Lineage-specific restraint of pituitary gonadotroph cell adenoma growth

Recent advancements in the molecular biology of pituitary adenomas

INTRODUCTION

Pituitary adenomas are a common and diverse group of intracranial tumors arising from the anterior pituitary that are usually slow-growing and benign, but still pose a significant healthcare burden to patients. Additionally, they are increasing in both incidence and prevalence, leading to a need for better understanding of molecular changes in the development of these tumors.

AREAS COVERED

A PubMed literature search was conducted using the terms 'pituitary adenoma' in combination with keywords related to secretory subtype: lactotroph, somatotroph, corticotroph, gonadotroph and null cell, in addition to their transcription factor expression: PIT1, TPIT, and SF-1. Articles resulting from this search were analyzed, as well as relevant articles cited as their references. In this review, we highlight recent advances in the genetic and epigenetic characterization of individual pituitary adenoma subtypes and the effect it may have on guiding future clinical treatment of these tumors.

EXPERT OPINION

Understanding the molecular biology of pituitary adenomas is a fundamental step toward advancing the treatment of these tumors. Yet crucial knowledge gaps exist in our understanding of the underlying molecular biology of pituitary adenomas which can potentially be addressed by turning to differentially activated molecular pathways in tumor relative to normal gland.

Architects of Pituitary Tumour Growth

The pituitary is a master gland responsible for the modulation of critical endocrine functions. Pituitary neuroendocrine tumours (PitNETs) display a considerable prevalence of 1/1106, frequently observed as benign solid tumours. PitNETs still represent a cause of important morbidity, due to hormonal systemic deregulation, with surgical, radiological or chronic treatment required for illness management. The apparent scarceness, uncommon behaviour and molecular features of PitNETs have resulted in a relatively slow progress in depicting their pathogenesis. An appropriate interpretation of different phenotypes or cellular outcomes during tumour growth is desirable, since histopathological characterization still remains the main option for prognosis elucidation. Improved knowledge obtained in recent decades about pituitary tumorigenesis has revealed that this process involves several cellular routes in addition to proliferation and death, with its modulation depending on many signalling pathways rather than being the result of abnormalities of a unique proliferation pathway, as sometimes presented. PitNETs can display intrinsic heterogeneity and cell subpopulations with diverse biological, genetic and epigenetic particularities, including tumorigenic potential. Hence, to obtain a better understanding of PitNET growth new approaches are required and the systematization of the available data, with the role of cell death programs, autophagy, stem cells, cellular senescence, mitochondrial function, metabolic reprogramming still being emerging fields in pituitary research. We envisage that through the combination of molecular, genetic and epigenetic data, together with the improved morphological, biochemical, physiological and metabolically knowledge on pituitary neoplastic potential accumulated in recent decades, tumour classification schemes will become more accurate regarding tumour origin, behaviour and plausible clinical results.

Overview of omics biomarkers in pituitary neuroendocrine tumors to design future diagnosis and treatment strategies

Pituitary neuroendocrine tumors (PitNETs) are the second most common type of intracranial neoplasia. Since their manifestation usually causes hormone hypersecretion, effective management of PitNETs is indisputably necessary. Most of the non-functioning PitNETs pose a real challenge in diagnosis as they grow without giving any signs. Despite the good response of prolactinomas to dopamine agonist therapy, some of these tumors persist or recur; also, about 20% are resistant and 10% behave aggressively. The silent corticotropinomas may not cause symptoms until the tumor mass causes a complication. In somatotropinomas, the possibility of recurrence after transsphenoidal resection is more common in pediatric patients than in adult patients. Therefore, detection of tumors at early stages or identification of recurrence and remission after transsphenoidal surgery would allow wiser management of the disease. Extensive studies have been performed to uncover potential signatures that can be used for preventive diagnosis and/or prognosis of PitNETs as well as for targeted therapy. These molecular signatures at multiple biological levels hold promise for the convergence of preventive approaches and patient-centered disease management and offer potential therapeutic strategies. In this review, we provide an overview of the omics-based biomarker research and highlight the multi-omics signatures that have been proposed as pitNET biomarkers. In addition, understanding the multi-omics data integration of current biomarker discovery strategies was discussed in terms of preventive, predictive, and personalized medicine. The topics discussed in this review will help to develop broader visions for pitNET research, diagnosis, and therapy, particularly in the context of personalized medicine.

Follicular cells in pituitary neuroendocrine tumors

Follicular cells (FCs) are thought to be agranular, non-hormone-producing stellate cells distributed throughout the adenohypophysis, occasionally arranged around colloid-filled follicles, and thought to be more prominent in the vicinity of necrosis and apoptotic cells. A distinct but similar cell type, the folliculostellate cell (FSC), is a sustentacular cell that is negative for keratins and stains for S100, GFAP, and SOX10. While several studies have examined FSCs in pituitary neuroendocrine tumors (PitNETs), the distribution and derivation of FCs in these lesions is unclear. We examined the presence and distribution of FCs in 104 PitNETs obtained by trans-sphenoidal surgery, using immunohistochemistry for keratins as well as the full complement of immunohistochemical stains for tumor characterization. The tumors included 9 somatotroph, 5 mammosomatotroph, 7 lactotroph, 7 immature PIT1-lineage, 2 acidophil stem cell, 17 corticotroph, 53 gonadotroph, 2 null cell, and 2 unusual plurihormonal tumors. CK-positive FCs were only identified in gonadotroph PitNETs and were found in 12 (23%) of those tumors; all other tumor types were negative for FCs. FCs express keratins identified by CAM5.2, AE1/AE3, CK18, and CK19 antibodies. FCs were identified scattered singly among hormone-producing neuroendocrine cells, in small clusters of 3-5 cells and surrounding colloid-filled follicles, as well as linearly along intratumoral blood vessels. Sequential stains showed that FCs express nuclear SF1 and GATA3, transcription factors of gonadotrophs, and multiplex immunohistochemistry confirmed colocalization of SF1 in the nucleus of keratin-positive FCs. In this series, FCs were exclusively found in gonadotroph PitNETs and occurred in 23% of those tumors. Co-expression of gonadotroph transcription factors in FCs supports the concept of cellular plasticity and transformation of neoplastic hormone-producing neuroendocrine cells to FCs. Further studies are required to determine if and why gonadotrophs alone undergo this transformation, the function of these cells and whether they have prognostic value.

