The histone methyltransferase EZH2, an oncogene common to benign and malignant parathyroid tumors

Whole-exome Sequencing of Atypical Parathyroid Tumors Detects Novel and Common Genes Linked to Parathyroid Tumorigenesis

CONTEXT

Atypical parathyroid tumor (APT) represents a neoplasm characterized by histological features typical of parathyroid carcinoma (PC) but lacking local infiltration and/or distant metastasis, leading to uncertainty regarding its malignant potential.

OBJECTIVE

To characterize the molecular landscape and deregulated pathways in APT.

METHODS

Whole-exome sequencing (WES) was conducted on 16 APTs. DNA from tumors and matched peripheral blood underwent WES using Illumina HiSeq3000.

RESULTS

A total of 192 nonsynonymous variants were identified. The median number of protein-altering mutations was 9. The most frequently mutated genes included BCOR, CLMN, EZH1, JAM2, KRTAP13-3, MUC16, MUC19, and OR1S1. Seventeen mutated genes belong to the Cancer Gene Census list. The most consistent hub genes identified through STRING network analysis were ATM, COL4A5, EZH2, MED12, MEN1, MTOR, PI3, PIK3CA, PIK3CB, and UBR5. Deregulated pathways included the PI3 K/AKT/mTOR pathway, Wnt signaling, and extracellular matrix organization. Variants in genes such as MEN1, CDC73, EZH2, PIK3CA, and MTOR, previously reported as established or putative/candidate driver genes in benign adenoma (PA) and/or PC, were also identified in APT.

CONCLUSION

APT does not appear to have a specific molecular signature but shares genomic alterations with both PA and PC. The incidence of CDC73 mutations is low, and it remains unclear whether these mutations are associated with a higher risk of recurrence. Our study confirms that PI3 K/AKT/mTOR and Wnt signaling represents the pivotal pathways in parathyroid tumorigenesis and also revealed mutations in key epigenetic modifier genes (BCOR, KDM2A, MBD4, and EZH2) involved in chromatin remodeling, DNA, and histone methylation.

The significance of an immunohistochemical marker-based panel in assisting the diagnosis of parathyroid carcinoma

PURPOSE

Parathyroid carcinoma (PC) is an endocrine malignancy with a poor prognosis. However, the diagnosis of PC is still a difficult problem. A model with immunohistochemical (IHC) staining of 5 biomarkers has been reported from limited samples for the differential diagnosis of PC. In the present study, a series of IHC markers was applied in relatively large samples to optimize the diagnostic model for PC.

METHODS

In this study, 44 patients with PC, 6 patients with atypical parathyroid tumors and 57 patients with parathyroid adenomas were included. IHC staining for parafibromin, Ki-67, galectin-3, protein-encoding gene product 9.5 (PGP9.5), E-cadherin, and enhancer of zeste homolog 2 (EZH2) was performed on formalin-fixed, paraffin-embedded tissue samples. The effects of clinical characteristics, surgical procedure, and IHC staining results of tumor tissues on the diagnosis and prognosis of PC were evaluated retrospectively.

RESULTS

A logistic regression model with IHC results of parafibromin, Ki-67, and E-cadherin was created to differentiate PC with an area under the curve of 0.843. Cox proportional hazards analysis showed that negative parafibromin staining (hazard ratio: 3.26, 95% confidence interval: 1.28-8.34, P = 0.013) was related to the recurrence of PC.

CONCLUSION

An IHC panel of parafibromin, Ki-67 and E-cadherin may help to distinguish PC from parathyroid neoplasms. Among the 6 IHC markers and clinical features examined, the risk factor related to PC recurrence was parafibromin staining loss.

KMT2A and chronic inflammation as potential drivers of sporadic parathyroid adenoma

BACKGROUND

Sporadic parathyroid adenoma (PA) is the most common cause of hyperparathyroidism, yet the mechanisms involved in its pathogenesis remain incompletely understood.

METHODS

Surgically removed PA samples, along with normal parathyroid gland (PG) tissues that were incidentally dissected during total thyroidectomy, were analysed using single-cell RNA-sequencing with the 10× Genomics Chromium Droplet platform and Cell Ranger software. Gene set variation analysis was conducted to characterise hallmark pathway gene signatures, and single-cell regulatory network inference and clustering were utilised to analyse transcription factor regulons. Immunohistochemistry and immunofluorescence were performed to validate cellular components of PA tissues. siRNA knockdown and gene overexpression, alongside quantitative polymerase chain reaction, Western blotting and cell proliferation assays, were conducted for functional investigations.

RESULTS

There was a pervasive increase in gene transcription in PA cells (PACs) compared with PG cells. This is associated with high expression of histone-lysine N-methyltransferase 2A (KMT2A). High KMT2A levels potentially contribute to promoting PAC proliferation through upregulation of the proto-oncogene CCND2, which is mediated by the transcription factors signal transducer and activator of transcription 3 (STAT3) and GATA binding protein 3 (GATA3). PA tissues are heavily infiltrated with myeloid cells, while fibroblasts, endothelial cells and macrophages in PA tissues are commonly enriched with proinflammatory gene signatures relative to their counterparts in PG tissues.

