Oncogene activation in pituitary tumors

A disintegrin and metalloproteinase 22 activates integrin β1 through its disintegrin domain to promote the progression of pituitary adenoma

BACKGROUND

Approximately 35% of pituitary adenoma (PA) display an aggressive profile, resulting in low surgical total resection rates, high recurrence rates, and worse prognosis. However, the molecular mechanism of PA invasion remains poorly understood. Although "a disintegrin and metalloproteinases" (ADAMs) are associated with the progression of many tumors, there are no reports on ADAM22 in PA.

METHODS

PA transcriptomics databases and clinical specimens were used to analyze the expression of ADAM22. PA cell lines overexpressing wild-type ADAM22, the point mutation ADAM22, the mutated ADAM22 without disintegrin domain, and knocking down ADAM22 were generated. Cell proliferation/invasion assays, flow cytometry, immunohistochemistry, immunofluorescence, co-immunoprecipitation, mass spectrometry, Reverse transcription-quantitative real-time PCR, phos-tag SDS-PAGE, and Western blot were performed for function and mechanism research. Nude mice xenograft models and rat prolactinoma orthotopic models were used to validate in vitro findings.

RESULTS

ADAM22 was significantly overexpressed in PA and could promote the proliferation, migration, and invasion of PA cells. ADAM22 interacted with integrin β1 (ITGB1) and activated FAK/PI3K and FAK/ERK signaling pathways through its disintegrin domain to promote PA progression. ADAM22 was phosphorylated by PKA and recruited 14-3-3, thereby delaying its degradation. ITGB1-targeted inhibitor (anti-itgb1) exerted antitumor effects and synergistic effects in combination with somatostatin analogs or dopamine agonists in treating PA.

CONCLUSIONS

ADAM22 was upregulated in PA and was able to promote PA proliferation, migration, and invasion by activating ITGB1 signaling. PKA may regulate the degradation of ADAM22 through post-transcriptional modification levels. ITGB1 may be a potential therapeutic target for PA.

Phosphorylated PTTG1 switches its subcellular distribution and promotes β-catenin stabilization and subsequent transcription activity

The Wnt/β-catenin signaling is usually abnormally activated in hepatocellular carcinoma (HCC), and pituitary tumor-transforming gene 1 (PTTG1) has been found to be highly expressed in HCC. However, the specific mechanism of PTTG1 pathogenesis remains poorly understood. Here, we found that PTTG1 is a bona fide β-catenin binding protein. PTTG1 positively regulates Wnt/β-catenin signaling by inhibiting the destruction complex assembly, promoting β-catenin stabilization and subsequent nuclear localization. Moreover, the subcellular distribution of PTTG1 was regulated by its phosphorylation status. Among them, PP2A induced PTTG1 dephosphorylation at Ser165/171 residues and prevented PTTG1 translocation into the nucleus, but these effects were effectively reversed by PP2A inhibitor okadaic acid (OA). Interestingly, we found that PTTG1 decreased Ser9 phosphorylation-inactivation of GSK3β by competitively binding to PP2A with GSK3β, indirectly leading to cytoplasmic β-catenin stabilization. Finally, PTTG1 was highly expressed in HCC and associated with poor patient prognosis. PTTG1 could promote the proliferative and metastasis of HCC cells. Overall, our results indicated that PTTG1 plays a crucial role in stabilizing β-catenin and facilitating its nuclear accumulation, leading to aberrant activation of Wnt/β-catenin signaling and providing a feasible therapeutic target for human HCC.

Pregnancies after Childhood Craniopharyngioma: Results of KRANIOPHARYNGEOM 2000/2007 and Review of the Literature

BACKGROUND

Data on female fertility, pregnancy, and outcome of offspring after childhood-onset craniopharyngioma (CP) are rare.

STUDY DESIGN

Observational study on pregnancy rate and offspring outcome in female CP patients recruited in KRANIOPHARYNGEOM 2000/2007 since 2000.

RESULTS

A total of 451 CP patients (223 female) have been recruited, and 269 (133 female) were postpubertal at study. Six of 133 female CP patients (4.5%) with a median age of 14.9 years at CP diagnosis had 9 pregnancies, giving birth to 10 newborns. Three patients achieved complete surgical resections. No patient underwent postoperative irradiation. Five natural pregnancies occurred in 3 CP patients without pituitary deficiencies. Four pregnancies in 3 CP patients with hypopituitarism were achieved under assisted reproductive techniques (ART) (median 4.5 cycles, range: 3-6 cycles). Median maternal age at pregnancy was 30 years (range: 22-41 years). Six babies (60%) were delivered by caesarean section. Median gestational age at delivery was 38 weeks (range: 34-43 weeks); median birth weight was 2,920 g (range: 2,270-3,520 g), the rate of preterm delivery was 33%. Enlargements of CP cysts occurred in 2 women during pregnancy. Other complications during pregnancy, delivery, and postnatal period were not observed.

CONCLUSIONS

Pregnancies after CP are rare and were only achieved after ART in patients with hypopituitarism. Close monitoring by an experienced reproductive physician is necessary. Due to a potentially increased risk for cystic enlargement, clinical, ophthalmological, and MRI monitoring are recommended in patients at risk. Severe perinatal complications, birth defects, and postnatal morbidity of mothers and offspring were not observed.

BRD4 as a therapeutic target for nonfunctioning and growth hormone pituitary adenoma

BACKGROUND

Nonfunctioning pituitary adenoma (NFPA) and growth hormone pituitary adenoma (GHPA) are major subtypes of pituitary adenomas (PAs). The primary treatment is surgical resection. However, radical excision remains challenging, and few effective medical therapies are available. It is urgent to find novel targets for the treatment. Bromodomain-containing protein 4 (BRD4) is an epigenetic regulator that leads to aberrant transcriptional activation of oncogenes. Herein, we investigated the pathological role of BRD4 and evaluated the effectiveness of BRD4 inhibitors in the treatment of NFPA and GHPA.

METHODS

The expression of BRD4 was detected in NFPA, GHPA, and normal pituitary tissues. The efficacies of BRD4 inhibitors were evaluated in GH3 and MMQ cell lines, patient-derived tumor cells, and in vivo mouse xenograft models of PA. Standard western blots, real-time PCR, and flow cytometry experiments were performed to investigate the effect of BRD4 inhibitors on cell cycle progression, apoptosis, and the expression patterns of downstream genes.

RESULTS

Immunohistochemistry studies demonstrated the overexpression of BRD4 in NFPA and GHPA. In vitro and in vivo studies showed that treatment with the BRD4 inhibitor ZBC-260 significantly inhibited the proliferation of PA cells. Further mechanistic studies revealed that ZBC-260 could downregulate the expression of c-Myc, B-cell lymphoma 2 (Bcl2), and related genes, which are vital factors in pituitary tumorigenesis.

CONCLUSION

In this study, we determined the overexpression of BRD4 in NFPA and GHPA and assessed the effects of BRD4 inhibitors on PA cells in vitro and in vivo. Our findings suggest that BRD4 is a promising therapeutic target for NFPA and GHPA.

Overview of the 2017 WHO Classification of Pituitary Tumors

This review focuses on discussing the main changes on the upcoming fourth edition of the WHO Classification of Tumors of the Pituitary Gland emphasizing histopathological and molecular genetics aspects of pituitary neuroendocrine (i.e., pituitary adenomas) and some of the non-neuroendocrine tumors involving the pituitary gland. Instead of a formal review, we introduced the highlights of the new WHO classification by answering select questions relevant to practising pathologists. The revised classification of pituitary adenomas, in addition to hormone immunohistochemistry, recognizes the role of other immunohistochemical markers including but not limited to pituitary transcription factors. Recognizing this novel approach, the fourth edition of the WHO classification has abandoned the concept of "a hormone-producing pituitary adenoma" and adopted a pituitary adenohypophyseal cell lineage designation of the adenomas with subsequent categorization of histological variants according to hormone content and specific histological and immunohistochemical features. This new classification does not require a routine ultrastructural examination of these tumors. The new definition of the Null cell adenoma requires the demonstration of immunonegativity for pituitary transcription factors and adenohypophyseal hormones Moreover, the term of atypical pituitary adenoma is no longer recommended. In addition to the accurate tumor subtyping, assessment of the tumor proliferative potential by mitotic count and Ki-67 index, and other clinical parameters such as tumor invasion, is strongly recommended in individual cases for consideration of clinically aggressive adenomas. This classification also recognizes some subtypes of pituitary neuroendocrine tumors as "high-risk pituitary adenomas" due to the clinical aggressive behavior; these include the sparsely granulated somatotroph adenoma, the lactotroph adenoma in men, the Crooke's cell adenoma, the silent corticotroph adenoma, and the newly introduced plurihormonal Pit-1-positive adenoma (previously known as silent subtype III pituitary adenoma). An additional novel aspect of the new WHO classification was also the definition of the spectrum of thyroid transcription factor-1 expressing pituitary tumors of the posterior lobe as representing a morphological spectrum of a single nosological entity. These tumors include the pituicytoma, the spindle cell oncocytoma, the granular cell tumor of the neurohypophysis, and the sellar ependymoma.

