SSX4

Gene Summary

Gene:SSX4; SSX family member 4
Aliases: CT5.4
Location:Xp11.23
Summary:The product of this gene belongs to the family of highly homologous synovial sarcoma X (SSX) breakpoint proteins. These proteins may function as transcriptional repressors. They are also capable of eliciting spontaneously humoral and cellular immune responses in cancer patients, and are potentially useful targets in cancer vaccine-based immunotherapy. SSX1, SSX2 and SSX4 genes have been involved in the t(X;18) translocation characteristically found in all synovial sarcomas. This translocation results in the fusion of the synovial sarcoma translocation gene on chromosome 18 to one of the SSX genes on chromosome X. Chromosome Xp11 contains a segmental duplication resulting in two identical copies of synovial sarcoma, X breakpoint 4, SSX4 and SSX4B, in tail-to-tail orientation. This gene, SSX4, represents the more telomeric copy. Two transcript variants encoding distinct isoforms have been identified for this gene. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:protein SSX4
Source:NCBIAccessed: 13 March, 2017

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 13 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 13 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (1)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Entity Topic PubMed Papers
Synovial Sarcomat(X;18)(p11.2;q11.2) SS18-SSX4 in Synovial Sarcoma
A SYT-SSX fusion gene resulting from the chromosomal translocation t(X;18)(p11;q11) is characteristic nearly all synovial sarcomas. This translocation fuses the SS18 (SYT) gene from chromosome 18 to one of three homologous genes at Xp11: SSX1, SSX2 or SSX4.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: SSX4 (cancer-related)

He L, Ji JN, Liu SQ, et al.
Expression of cancer-testis antigen in multiple myeloma.
J Huazhong Univ Sci Technolog Med Sci. 2014; 34(2):181-5 [PubMed] Related Publications
Recently, the immunotherapy has been highlighted among cancer treatments. Cancer-testis antigen (CTA) has been studied in a variety of solid tumors because of its specific expression in tumors, and testis, ovary and placenta tissues, but not in other normal tissues. In order to provide a new approach for multiple myeloma (MM) immunotherapy, we examined the CTA expression in MM cell lines, and primary myeloma cells in patients with MM. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the mRNA expression of MAGE-C1/CT7, SSX1, SSX2 and SSX4 in MM cell lines of RPMI-8226 and U266, and bone marrow (BM) cells of 25 MM patients and 18 healthy volunteers. The results showed that the 4 CTAs were expressed in RPMI-8226 and U266 cell lines. The positive expression rate of MAGE-C1/CT7, SSX1, SSX2 and SSX4 in the BM cells of 25 MM patients was 28% (7/25), 80% (20/25), 40% (10/25) and 68% (17/25), respectively. In contrast, the expression of any member of the CTAs was not detected in BM cells of 18 healthy volunteers. The expression of two or more CTAs was detected in 80% (20/25) MM patients, and that of at least one CTA in 88% (22/25). The mRNA expression levels of SSX1 and SSX4 were significantly higher in patients with MM at stage III than in those at stage I and II (P<0.05). No statistically significant differences were observed in the mRNA expression levels of MAGE-C1/CT7 and SSX2 in further stratified analyses by age, gender, MM types and percentage of MM cells in BM (P>0.05). In conclusion, our present study showed that MAGE-C1/CT7, SSX1, SSX2 and SSX4 were co-expressed in MM cell lines and the primary myeloma cells in MM patients, but not expressed in BM cells of healthy subjects. The mRNA levels of SSX1 and SSX4 are associated with MM clinical stage. This work may provide a new insight into MM immunotherapy in the future.

Greve KB, Pøhl M, Olsen KE, et al.
SSX2-4 expression in early-stage non-small cell lung cancer.
Tissue Antigens. 2014; 83(5):344-9 [PubMed] Related Publications
The expression of cancer/testis antigens SSX2, SSX3, and SSX4 in non-small cell lung cancers (NSCLC) was examined, since they are considered promising targets for cancer immunotherapy due to their immunogenicity and testis-restricted normal tissue expression. We characterized three SSX antibodies and performed immunohistochemical staining of 25 different normal tissues and 143 NSCLCs. The antibodies differed in binding to two distinctive splice variants of SSX2 that exhibited different subcellular staining patterns, suggesting that the two splice variants display different functions. SSX2-4 expression was only detected in 5 of 143 early-stage NSCLCs, which is rare compared to other cancer/testis antigens (e.g. MAGE-A and GAGE). However, further studies are needed to determine whether SSX can be used as a prognostic or predictive biomarker in NSCLC.

