Targeted Foxe1 Overexpression in Mouse Thyroid Causes the Development of Multinodular Goiter But Does Not Promote Carcinogenesis

Identification of Germline FOXE1 and Somatic MAPK Pathway Gene Alterations in Patients with Malignant Struma Ovarii, Cleft Palate and Thyroid Cancer

Germline variants in the FOXE1 transcription factor have been associated with thyroid ectopy, cleft palate (CP) and thyroid cancer (TC). Here, we aimed to clarify the role of FOXE1 in Portuguese families (F1 and F2) with members diagnosed with malignant struma ovarii (MSO), an ovarian teratoma with ectopic malignant thyroid tissue, papillary TC (PTC) and CP. Two rare germline heterozygous variants in the FOXE1 promoter were identified: F1) c.-522G>C, in the proband (MSO) and her mother (asymptomatic); F2) c.9C>T, in the proband (PTC), her sister and her mother (CP). Functional studies using rat normal thyroid (PCCL3) and human PTC (TPC-1) cells revealed that c.9C>T decreased FOXE1 promoter transcriptional activity in both cell models, while c.-522G>C led to opposing activities in the two models, when compared to the wild type. Immunohistochemistry and RT-qPCR analyses of patients' thyroid tumours revealed lower FOXE1 expression compared to adjacent normal and hyperplastic thyroid tissues. The patient with MSO also harboured a novel germline AXIN1 variant, presenting a loss of heterozygosity in its benign and malignant teratoma tissues and observable β-catenin cytoplasmic accumulation. The sequencing of the F1 (MSO) and F2 (PTC) probands' tumours unveiled somatic BRAF and HRAS variants, respectively. Germline FOXE1 and AXIN1 variants might have a role in thyroid ectopy and cleft palate, which, together with MAPK pathway activation, may contribute to tumours' malignant transformation.

Foxe1 Deletion in the Adult Mouse Is Associated With Increased Thyroidal Mast Cells and Hypothyroidism

CONTEXT

Foxe1 is a key thyroid developmental transcription factor. Germline deletion results in athyreosis and congenital hypothyroidism. Some data suggest an ongoing role for maintaining thyroid differentiation.

OBJECTIVE

We created a mouse model to directly examine the role of Foxe1 in the adult thyroid.

METHODS

A model of tamoxifen-inducible Cre-mediated ubiquitous deletion of Foxe1 was generated in mice of C57BL/6J background (Foxe1flox/flox/Cre-TAM). Tamoxifen or vehicle was administered to Foxe1flox/flox/Cre mice aged 6-8 weeks. Blood was collected at 4, 12, and 20 weeks, and tissues after 12 or 20 weeks for molecular and histological analyses. Plasma total thyroxine (T4), triiodothyronine, and thyrotropin (TSH) were measured. Transcriptomics was performed using microarray or RNA-seq and validated by reverse transcription quantitative polymerase chain reaction.

RESULTS

Foxe1 was decreased by approximately 80% in Foxe1flox/flox/Cre-TAM mice and confirmed by immunohistochemistry. Foxe1 deletion was associated with abnormal follicular architecture and smaller follicle size at 12 and 20 weeks. Plasma TSH was elevated in Foxe1flox/flox/Cre-TAM mice as early as 4 weeks and T4 was lower in pooled samples from 12 and 20 weeks. Foxe1 deletion was also associated with an increase in thyroidal mast cells. Transcriptomic analyses found decreased Tpo and Tg and upregulated mast cell markers Mcpt4 and Ctsg in Foxe1flox/flox/Cre-TAM mice.

CONCLUSION

Foxe1 deletion in adult mice was associated with disruption in thyroid follicular architecture accompanied by biochemical hypothyroidism, confirming its role in maintenance of thyroid differentiation. An unanticipated finding was an increase in thyroidal mast cells. These data suggest a possible explanation for previous human genetic studies associating alleles in/near FOXE1 with hypothyroidism and/or autoimmune thyroiditis.

Pathogenesis of Multinodular Goiter in Elderly XB130-Deficient Mice: Alteration of Thyroperoxidase Affinity with Iodide and Hydrogen Peroxide

