Expression of the PDGF alpha-receptor 1.5 kb transcript, OCT-4, and c-KIT in human normal and malignant tissues. Implications for the early diagnosis of testicular germ cell tumours and for our understanding of regulatory mechanisms

Oct4 reduction contributes to testicular injury of unilateral testicular torsion in mice model and apoptotic death of Sertoli cells through mediating CIP2A expression

This study explored the mechanism of ipsilateral testis injury after ipsilateral testicular torsion detorsion (T/D) and the potential testis-protective part of the octamer-binding transcription factor 4 (Oct4)-cancerous inhibitors of protein phosphatase 2A (CIP2A) axis in a T/D animal model and in ischemia-reperfusion (IR)-treated testicular Sertoli TM4 cells. Quantitative Polymerase chain reaction (PCR) and western blot (WB) confirmed the downregulation of both CIP2A and Oct4 expression in the testicular tissue from T/D mice compared with sham-operated mice. T/D model was then established in mice with upregulated Oct4 expression in the testis. Oct4 elevation restored CIP2A expression in testes after T/D treatment. Furthermore, we observed that an increase in Oct4 ameliorated the testicular damage caused by torsion in the testis. Biochemical analysis indicated that T/D treatment increased serum anti-sperm antibody levels, but reduced testosterone levels. Meanwhile, in testicular tissue, reactive oxygen species (ROS), malondialdehyde (MDA), and activity of testicular myeloperoxidase (MPO) enzymes were promoted, while glutathione peroxidase activity (GPx) was decreased by T/D injury. Notably, testicular Oct4 restoration partially counteracted the effect of T/D treatment on these biochemical indices. Hypoxia/reoxygenation (HR) treatment was applied to TM4 cells to mimic TT injury in vitro. A gain-of-function study showed that Oct4 overexpression partly counteracted the promoting role of HR in cell damage, apoptosis, and oxidative stress in TM4 cells. These observations provide novel insights into the possible biochemical mechanism underlying the mediation of the Oct4-CIP2A axis in T/D injury.

OCT4 Represses Inflammation and Cell Injury During Orchitis by Regulating CIP2A Expression

Octamer-binding transcription factor 4 (OCT4) and cancerous inhibitor of protein phosphatase 2A (CIP2A) are upregulated in testicular cancer and cell lines. However, its contribution to orchitis (testicular inflammation) is unclear and was thus, investigated herein. Cell-based experiments on a lipopolysaccharide (LPS)-induced orchitis mouse model revealed robust inflammation, apoptotic cell death, and redox disorder in the Leydig (interstitial), Sertoli (supporting), and, germ cells. Meanwhile, real-time quantitative PCR revealed low OCT4 and CIP2A levels in testicular tissue and LPS-stimulated cells. A gain-of-function study showed that OCT4 overexpression not only increased CIP2A expression but also repressed LPS-induced inflammation, apoptosis, and redox disorder in the aforementioned cells. Furthermore, the re-inhibition of CIP2A expression by TD-19 in OCT4-overexpressing cells counteracted the effects of OCT4 overexpression on inflammation, apoptosis, and redox equilibrium. In addition, our results indicated that the Keap1-Nrf2-HO-1 signaling pathway was mediated by OCT4 and CIP2A. These findings provide insights into the potential mechanism underlying OCT4- and CIP2A-mediated testicular inflammation.

Critical role of the fibroblast growth factor signalling pathway in Ewing's sarcoma octamer-binding transcription factor 4-mediated cell proliferation and tumorigenesis

Certain bone and soft tissue (BST) tumours harbour a chromosomal translocation [t(6;22)(p21;q12)], which fuses the Ewing's sarcoma (EWS) gene at 22q12 with the octamer-binding transcription factor 4 (Oct-4) gene at 6p21, resulting in the chimeric EWS-Oct-4 protein that possesses high transactivation ability. Although abnormal activation of signalling pathways can lead to human cancer development, the pathways underlying these processes in human BST tumours remain poorly explored. Here, we investigated the functional significance of fibroblast growth factor (FGF) signalling in human BST tumours. To identify the gene(s) involved in the FGF signalling pathway and potentially regulated by EWS-Oct-4 (also called EWS-POU5F1), we performed RNA-Seq analysis, electrophoretic mobility shift assays, chromatin immunoprecipitation assays, and xenograft assays. Treating GBS6 or ZHBTc4 cells-expressing EWS-Oct-4 with the small molecule FGF receptor (FGFR) inhibitors PD173074, NVPBGJ398, ponatinib, and dovitinib suppressed cellular proliferation. Gene expression analysis revealed that, among 22 Fgf and four Fgfr family members, Fgf-4 showed the highest upregulation (by 145-fold) in ZHBTc4 cells-expressing EWS-Oct-4. Computer-assisted analysis identified a putative EWS-Oct-4-binding site at +3017/+3024, suggesting that EWS-Oct-4 regulates Fgf-4 expression in human BST tumours. Fgf-4 enhancer constructs showed that EWS-Oct-4 transactivated the Fgf-4 gene reporter in vitro, and that overexpression of EWS-Oct-4 stimulated endogenous Fgf-4 gene expression in vivo. Finally, PD173074 significantly decreased tumour volume in mice. Taken together, these data suggest that FGF-4 signalling is involved in EWS-Oct-4-mediated tumorigenesis, and that its inhibition impairs tumour growth in vivo significantly.

Will Testicular Germ Cell Tumors Remain Untargetable?

Testicular Germ cell tumors (TGCT) represent the most common solid tumors affecting young men. They constitute a distinct entity because of their embryonic origin and their unique biological behavior. Recently, new preclinical data on genetic and epigenetic susceptibility profiles, biological signaling machinery as well as on molecular patterns of tumors and pathways of pathogenesis helped to elucidate the pathogenesis and the differentiation of TGCTs and to understand the mechanisms behind the development of resistance to treatment. In the present work, we have reviewed new clues to the development, differentiation and progression of TGCTs. We focus on the most important epigenetic and molecular biomarkers, and discussed their diagnostic and prognostic accuracy compared to the currently used biomarkers. The mechanisms underlying the development of resistance to cisplatin and commonly used chemotherapeutic agents are also discussed in detail. Finally, we summarize failed and ongoing clinical trials using targeted therapies in resistant TGCTs, and analyze the potential of new targeted therapies.

Loss of miR-514a-3p regulation of PEG3 activates the NF-kappa B pathway in human testicular germ cell tumors

Deregulation of microRNAs (miRNAs) contributes to the development and progression of many cancer types; however, their functions in the pathogenesis of testicular germ cell tumor (TGCT) remain unclear. Here, we determined miRNA expression profiles of TGCTs and normal testes using small RNA sequencing, and identified several deregulated miRNAs in TGCTs, including the miR-506~514 cluster. In functional studies in vitro we demonstrated that miR-514a-3p induced apoptosis through direct regulation of the paternally expressed gene 3 (PEG3), and ectopically expressed PEG3 could rescue the apoptotic effect of miR-514a-3p overexpression. Silencing of PEG3 or miR-514a-3p overexpression reduced nuclear accumulation of p50 and NF-κB reporter activity. Furthermore, PEG3 was co-immunoprecipitated with tumor necrosis factor receptor-associated factor 2 (TRAF2) in TGCT cell lysates. We propose a model of PEG3-mediated activation of NF-κB in TGCT. Loss of miR-514a-3p expression in TGCT increases PEG3 expression that recruits TRAF2 and activates the NF-kappa B pathway, which protects germ cells from apoptosis. Importantly, we observed strong expression of PEG3 and nuclear p50 in the majority of TGCTs (83% and 78%, respectively). In conclusion, our study describes a novel function for miR-514a-3p in TGCT and highlights an unrecognized mechanism of PEG3 regulation and NF-κB activation in TGCT.