PTTG promotes invasion in human breast cancer cell line by upregulating EMMPRIN via FAK/Akt/mTOR signaling

Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed at higher level in most of the tumors. PTTG overexpression correlates with lymph node infiltration and a higher degree of tumor recurrence in breast cancer. However, the cellular functions and precise signals elicited by PTTG in breast cancer are not fully understood. Here, we established a breast cancer cell line which stably overexpressed PTTG. In vitro experiments showed that overexpression of PTTG in MCF-7 cells was associated with enhanced cell migration and invasion as well as EMT. Our results also demonstrated that PTTG overexpression correlated with elevated EMMPRIN level, which mediated the enhanced cell migration, invasion and EMT. Moreover, our findings suggested that PTTG enhances metastatic potential of breast cancer cells by inducing EMMPRIN through activating FAK/Akt/mTOR pathway. Our findings may lead to a better understanding of the biological effect of PTTG and provide mechanistic insights for developing potential therapeutic strategies for inhibiting the invasion and metastasis of breast cancer.

Human Pituitary Adenoma Proteomics: New Progresses and Perspectives

Pituitary adenoma (PA) is a common intracranial neoplasm that impacts on human health through interfering hypothalamus-pituitary-target organ axis systems. The development of proteomics gives great promises in the clarification of molecular mechanisms of a PA and discovery of effective biomarkers for prediction, prevention, early-stage diagnosis, and treatment for a PA. A great progress in the field of PA proteomics has been made in the past 10 years, including (i) the use of laser-capture microdissection, (ii) proteomics analyses of functional PAs (such as prolactinoma), invasive and non-invasive non-functional pituitary adenomas (NFPAs), protein post-translational modifications such as phosphorylation and tyrosine nitration, NFPA heterogeneity, and hormone isoforms, (iii) the use of protein antibody array, (iv) serum proteomics and peptidomics, (v) the integration of proteomics and other omics data, and (vi) the proposal of multi-parameter systematic strategy for a PA. This review will summarize these progresses of proteomics in PAs, point out the existing drawbacks, propose the future research directions, and address the clinical relevance of PA proteomics data, in order to achieve our long-term goal that is use of proteomics to clarify molecular mechanisms, construct molecular networks, and discover effective biomarkers.

Thyroid hormone receptors and cancer

BACKGROUND

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that mediate the actions of the thyroid hormone (T3) in development, growth, and differentiation. The THRA and THRB genes encode several TR isoforms that express in a tissue- and development-dependent manner. In the past decades, a significant advance has been made in the understanding of TR actions in maintaining normal cellular functions. However, the roles of TRs in human cancer are less well understood. The reduced expression of TRs because of hypermethylation, or deletion of TR genes found in human cancers suggests that TRs could function as tumor suppressors. A close association of somatic mutations of TRs with human cancers further supports the notion that the loss of normal functions of TR could lead to uncontrolled growth and loss of cell differentiation.

SCOPE OF REVIEW

In line with the findings from association studies in human cancers, mice deficient in total functional TRs (Thra1(-/-)Thrb(-/-) mice) or with a targeted homozygous mutation of the Thrb gene (denoted PV; Thrb(PV/PV) mice) spontaneously develop metastatic thyroid carcinoma. This review will examine the evidence learned from these genetically engineered mice that provided strong evidence to support the critical role of TRs in human cancer.

MAJOR CONCLUSIONS

Loss of normal functions of TR by deletion or by mutations could contribute to cancer development, progression and metastasis.

GENERAL SIGNIFICANCE

Novel mechanistic insights are revealed in how aberrant TR activities lead to carcinogenesis. Mouse models of thyroid cancer provide opportunities to identify molecular targets as potential treatment modalities. This article is part of a Special Issue entitled Thyroid hormone signalling.

Cyclic AMP is both a pro-apoptotic and anti-apoptotic second messenger

The second messenger cyclic AMP (cAMP) can either stimulate or inhibit programmed cell death (apoptosis). Here, we review examples of cell types that show pro-apoptotic or anti-apoptotic responses to increases in cAMP. We also show that cells can have both such responses, although predominantly having one or the other. Protein kinase A (PKA)-promoted changes in phosphorylation and gene expression can mediate pro-apoptotic responses, such as in murine S49 lymphoma cells, based on evidence that mutants lacking PKA fail to undergo cAMP-promoted, mitochondria-dependent apoptosis. Mechanisms for the anti-apoptotic response to cAMP likely involve Epac (Exchange protein activated by cAMP), a cAMP-regulated effector that is a guanine nucleotide exchange factor (GEF) for the low molecular weight G-protein, Rap1. Therapeutic approaches that activate PKA-mediated pro-apoptosis or block Epac-mediated anti-apoptotisis may provide a means to enhance cell killing, such as in certain cancers. In contrast, efforts to block PKA or stimulate Epac have the potential to be useful in diseases settings (such as heart failure) associated with cAMP-promoted apoptosis.

Molecular aspects of thyroid hormone actions

Cellular actions of thyroid hormone may be initiated within the cell nucleus, at the plasma membrane, in cytoplasm, and at the mitochondrion. Thyroid hormone nuclear receptors (TRs) mediate the biological activities of T(3) via transcriptional regulation. Two TR genes, alpha and beta, encode four T(3)-binding receptor isoforms (alpha1, beta1, beta2, and beta3). The transcriptional activity of TRs is regulated at multiple levels. Besides being regulated by T(3), transcriptional activity is regulated by the type of thyroid hormone response elements located on the promoters of T(3) target genes, by the developmental- and tissue-dependent expression of TR isoforms, and by a host of nuclear coregulatory proteins. These nuclear coregulatory proteins modulate the transcription activity of TRs in a T(3)-dependent manner. In the absence of T(3), corepressors act to repress the basal transcriptional activity, whereas in the presence of T(3), coactivators function to activate transcription. The critical role of TRs is evident in that mutations of the TRbeta gene cause resistance to thyroid hormones to exhibit an array of symptoms due to decreasing the sensitivity of target tissues to T(3). Genetically engineered knockin mouse models also reveal that mutations of the TRs could lead to other abnormalities beyond resistance to thyroid hormones, including thyroid cancer, pituitary tumors, dwarfism, and metabolic abnormalities. Thus, the deleterious effects of mutations of TRs are more severe than previously envisioned. These genetic-engineered mouse models provide valuable tools to ascertain further the molecular actions of unliganded TRs in vivo that could underlie the pathogenesis of hypothyroidism. Actions of thyroid hormone that are not initiated by liganding of the hormone to intranuclear TR are termed nongenomic. They may begin at the plasma membrane or in cytoplasm. Plasma membrane-initiated actions begin at a receptor on integrin alphavbeta3 that activates ERK1/2 and culminate in local membrane actions on ion transport systems, such as the Na(+)/H(+) exchanger, or complex cellular events such as cell proliferation. Concentration of the integrin on cells of the vasculature and on tumor cells explains recently described proangiogenic effects of iodothyronines and proliferative actions of thyroid hormone on certain cancer cells, including gliomas. Thus, hormonal events that begin nongenomically result in effects in DNA-dependent effects. l-T(4) is an agonist at the plasma membrane without conversion to T(3). Tetraiodothyroacetic acid is a T(4) analog that inhibits the actions of T(4) and T(3) at the integrin, including angiogenesis and tumor cell proliferation. T(3) can activate phosphatidylinositol 3-kinase by a mechanism that may be cytoplasmic in origin or may begin at integrin alphavbeta3. Downstream consequences of phosphatidylinositol 3-kinase activation by T(3) include specific gene transcription and insertion of Na, K-ATPase in the plasma membrane and modulation of the activity of the ATPase. Thyroid hormone, chiefly T(3) and diiodothyronine, has important effects on mitochondrial energetics and on the cytoskeleton. Modulation by the hormone of the basal proton leak in mitochondria accounts for heat production caused by iodothyronines and a substantial component of cellular oxygen consumption. Thyroid hormone also acts on the mitochondrial genome via imported isoforms of nuclear TRs to affect several mitochondrial transcription factors. Regulation of actin polymerization by T(4) and rT(3), but not T(3), is critical to cell migration. This effect has been prominently demonstrated in neurons and glial cells and is important to brain development. The actin-related effects in neurons include fostering neurite outgrowth. A truncated TRalpha1 isoform that resides in the extranuclear compartment mediates the action of thyroid hormone on the cytoskeleton.

