Pituitary tumor transforming gene (PTTG) stimulates thyroid cell proliferation via a vascular endothelial growth factor/kinase insert domain receptor/inhibitor of DNA binding-3 autocrine pathway

'From Felix to the helix, and from the cradle to the grave - Semon's contribution to thyroid surgery', Royal Society of Medicine, 1 November 2019, London, UK

Mr President, Mr President Elect, Fellows and Members, Ladies and Gentleman, it is a pleasure to address the Section of Laryngology this morning and deliver the 94th Semon Lecture. I would like to thank the Semon Committee for their kind invitation. My lecture will discuss Sir Felix Semon (the man himself), highlight the history of head and neck surgery, and then discuss the requirements of a modern-day thyroid surgeon. I have no conflict of interest and nothing to declare.

Protein Expression of PTTG-1, OCT-4, and KLF-4 in Seminoma: A Pilot Study

Seminomas are the most frequent kind of testicular germ cell tumors (TGCTs), accounting for 50% of tumor diagnosis in young men, whereas non-seminomas account for 40% and mixed forms for 10% of cases. It is currently supposed that TGCTs evolve from a pre-invasive stage of carcinoma in situ (CIS). Octamer-binding transcription factor 4 (OCT4) is essential for self-renewal of stem cells. It is considered as a major regulator of cell pluripotency. Prior studies have shown that seminoma expresses OCT4. Transcription factor Krüppel-like factor 4 (KLF4) has moreover associated with embryonic stem cell maintenance. Finally, we previously demonstrated the expression of PTTG1 in CIS and seminomas. In this pilot study, we compared the combined expression of PTTG1 with KLF4 and OCT4 in seminoma, in order to validate our hypotesis that PTTG1 marks a specific population of stem cells in neoplastic tissue, strictly related with tumor. Formalin-fixed and paraffin-embedded testicular tissues by 5 patients who underwent an orchidectomy for seminoma have been collected and immunofluorescence analysis was performed using antibody rabbit monoclonal PTTG-1 and mouse monoclonal OCT4 or mouse monoclonal KLF4 antibody. In seminoma we observed that tumor cells strongly express OCT-4 in all seminomas and in the intratubular areas of seminoma. Expression of KLF-4 was observed in many tumor cells. PTTG1 marks some specific OCT4- and KLF4-positive tumor cells, mainly localized at the periphery of the neoplasm. In the intertubular infiltration areas nests of cells expressing both OCT4/KLF4 and PTTG1 have been observed. This is the first identification of a cell population in seminoma characterized for being OCT4, KLF4, and PTTG1 positive cells in seminoma, associated with cancer invasiveness. Further investigation is needed to elucidate if a functional abrogation of PTTG1 might be used in order to offer new therapeutic approaches in the clinical workout of seminoma.

The PTTG1-targeting miRNAs miR-329, miR-300, miR-381, and miR-655 inhibit pituitary tumor cell tumorigenesis and are involved in a p53/PTTG1 regulation feedback loop

Deregulation of the pituitary tumor transforming gene (PTTG1), a newly discovered oncogene, is a hallmark of various malignancies, including pituitary tumors. However, the mechanisms regulating PTTG1 expression are still needed to be explored. MicroRNAs (miRNAs) are a novel class of small RNA molecules that act as posttranscriptional regulators of gene expression and can play a significant role in tumor development. Here, we identified a series of miRNAs, namely, miR-329, miR-300, miR-381 and miR-655, which could target PTTG1 messenger RNA and inhibit its expression. Interestingly, all four miRNAs significantly that are downregulated in pituitary tumors were mapped to the 14q32.31 locus, which acts as a tumor suppressor in several cancers. Functional studies show that the PTTG1-targeting miRNAs inhibit proliferation, migration and invasion but induce apoptosis in GH3 and MMQ cells. Furthermore, overexpression of a PTTG1 expression vector lacking the 3′UTR partially reverses the tumor suppressive effects of these miRNAs. Next, we identified the promoter region of PTTG1-targeting miRNAs with binding sites for p53. In our hands, p53 transcriptionally activated the expression of these miRNAs in pituitary tumor cells. Finally, we found that PTTG1 could inhibit p53 transcriptional activity to the four miRNAs. These data indicate the existence of a feedback loop between PTTG1 targeting miRNAs, PTTG1 and p53 that promotes pituitary tumorigenesis. Together, these findings suggest that these PTTG1-targeting miRNAs are important players in the regulation of pituitary tumorigenesis and that these miRNAs may serve as valuable therapeutic targets for cancer treatment.

