A novel ETV6-NTRK3 gene fusion in congenital fibrosarcoma.

Congenital (or infantile) fibrosarcoma (CFS) is a malignant tumour of fibroblasts that occurs in patients aged two years or younger. CFS is unique among human sarcomas in that it has an excellent prognosis and very low metastatic rate. CFS is histologically identical to adult-type fibrosarcoma (ATFS); however, ATFS is an aggressive malignancy of adults and older children that has a poor prognosis. We report a novel recurrent t(12;15)(p13;q25) rearrangement in CFS that may underlie the distinctive biological properties of this tumour. By cloning the chromosome breakpoints, we show that the rearrangement fuses the ETV6 (also known as TEL) gene from 12p13 with the 15q25 NTRK3 neurotrophin-3 receptor gene (also known as TRKC). Analysis of mRNA revealed the expression of ETV6-NTRK3 chimaeric transcripts in all three CFS tumours analysed. These were not detected in ATFS or infantile fibromatosis (IFB), a histologically similar but benign fibroblastic proliferation occurring in the same age-group as CFS. ETV6-NTRK3 fusion transcripts encode the helix-loop-helix (HLH) protein dimerization domain of ETV6 fused to the protein tyrosine kinase (PTK) domain of NTRK3. Our studies indicate that a chimaeric PTK is expressed in CFS and this may contribute to oncogenesis by dysregulation of NTRK3 signal transduction pathways. Moreover, ETV6-NTRK3 gene fusions provide a potential diagnostic marker for CFS.

A second Ewing's sarcoma translocation, t(21;22), fuses the EWS gene to another ETS-family transcription factor, ERG.

The t(11;22)(q24;q12), present in 85% of Ewing's sarcoma and related tumours, fuses the EWS gene from chromosome 22q12 and the ETS family member, FLI-1. This results in the expression of a chimaeric protein containing the amino-terminal portion of EWS fused to the ETS DNA-binding domain of FLI-1. We have identified a second Ewing's sarcoma translocation, t(21;22)(q22;q12), that fuses EWS to a different ETS family member, the ERG gene located on band 21q22. Identical EWS nucleotide sequences found in the EWS/FLI-1 fusion transcripts are fused to portions of ERG encoding an ETS DNA-binding domain resulting in expression of a hybrid EWS/ERG protein. These findings suggest that fusion of EWS to different members of the ETS family of transcription factor genes may result in the expression of similar disease phenotypes.

Repression of the gene encoding the TGF-beta type II receptor is a major target of the EWS-FLI1 oncoprotein.

Chromosomal translocations resulting in the expression of chimaeric transcription factors are frequently observed in tumour cells, and have been suggested to be a common mechanism in human carcinogenesis. Ewing sarcoma and related peripheral primitive neuroectodermal tumours share recurrent translocations that fuse the gene EWSR1 (formerly EWS) from 22q-12 to FLI1 and genes encoding other ETS transcription factors (which bind DNA through the conserved ETS domain). It has been shown that transduction of the gene EWSR1-FLI1 (encoding EWS-FLI1 protein) can transform NIH3T3 cells, and that mutants containing a deletion in either the EWS domain or the DNA-binding domain in FLI1 lose this ability. This indicates that the EWS-FLI1 fusion protein may act as an aberrant transcription factor, but the exact mechanism of oncogenesis remains unknown. Because ETS transcription factors regulate expression of TGFBR2 (encoding the TGF-beta type II receptor, TGF-beta RII; Refs 9,14), a putative tumour suppressor gene, we hypothesized that TGFBR2 may be a target of the EWS-FLI1 fusion protein. We show here that Ewing sarcoma [corrected] (ES) cell lines with the EWSR1-FLI1 fusion have reduced TGF-beta sensitivity, and that fusion-positive ES cells and primary tumours both express low or undetectable levels of TGFBR2 mRNA and protein product. Co-transfection of FLI1 and the TGFBR2 promoter induces promoter activity, whereas EWSR1-FLI1 leads to suppression of TGFBR2 promoter activity and FLI1-induced promoter activity. Introduction of EWSR1-FLI1 into cells lacking the EWSR1-FLI1 fusion suppresses TGF-beta RII expression, whereas antisense to EWSR1-FLI1 in ES cell lines positive for this gene fusion restores TGF-beta RII expression. Furthermore, introduction of normal TGF-beta RII into ES cell lines restores TGF-beta sensitivity and blocks tumorigenicity. Our results implicate TGF-beta RII as a direct target of EWS-FLI1.

