Activation of Wnt/beta-catenin signaling in distinct histologic subtypes of human germ cell tumors

Beta-Catenin Alterations in Postchemotherapy Yolk Sac Tumor, Postpubertal-Type With Enteroblastic Features

Postchemotherapy postpubertal-type yolk sac tumors (YST) with glandular and solid phenotypes are aggressive and commonly resistant to systemic chemotherapy. These neoplasms show morphologic features that significantly overlap with those of somatic carcinomas with "enteroblastic" or "fetal" phenotype (the preferred terminology depends on the site of origin). They often present as late or very late recurrences, and their diagnosis is challenging because they frequently affect patients in an age group at risk for carcinomas of somatic origin. Recently, we incidentally identified examples of postchemotherapy glandular and solid YST with "enteroblastic" phenotypes and nuclear expression of beta-catenin, prompting us to further evaluate the prevalence of this phenomenon. We found nuclear expression of beta-catenin in 10 (29%) of 34 such tumors. A subset of cases with nuclear beta-catenin expression was further analyzed with a DNA sequencing panel (n = 6) and fluorescence in situ hybridization for isochromosome 12p [i(12p); n = 5]. Sequencing identified exon 3 CTNNB1 variants in 3 (50%) of 6 analyzed cases, and fluorescence in situ hybridization was positive for i(12p) in 5 of 5 cases. In conclusion, a significant subset of postchemotherapy YST with glandular or solid architecture and "enteroblastic" phenotype demonstrates beta-catenin alterations, suggesting that activation of Wnt signaling may play a role in the progression of these neoplasms. Moreover, nuclear beta-catenin expression in these tumors represents a potential diagnostic pitfall given that carcinomas of true somatic origin with overlapping morphology may also be positive for this marker.

Clinical Challenges in the Management of Malignant Ovarian Germ Cell Tumours

Nonepithelial ovarian cancers (NEOC) are a group of rare malignancies, including germ cell tumours (GCT) and sex cord-stromal tumours (SCST), along with small-cell carcinomas and sarcomas. GCTs represent 2-5% of ovarian cancers, with a yearly incidence of 4:100,000, and they usually affect young women and adolescents. Precursory germ cells of the ovary form the basis of GCT. They are histologically classified into primitive GCT, teratomas, and monodermal and somatic-type tumours associated with dermoid cysts. A primitive GCT can be either a yolk sac tumour (YST), dysgerminoma, or mixed germ cell neoplasm. Teratomas are either mature (benign) or immature (malignant). Given that malignant GCTs occur rarely compared to epithelial ovarian tumours (EOC), greater focus is required in their diagnosis and treatment. In this article, we review the epidemiology, clinical manifestations, diagnosis, and molecular biology, along with the management and therapeutic challenges.

Molecular Biology of Pediatric and Adult Ovarian Germ Cell Tumors: A Review

Ovarian germ cell tumors (OGCTs) are rare in adults; indeed, they occur predominantly in children, adolescents, and young adults, and they account for approximately 11% of cancer diagnoses in these groups. Because OGCTs are rare tumors, our current understanding of them is sparse; this is because few studies have investigated the molecular basis of pediatric and adult cancers. Here, we review the etiopathogenesis of OGCTs in children and adults, and we address the molecular landscape of these tumors, including integrated genomic analysis, microRNAs, DNA methylation, the molecular implications of treatment resistance, and the development of in vitro and in vivo models. An elucidation of potential molecular alterations may provide a novel field for understanding the pathogenesis, tumorigenesis, diagnostic markers, and genetic peculiarity of the rarity and complexity of OGCTs.

Analysis of the genomic landscape of yolk sac tumors reveals mechanisms of evolution and chemoresistance

Yolk sac tumors (YSTs) are a major histological subtype of malignant ovarian germ cell tumors with a relatively poor prognosis. The molecular basis of this disease has not been thoroughly characterized at the genomic level. Here we perform whole-exome and RNA sequencing on 41 clinical tumor samples from 30 YST patients, with distinct responses to cisplatin-based chemotherapy. We show that microsatellite instability status and mutational signatures are informative of chemoresistance. We identify somatic driver candidates, including significantly mutated genes KRAS and KIT and copy-number alteration drivers, including deleted ARID1A and PARK2, and amplified ZNF217, CDKN1B, and KRAS. YSTs have very infrequent TP53 mutations, whereas the tumors from patients with abnormal gonadal development contain both KRAS and TP53 mutations. We further reveal a role of OVOL2 overexpression in YST resistance to cisplatin. This study lays a critical foundation for understanding key molecular aberrations in YSTs and developing related therapeutic strategies.

A rare case of retroperitoneal teratoma with obstructed hemivagina and ipsilateral renal anomaly (OHVIRA) syndrome

A 9-month-old girl presented with progressive abdominal distension. Imaging revealed a huge cystic mass in the left retroperitoneum with solid components. The right kidney was absent and hydrometrocolpos was found. Tumour drainage and complete surgical excision were performed. A bulge in the right side of the uterus, suggestive of a uterine anomaly, was seen on laparoscopic observation. Pathology was consistent with teratoma with a small portion of immature neural tissue. The patient was discharged in good condition and was advised regular follow-up.

Primary intracranial pure endodermal sinus tumor: A retrospective series of 6 cases in a single center and a systematic review of overall survival

BACKGROUND

Primary intracranial pure endodermal sinus tumor (EST) is a rare malignant nongerminomatous germ cell tumor. There is still lack of knowledge about the treatment and prognosis.

