Multiple endocrine neoplasia type 1 gene maps to chromosome 11 and is lost in insulinoma

The dopamine receptor D2 genotype is associated with hyperprolactinemia

OBJECTIVE

To evaluate patients with hyperprolactinemia for the presence of dopamine receptor D2 polymorphisms.

DESIGN

Case-control study.

SETTING

Academic research environment.

PATIENT(S)

Women and men with pathologic hyperprolactinemia and healthy controls.

INTERVENTION(S)

DNA extraction of peripheral blood, polymerase chain reaction, single-strand conformation polymorphism, DNA sequencing, and restriction digest.

MAIN OUTCOME MEASURE(S)

Two polymorphisms in exon 7 of the dopamine receptor D2 (DRD2) gene. Polymorphism 1 involves nucleotide 3420 (C to T, 313 His), and polymorphism 2 involves nucleotide 3438 (C to T, 319 Pro).

RESULT(S)

The frequency of DRD2 polymorphism 1 alleles was increased in subjects with hyperprolactinemia. Analysis of the DRD2 genotypes demonstrates an odds ratio of 6.77 (2.39, 19.14; 95% confidence interval) for the polymorphism 1 homozygous state in hyperprolactinemia.

CONCLUSION(S)

A genetic predisposition to hyperprolactinemia is suggested by an excess homozygosity for polymorphism 1 in exon 7 of the DRD2 gene. Previous studies of lactotrophs from prolactinomas have found normal DRD2 receptors but differing isoform density. Homozygosity of polymorphism 1 may influence the distribution of the DRD2 isoforms on the lactotroph. Other potential mechanisms include an association with a molecular defect in a postreceptor signaling mechanism, such as a somatic inactivating mutation in a G1 protein, which could result in autonomous function of the lactotroph. Mutations could also result in different receptor-G protein interactions, such as a Gs instead of Gi, and result in autonomous lactotroph function.

Endocrine tumours of the gastrointestinal tract: aetiology, molecular pathogenesis and genetics

Endocrine tumours of the gut and pancreas originate from cells of the diffuse endocrine system and are characterised by the production of a wide variety of bioactive substances including growth factors. Two major tumour categories are distinguished-well-differentiated and poorly differentiated neoplasms-with distinct phenotypes and significantly diverse clinical behaviour. Here, genetic background data are summarised on an anatomical basis for tumours of foregut, midgut and hindgut derivatives. For well-differentiated tumours, independent techniques identified the abnormality of multiple chromosomal sites and genes, pointing to a complex genetic background. Differences in foregut tumours compared with midgut and hindgut tumours are, however, outlined. The multiple endocrine neoplasia syndrome type 1 (MEN1) gene is reported to be involved in about one-third of sporadic foregut endocrine tumours and exceptionally in midgut and hindgut tumours. Similarly, X chromosome markers are associated with malignant behaviour in foregut tumours only. For poorly differentiated carcinomas, a high degree of chromosomal instability is the common genetic trait independent of tumour site and frequently involving the p53 gene.

Clinical testing for multiple endocrine neoplasia type 1 in a DNA diagnostic laboratory

PURPOSE

Based on results of diagnostic MEN1 testing, we have attempted to further define the mutational spectrum of the MEN1 gene and the clinical features most frequently associated with MEN1 mutations.

METHODS

Mutation testing was performed on blood samples by PCR amplification and sequencing of exons 2 to 10 of the MEN1 gene and the corresponding intron-exon junctions. Pedigree phenotypic information was obtained by written questionnaire.

RESULTS

Among 288 presumably unrelated pedigrees, 73 independent mutations were found in 89 families. Five mutations were found in 2 pedigrees, and 4 mutations were seen in more than 2 pedigrees. There were 17 nonsense mutations (23.3%), 2 in-frame deletions (2.7%), 18 frameshift-deletion mutations (24.7%), 10 frameshift-insertion or -duplication mutations (13.7%), 13 splice-site mutations (17.8%), and 13 presumptive missense mutations (17.8%). Thirty-nine of 56 pedigrees with parathyroid and pancreatic islet neoplasia tested positive, compared with 4/24 and 8/32 pedigrees affected with hyperparathyroidism or hyperparathyroidism and pituitary tumors. MEN1 mutations were found in 6/20 sporadic patients, all of whom had both parathyroid and pancreatic neoplasms. Of 14 mutation-negative sporadic patients, 10 exhibited hyperparathyroidism and pituitary tumors without islet cell neoplasia. Somatic mosaicism was detected in 1 sporadic patient.

CONCLUSION

Patients from pedigrees with hyperparathyroidism and pancreatic islet tumors are most likely to test positive for MEN1 mutations. Mutations are less often detected in patients from pedigrees with hyperparathyroidism alone or in combination with pituitary tumors without pancreatic islet neoplasia. Sporadic cases are less likely to test positive than familial cases, in part due to somatic mosaicism.

Precursor lesions in patients with multiple endocrine neoplasia type 1-associated duodenal gastrinomas

BACKGROUND & AIMS

The identification of precursor lesions has a great impact on the understanding of tumorigenesis. Precursor lesions of endocrine tumors are known to occur in the setting of the MEN1 syndrome. The aim of this study was to test the hypothesis that MEN1-associated duodenal gastrinomas originate from diffuse preneoplastic gastrin cell changes. Precursor lesions may precede the development of duodenal gastrinomas because, in contrast to sporadic gastrinomas, these tumors are usually multiple.

METHODS

The distribution of endocrine cells in the nontumorous duodenal tissue was analyzed qualitatively and quantitatively for 25 patients operated on for a duodenal gastrinoma. MEN1 status was assessed clinically and by polymerase chain reaction-based mutational analysis.

RESULTS

Fourteen of 25 patients with gastrinoma had proliferative, hyperplastic lesions consisting of gastrin cells in the nontumorous duodenal mucosa, similar to the gastric enterochromaffin-like cell lesions observed in chronic atrophic gastritis. All patients with Zollinger-Ellison syndrome with proven MEN1 had such proliferative gastrin cell lesions, and all patients with Zollinger-Ellison syndrome without precursor lesions were MEN1 negative.

CONCLUSIONS

Duodenal gastrinomas in MEN1, but not sporadic duodenal gastrinomas, are associated with proliferative gastrin cell changes within the nontumorous mucosa. It is likely that these lesions precede the development of MEN1-associated duodenal gastrinomas.