Molecular rearrangements of the MLL gene are present in most cases of infant acute myeloid leukemia and are strongly correlated with monocytic or myelomonocytic phenotypes.

Cytogenetic studies have previously identified abnormalities of chromosome band 11q23 in many cases of infant acute leukemia. Recent studies by ourselves and others have demonstrated breakpoint clustering in acute leukemias bearing translocations involving 11q23, and a Drosophila trithorax gene homologue (called MLL, HRX, or ALL-1) has been shown to span the 11q23 breakpoints of these translocations. To determine if this gene is affected in infant acute myeloid leukemia (AML), we have analyzed 26 infant AML cases for molecular alterations of this 11q23 gene. 15 out of 26 cases studied (58%) showed rearrangement of the MLL gene at the molecular level, and these rearrangements were clustered within an approximately 11-kb region containing nine exons of this gene. Moreover, 14 of the 15 cases with 11q23 rearrangements (93%) had myelomonocytic or monocytic phenotypes (M4 or M5 FAB subtypes, respectively), both of which are associated with a poor prognosis in childhood AML. In contrast, only 1 of 11 nonrearranged cases had an M4 or M5 phenotype (P = 0.00002). Rearrangement also correlated significantly with hyperleukocytosis (P = 0.02), another clinical parameter associated with poor outcome in this disease. Our results demonstrate that molecular rearrangements of MLL are common in M4 or M5 infant AML, and suggest that alteration of this gene may result in abnormal control of proliferation and differentiation in monocytic progenitor cells.

Biphenotypic sarcomas with myogenic and neural differentiation express the Ewing's sarcoma EWS/FLI1 fusion gene.

Accurate diagnosis of primitive childhood sarcomas continues to be a formidable problem because these malignancies generally demonstrate very little morphological evidence of their tissue of origin. One of these tumor classes, the Ewing's sarcoma family of peripheral primitive neuroectodermal tumors (pPNETs), are thought to have a neural histogenesis based on evidence of neuroectodermal differentiation. Greater than 95% of pPNETs carry t(11;22) or t(21;22) chromosomal translocations which fuse the EWS gene from chromosome 22q12 in-frame with either FLI1 from chromosome 11q24 or ERG from chromosome 21q22. The pPNETs are considered to be histogenetically distinct from rhabdomyosarcomas, myogenic tumors lacking these EWS gene fusions and hypothesized to derive from immature skeletal muscle precursors. In the present study, we describe a unique set of childhood soft tissue sarcomas that show both neural and myogenic differentiation. These biphenotypic tumors express myogenic regulatory factors and muscle-specific antigens and also show neuroectodermal differentiation with ultrastructural evidence of neurosecretory granules and expression of neural-associated genes. Northern analysis and reverse transcriptase PCR reveal expression of EWS/FLI1 gene fusions in all biphenotypic sarcomas analyzed. Chimeric EWS/FLI1 transcripts and fusion proteins in these tumors are identical to those described for pPNETs. Our results provide evidence for a class of biphenotypic childhood sarcomas with myogenic and neural differentiation and suggest that these tumors may be related to the Ewing's sarcoma family of pPNETs.

The chimeric protein tyrosine kinase ETV6-NTRK3 requires both Ras-Erk1/2 and PI3-kinase-Akt signaling for fibroblast transformation.

