Heterogeneity at the 5'-end of MEN1 transcripts

Multiple Endocrine Neoplasia Type 1 (MEN1) 5'UTR Deletion, in MEN1 Family, Decreases Menin Expression

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by the occurrence of parathyroid, pancreatic and pituitary tumors, and is due to mutations in the coding region of the MEN1 gene, which encodes menin. We investigated a family with identical twins that had MEN1, with different MEN1 tumors. DNA sequence analysis of the MEN1 coding region had not identified any abnormalities and we hypothesized that deletions and mutations involving the untranslated regions may be involved. Informed consent and venous blood samples were obtained from five family members. Sanger DNA sequencing and multiplex ligation-dependent probe amplification (MLPA) analyses were performed using leukocyte DNA. This revealed a heterozygous 596bp deletion (Δ596bp) between nucleotides -1087 and -492 upstream of the translation start site, located within the MEN1 5' untranslated region (UTR), and includes the core promoter and multiple cis-regulatory regions. To investigate the effects of this 5'UTR deletion on MEN1 promoter activity, we generated luciferase reporter constructs, containing either wild-type 842bp or mutant 246bp MEN1 promoter, and transfected them into human embryonic kidney HEK293 and pancreatic neuroendocrine tumor BON-1 cells. This revealed the Δ596bp mutation to result in significant reductions by 37-fold (p < 0.0001) and 16-fold (p < 0.0001) in luciferase expression in HEK293 and BON-1 cells, respectively, compared to wild-type. The effects of this 5'UTR deletion on MEN1 transcription and translation were assessed using qRT-PCR and Western blot analyses, respectively, of mRNA and protein lysates obtained from Epstein-Barr-virus transformed lymphoblastoid cells derived from affected and unaffected individuals. This demonstrated the Δ596bp mutation to result in significant reductions of 84% (p < 0.05) and 88% (p < 0.05) in MEN1 mRNA and menin protein, respectively, compared to unaffected individuals. Thus, our results report the first germline MEN1 5'UTR mutation and highlight the importance of investigating UTRs in MEN1 patients who do not have coding region mutations. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Comprehensive Analysis of MEN1 Mutations and Their Role in Cancer

Simple Summary

Cancers are characterized by accumulation of genetic mutations in key cell cycle regulators that alter or disable the function of these genes. Such mutations can be inherited or arise spontaneously during the life of the individual. The MEN1 gene prevents uncontrolled cell division and it is considered a tumor suppressor. Inherited MEN1 mutations are associated with certain parathyroid and pancreatic syndromes while spontaneous mutations have been detected in cancer cells. We investigated whether inherited mutations appear in cancer cells which would suggest that patients with parathyroid and pancreatic syndromes have a predisposition to develop cancer. We find a weak correlation between the spectrum of inherited mutations and those appearing spontaneously. Thus, inherited MEN1 mutations may not be a good predictor of tumorigenesis.

Abstract

MENIN is a scaffold protein encoded by the MEN1 gene that functions in multiple biological processes, including cell proliferation, migration, gene expression, and DNA damage repair. MEN1 is a tumor suppressor gene, and mutations that disrupts MEN1 function are common to many tumor types. Mutations within MEN1 may also be inherited (germline). Many of these inherited mutations are associated with a number of pathogenic syndromes of the parathyroid and pancreas, and some also predispose patients to hyperplasia. In this study, we cataloged the reported germline mutations from the ClinVar database and compared them with the somatic mutations detected in cancers from the Catalogue of Somatic Mutations in Cancer (COSMIC) database. We then used statistical software to determine the probability of mutations being pathogenic or driver. Our data show that many confirmed germline mutations do not appear in tumor samples. Thus, most mutations that disable MEN1 function in tumors are somatic in nature. Furthermore, of the germline mutations that do appear in tumors, only a fraction has the potential to be pathogenic or driver mutations.

