An R201H activating mutation of the GNAS1 (Gsalpha) gene in a corticotroph pituitary adenoma

Pituitary Tumorigenesis-Implications for Management

Pituitary neuroendocrine tumors (PitNETs), the third most common intracranial tumor, are mostly benign. However, some of them may display a more aggressive behavior, invading into the surrounding structures. While they may rarely metastasize, they may resist different treatment modalities. Several major advances in molecular biology in the past few years led to the discovery of the possible mechanisms involved in pituitary tumorigenesis with a possible therapeutic implication. The mutations in the different proteins involved in the Gsa/protein kinase A/c AMP signaling pathway are well-known and are responsible for many PitNETS, such as somatotropinomas and, in the context of syndromes, as the McCune-Albright syndrome, Carney complex, familiar isolated pituitary adenoma (FIPA), and X-linked acrogigantism (XLAG). The other pathways involved are the MAPK/ERK, PI3K/Akt, Wnt, and the most recently studied HIPPO pathways. Moreover, the mutations in several other tumor suppressor genes, such as menin and CDKN1B, are responsible for the MEN1 and MEN4 syndromes and succinate dehydrogenase (SDHx) in the context of the 3PAs syndrome. Furthermore, the pituitary stem cells and miRNAs hold an essential role in pituitary tumorigenesis and may represent new molecular targets for their diagnosis and treatment. This review aims to summarize the different cell signaling pathways and genes involved in pituitary tumorigenesis in an attempt to clarify their implications for diagnosis and management.

Genetics of Cushing's disease

Corticotroph tumours are primarily sporadic monoclonal neoplasms and only rarely found in genetic syndromes. Recurrent mutations in the ubiquitin specific protease 8 (USP8) gene are found in around half of cases. Mutations in other genes such as USP48 and NR3C1 are less frequent, found in less than ~20% of cases. TP53 and ATXR mutations are reported in up to one out of four cases, when focusing in USP8 wild type or aggressive corticotroph tumours and carcinomas. At present, USP8 mutations are the primary driver alterations in sporadic corticotroph tumours, TP53 and ATXR mutations may indicate transition to more aggressive tumour phenotype. Next generation sequencing efforts have identified additional genomic alterations, whose role and importance in corticotroph tumorigenesis remains to be elucidated.

Genetic Basis of ACTH-Secreting Adenomas

Cushing's disease represents 60-70% of all cases of Cushing's syndrome, presenting with a constellation of clinical features associated with sustained hypercortisolism. Molecular alterations in corticotrope cells lead to the formation of ACTH-secreting adenomas, with subsequent excessive production of endogenous glucocorticoids. In the last few years, many authors have contributed to analyzing the etiopathogenesis and pathophysiology of corticotrope adenomas, which still need to be fully clarified. New molecular modifications such as somatic mutations of USP8 and other genes have been identified, and several case series and case reports have been published, highlighting new molecular alterations that need to be explored. To investigate the current knowledge of the genetics of ACTH-secreting adenomas, we performed a bibliographic search of the recent scientific literature to identify all pertinent articles. This review presents the most recent updates on somatic and germline mutations underlying Cushing's disease. The prognostic implications of these mutations, in terms of clinical outcomes and therapeutic scenarios, are still debated. Further research is needed to define the clinical features associated with the different genotypes and potential pharmacological targets.

Large Scale Molecular Studies of Pituitary Neuroendocrine Tumors: Novel Markers, Mechanisms and Translational Perspectives

Simple Summary

Pituitary neuroendocrine tumors are non-cancerous tumors of the pituitary gland, that may overproduce hormones leading to serious health conditions or due to tumor size cause chronic headache, vertigo or visual impairment. In recent years pituitary neuroendocrine tumors are studied with the latest molecular biology methods that simultaneously investigate a large number of factors to understand the mechanisms of how these tumors develop and how they could be diagnosed or treated. In this review article, we have studied literature reports, compiled information and described molecular factors that could affect the development and clinical characteristics of pituitary neuroendocrine tumors, discovered factors that overlap between several studies using large scale molecular analysis and interpreted the potential involvement of these factors in pituitary tumor development. Overall, this study provides a valuable resource for understanding the biology of pituitary neuroendocrine tumors.