FTY720 (Fingolimod) attenuates basal and sphingosine-1-phosphate-evoked thyroid cancer cell invasion

The bioactive lipid sphingosine-1-phosphate (S1P) is a potent inducer of ML-1 thyroid cancer cell migration and invasion. It evokes migration and invasion by activating S1P receptor 1 and 3 (S1P1,3) and downstream signaling intermediates as well as through cross-communication with vascular endothelial growth factor receptor 2 (VEGFR2). However, very little is known about the role of S1P receptors in thyroid cancer. Furthermore, the currently used treatments for thyroid cancer have proven to be rather unsuccessful. Thus, due to the insufficiency of the available treatments for thyroid cancer, novel and targeted therapies are needed. The S1P receptor functional antagonist FTY720, an immunosuppressive drug currently used for treatment of multiple sclerosis, has shown promising effects as an inhibitor of cancer cell proliferation and invasion. In this study, we investigated the effect of FTY720 on invasion and proliferation of several thyroid cancer cell lines. We present evidence that FTY720 attenuated basal as well as S1P-evoked invasion of these cell lines. Furthermore, FTY720 potently downregulated S1P1, protein kinase Cα(PKCα), PKCβI, and VEGFR2. It also attenuated S1P-evoked phosphorylation of ERK1/2. Our results also showed that FTY720 attenuated S1P-induced MMP2 intracellular expression, S1P-induced secretion of MMP2 and MMP9, and decreased basal MMP2 and MMP9 activity. Moreover, in FTY720-treated cells, proliferation was attenuated, p21 and p27 were upregulated, and the cells were arrested in the G1 phase of the cell cycle. FTY720 attenuated cancer cell proliferation in the chick embryo chorioallantoic membrane assay. Thus, we suggest that FTY720 could be beneficial in the treatment of thyroid cancer.

Gremlin, a bone morphogenetic protein antagonist, is a crucial angiogenic factor in pituitary adenoma

Gremlin is an antagonist of bone morphogenetic protein (BMP) and a major driving force in skeletal modeling in the fetal stage. Several recent reports have shown that Gremlin is also involved in angiogenesis of lung cancer and diabetic retinopathy. The purpose of this study was to investigate the role of Gremlin in tumor angiogenesis in pituitary adenoma. Double fluorescence immunohistochemistry of Gremlin and CD34 was performed in pituitary adenoma tissues obtained during transsphenoidal surgery in 45 cases (7 PRLoma, 17 GHoma, 2 ACTHoma, and 2 TSHoma). Gremlin and microvascular density (MVD) were detected by double-immunofluorescence microscopy in CD34-positive vessels from tissue microarray analysis of 60 cases of pituitary adenomas (6 PRLoma, 23 GHoma, 22 NFoma, 5 ACTHoma, and 4 TSHoma). In tissue microarray analysis, MVD was significantly correlated with an increased Gremlin level (linear regression: P < 0.005,  r (2) = 0.4958). In contrast, Gremlin expression showed no correlation with tumor subtype or Knosp score. The high level of expression of Gremlin in pituitary adenoma tissue with many CD34-positive vessels and the strong coherence of these regions indicate that Gremlin is associated with angiogenesis in pituitary adenoma cells.

Pituitary-tumour-transforming-gene 1 expression in testicular cancer

Genomic instability is a feature of germ cell tumours. The pituitary-tumour-transforming-gene 1 (PTTG1) is the major effector of chromosome segregation during mitosis, protecting the cell from aneuploidy. The protein expression of this gene has been evaluated in testicular tumours by immunohistochemistry. Formalin-fixed and paraffin-embedded specimens of testicular tissues from 83 patients undergoing therapeutic orchidectomy for seminomas (n = 53), embryonal carcinoma (n = 10), yolk sac tumour (n = 10) and teratoma (n = 10) were examined. Seminoma was associated with in situ carcinoma (CIS) in 23 samples. PTTG1 immunostaining was performed using rabbit anti-PTTG1 as a primary antibody. In CIS, only isolated cells showed nuclear staining for PTTG1. In the peripheral area of seminoma, PTTG1 was mostly detected as localised in the nucleus; in the central area of seminoma, PTTG1 staining was more intense in cytoplasm. PTTG1-positive cells were also present in the areas of seminoma infiltration. On the other hand, in embryonal carcinoma, cells had a diffuse positive immunostaining, mainly cytoplasmatic, while we did not observe an expression of PTTG1 in yolk sac tumour and mature teratoma. We firstly identified the PTTG1 expression pattern in normal testis, CIS and testicular cancer. Further investigation is needed to clarify the functional activity of PTTG1 in testicular oncogenesis.

