Novel oncogenic mutations in the WT1 Wilms' tumor suppressor gene: a t(11;22) fuses the Ewing's sarcoma gene, EWS1, to WT1 in desmoplastic small round cell tumor

Treatment of Desmoplastic Small round Cell Tumor with Image-Guided Intensity Modulated Radiation Therapy as a Component of Multimodality Treatment

Aims and background

The authors report the case of a 31-year-old black male diagnosed with a pelvic desmoplastic small round-cell tumor who was treated with a unique radiotherapy approach incorporating intensity-modulated radiotherapy and daily ultrasound localization to ensure accurate tumor targeting. Desmoplastic small round-cell tumor is a very rare tumor, most commonly presenting in the abdominopelvic regions of adolescents and young adults. It has generally been associated with a very poor prognosis.

Methods

The patient initially underwent biopsy of the mass and omentectomy for mesenteric implants followed by chemotherapy. Chemotherapy resulted in tumor shrinkage and was followed by a second-look laparotomy. Additional omental nodules were resected, but the primary tumor was adherent to the rectum and seminal vesicles. A radiation oncology consult was obtained, and a course of image-guided intensity-modulated radiotherapy ensued with daily ultrasound localization. This resulted in shrinkage of local disease, but a new lesion was identified. The patient was subsequently started on further chemotherapy, which has maintained the disease in a stable state for several months.

Conclusions

Image-guided intensity-modulated radiotherapy is a feasible option in the treatment of pelvic desmoplastic small round-cell tumor. Such therapy may permit escalation of conventional radiotherapy doses and could have a favorable impact on local control of disease. Confirmation of this belief will require additional data in the form of case reports like this. Pending such confirmation, we continue to be of the impression that desmoplastic small round-cell tumor has an overall unfavorable prognosis, regardless of treatment modalities employed.

Molecular strategies for detecting chromosomal translocations in soft tissue tumors (review)

Approximately one third of soft tissue tumors are characterized by chromosomal aberrations, in particular, translocations and amplifications, which appear to be highly specific. The identification of fusion transcripts not only supports the diagnosis, but provides the basis for the development of novel therapeutic strategies aimed at blocking the aberrant activity of chimeric proteins. Molecular biology, and in particular, cytogenetic and qualitative and quantitative polymerase chain reaction technologies, allow with high efficiency and specificity, the determination of specific fusion transcripts resulting from chromosomal translocations, as well as the analysis of gene amplifications. In this review, various molecular techniques that allow the identification of translocations and consequent fusion transcripts generated are discussed in the broad spectrum of soft tissue tumors.

The significance of Wilms Tumor Gene (WT1) and p53 expression in curettage specimens of patients with endometrial carcinomas

In this retrospective experimental study, we assessed the immunohistochemical expression of Wilms Tumor Gene (WT1) and p53 in endometrial biopsies of patients with endometrial cancer, and correlated their expression with the final pathological findings. Sixty-two patients with primary endometrial cancer who underwent surgical treatment were investigated. Immunohistochemical expression of Wilms Tumor Gene (WT1) and p53 was assessed in curettage specimens, and the final pathology reports from hysterectomy specimens were reviewed. The expression of these markers seems to play a role in curettage specimens as they correlate with the final tumor characteristics of hysterectomy specimens. Five out of sixty-two endometrial cancer specimens (8.1%) were WT1-positive, and 21 specimens (33.9%) were P53-positive. Positive expression of WT1 and P53 was significantly associated with the non-endometrioid type (p value of 0.019 and 0.005, respectively). Positive WT1 expression was significantly associated with high grade lesions, deep myometrial invasion, and advanced stage disease. Moreover, a statistically significant inverse relationship was observed between the positivity of WT1 and P53, and the positivity of ER and PR. We think that examination for WT1 and p53 in curettage specimens might help to predict the final pathological diagnosis in patients with endometrial cancer. This might be useful for the identification of high risk groups and, therefore, of candidates for more radical surgery.