Predicting recurrence of nonfunctioning pituitary adenomas

CONTEXT

Nonfunctioning pituitary adenomas are commonly diagnosed as large tumors. Most are detected incidentally during imaging studies or as a result of neurological manifestations. Depending on severity, most patients with large tumors require surgery and adjunctive therapies because of the high rate of tumor recurrence. The ability to predict the recurrence of a tumor at the time of the initial surgery would be helpful in deciding whether adjunctive therapy is necessary and decreasing morbidity. We investigated the use of several cellular markers for predicting the recurrence of nonfunctioning pituitary adenomas.

OBJECTIVE

A tissue array block was made using tissue from 35 cases of nonfunctioning pituitary adenomas (16 cases with early recurrence <or=4 yr after surgery, 10 cases with late recurrence >4 yr after surgery, and nine cases without recurrence). Levels of tumor tissue cellular markers associated with cell proliferation or apoptosis were analyzed, and immunohistochemical study of cellular markers was conducted using sectioned slides from the tissue array block.

RESULTS

High Ki-67 and TUNEL labeling indexes were associated with recurrent nonfunctioning pituitary adenomas. Tumors with a high level of expression of phospho-Akt, phospho-p44/42 MAPK, and PTTG1 were associated with early recurrence. However, high levels of expression of phospho-CREB and ZAC1 were inversely associated with recurrence.

CONCLUSIONS

Tumors with high levels of expression of phospho-Akt and phospho-p44/42 MAPK and low levels of expression of phospho-CREB and ZAC1 should be followed closely and may require adjunctive therapy to prevent tumor recurrence.

Novel non-genomic signaling of thyroid hormone receptors in thyroid carcinogenesis

The thyroid hormone receptors (TRs) are transcription factors that mediate the pleiotropic activities of the thyroid hormone, T3. Four T3-binding isoforms, TRalpha1, TRbeta1, TRbeta2, and TRbeta3, are encoded by two genes, THRA and THRB. Mutations and altered expression of TRs have been reported in human cancers. A targeted germ-line mutation of the Thrbeta gene in the mouse leads to spontaneous development of follicular thyroid carcinoma (TRbeta(PV/PV) mouse). The TRbetaPV mutant has lost T3-binding activity and displays potent dominant negative activity. The striking phenotype of thyroid cancer exhibited by TRbeta(PV/PV) mice has recently led to the discovery of novel non-genomic actions of TRbetaPV that contribute to thyroid carcinogenesis. These actions involve direct physical interaction of TRbetaPV with cellular proteins, namely the regulatory subunit of the phosphatidylinositol 3-kinase (p85alpha), the pituitary tumor transforming gene (PTTG) and beta-catenin, that are critically involved in cell proliferation, motility, migration, and metastasis. Thus, a TRbeta mutant (TRbetaPV), via a novel mode of non-genomic action, acts as an oncogene in thyroid carcinogenesis.

Diminished pancreatic beta-cell mass in securin-null mice is caused by beta-cell apoptosis and senescence

Pituitary tumor transforming gene (PTTG) encodes a securin protein critical in regulating chromosome separation. PTTG-null (PTTG(-/-)) mice exhibit pancreatic beta-cell hypoplasia and insulinopenic diabetes. We tested whether PTTG deletion causes beta-cell senescence, resulting in diminished beta-cell mass. We examined beta-cell mass, proliferation, apoptosis, neogenesis, cell size, and senescence in PTTG(-/-) and WT mice from embryo to young adulthood before diabetes is evident. The roles of cyclin-dependent kinase inhibitors and DNA damage in the pathogenesis of diabetes in PTTG(-/-) mice were also addressed. Relative beta-cell mass in PTTG(-/-) mice began to decrease at 2-3 wk, whereas beta-cell proliferation rate was initially normal but decreased in PTTG(-/-) mice beginning at 2 months. Apoptosis was also much more evident in PTTG(-/-) mice. At 1 month, beta-cell neogenesis was robust in wild-type mice but was absent in PTTG(-/-) mice. In addition, the size of beta-cells became larger and macronuclei were prominent in PTTG(-/-) animals. Senescence-associated beta-galactosidase was also active in PTTG(-/-) beta-cells at 1 month. Cyclin-dependent kinase inhibitor p21 was progressively up-regulated in PTTG(-/-) islets, and p21 deletion partially rescued PTTG(-/-) mice from development of diabetes. mRNA array showed that DNA damage-associated genes were activated in PTTG(-/-) islets. We conclude that beta-cell apoptosis and senescence contribute to the diminished beta-cell mass in PTTG(-/-) mice, likely secondary to DNA damage. Our results also suggest that ductal progenitor beta-cells are exhausted by excessive neogenesis induced by apoptosis in PTTG(-/-) mice.

PTTG: an important target gene for ovarian cancer therapy

Pituitary tumor transforming gene (PTTG), also known as securin is an important gene involved in many biological functions including inhibition of sister chromatid separation, DNA repair, organ development, and expression and secretion of angiogenic and metastatic factors. Proliferating cancer cells and most tumors express high levels of PTTG. Overexpression of PTTG in vitro induces cellular transformation and development of tumors in nude mice. The PTTG expression levels have been correlated with tumor progression, invasion, and metastasis. Recent studies show that down regulation of PTTG in tumor cell lines and tumors in vivo results in suppression of tumor growth, suggesting its important role in tumorigenesis. In this review, we focus on PTTG structure, sub-cellular distribution, cellular functions, and role in tumor progression with suggestions on possible exploration of this gene for cancer therapy.

Expression of pituitary tumor-transforming gene in endometrial cancer as a prognostic marker

The pituitary tumor-transforming gene (PTTG) is a novel oncogene expressed abundantly in most tumors, regulates basic fibroblast growth factor secretion, and induces angiogenesis. The objective of this study is to compare the expression rate of PTTG in endometrial cells, to correlate the level of expression of PTTG with the clinicopathologic parameters and overall survival, and to evaluate the possible use of PTTG as a prognostic marker of endometrial cancer. Forty patients diagnosed with endometrial cancer, 20 patients with endometrial hyperplasia, and 20 patients with normal endometrial tissues were included in the study. Immunohistochemical analyses on paraffin-embedded blocks were performed using a polyclonal anti-PTTG antibody. The decrease in expression of cytoplasmic and nuclear PTTG seen for endometrial cancer cells was statistically significant (P< 0.05). Cytoplasmic PTTG expression correlated with expression of progesterone receptor (P= 0.009) and FGF-2 (P= 0.007) but not with other parameters such as the expression of estrogen receptor, tumor grade, and surgical stage. Nuclear PTTG expression did not correlate with any parameters. The mean survival of patients with positive and negative cytoplasmic PTTG expression was 40.8 and 48.6 months (P= 0.78). In nuclear PTTG expression, the survival was 20.0 and 51.8 months, respectively (P= 0.04). Cytoplasmic PTTG expression was not associated with survival. Patients with nuclear PTTG overexpression showed a significant decrease in survival. The use of PTTG as a prognostic marker for endometrial cancer needs further investigation.

