Molecular analysis of p21 and p27 genes in human pituitary adenomas

Genetic analysis of the cooperative tumorigenic effects of targeted deletions of tumor suppressors Rb1, Trp53, Men1, and Pten in neuroendocrine tumors in mice

Genetic alterations of tumor suppressor genes (TSGs) are frequently observed to have cumulative or cooperative tumorigenic effects. We examined whether the TSGs Rb1, Trp53, Pten and Men1 have cooperative effects in suppressing neuroendocrine tumors (NETs) in mice. We generated pairwise homozygous deletions of these four genes in insulin II gene expressing cells using the Cre-LoxP system. By monitoring growth and examining the histopathology of the pituitary (Pit) and pancreas (Pan) in these mice, we demonstrated that pRB had the strongest cooperative function with PTEN in suppressing PitNETs and had strong cooperative function with Menin and TRP53, respectively, in suppressing PitNETs and PanNETs. TRP53 had weak cooperative function with PTEN in suppressing pituitary lesions. We also found that deletion of Pten singly led to prolactinomas in female mice, and deletion of Rb1 alone led to islet hyperplasia in pancreas. Collectively, our data indicated that pRB and PTEN pathways play significant roles in suppressing PitNETs, while the Menin-mediated pathway plays a significant role in suppressing PanNETs. Understanding the molecular mechanisms of these genes and pathways on NETs will help us understand the molecular mechanisms of neuroendocrine tumorigenesis and develop effective preclinical murine models for NET therapeutics to improve clinical outcomes in humans.

P21Waf1/Cip1 and p27Kip1 are correlated with the development and invasion of prolactinoma

Cell cycle control can prevent excessive proliferative response in the pituitary homeostasis. Cyclin dependent kinases (Cdks) are modulated by cyclins or Cdk inhibitors, such as p21 and p27, which can regulate cell cycle progression from the G1 to S phases. This study was conducted to evaluate the levels and the promoter region methylation status of p21 and p27 in prolactinomas (PRL) and analyze their association with clinicopathologic features. We found high-p21 level cases were featured by 5/23 and H-scores 142.3 ± 23.7 in invasive-PRL specimens, and 19/25 and 221.3 ± 45.4 in non-invasive specimens (x² = 14.11, p = 0.000), while high-p27 level cases were featured by 6/23 and H-scores 129.8 ± 31.1 in invasive-PRL specimens, and 18/25 and 197.1 ± 46.6 in non-invasive specimens (x² = 10.11, p = 0.001). A similar trend was also observed for p21 and p27 protein levels in PRL specimens through western-blot (P < 0.01, respectively). The Ki-67 index was much higher in invasive specimens than in non-invasive specimens (x² = 10.10, p = 0.001). Average 33 CpG sites per sample were analyzed by using MALDI-TOF Mass array, and 7/33 CpG sites methylation levels of p27 were higher than 50%. There existed significant differences in 4 CpG sites between invasive specimens and non-invasive specimens (p < 0.01). We found that D2 receptor was closely correlated with p21 levels (P < 0.05, r = 0.567) and p27 levels (P < 0.05, r = 0.591). In PRL, the deficiency in p21 and p27 contributed to the tumor proliferation and migration and Cdk inhibitors may be used as a new therapeutic approach.

Relation among Aromatase P450 and Tumoral Growth in Human Prolactinomas

The pituitary gland is part of hypothalamic-pituitary–gonadal axis, which controls development, reproduction, and aging in humans and animals. In addition, the pituitary gland is regulated mainly by hormones and neurotransmitters released from the hypothalamus and by systemic hormones secreted by target glands. Aromatase P450, the enzyme responsible for the catabolization of aromatizable androgens to estrogens, is expressed in different parts of body, including the pituitary gland. Moreover, aromatase P450 is involved in sexual dimorphism where alteration in the level of aromatase can initiate a number of diseases in both genders. On the other hand, the direct actions of estrogens, mainly estradiol, are well known for stimulating prolactin release. Numerous studies have shown that changes in the levels of estrogens, among other factors, have been implicated in the genesis and development of prolactinoma. The pituitary gland can produce estradiol locally in several types of endocrine cells, and it is possible that aromatase could be responsible for the maintenance of the population of lactotroph cells and the modulation of the action of central or peripheral regulators. Aromatase overexpression due to inappropriate gene regulation has clinical effects such as the pathogenesis of prolactinomas. The present study reports on the synthesis of pituitary aromatase, its regulation by gonadal steroids, and the physiological roles of aromatase on pituitary endocrine cells. The involvement of aromatase in the pathogenesis of pituitary tumors, mainly prolactinomas, through the auto-paracrine production of estradiol is reviewed.

