MEN1 and microRNAs: The link between sporadic pituitary, parathyroid and adrenocortical tumors?

MicroRNA Profile Alterations in Parathyroid Carcinoma: Latest Updates and Perspectives

Simple Summary

Despite the considerable development of diagnostic tools, distinguishing between benign and malignant parathyroid tumors poses a significant diagnostic challenge. Epigenetic regulations, including noncoding microRNAs (miRNAs), have recently emerged as a new and promising source of biomarkers. MiRNAs are post-transcriptional regulators of gene expression. These tissue-specific molecules are known to be deregulated between cancer and normal cells. This review delineates changes in miRNA expression in parathyroid carcinoma (PC), advancing our understanding of PC tumorigenesis and emphasizing, at the same time, that miRNAs can be further exploited for diagnostic and therapeutic purposes.

Abstract

Parathyroid tumors are a genetically heterogenous group with a significant variability in clinical features. Due to a lack of specific signs and symptoms and uncertain histopathological criteria, parathyroid carcinomas (PCs) are challenging to diagnose, both before and after surgery. There is a great interest in searching for accurate molecular biomarkers for early detection, disease monitoring, and clinical management. Due to improvements in molecular pathology, the latest studies have reported that PC tumorigenesis is strongly linked to the epigenetic regulation of gene expression. MicroRNA (miRNA) profiling may serve as a helpful adjunct in distinguishing parathyroid adenoma (PAd) from PC and provide further insight into regulatory pathways involved in PTH release and parathyroid tumorigenesis. So far, only a few studies have attempted to show the miRNA signature for PC, and very few overlaps could be found between these relatively similar studies. A global miRNA downregulation was detected in PC compared with normal glands among differentially expressed miRNAs. This review summarizes changes in miRNA expression in PC and discusses the future research directions in this area.

Microsatellite Instability-High, Malignant Insulinoma With Brain Metastasis

Insulinomas are the most common type of functional pancreatic neuroendocrine tumor. Although insulinomas usually are noninvasive or benign, 10% are deemed invasive or malignant. The pathologic mechanisms that lead to the malignant phenotype are not well elucidated. In this case report, we present a patient with stage 4 malignant insulinoma with metastasis to the liver, bone, and brain. Genetic analysis of the tumor showed that the tumor was mismatch-repair deficient and had a high rate of microsatellite instability. There was loss of MLH1- and PMS2-encoded protein expression, and MLH1 and MEN1 variants were identified. Notably, the liver metastasis showed considerable tumor heterogeneity (well differentiated) compared with the brain metastasis (poorly differentiated).

Role of miR-24 in Multiple Endocrine Neoplasia Type 1: A Potential Target for Molecular Therapy

Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal dominant inherited multiple cancer syndrome of neuroendocrine tissues. Tumors are caused by an inherited germinal heterozygote inactivating mutation of the MEN1 tumor suppressor gene, followed by a somatic loss of heterozygosity (LOH) of the MEN1 gene in target neuroendocrine cells, mainly at parathyroids, pancreas islets, and anterior pituitary. Over 1500 different germline and somatic mutations of the MEN1 gene have been identified, but the syndrome is completely missing a direct genotype-phenotype correlation, thus supporting the hypothesis that exogenous and endogenous factors, other than MEN1 specific mutation, are involved in MEN1 tumorigenesis and definition of individual clinical phenotype. Epigenetic factors, such as microRNAs (miRNAs), are strongly suspected to have a role in MEN1 tumor initiation and development. Recently, a direct autoregulatory network between miR-24, MEN1 mRNA, and menin was demonstrated in parathyroids and endocrine pancreas, showing a miR-24-induced silencing of menin expression that could have a key role in initiation of tumors in MEN1-target neuroendocrine cells. Here, we review the current knowledge on the post-transcriptional regulation of MEN1 and menin expression by miR-24, and its possible direct role in MEN1 syndrome, describing the possibility and the potential approaches to target and silence this miRNA, to permit the correct expression of the wild type menin, and thereby prevent the development of cancers in the target tissues.

Circulating and Tissue Expression Profile of MicroRNAs in Primary Hyperparathyroidism Caused by Sporadic Parathyroid Adenomas

We investigated the expression profile of selected microRNAs (miRs) in serum and tissue samples from patients with sporadic parathyroid adenomas (sPAs). This was a prospective, controlled cohort study. Forty patients with sPAs who had undergone parathyroidectomy (PTX) were included. MiR extraction was performed from (i) 40 formalin‐fixed paraffin‐embedded samples (FFPEs) of sPAs, (ii) 10 FFPEs of normal parathyroid tissue (NPT), (iii) serum samples of the 40 patients with sPAs (t1 = baseline; t2 = 2 months post‐PTX), and (vi) serum samples of 10 healthy individuals (controls; t1 = baseline and t2 = 2 months later). Ten miRs were selected based on their interaction with genes related to parathyroid tumorigenesis (miR‐17‐5p, miR‐24‐3p, miR‐29b‐3p, miR‐31‐5p, miR‐135b‐5p, miR‐186‐5p, miR‐195‐5p, miR‐330‐3p, miR‐483‐3p, and miR‐877‐5p). At tissue level, the relative expression of miR‐17‐5p, miR‐31‐5p, miR‐135b‐5p, miR‐186‐5p, and miR‐330‐3p was significantly decreased (fold change [FC]: 0.17, FC: 0.03, FC: 0.01, FC: 0.10, FC: 0.10, respectively; all p values <0.001), and the expression of miR‐24‐3p and miR‐29b‐3p was significantly increased (FC: 12.4, p < 0.001; FC: 18.5, p = 0.011, respectively) in sPA compared with NPT samples. The relative expression of miR‐135b‐5p was also significantly decreased in the serum samples of patients compared with controls (FC: 0.7, p = 0.035). No significant differences were found in the serum samples of patients before and after PTX. MiRs that regulate genes linked to parathyroid tumors such as menin 1 (miR‐24‐3p, miR‐29b‐3p), cyclin D1 (miR‐17‐5p), calcium sensing receptor (miR‐31‐5p, miR‐135b‐5p), cyclin‐dependent kinase inhibitors (miR‐186‐5p), and β‐catenin (miR‐330‐3p) were significantly deregulated in sPAs compared with NPT samples, suggesting a role for epigenetic changes in parathyroid tumorigenesis. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

[The role of non-coding RNAs in the pathogenesis of multiple endocrine neoplasia syndrome type 1]

Changes in the expression of non-coding ribonucleic acids (ncRNAs) take part in the formation of various tumors. Multiple endocrine neoplasia syndrome type 1 (MEN1) is a rare autosomal dominant disease caused by mutations of the MEN1 gene encoding the menin protein. This syndrome is characterized by the occurrence of parathyroid tumors, gastroenteropancreatic neuroendocrine tumors, pituitary adenomas, as well as other endocrine and non-endocrine tumors. The pathogenesis of MEN-1 associated tumors due to MEN1 mutations remains unclear. In the absence of mutations of the MEN1 gene in patients with phenotypically similar features, this condition is regarded as a phenocopy of this syndrome. The cause of the combination of several MEN-1-related tumors in these patients remains unknown. The possible cause is that changes in the expression of ncRNAs affect the regulation of signaling pathways in which menin participates and may contribute to the development of MEN-1-related tumors. The identification of even a small number of agents interacting with menin makes a significant contribution to the improvement of knowledge about its pathophysiological influence and ways of developing tumors within the MEN-1 syndrome and its phenocopies.