Fusion of the dominant negative transcription regulator CHOP with a novel gene FUS by translocation t(12;16) in malignant liposarcoma

Functional genomics in mice by tagged sequence mutagenesis

Most mammalian genes will soon be characterized as cDNA sequences with little information about their function. To utilize this sequence information for large-scale functional studies, a gene trap retrovirus shuttle vector has been developed to disrupt genes expressed in murine embryonic stem (ES) cells. A library of mutant clones was isolated, and regions of genomic DNA adjacent to 400 independent provirus inserts were cloned and sequenced. The flanking sequences, designated 'promoter-proximal sequence tags', or PSTs, identified 63 specific genes and anonymous cDNAs disrupted as a result of virus integration. The efficiency of tagged sequence mutagenesis suggests that many of the 10,000-20,000 genes expressed in ES cells can be targeted, providing defined mutations for the analysis of gene functions in vivo. In addition, PSTs provide the first expressed sequence tags derived from genomic DNA, and define gene features such as exon boundaries and promoters that are missing from cDNA sequences.

Complex genomic rearrangement within the 12q15 multiple aberration region induced by integrated human papillomavirus 18 in a cervical carcinoma cell line

Human papillomavirus (HPV) DNA is integrated into the host genome in cervical cancer. The cervical carcinoma cell line SW756 has integrated HPV-18 DNA in chromosome region 12q15, in the papillomavirus-associated locus-2 (PAL2). By polymerase chain reaction and hybridization of an arrayed cosmid library with oligonucleotides from the rearranged allele, we determined the pre-integration germline structure of the region. PAL2 was located approximately 10 kb from sequence-tagged site marker U27131, which was the marker most proximal to the 3' flank of the integrated viral DNA. HPV-18 DNA integration induced a complex genomic rearrangement resulting in inversion and deletion of cellular sequences. PAL2 is within the multiple aberration region, which has been shown to be affected in several types of benign tumors of mesenchymal origin. The integrated viral DNA was located 50 kb from a CpG island and 150 kb upstream of the high-mobility group I-C (HMGI-C) gene. The HMGI-C gene and the integrated HPV-18 DNA had opposite transcriptional orientations. No overexpression or altered message of the HMGI-C gene was detected in three cervical carcinoma cell lines. The integrated viral DNA did not affect any other known gene in the region and may be a marker for an unknown gene associated with malignant tumor phenotypes.

Characterization and chromosomal mapping of the human TFG gene involved in thyroid carcinoma

Homology searches in the Expressed Sequence Tag Database were performed using SPYGQ-rich regions as query sequences to find genes encoding protein regions similar to the N-terminal parts of the sarcoma-associated EWS and FUS proteins. Clone 22911 (T74973), encoding a SPYGQ-rich region in its 5' end, and several other clones that overlapped 22911 were selected. The combined data made it possible to assemble a full-length cDNA sequence. This cDNA sequence is 1677 bp, containing an initiation codon ATG, an open reading frame of 400 amino acids, a poly(A) signal, and a poly(A) tail. We found 100% identity between the 5' part of the consensus sequence and the 598-bp-long sequence named TFG. The TFG sequence is fused to the 3' end of NTRK1, generating the TRK-T3 fusion transcript found in papillary thyroid carcinoma. The cDNA therefore represents the full-length transcript of the TFG gene. TFG was localized to 3q11-q12 by fluorescence in situ hybridization. The 3' and the 5' ends of the TFG cDNA probe hybridized to a 2.2-kb band on Northern blot filters in all tissues examined.

Chromosomal translocations in human soft tissue sarcomas by interphase fluorescence in situ hybridization

In soft tissue sarcomas, clonal rearrangement of chromosomes has been shown by cytogenetic analysis to be unique and specific for tumor types. The development of fluorescence in situ hybridization (FISH) has allowed detection of chromosomal rearrangements in the interphase nuclei isolated from paraffin-embedded tissues. Three kinds of translocations in the interphase nuclei that were isolated from 47 cases of soft tissue sarcomas were examined by FISH with chromosome-specific DNA probes of centromeric and total probes. Of 47 soft tissue sarcomas 42 (89.4%) revealed tumor-specific translocations by retrospective cytogenetic analysis. Translocation t(X;18) was detected in 25/28 synovial sarcomas; translocation t(11;22) in 5/6 Ewing's sarcomas and primitive neuroectodermal tumors (PNET); and translocation t(12;16) was found in 12/13 liposarcomas, including 10 myxoid and two round cell types as clonal chromosomal aberrations specific for both subtypes. Based on the cytogenetic analysis, Ewing's sarcoma is related closely with PNET as shown by MIC2-protein reactivity. Other cytogenetic findings of translocation t(12;16) indicate that round cell liposarcomas share chromosomal changes with myxoid liposarcomas, and further suggest that both tumor subtypes of liposarcoma may possess common precursor cells. FISH is a useful aid in determining the tumor type of soft tissue sarcomas with regard to histogenetic origin.

A testicular antigen aberrantly expressed in human cancers detected by autologous antibody screening

Serological analysis of recombinant cDNA expression libraries (SEREX) using tumor mRNA and autologous patient serum provides a powerful approach to identify immunogenic tumor antigens. We have applied this methodology to a case of esophageal squamous cell carcinoma and identified several candidate tumor targets. One of these, NY-ESO-1, showed restricted mRNA expression in normal tissues, with high-level mRNA expression found only in testis and ovary tissues. Reverse transcription-PCR analysis showed NY-ESO-1 mRNA expression in a variable proportion of a wide array of human cancers, including melanoma, breast cancer, bladder cancer, prostate cancer, and hepatocellular carcinoma. NY-ESO-1 encodes a putative protein of Mr 17,995 having no homology with any known protein. The pattern of NY-ESO-1 expression indicates that it belongs to an expanding family of immunogenic testicular antigens that are aberrantly expressed in human cancers in a lineage-nonspecific fashion. These antigens, initially detected by either cytotoxic T cells (MAGE, BAGE, GAGE-1) or antibodies [HOM-MEL-40(SSX2), NY-ESO-1], represent a pool of antigenic targets for cancer vaccination.