The role of insulin-like growth factor system in soft tissue sarcomas: from physiopathology to targeted therapeutic approaches

Purpose/Results. Although surgical, chemo- and radiotherapeutic treatment regimens in patients with soft tissue sarcomas have constantly been refined over the past two decades, the survival rate for these patients is rather low.

Discussion. There is a great need to investigate the mechanisms for oncogenesis and to identify the factors involved in malignant transformation in sarcomas. Among these factors, IGFs are thought to play a pivotal role as progression factors in various types of sarcomas. The dysregulation of the IGF-II synthesis, e.g. by loss of imprinting which occurs in most types of sarcomas, is a permissive effect through the suppression of cell death. In addition, cells that overexpress the type I IGF receptors are more susceptible to transformation by oncogenes. As TP53 suppresses the activity of IGF-II P3 and P4, as well as the type I IGF receptor promoter, mutations of TP53 in sarcomas may alternatively lead to the activation of these factors. Finally, the phenomenon of non-islet cell tumour hypoglycaemia that occurs in patients with sarcomas, and which is related to the secretion of IGF-II prohormones, is discussed. Future therapeutic strategies may be based upon the application of antibodies or antisense oligonucleotides directed against the type I IGF receptors, with the common goal of inducing apoptosis in sarcoma cells. Ultimately, these and other therapeutic approaches may lead to a better outcome in patients suffering from sarcoma.

A novel EWS-WT1 gene fusion product in desmoplastic small round cell tumor is a potent transactivator of the insulin-like growth factor-I receptor (IGF-IR) gene

Desmoplastic small round cell tumor (DSRCT) is a primitive sarcoma characterized by a recurrent chromosomal translocation, t(11;22)(p13;q12), which fuses the 5' exons of the EWS gene to the 3' exons of the WT1 gene. EWS-WT1 chimeras are heterogeneous as a result of fusions of different regions of the EWS gene to the WT1 gene. We report here a rare and novel EWS-WT1 variant, EWS-WT1 5/10, in a 6-year-old boy diagnosed with DSRCT and analyze the potential transactivation effect of the fusion oncoprotein. The predicted product is comprised of the N-terminal transactivation domain of EWS and lacks any sequence derived from the WT1 gene product. Nonetheless, the truncated protein was able to stimulate expression of the insulin-like growth factor-I receptor gene, a potent antiapoptotic receptor tyrosine kinase with potentially important roles in DSRCT etiology. These findings raise the possibility that the oncogenic potential of EWS-WT1 fusions is not necessarily a consequence of the fusion protein product per se.

Adult human sarcomas. I. Basic science

When connective tissue undergoes malignant transformation, glioblastomas and sarcomas arise. However, the ancient biochemical mechanisms, which are now operational in sarcomas distorted by mutations and gene fusions in misaligned chromosomes, were originally acquired by those cells that emerged during the Cambrian explosion. Preserved throughout evolution up to the genus Homo, these mechanisms dictate the apoptosis- and senescence-resistant immortality of malignant cells. A 'retroviral paradox' distinguishes human sarcomas from those of the animal world. In contrast to the retrovirally induced sarcomatous transformation of animal (avian, murine, feline and simian) cells, human sarcomas have so far failed to yield a causative retroviral isolate. However, the proto-oncogenes/oncogenes transduced from their host cells by retroviruses of animals are the same that are active in human sarcomas. Since the encoded oncoproteins arise after birth, they are recognized frequently by the immune system of the host. Immune lymphocytes that kill autologous sarcoma cells in vitro commonly fail to do so in vivo. Sarcoma vaccines generate immune T- and natural killer cell reactions; even when vaccinated patients do not show a clinical response, their tumors become more sensitive to chemotherapy. The aim of this review is to lay a solid molecular biological foundation for the conclusion that targeting the sarcoma oncogenes will result in regression of the disease.