Abstract

Pituitary neuroendocrine tumors (PitNETs) are non-metastatic neoplasms of the pituitary, which overproduce hormones leading to systemic disorders, or tumor mass effects causing headaches, vertigo or visual impairment. Recently, PitNETs have been investigated in large scale (exome and genome) molecular analyses (transcriptome microarrays and sequencing), to uncover novel markers. We performed a literature analysis on these studies to summarize the research data and extrapolate overlapping gene candidates, biomarkers, and molecular mechanisms. We observed a tendency in samples with driver mutations (GNAS, USP8) to have a smaller overall mutational rate, suggesting driver-promoted tumorigenesis, potentially changing transcriptome profiles in tumors. However, direct links from drivers to signaling pathways altered in PitNETs (Notch, Wnt, TGF-β, and cell cycle regulators) require further investigation. Modern technologies have also identified circulating nucleic acids, and pinpointed these as novel PitNET markers, i.e., miR-143-3p, miR-16-5p, miR-145-5p, and let-7g-5p, therefore these molecules must be investigated in the future translational studies. Overall, large-scale molecular studies have provided key insight into the molecular mechanisms behind PitNET pathogenesis, highlighting previously reported molecular markers, bringing new candidates into the research field, and reapplying traditional perspectives to newly discovered molecular mechanisms.

The clinical aspects of pituitary tumour genetics

BACKGROUND

Pituitary tumours are usually benign and relatively common intracranial tumours, with under- and overexpression of pituitary hormones and local mass effects causing considerable morbidity and increased mortality. While most pituitary tumours are sporadic, around 5% of the cases arise in a familial setting, either isolated [familial isolated pituitary adenoma, related to AIP or X-linked acrogigantism], or in a syndromic disorder, such as multiple endocrine neoplasia type 1 or 4, Carney complex, McCune-Albright syndrome, phaeochromocytoma/paraganglioma with pituitary adenoma, DICER1 syndrome, Lynch syndrome, and USP8-related syndrome. Genetically determined pituitary tumours usually present at younger age and show aggressive behaviour, and are often resistant to different treatment modalities.

SUBJECT

In this practical summary, we take a practical approach: which genetic syndromes should be considered in case of different presentation, such as tumour type, family history, age of onset and additional clinical features of the patient.

CONCLUSION

The identification of the causative mutation allows genetic and clinical screening of relatives at risk, resulting in earlier diagnosis, a better therapeutic response and ultimately to better long-term outcomes.

Update on the Genetics of Pituitary Tumors

Pituitary adenomas are common intracranial neoplasms, with diverse phenotypes. Most of these tumors occur sporadically and are not part of genetic disorders. Over the last decades numerous genetic studies have led to identification of somatic and germline mutations associated with pituitary tumors, which has advanced the understanding of pituitary tumorigenesis. Exploring the genetic background of pituitary neuroendocrine tumors can lead to early diagnosis associated with better outcomes, and their molecular mechanisms should lead to novel targeted therapies even for sporadic tumors. This article summarizes the genes and the syndromes associated with pituitary tumors.

Clinical and Molecular Update on Genetic Causes of Pituitary Adenomas

Pituitary adenomas are benign tumors with variable functional characteristics that can have a significant impact on patients. The majority arise sporadically, but an inherited genetic susceptibility is increasingly being recognized. Recent advances in genetics have widened the scope of our understanding of pituitary tumorigenesis. The clinical and genetic characteristics of pituitary adenomas that develop in the setting of germline-mosaic and somatic GNAS mutations (McCune-Albright syndrome and sporadic acromegaly), germline MEN1 mutations (multiple endocrine neoplasia type 1), and germline PRKAR1A mutations (Carney complex) have been well described. Non-syndromic familial cases of isolated pituitary tumors can occur as familial isolated pituitary adenomas (FIPA); mutations/deletions of the AIP gene have been found in a minority of these. Genetic alterations in GPR101 have been identified recently as causing X-linked acro-gigantism (X-LAG) leading to very early-onset pediatric gigantism. Associations of pituitary adenomas with other tumors have been described in syndromes like multiple endocrine neoplasia type 4, pheochromocytoma-paraganglioma with pituitary adenoma association (3PAs) syndrome and some of their genetic causes have been elucidated. The genetic etiologies of a significant proportions of sporadic corticotropinomas have recently been identified with the discovery of USP8 and USP48 mutations. The elucidation of genetic and molecular pathophysiology in pituitary adenomas is a key factor for better patient management and effective follow-up.

GNAS mutated thyroid carcinoma in a patient with Mc Cune Albright syndrome

Mc Cune-Albright syndrome (MAS) is a rare disorder defined by the triad of polyostotic fibrous dysplasia, “café au lait” skin hyperpigmentation and hyperfunctioning endocrinopathies, such as precocious puberty.