CONCLUSIONS

We revealed the previously underappreciated involvement of the KMT2A‒STAT3/GATA3‒CCND2 axis and chronic inflammation in the pathogenesis of PA. These findings underscore the therapeutic promise of KMT2A inhibition and anti-inflammatory strategies, highlighting the need for future investigations to translate these molecular insights into practical applications.

HIGHLIGHTS

Single-cell RNA-sequencing reveals a transcriptome catalogue comparing sporadic parathyroid adenomas (PAs) with normal parathyroid glands. PA cells show a pervasive increase in gene expression linked to KMT2A upregulation. KMT2A-mediated STAT3 and GATA3 upregulation is key to promoting PA cell proliferation via cyclin D2. PAs exhibit a proinflammatory microenvironment, suggesting a potential role of chronic inflammation in PA pathogenesis.

EZH2 as a potential therapeutic target for gastrointestinal cancers

Gastrointestinal (GI) cancers continue to be a major cause of mortality and morbidity globally. Understanding the molecular pathways associated with cancer progression and severity is essential for creating effective cancer treatments. In cancer research, there is a notable emphasis on Enhancer of zeste homolog 2 (EZH2), a key player in gene expression influenced by its irregular expression and capacity to attach to promoters and alter methylation status. This review explores the impact of EZH2 signaling on various GI cancers, such as colorectal, gastric, pancreatic, hepatocellular, esophageal, and cholangiocarcinoma. The primary function of EZH2 signaling is to facilitate the accelerated progression of cancer cells. Additionally, EZH2 has the capacity to modulate the reaction of GI cancers to chemotherapy and radiotherapy. Numerous pathways, including long non-coding RNAs and microRNAs, serve as upstream regulators of EZH2 in these types of cancer. EZH2's enzymatic activity enables it to attach to target gene promoters, resulting in methylation that modifies their expression. EZH2 could be considered as an independent prognostic factor, with increased expression correlating with a worse disease prognosis. Additionally, a range of gene therapies including small interfering RNA, and anti-tumor agents are being explored to target EZH2 for cancer treatment. This comprehensive review underscores the current insights into EZH2 signaling in gastrointestinal cancers and examines the prospect of therapies targeting EZH2 to enhance patient outcomes.

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: molecular therapeutic targets

Parathyroid carcinoma (PC) is an extremely rare malignant tumor of the parathyroid glands, accounting for less than 1% of primary hyperparathyroidism, commonly characterized by severe and unmanageable hypercalcemia, aggressive behavior, high metastatic potential, and poor prognosis. PC manifests prevalently as a sporadic tumor and only occasionally it is part of congenital syndromic and non-syndromic endocrine diseases. Molecular pathogenesis of this form of parathyroid tumor is not fully elucidated and it appears to be caused by multiple genetic and epigenetic drivers, differing among affected patients and not yet clearly stated in distinguishing PC from the benign parathyroid adenoma (PA). Congenital forms of PC have been prevalently associated with germline heterozygous loss-of-function mutations of the CDC73 tumor suppressor gene, both in the context of the hyperparathyroidism jaw-tumor syndrome (HPT-JT) and of the isolated familial hyperparathyroidism (FIPH). Currently, surgical en bloc resection of affected gland(s) and other involved structures is the elective therapy for both primary and recurrent PC. However, it usually results ineffective for advance and metastatic disease, and a high percentage of post-operative recurrence is reported. Targeted medical therapies for surgically untreatable PC, based on the molecular profile of PC samples, are, therefore, needed. The characterization of genetic and epigenetic alterations and deregulated pathways in PC samples will be of fundamental importance to tailor treatment for each patient. Here, we reviewed main findings on molecular pathogenetic aspects of PC, and the current state of the art of therapies.

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.

Histone Modification on Parathyroid Tumors: A Review of Epigenetics

Parathyroid tumors are very prevalent conditions among endocrine tumors, being the second most common behind thyroid tumors. Secondary hyperplasia can occur beyond benign and malignant neoplasia in parathyroid glands. Adenomas are the leading cause of hyperparathyroidism, while carcinomas represent less than 1% of the cases. Tumor suppressor gene mutations such as MEN1 and CDC73 were demonstrated to be involved in tumor development in both familiar and sporadic types; however, the epigenetic features of the parathyroid tumors are still a little-explored subject. We present a review of epigenetic mechanisms related to parathyroid tumors, emphasizing advances in histone modification and its perspective of becoming a promising area in parathyroid tumor research.

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.

Analyzing Genetic Differences Between Sporadic Primary and Secondary/Tertiary Hyperparathyroidism by Targeted Next-Generation Panel Sequencing