Trautmann M, Sievers E, Aretz S, et al.
SS18-SSX fusion protein-induced Wnt/β-catenin signaling is a therapeutic target in synovial sarcoma.
Oncogene. 2014; 33(42):5006-16 [PubMed] Related Publications
Synovial sarcoma is a high-grade soft tissue malignancy characterized by a specific reciprocal translocation t(X;18), which leads to the fusion of the SS18 (SYT) gene to one of three SSX genes (SSX1, SSX2 or SSX4). The resulting chimeric SS18-SSX protein is suggested to act as an oncogenic transcriptional regulator. Despite multimodal therapeutic approaches, metastatic disease is often lethal and the development of novel targeted therapeutic strategies is required. Several expression-profiling studies identified distinct gene expression signatures, implying a consistent role of Wnt/β-catenin signaling in synovial sarcoma tumorigenesis. Here we investigate the functional and therapeutic relevance of Wnt/β-catenin pathway activation in vitro and in vivo. Immunohistochemical analyses of nuclear β-catenin and Wnt downstream targets revealed activation of canonical Wnt signaling in a significant subset of 30 primary synovial sarcoma specimens. Functional aspects of Wnt signaling including dependence of Tcf/β-catenin complex activity on the SS18-SSX fusion proteins were analyzed. Efficient SS18-SSX-dependent activation of the Tcf/β-catenin transcriptional complex was confirmed by TOPflash reporter luciferase assays and immunoblotting. In five human synovial sarcoma cell lines, inhibition of the Tcf/β-catenin protein-protein interaction significantly blocked the canonical Wnt/β-catenin signaling cascade, accompanied by the effective downregulation of Wnt targets (AXIN2, CDC25A, c-MYC, DKK1, CyclinD1 and Survivin) and the specific suppression of cell viability associated with the induction of apoptosis. In SYO-1 synovial sarcoma xenografts, administration of small molecule Tcf/β-catenin complex inhibitors significantly reduced tumor growth, associated with diminished AXIN2 protein levels. In summary, SS18-SSX-induced Wnt/β-catenin signaling appears to be of crucial biological importance in synovial sarcoma tumorigenesis and progression, representing a potential molecular target for the development of novel therapeutic strategies.

Caballero OL, Cohen T, Gurung S, et al.
Effects of CT-Xp gene knock down in melanoma cell lines.
Oncotarget. 2013; 4(4):531-41 [PubMed] Free Access to Full Article Related Publications
Cancer/testis (CT) genes are encoded by genes that are normally expressed only in the human germ line but which are activated in various malignancies. CT proteins are frequently immunogenic in cancer patients and their expression is highly restricted to tumors. They are thus important targets for anticancer immunotherapy. In several different tumor types, the expression of CT-X genes is associated with advanced disease and poor outcome, indicating that their expression might contribute to tumorigenesis. CT-X genes encoding members of the MAGE protein family on Xq28 have been shown to potentially influence the tumorigenic phenotype. We used small interfering RNA (siRNA) to investigate whether CT-X mapping to the short arm of the X-chromosome might also have tumorigenic properties and therefore be potentially targeted by functional inhibitors in a therapeutic setting. siRNAs specific to GAGE, SSX and XAGE1 were used in cell proliferation, migration and cell survival assays using cell lines derived from melanoma, a tumor type known to present high frequencies of expression of CT antigens. We found that of these, those specific to GAGE and XAGE1 most significantly impeded melanoma cell migration and invasion and those specific to SSX4 and XAGE1 decreased the clonogenic survival of melanoma cells. Our results suggest that GAGE, XAGE1 and SSX4 might each have a role in tumor progression and are possible therapeutic targets for the treatment of melanoma and other malignancies.

