Aggressive nonfunctioning pituitary neuroendocrine tumors

Nonfunctioning pituitary neuroendocrine tumors (NF-PitNETs) are tumors that are not associated with clinical evidence of hormonal hypersecretion. According to the World Health Organization (WHO), there are some subtypes of PitNETs that exhibit more aggressive behavior than others. Among the types of potentially aggressive PitNETs, three are nonfunctional: silent sparsely granulated somatotropinomas, silent corticotropinomas, and poorly differentiated PIT-1 lineage tumors. Several biological markers have been investigated in NF-PitNETs. However, there is no single biomarker able to independently predict aggressive behavior in NF-PitNETs. Thus, a more complex and multidisciplinary proposal of a comprehensive definition of aggressive NF-PitNETs is necessary. Here, we suggest a combined and more complete criterion for the NF-PitNETs classification. We propose that aggressiveness is due to a multifactorial combination, and we emphasize the need to include new emerging markers that are involved in the aggressiveness of NF-PitNETs and the need to identify.

The kinome, cyclins and cyclin-dependent kinases of pituitary adenomas, a look into the gene expression profile among tumors from different lineages

Background

Pituitary adenomas (PA) are the second most common intracranial tumors and are classified according to hormone they produce, and the transcription factors they express. The majority of PA occur sporadically, and their molecular pathogenesis is incompletely understood.

Methods

Here we performed transcriptome and proteome analysis of tumors derived from POU1F1 (GH-, TSH-, and PRL-tumors, N = 16), NR5A1 (gonadotropes and null cells adenomas, n = 17) and TBX19 (ACTH-tumors, n = 6) lineages as well as from silent ACTH-tumors (n = 3) to determine expression of kinases, cyclins, CDKs and CDK inhibitors.

Results

The expression profiles of genes encoding kinases were distinctive for each of the three PA lineage: NR5A1-derived tumors showed upregulation of ETNK2 and PIK3C2G and alterations in MAPK, ErbB and RAS signaling, POU1F1-derived adenomas showed upregulation of PIP5K1B and NEK10 and alterations in phosphatidylinositol, insulin and phospholipase D signaling pathways and TBX19-derived adenomas showed upregulation of MERTK and STK17B and alterations in VEGFA-VEGFR, EGF-EGFR and Insulin signaling pathways. In contrast, the expression of the different genes encoding cyclins, CDK and CDK inhibitors among NR5A1-, POU1F1- and TBX19-adenomas showed only subtle differences. CDK9 and CDK18 were upregulated in NR5A1-adenomas, whereas CDK4 and CDK7 were upregulated in POUF1-adenomas.

Conclusions

The kinome of PA clusters these lesions into three distinct groups according to the transcription factor that drives their terminal differentiation. And these complexes could be harnessed as molecular therapy targets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01206-y.

Integrated multi-omics profiling of nonfunctioning pituitary adenomas

PURPOSE

Genetic and epigenetic alterations are involved in pituitary adenoma pathogenesis, however the molecular basis of proliferative nonfunctioning pituitary adenomas (NFPAs) remains unclear. Here, we analyzed integrated multi-omics profiling including copy number variation (CNV), DNA methylation and gene expression of 8 NFPAs.

METHODS

We collected 4 highly proliferative (hpNFPA, Ki-67 ≥ 3) and 4 lowly proliferative (Ki-67 ≤ 1) NFPAs, and comprehensively assessed CNV, DNA methylation, and gene expression by Illumina HumanMethylation450 BeadChip and Affymetrix GeneChip PrimeView Human Gene Expression Array. We performed Ingenuity Pathway Analysis (IPA) for differentially expressed genes to illustrate aberrant pathways and delineated protein-protein networks of selected key genes in dysregulated pathways.

RESULTS

Aberrant arm level CNV, dysregulated DNA methylation, and associated impacts on gene expressions were observed in 2 early occurring hpNFPAs. Chromosomal losses were associated with attenuated expression of DNA methyltransferases, further altering global methylation in these 2 samples. Correlation analysis between DNA methylation and gene expression in 8 NFPAs indicates methylation in promoter and gene body regions are both involved in gene regulation. IPA showed PPARα/RXRα, dopamine receptor signaling, cAMP-mediated signaling, and calcium signaling were all activated, while p38 MAPK and ERK5 signaling were inhibited in hpNFPAs. Moreover, selected key gene networks in hpNFPAs exhibited concurrent methylation status and expression levels of adenylate cyclase genes, G protein subunits, HLA genes, CXCL12, and CCL2.

CONCLUSION

This study presents comprehensive multi-omics views of CNV, DNA methylation, and gene expression in 8 NFPAs. Pathway analysis and network maps of key genes provide clues to elucidate the molecular basis of hpNFPA.

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.

Integrated analysis of DNA methylation and mRNA expression profiles to identify key genes involved in the regrowth of clinically non-functioning pituitary adenoma

Tumour regrowth is a key characteristic of clinically non-functioning pituitary adenoma (NFPA). No applicable prognosis evaluation method is available for post-operative patients. We aimed to identify DNA methylation biomarkers that can facilitate prognosis evaluation. Genome-wide DNA methylation and mRNA microarray analyses were performed for tumour samples from 71 NFPA patients. Differentially expressed genes and methylated genes were identified based on the regrowth vs non-regrowth grouping. There were 139 genes that showed alterations in methylation status and expression level, and only 13 genes showed a negative correlation. The progression-free analysis found that FAM90A1, ETS2, STAT6, MYT1L, ING2 and KCNK1 are related to tumour regrowth. A prognosis-prediction model was built based on all 13 genes from integrated analysis, and the 6-gene model achieved the best area under the receiver operating characteristic curves (AUC) of 0.820, compared with 0.785 and 0.568 for the 13-gene and 7-gene models, respectively. Our prognostic biomarkers were validated by pyrosequencing and RT-PCR. FAM90A1 and ING2 was found to be independent prognostic factors of tumour regrowth with univariate Cox regression. The DNA methylation and expression levels of FAM90A1 and ING2 are associated with tumour regrowth, and may serve as biomarkers for predicting the prognosis of patients with NFPA.

SDF-1α/MicroRNA-134 Axis Regulates Nonfunctioning Pituitary Neuroendocrine Tumor Growth via Targeting VEGFA

BACKGROUND

Nonfunctioning pituitary neuroendocrine tumor (NF-PitNET) is difficult to resect. Except for surgery, there is no effective treatment for NF-PitNET. MicroRNA-134 (miR-134) has been reported to inhibit proliferation and invasion ability of tumor cells. Herein, the mechanism underlying the effect of miR-134 on alleviating NF-PitNET tumor cells growth is explored.

METHODS

Mouse pituitary αT3-1 cells were transfected with miR-134 mimics and inhibitor, followed by treatment with stromal cell-derived factor-1α (SDF-1α) in vitro. MiR-134 expression level: we used quantitative real-time PCR (qRT-PCR) to detect the expression of miR-134. Cell behavior level: cell viability and invasion ability were assessed using a cell counting kit-8 (CCK8) assay and Transwell invasion assay respectively. Cytomolecular level: tumor cell proliferation was evaluated by Ki-67 staining; propidium iodide (PI) staining analyzed the effect of miR-134 on cell cycle arrest; western blot analysis and immunofluorescence staining evaluated tumor migration and invasive ability. Additionally, we collected 27 NF-PitNET tumor specimens and related clinical data. The specimens were subjected to qRT-PCR to obtain the relative miR-134 expression level of each specimen; linear regression analysis was used to analyze the miR-134 expression level in tumor specimens and the age of the NF-PitNET population, gender, tumor invasion, prognosis, and other indicators.