Cell transformation mediated by homodimeric E2A-HLF transcription factors

The E2A-HLF fusion gene, created by the t(17;19)(q22;p13) chromosomal translocation in pro-B lymphocytes, encodes an oncogenic protein in which the E2A trans-activation domain is linked to the DNA-binding and protein dimerization domain of hepatic leukemia factor (HLF), a member of the proline- and acidic amino acid-rich (PAR) subfamily of bZIP transcription factors. This fusion product binds to its DNA recognition site not only as a homodimer but also as a heterodimer with HLF and two other members of the PAR bZIP subfamily, thyrotroph embryonic factor (TEF) and albumin promoter D-box binding protein (DBP). Thus, E2A-HLF could transform cells by direct regulation of downstream target genes, acting through homodimeric or heterodimeric complexes, or by sequestering normal PAR proteins into nonfunctional heterocomplexes (dominant-negative interference). To distinguish among these models, we constructed mutant E2A-HLF proteins in which the leucine zipper domain of HLF was extended by one helical turn or altered in critical charged amino acids, enabling the chimera to bind to DNA as a homodimer but not as a heterodimer with HLF or other PAR proteins. When introduced into NIH 3T3 cells in a zinc-inducible vector, each of these mutants induced anchorage-independent growth as efficiently as unaltered E2A-HLF, indicating that the chimeric oncoprotein can transform cells in its homodimeric form. Transformation also depended on an intact E2A activator region, providing further support for a gain-of-function contribution to oncogenesis rather than one based on a dominant-interfering or dominant-negative mechanism. Thus, the tumorigenic effects of E2A-HLF and its mutant forms in NIH 3T3 cells favor a straightforward model in which E2A-HLF homodimers bind directly to promoter/enhancer elements of downstream target genes and alter their patterns of expression in early B-cell progenitors.

Molecular and cytogenetics of soft tissue sarcomas

Molecular and cytogenetically soft tissue sarcomas are a well-characterized tumor entity with several tumor type specific changes understood also at the molecular level. Most likely, additional characteristic alterations will be detected, recurrent aberrations characterized at the molecular level, new clinical and histopathological correlations will be found, and little is known about how the genetic changes lead to tumor formation, promote progression and sometimes give tumor cells the ability to recur locally or distantly. The possibility to detect cells with these acquired genetic alterations may increase the reproducibility of tumor classification, yields promising possibilities for early diagnosis of tumor recurrences and/or metastasis, and may allow development of therapeutic regimens targeted at the genetically alterated cell.

EWS-Fli1 antisense oligodeoxynucleotide inhibits proliferation of human Ewing's sarcoma and primitive neuroectodermal tumor cells

The translocation t(11;22) is a common chromosomal abnormality detected both in Ewing's sarcoma and in primitive neuroectodermal tumor cells. The translocation results in an EWS-Fli1 fusion gene, made up of the 5' half of the EWS gene on chromosome 22 fused to the 3' half of the Fli1 gene on chromosome 11. Recent studies have evaluated possible roles of the fusion gene products. However, the biological significance of EWS-Fli1 is still unknown. Using a competitive polymerase chain reaction technique, we show here that there might be a correlation between the expression levels of the EWS-Fli1 fusion gene and the proliferative activities of Ewing's sarcoma and primitive neuroectodermal tumor cells. When the EWS-Fli1 expression is inhibited by antisense oligodeoxynucleotides against the fusion RNA, the growth of the tumor cells is significantly reduced both in vitro and in vivo. The data further indicate the growth inhibition of the cells by the antisense sequence might be mediated by G0/G1 block in the cell cycle progression. These results suggest that EWS-Fli1 may play an important role in the proliferation of the tumor cells, and the EWS-Fli1 fusion RNA could be used as a target to inhibit the growth of Ewing's sarcoma and primitive neuroectodermal tumor with the specific antisense oligonucleotide.

Interphase cytogenetic analysis of myxoid soft tissue tumors by fluorescence in situ hybridization and DNA flow cytometry using paraffin-embedded tissue

BACKGROUND

Myxoid liposarcoma is one of the major myxoid malignancies of soft tissue and its histologic differentiation from other myxoid tumors is sometimes difficult. Recent cytogenetic analysis revealed that a characteristic reciprocal chromosomal translocation of t(12;16)(q13;p11) occurs in myxoid liposarcomas. In this study, retrospective cytogenetic analysis by means of fluorescence in situ hybridization (FISH) and DNA flow cytometry were performed on free nuclei isolated from paraffin embedded myxoid liposarcoma cells, and they were compared with myxoid malignant fibrous histiocytomas (MFHs), low grade fibromyxoid sarcomas, and intramuscular myxomas.

METHODS

Nine myxoid liposarcomas, five myxoid MFHs, two low grade fibromyxoid sarcomas, and four intramuscular myxomas were examined. Chromosomal aberrations in chromosomes 12 and 16 were investigated by FISH, using both centromeric DNA probes and whole chromosome painting probes. Cellular DNA contents were determined by flow cytometry.

RESULTS

All nine myxoid liposarcomas were shown to be diploid by DNA flow cytometry and exhibited the translocation t(12; 16), as shown by FISH. Four of the five myxoid MFHs exhibited aneuploidy, as shown by flow cytometry, and remarkable numeric aberrations of chromosomes 12 and 16. No abnormal DNA content or chromosomal aberrations were identified in the two low grade fibromyxoid sarcomas or the four intramuscular myxomas.

CONCLUSIONS

FISH analysis performed on paraffin embedded materials can be used to differentiate myxoid liposarcomas from other myxoid soft tissue tumors.

Musculoskeletal oncology--advances in cytogenetics and molecular genetics and their clinical implications

Although musculoskeletal malignancies comprise a small group of cancers, a vast number of histological subtypes have been identified attesting to the heterogeneity of this class of tumours and the growing interest in their development. The mode of management for both bone and soft tissue sarcomas has been examined extensively and treatment guidelines have been proposed. Despite the intensive study and multidisciplinary treatment, a substantial proportion of tumours remain recalcitrant to therapy and recur locally and systemically. Improved methods of characterising these tumours may help in understanding their biology. Cytogenetic and molecular genetic techniques allow a subcellular dissection of these malignancies which may aid the identification of mechanisms that are important in tumorigenesis. Already candidate genes have been isolated which may play an important role in the deregulation of proliferation and or the adoption of a malignant phenotype, features which are fundamental in tumour development. By studying the molecular biology and cytogenetics of tumours it may be possible to improve diagnostic and prognostic accuracy thereby minimising over and under treatment.