MAS is caused by an activating post zygotic somatic mutation of GNAS gene, coding for the alpha-subunit of the stimulatory G protein (Gsalpha). In endocrine tissues, this mutation results in overproduction of hormones and endocrine cell hyperfunction and proliferation.

Whereas the association of hyperthyroidism and thyroid adenomas is well known in MAS, the relation with thyroid carcinoma has rarely been observed.

We report the occurrence of a thyroid carcinoma in an 18-years old woman with MAS, revealed by subclinical hyperthyroidism detected during her systematic annual follow-up. Ultrasound and thyroid scintigraphy revealed the presence of a nodule in the right lobe. Pathology on hemithyroidectomy revealed an unexpected thyroid follicular carcinoma. Neoplastic thyroid cells harbored the GNAS R201C activating mutation. This observation suggests that MAS may predispose patients to thyroid carcinomas and supports the importance of thyroid assessment by physical examination, hormonal blood test and ultrasound, in the follow-up of patients with MAS. Because ultrasound diagnostic is challenging in MAS, needle puncture of palpable nodules should be advised.

Cushing syndrome: Old and new genes

Cushing syndrome (CS) describes the signs and symptoms caused by exogenous or endogenous hypercortisolemia. Endogenous CS is caused by either ACTH-dependent sources (pituitary or ectopic) or ACTH-independent (adrenal) hypercortisolemia. Several genes are currently known to contribute to the pathogenesis of CS. Germline gene defects, such as MEN1, AIP, PRKAR1A and others, often present in patients with pituitary or adrenal involvement as part of a genetic syndrome. Somatic defects in genes, such as USP8, TP53, and others, are also involved in the development of pituitary or adrenal tumors in a large percentage of patients with CS, and give insight in pathways involved in pituitary or adrenal tumorigenesis.

The Genetics of Pituitary Adenomas

The genetic landscape of pituitary adenomas (PAs) is diverse and many of the identified cases remain of unclear pathogenetic mechanism. Germline genetic defects account for a small percentage of all patients and may present in the context of relevant family history. Defects in AIP (mutated in Familial Isolated Pituitary Adenoma syndrome or FIPA), MEN1 (coding for menin, mutated in Multiple Endocrine Neoplasia type 1 or MEN 1), PRKAR1A (mutated in Carney complex), GPR101 (involved in X-Linked Acrogigantism or X-LAG), and SDHx (mutated in the so called "3 P association" of PAs with pheochromocytomas and paragangliomas or 3PAs) account for the most common familial syndromes associated with PAs. Tumor genetic defects in USP8, GNAS, USP48 and BRAF are some of the commonly encountered tissue-specific changes and may explain a larger percentage of the developed tumors. Somatic (at the tumor level) genomic changes, copy number variations (CNVs), epigenetic modifications, and differential expression of miRNAs, add to the variable genetic background of PAs.

Genetics of Pituitary Tumours

Pituitary tumours are relatively common in the general population. Most often they occur sporadically, with somatic mutations accounting for a significant minority of somatotroph and corticotroph adenomas. Pituitary tumours can also develop secondary to germline mutations as part of a complex syndrome or as familial isolated pituitary adenomas. Tumours occurring in a familial setting may present at a younger age and can behave more aggressively with resistance to treatment. This chapter will focus on the genetics and molecular pathogenesis of pituitary tumours.

Neonatal McCune-Albright Syndrome: A Unique Syndromic Profile With an Unfavorable Outcome

Somatic gain‐of‐function mutations of GNAS cause a spectrum of clinical phenotypes, ranging from McCune‐Albright syndrome (MAS) to isolated disease of bone, endocrine glands, and more rarely, other organs. In MAS, a syndrome classically characterized by polyostotic fibrous dysplasia (FD), café‐au‐lait (CAL) skin spots, and precocious puberty, the heterogenity of organ involvement, age of onset, and clinical severity of the disease are thought to reflect the variable size and the random distribution of the mutated cell clone arising from the postzygotic mutation. We report a case of neonatal MAS with hypercortisolism and cholestatic hepatobiliary dysfunction in which bone changes indirectly emanating from the disease genotype, and distinct from FD, led to a fatal outcome. Pulmonary embolism of marrow and bone fragments secondary to rib fractures was the immediate cause of death. Ribs, and all other skeletal segments, were free of changes of typical FD and fractures appeared to be the result of a mild‐to‐moderate degree of osteopenia. The mutated allele was abundant in the adrenal glands and liver, but not in skin, muscle, and fractured ribs, where it could only be demonstrated using a much more sensitive PNA hybridization probe‐based FRET (Förster resonance energy transfer) technique. Histologically, bilateral adrenal hyperplasia and cholestatic disease matched the abundant disease genotype in the adrenals and liver. Based on this case and other sporadic reports, it appears that gain‐of‐function mutations of GNAS underlie a unique syndromic profile in neonates characterized by CAL skin spots, hypercortisolism, hyperthyroidism, hepatic and cardiac dysfunction, and an absence (or latency) of FD, often with a lethal outcome. Taken together, our and previous cases highlight the phenotypic severity and the diagnostic and therapeutic challenges of MAS in neonates. Furthermore, our case specifically points out how secondary bone changes, unrelated to the direct impact of the mutation, may contribute to the unfavorable outcome of very early‐onset MAS. © 2018 The Authors JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Overview of Genetically Determined Diseases/Multiple Endocrine Neoplasia Syndromes Predisposing to Endocrine Tumors