EWS–ETS oncoproteins: The linchpins of Ewing tumors

Ewing tumors, which comprise Ewing's sarcoma and peripheral primitive neuroectodermal tumors, are highly aggressive and mostly affect children and adolescents. Their molecular signature is a chromosomal translocation leading to the generation of EWS-ETS (or very rarely FUS-ETS) fusion proteins that are capable of transforming cells. These oncoproteins act as aberrant transcription factors due to the fusion of an ETS DNA binding domain to a highly potent EWS (or FUS) transactivation domain. Accordingly, many EWS-ETS target genes have been identified whose dysregulation could contribute to the development of tumor formation. Furthermore, EWS-ETS oncoproteins may impact on RNA splicing or affect other proteins through disturbing their ability to form functional complexes. The molecular knowledge gained so far from studying EWS-ETS oncoproteins has not only broadened our understanding of Ewing tumors but also improved the diagnosis of these highly undifferentiated tumors. In addition, several potential prognostic markers have been uncovered and novel therapies are suggested that may improve the still dismal survival rate of Ewing tumor patients.

Rapamycin induces apoptosis of JN-DSRCT-1 cells by increasing the Bax : Bcl-xL ratio through concurrent mechanisms dependent and independent of its mTOR inhibitory activity

Rapamycin, a complex macrolide and potent fungicide, immunosuppressant and anticancer agent, is a highly specific inhibitor of mammalian target of rapamycin (mTOR). Rapamycin has been shown to induce G1-phase cell cycle arrest in diverse tumor cell types, and its derivatives RAD001 and CCI-779 are currently in phase I and phase II clinical trials, respectively, as anticancer agents. In this study, we show that rapamycin induced the apoptotic death of JN-DSRCT-1 cells, the only available in vitro model for Desmoplastic Small Round Cell Tumors (DSRCT), while having only minor effects on their cell cycle. Rapamycin induced apoptosis by increasing the Bax : Bcl-xL ratio as a consequence of the concomitant downregulation of Bcl-xL and upregulation of Bax, both at the post-transcriptional level. Rapamycin also downregulated the levels of EWS/WT1, the fusion protein characteristic of DSRCT. Transient transfection studies using kinase-dead and rapamycin-resistant forms of mTOR demonstrated that only the downregulation of Bcl-xL was caused by the mTOR inhibitory action of rapamycin, which prevented cap-dependent translation initiation, whereas Bax upregulation was induced by rapamycin through a mechanism independent of its mTOR inhibitory activity. Moreover, rapamycin treatment downregulated the mRNA and protein levels of the 26S p44.5 proteasome subunit, suggesting the involvement of the proteasome complex in the mechanisms of rapamycin-induced apoptosis. Treatment of JN-DSRCT-1 cells with MG-132, a proteasome specific inhibitor, also resulted in the induction of apoptosis through a similar increase in the Bax : Bcl-xL ratio specifically caused by inhibiting Bax degradation and turnover. These results suggested that rapamycin induces apoptosis by preventing the degradation of the Bax protein by the proteasome, and that this process is independent of mTOR inhibition. Furthermore, these results strongly support the introduction of the use of rapamycin as a cytotoxic agent for the treatment of DSRCT.

Desmoplastic Small Round Cell Tumor of the Kidney

Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive, malignant tumor usually present with widespread abdominal serosal involvement. Isolated cases occur in limbs, head and neck, and brain. We present a case of primary DSRCT of the kidney in a 41-year-old man. The tumor showed morphologic, immunohistochemical, and molecular characteristics similar to DSRCTs arising in other sites. Epithelial and mesenchymal markers were coexpressed in the tumor cells. RT-PCR analysis showed EWS-WT1 fusion transcripts resulting from the t(11;22)(p13;q12) reciprocal translocation. DSRCT should be considered in the differential diagnosis of small blue round cell tumors of the kidney.

Wilms Tumor Gene (WT1) and p53 expression in endometrial carcinomas: a study of 130 cases using a tissue microarray

OBJECTIVE

With the exception of ovarian serous carcinoma, Wilms tumor suppressor gene (WT1) expression in common gynecologic carcinomas has not been described in detail. We studied a large number of endometrial carcinomas to determine the range of tumors that express WT1; this could have prognostic and therapeutic significance.