Molecular cloning and subcellular localisation of the snRNP-associated protein 69KD, a structural homologue of the proto-oncoproteins TLS and EWS with RNA and DNA-binding properties

We recently isolated and characterised a 69 kDa protein (69KD) found associated with spliceosomal small nuclear ribonucleoproteins (snRNPs). Here, we report the molecular cloning of a cDNA encoding this protein, its nucleic acid binding properties and its subcellular localisation. Sequence analysis of the 69KD cDNA revealed: (1) that 69KD shares structural similarity with the human RNA binding proteins TLS and EWS (95% and 65% identity, respectively), the products of two genes frequently targeted by tumour-specific chromosomal translocations; (2) that 69KD contains a consensus RNA binding domain (CS-RBD) and three Arg/Gly-rich RNA binding motifs, structural features typical of many RNA binding proteins, in particular of hnRNP proteins; and (3) that 69KD contains a single putative Cys2/Cys2 zinc finger domain, a characteristic of many DNA-binding proteins. Consistent with its possession of these motifs, 69KD display a general nucleic acid binding activity, with a strong preference for guanyl and uridyl-rich RNA sequences, as well as for single-stranded and double-stranded DNA. The functional significance of this affinity for nucleic acids remains unclear. However, based on the established association of 69KD with the Sm core domain of snRNPs in vivo, these motifs might help mediate 69KD binding to snRNPs or be involved in some, as yet, unknown aspect of RNA metabolism. Consistent with both possibilities, 69KD is detected within typical snRNP containing subnuclear structures referred to as speckles, and is also more widely distributed throughout the nucleoplasm, as observed for many hnRNP proteins.

Cytogenetic analysis of a case of myxoid liposarcoma with cartilaginous differentiation

The cytogenetic analysis of a patient with a myxoid liposarcoma exhibiting cartilaginous differentiation is presented. A complex translocation involving chromosome 12, 16, and 19 was found, instead of the t(12;16), specific for myxoid liposarcoma. The involvement of 19q13 in a tumor with cartilaginous differentiation, and the assignment of TGF beta 1 to 19q13.1-13.2, which appears to play a role in the formation of bone and cartilage, suggest a possible relation between both.

Tat-SF1: cofactor for stimulation of transcriptional elongation by HIV-1 Tat

Tat may stimulate transcriptional elongation by recruitment of a complex containing Tat-SF1 and a kinase to the human immunodeficiency virus-type 1 (HIV-1) promoter through a Tat-TAR interaction. A complementary DNA for the cellular activity, Tat-SF1, has been isolated. This factor is required for Tat trans-activation and is a substrate of an associated cellular kinase. Cotransfection with the complementary DNA for Tat-SF1 specifically modulates Tat activation. Tat-SF1 contains two RNA recognition motifs and a highly acidic carboxyl-terminal half. It is distantly related to EWS and FUS/TLS, members of a family of putative transcription factors with RNA recognition motifs that are associated with sarcomas.

Ectopic expression of CHOP (GADD153) induces apoptosis in M1 myeloblastic leukemia cells

CHOP (GADD153) is a member of the C/EBP family and a stress-induced protein. To investigate the role of CHOP in cellular growth, we expressed CHOP conditionally in M1 myeloblastic leukemia cells that do not express p53 protein. More than 60% of M1 cells died through apoptosis 72 h after CHOP induction. Site-directed mutagenesis revealed that this process requires leucine zipper domain but neither intact basic region nor trans-activation domain. CHOP-mediated apoptosis accompanied downregulation of bcl-2 mRNA and overexpression of Bcl-2 delayed the process. Our results indicate that CHOP can induce apoptosis in a p53-independent manner.

Genomic PCR detects tumor cells in peripheral blood from patients with myxoid liposarcoma

Myxoid liposarcoma (MLS) is the most common subtype of liposarcoma. The cytogenetic hallmark of MLS is the pathognomonic t(12;16)(q13;p11), present in more than 85% of cases. The translocation leads to the fusion of the CHOP and FUS genes at 12q13 and 16p11, respectively, and the generation of a FUS/CHOP hybrid protein. The presence of a tumor-specific chimeric gene makes it possible to identify MLS cells by polymerase chain reaction (PCR). We have analyzed peripheral blood samples obtained during a 10-year period at diagnosis of primary and/or recurrent disease in 19 MLS patients with t(12;16) and in one MLS patient with t(12;22;20), resulting in the fusion of the CHOP and EWS genes. Nested PCR on genomic DNA from blood samples amplified FUS/CHOP hybrid fragments in three patients and EWS/CHOP in the patient with t(12;22;20). There was no obvious association between PCR findings and clinical outcome, but larger series are needed to draw any firm conclusions.

The hybrid PAX3-FKHR fusion protein of alveolar rhabdomyosarcoma transforms fibroblasts in culture

Pediatric alveolar rhabdomyosarcoma is characterized by a chromosomal translocation that fuses parts of the PAX3 and FKHR genes. PAX3 codes for a transcriptional regulator that controls developmental programs, and FKHR codes for a forkhead-winged helix protein, also a likely transcription factor. The PAX3-FKHR fusion product retains the DNA binding domains of the PAX3 protein and the putative activator domain of the FKHR protein. The PAX3-FKHR protein has been shown to function as a transcriptional activator. Using the RCAS retroviral vector, we have introduced the PAX3-FKHR gene into chicken embryo fibroblasts. Expression of the PAX3-FKHR protein in these cells leads to transformation: the cells become enlarged, grow tightly packed and in multiple layers, and acquire the ability for anchorage-independent growth. This cellular transformation in vitro will facilitate studies on the mechanism of PAX3-FKHR-induced oncogenesis.

