In search of tumor suppressing functions of menin

Successful management of a multiple endocrine neoplasia type 1-associated thymic neuroendocrine neoplasms with acute chest pain as initial symptom: A rare case report

Key Clinical Message

Acute chest pain can be the first manifestation of multiple endocrine neoplasia type 1(MEN1)-associated thymic neuroendocrine neoplasms (NEN). Comprehensive treatment may be an effective strategy for MEN1-associated NEN.

Abstract

Multiple endocrine neoplasia type 1(MEN1)-associated thymic neuroendocrine neoplasms (NEN) is caused by the mutation of tumor suppressor MEN1 gene. Patients with MEN1-associated NEN initially presenting with acute chest pain are very rare. In the manuscript, we reported a case of a 45-year-old man who developed MEN1-associated NEN with acute chest pain as initial symptom. Thoracoscopic thymotomy was performed and thymic NEN was successfully removed. Genetic test showed a germline mutation of MEN1 gene in this patient. Immunohistochemical staining exhibited Syn(+), CgA(+), INSM1(+), CD56(+) and Ki67-positive cells (2%) in MEN1-associated NEN. Further evaluation unveiled MEN1-associated benign tumors including digestive NEN and pituitary gland adenoma. The 99mTc-HYNIC-TOC scintigraphy showed that focally increased radioactivity in the mid-upper abdomen. This patient was administered with 50Gy/25F of radiation dose to treat the postoperative lesions. Subsequently, sandostatin LAR (30 mg per week) was used as systemic therapy. He had no recurrence or metastasis for 6-month follow-up. Thus, acute chest pain can be the first manifestation of MEN1-associated NEN, and comprehensive treatment including surgery, radiation and systemic treatment may be an effective strategy for MEN1-associated NEN.

Loss of MEN1 leads to renal fibrosis and decreases HGF-Adamts5 pathway activity via an epigenetic mechanism

BACKGROUND

Renal fibrosis is a serious condition that results in the development of chronic kidney diseases. The MEN1 gene is an epigenetic regulator that encodes the menin protein and its role in kidney tissue remains unclear.

METHODS

Kidney histology was examined on paraffin sections stained with hematoxylin-eosin staining. Masson's trichrome staining and Sirius red staining were used to analyze renal fibrosis. Gene and protein expression were determined by quantitative real-time PCR (qPCR) and Western blot, respectively. Immunohistochemistry staining in the kidney tissues from mice or patients was used to evaluate protein levels. Flow cytometry was used to analyze the cell cycle distributions and apoptosis. RNA-sequencing was performed for differential expression genes in the kidney tissues of the Men1f/f and Men1∆/∆ mice. Chromatin immunoprecipitation sequencing (ChIP-seq) was carried out for identification of menin- and H3K4me3-enriched regions within the whole genome in the mouse kidney tissue. ChIP-qPCR assays were performed for occupancy of menin and H3K4me3 at the gene promoter regions. Luciferase reporter assay was used to detect the promoter activity. The exacerbated unilateral ureteral obstruction (UUO) models in the Men1f/f and Men1∆/∆ mice were used to assess the pharmacological effects of rh-HGF on renal fibrosis.

RESULTS

The expression of MEN1 is reduce in kidney tissues of fibrotic mouse and human diabetic patients and treatment with fibrotic factor results in the downregulation of MEN1 expression in renal tubular epithelial cells (RTECs). Disruption of MEN1 in RTECs leads to high expression of α-SMA and Collagen 1, whereas MEN1 overexpression restrains epithelial-to-mesenchymal transition (EMT) induced by TGF-β treatment. Conditional knockout of MEN1 resulted in chronic renal fibrosis and UUO-induced tubulointerstitial fibrosis (TIF), which is associated with an increased induction of EMT, G2/M arrest and JNK signaling. Mechanistically, menin recruits and increases H3K4me3 at the promoter regions of hepatocyte growth factor (HGF) and a disintegrin and metalloproteinase with thrombospondin motifs 5 (Adamts5) genes and enhances their transcriptional activation. In the UUO mice model, exogenous HGF restored the expression of Adamts5 and ameliorated renal fibrosis induced by Men1 deficiency.

CONCLUSIONS

These findings demonstrate that MEN1 is an essential antifibrotic factor in renal fibrogenesis and could be a potential target for antifibrotic 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.

DNMT1 as a therapeutic target in pancreatic cancer: mechanisms and clinical implications

BACKGROUND

Pancreatic cancer or pancreatic ductal adenocarcinoma (PDAC) is one of the most devastating cancer types with a 5-year survival rate of only 9%. PDAC is one of the leading causes of cancer-related deaths in both genders. Epigenetic alterations may lead to the suppression of tumor suppressor genes, and DNA methylation is a predominant epigenetic modification. DNA methyltransferase 1 (DNMT1) is required for maintaining patterns of DNA methylation during cellular replication. Accumulating evidence has implicated the oncogenic roles of DNMT1 in various malignancies including PDACs.

CONCLUSIONS

Herein, the expression profiles, oncogenic roles, regulators and inhibitors of DNMT1 in PDACs are presented and discussed. DNMT1 is overexpressed in PDAC cases compared with non-cancerous pancreatic ducts, and its expression gradually increases from pre-neoplastic lesions to PDACs. DNMT1 plays oncogenic roles in suppressing PDAC cell differentiation and in promoting their proliferation, migration and invasion, as well as in induction of the self-renewal capacity of PDAC cancer stem cells. These effects are achieved via promoter hypermethylation of tumor suppressor genes, including cyclin-dependent kinase inhibitors (e.g., p14, p15, p16, p21 and p27), suppressors of epithelial-mesenchymal transition (e.g., E-cadherin) and tumor suppressor miRNAs (e.g., miR-148a, miR-152 and miR-17-92 cluster). Pre-clinical investigations have shown the potency of novel non-nucleoside DNMT1 inhibitors against PDAC cells. Finally, phase I/II clinical trials of DNMT1 inhibitors (azacitidine, decitabine and guadecitabine) in PDAC patients are currently underway, where these inhibitors have the potential to sensitize PDACs to chemotherapy and immune checkpoint blockade therapy.

Phenotypes Associated With MEN1 Syndrome: A Focus on Genotype-Phenotype Correlations

Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal dominant inherited tumor syndrome, associated with parathyroid, pituitary, and gastro-entero-pancreatic (GEP) neuroendocrine tumors (NETs). MEN1 is usually consequent to different germline and somatic mutations of the MEN1 tumor suppressor gene, although phenocopies have also been reported. This review analyzed main biomedical databases searching for reports on MEN1 gene mutations and focused on aggressive and aberrant clinical manifestations to investigate the potential genotype-phenotype correlation. Despite efforts made by several groups, this link remains elusive to date and evidence that aggressive or aberrant clinical phenotypes may be related to specific mutations has been provided by case reports and small groups of MEN1 patients or families. In such context, a higher risk of aggressive tumor phenotypes has been described in relation to frameshift and non-sense mutations, and predominantly associated with aggressive GEP NETs, particularly pancreatic NETs. In our experience a novel heterozygous missense mutation at c.836C>A in exon 6 was noticed in a MEN1 patient operated for macro-prolactinoma, who progressively developed recurrent parathyroid adenomas, expanding gastrinomas and, long after the first MEN1 manifestation, a neuroendocrine uterine carcinoma. In conclusion, proof of genotype-phenotype correlation is limited but current evidence hints at the need for long-term interdisciplinary surveillance in patients with aggressive phenotypes and genetically confirmed MEN1.

