Expression, function, and regulation of the embryonic transcription factor TBX1 in parathyroid tumors

The Induction of Parathyroid Cell Differentiation from Human Induced Pluripotent Stem Cells Promoted Via TGF-α/EGFR Signaling

The parathyroid gland plays an essential role in mineral and bone metabolism. Cultivation of physiological human parathyroid cells has yet to be established and the method by which parathyroid cells differentiate from pluripotent stem cells remains uncertain. Therefore, it has been hard to clarify the mechanisms underlying the onset of parathyroid disorders, such as hyperparathyroidism. In this study, we developed a new method of parathyroid cell differentiation from human induced pluripotent stem (iPS) cells. Parathyroid cell differentiation occurred in accordance with embryologic development. Differentiated cells, which expressed the parathyroid hormone, adopted unique cell aggregation similar to the parathyroid gland. In addition, these differentiated cells were identified as calcium-sensing receptor (CaSR)/epithelial cell adhesion molecule (EpCAM) double-positive cells. Interestingly, stimulation with transforming growth factor-α (TGF-α), which is considered a causative molecule of parathyroid hyperplasia, increased the CaSR/EpCAM double-positive cells, but this effect was suppressed by erlotinib, which is an epidermal growth factor receptor (EGFR) inhibitor. These results suggest that TGF-α/EGFR signaling promotes parathyroid cell differentiation from iPS cells in a similar manner to parathyroid hyperplasia.

Molecular and Clinical Spectrum of Primary Hyperparathyroidism

Recent data suggest an increase in the overall incidence of parathyroid disorders, with primary hyperparathyroidism (PHPT) being the most prevalent parathyroid disorder. PHPT is associated with morbidities (fractures, kidney stones, chronic kidney disease) and increased risk of death. The symptoms of PHPT can be nonspecific, potentially delaying the diagnosis. Approximately 15% of patients with PHPT have an underlying heritable form of PHPT that may be associated with extraparathyroidal manifestations, requiring active surveillance for these manifestations as seen in multiple endocrine neoplasia type 1 and 2A. Genetic testing for heritable forms should be offered to patients with multiglandular disease, recurrent PHPT, young onset PHPT (age ≤40 years), and those with a family history of parathyroid tumors. However, the underlying genetic cause for the majority of patients with heritable forms of PHPT remains unknown. Distinction between sporadic and heritable forms of PHPT is useful in surgical planning for parathyroidectomy and has implications for the family. The genes currently known to be associated with heritable forms of PHPT account for approximately half of sporadic parathyroid tumors. But the genetic cause in approximately half of the sporadic parathyroid tumors remains unknown. Furthermore, there is no systemic therapy for parathyroid carcinoma, a rare but potentially fatal cause of PHPT. Improved understanding of the molecular characteristics of parathyroid tumors will allow us to identify biomarkers for diagnosis and novel targets for therapy.

Parathyroid Carcinoma: Update on Pathogenesis and Therapy

Parathyroid carcinoma (PC) is a very rare endocrine cancer with aggressive behavior, a high metastatic potential, and a poor prognosis. Surgical resection of affected gland(s) and other involved structures is the elective therapy. Pre-operative and intra-operative differential diagnosis with benign parathyroid adenoma remains a challenge. The lack of a clear pre-operative diagnosis does not allow one, in many cases, to choose the correct surgical approach to malignant PC, increasing persistence, the recurrence rate, and the risk of metastases. An initial wrong diagnosis of parathyroid adenoma, with a minimally invasive parathyroidectomy, is associated with over 50% occurrence of metastases after surgery. Genetic testing could help in identifying patients at risk of congenital PC (i.e., CDC73 gene) and in driving the choice of neck surgery extension. Targeted effective treatments, other than surgery, for advanced and metastatic PC are needed. The pathogenesis of malignant parathyroid carcinogenesis is still largely unknown. In the last few years, advanced molecular techniques allowed researchers to identify various genetic abnormalities and epigenetic features characterizing PC, which could be crucial for selecting molecular targets and developing novel targeted therapeutic agents. We reviewed current findings in PC genetics, epigenetics, and proteomics and state-of-the-art therapies.