METHODS

We studied the immunohistochemical expression of WT1 and p53 in 130 primary human endometrial carcinomas of various histological subtypes, grades, and stages using a tissue microarray. The clinical data were retrieved from the medical records.

RESULTS

WT1 was expressed in a wide variety of endometrial cancers and was most marked in malignant mixed Mullerian tumors (MMMTs) (70% positive). WT1 expression was significantly correlated with high histological grade, and there was a trend toward a worse clinical outcome for patients whose tumors expressed WT1. An association between expression of WT1 and p53 and between these and outcome was noted in a univariate analysis, but only stage and p53 status remained prognostically significant independent variables.

CONCLUSION

WT1 is expressed in appreciable numbers of endometrial cancers, particularly MMMTs. These findings support further investigation of WT1 as a possible therapeutic target in gynecologic malignancies.

Stimulation of hTAFII68 (NTD)-mediated transactivation by v-Src

The three genes hTAF(II)68, EWS, and TLS (called the TET family) encode related RNA binding proteins containing an RNA recognition motif and three glycine-, arginine-, and proline-rich regions in the C-terminus and a degenerated repeat containing the consensus sequence Ser-Tyr-Gly-Gln-Ser in the N-terminus. In many human cancers, the N-terminal portion of hTAF(II)68, EWS, or TLS is fused to the DNA binding domain of one of several transcription factors including Fli-1, ERG, ETV1, E1AF, WT1, ATF-1, CHOP, or TEC. We have recognized the presence of several potential tyrosine phosphorylation sites within the amino-terminal domain of hTAF(II)68 and have investigated the potential effects of cytoplasmic signaling on hTAF(II)68 function. Herein, we find that hTAF(II)68 is phosphorylated on tyrosine residue(s) by ectopic expression of v-Src protein tyrosine kinase in vitro and in vivo. The hTAF(II)68 protein can associated with the SH3 domains of several cell signaling proteins, including v-Src protein tyrosine kinase. We also document that full-length v-Src can stimulate hTAF(II)68-mediated transcriptional activation, whereas deletion mutants of v-Src are unable to exert this effect. In addition, cellular Src activity appears important for hTAF(II)68 function since hTAF(II)68-mediated transactivation is reduced in a dose-dependent fashion by ectopic overexpression of a dominant-negative mutant of Src. Taken together, our results suggest that the biological activities of hTAF(II)68 are linked to the cytoplasmic Src signal transduction pathway.

The IGFI receptor gene: a molecular target for disrupted transcription factors

The biological actions of the insulin-like growth factors, IGFI and IGFII, are mediated by their activation of the IGFI receptor (IGFIR), a transmembrane heterotetramer linked to the RAS-RAF-MAPK and PI3K-PKB/AKT signal transduction cascades. The IGFIR displays potent mitogenic, antiapoptotic, and transforming activities, and is a prerequisite for oncogenic transformation. A number of transcription factors have been identified that control the expression of this gene and therefore determine, to a significant extent, the proliferative status of the cell. The purpose of this review is to summarize data showing that, under normal physiological conditions, expression of the IGFIR is under inhibitory control by a family of negative growth regulators or tumor suppressors. Cells with a reduced number of cell-surface receptors are unable to progress through the cell cycle and remain in a postmitotic state. Loss-of-function mutation of tumor suppressors in certain cancers results in transcriptional derepression of the IGFIR gene, with ensuing increases in the levels of IGFIR and increased proliferative capacity. Understanding the molecular mechanisms responsible for transcriptional regulation of the IGFIR gene will prove important in designing novel therapies aimed at targeting the IGF axis.

Induction of BAIAP3 by the EWS-WT1 chimeric fusion implicates regulated exocytosis in tumorigenesis

Desmoplastic small round cell tumor (DSRCT) is defined genetically by the chimeric fusion of the Ewing's sarcoma and Wilms' tumor genes, generating a novel transcription factor, EWS-WT1. By using cells with inducible EWS-WT1 to screen high-density microarrays, we identified BAIAP3 as a transcriptional target of the chimera. The BAIAP3 promoter is specifically bound in vivo by the (-KTS) isoform of EWS-WT1, consistent with its activation in reporter assays. BAIAP3 encodes a protein implicated in regulated exocytosis, which is colocalized with a secreted growth factor within cytoplasmic organelles. Ectopic expression of BAIAP3 in tumor cells dramatically enhances growth in low serum and colony formation in soft agar. BAIAP3 therefore encodes a transcriptional target of an oncogenic fusion protein that implicates the regulated exocytotic pathway in cancer cell proliferation.