METHODS

We studied 6 cases of primary intracranial pure EST patients in Beijing Tiantan Hospital from June 2009 to June 2015. A comprehensive literature search was performed on Pubmed's electronic database using the search terms "primary intracranial endodermal sinus tumor", "primary intracranial yolk sac tumor" and "malignant germ cell tumor". Survival rates based on age, gender, tumor location, treatment, resection degree and metastatis were collected and analyzed.

RESULTS

Total resection was achieved in three patients and subtotal resection was achieved in three patients. Blood AFP level continuously decreased after tumor removal. In our case series, the longest survival time was 99 months; this patient received surgery+adjuvant therapy. Fifty-two cases were eligible and met the inclusion criteria for the review analysis. The majority of the population were in the young child to adolescent age and there is a male predominance in this study. In the Kaplan-Meier survival analysis, age, gender, tumor location and metastasis did not affect patients' OS. Better OS was found in patients who had subtotal and gross total resection of the tumor. Patients who had surgery combined with adjuvant therapy showed better OS compared to those who just had surgery.

CONCLUSION

Total resection of the tumor is necessary and EST is sensitive to adjuvant therapy.

Metastatic Mixed Germ Cell Tumour with Embryonal Carcinoma and Choriocarcinoma in a Female Eurasian Harvest Mouse (Micromys minutus)

Mixed germ cell tumours occur rarely in veterinary species. This report describes a case of metastatic mixed germ cell tumour in a female Eurasian harvest mouse (Micromys minutus). The tumour was extensive in one ovary and the uterus, and was characterized by two distinct tumour cell populations with features typical of embryonal carcinoma (EC) and choriocarcinoma (CC). Metastases of CC to the lungs and liver were observed. The exact origin of the CC was unclear, but the possibility of a non-gestational CC is favoured, given the context of a mixed germ cell tumour and lack of p53 expression. EC diagnosis was confirmed by immunohistochemical labelling of CD30 and lack of immunoreactivity for c-Kit. In addition, membranous β-catenin expression was present in the EC component, indicating an inactive Wnt/β-catenin pathway, which is required for the maintenance of pluripotency.

Predicting Gonadal Germ Cell Cancer in People with Disorders of Sex Development; Insights from Developmental Biology

The risk of gonadal germ cell cancer (GGCC) is increased in selective subgroups, amongst others, defined patients with disorders of sex development (DSD). The increased risk is due to the presence of part of the Y chromosome, i.e., GonadoBlastoma on Y chromosome GBY region, as well as anatomical localization and degree of testicularization and maturation of the gonad. The latter specifically relates to the germ cells present being at risk when blocked in an embryonic stage of development. GGCC originates from either germ cell neoplasia in situ (testicular environment) or gonadoblastoma (ovarian-like environment). These precursors are characterized by presence of the markers OCT3/4 (POU5F1), SOX17, NANOG, as well as TSPY, and cKIT and its ligand KITLG. One of the aims is to stratify individuals with an increased risk based on other parameters than histological investigation of a gonadal biopsy. These might include evaluation of defined susceptibility alleles, as identified by Genome Wide Association Studies, and detailed evaluation of the molecular mechanism underlying the DSD in the individual patient, combined with DNA, mRNA, and microRNA profiling of liquid biopsies. This review will discuss the current opportunities as well as limitations of available knowledge in the context of predicting the risk of GGCC in individual patients.

Human germ cell tumours from a developmental perspective

Human germ cell tumours (GCTs) are derived from stem cells of the early embryo and the germ line. They occur in the gonads (ovaries and testes) and also in extragonadal sites, where migrating primordial germ cells are located during embryogenesis. This group of heterogeneous neoplasms is unique in that their developmental potential is in effect determined by the latent potency state of their cells of origin, which are reprogrammed to omnipotent, totipotent or pluripotent stem cells. Seven GCT types, defined according to their developmental potential, have been identified, each with distinct epidemiological and (epi)genomic features. Heritable predisposition factors affecting the cells of origin and their niches likely explain bilateral, multiple and familial occurrences of the different types of GCTs. Unlike most other tumour types, GCTs are rarely caused by somatic driver mutations, but arise through failure to control the latent developmental potential of their cells of origin, resulting in their reprogramming. Consistent with their non-mutational origin, even the malignant tumours of the group are characterized by wild-type TP53 and high sensitivity for DNA damage. However, tumour progression and the rare occurrence of treatment resistance are driven by embryonic epigenetic state, specific (sub)chromosomal imbalances and somatic mutations. Thus, recent progress in understanding GCT biology supports a comprehensive developmental pathogenetic model for the origin of all GCTs, and provides new biomarkers, as well as potential targets for treatment of resistant disease.

New insights into germ cell tumor genomics

BACKGROUND

Testicular germ cell tumors (GCTs) represent the most common malignancy in young men. While GCTs represent a model for curable solid tumors due to exquisite chemosensitivity, mortality for patients with GCT comprises the most life years lost for non-pediatric malignancies. Given limited options for patients with platinum-resistant disease, improved insight into GCT biology could identify novel therapeutic options for patients with platinum-resistant disease. Recent studies into molecular characteristics of both early stage and advanced germ cell tumors suggest a role for rationally targeted agents and potentially immunotherapy.