RESULTS

In vitro experiment, miR-134 was observed to significantly inhibit αT3-1 cells proliferation characterized by inhibited cell viability and expressions of vascular endothelial growth factor A (VEGFA) and cell cycle transition from G1 to S phase (P < 0.01). VEGFA was verified as a target of miR-134. Additionally, miR-134-induced inhibition of αT3-1 cell proliferation and invasion was attenuated by SDF-1α and VEGFA overexpression (P < 0.01). In primary NF-PitNET tumor analysis, miR-134 expression level was negatively correlated with tumor invasion (P = 0.003).

CONCLUSION

The regulation of the SDF-1α/miR-134/VEGFA axis represents a novel mechanism in the pathogenesis of NF-PitNETs and may serve as a potential therapeutic target for the treatment of NF-PitNETs.

Identification of key genes in invasive clinically non-functioning pituitary adenoma by integrating analysis of DNA methylation and mRNA expression profiles

BACKGROUND

Tumor surrounding the internal carotid artery or invading to the cavernous sinus is an important characteristic of invasive pituitary adenoma, and a pivotal factor of tumor residue and regrowth. Without specific changes in serum hormone related to the adenohypophyseal cell of origin, clinically non-functioning pituitary adenoma is more likely to be diagnosed at invasive stages compared with functioning pituitary adenoma. The underlying mechanism of tumor invasion remains unknown. In this study, we aimed to identify key genes in tumor invasion by integrating analyses of DNA methylation and gene expression profiles.

METHOD

Genome-wide DNA methylation and mRNA microarray analysis were performed for tumor samples from 68 patients at the Beijing Tiantan Hospital. Differentially expressed genes and methylated probes were identified based on an invasive vs non-invasive grouping. Differentially methylated probes in the promoter region of targeted genes were assessed. Pearson correlation analysis was used to identify genes with a strong association between DNA methylation status and expression levels. Pyrosequencing and RT-PCR were used to validate the methylation status and expression levels of candidate genes, respectively.

RESULTS

A total of 8842 differentially methylated probes, located on 4582 genes, and 661 differentially expressed genes were identified. Both promoter methylation and expression alterations were observed for 115 genes with 58 genes showing a negative correlation between DNA methylation status and expression level. Nineteen genes that exhibited notably negative correlations between DNA methylation and gene expression levels, are involved in various gene ontologies and pathways, or played an important role in different diseases, were regarded as candidate genes. We found an increased methylation with a decreased expression of PHYHD1, LTBR, C22orf42, PRR5, ANKDD1A, RAB13, CAMKV, KIFC3, WNT4 and STAT6, and a decreased methylation with an increased expression of MYBPHL. The methylation status and expression levels of these genes were validated by pyrosequencing and RT-PCR.

CONCLUSIONS

The DNA methylation and expression levels of PHYHD1, LTBR, MYBPHL, C22orf42, PRR5, ANKDD1A, RAB13, CAMKV, KIFC3, WNT4 and STAT6 are associated with tumor invasion, and these genes may become the potential genes for targeted therapy.

Molecular Biology of Pituitary Adenomas

Pituitary adenomas are benign tumors, but still cause significant morbidity and in some cases increases in mortality. Surgical resection is not without risks, and approximately 40% of adenomas are incompletely resected. Medical therapies such as dopamine agonists, somatostatin analogues, and growth hormone antagonists are associated with numerous side effects. Understanding the molecular biology of pituitary adenomas may yield new therapeutic approaches. Additional studies are needed to help determine which genes or pathways are "drivers" of tumorigenesis and should be therapeutic targets. Further studies may also enable pituitary adenoma stratification to tailor treatment approaches.

Identification of Important Invasion-Related Genes in Non-functional Pituitary Adenomas

Non-functioning pituitary adenomas (NFPAs) are locally invasive with high morbidity. The objective of this study was to diagnose important genes and pathways related to the invasiveness of NFPAs and gain more insights into the underlying molecular mechanisms of NFPAs. The gene expression profiles of GSE51618 were downloaded from the Gene Expression Omnibus database with 4 non-invasive NFPA samples, 3 invasive NFPA samples, and 3 normal pituitary gland samples. Differentially expressed genes (DEGs) are screened between invasive NFPA samples and normal pituitary gland samples, followed by pathway and ontology (GO) enrichment analyses. Subsequently, a protein-protein interaction (PPI) network was constructed and analyzed for these DEGs, and module analysis was performed. In addition, a target gene-miRNA network and target gene-TF (transcription factor) network were analyzed for these DEGs. A total of 879 DEGs were obtained. Among them, 439 genes were upregulated and 440 genes were downregulated. Pathway enrichment analysis indicated that the upregulated genes were significantly enriched in cysteine biosynthesis/homocysteine degradation (trans-sulfuration) and PI3K-Akt signaling pathway, while the downregulated genes were mainly associated with docosahexaenoate biosynthesis III (mammals) and chemokine signaling pathway. GO enrichment analysis indicated that the upregulated genes were significantly enriched in animal organ morphogenesis, extracellular matrix, and hormone activity, while the downregulated genes were mainly associated with leukocyte chemotaxis, dendrites, and RAGE receptor binding. Subsequently, ESR1, SOX2, TTN, GFAP, WIF1, TTR, XIST, SPAG5, PPBP, AR, IL1R2, and HIST1H1C were diagnosed as the top hub genes in the upregulated and downregulated PPI networks and modules. In addition, HS3ST1, GPC4, CCND2, and SCD were diagnosed as the top hub genes in the upregulated and downregulated target gene-miRNA networks, while CISH, ISLR, UBE2E3, and CCNG2 were diagnosed as the top hub genes in the upregulated and downregulated target gene-TF networks. The new important DEGs and pathways diagnosed in this study may serve key roles in the invasiveness of NFPAs and indicate more molecular targets for the treatment of NFPAs.

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.

Prognostic and clinicopathological value of p16 protein aberrant expression in colorectal cancer: A PRISMA-compliant Meta-analysis

PURPOSE

Several studies have examined the potential role of p16 protein expression as a diagnostic and prognostic biomarker in various cancers. However, it remains unclear whether p16 protein expression is a prognostic and diagnostic factor for colorectal cancer. Therefore, this meta-analysis is conducted to evaluate the associations of p16 protein expression with overall survival (OS) and clinicopathological characteristics of colorectal cancer.

METHODS

According to PRISMA guideline, relevant literatures were identified by searching Medicine, Web of Science, WanFang, and CNKI databases. The pooled hazard ratios (HRs) with 95% confidence intervals (CIs) were extracted from included studies to assess the association between p16 protein expression and OS of patients with colorectal cancer. Other relevant data were extracted to evaluate the correlations of p16 protein expression with risk and clinicopathological characteristics of colorectal cancer. Stata 12.0 software was applied to calculate the strength of association between p16 protein expression and colorectal cancer.