There is increasing interest in the potential role of the NTRK family of neurotrophin receptors in human neoplasia. These receptor protein tyrosine kinases (PTKs) are well-known mediators of neuronal cell survival and differentiation, but altered NTRK signaling has also been implicated in mesenchymal, hematopoietic, and epithelial malignancies. We recently identified a novel gene fusion involving one of the neurotrophin receptor genes, NTRK3, in the pediatric solid tumor, congenital fibrosarcoma. In these tumors (and subsequently demonstrated in several other human malignancies), a t(12;15)(p13;q25) rearrangement fuses the 3' portion of the ETV6 gene with exons encoding the PTK domain of NTRK3. The resulting ETV6-NTRK3 fusion protein functions as a chimeric PTK with potent transforming activity. However, previous studies failed to detect interactions between ETV6-NTRK3 and molecules known to link wild-type NTRK3 to its two major effector pathways, namely the Ras-Raf1-Mek1-Erk1/2 mitogenic pathway or the phosphatidylinositol 3'-kinase pathway leading to activation of the AKT survival factor. Therefore, it remains unknown whether ETV6-NTRK3 transformation involves altered NTRK3 signaling. We now report that ETV6-NTRK3 expression in NIH3T3 cells leads to constitutive activation of Mek1 and Akt, as well as to constitutively high expression of cyclin D1. ETV6-NTRK3-induced soft agar colony formation was almost completely abolished by inhibition of either the Ras-Raf1-Mek1-Erk1/2 or the phosphatidylinositol 3'-kinase-Akt pathway. Moreover, this inhibition dramatically reduced expression of cyclin D1. Our results indicate that ETV6-NTRK3 transformation involves a link between known NTRK3 signaling pathways and aberrant cell cycle progression and that Mek1 and Akt activation act synergistically to mediate these effects.

ETV6-NTRK3 gene fusions and trisomy 11 establish a histogenetic link between mesoblastic nephroma and congenital fibrosarcoma.

Congenital mesoblastic nephroma (CMN) is an infantile spindle cell tumor of the kidney that is subdivided into "classical" and "cellular" forms based on the degree of cellularity and mitotic activity. The histogenesis of CMN remains obscure, but relationships to other pediatric renal neoplasms have been proposed. However, cellular CMN is virtually identical histologically to congenital fibrosarcoma (CFS), a malignant tumor of fibroblasts in children of the same age group. Moreover, cytogenetic studies have reported common trisomies in CFS and cellular CMN, particularly of chromosome 11. We show here that t(12;15)(p13;q25)-associated ETV6-NTRK3 gene fusions described in CFS are also present in cellular CMN. ETV6-NTRK3 chimeric transcripts were detected in 8 of 9 cellular CMNs and 2 of 2 mixed CMNs. In contrast, all of the four classical CMNs tested were negative, as were cases of Wilms' tumor and clear cell sarcoma of the kidney. Moreover, we found trisomy 11 only in cellular or mixed CMNs with the ETV6-NTRK3 gene fusion. Our studies indicate that classical and cellular CMN have different genetic features and support the concept that cellular CMN is histogenetically related to CFS. They also provide insight into potential mechanisms involved in the transformation of the classical into the cellular form of CMN.

The Ewing tumor family of peripheral primitive neuroectodermal tumors expresses human gastrin-releasing peptide.

The Ewing tumor family of peripheral primitive neuroectodermal tumors (pPNETs) are characterized by chromosomal translocations leading to EWS-ETS gene fusions. These hybrid genes express chimeric proteins that are thought to act as aberrant transcription factors. We therefore used differential display-PCR to compare gene expression patterns in pPNET cell lines with those of other small round cell tumors (SRCTs) of childhood. This technique detected differential expression of sequences corresponding to human gastrin-releasing peptide (GRP) in pPNET cell lines but not in other SRCT cell lines. Subsequent Northern and reverse transcription-PCR analysis of SRCT cell lines confirmed GRP positivity in all pPNET lines tested. Of primary tumors tested by reverse transcription-PCR, GRP expression was found in 7 (44%) of 16 pPNETs but in no other primary SRCTs examined. Expression of the GRP receptor gene was demonstrable in 55% of pPNET cell lines and 25% of primary pPNET tumors but also in several other SRCTs. Radioimmunoassays and immunohistochemistry confirmed expression of bioactive GRP peptide in pPNET cell lines and primary tumors, respectively. Moreover, in vitro growth of a pPNET cell line was slowed by treatment with a GRP receptor antagonist and accelerated by a GRP receptor agonist. GRP is a known autocrine growth factor in small cell lung cancer and other neuroendocrine tumors. Its expression in pPNETs provides further evidence for a neuroectodermal histogenesis of these tumors and suggests that autocrine growth of this family of tumors may be at least partially regulated by GRP.