Neumann F, Kaddu-Mulindwa D, Widmann T, et al.
EBV-transformed lymphoblastoid cell lines as vaccines against cancer testis antigen-positive tumors.
Cancer Immunol Immunother. 2013; 62(7):1211-22 [PubMed] Related Publications
EBV-transformed lymphoblastoid cell lines (LCL) are potent antigen-presenting cells. To investigate their potential use as cancer testis antigen (CTA) vaccines, we studied the expression of 12 cancer testis (CT) genes in 20 LCL by RT-PCR. The most frequently expressed CT genes were SSX4 (50 %), followed by GAGE (45 %), SSX1 (40 %), MAGE-A3 and SSX2 (25 %), SCP1, HOM-TES-85, MAGE-C1, and MAGE-C2 (15 %). NY-ESO-1 and MAGE-A4 were found in 1/20 LCL and BORIS was not detected at all. Fifteen of 20 LCL expressed at least one antigen, 9 LCL expressed ≥2 CT genes, and 7 of the 20 LCL expressed ≥4 CT genes. The expression of CT genes did not correlate with the length of in vitro culture, telomerase activity, aneuploidy, or proliferation state. While spontaneous expression of CT genes determined by real-time PCR and Western blot was rather weak in most LCL, treatment with DNA methyltransferase 1 inhibitor alone or in combination with histone deacetylase inhibitors increased CTA expression considerably thus enabling LCL to induce CTA-specific T cell responses. The stability of the CT gene expression over prolonged culture periods makes LCL attractive candidates for CT vaccines both in hematological neoplasias and solid tumors.

Yawata T, Maeda Y, Okiku M, et al.
Identification and functional characterization of glioma-specific promoters and their application in suicide gene therapy.
J Neurooncol. 2011; 104(2):497-507 [PubMed] Related Publications
Suicide gene therapy has been shown to be effective in inducing tumor regression. In this study, a human brain tumor-specific promoter was identified and used to develop transcriptionally targeted gene therapy. We searched for genes with brain tumor-specific expression. By in silico and reverse-transcription polymerase chain reaction screening, MAGE-A3 and SSX4 were found to be expressed in a tumor-specific manner. SSX4 gene promoter activity was high in human brain tumor cells but not in normal human astrocyte cells, whereas the MAGE-A3 promoter showed activity in both tumor and normal cells. A retrovirus vector carrying a suicide gene, the herpes simplex virus thymidine kinase gene controlled by the SSX4 promoter, was constructed to evaluate the efficacy of the promoter in tumor-specific gene therapy. Glioma and human telomerase catalytic subunit-immortalized fibroblast BJ-5ta cell lines transduced with retrovirus vectors were assayed for killing activity by ganciclovir. Glioma cell lines were effectively killed by ganciclovir in a concentration-dependent manner, whereas BJ-5ta cells were not. By contrast, MAGE-A3 promoter failed to induce cytotoxicity in a brain tumor-specific manner. In addition, mouse glioma RSV-M cells transduced with retrovirus vector also showed suppressed tumor formation activity in syngeneic mice in response to ganciclovir administration. Therefore, the SSX4 promoter is a candidate for brain tumor-specific gene therapy and supports the efficacy and safety of suicide gene therapy for malignant brain tumors.

Dimitriadis E, Rontogianni D, Kyriazoglou A, et al.
Novel SYT-SSX fusion transcript variants in synovial sarcoma.
Cancer Genet Cytogenet. 2009; 195(1):54-8 [PubMed] Related Publications
Synovial sarcoma (SS) is characterized by the t(X;18)(p11.2;q11.2) chromosomal translocation detected in >95% of cases. Through this translocation, one of the SYT genes, SYT4 on chromosome 18, is fused to one of the SSX genes on chromosome X. SYT4-SSX1 is the most common fusion subtype, present in approximately two thirds of the cases, followed by SYT4-SSX2 and, very rarely, SYT4-SSX4. Variant fusion transcripts occur less often, and most of the reported cases are the result of small insertions. Described here is a novel fusion variant containing a small deletion resulting in an alternative reading frame of the SSX part of the fusion gene. This fusion transcript may provide further insight into the oncogenic function of the SSX partner of the fusion gene.

Torres L, Lisboa S, Cerveira N, et al.
Cryptic chromosome rearrangement resulting in SYT-SSX2 fusion gene in a monophasic synovial sarcoma.
Cancer Genet Cytogenet. 2008; 187(1):45-9 [PubMed] Related Publications
Synovial sarcoma is cytogenetically characterized by the specific translocation t(X;18)(p11.2;q11.2), which results in the fusion of the SYT gene from chromosome 18 (18q11) with one of the genes from the X chromosome (Xp11) SSX1, SSX2, or SSX4. We present the case of a 51-year-old woman with a diagnosis of monophasic synovial sarcoma in which chromosome banding analysis did not reveal the presence of the typical t(X;18)(p11.2;q11.2), but instead found monosomy of chromosomes X and 18 and a marker chromosome. FISH analyses of the marker chromosome showed a rearrangement of the 5'SYT region and the presence of pericentromeric sequences of chromosomes 18 and X. Comparative genomic hybridization detected losses of Xq21qter, 18p, and 18q12qter, indicating that the marker also contained DNA sequences from Xp22q21, and reverse-transcription polymerase chain reaction demonstrated a SYT-SSX2 fusion transcript. We uncovered a complex cryptic rearrangement that gives rise to the characteristic SYT-SSX2 fusion gene in a monophasic synovial sarcoma.