MEN4 and CDKN1B mutations: the latest of the MEN syndromes

Multiple endocrine neoplasia (MEN) refers to a group of autosomal dominant disorders with generally high penetrance that lead to the development of a wide spectrum of endocrine and non-endocrine manifestations. The most frequent among these conditions is MEN type 1 (MEN1), which is caused by germline heterozygous loss-of-function mutations in the tumor suppressor gene MEN1 MEN1 is characterized by primary hyperparathyroidism (PHPT) and functional or nonfunctional pancreatic neuroendocrine tumors and pituitary adenomas. Approximately 10% of patients with familial or sporadic MEN1-like phenotype do not have MEN1 mutations or deletions. A novel MEN syndrome was discovered, initially in rats (MENX), and later in humans (MEN4), which is caused by germline mutations in the putative tumor suppressor CDKN1B The most common phenotype of the 19 established cases of MEN4 that have been described to date is PHPT followed by pituitary adenomas. Recently, somatic or germline mutations in CDKN1B were also identified in patients with sporadic PHPT, small intestinal neuroendocrine tumors, lymphoma and breast cancer, demonstrating a novel role for CDKN1B as a tumor susceptibility gene for other neoplasms. In this review, we report on the genetic characterization and clinical features of MEN4.

Genetic aspects of pituitary carcinoma: A systematic review

BACKGROUND

Pituitary carcinoma (PC) is a rare type of malignant intracranial neoplasm defined as distant metastasis of pituitary adenoma (PA). Although PC incidence is low because only 0.1% to 0.2% of PAs ultimately develop into PCs, the prognosis is poor and 66% of patients die within the first year. Existing therapeutic measures, including surgical removal, chemotherapy, and radiotherapy, have limited effectiveness. The lack of efficacy of current treatments is largely caused by the limited understanding of the molecular pathogenesis of PA and the malignant transformation to PC. Therefore, the aim of this systematic review was to summarize published research regarding gene and protein expression in PC to clarify the molecular mechanisms underlying PC genesis and development and identify new candidate diagnostic biomarkers and therapeutic targets for potential use in personalized treatment of PC.

METHODS

We followed the PRISMA guidelines to plan and conduct this systematic review. PubMed, Embase, and Web of Science databases were searched for relevant studies conducted before December 16, 2015 describing the association of PC with gene expression at the mRNA and protein levels. MeSH terms combined with free terms were used to retrieve the references.

RESULTS

In total, 207 records were obtained by primary search, and 32 were included in the systematic review. Compared with normal pituitary gland and/or PA, 30 and 18 genes were found to have higher or lower expression, respectively, in PCs using different analytical methods. Among them, we selected 9 upregulated and 7 downregulated genes for further analysis based on their identification as candidate treatment targets in other cancers, potential clinical application, or further research value.

CONCLUSION

Previous studies demonstrated that many genes promote PC malignant transformation, angiogenesis, invasion, metastasis, and recurrence. Although most of these genes and proteins have not been fully analyzed with regard to their downstream mechanisms or potential diagnostic and therapeutic application, they have the potential to become candidate PC biomarkers and/or molecular targets for guiding personalized treatment. Modern advanced technologies should be utilized in future research to identify more candidate genes for PC pathogenesis, as precisely targeted gene therapies against PC are urgently required.

Role of mTOR Inhibitors in Growth Hormone-Producing Pituitary Adenomas Harboring Different FGFR4 Genotypes

Pituitary adenomas (PAs) are common intracranial lesions. Available medical therapies are limited in PAs, and therefore, it is essential to identify treatments that control PA growth when surgery is not an option. Fibroblast growth factor 4 is implicated in PA pathogenesis; therefore, in this study, we used an isogenic mammosomatotroph cell line (GH4C1) harboring different fibroblast growth factor receptor (FGFR)-4 genotypes to establish and characterize intracranial xenograft mouse models that can be used for preclinical drug testing. We show that proliferating GH4C1 tumors have an average latency of 3 weeks to form. Histological analysis revealed that prototypic FGFR4 (G388) tumors express increased prolactin and less GH, whereas tumors possessing the polymorphic variant of FGFR4 (R388) express increased GH relative to prolactin. All tumors show abundant mammalian target of rapamycin (mTOR) signaling as confirmed using phosphorylated (p)-S6 and p-4E-binding protein 1 as downstream regulators of this pathway. We subsequently demonstrate that the mTOR inhibitor RAD001 decreases tumor growth rate and reduces p-S6 but not p-4E-binding protein 1 activation, regardless of FGFR4 status. More importantly, GH activity was significantly reduced after mTOR inhibition in the R388 polymorphic variant tumors. This reduction was also associated with a concomitant reduction in serum IGF-1 levels in the R388 group. In summary, we demonstrate that the GH4C1 FGFR polymorphic xenograft is a useful model for examining PAs. Furthermore, we show that RAD001 can efficiently reduce tumor growth rate by a reduction in mTOR signaling and more importantly results in control of GH expression and IGF-1 secretion, providing further support for using mTOR inhibitors in PA patients, in particular GH-producing adenomas.

Biomarkers of pituitary carcinomas

Pituitary carcinoma is a rare tumor originating from adenohypophyseal cells. Currently, diverse pathogenetic mechanisms, i.e. de novo versus malignant transformation from pituitary adenoma, remain obscure and require further investigation. During the last two decades, scientific research added new horizons not only in regards to general tumor concepts but also in next generation biomarker armamentarium that sheds light on alternate pathways in carcinogenesis. Areas covered: In this review, the impact of apoptotic and proliferative markers, angiogenesis, telomerase activity, H-ras, HIF-1, HER-2/neu, Rb gene, and microRNAs in pathogenetic mechanisms of pituitary carcinomas were revised. Expert commentary: It is becoming increasingly important for the need of standardization of new biomarkers but also for better comprehension of the diverse pathways in tumorigenesis. This can only be accomplished by tapping into the continuously expanding spectrum of new biomarkers.