Menin Coordinates C/EBPβ-Mediated TGF-β Signaling for Epithelial-Mesenchymal Transition and Growth Inhibition in Pancreatic Cancer

Menin displays either tumor suppression or promotion functions in a context-dependent manner. Previously, we proposed that Menin acts as a tumor suppressor by inhibiting cell growth in pancreatic ductal adenocarcinoma (PDAC), whereas the relationship between the Menin expression and overall survival rate of PDAC patients has not been completely elucidated, indicating the complexity of Menin functions in PDAC progression. Here, we identify Menin as a promoter of epithelial-mesenchymal transition (EMT), which is largely associated with cell migration or metastasis, with modest activity in cell growth inhibition. Ectopic expression of Menin suppresses the expression of CCAAT/enhancer-binding protein beta (CEBPB) and epithelial-specific genes by histone deacetylation and further enhances the TGF-β signaling-related EMT process. We also demonstrate that CCAAT/enhancer binding protein (C/EBP) beta (C/EBPβ; encoded by CEBPB) acts downstream of Menin and TGF-β signaling for balancing growth inhibition and EMT, and C/EBPβ overexpression could restore the anti-cancer functions of Menin in pancreatic cancer by cooperatively activating CDKN2A/B genes and antagonizing EMT processes. Taken together, our results suggest that Menin functions as an oncogene for cancer metastasis upon C/EBPβ depletion or acts as a tumor suppressor by cooperation with C/EBPβ to activate CDKN2A transcription.

Menin Associates With the Mitotic Spindle and Is Important for Cell Division

Menin is the protein mutated in patients with multiple endocrine neoplasia type 1 (MEN1) syndrome and their corresponding sporadic tumor counterparts. We have found that menin functions in promoting proper cell division. Here, we show that menin localizes to the mitotic spindle poles and the mitotic spindle during early mitosis and to the intercellular bridge microtubules during cytokinesis in HeLa cells. In our study, menin depletion led to defects in spindle assembly and chromosome congression during early mitosis, lagging chromosomes during anaphase, defective cytokinesis, multinucleated interphase cells, and cell death. In addition, pharmacological inhibition of the menin-MLL1 interaction also led to similar cell division defects. These results indicate that menin and the menin-MLL1 interaction are important for proper cell division. These results highlight a function for menin in cell division and aid our understanding of how mutation and misregulation of menin promotes tumorigenesis.

Insights into the biology and treatment strategies of pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PNETs) are the second most common primary pancreatic neoplasms after pancreatic ductal adenocarcinoma. PNETs present with widely various clinical manifestation and unfavorable survival rate. The recent advances in next generation sequencing have significantly increased our understanding of the molecular landscape of PNETs and help guide the development of targeted therapies. This review intends to outline a holistic picture of the tumors by discussing current understanding of clinical presentations, up-to-date treatment strategies, novel mouse models, and molecular biology of PNETs. Furthermore, we will provide insight into the future development of more effective targeted therapies that are necessary to manage PNETs.

UMD-MEN1 Database: An Overview of the 370 MEN1 Variants Present in 1676 Patients From the French Population

CONTEXT

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disease caused by mutations in the MEN1 gene characterized by a broad spectrum of clinical manifestations, of which the most frequent are primary hyperparathyroidism, pituitary adenomas, and neuroendocrine tumors.

OBJECTIVE

The aim of this work was to facilitate interpretation of variants and improve the genetic counseling and medical care of families of patients with MEN1.

DESIGN, SETTING, AND PATIENTS

The TENGEN network (Oncogenetics Network of Neuroendocrine Tumors) has interpreted and collected all allelic variants and clinical characteristics of the MEN1-positive patients identified through genetic testing performed in the French population from 1997 to 2015. Patients and their variants were registered in the locus-specific UMD-MEN1 database (www.umd.be/MEN1/).

MAIN OUTCOMES

Variant classification, age-related penetrance, and odds ratios.

RESULTS

A total of 370 distinct variants reported in 1676 patients, including 181 unpublished variants, have been registered. This database analysis revealed a low frequency (6.6%) of benign or likely benign missense variants in MEN1. Eight families (1.9%) had members with familial isolated hyperparathyroidism and harbored the same mutations as that found in families with authentic MEN1. An association existed between large rearrangements and an earlier onset of the disease, whereas no difference was observed between truncating and nontruncating variants.

CONCLUSION

The UMD-MEN1 database provides an exhaustive overview of the MEN1 variants present in the French population. For each variant, a classification is publicly available. Clinical data collections allow the determination of genotype-phenotype correlation and age-related penetrance of lesions in the cohort.

MiR-24-3p regulates cell proliferation and milk protein synthesis of mammary epithelial cells through menin in dairy cows

MiR-24-3p, a broadly conserved, small, noncoding RNA, is abundantly expressed in mammary tissue. However, its regulatory role in this tissue remains poorly understood. It was predicted that miR-24-3p targets the 3' untranslated region (3'-UTR) of multiple endocrine neoplasia type 1 (MEN1), an important regulatory factor in mammary tissue. The objective of this study was to investigate the function of miR-24-3p in mammary cells. Using a luciferase assay in mammary epithelial cells (MAC-T), miR-24-3p was confirmed to target the 3'-UTR of MEN1. Furthermore, miR-24-3p negatively regulated the expression of the MEN1 gene and its encoded protein, menin. miR-24-3p enhanced proliferation of MAC-T by promoting G1/S phase progression. MiR-24-3p also regulated the expression of key factors involved in phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin and Janus kinase/signal transducer and activators of transcription signaling pathways, therefore controlling milk protein synthesis in epithelial cells. Thus, miR-24-3p appears to act on MAC-T by targeting MEN1. The expression of miR-24-3p was controlled by MEN1/menin, indicating a negative feedback loop between miR-24-3p and MEN1/menin. The negatively inhibited expression pattern of miR-24-3p and MEN1 was active in mammary tissues at different lactation stages. The feedback mechanism is a new concept to further understand the lactation cycle of mammary glands and can possibly to be manipulated to improve milk yield and quality.

The Molecular and Clinical Landscape of Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors are rare tumors of the pancreas originating from the islets of the Langerhans. These tumors comprise 1% to 3% of all newly diagnosed pancreatic cancers every year and have a unique heterogeneity in clinical presentation. Whole-genome sequencing has led to an increased understanding of the molecular biology of these tumors. In this review, we will summarize the current knowledge of the signaling pathways involved in the tumorigenesis of pancreatic neuroendocrine tumors as well as the major studies targeting these pathways at preclinical and clinical levels.