Combined morphologic and karyotypic study of 28 myxoid liposarcomas. Implications for a revised morphologic typing, (a report from the CHAMP Group)

Cytogenetic analysis carried out in 28 adipose tissue tumors diagnosed microscopically as myxoid liposarcoma (ML) revealed a t(12;16)(q13:p11) chromosomal translocation in 26 of the 28 cases. Morphologically, these tumors were subclassified into the following categories: well-differentiated, six cases: poorly differentiated round cell type, 17 cases: poorly differentiated spindle cell type, five cases. Poorly differentiated ML behaved in a more aggressive fashion than the well-differentiated tumors. The results of this study confirm the consistency and specificity of the t(12;16)(q13:p11) translocation as the genetic marker of ML, support the contention that liposarcomas with round cells belong to the ML category, and confirm Stout's proposal for the existence of a poorly differentiated ML composed of spindle cells. Cytogenetic analysis may be helpful in the differential diagnosis of ML with atypical lipomatous tumors, which is characteristically associated with ring and giant marker chromosomes, and of ML with lipoblastoma, which is typically associated with 8q alterations. The existence of a mixed ML-atypical lipomatous tumor remains questionable. The genetic events associated with the greater aggressiveness of the poorly differentiated types of ML remain to be determined.

Signals from the stressed endoplasmic reticulum induce C/EBP-homologous protein (CHOP/GADD153)

The gene encoding C/EBP-homologous protein (CHOP), also known as growth arrest and DNA-damage-inducible gene 153 (GADD153), is activated by agents that adversely affect the function of the endoplasmic reticulum (ER). Because of the pleiotropic effects of such agents on other cellular processes, the role of ER stress in inducing CHOP gene expression has remained unclear. We find that cells with conditional (temperature-sensitive) defects in protein glycosylation (CHO K12 and BHK tsBN7) induce CHOP when cultured at the nonpermissive temperature. In addition, cells that are defective in initiating the ER stress response, because of overexpression of an exogenous ER chaperone, BiP/GRP78, exhibit attenuated inducibility of CHOP. Surprisingly, attenuated induction of CHOP was also noted in BiP-overexpressing cells treated with methyl methanesulfonate, an agent thought to activate CHOP by causing DNA damage. The roles of DNA damage and growth arrest in the induction of CHOP were therefore reexamined. Induction of growth arrest by culture to confluence or treatment with the enzymatic inhibitor N-(phosphonacetyl)-L-aspartate did not induce CHOP. Furthermore, both a DNA-damage-causing nucleoside analog (5-hydroxymethyl-2'-deoxyuridine) and UV light alone did not induce CHOP. These results suggest that CHOP is more responsive to ER stress than to growth arrest or DNA damage and indicate a potential role for CHOP in linking stress in the ER to alterations in gene expression.

The transcription factor Spi-1/PU.1 binds RNA and interferes with the RNA-binding protein p54nrb

The protooncogene for Spi-1/PU.1 is an Ets-related transcription factor overexpressed during Friend erythroleukemia. The molecular basis by which Spi-1/PU.1 is involved in the erythroleukemic process remains to be elucidated. By using an immobilized protein binding assay, we have identified a 55-kDa protein as a putative partner of Spi-1/PU.1 protein. Microsequence analysis revealed that this 55-kDa protein was p54nrb (nuclear RNA-binding protein, 54 kDa) a RNA-binding protein highly similar to the splicing factor PSF (polypyrimidine tract-binding protein-associated splicing factor). In this paper, we show that Spi-1/PU.1 impedes the binding of p54nrb to RNA and alters the splicing process in vitro. Moreover, we present evidence that the transcriptional factor Spi-1/PU.1, unlike other Ets proteins, is able to bind RNA. Altogether, these results raise the intriguing possibility that the functional interference observed between Spi-1/PU.1 and RNA-binding proteins might represent a novel mechanism in malignant erythropoiesis.

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.

Stress-induced binding of the transcriptional factor CHOP to a novel DNA control element

CHOP (GADD153) is a mammalian nuclear protein that dimerizes with members of the C/EBP family of transcriptional factors. Absent under normal conditions, CHOP is induced by the stress encountered during nutrient deprivation, the acute-phase response, and treatment of cells with certain toxins. The basic region of CHOP deviates considerably in sequence from that of other C/EBP proteins, and CHOP-C/EBP heterodimers are incapable of binding to a common class of C/EBP sites. With respect to such sites, CHOP serves as an inhibitor of the activity of C/EBP proteins. However, recent studies indicate that certain functions of CHOP, such as the induction of growth arrest by overexpression of the wild-type protein and oncogenic transformation by the TLS-CHOP fusion protein, require an intact basic region, suggesting that DNA binding by CHOP may be implicated in these activities. In this study an in vitro PCR-based selection assay was used to identify sequences bound by CHOP-C/EBP dimers. These sequences were found to contain a unique core element PuPuPuTGCAAT(A/C)CCC. Competition in DNA-binding assays, DNase 1 footprint analysis, and methylation interference demonstrate that the binding is sequence specific. Deletions in the basic region of CHOP lead to a loss of DNA binding, suggesting that CHOP participates in this process. Stress induction in NIH 3T3 cells leads to the appearance of CHOP-containing DNA-binding activity. CHOP is found to contain a transcriptional activation domain which is inducible by cellular stress, lending further support to the notion that the protein can function as a positively acting transcription factor. We conclude that CHOP may serve a dual role both as an inhibitor of the ability of C/EBP proteins to activate some target genes and as a direct activator of others.

Gains and losses of DNA sequences in liposarcomas evaluated by comparative genomic hybridization

Comparative genomic hybridization (CGH) was used to detect and map the regions of gain, high-level amplification, and loss of DNA sequences in 14 liposarcomas. Thirteen tumors showed DNA sequence copy number changes of one or more genomic regions (mean, six aberrations/tumor; range, 0-17). These aberrations were observed in almost every chromosome but some chromosomal regions were affected more often than others. DNA sequence gains were more frequent than losses. The most common gain was seen at 12q14-21 (50% of tumors). Other frequent gains (29%) were of 1q21-24, 8cen-q21.2, 19q, and 20q. High-level amplification was observed in six (43%) tumors and included as minimal common segments bands 12q15, 1q22, and 1q24. In five (36%) tumors, sequences at 1q21-24 and 1q32 were found to be gained simultaneously with 12q14-21, which means that in 71% of the tumors with gain at 12q, an increase of DNA sequence copy number at 1q was also observed. The most common losses of DNA sequences (21%) occurred from regions 9p21-pter and 13q21-qter. Most of the aforementioned regions have not previously been reported to be altered in liposarcomas. The detection of a novel recurring amplicon at 1q21-24 with high-level amplification at 1q22 and frequent simultaneous DNA sequence gain at 12q14-21 (high-level amplification at 12q15) suggests that genes linked to both these regions may play a significant role in the development and progression of liposarcomas.