Secondary hyperparathyroidism (SHPT) is characterized by excessive serum parathyroid hormone levels in response to decreasing kidney function, and tertiary hyperparathyroidism (THPT) is often the result of a long-standing SHPT. To date, several genes have been associated with the pathogenesis of primary hyperparathyroidism (PHPT). However, the molecular genetic mechanisms of uremic hyperparathyroidism (HPT) remain uncharacterized. To elucidate the differences in genetic alterations between PHPT and SHPT/THPT, the targeted next-generation sequencing of genes associated with HPT was performed using DNA extracted from parathyroid tissues. As a result, 26 variants in 19 PHPT or SHPT/THPT appeared as candidate pathogenic mutations, which corresponded to 9 (35%) nonsense, 8 (31%) frameshift, 6 (23%) missense, and 3 (11%) splice site mutations. The MEN1 (23%, 6/26), ASXL3 (15%, 4/26), EZH2 (12%, 3/26), and MTOR (8%, 2/26) genes were frequently mutated. Sixteen of 25 patients with PHPT (64%) had one or more mutations, whereas 3 (21%) of 21 patients with SHPT/THPT had only 1 mutation (p = 0.001). Sixteen of 28 patients (57%) with parathyroid adenoma (PA) had one or more mutations, whereas 3 of 18 patients (17%) with parathyroid hyperplasia (PH) had just one mutation (p = 0.003). Known driver mutations associated with parathyroid tumorigenesis such as CCND1/PRAD1, CDC73/HRPT2, and MEN1 were identified only in PA (44%, 7/16 with mutations). Our results suggest that molecular genetic abnormalities in SHPT/THPT are distinct from those in PHPT. These findings may help in analyzing the molecular pathogenesis underlying uremic HPT development.

EZH2 presents a therapeutic target for neuroendocrine tumors of the small intestine

Small intestinal neuroendocrine tumors (SI-NETs) are slow-growing tumors that seem genetically quite stable without highly recurrent mutations, but are epigenetically dysregulated. In contrast to the undetectable expression of the enhancer of zeste homolog 2 (EZH2) histone methyltransferase in the enterochromaffin cells of the small intestine, we found high and differential expression of EZH2 in primary SI-NETs and corresponding metastases. Silencing EZH2 in the SI-NET cell line CNDT2.5 reduced cell proliferation and induced apoptosis. Furthermore, EZH2 knockout inhibited tumor progression in a CNDT2.5 SI-NET xenograft mouse model, and treatment of SI-NET cell lines CNDT2.5 and GOT1 with the EZH2-specific inhibitor CPI-1205 decreased cell viability and promoted apoptosis. Moreover, CPI-1205 treatment reduced migration capacity of CNDT2.5 cells. The EZH2 inhibitor GSK126 also repressed proliferation of CNDT2.5 cells. Recently, metformin has received wide attention as a therapeutic option in diverse cancers. In CNDT2.5 and GOT1 cells, metformin suppressed EZH2 expression, and inhibited cell proliferation. Exposure of GOT1 three-dimensional cell spheroids to CPI-1205 or metformin arrested cell proliferation and decreased spheroid size. These novel findings support a possible role of EZH2 as a candidate oncogene in SI-NETs, and suggest that CPI-1205 and metformin should be further evaluated as therapeutic options for patients with SI-NETs.

The evolution and ecology of benign tumors

Tumors are usually classified into two main categories - benign or malignant, with much more attention being devoted to the second category given that they are usually associated with more severe health issues (i.e., metastatic cancers). Here, we argue that the mechanistic distinction between benign and malignant tumors has narrowed our understanding of neoplastic processes. This review provides the first comprehensive discussion of benign tumors in the context of their evolution and ecology as well as interactions with their hosts. We compare the genetic and epigenetic profiles, cellular activities, and the involvement of viruses in benign and malignant tumors. We also address the impact of intra-tumoral cell composition and its relationship with the tumoral microenvironment. Lastly, we explore the differences in the distribution of benign and malignant neoplasia across the tree of life and provide examples on how benign tumors can also affect individual fitness and consequently the evolutionary trajectories of populations and species. Overall, our goal is to bring attention to the non-cancerous manifestations of tumors, at different scales, and to stimulate research on the evolutionary ecology of host-tumor interactions on a broader scale. Ultimately, we suggest that a better appreciation of the differences and similarities between benign and malignant tumors is fundamental to our understanding of malignancy both at mechanistic and evolutionary levels.

Parathyroid Tumors: Molecular Signatures

Parathyroid tumors are rare endocrine neoplasms affecting 0.1–0.3% of the general population, including benign parathyroid adenomas (PAs; about 98% of cases), intermediate atypical parathyroid adenomas (aPAs; 1.2–1.3% of cases) and malignant metastatic parathyroid carcinomas (PCs; less than 1% of cases). These tumors are characterized by a variable spectrum of clinical phenotypes and an elevated cellular, histological and molecular heterogeneity that make it difficult to pre-operatively distinguish PAs, aPAs and PCs. Thorough knowledge of genetic, epigenetic, and molecular signatures, which characterize different parathyroid tumor subtypes and drive different tumorigeneses, is a key step to identify potential diagnostic biomarkers able to distinguish among different parathyroid neoplastic types, as well as provide novel therapeutic targets and strategies for these rare neoplasms, which are still a clinical and therapeutic challenge. Here, we review the current knowledge on gene mutations and epigenetic changes that have been associated with the development of different clinical types of parathyroid tumors, both in familial and sporadic forms of these endocrine neoplasms.

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.

