The pituitary tumour epigenome: aberrations and prospects for targeted therapy

CircVPS13C promotes pituitary adenoma growth by decreasing the stability of IFITM1 mRNA via interacting with RRBP1

CircRNAs play important roles in a variety of biological processes by acting as microRNA sponges and protein scaffolds or by encoding functional proteins. However, their functions and underlying mechanisms remain largely unknown. Distinctive circRNA patterns were explored by comparing nonfunctioning pituitary adenomas (NFPAs) and normal pituitary tissues with a circRNA array. The biological functions of selected circRNAs were determined in vitro and in vivo. RNA-seq and circRNA pulldown assays were applied to investigate the underlying mechanisms. The circRNA profile of NFPAs is tremendously different from that of normal pituitary tissues. CircVPS13C is significantly upregulated in NFPA samples and cell lines. Gain- and loss-of-function experiments demonstrate that silencing circVPS13C inhibits the proliferation of pituitary tumor cells in vitro and in vivo. Mechanistically, circVPS13C silencing increases the expression of IFITM1 and subsequently activates its downstream genes involved in MAPK- and apoptosis-associated signaling pathways. Rescue experiments show that IFITM1 overexpression partly reverses the biological effects of circVPS13C. Further studies reveal that circVPS13C inhibits IFITM1 expression through a novel mechanism mainly by competitively interacting with RRBP1, a ribosome-binding protein of the endoplasmic reticulum membrane, and thereby alleviating the stability of IFITM1 mRNA. Clinically, circVPS13C expression is markedly higher in high-risk NFPA samples and is downregulated in patient serum 7 days post-transsphenoidal adenoma resection. Our findings suggest that circVPS13C is a critical regulator in the proliferation and development of NFPAs through a novel mechanism, whereby regulating mRNA stability via interacting with ribosome-binding proteins on the endoplasmic reticulum membrane.

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.

Potential biomarkers and lncRNA-mRNA regulatory networks in invasive growth hormone-secreting pituitary adenomas

PURPOSE

Growth hormone-secreting pituitary adenomas (GH-PAs) are common subtypes of functional PAs. Invasive GH-PAs play a key role in restricting poor outcomes. The transcriptional changes in GH-PAs were evaluated.

METHODS

In this study, the transcriptome analysis of six different GH-PA samples was performed. The functional roles, co-regulatory network, and chromosome location of differentially expressed (DE) genes in invasive GH-PAs were explored.

RESULTS

Bioinformatic analysis revealed 101 DE mRNAs and 70 DE long non-coding RNAs (lncRNAs) between invasive and non-invasive GH-PAs. Functional enrichment analysis showed that epithelial cell differentiation and development pathways were suppressed in invasive GH-PAs, whereas the pathways of olfactory transduction, retinol metabolism, drug metabolism-cytochrome P450, and metabolism of xenobiotics by cytochrome P450 had an active trend. In the protein-protein interaction network, 11 main communities were characterized by cell- adhesion, -motility, and -cycle; transport process; phosphorus and hormone metabolic processes. The SGK1 gene was suggested to play a role in the invasiveness of GH-PAs. Furthermore, the up-regulated genes OR51B6, OR52E4, OR52E8, OR52E6, OR52N2, MAGEA6, MAGEC1, ST8SIA6-AS1, and the down-regulated genes GAD1-AS1 and SPINT1-AS1 were identified in the competing endogenous RNA network. The RT-qPCR results further supported the aberrant expression of those genes. Finally, the enrichment of DE genes in chromosome 11p15 and 12p13 regions were detected.

CONCLUSION

Our findings provide a new perspective for studies evaluating the underlying mechanism of invasive GH-PAs.

Demethylation Status of Somatic DNA Extracted From Pituitary Neuroendocrine Tumors Indicates Proliferative Behavior

BACKGROUND

Cytosine intermediaries 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), epigenetic hallmarks, have never been investigated in pituitary neuroendocrine tumors (PitNET).

OBJECTIVE

To examine methylation-demethylation status of global deoxyribonucleic acid (DNA) in PitNET tissues and to assess its correlation with clinical and biological parameters.

