Germ-line mutations in p27Kip1 cause a multiple endocrine neoplasia syndrome in rats and humans

Functional studies of menin through genetic manipulation of the Men1 homolog in mice

To investigate the physiological role of menin, the protein product of the MEN1 gene, several groups have utilized gene targeting strategies to delete one or both copies of the mouse homolog Men1. Mice that are homozygous null for Men1 die during embryogenesis. Heterozygous Men1 mice are viable and develop many of the same types of tumors as humans with MEN1. In addition to conventional knockouts of Men1, tissue-specific elimination of menin using cre-lox has been achieved in pancreatic beta cells, anterior pituitary, parathyroid, liver, neural crest and bone marrow, with varying results that are dependent on cell context. In this chapter, we compare the phenotypes of the different conventional Men1 knockouts, detail the similarities and differences between Men1 pathogenesis in mice and humans and highlight results from recent crossbreeding studies between Men1 mutants and mice with null mutations in genes within the retinoblastoma pathway, including p18(Inc4c), p27(Kip1) and Rb. In addition, we discuss not only how the Men1 mutants have shed light on the role of menin in endocrine tumor suppression, but also how Men1 mutant mice have helped uncover previously unrecognized roles for menin in development, leukemogenesis and gestational diabetes.

Deconstructing pancreas development to reconstruct human islets from pluripotent stem cells

There is considerable excitement about harnessing the potential of human stem cells to replace pancreatic islets that are destroyed in type 1 diabetes mellitus. However, our current understanding of the mechanisms underlying pancreas and islet ontogeny has come largely from the powerful genetic, developmental, and embryological approaches available in nonhuman organisms. Successful islet reconstruction from human pluripotent cells will require greater attention to "deconstructing" human pancreas and islet developmental biology and consistent application of conditional genetics, lineage tracing, and cell purification to stem cell biology.

Genetic screening for multiple endocrine neoplasia syndrome type 1 (MEN-1): when and how

Multiple endocrine neoplasia syndrome type 1 (MEN1) syndrome has benefited from the identification of the gene whose mutations account for the genetic susceptibility to develop endocrine tumors. Asymptomatic MEN1 mutant carriers need to be clearly recognized because the gene-related mutations confer a high risk of multiple primary cancers, occur at younger ages, and affect multiple family members who inherit the cancer-predisposing genetic mutation.

Cancer research in rat models

Rat has been the major model species used in several biomedical fields, notably in drug development and toxicology, including carcinogenicity testing. Rat is also a useful model in basic cancer research. Several rat models of monogenic (Mendelian) human hereditary cancers are available. Some were obtained spontaneously, while others were generated either by mutagenesis of tumor suppressor genes or by transgenesis of activated oncogenes (transgenesis can be performed efficiently in the rat). In addition, among the hundreds of inbred rat strains that have been isolated, some are highly susceptible or resistant to certain types of cancer, and these divergent phenotypes were shown to be polygenic. Numerous quantitative trait loci (QTLs) controlling cancer susceptibility/resistance have been defined in linkage analyses, and several of these QTLs were physically demonstrated in congenic strains. These studies led, in particular, to rapid translation to the human, with the identification of loci controlling susceptibility to a form of multiple endocrine neoplasia (monogenic trait) and to breast cancer (polygenic disease). The biology of cancer resistance has also been analyzed, and in some (but not all) cases, it was linked to regression of preneoplasic lesions. Rat tumors have been the subject of various types of analyses, and these studies led to important conclusions, including that tumors can be classified on the basis of the identity of the inducing agent, thereby suggesting that analyses of human tumors may be valuable in determining retrospectively the role of specific carcinogens in the formation of human cancers, and of human breast cancer in particular.

Caspase 8 and menin expressions are not correlated in human parathyroid tumors

Menin is lost by the sequential inactivation of both MEN1 alleles in subsets of non-hereditary endocrine tumors as well as those associated with multiple endocrine neoplasia type 1 (MEN1), an autosomal dominant hereditary cancer syndrome characterized by multiple tumors including parathyroid, pituitary and enteropancreatic endocrine tumors. Loss of menin has been reported to be associated with lowered caspase 8 expression and resistance to apoptosis in murine fibroblasts and in pancreatic islet tumors arising in heterozygous MEN1 gene knockout mice, the animal model of the human MEN1 syndrome. We confirmed by menin-knockdown experiments with specific siRNA that menin is crucial for caspase 8 expression in human culture cells while overexpression of menin did not increase caspase 8 protein over basal levels. We then examined expression of menin, caspase 8 and cyclin-dependent kinase inhibitors p27(Kip1) and p15(Ink4b) by Western blotting in human parathyroid tumors surgically resected from patients with MEN1 and those with non-hereditary primary hyperparathyroidism. The menin and p27(Kip1) expression levels were correlated with MEN1 mutation status that was confirmed by DNA analysis. The caspase 8 and p15(Ink4b) protein levels were variable among tumors, and were not correlated with menin protein levels. These findings suggest that human endocrine tumors lacking menin may not always exhibit lowered caspase 8 expression and hence may not be resistant to apoptosis-inducing therapy.