Genetic Alteration Profiles and Clinicopathological Associations in Atypical Parathyroid Adenoma

Genomic aberrations associated with atypical parathyroid adenoma (AA) are poorly understood. Thus, herein, we sought to expand our current understanding of the molecular basis of atypical parathyroid adenomas. We analyzed 134 samples that had been surgically obtained from parathyroid tumors, including parathyroid carcinomas, atypical parathyroid adenomas, and parathyroid adenomas. The tumors were harvested from formalin-fixed, paraffin-embedded tissues. Fifteen tumor-related genes from recently published genome sequencing data were subjected to targeted sequencing analysis, and an average sequencing depth of 500x was achieved. Sixteen (16/50, 32%) AA tumors harbored at least one of the following genomic alterations: CDC73 (12, 24%), EZH2 (4, 8%), HIC1 (1, 2%), and CDKN2A (1, 2%). Our study identified, for the first time, a relatively high frequency of genomic alterations in patients with AA in a Chinese population. This suggests that AA arises de novo, rather than developing from a parathyroid adenoma. Altogether, these findings will improve our understanding of the malignant potential of parathyroid tumors at the molecular level.

Parathyroid cancer: A systematic review of diagnostic biomarkers

INTRODUCTION

Parathyroid cancers are rare and difficult to distinguish from benign parathyroid tumours. Prediction of malignancy often relies on intraoperative assessment of invasion. Standard histology is also inadequate; especially in the absence of local invasion, lymph nodal disease and metastasis. The aim of this project was to systematically review published literature on potential bio-markers used for the diagnosis of parathyroid cancer.

METHODS

Pubmed, Web of Science and Medline databases were searched. Inclusion criteria included English language papers published after 1985 and reporting on biomarkers in human studies of parathyroid cancer and benign disease.

RESULTS

118 relevant papers were appraised; all were observational studies. At least 2 papers studied 8 serum, 4 urine and 27 tissue biomarkers on the diagnosis of parathyroid cancer. Of these, 5 serum and 13 tissue markers have been demonstrated in at least one study to be statistically different in benign and malignant disease. We present a synthesis of data for each biomarker and measures of diagnostic accuracy where possible.

CONCLUSIONS

Consideration should be given to the use of a panel of biomarkers to review patients with suspected parathyroid cancer. A profile including serum calcium and PTH levels and tissue expression of APC, Parafibromin, PGP9.5, Galectin 3 and Ki67 is proposed. Systematic Review Registration Number - CRD42019127833.

Genomics and Epigenomics in Parathyroid Neoplasia: from Bench to Surgical Pathology Practice

The majority of parathyroid disease encountered in routine practice is due to single parathyroid adenoma, of which the majority arise as sporadic tumors. This is usually a straightforward diagnosis in endocrine pathology when in the appropriate clinical setting, although subsets of cases will exhibit atypical histological features that may warrant additional immunohistochemical and genetic analyses to estimate the malignant potential. Parathyroid carcinomas on the other hand, are bona fide malignant tumors characterized by their unequivocal invasion demonstrated through routine histology or metastasis. The ultimate endpoint for any molecular marker discovered through laboratory investigations is to be introduced in clinical routine practice and guide the surgical pathologist in terms of diagnostics and prognostication. For parathyroid tumors, the two main diagnostic challenges include the distinction between parathyroid adenoma and parathyroid carcinoma, as well as the pinpointing of hereditable disease for familial screening purposes. While numerous markers on genetic, epigenetic, and protein levels have been proposed as discriminative in these aspects, this review aims to condense the scientific coverage of these enigmatic topics and to propose a focused surgical pathology approach to the subject.

Reduced Calcium Sensing Receptor (CaSR) Expression Is Epigenetically Deregulated in Parathyroid Adenomas

AIM

Reduced calcium sensing receptor (CaSR) expression has been implicated in parathyroid tumorigenesis, but the underlying mechanism remains elusive. Accordingly, we aimed to explore the epigenetic changes (DNA methylation and histone modifications) involved in CaSR regulation in sporadic parathyroid adenomas and correlate epigenetic state with disease indices.

EXPERIMENTAL DESIGN

Forty sporadic parathyroid adenomas and 10 control parathyroid tissues were studied. Real-time quantitative PCR (qPCR) for mRNA and immunohistochemistry for protein expression of CaSR were performed. The methylation status of the CaSR promoter 2 was determined by bisulphite sequencing analysis of sodium bisulphite-converted DNA. To determine the role of histone modifications in the CaSR regulation, chromatin immunoprecipitation-qPCR assay was performed.

RESULTS

Real-time qPCR revealed reduced CaSR mRNA expression with a fold reduction of 0.12 (P < 0.0001) in parathyroid adenomas. Immunohistochemistry revealed reduced protein expression of CaSR in 90% (36/40) of adenomas. The promoter 2 region of CaSR displayed significant hypermethylation in 45% (18/40) of the adenomas compared with the controls (6.7%; 1 of 10) (P < 0.002). Bisulphite sequencing analysis revealed maximum methylated CpG at glial cell missing 2 binding site on the CaSR promoter 2 compared to other CpG sites. The methylation status of CaSR correlated directly with plasma intact parathyroid hormone levels in patients with parathyroid adenoma. With chromatin immunoprecipitation-qPCR analysis, H3K9me3 levels showed increased enrichment by 10-fold in adenomas and correlated with CaSR-mRNA expression (r = 0.61; P < 0.003). Treatment with 5-aza-2'deoxycytidine restored the expression of CaSR in a parathyroid cell line.

CONCLUSION

Our data suggest that hypermethylation and increased H3K9me3 of the CaSR promoter 2 are involved in silencing CaSR expression in sporadic parathyroid adenoma.

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.

