Stable overexpression of MEN1 suppresses tumorigenicity of RAS

Menin signaling and therapeutic targeting in breast cancer

To date, mounting evidence have shown that patients with multiple endocrine neoplasia type 1 (MEN1) may face an increased risk for breast carcinogenesis. The product of the MEN1 gene, menin, was also indicated to be an important regulator in breast cancer signaling network. Menin directly interacts with MLL, EZH2, JunD, NF-κB, PPARγ, VDR, Smad3, β-catenin and ERα to modulate gene transcriptions leading to cell proliferation inhibition. Moreover, interaction of menin-FANCD2 contributes to the enhancement of BRCA1-mediated DNA repair mechanism. Ectopic expression of menin causes Bax-, Bak- and Caspase-8-dependent apoptosis. However, despite numbers of menin inhibitors were exploited in other cancers, data on the usage of menin inhibitors in breast cancer treatment remain limited. In this review, we focused on the menin associated signaling pathways and gene transcription regulations, with the aim of elucidating its molecular mechanisms and of guiding the development of novel menin targeted drugs in breast cancer therapy.

MEN1 promotes ferroptosis by inhibiting mTOR-SCD1 axis in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumor (pNET) is the second most common malignant tumors of the pancreas. Multiple endocrine neoplasia 1 ( MEN1) is the most frequently mutated gene in pNETs and MEN1-encoded protein, menin, is a scaffold protein that interacts with transcription factors and chromatin-modifying proteins to regulate various signaling pathways. However, the role of MEN1 in lipid metabolism has not been studied in pNETs. In this study, we perform targeted metabolomics analysis and find that MEN1 promotes the generation and oxidation of polyunsaturated fat acids (PUFAs). Meanwhile lipid peroxidation is a hallmark of ferroptosis, and we confirm that MEN1 promotes ferroptosis by inhibiting the activation of mTOR signaling which is the central hub of metabolism. We show that stearoyl-coA desaturase (SCD1) is the downstream of MEN1-mTOR signaling and oleic acid (OA), a metabolite of SCD1, recues the lipid peroxidation caused by MEN1 overexpression. The negative correlation between MEN1 and SCD1 is further verified in clinical specimens. Furthermore, we find that BON-1 and QGP-1 cells with MEN1 overexpression are more sensitive to everolimus, a widely used drug in pNETs that targets mTOR signaling. In addition, combined use everolimus with ferroptosis inducer, RSL3, possesses a more powerful ability to kill cells, which may provide a new strategy for the comprehensive therapy of pNETs.

HSP27/Menin Expression as New Prognostic Serum Biomarkers of Prostate Cancer Aggressiveness Independent of PSA

The screening of PCa is based on two tests, the total PSA test and the rectal examination. However, PSA is not specific for PCa stage confirmation, leading in false positive result and involving PCa over-diagnosis and over-treatment. HSP27 and Menin have been found to be overexpressed in a wide range of human cancers. Recent studies showed how HSP27 interacts with and stabilizes Menin to lead PCa progression and treatment resistance. The purpose of our study was to evaluate the correlation of HSP27 and Menin molecular expression, and their prognosis value in PCa with respect to clinicopathological features. Elisa was employed to measure serum HSP27 and Menin concentrations in 73 PCa patients and 80 healthy individuals. Immunohistochemistry (IHC) was used to determine HSP27 and Menin tissue expression in 57 tumors and 4 Benign Prostatic Hyperplasia (BPH) tissues. Serum HSP27 expression correlated with its tissue expression in all PCa patients, whereas serum Menin expression correlated only with tissue expression in aggressive PCa patients. Moreover, the results showed a positive correlation between HSP27 and Menin either in serum (r = 0.269; p = 0.021) or in tissue (r = 0.561; p < 0.0001). In aggressive PCa, serum expression of HSP27 and Menin was positively correlated (r = 0.664; R = 0.441; p = 0.001). The correlation between HSP27 and Menin expression in tissue was found only in patients with aggressive PCa (r = 0.606; R = 0.367; p = 0.004). Statistical analysis showed that the expression of both biomarkers was positively correlated with the hormone resistance or sensitivity, tumor aggressiveness, metastasis, Gleason Score, death and did not significantly correlate with age and PSA. Survival was illustrated by Kaplan−Meier curves; increased HSP27 and Menin expression correlated with shorter survival of PCa patients (p = 0.001 and p < 0.0001, respectively). Accuracy in predicting aggressiveness was quantified by the Area Under the Curve (AUC) of Receiver Operating Characteristic (ROC). We demonstrated that the combination of HSP27/Menin was statistically greater than PSA; it achieved an AUC of 0.824 (95% CI, 0.730−0.918; p < 0.0001). However, HSP27/Menin/PSA combination decreased the diagnostic value with an AUC of 0.569 (95% CI, 0.428−0.710; p = 0.645). Our work suggests the potential role of HSP27/Menin as diagnostic and prognostic biomarkers.

Molecular biology of pancreatic neuroendocrine tumors: From mechanism to translation

Pancreatic neuroendocrine tumors (pNETs) are a group of heterogeneous tumors originated from progenitor cells. As these tumors are predominantly non-functional, most of them display asymptomatic characteristics, making it difficult to be realized from early onset. Therefore, patients with pNETs are usually diagnosed with metastatic disease or at a late disease stage. The relatively low incidence also limits our understanding of the biological background of pNETs, which largely impair the development of new effective drugs. The fact that up to 10% of pNETs develop in patients with genetic syndromes have promoted researchers to focus on the gene mutations and driver mutations in MEN1, DAXX/ATRX and mTOR signaling pathway genes have been implicated in disease development and progression. Recent advances in sequencing technologies have further enriched our knowledge of the complex molecular landscape of pNETs, pointing out crucial roles of genes in DNA damage pathways, chromosomal and telomere alterations and epigenetic dysregulation. These novel findings may not only benefit early diagnosis of pNETs, but also help to uncover tumor heterogeneity and shape the future of translational medical treatment. In this review, we focus on the current molecular biology of pNETs and decipher how these findings may translate into future development of targeted therapy.