Molecular pathogenesis of human prolactinomas identified by gene expression profiling, RT-qPCR, and proteomic analyses

The molecular pathogenesis of prolactinomas has resisted elucidation; with the exception of a RAS mutation in a single aggressive prolactinoma, no mutational changes have been identified. In prolactinomas, a further obstacle has been the paucity of surgical specimens suitable for molecular analysis since prolactionomas are infrequently removed due to the availability and effectiveness of medical therapy. In the absence of mutational events, gene expression changes have been sought and detected. Using high-throughput analysis from a large bank of human pituitary adenomas, we examined these tumors according to their molecular profiles rather than traditional immunohistochemistry. We examined six prolactinomas and eight normal pituitary glands using oligonucleotide GeneChip microarrays, reverse transcription-real time quantitative polymerase chain reaction using 10 prolactinomas, and proteomic analysis to examine protein expression in four prolactinomas. Microarray analyses identified 726 unique genes that were statistically significantly different between prolactinomas and normal glands, whereas proteomic analysis identified four differently up-regulated and 19 down-regulated proteins. Several components of the Notch pathway were altered in prolactinomas, and there was an increased expression of the Pit-1 transcription factor, and the survival factor BAG1 but decreased E-cadherin and N-cadherin expression. Taken together, expression profiling and proteomic analyses have identified molecular features unique to prolactinomas that may contribute to their pathogenesis. In the current era of molecular medicine, these findings greatly enhance our understanding and supercede immunohistochemical diagnosis.

Evidence for cooperative transforming activity of the human pituitary tumor transforming gene and human T-cell leukemia virus type 1 Tax

Aneuploidy is frequent in cancers. Recently it was found that pituitary tumor transforming gene (PTTG; also called Pds1p or securin) is overexpressed in many different tumors. Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus that primarily infects CD4+ T lymphocytes and causes adult T-cell leukemia. Here, we report that overexpression of human PTTG cooperated with the HTLV-I Tax oncoprotein in cellular transformation. Coexpression of Tax and PTTG enhanced chromosomal instability and neoplastic changes to levels greater than overexpression of either factor singularly. Cells that overexpressed both PTTG and Tax induced tumors more robustly in nude mice than cells that expressed either PTTG alone or Tax alone.

Pituitary tumor-transforming gene: physiology and implications for tumorigenesis

Pituitary tumor-transforming gene-1 (PTTG1) is overexpressed in a variety of endocrine-related tumors, especially pituitary, thyroid, breast, ovarian, and uterine tumors, as well as nonendocrine-related cancers involving the central nervous, pulmonary, and gastrointestinal systems. Forced PTTG1 expression induces cell transformation in vitro and tumor formation in nude mice. In some tumors, high PTTG1 levels correlate with invasiveness, and PTTG1 has been identified as a key signature gene associated with tumor metastasis. Increasing evidence supports a multifunctional role of PTTG1 in cell physiology and tumorigenesis. Physiological PTTG1 properties include securin activity, DNA damage/repair regulation and involvement in organ development and metabolism. Tumorigenic mechanisms for PTTG1 action involve cell transformation and aneuploidy, apoptosis, and tumorigenic microenvironment feedback. This paper reviews recent advances in our understanding of PTTG1 structure and regulation and addresses known mechanisms of PTTG1 action. Recent knowledge gained from PTTG1-null mouse models and transgenic animals and their potential application to subcellular therapeutic targeting PTTG1 are discussed.

PTTG and PBF repress the human sodium iodide symporter

The ability of the thyroid to accumulate iodide provides the basis for radioiodine ablation of differentiated thyroid cancers and their metastases. Most thyroid tumours exhibit reduced iodide uptake, although the mechanisms accounting for this remain poorly understood. Pituitary tumour transforming gene (PTTG) is a proto-oncogene implicated in the pathogenesis of thyroid tumours. We now show that PTTG and its binding factor PBF repress expression of sodium iodide symporter (NIS) messenger RNA (mRNA), and inhibit iodide uptake. This process is mediated at least in part through fibroblast growth factor-2. In detailed studies of the NIS promoter in rat FRTL-5 cells, PTTG and PBF demonstrated specific inhibition of promoter activity via the human upstream enhancer element (hNUE). Within this approximately 1 kb element, a complex PAX8-upstream stimulating factor 1 (USF1) response element proved critical both to basal promoter activity and to PTTG and PBF repression of NIS. In particular, repression by PTTG was contingent upon the USF1, but not the PAX8, site. Finally, in human primary thyroid cells, PTTG and PBF similarly repressed the NIS promoter via hNUE. Taken together, our data suggest that the reported overexpression of PTTG and PBF in differentiated thyroid cancer has profound implications for activity of the NIS gene, and hence significantly impacts upon the efficacy of radioiodine treatment.

Novel functions of thyroid hormone receptor mutants: beyond nucleus-initiated transcription

Study of molecular actions of thyroid hormone receptor beta (TRbeta) mutants in vivo has been facilitated by creation of a mouse model (TRbetaPV mouse) that harbors a knockin mutant of TRbeta (denoted PV). PV, which was identified in a patient with resistance to thyroid hormone, has lost T3 binding activity and transcription capacity. The striking phenotype of thyroid cancer exhibited by TRbeta(PV/PV) mice has allowed the elucidation of novel oncogenic activity of a TRbeta mutant (PV) [PAS1] beyond nucleus-initiated transcription. PV was found to physically interact with the regulatory p85alpha subunit of phosphatidylinositol 3-kinase (PI3K) in both the nuclear and cytoplasmic compartments. This protein-protein interaction activates the PI3K signaling by increasing phosphorylation of AKT, mammalian target of rapamycin (mTOR), and p70(S6K). PV, via interaction with p85alpha, also activates the PI3K-integrin-linked kinase-matrix metalloproteinase-2 signaling pathway in the extra-nuclear compartment. The PV-mediated PI3K activation results in increased cell proliferation, motility, migration, and metastasis. In addition to affecting these membrane-initiated signaling events, PV affects the stability of the pituitary tumor-transforming gene (PTTG) product. PTTG (also known as securin), a critical mitotic checkpoint protein, is physically associated with TRbeta or PV in vivo. Concomitant with T3-induced degradation of TRbeta, PTTG is degraded by the proteasome machinery, but no such degradation occurs when PTTG is associated with PV. The degradation of PTTG/TRbeta is activated by the direct interaction of the T3-bound TRbeta with the steroid receptor coactivator-3 (SRC-3) that recruits a proteasome activator (PA28gamma). PV that does not bind T3 cannot interact directly with SRC-3/PA28gamma to activate proteasome degradation, and the absence of degradation results in an aberrant accumulation of PTTG. The PV-induced failure of timely degradation of PTTG results in mitotic abnormalities. PV, via novel protein-protein interaction and transcription regulation, acts to antagonize the functions of wild-type TRs and contributes to the oncogenic functions of this mutation.

B-RAF mutations are a rare event in pituitary adenomas

Pituitary tumors are a relatively common neoplasia whose pathogenesis is still largely unknown. Recent studies have revealed frequent activating mutations of the gene for B-RAF, an effector of Ras protein in the mitogen-activated protein kinase pathway, in several malignancies, including melanoma, thyroid, colorectal and ovarian cancer. However, analyses of B-RAF mutations in pituitary tumors have not been reported so far. Therefore, in the present study we have investigated the presence of the B-RAF mutations, by polymerase chain reaction (PCR) amplification of the hot spot exons 11 and 15, followed by direct sequencing, in 50 human pituitary adenomas, including 25 NFPA and 25 secreting adenomas (10 GH, 5 PRL, 6 LH and/or FSH, 4 GH/PRL). We found only one V600E mutation in a NFPA sample, suggesting that B-RAF mutations are a rare event in pituitary tumorigenesis.