The epigenetics of testicular germ cell tumors: looking for novel disease biomarkers

Testicular germ cell tumors (TGCT) are a group of heterogeneous, biologically diverse and clinically challenging neoplasms. Despite the relatively low incidence and mortality rates, a subgroup of patients with disseminated disease relapse after conventional therapy and have a dismal prognosis. Moreover, TGCT afflict mostly young men and have therapeutic peculiarities, with some patients showing resistance to cisplatin-based treatments and others being troubled by irreversible side effects, such as infertility. Most TGCT share a common tumorigenic pathway and are cytogenetically similar, making room for Epigenetics to explain its heterogeneity at pathological and clinical level. In this review, we summarize the foremost epigenetic alterations among TGCT focusing on their clinical potential as diagnostic, prognostic and predictive biomarkers.

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges

The production of spermatozoa relies on a pool of spermatogonial stem cells (SSCs), formed in infancy from the differentiation of their precursor cells, the gonocytes. Throughout adult life, SSCs will either self-renew or differentiate, in order to maintain a stem cell reserve while providing cells to the spermatogenic cycle. By contrast, gonocytes represent a transient and finite phase of development leading to the formation of SSCs or spermatogonia of the first spermatogenic wave. Gonocyte development involves phases of quiescence, cell proliferation, migration, and differentiation. Spermatogonia, on the other hand, remain located at the basement membrane of the seminiferous tubules throughout their successive phases of proliferation and differentiation. Apoptosis is an integral part of both developmental phases, allowing for the removal of defective cells and the maintenance of proper germ–Sertoli cell ratios. While gonocytes and spermatogonia mitosis are regulated by distinct factors, they both undergo differentiation in response to retinoic acid. In contrast to postpubertal spermatogenesis, the early steps of germ cell development have only recently attracted attention, unveiling genes and pathways regulating SSC self-renewal and proliferation. Yet, less is known on the mechanisms regulating differentiation. The processes leading from gonocytes to spermatogonia have been seldom investigated. While the formation of abnormal gonocytes or SSCs could lead to infertility, defective gonocyte differentiation might be at the origin of testicular germ cell tumors. Thus, it is important to better understand the molecular mechanisms regulating these processes. This review summarizes and compares the present knowledge on the mechanisms regulating mammalian gonocyte and spermatogonial differentiation.

Role of retinoic acid and platelet-derived growth factor receptor cross talk in the regulation of neonatal gonocyte and embryonal carcinoma cell differentiation

Neonatal gonocytes are direct precursors of spermatogonial stem cells, the cell pool that supports spermatogenesis. Although unipotent in vivo, gonocytes express pluripotency genes common with embryonic stem cells. Previously, we found that all-trans retinoic acid (RA) induced the expression of differentiation markers and a truncated form of platelet-derived growth factor receptor (PDGFR)β in rat gonocytes, as well as in F9 mouse embryonal carcinoma cells, an embryonic stem cell-surrogate that expresses somatic lineage markers in response to RA. The present study is focused on identifying the signaling pathways involved in RA-induced gonocyte and F9 cell differentiation. Mitogen-activated protein kinase kinase (MEK) 1/2 activation was required during F9 cell differentiation towards somatic lineage, whereas its inhibition potentiated RA-induced Stra8 expression, suggesting that MEK1/2 acts as a lineage specification switch in F9 cells. In both cell types, RA increased the expression of the spermatogonial/premeiotic marker Stra8, which is in line with F9 cells being at a stage before somatic-germline lineage specification. Inhibiting PDGFR kinase activity reduced RA-induced Stra8 expression. Interestingly, RA increased the expression of PDGFRα variant forms in both cell types. Together, these results suggest a potential cross talk between RA and PDGFR signaling pathways in cell differentiation. RA receptor-α inhibition partially reduced RA effects on Stra8 in gonocytes, indicating that RA acts in part via RA receptor-α. RA-induced gonocyte differentiation was significantly reduced by inhibiting SRC (v-src avian sarcoma [Schmidt-Ruppin A-2] viral oncogene) and JAK2/STAT5 (Janus kinase 2/signal transducer and activator of transcription 5) activities, implying that these signaling molecules play a role in gonocyte differentiation. These results suggest that gonocyte and F9 cell differentiation is regulated via cross talk between RA and PDGFRs using different downstream pathways.

Expression and differentiation between OCT4A and its Pseudogenes in human ESCs and differentiated adult somatic cells

The POU5F1 gene codes for the OCT4 transcription factor, which is one of the key regulators of pluripotency. Its transcription, alternative splicing, and alternative translation leading to the synthesis of the active, nuclear localized OCT4A has been described in detail. Much less, however, is known about actively transcribed OCT4 pseudogenes, several of which display high homology to OCT4A and can be expressed and translated into proteins. Using RT-PCR followed by pseudogene-specific restriction digestion, cloning, and sequencing we discriminate between OCT4A and transcripts for pseudogenes 1, 3 and 4. We show that expression of OCT4 and its pseudogenes follows a developmentally-regulated pattern in differentiating hESCs, indicating a tight regulatory relationship between them. We further demonstrate that differentiated human cells from a variety of tissues express exclusively pseudogenes. Expression of OCT4A can, however be triggered in adult differentiated cells by oxygen and FGF2-dependent mechanisms.

Control of mammalian germ cell entry into meiosis

Germ cells are unique in undergoing meiosis to generate oocytes and sperm. In mammals, meiosis onset is before birth in females, or at puberty in males, and recent studies have uncovered several regulatory steps involved in initiating meiosis in each sex. Evidence suggests that retinoic acid (RA) induces expression of the critical pre-meiosis gene Stra8 in germ cells of the fetal ovary, pubertal testis and adult testis. In the fetal testis, CYP26B1 degrades RA, while FGF9 further antagonises RA signalling to suppress meiosis. Failsafe mechanisms involving Nanos2 may further suppress meiosis in the fetal testis. Here, we draw together the growing knowledge relating to these meiotic control mechanisms, and present evidence that they are co-ordinately regulated and that additional factors remain to be identified. Understanding this regulatory network will illuminate not only how the foundations of mammalian reproduction are laid, but also how mis-regulation of these steps can result in infertility or germline tumours.

Recent advances in molecular and cell biology of testicular germ-cell tumors

Testicular germ-cell tumors (TGCTs) are the most frequent solid malignant tumors in men 20-40 years of age and the most frequent cause of death from solid tumors in this age group. TGCTs comprise two major histologic groups: seminomas and nonseminomas germ-cell tumors (NSGCTs). NSGCTs can be further divided into embryonal, carcinoma, Teratoma, yolk sac tumor, and choriocarcinoma. Seminomas and NSGCTs present significant differences in clinical features, therapy, and prognosis, and both show characteristics of the primordial germ cells. Many discovered biomarkers including OCT3/4, SOX2, SOX17, HMGA1, Nek2, GPR30, Aurora-B, estrogen receptor β, and others have given further advantages to discriminate between histological subgroups and could represent useful novel molecular targets for antineoplastic strategies. More insight into the pathogenesis of TGCTs is likely to improve disease management not only to better treatment of these tumors but also to a better understanding of stem cells and oncogenesis.