MATERIALS AND METHODS

Altogether, 57 PitNET and 25 corresponding plasma samples were collected. 5mC and 5hmC were investigated using liquid chromatography-tandem mass spectrometry. Expression of DNA methyltransferase 1 (DNMT1); tet methylcytosine dioxygenase 1 through 3 (TET1-3); and ubiquitin-like, containing PHD and RING finger domains 1 and 2 (UHRF1-2) were measured by reverse transcription-polymerase chain reaction. Levels of 5hmC and UHRF1-2 were explored by immunohistochemistry. Effect of demethylating agent decitabine was tested on pituitary cell lines.

RESULTS

5hmC/5mC ratio was higher in less differentiated PitNET samples. A negative correlation between Ki-67 proliferation index and 5hmC, 5hmC to 5mC ratio were revealed. Higher 5mC was observed in SF-1 + gonadotroph adenomas with a higher Ki-67 index. Expressions of TET2 and TET3 were significantly higher in adenomas with higher proliferation rate. UHRF1 showed gradually increased expression in higher proliferative adenoma samples, and a significant positive correlation was detected between UHRF2 expression and 5hmC level. Decitabine treatment significantly decreased 5mC and increased 5hmC levels in both cell lines, accompanied with decreased cell viability and proliferation.

CONCLUSION

The demethylation process negatively correlated with proliferation rate and the ratio of 5hmC to 5mC was higher in less differentiated adenomas. Therefore, epigenetic markers can be potential biomarkers for PitNET behavior. Altering the epigenome in adenoma cells by decitabine decreased proliferation, suggesting that this treatment might be a novel medical treatment for PitNET.

Exploring the Role of Novel Medical Therapies for Aggressive Pituitary Tumors: A Review of the Literature-"Are We There Yet?"

Aggressive pituitary tumors account for up to 10% of pituitary tumors and are characterized by resistance to medical treatment and multiple recurrences despite standard therapies, including surgery, radiotherapy, and chemotherapy. They are associated with increased morbidity and mortality, particularly pituitary carcinomas, which have mortality rates of up to 66% at 1 year after diagnosis. Novel targeted therapies under investigation include mammalian target of rapamycin (mTOR), tyrosine kinase, and vascular endothelial growth factor (VEGF) inhibitors. More recently, immune checkpoint inhibitors have been proposed as a potential treatment option for pituitary tumors. An increased understanding of the molecular pathogenesis of aggressive pituitary tumors is required to identify potential biomarkers and therapeutic targets. This review discusses novel approaches to the management of aggressive pituitary tumors and the role of molecular profiling.

Molecular Network Basis of Invasive Pituitary Adenoma: A Review

Cases with pituitary adenoma comprise 10-25% of intracranial neoplasm, being the third most common intracranial tumor, most of the adenomas are considered to be benign. About 35% of pituitary adenomas are invasive. This review summarized the known molecular basis of the invasiveness of pituitary adenomas. The study pointed out that hypoxia-inducible factor-1α, pituitary tumor transforming gene, vascular endothelial growth factor, fibroblast growth factor-2, and matrix metalloproteinases (MMPs, mainly MMP-2, and MMP-9) are core molecules responsible for the invasiveness of pituitary adenomas. The reason is that these molecules have the ability to directly or indirectly induce cell proliferation, epithelial-to-mesenchymal transition, angiogenesis, degradation, and remodeling of extracellular matrix. HIF-1α induced by hypoxia or apoplexy inside the adenoma might be the initiating factor of invasive transformation, followed with angiogenesis for overexpressed VEGF, EMT for overexpressed PTTG, degradation of ECM for overexpressed MMPs, creating a suitable microenvironment within the tumor. Together, they form a complex interactive network. More investigations are required to further elucidate the mechanisms underlying the invasiveness of pituitary adenomas.

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.

Genomic Alterations and Complex Subclonal Architecture in Sporadic GH-Secreting Pituitary Adenomas

PURPOSE

The molecular pathogenesis of growth hormone-secreting pituitary adenomas is not fully understood. Cytogenetic alterations might serve as alternative driver events in GNAS mutation-negative somatotroph tumors.

EXPERIMENTAL DESIGN

We performed cytogenetic profiling of pituitary adenomas obtained from 39 patients with acromegaly and four patients with sporadic gigantism by using array comparative genomic hybridization analysis. We explored intratumor DNA copy-number heterogeneity in two tumor samples by using DNA fluorescence in situ hybridization (FISH).