Single-cell transcriptome and genome analyses of pituitary neuroendocrine tumors

BACKGROUND

Pituitary neuroendocrine tumors (PitNETs) are the second most common intracranial tumor. We lacked a comprehensive understanding of the pathogenesis and heterogeneity of these tumors.

METHODS

We performed high-precision single-cell RNA sequencing for 2,679 individual cells obtained from 23 surgically resected samples of the major subtypes of PitNETs from 21 patients. We also performed single-cell multi-omics sequencing for 238 cells from 5 patients.

RESULTS

Unsupervised clustering analysis distinguished all tumor subtypes, which was in accordance with the classification based on immunohistochemistry and provided additional information. We identified three normal endocrine cell types: somatotrophs, lactotrophs and gonadotrophs. Comparisons of tumor and matched normal cells showed that differentially expressed genes of gonadotroph tumors were predominantly downregulated, while those of somatotroph and lactrotroph tumors were mainly upregulated. We identified novel tumor-related genes, such as AMIGO2, ZFP36, BTG1 and DLG5. Tumors expressing multiple hormone genes showed little transcriptomic heterogeneity. Furthermore, single-cell multi-omics analysis demonstrated that the tumor shad a relatively uniform pattern of genome with slight heterogeneity in copy number variations.

CONCLUSIONS

Our single-cell transcriptome and single-cell multi-omics analyses provide novel insights into the characteristics and heterogeneity of these complex neoplasms for the identification of biomarkers and therapeutic targets.

Involvement of histone deacetylase 1/2 in adrenocorticotropic hormone synthesis and proliferation of corticotroph tumor AtT-20 cells

Cushing's disease is mainly caused by autonomous production of adrenocorticotropic hormone (ACTH) from pituitary adenomas. In our previous study, a histone deacetylase (HDAC) inhibitor, trichostatin A, inhibited cell proliferation and ACTH production via decreased pituitary tumor-transforming gene 1 (PTTG1) in AtT-20 mouse corticotroph tumor cells. In the present study, we examined the effects of romidepsin, a potent and selective HDAC1/2 inhibitor, on cell proliferation and ACTH synthesis. To elucidate further potential mechanisms of romidepsin, we examined the effects of HDAC1/2 on proopiomelanocortin (Pomc) and Pttg1 mRNA levels and cell proliferation. Small interfering RNA-mediated knockdown was used to decrease HDAC1 or 2. Romidepsin treatment decreased Pomc and Pttg1 mRNA levels, and cell proliferation. The drug also increased Hdac1 and decreased Hdac2 mRNA levels. Hdac1 knockdown decreased basal Pttg1 mRNA levels and cell proliferation, but not Pomc mRNA levels. Romidepsin treatment decreases ACTH synthesis in corticotroph tumor cells. Romidepsin suppresses cell proliferation via PTTG1. HDAC1 is also involved in the proliferation of corticotroph cells via PTTG1.

The Repertoire of Glycan Alterations and Glycoproteins in Human Cancers

Cancer as the leading cause of death worldwide has many issues that still need to be addressed. Since the alterations on the glycan compositions or/and structures (i.e., glycosylation, sialylation, and fucosylation) are common features of tumorigenesis, glycomics becomes an emerging field examining the structure and function of glycans. In the past, cancer studies heavily relied on genomics and transcriptomics with relatively little exploration of the glycan alterations and glycoprotein biomarkers among individuals and populations. Since glycosylation of proteins increases their structural complexity by several orders of magnitude, glycome studies resulted in highly dynamic biomarkers that can be evaluated for cancer diagnosis, prognosis, and therapy. Glycome not only integrates our genetic background with past and present environmental factors but also offers a promise of more efficient patient stratification compared with genetic variations. Therefore, studying glycans holds great potential for better diagnostic markers as well as developing more efficient treatment strategies in human cancers. While recent developments in glycomics and associated technologies now offer new possibilities to achieve a high-throughput profiling of glycan diversity, we aim to give an overview of the current status of glycan research and the potential applications of the glycans in the scope of the personalized medicine strategies for cancer.

A Novel Expression Profile of Cell Cycle and DNA Repair Proteins in Nonfunctioning Pituitary Adenomas

The molecular mechanisms underlying the formation of nonfunctioning pituitary adenomas (NFAs) are largely unknown. In this study, we aimed to understand the relationship between NFAs and functional pituitary adenomas and the possible role of proteins involved in cell cycle, senescence, and DNA damage control mechanisms in the etiology of NFA. We analyzed pATM-S1981, pRb-S608, Rb, pE2F1-S364, p16, E2F1, p73, cyclin D1, and CHEK2 protein expression (in a group of 20 patients with acromegaly, 18 patients with Cushing's disease (CD), and 29 NFA patients) by immunohistochemistry and their relevant mRNA expression by qRT-PCR (in a group of 7 patients with acromegaly, 7 patients with CD, and 7 NFA patients). The clinical and histopathological results on the patients were statistically evaluated. pE2F1-S364 protein expression in the CD group was significantly lower than that in the NFA and acromegaly groups (p = 0.025, p = 0.034, respectively). However, the expression of the p16 protein was lower than in the NFA group than in the CD and acromegaly groups (p = 0.030, p = 0.033, respectively), and E2F1 protein expression was significantly higher in the NFA group than in the CD group (p = 0.025). p73 protein expression in patients with acromegaly was significantly higher (p = 0.031) than that in the CD group. CHEK2 mRNA expression in the CD group was significantly higher than that in the acromegaly group (p = 0.012). The selective and tumor-specific associations between E2F1, pE2F1-S364, CHEK2, and p73 mRNA and protein levels indicate their involvement in pituitary adenoma formation in NFA, CD, and acromegaly patients.