Gene expression profiles and pathway enrichment analysis to identification of differentially expressed gene and signaling pathways in epithelial ovarian cancer based on high-throughput RNA-seq data

Epithelial ovarian cancer (EOC) can be considered as a stressful and challenging disease among all women in the world, which has been associated with a poor prognosis and its molecular pathogenesis has remained unclear. In recent years, RNA Sequencing (RNA-seq) has become a functional and amazing technology for profiling gene expression. In the present study, RNA-seq raw data from Sequence Read Archive (SRA) of six tumor and normal ovarian sample was extracted, and then analysis and statistical interpretation was done with Linux and R Packages from the open-source Bioconductor. Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were applied for the identification of key genes and pathways involved in EOC. We identified 1091 Differential Expression Genes (DEGs) which have been reported in various studies of ovarian cancer as well as other types of cancer. Among them, 333 genes were up-regulated and 273 genes were down-regulated. In addition, Differentially Expressed Genes (DEGs) including RPL41, ALDH3A2, ERBB2, MIEN1, RBM25, ATF4, UPF2, DDIT3, HOXB8 and IL17D as well as Ribosome and Glycolysis/Gluconeogenesis pathway have had the potentiality to be used as targets for EOC diagnosis and treatment. In this study, unlike that of any other studies on various cancers, ALDH3A2 was most down-regulated gene in most KEGG pathways, and ATF4 was most up-regulated gene in leucine zipper domain binding term. In the other hand, RPL41 as a regulatory of cellular ATF4 level was up-regulated in many term and pathways and augmentation of ATF4 could justify the increase of RPL41 in the EOC. Pivotal pathways and significant genes, which were identified in the present study, can be used for adaptation of different EOC study. However, further molecular biological experiments and computational processes are required to confirm the function of the identified genes associated with EOC.

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.

Multiple Endocrine Neoplasia Syndromes from Genetic and Epigenetic Perspectives

Multiple endocrine neoplasia (MEN) syndromes are infrequent inherited disorders in which more than one endocrine glands develop noncancerous (benign) or cancerous (malignant) tumors or grow excessively without forming tumors. There are 3 famous and well-known forms of MEN syndromes (MEN 1, MEN 2A, and MEN 2B) and a newly documented one (MEN4). These syndromes are infrequent and occurred in all ages and both men and women. Usually, germ line mutations that can be resulted in neoplastic transformation of anterior pituitary, parathyroid glands, and pancreatic islets in addition to gastrointestinal tract can be an indicator for MEN1. The medullary thyroid cancer (MTC) in association with pheochromocytoma and/or multiple lesions of parathyroid glands with hyperparathyroidism can be pointer of MEN2 which can be subgrouped into the MEN 2A, MEN 2B, and familial MTC syndromes. There are no distinct biochemical markers that allow identification of familial versus nonfamilial forms of the tumors, but familial MTC usually happens at a younger age than sporadic MTC. The MEN1 gene (menin protein) is in charge of MEN 1 disease, CDNK1B for MEN 4, and RET proto-oncogene for MEN 2. The focus over the molecular targets can bring some hope for both diagnosis and management of MEN syndromes. In the current review, we look at this disease and responsible genes and their cell signaling pathway involved.

Current and emerging therapies for PNETs in patients with or without MEN1

Pancreatic neuroendocrine tumours (PNETs) might occur as a non-familial isolated endocrinopathy or as part of a complex hereditary syndrome, such as multiple endocrine neoplasia type 1 (MEN1). MEN1 is an autosomal dominant disorder characterized by the combined occurrence of PNETs with tumours of the parathyroids and anterior pituitary. Treatments for primary PNETs include surgery. Treatments for non-resectable PNETs and metastases include biotherapy (for example, somatostatin analogues, inhibitors of receptors and monoclonal antibodies), chemotherapy and radiological therapy. All these treatments are effective for PNETs in patients without MEN1; however, there is a scarcity of clinical trials reporting the efficacy of the same treatments of PNETs in patients with MEN1. Treatment of PNETs in patients with MEN1 is challenging owing to the concomitant development of other tumours, which might have metastasized. In recent years, preclinical studies have identified potential new therapeutic targets for treating MEN1-associated neuroendocrine tumours (including PNETs), and these include epigenetic modification, the β-catenin-wingless (WNT) pathway, Hedgehog signalling, somatostatin receptors and MEN1 gene replacement therapy. This Review discusses these advances.

Deletion of Menin in craniofacial osteogenic cells in mice elicits development of mandibular ossifying fibroma

Ossifying fibroma (OF) is a rare benign tumor of the craniofacial bones that can reach considerable and disfiguring dimensions if left untreated. Although the clinicopathological characteristics of OF are well established, the underlying etiology has remained largely unknown. Our work indicates that Men1-a tumor suppressor gene responsible of Multiple endocrine neoplasia type 1-is critical for OF formation and shows that mice with targeted disruption of Men1 in osteoblasts (Men1^Runx2Cre) develop multifocal OF in the mandible with a 100% penetrance. Using lineage-tracing analysis, we demonstrate that loss of Men1 arrests stromal osteoprogenitors in OF at the osterix-positive pre-osteoblastic differentiation stage. Analysis of Men1-lacking stromal spindle cells isolated from OF (OF-derived MSCs (OFMSCs)) revealed a downregulation of the cyclin-dependent kinase (CDK) inhibitor Cdkn1a, consistent with an increased proliferation rate. Intriguingly, the re-expression of Men1 in Men1-deficient OFMSCs restored Cdkn1a expression and abrogated cellular proliferation supporting the tumor-suppressive role of Men1 in OF. Although our work presents the first evidence of Men1 in OF development, it further provides the first genetic mouse model of OF that can be used to better understand the molecular pathogenesis of these benign tumors and to potentially develop novel treatment strategies.

EXPRESSION OF MENIN IN THE HUMAN THYROID GLAND

INTRODUCTION

The expression of menin in the thyroid gland has long been debated. Animal models with targeted inactivation of menin in the thyroid gland have shown that its inactivation might play a role in the progression to a more aggressive type of cancer. Human studies are conflicting, some have identified mutations in the MEN1 gene in a sub-type of oncocytic thyroid carcinomas, while others have not identified a higher prevalence of thyroid cancer in MEN1 patients.

OBJECTIVE

To analyze the immunohistochemical expression of menin in different types of thyroid carcinomas.

MATERIALS AND METHODS

48 thyroid tumours (12 papillary thyroid carcinomas (PTC), 6 anaplastic thyroid carcinomas (ATC), 12 poorly differentiated thyroid carcinomas (PDTC), 5 medullary thyroid carcinomas (MTC), 5 oncocytic follicular carcinomas (OC), 3 oncocytic adenomas (OA) and 5 goiters (G)) were tested for nuclear expression of menin using an anti-menin antibody. The expression was considered positive, negative or decreased.

RESULTS

The expression of menin was positive, identical to normal tissue, in 39 cases (81.25%). The expression was decreased (n=8) or absent (n=1) in 9 tumours (18.75% - 2 PTC, 5 PDTC, 2 OC) accounting for 42% (5/12) of the PDTC and 40% (2/5) of the OC.