RESULTS

Forty-one studies were included to evaluate the association between p16 protein expression and colorectal cancer. Nine studies involving 1731 patients with colorectal cancer found that there was no association between p16 protein expression and OS of colorectal cancer in the overall analysis (HR = 0.78, 95% CI: 0.55-1.10). However, p16 protein overexpression was significantly associated with a better prognosis in patients with colorectal cancer when cut-off value of p16 protein expression was <10% (HR = 0.23, 95% CI: 0.08-0.66). The results of subgroup analysis based on ethnicity indicated that p16 protein overexpression was a risk factor for the occurrence of colorectal cancer in Caucasians (odds ratio = 28.95, 95% CI: 6.08-137.89), but not in Asians. Furthermore, p16 protein overexpression was significantly associated with the Dukes stage, lymph node metastasis, tumor location, and Tumor Lymph Node Metastasis-stage of colorectal cancer.

CONCLUSIONS

p16 protein overexpression might be a useful biomarker to predict the clinicopathological progress and prognosis of colorectal cancer.

Microarray technology reveals potentially novel genes and pathways involved in non-functioning pituitary adenomas

Microarray data of non-functioning pituitary adenomas (NFPAs) were analyzed to disclose novel genes and pathways involved in NFPA tumorigenesis. Raw microarray data were downloaded from Gene Expression Omnibus. Data pre-treatment and differential analysis were conducted using packages in R. Functional and pathway enrichment analyses were performed using package GOs-tats. A protein-protein interaction (PPI) network was constructed using server STRING and Cytoscape. Known genes involved in pituitary adenomas (PAs), were obtained from the Comparative Toxicogenomics Database. A total of 604 differentially expressed genes (DEGs) were identifed between NFPAs and controls, including 177 up- and 427 down-regulated genes. Jak-STAT and p53 signaling pathways were significantly enriched by DEGs. The PPI network of DEGs was constructed, containing 99 up- and 288 down-regulated known disease genes (e.g. EGFR and ESR1) as well as 16 up- and 17 down-regulated potential novel NFPAs-related genes (e.g. COL4A5, LHX3, MSN, and GHSR). Genes like COL4A5, LHX3, MSN, and GHSR and pathways such as p53 signaling and Jak-STAT signaling, might participate in NFPA development. Although further validations are required, these findings might provide guidance for future basic and therapy researches.

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.

Molecular markers in pituitary tumors

PURPOSE OF REVIEW

This review summarizes our current understanding of the mechanisms and factors involved in pituitary tumorigenesis. It provides a comprehensive review on the role of genetic mutations, epigenetics, oncogenes, tumor suppressor genes, cell cycle deregulation, and highlights recent findings of altered micro-RNA and long noncoding RNA expression in pituitary tumors.

RECENT FINDINGS

This article provides a concise summary of our knowledge regarding oncogenes, tumor suppressor genes, and cell cycle deregulation in pituitary tumors. Additionally, it highlights new findings in epigenetics and altered micro-RNA and long noncoding RNA expression in pituitary tumors.

SUMMARY

Improved understanding of the mechanism(s) and candidates implicated in pituitary tumorigenesis may result in the identification of new therapeutic targets in pituitary tumors.

Molecular genetic advances in pituitary tumor development

Pituitary adenomas are a heterogeneous group of tumors that may occur as part of a complex syndrome or as an isolated endocrinopathy and both forms can be familial or non-familial. Studies of syndromic and non-syndromic pituitary adenomas have yielded important insights about the molecular mechanisms underlying tumorigenesis. Thus, syndromic forms, including multiple endocrine neoplasia type 1 (MEN1), MEN4, Carney Complex and McCune Albright syndrome, have been shown to be due to mutations of the tumor-suppressor protein menin, a cyclin-dependent kinase inhibitor (p27Kip1), the protein kinase A regulatory subunit 1-α, and the G-protein α-stimulatory subunit (Gsα), respectively. Non-syndromic forms, which include familial isolated pituitary adenoma (FIPA) and sporadic tumors, have been shown to be due to abnormalities of: the aryl hydrocarbon receptor-interacting protein; Gsα; signal transducers; cell cycle regulators; transcriptional modulators and miRNAs. The roles of these molecular abnormalities and epigenetic mechanisms in pituitary tumorigenesis, and their therapeutic implications are reviewed.

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.

Association between p16(CDKN2A) C540G polymorphism and tumor behavior in prolactinoma: A single-center study

Pituitary tumors usually originate as benign sporadic adenomas and develop into invasive and aggressive tumors such as prolactinomas, which are common functioning pituitary adenomas. The aim of the present study was to examine the association between the tumor behavior in prolactinomas and the p16(CDKN2A) gene polymorphism occurring at the 3'-untranslated region of exon 3 (C540G). A total of 104 patients with prolactinoma were included and assigned to two groups based on invasive vs. non-invasive tumor behavior. Ki67 indices were recorded according to histopathology results. Genotypic analysis of the p16(CDKN2A) C540G polymorphism was carried out using a modified polymerase chain reaction-restriction fragment length polymorphism assay. The corresponding frequencies for CC, CG and GG genotypes in non-invasive vs. invasive tumors were 61.5, 30.8, 7.7 and 64.1, 28.2, 7.7%, respectively (not significant). The observed CG genotype frequency was higher compared with previous studies. In addition, the patients with giant adenomas or a high Ki67 index had a higher frequency of the CG genotype as compared with the other subgroups, although the differences were not significant (46.2 and 42.9%, respectively). In conclusion, a higher frequency of the C540G CG genotype of the CDKN2A gene was found among patients with prolactinoma in comparison with previous studies. These frequencies were also higher in the subgroups with elevated Ki67 or giant adenomas. Further studies are required to improve the definition of the role of the CG genotype in the development and progression of tumors in prolactinomas.

A pilot genome-scale profiling of DNA methylation in sporadic pituitary macroadenomas: association with tumor invasion and histopathological subtype

Pituitary adenomas (PAs) are neoplasms that may cause a variety of neurological and endocrine effects. Although known causal contributors include heredity, hormonal influence and somatic mutations, the pathophysiologic mechanisms driving tumorigenesis and invasion of sporadic PAs remain unknown. We hypothesized that alterations in DNA methylation are associated with PA invasion and histopathology subtype, and that genome-scale methylation analysis may complement current classification methods for sporadic PAs. Twenty-four surgically-resected sporadic PAs with varying histopathological subtypes were assigned dichotomized Knosp invasion scores and examined using genome-wide DNA methylation profiling and RNA sequencing. PA samples clustered into subgroups according to functional status. Compared with hormonally-active PAs, nonfunctional PAs exhibited global DNA hypermethylation (mean beta-value 0.47 versus 0.42, P = 0.005); the most significant site of differential DNA methylation was within the promoter region of the potassium voltage-gated channel KCNAB2 (FDR = 5.11×10⁻¹⁰). Pathway analysis of promoter-associated CpGs showed that nonfunctional PAs are potentially associated with the ion-channel activity signal pathway. DNA hypermethylation tended to be negatively correlated with gene expression. DNA methylation analysis may be used to identify candidate genes involved in PA function and may potentially complement current standard immunostaining classification in sporadic PAs. DNA hypermethylation of KCNAB2 and downstream ion-channel activity signal pathways may contribute to the endocrine-inactive status of nonfunctional PAs.

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.

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.