The MENX syndrome and p27: relationships with multiple endocrine neoplasia

In the past 3 years new insight into the etiopathogenesis of hereditary endocrine tumors has emerged from studies conducted on MENX, a rat multiple endocrine neoplasia (MEN) syndrome. MENX spontaneously developed in a rat colony and was discovered by serendipity when these animals underwent complete necropsy, as they were found to consistently develop multiple endocrine tumors with a spectrum similar to both MEN type 1 (MEN1) and MEN2 human syndromes. Genetic studies identified a germline mutation in the Cdkn1b gene, encoding the p27 cell cycle inhibitor, as the causative mutation for the MENX syndrome. Capitalizing on these findings, we and others identified heterozygous germline mutations in the human homologue, CDKN1B, in patients with multiple endocrine tumors. As a consequence of these observations a novel human MEN syndrome, named MEN4, was recognized which is caused by mutations in p27. Altogether these studies identified Cdkn1b/CDKN1B as a novel tumor susceptibility gene for multiple endocrine tumors in both rats and humans. In this chapter we present the MENX syndrome and its phenotype, and we compare it to the human MEN syndromes; we discuss the current state of knowledge regarding the genes associated to inherited MEN, with a particular focus on CDKN1B; we present recent clinical and basic findings about the MEN4 syndrome and the functional characterization of the CDKN1B mutations identified. These findings are placed in the broader context of how p27 dysregulation might affect neuroendocrine cell function and trigger tumorigenesis.

Eye development

The vertebrate eye comprises tissues from different embryonic origins: the lens and the cornea are derived from the surface ectoderm, but the retina and the epithelial layers of the iris and ciliary body are from the anterior neural plate. The timely action of transcription factors and inductive signals ensure the correct development of the different eye components. Establishing the genetic basis of eye defects in zebrafishes, mouse, and human has been an important tool for the detailed analysis of this complex process. A single eye field forms centrally within the anterior neural plate during gastrulation; it is characterized on the molecular level by the expression of "eye-field transcription factors." The single eye field is separated into two, forming the optic vesicle and later (under influence of the lens placode) the optic cup. The lens develops from the lens placode (surface ectoderm) under influence of the underlying optic vesicle. Pax6 acts in this phase as master control gene, and genes encoding cytoskeletal proteins, structural proteins, or membrane proteins become activated. The cornea forms from the surface ectoderm, and cells from the periocular mesenchyme migrate into the cornea giving rise for the future cornea stroma. Similarly, the iris and ciliary body form from the optic cup. The outer layer of the optic cup becomes the retinal pigmented epithelium, and the main part of the inner layer of the optic cup forms later the neural retina with six different types of cells including the photoreceptors. The retinal ganglion cells grow toward the optic stalk forming the optic nerve. This review describes the major molecular players and cellular processes during eye development as they are known from frogs, zebrafish, chick, and mice-showing also differences among species and missing links for future research. The relevance to human disorders is one of the major aspects covered throughout the review.

Molecular genetics of the aip gene in familial pituitary tumorigenesis

Pituitary adenomas usually occur as sporadic tumors, but familial cases are now increasingly identified. As opposed to multiple endocrine neoplasia type 1 and Carney complex, in familial isolated pituitary adenoma (FIPA) syndrome no other disease is associated with the familial occurrence of pituitary adenomas. It is an autosomal dominant disease with incomplete variable penetrance. Approximately 20% of patients with FIPA harbour germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene located on 11q13. Patients with AIP mutations have an overwhelming predominance of somatotroph and lactotroph adenomas, which often present in childhood or young adulthood. AIP, originally identified as a molecular co-chaperone of several nuclear receptors, is thought to act as a tumor suppressor gene; overexpression of wild-type, but not mutant AIP, reduces cell proliferation while knockdown of AIP stimulates it. AIP is shown to bind various proteins, including the aryl hydrocarbon receptor, Hsp90, phosphodiesterases, survivin, RET and the glucocorticoid receptor, but currently it is not clear which interaction has the leading role in pituitary tumorigenesis. This chapter summarizes the available clinical and molecular data regarding the role of AIP in the pituitary gland.

Acromegaly pathogenesis and treatment

Dysregulated growth hormone (GH) hypersecretion is usually caused by a GH-secreting pituitary adenoma and leads to acromegaly - a disorder of disproportionate skeletal, tissue, and organ growth. High GH and IGF1 levels lead to comorbidities including arthritis, facial changes, prognathism, and glucose intolerance. If the condition is untreated, enhanced mortality due to cardiovascular, cerebrovascular, and pulmonary dysfunction is associated with a 30% decrease in life span. This Review discusses acromegaly pathogenesis and management options. The latter include surgery, radiation, and use of novel medications. Somatostatin receptor (SSTR) ligands inhibit GH release, control tumor growth, and attenuate peripheral GH action, while GH receptor antagonists block GH action and effectively lower IGF1 levels. Novel peptides, including SSTR ligands, exhibiting polyreceptor subtype affinities and chimeric dopaminergic-somatostatinergic properties are currently in clinical trials. Effective control of GH and IGF1 hypersecretion and ablation or stabilization of the pituitary tumor mass lead to improved comorbidities and lowering of mortality rates for this hormonal disorder.