In this chapter, we present an overview of multiple endocrine neoplasia syndromes including their most important clinical and molecular features. Multiple endocrine neoplasia type 1 and 2 syndromes (MEN1 and MEN2) are discussed in detail. Syndromes that are presented in other chapters are only briefly mentioned. We discuss the relevance of germline gene alterations in apparently sporadic endocrine tumors, e.g., medullary thyroid cancer, primary hyperparathyroidism, and neuroendocrine tumors. McCune-Albright syndrome that only exists in non-hereditary, sporadic forms is also discussed in detail, as tumors of several endocrine organs can develop in the same individual.

PATHOGENESIS OF CUSHING DISEASE: AN UPDATE ON THE GENETICS OF CORTICOTROPINOMAS

OBJECTIVE

Cushing disease is a rare severe condition caused by pituitary tumors that secrete adrenocorticotropic hormone (ACTH), leading to excessive endogenous glucocorticoid production. Tumors causing Cushing disease, also called corticotropinomas, are typically monoclonal neoplasms that mainly occur sporadically.

METHODS

Literature review.

RESULTS

Cushing disease is very rarely encountered in genetic familial syndromes. Oncogenes and tumor suppressor genes commonly associated with other tumor types are only rarely mutated in this tumor type. The advent of next-generation sequencing led to the identification of a single mutational hotspot in the ubiquitin-specific protease 8 ( USP8) gene in almost half of Cushing disease tumors.

CONCLUSION

The new discoveries showcase a novel mechanism responsible for corticotroph tumorigenesis and ACTH hypersecretion and highlight USP8 and its downstream signaling pathways as potential promising pharmacologic targets for the management of Cushing disease.

ABBREVIATIONS

ACTH = adrenocorticotropic hormone; BRG1 = Brahma-related gene 1; CABLES1 = CDK5 and ABL1 enzyme substrate 1; CD = Cushing disease; CNC = Carney complex; DICER1 = cytoplasmic endoribonuclease III; EGFR = epidermal growth factor receptor; GR = glucocorticoid receptor; IL = interleukin; MEN = multiple endocrine neoplasia; miRNA = microRNA; POMC = proopiomelanocortin; SSTR = somatostatin receptor; USP8 = ubiquitin-specific protease 8.

65 YEARS OF THE DOUBLE HELIX: Endocrine tumour syndromes in children and adolescents

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.

Genetics of Cushing's Syndrome

The knowledge on the molecular and genetic causes of Cushing's syndrome (CS) has greatly increased in the recent years. Somatic mutations leading to overactive 3',5'-cyclic adenosine monophosphate/protein kinase A and wingless-type MMTV integration site family/beta-catenin pathways are the main molecular mechanisms underlying adrenocortical tumorigenesis. Corticotropinomas are characterized by resistance to glucocorticoid negative feedback, impaired cell cycle control and overexpression of pathways sustaining ACTH secretion. Recognizing the genetic defects behind corticotroph and adrenocortical tumorigenesis proves crucial for tailoring the clinical management of CS patients and for designing strategies for genetic counseling and clinical screening to be applied in routine medical practice.

An update on the genetics of benign pituitary adenomas in children and adolescents

Pituitary adenomas in children and adolescents are rare tumors that often result from a tumor predisposition syndrome. Several inherited causes for pituitary adenomas have been identified in the last few years, including multiple endocrine neoplasia type 1 and 4, Carney's complex, Tuberous sclerosis, DICER1 syndrome, neurofibromatosis type 1, McCune Albright syndrome, familial isolated pituitary adenoma, and pituitary adenoma association due to defects in succinate dehydrogenase genes. Recently, our group discovered X-linked acrogigantism (X-LAG), a new pediatric disorder that is caused by an Xq26.3 genomic duplication (involving the GPR101 gene). Genes that predispose to pediatric Cushing disease, including CABLES1 and USP8, were also recently identified. Genetic screening and counseling of affected or at risk individuals is a key component of their comprehensive care. In this review, we provide an up-to-date discussion on the latest pediatric genetic discoveries associated with pituitary adenomas with a focus on familial syndromes.