Quantitative, genome-wide analysis of the DNA methylome in sporadic pituitary adenomas

DNA methylation is one of the several epigenetic modifications that together with genetic aberrations are hallmarks of tumorigenesis including those emanating from the pituitary gland. In this study, we examined DNA methylation across 27 578 CpG sites spanning more than 14 000 genes in the major pituitary adenoma subtypes. Genome-wide changes were first determined in a discovery cohort comprising non-functioning (NF), growth hormone (GH), prolactin (PRL)-secreting and corticotroph (CT) adenoma relative to post-mortem pituitaries. Using stringent cut-off criteria, we validated increased methylation by pyrosequencing in 12 of 16 (75%) genes. Overall, these criteria identified 40 genes in NF, 21 in GH, six in PRL and two in CT that were differentially methylated relative to controls. In a larger independent cohort of adenomas, for genes in which hypermethylation had been validated, different frequencies of hypermethylation were apparent, where the KIAA1822 (HHIPL1) and TFAP2E genes were hypermethylated in 12 of 13 NF adenomas whereas the COL1A2 gene showed an increase in two of 13 adenomas. For genes showing differential methylation across and between adenoma subtypes, pyrosequencing confirmed these findings. In three of 12 genes investigated, an inverse relationship between methylation and transcript expression was observed where increased methylation of EML2, RHOD and HOXB1 is associated with significantly reduced transcript expression. This study provides the first genome-wide survey of adenoma, subtype-specific epigenomic changes and will prove useful for identification of biomarkers that perhaps predict or characterise growth patterns. The functional characterisation of identified genes will also provide insight of tumour aetiology and identification of new therapeutic targets.

Estradiol partially recapitulates murine pituitary cell cycle response to pregnancy

Because pregnancy and estrogens both induce pituitary lactotroph hyperplasia, we assessed the expression of pituitary cell cycle regulators in two models of murine pituitary hyperplasia. Female mice were assessed during nonpregnancy, pregnancy, day of delivery, and postpartum. We also implanted estradiol (E(2)) pellets in female mice and studied them for 2.5 months. Pituitary weight in female mice increased 2-fold after E(2) administration and 1.4-fold at day of delivery, compared with placebo-treated or nonpregnant females. Pituitary proliferation, as assessed by proliferating cell nuclear antigen and/or Ki-67 staining, increased dramatically during both mid-late pregnancy and E(2) administration, and lactotroph hyperplasia was also observed. Pregnancy induced pituitary cell cycle proliferative and inhibitory responses at the G(1)/S checkpoint. Differential cell cycle regulator expression included cyclin-dependent kinase inhibitors, p21(Cip1), p27(Kip1), and cyclin D1. Pituitary cell cycle responses to E(2) administration partially recapitulated those effects observed at mid-late pregnancy, coincident with elevated circulating mouse E(2), including increased expression of proliferating cell nuclear antigen, Ki-67, p15(INK4b), and p21(Cip1). Nuclear localization of pituitary p21(Cip1) was demonstrated at mid-late pregnancy but not during E(2) administration, suggesting a cell cycle inhibitory role for p21(Cip1) in pregnancy, yet a possible proproliferative role during E(2) administration. Most observed cell cycle protein alterations were reversed postpartum. Murine pituitary meets the demand for prolactin during lactation associated with induction of both cell proliferative and inhibitory pathways, mediated, at least partially, by estradiol.

The pituitary tumour epigenome: aberrations and prospects for targeted therapy

Global and gene-specific changes in the epigenome are hallmarks of most tumour types, including those of pituitary origin. In contrast to genetic mutations, epigenetic changes (aberrant DNA methylation and histone modifications) are potentially reversible. Drugs that specifically target or inhibit DNA methyltransferases (DNMTs) and histone deacetylases (HDACs) can be used to restore the expression of epigenetically silenced genes. These drugs can potentially increase the sensitivity of tumour cells to conventional treatment modalities, such as chemotherapy and radiotherapy. Drug-induced reversal of transcriptional silencing can also be used to restore dopamine-D(2)-receptor-negative, hormone-refractory tumours to their previous receptor-positive, hormone-responsive status. Synergy between HDAC and DNMT inhibitors makes these pharmacological agents more therapeutically effective when administered in combination than when used alone. Studies in pituitary tumour cell lines show that drug-induced re-expression of the epigenetically silenced dopamine D(2) receptor leads to an increase in apoptosis mediated by a receptor agonist. Collectively, the use of drugs to directly or indirectly reverse gene-specific epigenetic changes, in combination with conventional therapeutic interventions, has potential for the clinical management of multiple tumour types-including those of pituitary origin. Furthermore, these drugs can be used to identify epigenetically regulated genes that could be novel, tumour-specific therapeutic targets.

Promoter methylation and loss of p16(INK4a) gene expression in head and neck cancer

BACKGROUND

Silencing of tumor suppressor genes plays a vital role in head and neck carcinogenesis. In this study we aimed to evaluate aberrant p16(INK4a) gene promoter methylation in patients with head and neck cancer.

METHODS

Methylation of the gene was investigated by bisulfite modification/methylation-specific polymerase chain reaction and gene expression levels were analyzed by quantitative reverse transcription-polymerase chain reaction in tumors and matched normal tissue samples from Turkish patients with head and neck cancer.

RESULTS

The promoter region of the p16(INK4a) gene was methylated in 67.5% and 28.6% of the primary tumors and the corresponding normal tissue, respectively. This difference was highly significant. In concordance, p16(INK4a) gene expression was downregulated in 67.5% of the tumor samples. Methylation and the absence of expression in the tumors were observed in 48% of the patients.

CONCLUSIONS

Our data indicate that methylation of the p16(INK4a) gene is a frequent event in primary head and neck cancer and that it plays a major role in the silencing of p16(INK4a) gene expression during tumor development.

Silencing of the imprinted DLK1-MEG3 locus in human clinically nonfunctioning pituitary adenomas

DLK1-MEG3 is an imprinted locus consisting of multiple maternally expressed noncoding RNA genes and paternally expressed protein-coding genes. The expression of maternally expressed gene 3 (MEG3) is selectively lost in clinically nonfunctioning adenomas (NFAs) of gonadotroph origin; however, expression status of other genes at this locus in human pituitary adenomas has not previously been reported. Using quantitative real-time RT-PCR, we evaluated expression of 24 genes from the DLK1-MEG3 locus in 44 human pituitary adenomas (25 NFAs, 7 ACTH-secreting, 7 GH-secreting, and 5 PRL-secreting adenomas) and 10 normal pituitaries. The effects on cell proliferation of five miRNAs whose expression was lost in NFAs were investigated by flow cytometry analysis. We found that 18 genes, including 13 miRNAs at the DLK1-MEG3 locus, were significantly down-regulated in human NFAs. In ACTH-secreting and PRL-secreting adenomas, 12 and 7 genes were significantly down-regulated, respectively; no genes were significantly down-regulated in GH-secreting tumors. One of the five miRNAs tested induced cell cycle arrest at the G2/M phase in PDFS cells derived from a human NFA. Our data indicate that the DLK1-MEG3 locus is silenced in NFAs. The growth suppression by miRNAs in PDFS cells is consistent with the hypothesis that the DLK1-MEG3 locus plays a tumor suppressor role in human NFAs.

Upregulation of CDKN2A and suppression of cyclin D1 gene expressions in ACTH-secreting pituitary adenomas

OBJECTIVE

Cushing's disease (CD) is usually caused by ACTH-secreting pituitary microadenomas, while silent corticotroph adenomas (SCA) are macroadenomas without Cushingoid features. However, the molecular mechanism(s) underlying their different tumor growth remains unknown. The aim of the current study was to evaluate and compare the gene expression profile of cell cycle regulators and cell growth-related transcription factors in CD, SCA, and non-functioning adenomas (NFA).