Ubiquitin-specific protease 8 inhibitor suppresses adrenocorticotropic hormone production and corticotroph tumor cell proliferation

Cushing's disease is primarily caused by autonomic hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. In Cushing's disease, mutations in the ubiquitin-specific protease 8 (USP8) have been detected. These mutations are associated with hyperactivation of USP8 that prevent epidermal growth factor receptor (EGFR) degradation. This leads to increased EGFR stability and results in the maintenance of EGFR signaling in Cushing's disease. USP8 inhibitors can suppress the growth of various tumors. In this study, the effects of a potent USP8 inhibitor, DUBs-IN-2, on ACTH production and cell proliferation were examined in mouse corticotroph tumor (AtT-20) cells. Proopiomelanocortin (Pomc) mRNA levels and ACTH levels were decreased in AtT-20 cells by DUBs-IN-2. Further, cell proliferation was inhibited, and apoptosis was induced by DUBs-IN-2. Transcript levels of pituitary tumor-transforming gene 1 (Pttg1), a pituitary tumor growth marker, were increased; and transcript levels of stress response growth arrest and DNA damage-inducible 45 (Gadd45β) and Cdk5 and ABL enzyme substrate 1 (Cables1) mRNA levels were increased in response to the drug. Gadd45β or Cables1 knockdown partially inhibited the DUBs-IN-2-induced decrease in cell proliferation, but not Pomc mRNA levels. Both GADD45β and CABLES1 may be responsible, at least in part, for the USP8-induced suppression of corticotroph tumor cell proliferation. USP-8 may be a new treatment target in Cushing's disease.

Lapatinib decreases the ACTH production and proliferation of corticotroph tumor cells

Cushing's disease is almost always caused by hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. A mutation in the deubiquitinase gene USP8 has been found in human ACTH-producing pituitary adenoma cells. This mutational hotspot hyperactivates USP8, rescuing epidermal growth factor receptor (EGFR) from lysosomal degradation and ensuring its sustained signaling in Cushing's disease. An EGFR inhibitor would be an effective anti-tumor agent in EGFR-related tumors. We investigated the effect of a potent dual tyrosine kinase inhibitor, lapatinib, on ACTH production and cell proliferation in AtT-20 mouse corticotroph tumor cells. Lapatinib decreased proopiomelanocortin (Pomc) mRNA levels and ACTH levels in AtT-20 cells and also inhibited cell proliferation, induced apoptosis, and decreased pituitary tumor-transforming gene 1 (Pttg1), a hallmark of pituitary tumors, mRNA levels. KSN/Slc nude mice were subcutaneously inoculated with AtT-20 cells. After 1 week, the mice were randomized either to control or lapatinib groups. The inhibitor decreased the tumor weight of AtT-20 allografts in vivo versus control mice. Lapatinib also significantly decreased Pomc and Pttg1 mRNA levels in the tumor and plasma ACTH and corticosterone levels in vivo. Thus, lapatinib decreases the ACTH production and proliferation of corticotroph tumor cells. An EGFR-targeting therapy could be an important treatment for Cushing's disease.

Attenuation of MAMLD1 Expression Suppresses the Growth and Migratory Properties of Gonadotroph Pituitary Adenomas

Gonadotroph pituitary adenomas (GPAs) constitute approximately 15-40% of pituitary tumors. Some GPAs can be highly infiltrative, making full surgical resection challenging and increasing the risk of recurrence. The transcriptional co-activator Mastermind-Like Domain Containing 1 (MAMLD1, CXorf6, F18) is involved in regulating signaling pathways important in pituitary tumorigenesis, including the Notch signaling pathway. However, MAMLD1's role in GPA remains unknown. GPA biopsies were collected from 96 patients following surgery, who were monitored until tumor recurrence. GPA tissue was used for immunohistochemistry. The murine GPA cell lines αT3 and LβT2 were used for in vitro experiments. Lentiviral constructs were employed for MAMLD1 knockdown (KD) and dominant negative (DN) mutant experiments. Quantitative real-time PCR (qPCR) and Western blotting of MAMLD1 and Notch2 were performed. MTT and Transwell assays were used to quantify proliferation and migration, respectively. An αT3 xenograft model was established in athymic nude mice followed by fluorescent IHC of xenograft tumors. MAMLD1 and Notch2 levels correlated positively with aggressive GPAs. Increased MAMLD1 levels correlated with shortened recurrence-free survival (RFS) in aggressive GPA patients. Moreover, MAMLD1 expression independently affected patient RFS according to multivariate Cox regression. In vitro, MAMLD1 KD in the murine GPA cell lines attenuated their proliferation and migration and Notch2 expression. Additionally, DN MAMLD1^L210X lowered their proliferative and migratory capacity. MAMLD1 KD suppressed tumor growth and Notch2 expression in murine xenografts. MAMLD1 may serve as a predictor of GPA patient outcome and may also be leveraged as a possible therapeutic target for aggressive GPA tumors.

Oxidative stress and mitochondrial adaptive shift during pituitary tumoral growth

The cellular transformation of normal functional cells to neoplastic ones implies alterations in the cellular metabolism and mitochondrial function in order to provide the bioenergetics and growth requirements for tumour growth progression. Currently, the mitochondrial physiology and dynamic shift during pituitary tumour development are not well understood. Pituitary tumours present endocrine neoplastic benign growth which, in previous reports, we had shown that in addition to increased proliferation, these tumours were also characterized by cellular senescence signs with no indication of apoptosis. Here, we show clear evidence of oxidative stress in pituitary cells, accompanied by bigger and round mitochondria during tumour development, associated with augmented biogenesis and an increased fusion process. An activation of the Nrf2 stress response pathway together with the attenuation of the oxidative damage signs occurring during tumour development were also observed which will probably provide survival advantages to the pituitary cells. These neoplasms also presented a progressive increase in lactate production, suggesting a metabolic shift towards glycolysis metabolism. These findings might imply an oxidative stress state that could impact on the pathogenesis of pituitary tumours. These data may also reflect that pituitary cells can modulate their metabolism to adapt to different energy requirements and signalling events in a pathophysiological situation to obtain protection from damage and enhance their survival chances. Thus, we suggest that mitochondria function, oxidative stress or damage might play a critical role in pituitary tumour progression.

Pathogenesis of non-functioning pituitary adenomas

The pathogenesis of non functioning pituitary adenomas (NFPA) is a complex process involving several factors, from molecular to genetic and epigenetic modifications, where tumor suppressor genes, oncogenes, cell cycle derangements have been demonstrated to play an important role. MicroRNAs (miRNAs) have also been identified as possible players in NFPA tumorigenesis and pituitary stem cells have been investigated for their potential role in pituitary tumor initiation. However, a critical role for paracrine signalling has also been highlighted. This review focuses on the current knowledge on the involvement of these factors in NFPA pathogenesis.