Targeting of herpes simplex virus 1 thymidine kinase gene sequences into the OCT4 locus of human induced pluripotent stem cells

The in vitro differentiation of human induced pluripotent stem cells (hiPSC) to generate specific types of cells is inefficient, and the remaining undifferentiated cells may form teratomas. This raises safety concerns for clinical applications of hiPSC-derived cellular products. To improve the safety of hiPSC, we attempted to site-specifically insert a herpes simplex virus 1 thymidine kinase (HSV1-TK) suicide gene at the endogenous OCT4 (POU5F1) locus of hiPSC. Since the endogenous OCT4 promoter is active in undifferentiated cells only, we speculated that the HSV1-TK suicide gene will be transcribed in undifferentiated cells only and that the remaining undifferentiated cells can be depleted by treating them with the prodrug ganciclovir (GCV) prior to transplantation. To insert the HSV1-TK gene at the OCT4 locus, we cotransfected hiPSC with a pair of plasmids encoding an OCT4-specific zinc finger nuclease (ZFN) and a donor plasmid harboring a promoter-less transgene cassette consisting of HSV1-TK and puromycin resistance gene sequences, flanked by OCT4 gene sequences. Puromycin resistant clones were established and characterized regarding their sensitivity to GCV and the site of integration of the HSV1-TK/puromycin resistance gene cassette. Of the nine puromycin-resistant iPSC clones analyzed, three contained the HSV1-TK transgene at the OCT4 locus, but they were not sensitive to GCV. The other six clones were GCV-sensitive, but the TK gene was located at off-target sites. These TK-expressing hiPSC clones remained GCV sensitive for up to 90 days, indicating that TK transgene expression was stable. Possible reasons for our failed attempt to selectively target the OCT4 locus are discussed.

Unravelling mechanisms of cisplatin sensitivity and resistance in testicular cancer

Testicular cancer is the most frequent solid malignant tumour type in men 20-40 years of age. At the time of diagnosis up to 50% of the patients suffer from metastatic disease. In contrast to most other metastatic solid tumours, the majority of metastatic testicular cancer patients can be cured with highly effective cisplatin-based chemotherapy. This review aims to summarise the current knowledge on response to chemotherapy and the biological basis of cisplatin-induced apoptosis in testicular cancer. The frequent presence of wild-type TP53 and the low levels of p53 in complex with the p53 negative feed-back regulator MDM2 contribute to cisplatin sensitivity. Moreover, the high levels of the pluripotency regulator Oct4 and as a consequence of Oct4 expression high levels of miR-17/106b seed family and pro-apoptotic Noxa and the low levels of cytoplasmic p21 (WAF1/Cip1) appear to be causative for the exquisite sensitivity to cisplatin-based therapy of testicular cancer. However, resistance of testicular cancer to cisplatin-based therapy does occur and can be mediated through aberrant levels of the above mentioned key players. Drugs targeting these key players showed, at least pre-clinically, a sensitising effect to cisplatin treatment. Further clinical development of such treatment strategies will lead to new treatment options for platinum-resistant testicular cancers.

Molecular biomarkers as potential targets for therapeutic strategies in human testicular germ cell tumors: an overview

Testicular germ cell tumors (TGCTs), the most common malignancy in males between 15 and 34 years of age and the most frequent cause of death from solid tumors in this age group. TGCTs can be subdivided into seminoma and non-seminoma germ cell tumors (NSGCTs), including embryonal cell carcinoma, choriocarcinoma, yolk sac tumor, and teratoma. Seminomas and NSGCTs do not only present distinctive clinical features, but they also show significant differences as far as therapy and prognosis are concerned. Seminomas are highly sensitive to both radiation and chemotherapy, with a good prognosis, non-seminomas are sensitive to platinum-based combination chemotherapy and are less susceptible to radiation, with the exception of teratomas. The different therapeutic outcome might be explained by inherent properties of the cells from which testicular neoplasia originate. The unique treatment sensitivity of TGCTs is unexplained so far, but it is likely to be related to intrinsic molecular characteristics of the PGCs/gonocytes, from which these tumors originate. Many discovered bio-markers including OCT3/4, SOX2, SOX17, HMGA1, HMGA2, PATZ1, GPR30, Aurora B, estrogen receptor β, and others have given further advantages to discriminate between histological subgroups. In addition, therapeutic approaches for the treatment of TGCTs have been proposed: humanized antibodies against receptors/surface molecules on cancer cells, inhibitors of serine-threonine, and tyrosine kinases, and others. The mini-review will be an overview on the molecular alterations identified in TGCTs and on novel targeted antineoplastic strategies that might help to treat chemotherapy resistant TGCTs.

Mutations in LRRC50 predispose zebrafish and humans to seminomas

Seminoma is a subclass of human testicular germ cell tumors (TGCT), the most frequently observed cancer in young men with a rising incidence. Here we describe the identification of a novel gene predisposing specifically to seminoma formation in a vertebrate model organism. Zebrafish carrying a heterozygous nonsense mutation in Leucine-Rich Repeat Containing protein 50 (lrrc50 also called dnaaf1), associated previously with ciliary function, are found to be highly susceptible to the formation of seminomas. Genotyping of these zebrafish tumors shows loss of heterozygosity (LOH) of the wild-type lrrc50 allele in 44.4% of tumor samples, correlating with tumor progression. In humans we identified heterozygous germline LRRC50 mutations in two different pedigrees with a family history of seminomas, resulting in a nonsense Arg488* change and a missense Thr590Met change, which show reduced expression of the wild-type allele in seminomas. Zebrafish in vivo complementation studies indicate the Thr590Met to be a loss-of-function mutation. Moreover, we show that a pathogenic Gln307Glu change is significantly enriched in individuals with seminoma tumors (13% of our cohort). Together, our study introduces an animal model for seminoma and suggests LRRC50 to be a novel tumor suppressor implicated in human seminoma pathogenesis.

Recent advances in the biology of germ cell tumors: implications for the diagnosis and treatment

Testicular germ cell tumors (TGCT), are the most frequent solid malignant tumors in men 20-40 yr of age, and the most frequent cause of death from solid tumors in this age group. TGCT can be subdivided into seminoma and nonseminoma germ cell tumors (NSGCT), including embryonal cell carcinoma, choriocarcinoma, yolk sac tumor, and teratoma. Seminomas and NSGCT do not only present distinctive clinical features, but they also show significant differences as far as therapy and prognosis are concerned. Many novel markers have given further advantages to discriminate between histological subgroups. In addition, therapeutic approaches for the treatment of TGCT have been proposed: humanized antibodies against receptors/surface molecules on cancer cells, inhibitors of serine-threonine, and tyrosine kinases, and others. The review will focus on the recent advances in the research of molecular alterations identified in TGCT and on novel targeted anti-neoplastic strategies that might help to treat chemotherapy-resistant TGCT.

Insights on neoplastic stem cells from gel-based proteomics of childhood germ cell tumors

BACKGROUND

Childhood germ cell tumors (cGCTs), believed to arise from transformed primordial germ cells by an unknown mechanism, provide a unique model system for investigating cell signaling, pluripotency, and the microenvironment of neoplastic stem cells (NSCs) in vivo. This is the first report of proteomics of cGCTs.