DESIGN AND METHODS

Tumor tissue specimens resected from 43 pituitary tumors were studied: CD (n=10), SCA (n=11), and NFA (n=22). The absolute transcript numbers of the following genes were quantified with real-time quantitative PCR assays: CDKN2A (or p16(INK4a)), cyclin family (A1, B1, D1, and E1), E2F1, RB1, BUB1, BUBR1, ETS1, and ETS2. Protein expressions of p16 and cyclin D1 were semi-quantitatively evaluated by immunohistochemical study.

RESULTS AND CONCLUSION

CDKN2A gene expression was about fourfold greater in CD than in SCA and NFA. The gene expressions of cyclins D1, E1, and B1, but not of A1, in CD were significantly suppressed than those in NFA. Cyclin D1 gene expression positively correlated with cyclins B1 and E1. The gene expressions of E2F1, RB1, BUB1, BUBR1, ETS1, and ETS2 did not differ between each group. Positive immunostaining for p16 and negative immunostaining for cyclin D1 were more frequent in CD than in NFA; there were positive correlations between mRNA and protein expressions of p16 and cyclin D1. Thus, it is suggested that upregulated CDKN2A with the concomitant downregulated cyclin gene family is partly involved in the small size of ACTH-secreting adenoma.

The genetics of pituitary adenomas

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

Frequent loss of the CDKN2C (p18INK4c) gene product in pituitary adenomas

Genomic alterations of cyclin-dependent kinase inhibitors have been demonstrated in a variety of tumor types including brain tumors. Among them, the cyclin-dependent kinase inhibitor 2A (CDKN2A or p16(INK4a)) gene has been shown to be frequently deleted or inactivated in astrocytic tumors. The CDKN2C (p18(INK4c)) gene is functionally related to CDKN2A. Moreover, mice with targeted disruption of CDKN2C alone or combined CDKN2C and cyclin-dependent kinase inhibitor 1B (CDKN1B or p27(Kip1)), or CDKN2C and TP53 gene disruption develop pituitary adenomas (PA) at high frequencies. The purpose of our study was to investigate genetic alterations of the CDKN2C gene by analysis of loss of heterozygosity (LOH), screening for mutations, analysis of promoter methylation, and protein expression in 38 PAs. In addition, genomic alterations and protein expression of the cell cycle genes CDKN2A and its alternatively spliced form, p14(ARF), as well as the retinoblastoma RB1 gene were investigated. LOH at the CDKN2C gene locus was detected in 25% of pituitary adenomas, whereas the RB1 and CDKN2A loci were altered in only 10%. No mutations were detected within the coding regions of the CDKN2C gene. However, 39.5% of adenomas displayed CDKN2C promoter methylation. The absence of CDKN2C protein was correlated with LOH of the CDKN2C locus on chromosome 1 and with methylation of the CDKN2C promoter. This is the first report to describe that the tumor suppressor gene CDKN2C is frequently targeted by genomic alterations in pituitary adenoma. The most common genetic alteration was promoter methylation suggesting that inactivation of CDKN2C by this mechanism may play an important role in pituitary adenoma development. Additional Supporting Information may be found in the online version of this article.

Familial pituitary adenomas

The majority of pituitary adenomas occur sporadically, however, about 5% of all cases occur in a familial setting, of which over half are due to multiple endocrine neoplasia type 1 (MEN-1) and Carney's complex (CNC). Since the late 1990s we have described non-MEN1/CNC familial pituitary tumours that include all tumour phenotypes, a condition named familial isolated pituitary adenomas (FIPA). The clinical characteristics of FIPA vary from those of sporadic pituitary adenomas, as patients with FIPA have a younger age at diagnosis and larger tumours. About 15% of FIPA patients have mutations in the aryl hydrocarbon receptor interacting protein gene (AIP), which indicates that FIPA may have a diverse genetic pathophysiology. This review describes the clinical features of familial pituitary adenomas like MEN1, the MEN 1-like syndrome MEN-4, CNC, FIPA, the tumour pathologies found in this setting and the genetic/molecular data that have been recently reported.

Genome-wide analysis in a murine Dnmt1 knockdown model identifies epigenetically silenced genes in primary human pituitary tumors

DNA methylation at promoter CpG islands (CGI) is an epigenetic modification associated with inappropriate gene silencing in multiple tumor types. In the absence of a human pituitary tumor cell line, small interfering RNA-mediated knockdown of the maintenance methyltransferase DNA methyltransferase (cytosine 5)-1 (Dnmt1) was used in the murine pituitary adenoma cell line AtT-20. Sustained knockdown induced reexpression of the fully methylated and normally imprinted gene neuronatin (Nnat) in a time-dependent manner. Combined bisulfite restriction analysis (COBRA) revealed that reexpression of Nnat was associated with partial CGI demethylation, which was also observed at the H19 differentially methylated region. Subsequent genome-wide microarray analysis identified 91 genes that were significantly differentially expressed in Dnmt1 knockdown cells (10% false discovery rate). The analysis showed that genes associated with the induction of apoptosis, signal transduction, and developmental processes were significantly overrepresented in this list (P < 0.05). Following validation by reverse transcription-PCR and detection of inappropriate CGI methylation by COBRA, four genes (ICAM1, NNAT, RUNX1, and S100A10) were analyzed in primary human pituitary tumors, each displaying significantly reduced mRNA levels relative to normal pituitary (P < 0.05). For two of these genes, NNAT and S100A10, decreased expression was associated with increased promoter CGI methylation. Induced expression of Nnat in stable transfected AtT-20 cells inhibited cell proliferation. To our knowledge, this is the first report of array-based "epigenetic unmasking" in combination with Dnmt1 knockdown and reveals the potential of this strategy toward identifying genes silenced by epigenetic mechanisms across species boundaries.

Selective loss of MEG3 expression and intergenic differentially methylated region hypermethylation in the MEG3/DLK1 locus in human clinically nonfunctioning pituitary adenomas

CONTEXT

MEG3 is an imprinted gene encoding a novel noncoding RNA that suppresses tumor cell growth. Although highly expressed in the normal human pituitary, it is unknown which of the normal pituitary cell types and pituitary tumors express MEG3.

OBJECTIVES

Our objectives were 1) to investigate cell-type- and tumor-type-specific expression of MEG3 in the human pituitary and 2) to investigate whether methylation in the intergenic differentially methylated region (IG-DMR) at the DLK1/MEG3 locus is involved in the loss of MEG3 expression in tumors.

DESIGN AND METHODS

RT-PCR, quantitative RT-PCR, Northern blot, and a combination of in situ hybridization and immunofluorescence were used to determine the cell-type- and tumor-type-specific MEG3 expression. Bisulfite treatment and PCR sequencing of genomic DNA were used to measure the CpG methylation status in the normal and tumor tissues. Five normal human pituitaries and 17 clinically nonfunctioning, 11 GH-secreting, seven prolactin-secreting, and six ACTH-secreting pituitary adenomas were used.