Surgical treatment of non-functioning pancreatic islet cell tumors

Pancreatic endocrine tumors (PETs) are rare neoplasms originating from the amine precursor uptake and decarboxylation (APUD) stem cells. Although the majority of PETs are sporadic, they frequently occur in familial syndromes. PETs may cause a variety of functional syndromes or symptoms of local progression if they are non-functional. General neuroendocrine tumor markers are highly sensitive in the diagnostic assessment of a PET. Imaging studies for tumor localization and staging include computer tomography (CT) scan, magnetic resonance imaging (MRI), In(111)-octreotide scan, MIBG, and endoscopic ultrasonography (EUS). Treatment of PETs often requires a multi-modality approach; however, surgical resection remains the only curative therapy for localized (non-metastatic) disease. Treatment of metastatic disease includes biologic agents, cytotoxic chemotherapy, and liver-directed therapies.

Novel mutations in the MEN1 gene in subjects with multiple endocrine neoplasia-1

OBJECTIVE

To identify MEN1 gene mutations and characterize clinical manifestations in Chinese kindred with multiple endocrine neoplasia type 1 (MEN1) in Taiwan.

PATIENTS AND METHODS

Eight unrelated subjects (one male and seven females, age range 26-70 years) with clinical manifestations of MEN1 were analysed. In addition, 45 relatives that included 10 affected (three males and seven females, age range 32-53 years) and 35 unaffected (17 males and 18 females, age range 15-80 years) subjects were evaluated. Genomic DNA extraction, polymerase chain reaction (PCR) and DNA sequence analysis were performed according to standard procedures.

RESULTS

We identified heterozygous MEN1 gene mutations in all eight probands and 10 affected subjects as well as in 13 clinically asymptomatic relatives. Novel mutations included a missense mutation in a heterozygous mutation in exon 9 (GAC --> CAC) resulting in a substitution of aspartic acid by histidine at codon 418 (family 1); a nonsense mutation at codon 556 of exon 10 (GAG --> TAG) resulting in a stop codon and termination (family 2); a missense mutation in exon 2 (GGG --> GAG) causing the substitution of glycine by glutamic acid at codon 110 (family 3); and a deletion/insertion mutation in nucleotide 1200 of exon 8 resulting in frameshift and early termination (family 4). Affected subjects in families 5-7 shared the same C insertion at nucleotide 1650 of exon 10, similar to that previously described as a hotspot for mutation, and proband 8 had a previously described mutation in intron 4 of the MEN1 gene (IVS4-9 G --> A). We also found that 18 (58%) of our 31 MEN1 mutant carriers had clinical symptoms, whereas four (13%) had biochemical abnormalities without clinical symptoms, and nine (29%) were unaffected both clinically and biochemically.

CONCLUSIONS

We have identified four novel mutations in the MEN1 gene in patients with MEN1 in Taiwan.

Familial Multiple Endocrine Neoplasia

In 1903, Erdheim described the case of an acromegalic patient with a pituitary adenoma and three enlarged parathyroid glands. Fifty years later, Underdahl et al reported 8 patients with a syndrome of pituitary, parathyroid, and pancreatic islet adenomas. In 1954, Wermer found that the syndrome was transmitted as a dominant trait. In 1959, Hazard et al described medullary (solid) thyroid carcinoma (MTC), a tumor that later was found to be a component of two endocrine syndromes. The first of these described by Sipple in 1961 comprised pheochromocytoma, MTC, and parathyroid adenoma. The second, described by Williams et al in 1966, was the combination of mucosal neuromas, pheochromocytoma, and MTC. In 1968, Steiner et al introduced the term "multiple endocrine neoplasia" (MEN) to describe disorders featuring combinations of endocrine tumors; they designated the Wermer syndrome as MEN 1 and the Sipple syndrome as MEN 2. In 1974, Sizemore et al concluded that the MEN 2 category included two groups of patients with MTC and pheochromocytoma: one with parathyroid disease and a normal appearance (MEN 2A) and the other without parathyroid disease but with mucosal neuromas and mesodermal abnormalities (MEN 2B). Later, additional nonendocrine conditions (von Recklinghausen neurofibromatosis and von Hippel-Lindau disease) were found accompanying other more recently described familial MEN syndromes, indicating that these diseases are very complicated disorders.

Hereditary cancer syndromes of the skin

Hereditary cancer syndromes are a group of disorders characterized by a genetic susceptibility to the development of malignant tumors. Multiple cancers in the family or an abnormally early onset for the given cancer may suggest an underlying inherited predisposition. Awareness of their associated dermatologic manifestations can facilitate early detection of risk for neoplasms. This article provides an update on the clinical features, diagnostic criteria, and the use of genetic analysis in the detection of causative mutations of those hereditary cancer syndromes with cutaneous manifestations.

Pancreatic insulinomas in multiple endocrine neoplasia, type I knockout mice can develop in the absence of chromosome instability or microsatellite instability

Multiple endocrine neoplasia, type I (MEN1) is an inherited cancer syndrome characterized by tumors arising primarily in endocrine tissues. The responsible gene acts as a tumor suppressor, and tumors in affected heterozygous individuals occur after inactivation of the wild-type allele. Previous studies have shown that Men1 knockout mice develop multiple pancreatic insulinomas, but this occurs many months after loss of both copies of the Men1 gene. These studies imply that loss of Men1 is not alone sufficient for tumor formation and that additional somatic genetic changes are most likely essential for tumorigenesis. The usual expectation is that such mutations would arise either by a chromosomal instability or microsatellite instability mechanism. In a study of more then a dozen such tumors, using the techniques of array-based comparative genomic hybridization, fluorescent in situ hybridization, loss of heterozygosity analysis using multiple microsatellite markers across the genome, and real time PCR to assess DNA copy number, it appears that many of these full-blown clonal adenomas remain remarkably euploid. Furthermore, the loss of the wild-type Men1 allele in heterozygous Men1 mice occurs by loss and reduplication of the entire mutant-bearing chromosome. Thus, the somatic genetic changes that are postulated to lead to tumorigenesis in a mouse model of MEN1 must be unusually subtle, occurring at either the nucleotide level or through epigenetic mechanisms.

Highly penetrant hereditary cancer syndromes

The past two decades have brought many important advances in our understanding of the hereditary susceptibility to cancer. Approximately 5-10% of all cancers are inherited, the majority in an autosomal dominant manner with incomplete penetrance. While this is a small fraction of the overall cancer burden worldwide, the molecular genetic discoveries that have resulted from the study of families with heritable cancer have not only changed the way these families are counselled and managed, but have shed light on molecular regulatory pathways important in sporadic tumour development as well. In this review, we consider 10 of the more highly penetrant cancer syndromes, with emphasis on those predisposing to breast, colon, and/or endocrine neoplasia. We discuss the prevalence, penetrance, and tumour spectrum associated with these syndromes, as well as their underlying genetic defects.