Transcriptional regulation of IGF-I receptor gene expression by novel isoforms of the EWS-WT1 fusion protein

The EWS family of genes is involved in numerous chromosomal translocations that are characteristic of a variety of sarcomas. A recently described member of this group is desmoplastic small round cell tumor (DSRCT), which is characterized by a recurrent t(11;22)(p13;q12) translocation that fuses the 5' exons of the EWS gene to the 3' exons of the WT1 gene. The originally described chimera comprises exons 1-7 of EWS and exons 8-10 of WT1. We have previously reported that the WT1 protein represses the expression of the IGF-I receptor gene, whereas the EWS(1-7)-WT1(8-10) fusion protein activates IGF-I receptor gene expression. It has recently become apparent that EWS-WT1 chimeras produced in DSCRT are heterogeneous as a result of fusions of different regions of the EWS gene to the WT1 gene. We have recently characterized additional EWS-WT1 translocations that involve the juxtaposition of EWS exons 7 or 8 to WT1 exon 8, and an EWS-WT1 chimera that lacks EWS exon 6. The chimeric transcription factors encoded by these various translocations differ in their DNA-binding characteristics and their ability to transactivate the IGF-I receptor promoter. These data suggest that the molecular pathology of DSRCT is more complex than previously appreciated, and that this diversity may provide the foundation for predictive genotype-phenotype correlations in the future.

Transcriptional regulation of IGF-I receptor gene expression by the PAX3-FKHR oncoprotein

Chromosomal translocations that disrupt the molecular organization of transcription factors are typical of a variety of solid and hematopoietic cancers. Alveolar rhabdomyosarcoma (ARMS), a paediatric soft tissue malignant tumour, is characterized by the recurrent translocation t(2;13)(q35;q14) that fuses the 5' DNA binding domain-encoding sequences of the Pax3 gene with the 3' sequences of the FKHR gene. The insulin-like growth factor (IGF) system has an important role in muscle development as well as in the aetiology of paediatric sarcomas, including ARMS. In the present study the potential regulation of the IGF-I receptor (IGF-I-R) gene by PAX3-FKHR at the transcriptional level was investigated. PAX3-FKHR was able to transactivate the IGF-I-R promoter in sarcoma-derived cell lines, whereas PAX3 exhibited a reduced potency in comparison to the fusion protein. Furthermore, transfection of the chimera induced a significant increase in the endogenous levels of IGF-I-R protein, suggesting that the IGF-I-R gene is a physiologically-relevant molecular target for the PAX3-FKHR oncogene.

Biology of EWS/ETS fusions in Ewing's family tumors

Tumor-associated chromosomal translocations lead to the formation of chimeric fusions between the EWS gene and one of five different ETS transcription factors in Ewing's family tumors (EFTs). The resultant EWS/ETS proteins promote oncogenesis in a dominant fashion in model systems and are necessary for continued growth of EFT cell lines. EWS belongs to a family of genes that encode proteins that may serve as adapters between the RNA polymerase II complex and RNA splicing factors. EWS/ETS fusions have biochemical characteristics of aberrant transcription factors and appear to promote abnormal cellular growth by transcriptionally modulating a network of target genes. Early evidence suggests that EWS/ETS proteins may also impact gene expression through alteration in RNA processing. Elucidation of EWS/ETS target gene networks in the context of other signaling pathways will hopefully lead to biology based therapeutic strategies for EFT.

