An essential role for Pax8 in the transcriptional regulation of cadherin-16 in thyroid cells

Perfluorooctanesulfonic acid (PFOS) disrupts cadherin-16 in the developing rat thyroid gland

Perfluorooctanesulfonic acid (PFOS) can disrupt the thyroid hormone (TH) system in rodents, potentially affecting perinatal growth and neurodevelopment. Some studies also suggest that gestational exposure to PFOS can lead to lower TH levels throughout life, indicating that PFOS may compromise thyroid gland development. To address this question, we utilized a rat thyroid gland ex vivo culture system to study direct effects of PFOS on the developing thyroid. No significant changes to follicular structure or size were observed with 1 µM or 10 µM PFOS exposure. However, the transcription factor Foxe1, together with Tpo and Lrp2, were upregulated, whereas the key transcription factor Pax8 and its downstream target gene Cdh16 were significantly downregulated at the transcript level, observed with both RT-qPCR and RNAscope. Notably, Cdh16 expression was not uniformly downregulated across Cdh16-postive cells, but instead displayed a patchy expression pattern across the thyroid gland. This is a significant change in expression pattern compared to control thyroids where Cdh16 is expressed relatively uniformly. The disrupted expression pattern was also seen at the protein level. This suggests that PFOS exposure can impact follicular growth and structure. Compromised follicle integrity, if irreversible, could help explain reduced TH synthesis postnatally. This view is supported by observed changes to Tpo and Lrp2 expression, two factors that play a role in TH synthesis.

Loss of CDH16 expression is a strong independent predictor for lymph node metastasis in Middle Eastern papillary thyroid cancer

Papillary Thyroid Cancer (PTC) is the most common type of thyroid cancer. The membrane-associated glycoprotein cadherin-16 (CDH16) plays a significant role in the embryonal development of thyroid follicles and cell adhesion. Previous studies have indicated a substantial downregulation of CDH16 in PTC. However, its role in Middle Eastern PTC has not been elucidated. We analyzed a tissue microarray comprising 1606 PTC and 240 normal thyroid tissues using immunohistochemistry to assess CDH16 expression and determine its clinico-pathological associations. We also conducted BRAF and TERT mutations analyses through Sanger sequencing. Disease-free survival (DFS) was assessed using Kaplan-Meier curves. CDH16 immunostaining was seen in 100% of normal thyroid tissues but only in 9.4% of PTC tissues (p < 0.0001). The loss of CDH16 expression was associated with aggressive PTC characteristics including bilaterality, multifocality, extrathyroidal extension, tall cell variant, lymph node metastasis (LNM) and distant metastasis. Additionally a correlation between loss of CDH16 expression and BRAF and TERT mutations was identified. Intriguingly, upon conducting multivariate logistic regression analysis, CDH16 was determined to be an independent predictor for LNM (Odds ratio = 2.46; 95% confidence interval = 1.60-3.79; p < 0.0001). Furthermore, CDH16 loss was associated with a shorter DFS (p = 0.0015). However, when we further subdivided CDH16 negative patients based on the co-existence of TERT and/or BRAF mutations, we found that patients with both CDH16 negative expression and TERT mutation exhibited the shortest DFS (p < 0.0001). In conclusion, our results suggest that CDH16 protein expression could serve as a valuable diagnostic tool for PTC. Furthermore, these findings demonstrate that the loss of CDH16 expression is an independent predictor of LNM and may contribute to the aggressiveness of PTC. Therefore, downregulation of CDH16 in PTC might be a potential target for designing novel therapeutic strategies to treat PTC.

GLIS3 regulates transcription of thyroid hormone biosynthetic genes in coordination with other thyroid transcription factors

BACKGROUND

Loss of the transcription factor GLI-Similar 3 (GLIS3) function causes congenital hypothyroidism (CH) in both humans and mice due to decreased expression of several thyroid hormone (TH) biosynthetic genes in thyroid follicular cells. Whether and to what extent, GLIS3 regulates thyroid gene transcription in coordination with other thyroid transcriptional factors (TFs), such as PAX8, NKX2.1 and FOXE1, is poorly understood.

METHODS

PAX8, NKX2.1, and FOXE1 ChIP-Seq analysis with mouse thyroid glands and rat thyrocyte PCCl3 cells was performed and compared to that of GLIS3 to analyze the co-regulation of gene transcription in thyroid follicular cells by these TFs.