RESULTS

All normal human pituitary cell types express MEG3. However, loss of MEG3 expression occurs only in nonfunctioning pituitary adenomas of a gonadotroph origin. All other pituitary tumor phenotypes examined express MEG3. Hypermethylation of the IG-DMR at the DLK1/MEG3 locus is present in nonfunctioning pituitary adenomas.

CONCLUSIONS

MEG3 is the first human gene identified expressed in multiple normal human pituitary cell types with loss of expression specifically restricted to clinically nonfunctioning pituitary adenomas. The IG-DMR hypermethylation may be an additional mechanism for MEG3 gene silencing in such tumors.

Expression of p16(INK4A) gene in human pituitary tumours

Pituitary adenomas comprise 10-15% of primary intracranial tumours but the mechanisms leading to tumour development are yet to be clearly established. The retinoblastoma pathway, which regulates the progression through the cell cycle, is often deregulated in different types of tumours. We studied the cyclin-dependent kinase inhibitor p16(INK4A) gene expression at mRNA level in human pituitary adenomas. Forty-six tumour specimens of different subtypes, 21 clinically non-functioning, 12 growth hormone-secreting, 6 prolactin-secreting, 6 adrenocorticotropin-secreting, and 1 thyrotropin-secreting tumours were studied. All clinically non-functioning and most of the hormone-secreting tumours were macroadenomas (38/46). The RT-PCR assay and electrophoresis of the PCR-products showed that p16(INK4A) mRNA was undetectable in: 62% of non-functioning, 8% of growth hormone-secreting, 17% of prolactin-secreting and 17% of adrenocorticotropin-secreting adenomas. Forty percent of all macroadenomas and 25% of microadenomas had negative p16(INK4A) mRNA, the latter results suggest that the absence of p16(INK4A) product might be an early event in tumours with no expression of this suppressor gene. Within the non-functioning adenomas 63% were "null cell" and 37% were positive for some hormone, both subgroups showed similar percentage of cases with absence of p16(INK4A) mRNA. Our results show that clinically non-functioning macroadenomas have impaired p16(INK4A) expression in a clearly higher proportion than any other pituitary tumour subtype investigated. Other regulatory pathways may be implicated in the development of tumours with positive p16(INK4A) expression.

Oncogenesis and mutagenesis of pituitary tumors

Although pituitary tumors may be present in up to 10% of the population, the pathophysiology of these lesions is not well characterized. Pituitary tumors are composed of monoclonal cell populations with disrupted control of replication pathways. The oncogenes and tumor suppressor genes that are common in other malignancies (i.e. jun, fos, myc, and p53) are rarely involved in the development of these tumors. However, oncogenes, such as gsp, can be present in up to 40% of hormonally active adenomas. The process of pituitary oncogenesis further appears to involve oncogenes such as cyclin E, cyclin D1, and the pituitary tumor transforming gene (PTTG). Finally, the cAMP signaling cascade plays a significant role in generation of both benign and malignant pituitary tumors. In this review, the biology of pituitary adenomas is explored with a special emphasis on potential targets for the development of targeted therapeutics.

Tumor suppressor loss in pituitary tumors

The current model of human neoplasia invokes a number of potential genomic alterations that impact cellular phenotype and proliferative rates. In the majority of human tumor models, the transformation from normal cells to neoplastic lesion is a multistep process. This review offers a specific overview of the involvement of tumor suppressor genes (TSGs) in the pathogenesis of human pituitary adenomas. TSG genetic lesions, such as BRCA1 in breast cancer and p53 in Li-Fraumeni Syndrome, have been identified in both sporadic and heritable human endocrine tumors. Familial neoplastic syndromes like multiple endocrine neoplasia type 1 (MEN1) that include pituitary tumor formation as part of a broad clinical spectrum of disease represent a unique opportunity to investigate the general mechanisms of tumorigenesis, and well as genes responsible for sporadic endocrine tumors. Similarly, homologous recombination knockout mice with selectively ablated candidate TSGs have also shed light on the molecular mechanisms of pituitary cell proliferation and tumor suppression. However, despite insights into pituitary tumorigenesis generated by heritable neoplasia syndromes and mouse knockout of critical TSGs that display a pituitary tumor phenotype, the molecular pathogenesis of human pituitary adenomas remains largely an enigma. Thus, the role of TSGs, if any, in sporadic pituitary adenoma formation has yet to be determined, despite our greater understanding of the molecular mechanisms underlying pituitary cell function and phenotype.

Abundant hypermethylation of SOCS-1 in clinically silent pituitary adenomas

Janus kinase (JAK)/signal transducers and activators of transcription (STAT) cascade are required for cytokines, growth factors, G-proteins and hormones (growth hormone and prolactin). Gatekeepers in this pathway are the suppressor of cytokine signalling (SOCS) family of proteins. Their expression level is epigenetically regulated by DNA methylation. We have investigated the CpG island methylation status of SOCS-1 in a cohort of pituitary adenomas (PA; n=57), craniopharyngiomas (CP; n=30) and normal pituitary tissue (NP; n=11) using methylation sensitive single-strand conformation polymorphism analysis (MS-SSCP) and direct sequencing. SOCS-1 hypermethylation was identified in 51% (29/57) of surgical specimens obtained from PA patients. 83% of these tumours were clinically silent. In contrast, no methylation of SOCS-1 was observed in CPs or NPs. Quantitative real-time PCR and western blot analysis confirmed reduced SOCS-1 expression in the majority of pituitary adenomas. The data is compatible with epigenetic silencing of the SOCS-1 gene and constitutive activation of the JAK-STAT pathway in PA. This appears to contribute particularly to those tumours characterized by a hormone-inactive status.

A novel apoptosis gene identified in the pituitary gland

Although multiple different cancers have been described, it is likely that these tumour types share a small, and common, number of newly acquired functional capabilities. Tumours that arise within the pituitary gland are no exception with respect to these new functional capabilities. Although compelling evidence for self-sufficiency in growth signals is presented, loss of functional tumour suppressor genes by classic mechanisms has not been clearly established. However, and in this context, methylation-mediated or -associated gene silencing, in particular of tumour suppressor genes, has been reported by numerous investigators in this tumour type. More recently, a search for novel genes on the basis of their inappropriate methylation has led to identification of a novel pro-apoptotic gene. Its pituitary tumour derivation and role in drug-induced apoptosis resulted in the acronym PTAG (pituitary tumour apoptosis gene) being assigned to this gene. In a model pituitary tumour cell line, AtT20, expression of PTAG per se had no discernible effects on proliferation, cell cycle profile or viability. However, enforced expression was associated with a significantly increased sensitivity to the apoptotic effects induced by bromocriptine challenge. Apoptosis was mediated through caspase activation and associated with DNA fragmentation as determined by TUNEL labelling. Similar findings are also evident in the rodent pituitary cell line, GH3 and our data shows that drugs other than bromocriptine, and that engage characterized receptors, elicit a PTAG-augmented apoptotic response. The isolation of novel genes, on the basis of their methylation status, offers a significant advantage with respect to our understanding of tumorigenesis in both the pituitary and other tumour types. The reversal of apparent gene silencing may lead to tumour cell 'sensitisation' to chemo- and radiotherapeutic treatment strategies.

The 2004 World Health Organization classification of pituitary tumors: what is new?

The classification of pituitary tumors is a dynamic area that changes with advances in cell biology that provide a deeper insight and clearer understanding of cell lineages and pathogenetic mechanisms. The 2004 edition of the World Heath Organization (WHO) text "Histological typing of endocrine tumors" reflects the progress that has been achieved since the previous edition of 2000. Here we review the new information and identify areas of concern for the next effort at classification of pituitary tumors.