Background: Multinodular goiter (MNG) is the most common disorder of the thyroid gland. Aging and genetic mutations that impair thyroid hormone (TH) production have been implicated in the development of MNG. XB130 is an adaptor/scaffold protein predominantly expressed in the thyroid gland. XB130 deficiency leads to transient postnatal growth retardation in mice due to congenital hypothyroidism. We studied the formation of MNG and possible mechanisms in elderly mice. Methods: Thyroid glands of male and female Xb130-knockout (Xb130^-/-), heterozygous (Xb130^+/-), and wild-type (Xb130^+/+) mice at the ages of 12-20 months were harvested for visual examination, histopathological, and immunohistological analyses. Blood and thyroid samples were collected after feeding elderly mice with a low iodine diet for ¹²⁵I uptake and perchlorate discharge assay. The activity of thyroperoxidase (Tpo) was examined by spectrophotometric evaluation of iodide oxidation. Results: While moderate MNG was seen in Xb130^+/+ and Xb130^+/- mice, severe MNG, characterized by multiple nodules intermixed with dilated colloid-rich macrofollicles, was found only in Xb130^-/- mice at 18 months. Thyrocyte cytoskeletal structure and cell adhesion molecules were disorganized, and TH production was significantly reduced. Reduced iodide organification was seen in elderly Xb130^+/+ mice and further enhanced in Xb130^-/- mice. In Xb130^+/+ mice, Tpo shows high affinity with hydrogen peroxide (H₂O₂) throughout aging, but reduced affinity with iodide in an age-dependent manner. By contrast, in elderly Xb130^-/- mice, the affinity of Tpo for iodide remained high, but the affinity of Tpo for H₂O₂ was reduced. Conclusions: The pathophysiological features in the thyroid glands of aged Xb130^-/- mice closely resemble the features of MNG in humans. Moderate MNG in elderly mice was dramatically aggravated by XB130 deficiency. Reduced affinity of Tpo for H₂O₂ may contribute to MNG development via oxidative stress. This could be specific to XB130 deficiency but also could be a common mechanism in MNG. Its clinical relevance should be further investigated.

Genetic Mutations and Variants in the Susceptibility of Familial Non-Medullary Thyroid Cancer

Thyroid cancer is the most frequent endocrine malignancy with the majority of cases derived from thyroid follicular cells and caused by sporadic mutations. However, when at least two or more first degree relatives present thyroid cancer, it is classified as familial non-medullary thyroid cancer (FNMTC) that may comprise 3-9% of all thyroid cancer. In this context, 5% of FNMTC are related to hereditary syndromes such as Cowden and Werner Syndromes, displaying specific genetic predisposition factors. On the other hand, the other 95% of cases are classified as non-syndromic FNMTC. Over the last 20 years, several candidate genes emerged in different studies of families worldwide. Nevertheless, the identification of a prevalent polymorphism or germinative mutation has not progressed in FNMTC. In this work, an overview of genetic alteration related to syndromic and non-syndromic FNMTC is presented.

The Contribution of Genetic Variants to the Risk of Papillary Thyroid Carcinoma in the Kazakh Population: Study of Common Single Nucleotide Polymorphisms and Their Clinicopathological Correlations

OBJECTIVE

Risk for developing papillary thyroid carcinoma (PTC), the most common endocrine malignancy, is thought to be mediated by lifestyle, environmental exposures and genetic factors. Recent progress in the genome-wide association studies of thyroid cancer leads to the identification of several genetic variants conferring risk to this malignancy across different ethnicities. We set out to elucidate the impact of selected single nucleotide polymorphisms (SNPs) on PTC risk and to evaluate clinicopathological correlations of these genetic variants in the Kazakh population for the first time.

METHODS

Eight SNPs were genotyped in 485 patients with PTC and 1,008 healthy control Kazakh subjects. The association analysis and multivariable modeling of PTC risk by the genetic factors, supplemented with rigorous statistical validation, were performed.

RESULT

Five of the eight SNPs: rs965513 (FOXE1/PTCSC2, P = 1.3E-16), rs1867277 (FOXE1 5'UTR, P = 7.5E-06), rs2439302 (NRG1 intron 1, P = 4.0E-05), rs944289 (PTCSC3/NKX2-1, P = 4.5E-06) and rs10136427 (BATF upstream, P = 9.8E-03) were significantly associated with PTC. rs966423 (DIRC3, P = 0.07) showed a suggestive association. rs7267944 (DHX35) was associated with PTC risk in males (P = 0.02), rs1867277 (FOXE1) conferred the higher risk in subjects older than 55 years (P = 7.0E-05), and rs6983267 (POU5F1B/CCAT2) was associated with pT3-T4 tumors (P = 0.01). The contribution of genetic component (unidirectional independent effects of rs965513, rs944289, rs2439302 and rs10136427 adjusted for age and sex) to PTC risk in the analyzed series was estimated to be 30-40%.

CONCLUSION

Genetic factors analyzed in the present work display significant association signals with PTC either on the whole group analysis or in particular clinicopathological groups and account for about one-third of the risk for PTC in the Kazakh population.