RESULTS

Analysis of the PAX8, NKX2.1, and FOXE1 cistromes identified extensive overlaps between these TF binding loci and those of GLIS3 indicating that GLIS3 shares many of the same regulatory regions with PAX8, NKX2.1, and FOXE1, particularly in genes associated with TH biosynthesis, induced by thyroid stimulating hormone (TSH), and suppressed in Glis3KO thyroid glands, including Slc5a5 (Nis), Slc26a4, Cdh16, and Adm2. ChIP-QPCR analysis showed that loss of GLIS3 did not significantly affect PAX8 or NKX2.1 binding and did not cause major alterations in H3K4me3 and H3K27me3 epigenetic signals.

CONCLUSIONS

Our study indicates that GLIS3 regulates transcription of TH biosynthetic and TSH-inducible genes in thyroid follicular cells in coordination with PAX8, NKX2.1, and FOXE1 by binding within the same regulatory hub. GLIS3 does not cause major changes in chromatin structure at these common regulatory regions. GLIS3 may induce transcriptional activation by enhancing the interaction of these regulatory regions with other enhancers and/or RNA Polymerase II (Pol II) complexes.

Cadherin‑16 inhibits thyroid carcinoma cell proliferation and invasion

Cadherin-16 (CDH16), a member of the cadherin family of adhesion molecules, serves an important role in the formation and maintenance of the thyroid follicular lumen. Decreased expression of CDH16 has been reported to be associated with tumor stage in papillary thyroid cancer (PTC); however, previous analyses have been limited and the biological role of CDH16 in different subtypes of TC is unknown. To investigate the role of CDH16 in the occurrence and development of TC, bioinformatic analysis of three TC subtypes (PTC, follicular cell-derived TC and anaplastic TC) was performed using an extended data set from the Gene Expression Omnibus database, with additional confirmation using data from The Cancer Genome Atlas, as well as biopsies from 35 patients with PTC and TC or follicular cell lines. According to the dataset analysis, CDH16 was downregulated in PTC and follicular cell-derived and anaplastic TC; the downregulation in PTC was independent of DNA copy number variation. Furthermore, low expression levels of CDH16 were significantly correlated with tumor size, lymph node metastasis status and disease stage in 35 patients with PTC. Gene Set Enrichment Analysis suggested that CDH16 participated in DNA replication and cell adhesion pathways. To evaluate CDH16 activity, CDH16 was overexpressed in TC-derived BCPAP cells. CDH16 overexpression inhibited cell proliferation, migration and invasion and induced apoptosis by downregulating proteins associated with DNA replication and cell adhesion. These results support the identification of CDH16 as a valuable target for TC prognosis and therapy and, to the best of our knowledge, represent the first direct demonstration of its mechanistic role in TC.

Epigenetic Dysregulation of the Homeobox A5 (HOXA5) Gene Associates with Subcutaneous Adipocyte Hypertrophy in Human Obesity

Along with insulin resistance and increased risk of type 2 diabetes (T2D), lean first-degree relatives of T2D subjects (FDR) feature impaired adipogenesis in subcutaneous adipose tissue (SAT) and subcutaneous adipocyte hypertrophy well before diabetes onset. The molecular mechanisms linking these events have only partially been clarified. In the present report, we show that silencing of the transcription factor Homeobox A5 (HOXA5) in human preadipocytes impaired differentiation in mature adipose cells in vitro. The reduced adipogenesis was accompanied by inappropriate WNT-signaling activation. Importantly, in preadipocytes from FDR individuals, HOXA5 expression was attenuated, with hypermethylation of the HOXA5 promoter region found responsible for its downregulation, as revealed by luciferase assay. Both HOXA5 gene expression and DNA methylation were significantly correlated with SAT adipose cell hypertrophy in FDR, whose increased adipocyte size marks impaired adipogenesis. In preadipocytes from FDR, the low HOXA5 expression negatively correlated with enhanced transcription of the WNT signaling downstream genes NFATC1 and WNT2B. In silico evidence indicated that NFATC1 and WNT2B were directly controlled by HOXA5. The HOXA5 promoter region also was hypermethylated in peripheral blood leukocytes from these same FDR individuals, which was further revealed in peripheral blood leukocytes from an independent group of obese subjects. Thus, HOXA5 controlled adipogenesis in humans by suppressing WNT signaling. Altered DNA methylation of the HOXA5 promoter contributed to restricted adipogenesis in the SAT of lean subjects who were FDR of type 2 diabetics and in obese individuals.