EWS-FLI1, EWS-ERG, and EWS-ETV1 oncoproteins of Ewing tumor family all suppress transcription of transforming growth factor beta type II receptor gene.

Ewing sarcoma-specific chromosomal translocations fuse the EWS gene to a subset of ets transcription factor family members, most commonly the FLI1 gene and less frequently ERG, ETV1, E1A-F, or FEV. These fusion proteins are thought to act as aberrant transcription factors that bind DNA through their ets DNA binding domain. Recently, we have shown (K-B. Hahm et al., Nat. Genet., 23: 222-227, 1999) that the transforming growth factor beta (TGF-beta) type II receptor (TGF-beta RII), a putative tumor suppressor gene, is a target of the EWS-FLI1 fusion protein. Here, we also examined effects of EWS-ETV1 and EWS-ERG on expression of the TGF-beta RII gene. We show that relative to the control, NIH-3T3 cell lines stably transfected with the EWS-FLI1, EWS-ERG, or EWS-ETV1 gene fusion express reduced levels of TGF-beta RII mRNA and protein, and that these cell lines have reduced TGF-beta sensitivity. Cotransfection of these fusion genes and the TGF-beta RII promoter suppresses TGF-beta RII promoter activity and also FLI1-, ERG-, or ETV1-induced promoter activity. These results indicate that transcriptional repression of TGF-beta RII is an important target of the EWS-FLI1, EWS-ERG, or EWS-ETV1 oncogene, and that EWS-ets fusion proteins may function as dominant negative forms of ets transcription factors.

The ETV6-NTRK3 gene fusion encodes a chimeric protein tyrosine kinase that transforms NIH3T3 cells.

The congenital fibrosarcoma t(12;15)(p13;q25) rearrangement splices the ETV6 (TEL) gene on chromosome 12p13 in frame with the NTRK3 (TRKC) neurotrophin-3 receptor gene on chromosome 15q25. Resultant ETV6-NTRK3 fusion transcripts encode the helix - loop - helix (HLH) dimerization domain of ETV6 fused to the protein tyrosine kinase (PTK) domain of NTRK3. We show here that ETV6-NTRK3 homodimerizes and is capable of forming heterodimers with wild-type ETV6. Moreover, ETV6-NTRK3 has PTK activity and is autophosphorylated on tyrosine residues. To determine if the fusion protein has transforming activity, NIH3T3 cells were infected with recombinant retroviral vectors carrying the full-length ETV6-NTRK3 cDNA. These cells exhibited a transformed phenotype, grew macroscopic colonies in soft agar, and formed tumors in severe combined immunodeficient (SCID) mice. We hypothesize that chimeric proteins mediate transformation by dysregulating NTRK3 signal transduction pathways via ligand-independent dimerization and PTK activation. To test this hypothesis, we expressed a series of ETV6-NTRK3 mutants in NIH3T3 cells and assessed their transformation activities. Deletion of the ETV6 HLH domain abolished dimer formation with either ETV6 or ETV6-NTRK3, and cells expressing this mutant protein were morphologically non-transformed and failed to grow in soft agar. An ATP-binding mutant failed to autophosphorylate and completely lacked transformation activity. Mutants of the three NTRK3 PTK activation-loop tyrosines had variable PTK activity but had limited to absent transformation activity. Of a series of signaling molecules well known to bind to wild-type NTRK3, only phospholipase-Cgamma (PLCgamma) associated with ETV6-NTRK3. However, a PTK active mutant unable to bind PLCgamma did not show defects in transformation activity. Our studies confirm that ETV6-NTRK3 is a transforming protein that requires both an intact dimerization domain and a functional PTK domain for transformation activity. Oncogene (2000) 19, 906 - 915.

The der(17)t(X;17)(p11;q25) of human alveolar soft part sarcoma fuses the TFE3 transcription factor gene to ASPL, a novel gene at 17q25.