CONCLUSIONS

Our results show that the expression of menin is generally preserved in human thyroid carcinomas, but it can be decreased or absent in certain types of thyroid cancer. Further molecular studies are needed to evaluate to potential of menin protein in tumorigenesis.

Genetics of multiple endocrine neoplasia type 1 syndrome: what's new and what's old

Despite its identification in 1997, the functions of the MEN1 gene-the main gene underlying multiple endocrine neoplasia type 1 syndrome-are not yet fully understood. In addition, unlike the RET-MEN2 causative gene-no hot-spot mutational areas or genotype-phenotype correlations have been identified. More than 1,300 MEN1 gene mutations have been reported and are mostly "private" (family specific). Even when mutations are shared at an intra- or inter-familial level, the spectrum of clinical presentation is highly variable, even in identical twins. Despite these inherent limitations for genetic counseling, identifying MEN1 mutations in individual carriers offers them the opportunity to have lifelong clinical surveillance schemes aimed at revealing MEN1-associated tumors and lesions, dictates the timing and scope of surgical procedures, and facilitates specific mutation analysis of relatives to define presymptomatic carriers.

MEN1, MEN4, and Carney Complex: Pathology and Molecular Genetics

Pituitary adenomas are a common feature of a subset of endocrine neoplasia syndromes, which have otherwise highly variable disease manifestations. We provide here a review of the clinical features and human molecular genetics of multiple endocrine neoplasia (MEN) type 1 and 4 (MEN1 and MEN4, respectively) and Carney complex (CNC). MEN1, MEN4, and CNC are hereditary autosomal dominant syndromes that can present with pituitary adenomas. MEN1 is caused by inactivating mutations in the MEN1 gene, whose product menin is involved in multiple intracellular pathways contributing to transcriptional control and cell proliferation. MEN1 clinical features include primary hyperparathyroidism, pancreatic neuroendocrine tumours and prolactinomas as well as other pituitary adenomas. A subset of patients with pituitary adenomas and other MEN1 features have mutations in the CDKN1B gene; their disease has been called MEN4. Inactivating mutations in the type 1α regulatory subunit of protein kinase A (PKA; the PRKAR1A gene), that lead to dysregulation and activation of the PKA pathway, are the main genetic cause of CNC, which is clinically characterised by primary pigmented nodular adrenocortical disease, spotty skin pigmentation (lentigines), cardiac and other myxomas and acromegaly due to somatotropinomas or somatotrope hyperplasia.

The role of tumor suppressor menin in IL-6 regulation in mouse islet tumor cells

Menin is a gene product of multiple endocrine neoplasia type1 (Men1), an inherited familial cancer syndrome characterized by tumors of endocrine tissues. To gain insight about how menin performs an endocrine cell-specific tumor suppressor function, we investigated the possibility that menin was integrated in a cancer-associated inflammatory pathway in a cell type-specific manner. Here, we showed that the expression of IL-6, a proinflammatory cytokine, was specifically elevated in mouse islet tumor cells upon depletion of menin and Men(-/-) MEF cells, but not in hepatocellular carcinoma cells. Histone H3 lysine (K) 9 methylation, but not H3 K27 or K4 methylation, was involved in menin-dependent IL-6 regulation. Menin occupied the IL-6 promoter and recruited SUV39H1 to induce H3 K9 methylation. Our findings provide a molecular insight that menin-dependent induction of H3 K9 methylation in the cancer-associated interleukin gene might be linked to preventing endocrine-specific tumorigenesis.

Multiple endocrine neoplasia type 1 associated with breast cancer: A case report and review of the literature

Multiple endocrine neoplasia type 1 (MEN1) is a cancer predisposition syndrome that includes a combination of endocrine and non-endocrine tumors. The present study reports a rare case of MEN1 associated with breast cancer with the MEN1 gene mutation. A 45-year-old female was diagnosed with breast cancer subsequent to presenting with a right breast mass. Pre-operative radiological studies indicated right breast cancer with a suspicious metastatic nodule of the lung. Further studies demonstrated bilateral thyroid nodules, a neuroendocrine tumor of the pancreas, paraganglioma, a left adrenal adenoma, gallstones, uterine subserosal myoma and pituitary macroadenoma. Laboratory examinations revealed hypercalcemia, hypophosphatemia and an increased intact parathyroid hormone level. The workup for the suspected MEN syndrome revealed an increased basal plasma level of insulin-like growth factor-1, prolactin and calcitonin, and an increased 24-h urinary free cortisol level. The patient underwent surgical removal of the breast cancer and the tumors of the pancreas, adrenal gland, thyroid and parathyroid glands, uterus, anterior mediastinum and lung. The pathological diagnosis of the resected breast was of invasive ductal carcinoma. Otherwise the pathological diagnosis was of calcitonin-producing pancreatic endocrine carcinoma, adrenal cortical adenoma, bilateral papillary thyroid carcinomas, parathyroid adenomas, uterine leiomyoma with adenomyosis, a thymic carcinoid tumor and lung hamatoma. Gene analysis was performed to determine the association between gene mutations and the development of tumors in this patient, and a germ-line MEN1 gene mutation was consequently detected. It could be assumed that MEN1 syndrome may have possibly predisposed the present patient to breast cancer. However, additional observations and further studies are required to demonstrate this association.

Hepatitis B spliced protein (HBSP) promotes the carcinogenic effects of benzo [alpha] pyrene by interacting with microsomal epoxide hydrolase and enhancing its hydrolysis activity

BACKGROUND

The risk of hepatocellular carcinoma (HCC) increases in chronic hepatitis B surface antigen (HBsAg) carriers who often have concomitant increase in the levels of benzo[alpha]pyrene-7,8-diol-9,10-epoxide(±) (BPDE)-DNA adduct in liver tissues, suggesting a possible co-carcinogenesis of Hepatitis B virus (HBV) and benzo[alpha]pyrene in HCC; however the exact mechanisms involved are unclear.

METHODS

The interaction between hepatitis B spliced protein (HBSP) and microsomal epoxide hydrolase (mEH) was confirmed using GST pull-down, co-immunoprecipitation and mammalian two-hybrid assay; the effects of HBSP on mEH-mediated B[alpha]P metabolism was examined by high performance liquid chromatography (HPLC); and the influences of HBSP on B[alpha]P carcinogenicity were evaluated by bromodeoxyuridine cell proliferation, anchorage-independent growth and tumor xenograft.