Shaping the thyroid: From peninsula to de novo lumen formation

A challenging and stimulating question in biology deals with the formation of organs from groups of undifferentiated progenitor cells. Most epithelial organs indeed derive from the endodermal monolayer and evolve into various shape and tridimensional organization adapted to their specialized adult function. Thyroid organogenesis is no exception. In most mammals, it follows a complex and sequential process initiated from the endoderm and leading to the development of a multitude of independent closed spheres equipped and optimized for the synthesis, storage and production of thyroid hormones. The first sign of thyroid organogenesis is visible as a thickening of the anterior foregut endoderm. This group of thyroid progenitors then buds and detaches from the foregut to migrate caudally and then laterally. Upon reaching their final destination in the upper neck region on both sides of the trachea, thyroid progenitors mix with C cell progenitors and finally organize into hormone-producing thyroid follicles. Intrinsic and extrinsic factors controlling thyroid organogenesis have been identified in several species, but the fundamental cellular processes are not sufficiently considered. This review focuses on the cellular aspects of the key morphogenetic steps during thyroid organogenesis and highlights similarities and common mechanisms with developmental steps elucidated in other endoderm-derived organs, despite different final architecture and functions.

Modelling of Epithelial Growth, Fission and Lumen Formation During Embryonic Thyroid Development: A Combination of Computational and Experimental Approaches

Organogenesis is the phase of embryonic development leading to the formation of fully functional organs. In the case of the thyroid, organogenesis starts from the endoderm and generates a multitude of closely packed independent spherical follicular units surrounded by a dense network of capillaries. Follicular organisation is unique and essential for thyroid function, i.e. thyroid hormone production. Previous in vivo studies showed that, besides their nutritive function, endothelial cells play a central role during thyroid gland morphogenesis. However, the precise mechanisms and biological parameters controlling the transformation of the multi-layered thyroid epithelial primordium into a multitude of single-layered follicles are mostly unknown. Animal studies used to improve understanding of organogenesis are costly and time-consuming, with recognised limitations. Here, we developed and used a 2-D vertex model of thyroid growth, angiogenesis and folliculogenesis, within the open-source Chaste framework. Our in silico model, based on in vivo images, correctly simulates the differential growth and proliferation of central and peripheral epithelial cells, as well as the morphogen-driven migration of endothelial cells, consistently with our experimental data. Our simulations further showed that reduced epithelial cell adhesion was critical to allow endothelial invasion and fission of the multi-layered epithelial mass. Finally, our model also allowed epithelial cell polarisation and follicular lumen formation by endothelial cell abundance and proximity. Our study illustrates how constant discussion between theoretical and experimental approaches can help us to better understand the roles of cellular movement, adhesion and polarisation during thyroid embryonic development. We anticipate that the use of in silico models like the one we describe can push forward the fields of developmental biology and regenerative medicine.

Altered PTPRD DNA methylation associates with restricted adipogenesis in healthy first-degree relatives of Type 2 diabetes subjects

Aim: First-degree relatives (FDR) of individuals with Type 2 diabetes (T2D) feature restricted adipogenesis, which render them more vulnerable to T2D. Epigenetics may contribute to these abnormalities. Methods: FDR pre-adipocyte Methylome and Transcriptome were investigated by MeDIP- and RNA-Seq, respectively. Results: Methylome analysis revealed 2841 differentially methylated regions (DMR) in FDR. Most DMR localized into gene-body and were hypomethylated. The strongest hypomethylation signal was identified in an intronic-DMR at the PTPRD gene. PTPRD hypomethylation in FDR was confirmed by bisulphite sequencing and was responsible for its upregulation. Interestingly, Ptprd-overexpression in 3T3-L1 pre-adipocytes inhibited adipogenesis. Notably, the validated PTPRD-associated DMR was significantly hypomethylated in peripheral blood leukocytes from the same FDR individuals. Finally, PTPRD methylation pattern was also replicated in obese individuals. Conclusion: Our findings indicated a previously unrecognized role of PTPRD in restraining adipogenesis. This abnormality may contribute to increase FDR proclivity toward T2D.

