Development of cystic glandular hyperplasia of the endometrium in Mullerian inhibitory substance type II receptor-pituitary tumor transforming gene transgenic mice

The pituitary tumor transforming gene (PTTG)/securin is an oncogene that is involved in cell cycle regulation and sister chromatid separation. PTTG is highly expressed in various tumors including ovarian tumors, suggesting that PTTG may play a role in ovarian tumorigenesis. Overexpression of PTTG resulted in induction of cellular transformation in vitro and tumor formation in nude mice. To ascertain PTTG function in ovarian tumorigenesis, we generated a transgenic mouse model of PTTG by cloning PTTG cDNA downstream of Mullerian inhibitory substance type II receptor gene promoter (MISIIR) in order to target the ovarian surface epithelium. By screening of transgenic animals, we identified five founders (four males and one female). Using the four male founders, we developed four transgenic lines. PTTG expression was increased in ovarian surface epithelium, ovarian granulosa cells, as well as in the pituitary gland. Transgenic females did not develop any visible ovarian tumors at 8-10 months of age; however, there was an overall increase in the corpus luteum mass in transgenic ovary, suggesting increased luteinization. These changes were associated with an increase in serum LH and testosterone levels. In addition, there was a generalized hypertrophy of the myometrium of MISIIR-PTTG transgenic uteri with cystic glandular and hyperplasia of the endometrium. Based on these results, we conclude that the overexpression of PTTG may be required to initiate precancerous conditions but is not sufficient to induce ovarian tumorigenesis and may require another partner to initiate cellular transformation.     

Pituitary tumor-transforming gene in endocrine and other neoplasms: a review and update

Pituitary tumor-transforming gene (PTTG) was only recently discovered. Its overexpression occurs in a wide variety of endocrine and non-endocrine tumors, including ones of pituitary, thyroid, ovary, breast, prostate, lung, esophagus, colon, and the central nervous system. It affects tumor invasiveness and recurrence in several systems, functions as a securin during cell cycle progression, and inhibits premature sister chromatid separation. PTTG is involved in multiple cellular pathways, including proliferation, DNA repair, transformation, angiogenesis induction, invasion, and the induction of genetic instability. In thyroid carcinomas, PTTG expression is a marker of invasiveness. PTTG is overexpressed in most pituitary adenomas, where it appears to correlate with recurrence and angiogenesis. Increasing evidence also points to the role of PTTG in endocrine organ development. For example, PTTG knockout mice show defective pancreatic beta-cell proliferation. Herein, we review the current knowledge regarding PTTG-mediated pathways based on evidence from in vivo and in vitro studies as well as knockout mice models. We also summarize the issue of PTTG expression and its correlation with clinicopathologic parameters in patients with neoplasms, particularly of endocrine organs. In addition, we discuss in vitro and in vivo therapeutic models targeting PTTG overexpression.     

The pituitary tumor transforming gene in thyroid cancer

The pituitary tumor transforming gene (PTTG) is a multifunctional proto-oncogene that is over-expressed in various tumors including thyroid carcinomas, where it is a prognostic indicator of tumor recurrence. PTTG has potent transforming capabilities in vitro and in vivo, and many studies have investigated the potential mechanisms by which PTTG contributes to tumorigenesis. As the human securin, PTTG is involved in critical mechanisms of cell cycle regulation, whereby aberrant expression induces aneuploidy. PTTG may further contribute to tumorigenesis through its role in DNA damage response pathways and via complex interactions with hormones and growth factors. Furthermore, PTTG over-expression negatively impacts upon the efficacy of radioiodine therapy in thyroid cancer, through repression of expression and function of the sodium iodide symporter. Given its various roles at all disease stages, PTTG appears to be an important oncogene in thyroid cancer. This review discusses the current knowledge of PTTG with particular focus on its role in thyroid cancer.     