Desmoplastic small round cell tumor presenting as a neck mass: a case report

An unusual case study of a desmoplastic small round cell tumor presenting as a 3.5-cm, firm, supraclavicular neck mass and diagnosed by fine-needle aspirate biopsy in a 16-yr-old male is reported. Clinical, cytologic, and immunocytochemical findings are described. Histologic, immunohistochemical, and genetic features are discussed. Desmoplastic small round cell tumor should be considered in the differential diagnosis of small round cell tumors of any site; the importance of ancillary studies in arriving at the correct diagnosis is emphasized.

EWS.Fli-1 fusion protein interacts with hyperphosphorylated RNA polymerase II and interferes with serine-arginine protein-mediated RNA splicing

Ewing's sarcoma displays a characteristic chromosomal translocation that results in fusion of the N-terminal domain of the Ewing's sarcoma protein (EWS) to the C-terminal DNA-binding domain of the ETS family transcription factor Fli-1 (Friend leukemia integration-1). EWS possesses structural motifs suggesting a role in transactivation as well as RNA binding. We demonstrate that wild-type EWS protein functions as an adapter molecule coupling transcription to RNA splicing by binding to hyperphosphorylated RNA polymerase II through the N-terminal domain of EWS and recruiting serine-arginine (SR) splicing factors through the C-terminal domain of EWS. The oncogenic EWS.Fli-1 fusion protein retains the ability to bind to hyperphosphorylated RNA polymerase II but lacks the ability to recruit SR proteins because of replacement of the C-terminal domain of EWS by Fli-1. In an in vivo splicing assay, the EWS.Fli-1 fusion protein inhibits SR protein-mediated E1A pre-mRNA splicing in a dominant-negative manner. These results indicate that EWS.Fli-1 interferes with the normal function of EWS and implicate uncoupling of gene transcription from RNA splicing in the pathogenesis of Ewing's sarcoma.

Regulation of the insulin-like growth factor-I receptor gene by oncogenes and antioncogenes: implications in human cancer

The insulin-like growth factor-I receptor (IGF-I-R) has a central role in normal cellular proliferation as well as in transformation processes. Transcription of the IGF-I receptor gene is controlled by a number of tumor suppressors, including WT1, p53, and BRCA1. It has been demonstrated that, in their wild-type form, these transcription factors can suppress the activity of the IGF-I-R promoter, with ensuing reduction in the levels of cell-surface IGF binding. On the other hand, a number of oncogenes, including mutant p53 and c-myb, and the fusion protein EWS-WT1 significantly stimulate promoter activity. Interactions between stimulatory and inhibitory transcription factors may determine the level of expression of the IGF-I-R gene and, consequently, the proliferative status of the cell.

Modulation of EWS/WT1 activity by the v-Src protein tyrosine kinase

Desmoplastic small round cell tumor (DSRCT) is a malignant human cancer that is associated with a specific t(11;22) chromosome translocation, where 265 amino acids from the EWS amino-terminus are fused to the DNA binding domain of the WT1 tumor suppressor gene. We have noticed the presence of several SH3 interacting domains within the amino-terminus of EWS and have assessed the potential of EWS/WT1 to interact with such motifs. We find that EWS/WT1 can associate with the SH3 domain of several proteins, including v-Src. Ectopic expression of v-Src phosphorylates EWS/WT1 in vivo, as well as enhances the transactivation ability of the EWS amino-terminal domain. Structural alteration of the v-Src SH2 or SH3 domains produced mutants that could not interact with EWS/WT1 nor augment the transcriptional properties of EWS. Taken together, our results suggest the possibility that some transcriptional properties of EWS/WT1 may be regulated by a cytoplasmic signaling pathway.

Biphenotypic sarcoma with characteristics of both a Ewing sarcoma and a desmoplastic small round cell tumor

BACKGROUND

The EWS gene, a transcription factor of unknown function, is involved in chromosomal translocations associated with a wide variety of tumors, particularly small round blue cell tumors such as Ewing sarcoma. It has previously been reported that desmoplastic small round blue cell tumor (DSRBCT) frequently has an associated t(11;22) abnormality resulting from fusion of the EWS and WT-1 genes.