RESULTS

Based on copy-number profiles, we found two groups of adenomas: a low-copy-number alteration (CNA) group (<12% of genomic disruption, 63% of tumors) and a high-CNA group (24% to 45% of genomic disruption, 37% of tumors). Arm-level CNAs were the most common abnormalities. GNAS mutation-positive adenomas belonged exclusively to the low-CNA group, whereas a subgroup of GNAS mutation-negative adenomas had a high degree of genomic disruption. We detected chromothripsis-related CNA profiles in two adenoma samples from an AIP mutation-positive patient with acromegaly and a patient with sporadic gigantism. RNA sequencing of these two samples identified 17 fusion transcripts, most of which resulted from chromothripsis-related chromosomal rearrangements. DNA FISH analysis of these samples demonstrated a subclonal architecture with up to six distinct cell populations in each tumor.

CONCLUSION

Somatotroph pituitary adenomas display substantial intertumor and intratumor DNA copy-number heterogeneity, as revealed by variable CNA profiles and complex subclonal architecture. The extensive cytogenetic burden in a subgroup of GNAS mutation-negative somatotroph adenomas points to an alternative tumorigenic pathway linked to genomic instability.

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.

Lactate dehydrogenase A promotes the invasion and proliferation of pituitary adenoma

Lactate dehydrogenase A (LDHA) has been reported to be involved in the initiation and progression of tumors. However, the potential role of LDHA in pituitary adenoma (PA) remains unknown. In this study, we showed that the expression levels of LDHA mRNA and protein were significantly elevated in invasive PA samples, and positively correlated with higher Ki-67 index. Overexpression of LDHA in a PA cell line (GH3) promoted glucose uptake through the upregulation of glucose transporter-1 (Glut1), lactate secretion and induced cellular invasion by upregulation of matrix metalloproteinase2 (MMP2). LDHA also promoted GH3 cell proliferation through induction of cell cycle progression via activation of the Akt-GSK-3β-cyclinD1 pathway. Accordingly, oxamate-induced inhibition of LDHA suppressed glucose uptake, lactate secretion, invasion and proliferation in GH3 cells via down regulation of Glut1 and MMP2 expression and inhibition of the Akt-GSK-3β-cyclinD1 pathway. Moreover, oxamate induced GH3 cell apoptosis by increasing mitochondrial reactive oxygen species (ROS) generation. In vivo, LDHA overexpression promoted tumor growth, and oxamate delayed tumor growth. In primary PA cell cultures, oxamate also effectively suppressed invasion and proliferation. Our data indicate that LDHA is involved in promoting the progression of PA, and oxamate might be a promising therapeutic agent for the treatment of PA.

Decoy receptor 1 (DCR1) promoter hypermethylation and response to irinotecan in metastatic colorectal cancer

Diversity in colorectal cancer biology is associated with variable responses to standard chemotherapy. We aimed to identify and validate DNA hypermethylated genes as predictive biomarkers for irinotecan treatment of metastatic CRC patients.

Candidate genes were selected from 389 genes involved in DNA Damage Repair by correlation analyses between gene methylation status and drug response in 32 cell lines. A large series of samples (n=818) from two phase III clinical trials was used to evaluate these candidate genes by correlating methylation status to progression-free survival after treatment with first-line single-agent fluorouracil (Capecitabine or 5-fluorouracil) or combination chemotherapy (Capecitabine or 5-fluorouracil plus irinotecan (CAPIRI/FOLFIRI)).

In the discovery (n=185) and initial validation set (n=166), patients with methylated Decoy Receptor 1 (DCR1) did not benefit from CAPIRI over Capecitabine treatment (discovery set: HR=1.2 (95%CI 0.7-1.9, p=0.6), validation set: HR=0.9 (95%CI 0.6-1.4, p=0.5)), whereas patients with unmethylated DCR1 did (discovery set: HR=0.4 (95%CI 0.3-0.6, p=0.00001), validation set: HR=0.5 (95%CI 0.3-0.7, p=0.0008)). These results could not be replicated in the external data set (n=467), where a similar effect size was found in patients with methylated and unmethylated DCR1 for FOLFIRI over 5FU treatment (methylated DCR1: HR=0.7 (95%CI 0.5-0.9, p=0.01), unmethylated DCR1: HR=0.8 (95%CI 0.6-1.2, p=0.4)).

In conclusion, DCR1 promoter hypermethylation status is a potential predictive biomarker for response to treatment with irinotecan, when combined with capecitabine. This finding could not be replicated in an external validation set, in which irinotecan was combined with 5FU. These results underline the challenge and importance of extensive clinical evaluation of candidate biomarkers in multiple trials.