RESULTS

HBSP could interact with mEH in vitro and in vivo, and this interaction was mediated by the N terminal 47 amino acid residues of HBSP. HBSP could greatly enhance the hydrolysis activity of mEH in cell-free mouse liver microsomes, thus accelerating the metabolism of benzo[alpha]pyrene to produce more ultimate carcinnogen, BPDE, and this effect of HBSP requires the intact HBSP molecule. Expression of HBSP significantly increased the formation of BPDE-DNA adduct in benzo[alpha]pyrene-treated Huh-7 hepatoma cells, and this enhancement was blocked by knockdown of mEH. HBSP could enhance the cell proliferation, accelerate the G1/S transition, and promote cell transformation and tumorigenesis of B[alpha]P-treated Huh-7 hepatoma cells.

CONCLUSIONS

Our results demonstrated that HBSP could promote carcinogenic effects of B[alpha]P by interacting with mEH and enhancing its hydrolysis activity.

Genetic and epigenetic mutations of tumor suppressive genes in sporadic pituitary adenoma

Human pituitary adenomas are the most common intracranial neoplasms. Approximately 5% of them are familial adenomas. Patients with familial tumors carry germline mutations in predisposition genes, including AIP, MEN1 and PRKAR1A. These mutations are extremely rare in sporadic pituitary adenomas, which therefore are caused by different mechanisms. Multiple tumor suppressive genes linked to sporadic tumors have been identified. Their inactivation is caused by epigenetic mechanisms, mainly promoter hypermethylation, and can be placed into two groups based on their functional interaction with tumor suppressors RB or p53. The RB group includes CDKN2A, CDKN2B, CDKN2C, RB1, BMP4, CDH1, CDH13, GADD45B and GADD45G; AIP and MEN1 genes also belong to this group. The p53 group includes MEG3, MGMT, PLAGL1, RASSF1, RASSF3 and SOCS1. We propose that the tumor suppression function of these genes is mainly mediated by the RB and p53 pathways. We also discuss possible tumor suppression mechanisms for individual genes.

Multiple endocrine neoplasia type 1 (MEN1) and type 4 (MEN4)

Multiple endocrine neoplasia (MEN) is characterized by the occurrence of tumors involving two or more endocrine glands within a single patient. Four major forms of MEN, which are autosomal dominant disorders, are recognized and referred to as: MEN type 1 (MEN1), due to menin mutations; MEN2 (previously MEN2A) due to mutations of a tyrosine kinase receptor encoded by the rearranged during transfection (RET) protoncogene; MEN3 (previously MEN2B) due to RET mutations; and MEN4 due to cyclin-dependent kinase inhibitor (CDNK1B) mutations. Each MEN type is associated with the occurrence of specific tumors. Thus, MEN1 is characterized by the occurrence of parathyroid, pancreatic islet and anterior pituitary tumors; MEN2 is characterized by the occurrence of medullary thyroid carcinoma (MTC) in association with phaeochromocytoma and parathyroid tumors; MEN3 is characterized by the occurrence of MTC and phaeochromocytoma in association with a marfanoid habitus, mucosal neuromas, medullated corneal fibers and intestinal autonomic ganglion dysfunction, leading to megacolon; and MEN4, which is also referred to as MENX, is characterized by the occurrence of parathyroid and anterior pituitary tumors in possible association with tumors of the adrenals, kidneys, and reproductive organs. This review will focus on the clinical and molecular details of the MEN1 and MEN4 syndromes. The gene causing MEN1 is located on chromosome 11q13, and encodes a 610 amino-acid protein, menin, which has functions in cell division, genome stability, and transcription regulation. Menin, which acts as scaffold protein, may increase or decrease gene expression by epigenetic regulation of gene expression via histone methylation. Thus, menin by forming a subunit of the mixed lineage leukemia (MLL) complexes that trimethylate histone H3 at lysine 4 (H3K4), facilitates activation of transcriptional activity in target genes such as cyclin-dependent kinase (CDK) inhibitors; and by interacting with the suppressor of variegation 3-9 homolog family protein (SUV39H1) to mediate H3K methylation, thereby silencing transcriptional activity of target genes. MEN1-associated tumors harbor germline and somatic mutations, consistent with Knudson's two-hit hypothesis. Genetic diagnosis to identify individuals with germline MEN1 mutations has facilitated appropriate targeting of clinical, biochemical and radiological screening for this high risk group of patients for whom earlier implementation of treatments can then be considered. MEN4 is caused by heterozygous mutations of CDNK1B which encodes the 196 amino-acid CDK1 p27Kip1, which is activated by H3K4 methylation.

FBP1 Is an Interacting Partner of Menin

Multiple endocrine neoplasia type 1 (MEN1) is a syndrome characterized by tumors in multiple endocrine tissues such as the parathyroid glands, the pituitary gland, and the enteropancreatic neuroendocrine tissues. MEN1 is usually caused by mutations in the MEN1 gene that codes for the protein menin. Menin interacts with proteins that regulate transcription, DNA repair and processing, and maintenance of cytoskeletal structure. We describe the identification of FBP1 as an interacting partner of menin in a large-scale pull-down assay that also immunoprecipitated RBBP5, ASH2, and LEDGF, which are members of complex proteins associated with SET1 (COMPASS), a protein complex that methylates histone H3. This interaction was confirmed by coimmunoprecipitation and Flag-pull-down assays. Furthermore, menin localized to the FUSE site on the MYC promoter, a site that is transactivated by FBP1. This investigation therefore places menin in a pathway that regulates MYC gene expression and has important implications for the biological function of menin.

Decoding information in cell shape

Shape is an indicator of cell health. But how is the information in shape decoded? We hypothesize that decoding occurs by modulation of signaling through changes in plasma membrane curvature. Using analytical approaches and numerical simulations, we studied how elongation of cell shape affects plasma membrane signaling. Mathematical analyses reveal transient accumulation of activated receptors at regions of higher curvature with increasing cell eccentricity. This distribution of activated receptors is periodic, following the Mathieu function, and it arises from local imbalance between reaction and diffusion of soluble ligands and receptors in the plane of the membrane. Numerical simulations show that transient microdomains of activated receptors amplify signals to downstream protein kinases. For growth factor receptor pathways, increasing cell eccentricity elevates the levels of activated cytoplasmic Src and nuclear MAPK1,2. These predictions were experimentally validated by changing cellular eccentricity, showing that shape is a locus of retrievable information storage in cells.

Menin: a scaffold protein that controls gene expression and cell signaling

The protein menin is encoded by the MEN1 gene, which is mutated in patients with multiple endocrine neoplasia type 1 (MEN1) syndrome. Although menin acts as a tumor suppressor in endocrine organs, it is required for leukemic transformation in mouse models. Menin possesses these dichotomous functions probably because it can both positively and negatively regulate gene expression, as well as interact with a multitude of proteins with diverse functions. Here, we review the recent progress in understanding the molecular mechanisms by which menin functions. The crystal structures of menin with different binding partners reveal that menin is a key scaffold protein that functionally crosstalks with various partners to regulate gene transcription and interplay with multiple signaling pathways.