Osteocalcin modulates parathyroid cell function in human parathyroid tumors

INTRODUCTION

The bone matrix protein osteocalcin (OC), secreted by osteoblasts, displays endocrine effects. We tested the hypothesis that OC modulates parathyroid tumor cell function.

METHODS

Primary cell cultures derived from parathyroid adenomas (PAds) and HEK293 cells transiently transfected with the putative OC receptor GPRC6A or the calcium sensing receptor (CASR) were used as experimental models to investigate γ-carboxylated OC (GlaOC) or uncarboxylated OC (GluOC) modulation of intracellular signaling.

RESULTS

In primary cell cultures derived from PAds, incubation with GlaOC or GluOC modulated intracellular signaling, inhibiting pERK/ERK and increasing active β-catenin levels. GlaOC increased the expression of PTH, CCND1 and CASR, and reduced CDKN1B/p27 and TP73. GluOC stimulated transcription of PTH, and inhibited MEN1 expression. Moreover, GlaOC and GluOC reduced staurosporin-induced caspase 3/7 activity. The putative OC receptor GPRC6A was detected in normal and tumor parathyroids at membrane or cytoplasmic level in cells scattered throughout the parenchyma. In PAds, the membrane expression levels of GPRC6A and its closest homolog CASR positively correlated; GPRC6A protein levels positively correlated with circulating ionized and total calcium, and PTH levels of the patients harboring the analyzed PAds. Using HEK293A transiently transfected with either GPRC6A or CASR, and PAds-derived cells silenced for CASR, we showed that GlaOC and GluOC modulated pERK/ERK and active β-catenin mainly through CASR activation.

CONCLUSION

Parathyroid gland emerges as a novel target of the bone secreted hormone osteocalcin, which may modulate tumor parathyroid CASR sensitivity and parathyroid cell apoptosis.

TBX1 regulates myogenic differentiation by activating the TGFβ-Smad2/3 pathway in myoblasts

TBX1 is systematically conserved in the T-box transcription factor family and regulates craniofacial muscle development during various stages of myogenesis, including commitment, proliferation, terminal differentiation, and survival. However, the role and mechanism by which TBX1 regulates the myogenic development of myoblasts remains unclear. In our study, we overexpressed TBX1 in mouse C2C12 myoblasts using a lentivirus method. We found that TBX1 inhibited cell proliferation and muscle differentiation, which had no effect on apoptosis. During myogenic differentiation, we also found that TBX1 overexpressing cells regulate myogenic differentiation by upregulating the expression levels of Smad2 and Smad3 and downregulating the expression level of MEF2C. After treatment with a specific inhibitor of Smad3 (SIS3), the myogenic differentiation of wild-type and TBX1 overexpressing cells increased. Thus, TBX1 may regulate myoblast muscle differentiation by enhancing the expression of Smad2 and Smad3. TBX1 may be a therapeutic target for muscular dystrophy.

TBX1 functions as a putative oncogene of breast cancer through promoting cell cycle progression

We have previously identified a genetic variant, rs34331122 in the 22q11.21 locus, as being associated with breast cancer risk in a genome-wide association study. This novel variant is located in the intronic region of the T-box transcription factor 1 (TBX1) gene. Cis-expression quantitative trait loci analysis showed that expression of TBX1 was regulated by the rs34331122 variant. In the current study, we investigated biological functions and potential molecular mechanisms of TBX1 in breast cancer. We found that TBX1 expression was significantly higher in breast cancer tumor tissues than adjacent normal breast tissues and increased with tumor stage (P < 0.05). We further knocked-down TBX1 gene expression in three breast cancer cell lines, MDA-MB-231, MCF-7 and T47D, using small interfering RNAs and examined consequential changes on cell oncogenicity and gene expression. TBX1 knock-down significantly inhibited breast cancer cell proliferation, colony formation, migration and invasion. RNA sequencing and flow cytometry analysis revealed that TBX1 knock-down in breast cancer cells induced cell cycle arrest in the G1 phase through disrupting expression of genes involved in the cell cycle pathway. Furthermore, survival analysis using the online Kaplan-Meier Plotter suggested that higher TBX1 expression was associated with worse outcomes in breast cancer patients, especially for estrogen receptor-positive breast cancer, with HRs (95% CIs) for overall survival (OS) and distant metastasis free survival (DMFS) of 1.5 (1.05-2.15) and 1.55 (1.10-2.18), respectively. In conclusion, our results suggest that the TBX1 gene may act as a putative oncogene of breast cancer through regulating expressions of cell cycle-related genes.