Downregulation of CDH16 in Papillary Thyroid Cancer and Its Potential Molecular Mechanism Analysed by qRT-PCR, TCGA and in silico Analysis

Objective

Thyroid cancer has the highest prevalence among the cancer types that affect the endocrine system; however, its molecular mechanisms are not yet determined. Cadherin-16 (CDH16) plays an important role in the tumorigenesis of human cancers, but its influence on papillary thyroid cancer (PTC) is poorly investigated. This study aimed to explore the role of CDH16 in PTC.

Methods

We performed quantitative real-time polymerase chain reaction to investigate CDH16 expression in PTC. The clinical significance of CDH16 expression in PTC was then evaluated using The Cancer Genome Atlas (TCGA) database. Bioinformatics analysis was also conducted to determine the potential molecular mechanisms of CDH16.

Results

CDH16 was remarkably downregulated in PTC tumors compared with that in corresponding normal thyroid tissues in the local and TCGA cohorts. This downregulation was associated with unfavorable clinicopathological features, including histological type, high tumor stage, aggressive lymph node metastasis (LNM), and advanced clinical stage. In addition, logistic analyses revealed that the reduced expression of CDH16 can aggravate the risk of LNM in PTC. Bioinformatics analysis indicated that the co-expressed CDH16 genes mainly participated in signaling the cancer-related pathways.

Conclusion

CDH16 is involved in PTC progression and acts as an LNM-related gene in PTC.

Development of the thyroid gland

Thyroid hormones are crucial for organismal development and homeostasis. In humans, untreated congenital hypothyroidism due to thyroid agenesis inevitably leads to cretinism, which comprises irreversible brain dysfunction and dwarfism. Elucidating how the thyroid gland - the only source of thyroid hormones in the body - develops is thus key for understanding and treating thyroid dysgenesis, and for generating thyroid cells in vitro that might be used for cell-based therapies. Here, we review the principal mechanisms involved in thyroid organogenesis and functional differentiation, highlighting how the thyroid forerunner evolved from the endostyle in protochordates to the endocrine gland found in vertebrates. New findings on the specification and fate decisions of thyroid progenitors, and the morphogenesis of precursor cells into hormone-producing follicular units, are also discussed.

Pax8 controls thyroid follicular polarity through cadherin-16

Organization of epithelial cells during follicular lumen formation is crucial for thyroid morphogenesis and function of the thyroid gland; however, the molecular mechanisms underlying this are poorly understood. To investigate this process, we established three-dimensional (3D) epithelial culture model systems using Fischer rat thyroid (FRT) cells or murine primary thyrocytes that developed polarized spherical structures with a central lumen, mimicking thyroid follicles. Using microarray-based differential expression analysis of FRT cells grown under 2D or 3D conditions, followed by RNA-mediated interference (RNAi) and morphogenetic analysis, we identified a key role for the thyroid transcription factor Pax8 and its target cadherin-16 (Cdh16) in the generation of polarized follicle-like structures. Silencing Pax8 expression inhibited the acquisition of apical–basal membrane polarity and impaired lumen formation. Both laminin and β1-integrin (Itgb1) expression was reduced, and cell cytoskeleton polarized distribution was altered. Silencing Cdh16 expression also led to the formation of defective structures characterized by very low laminin expression at the follicle–matrix interface, downregulation of Itgb1, and unpolarized distribution of cell cytoskeleton. Our results demonstrate that Pax8 controls apical–basal follicular polarization and follicle formation through Cdh16.

Summary: Using a 3D culture model of thyroid morphogenesis, it is revealed that thyroid follicular cell polarity depends on the Pax8 transcription factor and is linked to the β1-integrin–laminin pathway through Cdh16.

Pax8 modulates the expression of Wnt4 that is necessary for the maintenance of the epithelial phenotype of thyroid cells

Background

The transcription factor Pax8 is expressed during thyroid development and is involved in the morphogenesis of the thyroid gland and maintenance of the differentiated phenotype. In particular, Pax8 has been shown to regulate genes that are considered markers of thyroid differentiation. Recently, the analysis of the gene expression profile of FRTL-5 differentiated thyroid cells after the silencing of Pax8 identified Wnt4 as a novel target. Like the other members of the Wnt family, Wnt4 has been implicated in several developmental processes including regulation of cell fate and patterning during embryogenesis. To date, the only evidence on Wnt4 in thyroid concerns its down-regulation necessary for the progression of thyroid epithelial tumors.