Interplay between menin and K-Ras in regulating lung adenocarcinoma

MEN1, which encodes the nuclear protein menin, acts as a tumor suppressor in lung cancer and is often inactivated in human primary lung adenocarcinoma. Here, we show that the inactivation of MEN1 is associated with increased DNA methylation at the MEN1 promoter by K-Ras. On one hand, the activated K-Ras up-regulates the expression of DNA methyltransferases and enhances the binding of DNA methyltransferase 1 to the MEN1 promoter, leading to increased DNA methylation at the MEN1 gene in lung cancer cells; on the other hand, menin reduces the level of active Ras-GTP at least partly by preventing GRB2 and SOS1 from binding to Ras, without affecting the expression of GRB2 and SOS1. In human lung adenocarcinoma samples, we further demonstrate that reduced menin expression is associated with the enhanced expression of Ras (p < 0.05). Finally, excision of the Men1 gene markedly accelerates the K-Ras(G12D)-induced tumor formation in the Men1(f/f);K-Ras(G12D/+);Cre ER mouse model. Together, these findings uncover a previously unknown link between activated K-Ras and menin, an important interplay governing tumor activation and suppression in the development of lung cancer.

MEN1 gene replacement therapy reduces proliferation rates in a mouse model of pituitary adenomas

Multiple endocrine neoplasia type 1 (MEN1) is characterized by the combined occurrence of pituitary, pancreatic, and parathyroid tumors showing loss of heterozygosity in the putative tumor suppressor gene MEN1. This gene encodes the protein menin, the overexpression of which inhibits cell proliferation in vitro. In this study, we conducted a preclinical evaluation of MEN1 gene therapy in pituitary tumors of Men1(+/-) mice, using a recombinant nonreplicating adenoviral serotype 5 vector that contained the murine Men1 cDNA under control of a cytomegalovirus promoter (Men1.rAd5). Pituitary tumors in 55 Men1(+/-) female mice received a transauricular intratumoral injection of Men1.rAd5 or control treatments, followed by 5-bromo-2-deoxyuridine (BrdUrd) in drinking water for four weeks before magnetic resonance imaging (MRI) and immunohistochemical analysis. Immediate procedure-related and 4-week mortalities were similar in all groups, indicating that the adenoviral gene therapy was not associated with a higher mortality. Menin expression was higher in the Men1.rAd5-treated mice when compared with other groups. Daily proliferation rates assessed by BrdUrd incorporation were reduced significantly in Men1.rAd5-injected tumors relative to control-treated tumors. In contrast, apoptotic rates, immune T-cell response, and tumor volumes remained similar in all groups. Our findings establish that MEN1 gene replacement therapy can generate menin expression in pituitary tumors, and significantly reduce tumor cell proliferation.

Recent results of basic and clinical research in MEN1: opportunities to improve early detection and treatment

Due to the variable expression of multiple endocrine neoplasia type 1 (MEN1), it is difficult to predict the course of the disease. However, knowledge about the normal function of the MEN1 gene product, together with the effects of cellular derangement by subsequent genetic events, has increased considerably. At first, the possible existence of a genotype-phenotype correlation is discussed. Thus, mild- and late-onset phenotypes may be distinguished from more malignant phenotypes depending on the character of the primary MEN1 disease gene mutation. Subsequently, tumor-promoting factors such as gender, additional genetic mutations and ecogenetic factors may contribute to the course of the disease. New developments in management are based on the knowledge and experience of the multidisciplinary teams involved. Finally, the metabolic effects of MEN1 mutations in aged patients are discussed. Early identification of predisposition to the disease, together with knowledge about the natural history of specific mutations, risks of additional mutations and periodic clinical monitoring, allow early treatment and may improve life expectancy and quality of life.

Expression and subcellular localization of menin in human cancer cells

The aim of this study was to elucidate the expression and localization of menin, a protein encoded by the multiple endocrine neoplasia type I (MEN1) gene, in 13 human cancer cell lines. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the expression of the menin gene. The localization of the menin protein was detected by immunofluorescence microscopy. Western blotting was used to determine the quantity of menin in the nucleus, cytosol and membrane of the cells. RT-PCR revealed that menin was expressed in all the cell lines examined in this study. Immunofluorescence microscopy revealed that menin was located primarily in the nucleus. In the GES-1 (transformed human gastric epithelium), MCF-7 (breast cancer), SGH44 (brain glioma) and HeLa (cervical cancer) cell lines, menin was also found to be localized to the membrane, cytosol and nucleus. Moreover, in SGH44 cells more menin was located in the cytosol than the nucleus. Similar findings were obtained by western blotting. In the GES-1 and MKN-28 cells undergoing octreotide treatment, cytoplasmic menin was significantly increased compared with the control groups. Therefore, we suggest that menin is expressed in a number of human cancer cell lines and that the cytosolic distribution increases when the cells undergo octreotide treatment, indicating a new role for menin.

Variable clinical expression in patients with a germline MEN1 disease gene mutation: clues to a genotype-phenotype correlation

Multiple endocrine neoplasia type 1 is an inherited endocrine tumor syndrome, predominantly characterized by tumors of the parathyroid glands, gastroenteropancreatic tumors, pituitary adenomas, adrenal adenomas, and neuroendocrine tumors of the thymus, lungs or stomach. Multiple endocrine neoplasia type 1 is caused by germline mutations of the multiple endocrine neoplasia type 1 tumor suppressor gene. The initial germline mutation, loss of the wild-type allele, and modifying genetic and possibly epigenetic and environmental events eventually result in multiple endocrine neoplasia type 1 tumors. Our understanding of the function of the multiple endocrine neoplasia type 1 gene product, menin, has increased significantly over the years. However, to date, no clear genotype-phenotype correlation has been established. In this review we discuss reports on exceptional clinical presentations of multiple endocrine neoplasia type 1, which may provide more insight into the pathogenesis of this disorder and offer clues for a possible genotype-phenotype correlation.

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.

Potential roles for PA28beta in gastric adenocarcinoma development and diagnosis

PURPOSE

This study aimed to investigate the expression level of human proteasome activator PA28beta subunit (PA28beta) in gastric adenocarcinomas (GA) tissues and investigate its potential role in GA carcinogenesis.

METHODS

To investigate the expression profile of PA28beta in patients with GA, we employed immunohistochemistry for detection of 287 cases of paired GA and adjacent non-neoplastic tissues. To evaluate the role of PA28beta in GA cells, we measured cell growth, colony formation, soft agar, and nude mice tumorigenicity assays in MKN-45 GA cells pre- and post-PA28beta transfection.