Genetics of Cushing's disease

Cushing's disease (CD) is a rare disabling condition caused by Adrenocorticotropic hormone (ACTH)-secreting adenomas of the pituitary. The majority of corticotropic adenomas are monoclonal and occur sporadically. Only rarely does CD arise in the context of genetic familial syndromes. Targeted sequencing of oncogenes and tumour suppressor genes commonly mutated in other tumours did not identify recurrent mutations. In contrast, next generation sequencing allowed us recently to clarify the genetic basis of CD: we identified somatic driver mutations in the ubiquitin-specific protease 8 (USP8) gene in a significant portion of corticotropinomas. These mutations represent a novel and unique mechanism leading to ACTH excess. Inhibition of USP8 or its downstream signalling pathways could represent a new therapeutic approach for the management of CD. In this review, we will focus on this new evidence and its implication for clinical care of affected patients.

PRKAR1A mutation causing pituitary-dependent Cushing disease in a patient with Carney complex

CONTEXT

Carney complex (CNC) is an autosomal dominant condition caused, in most cases, by an inactivating mutation of the PRKAR1A gene, which encodes for the type 1 alpha regulatory subunit of protein kinase A. CNC is characterized by the occurrence of endocrine overactivity, myxomas and typical skin manifestations. Cushing syndrome due to primary pigmented nodular adrenocortical disease (PPNAD) is the most frequent endocrine disease observed in CNC.

CASE DESCRIPTION

Here, we describe the first case of a patient with CNC and adrenocorticotropic hormone (ACTH)-dependent Cushing disease due to a pituitary corticotroph adenoma. Loss-of-heterozygosity analysis of the pituitary tumour revealed loss of the wild-type copy of PRKAR1A, suggesting a role of this gene in the pituitary adenoma development.

CONCLUSION

PRKAR1A loss-of-function mutations can rarely lead to ACTH-secreting pituitary adenomas in CNC patients. Pituitary-dependent disease should be considered in the differential diagnosis of Cushing syndrome in CNC patients.

Recent advances in understanding Cushing disease: resistance to glucocorticoid negative feedback and somatic USP8 mutations

Cushing’s disease is a rare disease with a characteristic phenotype due to significant hypercortisolism driven by over-secretion of adrenocorticotropic hormone and to high morbidity and mortality if untreated. It is caused by a corticotroph adenoma of the pituitary, but the exact mechanisms leading to tumorigenesis are not clear. Recent advances in molecular biology such as the discovery of somatic mutations of the ubiquitin-specific peptidase 8 ( USP8) gene allow new insights into the pathogenesis, which could be translated into exciting and much-needed therapeutic applications.

Gene mutations in Cushing's disease

Cushing's disease (CD) is a severe (and potentially fatal) disease caused by adrenocorticotropic hormone (ACTH)-secreting adenomas of the pituitary gland (often termed pituitary adenomas). The majority of ACTH-secreting corticotroph tumors are sporadic and CD rarely appears as a familial disorder, thus, the genetic mechanisms underlying CD are poorly understood. Studies have reported that various mutated genes are associated with CD, such as those in menin 1, aryl hydrocarbon receptor-interacting protein and the nuclear receptor subfamily 3 group C member 1. Recently it was identified that ubiquitin-specific protease 8 mutations contribute to CD, which was significant towards elucidating the genetic mechanisms of CD. The present study reviews the associated gene mutations in CD patients.

Decoding the genetic basis of Cushing's disease: USP8 in the spotlight

Cushing's disease (CD) arises from pituitary-dependent glucocorticoid excess due to an ACTH-secreting corticotroph tumor. Genetic hits in oncogenes and tumor suppressor genes that afflict other pituitary tumor subtypes are not found in corticotrophinomas. Recently, a somatic mutational hotspot was found in up to half of corticotrophinomas in the USP8 gene that encodes a protein that impairs the downregulation of the epidermal growth factor receptor (EGFR) and enables its constitutive signaling. EGF is an important regulator of corticotroph function and its receptor is highly expressed in Cushing's pituitary tumors, where it leads to increased ACTH synthesis in vitro and in vivo. The mutational hotspot found in corticotrophinomas hyper-activates USP8, enabling it to rescue EGFR from lysosomal degradation and ensure its stimulatory signaling. This review presents new developments in the study of the genetics of CD and focuses on the USP8-EGFR system as trigger and target of corticotroph tumorigenesis.