Translational Diagnostics and Therapeutics in Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine tumors (PNET) are rare tumors, but have been increasing in incidence. Although typically thought of as indolent, more than half of patients present with metastatic disease. For many years, the only mutations commonly known in these tumors were those in the MEN1 gene. Recently, the genetics underlying PNETs have been further defined through exome sequencing. The most frequent alterations found in sporadic PNETs are in MEN1, DAXX/ATRX, and a variety of genes in the mTOR pathway. Confirmation of these mutations has prompted trials with a number of drugs active in these pathways, and two drugs were eventually approved in 2011-sunitinib and everolimus. New data additionally identify the MET and CD47 receptors as potential novel drug targets. Yet despite improvements in progression-free survival with sunitinib and everolimus, further studies defining when to use these agents and factors associated with limitations in their utility are needed. As more discoveries are made in the laboratory that elucidate additional molecular mechanisms important in the initiation and metastasis of PNETs, continued efforts to translate these discoveries into distinct new therapies will be needed to improve patient survival. Clin Cancer Res; 22(20); 5022-9. ©2016 AACR SEE ALL ARTICLES IN THIS CCR FOCUS SECTION, "ENDOCRINE CANCERS REVISING PARADIGMS".

Menin Modulates Mammary Epithelial Cell Numbers in Bovine Mammary Glands Through Cyclin D1

Menin, the protein encoded by the MEN1 gene, is abundantly expressed in the epithelial cells of mammary glands. Here, we found MEN1/menin expression slowly decreased with advancing lactation but increased by the end of lactation. It happened that the number of bovine mammary epithelial cells decreases since lactation, suggesting a role of menin in the control of mammary epithelial cell growth. Indeed, reduction of menin expression through MEN1-specific siRNA transfection in the bovine mammary epithelial cells caused cell growth arrest in G1/S phase. Decreased mRNA and protein expression of Cyclin D1 was observed upon MEN1 knockdown. Furthermore, menin was confirmed to physically bind to the promoter region of Cyclin D1 through a ChIP assay, indicating that menin plays a regulatory role in mammary epithelial cell cycle progression. Moreover, lower expression of MEN1/menin induced increased epithelial cell apoptosis and caused extracellular matrix remodeling by down-regulating its associated genes, such as DSG2 and KRT5, suggesting that menin's role may also be involved in the control of cell-cell adhesion in normal mammary glands. Taken together, our data revealed an unknown molecular function of menin in epithelial cell proliferation, which may be important in the regulation of lactation behavior of mammary glands.

Epigenetic regulation by the menin pathway

There is a trend of increasing prevalence of neuroendocrine tumors (NETs), and the inherited multiple endocrine neoplasia type 1 (MEN1) syndrome serves as a genetic model to investigate how NETs develop and the underlying mechanisms. Menin, encoded by the MEN1 gene, at least partly acts as a scaffold protein by interacting with multiple partners to regulate cellular homeostasis of various endocrine organs. Menin has multiple functions including regulation of several important signaling pathways by controlling gene transcription. Here, we focus on reviewing the recent progress in elucidating the key biochemical role of menin in epigenetic regulation of gene transcription and cell signaling, as well as posttranslational regulation of menin itself. In particular, we will review the progress in studying structural and functional interactions of menin with various histone modifiers and transcription factors such as MLL, PRMT5, SUV39H1 and other transcription factors including c-Myb and JunD. Moreover, the role of menin in regulating cell signaling pathways such as TGF-beta, Wnt and Hedgehog, as well as miRNA biogenesis and processing will be described. Further, the regulation of the MEN1 gene transcription, posttranslational modifications and stability of menin protein will be reviewed. These various modes of regulation by menin as well as regulation of menin by various biological factors broaden the view regarding how menin controls various biological processes in neuroendocrine organ homeostasis.

Menin localization in cell membrane compartment

Menin is encoded by the MEN1 gene, which is mutated in an inherited human syndrome, multiple endocrine neoplasia type 1(MEN1). Menin is primarily nuclear protein, acting as a tumor suppressor in endocrine organs, but as an oncogenic factor in the mixed lineage leukemia, in a tissue-specific manner. Recently, the crystal structures of menin with different binding partners reveal menin as a key scaffold protein that functionally interacts with various partners to regulate gene transcription in the nucleus. However, outside the nucleus, menin also regulates multiple signaling pathways that traverse the cell surface membrane. The precise nature regarding to how menin associates with the membrane fraction is poorly understood. Here we show that a small fraction of menin associates with the cell membrane fraction likely via serine palmitoylation. Moreover, the majority of the membrane-associated menin may reside inside membrane vesicles, as menin is protected from trypsin-mediated proteolysis, but disruption of the membrane fraction using detergent abolishes the detection. Consistently, cellular staining for menin also reveals the distribution of menin in the cell membrane and the punctate-like cell organelles. Our findings suggest that part of intracellular menin associates with the cell membrane peripherally as well as resides within the membrane vesicles.

MAJOR MOLECULAR GENETIC DRIVERS IN SPORADIC PRIMARY HYPERPARATHYROIDISM

Primary hyperparathyroidism is primarily due to a solitary parathyroid adenoma but multi-gland disease, parathyroid carcinoma, and ectopic parathyroid hormone production can occur. Although primary hyperparathyroidism mostly presents sporadically, strong familial predispositions also exist. Much is known about heritable genetic mutations responsible for these syndromes, including multiple endocrine neoplasia types 1 and 2A, hyperparathyroidism-jaw tumor syndrome, and familial hypocalciuric hypercalcemia. Acquired mutations in common sporadic hyperparathyroidism have also been discovered. Here we focus on the most common and well-established genetic drivers: 1) involvement of the oncogene cyclin D1 in human neoplasia was first established in parathyroid adenomas, followed by recognition of its importance in other tumor types including breast cancer and B-lymphoid malignancy; and 2) somatic mutation of the MEN1 gene, first identified as the source of pathogenic germline mutations in patients with familial endocrinopathies, is found in a substantial fraction of non-familial parathyroid adenomas.

PTCH 1 staining of pancreatic neuroendocrine tumor (PNET) samples from patients with and without multiple endocrine neoplasia (MEN-1) syndrome reveals a potential therapeutic target

Pancreatic neuroendocrine tumors (PNETs) are rare, indolent tumors that may occur sporadically or develop in association with well-recognized hereditary syndromes, particularly multiple endocrine neoplasia type 1 (MEN-1). We previously demonstrated that the hedgehog (HH) signaling pathway was aberrantly up-regulated in a mouse model that phenocopies the human MEN-1 syndrome, Men1l/l;RipCre, and that inhibition of this pathway suppresses MEN-1 tumor cell proliferation. We hypothesized that the HH signaling pathway is similarly upregulated in human PNETs. We performed immunohistochemical (IHC) staining for PTCH1 in human fresh and archival PNET specimens to examine whether human sporadic and MEN-1-associated PNETs revealed similar abnormalities as in our mouse model and correlated the results with clinical and demographic factors of the study cohort. PTCH1 staining was positive in 12 of 22 PNET patients (55%). Four of 5 MEN-1 patients stained for PTCH1 (p = 0.32 as compared with sporadic disease patients). Nine of 16 patients with metastatic disease stained for PTCH1 as compared with zero of 3 with localized disease only (p = 0.21). No demographic or clinical features appeared to be predictive of PTCH 1 positivity and PTCH 1 positivity per se was not predictive of clinical outcome. PTCH1, a marker of HH pathway up regulation, is detectable in both primary and metastatic tumors in more than 50% of PNET patients. Although no clinical or demographic factors predict PTCH1 positivity and PTCH1 positivity does not predict clinical outcome, the frequency of expression alone indicates that perturbation of this pathway with agents such as Vismodegib, an inhibitor of Smoothened (SMO), should be examined in future clinical trials.