Aberrant Epigenetic Alteration of PAX1 Expression Contributes to Parathyroid Tumorigenesis

CONTEXT

Primary hyperparathyroidism (PHPT) results from the hypersecretion of parathyroid hormone from parathyroid tumors. A transcription factor, namely Paired box1 (PAX1), is active in parathyroid gland development.

OBJECTIVE

We aimed to study potential epigenetic-mediated mechanism of PAX1 gene in sporadic parathyroid adenomas.

METHODS

In parathyroid adenomas tissues, we analyzed the DNA methylation via bisulfite-specific polymerase chain reaction (BSP) and histone modifications via chromatin immunoprecipitation in regulating the differential expression of PAX1.

RESULTS

The results showed that mRNA and protein expression of PAX1 was significantly reduced in parathyroid adenomas. Bisulfite sequencing demonstrated hypermethylation in the promoter region of PAX1 (35%; 14/40) and lower levels of histone 3 lysine 9 acetylation (H3K9ac) were observed on the promoter region of PAX1 (6-fold; P < .004) in parathyroid adenomas. Furthermore, upon treatment with a pharmacologic inhibitor, namely 5'aza-2 deoxycytidine, in rat parathyroid continuous cells, we found re-expression of PAX1 gene.

CONCLUSION

Our study not only reveals expression of PAX1 is epigenetically deregulated but also paves a way for clinical and therapeutic implications in patients with PHPT.

Genetics and Epigenetics of Parathyroid Carcinoma

Parathyroid carcinoma (PC) is an extremely rare malignancy, accounting less than 1% of all parathyroid neoplasms, and an uncommon cause of primary hyperparathyroidism (PHPT), characterized by an excessive secretion of parathyroid hormone (PTH) and severe hypercalcemia. As opposed to parathyroid hyperplasia and adenomas, PC is associated with a poor prognosis, due to a commonly unmanageable hypercalcemia, which accounts for death in the majority of cases, and an overall survival rate of 78-85% and 49-70% at 5 and 10 years after diagnosis, respectively. No definitively effective therapies for PC are currently available. The mainly employed treatment for PC is the surgical removal of tumoral gland(s). Post-surgical persistent or recurrent disease manifest in about 50% of patients. The comprehension of genetic and epigenetic bases and molecular pathways that characterize parathyroid carcinogenesis is important to distinguish malignant PCs from benign adenomas, and to identify specific targets for novel therapies. Germline heterozygote inactivating mutations of the CDC73 tumor suppressor gene, with somatic loss of heterozygosity at 1q31.2 locus, account for about 50-75% of familial cases; over 75% of sporadic PCs harbor biallelic somatic inactivation/loss of CDC73. Recurrent mutations of the PRUNE2 gene, a recurrent mutation in the ADCK1 gene, genetic amplification of the CCND1 gene, alterations of the PI3K/AKT/mTOR signaling pathway, and modifications of microRNA expression profile and gene promoter methylation pattern have all been detected in PC. Here, we review the current knowledge on gene mutations and epigenetic changes that have been associated with the development of PC, in both familial and sporadic forms of this malignancy.