RECENT DEVELOPMENTS

Recent GWAS meta-analyses have uncovered additional susceptibility loci for GCT and provide further evidence that GCT risk is polygenic. Chromosome arm level amplifications and reciprocal loss of heterozygosity have been described as significantly enriched in GCT compared to other cancer types. Contemporary analyses confirm ubiquitous gain of isochromosome 12 and mutations in addition to previously described GCT-associated genes such as KIT and KRAS. Alterations within the TP53-MDM2 signal transduction pathway appear to be enriched among patients with platinum-resistant disease. Potentially actionable targets, including alterations in TP53-MDM2, Wnt/β-catenin, PI3K, and MAPK signaling, are present in significant proportions of patients with platinum-resistant disease and may be exploited as therapeutic options. Pre-clinical and early clinical data also suggest a potential role for immunotherapy among patients with GCTs.

CONCLUSION

Molecular characterization of GCT patients may provide biologic rationale for novel treatment options in patients with platinum-resistant disease.

βcatenin is a marker of poor clinical characteristics and suppressed immune infiltration in testicular germ cell tumors

BACKGROUND

WNT/βcatenin (WNTβ) pathway is activated in early stages of embryonic development. We aimed to evaluate the significance of βcatenin in germ cell tumors (GCTs) and explore associations with the inflamed environment.

METHODS

Surgical specimens from 247 patients were analyzed. Βcatenin expression was detected in the tumor tissue by immunohistochemistry and correlated with clinical characteristics, outcome, PD-L1 expression and systemic immune-inflammation index (SII). The Ingenuity Pathway Analysis (IPA) was used to investigate the immune-cell related effects of βcatenin and PD-L1 encoding genes.

RESULTS

βcatenin was expressed in 86.2% of GCTs. The expression in seminomas was significantly lower compared to all subtypes of non-seminoma (all P <  0.0001). A high expression (weighted histoscore > 150) was associated with primary mediastinal non-seminoma (P = 0.035), intermediate/poor risk disease (P = 0.033) and high tumor markers (P = 0.035). We observed a positive correlation with the PD-L1 in tumor and an inverse correlation with the SII. IPA uncovered relationships of CTNNB (βcatenin) and CD274 (PD-L1) genes and their effects on differentiation, proliferation and activation of lymphocyte subtypes.

CONCLUSION

Herein, we showed that βcatenin is associated with male adult GCT characteristics as well as supressed immune environment.

EGF Receptor and mTORC1 Are Novel Therapeutic Targets in Nonseminomatous Germ Cell Tumors

Germ cell tumors (GCT) are malignant tumors that arise from pluripotent embryonic germ cells and occur in children and young adults. GCTs are treated with cisplatin-based regimens which, while overall effective, fail to cure all patients and cause significant adverse late effects. The seminoma and nonseminoma forms of GCT exhibit distinct differentiation states, clinical behavior, and response to treatment; however, the molecular mechanisms of GCT differentiation are not fully understood. We tested whether the activity of the mTORC1 and MAPK pathways were differentially active in the two classes of GCT. Here we show that nonseminomatous germ cell tumors (NSGCT, including embryonal carcinoma, yolk sac tumor, and choriocarcinoma) from both children and adults display activation of the mTORC1 pathway, while seminomas do not. In seminomas, high levels of REDD1 may negatively regulate mTORC1 activity. In NSGCTs, on the other hand, EGF and FGF2 ligands can stimulate mTORC1 and MAPK signaling, and members of the EGF and FGF receptor families are more highly expressed. Finally, proliferation of NSGCT cells in vitro and in vivo is significantly inhibited by combined treatment with the clinically available agents erlotinib and rapamycin, which target EGFR and mTORC1 signaling, respectively. These results provide an understanding of the signaling network that drives GCT growth and a rationale for therapeutic targeting of GCTs with agents that antagonize the EGFR and mTORC1 pathways. Mol Cancer Ther; 17(5); 1079-89. ©2018 AACR.

AXIN1 protects against testicular germ cell tumors via the PI3K/AKT/mTOR signaling pathway

Axis inhibition protein 1 (AXIN1) is characterized as a tumor suppressor in numerous types of cancer. However, the functional role of AXIN1 in the testicular germ cell tumors (TGCTs) remains unclear. The human embryonal carcinoma-derived cell line NTera2 was transfected with a recombinant AXIN1 expression vector (pcDNA3.1-AXIN1) and/or a small interfering RNA (siRNA) directed against AXIN1 (siAXIN). Following transfection, the mRNA and protein levels of AXIN1 were determined via reverse transcription-quantitative polymerase chain reaction analysis and western blotting, respectively. In addition, cell viability, apoptosis and the expression of apoptosis-associated proteins [apoptosis regulator Bax (Bax) and B-cell lymphoma (Bcl)-2] and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway proteins [phosphorylated (p)-mTOR, mTOR, p-AKT, AKT, P-70S ribosomal protein S6 (S6) and S6] were assessed. AXIN1 mRNA and protein levels were increased following transfection with pcDNA3.1-AXIN1 and decreased following transfection with siAXIN1 compared with their respective control groups. After overexpression of AXIN1, NTera2 cell viability and expression of Bcl-2, p-mTOR p-AKT and p-S6 protein was decreased, while apoptosis and Bax protein levels were increased, compared with the control group. However, there was no significant difference in AXIN1 mRNA expression, apoptosis or Bax/Bcl-2 protein expression when NTera2 cells were simultaneously transfected with pcDNA3.1-AXIN1+siAXIN1. In conclusion, the results of the present study indicate that overexpression of AXIN1 protects against TGCTs via inhibiting the PI3K/AKT/mTOR signaling pathway, suggesting that AXIN1 may be a potential target for gene therapy in TGCTs.