RESULTS

PA28beta had lower expression in 183 of 287 GA cases compared to paired normal samples (63.76%; P < or = 0.001). Decreased expression was dependent on histological type, TNM stage, and differentiation grade. Significantly decreased expression was correlated with a diffuse histological type (88/116, 75.86%) compared to an intestinal type (84/152, 55.26%; P < or = 0.001), with advanced TNM stages (T3: 44/59, 74.58%; T4:25/32, 78.13%) compared to earlier stages (T1: 25/47, 53.19%; T2: 90/149, 60.40%; P = 0.004), and poorer differentiation grade (poor: 68/90, 75.56%) compared to a higher grade (high: 9/18, 50%, moderate: 74/134, 55.22%) (P = 0.006). Over-expression of PA28beta inhibited cell growth, proliferation, and tumorigenicity of MKN-45 GA cells.

CONCLUSIONS

These results indicated that PA28beta might participate in the origin and progression of GA cancer through changes to cell proliferation activity and tumorigenicity. Therefore, PA28beta might be a novel biomarker for GA.

Primary hyperparathyroidism in patients with multiple endocrine neoplasia type 1

Primary hyperparathyroidism may occur as a part of an inherited syndrome in a combination with pancreatic endocrine tumours and/or pituitary adenoma, which is classified as Multiple Endocrine Neoplasia type 1 (MEN-1). This syndrome is caused by a germline mutation in MEN-1 gene encoding a tumour-suppressor protein, menin. Primary hyperparathyroidism is the most frequent clinical presentation of MEN-1, which usually appears in the second decade of life as an asymptomatic hypercalcemia and progresses through the next decades. The most frequent clinical presentation of MEN-1-associated primary hyperparathyroidism is bone demineralisation and recurrent kidney stones rarely followed by chronic kidney disease. The aim of this paper is to present the pathomechanism, screening procedures, diagnosis, and management of primary hyperparathyroidism in the MEN-1 syndrome. It also summarises the recent advances in the pharmacological therapy with a new group of drugs-calcimimetics.

Familial pituitary tumor syndromes

The vast majority of pituitary tumors are benign and occur sporadically; however, they can still result in significant morbidity and even premature mortality through mass effects and hormone dysfunction. The etiology of sporadic tumors is still poorly understood; by contrast, advances have been made in our understanding of familial pituitary adenoma syndromes in the past decade. Currently, four genes are known to be associated with familial pituitary tumor syndromes: MEN1, CDKN1B, PRKAR1A and AIP. The first three genes are associated with a variety of extrapituitary pathologies, for example, primary hyperparathyroidism with multiple endocrine neoplasia type 1, which might aid identification of these syndromes. By contrast, AIP mutations seem to occur in the setting of isolated familial pituitary adenomas, particularly of the growth-hormone-secreting subtype. Awareness and identification of familial pituitary tumor syndromes is important because of potential associated pathologies and important implications for family members. Here, we review the current knowledge of familial pituitary tumor syndromes.

MEN1 gene analysis in patients with primary hyperparathyroidism: 10-year experience of a single institution for thyroid and parathyroid care in Japan

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant hereditary disease. Primary hyperparathyroidism is known to occur at an early age in MEN1 patients. In MEN1 patients, special care regarding not only surgery for hyperparathyroidism but also other MEN1-related tumors is required. Between 1998 and 2007, 482 patients, including 16 whose hyperparathyroidism was discovered by family screening for MEN1, underwent surgical therapy for primary hyperparathyroidism at our institution. We recommended MEN1 gene analysis for patients having one of the following clinicopathological features: 1) age younger than 30 years old; 2) enlargement of multiple glands; 3) coexistence or presence of past history of MEN1-related tumors; or 4) family history of hyperparathyroidism or MEN1-related tumors. Sixty patients had at least one of the above features and were recommended for genetic analysis. Thirty-nine of these patients consented to undergo MEN1 genetic analysis and 16 (41%) showed MEN1 mutation. Pathological examination confirmed multiglandular parathyroid hyperplasia in 15 cases. Subject to this strategy, MEN1 index patients in Japan could be detected efficiently and selected for appropriate therapies for hyperparathyroidism and MEN1-related tumors.

Role of menin in neuroendocrine tumorigenesis

The menin protein encoded by the MEN1 tumor suppressor gene is ubiquitously expressed and highly conserved evolutionarily. The combination of findings from current in vitro and in vivo studies has not yielded a comprehensive understanding of the mechanisms of menin's tumor suppressor activity or the specific role for menin in endocrine tumorigenesis, although its diverse interactions suggest possible pivotal roles in transcriptional regulation, DNA processing and repair and cytoskeletal integrity. This manuscript summarizes recent research findings including studies of global gene expression in MEN1-associated neuroendocrine tumors and pivotal changes in intracellular signaling pathways associated with neuroendocrine tumorigenesis. Finally, the clinical applications provided by the understanding of the effects of MEN1 gene mutations on neuroendocrine tumor development in patients with this familial cancer syndrome are discussed.

Menin interacts with IQGAP1 to enhance intercellular adhesion of beta-cells

Multiple endocrine neoplasia type 1 (MEN1) is a dominantly inherited tumor syndrome that results from the mutation of the MEN1 gene that encodes protein menin. Stable overexpression of MEN1 has been shown to partially suppress the RAS-mediated morphological changes of NH3 fibroblast cells. Little is known about the molecular mechanisms by which menin decreases the oncogenic effects on cell morphology and other phenotypes. Here we showed that ectopic expression of menin in pretumor beta cells increases islet cell adhesion and reduces cell migration. Our further studies revealed that menin interacts with the scaffold protein, IQGAP1, reduces GTP-Rac1 interaction with IQGAP1 but increases E-cadherin/ß-catenin interaction with IQGAP1. Consistent with an essential role for menin in regulating ß cell adhesion in vivo, accumulations of β-catenin and E-cadherin are reduced at cell junctions in the islets from Men1-excised mice. Together, these results define a novel menin-IQGAP1 pathway that controls cell migration and cell-cell adhesion in endocrine cells.

Relation between menin expression and NF-kappaB activity in an intestinal cell line

In a previous study, we demonstrated that the Men1 gene is mainly expressed in the proliferative crypt compartment of the small intestine and that a reduction of menin expression in the crypt-like IEC-17 cell line induces an increase in proliferation rate concomitant with an increase in cyclin D1 expression. The aim of the present study was to test the hypothesis that the NF-kappaB pathway may be involved in cyclin D1 overexpression. Transcriptional activity of the cyclin D1 gene promoter was increased upon reduction of menin expression. Blockade of the NF-kappaB pathway restored proliferation, cell cycle, cyclin D1 gene transcription and cyclin D1 expression levels to those observed in the presence of menin. These data support a correlation between cyclin D1 expression, NF-kappaB activity and menin expression in this epithelial cell line and are relevant to the physiological function of menin in regulating proliferation in the intestinal epithelium.