Sphingosine 1-phosphate and cancer: lessons from thyroid cancer cells

Sphingomyelin is found in the cell membrane of all eukaryotic cells, and was for a long time considered merely as a structural component. However, during the last two decades, metabolites of sphingomyelin, especially sphingosine 1-phosphate (S1P), have proven to be physiologically significant regulators of cell function. Through its five different G protein-coupled receptors, S1P regulates a wide array of cellular processes, ranging from stimulating cellular proliferation and migration, to the inhibition of apoptosis and induction of angiogenesis and modulation of cellular calcium homeostasis. Many of the processes regulated by S1P are important for normal cell physiology, but may also induce severe pathological conditions, especially in malignancies like cancer. Thus, understanding S1P signaling mechanisms has been the aim of a multitude of investigations. Great interest has also been shown in understanding the action of sphingosine kinase (SphK), i.e., the kinase phosphorylating sphingosine to S1P, and the interactions between S1P and growth factor signaling. In the present review, we will discuss recent findings regarding the possible importance of S1P and SphK in the etiology of thyroid cancer. Although clinical data is still scarce, our in vitro findings suggest that S1P may function as a “double-edged sword”, as the receptor profile of thyroid cancer cells largely determines whether S1P stimulates or blocks cellular migration. We will also discuss the interactions between S1P- and VEGF-evoked signaling, and the importance of a S1P₁-VEGF receptor 2 complex in thyroid cancer cells.

Roles of microRNA on cancer cell metabolism

Advanced studies of microRNAs (miRNAs) have revealed their manifold biological functions, including control of cell proliferation, cell cycle and cell death. However, it seems that their roles as key regulators of metabolism have drawn more and more attention in the recent years. Cancer cells display increased metabolic autonomy in comparison to non-transformed cells, taking up nutrients and metabolizing them in pathways that support growth and proliferation. MiRNAs regulate cell metabolic processes through complicated mechanisms, including directly targeting key enzymes or transporters of metabolic processes and regulating transcription factors, oncogenes / tumor suppressors as well as multiple oncogenic signaling pathways. MiRNAs like miR-375, miR-143, miR-14 and miR-29b participate in controlling cancer cell metabolism by regulating the expression of genes whose protein products either directly regulate metabolic machinery or indirectly modulate the expression of metabolic enzymes, serving as master regulators, which will hopefully lead to a new therapeutic strategy for malignant cancer. This review focuses on miRNA regulations of cancer cell metabolism,including glucose uptake, glycolysis, tricarboxylic acid cycle and insulin production, lipid metabolism and amino acid biogenesis, as well as several oncogenic signaling pathways. Furthermore, the challenges of miRNA-based strategies for cancer diagnosis, prognosis and therapeutics have been discussed.

Regulation of human thyroid follicular cell function by inhibition of vascular endothelial growth factor receptor signalling

The potential autocrine role of human thyroid vascular endothelial growth factors (VEGFs) was examined using the VEGF receptor (VEGFR) inhibitor, ZM306416HCl. ZM306416HCl reduced VEGFR2 phosphorylation and inhibited endogenous, steady-state levels of p42/44 MAPK phosphorylation. It potently inhibited the secretion of plasminogen activators (PA) and increased (125)I uptake. Cell survival was compromised but rescued with insulin and TSH. Although the EGF receptor remained responsive to challenge by EGF in p42/44 MAPK assays, stimulatory effects of EGF on PA production were prevented by ZM306416HCl and those of protein kinase C stimulator, TPA reduced. In assays of (125)I uptake, ZM306416HCl prevented the inhibitory effects of EGF but not those of TPA. We conclude that autocrine VEGF may modulate thyroid function and that VEGFR inhibition increases iodide uptake and decreases PA production through regulation of p42/44 MAPK phosphorylation. VEGFR inhibition may have effects on thyroid function which may contribute to "off target" effects in clinical trials.

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.