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.

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.

Cyclin-dependent kinase inhibitor 1B (CDKN1B) gene variants in AIP mutation-negative familial isolated pituitary adenoma kindreds

Familial isolated pituitary adenoma (FIPA) occurs in families and is unrelated to multiple endocrine neoplasia type 1 and Carney complex. Mutations in AIP account only for 15-25% of FIPA families. CDKN1B mutations cause MEN4 in which affected patients can suffer from pituitary adenomas. With this study, we wanted to assess whether mutations in CDKN1B occur among a large cohort of AIP mutation-negative FIPA kindreds. Eighty-eight AIP mutation-negative FIPA families were studied and 124 affected subjects underwent sequencing of CDKN1B. Functional analysis of putative CDKN1B mutations was performed using in silico and in vitro approaches. Germline CDKN1B analysis revealed two nucleotide changes: c.286A>C (p.K96Q) and c.356T>C (p.I119T). In vitro, the K96Q change decreased p27 affinity for Grb2 but did not segregate with pituitary adenoma in the FIPA kindred. The I119T substitution occurred in a female patient with acromegaly. p27(I119T) shows an abnormal migration pattern by SDS-PAGE. Three variants (p.S56T, p.T142T, and c.605+36C>T) are likely nonpathogenic because In vitro effects were not seen. In conclusion, two patients had germline sequence changes in CDKN1B, which led to functional alterations in the encoded p27 proteins in vitro. Such rare CDKN1B variants may contribute to the development of pituitary adenomas, but their low incidence and lack of clear segregation with affected patients make CDKN1B sequencing unlikely to be of use in routine genetic investigation of FIPA kindreds. However, further characterization of the role of CDKN1B in pituitary tumorigenesis in these and other cases could help clarify the clinicopathological profile of MEN4.

Biomarkers of pituitary neoplasms: a review (Part II)

Several new markers have shown a capacity to predict the clinicopathological behavior of pituitary neoplasms; these markers have shown potential to correlate with tumor subtype and size and patient age and sex. These various markers are involved in a host of cellular functions, including cell-cycle progression, cell proliferation, apoptosis, cell adhesion, and tumor vascularity. In this companion article to our first review of Ki-67 as a marker of pituitary adenomas, we present and analyze the literature regarding matrix metalloproteinases and their inhibitors (tissue inhibitor metalloproteinases), vascular endothelial growth factor, fibroblast growth factor and its receptor, apoptotic markers and p53, as well as cyclooxygenase-2, galectin-3, and pituitary tumor transforming gene. Some of these markers, such as fibroblast growth factor and fibroblast growth factor receptor and matrix metalloproteinases, show particular promise in their ability to identify pituitary tumors that behave in an aggressive manner. We suggest the need for uniform design and application of methods and standardized criteria for the interpretation of results. A uniform approach will establish clinicopathological utility of emerging markers.

Cooperation between cyclin E and p27(Kip1) in pituitary tumorigenesis

Cushing's disease is caused by glucocorticoid-resistant pituitary corticotroph adenomas. We have previously identified the loss of nuclear Brg1 as one mechanism that may lead to partial glucocorticoid resistance: this loss is observed in about 33% of human corticotroph adenomas. We now show that Brg1 loss of function correlates with cyclin E expression in corticotroph adenomas and with loss of the cell cycle inhibitor p27(Kip1) expression. Because Brg1 is thought to have tumor suppressor activity, the present study was undertaken to understand the putative contribution of cyclin E derepression produced by loss of Brg1 expression on adenoma development. Overexpression of cyclin E in pituitary proopiomelanocortin cells leads to abnormal reentry into cell cycle of differentiated proopiomelanocortin cells and to centrosome instability. These alterations are consistent with the intermediate lobe hyperplasia and anterior lobe adenomas that were observed in these pituitaries. When combined with the p27(Kip1) knockout, overexpression of cyclin E increased the incidence of pituitary tumors, their size, and their proliferation index. These results suggest that cyclin E up-regulation and p27(Kip1) loss-of-function act cooperatively on pituitary adenoma development.

MEN-4 and other multiple endocrine neoplasias due to cyclin-dependent kinase inhibitors (p27(Kip1) and p18(INK4C)) mutations

Cyclin-dependent kinase inhibitors (CDKIs) are known targets to become deregulated in various tumour types, including endocrine tumours. Typically, these cell cycle regulators are somatically inactivated in sporadic endocrine tumours. Recently, it became known that certain CDKI genes cause inherited susceptibility to endocrine neoplasia. Multiple endocrine neoplasia type 4 (MEN4) emerged as a novel form of multiple endocrine neoplasia, caused by mutations in the CDKI gene CDKN1B/p27(Kip1). The MEN4 phenotype remains unclear, but all MEN4 patients identified thus far present with parathyroid involvement, and less typically with pituitary adenomas and other endocrine features. Moreover, the CDKI gene CDKN2C/p18(INK4C) has been also implicated in endocrine neoplasia susceptibility. This review presents the recent advances in these novel MEN-related states and summarises the current knowledge of how these CDKIs may be implicated in endocrine neoplasia. In addition, it briefly presents data from Cdkn1b/p27(Kip1) and Cdkn2c/p18(INK4C) murine models, which strongly support the protective role of these inhibitors against endocrine tumourigenesis.