Translocations in solid tumours

Specific chromosomal translocations have now been identified in a variety of solid tumour types. Recent developments in this field include the identification of novel genes involved in the t(X;18) synovial sarcoma translocation and the discovery that the high-mobility group protein gene, HMGI-C, is involved in the chromosome 12 rearrangements found in lipomas and uterine leiomyomas. These discoveries may have important implications for the strategies used in tumour diagnosis and treatment.

Detection of chromosomal translocations in leukemia-lymphoma cells by polymerase chain reaction

In recent years many chromosomal translocations involved in leukemia and lymphoma have been defined at the molecular level. In addition to advancing the understanding of pathological mechanisms underlying the transformation process, the cloning and sequencing of the genes altered by the translocations have provided new tools for diagnosis and monitoring of patients. In particular, the polymerase chain reaction (PCR) methodology yields rapid, sensitive and accurate diagnostic and prognostic information. As leukemias carrying certain translocations confer a higher risk of treatment failure, it is important to identify accurately all positive cases in order to give appropriate therapy. An important new initiative in the diagnostical setting and anti-leukemic therapy is the early detection of minimal residual disease (MRD). If MRD, implying an increased risk of relapse, is reliably detected during apparent clinical remission, alternative strategies could be applied early while the malignant cell burden is still minimal. The PCR assays are clearly more sensitive than other methods of MRD detection including morphology, immunophenotyping and cytogenetics; treatment failure is first detectable by PCR followed by cytogenetic relapse and finally clinical disease. PCR assays have been most often used in the MRD analysis of follicular lymphoma with t(14;18), chronic myeloid leukemia and acute lymphoblastic leukemia (ALL) with t(9;22), ALL with t(4;11), and acute myeloid leukemia (AML) with t(8;21) or t(15;17). PCR amplification is applicable to any other translocation provided the translocation is highly associated with the malignancy and the breakpoints are sufficiently clustered; a quickly increasing number of such specific molecular markers are now available for PCR assays. PCR still remains an experimental investigation for the detection of covert disease. However, the clinical relevance of MRD detection should be evaluated separately for each type of leukemia as significant prognostic differences between disease entities were found. This review describes the PCR assays available for the detection of leukemia cells with specific chromosomal translocations and summarizes the experience with the application of PCR techniques in monitoring patients during the course of the disease.

MDM2 gene amplification in bone and soft-tissue tumors: association with tumor progression in differentiated adipose-tissue tumors

We have studied 107 bone and soft-tissue sarcomas and 8 lipomas for amplification of the MDM2 gene. This gene was amplified in 3 out of 67 osteosarcomas, 3 out of 20 malignant fibrous histiocytomas, 4 out of 20 liposarcomas, and 4 out of 8 lipomas. The amplification was associated with overexpression of mRNA. In osteosarcomas, contrary to previous findings, all amplifications were observed in primary lesions. In liposarcomas, the amplification was seen exclusively in well-differentiated tumors with high frequency (4/5) but not in other subtypes (0/15). In addition, MDM2 amplification was also frequently found in deep-seated intra- or intermuscular lipomas (4/5). Hence, it is suggested that MDM2 amplification plays a significant role in the development of differentiated adipose-tissue tumors. Three well-differentiated liposarcomas with MDM2 amplification coexisted with high-grade dedifferentiated sarcomas, in which MDM2 amplification was also observed. Interestingly, in 2 of these cases, the grades of amplification correlated with the histological grades, indicating an important role of MDM2 overexpression in tumor progression.

Deletion in human chromosome region 12q13-15 by integration of human papillomavirus DNA in a cervical carcinoma cell line

In human cervical carcinomas papillomavirus DNA is frequently integrated in the cell genome. We have cloned the integration site of human papillomavirus-18 DNA in human chromosome region 12q13-15 present in the SW756 cervical carcinoma cell line. Viral DNA is broken from nucleotides 2643 to 3418 in the E1 and E2 open reading frames, resulting in a deletion of 775 bases of viral DNA. Cloning and sequence analysis of the rearranged and germline alleles shows that there is no homology between the target cellular and viral DNA, suggesting it is a nonhomologous recombination. The target cellular region is called papillomavirus associated locus 2 (PAL2). The 5'- and 3'-flanking probes derived from the hybrid viral-cellular clone detect completely different germline restriction fragments in DNA from cells with normal chromosome 12. There is no overlap between the restriction maps of the target germline clones obtained with 5'- and 3'-flanking probes. Probes from these germline clones beyond the breakpoint position do not detect any DNA rearrangement in SW756 cells DNA. These data prove that there is a deletion of cellular DNA as consequence of the integration, with an estimated minimum size of 14 kilobases. Both cellular flanking probes are outside the amplicon of this chromosome region identified in the OSA and RMS13 sarcoma cell lines, comprising SAS-CHOP-CDK4-MDM2 genes and where translocation breakpoints are located in liposarcomas. The integration at 12q13-15 might have been selected by its contribution to the tumor phenotype.

Cytogenetics of 158 patients with regional or disseminated melanoma. Subset analysis of near-diploid and simple karyotypes

We report on the cytogenetic analyses of 158 cases of metastatic malignant melanoma, comprised of 63 cases with regional disease (RD) and 95 cases with distant (metastatic) disease (DD). Clonal structural abnormalities were identified in 126 (80%) cases and were significantly increased ( < 0.01 after adjusting for multiple comparisons) on chromosomes (in order of frequency of involvement) 1, 6, 7, 11, 9, and 3. Clustering of breakpoints occurred at 1p36, 1p22-q21, 6p11-q21, 9p, 11q23-qter, 13p (especially for cases with DD), and 19q13. The most common clonal numerical abnormalities, in a subset of 49 near-diploid cases were -10, -22, -9, +7, -19, and -Y. Analysis of chromosome segment gains and losses (CSRP) showed frequent loss of chromosomes 6 and 10, followed by equal rates of involvement of chromosomes 1, 7, and 9. Whole or segmental losses of chromosome 9 (especially 9p) correlate well with recent molecular genetic studies identifying putative suppressor genes, and are also likely important genetic abnormalities. However, based on the frequency of abnormalities in this large series of metastatic melanomas, it is likely that structural abnormalities of 1 and 6, and 10 are important in the pathogenesis of sporadic advanced melanoma.

