Identification of syt-ssx fusion transcripts in both epithelial and spindle cell components of biphasic synovial sarcoma in small tissue samples isolated by membrane-based laser microdissection

SYT-SSX1 and SYT-SSX2 Interfere with Repression of E-Cadherin by Snail and Slug: A Potential Mechanism for Aberrant Mesenchymal to Epithelial Transition in Human Synovial Sarcoma

Synovial sarcoma is a primitive mesenchymal neoplasm characterized in almost all cases by a t(X;18) fusing the SYT transcriptional coactivator gene with either SSX1 or SSX2, with the resulting fusion gene encoding an aberrant transcriptional regulator. A subset of synovial sarcoma, predominantly cases with the SYT-SSX1 fusion, shows foci of morphologic epithelial differentiation in the form of nests of glandular epithelium. The striking spontaneous mesenchymal to epithelial differentiation in this cancer is reminiscent of a developmental switch, but the only clue to its mechanistic basis has been the observation that most cases of synovial sarcoma with glandular epithelial differentiation (GED) contain SYT-SSX1 instead of SYT-SSX2. We report here that SYT-SSX1 and SYT-SSX2 interact preferentially with Snail or Slug, respectively, and prevent these transcriptional repressors from binding to the proximal E-cadherin promoter as shown by coimmunoprecipitation and chromatin immunoprecipitation. Luciferase reporter assays reveal that SYT-SSX1 and SYT-SSX2 can respectively overcome the Snail- or Slug-mediated repression of E-cadherin transcription. This provides a mechanism by which E-cadherin expression, a prerequisite of epithelial differentiation, is aberrantly derepressed in synovial sarcoma and may also explain the association of GED with the SYT-SSX1 fusion because it interferes with Snail, the stronger repressor of the E-cadherin promoter. Thus, our data provide a mechanistic basis for the observed heterogeneity in the acquisition of epithelial characteristics in synovial sarcoma and highlight the potential role of differential interactions with Snail or Slug in modulating this phenotypic transition.

Modern classification of neoplasms: reconciling differences between morphologic and molecular approaches

BACKGROUND

For over 150 years, pathologists have relied on histomorphology to classify and diagnose neoplasms. Their success has been stunning, permitting the accurate diagnosis of thousands of different types of neoplasms using only a microscope and a trained eye. In the past two decades, cancer genomics has challenged the supremacy of histomorphology by identifying genetic alterations shared by morphologically diverse tumors and by finding genetic features that distinguish subgroups of morphologically homogeneous tumors.

DISCUSSION

The Developmental Lineage Classification and Taxonomy of Neoplasms groups neoplasms by their embryologic origin. The putative value of this classification is based on the expectation that tumors of a common developmental lineage will share common metabolic pathways and common responses to drugs that target these pathways. The purpose of this manuscript is to show that grouping tumors according to their developmental lineage can reconcile certain fundamental discrepancies resulting from morphologic and molecular approaches to neoplasm classification. In this study, six issues in tumor classification are described that exemplify the growing rift between morphologic and molecular approaches to tumor classification: 1) the morphologic separation between epithelial and non-epithelial tumors; 2) the grouping of tumors based on shared cellular functions; 3) the distinction between germ cell tumors and pluripotent tumors of non-germ cell origin; 4) the distinction between tumors that have lost their differentiation and tumors that arise from uncommitted stem cells; 5) the molecular properties shared by morphologically disparate tumors that have a common developmental lineage, and 6) the problem of re-classifying morphologically identical but clinically distinct subsets of tumors. The discussion of these issues in the context of describing different methods of tumor classification is intended to underscore the clinical value of a robust tumor classification.

SUMMARY

A classification of neoplasms should guide the rational design and selection of a new generation of cancer medications targeted to metabolic pathways. Without a scientifically sound neoplasm classification, biological measurements on individual tumor samples cannot be generalized to class-related tumors, and constitutive properties common to a class of tumors cannot be distinguished from uninformative data in complex and chaotic biological systems. This paper discusses the importance of biological classification and examines several different approaches to the specific problem of tumor classification.