Lidocaine Induces Apoptosis and Suppresses Tumor Growth in Human Hepatocellular Carcinoma Cells In Vitro and in a Xenograft Model In Vivo

Background

Recent epidemiologic studies have focused on the potential beneficial effects of regional anesthetics, and the differences in cancer prognosis may be the result of anesthetics on cancer biologic behavior. However, the function and underlying mechanisms of lidocaine in hepatocellular carcinoma both in vitro and in vivo have been poorly studied.

Methods

Human HepG2 cells were treated with lidocaine. Cell viability, colony formation, cell cycle, and apoptosis were assessed. The effects of lidocaine on apoptosis-related and mitogen-activated protein kinase protein expression were evaluated by Western blot analysis. The antitumor activity of lidocaine in hepatocellular carcinoma with or without cisplatin was investigated with in vitro experiments and also with animal experiments.

Results

Lidocaine inhibited the growth of HepG2 cells in a dose- and time-dependent manner. The authors also found that lidocaine arrested cells in the G0/G1 phase of the cell cycle (63.7 ± 1.7% vs. 72.4 ± 3.2%; P = 0.0143) and induced apoptosis (1.7 ± 0.3% vs. 5.0 ± 0.7%; P = 0.0009). Lidocaine may exert these functions by causing an increase in Bax protein and activated caspase-3 and a corresponding decrease in Bcl-2 protein through the extracellular signal-regulated kinase 1/2 and p38 pathways. More importantly, for the first time, xenograft experiments (n = 8 per group) indicated that lidocaine suppressed tumor development (P &lt; 0.0001; lidocaine vs. control) and enhanced the sensitivity of cisplatin (P = 0.0008; lidocaine plus cisplatin vs. cisplatin).

Conclusions

The authors’ findings suggest that lidocaine may exert potent antitumor activity in hepatocellular carcinoma. Furthermore, combining lidocaine with cisplatin may be a novel treatment option for hepatocellular carcinoma.

Current biomarkers of invasive sporadic pituitary adenomas

Though pituitary adenomas (PA) are considered benign, some of them exhibit invasive behaviors such as recurrence and low rate of total surgical resection. Reliable prognostic biomarkers for invasive PA are highly desired; however they remain to be identified. In this review, we summarize the current controversial findings of biomarkers for invasive sporadic PA, and we discuss the possible reasons for the controversies.

EZH2 is highly expressed in pituitary adenomas and associated with proliferation

Enhancer of zeste homolog 2 (EZH2) is a core epigenetic regulator, playing a crucial role in cell cycle regulation. The protein is known to be associated with proliferation and worse outcome in several tumor entities. In this study, we immunohistochemically investigated the expression pattern of EZH2 in a large cohort of pituitary tumors. These results were correlated with clinical features and double immunofluorescence stainings (DIS) were conducted to evaluate co-expression of EZH2 and proliferation marker Ki-67. Furthermore, we analyzed the effect of EZH2 inhibition on cell proliferation in vitro using the pituitary cell line AtT-20. While in the normal anterior pituitary EZH2 was almost absent, the cohort of tumors showed enhanced expression levels (p ≤ 0.0005). This was positively associated with Ki-67 indices (r = 0.834, p ≤ 0.0005) and DIF confirmed a predominant co-expression of both markers. In vitro experiments revealed a significant (p ≤ 0.05) decrease of tumor cell proliferation using the EZH2 inhibitor GSK126. Our results further support that epigenetic events are involved in the pathogenesis and biology of pituitary adenomas (PA). Therefore, EZH2 may function as a new potential target for therapeutic interventions in PA.

Epidrug mediated re-expression of miRNA targeting the HMGA transcripts in pituitary cells

INTRODUCTION

Transgenic mice overexpressing the high mobility group A (HMGA) genes, Hmga1 or Hmga2 develop pituitary tumours and their overexpression is also a frequent finding in human pituitary adenomas. In some cases, increased expression of HMGA2 but not that of HMGA1 is consequent to genetic perturbations. However, recent studies show that down-regulation of microRNA (miRNA), that contemporaneously target the HMGA1 and HMGA2 transcripts, are associated with their overexpression.