Results

Here we demonstrate that Pax8 is involved in the transcriptional modulation of Wnt4 gene expression directly binding to its 5’-flanking region, and that Wnt4 expression in FRTL-5 cells is TSH-dependent. Interestingly, we also show that in thyroid cells a reduced expression of Wnt4 correlates with the alteration of the epithelial phenotype and that the overexpression of Wnt4 in thyroid cancer cells is able to inhibit cellular migration.

Conclusions

We have identified and characterized a functional Pax8 binding site in the 5’-flanking region of the Wnt4 gene and we show that Pax8 modulates the expression of Wnt4 in thyroid cells. Taken together, our results suggest that in thyroid cells Wnt4 expression correlates with the integrity of the epithelial phenotype and is reduced when this integrity is perturbed. In the end, we would like to suggest that the overexpression of Wnt4 in thyroid cancer cells is able to revert the mesenchymal phenotype.

Mechanisms of thyroid development and dysgenesis: an analysis based on developmental stages and concurrent embryonic anatomy

Thyroid dysgenesis is the most common cause of congenital hypothyroidism that affects 1 in 3000 newborns. Although a number of pathogenetic mutations in thyroid developmental genes have been identified, the molecular mechanism of disease is unknown in most cases. This chapter summarizes the current knowledge of normal thyroid development and puts the different developmental stages in perspective, from the time of foregut endoderm patterning to the final shaping of pharyngeal anatomy, for understanding how specific malformations may arise. At the cellular level, we will also discuss fate determination of follicular and C-cell progenitors and their subsequent embryonic growth, migration, and differentiation as the different thyroid primordia evolve and merge to establish the final size and shape of the gland.

Genome-wide analysis of Pax8 binding provides new insights into thyroid functions

Background

The transcription factor Pax8 is essential for the differentiation of thyroid cells. However, there are few data on genes transcriptionally regulated by Pax8 other than thyroid-related genes. To better understand the role of Pax8 in the biology of thyroid cells, we obtained transcriptional profiles of Pax8-silenced PCCl3 thyroid cells using whole genome expression arrays and integrated these signals with global cis-regulatory sequencing studies performed by ChIP-Seq analysis

Results

Exhaustive analysis of Pax8 immunoprecipitated peaks demonstrated preferential binding to intragenic regions and CpG-enriched islands, which suggests a role of Pax8 in transcriptional regulation of orphan CpG regions. In addition, ChIP-Seq allowed us to identify Pax8 partners, including proteins involved in tertiary DNA structure (CTCF) and chromatin remodeling (Sp1), and these direct transcriptional interactions were confirmed in vivo. Moreover, both factors modulate Pax8-dependent transcriptional activation of the sodium iodide symporter (Nis) gene promoter. We ultimately combined putative and novel Pax8 binding sites with actual target gene expression regulation to define Pax8-dependent genes. Functional classification suggests that Pax8-regulated genes may be directly involved in important processes of thyroid cell function such as cell proliferation and differentiation, apoptosis, cell polarity, motion and adhesion, and a plethora of DNA/protein-related processes.

Conclusion

Our study provides novel insights into the role of Pax8 in thyroid biology, exerted through transcriptional regulation of important genes involved in critical thyrocyte processes. In addition, we found new transcriptional partners of Pax8, which functionally cooperate with Pax8 in the regulation of thyroid gene transcription. Besides, our data demonstrate preferential location of Pax8 in non-promoter CpG regions. These data point to an orphan CpG island-mediated mechanism that represents a novel role of Pax8 in the transcriptional output of the thyrocyte.

Role of the wnt pathway in thyroid cancer

Aberrant activation of Wnt signaling is involved in the development of several epithelial tumors. Wnt signaling includes two major types of pathways: (i) the canonical or Wnt/β-catenin pathway; and (ii) the non-canonical pathways, which do not involve β-catenin stabilization. Among these pathways, the Wnt/β-catenin pathway has received most attention during the past years for its critical role in cancer. A number of publications emphasize the role of the Wnt/β-catenin pathway in thyroid cancer. This pathway plays a crucial role in development and epithelial renewal, and components such as β-catenin and Axin are often mutated in thyroid cancer. Although it is accepted that altered Wnt signaling is a late event in thyroid cell transformation that affects anaplastic thyroid tumors, recent data suggest that it is also altered in papillary thyroid carcinoma (PTC) with RET/PTC mutations. Therefore, the purpose of this review is to summarize the main relevant data of Wnt signaling in thyroid cancer, with special emphasis on the Wnt/β-catenin pathway.