/iodide symporter promoter by histone deacetylase (HDAC) as a mechanism, simultaneously targeting BRAF V600E and HDAC could be a more effective strategy.

OBJECTIVES

The objective of the study was to test whether suppressing both BRAF V600E and HDAC could more effectively induce thyroid gene expression and RAI uptake in thyroid cancer cells.

RESEARCH DESIGN

We tested the BRAF V600E inhibitor PLX4032 (vemurafenib) and the HDAC inhibitor SAHA (vorinostat), two major anticancer drugs currently approved for clinical use, in inducing thyroid gene expression and RAI uptake in thyroid cancer cells.

RESULTS

PLX4032 alone induced a modest expression of thyroid genes and RAI uptake preferentially in thyroid cancer cells harboring BRAF V600E. SAHA showed an effect in a genetic-independent manner in all the cells. A robust synergistic effect on thyroid gene expression and RAI uptake was observed in BRAF V600E-positive thyroid cancer cells when the two inhibitors were simultaneously used. This was dramatically enhanced further by TSH; triple combination of PLX4032, SAHA, and TSH showed the most robust effect on thyroid gene expression and RAI uptake in cells harboring BRAF V600E. Abundant sodium/iodide symporter protein expression in thyroid cancer cells under these conditions was confirmed by immunofluorescent microscopy.

CONCLUSIONS

Simultaneously suppressing BRAF V600E and HDAC, particularly when cotreated with TSH, induced a far more robust expression of thyroid genes and RAI uptake in thyroid cancer cells than suppressing BRAF V600E alone. Triple combination of PLX4032, SAHA, and TSH is a specific robust regimen to restore RAI avidity in RAI-refractory BRAF V600E-positive thyroid cancer, which warrants clinical trials to confirm.

Histone deacetylation of NIS promoter underlies BRAF V600E-promoted NIS silencing in thyroid cancer

The BRAF V600E mutation causes impaired expression of sodium iodide symporter (NIS) and radioiodine refractoriness of thyroid cancer, but the underlying mechanism remains undefined. In this study, we hypothesized that histone deacetylation at the NIS (SLC5A5) promoter was the mechanism. Using the chromatin immunoprecipitation approach, we examined histone acetylation status on the lysine residues H3K9/14, H3K18, total H4, and H4K16 at the NIS promoter under the influence of BRAF V600E. We found that expression of stably or transiently transfected BRAF V600E inhibited NIS expression while the deacetylase inhibitor SAHA stimulated NIS expression in PCCL3 rat thyroid cells. Although BRAF V600E enhanced global histone acetylation, it caused histone deacetylation at the NIS promoter while SAHA caused acetylation in the cells. In human thyroid cancer BCPAP cells harboring homozygous BRAF V600E mutation, BRAF V600E inhibitor, PLX4032, and MEK inhibitor, AZD6244, increased histone acetylation of the NIS promoter, suggesting that BRAF V600E normally maintained histone in a deacetylated state at the NIS promoter. The regions most commonly affected with deacetylation by BRAF V600E were the transcriptionally active areas upstream of the translation start that contained important transcription factor binding sites, including nucleotides -297/-107 in the rat NIS promoter and -692/-370 in the human NIS promoter. Our findings not only reveal an epigenetic mechanism for BRAF V600E-promoted NIS silencing involving histone deacetylation at critical regulatory regions of the NIS promoter but also provide further support for our previously proposed combination therapy targeting major signaling pathways and histone deacetylase to restore thyroid gene expression for radioiodine treatment of thyroid cancer.

Modulation of sodium iodide symporter expression and function by LY294002, Akti-1/2 and Rapamycin in thyroid cells

The selective increase of Na(+)/I(-) symporter (NIS)-mediated active iodide uptake in thyroid cells allows the use of radioiodine I(131) for diagnosis and targeted treatment of thyroid cancers. However, NIS-mediated radioiodine accumulation is often reduced in thyroid cancers due to decreased NIS expression/function. As PI3K signaling is overactivated in many thyroid tumors, we investigated the effects of inhibitors for PI3K, Akt, or mTORC1 as well as their interplay on NIS modulation in thyroid cells under chronic TSH stimulation. PI3K inhibition by LY294002 increased NIS-mediated radioiodide uptake (RAIU) mainly through upregulation of NIS expression, however, mTORC1 inhibition by Rapamycin did not increase NIS-mediated RAIU despite increased NIS protein levels. In comparison, Akt inhibition by Akti-1/2 did not increase NIS protein levels, yet markedly increased NIS-mediated RAIU by decreasing iodide efflux rate and increasing iodide transport rate and iodide affinity of NIS. The effects of Akti-1/2 on NIS-mediated RAIU are not detected in nonthyroid cells, implying that Akti-1/2 or its derivatives may represent potential pharmacological reagents to selectively increase thyroidal radioiodine accumulation and therapeutic efficacy.