Autocrine IL-6 mediates pituitary tumor senescence

Cellular senescence is a stable proliferative arrest state. Pituitary adenomas are frequent and mostly benign, but the mechanism for this remains unknown. IL-6 is involved in pituitary tumor progression and is produced by the tumoral cells. In a cell autonomous fashion, IL-6 participates in oncogene-induced senescence in transduced human melanocytes. Here we prove that autocrine IL-6 participates in pituitary tumor senescence. Endogenous IL-6 inhibition in somatotroph MtT/S shRNA stable clones results in decreased SA-β-gal activity and p16INK4a but increased pRb, proliferation and invasion. Nude mice injected with IL-6 silenced clones develop tumors contrary to MtT/S wild type that do not, demonstrating that clones that escape senescence are capable of becoming tumorigenic. When endogenous IL-6 is silenced, cell cultures derived from positive SA-β-gal human tumor samples decrease the expression of the senescence marker. Our results establish that IL-6 contributes to maintain senescence by its autocrine action, providing a natural model of IL-6 mediated benign adenoma senescence.

Bioinformatic analysis of gene expression profiles of pituitary gonadotroph adenomas

The aim of the present study was to identify genes, microRNAs (miRNAs/miRs) or pathways associated with the development of pituitary gonadotroph adenomas. The array data of GSE23207, which included 16 samples of multiple endocrine neoplasia-associated rat pituitary homozygous mutations and 5 pituitary tissue samples from healthy rats, were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were analyzed prior to functional enrichment analysis and protein-protein interaction (PPI) network construction. miRNAs associated with DEGs were predicted, and an miRNA-target regulatory network was constructed. A total of 187 upregulated and 370 downregulated DEGs were identified in the pituitary gonadotroph adenoma group compared with the healthy (control) group. Cyclin-dependent kinase (Cdk) 1 exhibited the highest degree in the PPI network. The upregulated DEGs were predominately enriched in ‘neuroactive ligand-receptor interaction’ pathway, and downregulated DEGs were mainly enriched in ‘cell cycle’. The DEGs in module were predominately enriched in the ‘cell cycle’, whereas DEGs in module b and c were enriched in ‘neuroactive ligand-receptor interaction’. miR-374, −153, −145 and −33 were identified as important miRNAs in the regulation of the DEGs. Cdk1, cyclin (Ccn) A2, Ccnb1, ‘cell cycle’ and ‘neuroactive ligand-receptor interaction’ pathways may serve important roles in the development of pituitary gonadotroph adenomas; Ccna2 and Ccnb1 may contribute to this development via an effect on the ‘cell cycle’ pathway. Furthermore, miR-374 and −145 may contribute to the development of pituitary gonadotroph adenomas via regulation of the expression of target genes.

Atypical pituitary adenoma with MEN1 somatic mutation associated with abnormalities of DNA mismatch repair genes; MLH1 germline mutation and MSH6 somatic mutation

The mechanism of pituitary tumorigenesis remains largely unknown. Lynch syndrome is an autosomal, dominantly inherited syndrome caused by a defective mismatch repair (MMR) mechanism involved in the development of various tumors at an early age. In this case study, we showed the occurrence of pituitary tumors associated with Lynch syndrome for the first time and performed genetic and immunohistochemical analysis to evaluate the genetic aberrations that might be related to the tumorigenesis and proliferation. A 68-year-old female patient with Lynch syndrome due to mutL homolog 1 (MLH1) gene mutation suffered from hypersecretion of adrenocorticotrophic hormone (ACTH), hypercortisolism and a rapidly progressive pituitary tumor. We performed genetic analysis by whole genome sequencing with genomic DNA of the pituitary tumor and peripheral blood leukocytes, as well as immunohistochemical analysis of MMR proteins. Genetic analysis revealed that the tumor had homozygous gene mutation of MEN1 associated with pituitary tumorigenesis and mutS homolog 6 (MSH6) gene. Furthermore, immunohistochemical analysis showed that MLH1 and MSH6 immunoexpression were negative. We reveal for the first time that MMR abnormality could cause somatic mutation of MEN1 and pituitary tumor occurrence is associated with Lynch syndrome. We suggest that the identified gene mutations, especially those of MSH6 and MLH1 genes, may be involved in the pathogenesis and proliferation of pituitary tumor. The knowledge obtained from our case study is important to elucidate the pathogenesis and proliferation mechanisms of pituitary tumors.

Inhibitory effects of a selective Jak2 inhibitor on adrenocorticotropic hormone production and proliferation of corticotroph tumor AtT20 cells

Purpose

The primary cause of Cushing’s disease is adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. EGFR signaling induces POMC mRNA-transcript levels and ACTH secretion from corticotroph tumors. The Jak–STAT pathway is located downstream of EGFR signaling; therefore, a Jak2 inhibitor could be an effective therapy for EGFR-related tumors. In this study, we determined the effect of a potent and selective Jak2 inhibitor, SD1029, on ACTH production and proliferation in mouse AtT20 corticotroph tumor cells.

Materials and methods

AtT20 pituitary corticotroph tumor cells were cultured after transfection with PTTG1- or GADD45β-specific siRNA. Expression levels of mouse POMC, PTTG1, and GADD45β mRNAs were evaluated using quantitative real-time polymerase chain reaction. ACTH levels were measured using ACTH ELISA. Western blot analysis was performed to examine protein expression of phosphorylated STAT3/STAT3. Viable cells and DNA fragmentation were measured using a cell-proliferation assay and cell-death detection ELISA, respectively. Cellular DNA content was analyzed using fluorescence-activated cell sorting.

Results

SD1029 decreased POMC and PTTG1 mRNA and ACTH levels, while increasing GADD45β levels. The drug also decreased AtT20-cell proliferation and induced apoptosis, but did not alter cell-cycle progression. SD1029 also inhibited STAT3 phosphorylation. PTTG1 knockdown inhibited POMC mRNA levels and cell proliferation. However, combined treatment with PTTG1 knockdown and SD1029 had no additive effect on POMC mRNA levels or cell proliferation. GADD45β knockdown inhibited the SD1029-induced decrease in POMC mRNA levels and also partially inhibited the decrease in cell proliferation.

Conclusion

Both PTTG1 and GADD45β may be responsible, at least in part, for the Jak2-induced suppression of ACTH synthesis and cell proliferation. Accordingly, therapies that target EGFR-dependent Jak2/STAT3 may have clinical applications for treating Cushing’s disease.