Pediatric malignant germ cell tumors: A comparison of the neuro-oncology and solid tumor experience

Malignant germ cell tumors (GCT) arise from abnormal migration of primordial germ cells and are histologically identical whether they occur inside or outside the central nervous system (CNS). However, the treatment strategy for GCTs varies greatly depending on the location of the tumor. These differences are in part due to the increased morbidity of surgery in the CNS but may also reflect differential sensitivity of the tumors to chemotherapy and radiation therapy (RT) or not-yet-understood biologic differences between these tumors. Historically, specialists caring for extracranial and intracranial GCT in the United States have practiced separately without much cross communication. The focus of this review is a discussion of differences between the management of CNS and extra-CNS GCTs and opportunities for collaboration and future research.

Paediatric extracranial germ-cell tumours

Management of paediatric extracranial germ-cell tumours carries a unique set of challenges. Germ-cell tumours are a heterogeneous group of neoplasms that present across a wide age range and vary in site, histology, and clinical behaviour. Patients with germ-cell tumours are managed by a diverse array of specialists. Thus, staging, risk stratification, and treatment approaches for germ-cell tumours have evolved disparately along several trajectories. Paediatric germ-cell tumours differ from the adolescent and adult disease in many ways, leading to complexities in applying age-appropriate, evidence-based care. Suboptimal outcomes remain for several groups of patients, including adolescents, and patients with extragonadal tumours, high tumour markers at diagnosis, or platinum-resistant disease. Survivors have significant long-term toxicities. The challenge moving forward will be to translate new insights from molecular studies and collaborative clinical data into improved patient outcomes. Future trials will be characterised by improved risk-stratification systems, biomarkers for response and toxic effects, rational reduction of therapy for low-risk patients and novel approaches for poor-risk patients, and improved international collaboration across paediatric and adult cooperative research groups.

Understanding the Treatment Strategies of Intracranial Germ Cell Tumors: Focusing on Radiotherapy

Intracranial germ cell tumors (ICGCT) occur in 2-11% of children with brain tumors between 0-19 years of age. For treatment of germinoma, relatively low radiation doses with or without chemotherapy show excellent 10 year survival rate of 80-100%. Past studies showed that neoadjuvant chemotherapy combined with focal radiotherapy resulted in unacceptably high rates of periventricular tumor recurrence. The use of generous radiation volume which covers the whole ventricular space with later boost treatment to primary site is considered as standard treatment of intracranial germinomas. For non-germinomatous germ cell tumors (NGGCT), 10-year overall survival rate is still much inferior than that of intracranial germinoma despite intensive chemotherapy and high-dose radiotherapy. Craniospinal radiotherapy combined with cisplatin-based chemotherapy provides the best treatment outcome for NGGCT; 60-70% of overall survival rate. There is a debate on the surgical role whether surgery can contribute to improved treatment outcome of NGGCT when added to combined chemoradiotherapy. Because higher dose of radiotherapy is required for treatment of NGGCT than for germinoma, it is tested whether whole ventricular irradiation can replace craniospinal irradiation in intermediate risk group of NGGCT to minimize radiation-related late toxicity in the recent studies. To minimize the treatment-related neural deficit and late sequelae while maintaining long-term survival rate of ICGCT patients, optimized administration of chemotherapy and radiotherapy should be selected. Use of technically upgraded radiotherapy modalities such as intensity-modulated radiotherapy or proton beam therapy is expected to bring an improved neurocognitive outcome with longitudinal assessment of the patients.

Biology of childhood germ cell tumours, focussing on the significance of microRNAs

Genomic and protein-coding transcriptomic data have suggested that germ cell tumours (GCTs) of childhood are biologically distinct from those of adulthood. Global messenger RNA profiles segregate malignant GCTs primarily by histology, but then also by age, with numerous transcripts showing age-related differential expression. Such differences are likely to account for the heterogeneous clinico-pathological behaviour of paediatric and adult malignant GCTs. In contrast, as global microRNA signatures of human tumours reflect their developmental lineage, we hypothesized that microRNA profiles would identify common biological abnormalities in all malignant GCTs owing to their presumed shared origin from primordial germ cells. MicroRNAs are short, non-protein-coding RNAs that regulate gene expression via translational repression and/or mRNA degradation. We showed that all malignant GCTs over-express the miR-371-373 and miR-302/367 clusters, regardless of patient age, histological subtype or anatomical tumour site. Furthermore, bioinformatic approaches and subsequent Gene Ontology analysis revealed that these two over-expressed microRNAs clusters co-ordinately down-regulated genes involved in biologically significant pathways in malignant GCTs. The translational potential of this finding has been demonstrated with the detection of elevated serum levels of miR-371-373 and miR-302/367 microRNAs at the time of malignant GCT diagnosis, with levels falling after treatment. The tumour-suppressor let-7 microRNA family has also been shown to be universally down-regulated in malignant GCTs, because of abundant expression of the regulatory gene LIN28. Low let-7 levels resulted in up-regulation of oncogenes including MYCN, AURKB and LIN28 itself, the latter through a direct feedback mechanism. Targeting LIN28, or restoring let-7 levels, both led to effective inhibition of this pathway. In summary, paediatric malignant GCTs show biological differences from their adult counterparts at a genomic and protein-coding transcriptome level, whereas they both display very similar microRNA expression profiles. These similarities and differences may be exploited for diagnostic and/or therapeutic purposes.