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.

The Akt inhibitor MK2206 synergizes, but perifosine antagonizes, the BRAF(V600E) inhibitor PLX4032 and the MEK1/2 inhibitor AZD6244 in the inhibition of thyroid cancer cells

PURPOSE

The purpose of the study was to explore optimal combinations of currently actively developed drugs for dually targeting the Ras → Raf → MAPK kinase (MEK) → MAPK/ERK (MAPK) and the phosphatidylinositol 3-kinase/Akt pathways as effective treatments for thyroid cancer.

EXPERIMENTAL DESIGN

We tested the combinations of the Akt inhibitors MK2206 or perifosine with the BRAF(V600E) inhibitor PLX4032 or the MEK1/2 inhibitor AZD6244 in thyroid cancer cells harboring both the BRAF(V600E) and PIK3CA mutations.

RESULTS

We found that MK2206 could potently, when used alone, and synergistically, when combined with either PLX4032 or AZD6244, inhibit thyroid cancer cell growth with all the combination index values lower than 1. Perifosine could potently inhibit thyroid cancer cell growth when used alone, but a strong antagonism occurred between this drug and PLX4032 or AZD6244 in the inhibition of thyroid cancer cell growth with all combination index values higher than 1. Combinations of MK2206 with PLX4032 or AZD6244 dramatically enhanced G1 cell cycle arrest induced by each drug alone. However, G2 cell cycle arrest uniquely induced by perifosine alone and G1 cell cycle arrest induced by PLX4032 or AZD6244 were both reversed by combination treatments, providing a mechanism for their antagonism. All these drugs could correspondingly inhibit the MAPK and phosphatidylinositol 3-kinase/Akt signalings, confirming their expected target effects.

CONCLUSIONS

We demonstrated, unexpectedly, opposite outcomes of MK2206 and perifosine in their combinational treatments with BRAF(V600E)/MEK inhibitors in thyroid cancer cells. The data may help appropriate selection of these prominent drugs for clinical trials of combination therapies for thyroid cancer.

IQGAP1 plays an important role in the invasiveness of thyroid cancer

PURPOSE

This study was designed to explore the role of IQGAP1 in the invasiveness of thyroid cancer and its potential as a novel prognostic marker and therapeutic target in this cancer.

EXPERIMENTAL DESIGN

We examined IQGAP1 copy gain and its relationship with clinicopathologic outcomes of thyroid cancer and investigated its role in cell invasion and molecules involved in the process.

RESULTS

We found IQGAP1 copy number (CN) gain ≥ 3 in 1 of 30 (3%), 24 of 74 (32%), 44 of 107 (41%), 8 of 16 (50%), and 27 of 41 (66%) of benign thyroid tumor, follicular variant papillary thyroid cancer (FVPTC), follicular thyroid cancer (FTC), tall cell papillary thyroid cancer (PTC), and anaplastic thyroid cancer, respectively, in the increasing order of invasiveness of these tumors. A similar tumor distribution trend of CN ≥ 4 was also seen. IQGAP1 copy gain was positively correlated with IQGAP1 protein expression. It was significantly associated with extrathyroidal and vascular invasion of FVPTC and FTC and, remarkably, a 50%-60% rate of multifocality and recurrence of BRAF mutation-positive PTC (P = 0.01 and 0.02, respectively). The siRNA knockdown of IQGAP1 dramatically inhibited thyroid cancer cell invasion and colony formation. Coimmunoprecipitation assay showed direct interaction of IQGAP1 with E-cadherin, a known invasion-suppressing molecule, which was upregulated when IQGAP1 was knocked down. This provided a mechanism for the invasive role of IQGAP1 in thyroid cancer. In contrast, IQGAP3 lacked all these functions.

CONCLUSIONS

IQGAP1, through genetic copy gain, plays an important role in the invasiveness of thyroid cancer and may represent a novel prognostic marker and therapeutic target for this cancer.