Pituitary tumor-transforming gene and its binding factor in endocrine cancer

The pituitary tumor-transforming gene (PTTG1) encodes a multifunctional protein (PTTG) that is overexpressed in numerous tumours, including pituitary, thyroid, breast and ovarian carcinomas. PTTG induces cellular transformation in vitro and tumourigenesis in vivo, and several mechanisms by which PTTG contributes to tumourigenesis have been investigated. Also known as the human securin, PTTG is involved in cell cycle regulation, controlling the segregation of sister chromatids during mitosis. This review outlines current information regarding PTTG structure, expression, regulation and function in the pathogenesis of neoplasia. Recent progress concerning the use of PTTG as a prognostic marker or therapeutic target will be considered. In addition, the PTTG binding factor (PBF), identified through its interaction with PTTG, has also been established as a proto-oncogene that is upregulated in several cancers. Current knowledge regarding PBF is outlined and its role both independently and alongside PTTG in endocrine and related cancers is discussed.

Fifteen years' experience in thyroid surgery

INTRODUCTION

Thyroid disease is common, thyroid cancer is uncommon. Most goitres are investigated using blood tests, fine needle aspiration cytology together with ultrasound. Surgery usually entails either lobectomy or total thyroidectomy, and for malignancy, patients may need a neck dissection. Recently, significant advances have been made regarding mechanisms involved in both thyroid growth and function (goitrogenesis) and carcinogenesis at a molecular level.

PATIENTS AND METHODS

In the study cohort, 1113 patients had benign disease and 387 malignancy. For benign disease, 716 patients had lobectomy or isthmusectomy, 44 had near-total thyroidectomy and 318 a total thyroidectomy. For malignancy, patients received initial lobectomy (180) or total thyroidectomy (152). One hundred and eleven had completion surgery. Thirty patients had extensive surgery. Thyroid growth and function was investigated using 500 human thyroid cell primary cultures obtained at surgery, as well as in three animal models. The role of pituitary tumour transforming gene (PTTG), PTTG binding factor (PBF) and sodium iodide symporter (NIS) in thyroid cell function was then evaluated.

RESULTS

Temporary and permanent recurrent laryngeal nerve palsy rates were 2.4% and 0.4%. Other complications included temporary (21%) and permanent (3%) hypoparathyroidism, wound infection (1.2%), haematoma (1.2%) and poor scar (0.8%). Six patients have died. Regarding thyroid growth and function, TSH represents (either directly or indirectly) the main factor mediating thyroid follicular cell growth. For carcinogenesis, over-expression of the proto-oncogenes PTTG and PBF induces tumours in nude mice, and PTTG can induce proliferation of human thyroid cells and, in addition, both repress expression and function of NIS.

New targeted molecular therapies for dedifferentiated thyroid cancer

Dedifferentiated thyroid cancer (DeTC) derived from follicular epithelium is often incurable because it does not respond to radioiodine, radiotherapy, or chemotherapy. In cases, RET/PTC rearrangements are found in 30%–40%, RAS mutations in about 10%, and BRAF mutations in around 40%–50%, with no overlap between these mutations results in papillary thyroid cancer, while a higher prevalence of BRAF mutations (up to 70%) has been observed in DeTC. The identification of these activating mutations in DeTC makes this malignancy an excellent model to examine the effect of tyrosine kinase inhibitors (TKIs). Clinical trials with several TKIs targeting RET, and to a lesser extent BRAF, and other TKRs have shown positive results, with about one-third of DeTC showing a reduction in tumor size up to 50%, with the longest treatment duration of approximately three-four years. Angiogenesis inhibitors have also shown promising activity in DeTC. Progress is being made toward effective targeted DeTC therapy. The possibility of testing the sensitivity of primary DeTC cells from each subject to different TKIs could increase the effectiveness of the treatment.

Immunohistochemical expression of pituitary tumor transforming gene (PTTG) in pituitary adenomas: a correlative study of tumor subtypes

OBJECTIVE

We investigated the correlation between immunohistochemical expression of the pituitary tumor transforming gene (PTTG) and pituitary adenoma subtype.

METHODS

Pituitary adenomas (n = 89) were stained for PTTG using the streptavidin-biotin-peroxidase complex method and a monoclonal PTTG antibody.

RESULTS

PTTG staining was found to be cytoplasmic with a pronounced paranuclear expression pattern. Reactivity was highest in growth hormone (GH) adenomas as compared with other tumors, including prolactin (PRL), follicle-stimulating hormone/luteinizing hormone/alpha subunit, as well as adrenocorticotrophic hormone-secreting adenomas. PRL adenomas exhibited the lowest expression levels. Among GH adenomas, untreated tumors demonstrated significantly higher PTTG levels than octreotide-treated examples. Although dopamine agonist-treated PRL adenomas tended to show lower expression levels, statistical significance was not reached.

