Role of NKX2-1 in N-bis(2-hydroxypropyl)-nitrosamine-induced thyroid adenoma in mice

Establishment and Characterization of Amitrole-Induced Mouse Thyroid Adenomatous Nodule-Derived Cell Lines

Background: Thyroid cancer cell lines have been of great value for the study of thyroid cancer. However, the availability of benign thyroid adenoma cell lines is limited. Methods: Cell lines were established from thyroid adenomatous nodules that developed in mice treated with the goitrogen amitrole. Expression of epithelial, mesenchymal, and thyroid markers of these established cell lines was determined, and the effect of lentivirus-transduced overexpression of NKX2-1, a master regulator of thyroid development, on the thyroid marker expression was examined. Signal transduction and cell proliferation were evaluated after treatment with insulin-like growth factor-I (IGF-I) and the selective IGF-I receptor (IGF-IR) inhibitor NVP-ADW742. Xenograft studies were performed to examine tumorigenicity of the cells in mice. Whole-genome sequencing (WGS) was used to comprehensively determine the genetic mutations in the established two cell lines. Results: Five mouse thyroid adenomatous nodules-derived cell lines named CAT (cells from amitrole-treated thyroids) were established. Among these, two cell lines, CAT458/458s (CAT458s: a subline of CAT458) and CAT459, were found to be positive for epithelial markers and negative for a mesenchymal marker. NKX2-1-positive CAT459 cells showed higher messenger RNA (mRNA) expression of some thyroid differentiation markers than NKX2-1-negative CAT458s cells, and NKX2-1 overexpression increased and/or induced their expression. IGF-I signaling was transduced in thyrotropin receptor (Tshr)-negative CAT458s and 459 cells, and NVP-ADW742 suppressed their proliferation. No tumors developed in mice after subcutaneous injection of CAT458s or 459 cells. The WGS analysis revealed the presence of missense mutations in the tumor suppressor genes such as Polk (encoding DNA polymerase kappa) and Tgfb1 (encoding transforming growth factor beta 1), while no mutations were found in the prominent thyroid cancer-related genes Braf, Trp53 (encoding p53), and Tert (encoding telomerase reverse transcriptase). Conclusions: Two mouse thyroid adenomatous nodule-derived cell lines with different thyroid differentiation marker expression were established. NKX2-1 induced partial differentiation of these cell lines. They lacked tumorigenicity and prominent gene mutations involved in thyroid cancer development, while missense mutations were found in some tumor suppressors as revealed by WGS. The CAT458s and 459 provide a new tool to further clarify the process of thyroid multistep carcinogenesis and differentiation.

NKX2-1 re-expression induces cell death through apoptosis and necrosis in dedifferentiated thyroid carcinoma cells

NK2 homeobox 1 (NKX2-1) is a thyroid transcription factor essential for proper thyroid formation and maintaining its physiological function. In thyroid cancer, NKX2-1 expression decreases in parallel with declined differentiation. However, the molecular pathways and mechanisms connecting NKX2-1 to thyroid cancer phenotypes are largely unknown. This study aimed to examine the effects of NKX2-1 re-expression on dedifferentiated thyroid cancer cell death and explore the underlying mechanisms. A human papillary thyroid carcinoma cell line lacking NKX2-1 expression was infected with an adenoviral vector containing Nkx2-1. Cell viability decreased after Nkx2-1 transduction and apoptosis and necrosis were detected. Arginase 2 (ARG2), regulator of G protein signaling 4 (RGS4), and RGS5 mRNA expression was greatly increased in Nkx2-1-transducted cells. After suppressing these genes by siRNA, cell death, apoptosis, and necrosis decreased in RGS4 knockdown cells. These findings demonstrated that cell death was induced via apoptosis and necrosis by NKX2-1 re-expression and involves RGS4.

