MEN1 tumor-suppressor protein localizes to telomeres during meiosis

Fyn-mediated phosphorylation of Menin disrupts telomere maintenance in stem cells

Telomeres protect chromosome ends and determine the replication potential of dividing cells. The canonical telomere sequence TTAGGG is synthesized by telomerase holoenzyme, which maintains telomere length in proliferative stem cells. Although the core components of telomerase are well-defined, mechanisms of telomerase regulation are still under investigation. We report a novel role for the Src family kinase Fyn, which disrupts telomere maintenance in stem cells by phosphorylating the scaffold protein Menin. We found that Fyn knockdown prevented telomere erosion in human and mouse stem cells, validating the results with four telomere measurement techniques. We show that Fyn phosphorylates Menin at tyrosine 603 (Y603), which increases Menin's SUMO1 modification, C-terminal stability, and importantly, its association with the telomerase RNA component (TR). Using mass spectrometry, immunoprecipitation, and immunofluorescence experiments we found that SUMO1-Menin decreases TR's association with telomerase subunit Dyskerin, suggesting that Fyn's phosphorylation of Menin induces telomerase subunit mislocalization and may compromise telomerase function at telomeres. Importantly, we find that Fyn inhibition reduces accelerated telomere shortening in human iPSCs harboring mutations for dyskeratosis congenita.

Integrated mutational landscape analysis of uterine leiomyosarcomas

Uterine leiomyosarcomas (uLMS) are aggressive tumors arising from the smooth muscle layer of the uterus. We analyzed 83 uLMS sample genetics, including 56 from Yale and 27 from The Cancer Genome Atlas (TCGA). Among them, a total of 55 Yale samples including two patient-derived xenografts (PDXs) and 27 TCGA samples have whole-exome sequencing (WES) data; 10 Yale and 27 TCGA samples have RNA-sequencing (RNA-Seq) data; and 11 Yale and 10 TCGA samples have whole-genome sequencing (WGS) data. We found recurrent somatic mutations in TP53, MED12, and PTEN genes. Top somatic mutated genes included TP53, ATRX, PTEN, and MEN1 genes. Somatic copy number variation (CNV) analysis identified 8 copy-number gains, including 5p15.33 (TERT), 8q24.21 (C-MYC), and 17p11.2 (MYOCD, MAP2K4) amplifications and 29 copy-number losses. Fusions involving tumor suppressors or oncogenes were deetected, with most fusions disrupting RB1, TP53, and ATRX/DAXX, and one fusion (ACTG2-ALK) being potentially targetable. WGS results demonstrated that 76% (16 of 21) of the samples harbored chromoplexy and/or chromothripsis. Clinically actionable mutational signatures of homologous-recombination DNA-repair deficiency (HRD) and microsatellite instability (MSI) were identified in 25% (12 of 48) and 2% (1 of 48) of fresh frozen uLMS, respectively. Finally, we found olaparib (PARPi; P = 0.002), GS-626510 (C-MYC/BETi; P < 0.000001 and P = 0.0005), and copanlisib (PIK3CAi; P = 0.0001) monotherapy to significantly inhibit uLMS-PDXs harboring derangements in C-MYC and PTEN/PIK3CA/AKT genes (LEY11) and/or HRD signatures (LEY16) compared to vehicle-treated mice. These findings define the genetic landscape of uLMS and suggest that a subset of uLMS may benefit from existing PARP-, PIK3CA-, and C-MYC/BET-targeted drugs.

Future Directions in the Biology of Neuroendocrine Tumors

The neuroendocrine field is experiencing an ever-accelerating expansion of data about the makeup of these tumors whose biology has long been opaque. Genome sequencing and epigenetic data regarding copy number variations, methylation events, and expression profiling are increasingly available for small bowel and pancreatic neuroendocrine tumors. However, in addition to building larger and more robust genetic and epigenetic datasets, the remaining challenge is moving beyond the data toward meaningful information, knowledge, and wisdom. Herein, we will offer perspectives on the existing data and thoughts on future directions.

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.

