Subset Of Germ Cell Tumors Research Articles

Abstract 2528: Mechanism and role of SOX2 repression in human germline specification

Abstract The core pluripotency regulatory master transcription factor SOX2 is repressed in human primordial germ cells (PGCs) and in the seminoma (SEM) subset of human germ cell tumors (GCTs), which arises by transformation of PGCs. Neither the mechanism of this repression not its significance to GC and GCT development have so far been clarified. Here we show that SOX2 repression in TCam-2 SEM cells is mediated by the presence of the Polycomb repressive complex (PcG) and by the H3K27me3 chromatin mark at the SOX2 transcription start site. Moreover, repression can be abrogated by recruitment of the H3K27 demethylase UTX to the SOX2 promoter through retinoid signaling. SOX2-activated TCam-2 cells express neuronal and other lineage genes, consistent with the gene's function as a neurectodermal effector. Based on the recent discovery that SOX17 initiates human PGC specification, with its downstream target PRDM1 acting to suppress mesendodermal genes, we propose that SOX2 repression is required for PGC specification to suppress neuroectodermal genes. Overt pluripotency is initiated in latently pluripotent transformed PGCs presenting as the SOX2 upregulated embryonal carcinoma (EC) subset of GCTs; by gene expression profiling analysis we characterize the functional pathways that distinguish PGC-like unipotent SEM from blastocyst-like pluripotent EC. Citation Format: Kushwaha Ritu, Nirmala Jagadish, George Bosl, Raju Chaganti. Mechanism and role of SOX2 repression in human germline specification. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2528.

Mechanism and Role of SOX2 Repression in Seminoma: Relevance to Human Germline Specification

SummaryHuman male germ cell tumors (GCTs) are derived from primordial germ cells (PGCs). The master pluripotency regulator and neuroectodermal lineage effector transcription factor SOX2 is repressed in PGCs and the seminoma (SEM) subset of GCTs. The mechanism of SOX2 repression and its significance to GC and GCT development currently are not understood. Here, we show that SOX2 repression in SEM-derived TCam-2 cells is mediated by the Polycomb repressive complex (PcG) and the repressive H3K27me3 chromatin mark that are enriched at its promoter. Furthermore, SOX2 repression in TCam-2 cells can be abrogated by recruitment of the constitutively expressed H3K27 demethylase UTX to the SOX2 promoter through retinoid signaling, leading to expression of neuronal and other lineage genes. SOX17 has been shown to initiate human PGC specification, with its target PRDM1 suppressing mesendodermal genes. Our results are consistent with a role for SOX2 repression in normal germline development by suppressing neuroectodermal genes.

PAX5 Is Focally Expressed in a Subset of Germ Cell Tumors: A Potential Diagnostic Pitfall

PAX5 Is Focally Expressed in a Subset of Germ Cell Tumors: A Potential Diagnostic Pitfall

Fusion of the Tumor-Suppressor Gene CHEK2 and the Gene for the Regulatory Subunit B of Protein Phosphatase 2 PPP2R2A in Childhood Teratoma

We characterized the molecular genetic consequences of a balanced chromosome translocation t(8;22)(p21; q12), which occurred as the sole cytogenetic aberration in short-term cultured cells from an intrathoracic mature teratoma in a 15-year-old girl. Fluorescence in situ hybridization and reverse transcription- polymerase chain reaction disclosed that t(8;22) resulted in the fusion of the genes PPP2R2A and CHEK2, with an inserted fragment belonging to class I endogenous retrovirus-related sequences at the junction. Sequencing of the two genes did not reveal any additional mutation. None of the three detected PPP2R2A/CHEK2 fusion transcripts resulted in an in-frame PPP2R2A/CHEK2 chimerical open reading frame; however, in all of them, the known open reading frame of CHEK2 was preserved. Thus, promoter swapping leading to deregulated CHEK2 expression would be the most likely oncogenic mechanism. Whereas inactivating mutations of CHEK2 previously have been described in a variety of sporadic tumors and in inherited cancer-predisposing syndromes, PPP2R2A, encoding a regulatory subunit of the multimeric enzyme phosphatase 2, has not been directly implicated in tumorigenesis. Our findings suggest that deregulation of CHEK2 and/or PPP2R2A is of pathogenetic importance in at least a subset of germ cell tumors.