Multiple endocrine neoplasia type 1: clinical correlates of MEN1 gene methylation

Multiple endocrine neoplasia type 1 (MEN 1) has marked severity variation between individuals with the same mutation. To investigate any relationship between promoter methylation and clinical features, blood and tissue samples were collected from 16 members of the Tasman 1 MEN 1 kindred carrying a common splice site mutation and 7 patients with sporadic MEN 1. Methylation at 39 CpGs in the MEN1 promoter were assessed in formalin fixed, paraffin embedded parathyroid tissue. Clinical disease severity markers included age at first parathyroid operation, parathyroid hormone level and corrected serum calcium levels. Six patients with sporadic hyperparathyroidism were used for comparison. Minimal methylation was observed in all patients across CpG sites 1-23. In contrast, hypermethylation was observed at CpG sites 24-31 in MEN 1 patients, a pattern not observed in patients with non-MEN 1 parathyroid disease. Mean methylation at sites 24-31 was significantly correlated with age at first parathyroid operation (r = 0.652, p = 0.041). A permutation test, utilising the mean correlation coefficient (r = -0.401) revealed a possible association between relative PHPT severity and methylation score for each significant CpG site (p < 0.103). This novel study reveals evidence supporting a possible association between altered MEN1 promoter methylation and clinical severity of disease.

A Review of the Scaffold Protein Menin and its Role in Hepatobiliary Pathology

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome with neuroendocrine tumorigenesis of the parathyroid glands, pituitary gland, and pancreatic islet cells. The MEN1 gene codes for the canonical tumor suppressor protein, menin. Its protein structure has recently been crystallized, and it has been investigated in a multitude of other tissues. In this review, we summarize recent advancements in understanding the structure of the menin protein and its function as a scaffold protein in histone modification and epigenetic gene regulation. Furthermore, we explore its role in hepatobiliary autoimmune diseases, cancers, and metabolic diseases. In particular, we discuss how menin expression and function are regulated by extracellular signaling factors and nuclear receptor activation in various hepatic cell types. How the many signaling pathways and tissue types affect menin's diverse functions is not fully understood. We show that small-molecule inhibitors affecting menin function can shed light on menin's broad role in pathophysiology and elucidate distinct menin-dependent processes. This review reveals menin's often dichotomous function through analysis of its role in multiple disease processes and could potentially lead to novel small-molecule therapies in the treatment of cholangiocarcinoma or biliary autoimmune diseases.

Multiple endocrine neoplasia type 1 (MEN1): An update of 208 new germline variants reported in the last nine years

This review will focus on the germline MEN1 mutations that have been reported in patients with MEN1 and other hereditary endocrine disorders from 2007 to September 2015. A comprehensive review regarding the analysis of 1336 MEN1 mutations reported in the first decade following the gene's identification was performed by Lemos and Thakker in 2008. No other similar papers are available in literature apart from these data. We also checked for the list of Locus-Specific DataBases (LSDBs) and we found five MEN1 free-online mutational databases. 151 articles from the NCBI PubMed literature database were read and evaluated and a total of 75 MEN1 variants were found. On the contrary, 67, 22 and 44 novel MEN1 variants were obtained from ClinVar, MEN1 at Café Variome and HGMD (The Human Gene Mutation Database) databases respectively. A final careful analysis of MEN1 mutations affecting the coding region was performed.

Molecular alterations in sporadic primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a frequent endocrine disorder characterized by an excessive autonomous production and release of parathyroid hormone (PTH) by the parathyroid glands. This endocrinopathy may result from the development of a benign lesion (adenoma or hyperplasia) or from a carcinoma. Most of the PHPT cases occur sporadically; however, approximately 10% of the patients present a familial form of the disease. The molecular mechanisms underlying the pathogenesis of sporadic PHPT are incompletely understood, even though somatic alterations in MEN1 gene and CCND1 protein overexpression are frequently observed. The MEN1 gene is mutated in about 30% of the parathyroid tumours and the protooncogene CCND1 is implicated in parathyroid neoplasia by rearrangements, leading to an overexpression of CCND1 protein in parathyroid cells. The aim of this work is to briefly update the molecular alterations underlying sporadic primary hyperparathyroidism.

Multiple endocrine neoplasia type 1 (MEN1)