Genetic Aspects of Pituitary Adenomas

Although most of pituitary adenomas are benign, they may cause significant burden to patients. Sporadic adenomas represent the vast majority of the cases, where recognized somatic mutations (eg, GNAS or USP8), as well as altered gene-expression profile often affecting cell cycle proteins have been identified. More rarely, germline mutations predisposing to pituitary adenomas -as part of a syndrome (eg, MEN1 or Carney complex), or isolated to the pituitary (AIP or GPR101) can be identified. These alterations influence the biological behavior, clinical presentations and therapeutic responses, and their full understanding helps to provide appropriate care for these patients.

Programmed cell senescence: role of IL-6 in the pituitary

IL-6 is a pleiotropic cytokine with multiple pathophysiological functions. As a key factor of the senescence secretome, it can not only promote tumorigenesis and cell proliferation but also exert tumor suppressive functions, depending on the cellular context. IL-6, as do other cytokines, plays important roles in the function, growth and neuroendocrine responses of the anterior pituitary gland. The multiple actions of IL-6 on normal and adenomatous pituitary function, cell proliferation, angiogenesis and extracellular matrix remodeling indicate its importance in the regulation of the anterior pituitary. Pituitary tumors are mostly benign adenomas with low mitotic index and rarely became malignant. Premature senescence occurs in slow-growing benign tumors, like pituitary adenomas. The dual role of IL-6 in senescence and tumorigenesis is well represented in pituitary tumor development, as it has been demonstrated that effects of paracrine IL-6 may allow initial pituitary cell growth, whereas autocrine IL-6 in the same tumor triggers senescence and restrains aggressive growth and malignant transformation. IL-6 is instrumental in promotion and maintenance of the senescence program in pituitary adenomas.

PTTG regulates the metabolic switch of ovarian cancer cells via the c-myc pathway

Human pituitary tumor-transforming gene (PTTG) is a proto-oncogene involved in the development, invasion, and metastasis of many types of cancer, including ovarian cancer. However, little is known about the role of PTTG in the metabolic shift of ovarian cancer cells. In our study, we show that PTTG expression was positively correlated with the differentiation degree of ovarian cancer tissue. In addition, PTTG suppression by specific shRNA could inhibit the proliferation of ovarian cancer cells A2780 and SKOV-3. Furthermore, aerobic glycolysis was suppressed and oxidative phosphorylation was increased in ovarian cancer cells after PTTG suppression. We further found that the expression of c-myc and several crucial enzymes involved in aerobic glycolysis (e.g., PKM2, LDHA, and glucose transporter 1 (GLUT-1)) were downregulated by PTTG knockwown. Overexpression of c-myc could prevent the metabolic shift induced by PTTG knockwown. Together, our findings suggest that the oncogene PTTG promotes the progression of ovarian cancer cells, and its loss resists tumor development, in part, by regulating cellular metabolic reprogramming that supports cell growth and proliferation via c-myc pathway.

Prolactinomas: evolution after menopause

OBJETIVE

The aim was to assess the evolution of tumor size and prolactin (PRL) levels in patients with micro and macroprolactinomas diagnosed and treated with dopamine agonists during fertile age, and the effects of suspension of drugs after menopause.

SUBJECTS AND METHODS

Retrospective study, 29 patients with prolactinomas, 22 microadenomas and 7 macroadenomas, diagnosed during their fertile age were studied in their menopause; treatment was stopped in this period. Age at menopause was 49 ± 3.6 years. The average time of treatment was 135 ± 79 months. The time of follow-up after treatment suspension was 4 to 192 months. Results: Pre-treatment PRL levels in micro and macroadenomas were 119 ± 57 ng/mL and 258 ± 225 ng/mL, respectively. During menopause after treatment suspension, and at the latest follow-up: in microadenomas PRL levels were 23 ± 13 ng/mL and 16 ± 5.7 ng/mL, respectively; in macroadenomas, PRL levels were 20 ± 6.6 ng/mL 5t5and 25 ± 18 ng/mL, respectively. In menopause after treatment suspension, the microadenomas had disappeared in 9/22 and had decreased in 13/22. In the group of patients whose tumor had decreased, in the latest follow-up, tumors disappeared in 7/13 and remained unchanged in 6/13. In macroadenomas, after treatment suspension 3/7 had disappeared, 3/7 decreased and 1/7 remained unchanged. In the latest control in the 3 patients whose tumor decreased, disappeared in 1/3, decreased in 1/3 and there was no change in the remaining.

CONCLUSIONS

Normal PRL levels and sustained reduction or disappearance of adenomas were achieved in most of patients, probably due to the decrease of estrogen levels. Dopamine agonists might be stopped after menopause in patients with prolactinomas.

Inhibition of heat shock protein 90 decreases ACTH production and cell proliferation in AtT-20 cells

PURPOSE

Cushing's disease is primarily caused by adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. If excision of the tumor from the pituitary, which is the primary treatment for Cushing's disease, is unsuccessful, further medical therapy is needed to treat the resultant hypercortisolism. Some of the drugs used to treat this condition have shown potential therapeutic benefits, but a more effective treatment should be explored for the treatment of Cushing's disease. In the present study, we determined the effect of heat shock protein 90 inhibitors on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells.

METHODS

AtT-20 pituitary corticotroph tumor cells were cultured. The expression levels of mouse proopiomelanocortin (POMC) and pituitary tumor transforming gene 1 (PTTG1) mRNA were evaluated using quantitative real-time PCR. Cellular DNA content was analyzed with fluorescence-activated cell sorting (FACS) analysis. The protein levels were determined by Western blot analysis.

RESULTS

Both 17-allylamino-17-demethoxygeldanamycin and CCT018159 decreased POMC mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that both drugs suppress ACTH synthesis and secretion in corticotroph tumor cells. Both drugs also decreased cell proliferation and induced apoptosis. FACS analyses revealed that both agents increased the percentage of AtT-20 cells in the G2/M phase. These drugs decreased cell proliferation, presumably due to the induction of cell death and arrest of the cell cycle in AtT-20 cells. Tumor weight in mice xenografted with AtT-20 cells and treated with CCT018159 was lower than in AtT-20-xenografted control mice. CCT018159 also decreased plasma ACTH levels, and POMC and PTTG1 mRNA levels in the tumor cells.