Hyperparathyroidism and multiple endocrine neoplasia

Multiple endocrine neoplasia (MEN) syndromes comprise the group of heritable endocrinopathies, MEN 1, MEN 2A, and MEN 2B. Primary hyperparathyroidism caused by multiglandular involvement is usually the initial manifestation in MEN 1, occurring in more than 90% of patients. In patients with MEN 2A, hyperparathyroidism develops less commonly and is usually milder than in MEN 1. Advances in genetics and molecular biology aid in confirming the diagnosis and screening relatives who are carriers or at risk for the disease. Surgery plays an important role in the management of hyperparathyroidism in both MEN 1 and MEN 2A,although the timing and extent of surgery are areas of controversy.Long-term follow-up reveals a high rate of recurrent hyperparathyroidism in MEN 1 despite surgical intervention.

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.

Menin missense mutants associated with multiple endocrine neoplasia type 1 are rapidly degraded via the ubiquitin-proteasome pathway

MEN1 is a tumor suppressor gene that is responsible for multiple endocrine neoplasia type 1 (MEN1) and that encodes a 610-amino-acid protein, called menin. While the majority of germ line mutations identified in MEN1 patients are frameshift and nonsense mutations resulting in truncation of the menin protein, various missense mutations have been identified whose effects on menin activity are unclear. For this study, we analyzed a series of menin proteins with single amino acid alterations and found that all of the MEN1-causing missense mutations tested led to greatly diminished levels of the affected proteins in comparison with wild-type and benign polymorphic menin protein levels. We demonstrate here that the reduced levels of the mutant proteins are due to rapid degradation via the ubiquitin-proteasome pathway. Furthermore, the mutants, but not wild-type menin, interact both with the molecular chaperone Hsp70 and with the Hsp70-associated ubiquitin ligase CHIP, and the overexpression of CHIP promotes the ubiquitination of the menin mutants in vivo. These findings reveal that MEN1-causing missense mutations lead to a loss of function of menin due to enhanced proteolytic degradation, which may be a common mechanism for inactivating tumor suppressor gene products in familial cancer.

Molecular biology of primary hyperparathyroidism

As molecular biology and genetic mapping receive wider application to human disease, genetic alterations have been identified with increased frequency in some patients with primary hyperparathyroidism(HPT). These alterations have been found in molecules related to cellular signaling and growth (RET proto-oncogene)and in tumor suppressors that control cell cycle progression and gene transcription (cyclin D1 and the MEN1 gene product. Although primary HPT can usually be treated surgically without knowledge of which specific genetic alteration has occurred, this information may assist clinicians in identifying which patients will go on to develop multiglandular or recurrent disease. In addition,such an approach would facilitate more appropriate postoperative surveillance, as well as counseling and screening of family members who may be at high risk for HPT.

Hereditary pancreatic endocrine tumours

The two main types of hereditary pancreatic neuroendocrine tumours are found in multiple endocrine neoplasia type 1 (MEN-1) and von Hippel-Lindau disease (VHL), but also in the rarer disorders of neurofibromatosis type 1 and tuberous sclerosis. This review considers the major advances that have been made in genetic diagnosis, tumour localization, medical and surgical treatment and palliation with systemic chemotherapy and radionuclides. With the exception of the insulinoma syndrome, all of the various hormone excess syndromes of MEN-1 can be treated medically. The role of surgery however remains controversial ranging from no intervention (except enucleation for insulinoma), intervening for tumours diagnosed only by biochemical criteria, intervening in those tumours only detected radiologically (1-2 cm in diameter) or intervening only if the tumour diameter is > 3 cm in diameter. The extent of surgery is also controversial, although radical lymphadenectomy is generally recommended. Pancreatic tumours associated with VHL are usually non-functioning and tumours of at least 2 cm in diameter should be resected. Practice guidelines recommend that screening in patients with MEN-1 should commence at the age of 5 years for insulinoma and at the age of 20 years for other pancreatic neuroendocrine tumours and variously at 10-20 years of age for pancreatic tumours in patients with VHL. The evidence is increasing that the life span of patients may be significantly improved with surgical intervention, mandating the widespread use of tumour surveillance and multidisciplinary team management.

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.

Familial acromegaly

Most pituitary tumors are sporadic, though a few occur with a familial aggregation. Three distinct syndromes have been recognized to date: multiple endocrine neoplasia, type I (MEN-1), Carney complex (CNC), and isolated familial somatotropinomas (IFS). Pituitary tumor types in MEN-1 are similar to those occurring sporadically. The largest percentage are prolactin-secreting or non-functioning and only about 10% are growth hormone (GH)-secreting (somatotropinomas). In contrast, tumors types in CNC and IFS are invariably somatotropinomas, though there are differences in both clinical and histological features. Each of the familial syndromes is associated with a tumor-suppressor gene that was initially recognized by an observed loss of heterozygosity on chromosome 11q13 in MEN-1 and IFS and on chromosome 17q in CNC. The MEN-1 gene, which codes for the nuclear protein, menin, has been identified and a large number of inactivating mutations have been recognized. The gene associated with CNC codes for the protein kinase A regulatory subunit 1, inactivation of which leads to enhanced activity of the GH-releasing hormone-induced signal transduction pathway. This pathway exerts proliferative effects in somatotropes. The gene associated with IFS is distinct from the MEN-1 gene, though it is located in close proximity, and is contained in a candidate region of approximately 10 Mb. Identification of the IFS gene should provide new insight into the pathogenesis of somatotropinomas, not only in IFS but also in sporadic tumors, where there is an up to 40% allelic loss on chromosome 11q13.

JunD-menin interaction regulates c-Jun-mediated AP-1 transactivation

The gene responsible for multiple endocrine neoplasia type 1, MEN1, encodes the 610-amino acid-protein, menin. Although menin has been reported to bind AP-1 transcription factor JunD and suppress its transcriptional activity, little is known about its molecular mechanisms and physiological role. To better understand the function of menin and its significance in tumorigenesis, we investigated the effect of wild-type and mutant menin proteins on AP-1 transactivation. In COS cells, wild-type menin suppressed JunD-mediated transactivation in a dose-dependent manner, while it augmented c-Jun-mediated transactivation also in a dose-dependent manner. These effects were lost or reduced in all menin mutants examined. Electrophoretic mobility shift assay using AP-1 binding elements as a probe revealed that menin does not affect binding of c-Jun to DNA. Coexpression of menin mutants did not affect the function of wild-type menin. Coexpression of JunD amino-terminal fragment abolished menin-mediated enhancement of c-Jun transactivation, suggesting that Menin-JunD interaction may negatively regulate the enhancing effect of menin on c-Jun-mediated transactivation in COS cells.