Molecular characteristics of malignant ovarian germ cell tumors and comparison with testicular counterparts: implications for pathogenesis

This review focuses on the molecular characteristics and development of rare malignant ovarian germ cell tumors (mOGCTs). We provide an overview of the genomic aberrations assessed by ploidy, cytogenetic banding, and comparative genomic hybridization. We summarize and discuss the transcriptome profiles of mRNA and microRNA (miRNA), and biomarkers (DNA methylation, gene mutation, individual protein expression) for each mOGCT histological subtype. Parallels between the origin of mOGCT and their male counterpart testicular GCT (TGCT) are discussed from the perspective of germ cell development, endocrinological influences, and pathogenesis, as is the GCT origin in patients with disorders of sex development. Integrated molecular profiles of the 3 main histological subtypes, dysgerminoma (DG), yolk sac tumor (YST), and immature teratoma (IT), are presented. DGs show genomic aberrations comparable to TGCT. In contrast, the genome profiles of YST and IT are different both from each other and from DG/TGCT. Differences between DG and YST are underlined by their miRNA/mRNA expression patterns, suggesting preferential involvement of the WNT/β-catenin and TGF-β/bone morphogenetic protein signaling pathways among YSTs. Characteristic protein expression patterns are observed in DG, YST and IT. We propose that mOGCT develop through different developmental pathways, including one that is likely shared with TGCT and involves insufficient sexual differentiation of the germ cell niche. The molecular features of the mOGCTs underline their similarity to pluripotent precursor cells (primordial germ cells, PGCs) and other stem cells. This similarity combined with the process of ovary development, explain why mOGCTs present so early in life, and with greater histological complexity, than most somatic solid tumors.

EPCAM-A novel molecular target for the treatment of pediatric and adult germ cell tumors

Germ cell tumors (GCTs) are thought to develop from totipotent primordial germ cells. Although the epithelial cell adhesion molecule (EPCAM) is expressed on embryonic stem cells as well as different tumor cells, it has not yet been extensively studied in GCTs. We analyzed EPCAM expression by quantitative RT-PCR in 48 fresh-frozen GCT specimens of different histology (10 mature teratoma, MT; 6 immature teratoma, IT; 7 dysgerminoma; 6 mixed malignant GCTs; 19 yolk sac tumor, YST) and in the GCT cell lines NCCIT, TE76.T, JAR and 2102Ep, and correlated its expression with AFP and hCG protein levels, histologic differentiation, and clinical follow-up data. EPCAM protein was visualized by immunohistochemistry of selected corresponding paraffin embedded tumor tissues. EPCAM was expressed in malignant but not in benign GCTs irrespective of age, sex, site and clinical stage of tumor (P = 0.001). In primary teratomas, EPCAM expression increased with their grade of immaturity (mean 2(-ΔCt) values: MT 0.23, IT 1.61, P = 0.007) and significantly correlated with serum AFP (P = 0.03) and hCG (P = 0.03) levels in malignant GCTs. Particularly high EPCAM levels were found in nonseminomatous GCTs such as YSTs (8.49) and choriocarcinoma (13.54). Immunohistochemical analysis verified gene expression data showing a distinct EPCAM staining in YST. Similarly in vitro, highest EPCAM expression was measured in GCT cell lines comprising yolk sac (2102Ep: 5.59) or choriocarcinoma (JAR: 10.65) components. This first comprehensive analysis of EPCAM in GCTs revealed high EPCAM expression in YSTs and choriocarcinomas. Thus, these nonseminomatous GCTs may be interesting targets for EPCAM immunotherapy, which has to be evaluated in further studies.

Mutation in the type IB bone morphogenetic protein receptor Alk6b impairs germ-cell differentiation and causes germ-cell tumors in zebrafish

Germ-cell tumors (GCTs), which arise from pluripotent embryonic germ cells, exhibit a wide range of histologic differentiation states with varying clinical behaviors. Although testicular GCT is the most common cancer of young men, the genes controlling the development and differentiation of GCTs remain largely unknown. Through a forward genetic screen, we previously identified a zebrafish mutant line, tgct, which develops spontaneous GCTs consisting of undifferentiated germ cells [Neumann JC, et al. (2009) Zebrafish 6:319-327]. Using positional cloning we have identified an inactivating mutation in alk6b, a type IB bone morphogenetic protein (BMP) receptor, as the cause of the zebrafish GCT phenotype. Alk6b is expressed in spermatogonia and early oocytes, and alk6b mutant gonads display impaired BMP signal transduction, altered expression of BMP target genes, and abnormal germ-cell differentiation. We find a similar absence of BMP signaling in undifferentiated human GCTs, such as seminomas and embryonal carcinoma, but not in normal testis or in differentiated GCTs. These results indicate a germ-cell-autonomous role for BMP signal transduction in germ-cell differentiation, and highlight the importance of the BMP pathway in human GCTs.

Bone morphogenetic protein signalling activity distinguishes histological subsets of paediatric germ cell tumours

Germ cell tumours (GCTs) are cancers of the testis, ovary or extragonadal sites that occur in infants, children and adults. Testicular GCT is the most common cancer in young men aged 15-40 years. Abnormalities in developmental signalling pathways such as wnt/β-catenin, TGF-β/BMP and Hedgehog have been described in many childhood tumours. To date, however, the status of BMP signalling in GCTs has not been described. Herein, we examine BMP-SMAD signalling in a set of clinically-annotated paediatric GCTs. We find that BMP signalling activity is absent in undifferentiated tumours such as seminomas and dysgerminomas, but robustly present in most yolk sac tumours, a differentiated tumour type. Gene expression profiling of TGF-β/BMP pathway genes in germinomas and yolk sac tumours reveals a set of genes that distinguish the two tumour types. There is significant intertumoural heterogeneity between tumours of the same histological subclass, implying that the BMP pathway can be differentially regulated in individual tumours. Finally, through miRNA expression profiling, we identify differential regulation of a set of miRNAs predicted to target the TGF-β/BMP pathway at multiple sites. Taken together, these results suggest that the BMP signalling pathway may represent a new therapeutical target for childhood GCTs.