Molecular pathogenesis of parathyroid tumours

Parathyroid tumors represent an elusive endocrine neoplasia, which lead to primary hyperparathyroidism, pHPT, a common endocrine calcium disorder characterized by hypercalcemia and normal-high parathormone secretion. Parathyroid tumours are benign adenomas or multiple glands hyperplasia in the vast majority (>99% of cases), while malignant neoplasms are rare (less than 1%). Despite pHPT is a common disorder, our knowledge about the genetic predisposition and molecular pathophysiology is limited to the familial syndromic forms of parathyroid tumour, that, however, represent not more than the 10% of all the cases; instead, the pathophysiology of sporadic forms remains an open field, although data about epigenetic mechanisms or private genes have been supposed. Here we present an overview of more recent acquisitions about the genetic causes along with their molecular mechanisms of benign, but also, malignant parathyroid tumours either in sporadic and familial presentation.

Alterations of DNA methylation in parathyroid tumors

Parathyroid tumors are common endocrine neoplasias associated with primary hyperparathyroidism, a metabolic disorder characterized by parathormone hypersecretion. Parathyroid neoplasia are frequently benign adenomas or multiple glands hyperplasia, while malignancies are rare. The epigenetic scenario in parathyroid tumors has just begun to be decoded: DNA methylation, histones and chromatin modifiers expression have been investigated so far. The main findings suggest that DNA methylation and chromatin remodeling are active and deregulated in parathyroid tumors, cooperating with genetic alterations to drive the tumor phenotype: the tumor suppressors menin and parafibromin, involved in parathyroid tumorigenesis, interact with chromatin modifiers, defining distinct epigenetic derangements. Many epigenetic alterations identified in parathyroid tumors are common to those in human cancers; moreover, some aspects of the epigenetic profile resemble epigenetic features of embryonic stem cells. Epigenetic profile may contribute to define the heterogeneity of parathyroid tumors and to provide targets for new therapeutic approaches.

Epigenetic processes in sporadic parathyroid neoplasms

Parathyroid tumors (PTs) are highly variable in their genetic background. Increasing evidence demonstrates that endocrine diseases can be caused by epigenetic alterations. The present review is focused on epigenetic aberrations related to PTs. DNA methylation, posttranslational histone modification, and noncoding RNAs are epigenetic mechanisms involved in parathyroid tumorigenesis. The information in this review has the potential to define epigenetic signatures associated with PTs for future use as diagnostic markers and lead to the development of new epigenetic drugs with therapeutic applications for these tumors. However, several epigenetic aspects regarding the biomarkers involved and their interactions in tumorigenesis on PTs are still unknown. Key to future epigenetic research would be a focus on global epigenetic identification of biomarkers in the different types of PTs, especially in parathyroid carcinoma. Better understanding may be useful for diagnostic and therapeutic uncertainty.

Molecular genetics of syndromic and non-syndromic forms of parathyroid carcinoma

Parathyroid carcinoma (PC) may occur as part of a complex hereditary syndrome or an isolated (i.e., non-syndromic) non-hereditary (i.e., sporadic) endocrinopathy. Studies of hereditary and syndromic forms of PC, which include the hyperparathyroidism-jaw tumor syndrome (HPT-JT), multiple endocrine neoplasia types 1 and 2 (MEN1 and MEN2), and familial isolated primary hyperparathyroidism (FIHP), have revealed some genetic mechanisms underlying PC. Thus, cell division cycle 73 (CDC73) germline mutations cause HPT-JT, and CDC73 mutations occur in 70% of sporadic PC, but in only ∼2% of parathyroid adenomas. Moreover, CDC73 germline mutations occur in 20%-40% of patients with sporadic PC and may reveal unrecognized HPT-JT. This indicates that CDC73 mutations are major driver mutations in the etiology of PCs. However, there is no genotype-phenotype correlation and some CDC73 mutations (e.g., c.679_680insAG) have been reported in patients with sporadic PC, HPT-JT, or FIHP. Other genes involved in sporadic PC include germline MEN1 and rearranged during transfection (RET) mutations and somatic alterations of the retinoblastoma 1 (RB1) and tumor protein P53 (TP53) genes, as well as epigenetic modifications including DNA methylation and histone modifications, and microRNA misregulation. This review summarizes the genetics and epigenetics of the familial syndromic and non-syndromic (sporadic) forms of PC.

Epigenetics of human parathyroid tumors

Parathyroid tumors are common endocrine neoplasia associated with primary hyperparathyroidism, a metabolic disorder sustained by parathormone hypersecretion. The epigenetic scenario in parathyroid tumors is beginning to be decoded. Here, main findings are reviewed: hypermethylation of specific DNA CpG islands has been described, despite global DNA promoter hypomethylation was not detectable; embryonic-related miRNAs, belonging to the C19MC and miR‐371-373 clusters, and miR‐296, are deregulated; expression of histone H1.2 and H2B is increased; expression of histone methyltransferase EZH2, BMI1 and RIZ1 is impaired; the tumor suppressor HIC1, MEN1 and CDC73 gene products, key molecules in parathyroid tumorigenesis, may be involved in epigenetic aberrant changes. Epigenetic changes are more frequent and more consistent in parathyroid malignancies, and positively correlated with severity of primary hyperparathyroidism.