Mutational analysis of transforming growth factor-beta receptor type II and Smad3 tumor suppressor genes in prolactinomas

The presence of transforming growth factor-beta receptor type II and Smad3 gene abnormality was examined in human prolactinomas by single-strand conformation polymorphism screening for gene abnormality and band shift in tumor tissue and peripheral blood samples obtained from 14 patients treated for prolactinoma. Direct sequencing of exon 4 of the transforming growth factor-beta receptor type II gene, which showed a band shift by single-strand conformation polymorphism, disclosed a single nucleotide polymorphism (rs2228048) (alleles A/G; average allele frequency, G:0.817, A:0.183) and not an active mutation. Seven of the 14 cases showed base substitution (G --> A) of the single nucleotide polymorphism. Two of these 7 cases showed base substitution (G --> A) in the blood sample in accordance with neoplastic transformation. Direct sequencing of exon 2 of the Smad3 gene, which showed band shift by single-strand conformation polymorphism, disclosed single nucleotide polymorphism (rs1065080) (alleles C/T; average allele frequency, C:0.947, T:0.053) and no active mutation. Four of the 14 cases showed base substitution (C --> T) of the single nucleotide polymorphism. Blood samples were available for 2 of these 4 cases, and 1 of these 2 cases showed base substitution (C --> T) in accordance with neoplastic transformation. Estimation of the drug sensitivity of pituitary adenoma based on analysis of peripheral blood cells needs special care.

Promoter hypermethylation profile of cell cycle regulator genes in pituitary adenomas

Aberrant hypermethylation of CpG islands in the promoter region plays a causal role in the inactivation of various key genes involved in the cell cycle regulatory cascade, which could result in a loss of cell cycle control. The aim of the present study was to examine in more detail the prevalence and role of the promoter methylation of genes with a proven involvement in the cell cycle regulation of pituitary adenomas, since their tumorigenesis has not yet been clearly defined. We profiled the CpG island methylation status of a series of well-characterized cell cycle regulation genes: the RB1, p14(ARF), p15(INK4b), p16(INK4a), p21(Waf1/Cip1), p27(Kip1), and p73 genes, in 34 pituitary adenomas as determined by a methylation-specific polymerase chain reaction assay. Promoter hypermethylation of the RB1, p14(ARF), p15(INK4b), p16(INK4a), p21(Waf1/Cip1), p27(Kip1), and p73 genes was detected in 12 (35%), 2 (6%), 11 (32%), 20 (59%), 1 (3%), 0 (0%), and 4 (12%) of the adenomas, respectively. In total, 88% (30 of 34) of the adenomas displayed methylation of at least one of such cell cycle regulatory genes, especially methylation of the member genes of the RB1 pathway (29 of 34; 85%). Promoter hypermethylation of p15(INK4b) coincided with RB1 and/or p16(INK4a) methylation, whereas RB1 and p16(INK4a) methylations tended to be mutually exclusive (p = 0.0048). Furthermore, promoter hypermethylations of p14(ARF), p21(Waf1/Cip1), and p73 (not belonging to the member genes of the RB1 pathway) were also coincident with RB1 and/or p16(INK4a) methylation except in one p73 methylated case. In contrast, none of the clinicopathological features, including the cell proliferation index, was significantly correlated with any particular methylation status. Our results suggested that aberrant hypermethylation of the key cell cycle regulatory genes occurs at a relatively high frequency in pituitary adenomas, especially in RB1 pathway genes with promoter hypermethylation of the p16(INK4a) gene being the most common deregulation. We further obtained evidence to indicate that RB1 and p16(INK4a) methylations tended to be mutually exclusive, but did occasionally coincide with other cell cycle regulation gene methylations.

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.

Aggressive vestibular schwannomas showing postoperative rapid growth - their association with decreased p27 expression

Vestibular schwannomas (VSs) are relatively slow growing tumors. However, some rapidly regrow or recur after surgical resection. The objective of this study was to identify those molecular characteristics predicting rapid recurrence after surgical resection. Immunohistochemically determined expressions of several cell cycle regulators and apoptosis-associated proteins in 12 cases of aggressive VS (AVS) and in 15 control cases of usual VS (UVS) cases were compared. The expressions of p53 and Bax (pro-apoptotic protein), Bcl-2 (anti-apoptotic protein), Fas, and Fas-L (apoptotic death receptor and ligand), caspase 3 (apoptotic effector caspase proteins), and p27 and p21 (cyclin-dependent kinase inhibitors) were analyzed using tissue array blocks. Loss of p27 expression was observed in 8 of 12 AVS cases (67%) and in 3 UVS cases (20%); p21 was expressed in all cases. Loss of Bax was observed in 3 AVS and 3 UVS cases. The anti-apoptotic protein, Bcl-2, was expressed in 9 AVS (75%) and 11 UVS (73%), and p53, Fas-L, and caspase 3 were negative and Fas was positive in all AVS and UVS cases. Of these, only the loss of p27 was statistically significant (P = 0.02). The loss of p27 in AVS may explain the unusually high proliferative potential of AVS versus UVS, and p27 may be a predictor of VS aggressiveness. The expressions of other apoptosis associated proteins were not significantly different in the two groups. This may be the first report to identify a molecular entity associated with aggressive VS. However, further studies are required.