Regulation of the human catalytic subunit of telomerase (hTERT)

Over the past decade, there has been much interest in the regulation of telomerase, the enzyme responsible for maintaining the integrity of chromosomal ends, and its crucial role in cellular immortalization, tumorigenesis, and the progression of cancer. Telomerase activity is characterized by the expression of the telomerase reverse transcriptase (TERT) gene, suggesting that TERT serves as the major limiting agent for telomerase activity. Recent discoveries have led to characterization of various interactants that aid in the regulation of human TERT (hTERT), including numerous transcription factors; further supporting the pivotal role that transcription plays in both the expression and repression of telomerase. Several studies have suggested that epigenetic modulation of the hTERT core promoter region may provide an additional level of regulation. Although these studies have provided essential information on the regulation of hTERT, there has been ambiguity of the role of methylation within the core promoter region and the subsequent binding of various activating and repressive agents. As a result, we found it necessary to consolidate and summarize these recent developments and elucidate these discrepancies. In this review, we focus on the co-regulation of hTERT via transcriptional regulation, the presence or absence of various activators and repressors, as well as the epigenetic pathways of DNA methylation and histone modifications.

Human telomerase expression regulation

Since telomerase has been recognized as a relevant factor distinguishing cancer cells from normal cells, it has become a very promising target for anti-cancer therapy. A correlation between short telomere length and increased mortality was revealed in many studies. The telomerase expression/activity appears to be one of the most crucial factors to study to improve cancer therapy and prevention. However, this multisubunit enzymatic complex can be regulated at various levels. Thus, several strategies have been proposed to control telomerase in cancer cells such as anti-sense technology against TR and TERT, ribozymes against TERT, anti-estrogens, progesterone, vitamin D, retinoic acid, quadruplex stabilizers, telomere and telomerase targeting agents, modulation of interaction with other proteins involved in the regulation of telomerase and telomeres, etc. However, the transcription control of key telomerase subunits seems to play the crucial role in whole complexes activity and cancer cells immortality. Thus, the research of telomerase regulation can bring significant insight into the knowledge concerning stem cells metabolism but also ageing. This review summarizes the current state of knowledge of numerous telomerase regulation mechanisms at the transcription level in human that might become attractive anti-cancer therapy targets.

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.

Menin: the protein behind the MEN1 syndrome

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

Inherited pancreatic endocrine tumor syndromes: advances in molecular pathogenesis, diagnosis, management, and controversies

Pancreatic endocrine tumors (PETs) can occur as part of 4 inherited disorders, including Multiple Endocrine Neoplasia type 1 (MEN1), von Hippel-Lindau disease (VHL), neurofibromatosis 1 (NF-1) (von Recklinghausen disease), and the tuberous sclerosis complex (TSC). The relative frequency with which patients who have these disorders develop PETs is MEN1>VHL>NF-1>TSC. Over the last few years, there have been major advances in the understanding of the genetics and molecular pathogenesis of these disorders as well in the localization and the medical and surgical treatment of PETs in such patients. The study of PETs in these disorders not only has provided insights into the possible pathogenesis of sporadic PETs but also has presented several unique management and treatment issues, some of which are applicable to patients with sporadic PETs. Therefore, the study of PETs in these uncommon disorders has provided valuable insights that, in many cases, are applicable to the general group of patients with sporadic PETs. In this article, these areas are reviewed briefly along with the current state of knowledge of the PETs in these disorders, and the controversies that exist in their management are summarized briefly and discussed.

Multiple endocrine neoplasms

Multiple endocrine neoplasia type 1 (MEN1) and type 2 (MEN2) are rare autosomal-dominant disorders characterized by primary tumours in at least two different endocrine tissues. Both syndromes present as sporadic (a single case with two of the characteristic endocrine tumours) or familial form (an MEN case plus at least one first-degree relative showing one of the characteristic endocrine tumours). MEN1 is characterized by the occurrence of parathyroid, gastro-entero-pancreatic and anterior pituitary tumours, but it can include various combinations of more than 20 endocrine and non-endocrine tumours. Generally, tumours in MEN1 are benign, although gastrinomas and foregut carcinoids may exhibit a malignant course. MEN2 is characterized by medullary thyroid carcinoma (MTC), uni- or bi-lateral pheochromocytoma, and other tumours of different endocrine tissues. If not diagnosed precociously, MTC can be fatal. MEN1 develops after tissue inactivation of both MEN1 gene copies. Activating mutations of c-RET proto-oncogene causes MEN2.

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.