Multiple Endocrine Neoplasia type 1

The co-occurrence of parathyroid hyperplasia with pancreatic endocrine tumours and/or pituitary adenoma is classified as Multiple Endocrine Neoplasia type 1 (MEN-1) and is caused by a germ-line mutation in MEN-1 gene encoding a tumour suppressor protein, menin. This review presents clinical expressions, diagnosis and management of the MEN-1 syndrome. Properties and mechanisms of menin functions are also reviewed.

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.

Multiple endocrine neoplasia type 1 interacts with forkhead transcription factor CHES1 in DNA damage response

Multiple endocrine neoplasia type 1 (MEN1) is a cancer susceptibility syndrome affecting several endocrine tissues. Investigations of the biochemical function of the MEN1 protein, menin, have suggested a role as a transcriptional comodulator. The mechanism by which MEN1 inactivation leads to tumor formation is not fully understood. MEN1 was implicated to function in both regulation of cell proliferation and maintenance of genomic integrity. Here, we investigate the mechanism by which MEN1 affects DNA damage response. We found that Drosophila larval tissue and mouse embryonic fibroblasts mutant for the MEN1 homologue were deficient for a DNA damage-activated S-phase checkpoint. The forkhead transcription factor CHES1 (FOXN3) was identified as an interacting protein by a genetic screen, and overexpression of CHES1 restored both cell cycle arrest and viability of MEN1 mutant flies after ionizing radiation exposure. We showed a biochemical interaction between human menin and CHES1 and showed that the COOH terminus of menin, which is frequently mutated in MEN1 patients, is necessary for this interaction. Our data indicate that menin is involved in the activation of S-phase arrest in response to ionizing radiation. CHES1 is a component of a transcriptional repressor complex, that includes mSin3a, histone deacetylase (HDAC) 1, and HDAC2, and it interacts with menin in an S-phase checkpoint pathway related to DNA damage response.

In search of tumor suppressing functions of menin

Human hereditary tumor syndromes serve as an ideal model for studying molecular pathways regulating tumorigenesis. Multiple endocrine neoplasia type 1 (MEN1), a human familial tumor syndrome, results from mutations in the Men1 gene. Men1 encodes a novel tumor suppressor, menin, of unknown biochemical function. Recently, significant progress has been made in identifying menin as a regulator of gene transcription, cell proliferation, apoptosis, and genome stability, leading to a new model of understanding menin's tumor-suppressing function. These findings suggest that menin's diverse functions depend on its association with chromatin and its control over gene transcription. This knowledge will likely be translated into new strategies to improve therapeutic interventions against MEN1 and other related cancers.

Adrenal involvement in multiple endocrine neoplasia type 1: results of 7 years prospective screening

BACKGROUND

Adrenal tumors are a common manifestation of the multiple endocrine neoplasia type 1 (MEN-1) syndrome. Prevalence in recent studies varies between 9 and 45%. A genotype-phenotype correlation has been described as well as the development of adrenocortical carcinomas. Long-term prospective data are still lacking.

MATERIALS AND METHODS

Thirty-eight MEN-1 patients with proven germline mutations have been prospectively observed in a regular screening program in our hospital. Adrenal glands have been screened by biochemical analysis and either by endoscopic ultrasound (EUS) or computed tomography (CT) or both. Median follow-up was 48 months (12-108 months). Age at diagnosis of MEN-1, type of adrenal tumor, genotype, therapy, and clinical characteristics have been analyzed.

RESULTS

In 21 (55%) patients, adrenal involvement of the disease was detected. Adrenal lesions were detected in average 6.9 years after the initial diagnosis of MEN-1. Median tumor size was 12 mm (5-40 mm). Tumor size smaller than 10 mm was observed in 11 patients. Twelve patients had unilateral while nine had bilateral adrenal lesions. EUS detected all adrenal tumors, whereas CT failed in seven cases. In three patients, functioning tumors (one pheochromocytoma, one bilateral Cushing adenoma, and one adrenocortical carcinoma) and one nonfunctioning adenoma were diagnosed by histology and biochemical assessment. Two laparoscopic adrenalectomies and one laparoscopic subtotal resection were performed. Nonfunctioning adrenal lesions, not characterized by histology yet, were found in 18 patients. There was no statistical difference with regard to adrenal involvement between patients with germline mutations in exons 2 and 10 (12/21) and those with mutations in exons 3-9 (6/11).

CONCLUSION

MEN-1-associated adrenal tumors are mostly small, benign, and nonfunctioning and much more common than previously reported. EUS was the most sensitive imaging procedure. The genotype-pheotype correlation previously suggested by our group could not be confirmed.

Reconstituted expression of menin in Men1-deficient mouse Leydig tumour cells induces cell cycle arrest and apoptosis

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary syndrome caused by the inactivation of the responsible gene, MEN1. To date, the lack of MEN1-deficient cell lines derived directly from MEN1 tumours has hampered the detailed study of the MEN1 gene. We have established several stable Men1-deficient Leydig cell tumour (LCT) lines derived from a Leydig cell tumour developed in a male heterozygous Men1 mutant mouse. Our data show that these cell lines maintain the basic characteristics of Leydig cells in terms of both androgen synthesis and gene expression. Interestingly, reconstituted menin expression in one of Men1-deficient LCT cell lines resulted in cell growth inhibition, suggesting that the function of cell growth suppression of the menin pathway, apart from menin itself, is essentially preserved in these cells. Furthermore, we show that menin re-expression in these Men1-deficient cells leads to a block in the transition from G0/G1 to S phase of the cell cycle and an increase in apoptosis, accompanied by a marked increase of p18INK4C and p27Kip1 expression. The current study therefore highlights the importance of menin expression in cell cycle and cell survival control in endocrine cells, and may provide insights into the mechanisms of tumour suppression by menin in related endocrine tumours.