Mouse models of sporadic thyroid cancer derived from BRAFV600E alone or in combination with PTEN haploinsufficiency under physiologic TSH levels

The BRAF^V600E mutation is the most prevalent driver mutation of sporadic papillary thyroid cancers (PTC). It was previously shown that prenatal or postnatal expression of BRAF^V600E under elevated TSH levels induced thyroid cancers in several genetically engineered mouse models. In contrast, we found that postnatal expression of BRAF^V600E under physiologic TSH levels failed to develop thyroid cancers in conditional transgenic Tg(LNL-Braf^V600E) mice injected in the thyroid with adenovirus expressing Cre under control of the thyroglobulin promoter (Ad-TgP-Cre). In this study, we first demonstrated that Braf^CA/+ mice carrying a Cre-activated allele of Braf^V600E exhibited higher transformation efficiency than Tg(LNL-Braf^V600E) mice when crossed with TPO-Cre mice. As a result, most Braf^CA/+ mice injected with Ad-TgP-Cre developed thyroid cancers in 1 year. Histologic examination showed follicular or cribriform-like structures with positive TG and PAX staining and no colloid formation. Some tumors also had papillary structure component with lower TG expression. Concomitant PTEN haploinsufficiency in injected Braf^CA/+;Pten^f/+ mice induced tumors predominantly exhibiting papillary structures and occasionally undifferentiated solid patterns with normal to low PAX expression and low to absent TG expression. Typical nuclear features of human PTC and extrathyroidal invasion were observed primarily in the latter mice. The percentages of pERK-, Ki67- and TUNEL-positive cells were all higher in the latter. In conclusion, we established novel thyroid cancer mouse models in which postnatal expression of BRAF^V600E alone under physiologic TSH levels induces PTC. Simultaneous PTEN haploinsufficiency tends to promote tumor growth and de-differentiation.

Genetic Polymorphism Predisposing to Differentiated Thyroid Cancer: A Review of Major Findings of the Genome-Wide Association Studies

Thyroid cancer has one of the highest hereditary component among human malignancies as seen in medical epidemiology investigations, suggesting the potential meaningfulness of genetic studies. Here we review researches into genetic variations that influence the chance of developing non-familial differentiated thyroid cancer (DTC), focusing on the major findings of the genome-wide association studies (GWASs) of common single-nucleotide polymorphisms (SNPs). To date, eight GWAS have been performed, and the association of a number of SNPs have been reproduced in dozens of replication investigations across different ethnicities, including Korea and Japan. Despite the cumulative effect of the strongest SNPs demonstrates gradual increase in the risk for cancer and their association signals are statistically quite significant, the overall prediction ability for DTC appears to be very limited. Thus, genotyping of common SNPs only would be insufficient for evidence-based counseling in clinical setting at present. Further studies to include less significant and rare SNPs, non-SNP genetic information, gene-gene interactions, ethnicity, non-genetic and environmental factors, and development of more advanced computational algorithms are warranted to approach to personalized disease risk prediction and prognostication.

Does the Polymorphism in the Length of the Polyalanine Tract of FOXE1 Gene Influence the Risk of Thyroid Dysgenesis Occurrence?

Background. Recent data have suggested that polymorphisms in the length of the polyalanine tract (polyA) of FOXE1 gene may act as a susceptibility factor for thyroid dysgenesis. The main purpose of this study was to investigate the influence of polyA of FOXE1 gene on the risk of thyroid dysgenesis. Method. A case-control study was conducted in a sample of 90 Brazilian patients with thyroid dysgenesis and 131 controls without family history of thyroid disease. Genomic DNA was isolated from peripheral blood samples and the genotype of each individual was determined by automated sequencing. Results. More than 90% of genotypes found in the group of patients with thyroid dysgenesis and in controls subjects were represented by sizes 14 and 16 polymorphisms in the following combinations: 14/14, 14/16, and 16/16. Genotypes 14/16 and 16/16 were more frequent in the control group, while genotype 14/14 was more frequent in the group of patients with thyroid dysgenesis. There was no difference between agenesis group and control group. Genotype 14/14 when compared to genotypes 14/16 and 16/16A showed an association with thyroid dysgenesis. Conclusion. PolyA of FOXE1 gene alters the risk of thyroid dysgenesis, which may explain in part the etiology of this disease.