Alveolar soft part sarcoma (ASPS) is an unusual tumor with highly characteristic histopathology and ultrastructure, controversial histogenesis, and enigmatic clinical behavior. Recent cytogenetic studies have identified a recurrent der(17) due to a non-reciprocal t(X;17)(p11.2;q25) in this sarcoma. To define the interval containing the Xp11.2 break, we first performed FISH on ASPS cases using YAC probes for OATL1 (Xp11.23) and OATL2 (Xp11.21), and cosmid probes from the intervening genomic region. This localized the breakpoint to a 160 kb interval. The prime candidate within this previously fully sequenced region was TFE3, a transcription factor gene known to be fused to translocation partners on 1 and X in some papillary renal cell carcinomas. Southern blotting using a TFE3 genomic probe identified non-germline bands in several ASPS cases, consistent with rearrangement and possible fusion of TFE3 with a gene on 17q25. Amplification of the 5' portion of cDNAs containing the 3' portion of TFE3 in two different ASPS cases identified a novel sequence, designated ASPL, fused in-frame to TFE3 exon 4 (type 1 fusion) or exon 3 (type 2 fusion). Reverse transcriptase PCR using a forward primer from ASPL and a TFE3 exon 4 reverse primer detected an ASPL-TFE3 fusion transcript in all ASPS cases (12/12: 9 type 1, 3 type 2), establishing the utility of this assay in the diagnosis of ASPS. Using appropriate primers, the reciprocal fusion transcript, TFE3-ASPL, was detected in only one of 12 cases, consistent with the non-reciprocal nature of the translocation in most cases, and supporting ASPL-TFE3 as its oncogenically significant fusion product. ASPL maps to chromosome 17, is ubiquitously expressed, and matches numerous ESTs (Unigene cluster Hs.84128) but no named genes. The ASPL cDNA open reading frame encodes a predicted protein of 476 amino acids that contains within its carboxy-terminal portion of a UBX-like domain that shows significant similarity to predicted proteins of unknown function in several model organisms. The ASPL-TFE3 fusion replaces the N-terminal portion of TFE3 by the fused ASPL sequences, while retaining the TFE3 DNA-binding domain, implicating transcriptional deregulation in the pathogenesis of this tumor, consistent with the biology of several other translocation-associated sarcomas. Oncogene (2001) 20, 48 - 57.

Common and variant gene fusions predict distinct clinical phenotypes in rhabdomyosarcoma.

PURPOSE: We evaluated the clinical features of the common PAX3-FKHR and variant PAX7-FKHR gene fusions observed in rhabdomyosarcoma. PATIENTS AND METHODS: Reverse-transcriptase polymerase chain reaction (RT-PCR) assays were used to detect the gene fusions in 34 cases of rhabdomyosarcoma. Clinical data were obtained retrospectively and compared with the molecular results. RESULTS: The PAX3-FKHR and PAX7-FKHR gene fusions were present in tumors from 18 and 16 patients, respectively. The group with a PAX7-FKHR fusion was younger (P = .01) and presented more often with an extremity lesion (82% v 22%; P = .001). PAX7-FKHR tumors were more often localized than PAX3-FKHR tumors (P = .03). In patients with metastatic disease at diagnosis, the patterns were different: PAX7-FKHR patients had metastatic disease that involved only bone (n = 2) and distant nodes (n = 2), while the PAX3-FKHR group had multiple sites involved, including bone (n = 7), marrow (n = 7), lungs (n = 3), distant nodes (n = 2), skin (n = 1), and brain (n = 1). No significant difference in relapse rate was observed. A trend toward improved overall survival in the PAX7-FKHR group was noted (P = .09). Event-free survival for this PAX7-FKHR group was significantly longer (P = .04). CONCLUSION: Our results suggest that the common PAX3-FKHR and the variant PAX7-FKHR fusions are associated with distinct clinical phenotypes. Identification of fusion gene status may be a useful diagnostic tool in rhabdomyosarcoma.

Peripheral primitive neuroectodermal tumors in adults: documentation by molecular analysis.