CONCLUSIONS

CCT018159 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.

Evidence of cellular senescence during the development of estrogen-induced pituitary tumors

Although pituitary adenomas represent 25% of intracranial tumors, they are usually benign, with the mechanisms by which these tumors usually avoid an invasive profile and metastatic growth development still remaining unclear. In this context, cellular senescence might constitute a plausible explanation for the benign nature of pituitary adenomas. In this study, we investigated the emergence of cellular senescence as a growth control mechanism during the progression of estrogen-induced pituitary tumors. The quantification of Ki67-immunopositive cells in the pituitaries of estrogenized male rats after 10, 20, 40, and 60 days revealed that the mitogenic potential rate was not sustained for the whole period analyzed and successively decreased after 10 days of estrogen exposure. In addition, the expression of cellular senescence features, such as the progressive rise in the enzymatic senescence-associated b-galactosidase (SA-b-gal) activity, IL6, IL1b, and TGFb expression, was observed throughout pituitary tumor development. Furthermore, tumoral pituitary cells also displayed nuclear pATM expression, indicating activated DNA damage signaling, with a significant increase in p21 expression also being detected. The associations among DNA damage signaling activation, SA-b-gal expression, and p21 may provide a reliable combination of senescence-associated markers for in vivo pituitary senescence detection. These results suggest a role for this cellular process in the regulation of pituitary cell growth. Thus, cellular senescence should be conceived as a contributing component to the benign nature of pituitary adenomas, thereby influencing the capability of the pituitary gland to avoid unregulated cell proliferation.

Pituitary tumors

Pituitary tumors are commonly encountered intracranial neoplasms that are invariably benign. Classic oncogene mutations are not encountered in these tumors, and disrupted cell cycle control and growth factor signaling likely contribute to pathogenesis and natural history. They have unique clinical features that are determined by the secreted hormone gene product.

A structural and functional acromegaly classification

CONTEXT

GH-secreting pituitary adenomas exhibit heterogeneous natural history ranging from small tumors to large aggressive adenomas.

OBJECTIVE

To rigorously classify an acromegaly patient cohort defined by clinical, radiological, histopathological, and outcome characteristics.

DESIGN

Cross-sectional study.

SETTING

Tertiary referral pituitary center.

PATIENTS

Subjects were selected from a pituitary tumor research registry that includes 1178 patients with pituitary disease. Cluster analysis was performed on 338 acromegaly patients.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Biochemically active disease with elevated IGF-1 levels at follow-up.

RESULTS

Cluster analysis of all patients yielded 292 who were rigorously classified to three acromegaly types. Type 1 (50%) comprised older patients with the longest follow-up and most favorable outcomes, characterized by densely granulated, nonaggressive microadenomas and macroadenomas. Type 1 tumors extend to the sphenoid sinus more frequently than suprasellar extension (concave tumor image) and express abundant immunoreactive p21 and somatostatin receptor 2. Type 2 (19%) comprised noninvasive, densely or sparsely granulated macroadenomas, without significant extension (flat tumor image), with intermediate biochemical outcome. Type 3 (31%) was characterized by sparsely granulated aggressive macroadenomas and comprised patients with adverse therapeutic outcomes, despite receiving more treatments. These tumors extend to both the sphenoid sinus and suprasellar regions with commonly encountered optic chiasm compression ("peanut" magnetic resonance image), with low tumor p21 and somatostatin receptor 2 expression.

CONCLUSIONS

After validation, this classification may be useful to accurately identify acromegaly patients with distinctive patterns of disease aggressiveness and outcome, as well as to provide an accurate tool for selection criteria in clinical studies.

Inhibitory effects of trichostatin A on adrenocorticotropic hormone production and proliferation of corticotroph tumor AtT-20 cells

Cushing's disease is primarily caused by adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. Pituitary tumor-transforming gene 1 (PTTG1) expression, a hallmark of pituitary tumors, stimulates pituitary cell proliferation. Histone deacetylases (HDACs) play an important role in regulating gene transcription and HDAC inhibitors induce cellular differentiation and suppress tumor cell proliferation. HDAC inhibitors also repress PTTG1 mRNA levels. Trichostatin A (TSA) is a potent cell-permeable HDAC inhibitor that blocks cell cycle progression. In the present study, we determined the effect of TSA on ACTH production and cellular proliferation in mouse AtT-20 corticotroph tumor cells. TSA decreased proopiomelanocortin (POMC) mRNA levels in AtT-20 cells and reduced ACTH levels in the culture medium of these cells. The TSA-induced decreases in POMC mRNA levels were not modulated when TSA and dexamethasone were simultaneously administered. Drug treatment also decreased AtT-20 cell proliferation, induced apoptosis, and increased the percentage of cells in G0/G1 phase using flow cytometry. TSA decreased PTTG1 mRNA levels. Furthermore, PTTG1 knockdown inhibited cellular proliferation. Its knockdown also inhibited POMC mRNA and ACTH levels. TSA inhibits ACTH production and corticotroph tumor cell proliferation. TSA may inhibit cellular proliferation, and ACTH synthesis and secretion by decreasing PTTG1 expression.

Aggressive pituitary tumors

Pituitary adenomas are common intracranial tumors that are mainly considered as benign. Rarely, these tumors can exhibit an aggressive behavior, characterized by gross invasion of the surrounding tissues, resistance to conventional treatment leading to early and frequent recurrences. Even more rarely, pituitary tumors can give rise to cerebrospinal or systemic metastases qualifying as pituitary carcinomas according to the latest WHO definition. In the same classification, a subset of tumors with relatively distinct histopathological features was identified and defined as atypical adenomas designated to follow a more aggressive clinical course. This classification, although clinically useful, does not provide an accurate correlation between histopathological findings and the clinical behavior of these tumors, neither is it adequate to convey the precise features of 'aggressive' tumors. Thus, 'aggressive' pituitary adenomas need to be properly defined with clinical, radiological, histological and molecular markers in order to identify patients at increased risk of early recurrence or subsequent tumor progression. At present, no single marker or classification system of pituitary tumor aggressiveness exists, and clinically useful information in the literature is insufficient to guide diagnostic and therapeutic decisions. Treatment of patients with aggressive pituitary tumors is challenging since conventional treatments often fail, necessitating multiple surgical procedures with additional radiotherapy. Although traditional chemotherapy applied in other neuroendocrine tumors has not been shown to be efficacious, newer agents, particularly temozolomide, have shown promising results and are currently used despite the lack of data from a randomized prospective trial. Molecular targeted therapies such as mTOR and epidermal growth factor inhibitors have also been applied and might prove to be useful in the management of these patients. In the present review, we provide information regarding the epidemiology and clinical, histopathological and molecular features of aggressive pituitary tumors using recent employed definitions. In addition, we review currently employed therapeutic means providing a therapeutic algorithm and highlight the need to identify more specific disease-related and prognostic markers and the necessity for central registration of these tumors.