The Hox11 gene is essential for cell survival during spleen development

The HOX11 homeobox gene was identified via the translocation t(10;14) in T cell leukaemia. To determine the function of this gene in mice, null mutations were made using homologous recombination in ES cells to incorporate lacZ into the hox11 transcription unit. Production of beta-galactosidase from the recombinant hox11 allele in +/− mutants allowed identification of sites of hox11 expression which included the developing spleen. Newborn hox11 −/− mice exhibit asplenia. Spleen formation commences normally at E11.5 in hox11 −/− mutant embryos but the spleen anlage undergoes rapid and complete resorption between E12.5 and E13.5. Dying spleen cells exhibit molecular features of apoptosis, suggesting that programmed cell death is initiated at this stage of organ development in the absence of hox11 protein. Thus hox11 is not required to initiate spleen development but is essential for the survival of splenic precursors during organogenesis. This function for hox11 suggests that enhanced cell survival may result from the t(10;14) which activates HOX11 in T cell leukaemias, further strengthening the association between oncogene-induced cell survival and tumorigenesis.

Regional fine mapping of the multiple-aberration region involved in uterine leiomyoma, lipoma, and pleomorphic adenoma of the salivary gland to 12q15

Cytogenetic aberrations involving 12q13-15 are frequently observed in a variety of benign solid tumors. Using a chromosome walking approach combined with fluorescence in situ hybridization analysis, we were able to show that the chromosome 12 breakpoints involved in uterine leiomyoma, pleomorphic adenoma of the salivary gland, and lipoma cluster to the same chromosomal region, which we therefore designated MAR (multiple-aberration region). By comparing the G-banding pattern of prometaphase chromosomes of amniotic fluid cells and lymphocytes to the position of hybridization signals obtained with a cosmid pool encompassing this breakpoint hot spot region, MAR was assigned to 12q15. We conclude that, despite the cytogenetic breakpoint assignment to the three bands 12q13-15 in individual uterine leiomyomas, lipomas, and pleomorphic adenomas of the salivary glands in the past, most likely 12q15 is the only 12q breakpoint site in these three distinct solid tumor types.

Association of SARFH (sarcoma-associated RNA-binding fly homolog) with regions of chromatin transcribed by RNA polymerase II

Many oncogenes associated with human sarcomas are composed of a fusion between transcription factors and the N-terminal portions of two similar RNA-binding proteins, TLS and EWS. Though the oncogenic fusion proteins lack the RNA-binding domain and do not bind RNA, the contribution from the N-terminal portion of the RNA-binding protein is essential for their transforming activity. TLS and EWS associate in vivo with RNA polymerase II (Pol II) transcripts. To learn more about the target gene specificity of this interaction, the localization of a Drosophila melanogaster protein that has extensive sequence identity to the C-terminal RNA-binding portions of TLS and EWS was studied in preparations of Drosophila polytene nuclei. cDNA clones encoding the full-length Drosophila TLS-EWS homolog, SARFH (stands for sarcoma-associated RNA-binding fly homolog), were isolated. Functional similarity to TLS and EWS was revealed by the association of SARFH with Pol II transcripts in mammalian cells and by the ability of SARFH to elicit homologous down-regulation of the levels of the mammalian proteins. The SARFH gene is expressed in the developing Drosophila embryo from the earliest stages of cellularization and is subsequently found in many cell types. In preparations of polytene chromosomes from salivary gland nuclei, SARFH antibodies recognize their target associated with the majority of active transcription units, revealed by colocalization with the phosphorylated form of RNA Pol II. We conclude that SARFH and, by homology, EWS and TLS participate in a function common to the expression of most genes transcribed by RNA Pol II.

Recurrent rearrangements in the high mobility group protein gene, HMGI-C, in benign mesenchymal tumours

We recently showed that the 1.7 megabase multiple aberration region (MAR) on human chromosome 12q15 harbours recurrent breakpoints frequently found in a variety of benign solid tumours. We now report a candidate gene within MAR suspected to be of pathogenetical relevance. Using positional cloning, we have identified the high mobility group protein gene HMGI-C within a 175 kilobase segment of MAR and characterized its genomic organization. By FISH analysis, we show the majority of the breakpoints of eight different benign solid tumour types fall within this gene. By Southern blot and 3'-RACE analysis, we demonstrate consistent rearrangements in HMGI-C and/or expression of altered HMGI-C transcripts. These results suggest a link between a member of the HMG gene family and benign solid tumour development.

Identification of target genes for the Ewing's sarcoma EWS/FLI fusion protein by representational difference analysis

The EWS/FLI-1 fusion gene results from the 11;22 chromosomal translocation in Ewing's sarcoma. The product of the gene is one of a growing number of structurally altered transcription factors implicated in oncogenesis. We have employed a subtractive cloning strategy of representational difference analysis in conjunction with a model transformation system to identify genes transcribed in response to EWS/FLI. We have characterized eight transcripts that are dependent on EWS/FLI for expression and two transcripts that are repressed in response to EWS/FLI. Three of the former were identified by sequence analysis as stromelysin 1, a murine homolog of cytochrome P-450 F1 and cytokeratin 15. Stromelysin 1 is induced rapidly after expression of EWS/FLI, suggesting that the stromelysin 1 gene may be a direct target gene of EWS/FLI. These results demonstrate that expression of EWS/FLI leads to significant changes in the transcription of specific genes and that these effects are at least partially distinct from those caused by expression of germ line FLI-1. The representational difference analysis technique can potentially be applied to investigate transformation pathways activated by a broad array of genes in different tumor systems.