Interplay between menin and Dnmt1 reversibly regulates pancreatic cancer cell growth downstream of the Hedgehog signaling pathway

Menin, the product of the Men1 gene, which is frequently mutated in pancreatic neuroendocrine tumors, acts as a chromatin-remodeling factor to modulate the transcription of cell cycle regulators by interacting with histone modification factors. However, the function of menin and its underlying mechanisms in pancreatic ductal adenocarcinoma remain unknown. Here, we found that menin inhibited pancreatic cancer cell growth in vitro and in vivo and that its expression was gradually lost during pancreatic carcinogenesis. Menin overexpression significantly activated the expression of the cyclin-dependent kinase (CDK) inhibitors p18 and p27, accompanied with a decrease in DNA methylation levels of p18 and p27 promoters. Mechanistically, we found that interaction of menin with DNA methyltransferase 1 (Dnmt1) competitively pulled down Dnmt1 from p18 and p27 promoters, leading to the downregulation of DNA methylation levels. Moreover, menin expression was suppressed by Dnmt1 downstream of the Hedgehog signaling pathway, and menin overexpression strongly antagonized the promotion effect of hedgehog signaling on pancreatic cancer cell proliferation. Taken together, the interaction between menin and Dnmt1 reversibly regulates pancreatic cancer cell growth downstream of Hedgehog pathways with complex mutual modulation networks, suggesting that the Hedgehog/Dnmt1/menin axis is a potential molecular target for pancreatic cancer therapy.

Identification of CD34+ and CD34- leukemia-initiating cells in MLL-rearranged human acute lymphoblastic leukemia

Translocation of the mixed-lineage leukemia (MLL) gene with AF4, AF9, or ENL results in acute leukemia with both lymphoid and myeloid involvement. We characterized leukemia-initiating cells (LICs) in primary infant MLL-rearranged leukemia using a xenotransplantation model. In MLL-AF4 patients, CD34(+)CD38(+)CD19(+) and CD34(-)CD19(+) cells initiated leukemia, and in MLL-AF9 patients, CD34(-)CD19(+) cells were LICs. In MLL-ENL patients, either CD34(+) or CD34(-) cells were LICs, depending on the pattern of CD34 expression. In contrast, in patients with these MLL translocations, CD34(+)CD38(-)CD19(-)CD33(-) cells were enriched for normal hematopoietic stem cells (HSCs) with in vivo long-term multilineage hematopoietic repopulation capacity. Although LICs developed leukemic cells with clonal immunoglobulin heavy-chain (IGH) rearrangement in vivo, CD34(+)CD38(-)CD19(-)CD33(-) cells repopulated recipient bone marrow and spleen with B cells, showing broad polyclonal IGH rearrangement and recipient thymus with CD4(+) single positive (SP), CD8(+) SP, and CD4(+)CD8(+) double-positive (DP) T cells. Global gene expression profiling revealed that CD9, CD32, and CD24 were over-represented in MLL-AF4, MLL-AF9, and MLL-ENL LICs compared with normal HSCs. In patient samples, these molecules were expressed in CD34(+)CD38(+) and CD34(-) LICs but not in CD34(+)CD38(-)CD19(-)CD33(-) HSCs. Identification of LICs and LIC-specific molecules in primary human MLL-rearranged acute lymphoblastic leukemia may lead to improved therapeutic strategies for MLL-rearranged leukemia.

Menin-mediated regulation of miRNA biogenesis uncovers the IRS2 pathway as a target for regulating pancreatic beta cells

Menin, a protein encoded by the MEN1 gene, is mutated in patients with multiple endocrine neoplasia type 1 (MEN1). Menin acts as a tumor suppressor in endocrine organs while it is also required for transformation of a subgroup of leukemia. The recently solved crystal structure of menin with different binding partners reveals that menin is a key scaffold protein that cross-talks with various partners, including transcription factors, to regulate gene transcription. Our recent findings unravel a previously undiscovered mechanism for menin-mediated control of gene expression via processing of certain microRNA's, thus adding to the plethora of ways in which menin regulates gene expression. By interacting with ARS2, an RNA binding protein, menin facilitates the processing of pri-let 7a and pri-miR155 to pre-let 7a and pre-miR155 respectively. Consistently, excision of the Men1 gene results in upregulation of IRS2, a let-7a target. As IRS2 is known to mediate both insulin signaling and insulin-induced cell proliferation, and let-7a targets include oncogenes like RAS and HMGA2, a deeper understanding of the menin-ARS2 complex in regulating miRNA biogenesis will yield further insights into the pathogenesis of the MEN1 syndrome and other menin-associated malignancies.

p27 Loss Is Associated with Poor Prognosis in Gastroenteropancreatic Neuroendocrine Tumors

Purpose

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a heterogeneous disease group originating from the neuroendocrine cells. Identification of prognostic markers, related to neuroendocrine tissue-selective tumorigenesis, is necessary to find therapeutic targets.

Materials and Methods

A total of 327 patients with GEP-NETs were included in this study; there were 49 gastric, 29 duodenal, 49 pancreatic, 12 hepatobiliary, 33 appendiceal, 5 proximal colon, and 150 distal colon cases. We performed immunostaining with the tissue microarray method for menin, p27, and p18.

Results

We observed negative staining for menin, p27, and p18 in 34%, 21%, and 56% of GEP-NETs, respectively. The loss of p27, but not menin, was positively correlated with the grade of Ki-67. Menin–/p27–, menin–/p27+, menin+/p27–, and menin+/p27+ phenotype groups included 13%, 22%, 8%, and 57% of patients, respectively. A dichotomized comparison showed that menin– or p27– tumors were significantly associated with foregut and midgut localizations, high World Health Organization (WHO) grade, lymph node metastasis, and more advanced stage as compared to menin+/p27+ patients. Kaplan-Meier analysis for the overall survival showed that p27 loss was significantly associated with decreased survival. Multivariate analysis showed that p27 loss is an independent factor for poor overall survival.

Conclusion

Our results revealed that the loss of p27 is associated with poor prognosis and the menin-p27 pathway is important in the tumorigenesis of GEP-NETs.

p.Ala541Thr variant of MEN1 gene: a non deleterious polymorphism or a pathogenic mutation?

CONTEXT

Multiple Endocrine Neoplasia Type 1 (MEN1) is an autosomal dominant inherited syndrome, related to mutations in the MEN1 gene. Controversial data suggest that the nonsynonymous p.Ala541Thr variant, usually considered as a non-pathogenic polymorphism, may be associated with an increased risk of MEN1-related lesions in carriers.

OBJECTIVE

The aim of this study was to evaluate the pathogenic influence of the p.Ala541Thr variant on clinical and functional outcomes.

PATIENTS AND METHODS

We analysed a series of 55 index patients carrying the p.Ala541Thr variant. Their clinical profile was compared to that of 117 MEN1 patients. The biological impact of the p.Ala541Thr variant on cell growth was additionally investigated on menin-deficient Leydig cell tumour (LCT)10 cells generated from Men1+/Men1- heterozygous knock-out mice, and compared with wild type (WT).

RESULTS

The mean age at first appearance of endocrine lesions was similar in both p.Ala541Thr carriers and MEN1 patients, but no p.Ala541Thr patient had more than one cardinal MEN1 lesion at initial diagnosis. A second MEN1 lesion was diagnosed in 13% of MEN1 patients and in 7% of p.Ala541Thr carriers in the year following preliminary diagnosis. Functional studies on LCT10 cells showed that overexpression of the p.Ala541Thr variant did not inhibit cell growth, which is in direct contrast to results obtained from investigation of WT menin protein.