Co-exposure to BPA and DEHP enhances susceptibility of mammary tumors via up-regulating Esr1/HDAC6 pathway in female rats

Breast cancer (BrCa) as one of the major malignancies threatening women's health worldwide occurs due to the genetic and environmental interactions. Epidemiological studies have suggested that exposure to endocrine disrupting chemicals (EDCs) can elevate the risk of breast cancer. Di-(2-ethylhexyl)-phthalate (DEHP) and bisphenol A (BPA) are known as two typical EDCs. Although several studies have implied that there appear to have adverse effects of exposure to BPA or DEHP alone on breast development, no study to date has demonstrated the exact toxic effect of combined exposure to DEHP and BPA on breast tumorigenesis. In the present study, we performed an in vivo experiment including 160 female Sprague-Dawley (SD) rats, in which 80 rats were randomly allocated to 4 groups including control group given to normal diet, DEHP (150 mg/kg body weight/day), BPA (20 mg/kg body weight/day), and DEHP (150 mg/kg body weight/day) combined with BPA (20 mg/kg body weight/day) by gavage for 30 weeks. Additionally, a DEN/MNU/DHPN (DMD)-induced carcinogenesis animal model was also established to assess their effect on tumor promotion. Namely, the other 80 SD rats were separated into another 4 groups: in addition to DMD initiation each group treated with vehicle, DEHP, BPA and the combination of BPA and DEHP respectively. Our data demonstrated that BPA alone or in combination with DEHP may induce hyperplasia of mammary glands, including the proliferation of ductal epithelial cells and an increase in the number of lobules and acinus after a 30-week exposure. Notably, co-exposure to DEHP and BPA increased the incidence and reduced the latency of mammary tumor, which seemed to enhance the susceptibility of carcinogens-induced tumor. Mechanistically, our results supported the hypothesis that exposure to BPA and DEHP might promote breast cancer dependent on Esr1 and HDAC6 as pivotal factors, and further lead to the activation of oncogene c-Myc. Our study suggested that BPA combined with DEHP facilitate the occurrence of mammary tumors, which contributed to advance our understanding in the complex effects of compound exposure to endocrine disrupting chemicals.

Mouse models of thyroid cancer: Bridging pathogenesis and novel therapeutics

Due to a global increase in the incidence of thyroid cancer, numerous novel mouse models were established to reveal thyroid cancer pathogenesis and test promising therapeutic strategies, necessitating a comprehensive review of translational medicine that covers (i) the role of mouse models in the research of thyroid cancer pathogenesis, and (ii) preclinical testing of potential anti-thyroid cancer therapeutics. The present review article aims to: (i) describe the current approaches for mouse modeling of thyroid cancer, (ii) provide insight into the biology and genetics of thyroid cancers, and (iii) offer guidance on the use of mouse models for testing potential therapeutics in preclinical settings. Based on research with mouse models of thyroid cancer pathogenesis involving the RTK, RAS/RAF/MEK/ERK, PI3K/AKT/mTOR, SRC, and JAK-STAT signaling pathways, inhibitors of VEGFR, MEK, mTOR, SRC, and STAT3 have been developed as anti-thyroid cancer drugs for "bench-to-bedside" translation. In the future, mouse models of thyroid cancer will be designed to be ''humanized" and "patient-like," offering opportunities to: (i) investigate the pathogenesis of thyroid cancer through target screening based on the CRISPR/Cas system, (ii) test drugs based on new mouse models, and (iii) explore the underlying mechanisms based on multi-omics.

An in vivo model for thyroid regeneration and folliculogenesis

While thyroid is considered to be a dormant organ, when required, it can regenerate through increased cell proliferation. However, the mechanism for regeneration remains unknown. Nkx2-1(fl/fl);TPO-cre mouse thyroids exhibit a very disorganized appearance because their thyroids continuously degenerate and regenerate. In mouse thyroids, a cluster of cells are found near the tracheal cartilage and muscle, which are positive for expression of NKX2-1, the master transcription factor governing thyroid development and function. In the present study, we propose that this cluster of NKX2-1-positive cells may be the precursor cells that mature to become thyroid follicular cells, forming thyroid follicles. We also found that phosphorylation of AKT is induced by NKX2-1 in the proposed thyroid progenitor-like side-population cell-derived thyroid cell line (SPTL) cells, suggesting the possibility that NKX2-1 plays a role in differentiation through the modulation of AKT signaling. This study revealed that Nkx2-1(fl/fl);TPO-cre mice provide a suitable model to study in vivo regeneration and folliculogenesis of the thyroid.