Sensitive detection of occult Ewing's cells by the reverse transcriptase-polymerase chain reaction

Recently, Ewing's tumours have been shown to carry specific hybrid transcripts resulting from the fusion of the EWS gene with FLI-1 or ERG genes. Based on the sensitivity and specificity of the detection of these alterations by the reverse transcriptase-polymerase chain reaction technique, we have developed an assay to search for small numbers of Ewing cells in various sites from patients with Ewing's tumour. This method enables the detection of fewer than one tumour cell per million blood mononuclear cells. A total of 28 primary sites and 51 peripheral samples from 36 patients were investigated. Tumour cells could be detected in 4/18 blood samples, 4/15 bone marrow aspirates and 2/18 peripheral stem cell harvests. EWS/FLI-1 and EWS/ERG transcripts being observed in eight and two cases respectively. The type of fusion transcript detected in peripheral site(s) was identical to that observed in the primary site. At diagnosis 5/16 patients (31%) demonstrated either circulating tumour cells or/and occult bone marrow metastasis. After induction therapy, tumour cells were detected in 3/21 patients. This highly sensitive method should be a relevant tool to allow a more accurate clinical assessment of the dissemination of Ewing's tumours.

Cytogenetics and molecular genetics of human solid tumours

It is generally accepted that cancer is a genetic disease resulting from the accumulation of multiple genomic rearrangements. These rearrangements involve gross chromosomal abnormalities (e.g. translocations and deletions) as well as submicroscopic mutations affecting both oncogenes and tumour suppressor genes. Recent studies of several tumour specific translocations in sarcomas have shown that the translocations result in so-called fusion genes. In this review we will discuss the specificity and implications of different genetic alterations in both sporadic and hereditary human solid tumours, and provide examples of how these changes can be used as tumour specific markers of both diagnostic and prognostic significance.

Establishment and characterization of IRTA17 and IRTA21, two novel acute non-lymphocytic leukaemia cell lines with t(16;21) translocation

The t(16;21)(p11;q22) translocation is an infrequent chromosomal abnormality, but seems specific to acute non-lymphocytic leukaemia (ANLL). We established two cell lines with t(16;21)(p11;q22) from the bone marrow of a patient with ANL in relapse. Their morphological, karyotypic, immunohistochemical and genetic features are examined. Although both cell lines show monocytoid features morphologically, they express only CD13 (My7) and CD34, and neither expressed monocytoid or lymphoid markers. Reverse transcription-polymerase chain reaction showed that both cell lines expressed a similar TLS-ERG chimaeric mRNA as a result of the t(16;21)(p11;q22) translocation. As far as we know, there is no report of a leukaemia cell line with t(16;21). These cell lines represent a useful tool for leukaemia research.

Molecular characterization of MAR, a multiple aberration region on human chromosome segment 12q13-q15 implicated in various solid tumors

Chromosome arm 12q breakpoints in seven cell lines derived from primary pleomorphic salivary gland adenomas were mapped by FISH analysis relative to nine DNA probes. These probes all reside in a 2.8 Mb genomic DNA region of chromosome segment 12q13-q15 and correspond to previously published sequence-tagged sites (STS). Their relative positions were established on the basis of YAC cloning and long range physical and STS content mapping. The 12q breakpoints of five of the cell lines were found to be mapping within three different subregions of the 445 kb DNA interval that was recently defined as the uterine leiomyoma cluster region of chromosome 12 breakpoints (ULCR12) between STS RM33 and RM98. All seven breakpoints appeared to map within the 1.7 Mb DNA region between STS RM36 and RM103. Furthermore, the chromosome 12 breakpoints of three primary pleomorphic salivary gland adenomas were also found to be mapping between RM36 and RM103. Finally, FISH analysis of two lipoma cell lines with 12q13-q15 aberrations pinpointed the breakpoints of these to relatively small and adjacent DNA segments which, as well as those of two primary lipomas, appeared to be located also between RM36 and RM103. We conclude from the observed clustering of the 12q breakpoints of the three distinct solid tumor types that the 1.7 Mb DNA region of the long arm of chromosome 12 between RM36 and RM103 is a multiple aberration region which we designate MAR.

Cabeza, a Drosophila gene encoding a novel RNA binding protein, shares homology with EWS and TLS, two genes involved in human sarcoma formation

We have previously described a partial Drosophila cDNA, clone P19, which bears homology to members of the RNA recognition motif (RRM) family of proteins [Haynes et al. (1987) Proc. Natl. Acad. Sci. USA, 84, 1819-1823]. RNA binding as well as involvement in RNA processing has been demonstrated for some RRM proteins. We report here the further characterization of P19, which we renamed cabeza (caz). caz is located on the X chromosome at position 14B. Using Northern analysis, at least four transcripts from the caz gene were observed at varying levels during development. caz mRNA and protein are enriched in the brain and central nervous system during embryogenesis. In addition, the protein is enriched in the adult head. UV crosslinking was used to demonstrate in vitro RNA binding activity for full-length recombinant caz protein and for the caz RRM domain. Sequence analysis revealed caz is related to two human genes, EWS and TLS, which are involved in chromosomal translocations. The fusion of EWS and TLS to other cellular genes results in sarcoma formation. In addition to their overall structural organization and sequence similarity, these three genes share an RRM which is divergent from typical RRMs. Therefore, it appears that these genes constitute a new sub-family of RNA binding proteins.

The PAX3-FKHR fusion protein created by the t(2;13) translocation in alveolar rhabdomyosarcomas is a more potent transcriptional activator than PAX3

Alveolar rhabdomyosarcomas are pediatric solid tumors with a hallmark cytogenetic abnormality: translocation of chromosomes 2 and 13 [t(2;13) (q35;q14)]. The genes on each chromosome involved in this translocation have been identified as the transcription factor-encoding genes PAX3 and FKHR. The NH2-terminal paired box and homeodomain DNA-binding domains of PAX3 are fused in frame to COOH-terminal regions of the chromosome 13-derived FKHR gene, a novel member of the forkhead DNA-binding domain family. To determine the role of the fusion protein in transcriptional regulation and oncogenesis, we identified the PAX3-FKHR fusion protein and characterized its function(s) as a transcription factor relative to wild-type PAX3. Antisera specific to PAX3 and FKHR were developed and used to examine PAX3 and PAX3-FKHR expression in tumor cell lines. Sequential immunoprecipitations with anti-PAX3 and anti-FKHR sera demonstrated expression of a 97-kDa PAX3-FKHR fusion protein in the t(2;13)-positive rhabdomyosarcoma Rh30 cell line and verified that a single polypeptide contains epitopes derived from each protein. The PAX3-FKHR protein was localized to the nucleus in Rh30 cells, as was wild-type PAX3, in t(2;13)-negative A673 cells. In gel shift assays using a canonical PAX binding site (e5 sequence), we found that DNA binding of PAX3-FKHR was significantly impaired relative to that of PAX3 despite the two proteins having identical PAX DNA-binding domains. However, the PAX3-FKHR fusion protein was a much more potent transcriptional activator than PAX3 as determined by transient cotransfection assays using e5-CAT reporter plasmids. The PAX3-FKHR protein may function as an oncogenic transcription factor by enhanced activation of normal PAX3 target genes.