The molecular pathogenesis of corticotroph tumours

BACKGROUND

The pathogenesis of tumour formation in the anterior pituitary including adrenocorticotropic hormone (ACTH)-secreting tumours has been intensively studied, but the causative mechanisms involved in pituitary cell transformation and tumourigenesis remain unclear.

MATERIALS AND METHODS

We searched PubMed on any paper related with molecular pathology of pituitary corticotroph adenomas and have included to this review all relevant references published up to June 2011.

RESULTS

Current studies increased our knowledge on the genetic basis of McCune-Albright syndrome (MAS), multiple endocrine neoplasia type 1 (MEN1), Carney complex (CNC), pituitary adenoma predisposition syndromes and tuberous sclerosis, but they have performed little to elucidate the causes of sporadic pituitary tumours including Cushing disease.

DISCUSSION

The aim of this review was to focus on the most recently published advances in the molecular pathology of corticotroph adenomas, which are presented in the context of changes seen in all types of pituitary adenomas, as well as in terms of corticotrophin-releasing hormone/ACTH/cortisol-specific pathways.

CONCLUSIONS

We would expect that over the next 5 years, more detailed analysis of inter-cellular communication pathways between pituitary cells, including the cadherins and integrins, and their interactions with other signalling pathways such as the β-catenin cascade will help elucidate what exactly goes awry in the formation of a benign corticotroph adenoma. This should in turn predict novel forms of pharmacological tumour control.

The genetics of pituitary adenomas

Pituitary adenomas are one of the most frequent intracranial tumors with a prevalence of clinically-apparent tumors close to 1:1000 of the general population. They are clinically significant because of hormone overproduction and/or tumor mass effects in addition to the need for neurosurgery, medical therapies and radiotherapy. The majority of pituitary adenomas have a sporadic origin with recognized genetic mutations seldom being found; somatotropinomas are an exception, presenting frequent somatic GNAS mutations. In this and other phenotypes, tumorigenesis could possibly be explained by altered function of genes implicated in cell cycle regulation, growth factors or their receptors, cell-signaling pathways, specific hormonal factors or other molecules with still unclear mechanisms of action. Genetic changes, such as allelic loss or gene amplification, and epigenetic changes, usually by promoter methylation, have been implicated in abnormal gene expression, but alternative mechanisms may be present. Familial cases of pituitary adenomas represent 5% of all pituitary tumors. MEN1 mutations cause multiple endocrine neoplasia type 1 (MEN1), while the Carney complex (CNC) is characterized by mutations in the protein kinase A regulatory subunit-1alpha (PRKAR1A) gene or changes in a locus at 2p16. Recently, a MEN1-like condition, MEN4, was found to be related to mutations in the CDKN1B gene. The clinical entity of familial isolated pituitary adenomas (FIPA) is characterized by genetic defects in the aryl hydrocarbon receptor interacting protein (AIP) gene in about 15% of all kindreds and 50% of homogenous somatotropinoma families. Identification of familial cases of pituitary adenomas is important as these tumors may be more aggressive than their sporadic counterparts.

Signalling pathway mediated by CXCR7, an alternative chemokine receptor for stromal-cell derived factor-1α, in AtT20 mouse adrenocorticotrophic hormone-secreting pituitary adenoma cells

Stromal cell-derived factor (SDF)-1 and its receptor, CXCR4, have been identified in both neurones and glia of many brain areas. Previous studies have mainly focused on the role of SDF-1 and CXCR4 in modulating the hypothalamic-pituitary axis and their possible involvement in the development of pituitary adenomas. An alternative SDF-1 receptor, CXCR7, has recently been identified, but it has not been studied in the context of pituitary adenomas. The present study aimed to investigate the distribution and function of CXCR7 in pituitary adenomas. The expression of CXCR7, normalised to β-actin, was assessed by tissue microarray analysis of 62 adenomas, including 23 growth hormone (GH)-producing adenomas, 22 nonfunctioning adenomas, seven prolactin (PRL)-producing adenomas, six adrenocorticotrophic hormone-producing adenomas and four thyroid-stimulating hormone-producing adenomas. In vitro functional studies used RNA interference (RNAi) and cDNA microarray analysis to evaluate the CXCR7 signalling pathway in AtT-20 mouse pituitary adenoma cells treated with recombinant mouse SDF-1α and transfected with RNAi against Cxcr7 or control RNAi. In tissue microarray analysis, prominent expression of CXCR7 was observed in GH-producing adenomas and PRL-producing adenomas, and in macroadenomas (P < 0.05). Intracellular signalling via CXCR7 up-regulated Bub1, Cdc29 and Ccnb1, and down-regulated Asns, Gpt, Pycr1, Cars and Dars. The present study demonstrates that the SDF-1α ⁄ CXCR7 signalling pathway regulates genes involved in cell cycle control, amino acid metabolism and ligase activity, which comprise targets that are distinct from those of CXCR4.