Pituitary action of cytokines: focus on BMP-4 and gp130 family

The anterior pituitary can develop benign tumors of different sizes, classified as micro- and macroadenomas, frequently associated with high levels of hormone production, leading to different associated syndromes like Cushing's disease, acromegaly or prolactinomas. Much work has been done in order to understand the signaling pathways and the factors and hormones involved in the pituitary tumorigenic process. In recent years, much evidence has been collected and it is now well documented that cytokines of the gp130 family, such as interleukin-6, that use gp130 as a common signaling protein stimulate not only the proliferation but also the hormone secretion of pituitary cells. Experiments in vivo have shown that the overexpression of the gp130 receptor resulted in pituitary abnormal growth. Moreover, it has been recently described that bone morphogenetic protein-4 (BMP-4), a member of the TGF-beta family, has a stimulatory role on lactosomatotropic cells promoting the development of prolactinomas but it has an inhibitory action on the corticotropic lineage. This inhibitory action prevents Cushing's disease progression. Furthermore, BMP-4 mediates the antiproliferative action of retinoic acid in these cells. The present review highlights the most recent work about gp130 and TGF-beta cytokine families and their role in pituitary tumorigenesis.

Aberrant accumulation of PTTG1 induced by a mutated thyroid hormone beta receptor inhibits mitotic progression

Overexpression of pituitary tumor-transforming 1 (PTTG1) is associated with thyroid cancer. We found elevated PTTG1 levels in the thyroid tumors of a mouse model of follicular thyroid carcinoma (TRbeta(PV/PV) mice). Here we examined the molecular mechanisms underlying elevated PTTG1 levels and the contribution of increased PTTG1 to thyroid carcinogenesis. We showed that PTTG1 was physically associated with thyroid hormone beta receptor (TRbeta) as well as its mutant, designated PV. Concomitant with thyroid hormone-induced (T3-induced) degradation of TRbeta, PTTG1 proteins were degraded by the proteasomal machinery, but no such degradation occurred when PTTG1 was associated with PV. The degradation of PTTG1/TRbeta was activated by the direct interaction of the liganded TRbeta with steroid receptor coactivator 3 (SRC-3), which recruits proteasome activator PA28gamma. PV, which does not bind T3, could not interact directly with SRC-3/PA28gamma to activate proteasome degradation, resulting in elevated PTTG1 levels. The accumulated PTTG1 impeded mitotic progression in cells expressing PV. Our results unveil what we believe to be a novel mechanism by which PTTG1, an oncogene, is regulated by the liganded TRbeta. The loss of this regulatory function in PV led to an aberrant accumulation of PTTG1 disrupting mitotic progression that could contribute to thyroid carcinogenesis.

Large-scale transcriptional analysis of bovine embryo biopsies in relation to pregnancy success after transfer to recipients

The purpose of this work is to address the relationship between transcriptional profile of embryos and the pregnancy success based on gene expression analysis of blastocyst biopsies taken prior to transfer to recipients. Biopsies (30-40% of the intact embryo) were taken from in vitro-produced day 7 blastocysts (n = 118), and 60-70% were transferred to recipients after reexpansion. Based on the success of pregnancy, biopsies were pooled in three groups (each 10 biopsies) namely: those resulting in no pregnancy (G1), resorbed embryos (G2), and those resulting in calf delivery (G3). Gene expression analysis of these groups was performed using home-made bovine preimplantation-specific cDNA array (219 clones) and BlueChip (with approximately 2,000 clones). Microarray data analysis results revealed a total of 52 and 58 genes were differentially regulated during comparison between G1 vs. G3 and G2 vs. G3. Biopsies resulted in calf delivery were enriched with genes necessary for implantation (COX2 and CDX2), carbohydrate metabolism (ALOX15), growth factor (BMP15), signal transduction (PLAU), and placenta-specific 8 (PLAC8). Biopsies from embryos resulting in resorption are enriched with transcripts involved protein phosphorylation (KRT8), plasma membrane (OCLN), and glucose metabolism (PGK1 and AKR1B1). Biopsies from embryos resulting in no pregnancy are enriched with transcripts involved inflammatory cytokines (TNF), protein amino acid binding (EEF1A1), transcription factors (MSX1, PTTG1), glucose metabolism (PGK1, AKR1B1), and CD9, which is an inhibitor of implantation. In conclusion, we generated direct candidates of blastocyst-specific genes which may play an important role in determining the fate of the embryo after transfer.

The emerging role of pituitary tumor transforming gene in tumorigenesis

Pituitary tumor transforming gene (PTTG) is a newly discovered oncogene, and serves as a marker of malignancy grades in several forms of cancer, particularly endocrine malignancies such as pituitary adenomas. PTTG appears also to have a role in the genesis of some types of cancer. Also known as a human form of securin, PTTG is an anaphase inhibitor that prevents premature chromosome separation through inhibition of separase activity; hence, its degradation is required to start anaphase. Through this important function, PTTG participates in several key cellular events such as mitosis, cell cycle progression, DNA repair and apoptosis. The physiological importance of PTTG is indicated by the study of PTTG-null mice that have cell growth abnormalities in testis and pancreatic beta cells. Overexpression of PTTG has been observed in thyroid and colon cancers. In addition, 90% of pituitary adenomas overexpress PTTG, qualifying it as the best available marker for this disease. Although the exact mechanism is unknown, PTTG participates in the pathogenesis of various tumors, including pituitary tumors, by inducing aneuploidy and upregulating FGF-2, a potent mitogenic and angiogenic factor. Various growth factors, nuclear factors and hormones regulate PTTG expression in different tumor cells, which could be important to understand in order to obtain insight into the tumorigenic and tumor progression process. Here, we review the current knowledge of the biological and pathophysiological roles of PTTG.

Patterns of gene expression in pituitary carcinomas and adenomas analyzed by high-density oligonucleotide arrays, reverse transcriptase-quantitative PCR, and protein expression

Very few of the genes that are important in pituitary tumor initiation, progression, and metastasis have been identified to date. To identify potential genes that may be important in pituitary tumor progression and carcinoma development, we used Affymetrix GeneChip HGU-133A-oligonucleotide arrays, which contain more than 15,000 characterized genes from the human genome to study gene expression in an ACTH pituitary carcinoma metastatic to the liver and four pituitary adenomas. Reverse-transcriptase real-time quantitative- PCR (RT-qPCR) was then used to analyze 4 nonneoplastic pituitaries, 19 adenomas, and the ACTH carcinoma. A larger series of pituitary adenomas and carcinomas were also analyzed for protein expression using tissue microarrays (TMA) (n = 233) and by Western blotting (n = 18). There were 4298 genes that were differentially expressed among the adenomas compared to the carcinoma, with 2057 genes overexpressed and 2241 genes underexpressed in the adenomas. The beta-galactoside binding protein galactin-3 was underexpressed in some adenomas compared to the carcinomas. Prolactin (PRL) and ACTH tumors had the highest levels of expression of galectin-3. The human achaetescute homolog-1 ASCL1 (hASH-1) gene was also underexpressed in some adenomas compared to the carcinoma. Prolactin and ACTH tumors had the highest levels of expression of hASH-1. ID2, which has an important role in cell development and tumorigenesis, was underexpressed in some adenomas compared to the carcinomas. Transducin-like enhancer of split four/ Groucho (TLE-4) was over-expressed in adenomas compared to the ACTH carcinoma. The differential expression of these genes was validated by RT-qPCR, by immunohistochemistry using TMA and by Western blotting. These results indicate that the LGALS3, hASH1, ID2, and TLE-4 genes may have important roles in the development of pituitary carcinomas.

Bone morphogenetic protein-4 inhibits corticotroph tumor cells: involvement in the retinoic acid inhibitory action

The molecular mechanisms governing the pathogenesis of ACTH-secreting pituitary adenomas are still obscure. Furthermore, the pharmacological treatment of these tumors is limited. In this study, we report that bone morphogenetic protein-4 (BMP-4) is expressed in the corticotrophs of human normal adenohypophysis and its expression is reduced in corticotrophinomas obtained from Cushing's patients compared with the normal pituitary. BMP-4 treatment of AtT-20 mouse corticotrophinoma cells has an inhibitory effect on ACTH secretion and cell proliferation. AtT-20 cells stably transfected with a dominant-negative form of the BMP-4 signal cotransducer Smad-4 or the BMP-4 inhibitor noggin have increased tumorigenicity in nude mice, showing that BMP-4 has an inhibitory role on corticotroph tumorigenesis in vivo. Because the activation of the retinoic acid receptor has an inhibitory action on Cushing's disease progression, we analyzed the putative interaction of these two pathways. Indeed, retinoic acid induces both BMP-4 transcription and expression and its antiproliferative action is blocked in Smad-4dn- and noggin-transfected Att-20 cells that do not respond to BMP-4. Therefore, retinoic acid induces BMP-4, which participates in the antiproliferative effects of retinoic acid. This new mechanism is a potential target for therapeutic approaches for Cushing's disease.