Accelerated Maturation, Exhaustion, and Senescence of T cells in 22q11.2 Deletion Syndrome

PURPOSE

22q11.2 deletion syndrome (22q11.2DS) is a primary immunodeficiency characterized chiefly by the hypoplasia of the thymus resulting in T cell lymphopenia, increased susceptibility to infections, and higher risk of autoimmune diseases. The irregular thymic niche of T cell development may contribute to autoimmune and atopic complications, whereas the compensatory mechanism of homeostatic T cell proliferation and continuous immune stimulation may result in T cell senescence and exhaustion, further aggravating the immune system dysregulation.

METHODS

We used flow cytometry to investigate T cell maturation, delineation, proliferation, activation, and expression of senescence and exhaustion-associated markers (PD1, KLRG1, CD57) in 17 pediatric and adolescent patients with 22q11.2DS and age-matched healthy donors.

RESULTS

22q11.2DS patients aged 0-5 years had fewer naïve but more effector memory T cells with a tendency to approach normal values with increasing age. Young patients in particular had a higher percentage of proliferating T cells and increased expression of PD1, KLRG1, and CD57, as well as cells co-expressing several exhaustion-associated molecules (PD1, KLRG1, Tbet, Eomes, Helios). Additionally, high-risk 22q11.2DS patients with very low numbers of CD4 T cells had significantly higher percentage of Th1 and Th17 T cells, driven in part by higher proportion of mature T cell forms.

CONCLUSION

The low thymic output and accelerated T cell differentiation remain the principal features of 22q11.2DS patient immunity, especially in young patients of < 5 years. Later in life, homeostatic proliferation drives expression of T cell exhaustion and senescence-associated markers, suggesting functional aberrations in addition to numeric T cell deficiency.

SNP-mediated binding of TBX1 to the enhancer element of IL-10 reduces the risk of Behçet's disease

Aims: The genetic association between Behçet's disease susceptibility and IL-10 has been confirmed in multiple cohorts, but the underlying mechanism of this association remains unclear. Materials & methods: We combined public resources and laboratory experiments (electrophoretic mobility shift assays, chromatin immunoprecipitation, luciferase reporter gene and CRISPR/Cas9 genome editing) to analyze transcription factor binding and enhancer activity controlling IL-10 expression. Results & conclusion: The T allele of noncoding rs3024490 within super-enhancer elements is able to specifically bind TBX1 and, in turn, promotes the enhancer activity and increased expression of IL-10. However, a relative deficiency in TBX1 in Behçet's disease patients leads to the low expression of IL-10 and increased risk of developing Behçet's disease.

The Core Stem Genes SOX2, POU5F1/OCT4, and NANOG Are Expressed in Human Parathyroid Tumors and Modulated by MEN1, YAP1, and β-catenin Pathways Activation

Tumors of the parathyroid glands are the second most common endocrine neoplasia. Epigenetic studies revealed an embryonic signature involved in parathyroid tumorigenesis. Here, we investigated the expression of the stem core genes SOX2, POU5F1/OCT4, and NANOG. Rare cells within normal parathyroid glands expressed POU5F1/OCT4 and NANOG, while SOX2 was undetectable. Nuclear SOX2 expression was detectable in 18% of parathyroid adenomas (PAds, n = 34) involving 5–30% of cells, while OCT4 and NANOG were expressed at the nuclear level in a more consistent subset of PAds involving 15–40% of cells. Most parathyroid carcinomas expressed the core stem genes. SOX2-expressing cells co-expressed parathormone (PTH). In PAds-derived primary cultures, silencing of the tumor suppressor gene MEN1 induced the expression of SOX2, likely through a MEN1/HAR1B/SOX2 axis, while calcium-sensing receptor activation increased SOX2 mRNA levels through YAP1 activation. In addition, inducing nuclear β-catenin accumulation in PAds-derived primary cultures by short-term incubation with lithium chloride (LiCl), SOX2 and POU5F1/OCT4 expression levels increased, while NANOG transcripts were reduced, and LiCl long-term incubation induced an opposite pattern of gene expression. In conclusion, detection of the core stem genes in parathyroid tumors supports their embryogenic signature, which is modulated by crucial genes involved in parathyroid tumorigenesis.