PROCEDURE

We report a case of a small round blue cell tumor with characteristics of both Ewing sarcoma and DSRBCT with a t(11;22) translocation leading to fusion of the EWS and FLI1genes.

RESULTS

The translocation point and fusion products were confirmed by polymerase chain reaction amplification and restriction fragment mapping of the products.

CONCLUSIONS

The biphenotypic nature of this case and the apparent promiscuity of the EWS gene in tumor-associated translocations coupled with other reports of biphenotypic childhood sarcomas has potential implications for the relationship between small round blue cell tumors and the mechanism of EWS/FLI1 oncogenesis.

A KRAB zinc finger protein gene is the potential target of 19q13 translocation in benign thyroid tumors

In an attempt to identify the target gene of specific translocations involving chromosomal band 19q13 in benign follicular thyroid tumors, we have used two cell lines derived from benign thyroid tumors showing translocations with 19q13 breakpoints for fluorescence in situ hybridization mapping studies with cosmid and PAC clones located in a 400-kbp region. The breakpoints of the chromosome 19 abnormalities mapped within a 140-kb segment covered by a single PAC clone. Sequencing of part of this PAC clone allowed us to establish the cDNA sequence and the genomic structure of a candidate gene located in close vicinity to the breakpoints. The gene that we tentatively refer to as RITA (rearranged in thyroid adenomas) belongs to the KRAB zinc finger protein coding genes. From our results we have concluded that in the two cell lines investigated the breaks have occurred either within the 5' untranslated region of RITA or in its close 5' vicinity. By Northern blot analyses two transcripts of about 4.7 kbp and 5 kbp were detected in normal thyroid tissue as well as in other normal tissues tested. An additional 2.1-kbp transcript was found only in testicular tissue. In contrast to all normal tissues, both cell lines with 19q aberrations expressed larger transcripts of approximately 5.5 kbp and 6.2 kbp. From the close vicinity to the breakpoint region, the expression patterns of the gene, and its type, we consider RITA a strong candidate target gene of the specific 19q aberrations in benign thyroid tumors.

Modification of EWS/WT1 functional properties by phosphorylation

In many human cancers, tumor-specific chromosomal rearrangements are known to create chimeric products with the ability to transform cells. The EWS/WT1 protein is such a fusion product, resulting from a t(11;22) chromosomal translocation in desmoplastic small round cell tumors, where 265 aa from the EWS amino terminus are fused to the DNA binding domain of the WT1 tumor suppressor gene. Herein, we find that EWS/WT1 is phosphorylated in vivo on serine and tyrosine residues and that this affects DNA binding and homodimerization. We also show that EWS/WT1 can interact with, and is a substrate for, modification on tyrosine residues by c-Abl. Tyrosine phosphorylation of EWS/WT1 by c-Abl negatively regulates its DNA binding properties. These results indicate that the biological activity of EWS/WT1 is closely linked to its phosphorylation status.

Molecular genetics of chromosome translocations involving EWS and related family members

Many types of sarcomas are characterized by specific chromosomal translocations that appear to result in the production of novel, tumor-specific chimeric transcription factors. Many of these show striking similarities: the emerging picture is that the amino-terminal domain of the fusion product is donated by the Ewing's sarcoma gene (EWS) or a related member from the same gene family, whereas the carboxy-terminal domain often consists of a DNA-binding domain derived from one of a number of transcription factors. Given the observation that the different translocation partners of the EWS protooncogene are associated with distinct types of sarcomas, the functional consequence of fusing EWS (or a related family member) to a different DNA-binding domain can only be understood in the context of functional studies that define the specificity of action of the different fusion products. An understanding of the molecular structure and function of these translocations provides new methods for diagnosis and novel targets for therapeutics.