CONCLUSIONS

Our finding that PTTG was differentially expressed in pituitary adenoma subtypes suggests a cell-specific function for PTTG. Moreover, treatment of GH adenomas with somatostatin analogues lowered PTTG expression. Further investigation into mechanisms mediating cell-specific expression of PTTG is warranted.

Thyroid hormone receptors are tumor suppressors in a mouse model of metastatic follicular thyroid carcinoma

Aberrant expression and mutations of thyroid hormone receptor genes (TRs) are closely associated with several types of human cancers. To test the hypothesis that TRs could function as tumor suppressors, we took advantage of mice with deletion of all functional TRs (TRalpha1(-/-)TRbeta(-/-) mice). As these mice aged, they spontaneously developed follicular thyroid carcinoma with pathological progression from hyperplasia to capsular invasion, vascular invasion, anaplasia and metastasis to the lung, similar to human thyroid cancer. Detailed molecular analysis revealed that known tumor promoters such as pituitary tumor-transforming gene were activated and tumor suppressors such as peroxisome proliferator-activated receptor gamma and p53 were suppressed during carcinogenesis. In addition, consistent with the human cancer, AKT-mTOR-p70(S6K) signaling and vascular growth factor and its receptor were activated to facilitate tumor progression. This report presents in vivo evidence that functional loss of both TRalpha1 and TRbeta genes promotes tumor development and metastasis. Thus, TRs could function as tumor suppressors in a mouse model of metastatic follicular thyroid cancer.

VEGF modulates the effects of gonadotropins in granulosa cells

Follicle selection is associated with an increase in the expression of vascular endothelial growth factor (VEGF) and its receptors in granulosa cells, however, the roles of VEGF in regulating the function of these or other non-endothelial cells in the ovary have not been explored in detail. The current study used bovine cell cultures to investigate potential roles of VEGF in the regulation of granulosa cell function during follicle development. Granulosa cells were obtained from morphologically healthy follicles 4 to 8 mm or 9 to 14 mm in diameter (corresponding to diameters before and after the establishment of dominance, respectively, during a bovine follicular wave) and exposed to a range of VEGF concentrations (1 to 100 ng/mL) encompassing concentrations found naturally in bovine dominant follicles. A concentration of VEGF of 1 ng/mL induced significant proliferation of granulosa cells from 4- to 8-mm follicles (P=0.024) and increased the proliferative response of these cells to follicle-stimulating hormone (FSH; P=0.045); whereas higher doses of VEGF had no effect on proliferation (P=0.9). Treatment with VEGF induced an overall increase in mean extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation (P=0.02). In contrast, VEGF, alone or in combination with FSH, had no effect on expression of the steroidogenic enzyme, CYP11A1, by cells from 4- to 8-mm follicles (P=0.9). Granulosa cells from 9- to 14-mm follicles responded to 1 ng/mL VEGF with an increase in expression of the ovulation-associated gene, PTGS2 (P=0.003) but higher VEGF doses had no effect (P=0.9). The PTGS2 response to 1 ng/mL VEGF was similar to that induced by treatment with luteinizing hormone (LH). Interestingly, the stimulatory effects of LH on ERK1/2 phosphorylation (P=0.003) and PTGS2 expression (P<0.01) in granulosa cells from 9- to 14-mm follicles were abolished (P=0.2) by specific chemical inhibition of VEGF receptor 2 (VEGFR2). These results suggest novel and important roles of VEGF and its receptor, VEGFR2, in mediating and/or enhancing the effects of gonadotropins in granulosa cells.

Targeting vascular endothelial growth factor receptor in thyroid cancer: the intracellular and extracellular implications

Our understanding of the molecular pathophysiology of differentiated thyroid cancer (DTC) has developed considerably over the last 10 years. Aberrant signaling through B-Raf and Akt has been implicated in the tumorigenesis of DTC. Moreover, these highly vascular tumors have proven to be sensitive to the inhibition of vascular endothelial growth factor receptor (VEGFR-2). It is likely that the multikinase inhibitors, sorafenib, sunitinib, axitinib, and motesanib, whose targets include VEGFR-2, exert their effects primarily through inhibition of endothelial cells. However, as VEGFR-2 is expressed on DTC cells, these compounds may have direct antitumor action. This review will discuss the key signaling pathways involved in thyroid cancer and their implications for targeted therapy.