PROCEDURE

Four dysgerminomas (DYSs) and four childhood endodermal sinus tumors (cESTs), resembling self-renewing and differentiating NSCs, respectively, were selected. Proteomic studies were performed by 2-DE, SDS-PAGE, and cLC/MS/MS with protein database searching.

RESULTS

2-DE: 9 of 941 spots were differentially regulated with greater than a twofold change in spot volume for at least three of four gels in each group. Two of nine spots had P values for the t-test analysis of comparisons less than 0.001, while the remaining spots had P values from 0.013 to 0.191. Top-ranked proteins were identified in nine of nine spots with 4.0-38% sequence coverage. APOA1, CRK, and PDIA3 were up-regulated in cESTs. TFG, TYMP, VCP, RBBP, FKBP4, and BiP were up-regulated in DYSs. SDS-PAGE: Up-regulation of NF45 and FKBP4 was observed in four of four cESTs and DYSs, respectively. The fold-changes observed correspond with characteristic genetic changes.

CONCLUSION

Differential regulation of FKBP4 and NF45, combined with previous research on immunosuppressant binding, suggests that glucocorticoid receptor signaling merits further investigation in cGCTs and NSCs.

Histone methylation is a critical regulator of the abnormal expression of POU5F1 and RASSF1A in testis cancer cell lines

DNA and histone methylation are epigenetic modifications functioning in transcriptional control and have been implicated in the deregulation of gene expression in cancer. As a first step to determine if histone methylation could be involved in testis cancer pathogenesis, we performed immunofluorescent localization of histone H3 methylation at lysine 4 (H3-K4; gene activating) and lysine 9 (H3-K9; gene silencing) in healthy testis tissue and in samples of non-seminoma germ-cell tumours. In healthy testis, the distribution of histone H3 methylation was dependent on the developmental stage of spermatogenic cells and in non-seminoma, histone H3-K4 and K9 methylation was detected in all histological subtypes. This suggested that histone H3-K4 and K9 methylation could be associated with abnormal gene expression in non-seminoma. To determine the gene-specific function of histone H3 methylation, we proceeded to define the epigenetic status of key genes implicated in the pathogenesis of non-seminoma, namely the proto-oncogene POU5F1, which is overexpressed in testis cancer, and the tumour suppressor RASSF1A, which is aberrantly silenced. Cell lines representative of non-seminoma were treated with the chromatin-modifying drug, 5-aza-2'-deoxycytidine (5-aza-dC). Chromatin immunoprecipitation and real-time polymerase chain reaction analyses revealed that treatment with 5-aza-dC restored RASSF1A expression through a loss of gene silencing H3-K9 methylation and by retention of gene activating H3-K4 tri-methylation in the promoter region. In contrast, the expression of POU5F1 was reduced by 5-aza-dC and was associated with a loss of gene activating H3-K4 di-methylation in the promoter region. Analysis of DNA methylation revealed a slight reduction in DNA hypermethylation at the RASSF1A promoter, whereas the POU5F1 promoter remained mostly unmethylated and unaffected. Our results indicate that the effects of 5-aza-dC on histone methylation profiles are gene-specific and that aberrant histone modifications may serve as a principal means of misregulation of RASSF1A and POU5F1 expression in testis cancer.

Expression and interdependencies of pluripotency factors LIN28, OCT3/4, NANOG and SOX2 in human testicular germ cells and tumours of the testis

OCT3/4, NANOG, SOX2 and, most recently, LIN28 have been identified as key regulators of pluripotency in mammalian embryonic and induced stem cells, and are proven to be crucial for generation of the mouse germ-cell lineage. These factors are a hallmark of certain histological types of germ-cell tumours (GCTs). Here, we report novel information on the temporal and spatial expression pattern of LIN28 during normal human male germ-cell development as well as various types of GCTs. To investigate LIN28 expression, immunohistochemical analyses and quantitative proximity ligation assay-based TaqMan protein assays were applied on snap-frozen and formalin-fixed, paraffin-embedded samples as well as representative cell lines. LIN28 was found in primordial germ cells, gonocytes and pre-spermatogonia, in contrast to OCT3/4 and NANOG, which were found only in the first two stages. LIN28 was also found in all precursor lesions (carcinoma in situ and gonadoblastoma) of type II GCTs, as well as the invasive components seminoma and the non-seminomatous elements embryonal carcinoma and yolk sac tumour. Choriocarcinoma showed a heterogeneous pattern, while teratomas and spermatocytic seminomas (type III GCTs) were negative. This expression pattern suggests that LIN28 is associated with malignant behaviour of type II GCTs. Cell line experiments involving siRNA knockdown of LIN28, OCT3/4 and SOX2 showed that LIN28 plays a role in the maintenance of the undifferentiated state of both seminoma and embryonal carcinoma, closely linked to, and likely upstream of OCT3/4 and NANOG. In conclusion, LIN28 regulates the differentiation status of seminoma and embryonal carcinoma and is likely to play a related role in normal human germ-cell development.

Expression of OCT4 pseudogenes in human tumours: lessons from glioma and breast carcinoma

The POU family transcription factor OCT4 is required for maintaining the pluripotency of embryonic stem cells and for generating induced pluripotent stem cells. Although OCT4 is clearly shown to be expressed in some pluripotent germ cell tumours, its expression in human somatic tumours remains controversial. Some studies have shown that OCT4 is expressed in adult stem cells, somatic cancers and, further, cancer stem cells, while other studies failed to make such an observation. It is thus important to ascertain whether OCT4 is expressed in human somatic tumours. By using RT-PCR and sequencing analysis, three OCT4 pseudogenes, viz. OCT4-pg1, OCT4-pg3 and OCT4-pg4 but excluding the OCT4 gene, were found to be expressed in two types of human solid tumours, glioma and breast carcinoma, from which cancer stem cells had earlier been isolated. The protein expression of these pseudogenes was further demonstrated by immunochemistry and western blotting. Along with this, it was shown that OCT4 pseudogenes lacked OCT4-like activities. The expression of OCT4 splicing variant and various pseudogenes at both the mRNA and protein levels in human somatic tumours might call into question the reliability of the results regarding OCT4 expression and function in tumourigenesis. Hence, in investigations of OCT4 expression in cancers and stem cells, different approaches with appropriate controls would be desirable to exclude possibility of false-positive results.

Role of platelet-derived growth factors in the testis

Normal development and function of the testis are controlled by endocrine and paracrine signaling pathways. Platelet-derived growth factors (PDGFs) are growth factors that mediate epithelial-mesenchymal interactions in various tissues during normal and abnormal processes such as embryo development, wound healing, tissue fibrosis, vascular disorders, and cancer. PDGFs and their receptors (PDGFRs) have emerged as key players in the regulation of embryonic and postnatal development of the male gonad. Cells that express PDGFs and PDGFRs are found in the testis of mammals, birds, and reptiles, and their distribution, regulation, and function vary across species. Testicular PDGFs and PDGFRs appear after the process of sex determination in animals that use either genetic sex determination or environmental sex determination. Sertoli cells are the main PDGF-producing cells during the entire period of prenatal and postnatal testis development. Fetal Leydig cells and their precursors, adult Leydig cells and their stem cell precursors, peritubular myoid cells, cells of the blood vessels, and gonocytes are the testicular cell types expressing PDGFRs. Genetically targeted deletions of PDGFs, PDGFRs, PDGFR target genes or pharmacological silencing of PDGF signaling produce profound damage on the target cells that, depending on the developmental period, are under direct or indirect control of PDGF. PDGF signaling may also serve diverse functions outside of the realm of testis development, including testicular tumors. In this review, we provide a framework of the current knowledge to clarify the useful information regarding how PDGFs function in individual cells of the testis.