Transcriptomic analyses of gastrulation-stage mouse embryos with differential susceptibility to alcohol

Genetics are a known contributor to differences in alcohol sensitivity in humans with fetal alcohol spectrum disorders (FASDs) and in animal models. Our study profiled gene expression in gastrulation-stage embryos from two commonly used, genetically similar mouse substrains, C57BL/6J (6J) and C57BL/6NHsd (6N), that differ in alcohol sensitivity. First, we established normal gene expression patterns at three finely resolved time points during gastrulation and developed a web-based interactive tool. Baseline transcriptional differences across strains were associated with immune signaling. Second, we examined the gene networks impacted by alcohol in each strain. Alcohol caused a more pronounced transcriptional effect in the 6J versus 6N mice, matching the increased susceptibility of the 6J mice. The 6J strain exhibited dysregulation of pathways related to cell death, proliferation, morphogenic signaling and craniofacial defects, while the 6N strain showed enrichment of hypoxia and cellular metabolism pathways. These datasets provide insight into the changing transcriptional landscape across mouse gastrulation, establish a valuable resource that enables the discovery of candidate genes that may modify alcohol susceptibility that can be validated in humans, and identify novel pathogenic mechanisms of alcohol. This article has an associated First Person interview with the first author of the paper.

Yes-Associated Protein 1 Is a Novel Calcium Sensing Receptor Target in Human Parathyroid Tumors

The Hippo pathway is involved in human tumorigenesis and tissue repair. Here, we investigated the Hippo coactivator Yes-associated protein 1 (YAP1) and the kinase large tumor suppressor 1/2 (LATS1/2) in tumors of the parathyroid glands, which are almost invariably associated with primary hyperparathyroidism. Compared with normal parathyroid glands, parathyroid adenomas (PAds) and carcinomas show variably but reduced nuclear YAP1 expression. The kinase LATS1/2, which phosphorylates YAP1 thus promoting its degradation, was also variably reduced in PAds. Further, YAP1 silencing reduces the expression of the key parathyroid oncosuppressor multiple endocrine neoplasia type 1(MEN1), while MEN1 silencing increases YAP1 expression. Treatment of patient-derived PAds-primary cell cultures and Human embryonic kidney 293A (HEK293A) cells expressing the calcium-sensing receptor (CASR) with the CASR agonist R568 induces YAP1 nuclear accumulation. This effect was prevented by the incubation of the cells with RhoA/Rho-associated coiled-coil-containing protein kinase (ROCK) inhibitors Y27632 and H1152. Lastly, CASR activation increased the expression of the YAP1 gene targets CYR61, CTGF, and WNT5A, and this effect was blunted by YAP1 silencing. Concluding, here we provide preliminary evidence of the involvement of the Hippo pathway in human tumor parathyroid cells and of the existence of a CASR-ROCK-YAP1 axis. We propose a tumor suppressor role for YAP1 and LATS1/2 in parathyroid tumors.

T-box transcription factor TBX1, targeted by microRNA-6727-5p, inhibits cell growth and enhances cisplatin chemosensitivity of cervical cancer cells through AKT and MAPK pathways

Cervical cancer (CC) is the fourth most common cancers among women worldwide. T-box transcription factor 1 (TBX1), a member of the T-box family, has anti-tumor effects in some types of cancer, but its role in CC is yet unknown. The aim of this study is to investigate the functions and underlying mechanisms of TBX1 in CC. Online database UALCAN showed that TBX1 was down-regulated in CC tissues compared with normal tissues and patients with lower TBX1 expression level had a poor prognosis. TBX1 overexpression significantly decreased the proliferation, migration, and invasion of Hela and SiHa cells. Conversely, cell apoptosis and chemosensitivity to cisplatin were promoted in TBX1-overexpressing CC cells. Moreover, up-regulation of TBX1 inhibited both AKT and MAPK signaling pathways. Furthermore, dual luciferase report assay indicated that TBX1 could directly bind to miR-6727-5p. In addition, TBX1 expression was inhibited by miR-6727-5p mimic and up-regulated by miR-6727-5p inhibitor. Knockdown of TBX1 reversed the inhibitory effect of the miR-6727-5p inhibitor on CC cells. This study demonstrates that TBX1, a target gene of miR-6727-5p, acts as a tumor suppressor in CC, indicating that TBX1 may be a new target for CC therapy.