Prevalence of gsp oncogene in somatotropinomas and clinically non-functioning pituitary adenomas: our experience

The purpose of the present study is to evaluate the prevalence of the gsp oncogene in Brazilian patients harboring somatotropinomas and non-functioning pituitary adenomas (NFPA). Patients and methods Deoxyribonucleic acid was extracted from 54 somatotropinomas and 14 NFPA. Exons 8 and 9 (including codons 201 and 227, respectively) of the GNAS gene were amplified by polymerase chain reaction (PCR). The PCR products were then purified and sequenced using the same primers. Results The gsp oncogene was found in nine tumors (eight somatotropinomas). The prevalence among somatotropinomas was 15% and among NFPA was 7%. The mutation was found in codon 201 in eight tumors and in codon 227 in one tumor (a somatotropinoma). No differences were found in age, sex, GH, and IGF-I levels or tumor volume at diagnosis between gsp+ and gsp- patients. Conclusion We found a lower than expected prevalence of gsp mutations in somatotropinomas and a similar prevalence in NFPA compared to previous studies from other countries.

Laryngeal squamous cell carcinoma in a 13 year-old child associated with human papillomaviruses 16 and 18: a case report and review of the literature

Squamous cell carcinoma (SCC) of the larynx is extremely rare in adolescents and typically has an aggressive nature. The mechanism of laryngeal oncogenesis is complex and little is known about the role that human papillomavirus (HPV) plays in SCC in adolescents. We report a case of invasive laryngeal SCC that co-expressed HPV DNA subtypes 16 and 18 in a 13 year-old boy. Detection of HPV DNA types 6, 11, 16, 18, 31, 33, and 51 was performed by in situ hybridization, with confirmation by polymerase chain reaction. Immunohistochemical staining with p16 and HPV 16/18 revealed diffusely positive staining in the tumor cells. Coinfection by HPV DNA types 16 and 18 has not been previously reported, but our case suggests that HPV is a risk factor in developing laryngeal SCC in children and adolescents. Future studies evaluating HPV in the pathogenesis of these lesions is recommended to determine its prognostic significance.

Clinical and molecular genetics of acromegaly: MEN1, Carney complex, McCune-Albright syndrome, familial acromegaly and genetic defects in sporadic tumors

Pituitary tumors are among the most common neoplasms in man; they account for approximately 15% of all primary intracranial lesions (Jagannathan et al., Neurosurg Focus, 19:E4, 2005). Although almost never malignant and rarely clinically expressed, pituitary tumors may cause significant morbidity in affected patients. First, given the critical location of the gland, large tumors may lead to mass effects, and, second, proliferation of hormone-secreting pituitary cells leads to endocrine syndromes. Acromegaly results from oversecretion of growth hormone (GH) by the proliferating somatotrophs. Despite the significant efforts made over the last decade, still little is known about the genetic causes of common pituitary tumors and even less is applied from this knowledge therapeutically. In this review, we present an update on the genetic syndromes associated with pituitary adenomas and discuss the related genetic defects. We next review findings on sporadic, non-genetic, pituitary tumors with an emphasis on pathways and animal models of pituitary disease. In conclusion, we attempt to present an overall, integrative approach to the human molecular genetics of both familiar and sporadic pituitary tumors.

Molecular genetics of the cAMP-dependent protein kinase pathway and of sporadic pituitary tumorigenesis