Inhibitory effects of SOM230 on adrenocorticotropic hormone production and corticotroph tumor cell proliferation in vitro and in vivo

Adrenocorticotropic hormone (ACTH) production by pituitary corticotroph adenomas is the main cause of Cushing's disease. A drug that targets pituitary ACTH-secreting adenomas would aid treatment of Cushing's disease. Octreotide, a somatostatin receptor type 2 (SSTR2)-preferring somatostatin analogue, has no effect on ACTH secretion in patients with Cushing's disease. The multiligand SOM230 (pasireotide) displays a much higher affinity for SSTR1 and SSTR5 than octreotide and suppresses ACTH secretion in cultures of human corticotroph tumors to a greater extent than octreotide. In the present in vitro and in vivo study, we determined the effect of SOM230 on ACTH production and cell proliferation of AtT-20 corticotroph tumor cells. SOM230 decreased proopiomelanocortin (POMC) mRNA levels in AtT-20 cells and ACTH levels in the culture medium of these cells, suggesting that SOM230 suppresses ACTH synthesis and secretion in corticotroph tumor cells. SOM230 also decreased cell proliferation and both cyclic adenosine monophosphate response element-binding protein and Akt phosphorylation in AtT-20 cells. SSTR5 knockdown inhibited the SOM230-induced decreases in cell proliferation. Fluorescence-activated cell sorting analyses revealed that SOM230 did not attenuate cell cycle progression. Tumor weight in mice xenografted with AtT-20 cells and treated with SOM230 was significantly lower than in AtT-20-xenografted control mice. SOM230 also significantly decreased plasma ACTH levels, and POMC and pituitary tumor transforming gene mRNA levels in the tumor cells. Thus, SOM230 inhibits ACTH production and corticotroph tumor cell proliferation in vitro and in vivo.

Regulation of LH/FSH expression by secretoglobin 3A2 in the mouse pituitary gland

Secretoglobin (SCGB) 3A2 was originally identified as a downstream target for the homeodomain transcription factor NKX2-1 in the lung. NKX2-1 plays a role in the genesis and expression of genes in the thyroid, lung and ventral forebrain; Nkx2-1-null mice have no thyroid and pituitary and severely hypoplastic lungs and hypothalamus. To demonstrate whether SCGB3A2 plays any role in pituitary hormone production, NKX2-1 and SCGB3A2 expression in the mouse pituitary gland was examined by immunohistochemical analysis and RT-PCR. NKX2-1 was localized in the posterior pituitary lobe, whereas SCGB3A2 was observed in both anterior and posterior lobes as shown by immunohistochemistry and RT-PCR. Expression of CCAAT-enhancer binding proteins (C/EBPs), which regulate mouse Scgb3a2 transcription, was also examined by RT-PCR. C/EBPβ, γ, δ and ζ were expressed in the adult mouse pituitary gland. SCGB3A2 was expressed in the anterior and posterior lobes from postnatal days 1 and 5, respectively and the areas where SCGB3A2 expression was found coincided with the area where FSH-secreting cells were found. Double-staining for SCGB3A2 and pituitary hormones revealed that SCGB3A2 was mainly localized in gonadotrophs in 49 % of FSH-secreting cells and 47 % of LH-secreting cells. In addition, SCGB3A2 dramatically inhibited LH and FSH mRNA expression in rat pituitary primary cell cultures. These results suggest that SCGB3A2 regulates FSH/LH production in the anterior pituitary lobe and that transcription factors other than NKX2-1 may regulate SCGB3A2 expression.

Characterization of MENX-associated pituitary tumours

AIMS

The aim of this study is to evaluate the pathological features, serum hormone levels and ex vivo cultures of pituitary adenomas that occur in rats affected by MENX syndrome. MENX is multiple endocrine neoplasia syndrome caused by a germline mutation in the cell cycle inhibitor p27. Characterization of MENX adenomas is a prerequisite to exploit this animal model for molecular and translational studies of pituitary adenomas.

METHODS

We investigated MENX pituitary adenomas with immunohistochemistry, double immunofluorescence, electron microscopy, reverse transcription polymerase chain reaction (RT-PCR), measurement of serum hormone levels and ex vivo cultures.

RESULTS

Adenomas in MENX rats belong to the gonadotroph lineage. They start from 4 months of age as multiple neoplastic nodules and progress to become large lesions that efface the gland. Adenomas are composed of chromophobic cells predominantly expressing the glycoprotein alpha-subunit (αGSU). They show mitotic activity and high Ki67 labelling. A few neoplastic cells co-express gonadotropins and the transcription factor steroidogenic factor 1, together with growth hormone or prolactin and Pit-1, suggesting that they are not fully committed to one cell lineage. Ex vivo cultures show features similar to the primary tumour.

CONCLUSIONS

Our results suggest that p27 function is critical to regulate gonadotroph cells growth. The MENX syndrome represents a unique model to elucidate the physiological and molecular mechanisms mediating the pathogenesis of gonadotroph adenomas.