TBX1 Functions as a Tumor Activator in Prostate Cancer by Promoting Ribosome RNA Gene Transcription

TBX1 belongs to an evolutionarily conserved family of transcription factors involved in organ development. TBX1 has been reported to have a hypermethylated cytosine guanine dinucleotide island around its second exon, which was related to prostate cancer (PCa) progression. However, the role and exact mechanism of TBX1 in PCa remains unknown. Using human prostate samples, online data mining and multiple in vitro and in vivo models, we examined the biological role and underlying mechanisms of TBX1 in PCa. TBX1 was highly expressed in PCa tissues, and high TBX1 expression was positively associated with Gleason score, pathological tumor stage, pathological lymph node stage, extraprostatic extension and disease/progression-free survival. In vitro and in vivo data demonstrated that TBX1 silencing inhibits PCa cell proliferation and colony formation and increases the cell population at the G0/G1 phase. The exogenous expression of TBX1 rescued these phenotypes. Mechanistically, TBX1 silencing suppressed the expression of 45S ribosomal RNA (rRNA), which was rescued by the exogenous expression of TBX1. TBX1 silencing inhibited the monomethylation of histone 3 lysine 4 (H3K4me1) binding with the non-coding intergenic spacer (IGS) regions of ribosomal DNA (rDNA) and the recruitment of upstream binding factor to the promoter and IGS regions of rDNA. The drug-induced enhancement of H3K4me1 counteracted the effect of TBX1 silencing. These findings indicate that TBX1 exerts its tumor activator function in PCa cells via epigenetic control, thereby promoting rRNA gene transcription. Thus, TBX1 may represent a prognostic biomarker and therapeutic target for PCa patients.

Intratumor heterogeneity in human parathyroid tumors

Parathyroid tumors are the second most common endocrine neoplasia after thyroid neoplasia. They are mostly associated with impaired parathormone (PTH) synthesis and release determining the metabolic and clinical condition of primary hyperparathyroidism (PHPT). PHPT is the third most prevalent endocrine disorder, mainly affecting postmenopausal women. Parathyroid benign tumors, both adenomas of a single gland or hyperplasia involving all the glands, are the main histotypes, occurring in more than 95% of PHPT cases. The differential diagnosis between benign and malignant parathyroid lesions is a challenge for clinicians. It relies on histologic features, which display significant overlap between the histotypes with different clinical outcomes. Parathyroid adenomas and hyperplasia have been considered so far as a unique monoclonal/polyclonal entity, while accumulating evidence suggest great heterogeneity. Intratumor parathyroid heterogeneity involves tumor cell type, as well as tumor cell function, in terms of PTH synthesis and secretion, and of expression patterns of membrane and nuclear receptors (calcium sensing receptor, vitamin D receptor, α-klotho receptor and others). Intratumor heterogeneity can also interfere with cell molecular biology, in regard to clonality, oncosuppressor gene expression (such as MEN1 and HRPT2/CDC73), transcription factors (GCM2, TBX1) and microRNA expression. Such heterogeneity is likely involved in the phenotypic variability of the parathyroid tumors, and it should be considered in the clinical management, though at present target therapies are not available, with the exception of the calcium sensing receptor agonists.