RESULTS

In a cohort of primary pituitary adenoma we determine the impact of epigenetic modifications on the expression of HMGA-targeting miRNA. For these miRNAs, chromatin immunoprecipitations showed that transcript down-regulation is correlated with histone tail modifications associated with condensed silenced genes. The functional impact of epigenetic modification on miRNA expression was determined in the rodent pituitary cell line, GH3. In these cells, histone tail, miRNA-associated, modifications were similar to those apparent in human adenoma and likely account for their repression. Indeed, challenge of GH3 cells with the epidrugs, zebularine and TSA, led to enrichment of the histone modification, H3K9Ac, associated with active genes, and depletion of the modification, H3K27me3, associated with silent genes and re-expression of HMGA-targeting miRNA. Moreover, epidrugs challenges were also associated with a concomitant decrease in hmga1 transcript and protein levels and concurrent increase in bmp-4 expression.

CONCLUSIONS

These findings show that the inverse relationship between HMGA expression and targeting miRNA is reversible through epidrug interventions. In addition to showing a mechanistic link between epigenetic modifications and miRNA expression these findings underscore their potential as therapeutic targets in this and other diseases.

The role of genetic and epigenetic changes in pituitary tumorigenesis

Pituitary adenomas are one of the most common intracranial tumors. Despite their benign nature, dysregulation of hormone secretion causes systemic metabolic deterioration, resulting in high mortality and an impaired quality of life. Tumorigenic pathogenesis of pituitary adenomas is mainly investigated by performing genetic analyses of somatic mutations in the tumor or germline mutations in patients. Genetically modified mouse models, which develop pituitary adenomas, are also used. Genetic analysis in rare familial pituitary adenomas, including multiple endocrine neoplasia type 1 and type 4, Carney complex, familial isolated pituitary adenomas, and succinate dehydrogenases (SDHs)-mediated paraganglioma syndrome, revealed several causal germline mutations and sporadic somatic mutations in these genes. The analysis of genetically modified mouse models exhibiting pituitary adenomas has revealed the underlying mechanisms, where cell cycle regulatory molecules, tumor suppressors, and growth factor signaling are involved in pituitary tumorigenesis. Furthermore, accumulating evidence suggests that epigenetic changes, including deoxyribonucleic acid (DNA) methylation, histone modification, micro ribonucleic acids (RNAs), and long noncoding RNAs play a pivotal role. The elucidation of precise mechanisms of pituitary tumorigenesis can contribute to the development of novel targeted therapy for pituitary adenomas.

Pathogenesis analysis of pituitary adenoma based on gene expression profiling

The aim of the current study was to investigate the pathogenesis of pituitary adenoma through screening of the differentially-expressed genes (DEGs) and proteins in normal pituitary and pituitary adenoma tissues, and analyzing the interactions among them. Following the acquisition of gene expression profiling data from a public functional genomics data repository, Gene Expression Omnibus, DEGs were screened in normal pituitary and pituitary adenoma tissues. Upregulated and downregulated DEGs were further identified through gene ontology functional enrichment analysis. Subsequently, the DEGs were mapped to the Search Tool for the Retrieval of Interacting Genes database, and the protein-protein interaction (PPI) networks of the upregulated and downregulated DEGs were constructed. Finally, the functional modules of the PPI network of the downregulated DEGs were analyzed. In total, 211 upregulated and 413 downregulated DEGs were screened between the normal pituitary and pituitary adenoma samples. Downregulated DEGs were associated with certain functions, including the immune response, hormone regulation and cell proliferation. Upregulated genes were associated with cation transport functions. Five modules were acquired from the PPI network of the downregulated DEGs. Transcription factors, including signal transducer and activator of transcription 3 (STAT3), interleukin 6 (IL-6), B-cell lymphoma 6 protein, early growth response 1, POU1F1, jun B proto-oncogene and FOS were the core nodes in the functional modules. In summary, the DEGs and proteins were identified through screening gene expression profiling and PPI networks. The results of the present study indicated that low expression levels of hormone- and immune-related genes facilitated the occurrence of pituitary adenoma. Low expression levels of IL-6 and STAT3 were significant in the dysimmunity of pituitary adenoma. Furthermore, the low expression level of POU1F1 contributed to the reduction in pituitary hormone secretion.

Epigenetics of pituitary tumours: an update

PURPOSE OF REVIEW

To review recent advances in our knowledge and understanding of aberrations that target the epigenome in sporadic pituitary adenomas.