CONCLUSION

Taken together, these data raise the question of a potential pathogenicity of the p.Ala541Thr missense variant of menin that commonly occurs within the general population. Additional studies are required to investigate whether it may be involved in a low-penetrance MEN1 phenotype.

Challenges and opportunities in targeting the menin-MLL interaction

Menin is an essential co-factor of oncogenic MLL fusion proteins and the menin-MLL interaction is critical for development of acute leukemia in vivo. Targeting the menin-MLL interaction with small molecules represents an attractive strategy to develop new anticancer agents. Recent developments, including determination of menin crystal structure and development of potent small molecule and peptidomimetic inhibitors, demonstrate the feasibility of targeting the menin-MLL interaction. On the other hand, biochemical and structural studies revealed that MLL binds to menin in a complex bivalent mode engaging two MLL motifs, and therefore inhibition of this protein-protein interaction represents a challenge. This review summarizes the most recent achievements in targeting the menin-MLL interaction as well as discusses potential benefits of blocking menin in cancer.

Menin is required for optimal processing of the microRNA let-7a

Multiple endocrine neoplasia type I (MEN1) is an inherited syndrome that includes susceptibility to pancreatic islet hyperplasia. This syndrome results from mutations in the MEN1 gene, which encodes menin protein. Menin interacts with several transcription factors, including JunD, and inhibits their activities. However, the precise mechanism by which menin suppresses gene expression is not well understood. Here, we show that menin interacts with arsenite-resistant protein 2 (ARS2), a component of the nuclear RNA CAP-binding complex that is crucial for biogenesis of certain miRNAs including let-7a. The levels of primary-let-7a (pri-let-7a) are not affected by menin; however, the levels of mature let-7a are substantially decreased upon Men1 excision. Let-7a targets, including Insr and Irs2, pro-proliferative genes that are crucial for insulin-mediated signaling, are up-regulated in Men1-excised cells. Inhibition of let-7a using anti-miRNA in wild type cells is sufficient to enhance the expression of insulin receptor substrate 2 (IRS2) to levels observed in Men1-excised cells. Depletion of menin does not affect the expression of Drosha and CBP80, but substantially impairs the processing of pri-miRNA to pre-miRNA. Ars2 knockdown decreased let-7a processing in menin-expressing cells but had little impact on let-7a levels in menin-excised cells. As IRS2 is known to mediate insulin signaling and insulin/mitogen-induced cell proliferation, these findings collectively unravel a novel mechanism whereby menin suppresses cell proliferation, at least partly by promoting the processing of certain miRNAs, including let-7a, leading to suppression of Irs2 expression and insulin signaling.

Causes of death and prognostic factors in multiple endocrine neoplasia type 1: a prospective study: comparison of 106 MEN1/Zollinger-Ellison syndrome patients with 1613 literature MEN1 patients with or without pancreatic endocrine tumors

Multiple endocrine neoplasia type 1 (MEN1) is classically characterized by the development of functional or nonfunctional hyperplasia or tumors in endocrine tissues (parathyroid, pancreas, pituitary, adrenal). Because effective treatments have been developed for the hormone excess state, which was a major cause of death in these patients in the past, coupled with the recognition that nonendocrine tumors increasingly develop late in the disease course, the natural history of the disease has changed. An understanding of the current causes of death is important to tailor treatment for these patients and to help identify prognostic factors; however, it is generally lacking.To add to our understanding, we conducted a detailed analysis of the causes of death and prognostic factors from a prospective long-term National Institutes of Health (NIH) study of 106 MEN1 patients with pancreatic endocrine tumors with Zollinger-Ellison syndrome (MEN1/ZES patients) and compared our results to those from the pooled literature data of 227 patients with MEN1 with pancreatic endocrine tumors (MEN1/PET patients) reported in case reports or small series, and to 1386 patients reported in large MEN1 literature series. In the NIH series over a mean follow-up of 24.5 years, 24 (23%) patients died (14 MEN1-related and 10 non-MEN1-related deaths). Comparing the causes of death with the results from the 227 patients in the pooled literature series, we found that no patients died of acute complications due to acid hypersecretion, and 8%-14% died of other hormone excess causes, which is similar to the results in 10 large MEN1 literature series published since 1995. In the 2 series (the NIH and pooled literature series), two-thirds of patients died from an MEN1-related cause and one-third from a non-MEN1-related cause, which agrees with the mean values reported in 10 large MEN1 series in the literature, although in the literature the causes of death varied widely. In the NIH and pooled literature series, the main causes of MEN1-related deaths were due to the malignant nature of the PETs, followed by the malignant nature of thymic carcinoid tumors. These results differ from the results of a number of the literature series, especially those reported before the 1990s. The causes of non-MEN1-related death for the 2 series, in decreasing frequency, were cardiovascular disease, other nonendocrine tumors > lung diseases, cerebrovascular diseases. The most frequent non-MEN1-related tumor deaths were colorectal, renal > lung > breast, oropharyngeal. Although both overall and disease-related survival are better than in the past (30-yr survival of NIH series: 82% overall, 88% disease-related), the mean age at death was 55 years, which is younger than expected for the general population.Detailed analysis of causes of death correlated with clinical, laboratory, and tumor characteristics of patients in the 2 series allowed identification of a number of prognostic factors. Poor prognostic factors included higher fasting gastrin levels, presence of other functional hormonal syndromes, need for >3 parathyroidectomies, presence of liver metastases or distant metastases, aggressive PET growth, large PETs, or the development of new lesions.The results of this study have helped define the causes of death of MEN1 patients at present, and have enabled us to identify a number of prognostic factors that should be helpful in tailoring treatment for these patients for both short- and long-term management, as well as in directing research efforts to better define the natural history of the disease and the most important factors determining long-term survival at present.

Menin epigenetically represses Hedgehog signaling in MEN1 tumor syndrome

Multiple endocrine neoplasia type 1 (MEN1) is an inherited tumor syndrome that includes susceptibility to pancreatic islet tumors. This syndrome results from mutations in the MEN1 gene, encoding menin. Although menin acts as an oncogenic cofactor for mixed lineage leukemia (MLL) fusion protein-mediated histone H3 lysine 4 methylation, the precise basis for how menin suppresses gene expression and proliferation of pancreatic beta cells remains poorly understood. Here, we show that menin ablation enhances Hedgehog signaling, a proproliferative and oncogenic pathway, in murine pancreatic islets. Menin directly interacts with protein arginine methyltransferase 5 (PRMT5), a negative regulator of gene transcription. Menin recruits PRMT5 to the promoter of the Gas1 gene, a crucial factor for binding of Sonic Hedgehog (Shh) ligand to its receptor PTCH1 and subsequent activation of the Hedgehog signaling pathway, increases repressive histone arginine symmetric dimethylation (H4R3m2s), and suppresses Gas1 expression. Notably, MEN1 disease-related menin mutants have reduced binding to PRMT5, and fail to impart the repressive H4R3m2s mark at the Gas1 promoter, resulting in its elevated expression. Pharmacologic inhibition of Hedgehog signaling significantly reduces proliferation of insulinoma cells, and expression of Hedgehog signaling targets including Ptch1, in MEN1 tumors of mice. These findings uncover a novel link between menin and Hedgehog signaling whereby menin/PRMT5 epigenetically suppresses Hedgehog signaling, revealing it as a target for treating MEN1 tumors.