Subcellular localization of Apaf-1 in apoptotic rat pituitary cells

A key step in the intrinsic apoptotic pathway is the assembly of the apoptosome complex. The apoptosome components are well known; however, the physiology of the assembly of the apoptosome complex at the cellular level is still poorly defined. The aim of this work was to study the subcellular distribution of the apoptosome scaffold protein apoptotic protease-activating factor 1 (Apaf-1) before and after triggering apoptosis in single somatotrophs. Somatotrophs are the subject of extensive pituitary tissue remodeling in different physiological situations in which the quality and the number of pituitary cells are determined by cell proliferation and apoptosis. We show herein that 2 h after triggering apoptosis with rotenone, Apaf-1 redistributed to the proximity of mitochondria. In addition, the degree of colocalization between Apaf-1 and fluorescently labeled caspase-9 significantly increased during the same period. Furthermore, we show herein for the first time in single cells that the colocalization between Apaf-1 and cytochrome c increases only transiently, indicating a transient interaction between cytochrome c and Apaf-1 during the activation of apoptosis in these cells.

Pituitary tumors: prognostic indicators

Many factors influence the proliferation of pituitary adenomas: angiogenesis, apoptosis, growth factors, oncogenes, tumor suppressor genes, and hormone receptors. These elements can be demonstrated by immunohistochemistry and/or molecular pathology but no single factor can be used for determination of biological behavior resp. prognosis. Pituitary adenomas can be enclosed or invasive and may be very large or may be microadenomas, but the most important point for prognosis is the total resection in the first or second surgery or the reaction on treatments by drugs. Especially for residual tumor tissue proliferation, markers are important because they may indicate the growth rate and the aggressiveness of the tumor. Radiation therapy is indicated in many of these recurrent tumors and can improve the prognosis.

DNA microarrays: recent developments and applications to the study of pituitary tissues

Many new techniques are rapidly being developed and applied to the study of normal and neoplastic pituitary. DNA microarrays are a uniquely efficient method for simultaneously assessing the expression levels of thousands of genes, identifying disease subphenotypes, and predicting disease progression. This article reviews the utility of DNA microarray-based tumor profiling including recent developments and applications to pituitary biology in order to demonstrate how these new techniques are providing insights about basic aspects, clinical knowledge, and pharmacologic knowledge of the pituitary gland and about pituitary tumors.

Metastatic prolactinoma: case report with immunohistochemical assessment for p53 and Ki-67 antigens

Pituitary carcinomas are rare neoplasms characterized by craniospinal and/or systemic metastases originated from the pituitary. Their histopathology is frequently indistinguishable from that of benign adenomas. The development of markers that better reflect their behavior is desirable. We present the case of a 47 year-old man with a prolactin-secreting macroadenoma who was submitted to surgeries, cranial radiation therapy, and bromocriptine treatment, but evolved to a fatal outcome after the disclosure of intracranial metastases. Tumor samples underwent p53 and Ki-67 immunohistochemical assessment. p53 was absent in all samples, a rare finding among pituitary carcinomas. Ki-67 proliferative index was 2.80% in the original tumor, 4.40% in the relapse, and 4.45% in the metastasis. The figure in the relapse is higher than the expected for a noninvasive adenoma. In conclusion, p53 staining is not positive in all pituitary carcinomas. A high Ki-67 proliferative index in a pituitary adenoma might indicate a more aggressive behavior.

Insulin and IGF-1 regulate the expression of the pituitary tumor transforming gene (PTTG) in breast tumor cells

The pituitary tumor transforming Gene (PTTG) is an oncogene that is highly expressed in most tumors analyzed to date. Here, we report the effects of insulin and the insulin like growth factor-1 (IGF-1) on the expression of PTTG. Using MCF-7 cells, a human breast cancer cell line, we observed that both insulin and IGF-1 upregulate the expression of PTTG mRNA by approximately 2.5-fold. Induction of PTTG mRNA expression by insulin or IGF-1 was completely blocked by the specific phosphatidylinositol (PI) 3 kinase inhibitor LY294002, but partially blocked by the MAP kinase inhibitor PD98059. Pretreatment of MCF-7 cells with actinomycin D completely blocked the stimulatory effect of insulin. Transfection of MCF-7 cells with a PTTG promoter-luciferase reporter construct revealed the dose-dependent stimulation of PTTG promoter activity by insulin, suggesting that the increase in PTTG expression by insulin is a result of activation of transcription of the PTTG gene. Taken together, our results suggest that insulin and IGF-1 regulate the expression of PTTG in MCF-7 cells primarily through the activation of PI3K/AKT cascade.

Pituitary tumor transforming gene binding factor: a novel transforming gene in thyroid tumorigenesis

CONTEXT

There are currently no clear markers for the detection of differentiated thyroid cancer and its recurrence. Pituitary tumor transforming gene (PTTG) is a protooncogene implicated in the pathogenesis of multiple tumor types, which stimulates fibroblast growth factor-2 secretion via PTTG binding factor (PBF).

OBJECTIVE

The aim of this study was to ascertain whether PBF expression is associated with thyroid cancer outcome.

DESIGN

PBF expression was measured at the mRNA and protein level. Tissue was collected during surgery, with normal samples being taken from the contralateral lobe. In vitro studies ascertained the ability of PBF to transform cells and form tumors in nude mice and its subcellular localization.

SETTING

The study was conducted at a primary care/referral center.

PATIENTS

Thyroid tumors were collected from a series of 27 patients undergoing surgical excision of papillary and follicular thyroid tumors.

INTERVENTION

No intervention was conducted.

MAIN OUTCOME MEASURE

The expression of PBF in thyroid cancers compared with normal thyroid, hypothesized before the investigation to be raised in tumors, was the main outcome measure.

RESULTS

PBF mRNA expression was higher in differentiated thyroid carcinomas than in normal thyroid (P < 0.001; n = 27) and was independently associated with tumor recurrence (P = 0.002; R(2) = 0.49). PTTG was able to up-regulate PBF mRNA expression in vitro (P < 0.001; n = 12), and stable overexpression of PBF in NIH3T3 cells resulted in significant colony formation (P < 0.001; n = 12). In vivo, stable sc overexpression of PBF induced tumor formation in athymic nude mice.

CONCLUSIONS

PBF is an additional prognostic indicator in differentiated thyroid cancer that is transforming in vitro and tumorigenic in vivo.

Transforming activity of MECT1-MAML2 fusion oncoprotein is mediated by constitutive CREB activation

Salivary gland tumors, a group of histologically diverse benign and malignant neoplasms, represent a challenging problem for diagnosis and treatment. A specific recurring t(11;19)(q21;p13) translocation is associated with two types of salivary gland tumors, mucoepidermoid carcinomas and Warthin's tumors. This translocation generates a fusion protein comprised of the N-terminal CREB (cAMP response element-binding protein)-binding domain of the CREB regulator MECT1 (Mucoepidermoid carcinoma translocated-1) and the C-terminal transcriptional activation domain of the Notch coactivator Mastermind-like 2 (MAML2). Here, we demonstrate that the MECT1-MAML2 fusion protein induces expression of multiple genes known to be CREB transcriptional targets. MECT1-MAML2 was found to bind to CREB, recruit p300/CBP into the CREB complex through a binding domain on MAML2, and constitutively activate CREB-dependent transcription. The transforming activity of MECT1-MAML2 was markedly reduced by blocking CREB DNA binding. Thus, this fusion oncogene mimics constitutive activation of cAMP signaling, by activating CREB directly. This study has identified a novel, critical mechanism of transformation for an oncogene associated very specifically with salivary gland tumors, and identified potential targets for the development of novel therapies.