Analysis of the adenomatous polyposis coli (APC) gene in childhood and adolescent germ cell tumors

BACKGROUND

Aberrant Wnt signaling due to deregulation of Wnt regulators is implicated in the development and progression of numerous embryonal tumors. This study addresses the questions if activation of Wnt signaling in germ cell tumors (GCTs) arising during childhood and adolescence is associated with aberrations of the tumor suppressor adenomatous polyposis coli (APC), and whether APC aberrations might be responsible for progression from benign teratoma to malignant yolk sac tumor (YST).

PROCEDURE

Forty-eight GCTs were analyzed, including mature (n = 5) and immature (n = 7) teratomas, mixed malignant GCTs (n = 10), YSTs (n = 17) as well as dysgerminomas (n = 9). To screen APC for genetic aberrations, we conducted direct sequencing of the mutation cluster region (MCR), loss of heterozygosity analyses (LOH) and protein truncation test. Epigenetic analyses included methylation specific PCR and bisulfite genomic sequencing of the APC 1a promoter. Gene expression was determined by quantitative real-time PCR.

RESULTS

Aberrant promoter methylation was detected in YSTs, teratomas and mixed malignant GCTs, with a pronounced hypermethylation exclusively in YSTs (11/13) while dysgerminomas were not methylated (0/9). Teratomas (2/2) and YSTs (4/5) show LOH at the APC locus. However, neither mutations within the MCR nor truncated protein were detected. APC expression did not significantly vary between the different histological subgroups.

CONCLUSIONS

Methylation of APC and LOH 5q21-22 in YSTs and teratomas provide evidence for involvement of APC in the accumulation of β-catenin and activation of the WNT pathway. Our additional analyses suggest that APC is unlikely to be solely responsible for the formation and progression of childhood GCTs.

Pediatric primary central nervous system germ cell tumors of different prognosis groups show characteristic miRNome traits and chromosome copy number variations

Background

Intracranial pediatric germ cell tumors (GCTs) are rare and heterogeneous neoplasms and vary in histological differentiation, prognosis and clinical behavior. Germinoma and mature teratoma are GCTs that have a good prognosis, while other types of GCTs, termed nongerminomatous malignant germ cell tumors (NGMGCTs), are tumors with an intermediate or poor prognosis. The second group of tumors requires more extensive drug and irradiation treatment regimens. The mechanisms underlying the differences in incidence and prognosis of the various GCT subgroups are unclear.

Results

We identified a distinct mRNA profile correlating with GCT histological differentiation and prognosis, and also present in this study the first miRNA profile of pediatric primary intracranial GCTs. Most of the differentially expressed miRNAs were downregulated in germinomas, but miR-142-5p and miR-146a were upregulated. Genes responsible for self-renewal (such as POU5F1 (OCT4), NANOG and KLF4) and the immune response were abundant in germinomas, while genes associated with neuron differentiation, Wnt/β-catenin pathway, invasiveness and epithelial-mesenchymal transition (including SNAI2 (SLUG) and TWIST2) were abundant in NGMGCTs. Clear transcriptome segregation based on patient survival was observed, with malignant NGMGCTs being closest to embryonic stem cells. Chromosome copy number variations (CNVs) at cytobands 4q13.3-4q28.3 and 9p11.2-9q13 correlated with GCT malignancy and clinical risk. Six genes (BANK1, CXCL9, CXCL11, DDIT4L, ELOVL6 and HERC5) within 4q13.3-4q28.3 were more abundant in germinomas.

Conclusions

Our results integrate molecular profiles with clinical observations and provide insights into the underlying mechanisms causing GCT malignancy. The genes, pathways and microRNAs identified have the potential to be novel therapeutic targets.

Wnt pathway reprogramming during human embryonal carcinoma differentiation and potential for therapeutic targeting

Background

Testicular germ cell tumors (TGCTs) are classified as seminonas or non-seminomas of which a major subset is embryonal carcinoma (EC) that can differentiate into diverse tissues. The pluripotent nature of human ECs resembles that of embryonic stem (ES) cells. Many Wnt signalling species are regulated during differentiation of TGCT-derived EC cells. This study comprehensively investigated expression profiles of Wnt signalling components regulated during induced differentiation of EC cells and explored the role of key components in maintaining pluripotency.

Methods

Human embryonal carcinoma cells were stably infected with a lentiviral construct carrying a canonical Wnt responsive reporter to assess Wnt signalling activity following induced differentiation. Cells were differentiated with all-trans retinoic acid (RA) or by targeted repression of pluripotency factor, POU5F1. A Wnt pathway real-time-PCR array was used to evaluate changes in gene expression as cells differentiated. Highlighted Wnt pathway genes were then specifically repressed using siRNA or stable shRNA and transfected EC cells were assessed for proliferation, differentiation status and levels of core pluripotency genes.

Results

Canonical Wnt signalling activity was low basally in undifferentiated EC cells, but substantially increased with induced differentiation. Wnt pathway gene expression levels were compared during induced differentiation and many components were altered including ligands (WNT2B), receptors (FZD5, FZD6, FZD10), secreted inhibitors (SFRP4, SFRP1), and other effectors of Wnt signalling (FRAT2, DAAM1, PITX2, Porcupine). Independent repression of FZD5, FZD7 and WNT5A using transient as well as stable methods of RNA interference (RNAi) inhibited cell growth of pluripotent NT2/D1 human EC cells, but did not appreciably induce differentiation or repress key pluripotency genes. Silencing of FZD7 gave the greatest growth suppression in all human EC cell lines tested including NT2/D1, NT2/D1-R1, Tera-1 and 833K cells.