Mutational Analysis of ZFY in Sporadic Parathyroid Adenomas

Context:

The molecular pathogenesis of sporadic parathyroid adenomas is incompletely understood, with alterations in cyclin D1/PRAD1 and MEN1 most firmly established as genetic drivers. The gene encoding the X-linked zinc finger protein (ZFX) has recently been implicated in the pathogenesis of a subset of parathyroid adenomas after recurrent, hotspot-focused somatic mutations were identified. ZFX escapes X inactivation and is transcribed from both alleles in women, and a highly homologous gene encoding the Y-linked zinc finger protein (ZFY) provides dosage compensation in males.

Objective:

We sought to investigate the role of ZFY mutation in sporadic parathyroid adenoma.

Intervention:

Polymerase chain reaction and Sanger sequencing were used to examine DNA from typically presenting, sporadic (nonfamilial, nonsyndromic) parathyroid adenomas from male patients for mutations within the ZFY gene.

Results:

No mutations were identified among 117 adenomas.

Conclusions:

The absence of ZFY mutations in this series suggests that ZFY rarely, if ever, acts as a driver oncogene in sporadic parathyroid adenomas. The apparent differences in tumorigenic capabilities between the closely related zinc finger proteins ZFX and ZFY suggest that structure-function studies could represent an opportunity to gain insight into neoplastic processes in the parathyroid glands.

Mice deleted for cell division cycle 73 gene develop parathyroid and uterine tumours: model for the hyperparathyroidism-jaw tumour syndrome

The hyperparathyroidism-jaw tumour (HPT-JT) syndrome is an autosomal dominant disorder characterized by occurrence of parathyroid tumours, often atypical adenomas and carcinomas, ossifying jaw fibromas, renal tumours and uterine benign and malignant neoplasms. HPT-JT is caused by mutations of the cell division cycle 73 (CDC73) gene, located on chromosome 1q31.2 and encodes a 531 amino acid protein, parafibromin. To facilitate in vivo studies of Cdc73 in tumourigenesis we generated conventional (Cdc73^+/-) and conditional parathyroid-specific (Cdc73^+/L/PTH-Cre and Cdc73^L/L/PTH-Cre) mouse models. Mice were aged to 18-21 months and studied for survival, tumour development and proliferation, and serum biochemistry, and compared to age-matched wild-type (Cdc73^+/+ and Cdc73^+/+/PTH-Cre) littermates. Survival of Cdc73^+/- mice, when compared to Cdc73^+/+ mice was reduced (Cdc73^+/-=80%; Cdc73^+/+=90% at 18 months of age, P<0.05). Cdc73^+/-, Cdc73^+/L/PTH-Cre and Cdc73^L/L/PTH-Cre mice developed parathyroid tumours, which had nuclear pleomorphism, fibrous septation and increased galectin-3 expression, consistent with atypical parathyroid adenomas, from 9 months of age. Parathyroid tumours in Cdc73^+/-, Cdc73^+/L/PTH-Cre and Cdc73^L/L/PTH-Cre mice had significantly increased proliferation, with rates >fourfold higher than that in parathyroid glands of wild-type littermates (P<0.0001). Cdc73^+/-, Cdc73^+/L/PTH-Cre and Cdc73^L/L/PTH-Cre mice had higher mean serum calcium concentrations than wild-type littermates, and Cdc73^+/- mice also had increased mean serum parathyroid hormone (PTH) concentrations. Parathyroid tumour development, and elevations in serum calcium and PTH, were similar in males and females. Cdc73^+/- mice did not develop bone or renal tumours but female Cdc73^+/- mice, at 18 months of age, had uterine neoplasms comprising squamous metaplasia, adenofibroma and adenomyoma. Uterine neoplasms, myometria and jaw bones of Cdc73^+/- mice had increased proliferation rates that were 2-fold higher than in Cdc73^+/+ mice (P<0.05). Thus, our studies, which have established mouse models for parathyroid tumours and uterine neoplasms that develop in the HPT-JT syndrome, provide in vivo models for future studies of these tumours.

Epigenetic Alterations in Parathyroid Cancers

Parathyroid cancers (PCas) are rare malignancies representing approximately 0.005% of all cancers. PCas are a rare cause of primary hyperparathyroidism, which is the third most common endocrine disease, mainly related to parathyroid benign tumors. About 90% of PCas are hormonally active hypersecreting parathormone (PTH); consequently patients present with complications of severe hypercalcemia. Pre-operative diagnosis is often difficult due to clinical features shared with benign parathyroid lesions. Surgery provides the current best chance of cure, though persistent or recurrent disease occurs in about 50% of patients with PCas. Somatic inactivating mutations of CDC73/HRPT2 gene, encoding parafibromin, are the most frequent genetic anomalies occurring in PCas. Recently, the aberrant DNA methylation signature and microRNA expression profile have been identified in PCas, providing evidence that parathyroid malignancies are distinct entities from parathyroid benign lesions, showing an epigenetic signature resembling some embryonic aspects. The present paper reviews data about epigenetic alterations in PCas, up to now limited to DNA methylation, chromatin regulators and microRNA profile.