Amary MF, Berisha F, Bernardi Fdel C, et al.
Detection of SS18-SSX fusion transcripts in formalin-fixed paraffin-embedded neoplasms: analysis of conventional RT-PCR, qRT-PCR and dual color FISH as diagnostic tools for synovial sarcoma.
Mod Pathol. 2007; 20(4):482-96 [PubMed] Related Publications
Synovial Sarcoma consistently harbors t(X;18) resulting in SS18-SSX1, SS18-SSX2 and rarely SS18-SSX4 fusion transcripts. Of 328 cases included in our study, synovial sarcoma was either the primary diagnosis or was very high in the differential diagnosis in 134 cases: of these, amplifiable cDNA was obtained from 131. SS18-SSX fusion products were found in 126 (96%) cases (74 SS18-SSX1, 52 SS18-SSX2), using quantitative and 120 by conventional reverse transcriptase-polymerase chain reaction (RT-PCR). One hundred and one cases in a tissue microarray, analyzed by fluorescence in situ hybridization (FISH), revealed that 87 (86%) showed SS18 rearrangement: four RT-PCR positive cases, reported as negative for FISH, showed loss of one spectrum green signal, and 15 cases had multiple copies of the SS18 gene: both findings are potentially problematic when interpreting results. One of three cases, not analyzed by RT-PCR reaction owing to poor quality RNA, was positive by FISH. SS18-SSX1 was present in 56 monophasic and 18 biphasic synovial sarcoma: SS18-SSX2 was detected in 41 monophasic and 11 biphasic synovial sarcoma. Poorly differentiated areas were identified in 44 cases (31%). There was no statistically significant association between biphasic, monophasic and fusion type. Five cases were negative for SS18 rearrangement by all methods, three of which were pleural-sited neoplasms. Following clinical input, a diagnosis of mesothelioma was favored in one case, a sarcoma, not otherwise specified in another and a solitary fibrous tumor in the third case. The possibility of a malignant peripheral nerve sheath tumor could not be excluded in the other two cases. We concluded that the employment of a combination of molecular approaches is a powerful aid to diagnosing synovial sarcoma giving at least 96% sensitivity and 100% specificity but results must be interpreted in the light of other modalities such as clinical findings and immunohistochemical data.

Subramaniam MM, Noguera R, Piqueras M, et al.
Evaluation of genetic stability of the SYT gene rearrangement by break-apart FISH in primary and xenotransplanted synovial sarcomas.
Cancer Genet Cytogenet. 2007; 172(1):23-8 [PubMed] Related Publications
Synovial sarcomas (SS) are infrequent and morphologically heterogeneous soft tissue sarcomas. The t(X;18)(p11.2;q11.2), which results in fusion of the SYT gene at 18q11 with the SSX1, SSX2, or (rarely) SSX4 gene is a primary genetic event in 90% of SS. To determine whether the t(X;18) present in the original tumor is maintained in its passages, a dual-color break-apart FISH assay for SYT gene disruption was performed in two tissue microarrays (TMA) comprising eight molecularly confirmed primary SSs and their xenografts, which were followed for several generations. A simplified scoring system was applied to the FISH results of the primary and xenotransplanted SS to classify the FISH data into distinct groups. SYT disruption was identified in all eight primary SS and in all their passages without any significant differences among them, despite wide variations in xenotransplantation time between the primary tumors and their xenografts. The TMA-based FISH assay demonstrated genetic stability related to SYT gene rearrangement in primary and xenografted SS.