Growth hormone is a cellular senescence target in pituitary and nonpituitary cells

Premature proliferative arrest in benign or early-stage tumors induced by oncoproteins, chromosomal instability, or DNA damage is associated with p53/p21 activation, culminating in either senescence or apoptosis, depending on cell context. Growth hormone (GH) elicits direct peripheral metabolic actions as well as growth effects mediated by insulin-like growth factor 1 (IGF1). Locally produced peripheral tissue GH, in contrast to circulating pituitary-derived endocrine GH, has been proposed to be both proapoptotic and prooncogenic. Pituitary adenomas expressing and secreting GH are invariably benign and exhibit DNA damage and a senescent phenotype. We therefore tested effects of nutlin-induced p53-mediated senescence in rat and human pituitary cells. We show that DNA damage senescence induced by nutlin triggers the p53/p21 senescent pathway, with subsequent marked induction of intracellular pituitary GH in vitro. In contrast, GH is not induced in cells devoid of p53. Furthermore we show that p53 binds specific GH promoter motifs and enhances GH transcription and secretion in senescent pituitary adenoma cells and also in nonpituitary (human breast and colon) cells. In vivo, treatment with nutlin results in up-regulation of both p53 and GH in the pituitary gland, as well as increased GH expression in nonpituitary tissues (lung and liver). Intracrine GH acts in pituitary cells as an apoptosis switch for p53-mediated senescence, likely protecting the pituitary adenoma from progression to malignancy. Unlike in the pituitary, in nonpituitary cells GH exerts antiapoptotic properties. Thus, the results show that GH is a direct p53 transcriptional target and fulfills criteria as a p53 target gene. Induced GH is a readily measurable cell marker for p53-mediated cellular senescence.

Silencing of RASSF3 by DNA hypermethylation is associated with tumorigenesis in somatotroph adenomas

The pathogenic mechanisms underlying pituitary somatotroph adenoma formation, progression are poorly understood. To identify candidate tumor suppressor genes involved in pituitary somatotroph adenoma tumorigenesis, we used HG18 CpG plus Promoter Microarray in 27 human somatotroph adenomas and 4 normal human adenohypophyses. RASSF3 was found with frequent methylation of CpG island in its promoter region in somatotroph adenomas but rarely in adenohypophyses. This result was confirmed by pyrosequencing analysis. We also found that RASSF3 mRNA level correlated negatively to its gene promoter methylation level. RASSF3 hypermethylation and downregulation was also observed in rat GH3 and mouse GT1.1 somatotroph adenoma cell lines. 5-Aza-2′ deoxycytidine and trichostatin-A treatment induced RASSF3 promoter demethylation, and restored its expression in GH3 and GT1.1 cell lines. RASSF3 overexpression in GH3 and GT1.1 cells inhibited proliferation, induced apoptosis accompanied by increased Bax, p53, and caspase-3 protein and decreased Bcl-2 protein expression. We also found that the antitumor effect of RASSF3 was p53 dependent, and p53 knockdown blocked RASSF3-induced apoptosis and growth inhibition. Taken together, our results suggest that hypermethylation-induced RASSF3 silencing plays an important role in the tumorigenesis of pituitary somatotroph adenomas.

Clusterin and FOXL2 act concordantly to regulate pituitary gonadotroph adenoma growth

Pituitary tumors grow slowly and despite their high prevalence are invariably benign. We therefore studied mechanisms underlying pituitary tumor growth restraint. Pituitary tumor transforming gene (PTTG), the index human securin, a hallmark of pituitary tumors, triggers pituitary cell proliferation and murine pituitary tumor development. We show that human gonadotroph cell pituitary tumors, unlike other secreting tumor types, express high levels of gonadotroph-specific forkhead transcription factor FOXL2, and both PTTG and Forkhead box protein L2 (FOXL2) stimulate gonadotroph clusterin (Clu) expression. Both Clu RNA isoforms are abundantly expressed in these nonhormone-secreting human tumors, and, when cultured, these tumor cells release highly abundant levels of secreted Clu. FOXL2 directly stimulates the Clu gene promoter, and we show that PTTG triggers ataxia telangiectasia mutated kinase/IGF-I/p38MAPK DNA damage/chromosomal instability signaling, which in turn also induces Clu expression. Consequently, Clu restrains pituitary cell proliferation by inducing cyclin dependent kinase inhibitors p16 and p27, whereas Clu deletion down-regulates p16 and p27 in the Clu(-/-) mouse pituitary. FOXL2 binds and suppresses the PTTG promoter, and Clu also suppresses PTTG expression, thus neutralizing protumorigenic PTTG gonadotroph tumor cell properties. In vivo, murine gonadotroph LβT2 tumor cell xenografts overexpressing Clu and FOXL2 both grow slower and elicit smaller tumors. Thus, gonadotroph tumor cell proliferation is determined by the interplay between cell-specific FOXL2 with PTTG and Clu.

PI3K/Akt/mTOR and Raf/MEK/ERK signaling pathways perturbations in non-functioning pituitary adenomas

Non-functioning pituitary adenomas (NFPAs) comprise a heterogeneous group, which are considered the most common pituitary tumor. As no clinically hormone hypersecretion is apparent, non-functioning pituitary adenomas are often diagnosed only when they are large enough to cause tumor mass effects, such as hypopituitarism, visual field defects or headaches. Efficient medical therapy for NFPAs is currently unavailable and surgical treatment of these tumors is not always satisfactory. Characterization of signaling regulatory events in the context of NFPAs may enable the development of new attractive novel strategies. Although data regarding gene expression profiling of signaling pathways in NFPAs have accumulated, studies aimed at fine-classification of NFPAs-specific signaling regulatory mechanisms and feedback loops are scarce.

Cell-type specific modulation of pituitary cells by activin, inhibin and follistatin

Activins are multifunctional proteins and members of the TGF-β superfamily. Activins are expressed locally in most tissues and, analogous to the actions of other members of this large family of pleiotropic factors, play prominent roles in the regulation of diverse biological processes in both differentiated and embryonic stem cells. They have an essential role in maintaining tissue homeostasis in the adult and are known to contribute to the developmental programs in the embryo. Activins are further implicated in the growth and metastasis of tumor cells. Through distinct modes of action, inhibins and follistatins function as antagonists of activin and several other TGF-β family members, including a subset of BMPs/GDFs, and modulate cellular responses and the signaling cascades downstream of these ligands. In the pituitary, the activin pathway is known to regulate key aspects of gonadotrope functions and also exert effects on other pituitary cell types. As in other tissues, activin is produced locally by pituitary cells and acts locally by exerting cell-type specific actions on gonadotropes. These local actions of activin on gonadotropes are modulated by the autocrine/paracrine actions of locally secreted follistatin and by the feedback actions of gonadal inhibin. Knowledge about the mechanism of activin, inhibin and follistatin actions is providing information about their importance for pituitary function as well as their contribution to the pathophysiology of pituitary adenomas. The aim of this review is to highlight recent findings and summarize the evidence that supports the important functions of activin, inhibin and follistatin in the pituitary.