Menin is required for bone morphogenetic protein 2- and transforming growth factor beta-regulated osteoblastic differentiation through interaction with Smads and Runx2

Menin, the product of the multiple endocrine neoplasia type 1 (MEN1) gene, is required for commitment of multipotential mesenchymal stem cells to the osteoblast lineage, however, it inhibits their later differentiation (Sowa, H., Kaji, H., Canaff, L., Hendy, G.N., Tsukamoto, T., Yamaguchi, T., Miyazono, K., Sugimoto, T., and Chihara, K. (2003) J. Biol. Chem. 278, 21058-21069). Here, we have examined the mechanism of action of menin in regulating osteoblast differentiation using the mouse bone marrow stromal ST2 and osteoblast MC3T3-E1 cell lines. In ST2 cells, reduced menin expression achieved by transfection of menin antisense DNA (AS) antagonized bone morphogenetic protein (BMP)-2-induced alkaline phosphatase activity and osteocalcin and Runx2 mRNA expression. Menin was co-immunoprecipitated with Smad1/5 in ST2 and MC3T3-E1 cells, and inactivation of menin antagonized BMP-2-induced transcriptional activity of Smad1/5 in ST2 cells, but not MC3T3-E1 cells. Menin was co-immunoprecipitated with the key osteoblast regulator, Runx2, and AS antagonized Runx2 transcriptional activity and the ability of Runx2 to stimulate alkaline phosphatase activity only in ST2 cells but not in MC3T3-E1 cells. In the osteoblast MC3T3-E1 cells, transforming growth factor-beta and its signaling molecule, Smad3, negatively regulated Runx2 transcriptional activity. Menin and Smad3 were co-immunoprecipitated, and combined menin and Smad3 overexpression antagonized, whereas menin and the dominant-negative Smad3DeltaC together enhanced BMP-2-induced transcriptional activity of Smad1/5 and Runx2. Smad3 alone had no effect. Therefore, menin interacts physically and functionally with Runx2 in uncommitted mesenchymal stem cells, but not in well differentiated osteoblasts. In osteoblasts the interaction of menin and the transforming growth factor-beta/Smad3 pathway negatively regulates the BMP-2/Smad1/5- and Runx2-induced transcriptional activities leading to inhibition of late-stage differentiation.

Menin inactivation leads to loss of transforming growth factor beta inhibition of parathyroid cell proliferation and parathyroid hormone secretion

Primary hyperparathyroidism is a common endocrine disorder caused by parathyroid gland enlargement and excessive parathyroid hormone (PTH) secretion. However, the precise mechanisms of tumorigenesis of the parathyroids are unknown. Here we have investigated the roles of transforming growth factor (TGF)-beta and menin, the product of the multiple endocrine neoplasia type 1 (Men1) gene, in the proliferation and PTH production of parathyroid cells from either patients with secondary hyperparathyroidism or Men1. TGF-beta was expressed in the parathyroid endocrine cells. Addition of TGF-beta to parathyroid cells from patients with secondary hyperparathyroidism inhibited their proliferation and PTH secretion. These responses to TGF-beta were lost when menin was specifically inactivated by antisense oligonucleotides. Moreover, TGF-beta did not affect the proliferation and PTH production of parathyroid cells from a Men1 patient. These results indicate that menin is required for TGF-beta action in the parathyroid. We conclude that TGF-beta is an important autocrine/paracrine negative regulator of parathyroid cell proliferation and PTH secretion and that loss of TGF-beta signaling due to menin inactivation contributes to parathyroid tumorigenesis.

Primary hyperparathyroidism associatiated with aldosterone-producing adrenocortical adenoma and breast cancer: relation to MEN1 gene

A rare case of primary hyperparathyroidism associated with primary aldosteronism and breast cancer is reported. A 44-year-old woman was admitted to our hospital to undergo surgical removal of breast cancer. She had hypertension with low serum potassium, and slightly but significantly elevated serum calcium levels. Further studies demonstrated an enlarged left superior parathyroid gland and a left aldosterone-producing adrenocortical adenoma. Blood pressure was controlled with spironolactone and nifedipine, and left mastectomy was done for breast cancer. The pathological diagnosis was scirrhous breast carcinoma. Although the postoperative course was uneventful, her serum calcium gradually and progressively rose to higher levels. Left superior parathyroidectomy and left adrenalectomy were then performed simultaneously. The pathological diagnoses of the resected parathyroid gland and adrenal gland were parathyroid chief cell adenoma and adrenocortical adenoma with hyperplasia of zona glomerulosa, respectively. To clarify if the occurence of these tumors may be related to MEN1 gene mutations, we analyzed MEN1 gene in this patient, and found a loss of heterozygosity of the MEN1 locus in the parathyroid adenoma and breast cancer. Thus, we conclude that an alteration of the MEN1 gene and/or another tumor suppressor gene located at the MEN1 locus on chromosome 11q13 may be responsible for the development of parathyroid adenoma and breast cancer in our patient suggesting that the clinical spectrum of MEN1 might include breast cancer. In addition, serum calcium should be interpreted with caution in primary aldosteronism, because hypercalcemia may be masked in the presence of aldosterone excess.

Reduction of menin expression enhances cell proliferation and is tumorigenic in intestinal epithelial cells

Menin, the product of the tumor suppressor gene MEN1, is widely expressed in mammalian endocrine and non-endocrine tissues, including intestine. Its known abundant expression in several types of cells with high proliferative capacity led us to investigate the physiological function of the protein menin in intestinal epithelium, one of the most rapidly growing epithelia. Here we showed that the Men1 gene is mainly expressed in the crypt compartment of the proximal small intestine and that its expression was increased during fasting in vivo, both suggesting a role of menin in the control of cell growth. Indeed, specific reduction of menin expression by transfected antisense cDNA in the rat duodenal crypt-like cell line, IEC-17, increased cell proliferation. The latter is correlated to a loss of cell-cycle arrest in G(1) phase by resting cells and an overexpression of cyclin D1 and cyclin-dependent kinase (Cdk)-4. Furthermore, these cells lost the inhibition of proliferation induced by transforming growth factor-beta1, associated with a decrease of transforming growth factor-beta type II receptor expression. As a result of deregulated proliferation, antisense menin transfected IEC-17 cells became tumorigenic as shown in vitro as well as in vivo in immunosuppressed animals. These results indicate that menin contributes to proliferation control in intestinal epithelial cells. The present study reveals an unknown physiological function for menin in intestine that may be important in the regulation of epithelial homeostasis.