Adenomas hipofisários produtores de glicoproteínas: patogênese, diagnóstico e tratamento

Os adenomas hipofisários produtores de glicoproteínas compreendem duas entidades clínicas e patológicas distintas: os adenomas gonadotróficos e os tirotróficos. Embora possam ser agrupados por produzirem hormônios e/ou sub-unidades que são glicoproteínas, esses tumores se originam em tipos celulares distintos (gonadotrofos e tirotrofos) que são apenas remotamente relacionados. Os gonadotróficos estão entre os adenomas hipofisários mais comuns, correspondendo à grande maioria dos assim chamados adenomas "não-funcionantes", silenciosos ou clinicamente não-secretores, enquanto os tirotróficos são extremamente raros e clinicamente se apresentam com hipertiroidismo por secreção inapropriada de TSH. Nesse artigo, os autores revisam aspectos epidemiológicos, patológicos, patogenéticos, clínicos, diagnósticos e terapêuticos desses adenomas. Uma ênfase maior foi dada à patogênese molecular dos tumores hipofisários em geral, buscando, sempre que possível, contrastar as alterações moleculares encontradas nesses adenomas com outros tipos de adenomas hipofisários. No lado mais prático, a experiência dos autores de mais de duas décadas no diagnóstico e tratamento desses tumores na Unidade de Neuroendocrinologia da Unifesp, foi criteriosamente utilizada para discutir a literatura disponível nesses tópicos.

Differential gene expression in pituitary adenomas by oligonucleotide array analysis

OBJECTIVES

Microarray technology allows for the expression profile of many thousands of genes to be quantified at the same time, and has resulted in novel discoveries about the tumour biology of a number of cancers. We sought to do this in pituitary adenomas, the most common intracranial neoplasm.

METHODS

Affymetrix GeneChip HG-U133A oligonucleotide arrays covering 14 500 well-characterised genes from the human genome were used to study pooled RNA for each of the four major pituitary adenoma subtypes. Individual gene-expression levels in the tumours were compared relative to the expression profile in normal pooled pituitary RNA. Three differentially expressed genes with potential importance in tumourigenesis were chosen for validation by real-time quantitative PCR on the original tumours and on an additional 26 adenomas.

RESULTS

Bioinformatic analysis showed that 3906 genes and 351 expressed sequence tags were differentially expressed among all pituitary tumour subtypes. Lysosomal-associated protein transmembrane- 4-beta (LAPTM4B), a novel gene upregulated in hepatocellular carcinoma, was significantly over-expressed in adrenocorticotrophin (ACTH)-secreting adenomas and non-functioning pituitary adenomas (NFPAs). Bcl-2-associated athanogene (BAG1), an anti-apoptotic protein found at high levels in a number of human cancers, was significantly over-expressed in growth hormone-secreting and prolactin-secreting adenomas and NFPAs. The cyclin-dependent kinase inhibitor p18, in which murine gene deletion has been shown to produce pituitary ACTH cell hyperplasia and adenomas, was significantly under-expressed in ACTH-secreting adenomas.

CONCLUSIONS

Expression array analysis of pituitary adenomas using the Affymetrix GeneChip HG-U133A arrays appears to be a valid method of identifying genes that may be important in tumour pathogenesis.

The p15(INK4b)/p16(INK4a)/RB1 pathway is frequently deregulated in human pituitary adenomas

Pituitary adenomas are common benign intracranial neoplasms. However, their tumorigenesis is not yet clearly defined. Inactivation of genes involved in the negative cell-cycle regulatory p15(INK4b) - p16(INK4a) -cyclin D/CDK4-RB1-mediated pathway (RB1 pathway) is one of the most common and important mechanisms in the growth advantage of tumor cells. Recently, much attention has been focused on the importance of alternative mechanisms of gene inactivation, particularly promoter hypermethylation in the transcriptional silencing of such tumor-suppressor genes. Based on the rare occurrence of inactivation by gene mutations and deletions of the RB1 pathway in pituitary adenomas, we investigated the deregulation of the RB1 pathway in 42 sporadic human pituitary adenomas, especially focusing on the methylation status of this pathway as determined by a methylation-specific polymerase chain reaction assay. Homozygous deletion of the p15(INK4b) or p16(INK4a) gene was detected in one adenoma each. Amplification of the CDK4 gene was not apparent in any of the pituitary adenomas presently examined. Promoter hypermethylation of the p15(INK4b), p16(INK4a), and RB1 genes was detected in 15 (35.7%), 30 (71.4%), and 12 (28.6%) of the adenomas, respectively. Promoter hypermethylation of the p15(INK4b) gene coincided with p16(INK4a) alteration and/or RB1 methylation, whereas p16(INK4a) and RB1 methylations tended to be mutually exclusive (p = 0.019). Thus, the vast majority of the adenomas (38 of 42, 90.5%) displayed alterations of the RB1 pathway. None of the clinicopathologic features, including the proliferation cell index, was significantly correlated with any particular methylation status. Our results suggest that inactivation of the RB1 pathway may play a causal role in pituitary tumorigenesis, with hypermethylation of the p16(INK4a) gene being the most common deregulation, and further provide evidence that RB1 and p16(INK4a) methylations tend to be mutually exclusive but occasionally coincide with p15(INK4b) methylation.

Pathogenesis of prolactinomas

In recent years the demonstration that human pituitary adenomas are monoclonal in origin provides further evidence that pituitary neoplasia arise from the replication of a single mutated cell in which growth advantage results from either activation of proto-oncogenes or inactivation of tumor suppressor genes. However, with the exception of one RAS mutation identified in a single unusually aggressive prolactinoma resistant to dopaminergic inhibition that resulted to be lethal, no mutational changes have been so far detected in prolactinomas. In the absence of genetic changes, modifications in the level of expression of oncogenes or tumor suppressor genes have been detected in these tumors, although it is unknown whether these changes have a causative role or are a secondary event. Indeed, our knowledge on the molecular events involved in lactotroph proliferation is even more limited in comparison to the other tumor types, since these tumors are very infrequently surgically removed and therefore available for molecular biology studies. In this respect, it is worth noting that the molecular and biological abnormalities so far described in prolactinomas mainly concern aggressive and atypical tumors and likely do not apply to the typical prolactinomas, that are characterized by good response to medical treatment and a very low growth rate.

Molecular pathology shows p16 methylation in nonadenomatous pituitaries from patients with Cushing's disease

PURPOSE

The majority of cases of Cushing's disease are due to the presence of a corticotroph microadenoma. Less frequently no adenoma is found and histology shows either corticotroph hyperplasia, or apparently normal pituitary. In this study we have used molecular pathology to determine whether the tissue labeled histologically as "normal" is indeed abnormal.

EXPERIMENTAL DESIGN

Tissue from 31 corticotroph adenomas and 16 nonadenomatous pituitaries were subject to methylation-sensitive PCR to determine the methylation status of the p16 gene CpG island. The proportion of methylated versus unmethylated CpG island was determined using combined bisulphite restriction analysis. Methylation status was correlated with immunohistochemical detection of p16.