The protooncogene CHOP/GADD153, involved in growth arrest and DNA damage response, is amplified in a subset of human sarcomas

The C/EBP-homologous transcription factor CHOP (GADD153) is inducible by growth inhibition or DNA damage, and has been shown to be oncogenically activated by the specific (12;16) translocation in human myxoid liposarcoma. We have now found CHOP amplification in two sarcoma cell lines with previously reported amplification of the nearby GLI gene. Among 98 other human sarcomas of various types, CHOP was amplified in a hemangiopericytoma, a liposarcoma, and two osteosarcoma. High constitutive expression levels of CHOP were observed in tumors with gene amplification, but also in some other samples. The nearby MDM2 gene, which codes for a protein that may inactivate wild-type p53, has previously been reported to be frequently amplified in sarcoma. In our sarcoma panel, MDM2 was amplified in 9 cases. MDM2 and CHOP were co-amplified in two of these, whereas the two osteosarcomas had amplified CHOP but not MDM2. CHOP was amplified in both cell lines with GLI amplification, and MDM2 only in one. No mutations in the TP53 gene have been found in samples with amplification of MDM2. In contrast, the cell line in which CHOP but not MDM2 was amplified had mutated TP53, suggesting that selection of this amplicon was not mediated through p53 inactivation.

Fusion of the FUS gene with ERG in acute myeloid leukemia with t(16;21)(p11;q22)

It has been shown that the gene ERG in 21q22 is rearranged in the t(16;21)(p11;q22) associated with acute myeloid leukemia (AML). ERG is a member of the ETS gene family and is fused with EWS in a subset of Ewing's sarcomas. EWS in 22q12 has a very high homology with FUS (also called TLS) in 16p11; the latter gene is rearranged in the t(12;16)(q13;p11) that characterizes myxoid liposarcoma. To investigate whether FUS is involved in the t(16;21) of AML, we used the Southern blot technique and polymerase chain reaction (PCR) to examine the bone marrow of a 3-year-old boy with a t(16;21)(p11;q22)-positive AML. Hybridization of Southern blot filters containing digested DNA with probes for FUS and ERG showed both germline and aberrant fragments. Using specific primers for the 5' part of FUS and the 3' part of ERG, we amplified a 4.4 kb genomic FUS/ERG DNA fragment from the leukemic sample. In a second PCR experiment, in which we used primers upstream of the 5' part of ERG and downstream of the 3' part of FUS, a 5.6 kb fragment was amplified. Blotting and hybridization with specific probes for FUS and ERG revealed that the amplified fragments consisted of FUS/ERG and ERG/FUS hybrid DNA. Both PCR fragments, when used as probes, detected germline ERG and FUS as well as aberrant fragments on Southern blot filters. The results suggest that the t(16;21) in AML leads to rearrangement and fusion of the FUS and ERG genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytogenetics of tumors of soft tissue and bone. Implication for pathology

Pathologists should be aware of the existence of diagnostically useful chromosomal rearrangements in several soft tissue and bone tumors. They include rearrangement of 8q12 in lipoblastomas, ring chromosomes in atypical lipomas, ring and giant marker chromosomes in well differentiated liposarcomas, t(12;16)(q13;p11) in myxoid liposarcomas, rearrangement of 7p21-22 in low-grade endometrial stromal sarcomas, t(2;13)(q37;q14) in alveolar rhabdomyosarcomas, t(X;18)(p11.2;q11.2) in synovial sarcomas, t(12;22) (q13;q13) in clear cell sarcomas, t(11;22)(q24;q12) in Ewing's sarcomas and peripheral neuroepitheliomas, and t(9;22)(q21-31;q11-12) in extraskeletal myxoid chondrosarcomas.

Chromosomal translocations in human cancer

Chromosomal abnormalities in tumours were recognized at the end of the last century but their significance has only recently become clear. Distinct translocations in leukaemias and in solid tumours lead to the activation of proto-oncogene products or, more commonly, creation of tumour-specific fusion proteins. The proteins in both categories are often transcription factors and thus disruption of transcriptional control plays a major role in the aetiology of cancer. Fusion proteins formed after chromosomal translocations are common in a range of tumour types; these are unique tumour antigens and are therefore potential targets for therapy design.

A novel effector domain from the RNA-binding protein TLS or EWS is required for oncogenic transformation by CHOP

In human myxoid liposarcoma, a chromosomal rearrangement leads to fusion of the growth-arresting and DNA-damage-inducible transcription factor CHOP (GADD153) to a peptide fragment encoded by the TLS gene. We have found that wild-type TLS and a closely related sarcoma-associated protein, EWS, are both abundant nuclear proteins that associate in vivo with products of RNA polymerase II transcription. This association leads to the formation of a ternary complex with other heterogeneous RNA-binding proteins (hnRNPs), such as A1 and C1/C2. An NIH-3T3-based transformation assay was used to study the oncogenic role of the sarcoma-associated domain of these RNA-binding proteins. Transduction of the TLS-CHOP oncogene into cells by means of a retroviral expression vector leads to loss of contact inhibition, acquisition of the ability to grow as colonies in soft agar, and tumor formation in nude mice. Mutations that interfere with the function of the leucine zipper dimerization domain or the adjacent basic region of CHOP abolish transformation. The essential role of the TLS component was revealed by the inability of truncated forms to fully transform cells. Domain swap between TLS- and EWS-associated oncogenes demonstrated that the component contributed by the RNA-binding proteins are functionally interchangeable, whereas the transcription factor component specifies tumor phenotype. The sarcoma-associated component of TLS and EWS contribute a strong transcriptional activation domain to the fusion proteins; however, transforming activity cannot be fully substituted by fusion of CHOP to other strong trans-activators. The juxtaposition of a novel effector domain from sarcoma-associated RNA-binding proteins to the targeting domain of transcription factors such as CHOP leads to the creation of a potent oncogene.