Elevated HMGN4 expression potentiates thyroid tumorigenesis

Thyroid cancer originates from genetic and epigenetic changes that alter gene expression and cellular signaling pathways. Here, we report that altered expression of the nucleosome-binding protein HMGN4 potentiates thyroid tumorigenesis. Bioinformatics analyses reveal increased HMGN4 expression in thyroid cancer. We find that upregulation of HMGN4 expression in mouse and human cells, and in the thyroid of transgenic mice, alters the cellular transcription profile, downregulates the expression of the tumor suppressors Atm, Atrx and Brca2, and elevates the levels of the DNA damage marker γH2AX. Mouse and human cells overexpressing HMGN4 show increased tumorigenicity as measured by colony formation, by tumor generation in nude mice, and by the formation of preneoplastic lesions in the thyroid of transgenic mice. Our study identifies a novel epigenetic factor that potentiates thyroid oncogenesis and raises the possibility that HMGN4 may serve as an additional diagnostic marker, or therapeutic target in certain thyroid cancers.

Is dietary nitrate/nitrite exposure a risk factor for development of thyroid abnormality? A systematic review and meta-analysis

The potential effects of inorganic nitrate/nitrite on global health are a much debated issue. In addition to possible methemoglobinemia and carcinogenic properties, anti-thyroid effects of nitrate/nitrite have been suggested. Considering the growing significance of nitrate/nitrite and since there is no comprehensive review in data available, clarifying the effect of nitrate/nitrite on thyroid disorder outcomes is essential. Therefore, we conducted this systematic review of experimental and clinical studies, and a meta-analysis of relevant cohort and cross-sectional studies investigating the association of nitrate/nitrite exposure and thyroid function. Most animal studies show that high exposure (~10-600 times of acceptable daily intake) to nitrate/nitrite induces anti-thyroid effects, including decreased serum level of thyroid hormones and histomorphological changes in thyroid gland; however no similar observations have been documented in humans. Based on our meta-analysis, no significant association was observed between nitrate exposure and the risk of thyroid cancer, hyper- and hypothyroidism; findings from three cohort studies however showed a significant association between higher exposure to nitrite and the risk of thyroid cancer (risk = 1.48, 95% confidence interval = 1.09-2.02, P = 0.012). Additional research is needed to clarify the association between nitrate/nitrite exposures and both thyroid function and cancer.

The common genetic variant rs944289 on chromosome 14q13.3 associates with risk of both malignant and benign thyroid tumors in the Japanese population

BACKGROUND

Several single nucleotide polymorphisms (SNP) have been identified to be associated with the risk for differentiated thyroid cancer in populations of distinct ethnic background. The relationship of these genetic markers to a benign tumor of the thyroid, follicular adenoma (FA), is not well established.

METHODS

In a multicenter retrospective case-control study, five thyroid cancer-related SNPs-rs966513 (9q22.33, FOXE1), rs944289 (14q13.3, PTCSC3), rs2439302 (8p12, NRG1), rs1867277 (9q22.23, FOXE1), and rs6983267 (8q24, POU5F1B)-were genotyped in 959 cases of histologically verified FA, 535 papillary thyroid carcinomas (PTC), and 2766 population controls.