Effect of PTTG on endogenous gene expression in HEK 293 cells

Background

Pituitary tumor transforming gene (PTTG), also known as securin, is highly expressed in various tumors including pituitary, thyroid, colon, ovary, testis, lung, and breast. An overexpression of PTTG enhances cell proliferation, induces cellular transformation in vitro, and promotes tumor development in nude mice. PTTG also inhibits separation of sister chromatids leading to aneuploidy and genetic instability. A great amount of work has been undertaken to understand the biology of PTTG and its expression in various tumors. However, mechanisms by which PTTG mediates its tumorigenic function are not fully understood. To utilize this gene for cancer therapy, identification of the downstream signaling genes regulated by PTTG in mediation of its tumorigenic function is necessary. For this purpose, we expressed PTTG in human embryonic kidney (HEK293) cells that do not express PTTG and analyzed the downstream genes using microarray analysis.

Results

A total of 22,277 genes printed on an Affymetrix HG-U133A 2.0 GeneChip™ array were screened with labeled cRNA prepared from HEK293 cells infected with adenovirus vector expressing PTTG cDNA (AdPTTG cDNA) and compared with labeled cRNA prepared from HEK293 cells infected with control adenovirus (control Ad) or adenovirus vector expressing GFP (AdGFP). Out of 22,277 genes, 71 genes were down-regulated and 35 genes were up-regulated with an FDR corrected p-value of ≤ 0.05 and a fold change of ≥2. Most of the altered genes identified are involved in the cell cycle and cell apoptosis; a few are involved in mRNA processing and nitrogen metabolism. Most of the up-regulated genes belong to the histone protein family.

Conclusion

PTTG is a well-studied oncogene for its role in tumorigenesis. In addition to its importance in regulation of the cell cycle, this gene has also been recently shown to play a role in the induction of cell apoptosis. The microarray analysis in the present study demonstrated that PTTG may induce apoptosis by down-regulation of oncogenes such as v-Jun and v-maf and up-regulation of the histone family of genes.

Oct-1 induces pituitary tumor transforming gene expression in endocrine tumors

As human pituitary tumor transforming gene (hPTTG1) is upregulated in endocrine tumors, we studied regulatory mechanisms for hPTTG1 expression. We identified Oct-1-binding motifs in the hPTTG1 promoter region and show Oct-1-specific binding to the hPTTG1 promoter using chromatin immunoprecipitation. We overexpressed Oct-1 and observed approximately 2.5-fold activation of hPTTG1 promoter luciferase constructs (-2642/-1 and -1717/-1). Transcriptional activation was abrogated by co-transfection of an inactive Oct-1 form lacking the POU domain or by utilizing mutated hPTTG1 promoters or mutants devoid of two Oct-1-binding motifs (-1717/-1mut, -637/-1 or -433/-1). Using biotin-streptavidin pull-down assays, we confirmed Oct-1 binding to the two octamer motifs in the hPTTG1 promoter (-1669/-1631 and -1401/-1361). Endogenous hPTTG1 mRNA and protein increased up to approximately fourfold in Oct-1 transfectants, as measured by real-time PCR and western blot. In contrast, siRNA-mediated suppression of endogenous Oct-1 attenuated both the hPTTG1 mRNA and protein levels. Using confocal immunofluorescence imaging, Oct-1 and hPTTG1 were concordantly upregulated in pituitary (57 and 62%, n=79, P<0.01) and breast tumor specimens (57 and 42%, n=77, P<0.05) respectively. The results show that Oct-1 transactivates hPTTG1, and both proteins are concordantly overexpressed in endocrine tumors, thus offering a mechanism for endocrine tumor hPTTG1 abundance.

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.

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.

Human microRNA genes are frequently located at fragile sites and genomic regions involved in cancers

A large number of tiny noncoding RNAs have been cloned and named microRNAs (miRs). Recently, we have reported that miR-15a and miR-16a, located at 13q14, are frequently deleted and/or down-regulated in patients with B cell chronic lymphocytic leukemia, a disorder characterized by increased survival. To further investigate the possible involvement of miRs in human cancers on a genome-wide basis, we have mapped 186 miRs and compared their location to the location of previous reported nonrandom genetic alterations. Here, we show that miR genes are frequently located at fragile sites, as well as in minimal regions of loss of heterozygosity, minimal regions of amplification (minimal amplicons), or common breakpoint regions. Overall, 98 of 186 (52.5%) of miR genes are in cancer-associated genomic regions or in fragile sites. Moreover, by Northern blotting, we have shown that several miRs located in deleted regions have low levels of expression in cancer samples. These data provide a catalog of miR genes that may have roles in cancer and argue that the full complement of miRs in a genome may be extensively involved in cancers.