Molecular genetics and epigenetics of nonfamilial (sporadic) parathyroid tumours

Primary hyperparathyroidism (pHPT) is a common endocrine disease characterized by excessive secretion of parathyroid hormone and an increased level of serum calcium. Overall, 80-85% of pHPT cases are due to a benign, single parathyroid adenoma (PA), and 15% to multiglandular disease (multiple adenomas/hyperplasia). Parathyroid carcinoma (PC) is rare, accounting for <0.5-1% of pHPT cases. Secondary hyperparathyroidism (sHPT) is a complication of renal failure, with the development of parathyroid tumours and hypercalcaemia. Recurrent mutations in the MEN1 gene have been confirmed by the whole-exome sequencing in 35% of PAs, suggesting that non-protein-coding genes, regulatory elements or epigenetic derangements may also have roles in the majority of PAs. DNA translocations with cyclin D1 overexpression occur in PAs (8%). In PCs, mutations in CDC73/HRPT2 are common. Activation of the WNT/β-catenin signalling pathway (accumulation of nonphosphorylated β-catenin) by an aberrantly truncated LRP5 receptor has been seen for the majority of investigated PAs and sHPT tumours, and possibly by APC inactivation through promoter methylation in PCs. Promoter methylation of several other genes and repressive histone H3 lysine 27 trimethylation by EZH2 of the HIC1 gene may also contribute to parathyroid tumorigenesis. It is possible that a common pathway exists for parathyroid tumour development. CCND1 (cyclin D1) and EZH2 overexpression, accumulation of nonphosphorylated β-catenin and repression of HIC1 have all been observed to occur in PAs, PCs and sHPT tumours. In addition, hypermethylation has been observed for the same genes in PAs and PCs (e.g. SFRP1, CDKN2A and WT1). Whether β-catenin represents a 'hub' in parathyroid tumour development will be discussed.

EZH2 is overexpressed in adrenocortical carcinoma and is associated with disease progression

Adrenal Cortex Carcinoma (ACC) is an aggressive tumour with poor prognosis. Common alterations in patients include constitutive WNT/β-catenin signalling and overexpression of the growth factor IGF2. However, the combination of both alterations in transgenic mice is not sufficient to trigger malignant tumour progression, suggesting that other alterations are required to allow development of carcinomas. Here, we have conducted a study of publicly available gene expression data from three cohorts of ACC patients to identify relevant alterations. Our data show that the histone methyltransferase EZH2 is overexpressed in ACC in the three cohorts. This overexpression is the result of deregulated P53/RB/E2F pathway activity and is associated with increased proliferation and poorer prognosis in patients. Inhibition of EZH2 by RNA interference or pharmacological treatment with DZNep inhibits cellular growth, wound healing and clonogenic growth and induces apoptosis of H295R cells in culture. Further growth inhibition is obtained when DZNep is combined with mitotane, the gold-standard treatment for ACC. Altogether, these observations suggest that overexpression of EZH2 is associated with aggressive progression and may constitute an interesting therapeutic target in the context of ACC.

5-Hydroxymethylcytosine discriminates between parathyroid adenoma and carcinoma

Background

Primary hyperparathyroidism is characterized by enlarged parathyroid glands due to an adenoma (80–85 %) or multiglandular disease (~15 %) causing hypersecretion of parathyroid hormone (PTH) and generally hypercalcemia. Parathyroid cancer is rare (<1–5 %). The epigenetic mark 5-hydroxymethylcytosine (5hmC) is reduced in various cancers, and this may involve reduced expression of the ten-eleven translocation 1 (TET1) enzyme. Here, we have performed novel experiments to determine the 5hmC level and TET1 protein expression in 43 parathyroid adenomas (PAs) and 17 parathyroid carcinomas (PCs) from patients who had local invasion or metastases and to address a potential growth regulatory role of TET1.

Results

The global 5hmC level was determined by a semi-quantitative DNA immune-dot blot assay in a smaller number of tumors. The global 5hmC level was reduced in nine PCs and 15 PAs compared to four normal tissue samples (p < 0.05), and it was most severely reduced in the PCs. By immunohistochemistry, all 17 PCs stained negatively for 5hmC and TET1 showed negative or variably heterogeneous staining for the majority. All 43 PAs displayed positive 5hmC staining, and a similar aberrant staining pattern of 5hmC and TET1 was seen in about half of the PAs. Western blotting analysis of two PCs and nine PAs showed variable TET1 protein expression levels. A significantly higher tumor weight was associated to PAs displaying a more severe aberrant staining pattern of 5hmC and TET1. Overexpression of TET1 in a colony forming assay inhibited parathyroid tumor cell growth.

Conclusions

5hmC can discriminate between PAs and PCs. Whether 5hmC represents a novel marker for malignancy warrants further analysis in additional parathyroid tumor cohorts. The results support a growth regulatory role of TET1 in parathyroid tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0197-2) contains supplementary material, which is available to authorized users.

Mutation spectra of histone methyltransferases with canonical SET domains and EZH2-targeted therapy

Germline mutations in canonical SET-methyltransferases have been identified in autism and intellectual disability syndromes and gain-of-function somatic alterations in EZH2, MLL3, NSD1, WHSC1 (NSD2) and WHSC1L1 (NSD3) in cancer. EZH2 interacts with AR, ERα, β-catenin, FOXP3, NF-κB, PRC2, REST and SNAI2, resulting in context-dependent transcriptional activation and repression. Pharmacological EZH2 inhibitors are currently in clinical trials for the treatment of B-cell lymphomas and solid tumors. EZH2 inhibitors might also be applicable in the treatment of SWI/SNF-mutant cancers, reflecting the reciprocal expression of and functional overlap between EZH2 and SMARCA4. Because of the risks for autoimmune diseases, cognitive impairment, cardiomyopathy and myelodysplastic syndrome, EZH2 inhibitors should be utilized for cancer treatment in patients receiving long-term surveillance but not for cancer chemoprevention.