RECENT FINDINGS

A more complete understanding of the pituitary epigenome has been facilitated by advances in technologies for exploring the tumour-associated epigenomic landscape, and has revealed aberration to the principle targets of these changes, namely, methylation of CpG dinucleotides, modification of histone tails and the expression of target-specific miRNA. Genome-wide investigations, of sporadic pituitary adenoma, have identified novel methylated genes that in some cases are subtype-specific. Recent studies have also shown that silenced genes may be reactivated through epidrug challenges. Moreover, in experimental settings, wherein enforced expression of specific miRNA has been employed, these have been shown to inhibit pituitary cell proliferation in vitro and in vivo.

SUMMARY

Candidate gene and genome-wide studies reveal frequent epigenetic changes in pituitary adenomas. Aberrations, concurrent with their impact on functional end-points, may display subtype specificity, whereas others appear to be independent of adenoma subtype. Changes to the epigenomic landscape, and apparent as CpG island methylation and/or as histone tail modifications, show sensitivity to epidrug-induced re-expression that concomitantly impacts on cell proliferation. Similarly, enforced expression of silenced miRNA in model systems is also associated with similar end-points. Collectively, emerging data show that these types of manipulation, alone or in combination with a more conventional therapeutic option, offer new avenues for the medical management of these tumours.

Mir-23b and miR-130b expression is downregulated in pituitary adenomas

MicroRNA (miRNA) deregulation plays a critical role in tumorigenesis. miR-23b and miR-130b are induced by thyrotropin in thyroid cells in a cAMP-dependent manner. The aim of our work has been to investigate the possible role of miR-23b and miR-130b in pituitary tumorigenesis. We have analyzed their expression in a panel of pituitary adenomas (PAs) including GH and NFPA adenomas. We report that miR-23b and miR-130b are drastically reduced in GH, gonadotroph and NFPA adenomas in comparison with normal pituitary gland. Interestingly, the overexpression of miR-23b and miR-130b inhibits cell proliferation arresting the cells in the G1 and G2 phase of the cell cycle, respectively. Moreover, we demonstrate that miR-23b and miR-130b target HMGA2 and cyclin A2 (CCNA2) genes, respectively. Finally, downregulation of miR-23b and miR-130b expression is associated with increased levels of their respective targets in human PAs. These findings suggest that miR-23b and miR-130b downregulation may contribute to pituitary tumorigenesis.

Genetic and epigenetic mutations of tumor suppressive genes in sporadic pituitary adenoma

Human pituitary adenomas are the most common intracranial neoplasms. Approximately 5% of them are familial adenomas. Patients with familial tumors carry germline mutations in predisposition genes, including AIP, MEN1 and PRKAR1A. These mutations are extremely rare in sporadic pituitary adenomas, which therefore are caused by different mechanisms. Multiple tumor suppressive genes linked to sporadic tumors have been identified. Their inactivation is caused by epigenetic mechanisms, mainly promoter hypermethylation, and can be placed into two groups based on their functional interaction with tumor suppressors RB or p53. The RB group includes CDKN2A, CDKN2B, CDKN2C, RB1, BMP4, CDH1, CDH13, GADD45B and GADD45G; AIP and MEN1 genes also belong to this group. The p53 group includes MEG3, MGMT, PLAGL1, RASSF1, RASSF3 and SOCS1. We propose that the tumor suppression function of these genes is mainly mediated by the RB and p53 pathways. We also discuss possible tumor suppression mechanisms for individual genes.

Advances in understanding pituitary tumors

Pituitary tumors are common in the general population. Since neuroimaging techniques have improved, pituitary tumors are more often diagnosed incidentally. About 16.7% of the general population show changes in the pituitary gland. Predominantly, pituitary tumors are benign pituitary adenomas. Pituitary carcinomas or aggressive pituitary tumors are extremely rare. They might develop from benign adenomas. New genetic and epigenetic abnormalities help us to understand pituitary tumorigenesis and might lead to therapeutical targeting drugs in the future. Macroadenomas (>1 cm) can lead to visual field disturbances, compression of cranial nerves, hypopituitarism, and infiltration of the cavernous sinuses. The functional status of the pituitary tumor is important. About half to one third of all pituitary tumors are non-functioning pituitary adenomas. The other pituitary tumors show a specific pattern of hormone secretion. About 25% to 41% of all pituitary tumors are prolactinomas, acromegaly with production of growth hormone represents 10% to 15% of adenomas, Cushing's disease with production of adrenocorticotropic hormone accounts for 10%, and other hormonal characteristics are less common. Transsphenoidal resection and total adenomectomy are desirable. Radiosurgery has enriched the surgical treatment options. Surgical treatment is the intervention of choice except for prolactinomas, where pharmaceutical treatment is recommended. Pharmaceutical treatment consists of dopamine agonists such as cabergoline and somatostatin analogues that include octreotide and pasireotide; retinoic acid is of theoretical interest while peroxisome proliferator-activated receptor-gamma-ligands are not clinically useful. In acromegaly, pegvisomant is a further treatment option. Temozolomide should be considered in aggressive pituitary tumors. In general, pharmaceutical options developed recently have extended the repertoire of treatment possibilities of pituitary tumors.

