Germline mutations of the aryl hydrocarbon receptor (AHR)-interacting protein (AIP) gene confer a predisposition to pituitary adenomas (PA), usually in the setting of familial isolated PA. To provide further insights into the possible role of AIP in pituitary tumour pathogenesis, the expression of AIP and AHR was determined by real-time RT-PCR and/or immunohistochemistry (IHC) in a large series of PA (n=103), including 17 with AIP mutations (AIP mut). Variable levels of AIP and AHR transcripts were detected in all PA, with a low AHR expression (P<0.0001 versus AIP). Cytoplasmic AIP and AHR were detected by IHC in 84.0 and 38.6% of PA respectively, and significantly correlated with each other (P=0.006). Nuclear AHR was detected in a minority of PA (19.7%). The highest AIP expression was observed in somatotrophinomas and non-secreting (NS) PA, and multivariate analysis in somatotrophinomas showed a significantly lower AIP immunostaining in invasive versus non-invasive cases (P=0.019). AIP expression was commonly low in other secreting PA. AIP immunostaining was abolished in a minority of AIP mut PA, with a frequent loss of cytoplasmic AHR and no evidence of nuclear AHR. In contrast, AIP overexpression in a subset of NS PA could be accompanied by nuclear AHR immunopositivity. We conclude that down-regulation of AIP and AHR may be involved in the aggressiveness of somatotrophinomas. Overall, IHC is a poorly sensitive tool for the screening of AIP mutations. Data obtained on AHR expression suggest that AHR signalling may be differentially affected according to PA phenotype.
Marie-Lise Jaffrain-Rea, Mariolina Angelini, Donatella Gargano, Maria A Tichomirowa, Adrian F Daly, Jean-François Vanbellinghen, Emanuela D'Innocenzo, Anne Barlier, Felice Giangaspero, Vincenzo Esposito, Luca Ventura, Antonietta Arcella, Marily Theodoropoulou, Luciana A Naves, Carmen Fajardo, Sabina Zacharieva, Vincent Rohmer, Thierry Brue, Alberto Gulino, Giampaolo Cantore, Edoardo Alesse, and Albert Beckers
R Formosa, J Borg, and J Vassallo
Pituitary adenomas (PA) represent the largest group of intracranial neoplasms and yet the molecular mechanisms driving this disease remain largely unknown. The aim of this study was to use a high-throughput screening method to identify molecular pathways that may be playing a significant and consistent role in PA. RNA profiling using microarrays on eight local PAs identified the aryl hydrocarbon receptor (AHR) signalling pathway as a key canonical pathway downregulated in all PA types. This was confirmed by real-time PCR in 31 tumours. The AHR has been shown to regulate cell cycle progression in various cell types; however, its role in pituitary tissue has never been investigated. In order to validate the role of AHR in PA behaviour, further functional studies were undertaken. Over-expression of AHR in GH3 cells revealed a tumour suppressor potential independent of exogenous ligand activation by benzo α-pyrene (BαP). Cell cycle analysis and quantitative PCR of cell cycle regulator genes revealed that both unstimulated and BαP-stimulated AHR reduced E2F-driven transcription and altered expression of cell cycle regulator genes, thus increasing the percentage of cells in G0/G1 phase and slowing the proliferation rate of GH3 cells. Co-immunoprecipitation confirmed the interaction between AHR and retinoblastoma (Rb1) protein supporting this as a functional mechanism for the observed reduction. Endogenous Ahr reduction using silencing RNA confirmed the tumour suppressive function of the Ahr. These data support a mechanistic pathway for the putative tumour suppressive role of AHR specifically in PA, possibly through its role as a cell cycle co-regulator, even in the absence of exogenous ligands.
H E Turner, N R Moore, J V Byrne, and J A H Wass
The use of increasingly sophisticated imaging techniques has produced a new clinical problem: namely the evaluation and management of the serendipitously discovered mass-‘incidentaloma’. In the last 50 years of endocrinology, these lesions have been described mainly in the adrenal and pituitary glands by pathologists on the basis of autopsy series of patients assumed to have been asymptomatic. The current challenge is the investigation of these common lesions which are now more commonly detected during life, to allow not only the correct identification and investigation of those with a hypersecretory syndrome whether it be clinically apparent or subclinical, but also the correct identification of those masses which are malignant and which may therefore produce significant problems in the future. As more experience is gained on the natural history of the true incidentaloma, appropriate follow-up and treatment can be instigated as necessary. The rationale of investigations therefore should be to evaluate most accurately and cost-effectively which patients do not have an incidentaloma, but a lesion that requires further active treatment.