Atanackovic D, Arfsten J, Cao Y, et al.
Cancer-testis antigens are commonly expressed in multiple myeloma and induce systemic immunity following allogeneic stem cell transplantation.
Blood. 2007; 109(3):1103-12 [PubMed] Related Publications
Immunotherapies using cancer-testis (CT) antigens as targets represent a potentially useful treatment in patients with multiple myeloma (MM) who commonly show recurrent disease following chemotherapy. We analyzed the expression of 11 CT antigens in bone marrow samples from patients with MM (n=55) and healthy donors (n=32) using reverse transcriptase-polymerase chain reaction (RT-PCR). CT antigens were frequently expressed in MM with 56% (MAGEC2), 55% (MAGEA3), 35% (SSX1), 20% (SSX4, SSX5), 16% (SSX2), 15% (BAGE), 7% (NY-ESO-1), and 6% (ADAM2, LIPI) expressing the given antigen. Importantly, CT antigens were not expressed in healthy bone marrow. Analyzing patients with MM (n=66) for antibody responses against MAGEA3, SSX2, and NY-ESO-1, we found strong antibody responses against CT antigens preferentially in patients who had received allogeneic stem cell transplantation (alloSCT). Antibody responses against NY-ESO-1 correlated with NY-ESO-1-specific CD4+ and CD8+ T-cell responses against peptide NY-ESO-1(51-62) and CD4+ responses against NY-ESO-1(121-140) in 1 of these patients. These allogeneic immune responses were not detectable in pretransplantation samples and in the patients' stem cell donors, indicating that CT antigens might indeed represent natural targets for graft-versus-myeloma effects. Immune responses induced by alloSCT could be boosted by active CT antigen-specific immunotherapy, which might help to achieve long-lasting remissions in patients with MM.

Gure AO, Chua R, Williamson B, et al.
Cancer-testis genes are coordinately expressed and are markers of poor outcome in non-small cell lung cancer.
Clin Cancer Res. 2005; 11(22):8055-62 [PubMed] Related Publications
PURPOSE: Cancer-testis genes mapping to the X chromosome have common expression patterns and show similar responses to modulators of epigenetic mechanisms. We asked whether cancer-testis gene expression occurred coordinately, and whether it correlated with variables of disease and clinical outcome of non-small cell lung cancer (NSCLC).
EXPERIMENTAL DESIGN: Tumors from 523 NSCLC patients undergoing surgery were evaluated for the expression of nine cancer-testis genes (NY-ESO-1, LAGE-1, MAGE-A1, MAGE-A3, MAGE-A4, MAGE-A10, CT7/MAGE-C1, SSX2, and SSX4) by semiquantitative PCR. Clinical data available for 447 patients were used to correlate cancer-testis expression to variables of disease and clinical outcome.
RESULTS: At least one cancer-testis gene was expressed by 90% of squamous carcinoma, 62% of bronchioloalveolar cancer, and 67% of adenocarcinoma samples. Statistically significant coexpression was observed for 34 of the 36 possible cancer-testis combinations. Cancer-testis gene expression, either cumulatively or individually, showed significant associations with male sex, smoking history, advanced tumor, nodal and pathologic stages, pleural invasion, and the absence of ground glass opacity. Cox regression analysis revealed the expression of NY-ESO-1 and MAGE-A3 as markers of poor prognosis, independent of confounding variables for adenocarcinoma of the lung.
CONCLUSIONS: Cancer-testis genes are coordinately expressed in NSCLC, and their expression is associated with advanced disease and poor outcome.

Taylor BJ, Reiman T, Pittman JA, et al.
SSX cancer testis antigens are expressed in most multiple myeloma patients: co-expression of SSX1, 2, 4, and 5 correlates with adverse prognosis and high frequencies of SSX-positive PCs.
J Immunother. 2005 Nov-Dec; 28(6):564-75 [PubMed] Related Publications
Cancer testis antigens (CTAs) are tumor-specific antigens that may be useful targets for cancer vaccines. Here, CTA expression was examined in multiple myeloma (MM), a B-cell cancer characterized by malignant plasma cells (PCs) in the bone marrow (BM), and monoclonal gammopathy of undetermined significance (MGUS), a condition that can progress to MM. We screened a panel of patient BMs at different stages of malignancy for CTA expression by reverse transcription polymerase chain reaction RT-PCR. Here, SSX (synovial sarcoma, X chromosome) emerged as a promising candidate for an MM vaccine, having a profile similar to currently studied CTA, NY-ESO-1, and MAGE. SSX1, 2, 4, and 5 expression was studied further in 114 MM (total SSX, 61% of patients; SSX1, 42%; SSX2, 23%; SSX4, 38%; SSX5, 35%), 45 MGUS (total SSX, 24% of patients; SSX1, 9%; SSX4, 20%), and 12 control (0/12, 0%) subjects. Several expression patterns were observed, the most predominant being co-expression of SSX1, 2, 4, and 5 (called group A expression, in 20% of MM), which correlated with reduced survival (P=0.0006). Of the four genes, SSX2 had the strongest association with reduced survival (P=0.0001). SSX protein expression ranged from 13.5% of PCs in an SSX1/SSX4 co-expressor to as high as 88% of PCs in group A expressor, exceeding reported frequencies of NY-ESO-1 and MAGE in MM. In single PCs from group A patients, we detected variable degrees of SSX co-expression, emphasizing the heterogeneity of CTA expression within tumor cell populations. These results demonstrate that SSX is a frequently expressed CTA in MM and highlight its potential as an MM vaccine candidate.