Cytoplasmic p21 expression levels determine cisplatin resistance in human testicular cancer

Platinum-based chemotherapies such as cisplatin are used as first-line treatment for many cancers. Although there is often a high initial responsiveness, the majority of patients eventually relapse with platinum-resistant disease. For example, a subset of testicular cancer patients still die even though testicular cancer is considered a paradigm of cisplatin-sensitive solid tumors, but the mechanisms of chemoresistance remain elusive. Here, we have shown that one key determinant of cisplatin-resistance in testicular embryonal carcinoma (EC) is high cytoplasmic expression of the cyclin-dependent kinase (CDK) inhibitor p21. The EC component of the majority of refractory testicular cancer patients exhibited high cytoplasmic p21 expression, which protected EC cell lines against cisplatin-induced apoptosis via CDK2 inhibition. Localization of p21 in the cytoplasm was critical for cisplatin resistance, since relocalization of p21 to the nucleus by Akt inhibition sensitized EC cell lines to cisplatin. We also demonstrated in EC cell lines and human tumor tissue that high cytoplasmic p21 expression and cisplatin resistance of EC were inversely associated with the expression of Oct4 and miR-106b seed family members. Thus, targeting cytoplasmic p21, including by modulation of the Oct4/miR-106b/p21 pathway, may offer new strategies for the treatment of chemoresistant testicular and other types of cancer.

Identification of a heritable model of testicular germ cell tumor in the zebrafish

Germ cell tumors (GCTs) affect infants, children, and adults and are the most common cancer type in young men. Progress in understanding the molecular basis of GCTs has been hampered by a lack of suitable animal models. Here we report the identification of a zebrafish model of highly penetrant, heritable testicular GCT isolated as part of a forward genetic screen for cancer susceptibility genes. The mutant line develops spontaneous testicular tumors at a median age of 7 months, and pedigree analysis indicates dominant inheritance of the GCT susceptibility trait. The zebrafish model exhibits disruption of testicular tissue architecture and the accumulation of primitive, spermatogonial-like cells with loss of spermatocytic differentiation. Radiation treatment leads to apoptosis of the tumor cells and tumor regression. The GCT-susceptible line can serve as a model for understanding the mechanisms regulating germ cells in normal development and disease and as a platform investigating new therapeutic approaches for GCTs.

EWS-Oct-4B, an alternative EWS-Oct-4 fusion gene, is a potent oncogene linked to human epithelial tumours

BACKGROUND

Characterisation of EWS-Oct-4 translocation fusion product in bone and soft-tissue tumours revealed a chimeric gene resulting from an in-frame fusion between EWS (Ewing's sarcoma gene) exons 1-6 and Oct-4 exons 1-4. Recently, an alternative form of the fusion protein between the EWS and Oct-4 genes, named EWS-Oct-4B, was reported in two types of epithelial tumours, a hidradenoma of the skin and a mucoepidermoid carcinoma of the salivary glands. As the N-terminal and POU domains of the EWS-Oct-4 and EWS-Oct-4B proteins are not structurally identical, we decided to investigate the functional consequences of the EWS-Oct-4B fusion.

METHODS

In this report, we have characterised the EWS-Oct-4B fusion protein. To investigate how the EWS-Oct-4B protein contributes to tumourigenesis in human cancers, we analysed its DNA-binding activity, subcellular localisation, transcriptional activation behaviour, and oncogenic properties.

RESULTS

We found that this new chimeric gene encodes a nuclear protein that binds DNA with the same sequence specificity as the parental Oct-4 protein or the fusion EWS-Oct-4 protein. We show that the nuclear localisation signal of EWS-Oct-4B is dependent on the POU DNA-binding domain, and we identified a cluster of basic amino acids, (269)RKRKR(273), in the POU domain that specifically mediates the nuclear localisation of EWS-Oct-4B. Comparison of the properties of EWS-Oct-4B and EWS-Oct-4 indicated that EWS-Oct-4B is a less-potent transcriptional activator of a reporter construct carrying the Oct-4-binding sites. Deletion analysis of the functional domains of EWS-Oct-4B revealed that the EWS N-terminal domain (NTD)(B), POU, and C-terminal domain (CTD) are necessary for its full transactivation potential. Despite its reduced activity as a transcriptional activator, EWS-Oct-4B regulated the expression of fgf-4 (fibroblast growth factor-4) and nanog, which are potent mitogens, as well as of Oct-4 downstream target genes, the promoters of which contain potential Oct-4-binding sites. Finally, ectopic expression of EWS-Oct-4B in Oct-4-null ZHBTc4 ES cells resulted in increased tumourigenic growth potential in nude mice.

CONCLUSION

These results suggest that the oncogenic effect of the t(6;22) translocation is due to the EWS-Oct-4B chimeric protein, and that alternative fusion of the EWS amino terminal domain to the Oct-4 DNA-binding domain produces another transforming chimeric product in human epithelial tumours.

Oct4 is expressed in human gliomas and promotes colony formation in glioma cells

There is increasing evidence that self-renewal capacity of cancer cells is critical for carcinogenesis; hence, it is vital to examine the expression and involvement of self-renewal regulatory genes in these cells. Here, we reported that Oct4, a well-known regulator of self-renewal in embryonic stem cells, was highly expressed in human gliomas and glioma cell lines, and the expression levels were increased in parallel with increasing glioma grades. In in vitro cell cultures, Oct4 was only expressed in rat C6 glioma cells and rat neural stem cells but not in rat brain differentiated cells. Downregulation of Oct4 expression by RNA interference in C6 cells was associated with reduced cell proliferation and colony formation. Further analysis revealed that Oct4 could upregulate phosphorylation of Stat3 to promote tumor cell proliferation. Overexpression of Oct4 in C6 cells increased the expression of nestin but decreased the expression of GFAP suggesting that Oct4 might inhibit the differentiation of glioma cells. Our findings may provide further evidence for the stem cell theory of carcinogenesis. In contrast, the results might also imply that Oct4 contributes to the existence of undifferentiated cells in gliomas.

Mutation in the DNA-binding domain of the EWS-Oct-4 oncogene results in dominant negative activity that interferes with EWS-Oct-4-mediated transactivation

The EWS-Oct-4 protein is a chimeric molecule in which the amino terminal domain (NTD) of the EWS becomes fused to the carboxy terminal domain (CTD) of the Oct-4 transcription factor. It was identified in human bone and soft-tissue tumors associated with t(6;22)(p21;q12). Using in vitro and in vivo systems, we found that the EWS-Oct-4 protein self-associates. The major domains required for self-association mapped to the EWS NTD (amino acids 70-163) and the POU DNA-binding domain. EWS-Oct-4 protein also associated with EWS-Oct-4 (V351P), which contains a mutation in the POU DNA-binding domain. Using electrophoretic mobility shift assays, we found that the EWS-Oct-4 (V351P) mutant interfered with wild-type EWS-Oct-4 DNA-binding activity. In addition, we found that EWS-Oct-4-mediated transcriptional activation was inhibited by EWS-Oct-4 (V351P) protein in vivo. Thus, this mutation in the POU DNA-binding domain results in a dominant negative protein. These findings suggest that the biological functions of the EWS-Oct-4 oncogene can be modulated by the dominant negative mutant EWS-Oct-4 (V351P).