Multiple endocrine neoplasia (MEN)-associated tumours

The pathological changes of tumours associated with the two main MEN syndromes, types 1 and 2, and their relation with the genetic defects responsible for the individual syndromes are reviewed. MEN 1-associated tumours, affecting mainly the pituitary, the parathyroids and the pancreas, are due to inactivation of the MEN 1 oncosuppressor gene located in 11q13. Although at least one peculiar phenotype of MEN 1 syndrome is known, no genotype-phenotype relation has been disclosed. MEN 2-associated tumours, affecting mainly the thyroid C cells, the parathyroids and the adrenal medulla, are due to oncogenic point mutations of the RET proto-oncogene located in 10q11.2. The two main phenotypes of the MEN 2 syndrome, known as MEN 2A and MEN 2B, are associated with different mutations of the RET oncogene, mostly located on exons 10 or 11 in MEN 2A and in codon 918 of exon 16 in MEN 2B. Independent of the type of MEN disease, the development of tumours follows a substantially similar pattern in all MEN target organs. The initial lesion is a diffuse hyperplastic proliferation of the affected endocrine tissue with bilateral involvement of pair organs, followed by development of multiple micro- and, eventually, macronodular lesions. Such association of endocrine hyperplastic changes and tumours is suggestive of a MEN condition in patients with apparently sporadic tumours. LOH investigations in MEN 1 cases indicate that each multiple tumour is the result of an independent genetic event.

Clinical and genetic features of patients with multiple endocrine tumors who have neither family history nor MEN1 germline mutations

Multiple endocrine neoplasia type 1 (MEN1) is an hereditary tumor syndrome that involves specific endocrine organs such as parathyroids, anterior pituitary gland, and endocrine pancreas. The responsible gene for this syndrome, MEN1, has been isolated and that enabled genetic diagnosis for patients with endocrine tumors and early detection of asymptomatic gene carriers in affected families. Nevertheless, there are a considerable number of patients with MEN1 who have neither family history nor germline MEN1 mutations. In this article, clinical features of such patients are described. Among 53 MEN1 patients we have seen during the last 20 yr, five patients who did not have either MEN1 germline mutation or family history were categorized as MEN1 phenocopy. During the same period, we have also experienced three patients who had primary hyperparathyroidism and adrenocortical tumor but had no apparent family history of endocrine tumors. These patients were considered as MEN1 phenocopy variants and included in the study. The mean age of MEN1 phenocopy patients (including variants) at diagnosis was 48 yr, which was not significantly different from that of probands of familial MEN1 (46 yr) who carry heterozygous MEN1 gene mutations. In the majority of MEN1 phenocopy patients, primary hyperparathyroidism was due to a single parathyroid adenoma. In contrast to a previous report, we found that MEN1 phenocopy patients are not necessarily older than probands of familial MEN1. Phenotypic expression of such patients is variable, thus differentiation of familial MEN1 and MEN1 phenocopy cannot be made based on age and clinical phenotype alone.

Quality of life in patients with multiple endocrine neoplasia type 1 (MEN 1)

To study quality of life among patients living with a hereditary tumor syndrome, the small group with multiple endocrine neoplasia type 1 (MEN1) was selected. It is characterized by multifocal adenomas of the pancreas, parathyroid, anterior pituitary and other endocrine glands. Patients were assessed at an in-hospital stay and six months later at home. Patients at a specialist ward for MEN1 were recruited consecutively (n = 36) during one year. Eighty-one percent participated (n = 29). Four questionnaires were used: the Hospital Anxiety and Depression Scale (HADS), the Impact of Event Scale (IES), the Life Orientation Test (LOT) and the Short Form-36 (SF-36). Psychosocial outcome measures (anxiety, depression, intrusion, avoidance) changed only marginally between the in hospital stay and six months later at home. However, depression increased for patients categorized as having a high burden of disease and treatment. Compared to population-based norm values, the SF-36 scores of the patient group MEN1were lower for General Health and Social Functioning. Optimism assessed at the hospital was a predictor of Mental Health six months later. Most MEN 1 patients (70%) were pessimists. Patients having a higher burden of disease and treatment are in need of support after discharge. Patients could easily be monitored with questionnaires and, when indicated, offered help for their psychosocial distress.

[Multiple endocrine neoplasias. Recent advances in clinical and genetic diagnosis]

PURPOSE

Multiple endocrine neoplasias (MEN) are autosomal dominant inherited syndromes characterized by the association of different glandular lesions in several members of the same kindred. The main clinical features of MEN 1 include primary hyperparathyroidism, pancreatic islet cell tumors and pituitary adenomas; less common features are adrenal adenomas, thymic and bronchial carcinoid tumors, lipomas and various cutaneous lesions. The MEN 2 syndromes (MEN 2A, MEN 2B and familial medullary thyroid carcinomas) are characterized by high penetrance of medullary thyroid carcinoma and differ in their variable expression of pheochromocytoma, hyperparathyroidism and other clinical features.

CURRENT KNOWLEDGE AND KEY POINTS

MEN 1 tumor suppressor gene encodes a nuclear protein, menin, which interacts with different regulation transcription factors. The MEN 2 syndromes are caused by germ-line mutations of the RET proto-oncogene, which encodes a transmembrane tyrosine kinase. Genetic testing for mutations in these 2 genes allows identification of individuals predisposed to the disease, early diagnosis, and clinical and therapeutic management.

FUTURE PROSPECTS AND PROJECTS

Fundamental approach will allow a best comprehension of physiopathogenic mechanisms of these disorders and the improvement of therapeutic management.

Prevalence of multiple endocrine neoplasia type 1 in young patients with apparently sporadic primary hyperparathyroidism or pancreaticoduodenal endocrine tumours

Background

The appropriate treatment for a sporadic endocrine tumour may be different from those that present as part of the multiple endocrine neoplasia type 1 (MEN1) syndrome. As primary hyperparathyroidism (pHPT) and pancreaticoduodenal endocrine tumours (PETs) are the most common organ manifestations of MEN1, the prevalence of germline mutations in the MEN1 gene was determined in young patients with apparently sporadic pHPT or PETs.