Ectopic expression of PTTG1/securin promotes tumorigenesis in human embryonic kidney cells

Background

Pituitary tumor transforming gene1 (PTTG1) is a novel oncogene that is expressed in most tumors. It encodes a protein that is primarily involved in the regulation of sister chromatid separation during cell division. The oncogenic potential of PTTG1 has been well characterized in the mouse, particularly mouse fibroblast (NIH3T3) cells, in which it induces cell proliferation, promotes tumor formation and angiogenesis. Human tumorigenesis is a complex and a multistep process often requiring concordant expression of a number of genes. Also due to differences between rodent and human cell biology it is difficult to extrapolate results from mouse models to humans. To determine if PTTG1 functions similarly as an oncogene in humans, we have characterized its effects on human embryonic kidney (HEK293) cells.

Results

We report that introduction of human PTTG1 into HEK293 cells through transfection with PTTG1 cDNA resulted in increased cell proliferation, anchorage-independent growth in soft agar, and formation of tumors after subcutaneous injection of nu/nu mice. Pathologic analysis revealed that these tumors were poorly differentiated. Both analysis of HEK293 cells transiently transfected with PTTG1 cDNA and analysis of tumors developed on injection of HEK293 cells that had been stably transfected with PTTG1 cDNA indicated significantly higher levels of secretion and expression of bFGF, VEGF and IL-8 compared to HEK293 cells transfected with pcDNA3.1 vector or uninvolved tissues collected from the mice. Mutation of the proline-rich motifs at the C-terminal of PTTG1 abolished its oncogenic properties. Mice injected with this mutated PTTG1 either did not form tumors or formed very small tumors. Taken together our results suggest that PTTG1 is a human oncogene that possesses the ability to promote tumorigenesis in human cells at least in part through the regulation of expression or secretion of bFGF, VEGF and IL-8.

Conclusions

Our results demonstrate that PTTG1 is a potent human oncogene and has the ability to induce cellular transformation of human cells. Overexpression of PTTG1 in HEK293 cells leads to an increase in the secretion and expression of bFGF, VEGF and IL-8. Mutation of C-terminal proline-rich motifs abrogates the oncogenic function of PTTG1. To our knowledge, this is the first study demonstrating the importance of PTTG1 in human tumorigenesis.

Prognostic indicators in pituitary tumors

Recent advances in molecular pathology have shed light not only on the cellular composition and derivation of various tumors, but also on their growth potential, likelihood of recurrence, and prognosis. The development of reliable and prognostically informative methods of assessing tumor behavior is particularly important in pituitary tumors, where no precise correlation exists between morphology and clinical aggressiveness. Among the numerous morphologic techniques that have been introduced in the last three decades, some have gained popularity due to their reliability and ease of performance, whereas others have fallen from favor due to their inconsistency and insensitivity in distinguishing indolent from aggressive pituitary tumors. Yet others, due to cost and complexity, never came into general use. We predict that the immunohistochemical methods now in use for assessment of tumor behavior will be complemented and partly replaced by molecular genetic procedures in the future.

Diagnosis and treatment of pituitary tumors

PURPOSE OF REVIEW

Treatment of pituitary adenomas remains an interdisciplinary challenge involving neurosurgeons, endocrinologists and radiation oncologists. The different disciplines inaugurated advanced techniques to improve the already relatively high standard of outcome for the benefit of patients, covering molecular pathogenesis, novel therapeutic strategies for the different adenoma subtypes, developments in perioperative magnetic resonance imaging and radiosurgical management of pituitary adenomas.

RECENT FINDINGS

Despite the progress achieved in medical treatment of hormone-secreting pituitary adenomas throughout recent years, surgery remains the primary therapy of choice except for prolactinomas. Recent studies in molecular pathogenesis aiming to find novel therapy targets and reports on new pharmacological drugs effecting GH-secreting pituitary adenomas are reviewed (for example, lanreotide 60, SOM320 and pegvisomant). Advances in surgical treatment of pituitary macroadenomas are obtained by pre- and especially by intraoperative (high-field) MRI offering a higher rate of safe and complete tumor removal. Therapy pitfalls mentioned in the literature throughout the last year as well as key points in the management of pituitary adenomas with focus on acromegaly and Cushing's disease are reported. Adjuvant irradiation for recurrent or residual adenomas is often a necessity. In comparison to standard conventional radiation strategies an increasing number of radiation oncologists and neurosurgeons report their experience with radiosurgery especially for smaller tumor remnants in pituitary adenomas.

SUMMARY

Recent molecular studies suggest a new level of complexity in the tumorigenisis of pituitary adenomas in terms of possible cell-type-specific molecular changes. Except for prolactinomas surgery remains the primary treatment for pituitary adenomas. New pharmacological drugs achieve very encouraging endocrine results although no long-term follow-up is available so far. The results of trans-sphenoidal surgery will further improve by modern imaging techniques, especially by applying intraoperative high-field magnetic resonance imaging and neuronavigation. The results of radiosurgical techniques with regard to tumor control are mostly convincing, but definitive conclusions on long-term recurrence and/or late complications are not reliable so far.

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.

PTTG/securin activates expression of p53 and modulates its function

BACKGROUND

Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed abundantly in most tumors. Overexpression of PTTG induces cellular transformation and promotes tumor formation in nude mice. PTTG has been implicated in various cellular processes including sister chromatid separation during cell division as well as induction of apoptosis through p53-dependent and p53-independent mechanisms. The relationship between PTTG and p53 remains unclear, however.

RESULTS

Here we report the effects of overexpression of PTTG on the expression and function of p53. Our results indicate that overexpression of PTTG regulates the expression of the p53 gene at both the transcriptional and translational levels and that this ability of PTTG to activate the expression of p53 gene is dependent upon the p53 status of the cell. Deletion analysis of the p53 gene promoter revealed that only a small region of the p53 gene promoter is required for its activation by PTTG and further indicated that the activation of p53 gene by PTTG is an indirect effect that is mediated through the regulation of the expression of c-myc, which then interacts with the p53 gene promoter. Our results also indicate that overexpression of PTTG stimulates expression of the Bax gene, one of the known downstream targets of p53, and induces apoptosis in a human embryonic kidney cell line (HEK293). This stimulation of bax expression by PTTG is indirect and is mediated through modulation of p53 gene expression.

CONCLUSIONS

Overexpression of PTTG activates the expression of p53 and modulates its function, with this action of PTTG being mediated through the regulation of c-myc expression. PTTG also up-regulates the activity of the bax promoter and increases the expression of bax through modulation of p53 expression.

Expression of hPTTG1 and bFGF in gallbladder carcinoma tissue and their correlation with angiogenesis

AIM: To investigate the expression of hPTTG1 and bFGF in human gallbladder carcinoma tissues and their correlation with angiogenesis and other clinicobiological behaviors.

METHODS: The expression of hPTTG1 and bFGF in 41 cases of human gallbladder carcinoma and 22 cases of chronic cholecystitis was detected by immunohistochemical staining (SP method). The microvessels were highlighted by immunohistochemical staining (SP method) to detect antigen of CD34. Angiogenesis was represented by intratumor microvessel density (MVD).

RESULTS: In the gallbladder carcinoma, the positive rates of hPTTG1 and bFGF were 82.9% and 75.6% respectively, which were significantly higher than those in the chronic cholecystitis (P = 0.002 and 0.006). The expression of hPTTG1 was significantly associated with clinical stages and lymph node metastasis status (P = 0.025, 0.007), but not with histological differentiation (P = 0.144). The expression of bFGF was significantly correlated with clinical stages and histological differentiation (P = 0.019, 0.015), but not with lymph node metastasis status (P = 0.081). There was a significant correlation between the expression of hPTTG1 and bFGF (r = 0.648, P = 0.000). Neither of them had relation with age, sex, histological type and cholelithiasis. The value of MVD in the gallbladder carcinoma was significantly higher than that in the chronic cholecystitis (t = 3.684, P = 0.001). The expression of hPTTG1 and bFGF was correlated with MVD in gallbladder carcinoma (P = 0.000, 0.000). MVD in the gallbladder carcinoma was significantly associated with clinical stages and lymph node metastasis status (P = 0.007, 0.024), but not with age, sex, histological type, histological differentiation and cholelithiasis.