Menin mediates epigenetic regulation via histone H3 lysine 9 methylation

Menin, encoded by the multiple endocrine neoplasia type 1 (MEN1) gene, is a tumor suppressor that leads to multiple endocrine tumors upon loss of its function. Menin functions as a transcriptional activator by tethering MLL complex to mediate histone H3 K4 methylation. It also functions as a repressor. However, the molecular mechanism of how menin contributes to the opposite outcome in gene expression is largely unknown. Here, we investigated the role of menin in the epigenetic regulation of transcription mediated by histone covalent modification. We show that the global methylation level of histone H3 K9, as well as H3 K4, was decreased in Men1(-/-) MEF cells. Consistently, menin was able to interact with the suppressor of variegation 3-9 homolog family protein, SUV39H1, to mediate H3 K9 methylation. This interaction decreased when patient-derived MEN1 mutation was introduced into the SUV39H1-interaction domain. We show that menin mediated different chromatin changes depending on target genes. Chromatin immunoprecipitation studies showed that menin directly associated with the GBX2 promoter and menin-dependent recruitment of SUV39H1 was essential for chromatin remodeling and transcriptional regulation. These results provide a molecular basis of how menin functions as a transcriptional repressor and suggest that menin-dependent integration of H3 K9 methylation might play an important role in preventing tumors.

Molecular and cellular biology of neuroendocrine lung tumors: evidence for separate biological entities

Pulmonary neuroendocrine tumors (NETs) are traditionally described as comprising a spectrum of neoplasms, ranging from low grade typical carcinoids (TCs) via the intermediate grade atypical carcinoids (ACs) to the highly malignant small cell lung cancers (SCLCs) and large cell neuroendocrine carcinomas (LCNECs). Recent data, however, suggests that two categories can be distinguished on basis of molecular and clinical data, i.e. the high grade neuroendocrine (NE) carcinomas and the carcinoid tumors. Bronchial carcinoids and SCLCs may originate from the same pulmonary NE precursor cells, but a precursor lesion has only been observed in association with carcinoids, termed diffuse idiopathic pulmonary neuroendocrine cell hyperplasia. The occurrence of mixed tumors exclusively comprising high grade NE carcinomas also supports a different carcinogenesis for these two groups. Histopathologically, high grade NE lung tumors are characterized by high mitotic and proliferative indices, while carcinoids are defined by maximally 10 mitoses per 2mm(2) (10 high-power fields) and rarely have Ki67-proliferative indices over 10%. High grade NE carcinomas are chemosensitive tumors, although they usually relapse. Surgery is often not an option due to extensive disease at presentation and early metastasis, especially in SCLC. Conversely, carcinoids are often insensitive to chemo- and radiation therapy, but cure can usually be achieved by surgery. A meta-analysis of comparative genomic hybridization studies performed for this review, as well as gene expression profiling data indicates separate clustering of carcinoids and carcinomas. Chromosomal aberrations are much more frequent in carcinomas, except for deletion of 11q, which is involved in the whole spectrum of NE lung tumors. Deletions of chromosome 3p are rare in carcinoids but are a hallmark of the high grade pulmonary NE carcinomas. On the contrary, mutations of the multiple endocrine neoplasia type 1 (MEN1) gene are restricted to carcinoid tumors. Many of the differences between carcinoids and high grade lung NETs can be ascribed to tobacco consumption, which is strongly linked to the occurrence of high grade NE carcinomas. Smoking causes p53 mutations, very frequently present in SCLCs and LCNECs, but rarely in carcinoids. It further results in other early genetic events in SCLCs and LCNECs, such as 3p and 17p deletions. Smoking induces downregulation of E-cadherin and associated epithelial to mesenchymal transition. Also, high grade lung NETs display higher frequencies of aberrations of the Rb pathway, and of the intrinsic and extrinsic apoptotic routes. Carcinoid biology on the other hand is not depending on cigarette smoke intake but rather characterized by aberrations of other specific genetic events, probably including Menin or its targets and interaction partners. This results in a gradual evolution, most likely from proliferating pulmonary NE cells via hyperplasia and tumorlets towards classical carcinoid tumors. We conclude that carcinoids and high grade NE lung carcinomas are separate biological entities and do not comprise one spectrum of pulmonary NETs. This implies the need to reconsider both diagnostic as well as therapeutic approaches for these different groups of malignancies.

Novel mutations in MEN1, CDKN1B and AIP genes in patients with multiple endocrine neoplasia type 1 syndrome in Spain

CONTEXT

Multiple endocrine neoplasia type 1 (MEN1) is a rare autosomal dominant disorder mostly owing to a genetic defect in MEN1 gene. Not all patients with MEN1 phenotype present a defect in this gene. Thus, other genes like CDKN and AIP have been showed to be involved in MEN1-like patients.

OBJECTIVE

The aim of this study was to perform a genetic screening in our cohort or patients with suspected MEN1 syndrome by direct sequencing analysis of MEN1, CDKN1B and AIP, and dosage analysis of MEN1 and AIP.

RESULTS

A total of 79 different sporadic and familial cases with the MEN1 phenotype have been studied, in which 34 of them (48%) present a mutation in MEN1 gene. In two patients without a detectable mutation in MEN1 gene, we have identified a novel missense mutation (c.163G>A/p.Ala55Thr) in CDKN1B gene and a novel frameshift mutation (c.825_845delCGCGGCCGTGTGGAATGCCCA/p. His275GlnfsX49) in AIP gene, respectively.

CONCLUSIONS

Our data support that MEN1 gene is the main target for genetic analysis in clinical MEN1 syndrome. We confirm that in those patients without MEN1 gene mutation, other genes such as CDKN1B/p27Kip, or AIP in those including pituitary tumours should also be tested.

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.

The same pocket in menin binds both MLL and JUND but has opposite effects on transcription

Menin is a tumour suppressor protein whose loss or inactivation causes multiple endocrine neoplasia 1 (MEN1), a hereditary autosomal dominant tumour syndrome that is characterized by tumorigenesis in multiple endocrine organs. Menin interacts with many proteins and is involved in a variety of cellular processes. Menin binds the JUN family transcription factor JUND and inhibits its transcriptional activity. Several MEN1 missense mutations disrupt the menin-JUND interaction, suggesting a correlation between the tumour-suppressor function of menin and its suppression of JUND-activated transcription. Menin also interacts with mixed lineage leukaemia protein 1 (MLL1), a histone H3 lysine 4 methyltransferase, and functions as an oncogenic cofactor to upregulate gene transcription and promote MLL1-fusion-protein-induced leukaemogenesis. A recent report on the tethering of MLL1 to chromatin binding factor lens epithelium-derived growth factor (LEDGF) by menin indicates that menin is a molecular adaptor coordinating the functions of multiple proteins. Despite its importance, how menin interacts with many distinct partners and regulates their functions remains poorly understood. Here we present the crystal structures of human menin in its free form and in complexes with MLL1 or with JUND, or with an MLL1-LEDGF heterodimer. These structures show that menin contains a deep pocket that binds short peptides of MLL1 or JUND in the same manner, but that it can have opposite effects on transcription. The menin-JUND interaction blocks JUN N-terminal kinase (JNK)-mediated JUND phosphorylation and suppresses JUND-induced transcription. In contrast, menin promotes gene transcription by binding the transcription activator MLL1 through the peptide pocket while still interacting with the chromatin-anchoring protein LEDGF at a distinct surface formed by both menin and MLL1.