Methods

Eighteen of 705 patients with pHPT and 11 of 93 patients with PETs operated on between 1987 and 2001 had no family history of MEN1, only one organ manifestation and were aged 40 years or less at the time of diagnosis. Fifteen patients with pHPT and eight with PETs agreed to MEN1 gene mutation analysis, which was performed by single-strand conformational variant analysis and direct DNA sequencing.

Results

Two of 15 patients (13·3 (95 per cent confidence interval (c.i.) 1·6 to 40·4) per cent) with apparently sporadic pHPT had a MEN1 germline mutation. Both mutations were found in patients with pHPT due to multiglandular disease, whereas the remaining 13 patients had a solitary adenoma. None of the eight patients with PETs carried a MEN1 germline mutation.

Conclusion

Sporadic pHPT due to multiglandular disease in patients younger than 40 years may represent the first organ manifestation of MEN1 despite a negative family history.

Menin, a tumor suppressor, associates with nonmuscle myosin II-A heavy chain

MEN1 is a likely tumor suppressor gene that encodes a novel protein, menin. Menin is a 610 amino-acid residue protein with as yet unknown function(s). We have used tandem affinity purification and mass spectroscopy to isolate and identify proteins associating with menin from cultured HeLa cell extracts. This strategy has resulted in the isolation and identification of nonmuscle myosin type II-A heavy chain (NMHC II-A) as a menin interacting protein. This interaction was confirmed by glutathione-S-transferase pulldown assays, by coimmunoprecipitation, and by actin selection of myosin. We have further identified the amino-terminal region of menin and the head domain of NMHC II-A to be regions required for this interaction. Moreover menin was seen to colocalize with this myosin isoform in the cleavage furrow of dividing cells by indirect immunofluoresence. These data indicate that menin through binding to NMHC II-A could participate in cell division and in other processes that involve NMHC II-A.

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

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

Of mice and MEN1: Insulinomas in a conditional mouse knockout

Patients with multiple endocrine neoplasia type 1 (MEN1) develop multiple endocrine tumors, primarily affecting the parathyroid, pituitary, and endocrine pancreas, due to the inactivation of the MEN1 gene. A conditional mouse model was developed to evaluate the loss of the mouse homolog, Men1, in the pancreatic beta cell. Men1 in these mice contains exons 3 to 8 flanked by loxP sites, such that, when the mice are crossed to transgenic mice expressing cre from the rat insulin promoter (RIP-cre), exons 3 to 8 are deleted in beta cells. By 60 weeks of age, >80% of mice homozygous for the floxed Men1 gene and expressing RIP-cre develop multiple pancreatic islet adenomas. The formation of adenomas results in elevated serum insulin levels and decreased blood glucose levels. The delay in tumor appearance, even with early loss of both copies of Men1, implies that additional somatic events are required for adenoma formation in beta cells. Comparative genomic hybridization of beta cell tumor DNA from these mice reveals duplication of chromosome 11, potentially revealing regions of interest with respect to tumorigenesis.

Clinical and molecular aspects of adrenocortical tumourigenesis

Adrenal masses are a common problem affecting 3-7% of the population. The majority turn out to be benign adrenocortical adenomas, which may be functional or non-functional. Much more rarely, these masses represent a primary adrenal carcinoma. It is becoming increasingly recognized that of the benign functioning adenomas or hyperplasias, the majority will hypersecrete aldosterone and this will be more frequently detected when hypertensive populations are screened for this disease. In contrast, the incidence of primary adrenocortical carcinoma has remained steady and for this disease, surgery represents the mainstay of treatment. The advent of laparoscopic adrenal surgery has lowered the threshold size for recommending surgery for asymptomatic adrenal masses and as such, an increased proportion of adrenocortical cancers are being resected and detected at an earlier stage. Recent progress has been made in our understanding of the key genetic changes which underpin the biology of this disease. Progression from adrenal adenoma to carcinoma involves a monoclonal proliferation of cells which, among other defects, have undergone chromosomal duplication at the 11p15.5 locus leading to overexpression of the IGF2 gene and abrogation of expression of the CDKN1C and H19 genes. TP53 is involved in progression to carcinoma in a subset of patients and the frequency of ACTH receptor deletion needs to be more fully explored. Other key oncogenes and tumour suppressor genes remain to be identified although the chromosomal loci in which they lie can be identified at 17p, 1p, 2p16 and 11q13 for tumour suppressor genes and chromosomes 4, 5 and 12 for oncogenes.

Carcinoid tumors of the stomach

Interest in gastric carcinoid tumors has in recent time amplified considerably as the understanding of both their biological background and clinical significance has developed. The increase in identification associated with the widespread availability of upper gastrointestinal endoscopy has facilitated diagnosis. In addition concern related to the consequences of long-standing hypergastrinemia generated by the use of potent acid-suppressive medications has augmented both clinical and scientific focus on gastric neuro endocrine issues. The elucidation of the regulatory mechanisms of the progenitor cell (ECL cell) of the gastric carcinoid tumor, the refinement of a pathological grading system for ECL cell proliferation, and the availability of specific immunohistologic identification techniques have further amplified the characterization of this lesion. Although the putative malignant potential of gastric carcinoids may ultimately be of only modest concern in a background of hypergastrinemia its relationship to gastric adenocarcinoma is still enigmatic and worthy of further consideration. This review will describe the molecular interrelationship between low-acid states, gastrin, and ECL cell proliferation and will discuss the pathological classification of the distinct types of gastric carcinoid tumors. In addition, the clinical rationale of current diagnostic and therapeutic strategies will be examined, providing a logical basis for the formulation of appropriate management strategies for patient care.

Germline mutations of the MEN1 gene in Korean families with multiple endocrine neoplasia type 1 (MEN1) or MEN1-related disorders

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome characterized by the combined occurrence of tumours of the parathyroid glands, pancreatic islet cells and anterior pituitary gland. Mutation analysis of the MEN1 gene has enabled the genetic diagnosis of patients with MEN1. Two MEN1-related disorders - familial isolated hyperparathyroidism (FIHP) and familial pituitary adenoma - are considered to be variants of MEN1, or at least to be incompletely expressed variants. Germline mutations of the MEN1 gene have been reported in some with FIHP, but familial pituitary adenoma usually lacks the MEN1 mutation and has been described as a genetically distinct disorder. In this work, we investigated five Korean families with MEN1, one family with FIHP and one family with familial pituitary adenoma. Polymerase chain reaction (PCR)-based single-strand conformation polymorphism (PCR-SSCP) analysis, denaturing high-performance liquid chromatography (DHPLC) and sequencing were used to detect the MEN1 mutations. Screening of the genetic variations of the MEN1 gene revealed four germline mutations in five typical MEN1 families. All four germline mutations led to truncated proteins or a change in the amino acids of the functional domains. In this study, we identified three novel MEN1 germline mutations (969C >A, 973G >C and 1213C >T) and one previously reported mutation (200-201insAGCCC). The frequency of the MEN1 germline mutation in Korean MEN1 families (four of five; 80%) was similar to those reported previously. In accordance with previous studies, no MEN1 germline mutation was detected in two families with FIHP or familial pituitary adenoma.