Multiple Endocrine Neoplasia type 1 (MEN1) is an autosomal-dominant disorder characterised by the occurrence of tumours of the parathyroids, pancreas and anterior pituitary. The MEN1 gene, consists of 10 exons that encode a 610-amino acid protein referred to as Menin. Menin is predominantly a nuclear protein that has roles in transcriptional regulation, genome stability, cell division and proliferation. Germ-line mutations usually result in MEN1 or occasionally in an allelic variant referred to as Familial Isolated Hyperparathyroidism (FIHP). MEN1 tumours frequently have loss of heterozygosity (LOH) of the MEN1 locus, which is consistent with a tumour suppressor role of MEN1. Furthermore, somatic abnormalities of MEN1 have been reported in MEN1 and non-MEN1 endocrine tumours. To date, over 1300 mutations have been reported, and the majority (>70%) of these are predicted to lead to truncated forms of Menin. The mutations are scattered throughout the >9 kb genomic sequence of the MEN1 gene. Four, which consist of c.249_252delGTCT (deletion at codons 83-84), c.1546_1547insC (insertion at codon 516), c.1378C>T (Arg460Ter) and c.628_631delACAG (deletion at codons 210-211) have been reported to occur frequently in 4.5%, 2.7%, 2.6% and 2.5% of families, respectively. However, a comparison of the clinical features in patients and their families with the same mutations reveals an absence of phenotype-genotype correlations. The majority of MEN1 mutations are likely to disrupt the interactions of Menin with other proteins and thereby alter critical events in cell cycle regulation and proliferation.

Multiple endocrine neoplasia type 1 knockout mice develop parathyroid, pancreatic, pituitary and adrenal tumours with hypercalcaemia, hypophosphataemia and hypercorticosteronaemia

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized in man by parathyroid, pancreatic, pituitary and adrenal tumours. The MEN1 gene encodes a 610-amino acid protein (menin) which is a tumour suppressor. To investigate the in vivo role of menin, we developed a mouse model, by deleting Men1 exons 1 and 2 and investigated this for MEN1-associated tumours and serum abnormalities. Men1(+/-) mice were viable and fertile, and 220 Men1(+/-) and 94 Men1(+/+) mice were studied between the ages of 3 and 21 months. Survival in Men1(+/-) mice was significantly lower than in Men1(+/+) mice (<68% vs >85%, P<0.01). Men1(+/-) mice developed, by 9 months of age, parathyroid hyperplasia, pancreatic tumours which were mostly insulinomas, by 12 months of age, pituitary tumours which were mostly prolactinomas, and by 15 months parathyroid adenomas and adrenal cortical tumours. Loss of heterozygosity and menin expression was demonstrated in the tumours, consistent with a tumour suppressor role for the Men1 gene. Men1(+/-) mice with parathyroid neoplasms were hypercalcaemic and hypophosphataemic, with inappropriately normal serum parathyroid hormone concentrations. Pancreatic and pituitary tumours expressed chromogranin A (CgA), somatostatin receptor type 2 and vascular endothelial growth factor-A. Serum CgA concentrations in Men1(+/-) mice were not elevated. Adrenocortical tumours, which immunostained for 3-beta-hydroxysteroid dehydrogenase, developed in seven Men1(+/-) mice, but resulted in hypercorticosteronaemia in one out of the four mice that were investigated. Thus, these Men1(+/-) mice are representative of MEN1 in man, and will help in investigating molecular mechanisms and treatments for endocrine tumours.

Menin: the protein behind the MEN1 syndrome

The cloning of the MEN1 gene in 1997 led to the characterization of menin, the protein behind the multiple endocrine neoplasia Type 1 syndrome. Menin, a novel nuclear protein with no homology to other gene products, is expressed ubiquitously. MEN1 missense mutations are dispersed along the coding region of the gene but are more common in the most conserved regions. Likewise, domains of protein interaction often correspond to the more conserved segments of menin. These protein interactions are generally facilitated by multiple domains or encompass a large portion of menin. The exception to this rule is a small stretch of amino acids mediating the interaction of menin with the mSin3A corepressor and histone deacetylase complexes. The C-terminal region of menin harbors several nuclear localization signals that play redundant functions in the localization of menin to the nuclear compartment. The nuclear localization signals are also important for the interaction of menin with the nuclear matrix. Menin is the target of several kinases and a candidate substrate of the ATM/ATR kinases, implying a role for this tumor suppressor in the DNA damage response. Menin is highly conserved from Drosophila to human but is absent in the nematode and in yeast.

MEN1 missense mutations impair sensitization to apoptosis induced by wild-type menin in endocrine pancreatic tumor cells

BACKGROUND & AIMS

Missense mutations account for 30% of mutations identified in patients with the multiple endocrine neoplasia type 1 (MEN1) syndrome. They raise several issues: the distinction between pathogenic mutations and polymorphisms is sometimes difficult and the functional effects of missense mutations are unclear. We aimed to evaluate the functional consequences of missense MEN1 mutations in an appropriate endocrine cellular context.