Key signaling molecules in pituitary tumors

In pituitary tumorigenesis there is cross-talk between fine deregulation of intracellular pathways and complex microenvironmental factors, processes that can be modulated at various levels. The signaling pathways of growth, angiogenic factors and hormones are intricate; therefore, alterations induced upon node-molecules can lead to aberrant proliferation. The demonstrated overactivity of AKT and MAPK pathways qualifies them as valuable targets for inhibition mediated by somatostatin analogues. An increasing body of evidence suggests clinically significant implications of PTTG1 in correlation with aggressive phenotypes or survival rate, thus PTTG1 is an interesting candidate biomarker for malignancy, tumor staging and subsequent therapeutic interventions. Future work should focus on understanding the molecular mechanisms that control pituitary tumor transformation, where intracellular signaling molecules will constitute not only diagnostic/prognostic markers but also novel therapeutic targets.

The expression of AIP-related molecules in elucidation of cellular pathways in pituitary adenomas

Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to the development of pituitary adenomas. Here, we characterized AIP mutation positive (AIPmut+) and AIP mutation negative (AIPmut-) pituitary adenomas by immunohistochemistry. The expressions of the AIP-related proteins aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT), cyclin-dependent kinase inhibitor 1B encoding p27(Kip1), and hypoxia-inducible factor 1-alpha were examined in 14 AIPmut+ and 53 AIPmut- pituitary adenomas to detect possible expression differences. In addition, the expression of CD34, an endothelial and hematopoietic stem cell marker, was analyzed. We found ARNT to be less frequently expressed in AIPmut+ pituitary adenomas (P = 0.001), suggesting that AIP regulates the ARNT levels. AIP small interfering RNA-treated HeLa, HEK293, or Aip-null mouse embryonic fibroblast cells did not show lowered expression of ARNT. Instead, in the pituitary adenoma cell line GH3, Aip silencing caused a partial reduction of Arnt and a clear increase in cell proliferation. We also observed a trend for increased expression of nuclear AHR in AIPmut+ samples, although the difference was not statistically significant (P = 0.06). The expressions of p27(Kip1), hypoxia-inducible factor 1-alpha, or CD34 did not differ between tumor types. The present study shows that the expression of ARNT protein is significantly reduced in AIPmut+ tumors. We suggest that the down-regulation of ARNT may be connected to an imbalance in AHR/ARNT complex formation arising from aberrant cAMP signaling.

The pathophysiology of pituitary adenomas

The pathogenesis of tumour formation in the anterior pituitary has been intensively studied, but the causative mechanisms involved in pituitary cell transformation and tumourigenesis remain elusive. Most pituitary tumours are sporadic, but some arise as a component of genetic syndromes such as the McCune-Albright syndrome, multiple endocrine neoplasia type 1, Carney complex and, the most recently described, a MEN1-like phenotype (MEN4) and pituitary adenoma predisposition syndromes. Some specific genes have been identified that predispose to pituitary neoplasia (GNAS, MEN1, PRKAR1A, CDKN1B and AIP), but these are rarely involved in the pathogenesis of sporadic tumours. Mutations of tumour suppressor genes or oncogenes, as seen in more common cancers, do not seem to play an important role in the great majority of pituitary adenomas. The pituitary tumour transforming gene (PTTG; securin) was the first transforming gene found to be highly expressed in pituitary tumour cells, and seems to play an important role in the process of oncogenesis. Many tumour suppressor genes, especially those involved in the regulation of the cell cycle, are under-expressed, most often by epigenetic modulation - usually promoter hypermethylation - but the regulator of these co-ordinated series of methylations is also unclear. Cell signalling abnormalities have been identified in pituitary tumours, but their genetic basis is unknown. Both Raf/MEK/ERK and PI3K/Akt/mTOR pathways are over-expressed and/or over-activated in pituitary tumours: these pathways share a common root, including initial activation related to the tyrosine kinase receptor, and we speculate that a change to these receptors or their relationship to membrane matrix-related proteins may be an early event in pituitary tumourigenesis.

The epidemiology and genetics of pituitary adenomas

According to data derived from autopsy and radiological imaging series, pituitary tumours occur very commonly in the general population; however, most of these tumours are incidental findings with no obvious clinical impact. The historical data on the prevalence of pituitary adenomas in the clinical setting are scant and point to such tumours being relatively rare. Recent studies have shown that the prevalence of clinically relevant pituitary adenomas is 3-5 times higher than previously reported, which adds impetus to research into the aetiology of these tumours. Although the majority of pituitary adenomas are sporadic, approximately 5% of all cases occur in a familial setting and over half of these are due to Multiple Endocrine Neoplasia Type 1 (MEN-1) and Carney's Complex (CNC) disorders. Since the late 1990 s, we have described non-MEN1/CNC familial pituitary tumours that include all tumour phenotypes as a condition termed Familial Isolated Pituitary Adenomas (FIPAs). The clinical characteristics of the FIPAs vary from those sporadic pituitary adenomas, as patients with FIPAs have a younger age at diagnosis and larger tumours. About 15% of the FIPA patients have mutations in the aryl hydrocarbon receptor-interacting protein gene (AIP), which indicates that the FIPA may have a diverse genetic pathophysiology.