Establishment and characterization of a biphasic synovial sarcoma cell line, SYO-1

We describe here the establishment of a new synovial sarcoma cell line, SYO-1, derived from a biphasic synovial sarcoma that developed in the groin of a 19-year-old female. The cell line was maintained for more than 70 passages (more than 24 months) in vitro. The SYO-1 cells in monolayer culture exhibited a spindle shape without conspicuous pleomorphism. Immunohistochemically, the cells were positive for vimentin, type IV collagen, S-100, mdm2, bcl-2, c-Met and c-Kit. Tumors developed by their implantation in nude mice histologically showed biphasic features that were composed of areas of fascicles of spindle cells and areas of compact proliferation of polygonal to ovoid cells, which occasionally formed epithelial plaque and expressed cytokeratin and EMA. SYO-1 cells harbored the characteristic t(X;18)(p11.2;q11.2) translocation by chromosome analysis and SYT-SSX2 chimeric transcript by RT-PCR. The SYO-1 cells, the first characterized cell line derived from biphasic synovial sarcoma retaining the characteristic genetic and phenotypic features of the tumor, will be useful for various investigations on synovial sarcoma, especially for its epithelial differentiation.

Tumor classification: molecular analysis meets Aristotle

Background

Traditionally, tumors have been classified by their morphologic appearances. Unfortunately, tumors with similar histologic features often follow different clinical courses or respond differently to chemotherapy. Limitations in the clinical utility of morphology-based tumor classifications have prompted a search for a new tumor classification based on molecular analysis. Gene expression array data and proteomic data from tumor samples will provide complex data that is unobtainable from morphologic examination alone. The growing question facing cancer researchers is, "How can we successfully integrate the molecular, morphologic and clinical characteristics of human cancer to produce a helpful tumor classification?"

Discussion

Current efforts to classify cancers based on molecular features ignore lessons learned from millennia of experience in biological classification. A tumor classification must include every type of tumor and must provide a unique place for each tumor within the classification. Groups within a classification inherit the properties of their ancestors and impart properties to their descendants. A classification was prepared grouping tumors according to their histogenetic development. The classification is simple (reducing the complexity of information received from the molecular analysis of tumors), comprehensive (providing a place for every tumor of man), and consistent with recent attempts to characterize tumors by cytogenetic and molecular features. The clinical and research value of this historical approach to tumor classification is discussed.

Summary

This manuscript reviews tumor classification and provides a new and comprehensive classification for neoplasia that preserves traditional nomenclature while incorporating information derived from the molecular analysis of tumors. The classification is provided as an open access XML document that can be used by cancer researchers to relate tumor classes with heterogeneous experimental and clinical tumor databases.

Establishment and characterization of a novel human desmoplastic small round cell tumor cell line, JN-DSRCT-1

The exact nature of the desmoplastic small round cell tumor (DSRCT) remains controversial. More detailed analyses might be facilitated by the establishment of permanent DSRCT cell lines. To date, however, no human DSRCT cell line has been reported. In this study, we report the establishment of a new human cell line, JN-DSRCT-1, from the pleural effusion of a 7-year-old boy with pulmonary metastasis from a typical intra-abdominal DSRCT. JN-DSRCT-1 cells were small round or spindle shaped with oval nuclei and have been maintained continuously in vitro for over 190 passages during more than 40 months. Histologic features of the heterotransplanted tumors in severe combined immunodeficiency mouse were essentially the same as those of the original DSRCT, revealing nests or clusters of small round cells embedded in an abundant desmoplastic stroma. Both in vitro and in vivo, the cells exhibited immunopositive reactions for vimentin, desmin, cytokeratins (AE1/AE3 and CAM 5.2), epithelial membrane antigen, neuron-specific antigen, and CD57 (Leu-7). JN-DSRCT-1 cells exhibited a pathognomonic t(11;22)(p13;q12) translocation by cytogenetic analysis. In addition, RT-PCR and sequencing analysis revealed a chimeric transcriptional message of the Ewing's sarcoma gene exon 10 fused to the Wilms' tumor gene exon 8. To our knowledge, this is the first permanent human DSRCT cell line. The JN-DSRCT-1 cell line, which exhibits the unique morphologic and genetic characteristics of DSRCT, will be extremely useful for a variety of important studies such as the pathogenic mechanism, biologic behavior, and therapeutic model of human DSRCT.