METHODS

From the INS-1 insulinoma cell line, we established clones conditionally over expressing wild-type (WT) menin or its A160T, H317Y, and A541T variants. We compared the consequences of WT or variant menin over expression on apoptotic response after gamma-irradiation and analyzed the interactions of these proteins with p53.

RESULTS

WT menin over expression sensitized INS-r3 cells to apoptosis through amplification of caspase-3 activation, increased p53 acetylation, and accelerated p21 activation; moreover, over expressed WT menin could be recovered in p53-containing complexes. For all 3 missense mutations tested, the functional effects observed with WT were impaired significantly and only low amounts of variant menin proteins were recovered in p53-containing complexes.

CONCLUSIONS

Taking advantage of a new endocrine cellular model, we show a loss of function for 2 missense disease-related menin mutants and for a controversial variant as well. Furthermore, our results suggest the existence of functional interactions between p53 and menin for the control of apoptosis, which may cast new light on the mechanisms of endocrine tumorigenesis.

Clinical and molecular genetics of acromegaly: MEN1, Carney complex, McCune-Albright syndrome, familial acromegaly and genetic defects in sporadic tumors

Pituitary tumors are among the most common neoplasms in man; they account for approximately 15% of all primary intracranial lesions (Jagannathan et al., Neurosurg Focus, 19:E4, 2005). Although almost never malignant and rarely clinically expressed, pituitary tumors may cause significant morbidity in affected patients. First, given the critical location of the gland, large tumors may lead to mass effects, and, second, proliferation of hormone-secreting pituitary cells leads to endocrine syndromes. Acromegaly results from oversecretion of growth hormone (GH) by the proliferating somatotrophs. Despite the significant efforts made over the last decade, still little is known about the genetic causes of common pituitary tumors and even less is applied from this knowledge therapeutically. In this review, we present an update on the genetic syndromes associated with pituitary adenomas and discuss the related genetic defects. We next review findings on sporadic, non-genetic, pituitary tumors with an emphasis on pathways and animal models of pituitary disease. In conclusion, we attempt to present an overall, integrative approach to the human molecular genetics of both familiar and sporadic pituitary tumors.

Multiple endocrine neoplasia type 1 (MEN1): analysis of 1336 mutations reported in the first decade following identification of the gene

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by the occurrence of tumors of the parathyroids, pancreas, and anterior pituitary. The MEN1 gene, which was identified in 1997, consists of 10 exons that encode a 610-amino acid protein referred to as menin. Menin is predominantly a nuclear protein that has roles in transcriptional regulation, genome stability, cell division, and proliferation. Germline mutations usually result in MEN1 or occasionally in an allelic variant referred to as familial isolated hyperparathyroidism (FIHP). MEN1 tumors frequently have loss of heterozygosity (LOH) of the MEN1 locus, which is consistent with a tumor suppressor role of MEN1. Furthermore, somatic abnormalities of MEN1 have been reported in MEN1 and non-MEN1 endocrine tumors. The clinical aspects and molecular genetics of MEN1 are reviewed together with the reported 1,336 mutations. The majority (>70%) of these mutations are predicted to lead to truncated forms of menin. The mutations are scattered throughout the>9-kb genomic sequence of the MEN1 gene. Four, which consist of c.249_252delGTCT (deletion at codons 83-84), c.1546_1547insC (insertion at codon 516), c.1378C>T (Arg460Ter), and c.628_631delACAG (deletion at codons 210-211) have been reported to occur frequently in 4.5%, 2.7%, 2.6%, and 2.5% of families, respectively. However, a comparison of the clinical features in patients and their families with the same mutations reveals an absence of phenotype-genotype correlations. The majority of MEN1 mutations are likely to disrupt the interactions of menin with other proteins and thereby alter critical events in cell cycle regulation and proliferation.

Functional Characterization of a Promoter Region in the Human MEN1 Tumor Suppressor Gene