The role of epigenetic modification in tumorigenesis and progression of pituitary adenomas: a systematic review of the literature

Background

Pituitary adenomas (PAs) are commonly occurring neoplasms with diverse endocrine and neurological effects. Although somatic gene mutations are uncommon in sporadic PAs, recent studies lend support to epigenetic modification as a potential cause of tumorigenesis and tumor progression.

Methods

A systematic literature review of the PubMed and Google Scholar databases was conducted to identify abstracts (n=1,082) pertaining to key targets and mechanisms implicated in epigenetic dysregulation of PAs published between 1993-2013. Data regarding histopathological subtype, target genes, mode of epigenetic modification, and clinical correlation were recorded and analyzed.

Results

Of the 47 that studies met inclusion criteria and focused on epigenomic assessment of PAs, only 2 were genome-scale analyses. Current evidence supports epigenetic alteration in at least 24 PA genes, which were categorized into four groups based on function and epigenetic alteration: 1) Sixteen tumor suppressor genes silenced via DNA methylation; 2) Two oncogenes overexpressed via histone acetylation and hypomethylation; 3) Three imprinted genes with selective allelic silencing; and 4) One epigenome writer inducing abnormal genome-scale activity and 5) Two transcription regulators indirectly modifying the genome. Of these, 5 genes (CDKN2A, GADD45y, FGFR2, caspase-8, and PTAG) showed particular susceptibility to epigenetic modification, with abnormal DNA methylation in >50% of PA samples. Several genes displayed correlations between epigenetic modification and clinically relevant parameters, including invasiveness (CDKN2A; DAPK; Rb1), sex (MAGE-A3), tumor size (GNAS1), and histopathological subtype (CDKN2A; MEG3; p27; RASSF1A; Rb1).

Conclusions

Epigenetic modification of selected PA genes may play a key role in tumorigenesis and progression, which may translate into important diagnostic and therapeutic applications.

Regulation of the Nrf2 antioxidant pathway by microRNAs: New players in micromanaging redox homeostasis

MicroRNAs are now thought to play a central role in the regulation of many diverse aspects of cell biology; however, it remains to be fully elucidated how microRNAs can orchestrate cellular redox homeostasis, which plays a central role in a multitude of physiological and pathophysiological processes. The redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) serves as a "master regulator" of cell survival through the coordinated induction of phase II and antioxidant defense enzymes to counteract oxidative stress and modulate redox signaling events. MicroRNAs are able to "fine-tune" the regulation of processes including those directly interacting with the Nrf2 pathway and the generation of reactive oxygen species (ROS). This review highlights that cellular redox homeostasis can be regulated by microRNAs through their modulation of Nrf2-driven antioxidant gene expression as well as key enzymes that generate ROS, which in turn can alter the biogenesis and processing of microRNAs. Therefore redox sensitive microRNAs or "redoximiRs" add an important regulatory mechanism for redox signaling beyond the well-characterized actions of Nrf2. The potential exists for microRNA-based therapies where diminished antioxidant defenses and dysregulated redox signaling can lead to cardiovascular diseases, cancers, neurodegeneration, and accelerated aging.