CONCLUSION: Overexpression of hPTTG1 is related to the tumorigenesis and angiogenesis in gallbladder carcinoma, which may provide a new target for therapy of gallbladdercarcinoma.

Mechanisms for pituitary tumorigenesis: the plastic pituitary

The anterior pituitary gland integrates the repertoire of hormonal signals controlling thyroid, adrenal, reproductive, and growth functions. The gland responds to complex central and peripheral signals by trophic hormone secretion and by undergoing reversible plastic changes in cell growth leading to hyperplasia, involution, or benign adenomas arising from functional pituitary cells. Discussed herein are the mechanisms underlying hereditary pituitary hypoplasia, reversible pituitary hyperplasia, excess hormone production, and tumor initiation and promotion associated with normal and abnormal pituitary differentiation in health and disease.

Overexpressed pituitary tumor-transforming gene causes aneuploidy in live human cells

The mammalian securin, pituitary tumor-transforming gene (PTTG), is overexpressed in several tumors and transforms cells in vitro and in vivo. To test the hypothesis that PTTG overexpression causes aneuploidy, enhanced green fluorescent protein (EGFP)-tagged PTTG (PTTG-EGFP) was expressed in human H1299 cancer cells (with undetectable endogenous PTTG expression) and mitosis of individual live cells observed. Untransfected cells and cells expressing EGFP alone exhibited appropriate mitosis. PTTG-EGFP markedly prolonged prophase and metaphase, indicating that PTTG blocks progression of mitosis to anaphase. In cells that underwent apparently normal mitosis (35 of 65 cells), PTTG-EGFP was degraded about 1 min before anaphase onset. Cells that failed to degrade PTTG-EGFP exhibited asymmetrical cytokinesis without chromosome segregation (18 of 65 cells) or chromosome decondensation without cytokinesis (9 of 65 cells), resulting in appearance of a macronucleus. Fifty-one of 55 cells expressing a nondegradable mutant PTTG exhibited asymmetrical cytokinesis without chromosome segregation, and some (4 of 55) decondensed chromosomes, both resulting in macronuclear formation. During this abnormal cytokinesis, all chromosomes and spindles and both centrosomes moved to one daughter cell, suggesting potential chaos in the subsequent mitosis. In conclusion, failure of PTTG degradation or enhanced PTTG accumulation, as a consequence of overexpression, inhibits mitosis progression and chromosome segregation but does not directly affect cytokinesis, resulting in aneuploidy. These results demonstrate that PTTG induces aneuploidy in single, live, human cancer cells.

Targeted overexpression of luteinizing hormone causes ovary-dependent functional adenomas restricted to cells of the Pit-1 lineage

The majority of pituitary adenomas in humans are nonmetastasizing, monoclonal neoplasms that occur in approximately 20% of the general population. Their development has been linked to a combination of extrinsic factors and intrinsic defects. We now demonstrate with transgenic mice that targeted and chronic overexpression of LH causes ovarian hyperstimulation and subsequent hyperproliferation of Pit-1-positive cells that culminates in the appearance of functional pituitary adenomas ranging from focal to multifocal expansion of lactotropes, somatotropes, and thyrotropes. Tumors fail to develop in ovariectomized mice, indicating that contributions from the ovary are necessary for adenoma development. Although the link between chronic ovarian hyperstimulation and PRL-secreting adenomas was expected, the involvement of somatotropes and thyrotropes was surprising and suggests that multiple ovarian hormones may contribute to this unusual pathological consequence. In support of this idea, we have found that ovariectomy followed by estrogen replacement results in the expansion of lactotropes selectively in LH overexpressing mice, but not somatotropes and thyrotropes. Collectively, these data indicate that estrogen is sufficient for the formation of lactotrope adenomas only in animals with a hyperstimulated ovary, whereas the appearance of GH- and TSH-secreting adenomas depends on multiple ovarian hormones. Together, our data expand current models of pituitary tumorigenesis by suggesting that chronic ovarian hyperstimulation may underlie the formation of a subset of pituitary adenomas containing lactotropes, somatotropes, and thyrotropes.

A potential role for PTTG/securin in the developing human fetal brain

Human securin, known also as PTTG, has established oncogenic and cell cycle regulatory functions. PTTG/securin transforms cells in vitro, inhibits sister chromatid separation, and regulates secretion of fibroblast growth factor-2. FGF-2 is a key regulator of CNS development and PTTG/securin expression has been reported in murine fetal brain. We examined the expression and function of securin and FGF-2 in the developing human fetal brain and in a fetal neuronal cell line (NT 2). Securin expression was significantly reduced in first and second trimester fetal cerebral cortex compared with adult cerebral cortex, where immunocytochemistry revealed intense securin staining in neuronal cell bodies. FGF-2 protein was concordantly lower in fetal cortex, whereas pretranslational expression of PTTG binding factor (PBF) was not significantly altered in fetal brain compared with adult. PCNA expression demonstrated that high securin levels in adult cortex were associated with absent cell proliferation. In NT-2 cells, securin stimulated FGF-2 expression, which could be abrogated by a carboxyl-terminal mutation. Low transient expression of securin resulted in a significant proliferative effect, whereas high levels of securin expression inhibited cell turnover. We propose a potential role for human PTTG/securin in modulating cell proliferation and FGF-2 expression during human neurogenesis.

Best Practice No 172: pituitary gland pathology

This article reviews published evidence on the diagnosis and classification of pituitary gland tumours and the relevance of histological and genetic features to prognosis. Much of the literature is devoted to the histological, ultrastructural, and immunocytochemical classification of pituitary adenomas (extensively supported by multicentre studies), with little consensus on the identification of prognostic features in adenomas, particularly in relation to invasion. There is a lack of correspondence between clinical and pathological criteria to identify and classify invasion, and a need to reassess the nomenclature and diagnostic criteria for invasive adenomas and carcinomas. Recent cytogenetic, genetic, and molecular biological studies have identified no consistent abnormalities in relation to pituitary tumour progression, although many genes are likely to be involved. In light of these uncertainties, an approach to the diagnosis and classification of pituitary adenomas is suggested, based on robust criteria from earlier studies and incorporating provisional data that require reassessment in large prospective studies with an adequate clinicopathological database.

Genome-wide amplification and allelotyping of sporadic pituitary adenomas identify novel regions of genetic loss

Through the use of a candidate gene approach, several previous studies have identified loss of heterozygosity (LOH) at putative tumor-suppressor gene (TSG) loci in sporadic pituitary tumors. This study reports a genome-wide allelotyping by use of 122 microsatellite markers in a large cohort of tumors, consisting of somatotrophinomas and non-functioning adenomas. Samples were first subject to prior whole genome amplification by primer extension pre-amplification (PEP) to circumvent limitations imposed by insufficient DNA for whole-genome analysis with this number of microsatellite markers. The overall mean frequency of loss in invasive tumors was significantly higher than that in their non-invasive counterparts (7 vs. 3% somatotrophinomas; 6 vs. 3% non-functioning adenomas, respectively). Analysis of the mean frequency of LOH, across all markers to individual chromosomal arms, identified 13 chromosomal arms in somatotrophinomas and 10 in non-functioning tumors, with LOH greater than the 99% upper confidence interval calculated for the rate of overall random allelic loss. In the majority of cases, these losses were more frequent in invasive tumors than in their non-invasive counterparts, suggesting these to be markers of tumor progression. Other regions showed similar frequencies of LOH in both invasive and non-invasive tumors, implying these to be early changes in pituitary tumorigenesis. This genome-wide study also revealed chromosomal regions where losses were frequently associated with an individual marker, for example, chromosome arm 1q (LOH > 30%). In some cases, these losses were subtype-specific and were found at a higher frequency in invasive tumors than in their non-invasive counterparts. Identification of these regions of loss provides the first preliminary evidence for the location of novel putative TSGs involved in pituitary tumorigenesis that are, in some cases, subtype-specific. This investigation provides an unbiased estimate of global aberrations in sporadic pituitary tumors as assessed by LOH analysis. The identification of multiple "hotspots" throughout the genome may be a reflection of an unstable chromatin structure that is susceptible to a deletion or epigenetic-mediated gene-silencing events.