Xiao-Hua Jiang, Jie-Li Lu, Bin Cui, Yong-Ju Zhao, Wei-qing Wang, Jian-Min Liu, Wen-Qiang Fang, Ya-Nan Cao, Yan Ge, Chang-xian Zhang, Huguette Casse, Xiao-Ying Li, and Guang Ning
Multiple endocrine neoplasia type 1 (MEN1) is an inherited tumour syndrome characterized by the development of tumours of the parathyroid, anterior pituitary and pancreatic islets, etc. Heterozygous germ line mutations of MEN1 gene are responsible for the onset of MEN1. We investigated the probands and 31 family members from eight unrelated Chinese families associated with MEN1 and identified four novel mutations, namely 373_374ins18, 822delT, 259delT and 1092delC, as well as three previously reported mutations, such as 357_360delCTGT, 427_428delTA and R108X (CGA>TGA) of MEN1 gene. Furthermore, we detected a loss of heterozygosity (LOH) at chromosome 11q in the removed tumours, including gastrinoma, insulinoma and parathyroid adenoma from two probands of MEN1 families. RT-PCR and direct sequencing showed that mutant MEN1 transcripts remained in the MEN1-associated endocrine tumours, whereas normal menin proteins could not be detected in those tumours by either immunohistochemistry or immunoblotting. In conclusion, MEN1 heterozygous mutations are associated with LOH and menin absence, which are present in MEN1-associated endocrine tumours.
Kerong Shi, Vaishali I Parekh, Swarnava Roy, Shruti S Desai, and Sunita K Agarwal
The multiple endocrine neoplasia type 1 (MEN1) syndrome is caused by germline mutations in the MEN1 gene encoding menin, with tissue-specific tumors of the parathyroids, anterior pituitary, and enteropancreatic endocrine tissues. Also, 30–40% of sporadic pancreatic endocrine tumors show somatic MEN1 gene inactivation. Although menin is expressed in all cell types of the pancreas, mouse models with loss of menin in either pancreatic α-cells, or β-cells, or total pancreas develop β-cell-specific endocrine tumors (insulinomas). Loss of widely expressed tumor suppressor genes may produce tissue-specific tumors by reactivating one or more embryonic-specific differentiation factors. Therefore, we determined the effect of menin overexpression or knockdown on the expression of β-cell differentiation factors in a mouse β-cell line (MIN6). We show that the β-cell differentiation factor Hlxb9 is posttranscriptionally upregulated upon menin knockdown, and it interacts with menin. Hlxb9 reduces cell proliferation and causes apoptosis in the presence of menin, and it regulates genes that modulate insulin level. Thus, upon menin loss or from other causes, dysregulation of Hlxb9 predicts a possible combined mechanism for β-cell proliferation and insulin production in insulinomas. These observations help to understand how a ubiquitously expressed protein such as menin might control tissue-specific tumorigenesis. Also, our findings identify Hlxb9 as an important factor for β-cell proliferation and insulin regulation.
M T Barakat, K Meeran, and S R Bloom
Neuroendocrine tumours are a heterogeneous group including, for example, carcinoid, gastroenteropancreatic neuroendocrine tumours, pituitary tumours, medullary carcinoma of the thyroid and phaeochromocytomas. They have attracted much attention in recent years, both because they are relatively easy to palliate and because they have indicated the chronic effect of the particular hormone elevated. As neuroendocrine phenotypes became better understood, the definition of neuroendocrine cells changed and is now accepted as referring to cells with neurotransmitter, neuromodulator or neuropeptide hormone production, dense-core secretory granules, and the absence of axons and synapses. Neuroendocrine markers, particularly chromogranin A, are invaluable diagnostically. Study of several neuroendocrine tumours has revealed a genetic etiology, and techniques such as genetic screening have allowed risk stratification and prevention of morbidity in patients carrying the particular mutation. Pharmacological therapy for these often slow-growing tumours, e.g. with somatostatin analogues, has dramatically improved symptom control, and radiolabelled somatostatin analogues offer targeted therapy for metastatic or inoperable disease. In this review, the diagnosis and management of patients with carcinoid, gut neuroendocrine tumours, multiple endocrine neoplasia types 1 and 2, and isolated phaeochromocytoma are evaluated.