Cell lineage-specific interactions between Men1 and Rb in neuroendocrine neoplasia

Inactivation of multiple endocrine neoplasia (MEN) type 1 gene (Men1) results in development of multiple endocrine tumors in Men1(+/-) mice and in humans. Intriguingly, loss of the wild-type retinoblastoma 1 (Rb) gene also leads to MEN-like phenotype in Rb(+/-) mice. To evaluate potential genetic interactions between these genes, we prepared and characterized Men1(+/-)Rb(+/-) compound mice in parallel with their parental genotypes. Men1 and Rb did not cooperate in tumor suppression, as demonstrated by comparable survival rates of Rb(+/-) and Men1(+/-)Rb(+/-) mice, absence of tumor growth acceleration and lack of novel neoplasms. Notably, the loss of the remaining copy of the wild-type Men1 and Rb was mutually exclusive in all tumors of Men1(+/-)Rb(+/-) mice, including pituitary anterior lobe and adrenal medulla neoplasms shared by Rb- and Men1-deficient phenotypes. Down-regulation of Men1 targets p18 and p27 and increased presence of phosphorylated-Rb were observed in Men1-deficient pheochromocytomas of Men1(+/-)Rb(+/-) and Men1(+/-) mice. At the same time, the RNA interference (RNAi) knock-down of Men1 mRNA resulted in increased apoptosis of Rb-deficient medullary thyroid carcinoma cells. These results demonstrate that, depending on cell lineage context, combined Men1 and Rb deficiency may be either redundant or detrimental to neoplastic growth. Identification of cell lineage-specific interactions between Men1 and Rb may have important implications for development of rationally designed therapeutic approaches.

Menin and its interacting proteins: elucidation of menin function

The multiple endocrine neoplasia type 1 (MEN1) gene is a tumor suppressor gene encoding a 610 amino acid nuclear protein, menin. Although mutations of the MEN1 gene are responsible for MEN 1 syndrome, the intracellular functions of menin have not been fully elucidated. Recent data suggest that interactions between menin and menin-interacting proteins have a role in physiological regulation of cell growth, control of the cell cycle and genome stability, and are potentially important in bone development and multipotent mesenchymal stem cell differentiation. Loss of these interactions might also contribute to the development of MEN 1 syndrome.

Hereditary hormone excess: genes, molecular pathways, and syndromes

Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.

Analysis of the cytogenetic stability of the human embryonal kidney cell line 293 by cytogenetic and STR profiling approaches

We have characterized the cytogenetic alterations of the human embryonal cell line 293 by spectral karyotyping and G-banding analysis. To investigate its genomic stability, we compared the karyotypes of 293 and its daughter line EcR-293. Genotype profiling through short tandem repeats complemented the analysis. While displaying almost identical STR profiles and thus verifying their origin and their close relation, the two lines were remarkably different in their number of chromosomes and setup of aberrant chromosomes. However, the cell lines retained a stable karyotype in long term culture. The establishment of subclones from EcR-293, expressing inducible lacZ or MEN1 transgenes, only added minor changes to the karyotype. Our study shows that the cytogenetic constitution of a clonal cell line of the 293 origin appears to be sufficiently stable. However, care should be taken when comparing the properties of independent 293 lineages, since clonal variations might be substantial.

Hypermutability in a Drosophila model for multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type I (MEN1) is an autosomal dominant cancer predisposition syndrome, the gene for which encodes a nuclear protein, menin. The biochemical function of this protein has not been completely elucidated, but several studies have shown a role in transcriptional modulation through recruitment of histone deacetylase. The mechanism by which MEN1 mutations cause tumorigenesis is unknown. The Drosophila homolog of MEN1, Mnn1, encodes a protein 50% identical to human menin. In order to further elucidate the function of MEN1, we generated a null allele of this gene in Drosophila and showed that homozygous inactivation results in morphologically normal flies that are hypersensitive to ionizing radiation and two DNA cross-linking agents, nitrogen mustard and cisplatinum. The spectrum of agents to which mutant flies are sensitive and analysis of the molecular mechanisms of this sensitivity suggest a defect in nucleotide excision repair. Drosophila Mnn1 mutants have an elevated rate of both sporadic and DNA damage-induced mutations. In a genetic background heterozygous for lats, a Drosophila and vertebrate tumor suppressor gene, homozygous inactivation of Mnn1 enhanced somatic mutation of the second allele of lats and formation of multiple primary tumors. Our data indicate that Mnn1 is a novel member of the class of autosomal dominant cancer genes that function in maintenance of genomic integrity, similar to the BRCA and HNPCC genes.