Pituitary tumors are among the most common human neoplasms. Although these common lesions rarely become clinically manifest and they are almost never malignant, they are the cause of significant morbidity in affected patients. The genetic causes of common pituitary tumors remain for the most part unknown; progress has been limited to the elucidation of the molecular etiology of four genetic syndromes predisposing to pituitary neoplasias: McCune-Albright syndrome, multiple endocrine neoplasia type 1, Carney complex and, most recently, familial acromegaly and prolactinomas and other tumors caused by mutations in the GNAS, menin, PRKAR1A, AIP, and p27 (CDKN1B) genes, respectively. Intense molecular studies of sporadic pituitary tumors from patients with negative family histories and no other neoplasms have yielded interesting findings with abnormalities in growth factor expression and cell cycle control dysregulation. To add to the difficulties in understanding pituitary tumorigenesis in man, good murine models of these neoplasms simply do not exist: pituitary tumors are common in rodents, but their histologic origin (mostly from the intermediate lobe), age of presentation (late in murine life) and clinical course make them hardly models of their human counterparts. The present report reviews the clinical and molecular genetics of the cAMP-dependent protein kinase pathway in human pituitary tumors; it also reviews briefly other pathways that have been involved in sporadic pituitary neoplasms. At the end, we attempt a unifying hypothesis for pituitary tumorigenesis, taking into account data that are also discussed elsewhere in this issue.

Genetics of McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a rare proteiform disease due to postzygotic, somatic mutations at codon R201 of the GNAS1 gene that results in cellular mosaicism. Different methods have been used in the molecular analysis of DNA samples from several tissues of patients with one or more MAS signs, with various mutation detection rates. We review data from the literature to investigate whether patient inclusion criteria for GNAS1 analysis, the molecular methods used to search for R201 mutations, and the type of tissues analysed, can influence the mutation detection rate in MAS. Our study indicates that to overcome the problems related to GNAS1 analysis in MAS, sensitive and specific molecular methods must be used to look for the mutation from all available affected tissues and from easily accessible tissues, and even more so in the presence of atypical and monosymptomatic forms of MAS.

A case of McCune-Albright syndrome associated with Gs alpha mutation in the bone tissue

The syndrome of McCune-Albright syndrome (MAS) is clasically defined as a triad presentation with the findings of polyostotic fibrous dysplasia, café-au-lait spots, and sexual precocity. However, not all patients present with complete symptoms. A 52-year-old man was diagnosed as having a variant of McCune-Albright syndrome with the following findings: polyostotic fibrous dysplasia, acromegaly due to pituitary tumor and subclinical hyperthyroidism due to toxic multinodular goiter. Sexual precocity and café-au-lait spots were not noted. Acromegaly was confirmed by laboratory examination (IGF-1, glucose suppression test and TRH stimulation test). Long acting somatostatin analogue was used as treatment. Although the pituitary tumor could not be removed due to technical problems, mass lesions on the cranium were removed subtotally. Histopathological evaluation demonstrated that the lesion complied with fibrous dysplasia. Genomic DNAs were isolated from the craniofacial bones and peripheral leucocytes of the patient. After amplifying the related regions, Gs alpha (Gs alpha) gene was analysed by automatic DNA sequence analysis. An activating mutation of the Gs alpha gene (Arg 201 Cys) was found in the genomic DNA isolated from the bone tissue of the patient, but not in the genomic DNA isolated from the blood. We described a case of MAS associated with Gs alpha mutation in the bone tissue, presenting with polyostotic fibrous dysplasia, subclinical hyperthyroidism and acromegaly.

Mammalian G proteins and their cell type specific functions

Heterotrimeric G proteins are key players in transmembrane signaling by coupling a huge variety of receptors to channel proteins, enzymes, and other effector molecules. Multiple subforms of G proteins together with receptors, effectors, and various regulatory proteins represent the components of a highly versatile signal transduction system. G protein-mediated signaling is employed by virtually all cells in the mammalian organism and is centrally involved in diverse physiological functions such as perception of sensory information, modulation of synaptic transmission, hormone release and actions, regulation of cell contraction and migration, or cell growth and differentiation. In this review, some of the functions of heterotrimeric G proteins in defined cells and tissues are described.

[Endocrine tumors associated to protein Gsalpha/Gi2alpha mutations]

Many oncogenic mutations promote tumor growth by inducing autonomous activity of proteins that normally transmit proliferative signal initiated by extracellular factors. G proteins are a family of guanine nucleotide binding proteins, which are structurally homologous and widely distributed in eukaryotic cells. They are composed of three different subunits (alpha, beta e gamma). The alpha subunit, which contains the guanine nucleotide-binding site, is unique to each G protein. The G proteins couple an array of seven transmembrane receptors at the cell surface with a variety of intracellular effectors, which produce second messenger molecules. A subset of endocrine tumors, such as GH- or ACTH-secreting pituitary adenomas, functioning thyroid adenomas, adrenocortical and gonadal tumors were associated with somatic activating mutations in the highly conserved codons of the Gs (Arg201 and Gln227) and Gi (Arg179 and Gln205) proteins. These findings indicated that the G proteins play a role as oncogenes, contributing with the human endocrine tumorigenesis.