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.

Elevated expression of p21 (WAF1/Cip1) in hormonally active pituitary adenomas

Although most pituitary adenomas arise sporadically, molecular studies show alterations of known oncogenes and/or tumor suppressor genes in a small percentage of adenomas, and the molecular pathology of most is unknown. The p21 gene is a universal inhibitor of cyclin-dependent kinases and serves as a cell-cycle blocker and cell-growth inhibitor. Pituitary adenomas (n = 54) were immunophenotyped for hormone production (prolactin, growth hormone, adrenocorticotropin, thyrotropin, follicle-stimulating hormone, and luteinizing hormone), and expression of p21 was determined by immunohistochemistry. The percentage of cells expressing p21 for each tumor was evaluated blindly with regard to hormone status, and expression of p21 was then correlated with the results of hormone immunotyping. Results show a striking difference in the expression of p21 between immunonegative adenomas and hormone-producing tumors. Whereas 71% (10/14) of nonfunctional adenomas exhibit p21 expression in fewer than 5% of cells, 77% (31/40) of hormone-producing adenomas show expression in more than 25% of cells, and of these, 68% (21/31) show expression in more than 75% of cells. Overexpression of p21 is particularly striking for growth hormone-producing tumors, of which 92% (11/12) show expression in more than 75% of cells. Hormone-producing pituitary adenomas express much more p21 than do immunonegative adenomas. These high levels of p21 expression represent the most widespread molecular genetic alteration demonstrated to date in pituitary adenomas.

Infrequent mutation of APC, AXIN1, and GSK3B in human pituitary adenomas with abnormal accumulation of CTNNB1

We analyzed mutation of the APC, AXIN1, and GSK3genes in 14 pituitary adenomas with abnormal nuclear accumulations of CTNNB1. These tumors did not harbor mutation of the CTNNB1 gene. The genes analyzed encode proteins associated with ubiquitin-mediated degradation of CTNNB1. Although the regions encoding functional domains of these protein products were analyzed, no significant genetic alterations were found. Furthermore, the antibody for the C-terminus of APC detected normal expression of the APC protein in these pituitary adenomas. Our present results imply that an unknown mechanism(s) accelerates the accumulation of CTNNB1 that plays an important role in the pathogenesis of human pituitary adenomas. However, the possibility that mutation of regions outside of our survey or epigenetic mechanism play an important role cannot be excluded.

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.

Molecular defects in the pathogenesis of pituitary tumours

The majority of pituitary adenomas are trophically stable and change relatively little in size over many years. A comparatively small proportion behave more aggressively and come to clinical attention through inappropriate hormone secretion or adverse effects on surrounding structures. True malignant behaviour with metastatic spread is very atypical. Pituitary adenomas that come to surgery are predominantly monoclonal in origin and roughly half are aneuploid, indicating either ongoing genetic instability or transition through a period of genetic instability at some time during their development. Few are associated with the classical mechanisms of tumour formation but it is generally believed that the majority harbour quantitative if not qualitative differences in molecular composition compared to the normal pituitary. Despite their prevalence and the ready availability of biopsy material, at the present time, the precise molecular pathogenesis of the majority of pituitary adenomas remains unclear. This review summarizes current thinking.

Clinicopathologic study of 123 cases of prolactin-secreting pituitary adenomas with special reference to multihormone production and clonality of the adenomas

BACKGROUND

Prolactinoma is the most invasive type of pituitary adenoma and is generally believed to be well-differentiated adenoma and to produce only prolactin (PRL). The factors related to the various biologic behaviors occurring in patients of different ages and sexes await clarification. Since different immunophenotypes of adenoma may show different biologic behaviors and responses to medical agents, the authors examined hormone production and tried to clarify the clonality of plurihormonal prolactinoma.

METHODS

Clinicopathologic factors were studied in 123 patients with prolactinomas (40 males and 83 females). The specimens were fixed in either 10% neutral buffered formalin or 70% alcohol and used for light microscopy. Alcohol-fixed tissue was used to extract DNA from 26 samples obtained from female patients for human androgen receptor gene (HUMARA) assay.