The notch target gene HES1 regulates cell cycle inhibitor expression in the developing pituitary

The pituitary is an endocrine gland responsible for the release of hormones, which regulate growth, metabolism, and reproduction. Diseases such as hypopituitarism or pituitary adenomas are able to disrupt pituitary function leading to suboptimal function of the entire endocrine system. Growth of the pituitary during development and adulthood is a tightly regulated process. Hairy and enhancer of split (HES1), a transcription factor whose expression is initiated by the Notch signaling pathway, is a repressor of cell cycle inhibitors. We hypothesize that with the loss of Hes1, pituitary progenitors are no longer maintained in a proliferative state, choosing instead to exit the cell cycle. To test this hypothesis, we examined the expression of cell cycle regulators in wild-type and Hes1-deficient pituitaries. Our studies indicate that in early pituitary development [embryonic day (e) 10.5], cells contained in the Rathke's pouch of Hes1 mutants have decreased proliferation, indicated by changes in phosphohistone H3 expression. Furthermore, pituitaries lacking Hes1 have increased cell cycle exit, shown by significant increases in the cyclin-dependent kinase inhibitors, p27 and p57, from e10.5 to e14.5. Additionally, Hes1 mutant pituitaries have ectopic expression of p21 in Rathke's pouch progenitors, an area coincident with increased cell death. These observations taken together indicate a role for HES1 in the control of cell cycle exit and in mediating the balance between proliferation and differentiation, allowing for the properly timed emergence of hormone secreting cell types.

Familial pituitary tumor syndromes

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

[Molecular aspects of pituitary tumorigenesis]

Pituitary tumors, almost invariably adenomas, are of frequent occurrence, accounting for 10% to 15% of all the intracranial neoplasm. They are classified as microadenomas (< 10 mm) or macroadenomas (> 10 mm) and as secreting or clinically non-secreting (or not functioning) adenomas. These tumors are autonomously capable to release pituitary hormones such as the growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone (ACTH), thyroid stimulating hormone (TSH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The occurrence of metastases, characterizing a pituitary carcinoma, is exceedingly rare. However tumors with aggressive behavior, leading to local invasion, are relatively common. Although the pathogenesis of pituitary tumors is fully characterized, many molecular mechanisms of pituitary tumorigenesis had already been revealed. This review intends to describe advances in the understanding of the involved advances that have been made in the last decade concerning pituitary tumors progression, including the participation of oncogenes, tumor suppressor genes and growth factors.

Multiple endocrine neoplasias: advances and challenges for the future

Several important advances have been made over the last 2 years, since the last international workshop on multiple endocrine neoplasias (MENs) that was held in Marseilles, France (MEN2006). The series of articles that are included in this issue summarize the most important of these advances as they were presented in Delphi, Greece, during the 11th International Workshop on MENs, September 25-27, 2008 (MEN2008). This editorial summarizes some of these advances: the identification of the AIP, and the PDE11A and PDE8B genes by genome-wide association (GWA) studies as predisposing genes for pituitary and adrenal tumours, respectively, the discovery of p27 mutations in a new form of MEN similar to MEN type 1 (MEN 1) that is now known as MEN 4, the molecular investigations of Carney triad (CT), a disorder that associates paragangliomas (PGLs), gastrointestinal stromal tumour (GISTs), and pulmonary chondromas (PCH) with pheochromocytomas and adrenocortical adenomas and other lesions, and the molecular elucidation of the association of GISTs with paragangliomas (Carney-Stratakis syndrome) that is now known to be because of SDHB, SDHC, and SDHD mutations. Molecular investigations in Carney complex (another MEN also described by Dr. Carney, who during the meeting, along with Dr. Charles E. ('Gene') Jackson was honoured for his life-long and many contributions to the field) have also revealed the role of cyclic AMP signalling in tumorigenesis. As our knowledge of the molecular causes of MENs increases, the challenge is to translate these discoveries in better treatments for our patients. Indeed, new advances in the preventive diagnosis and molecular treatment of MEN 1 and MEN 2, respectively, continued unabated, and an update on this front was also presented at MEN2008 and is included in this issue.

Multiple endocrine neoplasia type 1: a chromatin writer's block

Multiple endocrine neoplasia type 1 (MEN1) is caused by inactivating germ line mutations of the MEN1 tumour suppressor gene. The MEN1 gene product, menin, participates in many cellular processes, including regulation of gene transcription. As part of a protein complex that writes a trimethyl mark on lysine 4 of histone H3 (H3K4me3), menin is involved in activating gene transcription. Several functions of the menin histone methyltransferase complex have been discovered through protein interaction studies. Menin can interact with nuclear receptors and regulate transcription of hormone responsive target genes. Menin regulates transcription of cyclin-dependent kinase inhibitor and Hox genes via the chromatin-associated factor LEDGF. Aberrant expression of menin target genes in tumours in MEN1 patients suggests that loss of writing of the H3K4me3 mark contributes to MEN1 tumourigenesis. At present, drugs are being developed that target chromatin modifications. The identification of compounds that could restore H3K4me3 on menin target genes would provide new therapeutic strategies for MEN1 patients.

Familial pituitary adenomas

The majority of pituitary adenomas occur sporadically, however, about 5% of all cases occur in a familial setting, of which over half are due to multiple endocrine neoplasia type 1 (MEN-1) and Carney's complex (CNC). Since the late 1990s we have described non-MEN1/CNC familial pituitary tumours that include all tumour phenotypes, a condition named familial isolated pituitary adenomas (FIPA). The clinical characteristics of FIPA vary from those of sporadic pituitary adenomas, as patients with FIPA have a younger age at diagnosis and larger tumours. About 15% of FIPA patients have mutations in the aryl hydrocarbon receptor interacting protein gene (AIP), which indicates that FIPA may have a diverse genetic pathophysiology. This review describes the clinical features of familial pituitary adenomas like MEN1, the MEN 1-like syndrome MEN-4, CNC, FIPA, the tumour pathologies found in this setting and the genetic/molecular data that have been recently reported.

Multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal-dominant inherited tumor syndrome characterized by hyperplasia and/or tumors in the parathyroid glands, the pancreatic islets, the anterior pituitary and adrenal glands, as well as neuroendocrine tumors in the thymus, lungs and stomach, and tumors in nonendocrine tissues. In 1997, the responsible MEN1 gene was identified as a tumor-suppressor gene and its product was named menin. In this review, guidelines for early diagnosis, including MEN1 gene mutation analysis, and treatment, including periodic clinical monitoring, have been formulated, enabling improvement of life expectancy and quality of life. Identification of menin-interacting proteins has provided new insights into the function of menin, notably involving regulation of gene transcription related to proliferation and apoptosis, genome stability and DNA repair, and endocrine/metabolic homeostasis. In the near future, target-directed intervention may prevent or delay the onset of MEN 1-related tumors.

Mutation analysis of MEN1, HRPT2, CASR, CDKN1B, and AIP genes in primary hyperparathyroidism patients with features of genetic predisposition

OBJECTIVE

Primary hyperparathyroidism (PHPT), a common endocrine condition, is usually caused by sporadically occurring parathyroid adenoma. A subset of patients carry germline mutations in genes such as MEN1 (multiple endocrine neoplasia type 1), HRPT2 (hyperparathyroidism 2), and CASR (calcium-sensing receptor) predisposing to syndromic forms of PHPT or familial isolated hyperparathyroidism (FIHP). Recently, germline mutations in two novel genes AIP (aryl hydrocarbon receptor-interacting protein) and CDKN1B (cyclin-dependent kinase inhibitor 1B) have been found to be associated with endocrine tumors. The purpose of this study was to evaluate the role of MEN1, HRPT2, CASR, AIP, and CDKN1B genes in PHPT patients with clinical features suggestive of genetic predisposition.

PATIENTS AND DESIGN

Medical records of patients treated for PHPT from 1974 to 2001 at Oulu University Hospital were reviewed. Patients with multiglandular or recurrent/persistent disease, other MEN1- related manifestations, aged 40 yr or younger at onset or with a family history of PHPT/MEN1-related tumor were invited to the study. Twenty patients with previously diagnosed MEN1 were excluded. Participants were interviewed and blood samples obtained for biochemical screening and mutation analysis of MEN1, HRPT2, CASR, AIP, and CDKN1B.

RESULTS

Of the 56 invited patients, 29 took part in the study. One patient was found to carry the c. 1356_1367del12 MEN1 founder mutation. Mutations in other genes were not detected.

CONCLUSIONS

Apart from MEN1, mutations in other genes predisposing to PHPT seem to be rare or non-existing in Northern Finnish PHPT patients. No evidence was found for a role of AIP or CDKN1B in PHPT predisposition.

Rare germline mutations in cyclin-dependent kinase inhibitor genes in multiple endocrine neoplasia type 1 and related states

CONTEXT

Germline mutation in the MEN1 gene is the usual cause of multiple endocrine neoplasia type 1 (MEN1). However, the prevalence of identifiable germline MEN1 mutations in familial MEN1 cases is only 70%. Some cases may have a germline mutation in another gene such as the p27 cyclin-dependent kinase inhibitor (CDKI).

OBJECTIVE

The aim of the study was to investigate cases of MEN1 or related states for germline mutations in all CDKI genes.

METHODS

A total of 196 consecutive index cases were selected with clear or suspected MEN1 and no identifiable germline MEN1 mutation. Every case was analyzed for germline mutation in each of the seven CDKI genes.

RESULTS

We identified benign polymorphisms of the CDKI genes and also 15 other initially unclassified sequence variants. After detailed gene/protein analysis, seven of these 15 variants were classified as probably pathological mutations. Three of these seven were probable mutations of p27. The remaining four were probable pathological mutations in three of the other CDKI genes, thereby implicating these three genes in the germline of human tumors. The identification rates for probably pathological mutations among the 196 index cases were similarly low for each of four CDKI genes: p15 (1%), p18 (0.5%), p21 (0.5%), and p27 (1.5%). No characteristic clinical subtype related to MEN1 was identified among the seven index cases and their families.

CONCLUSION

Rare germline mutation in any among four (p15, p18, p21, and p27) of the seven CDKIs is a probable cause of MEN1 or of some related states.