Amelanotic Anorectal Malignant Melanoma: Case Report with Immunohistochemical Study and Literature Review

Epithelioid cell tumors presenting in the gastrointestinal tract are uncommon, but when they arise, arriving at a correct diagnosis is important. We report a case of anal malignant melanoma in an 82-year-old man who microscopically showed an epithelioid malignant tumor simulating a gastrointestinal stromal tumor. C-kit stain and Melan-A were diffusely and strongly positive, while HMB-45 was focally positive. This case illustrates the potential pitfall of relying on a single antibody or inadequate panel of immunohistochemical stains to confirm the diagnosis. We recommend to apply an adequate immunohistochemical panel which includes S-100 protein, HMB-45 and Melan-A in order to make an accurate diagnosis, and discuss the differential diagnosis and surgical treatment modalities.

Molecular and cell biology of testicular germ cell tumors

Although testicular germ cell tumors (TGCTs) are relatively uncommon, they are particularly important as they tend to affect children and young men, representing the most common tumor in male aged from 20 to 40years. TGCTs are a heterogeneous group of tumors, with specific peculiarities reflecting on epidemiologic distribution and clinic-pathological features. TGCTs show a high-cure rates in both seminomas and nonseminomas and represent the model of a curable neoplasia: sensitive serum tumor markers, accurate prognostic classification, contribute to a high effectiveness of cancer therapy. However, up to 30% of patients diagnosed with metastatic nonseminomas do not achieve a durable remission, and in metastatic teratomas cisplatin-based treatment resistance has been observed. These different prognostic and therapeutic features of TGCTs highlight the need for a better understanding of the molecular biology of TGCT, that could help to improve disease management and to tailor aggressiveness of treatment to the severity of the prognosis.

Neuron-like differentiation and selective ablation of undifferentiated embryonic stem cells containing suicide gene with Oct-4 promoter

In vivo transplantation of undifferentiated embryonic stem (ES) cells can produce teratomas with uncontrolled cell proliferation. Although ES cells may be attractive candidates for human cell-replacement therapy in the future, the major limitation of its application to the therapy is teratoma formation. In the present study, ES cells containing herpes simplex virus-thymidine kinase (HSV-tk) transgene for a suicide gene expression under the control of the Oct-4 promoter was used for ablation of undifferentiated ES cells, which may produce teratomas, using three-dimensional cell culture system allowing a multilayer cell construct. Selective ablation of undifferentiated ES cells expressing HSV-tk gene under the control of Oct-4 promoter was achieved by ganciclovir treatment. Surviving ES cells after ganciclovir treatment expressed several neuron-associated markers such as synaptophysin, beta-tubulin, vesicular glutamate transporter 1, syntaxin, protein kinase C and glial fibrillary acidic protein (GFAP) but not Oct-4. Coexpression of synaptophysin as a marker of neuronal synapse and GFAP as that of glial fibers in the surviving ES cells revealed finely structured neuronal network. Furthermore, decrease of Ki-67 proliferative index was detected in the surviving ES cells. In conclusion, selective ablation of undifferentiated ES cells by a suicide gene decreases proliferative activity and induces neuron-like differentiation in ES cells.

[Value of targeted treatment for testicular cancer: from molecular approaches to clinical possibilities]

Due to the introduction of tyrosine kinase-inhibitors in the treatment of metastatic renal cell cancer, targeted therapy raises hopes for other urological tumors as well. Even if excellent cure rates, achieved by standardization of diagnosis und therapy, have made testicular cancer a curable disease, up to 6% of young patients still die from tumors refractory to therapy. The quality of life of patients in advanced stages needing aggressive treatment should be improved by new therapies with reduced side effects. The role of tyrosine kinase inhibitors and angiogenesis inhibitors as well as intervention in the cell cycle and induction of apoptosis are discussed.

Application of stem cell markers in search for neoplastic germ cells in dysgenetic gonads, extragonadal tumours, and in semen of infertile men

Germ cell tumours (GCTs) are a complex entity. Current areas of attention include early detection and avoidance of unnecessary over-treatment. Novel findings regarding diagnosis of GCTs located in various anatomical sites are described, particularly testicular GCTs and their common progenitor, carcinoma in situ (CIS). Recognition of CIS enables intervention before tumour development, but nevertheless, testicular GCTs are sporadically diagnosed at the pre-invasive stage where minimal treatment is necessary. As presence of CIS is asymptomatic, a simple screening method is needed when CIS is suspected (i.e. in males investigated for infertility). To develop approaches for early detection CIS gene expression studies have been performed showing many similarities with embryonic stem cells with confirmation of established markers (i.e. PLAP, OCT-3/4, KIT) and identification of novel markers (i.e. AP-2 gamma, NANOG). We have reported a very promising new approach of AP-2 gamma (or OCT3/4) based immunocytological semen analysis (specificity 93.6%, sensitivity 54.5%). Comparative studies of gonadal/extragonadal GCTs have revealed resemblance pointing towards similar, but not identical, origins. Moreover, infertility and testicular cancer are connected in the 'Testicular Dysgenesis Syndrome' and 25% of contralateral testes from testicular GCT patients harbour dysgenetic features, including impaired spermatogenesis. Thus, recent data have provided potential diagnostic tools including CIS detection in semen, microarray-based tumour classification, additional serological GCT markers, and novel stem cell markers for immunohistochemical diagnosis of gonadal and extragonadal GCTs. Many CIS candidate genes are yet uninvestigated, and information from these could increase knowledge about CIS tumour initiation/progression and be used for optimisation of a non-invasive detection method.

Sequence variation in the human transcription factor gene POU5F1

Background

POU5F1 expression is required to maintain stem cell pluripotency and for primordial germ cells to retain proliferative capability in embryonic development. Recent evidence suggests that POU5F1 may also be a testicular germ cell carcinoma (TGCC) oncogene, and POU5F1 variation may influence TGCC risk. As an important first step to a genetic association study, we sought to identify all common sequence variants in an 11.3 kb region containing POU5F1, and to describe the linkage disequilibrium patterns, using DNA from individuals of African-descent (AD) and European-descent (ED).

Results

A higher number of polymorphisms was observed in the AD (n = 102) versus ED (n = 82) population. Among the 41 observed haplotypes, 21 (51%) and 12 (29%) were unique to the AD and ED populations, respectively, while 8 (20%) were observed in both. The number of tagging polymorphisms necessary to explain at least 80% of common variation (minor allele frequency ≥ 0.10) due to the remaining untyped polymorphisms was 17 for an AD and 10 for an ED population, providing a 4.0- and 7.0-fold gain in genotyping efficiency for characterizing nucleotide variation, respectively.

Conclusion

POU5F1 is highly polymorphic, however a smaller subset of polymorphisms can tag the observed genetic variation with little loss of information.