RESULTS

Sixty one cases (50%) were pure prolactinoma and 62 cases (50%) were plurihormonal prolactinoma. Spearman rank correlation analysis revealed a significant relationship between age and serum PRL level (P = 0.0002), age and tumor volume (P < 0.0001), and tumor volume and serum PRL level (P < 0.0001). Multiple regression analysis showed a significant correlation only between tumor volume and serum PRL level. The Mann-Whitney U test revealed that prolactinomas associated with higher PRL levels, larger adenomas, and higher ages were significantly more invasive to the cavernous sinus and that male patients had significantly higher PRL levels and larger adenomas. The HUMARA assay disclosed that 11 of 13 plurihormonal prolactinomas (85%) were compatible with monoclonal origin.

CONCLUSIONS

The current results suggest that not only can various hormones other than PRL be secreted by prolactinoma, but also that most multihormone-producing prolactinomas are monoclonal in origin.

Morphologic and molecular analysis of estrogen-induced pituitary tumorigenesis in targeted disruption of transforming growth factor-beta receptor type II and/or p27 mice

The critical genes and products involved in estrogen-induced tumorigenesis of the pituitary gland were investigated in heterozygous transforming growth factor-beta (TGF-beta) receptor type II and p27 knockout mouse models. Tgfbr2(+/-), p27(+/-); Tgfbr2(+/-), and p27(+/-) mice and C57BL/6J wild-type mice received sc implantation of estrogen or placebo pellets for 16 or 25 wk, after which the mice were sacrificed and their pituitary glands removed for examination. The bromodeoxyuridine labeling indexes in tissue from both the anterior and intermediate pituitary lobes from p27 (+/-) and Tgfbr2(+/-); p27(+/-) mice were significantly higher than those from wild-type and Tgfbr2(+/-) mice after treatment with estrogen for 16 wk. Pituitary tumorigenesis was significantly accelerated in Tgfbr2(+/-), p27(+/-), and Tgfbr2(+/-); p27(+/-) mice compared with wild-type mice after treatment with estrogen for 16 wk. Pituitary tumorigenesis was not accelerated in Tgfbr2(+/-); p27(+/-) mice compared with Tgfbr2(+/-) or p27(+/-) mice. Expression of TGF-beta receptor type II mRNA was lower in the pituitary gland of Tgfbr2(+/-) mice than in wild-type mice before estrogen treatment and was significantly reduced after treatment. Pituitary tumorigenesis is accelerated in mice with severe TGF-beta resistance, and greatly accelerated in mice with TGF-beta resistance combined with decreased p27 expression compared with wild-type mice. Both the TGF-beta receptor type II gene and p27 gene and their products are involved in estrogen-induced tumorigenesis.

Mdm2 and the p53 pathway in human pituitary adenomas

OBJECTIVE

Studies on pituitary tumours have failed to identify mutations in the tumour suppressor gene p53 suggesting that the protein identified is wild type. p21(WAF--1) is a downstream effector of p53 which promotes growth arrest. Mdm2 (mouse double minute) is a protein induced by wild type p53 and forms an autoregulatory feedback loop suppressing wild type p53 activity. The purpose of this study was to examine a group of pituitary tumours for expression of p53 and its two downstream effector proteins p21(WAF--1) and mdm2 and to compare this with their radiological invasive status and proliferative potential as assessed by Ki-67 expression.

SUBJECTS AND METHODS

Sixty-nine tumours removed at transsphenoidal surgery were examined by immunocytochemistry using antibodies against p53, p21(WAF--1), mdm2 and Ki-67 (MIB-1). The invasive status of the tumours was determined from the preoperative CT/MRI scans.

RESULTS

p53 was expressed in 42 of 69 (61%) pituitary adenomas but there was no relationship with either pituitary tumour invasive status (P = 0.71) or volume (P = 0.33). p53 expression correlated, however, with the proliferative state of the tumours as assessed by the MIB-1 labelling index (P = 0.0065). Invasive tumours had a higher growth fraction than non-invasive ones (P = 0.027). p21(WAF--1) was expressed in the nuclei of 58/69 (84%) pituitary adenomas and its expression correlated with that of p53 (r = 0.26, P = 0.03). Mdm2 was expressed in the cytoplasm of 46/69 (67%) tumours and this correlated with the nuclear staining for p53 (P = 0.022) while nuclear staining was seen in 32/69 (46%) tumours but this did not correlate significantly with nuclear p53 staining (P = 0.096).

CONCLUSIONS

These results suggest that p53, p21(WAF--1) and mdm2 are all expressed in pituitary tumours suggesting that the p53 protein detected by immunocytochemistry is wild type. Expression of p53 is associated with tumours which have a higher proliferative status. The p53 activity is probably the result of upstream signals of local stresses mediated through either genetic change, cytokines, hypoxia or hormonal factors. Our results suggest, however, that the downstream pathway mediated through the activities of p21(WAF--1) and mdm2 may be dysfunctional in these tumours.

Frequent nuclear accumulation of beta-catenin in pituitary adenoma

BACKGROUND

Beta-catenin (CTNNB1) is known to be a member of the cadherin-catenin superfamily and to function in cell-cell adhesion. However, it also has been reported that CTNNB1 plays an important role in carcinogenesis. In the current study, the authors observed expression of the CTNNB1 protein in primary pituitary adenomas to investigate the role of CTNNB1 in the development of pituitary adenomas.