Anna Angelousi, Eva Kassi, Narjes Ansari-Nasiri, Harpal Randeva, Gregory Kaltsas, and George Chrousos
Circadian rhythms at a central and peripheral level are operated by transcriptional/translational feedback loops involving a set of genes called ‘clock genes’ that have been implicated in the development of several diseases, including malignancies. Dysregulation of the Clock system can influence cancer susceptibility by regulating DNA damage and repair mechanisms, as well as apoptosis. A number of oncogenic pathways can be dysregulated via clock genes’ epigenetic alterations, including hypermethylation of clock genes’ promoters or variants of clock genes. Clock gene disruption has been studied in breast, lung and prostate cancer, and haematological malignancies. However, it is still not entirely clear whether clock gene disruption is the cause or the consequence of tumourigenesis and data in endocrine neoplasms are scarce. Recent findings suggest that clock genes are implicated in benign and malignant adrenocortical neoplasias. They have been also associated with follicular and papillary thyroid carcinomas and parathyroid adenomas, as well as pituitary adenomas and craniopharyngiomas. Dysregulation of clock genes is also encountered in ovarian and testicular tumours and may also be related with their susceptibility to chemotherapeutic agents. The most common clock genes that are implicated in endocrine neoplasms are PER1, CRY1; in most cases their expression is downregulated in tumoural compared to normal tissues. Although there is still a lot to be done for the better understanding of the role of clock genes in endocrine tumourigenenesis, existing evidence could guide research and help identify novel therapeutic targets aiming mainly at the peripheral components of the clock gene system.
Catherine Goudie, Fady Hannah-Shmouni, Mahmure Kavak, Constantine A Stratakis, and William D Foulkes
As medicine is poised to be transformed by incorporating genetic data in its daily practice, it is essential that clinicians familiarise themselves with the information that is now available from more than 50 years of genetic discoveries that continue unabated and increase by the day. Endocrinology has always stood at the forefront of what is called today ‘precision medicine’: genetic disorders of the pituitary and the adrenal glands were among the first to be molecularly elucidated in the 1980s. The discovery of two endocrine-related genes, GNAS and RET, both identified in the late 1980s, contributed greatly in the understanding of cancer and its progression. The use of RET mutation testing for the management of medullary thyroid cancer was among the first and one of most successful applications of genetics in informing clinical decisions in an individualised manner, in this case by preventing cancer or guiding the choice of tyrosine kinase inhibitors in cancer treatment. New information emerges every day in the genetics or system biology of endocrine disorders. This review goes over most of these discoveries and the known endocrine tumour syndromes. We cover key genetic developments for each disease and provide information that can be used by the clinician in daily practice.
D M Robertson, H G Burger, and P J Fuller
Inhibin and activin are members of the transforming growth factor beta (TGFbeta) family of cytokines produced by the gonads, with a recognised role in regulating pituitary FSH secretion. Inhibin consists of two homologous subunits, alpha and either betaA or betaB (inhibin A and B). Activins are hetero- or homodimers of the beta-subunits. Inhibin and free alpha subunit are known products of two ovarian tumours (granulosa cell tumours and mucinous carcinomas). This observation has provided the basis for the development of a serum diagnostic test to monitor the occurrence and treatment of these cancers. Transgenic mice with an inhibin alpha subunit gene deletion develop stromal/granulosa cell tumours suggesting that the alpha subunit is a tumour suppressor gene. The role of inhibin and activin is reviewed in ovarian cancer both as a measure of proven clinical utility in diagnosis and management and also as a factor in the pathogenesis of these tumours. In order to place these findings into perspective the biology of inhibin/activin and of other members of the TGFbeta superfamily is also discussed.
Rachel S van Leeuwaarde, Joanne M de Laat, Carolina R C Pieterman, Koen Dreijerink, Menno R Vriens, and Gerlof D Valk
Multiple endocrine neoplasia type 1 is a rare autosomal inherited disorder associated with a high risk for patients to simultaneously develop tumors of the parathyroid glands, duodenopancreatic neuroendocrine tumors and tumors of the anterior pituitary gland. Early identification of MEN1 in patients enables presymptomatic screening of manifestations, which makes timely interventions possible with the intention to prevent morbidity and mortality. Causes of death nowadays have shifted toward local or metastatic progression of malignant neuroendocrine tumors. In early cohorts, complications like peptic ulcers in gastrinoma, renal failure in hyperparathyroidism, hypoglycemia and acute hypercalcemia were the primary causes of early mortality. Improved medical treatments of these complications led to a significantly improved life expectancy. The MEN1 landscape is still evolving, considering the finding of breast cancer as a new MEN1-related manifestation and ongoing publications on follow-up and medical care for patients with MEN1. This review aims at summarizing the most recent insights into the follow-up and medical care for patients with MEN1 and identifying the gaps for future research.