A novel deletion of the MEN1 gene in a large family of multiple endocrine neoplasia type 1 (MEN1) with aggressive phenotype

CONTEXT

The MEN1 syndrome is associated with parathyroid, pancreatic and pituitary tumours and is caused by mutations in the MEN1 gene. In general, there is no genotype-phenotype correlation.

OBJECTIVES

To characterize a large family with MEN1 with aggressive tumour behaviour: malignant pancreatic endocrine tumours were present in five affected subjects and were the presenting features in three subjects.

DESIGN

The coding region of MEN1 was sequenced. Gene copy number analysis was performed by multiplex ligation-dependent probe amplification (MLPA) and array comparative genomic hybridization (aCGH). Loss of heterozygosity (LOH) in tumour tissue was studied by microsatellite analysis. Insulin-like growth factor II (IGF-II) and CDKN1C/p57KIP2 expression were investigated by immunohistochemistry.

RESULTS

Mutation screening by conventional PCR sequence analysis of patients' peripheral blood DNA did not reveal any mutation in the MEN1 or CDKN1B gene. Gene copy number analysis by MLPA and aCGH demonstrated a novel monoallelic deletion of 5 kb genomic DNA involving the MEN1 promoter and exons 1 and 2. LOH analysis indicated somatic deletion of maternal chromosome 11, including MEN1 locus (11q13) and 11p15 imprinting control regions (ICR). Methylation analysis of ICR demonstrated ICR1 hypermethylation and ICR2 hypomethylation in the tumour specimens. ICR1 and ICR2 control the expression of IGF-2 and CDKN1C/p57KIP2, respectively. Immunohistochemistry showed that expression of paternally expressed IGF-2 was up-regulated and the maternally expressed CDKN1C/p57KIP2 was lost in the pancreatic endocrine tumours.

CONCLUSIONS

Gene copy number analysis by MLPA should be considered in patients with negative conventional mutation screening. Although large MEN1 deletion causes MEN1, disruption of imprinted CDKN1C/p57KIP2 and IGF-2 gene expression may contribute to tumour progression and aggressive phenotype.

Trithorax group proteins: switching genes on and keeping them active

Cellular memory is provided by two counteracting groups of chromatin proteins termed Trithorax group (TrxG) and Polycomb group (PcG) proteins. TrxG proteins activate transcription and are perhaps best known because of the involvement of the TrxG protein MLL in leukaemia. However, in terms of molecular analysis, they have lived in the shadow of their more famous counterparts, the PcG proteins. Recent advances have improved our understanding of TrxG protein function and demonstrated that the heterogeneous group of TrxG proteins is of critical importance in the epigenetic regulation of the cell cycle, senescence, DNA damage and stem cell biology.

Unique gene expression profile associated with an early-onset multiple endocrine neoplasia (MEN1)-associated pituitary adenoma

CONTEXT

Multiple endocrine neoplasia type 1 (MEN1) is caused by mutations in the menin (MEN1) gene. The mechanism(s) by which MEN1 mutations lead to pituitary tumor formation remain(s) unknown.

OBJECTIVE

The aim of the study was to identify the pediatric MEN1-associated pituitary tumor transcriptome.

PATIENTS AND METHODS

A patient harboring a MEN1 mutation (c.525C>G; p.H139D) who presented with an early-onset mammosomatotroph pituitary adenoma was studied. Microarray analysis was performed in the tumor sample and compared with the profile observed in normal pituitaries and in a sporadic mammosomatotropinoma. Validation of the microarray results was performed using quantitative real-time PCR and immunohistochemical analysis for selected genes.

RESULTS

In the MEN1-associated pituitary adenoma, 59 and 24 genes were found to be significantly up- and down-regulated, respectively. The up-regulated genes included those involved in cell growth and maintenance, apoptosis, growth arrest, and tumorigenesis. Moreover, we observed decreased expression in genes neuroendocrine in nature and related to growth or apoptosis. Only 21 of the 59 genes differentially expressed in the MEN1-associated adenoma showed a similar expression profile to that seen in the sporadic mammosomatotropinoma; for some genes an opposite expression profile was observed.

CONCLUSIONS

We identified changes in the transcriptome that occur in pituitary GH- and PRL-producing cells after the loss of menin expression; some of the gene changes are necessary for tumor evolution, and others may be tertiary. Nevertheless, the rare overlap between the expression profiles of the MEN1 tumor vs. that of its sporadic counterpart suggests that these tumors evolve along different molecular pathways.

Genomics in pediatric endocrinology-genetic disorders and new techniques

In the last few years, there have been remarkable advances in the development of new and more sophisticated genetic techniques. These have allowed a better understanding of the molecular mechanisms of genetically determined pediatric endocrine disorders and are paving the way for a radical change in diagnosis and treatment. This article introduces some of these concepts and some of the genetic techniques being used.

Crystal structure of menin reveals binding site for mixed lineage leukemia (MLL) protein

Menin is a tumor suppressor protein that is encoded by the MEN1 (multiple endocrine neoplasia 1) gene and controls cell growth in endocrine tissues. Importantly, menin also serves as a critical oncogenic cofactor of MLL (mixed lineage leukemia) fusion proteins in acute leukemias. Direct association of menin with MLL fusion proteins is required for MLL fusion protein-mediated leukemogenesis in vivo, and this interaction has been validated as a new potential therapeutic target for development of novel anti-leukemia agents. Here, we report the first crystal structure of menin homolog from Nematostella vectensis. Due to a very high sequence similarity, the Nematostella menin is a close homolog of human menin, and these two proteins likely have very similar structures. Menin is predominantly an α-helical protein with the protein core comprising three tetratricopeptide motifs that are flanked by two α-helical bundles and covered by a β-sheet motif. A very interesting feature of menin structure is the presence of a large central cavity that is highly conserved between Nematostella and human menin. By employing site-directed mutagenesis, we have demonstrated that this cavity constitutes the binding site for MLL. Our data provide a structural basis for understanding the role of menin as a tumor suppressor protein and as an oncogenic co-factor of MLL fusion proteins. It also provides essential structural information for development of inhibitors targeting the menin-MLL interaction as a novel therapeutic strategy in MLL-related leukemias.

Menin represses tumorigenesis via repressing cell proliferation

Multiple endocrine neoplasia type 1 (MEN1) results from mutations in the tumor suppressor gene, MEN1, which encodes nuclear protein menin. Menin is important for suppressing tumorigenesis in various endocrine and certain non-endocrine tissues. Although menin suppresses MEN1 through a variety of mechanisms including regulating apoptosis and DNA repair, the role of menin in regulating cell proliferation is one of the best-studied functions. Here, we focus on reviewing various mechanisms underlying menin-mediated inhibition of cell proliferation. Menin inhibits cell proliferation to repress MEN1 through multiple mechanisms. 1) Menin interacts with various histonemodifying enzymes, such as MLL, EZH2 and HDACs, to affect gene transcription, leading to repression of cell proliferation. 2) Menin also interacts with various transcription factors, such as JunD, NF-κB, PPARγ and VDR, to induce or suppress gene transcription. As these various transcription factors are known to regulate cell proliferation, their interaction with menin may be relevant to menin's role in inhibiting cell proliferation. 3) Menin inhibits cell proliferation via TGF-β signaling and Wnt/β-catenin signaling pathways. 4) Menin represses certain pro-proliferative factors involved in endocrine tumors such as IGFBP-2, IGF2 and PTHrP to repress cell proliferation. 5) Menin affects cell cycle progression to inhibit cell proliferation. This review is helpful in our understanding of the comprehensive mechanisms whereby menin represses MEN1 through inhibiting cell proliferation.