METHODS

A total of 37 pituitary adenomas were analyzed. Expression of CTNNB1 and the cell proliferation marker Ki-67 were observed immunohistochemically. In addition, the authors performed direct sequencing to detect somatic mutations of exon 3 of the CTNNB1 gene.

RESULTS

Twenty-one of 37 pituitary adenomas (57%) demonstrated abnormal nuclear accumulation of CTNNB1. It is interesting to note that tumors with an accumulation of CTNNB1 in the nucleus showed a statistical tendency toward an association with increased immunoreactivity of Ki-67 (P < 0.05) whereas no significant correlation was detected between the status of CTNNB1 and other clinicopathologic features. Missense mutations in exon 3 of the CTNNB1 gene also were detected in the cases with abnormal nuclear accumulation of the CTNNB1 protein.

CONCLUSIONS

The results of the current study suggest that up-regulation of the Wnt signaling pathway, including accumulation of mutant CTNNB1 in the nuclei, plays an important role in the tumorigenesis and development of adenoma in the pituitary gland.

Immunohistochemical analysis of p27 (Kip1) in human pituitary glands and in various types of pituitary adenomas

p27 (Kip1) plays regulatory roles in the cell cycle by inhibiting the activity of cyclin dependent kinases (CDKs). This immunohistochemical study is aimed at elucidating the expression of p27 in human pituitary and in various types of pituitary adenomas in order to clarify its role in the regulation of proliferation. Sixteen normal pituitary glands and 179 human pituitary adenomas were used for immunohistochemical studies. The tissues were fixed in 10% formalin and embedded in paraffin. Indirect peroxidase method was performed after heat-induced antigen retrieval using a monoclonal antibody against p27 protein. p27 protein was expressed in the nuclei of all 16 normal human pituitary glands. p27 protein was also expressed in 128 of 179 cases of pituitary adenomas (71.5%). A marked decrease of p27 expression was noted in ACTH-secreting adenomas, 8/20 (40.0%), compared with other types of pituitary adenomas--GH-secreting adenomas, 35/46 (76.1%); PRL-secreting adenomas, 22/33 (66.7%); TSH-secreting adenomas, 8/11 (72.7%); and nonfunctioning adenomas, 55/69 (79.7%). These results suggest that p27 may play some role in the regulation of proliferation in all types of pituitary adenomas. The lower levels of p27 in ACTH-secreting adenoma is of particular interest with respect to the intermediate lobe-derived pituitary tumor developed in p27 knockout mice.

p27Kip1-deficient mice exhibit accelerated growth hormone-releasing hormone (GHRH)-induced somatotrope proliferation and adenoma formation

p27Kip1 (p27) controls cell cycle progression by binding to and inhibiting the activity of cyclin dependent kinases. Disruption of the p27 gene in mice (p27-/-) results in increased body growth with a disproportionate enlargement of the spleen, thymus, testis, ovary and pituitary. The increase in pituitary size is due to selective hyperplasia of the intermediate lobe (IL) while the anterior lobe (AL) is not overtly affected. p27 heterozygous mice (p27+/-), as well as p27-/- mice, are hypersensitive to radiation- and chemical-induced tumors compared to wildtype (p27+/+) littermates. Therefore, unlike classical tumor suppressors, only a reduction in p27 levels is necessary to predispose tissues to secondary tumor promoters. Consistent with these studies is the fact that the p27 gene sequence and mRNA levels appear normal in human pituitary adenomas while p27 protein levels are decreased. Therefore, a reduction in p27 levels could be sufficient to sensitize pituitary cells to tumorigenic factors. To test this hypothesis, metallothionein promoter-driven, human growth hormone-releasing hormone (MT-hGHRH) transgenic mice, that exhibit somatotrope hyperplasia before 9 months of age and subsequent adenoma formation with 30 - 40% penetrance, were crossbred with p27+/- mice for two successive generations to produce p27+/+, p27+/- and p27-/- mice that expressed the hGHRH transgene. At 10 - 12 weeks of age, p27-/- and p27+/+, hGHRH mice were larger than their p27+/+ littermates and displayed characteristic hyperplasia of the IL and AL, respectively. Expression of the hGHRH transgene in both p27+/- and p27-/- mice selectively expanded the population of somatotropes within the AL, where pituitaries of p27+/-, hGHRH and p27-/-, hGHRH mice were two- and fivefold larger than p27+/+, hGHRH pituitaries, respectively. There was also a synergistic effect of hGHRH transgene expression and p27-deficiency on liver, spleen and ovarian growth. At 6 - 8 months of age, 83% of p27+/-, hGHRH mice displayed macroscopic AL adenomas (>100 mg), while all pituitaries from p27+/+, hGHRH mice remained hyperplastic (<20 mg). In contrast to the dramatic effects of p27-deficiency on hGHRH-induced organ growth, elimination of p53, by crossbreeding MT-hGHRH mice to p53-deficient mice, did not augment the hyperplastic/tumorigenic effects of hGHRH transgene expression. Taken together these results demonstrate that a reduction in p27 expression is sufficient to sensitize somatotropes to the proliferative actions of excess GHRH, resulting in the earlier appearance and increased penetrance of hGHRH-induced pituitary tumors.