Conclusion

During induced differentiation of human EC cells, the Wnt signalling pathway is reprogrammed and canonical Wnt signalling induced. Specific species regulating non-canonical Wnt signalling conferred growth inhibition when targeted for repression in these EC cells. Notably, FZD7 repression significantly inhibited growth of human EC cells and is a promising therapeutic target for TGCTs.

Pediatric malignant germ cell tumors show characteristic transcriptome profiles

Malignant germ cell tumors (GCT) of childhood are rare and heterogeneous neoplasms thought to arise from primordial germ cells. They vary substantially in their natural history and show important clinical differences from their adult counterparts. To address the biological basis for these observations, we have undertaken a comprehensive analysis of global gene expression patterns in pediatric malignant GCTs and compared these findings with published data on adult testicular GCTs (TGCT). Our study included 27 primary tumors and assessed the principal malignant histologic types of pediatric GCT, yolk sac tumor (YST; n = 18), and seminoma (n = 9). Analysis of Affymetrix U133A GeneChip data was performed using the statistical software environment R, including gene set enrichment analysis, with cross-validation at the RNA and protein level. Unsupervised analysis showed complete separation of YSTs and seminomas by global gene expression profiles and identified a robust set of 657 discriminatory transcripts. There was no segregation of tumors of the same histology arising at different sites or at different ages within the pediatric range. In contrast, there was segregation of pediatric malignant GCTs and adult malignant TGCTs, most notably for the YSTs. The pediatric seminomas were significantly enriched for genes associated with the self-renewing pluripotent phenotype, whereas the pediatric YSTs were significantly enriched for genes associated with a differentiation and proliferation phenotype. We conclude that histologic type is the key discriminator in pediatric malignant GCTs and that the observed clinical differences between malignant GCTs of children and adults are mirrored by significant differences in global gene expression.

Dickkopf-1 secreted by decidual cells promotes trophoblast cell invasion during murine placentation

Dickkopf-1 (Dkk1) is one of the secreted antagonists in the canonical Wnt signaling pathway. It plays important roles in diverse developmental processes. However, the role of Dkk1 in trophoblast cell invasion during placentation remains unclear. In this study, we found that Dkk1 was mainly expressed in maternal decidual tissue but trivially in ectoplacental cones (EPCs) in day 8 post coitum (p.c.) pregnant mouse uterus and that the efficiency of EPC attachment and outgrowth was increased when co-cultured with decidual cells, which secreted Dkk1, and this enhancement was abolished by pretreating decidual cells with Dkk1 blocking antibody before co-culture experiment. This indicates that Dkk1 secreted by decidual cells plays an important role in trophoblast cell invasion. Indeed, when recombinant mouse Dkk1 was added to EPCs in vitro, the efficiency of attachment and outgrowth was increased. Migration of EPCs toward the decidua was retarded when antisense Dkk1 oligonucleotide (ODN) was administered via intrauterine injection in vivo. Furthermore, the active beta-catenin nuclear location was lost when we treated cultured EPCs with recombinant mouse Dkk1, and the efficiency of EPCs attachment and outgrowth was obviously increased when we treated cultured EPCs with antisense beta-catenin ODN. Taken together, Dkk1 secreted by decidual cells may induce trophoblast cell invasion in the mouse and beta-catenin may be involved in such functions of Dkk1.

Participation of OCT3/4 and beta-catenin during dysgenetic gonadal malignant transformation

Gonadoblastoma (GB) is an in situ tumor consisting of a heterogeneous population of mature and immature germ cells, other cells resembling immature Sertoli/granulosa cells, and Leydig/lutein-like cells, may also be present. GB almost exclusively affects a subset of patients with intersex disorders and in 30% of them overgrowth of the germinal component of the tumor is observed and the lesion is term dysgerminoma/seminoma. Several pathways have been proposed to explain the malignant process, and abnormal OCT3/4 expression is the most robust risk factor for malignant transformation. Some authors have suggested that OCT3/4 and beta-catenin might both be involved in the same oncogenic pathway, as both genes are master regulators of cell differentiation and, overexpression of either gene may result in cancer development. The mechanism by which beta-catenin participates in GB transformation is not completely clear and exploration of the E-cadherin pathway did not conclusively show that this pathway participated in the molecular pathogenesis of GB. Here we analyze seven patients with mixed gonadal dysgenesis and GB, in an effort to elucidate the participation of beta-catenin and E-cadherin, as well as OCT3/4, in the oncogenic pathways involved in the transformation of GB into seminoma/dysgerminoma. We conclude that the proliferation of immature germ cells in GB may be due to an interaction between OCT3/4 and accumulated beta-catenin in the nuclei of the immature germ cells.