Multiple endocrine neoplasia type 1

Multiple Endocrine Neoplasia type 1 (MEN1) is a rare autosomal dominant hereditary cancer syndrome presented mostly by tumours of the parathyroids, endocrine pancreas and anterior pituitary, and characterised by a very high penetrance and an equal sex distribution. It occurs in approximately one in 30,000 individuals. Two different forms, sporadic and familial, have been described. The sporadic form presents with two of the three principal MEN1-related endocrine tumours (parathyroid adenomas, entero-pancreatic tumours and pituitary tumours) within a single patient, while the familial form consists of a MEN1 case with at least one first degree relative showing one of the endocrine characterising tumours. Other endocrine and non-endocrine lesions, such as adrenal cortical tumours, carcinoids of the bronchi, gastrointestinal tract and thymus, lipomas, angiofibromas, collagenomas have been described. The responsible gene, MEN1, maps on chromosome 11q13 and encodes a 610 aminoacid nuclear protein, menin, with no sequence homology to other known human proteins. MEN1 syndrome is caused by inactivating mutations of the MEN1 tumour suppressor gene. This gene is probably involved in the regulation of several cell functions such as DNA replication and repair and transcriptional machinery. The combination of clinical and genetic investigations, together with the improving of molecular genetics knowledge of the syndrome, helps in the clinical management of patients. Treatment consists of surgery and/or drug therapy, often in association with radiotherapy or chemotherapy. Currently, DNA testing allows the early identification of germline mutations in asymptomatic gene carriers, to whom routine surveillance (regular biochemical and/or radiological screenings to detect the development of MEN1-associated tumours and lesions) is recommended.

Tumor suppressor menin: the essential role of nuclear localization signal domains in coordinating gene expression

Menin is encoded by the tumor suppressor gene MEN1 that is mutated in patients with an inherited tumor syndrome, multiple endocrine neoplasia type 1 (MEN1). Although menin is a nuclear protein and directly binds to DNA through its nuclear localization signals (NLSs), the precise role for each of the NLSs in nuclear translocation and gene expression remains to be elucidated. Here, we show that point mutations in three individual NLSs, NLS1, NLS2, and a novel accessory NLS, NLSa, do not block nuclear translocation, but compromise the ability of menin to repress expression of the endogenous insulin-like growth factor binding protein-2 (IGFBP-2) gene. This repression is not released by an inhibitor of histone deacetylases. Although subtle mutations in menin NLSs do not affect menin association with chromatin, they abolish menin binding to the IGFBP-2 promoter in vivo. Furthermore, each of the NLSs is also crucial for menin-mediated induction of caspase 8 expression. Together, these results suggest that menin may act as a scaffold protein in coordinating activation and repression of gene transcription and that its NLSs play a more important role in controlling gene transcription than merely targeting menin into the nucleus.

Génétique des tumeurs endocrines

Major advances have been made in the understanding of the genetic mechanisms underlying endocrine tumorigenesis, through the study of several syndromes of genetic predisposition and the identification of the genes involved. The syndrome of type 1 multiple endocrine neoplasia (MEN-1) is one of the best known; this autosomal dominant hereditary syndrome predisposes to the development of endocrine tumors of the pituitary, the parathyroids, the foregut and the adrenals. The responsible gene, known as MEN-1, encodes an original protein, menin, involved in several major cellular functions, such as the control of cell proliferation and differentiation. Type 2 multiple endocrine neoplasia (MEN-2) is an autosomal dominant hereditary syndrome associated with the development of medullary carcinomas of the thyroid, pheochromocytomas and hyperparathyroidism; the corresponding gene, RET, encodes a transmembrane receptor with tyrosine kinase activity. Endocrine tumors are also associated with non Hippel-Lindau disease and with phacomatoses, such as type 1 neurofibromatosis and tuberous sclerosis. Finally, isolated familial syndromes of endocrine tumors have been described: isolated familial hyperparathyroidism type II (HRPT2), associated with alterations in a gene coding for an original protein, parafibromin, or isolated familial syndromes of pheochromocytomas and paragangliomas (PRG) associated with mutations in the genes SDHB, SDHC or SDHD, which encode succinate-dehydrogenase subunits. The understanding of the genetic mechanisms underlying these syndromes of predisposition is essential for the diagnosis and management of these patients and their family; it also gives insight on the molecular mechanisms of endocrine tumorigenesis.

Molecular genetics of multiple endocrine neoplasia types 1 and 2

Six multiple endocrine neoplasia (MEN) syndromes have received a level of attention that might seem disproportionate to their low prevalence. The attention has been given because their hormonal excesses cause striking metabolic expressions and because they might clarify pathways disrupted in more common tumours. The recent discovery of the main gene in each MEN syndrome has furthered our understanding of not only hereditary but also sporadic tumours and has fostered new avenues of research.

Functional interaction between tumor suppressor menin and activator of S-phase kinase

Multiple endocrine neoplasia type I (MEN1), a hereditary tumor syndrome, is characterized by the development of tumors in multiple endocrine organs. The gene mutated in MEN1 patients, Men1, encodes a tumor suppressor, menin. Overexpression of menin leads to inhibition of Ras-transformed cells. However, it is unclear whether menin is essential for repression of cell proliferation, and if it is, how it inhibits cell proliferation. Here, we show that targeted disruption of the Men1 gene leads to enhanced cell proliferation, whereas complementation of menin-null cells with menin reduces cell proliferation. Moreover, menin interacts with activator of S-phase kinase (ASK), a component of the Cdc7/ASK kinase complex that is crucial for cell proliferation, but does not appear to alter Cdc7 kinase activity in in vitro kinase assays. We identify the COOH terminus of menin as the domain that mediates the specific interaction with ASK. Notably, wild-type menin completely represses ASK-induced cell proliferation, although it does not obviously affect the steady-state cell cycle profile of ASK-infected cells. Interestingly, disease-related COOH-terminal menin mutants that do not interact with ASK completely fail to repress ASK-induced cell proliferation. Together, these findings demonstrate a functional link between menin and ASK in the regulation of cell proliferation.

Direct binding of DNA by tumor suppressor menin

Menin is a tumor suppressor that is mutated in patients with multiple endocrine neoplasia type I (MEN1), an inherited tumor-prone syndrome. Because there is no obvious conserved structural domain in menin that suggests a biochemical function, little is known as to how menin suppresses tumorigenesis. Although menin interacts with a variety of nuclear proteins including transcription factors, it is unknown whether menin itself can directly bind DNA. Here we show that menin directly binds to double-stranded DNA. It also binds a variety of DNA structures, including Y-structures, branched structures, and 4-way junction structures. The COOH terminus of menin mediates binding to DNA, but MEN1 disease-derived mutations in the COOH terminus abolish the ability of menin to bind DNA. Importantly, these MEN1 disease-related menin mutants also fail to repress cell proliferation as well as cell cycle progression at the G2/M phase. Furthermore, detailed mutagenesis studies indicate that positively charged residues in two nuclear localization signals mediate direct DNA binding as well as repression of cell proliferation. Collectively, these results demonstrate, for the first time, a novel biochemical activity of menin, binding to DNA, and link its DNA binding to the regulation of cell proliferation.