RESULTS

Seventeen of 31 adenomas (54.8%), 4 of 6 cases of corticotroph hyperplasia, and 7 of 10 apparently normal pituitaries showed p16 methylation. Ten of 14 (71%; P = 0.01) adenomas and 2 of 3 cases of corticotroph hyperplasia, which were methylated, failed to express p16 protein. However, only 2 of 7 apparently normal pituitaries that were methylated failed to express p16 protein. Quantitative analysis of methylation using combined bisulphite restriction analysis showed only unmethylated CpG islands in postmortem normal pituitaries; however, in adenomas 80-90% of the cells within a specimen were methylated. The reverse was true for corticotroph hyperplasia and apparently normal pituitaries where only 10-20% of the cells were methylated. Thus, the decreased proportion of cells that were methylated, particularly in those cases of apparently normal pituitary, is the most likely explanation for the lack of association between this change and loss of cognate protein in these cases.

CONCLUSIONS

To our knowledge this is the first report that describes an intrinsic molecular change, namely methylation of the p16 gene CpG island, common to all three histological patterns associated with Cushing's disease. Thus, the use of molecular pathology reveals abnormalities undetected by routine pathological investigation. In cases of "apparently" normal pituitaries it is not possible to determine whether the change is associated with adenoma cells "scattered" throughout the gland, albeit few in number, or with the ancestor-clonal origin of these tumor cells.

Bases moleculares dos adenomas hipofisários com ênfase nos somatotropinomas

Esta revisão descreve as bases moleculares dos adenomas hipofisários com ênfase nos tumores secretores de GH (somatotropinomas). São discutidos os papéis de genes de supressão tumoral (como RB1, MEN-1) e de oncogenes (como gsp, PTTG) na iniciação e progressão destes tumores. A caracterização destes marcadores moleculares pode ajudar na compreensão do comportamento tumoral, auxiliando a conduta terapêutica. Entretanto, apesar dos recentes avanços, ainda não é totalmente conhecida a seqüência de alterações genéticas envolvidas na patogênese destes adenomas.

Isolation and characterization of a novel pituitary tumor apoptosis gene

To determine mechanisms for pituitary neoplasia we used methylation-sensitive arbitrarily primed-PCR to isolate novel genes that are differentially methylated relative to normal pituitary. We report the isolation of a novel differentially methylated chromosome 22 CpG island-associated gene (C22orf3). Sodium bisulfite sequencing of pooled tumor cohorts, used in the isolation of this gene, showed that only a proportion of the adenomas within the pools were methylated; however, expression analysis by quantitative RT-PCR of individual adenoma irrespective of subtype showed the majority (30 of 38; 79%) failed to express this gene relative to normal pituitary. Sodium bisulfite sequencing of individual adenomas showed that 6 of 30 (20%) that failed to express pituitary tumor apoptosis gene (PTAG) were methylated; however, genetic change as determined by loss of heterozygosity and sequence analysis was not apparent in the remaining tumors that failed to express this gene. In those cases where the CpG island of these genes was methylated it was invariably associated with loss of transcript expression. Enforced expression of C22orf3 in AtT20 cells had no measurable effects on cell proliferation or viability; however, in response to bromocriptine challenge (10-40 microm) cells expressing this gene showed a significantly augmented apoptotic response as determined by both acridine orange staining and TUNEL labeling. The apoptotic response to bromocriptine challenge was inhibited in coincubation experiments with the general caspase inhibitor z-VAD-fmk. In addition, in time course experiments, direct measurement of active caspases by fluorochrome-labeled inhibition of caspases, showed an augmented increase (approximately 2.4 fold) in active caspases in response to bromocriptine challenge in cells expressing C22orf3 relative to those harboring an empty vector control. The pituitary tumor derivation and its role in apoptosis of this gene led us to assign the acronym PTAG to this gene and its protein product. The ability of cells, showing reduced expression of PTAG, to evade or show a blunted apoptotic response may underlie oncogenic transformation in both the pituitary and other tumor types.

Loss of expression of the growth inhibitory gene GADD45gamma, in human pituitary adenomas, is associated with CpG island methylation

Inappropriate expression of cell-cycle regulatory genes and/or their protein products are a frequent finding in pituitary tumours; however, genetic changes associated with or responsible for their dysregulation are in general uncommon. In a search for novel genes, and employing cDNA-representational difference analysis, the gene encoding GADD45gamma was recently isolated and identified as being under-represented in pituitary adenomas. GADD45gamma is a member of a family of genes that are induced by DNA damage and function in the negative regulation of cell growth. In this study, we further confirm this initial report that the majority of pituitary adenomas (22 of 33; 67%) do not express GADD45gamma as determined by RT-PCR analysis. Loss of expression was not associated with either loss of heterozygosity or mutations within the coding region of this gene. In marked contrast, epigenetic change, namely methylation of the GADD45gamma genes CpG island, was a frequent finding (19 of 33 adenoma; 58%) and was significantly associated with tumours in which GADD45gamma transcript was not expressed (18 of 22; 82%; P=0.002). In common with the primary tumours, methylation-associated gene silencing of the GADD45gamma gene was also found in the pituitary tumour cell line AtT20. The treatment of AtT20 cells with the demethylating agent, 5-Aza-2'-deoxycytidine, induced the re-expression of this gene. These findings show that silencing of the GADD45gamma gene in pituitary tumours is primarily associated with methylation of the genes CpG island. Methylation has functional importance since reversal of this epigenetic change in a pituitary-derived cell line is associated with re-expression. Silencing of GADD45gamma, a negative regulator of cell growth, is most likely responsible for conferring a selective growth advantage during tumour evolution and outgrowth.

Genetics of pituitary tumors: Focus on G-protein mutations

In recent years the demonstration that human pituitary adenomas are monoclonal in origin has provided further evidence that pituitary neoplasia arise from the replication of a single mutated cell in which growth advantage results from either activation of proto-oncogenes or inactivation of tumor suppressor genes. While common oncogenes, such as Ras, are only exceptionally involved, the only mutations identified in a significant proportion of pituitary tumors, and particular in GH-secreting adenomas, occur in the Gsalpha gene (GNAS1) and cause constitutive activation of the cAMP pathway (gsp oncogene). Moreover, pituitary tumors overexpress hypothalamic releasing hormones, growth factors, and their receptors as well as cyclins involved in cell cycle progression. As far as the role of tumor suppressor genes in pituitary tumorigenesis is concerned, reduced expression of these genes seems to frequently occur in pituitary tumors as a consequence of abnormal methylation processes. Although the only mutational change so far identified in pituitary tumors is the gsp oncogene, this oncogene is not associated with a clear phenotype in patients bearing positive tumors. Mechanisms able to counteract the cAMP pathway, such as high sensitivity to somatostatin, and induction of genes with opposite actions, such as phosphodiesterases, CREB end ICER, or instability of mutant Gsalpha, have been proposed to account for the lack of genotype/phenotype relationships.

Genomic instability--the engine of tumorigenesis?

Human cancers harbour numerous mutations and it has been proposed that these result from some form of inherent genomic instability. Some cancers have proven genomic instability or features that are indicative of this. Inherited cancer syndromes exist that are caused by deficient DNA repair or chromosomal integrity. By contrast, theoretical analysis and experimental data from sporadic colorectal tumours provide little general evidence of genomic instability in early lesions. These apparently conflicting data raise the question of whether or not genomic instability is necessary for driving tumour growth, and whether or not it is the usual initiating event in tumorigenesis.