RESULTS

A significant association was found between FA and rs944289 (p=0.002; OR 1.176 [CI 1.064-1.316]), and suggestively with rs2439302 (p=0.033; OR 1.149 [CI 1.010-1.315]). In PTC, significant associations were confirmed for rs965513 (p=4.21E-04; OR 1.587 [CI 1.235-2.000]) and rs944289 (p=0.003; OR 1.234 [CI 1.075-1.408]), newly found for rs2439302 (p=0.003; OR 1.266 [CI 1.087-1.493]) and rs1867277 (p=1.17E-04; OR 1.492 [CI 1.235-1.818]), and was not replicated for rs6983267 (p=0.082; OR 1.136 [CI 0.980-1.316]) in this series. A significant correlation between rs2439302 genotype and relative expression of NRG1 was detected in normal and tumor counterparts of PTC (about 10% decrease per each risk allele). NRG1 expression also significantly correlated with that of PTCSC3.

CONCLUSIONS

Association of rs944289, which was previously known to confer risk for thyroid cancer, with FA, and the correlation between PTCSC3 and NRG1 expression demonstrates that predisposing genetic factors are partly common for benign and malignant thyroid tumors, and imply broader roles of the pathways they underlie in thyroid tumorigenesis, not limited to carcinogenesis.

Are the SNPs of NKX2-1 associated with papillary thyroid carcinoma in the Han population of Northern China?

Papillary thyroid carcinoma (PTC) is one of the most common tumors of the thyroid gland. The common risk factors of PTC include ionizing radiation, positive family history, and thyroid nodular disease. PTC was identified in Europeans by conducting a genome-wide association study, and a strong association signal with PTC was observed in rs944289 and NKX2-1 (located at the 14q13.3 locus), which was probably the genetic risk factor of PTC. This study aimed to examine the association of this gene with PTC in Chinese. A total of 354 patients with PTC and 360 healthy control subjects from the Han population of Northern China were recruited in the study. These individuals were genotyped to determine rs12589672, rs12894724, rs2076751, and rs944289. The association of rs944289 with PTC was obtained (C vs. T, P = 0.027, OR = 1.264, 95% CI = 1.026 - 1.557; and C/C - C/T vs. T/T, P = 0.034, OR = 1.474, 95% CI = 1.028 - 2.112). Conducting a subgroup analysis, we found a marginal difference in the allele frequency distribution of rs944289 (adjusted P = 0.062) between the patients with PTC and multi-nodular goiter and the control subjects. We also observed an interaction (P = 0.029; OR = 2.578, 95% CI = 1.104 - 6.023) between rs944289 and diabetes in patients with PTC. In conclusion, rs944289 was associated with an increased risk of PTC in the Han population of Northern China, but no clear association was observed in either of the tag single nucleotide polymorphisms of NKX2-1.

The complexity of thyroid transcription factor 1 with both pro- and anti-oncogenic activities

After the original identification of thyroid transcription factor 1 (TTF-1 or NKX2-1) biochemical activity as a transcriptional regulator of thyroglobulin in 1989, the bulk of the ensuing research has concentrated on elucidating the roles of NKX2-1 in the development of lung and thyroid tissues. Motivated by its specific expression pattern, pathologists adopted the NKX2-1 immunoreactivity to distinguish pulmonary from nonpulmonary nonthyroid adenocarcinomas. Interestingly, the concept of NKX2-1 as an active participant in lung tumorigenesis did not take hold until 2007. This minireview contrasts the recent advancements of NKX2-1-related observations primarily in the realm of pulmonary malignancies.

Nkx2-1 represses a latent gastric differentiation program in lung adenocarcinoma

Tissue-specific differentiation programs become dysregulated during cancer evolution. The transcription factor Nkx2-1 is a master regulator of pulmonary differentiation that is downregulated in poorly differentiated lung adenocarcinoma. Here we use conditional murine genetics to determine how the identity of lung epithelial cells changes upon loss of their master cell-fate regulator. Nkx2-1 deletion in normal and neoplastic lungs causes not only loss of pulmonary identity but also conversion to a gastric lineage. Nkx2-1 is likely to maintain pulmonary identity by recruiting transcription factors Foxa1 and Foxa2 to lung-specific loci, thus preventing them from binding gastrointestinal targets. Nkx2-1-negative murine lung tumors mimic mucinous human lung adenocarcinomas, which express gastric markers. Loss of the gastrointestinal transcription factor Hnf4α leads to derepression of the embryonal proto-oncogene Hmga2 in Nkx2-1-negative tumors. These observations suggest that loss of both active and latent differentiation programs is required for tumors to reach a primitive, poorly differentiated state.