Malignant retroperitoneal and abdominal germ cell tumors: An intergroup study

Background/Purpose: This randomized study examined survival (S) and event-free survival (EFS) rates using high-or standard-dose cisplatin-based combination chemotherapy and surgical resection for this subset of germ cell tumors. Methods: Twenty-six of 317 patients enrolled on the POG 9049/COG 8882 intergroup study for malignant germ cell tumors had abdomen or retroperitoneum as the primary site. Twenty-five of 26 were eligible for inclusion (n = 25). Patients had biopsy or resection at diagnosis and randomization to chemotherapy including etoposide, bleomycin, and either standard-dose (PEB) or high-dose cisplatin (HDPEB). In patients with initial biopsy, delayed resection was planned. Results: Median age was 26 months. There were 14 girls and 11 boys. There were 3 stage I to II, 5 stage III, and 17 stage IV patients. Surgical management included primary resection in 5, resection after chemotherapy in 13, and biopsy or partial resection in 7 patients. Overall 6-year EFS rate was 82.8% ± 10.9%, and 6-year survival rate was 87.6% ± 9.3%. By group, 6-year survival rate was 90.0% ± 11.6% for PEB and 85.7 ± 14.5% for HDPEB. Deaths include one from sepsis, one from malignant tumor progression, and one from bulky disease caused by benign components despite response of the malignant elements to chemotherapy. Conclusions: Malignant germ cell tumors arising in the abdomen and retroperitoneum have an excellent prognosis despite advanced stage in most children. Aggressive resection need not be undertaken at diagnosis, but a concerted attempt at complete surgical removal after chemotherapy is important to distinguish viable tumor from necrotic tumor or benign elements that will not benefit from further chemotherapy. J Pediatr Surg 38:315-318. Copyright 2003, Elsevier Science (USA). All rights reserved.

FGF4 dissociates anti-tumorigenic from differentiation signals of retinoic acid in human embryonal carcinomas.

A subset of male germ cell cancers presenting with advanced stage abundantly express the fibroblast growth factor-4 (FGF4). FGF4 expression is restricted in vitro to undifferentiated embryonal carcinomas (ECs). During induced differentiation, FGF4 expression is repressed in maturation sensitive but not resistant human ECs, suggesting FGF4 plays an important role in malignant growth or differentiation of ECs. To explore these FGF4 signals in male germ cell cancers, the multipotent human EC NTERA-2 clone D1 (NT2/D1) cell line was studied. All-trans-retinoic acid (RA)-treatment of these cells induces a neuronal phenotype and represses tumorigenicity and FGF4 expression. In contrast, RA-treatment of retinoid resistant lines derived from NT2/D1 cells failed to repress FGF4 expression. This implicated FGF4 directly in regulating human EC growth or differentiation. To evaluate further this FGF4 role, FGF4 was constitutively over-expressed in NT2/D1 cells using a CMV-driven expression vector containing the neomycin resistance gene. Three stable transfectants expressing exogenous FGF4 were studied as was a control transfectant only expressing the neomycin resistance gene. RA-treatment repressed endogenous but not exogenous FGF4 expression. RA-treatment of these transfectants induced morphologic and immunophenotypic maturation, changes in RA-regulated genes, and a G1 cell cycle arrest in a manner similar to parental NT2/D1 cells. This indicated FGF4 over-expression did not block RA-mediated differentiation. As expected, RA-treatment repressed tumorigenicity of the control transfectant after subcutaneous injection into athymic mice. Despite RA-treatment, this repressed tumorigenicity was overcome in all the transfectants over-expressing FGF4. The histopathology and neovascularization did not appreciably differ between xenograft tumors derived from FGF4 over-expressing versus control transfectants. FGF4 expression studies were extended to patient-derived germ cell tumors using total cellular RNA Northern analysis and an immunohistochemical assay developed to detect FGF4 protein expression. Germ cell tumors with EC components were significantly more likely to express FGF4 mRNA (P < or = 0.0179) than other examined germ cell tumors without EC components. Immunohistochemical results from 43 germ cell tumors demonstrated increased FGF4 expression especially in non-seminomas having EC components. Thus, FGF4 promotes directly malignant growth of cultured ECs, overcomes the antitumorigenic actions of RA, and is selectively expressed in specific histopathologic subsets of germ cell tumors. Taken together, these findings indicate how differentiation and anti-tumorigenic retinoic acid signals can be dissociated in germ cell cancer.

Pediatric germ cell tumors.

Germ cell tumors historically have been considered to be a single nosologic category comprising tumors with different histologic manifestations and different degrees of malignancy and arising at different sites of origin. Only in the last decade has the biologic heterogeneity of germ cell tumors been recognized and addressed. Therapy tailored for the many biologically distinct subsets of germ cell tumors has yet to be defined. Because many categories exclusively involve children, this challenge has been assumed by pediatric oncologists, resulting in the multi-institutional and multinational cooperative studies currently in progress. Current protocols utilize regimens that have been effective in adult germ cell tumors. The probability that the biologically unique pediatric subsets may be best treated by other regimens awaits future protocols.