Multiple endocrine neoplasia type 1 (MEN1): genetic and clinical analysis in the Southern Chinese

OBJECTIVE

Multiple endocrine neoplasia type 1 (MEN1) is characterized by a triad of neoplasia affecting the parathyroid glands, enteropancreatic endocrine tissue and the anterior pituitary gland.

DESIGN

In order to define the prevalence of MEN1 germ-line mutations in Southern Chinese patients with MEN1 syndrome, we performed direct sequencing of the entire open reading frame of the MEN1 gene for 12 index patients and their first-degree relatives.

RESULTS

Six patients had familial MEN1 syndrome and six had apparently sporadic disease. Nine different germ-line mutations at the MEN1 gene were identified, including three novel mutations [248-249delTT in exon 2, K559X(AAG --> TAG) in exon 10 and IVS 2nt + 2(G --> T) in intron 2]. All patients with familial MEN1 syndrome were heterozygous carriers of a germ-line mutation and MEN1-related disorders were only evident in their first-degree relatives who also carried the mutation. All patients with an enteropancreatic lesion were mutation carriers and the absence of mutation in three apparently sporadic MEN1 patients with only hyperparathyroidism and pituitary microadenoma might represent the presence of MEN1 phenocopy.

CONCLUSIONS

The finding of MEN1 germ-line mutation in all patients with familial MEN1 syndrome suggests that genetic screening should be useful in our population to identify affected individuals within a kindred and allow early detection of MEN1-related tumours.

Inactivation of menin, the product of the multiple endocrine neoplasia type 1 gene, inhibits the commitment of multipotential mesenchymal stem cells into the osteoblast lineage

The physiological roles of menin, the product of the multiple endocrine neoplasia type 1 gene, are not known. Homozygous menin knockout mice exhibit cranial and facial hypoplasia. We, therefore, investigated the role of menin in the regulation of osteoblastic differentiation. Menin antisense oligonucleotides (AS-oligo) reduced endogenous menin expression in the C3H10T1/2 (10T1/2) mouse mesenchymal stem cells and antagonized alkaline phosphatase (ALP) activity and the expression of type I collagen, Runx2/cbfa1 (Runx2), and osteocalcin (OCN) induced by bone morphogenetic protein 2 (BMP-2). AS-oligo did not affect adipogenic markers (Oil red staining and PPARgamma expression) and chondrogenic markers (Alcian blue staining and type IX collagen) induced by BMP-2 in 10T1/2 cells. Menin co-immunoprecipitated with Smad1 and Smad5, and inactivation of menin antagonized BMP-2-induced transcriptional activity of Smad1/5. In osteoblastic MC3T3-E1 cells, AS-oligo affected neither BMP-2-stimulated ALP activity nor the expression of Runx2 and OCN. Stable inactivation of menin in MC3T3-E1 cells increased ALP activity, mineralization, and the expression of type I collagen and OCN. In 21-day cultures of MC3T3-E1 cells and BMP-2-treated 10T1/2 cells, endogenous menin expression increased up to day 14 and declined thereafter. These data indicate that menin inactivation specifically inhibits the commitment of pluripotent mesenchymal stem cells to the osteoblast lineage, mediated by menin and Smad1/5 interactions. Menin is important for both early differentiation of osteoblasts and inhibition of their later differentiation, and it might be crucial for intramembranous ossification.

Multiple endocrine neoplasia type 1: duodenopancreatic tumours

The pancreaticoduodenal disease in Multiple endocrine neoplasia type 1 (MEN1) is the most frequent cause of death due to the syndrome, and the most controversial with regard to its management. This article discusses the current data and recommendations with respect to disease screening, functional tumour diagnosis, natural history, preoperative imaging, operative strategy and follow-up.

Functional studies of the MEN1 gene

Multiple endocrine neoplasia type 1 is an autosomal dominant cancer syndrome affecting primarily parathyroid, enteropancreatic endocrine and pituitary tissues. The inactivating germline and somatic mutations spread throughout the gene and the accompanying loss of the second allele in tumours show that the MEN1 gene is a tumour suppressor. The MEN1-encoded protein, menin, is a novel nuclear protein. Menin binds and alters JunD-, NF-kappaB-, Smad3-mediated transcriptional activation. The mouse Men1 knockout model mimicks the human MEN1 condition contributing to the understanding of tumorigenesis in MEN1.

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.

Multiple endocrine neoplasia type 1

Rare and unpredictable

Menin interacting proteins as clues toward the understanding of multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome characterized mostly by tumors of the parathyroids, pancreas and anterior pituitary. The gene responsible, MEN1, encodes Menin, a 610 aminoacid nuclear protein with no sequence homology to other proteins. Although a mouse knock-out model is available, the function of Menin is still elusive. Proteins of known function are shown to interact with Menin: JunD, nuclear factor-KappaB, Smad3, Pem, Nm23H1, glial fibrillary acidic protein, Vimentin, and probably P53. Their partnership with Menin may correspond to a regulation of their activity, but their relevance to the various traits of MEN1 pathogenicity is not established. This raises fundamental issues on the regulation pathways implicated in this complex endocrine disease.

