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.
E Kim, E M Rath, V H M Tsang, A P Duff, B G Robinson, W B Church, D E Benn, T Dwight, and R J Clifton-Bligh
Mitochondrial dysfunction, due to mutations of the gene encoding succinate dehydrogenase (SDH), has been implicated in the development of adrenal phaeochromocytomas, sympathetic and parasympathetic paragangliomas, renal cell carcinomas, gastrointestinal stromal tumours and more recently pituitary tumours. Underlying mechanisms behind germline SDH subunit B (SDHB) mutations and their associated risk of disease are not clear. To investigate genotype–phenotype correlation of SDH subunit B (SDHB) variants, a homology model for human SDH was developed from a crystallographic structure. SDHB mutations were mapped, and biochemical effects of these mutations were predicted in silico. Results of structural modelling indicated that many mutations within SDHB are predicted to cause either failure of functional SDHB expression (p.Arg27*, p.Arg90*, c.88delC and c.311delAinsGG), or disruption of the electron path (p.Cys101Tyr, p.Pro197Arg and p.Arg242His). GFP-tagged WT SDHB and mutant SDHB constructs were transfected (HEK293) to determine biological outcomes of these mutants in vitro. According to in silico predictions, specific SDHB mutations resulted in impaired mitochondrial localisation and/or SDH enzymatic activity. These results indicated strong genotype–functional correlation for SDHB variants. This study reveals new insights into the effects of SDHB mutations and the power of structural modelling in predicting biological consequences. We predict that our functional assessment of SDHB mutations will serve to better define specific consequences for SDH activity as well as to provide a much needed assay to distinguish pathogenic mutations from benign variants.
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.
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.
A Falchetti and M L Brandi
Multiple Endocrine Neoplasias type 1 (MEN 1) and type 2 (MEN 2) represent complex inherited (autosomal dominant traits) syndromes characterized by occurrence of distinct proliferative disorders of endocrine tissues, varying from hyperplasia to adenoma and carcinoma.
MEN 1 syndrome is characterized by parathyroid gland, anterior pituitary and endocrine pancreas tumors. Other endocrine and non endocrine tumors, such as carcinoids, lipomas, pinealomas, adrenocortical and thyroid follicular tumors, have been also described in MEN 1 patients occurring at higher frequency than in general population (Brandi ML et al. 1987). Recently also a spinal ependymoma has been found in a patient with MEN 1 syndrome (Kato H et al 1997)
MEN 2 syndromes recognize three main clinical entities, MEN 2A, characterized by medullary thyroid carcinoma (MTC), primary hyperparathyroidism (PHPT) and pheochromocytoma (PHEO); MEN 2B that exhibits MTC, usually developing sooner than the MEN 2A- associated one, pheochromocytoma, multiple neuromas of gastroenteric mucosa, myelinated corneal nerves (Gorlin RJ et al. 1968) and a typical marphanoid habitus; and familial medullary thyroid carcinoma only (FMTC) featuring by families with at least four members with MTC and no objective evidence of pheochromocytoma and parathyroid disease on screening of affected and at-risk members, as stated by the International RET Mutation Consortium (Larsson C et al. 1994).
This work was supported by grants of the Associazione Italiana per la Ricerca sul Cancro (to MLB), from CNR/PF ACRO (INV. 95.00316 PF 39) and by MURST 60% (to MLB).
Gregory A Kaltsas, Jane Evanson, Alexandra Chrisoulidou, and Ashley B Grossman
The sellar and parasellar region is an anatomically complex area where a number of neoplastic, inflammatory, infectious, developmental and vascular diseases can develop. Although most sellar lesions are due to pituitary adenomas, a number of other pathologies involving the parasellar region can present in a similar manner. The diagnosis of such lesions involves a multidisciplinary approach, and detailed endocrinological, ophthalmological, neuroimaging, neurological and finally histological studies are required. Correct diagnosis prior to any intervention is essential as the treatment of choice will be different for each disorder, particularly in the case of primary malignant parasellar tumours. The complexity of structures that define the parasellar region can produce a variety of neoplastic processes, the malignant potential of which relies on histological grading. In the majority of parasellar tumours, a multimodal therapeutic approach is frequently necessary including surgery, radiotherapy, primary or adjuvant medical treatment and replacement of apparent endocrine deficits. Disease-specific medical therapies are mandatory in order to prevent recurrence or further tumour growth. This is particularly important as neoplastic lesions of the parasellar region tend to recur after prolonged follow-up, even when optimally treated. Apart from the type of treatment, identification of clinical and radiological features that could predict patients with different prognosis seems necessary in order to identify high-risk patients. Due to their rarity, central registration of parasellar tumours is required in order to be able to provide evidence-based diagnostic and mainly therapeutic approaches.
G Carreno, J K R Boult, J Apps, J M Gonzalez-Meljem, S Haston, R Guiho, C Stache, L S Danielson, A Koers, L M Smith, A Virasami, L Panousopoulos, M Buchfelder, T S Jacques, L Chesler, S P Robinson, and J P Martinez-Barbera
Pharmacological inhibition of the sonic hedgehog (SHH) pathway can be beneficial against certain cancers but detrimental in others. Adamantinomatous craniopharyngioma (ACP) is a relevant pituitary tumour, affecting children and adults, that is associated with high morbidity and increased mortality in long-term follow-up. We have previously demonstrated overactivation of the SHH pathway in both human and mouse ACP. Here, we show that this activation is ligand dependent and induced by the expression of SHH protein in a small proportion of tumour cells. We investigate the functional relevance of SHH signalling in ACP through MRI-guided preclinical studies using an ACP mouse model. Treatment with vismodegib, a clinically approved SHH pathway inhibitor, results in a significant reduction in median survival due to premature development of highly proliferative and vascularised undifferentiated tumours. Reinforcing the mouse data, SHH pathway inhibition in human ACP leads to a significant increase in tumour cell proliferation both ex vivo, in explant cultures, and in vivo, in a patient-derived xenograft model. Together, our results demonstrate a protumourigenic effect of vismodegib-mediated SHH pathway inhibition in ACP.
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.