Biomarkers for exposure to estrogenic compounds: gene expression analysis in zebrafish (Danio rerio)

Gene expression analyses in male zebrafish (Danio rerio) were carried out using microarray technique and quantitative polymerase chain reaction. Genes responding to the exposure to 17beta-estradiol, bisphenol A and genistein were identified, among them genes involved in metabolism, reproductional and developmental processes. Threshold levels of 17beta-estradiol (200 ng/L), bisphenol A (2000 microg/L), and genistein (5000 microg/L) for the upregulation of the vtg1 gene in short-time exposures (11 days) were determined by qPCR. 14k microarrays were used to generate complete lists of genes regulated by these estrogenic compounds. For this purpose, liver samples from 10 exposed zebrafish and 10 controls were processed. In this case the expressions of 211 genes were significantly regulated by 17beta-estradiol, 47 by bisphenol A and 231 by genistein. Furthermore, it is shown that fish exposed to 17beta-estradiol and genistein have similarities in their gene expression patterns, whereas bisphenol A apparently affected gene expression in a different way. Only genes coding for egg-yolk precursor protein vitellogenin were found to be regulated by all three compounds, which shows that these genes are the only suitable markers for exposure to different estrogenic compounds. The regulated genes were assigned to gene ontology classes. All three estrogenic compounds regulated genes mainly involved in primary and cellular metabolism, but genistein regulated several genes involved in cell cycle-regulation and bisphenol A several genes involved in protein biosynthesis. Genistein also upregulated the expression of four eggshell proteins, which can be used as biomarkers for exposure to this chemical.

Genetic alterations of E-cadherin and beta-catenin in germinoma and teratoma: report of two central nervous system cases

The genetic basis as well as mechanisms of development of germ cell tumors of the CNS are still unexplained. In the present article changes of Ecadherin (CDH1) and beta-catenin (CTNNB1) genes in two CNS germ cell tumors are reported. Both gene products are components of adherens junctions, but are also involved in the Wnt signaling pathway. A case of germinoma of the central nervous system and a case of spinal channel teratoma were tested for loss of heterozygosity (LOH) of E-cadherin gene by PCR amplification of tetranucleotide polymorphism (D16S752). Changes of beta-catenin were tested by heteroduplex method. Both germ cell tumors analyzed demonstrated LOH of the CDH1 gene. Analysis of exon 3 of the CTNNB1 gene showed additional band in the germinoma, suggesting that this sample harbors mutation in the beta-catenin gene. Immunostaining showed that LOHs in our samples were accompanied with the absence of E-cadherin protein. We also investigated E-cadherin expression in four other germinomas, of which three were negative and one was mildly positive. Our findings may contribute to better understanding of the genetic profile of germ cell tumors.

Transcriptional regulation of livin by beta-catenin/TCF signaling in human lung cancer cell lines

Wnt/beta-catenin signaling emerged as a critical pathway in human lung carcinogenesis by regulating the livin promoter activity. This study clarified that livin was a direct target gene of beta-catenin/TCF signaling pathway in non-small cell lung cancer (NSCLC) cells. First, we observed that livin mRNA was up-regulated by LiCl treatment in culture of A549 and 103H cell lines. In addition we found that the activity of livin promoter is increased considerably by activation of beta-catenin and could be blocked by a dominant negative form of DeltaTCF4. Furthermore, we identified a TCF binding site located at -1476/-1470 of the livin promoter which is crucial to the response of beta-catenin. At last, chromatin immunoprecipitation (ChIP) assay was performed and the result indicated that beta-catenin/TCF complex binds to the putative TCF binding site of the livin promoter in A549 and 103H cell lines. Our results suggest that livin is transcriptionally regulated by beta-catenin/TCF signaling in human NSCLC cell lines.

Transcriptional regulation of livin by beta-catenin/TCF signaling in human lung cancer cell lines

Wnt/beta-catenin signaling emerged as a critical pathway in human lung carcinogenesis by regulating the livin promoter activity. This study clarified that livin was a direct target gene of beta-catenin/TCF signaling pathway in non-small cell lung cancer (NSCLC) cells. First, we observed that livin mRNA was up-regulated by LiCl treatment in culture of A549 and 103H cell lines. In addition we found that the activity of livin promoter is increased considerably by activation of beta-catenin and could be blocked by a dominant negative form of DeltaTCF4. Furthermore, we identified a TCF binding site located at -1476/-1470 of the livin promoter which is crucial to the response of beta-catenin. At last, chromatin immunoprecipitation (ChIP) assay was performed and the result indicated that beta-catenin/TCF complex binds to the putative TCF binding site of the livin promoter in A549 and 103H cell lines. Our results suggest that livin is transcriptionally regulated by beta-catenin/TCF signaling in human NSCLC cell lines.

The soluble wnt receptor Frizzled8CRD-hFc inhibits the growth of teratocarcinomas in vivo

Wnt signaling is important for normal cell proliferation and differentiation, and mutations in pathway components are associated with human cancers. Recent studies suggest that altered wnt ligand/receptor interactions might also contribute to human tumorigenesis. Therefore, agents that antagonize wnt signaling at the extracellular level would be attractive therapeutics for these cancers. We have generated a soluble wnt receptor comprising the Frizzled8 cysteine-rich domain (CRD) fused to the human Fc domain (F8CRDhFc) that exhibits favorable pharmacologic properties in vivo. Potent antitumor efficacy was shown using the mouse mammary tumor virus-Wnt1 tumor model under dosing conditions that did not produce detectable toxicity in regenerating tissue compartments. In vitro, F8CRDhFc inhibited autocrine wnt signaling in the teratoma cell lines PA-1, NTera-2, Tera-2, and NCCIT. In vivo, systemic administration of F8CRDhFc significantly retarded the growth of tumor xenografts derived from two of these cell lines, PA-1 and NTera-2. Pharmacodynamic markers of wnt signaling, identified by gene expression analysis of cultured teratoma cells, were also modulated in the tumor xenografts following treatment with F8CRDhFc. Additionally, these markers could be used as indicators of treatment efficacy and might also be useful in identifying patients that would benefit from the therapeutic agent. This is the first report showing the efficacy of a soluble wnt receptor as an antitumor agent and suggests that further development of wnt antagonists will have utility in treating human cancer.