Expression of WT1 in pediatric small cell tumors: report of two cases with a possible mesothelial origin

The WT1 gene is normally expressed in fetal kidney and mesothelium, and its expression has been suggested as a marker for Wilms tumor and mesothelioma. We examined WT1 expression levels by reverse-transcriptase polymerase chain reaction (RT-PCR) in 38 childhood small-cell tumors including Wilms tumor, embryonal and alveolar rhabdomyosarcoma, Ewing sarcoma, lymphoma, desmoplastic small round-cell tumor (DSRCT), synovial sarcoma, extrarenal rhabdoid tumor, and two tumors that were atypical for this group of tumors. WT1 expression was only detected in Wilms tumor, rhabdoid tumor, and in these two cases of uncertain histogenesis. Both arose in the peritoneal cavity and by immunohistochemistry were diffusely positive for vimentin, keratin, and desmin. Tonofilaments were identified by electron microscopy in one of the cases. RT-PCR failed to detect the t(11;22) translocation associated with DSRCT in either case. Our results suggest that WT1 expression is an unusual feature of childhood non-Wilms tumors and, in the right setting, it may indicate a mesothelial origin. The expression of WT1 may play a role in mesodermal cells acquiring epithelial characteristics, a concept supported by the mixed epithelial and mesenchymal phenotype of these two cases.

Novel breakpoints of the EWS gene and the WT1 gene in a desmoplastic small round cell tumor

We report here a 15-year-old boy with an intraabdominal desmoplastic small round cell tumor (DSRCT). Cytogenetic analysis of the tumor cells showed the chromosomal translocation (11;22). Reverse-transcriptase polymerase chain reaction and sequencing analysis revealed a chimeric transcriptional message of the EWS gene exon 10 fused to the WT1 gene exon 8. The typical chimeric transcript seen in DSRCT is an in-frame fusion of EWS exon 7 to WT1 exon 8. The tumor in this case had a novel and longer chimeric transcript, which should be a potent transcription factor. Genetic analysis is a very powerful and specific aid in the differential diagnosis of small round cell tumors.

Molecular genetics in the diagnosis and prognosis of solid pediatric tumors

The field of molecular genetics continues to see an ever increasing number of applications to pediatric tumor analysis. Studies in pediatric tumors have identified novel genes and other genetic changes, a large number of which reflect one of the following mechanisms: (1) activation of proto-oncogenes; (2) loss of tumor suppressor genes; or (3) creation of novel fusion proteins. At least one of these mechanisms is operational in each of the following pediatric tumors: neuroblastoma, Ewing sarcoma and peripheral primitive neuroectodermal tumor (pPNET), intra-abdominal desmoplastic small-cell tumor, rhabdomyosarcoma, synovial sarcoma, and Wilms tumor. Out of this research has come not only an increased understanding of oncogenesis but also, for each of the tumors listed above, diagnostic and/or prognostic markers that can be used by the pathologist and oncologist to improve overall patient management.

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.

The IGF-I receptor gene promoter is a molecular target for the Ewing's sarcoma-Wilms' tumor 1 fusion protein

Desmoplastic small round cell tumor (DSRCT) is an abdominal malignancy in children which is characterized by a recurrent chromosomal translocation, t(11;22)(p13;q12). This rearrangement results in the fusion of the ubiquitously expressed EWS1 gene to the Wilms' tumor suppressor (WT1) gene. The chimeric protein contains the N-terminal domain of EWS1 fused to the DNA-binding domain of WT1, including zinc fingers 2-4. Because WT1 has been shown previously to bind and repress the insulin-like growth factor I (IGF-I-R) promoter, we investigated whether this promoter is, in addition, a target for the aberrant EWS/WT1 transcription factor. EWS/WT1 activated the IGF-I-R promoter approximately 340%, whereas a fusion protein containing a three-amino acid insert (KTS) between zinc fingers 3 and 4 had no effect. On the other hand, expression vectors encoding either WT1 or EWS1 reduced the activity of the promoter to 46 and 58% of control values, respectively. Results of gel shift assays indicate that the binding affinity of EWS/WT1 to a fragment of the 5'-flanking region of the receptor promoter was higher than the affinity of WT1 itself. Consistent with the results of functional assays, the binding of EWS/WT1(+KTS) was significantly reduced. Due to the central role of the IGF-I-R in tumorigenesis, activation of the receptor promoter by EWS/WT1 may constitute a potential mechanism for the etiology and/or progression of DSRCT.