Preincubation of pituitary tumor cells with the epidrugs zebularine and trichostatin A are permissive for retinoic acid-augmented expression of the BMP-4 and D2R genes

Retinoic acid (RA)-induced expression of bone morphogenetic protein-4 (BMP-4) inhibits in vitro and in vivo cell proliferation and ACTH synthesis in corticotroph-derived tumor cells. Reduced expression of BMP-4 in this adenoma subtype is associated with epigenomic silencing, and similar silencing mechanisms are also associated with the RA-responsive dopamine D2 receptor (D2R) in somatolactotroph cells. We now show that preincubation with the epidrugs zebularine and trichostatin A is obligate and permissive for RA-induced expression of the BMP-4 and the D2R genes in pituitary tumor cells. Combined epidrug challenges are associated with marginal reduction in CpG island methylation. However, significant change to histone tail modifications toward those associated with expression-competent genes is apparent, whereas RA challenge alone or in combined incubations does not have an impact on these modifications. Epidrug-mediated and RA-augmented expression of endogenous BMP-4 increased or decreased cell proliferation and colony-forming efficiency in GH3 and AtT-20 pituitary tumor cells, respectively, recapitulating recent reports of challenges of these cells with exogenous ligand. The specificity of the BMP-4-mediated effects was further supported by knock-down experiments of the BMP-4 antagonist noggin (small interfering RNA [siRNA]). Knock-down of noggin, in the absence and the presence of epidrugs, induced and augmented BMP-4 expression, respectively. In cell proliferation assays, challenge with either epidrugs or siRNA led to significant increase in cell numbers at the 72-hour time point; however, in siRNA-treated cells coincubated with epidrugs, a significant increase was apparent at the 48-hour time point. These studies show the potential of combined drug challenges as a treatment option, where epidrug renders silenced genes responsive to conventional therapeutic options.

Approach to the Cushing's disease patient with persistent/recurrent hypercortisolism after pituitary surgery

Although it is the ideal treatment, pituitary surgery is not always successful, and success is not always lasting. Close surveillance, clinical and biological, will detect immediate failure or late recurrence. The reason must be thoroughly explored with the somewhat dogmatic rule that the patient should be offered the best surgery in expert hands, and a repeat surgical attempt must be systematically discussed. When repeat pituitary surgery is not indicated or has failed, then comes the difficult task to choose between a number of options directed toward different targets: directly suppress tumor ACTH by pituitary radiotherapy (conventional or stereotaxic) or with medications (somatostatin analog such as pasireotide, or dopaminergic drug such as cabergoline), directly suppress adrenocortical activity with medications (inhibitors of adrenal steroidogenesis such as ketoconazole or metyrapone, or the adrenolytic Lysodren), or by surgery (bilateral adrenalectomy), and finally oppose peripheral cortisol action with the antiglucocorticoid mifepristone. No single option is ideal, able to provide at the same time a high success rate and a rapid onset of action, to restore a normal pituitary adrenal axis, and to have good tolerability. Close follow-up and thorough evaluation of the cortisolic status will eventually dictate a switch in treatment options and/or combination strategies over time. The tumor status and its possible oncogenic threat, the severity of the hypercortisolism, and the patient perspectives (wish of fertility) are among the major parameters that can help a multidisciplinary approach toward the best option.

The EFEMP1 gene: a frequent target for epigenetic silencing in multiple human pituitary adenoma subtypes

BACKGROUND/AIMS

In a genome-wide investigation we recently identified the EGF-containing fibulin-like extracellular matrix protein 1 gene, EFEMP1, as hypermethylated in growth hormone-secreting adenoma.

METHODS

In an independent cohort we determined expression of EFEMP1, CpG island methylation and histone tail modification status. The causal consequences of epigenetic modification were determined through epidrug-induced reversal and enforced EFEMP1 expression in GH3 cells.

RESULTS

The majority of adenomas, irrespective of subtype, show reduced EFEMP1 expression. However, epigenetic change, as determined by CpG island methylation, was not invariantly associated with decreased EFEMP1 expression. Conversely, chromatin immunoprecipitation assays revealed enrichment for modifications associated with either active or silenced genes in adenoma that did or did not express EFEMP1 respectively. In AtT-20 and GH3 cells a causal relationship between epigenetic silencing and expression of EFEMP1 was established where co-incubation with the epidrugs zebularine and TSA induced expression of EFEMP1 and concomitant histone tail modifications toward those associated with expressed genes. Enforced expression of EFEMP1 in GH3 cells was without effect on cell proliferation or apoptotic end-points, however inhibition of endogenous matrix metalloproteinase (MMP)-2 expression was apparent. Primary adenomas did not show this relationship, however a positive correlation was apparent with the MMP7 transcript and perhaps reflects cell or species differences.

CONCLUSIONS

The protein product of the EFEMP1 gene, fibulin-3, is reported to impact on multiple pathways in a cell-specific context. Subtype-independent loss of EFEMP1 expression in the majority of primary adenomas should prompt more detailed investigation in this tumour type.