The Role of Lithium in Management of Endocrine Tumors-A Comprehensive Review

Background: Epidemiological data reveal that treatment with lithium, a mood stabilizer, is associated with decreased incidence and mortality of certain cancer types, such as melanoma. Therefore, repositioning of lithium as an anticancer agent has emerged as a promising strategy in oncology. Since lithium affects the physiology of several endocrine tissues, the goal of this study was to analyze the role of lithium in the pathogenesis and treatment of tumors of the endocrine system. Methods: The databases of PubMed, EMBASE, MEDLINE, were searched from January 1970 through February 2019 for articles including the keywords "lithium and"-"thyroid cancer," "thyroid nodule," "parathyroid adenoma," "parathyroid carcinoma," "pituitary adenoma," "pituitary neuroendocrine tumor," "neuroendocrine tumor," "carcinoid," "adrenal adenoma," "adrenal carcinoma," "pheochromocytoma/paraganglioma." Preclinical in vitro and in vivo studies as well as case series, retrospective cohort studies and prospective trials were selected for the analysis. Results: Treatment with lithium has been associated with a higher prevalence of thyroid enlargement, hypothyroidism and increased calcium levels due to parathyroid adenoma or hyperplasia, as one of the mechanisms of its action is to stimulate proliferation of normal follicular thyroid and parathyroid cells via activation of the Wnt signaling pathway. Supratherapeutic concentrations of lithium decrease the activity of glycogen synthase kinase-3β (GSK-3β), leading to cell cycle arrest in several in vitro cancer models including medullary thyroid cancer (TC), pheochromocytoma/paraganglioma and carcinoid. Growth inhibitory effects of lithium in vivo have been documented in medullary TC xenograft mouse models. Clinically, lithium has been used as an adjuvant agent to therapy with radioactive iodine (RAI), as it increases the residence time of RAI in TC. Conclusion: Patients chronically treated with lithium need to be screened for hypothyroidism, goiter, and hyperparathyroidism, as the prevalence of these endocrine abnormalities is higher in lithium-treated patients than in the general population. The growth inhibitory effects of lithium in medullary TC, pheochromocytoma/paraganglioma and carcinoid were achieved with supratherapeutic concentrations of lithium thus limiting its translational perspective. Currently available clinical data on the efficacy of lithium in the therapy of endocrine tumors in human is limited and associated with conflicting results.

TBX1 Functions as a Tumor Suppressor in Thyroid Cancer Through Inhibiting the Activities of the PI3K/AKT and MAPK/ERK Pathways

BACKGROUND

TBX1 is a member of the T-box family of transcription factors characterized by a conserved DNA binding domain termed T-box. TBX1 has been reported to be downregulated in mouse skin tumors and is considered a negative regulator of tumor cell growth in mice. However, its role and exact mechanism in human cancers, including thyroid cancer, remain totally unknown.

METHODS

Quantitative reverse transcription polymerase chain reaction and Western blot assays were performed to evaluate the expression of investigated genes. Methylation-specific polymerase chain reaction and pyrosequencing were used to analyze TBX1 promoter methylation. The biological functions of TBX1 in thyroid cancer cells were determined by a series of in vitro and in vivo experiments. Chromatin immunoprecipitation sequencing and dual-luciferase reporter assays were used to identify its downstream targets.

RESULTS

This study demonstrates that TBX1 is frequently downregulated by promoter methylation in both papillary thyroid cancers and thyroid cancer cell lines. Ectopic expression of TBX1 in thyroid cancer cells dramatically inhibits cell viability, colony formation, and tumorigenic potential in nude mice, and induces cell-cycle arrest and apoptosis through modulating a panel of cell-cycle and apoptosis-related genes. In addition, ectopic expression of TBX1 significantly decreases the migration and invasion potential of thyroid cancer cells through inhibiting the process of epithelial-mesenchymal transition and the expression of matrix metalloproteinases. On the other hand, TBX1 knockdown markedly promotes thyroid cancer cell viability and invasiveness. Mechanistically, TBX1 exerts its tumor suppressor function in thyroid cancer cells through inhibiting phosphorylation of AKT at Ser473 and ERK via regulating its downstream targets such as RNF41, PARK2, and PHLPP2.

CONCLUSIONS

The data show that TBX1 is frequently inactivated by promoter methylation and functions as a potential tumor suppressor in thyroid cancer through inhibiting the activities of the PI3K/AKT and MAPK/ERK signaling pathways.