Overexpression of pituitary tumor-transforming gene-1 in hepatocellular carcinoma

BACKGROUND/AIMS: Pituitary tumor-transforming gene-1, a recently identified proto-oncogene, was reported to be highly expressed in various tumors, such as tumors of the pituitary gland, adrenal gland, colon, ovary, endometrium, uterus, and kidney. The purpose of this study was to investigate the clinicopathologic significance of PTTG1 expression in hepatocellular carcinoma. METHODOLOGY: Expression of PTTG1 mRNA was evaluated by RT-PCR in 147 HCCs and 103 paired nontumorous liver tissues. RESULTS: PTTG1 was found overexpressed in 80 of 147 (61%) HCCs. Overexpression of PTTG1 correlated with alpha-fetoprotein elevation (p<0.022) and higher tumor stage (stage IIIB-IV) tumors (p<0.009), but not with tumor grade, size, and survival. CONCLUSIONS: The results show that PTTG1 is overexpressed frequently in HCC, and correlated high stage tumors, indicating that overexpression of PTTG1 plays a role in the development and progression of HCC.     

Adenovirus-mediated transfer of siRNA against PTTG1 inhibits liver cancer cell growth in vitro and in vivo

The pituitary tumor transforming (PTTG) gene family comprises PTTG1, 2, and 3. Forced expression of PTTG1 (securin) induces cellular transformation and promotes tumor development in animal models. PTTG1 is overexpressed in various human cancers. However, the expression and pathogenic implications of the PTTG gene family in hepatocellular carcinoma are largely unknown. Gene silencing using short interfering RNA (siRNA) has become an efficient means to study the functions of genes and has been increasingly used for cancer gene therapy approaches. We report that PTTG1, but not PTTG2 and 3, was highly and frequently expressed in liver cancer tissues from patients and highly in SH-J1, SK-Hep1, and Huh-7 hepatoma cell lines. Adenoviral vector encoding siRNA against PTTG1 (Ad.PTTG1-siRNA) depleted PTTG1 specifically and efficiently in SH-J1 hepatoma cells, which resulted in activation of p53 that led to increased p21 expression and induction of apoptosis. The depletion of PTTG1 in HCT116 colorectal cancer cells exhibited a cytotoxic effect in a p53-dependent manner. Ad.PTTG1-siRNA-mediated cytotoxic effect was dependent on expression levels of PTTG1 and p53 in hepatoma cell lines. Huh-7 hepatoma cells, once transduced with Ad.PTTG1-siRNA, displayed markedly attenuated growth potential in nude mice. Intra-tumor delivery of Ad.PTTG1-siRNA led to significant inhibition of tumor growth in SH-J1 tumor xenograft established in nude mice. In conclusion, PTTG1 overexpressed in hepatoma cell lines negatively regulates the ability of p53 to induce apoptosis. PTIG1 gene silencing using siRNA may be an effective modality to treat liver cancer, in which PTTG1 is abundantly expressed. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/ suppmat/index.html).     

Vascular endothelial growth factor,its receptor KDR/Flk-1, and pituitary tumor transforming gene in pituitary tumors

Pituitary tumorigenesis is a poorly understood process involving dysregulation of the cell cycle, proliferation, and angiogenesis. The novel securin pituitary tumor transforming gene (PTTG) disrupts cell division and stimulates fibroblast growth factor (FGF)-2-mediated angiogenesis. We investigated expression of the angiogenic vascular endothelial growth factor (VEGF) and its receptor KDR/Flk-1 in 103 human pituitary tumors, and we assessed functional relationships between these genes in vitro. Nonfunctioning tumors (n = 81) demonstrated markedly raised VEGF mRNA (3.2-fold, P < 0.05) and protein concentrations, compared with normal pituitaries (n = 10). KDR was also highly induced in nonfunctioning tumors (14-fold, P < 0.001, n = 78) as well as in the whole cohort of pituitary tumors, compared with normal pituitary samples (14-fold, P < 0.0001, n = 100). In vitro, PTTG induced VEGF, but not KDR, expression in fetal neuronal NT2 cells (2.7-fold, P < 0.001, n = 8), MCF-7 breast carcinoma cells (1.9-fold, P = 0.03, n = 10), and choriocarcinoma JEG-3 cells (P = 0.0002, n = 8). A mutated PTTG construct that cannot be phosphorylated showed identical VEGF up-regulation (2.9-fold, P < 0.001, n = 8) in NT2 cells, compared with wild-type PTTG, but a further mutated construct with abrogation of the key protein:protein interaction domain of PTTG resulted in a significant reduction in VEGF stimulation, compared with wild-type (0.37-fold reduction, P < 0.001, n = 8). FGF-2 findings mirrored those of VEGF, although antibody depletion of secreted FGF-2 in the cell medium failed to influence VEGF up-regulation by PTTG. Overall, our findings implicate altered VEGF and KDR signaling in pituitary tumorigenesis, and we propose that PTTG stimulation of FGF-2 and VEGF expression in the presence of up-regulated growth factor receptors may account for angiogenic growth and progression of human pituitary tumors.     