Our previous studies on the human MEN1 (multiple endocrine neoplasia type 1) gene revealed heterogeneity of MEN1 2.8 kb transcripts related to variation in their 5' UTR only. Six distinct exons 1 (e1A-e1F) were isolated that suggested the existence of multiple but not already identified transcriptional start sites (TSS) and of a complex transcriptional control. Identification of a minimal promoter region and its adjacent regulatory regions appears an inescapable step to the understanding of MEN1 gene transcriptional regulation in normal and pathological situations. For this purpose, we subcloned the approximately 2000 bp region situated directly upstream of the exon 2 in front of a luciferase reporter gene, and we analyzed functional consequences of 5' and 3' serial deletions, comparatively in a series of endocrine versus non-endocrine cell lines. Primer extension and RPA experiments demonstrate that in HEK293 cells transcription initiated simultaneously at several points in endogenous MEN1 promoter as well as in transfected promoter fragments in reporter plasmids, mainly in Inr elements that are efficiently employed to synthetize previously described exons e1A-e1D. Functional consequences of TSS deletion are directly related to cellular context. The minimal promoter region is localized between -135 and -36. Five large adjacent cis-regulatory regions (UR1-UR5) exist upstream of this minimal promoter region, whose activity depend not only on the cellular context but also on the presence of a downstream sequence DR1. Five small cis-regulatory elements (C1-C5) are localized between -325 and -107. Overexpression of exogenous menin, the MEN1 gene's product, in mouse embryonic fibroblasts from Men1(-/-) knock-out mice dose-dependently decreases MEN1 promoter activity, through sequences surrounding the minimal promoter. Our data highlight the existence of a complex transcriptional regulation of the MEN1 gene, whose activity is clearly modulated depending not only on the cellular context but also on menin intracellular levels. They are the molecular bases required for a future understanding of a potential specific transcription control in endocrine cells.

Germline mutation profile of MEN1 in multiple endocrine neoplasia type 1: search for correlation between phenotype and the functional domains of the MEN1 protein

Multiple Endocrine Neoplasia type 1 (MEN1) is an autosomal dominant disease characterized by endocrine tumors of the parathyroids, the pancreatic islets, and the anterior pituitary. The MEN1 gene encodes menin, a nuclear protein interacting with JunD/AP1, Smad3, NFkappaB, and other proteins involved in transcription and cell growth regulation. Here, by exhaustive sequence analysis of 170 probands/families collected through a French clinical network, we identified 165 mutations located in coding parts of the MEN1 gene, which represent 114 distinct MEN1 germline alterations. These mutations have been included in a MEN1-locus specific database available on the world wide web together with approximately 240 germline and somatic MEN1 mutations listed from international published data. Our mutation series included 56 frameshifts, 23 nonsense, 27 missense, and eight deletion or insertion in-frame mutations. Mutations were spread over the entire coding sequence. Taken together, most missense and in-frame MEN1 genomic alterations affect one or all domains of menin interacting with JunD [codons 1-40; 139-242; 323-428], Smad3 [distal to codon 478], and NFkappaB [codons 276-479], three major effectors in transcription and cell growth regulation. No correlation has been observed between genotype and MEN1 phenotype. We suggest that the knowledge of structure and location of a specific mutation has not been useful in clinical practice for the follow-up of affected patients and asymptomatic gene carriers. Our results provide the largest series of MEN1 mutations published to date. They will be a useful tool for further studies focusing on the functional effects of missense mutations and understanding which mechanisms or pathways related to multiple menin interactions might be involved in tumorigenesis of endocrine cells.

Deregulation of genetic pathways in neuroendocrine tumors

Complexity and redundancy of functional pathways controlled by the human genome explain that a single type of tumor can be induced by independant defective mutations in various genes that encode proteins acting in different parts of the cell physiology. Neuroendocrine tumors represent a powerful model for understanding such a complexity from the fact that at least six unrelated genetic syndromes have been characterized in the last decade which predispose to endocrine cell proliferation with variable penetrance and expressivity. Multiple Endocrine Neoplasia, von Hippel-Lindau. Carney and uncommonly Recklinghausen and Tuberous Sclerosis syndromes represent almost the whole panel of genetic diseases for which genes have been cloned and most of the functional knowledge has been collected. All the endocrine glands are concerned in these diseases, but the cellular pathways that are deregulated downstream from the deleterious mutations occurring in the genes of these autosomal dominant syndromes. might be related to each step of the cell life, from mitosis to DNA transcription, membrane receptor signalling and growth factor production, protein catabolism and extracellular matrix synthesis, and from transcription regulation to apoptosis and response to hypoxia and cellular stress. Here, we present an overview of genes involved in genetic predisposition to neuroendocrine tumors and highlight the complexity of pathways involved and the need of further studies focussing on genes involved in tumoral progression, most neuroendocrine tumors being benign at initial diagnosis but able to produce highly malignant cellular clones related to secondary genetic alterations or deregulation of growth factor production or cell cell adhesion processes.