Synovial sarcoma with a secondary chromosome change der(22)t(17;22)(q12;q12)

A consistent, pathognomonic translocation, most commonly a balanced reciprocal translocation, t(X;18) (p11.2;q11.2), is found in more than 90% of synovial sarcomas. We report here a secondary chromosome change, der(22)t(17;22)(q12;q12), in addition to the primary t(X;18)(p11.2;q11.2) in a biphasic synovial sarcoma that occurred in the thigh of a 34-year-old woman. Although the karyotype of the primary tumor exhibited 46,X,t(X;18)(p11.2;q11.2), the recurrent tumor showed 46,X,der(X)t(X;18)(p11.2;q11.2),der(22) t(17;22)(q12;q12). The SYT-SSX1 fusion transcript was demonstrated in the primary and recurrent tumors using a reverse transcriptase polymerase chain reaction (RT-PCR). Southern blot analysis also confirmed that the detected messages were derived from the SYT-SSX fusion gene. However, we could not detect the EWS-E1AF fusion gene that has been reported to be generated through a t(17;22)(q12;q12) by RT-PCR. Furthermore, fluorescence in situ hybridization (FISH) with cosmid probes corresponding to loci flanking the EWSR1 region demonstrated no split of chromosome 22 in all analyzed interphase nuclei. To our knowledge, this is the first reported case of synovial sarcoma in which an additional (secondary) chromosome change, der(22)t(17;22)(q12;q12), has been demonstrated.

Losses in chromosomes 17, 19, and 22q in neurofibromatosis type 1 and sporadic neurofibromas: a comparative genomic hybridization analysis

Neurofibromatosis type 1 (von Recklinghausen's NF1) is an autosomal dominant disease associated with an increased risk of benign and malignant neoplasia including malignant peripheral nerve sheath tumors (MPNSTs). In this study, we employed comparative genomic hybridization (CGH) to determine changes in the relative chromosome copy number in 24 patients with neurofibromas, including 12 NF1-associated and 12 sporadic cases. Differences in the frequency and distribution of chromosomal imbalances were observed in both NF1-asociated and sporadic neurofibromas. Chromosomal imbalances were more common in NF1-associated tumors than in sporadic neurofibromas. In both groups, the number of losses was higher than the number of gains, suggesting a predominant role of tumor suppressor gene in tumorigenesis. A number of new chromosomal imbalances were noted including chromosomes 17, 19, and chromosome arm 22q, which may be related to oncogenes or tumor suppressor genes in neurofibromas. In NF1-associated neurofibromas, the most frequent losses were found in chromosome 17 (the minimal common regions were 17p11.2-->p13 in nine cases and 17q24-->q25 in six cases) and 19p (19p13.2 in nine cases). In addition, both NF1-associated and sporadic neurofibromas often exhibited losses at chromosome arms 19q and 22q (in NF1 tumors, the minimal common regions were 19q13.2-->qter in seven cases).

Chromosomal translocations and sarcomas

This review examines how the identification of tumor-specific translocations and fusion proteins has advanced the basic scientific and clinical understanding of sarcomas. Recent genetic advances, including the ASPL-TFE3 fusion of alveolar soft part sarcoma, the JAZF1-JJAZ1 fusion of endometrial stromal sarcoma, and HMGIC fusions in liposarcoma, are discussed. Next, the review addresses the ways in which molecular genetic data have influenced diagnostic and prognostic paradigms. For example, recent studies describe the detection of occult tumor cells and the identification of primary renal neoplasms that are genetically related to alveolar soft part sarcoma. In addition, the review discusses potential therapies based on the targeting of sarcoma-specific fusion proteins. These reports describe the potential use of Gleevec (STI571) for dermatofibrosarcoma protuberans and the use of tumor-specific fusion proteins as potential targets for immunotherapy. Finally, basic scientific findings are reviewed that elucidate, for example, the aberrant functions of SYT-SSX in chromatin remodeling and of EWS-FLI1 in transcription and mRNA splicing. These and other emerging models of tumorigenesis will help identify new therapeutic targets.