Pituitary tumor-transforming gene regulates multiple downstream angiogenic genes in thyroid cancer

CONTEXT: Pituitary tumor-transforming gene (PTTG) is a multifunctional protein involved in several tumorigenic mechanisms, including angiogenesis. PTTG has been shown to promote angiogenesis, a key rate-limiting step in tumor progression, by up-regulation of fibroblast growth factor-2 and vascular endothelial growth factor. OBJECTIVE: To investigate whether PTTG regulates other angiogenic genes in thyroid cells, we performed angiogenesis-specific cDNA arrays after PTTG transfection. Two of the genes [inhibitor of DNA binding-3 (ID3) and thrombospondin-1 (TSP-1)] which showed differential expression in primary thyroid cells were validated in vitro and in vivo. RESULTS: TSP-1 showed a 2.5-fold reduction and ID3 showed a 3.5-fold induction in expression in response to PTTG overexpression in vitro. Conversely, suppression of PTTG with small interfering RNA was associated with a 2-fold induction of TSP-1 and a 2.2-fold reduction in ID3 expression. When we examined TSP-1 and ID3 expression in 34 differentiated thyroid cancers, ID3 was significantly increased in tumors compared with normal thyroid tissue. Furthermore, ID3 expression was significantly higher in follicular thyroid tumors than in papillary tumors. Although mean TSP-1 expression was not altered in cancers compared with normal thyroids, we observed a significant independent association between TSP-1 expression and early tumor recurrence, with recurrent tumors demonstrating 4.2-fold lower TSP-1 expression than normal thyroid tissues. CONCLUSION: We have identified ID3 and TSP-1 as two new downstream targets of PTTG in thyroid cancer. We propose that PTTG may promote angiogenesis by regulating the expression of multiple genes with both pro- and antiangiogenic properties and may thus be a key gene in triggering the angiogenic switch in thyroid tumorigenesis.     

Cell cycle control of pituitary development and disease

The pituitary gland regulates diverse physiological functions, including growth, metabolism, reproduction, stress response, and ageing. Early genetic models in the mouse taught us that the pituitary is highly sensitive to genetic alteration of specific cell cycle regulators such as the retinoblastoma protein (pRB) or the cell cycle inhibitor p27(Kip1). The molecular analysis of human pituitary neoplasias has now corroborated that cell cycle deregulation is significantly implicated in pituitary tumorigenesis. In particular, proteins involved in cyclin-dependent kinase regulation or the pRB pathway are altered in nearly all human pituitary tumors. Additional cell cycle regulators such as PTTG1/securin may have critical roles in promoting genomic instability in pituitary neoplasias. Recent experimental data suggest that these cell cycle regulators may have significant implications in the biology of putative progenitor cells and pituitary homeostasis. Understanding how cell cycle regulation controls pituitary biology may provide us with new therapeutic approaches against pituitary diseases.     