PURPOSE: The Ewing tumor (ET) family of peripheral primitive neuroectodermal tumors (pPNETs) are primitive small round-cell tumors (SRCTs) of the bone and soft tissue that occur predominantly in children and adolescents. However, pPNETs only rarely enter the differential diagnosis of bone and soft tissue SRCTs in adults. Recently, gene fusions between the EWS gene and different members of the ETS transcription factor family have been shown to occur in virtually all pPNETs and thus constitute a pathognomonic marker for this tumor subclass. The aim of the present study was to document EWS/ETS fusion gene expression in suspected pPNETs of adults as objective evidence for the existence of this tumor family in older patients. PATIENTS AND METHODS: The three contributing molecular diagnostic laboratories retrospectively compiled a cohort of all SRCT cases in which EWS/ETS gene fusions had been shown by molecular analysis. This cohort was surveyed for cases that occurred in patients aged 40 years or older, which were then analyzed for their clinical and pathologic features. RESULTS: Nine patients between 40 and 65 years of age were found to have tumors positive for EWS/ETS gene fusions. Standard histopathologic and clinical features of these cases, other than age, were similar to those of childhood pPNETs. Patients were initiated on appropriate therapy after molecular analysis confirmed the diagnosis of pPNET. CONCLUSION: Identification of an EWS/ETS gene fusion is useful in providing objective evidence of the diagnosis of pPNET in patients over the age of 40 years. This diagnosis should be considered in adults who present with bone and soft tissue SRCTs and appropriate biopsy specimens should be collected for molecular analysis at the time of diagnosis.

EWS-FLI1 and EWS-ERG gene fusions are associated with similar clinical phenotypes in Ewing's sarcoma.

PURPOSE: There are a variety of solid tumors in which alternative chromosomal translocations generate related fusion products. In alveolar rhabdomyosarcoma and synovial sarcoma, these variant fusions have been found to have major clinical significance. We investigated whether the two alternative gene fusion products, EWS-FLI1 and EWS-ERG, define different clinical subsets within the Ewing's sarcoma family of tumors. PATIENTS AND METHODS: We selected 30 cases of Ewing's sarcoma with the EWS-ERG gene fusion and 106 cases with the EWS-FLI1 fusion. Clinical data were obtained for each case and compared with the molecular diagnostic findings. RESULTS: There were no significant clinical differences observed between the two groups in age of diagnosis, sex, metastasis at diagnosis, primary site, event-free survival, or overall survival. CONCLUSION: Differences in the C-terminal partner in the Ewing's sarcoma family gene fusions are not associated with significant phenotypic differences.

EWS-FLI1 fusion transcript structure is an independent determinant of prognosis in Ewing's sarcoma.

PURPOSE: More than 90% of Ewing's sarcomas (ES) contain a fusion of the EWS and FLI1 genes, due to the t(11;22)(q24;q12) translocation. At the molecular level, the EWS-FLI1 rearrangements show great diversity. Specifically, many different combinations of exons from EWS and FLI1 encode in-frame fusion transcripts and result in differences in the length and composition of the chimeric protein, which functions as an oncogenic aberrant transcription factor. In the most common fusion type (type 1), EWS exon 7 is linked in frame with exon 6 of FLI1. As the fundamental pathogenetic lesion in ES, the molecular heterogeneity of these fusion transcripts may have functional and clinical significance. PATIENTS AND METHODS: We performed a clinical and pathologic analysis of 112 patients with ES in which EWS-FLI1 fusion transcripts were identified by reverse-transcriptase polymerase chain reaction (RT-PCR). Adequate treatment and follow-up data were available in 99 patients treated with curative intent. Median follow-up in these 99 patients was 26 months (range, 1 to 140 months). Univariate and multivariate survival analyses were performed that included other prognostic factors, such as age, tumor location, size, and stage. RESULTS: Among the 99 patients suitable for survival analysis, the tumors in 64 patients contained the type 1 fusion and in 35 patients contained less common fusion types. Stage at presentation was localized in 74 patients and metastatic in 25. Metastases (relative risk [RR] = 2.6; P = .008), and type 1 EWS-FLI1 fusion (RR = 0.37; P = .014) were, respectively, independent negative and positive prognostic factors for overall survival by multivariate analysis. Among 74 patients with localized tumors, the type 1 EWS-FLI1 fusion was also a significant positive predictor of overall survival (RR = 0.32; P = .034) by multivariate analysis. CONCLUSION: EWS-FLI1 fusion type appears to be prognostically relevant in ES, independent of tumor site, stage, and size. Further studies are needed to clarify the biologic basis of this phenomenon.