Molecular pathology of the MEN1 gene

Multiple endocrine neoplasia type 1 (MEN1), among all syndromes, causes tumors in the highest number of tissue types. Most of the tumors are hormone producing (e.g., parathyroid, enteropancreatic endocrine, anterior pituitary) but some are not (e.g., angiofibroma). MEN1 tumors are multiple for organ type, for regions of a discontinuous organ, and for subregions of a continuous organ. Cancer contributes to late mortality; there is no effective prevention or cure for MEN1 cancers. Morbidities are more frequent from benign than malignant tumor, and both are indicators for screening. Onset age is usually earlier in a tumor type of MEN1 than of nonhereditary cases. Broad trends contrast with those in nonneoplastic excess of hormones (e.g., persistent hyperinsulinemic hypoglycemia of infancy). Most germline or somatic mutations in the MEN1 gene predict truncation or absence of encoded menin. Similarly, 11q13 loss of heterozygosity in tumors predicts inactivation of the other MEN1 copy. MEN1 somatic mutation is prevalent in nonhereditary, MEN1-like tumor types. Compiled germline and somatic mutations show almost no genotype/phenotype relation. Normal menin is 67 kDa, widespread, and mainly nuclear. It may partner with junD, NF-kB, PEM, SMAD3, RPA2, FANCD2, NM23beta, nonmuscle myosin heavy chain II-A, GFAP, and/or vimentin. These partners have not clarified menin's pathways in normal or tumor tissues. Animal models have opened approaches to menin pathways. Local overexpression of menin in Drosophila reveals its interaction with the jun-kinase pathway. The Men1+/- mouse has robust MEN1; its most important difference from human MEN1 is marked hyperplasia of pancreatic islets, a tumor precursor stage.

Knockout mice provide novel insights into meiotic chromosome and telomere dynamics

Meiosis is a succession of two specialized cell divisions that leads to the formation of gametes and thereby compensates for genome doubling at fertilization. During the extended prophase of the first meiotic division chromosomes assemble protein cores (axial elements) that attach their ends to the nuclear envelope. These ends transiently gather at a limited sector of the nuclear periphery (bouquet stage) at a time when meiotic recombination is initiated and when chromosomes initiate stable pairing (synapsis). This review discusses novel insights into the relation between recombinational DNA repair and meiotic telomere dynamics that have arrived from recent studies of transchromosomal mice and knockout mice. Analysis of mice deficient for A-type lamins, histone H2AX, Suv39h HMTases, and the AE protein SYCP3 suggests that entry into prophase I requires heterochromatin integrity and lamin A expression. Initiation of meiotic telomere clustering represents an early recombination-independent event in first meiotic prophase, while exit from the bouquet stage depends on signals that emanate from the progress of recombinational DNA repair as sensed by ATM kinase and relayed through histone H2AX.

Genetic ablation of the tumor suppressor menin causes lethality at mid-gestation with defects in multiple organs

Patients suffering from multiple endocrine neoplasia type 1 (MEN1) are predisposed to multiple endocrine tumors. The MEN1 gene product, menin, is expressed in many embryonic, as well as adult tissues, and interacts with several proteins in vitro and in vivo. However, the biological function of menin remains largely unknown. Here we show that disruption of the Men1 gene in mice causes embryonic lethality at E11.5-E13.5. The Men1 null mutant embryos appeared smaller in size, frequently with body haemorrhages and oedemas, and a substantial proportion of them showed disclosure of the neural tube. Histological analysis revealed an abnormal development of the nervous system and heart hypotrophy in some Men1 null embryos. Furthermore, Men1 null livers generally displayed an altered organization of the epithelial and hematopoietic compartments associated with enhanced apoptosis. Chimerism analysis of embryos generated by injection of Men1 null ES cells, showed that cells lacking menin do not seem to have a general cell-autonomous defect. However, primary Men1 null embryonic fibroblasts entered senescence earlier than their wild-type counterparts. Despite normal proliferation ability, Men1 null ES cells exhibited a deficiency to form embryoid bodies, suggesting an impaired differentiation capacity in these cells. The present study demonstrates that menin plays an important role in the embryonic development of multiple organs in addition to its proposed role in tumor suppression.