The MEN1 gene and pituitary tumours

Sporadic multiple endocrine neoplasia type 1 (MEN1) is defined as the occurrence of tumours in two of three main endocrine tissue types: parathyroid, pituitary and pancreaticoduodenal. A prolactinoma variant or Burin variant of MEN1 was found to occur in three large kindreds, with more prolactinomas and fewer gastrinomas than typical MEN1. MEN1 tumours differ from common tumours by showing features from the MEN1 gene (e.g. larger pituitary tumours). They also show various expressions of tumour multiplicity; however, pituitary tumour in MEN1 is usually solitary. Diagnosis in MEN1 carriers during childhood is not directed at cancers but at benign morbid tumours. Morbid prolactinoma occurred at the age of 5 years in one MEN1 individual; hence, this is the earliest age at which to recommend tumour surveillance in carriers. The MEN1 gene shows biallelic inactivation in 30% of some types of common variety endocrine tumours (e.g. parathyroid adenoma, gastrinoma, insulinoma and bronchial carcinoid), but in only 1-5% of common pituitary tumours. Heterozygous knockout of MEN1 in mice provides a robust model of MEN1 and has been found to support further research on anti-angiogenesis therapy for pituitary tumours. The rarity of MEN1 mutations in some MEN1-like states aids the identification of other mutated genes, such as AIP, HRPT2 and p27(Kip1). We present recent clinical and basic findings about the MEN1 gene, particularly concerning hereditary vs. common variety pituitary tumours.

Endocrine dysfunction in p27Kip1 deficient mice and susceptibility to Wnt-1 driven breast cancer

The cyclin-dependent kinase (Cdk) inhibitor p27(Kip1) (p27) is a marker of prognosis in many cancers, including breast cancer. Low p27 expression correlates with poor prognosis, especially in hormone receptor positive breast tumors. This association suggests a role for p27 in hormone-dependent cancer. We used the Wnt-1 transgenic mouse model to further explore the role of p27 in hormone-driven breast cancer. We found that p27 deficiency did not alter breast cancer rate in either male or female Wnt-1 mice. However, we did find p27-/- females had reduced levels of serum progesterone (P) and increased variability in estradiol (E), which could have affected their cancer susceptibility. To equalize hormone levels, an additional cohort of Wnt-1 female mice was ovariectomized and implanted with slow release pellets of E and P. Although this treatment did not alter the breast cancer rate, it did accelerate the development of pituitary and gastric tumors in p27-/- mice. This study shows that while not a significant inhibitor of Wnt-1-driven breast cancer, p27 inhibits gastric tumors, whose latency is modulated by sex steroids.

Assessment of p27 (cyclin-dependent kinase inhibitor 1B) and aryl hydrocarbon receptor-interacting protein (AIP) genes in multiple endocrine neoplasia (MEN1) syndrome patients without any detectable MEN1 gene mutations

OBJECTIVE

Germline mutations in the MEN1 gene predispose to the multiple endocrine neoplasia (MEN1) syndrome; however, approximately 10-20% of patients with MEN1 do not have a detectable MEN1 mutation. A rat strain with multiple endocrine tumours, a phenotypic overlap of both MEN1 and MEN2, has been reported to have a homozygous germline p27 (CDKN1B) mutation. Recently, two MEN1 mutation-negative MEN1 syndrome patients have been identified to harbour a germline CDKN1B mutation. The recently identified gene AIP can also cause familial isolated pituitary adenoma, but no other specific tumour is associated with this syndrome. The objective of this study was to evaluate the possible contribution of CDKN1B and AIP germline mutations in a cohort of MEN1 mutation-negative MEN1 syndrome patients.

PATIENTS

Eighteen sporadic and three familial cases of MEN1 mutation-negative MEN1 syndrome were studied (18 pituitary adenomas, 12 hyperparathyroidism, 10 neuroendocrine tumours including 2 ACTH-secreting lesions and one adrenal nodular hyperplasia). Clinical data and genomic DNA were analysed for mutations in the CDKN1B and AIP genes.

RESULTS

There were no mutations in the coding region or exon/intron junction of the CDKN1B and AIP genes in any patient. Although we have a limited number of patients in our cohort, our data is consistent with others in the literature suggesting that CDKN1B and AIP mutations are extremely rare in MEN1 syndrome.

CONCLUSION

Our results suggest that mutations in the CDKN1B and AIP genes are relatively uncommon in MEN1 mutation-negative MEN1 syndrome patients.

MEN1 gene and its mutations: basic and clinical implications

Heterozygous germline mutations of the tumor-suppressor gene MEN1 are responsible for multiple endocrine neoplasia type 1 (MEN1), a dominantly inherited familial cancer syndrome characterized by pituitary, parathyroid, and enteropancreatic tumors. Various mutations have been identified throughout the entire gene region in patients with MEN1 and related disorders. Neither mutation hot spot nor phenotype–genotype correlation has been established in MEN1 although some missense mutations may be specifically associated with a phenotype of familial isolated hyperparathyroidism. The gene product menin has been implicated in multiple roles, including gene transcription, maintenance of genomic integrity, and control of cell division and differentiation. These multiple functions are likely to be conferred by association with multiple protein factors. Occurrence of MEN1-causing missense mutations throughout menin also suggests the requirement of multiple binding factors for its full tumor-suppressive activity. The effect of menin depletion is highly tissue specific, but its underlying mechanism remains to be elucidated. A DNA test for MEN1 germline mutations is a useful tool for diagnosis of MEN1 although it needs further improvements

Diagnosis of asymptomatic primary hyperparathyroidism: proceedings of the third international workshop

OBJECTIVE

Asymptomatic primary hyperparathyroidism (PHPT) is a common clinical problem. The purpose of this report is to guide the use of diagnostic tests for this condition in clinical practice.

PARTICIPANTS

Interested professional societies selected a representative for the consensus committee and provided funding for a one-day meeting. A subgroup of this committee set the program and developed key questions for review. Consensus was established at a closed meeting that followed. The conclusions were then circulated to the participating professional societies.