Lessons from Fukushima: Latest Findings of Thyroid Cancer After the Fukushima Nuclear Power Plant Accident

The increase in risk for late-onset thyroid cancer due to radiation exposure is a potential health effect after a nuclear power plant accident mainly due to the release of radioiodine in fallout. The risk is particularly elevated in those exposed during infancy and adolescence. To estimate the possibility and extent of thyroid cancer occurrence after exposure, it is of utmost importance to collect and analyze epidemiological information providing the basis for evaluation of radiation risk, and to consider radiobiology and molecular genetics. In this regard, the dose-response of cancer risk, temporal changes in the rates of thyroid cancer, its histopathological types and subtypes, and frequency of underlying genetic abnormalities are important. At present, however, it is difficult or impossible to distinguish radiation-induced thyroid cancer from spontaneous/sporadic thyroid cancer because molecular radiation signatures, biomarkers of radiation exposure, or genetic factors specific to radiation-induced cancer have not yet been identified. The large-scale ultrasound screening in Fukushima Prefecture of Japan demonstrated a high detection rate of thyroid cancer in young individuals, revealing 116 and 71 cases in the first and second rounds, respectively, among the same cohort of approximately 300,000 subjects. These findings raised concerns among residents and the public that it might be due to putative exposure to radiation from the accident at Fukushima Daiichi Nuclear Power Plant. This review summarizes evaluations by international organizations and reviews scientific publications by the authors and others on childhood thyroid cancer, especially those relevant to radiation, including basic studies on molecular mechanisms of thyroid carcinogenesis. Clinical details are also provided on surgical cases in Fukushima Prefecture, and the effect of thyroid ultrasound screening is discussed. Correct understanding of issues relating to radiation and the thyroid are essential for interpretation of thyroid cancer in Fukushima.

Interaction Landscape of Inherited Polymorphisms with Somatic Events in Cancer

Recent studies have characterized the extensive somatic alterations that arise during cancer. However, the somatic evolution of a tumor may be significantly affected by inherited polymorphisms carried in the germline. Here, we analyze genomic data for 5,954 tumors to reveal and systematically validate 412 genetic interactions between germline polymorphisms and major somatic events, including tumor formation in specific tissues and alteration of specific cancer genes. Among germline-somatic interactions, we found germline variants in RBFOX1 that increased incidence of SF3B1 somatic mutation by 8-fold via functional alterations in RNA splicing. Similarly, 19p13.3 variants were associated with a 4-fold increased likelihood of somatic mutations in PTEN. In support of this association, we found that PTEN knockdown sensitizes the MTOR pathway to high expression of the 19p13.3 gene GNA11 Finally, we observed that stratifying patients by germline polymorphisms exposed distinct somatic mutation landscapes, implicating new cancer genes. This study creates a validated resource of inherited variants that govern where and how cancer develops, opening avenues for prevention research.Significance: This study systematically identifies germline variants that directly affect tumor evolution, either by dramatically increasing alteration frequency of specific cancer genes or by influencing the site where a tumor develops. Cancer Discovery; 7(4); 410-23. ©2017 AACR.See related commentary by Geeleher and Huang, p. 354This article is highlighted in the In This Issue feature, p. 339.

Genotype Analyses in the Japanese and Belarusian Populations Reveal Independent Effects of rs965513 and rs1867277 but Do Not Support the Role of FOXE1 Polyalanine Tract Length in Conferring Risk for Papillary Thyroid Carcinoma

BACKGROUND

Several functional single-nucleotide polymorphisms (SNPs) at the FOXE1 locus on chromosome 9q22.33 have been associated with the risk for papillary thyroid carcinoma (PTC). This study set out to elucidate whether their effects are independent, using genotyping results in populations of Asian and European descent.

METHODS

SNPs rs965513 and rs1867277 and a polymorphic region determining the length of the FOXE1 polyalanine (poly-Ala) tract were genotyped in 501 patients with PTC and 748 healthy individuals from Japan, and in 660 patients and 820 population controls from Belarus. Functional analysis of transactivation activities of FOXE1 isoforms with varying number of alanine repeats was performed by a Dual-Luciferase^® Assay.

RESULTS

All three polymorphisms were significantly associated with PTC in both populations on univariate analysis. However, conditional analysis revealed independent effects of rs965513 and rs1867277 SNPs but not of the FOXE1 poly-Ala polymorphism. The independent effect of the lead rs965513 SNP was observed in both populations, while that of rs1867277 was only identified in the Japanese population, in which linkage disequilibrium between the three polymorphisms is markedly weaker. Despite the strong decrease in transcriptional activity with increasing FOXE1 poly-Ala tract length, no difference in transactivation potential of the FOXE1 poly-Ala isoforms could be seen after adjustment for the minimal promoter activity in the reporter vectors. Plasmids encoding FOXE1 isoforms of increasing poly-Ala tract length were also found to produce less FOXE1 protein after cell transfection.

CONCLUSIONS

The functional variants rs965513 and rs1867277 independently contribute to genetic predisposition to PTC, while a contributing role of the FOXE1 poly-Ala polymorphism could not be confirmed.