Multiple functions of p27(Kip1) and its alterations in tumor cells: a review

Cyclin-dependent kinases (CDKs), together with cyclins, their regulatory subunits, govern cell-cycle progression in eukaryotic cells. p27(Kip1) is a member of a family of CDK inhibitors (CDIs) that bind to cyclin/CDK complexes and arrest cell division. There is considerable evidence that p27(Kip1) plays an important role in multiple fundamental cellular processes, including cell proliferation, cell differentiation, and apoptosis. Moreover, p27(Kip1) is a putative tumor-suppressor gene that appears to play a critical role in the pathogenesis of several human malignancies and its reduced expression has been shown to correlate with poor prognosis in cancer patients. This study reviews current information on the functions of p27(Kip1), its abnormalities found in human tumors, and the possible clinical implications of these findings with respect to the management of cancer patients.

p27(kip1) and Other Cell-Cycle Protein Expression in Normal and Neoplastic Endocrine Tissues

Endocrine tumors are often diagnostic challenges. Recent studies have suggested that proteins that regulate cell cycle may have diagnostic and prognostic utility in endocrine tumors. p27(kip1) (p27) is a cyclin-dependent kinase inhibitor that regulates the transition from the G1 to the S phase of the cell cycle. p27 and other cell-cycle proteins are becoming increasingly important in assessing the biologic behavior of endocrine neoplasms, classifying hyperplastic and neoplastic endocrine tissues, and in the progression of endocrine tumors. p27 appears to separate normal from neoplastic endocrine tissues and, in some cases, benign from malignant endocrine tumors. However, there is overlap in p27 expression among individual cases of benign and malignant tumors, and p27 has only limited prognostic utility in endocrine tumors compared to some epithelial tumors such as breast and prostate neoplasms. Thus, more effective molecular and cellular markers that can be used for diagnostic and prognostic purposes in endocrine pathology are needed.

Low expression of the cell cycle inhibitor p27Kip1 in normal corticotroph cells, corticotroph tumors, and malignant pituitary tumors

The cell cycle is regulated by a number of inhibitors, including p27Kip1 (p27), which belongs to the kip1 family. By binding to the cyclin/cyclin-dependent kinase complexes, it regulates progression of G1 to S phase in the cell cycle. It has been reported that p27 knockout mice develop multiorgan hyperplasia and intermediate lobe pituitary tumors secreting ACTH. Previously, we and others have been unable to show any consistent change in messenger RNA expression or genomic mutations for p27 in human corticotroph adenomas. However, dysregulation at the protein level has been reported in nonendocrine tumors, and we, therefore, investigated the expression of p27 in a range of benign and metastatic pituitary tumors. We studied a total of 107 pituitaries, including normal pituitary (n = 20), Cushing's disease (n = 21), acromegaly (n = 19), nonfunctioning adenomas (n = 18), prolactinomas (n = 7), TSH-omas (n = 2), FSH-omas (n = 6), aggressive tumors showing invasiveness and recurrence (n = 9), and metastatic pituitary carcinomas (n = 5). Using standard immunohistochemical techniques with a highly specific monoclonal antibody, p27 expression was determined quantitatively as the percentage of cells showing strongly positive, weak, or negative staining. In each sample, approximately 500 cells were analyzed. We also analyzed normal pituitaries using double-labeling for p27 and each of the pituitary hormones to characterize the expression of p27 in each cell type. p27 was expressed in normal pituitary cells; in tumors expressing GH, prolactin, TSH, and FSH; and in aggressive tumors, but markedly reduced expression of p27 was seen in corticotroph tumors and pituitary carcinomas. In the normal pituitary, somatotroph, lactotroph, and thyrotroph cells showed strong p27 staining, whereas normal corticotroph cells showed a much lower level of p27 staining (P < 0.001). Somatotroph, lactotroph, gonadotroph, and thyrotroph adenomas showed a lower level of p27 expression compared with normal somatotrophs (P = 0.02), lactotrophs (P = 0.03), gonadotrophs (P = 0.01), and thyrotrophs, respectively, whereas the lower level of p27 expression present in normal corticotrophs virtually disappeared in corticotroph adenomas (P = 0.001). We conclude that pituitary adenomas show a lower level of p27 protein expression than the normal cells from which they are derived, with malignant transformation leading to complete loss of p27 immunoreactivity. Corticotrophs are quite different to other pituitary cell types in terms of p27 immunoreactivity because both normal and tumorous corticotrophs have low p27 staining, and we speculate that this may relate to their inherent control mechanisms.

Estrogen-induced tumorigenesis in the pituitary gland of TGF-beta(+/-) knockout mice

Transforming growth factor (TGF)-beta receptor type II gene (Tgfbr2) knockout and wild type mice underwent chronic estrogen exposure using estradiol pellets. Histological examination of the pituitary glands found 38 adenomas in 14 Tgfbr2(+/-) mice but only one tumor in ten wild type mice. Pituitary tumorigenesis is greatly accelerated in Tgfbr2(+/-) mice by estrogen treatment.