Clinicopathological correlates of hyperparathyroidism

Hyperparathyroidism is a common endocrine disorder with potential complications on the skeletal, renal, neurocognitive and cardiovascular systems. While most cases (95%) occur sporadically, about 5% are associated with a hereditary syndrome: multiple endocrine neoplasia syndromes (MEN-1, MEN-2A, MEN-4), hyperparathyroidism-jaw tumour syndrome (HPT-JT), familial hypocalciuric hypercalcaemia (FHH-1, FHH-2, FHH-3), familial hypercalciuric hypercalcaemia, neonatal severe hyperparathyroidism and isolated familial hyperparathyroidism. Recently, molecular mechanisms underlying possible tumour suppressor genes (MEN1, CDC73/HRPT2, CDKIs, APC, SFRPs, GSK3β, RASSF1A, HIC1, RIZ1, WT1, CaSR, GNA11, AP2S1) and proto-oncogenes (CCND1/PRAD1, RET, ZFX, CTNNB1, EZH2) have been uncovered in the pathogenesis of hyperparathyroidism. While bi-allelic inactivation of CDC73/HRPT2 seems unique to parathyroid malignancy, aberrant activation of cyclin D1 and Wnt/β-catenin signalling has been reported in benign and malignant parathyroid tumours. Clinicopathological correlates of primary hyperparathyroidism include parathyroid adenoma (80-85%), hyperplasia (10-15%) and carcinoma (<1-5%). Secondary hyperparathyroidism generally presents with diffuse parathyroid hyperplasia, whereas tertiary hyperparathyroidism reflects the emergence of autonomous parathyroid hormone (PTH)-producing neoplasm(s) from secondary parathyroid hyperplasia. Surgical resection of abnormal parathyroid tissue remains the only curative treatment in primary hyperparathyroidism, and parathyroidectomy specimens are frequently encountered in this setting. Clinical and biochemical features, including intraoperative PTH levels, number, weight and size of the affected parathyroid gland(s), are crucial parameters to consider when rendering an accurate diagnosis of parathyroid proliferations. This review provides an update on the expanding knowledge of hyperparathyroidism and highlights the clinicopathological correlations of this prevalent disease.

Epigenetic alterations in human parathyroid tumors

Epigenetics alterations are involved in tumorigenesis and have been identified in endocrine neoplasia. In particular, DNA methylation, microRNAs deregulations and histone methylation impairment are detected in tumors of the parathyroid glands. Parathyroid tumors are the second most common endocrine neoplasia following thyroid cancer in women, and it is associated with primary hyperparathyroidism, a disease sustained by PTH hypersecretion. Despite the hallmark of global promoter hypomethylations was not detectable in parathyroid tumors, increase of hypermethylation in specific CpG islands was detected in the progression from benign to malignant parathyroid tumors. Furthermore, deregulation of a panel of embryonic-related microRNAs (miRNAs) was documented in parathyroid tumors compared with normal glands. Impaired expression of the histone methyltransferases EZH2, BMI1, and RIZ1 have been described in parathyroid tumors. Moreover, histone methyltransferases have been shown to be modulated by the oncosuppressors HIC1, MEN1, and HRPT2/CDC73 gene products that characterize tumorigenesis of parathyroid adenomas and carcinomas, respectively. The epigenetic scenario in parathyroid tumors have just began to be decoded but emerging data highlight the involvement of an embryonic gene signature in parathyroid tumor development.

Primary Hyperparathyroidism Focused on Molecular Pathogenesis

Primary hyperparathyroidism (PHPT) is a common cause of hypercalcaemia. The most common lesion found in patients is the solitary benign parathyroid adenoma. Multiple parathyroid adenomas have also been reported. Parathyroid carcinomas are an uncommon cause of PHPT. In 15% of patients, all four parathyroid glands are involved and it may be associated with a familial hereditary syndrome, such as multiple endocrine neoplasia, types 1, 2A and 4. PHPT jaw tumour syndrome is associated with fibromas in the mandible and tumours can also be present in the kidneys and the uterus. No predisposing germline DNA variants in parathyroid adenomas have been demonstrated and only a few clonally altered genes that drive parathyroid tumorigenesis have been identified. Frequently parathyroid adenomas have HRPT2 gene mutations that are likely to be of pathogenetic importance. Mutations in the MEN1 gene (localised to 11q13) are responsible for multiple endocrine neoplasia 1. Multiple endocrine neoplasia 2A, which can be associated with medullary thyroid cancer, is due to a germline mutation of the RET proto-oncogene located on chromosome 10. In MEN1-like negative patients some of the germline mutations in this new susceptibility gene were due to gene CDKN1B (12p13). This new syndrome was classified as multiple endocrine neoplasia 4. In PHPT jaw tumour syndrome, HRPT2, the gene on the long arm of chromosome 1, is responsible for the syndrome. It is suggested to perform genetic testing in patients with PHPT below the age of 30 years, but at any age in patients presenting with multigland parathyroid disease.