EVIDENCE

Each question was addressed by a relevant literature search (on PubMed), and the data were presented for discussion at the group meeting.

CONSENSUS PROCESS

Consensus was achieved by a group meeting. Statements were prepared by all authors, with comments relating to accuracy from the diagnosis subgroup and by representatives from the participating professional societies.

CONCLUSIONS

We conclude that: 1) reference ranges should be established for serum PTH in vitamin D-replete healthy individuals; 2) second- and third-generation PTH assays are both helpful in the diagnosis of PHPT; 3) DNA sequence testing can be useful in familial hyperparathyroidism or hypercalcemia; 4) normocalcemic PHPT is a variant of the more common presentation of PHPT with hypercalcemia; 5) serum 25-hydroxyvitamin D levels should be measured and, if vitamin D insufficiency is present, it should be treated as part of any management course; and 6) the estimated glomerular filtration rate should be used to determine the level of kidney function in PHPT: an estimated glomerular filtration rate of less than 60 ml/min.1.73 m2 should be a benchmark for decisions about surgery in established asymptomatic PHPT.

Glucagon cell adenomatosis: a newly recognized disease of the endocrine pancreas

BACKGROUND

Glucagon-producing tumors are either solitary neoplasms of the pancreas, occasionally associated with a glucagonoma syndrome, or multiple neoplasms associated with multiple endocrine neoplasia type 1 (MEN1). We observed a previously undescribed multicentric glucagon-producing tumor disease that is not related to MEN1.

METHODS

Pancreatic tissue from four patients showing multiple neuroendocrine microadenomas and in two cases also macrotumors were screened for hormones using immunohistochemical and morphometric methods. MEN1, von Hippel-Lindau, and p27 germ line and somatic mutation analysis was performed. Deletion of MEN1 (11q13), von Hippel-Lindau (3p25), and the centromere 11 and 3 gene locus was determined by fluorescence in situ hybridization. DNA copy number changes were studied using array comparative genomic hybridization.

RESULTS

The pancreatic tissue from the four patients contained more than 870 microadenomas and 10 macrotumors, all of which expressed exclusively glucagon and none of which showed evidence of malignancy. In addition, many islets were unusually large and showed glucagon cell hyperplasia. There was no clinical or molecular evidence of any hereditary tumor disease, and changes in the MEN1 gene were only seen in individual tumors. Array comparative genomic hybridization of one macrotumor and 20 pooled microadenomas revealed a homogeneous diploid chromosome set.

CONCLUSIONS

The findings are sufficiently distinctive to suggest a new neoplastic disease of the endocrine pancreas that we recommend calling glucagon cell adenomatosis. Clinically, this disease may be an incidental finding, or it may lead to a glucagonoma syndrome.

Pituitary gland and beta-catenin signaling: from ontogeny to oncogenesis

Although pituitary tumors are mostly benign, they share certain molecular events with more malignant neoplasia, although their precise pathogenesis is far from established. The acquisition of new functional characteristics during their evolution suggests a multistep process that leads to tumor transformation. Mutations in classical tumor suppressor genes or oncogenes are infrequently associated with pituitary tumorigenesis. However, alterations in different signaling pathways, especially those involved in pituitary gland development, have emerged as significant features in pituitary adenomas. In particular, changes in inhibitory components of the beta-catenin pathway and its relationship to the cadherin family of peptides may well play an important role in tumorigenesis. We review and assess the role of the beta-catenin signaling pathway in the pathogenesis of pituitary adenomas.

Hypercalcitoninemia is not pathognomonic of medullary thyroid carcinoma

Hypercalcitoninemia has frequently been reported as a marker for medullary thyroid carcinoma. Currently, calcitonin measurements are mostly useful in the evaluation of tumor size and progression, and as an index of biochemical improvement of medullary thyroid carcinomas. Although measurement of calcitonin is a highly sensitive method for the detection of medullary thyroid carcinoma, it presents a low specificity for this tumor. Several physiologic and pathologic conditions other than medullary thyroid carcinoma have been associated with increased levels of calcitonin. Several cases of thyroid nodules associated with increased values of calcitonin are not medullary thyroid carcinomas, but rather are related to other conditions, such as hypercalcemias, hypergastrinemias, neuroendocrine tumors, renal insufficiency, papillary and follicular thyroid carcinomas, and goiter. Furthermore, prolonged treatment with omeprazole (>2-4 months), beta-blockers, glucocorticoids and potential secretagogues, have been associated with hypercalcitoninemia. An association between calcitonin levels and chronic auto-immune thyroiditis remains controversial. Patients with calcitonin levels >100 pg/mL have a high risk for medullary thyroid carcinoma (approximately 90%-100%), whereas patients with values from 10 to 100 pg/mL (normal values: <8.5 pg/mL for men, <5.0 pg/mL for women; immunochemiluminometric assay) have a <25% risk for medullary thyroid carcinoma.In multiple endocrine neoplasia type 2 (MEN2), RET mutation analysis is the gold-standard for the recommendation of total preventive thyroidectomy to relatives at risk of harboring a germline RET mutation (50%). False-positive calcitonin results within MEN2 families have led to incorrect indications of preventive total thyroidectomy to RET mutation negative relatives. In this review, we focus on the differential diagnosis of hypercalcitoninemia, underlining its importance for the avoidance of misdiagnosis of medullary thyroid carcinoma and consequent incorrect recommendation for thyroid surgery.