Expression of pituitary tumor transforming gene (PTTG) and its binding protein in human astrocytes and astrocytoma cells: function and regulation of PTTG in U87 astrocytoma cells

Human securin, pituitary tumor transforming gene (PTTG), is a protooncogene. Here we report expressions of PTTG and its interacting protein, PTTG-binding factor in human astrocytic cells. PTTG expression was higher in malignant cells than in primary astrocytes, whereas PTTG-binding factor was not. Using a xenotransplantable, glioma cell line (U87), we observed that knocking down PTTG mRNA by RNA silencing inhibited serum-induced proliferation by approximately 50%. Furthermore, in U87 cells PTTG expression was up-regulated by promalignant ligands epithelial growth factor (EGF) and TGFalpha, both at the protein and mRNA levels. PTTG induction by EGF receptor (EGFR) ligands could be blocked by the specific EGFR inhibitor, AG1478. Hepatocyte growth factor (HGF) also induced PTTG but to a lesser extent than EGF. Although EGF stimulates HGF secretion in U87 cells, the effect of EGF on PTTG mRNA expression is independent of HGF as neutralizing antibody against HGF failed to abolish EGF-induced up-regulation of PTTG mRNA. PTTG mRNA was unchanged by incubating U87 cells with the promalignant growth factor TGFbeta, apoptosis inducing TNFalpha and ligands for nuclear receptors, such as retinoic acid and retinoid X receptors and peroxisome proliferator-activated receptor-gamma, known for their growth-inhibitory and apoptosis-inducing effects on gliomas. In addition, 17beta-estradiol and Ca2+, known to activate PTTG expression, did not change PTTG mRNA levels in U87 cells. In summary, we show higher PTTG expression in astrocytoma than normal astrocytes and secondly, PTTG is involved in glioma cell growth. Finally, regulation of its expression has glioma-specific features and is selectively regulated by promalignant cytokines including EGFR ligands and HGF.     

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.     

Survivin基因沉默对结直肠癌PTTG mRNA的影响

目的探讨重组载体介导的Survivin小干扰RNA(siRNA)对人结肠癌细胞株Lovo中PTTG mRNA的影响。方法前期成功构建的Survivin特异性siRNA真核表达载体转染结肠癌Lovo细胞后,采用实时荧光定量PCR检测PTTG mRNA的表达水平。结果 Survivin基因沉默后24～72 h,与正常对照组相比,Survivin mRNA表达明显降低(P<0.05);基因沉默24和48 h后,pGenesil-2-Survivin 1组和pGenesil-2-Survivin 2组PT-TG mRNA表达显著低于正常对照组(P<0.05)。结论 Survivin基因沉默后结直肠癌细胞PTTG mRNA表达显著下调,提示Survivin和PTTG可能相互促进共同参与结直肠癌的发生发展。     

Expression and function of pituitary tumour transforming gene for T-lymphocyte activation

Pituitary tumour transforming gene (PTTG) isolated from pituitary tumour cells transforms cells in vitro and causes in vivo tumour formation. PTTG is expressed in several human tumours and cell lines. In normal adult tissues, the testis expresses abundant levels of PTTG mRNA comparable to that found in tumour cells. Although PTTG is not expressed in resting T cells, we showed here that activation of normal adult human T cells using either immobilized anti-CD3 antibodies or phytohaemagglutinin was accompanied by marked PTTG induction, reaching levels observed in human tumour cells. Inhibitors of T-cell functions, such as cyclosporin A and hydrocortisone, decreased induction of PTTG mRNA expression. During T-cell activation, PTTG mRNA abundance corresponded with the increase in S-phase cells, suggesting PTTG involvement in cell cycle-dependent processes. These results showed that PTTG-1 expression follows cell cycling patterns in T lymphocytes, providing a convenient model for studying PTTG functions in normal cells.     

The emerging role of pituitary tumour transforming gene (PTTG) in endocrine tumourigenesis

It is now 10 years since PTTG was first cloned and isolated. Perhaps the major story of the intervening decade of work performed by numerous groups around the world is the sheer multifunctionality ascribed to this gene. PTTG has been implicated in mechanisms of gene transactivation, cell transformation, angiogenesis, metabolism, apoptosis, DNA repair, genetic instability and mitotic control, both in endocrine and non-endocrine settings. In the current review, we cast a critical eye over a decade of PTTG research within the field of endocrine neoplasia.