Kras(G12D) and Nkx2-1 haploinsufficiency induce mucinous adenocarcinoma of the lung

Mucinous adenocarcinoma of the lung is a subtype of highly invasive pulmonary tumors and is associated with decreased or absent expression of the transcription factor NK2 homeobox 1 (NKX2-1; also known as TTF-1). Here, we show that haploinsufficiency of Nkx2-1 in combination with oncogenic Kras(G12D), but not with oncogenic EGFR(L858R), caused pulmonary tumors in transgenic mice that were phenotypically similar to human mucinous adenocarcinomas. Gene expression patterns distinguished tumor goblet (mucous) cells from nontumorigenic airway and intestinal goblet cells. Expression of NKX2-1 inhibited urethane and oncogenic Kras(G12D)-induced tumorigenesis in vivo. Haploinsufficiency of Nkx2-1 enhanced Kras(G12D)-mediated tumor progression, but reduced EGFR(L858R)-mediated progression. Genome-wide analysis of gene expression demonstrated that a set of genes induced in mucinous tumors was shared with genes induced in a nontumorigenic chronic lung disease, while a distinct subset of genes was specific to mucinous tumors. ChIP with massively parallel DNA sequencing identified a direct association of NKX2-1 with the genes induced in mucinous tumors. NKX2-1 associated with the AP-1 binding element as well as the canonical NKX2-1 binding element. NKX2-1 inhibited both AP-1 activity and tumor colony formation in vitro. These data demonstrate that NKX2-1 functions in a context-dependent manner in lung tumorigenesis and inhibits Kras(G12D)-driven mucinous pulmonary adenocarcinoma.

Functional inactivation of thyroid transcription factor-1 in PCCl3 thyroid cells

Thyroid transcription factor-1 (TTF-1) is a key regulator of thyroid development and function. In order to identify the genes whose expression depends on TTF-1 transcriptional activity within the thyrocyte we analyzed the consequence of the functional inactivation of this factor in PCCl3 cells. The expression of a fusion protein composed of the DNA binding domain of TTF-1 and of the strong repressive domain of the engrailed protein resulted in a dramatic loss of epithelial cell morphology and in proliferation arrest. These changes were reversed when the inhibition of endogenous TTF-1 was relieved. No change was observed when a similar fusion protein containing point mutations abolishing DNA binding activity was produced in the cells. Besides the expected down-regulation of expression of the main genes linked to the differentiated thyroid function, we observed a decreased expression of the transcription factors Hhex, Pax 8 and TTF-2 and of E-cadherin. By contrast, both ThOX-1 and DUOXA-1 genes were up-regulated, as well as the ones encoding vimentin and several proteins involved in cell cycle arrest. Our data thus extend the known roles of TTF-1 in thyroid development and in the expression of differentiated function in the adult organ to the control of epithelial morphology and of cell division in mature thyrocytes.

Thyroid-specific transcription factors and their roles in thyroid cancer

Homeodomain, forkhead domain, and paired domain-containing transcription factors play a major role in development, tissue-specific gene expression, and tissue homeostasis in organs where they are expressed. Recently, their roles in stem cell and cancer biology are emerging. In the thyroid, NKX2-1, FOXE1, and PAX8 transcription factors are responsible for thyroid organogenesis and expression of thyroid-specific genes critical for thyroid hormone synthesis. In contrast to their known roles in gene regulation, thyroid development and homeostasis, their involvement in stem cell, and/or cancer biology are still elusive. In order to further understand the nature of thyroid cancer, it is critical to determine their roles in thyroid cancer.