Loss of the tumor suppressor Hace1 leads to ROS-dependent glutamine addiction.

Cellular transformation is associated with altered glutamine (Gln) metabolism. Tumor cells utilize Gln in the tricarboxylic acid (TCA) cycle to maintain sufficient pools of biosynthetic precursors to support rapid growth and proliferation. However, Gln metabolism also generates NADPH, and Gln-derived glutamate is used for synthesis of glutathione (GSH). As both NADPH and GSH are antioxidants, Gln may also contribute to redox balance in transformed cells. The Hace1 E3 ligase is a tumor suppressor inactivated in diverse human cancers. Hace1 targets the Rac1 GTPase for degradation at Rac1-dependent NADPH oxidase complexes, blocking superoxide generation by the latter. Consequently, loss of Hace1 increases reactive oxygen species (ROS) levels in vitro and in vivo. Given the link between Hace1 loss and increased ROS, we investigated whether genetic inactivation of Hace1 alters Gln metabolism. We demonstrate that mouse embryonic fibroblasts (MEFs) derived from Hace1(-/-) mice are highly sensitive to Gln withdrawal, leading to enhanced cell death compared with wild-type (wt) MEFs, and Gln depletion or chemical inhibition of Gln uptake blocks soft agar colony formation by Hace1(-/-) MEFs. Hace1(-/-) MEFs exhibit increased Gln uptake and ammonia secretion, and metabolic labeling using (13)C-Gln revealed that Hace1 loss increases incorporation of Gln carbons into the TCA cycle intermediates. Gln starvation markedly increases ROS levels in Hace1(-/-) but not in wt MEFs, and treatment with the antioxidant N-acetyl cysteine or the TCA cycle intermediate oxaloacetate efficiently rescues Gln starvation-induced ROS elevation and cell death in Hace1(-/-) MEFs. Finally, Gln starvation increases superoxide levels in Hace1(-/-) MEFs, and NADPH oxidase inhibitors block the induction of superoxide and cell death by Gln starvation. Together, these results suggest that increased ROS production due to Hace1 loss leads to Gln addiction as a mechanism to cope with increased ROS-induced oxidative stress.

Molecular detection of the ETV6-NTRK3 gene fusion differentiates congenital fibrosarcoma from other childhood spindle cell tumors.

Congenital fibrosarcoma (CFS) is a pediatric spindle cell tumor of the soft tissues that usually presents before the age of 2 years. Although these tumors display histologic features of malignancy and frequently recur, they have a relatively good prognosis and only rarely metastasize. CFS must therefore be differentiated from more aggressive spindle cell sarcomas that occur during childhood, particularly adult-type fibrosarcoma (ATFS), which can have an identical morphology. CFS must also be distinguished from benign but cellular fibroblastic lesions of the same age group, including infantile fibromatosis (IFB) and myofibromatosis (MFB). Unfortunately, standard pathologic examination often does not differentiate CFS from these other conditions. The authors recently identified a novel chromosomal translocation in CFS, t(12;15)(p13;q25), which gives rise to an ETV6-NTRK3 gene fusion. They subsequently developed reverse transcription-polymerase chain reaction (RT-PCR) assays that can detect ETV6-NTRK3 fusion transcripts in CFS frozen or paraffin-embedded tumor specimens. To confirm the use of this assay in the differential diagnosis of CFS, they have screened a larger series of childhood pediatric spindle cell lesions for ETV6-NTRK3 gene fusions, including 11 cases of CFS, 13 malignant spindle cell tumors (including ATFS), and 38 benign spindle cell tumors (including IFB and MFB). Of the 11 cases diagnosed as CFS, 10 showed the ETV6-NTRK3 gene fusion, whereas none of the 51 other malignant or benign spindle cell tumors demonstrated this fusion gene. They also compared their RT-PCR findings with those of conventional cytogenetics and with immunohistochemical detection of the ETV6-NTRK3 protein using antisera to NTRK3. They conclude that RT-PCR analysis is superior to these techniques for the detection of the ETV6-NTRK3 gene fusion in pediatric spindle cell tumors, and it is a reliable and specific modality for the diagnosis of CFS.