Parathyroid carcinoma

Parathyroid carcinoma (PC) is a rare disease with an indolent behavior due to the low malignant potential. The etiology is unknown. Somatic mutations of CDC73 gene, the same gene involved in the hyperparathyroidism-jaw tumor syndrome, can be identified in up to 70% of patients with PC and in one-third of cases the mutations are germline. Therefore, in patients who carry germline CDC73 gene mutations, its finding permits to identify the carriers among relatives and sometimes to early detect a parathyroid lesion in such subjects. The diagnosis of PC is commonly made after surgery, however there are some clinical/biochemical features that should raise the suspicion of PC, namely markedly elevated serum calcium and PTH levels, a large parathyroid lesion with suspected ultrasonographic features of malignancy, the damages of kidney and bones. The best chance of cure is the complete surgical resection with the en-bloc excision at the first operation, however several recurrences are often observed during the follow-up. Since PC is an indolent tumor with long-lasting survival and the death is due to complications of untreatable hypercalcemia, multiple surgical interventions with debulking of tumoral tissues along with medical treatment for reducing hypercalcemia are often needed. Patients with PC should be followed up along their lifetime.

MicroRNA-451a acts as tumor suppressor in cutaneous basal cell carcinoma

Background

Basal cell carcinoma (BCC) is the most common type of skin cancer. The underlying mechanism leading to BCC formation is not fully uncovered. The aim of this study was to characterize miRNA‐451a as a novel tumor suppressor in cutaneous BCC.

Methods

We first evaluated miRNA‐451a level in human BCC clinical tissues and inducible BCC mouse model. Then we studied the impact of overexpressing or inhibiting miR‐451a in cell proliferation, colony formation potential, and cell cycle pattern. Next, we employed luciferase reporter assay and western blotting to evaluate TBX1 as a downstream target of miRNA‐451a. Lastly, we confirmed TBX1 expressional change in BCC tissues by qPCR.

Results

miRNA‐451a was significantly reduced in human BCC tissues. The downregulation of miRNA‐451a was also confirmed in BCC mouse model. Overexpressing miRNA‐451a in tumor cells markedly suppressed cell growth through G1 cell cycle arrest. However, inhibiting miRNA‐451a in primary cells promoted cell growth and colony formation capacity. TBX1 (602054) was predicted as a downstream target of miRNA‐451a and this was confirmed by luciferase assay and protein expression. Finally, TBX1 level was shown upregulated in BCC tissues as inversely to miR451a.

Conclusion

Our studies revealed that miRNA‐451a/TBX1 axis played a pivotal role in BCC tumorigenesis.

The aberrantly expressed miR-372 partly impairs sensitivity to apoptosis in parathyroid tumor cells

Parathyroid tumors deregulate microRNAs belonging to the two clusters on the chromosome 19, the C19MC and miR-371-373 clusters. Here, we report that the embryonic miR-372 is aberrantly expressed in half of parathyroid adenomas (PAds) in most of atypical adenomas and carcinomas (n = 15). Through in situ hybridization, we identified that miR-372-positive parathyroid tumor cells were scattered throughout the tumor parenchyma. In PAd-derived cells, ectopic miR-372 inhibited the expression of its targets CDKN1A/p21 and LATS2 at both mRNA and protein levels. Although the viability of parathyroid cells was not affected by miR-372 overexpression, the miRNA blunted camptothecin-induced apoptosis in primary PAd-derived cultures. miR-372 overexpression in parathyroid tumor cells increased parathormone (PTH) mRNA levels, and it positively correlated in vivo with circulating PTH levels. Conversely, the parathyroid-specific genes TBX1 and GCM2 were not affected by miR-372 mimic transfection. Finally, miR-372 dampened the Wnt pathway in parathyroid tumor cells through DKK1 upregulation. In conclusion, miR-372 is a novel mechanism exploited by a subset of parathyroid tumor cells to partially decrease sensitivity to apoptosis, to increase PTH synthesis and to deregulate Wnt signaling.