Unusual clinical and pathological presentation of a neuroendocrine tumor in a patient with multiple endocrine neoplasia type 1

Neuroendocrine tumors develop in various organs in patients with multiple endocrine neoplasia type 1 (MEN1). Among those, tumors developed in upper gastrointestinal tract, thymus and bronchus have historically been called "carcinoid tumor". Occurrence of "carcinoid tumor" in other region is very rare and molecular pathogenesis of such tumors is unknown. We have experienced a patient with MEN1 who have developed an "ectopic" retroperitoneal neuroendocrine tumor. Genetic analysis of the MEN1 gene in tumor cells revealed a somatic mutation in exon 9 as well as a germline mutation in exon 10. Allele-specific amplification followed by sequence analysis revealed these two mutations exist on the different allele, indicating both alleles are functionally inactivated. Immunohistochemical staining with an anti-menin antibody revealed that wild-type menin is not expressed in tumor cells. Expression of p27(Kip1) protein is not observed in tumor cells, either. These results confirmed the inactivation of the MEN1 gene as a genetic cause of an ectopically developed neuroendocrine tumor in a patient with MEN1.

Novel germline mutations of the MEN1 gene in Greek families with multiple endocrine neoplasia type 1

INTRODUCTION

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant hereditary disorder associated with mutations of the MEN1 gene and characterized by the combined occurrence of tumours of the parathyroid glands, the pancreatic islet cells and the anterior pituitary.

AIM

To identify MEN1 gene mutations and characterize clinical manifestations in Greek patients with MEN1.

PATIENTS AND METHODS

We studied four unrelated index patients with MEN1, 17 relatives and 100 control subjects. Among the relatives, seven were clinically and/or biochemically affected, while 10 were unaffected. DNA extraction, polymerase chain reaction (PCR) and direct sequencing of the MEN1 exons 2-10 and exon/intron boundaries were performed according to standard procedures.

RESULTS

We identified novel MEN1 gene mutations in three out of four index patients (75%) and in all affected (100%) relatives. Novel mutations included: a frameshift mutation in exon 4 (c.684_685insG) at codon 229 (index patient A); a frameshift mutation in exon 8 (c.1160_1170dupAGGAGCGGCCG) involving codons 387-390 (index patient B); and a missense mutation in exon 4 (c.776T > C), which substitutes leucine with proline at codon 259 (L259P) (index patient C). In the fourth index patient, a common polymorphism (D418D) was detected.

CONCLUSIONS

This is the first report to reveal a high prevalence of novel MEN1 gene mutations among Greek MEN1 patients with apparent absence of genotype-phenotype correlation. Because of the small number of patients examined, the high prevalence detected might be a chance phenomenon.

Update on the treatment of pituitary adenomas: familial and genetic considerations

Clinically-relevant pituitary adenomas occur with a prevalence of approximately 1 per 1000 population in Belgium. Pituitary adenomas that occur in families are likely to have an important genetic pathophysiological basis. Currently about 5% of all pituitary adenoma cases have a family history of pituitary adenomas, classically due to multiple endocrine neoplasia type 1 (MEN1) and Carney complex (CNC). Over the last decade we have described non-MEN1/CNC familial pituitary tumours that include all tumour phenotypes, a condition named 'familial isolated pituitary adenoma' (FIPA). Clinical features of FIPA differ from those of sporadic pituitary adenomas in that patients with FIPA are often younger and have larger tumours at diagnosis. Approximately 15% of FIPA patients have mutations in the aryl hydrocarbon receptor interacting protein gene (AIP), which indicates that FIPA may have a diverse genetic pathophysiology. In this review we examine new findings on the epidemiology of pituitary adenomas and we review familial causes of pituitary adenomas with a particular emphasis on modern clinical testing. In addition, the clinical and genetic features of FIPA are described as FIPA represents a useful framework to study the features of pituitary adenomas that occur in a familial setting.

A functional genome-wide RNAi screen identifies TAF1 as a regulator for apoptosis in response to genotoxic stress

Evasion from apoptotic cell death is a characteristic of cancer; genes that modulate this process may be optimal for therapeutic attack. Identifying key regulators of apoptosis is thus a central goal in cancer therapy. Here, we describe a loss-of-function screen that uses RNA interference libraries to identify genes required for induction of apoptosis. We used a short-hairpin RNA expressing vector with high gene-expression silencing activity that contained fetal brain cDNAs. Survived cells from genotoxic stress were isolated to determine knock-down of molecules that are crucial for induction of apoptosis. We identified TBP-associated factor 1 (TAF1), a gene previously implicated as an essential component of transcription machinery. Depletion of TAF1 was associated with substantial attenuation of apoptosis induced by oxidative as well as genotoxic stress. Microarray analysis further demonstrated that a number of genes were transcriptionally declined in cells silenced for TAF1. Surprisingly, knocking down TAF1 exhibited a marked decrease in p27(Kip1) expression, allowing cells resistant from oxidative stress-induced apoptosis. These results suggest that TAF1 regulates apoptosis by controlling p27(Kip1) expression. Our system provides a novel approach to identifying candidate genes that modulate apoptosis.