Imaging of cancer predisposition syndromes in children

The term cancer predisposition syndrome (CPS) encompasses a multitude of familial cancers in which a clear mode of inheritance can be established, although a specific gene defect has not been described in all cases. Advances in genetics and the development of new imaging techniques have led to better understanding and early detection of these syndromes and offer the potential for preclinical diagnosis of any associated tumors. As a result, imaging has become an essential component of the clinical approach to management of CPSs and the care of children suspected of having a CPS or with a confirmed diagnosis. Common CPSs in children include neurofibromatosis type 1, Beckwith-Wiedemann syndrome, multiple endocrine neoplasia, Li-Fraumeni syndrome, von Hippel-Lindau syndrome, and familial adenomatous polyposis. Radiologists should be familiar with these syndromes, their common associated tumors, the new imaging techniques that are available, and current screening and surveillance recommendations to optimize the assessment of affected children.

A new mutation in the menin gene causes the multiple endocrine neoplasia type 1 syndrome with adrenocortical carcinoma

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant tumor syndrome that may be caused by mutations in the MEN1 gene on 11q13. Loss of function of the tumor suppressor gene MEN1 leads to synchronous or metachronous appearance of neuroendocrine tumors arising from neuroendocrine cells of the parathyroid and pituitary glands, the duodenum and pancreatic islets, and other endocrine organs such as the adrenal cortex. We here present a patient with MEN1 who developed hyperparathyroidism, multiple well differentiated functionally inactive neuroendocrine tumors of the pancreas and an adrenal carcinoma. We describe a new mutation at codon 443 in the coding region of exon 9 in the MEN1 gene, where a cytosine residue was exchanged for adenosine (TCC > TAC) and, consequently, serine for tyrosine (p.Ser443Tyr; c.1328C > A). [corrected] Also, we provide clinical data that may add to the genotype-phenotype discussion. We conclude that the novel mutation in the MEN1 gene described herein was clinically relevant.

The tumor suppressor protein menin inhibits AKT activation by regulating its cellular localization

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder associated mainly with tumors of multiple endocrine organs. Mutations in the MEN1 gene that encodes for the menin protein are the predominant cause for hereditary MEN1 syndrome. Though menin is a tumor suppressor, its molecular mechanism of action has not been defined. Here, we report that menin interacts with AKT1 in vitro and in vivo. Menin downregulates the level of active AKT and its kinase activity. Through interaction with AKT1, menin suppresses both AKT1-induced proliferation and antiapoptosis in nonendocrine and endocrine cells. Confocal microscopy analysis revealed that menin regulates AKT1 in part by reducing the translocation of AKT1 from the cytoplasm to the plasma membrane during growth factor stimulation. Our findings may be generalizable to other cancers, insofar as we found that loss of menin expression was also associated with AKT activation in a mouse model of pancreatic islet adenoma. Together, our results suggest menin as an important novel negative regulator of AKT kinase activity.

Molecular pathogenesis of pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PNETs) are rare primary neoplasms of the pancreas and arise sporadically or in the context of genetically determined syndromes. Depending on hormone production and sensing, PNETs clinically manifest due to a hormone-related syndrome (functional PNET) or by symptoms related to tumor bulk effects (non-functional PNET). So far, radical surgical excision is the only therapy to cure the disease. Development of tailored non-surgical approaches has been impeded by the lack of experimental laboratory models and there is, therefore, a limited understanding of the complex cellular and molecular biology of this heterogeneous group of neoplasm. This review aims to summarize current knowledge of tumorigenesis of familial and sporadic PNETs on a cellular and molecular level. Open questions in the field of PNET research are discussed with specific emphasis on the relevance of disease management.

Neuroendocrine tumors and tumor syndromes in childhood

Endocrine and neuroendocrine cells form a large and diverse array of cell types. They are present in the form of specialized organs, such as the pituitary, parathyroid, thyroid, and adrenal gland, or in the form of the diffuse neuroendocrine system in the respiratory and digestive tracts. Neuroendocrine tumors are a heterogeneous group of neoplasms, yet they present certain unifying features. These include frequent hormonal overproduction that leads to specific symptoms and a typical immunohistochemical staining profile with chromogranin A and synaptophysin reactivity. Over the past decades, many neuroendocrine tumors have been described in the context of heritable tumor syndromes, and there exist several syndromes that are almost entirely composed of neuroendocrine tumors. Tumors occurring as part of these hereditary syndromes are characterized by specific genetic abnormalities that have helped our understanding of tumorigenesis, and they frequently appear at a young age. It is therefore important for the pediatric pathologist to be aware of specific histologic characteristics of neuroendocrine tumors in childhood and of their association with specific tumor syndromes. This may alert other clinicians to the possibility of multiple tumors in the patient or his family members. This review focuses on hereditary syndromes with neuroendocrine tumors, including multiple endocrine neoplasia types 1 and 2, Von Hippel-Lindau disease, neurofibromatosis type 1, Carney complex, pheochromocytoma-paraganglioma syndrome, and familial nonmedullary thyroid carcinoma. In addition, several individual neuroendocrine tumors are described, such as medullary thyroid carcinoma, gastroenteropancreatic tumors, pheochromocytoma, and paraganglioma, emphasizing specific histopathologic characteristics.

Characterisation of prostate cancer lesions in heterozygous Men1 mutant mice

Background

Mutations of the MEN1 gene predispose to multiple endocrine neoplasia type 1 (MEN1) syndrome. Our group and others have shown that Men1 disruption in mice recapitulates MEN1 pathology. Intriguingly, rare lesions in hormone-dependent tissues, such as prostate and mammary glands, were also observed in the Men1 mutant mice.

Methods

To study the occurrence of prostate lesions, we followed a male mouse cohort of 47 Men1^+/- mice and 23 age-matched control littermates, starting at 18 months of age, and analysed the prostate glands from the cohort.

Results

Six Men1^+/- mice (12.8%) developed prostate cancer, including two adenocarcinomas and four in situ carcinomas, while none of the control mice developed cancerous lesions. The expression of menin encoded by the Men1 gene was found to be drastically reduced in all carcinomas, and partial LOH of the wild-type Men1 allele was detected in three of the five analysed lesions. Using immunostaining for the androgen receptor and p63, a basal epithelial cell marker, we demonstrated that the menin-negative prostate cancer cells did not display p63 expression and that the androgen receptor was expressed but more heterogeneous in these lesions. Furthermore, our data showed that the expression of the cyclin-dependent kinase inhibitor CDKN1B (p27), a Men1 target gene known to be inactivated during prostate cell tumorigenesis, was notably decreased in the prostate cancers that developed in the mutant mice.

Conclusion

Our work suggests the possible involvement of Men1 inactivation in the tumorigenesis of the prostate gland.