The 32-kilodalton subunit of replication protein A interacts with menin, the product of the MEN1 tumor suppressor gene

Menin is a 70-kDa protein encoded by MEN1, the tumor suppressor gene disrupted in multiple endocrine neoplasia type 1. In a yeast two-hybrid system based on reconstitution of Ras signaling, menin was found to interact with the 32-kDa subunit (RPA2) of replication protein A (RPA), a heterotrimeric protein required for DNA replication, recombination, and repair. The menin-RPA2 interaction was confirmed in a conventional yeast two-hybrid system and by direct interaction between purified proteins. Menin-RPA2 binding was inhibited by a number of menin missense mutations found in individuals with multiple endocrine neoplasia type 1, and the interacting regions were mapped to the N-terminal portion of menin and amino acids 43 to 171 of RPA2. This region of RPA2 contains a weak single-stranded DNA-binding domain, but menin had no detectable effect on RPA-DNA binding in vitro. Menin bound preferentially in vitro to free RPA2 rather than the RPA heterotrimer or a subcomplex consisting of RPA2 bound to the 14-kDa subunit (RPA3). However, the 70-kDa subunit (RPA1) was coprecipitated from HeLa cell extracts along with RPA2 by menin-specific antibodies, suggesting that menin binds to the RPA heterotrimer or a novel RPA1-RPA2-containing complex in vivo. This finding was consistent with the extensive overlap in the nuclear localization patterns of endogenous menin, RPA2, and RPA1 observed by immunofluorescence.

Determination of allelic deletion of multiple endocrine neoplasm type 1 (MEN1) gene in acute myeloid leukemia (AML) by application of FISH-TSA technique

We have used the single and dual color fluorescence in situ hybridization (FISH) technique combined with a new detection system, tyramide signal amplification (TSA), by using the multiple endocrine neoplasm type 1 (MEN1) gene and chromosome 11 specific alpha satellite DNA probes for the study of the allelic deletion of the MEN1 gene. The MEN1 gene is a new tumor suppressor gene and has been recently cloned on chromosome 11q13. FISH combined with the TSA detection system was performed on bone marrow interphase nuclei of 22 patients with acute myeloid leukemia (AML). The FISH-TSA analysis revealed the mono allelic deletion of the MEN1 gene in 4 out of 22 patients (18.18%), 2 of 9 AML-M2 patients (22.2%), 1 of 6 AML-M4 patients (16.6%), and 1 of 4 AML-M5 patients (25.0%). Our study indicates that allelic deletion of the MEN1 gene is not a major cause or a primary event in tumorigenesis of AML, although the long arm (q13 region) of chromosome 11 involves a chromosomal rearrangement in AML.

Multiple endocrine neoplasia type 1: fresh perspective on clinical features and penetrance

Multiple endocrine neoplasia type 1 (MEN-1) is an interesting genetic syndrome of polyendocrinopathies. Clinical knowledge about MEN-1 is essential as it appears to be significantly under-diagnosed. New data from several prospective series shows not only that as a many as 40% of patients manifest a first feature of MEN-1 after age 40, but also that as many as a third of gene carriers do not present with hyperparathyroidism as the first feature, as previously believed. Mutational analysis for frequently involved exons of the gene menin on chromosome 11 is now available, but negative results should be interpreted with caution in patients with clinical MEN-1. Disease-specific mortality is significant, arises largely from pancreatic islet carcinoma and malignant thymic carcinoid, and renders this disorder worthy of careful and early prospective diagnosis and treatment.

Menin, the multiple endocrine neoplasia type 1 gene product, exhibits GTP-hydrolyzing activity in the presence of the tumor metastasis suppressor nm23

MEN1, the gene responsible for multiple endocrine neoplasia type 1, is a tumor suppressor gene that encodes a protein called menin, of unknown function with no homology to any known protein. Here we demonstrate that menin interacts with a putative tumor metastasis suppressor nm23H1/nucleoside diphosphate (NDP) kinase A in mammalian cells. Given the roles of nm23 as a multi-functional protein, we searched for the possible function of menin. Menin has no effect on the known activities of nm23; that is, nucleoside diphosphate kinase, protein kinase, or GTPase-activating protein for Ras-related GTPase Rad. However, we found that menin hydrolyzes GTP to GDP efficiently in the presence of nm23, whereas nm23 or menin alone shows little or no detectable GTPase activity. Furthermore, menin contains sequence motifs similar to those found in all known GTPases or GTP-binding proteins and shows low affinity but specific binding to GTP/GDP. These results suggest that menin is an atypical GTPase stimulated by nm23.

MEN1 tumor-suppressor protein localizes to telomeres during meiosis

Multiple endocrine neoplasia type 1 is an autosomal dominant cancer predisposition syndrome caused by mutations in the tumor-suppressor gene MEN1. The gene encodes a nuclear protein, menin, with no recognized functional motifs. Menin has been shown negatively to regulate transcriptional activation mediated by JunD, although the significance of this interaction in normal cell physiology and how the absence of menin leads to tumorigenesis are unknown. Menin is highly expressed in testes. We used immunocytochemistry to explore its role in meiosis and found that it localizes exclusively at telomeres. JunD was not found at telomeres in meiotic cells. In view of elevated telomerase activity or abnormal telomere structure in virtually all malignancies, regulation of telomere function would be an appealing role for a tumor suppressor. However, menin does not specifically associate with telomeres in somatic cells, as indicated by lack of co-localization with the known telomeric protein TRF2. Cells overexpressing menin had normal telomerase activity, and tumors with homozygous MEN1 mutations showed no aberrations in telomere length, indicating that menin does not directly regulate telomerase activity. The role of menin at meiotic telomeres appears to be independent of JunD and may not have a counterpart in somatic cells. These results suggest that menin may play different roles in different tissues through interactions with different proteins.

Descobrindo Genes no Século XXI: Enfoque na Área de Onco-Endocrinologia

A área de endocrinologia genética e oncológica tem sido alvo de enorme avanço nos anos recentes. A descoberta de genes responsáveis por neoplasias hereditárias nas últimas décadas representou uma fonte importante de informações concernentes à avaliação de risco, prevenção e aconselhamento genético. Neste particular, a caracterização do gene responsável pela neoplasia endócrina múltipla tipo 2 (MEN 2) representou a "pedra angular" para o desenvolvimento do campo de oncogenética clínica. Portanto, estima-se que o estudo genético e funcional das neoplasias hereditárias será igualmente capaz de liderar o avanço para um melhor manuseio clínico e terapêutico destas doenças. Um dos grandes desafios do futuro reside em se entender o intrincado mecanismo de interação entre genes e proteínas no controle do desenvolvimento e regulação dos diferentes sistemas biológicos. Uma das conseqüências mais antecipadas deste avanço é a sua aplicação para o tratamento específico e "individualizado" de todas as doenças humanas. Esta breve revisão tratará de aspectos gerais que envolvem o processo de identificação de novos genes e sua associação com condições clínicas específicas. As técnicas clássicas de clonagem serão apresentadas ao lado de estratégias modernas de identificação e análise de genes. O papel da bioinformática no Projeto Genoma Humano e o imenso potencial que esta informação traz para acelerar o processo de caracterização de novos grupos de genes serão brevemente discutidos.