Absence of OCT4 expression in somatic tumor cell lines

The POU-domain transcription factor OCT4 is associated with the pluripotent state of cells comprising the inner cell mass of pre-implantation embryos and has been known to play a critical role in the maintenance of pluripotency of embryonic stem cells. Reactivation of OCT4 expression is postulated to occur in differentiated cells that have undergone carcinogenesis, or tumor formation. In contrast to earlier studies, recent reports describe OCT4 expression in several human tumor cell lines. To resolve the apparent discrepancy in OCT4 expression between earlier and recent studies, we determined OCT4 expression in the cervical carcinoma cell line HeLa and the breast cancer cell line MCF7 in comparison with the human teratoma cell line nTera by immunofluorescence, Western blot, and RT-PCR analyses. We were unable to detect staining of the OCT4 transcription factor in the nucleus of HeLa and MCF7 cells by immunofluorescence using two different monoclonal antibodies. Faint cytoplasmic staining in HeLa and MCF7 cells was observed; however, no OCT4 signal could be detected by Western blot analysis. In addition, we were unable to detect significant levels of OCT4 mRNA in HeLa and in MCF7 cells by RT-PCR. Furthermore, the OCT4 promoter region is highly methylated in HeLa and MCF7 cells. We argue that recent reports of OCT4 expression in these and other cancer cell lines could actually be attributed to OCT4 pseudogene expression or misinterpretation of background signals in immunofluorescence experiments. In conclusion, we emphasize the need for adequate controls in investigations of OCT4 expression in somatic cell lines by immunofluorescence and RT-PCR.

The EWS-Oct-4 fusion gene encodes a transforming gene

The t(6;22)(p21;q12) translocation associated with human bone and soft-tissue tumours results in a chimaeric molecule fusing the NTD (N-terminal domain) of the EWS (Ewing's sarcoma) gene to the CTD (C-terminal domain) of the Oct-4 (octamer-4) embryonic gene. Since the N-terminal domains of EWS and Oct-4 are structurally different, in the present study we have assessed the functional consequences of the EWS-Oct-4 fusion. We find that this chimaeric gene encodes a nuclear protein which binds DNA with the same sequence specificity as the parental Oct-4 protein. Comparison of the transactivation properties of EWS-Oct-4 and Oct-4 indicates that the former has higher transactivation activity for a known target reporter gene containing Oct-4 binding. Deletion analysis of the functional domains of EWS-Oct-4 indicates that the EWS (NTD), the POU domain and the CTD of EWS-Oct-4 are necessary for full transactivation potential. EWS-Oct-4 induced the expression of fgf-4 (fibroblast growth factor 4) and nanog, which are potent mitogens as well as Oct-4 downstream target genes whose promoters contain potential Oct-4-binding sites. Finally, ectopic expression of EWS-Oct-4 in Oct-4-null ZHBTc4 ES (embryonic stem) cells resulted in increased tumorigenic growth potential in nude mice. These results suggest that the oncogenic effect of the t(6;22) translocation is due to the EWS-Oct-4 chimaeric protein and that fusion of the EWS NTD to the Oct-4 DNA-binding domain produces a transforming chimaeric product.

Transcriptional regulation of a new variant of human platelet-derived growth factor receptor alpha transcript by E2F-1

Platelet-derived growth factors (PDGFs) and their receptors play an important role in cell proliferation, angiogenesis, and differentiation during normal development, and have also been implicated in tumorigenesis. In this study, we identified a novel variant of human PDGF receptor alpha mRNA (type II), which contains the same open reading frame as the known PDGF receptor alpha mRNA (type I) but a different 5'-untranslated region (5'-UTR). The 5'-UTR of the type II transcript was identified as a 363-bp exon located in intron 1 at position +1,210 to +1,572 relative to the transcriptional initiation site of the type I transcript. This type II transcript was expressed in a subset of human cell lines, such as MG-63 and MNNG/HOS cells. Moreover, transcription of the type II, but not the type I, was regulated by E2F-1 through an E2F-1-responsive site located at position +1,086/+1,093 downstream of the transcriptional initiation site of the type I transcript. Furthermore, epigenetic modulation might be involved in the expression of the type II transcript. Our findings provide new insights into the regulatory mechanism of PDGF receptor alpha transcription in normal and tumor cells.

OCT4: biological functions and clinical applications as a marker of germ cell neoplasia

Germ cell tumours (GCTs) are a heterogeneous group of neoplasms, which develop in the gonads as well as in extragonadal sites, that share morphological patterns and an overall good prognosis, owing to their responsiveness to current surgical, chemotherapeutic, and radiotherapeutic measures. GCTs demonstrate extremely interesting biological features because of their close relationships with normal embryonal development as demonstrated by the pluripotentiality of some undifferentiated GCT variants. The similarities between GCTs and normal germ cell development have made it possible to identify possible pathogenetic pathways in neoplastic transformation and progression of GCTs. Genotypic and immunophenotypic profiles of these tumours are also useful in establishing and narrowing the differential diagnosis in cases of suspected GCTs. Recently, OCT4 (also known as OCT3 or POU5F1), a transcription factor that has been recognized as fundamental in the maintenance of pluripotency in embryonic stem cells and primordial germ cells, has been proposed as a useful marker for GCTs that exhibit features of pluripotentiality, specifically seminoma/dysgerminoma/germinoma and embryonal carcinoma. The development of commercially available OCT4-specific antibodies suitable for immunohistochemistry on paraffin-embedded specimens has generated increasing numbers of reports of OCT4 expression in a wide variety of gonadal and extragonadal GCTs. OCT4 immunostaining has been shown to be a sensitive and specific marker for seminomatous/(dys)germinomatous tumours and in embryonal carcinoma variants of non-seminomatous GCTs, whether in primary gonadal or extragonadal sites or in metastatic lesions. Therefore, OCT4 immunohistochemistry is an additional helpful marker both in the differential diagnosis of specific histological subtypes of GCTs and in establishing a germ cell origin for some metastatic tumours of uncertain primary. OCT4 expression has also been reported in pre-invasive conditions such as intratubular germ cell neoplasia, unclassified (IGCNU) and the germ cell component of gonadoblastoma. Additionally, OCT4 immunostaining shows promise as a useful tool in managing patients known to be at high risk for the development of invasive GCTs.

Developmental model for the pathogenesis of testicular carcinoma in situ: genetic and environmental aspects

Carcinoma in situ testis (CIS), also known as intratubular germ cell neoplasia (ITGCN), is a pre-invasive precursor of testicular germ cell tumours, the commonest cancer type of male adolescents and young adults. In this review, evidence supporting the hypothesis of developmental origin of testicular germ cell cancer is summarized, and the current concepts regarding aetiology and pathogenesis of this disease are critically discussed. Comparative studies of cell surface proteins (e.g. PLAP and KIT), some of the germ cell-specific markers (e.g. MAGEA4, VASA, TSPY and NY-ESO-1), supported by studies of regulatory elements of the cell cycle (e.g. p53, CHK2 and p19-INK4d) demonstrated a close similarity of CIS to primordial germ cells and gonocytes, consistent with the pre-meiotic origin of CIS. Recent gene expression profiling studies showed that CIS cells closely resemble embryonic stem cells (ESCs). The abundance of factors associated with pluripotency (NANOG and OCT-3/4) and undifferentiated state (AP-2gamma) may explain the remarkable pluripotency of germ cell neoplasms, which are capable of differentiating to various somatic tissue components of teratomas. Impaired gonadal development resulting in the arrest of gonocyte differentiation and retention of its embryonic features, associated with an increasing genomic instability, is the most probable model for the pathogenesis of CIS. Genomic amplification of certain chromosomal regions, e.g. 12p, may facilitate survival of CIS and further invasive progression. Genetic studies, have so far not identified gene polymorphisms predisposing to the most common non-familial testicular cancer, but this research has only recently begun. Association of CIS with other disorders, such as congenital genital malformations and some forms of impaired spermatogenesis, all rising in incidence in a synchronous manner, led to the hypothesis that CIS might be a manifestation of testicular dysgenesis syndrome (TDS). The aetiology of TDS including testicular cancer remains to be elucidated, but epidemiological trends suggest a primary role for environmental factors, probably combined with genetic susceptibility.