Detection of the EWS/WT1 gene fusion by reverse transcriptase-polymerase chain reaction in the diagnosis of intra-abdominal desmoplastic small round cell tumor.

We report two cases of intra-abdominal desmoplastic small round cell tumor with characteristic clinical, histological, immunohistochemical, and ultrastructural features. Fusion of the EWS gene on chromosome 22 and the WT1 gene on chromosome 11, resulting from the chromosomal translocation t(11;22)(p13;q12), was detected by reverse transcriptase polymerase chain reaction (RT-PCR) in both cases. This translocation has been previously reported in this type of tumor using either cytogenetic or molecular biological techniques. Tumor tissue from both cases revealed no chimeric fusion transcripts characteristic of the Ewing sarcoma family of peripheral primitive neuroectodermal tumors or of alveolar rhabdomyosarcoma, two tumors in the differential diagnosis of intra-abdominal desmoplastic small round cell tumor. This report demonstrates the utility of molecular studies as an adjunct in the diagnosis of this rare and aggressive tumor.

Absence of detectable EWS/FLI1 expression after therapy-induced neural differentiation in Ewing sarcoma.

Ewing sarcoma and other peripheral primitive neuroectodermal tumors (pPNETs) display limited neural differentiation and are thought to have a neural crest origin Greater than 95% of these tumors share common t(11;22)(q24;q12) ort(21;22)(q22;q12) chromosomal translocations leading to ES/FLI1 or EWS/ERG gene fusions, respectively. The resulting chimeric oncoproteins seem to function as aberrant transcription factors. However, whether these molecules contribute to the limited neural differentiation observed in pPNETs or actually inhibit differentiation remains unclear. We report a Ewing sarcoma case from the forearm of a 10-year-old girl which expressed EWS/FLI1 fusion transcripts. The tumor was treated with surgery, chemotherapy, and local radiation, but residual tumor was detected within a year as a well-differentiated peripheral neural tumor lacking detectable EWS/FLI1 expression. Further studies suggested that the primary and residual tumors were clonally related. This association between apparent therapy-induced differentiation in Ewing sarcoma and absence of detectable fusion transcripts in the residual tumor provides presumptive evidence that EWS/FLI1 expression may inhibit differentiation in tumour cells.

Mixed epithelial and stromal tumor of the kidney lacks the genetic alterations of cellular congenital mesoblastic nephroma.

Mixed epithelial and stromal tumor of the kidney is a recently recognized neoplasm that occurs almost exclusively in perimenopausal women. Because it frequently contains areas of smooth muscle in which epithelial structures are embedded, some have concluded that it is the adult form of congenital mesoblastic nephroma. Others have concluded that the morphology and epidemiology of mixed epithelial and stromal tumor indicate that it is unrelated to congenital mesoblastic nephroma. Although the genetic alterations of mixed epithelial and stromal tumor have not been previously elucidated, much is known about the genetic alterations of cellular congenital mesoblastic nephroma. The present study was undertaken to determine if mixed epithelial and stromal tumors have any of the genetic alterations recognized as typical of cellular congenital mesoblastic nephroma. RNA extraction was performed on formalin-fixed, paraffin-embedded tissue from 7 mixed epithelial and stromal tumors followed by reverse-transcription polymerase chain reaction to detect the ETV6-NTRK3 gene fusion. Fluorescent in situ hybridization with centromere-specific probes for chromosomes 8, 11, and 17 was performed to evaluate polyploidy of these chromosomes in 11 cases of mixed epithelial and stromal tumor. None of the mixed epithelial and stromal tumors showed any of these genetic alterations. We conclude that mixed epithelial and stromal tumor of the kidney lacks the genetic alterations typical of cellular congenital mesoblastic nephroma, is unrelated to it, and the appellation "adult mesoblastic nephroma" should not be used for these tumors.