Amplification and Overexpression of the KIT Gene Is Associated with Progression in the Seminoma Subtype of Testicular Germ Cell Tumors of Adolescents and Adults

We have previously identified amplification at 4q12 in testicular germ cell tumors of adolescents and adults centered around the KIT gene encoding a tyrosine kinase transmembrane receptor. Analysis of primary testicular germ cell tumors totaling 190 cases revealed 21% of the seminoma subtype with an increased copy number of KIT whereas this change was rarely found in the nonseminomas. In most cases, gain of KIT did not include the immediately flanking noncoding DNA or the flanking genes KDR and PDGFRA. Increased copy number of KIT was not found in the putative precursor lesion, carcinoma in situ (CIS), adjacent to tumor with this change. KIT overexpression was found independent of gain and KIT immunostaining was stronger in selected cases with gain of KIT compared to those without. Taken together with activating mutations of KIT in exon 17 identified in 13% of seminomas, this suggests that the KIT gene product plays a role in the progression of CIS towards seminoma, the further understanding of which may lead to novel less toxic therapeutic approaches.

Testicular germ cell tumours: the paradigm of chemo-sensitive solid tumours

Testicular germ cell tumours (TGCTs) are the most frequent solid malignant tumour in men 20-40 years of age and the most frequent cause of death from solid tumours in this age group. Up to 50% of the patients suffer from metastatic disease at diagnosis. The majority of metastatic testicular cancer patients, in contrast to most other metastatic solid tumours, can be cured with highly effective cisplatin-based chemotherapy. From a genetic point of view, almost all TGCTs in contrast to solid tumours are characterised by the presence of wild type p53. High p53 expression levels are associated with elevated Mdm2 levels and a loss of p21(Waf1/Cip1) expression suggesting a changed functionality of p53. Expression levels of other proteins involved in the regulation of cell cycle progression indicate a deregulated G1-S phase checkpoint in TGCTs. After cisplatin-induced DNA damage, the increasing levels of p53 lead to the trans-activation of a number of genes but not of p21(Waf1/Cip1), preferentially directing TGCT cells into apoptosis or programmed cell death, both via the mitochondrial and the death receptor apoptosis pathways. The sensitivity of TGCTs to chemotherapeutic drugs may lay in the susceptibility of germ cells to apoptosis. Taken together, this provides TGCT as a tumour type model to investigate and understand the molecular determinants of chemotherapy sensitivity of solid tumours. This review aims to summarise the current knowledge on the biological basis of cisplatin-induced apoptosis and response to chemotherapy in TGCTs.

Stimulation of Oct-4 Activity by Ewing's Sarcoma Protein

The Oct-4 gene encodes a transcription factor that is expressed in embryonic stem (ES) cells and germ cells. Oct-4 is known to function as a transcriptional activator of genes involved in maintaining an undifferentiated totipotent state and possibly in preventing expression of genes activated during differentiation. In addition, it is a putative proto-oncogene and a critical player in the genesis of human testicular germ cell tumors. Although much effort has gone toward characterizing Oct-4, there is still little known about the molecular mechanisms and the proteins that regulate Oct-4 function. To identify cofactors that control Oct-4 function in vivo, we used a recently developed bacterial two-hybrid screening system and isolated a novel ES cell-derived cDNA encoding Ewing's sarcoma protein (EWS). EWS is a proto-oncogene and putative RNA-binding protein involved in human cancers. By using glutathione-S-transferase (GST) pull-down assays, we were able to confirm the interaction between Oct-4 and EWS in vitro, and moreover, coimmunoprecipitation and colocalization studies have shown that these proteins also associate in vivo. We have mapped the EWS-interacting region to the POU domain of Oct-4. In addition, three independent sites on EWS are involved in binding to Oct-4. In this study, we report that Oct-4 and EWS are coexpressed in the pluripotent mouse and human ES cells. Consistent with its ability to bind to and colocalize with Oct-4, ectopic expression of EWS enhances the transactivation ability of Oct-4. Moreover, a chimeric protein generated by fusion of EWS (1-295) to the GAL4 DNA-binding domain significantly increases promoter activity of a reporter containing GAL4 DNA-binding sites, suggesting the presence of a strong activation domain within EWS. Taken together, our results suggest that Oct-4-mediated transactivation is stimulated by EWS.

Expression and mutational analysis of tyrosine kinase receptors c-kit, PDGFRalpha, and PDGFRbeta in ovarian cancers

Most women with epithelial ovarian cancer are diagnosed with advanced disease. Despite surgery and initial tumor reduction by standard chemotherapy, the tumors frequently recur and the patients eventually die of their disease. New drugs that inhibit tyrosine kinase receptors (TKRs) are being investigated for treatment and this study was undertaken to determine the expression and mutational state for 3 TKRs (c-kit, platelet-derived growth factor receptor [PDGFR] alpha, and PDGFR beta) in ovarian cancer. Tissue arrays containing 84 epithelial ovarian tumors were studied by immunohistochemistry with antibodies specific for c-kit, PDGFR alpha, and PDGFR beta. Immunoreactivity was detected in 78% of the tumor to at least one TKR. PDGFR alpha was expressed in the largest percentage of ovarian tumors (58%) whereas 29% expressed PDGFR beta. Two commercial antibodies against c-kit were studied and 33% of the tumors stained with one but only 6% were interpreted as positive with the second antibody. Activation of TKRs may occur through mutations but, by sequence analysis, no mutations were detected in 6 ovarian tumors with elevated immunoreactivity for each of the TKRs (c-kit, PDGFR alpha, and PDGFR beta). Tyrosine kinase receptors could also be activated through autocrine or paracrine stimulation of receptor by its ligand. Of 43 (35%) tumors tested for both c-kit receptor and its ligand (stem cell factor), 15 expressed both proteins indicating the possibility that this autocrine stimulation feedback loop is a factor in the growth of some ovarian cancers. This study demonstrates that PDGFR alpha, PDGFR beta, and c-kit are expressed in a high percentage of epithelial ovarian cancers suggesting that tyrosine kinase inhibitors may be useful in the treatment of these tumors.

Testicular germ-cell tumours in a broader perspective

The germ-cell tumours are a fascinating group of neoplasms because of their unusual biology and the spectacular therapeutic results that have been obtained in these tumours. Traditionally, this group of neoplasms is presented in an organ-oriented approach. However, recent clinical and experimental data convincingly demonstrate that these neoplasms are one disease with separate entities that can manifest themselves in different anatomical sites. We propose five entities, in which the developmental potential is determined by the maturation stage and imprinting status of the originating germ cell. Recent progress begins to explain the apparent unpredictable development of germ-cell tumours and offers a basis for understanding their exquisite sensitivity to therapy.