Hasegawa K, Koizumi F, Noguchi Y, et al.
SSX expression in gynecological cancers and antibody response in patients.
Cancer Immun. 2004; 4:16 [PubMed] Related Publications
The SSX genes are members of the cancer-testis (CT) antigen family. SSX2, the prototype SSX gene, was found by serological analysis of antigens by recombinant expression cloning (SEREX). Since little is known about SSX expression in gynecological malignancies, we investigated SSX mRNA expression in 115 gynecological cancer specimens and 25 normal control samples by RT-PCR. We also tested the humoral immune response to SSX2 and SSX4 using recombinant proteins. We found relatively high SSX4 mRNA expression in endometrial cancer (24%), ovarian cancer (13%), and cervical cancer (20%). In contrast, SSX1 and SSX2 mRNA expression was detected in not more than 4% of the gynecological cancer specimens analysed. No SSX mRNA expression was found in 25 normal specimens. Two gynecological cancer patients had antibodies against SSX4, whereas no antibody reactivity to SSX4 was found in the sera of 40 normal individuals. This suggests that SSX4 is a potential target for cancer vaccines in gynecological cancer patients.

Koković I, Bracko M, Golouh R, et al.
Are there geographical differences in the frequency of SYT-SSX1 and SYT-SSX2 chimeric transcripts in synovial sarcoma?
Cancer Detect Prev. 2004; 28(4):294-301 [PubMed] Related Publications
Synovial sarcoma (SS) is characterized by the t(X;18)(p11.2;q11.2) chromosomal translocation, which results in generating either SYT-SSX1, SYT-SSX2 or, infrequently, SYT-SSX4 fusion gene. The ratio of SYT-SSX1:SYT-SSX2 fusions is close to 2:1 in the majority of studies, and SYT-SSX2 fusion has been only rarely observed in biphasic SS. In the present study, we compared two series of patients with SS, Slovenian (37 cases) and Dutch (14 cases), with respect to clinical, pathological and molecular findings. The two groups did not differ with regard to clinicopathological features. Whereas the frequency of different SYT-SSX fusions in the Dutch group was similar to that reported in the literature, we found an unexpectedly high number of tumors with SYT-SSX2 fusion in the Slovenian group. The ratio of SYT-SSX1:SYT-SSX2 fusion was 7:18 for monophasic and 2:7 for biphasic tumors in the Slovenian group. This distribution differs significantly from that observed in the Dutch group in the present study (P = 0.041) as well as from data reported in the recent large multi-institutional study on 243 patients (P = 0.0001). Our findings indicate possible geographical differences in the frequency of two SYT-SSX fusion transcripts in patients with synovial sarcoma.

Surace C, Panagopoulos I, Pålsson E, et al.
A novel FISH assay for SS18-SSX fusion type in synovial sarcoma.
Lab Invest. 2004; 84(9):1185-92 [PubMed] Related Publications
Synovial sarcoma is a morphologically, clinically and genetically distinct entity that accounts for 5-10% of all soft tissue sarcomas. The t(X;18)(p11.2;q11.2) is the cytogenetic hallmark of synovial sarcoma and is present in more than 90% of the cases. It produces three types of fusion gene formed in part by SS18 from chromosome 18 and by SSX1, SSX2 or, rarely, SSX4 from the X chromosome. The SS18-SSX fusions do not seem to occur in other tumor types, and it has been shown that in synovial sarcoma a clear correlation exists between the type of fusion gene and histologic subtype and, more importantly, clinical outcome. Previous analyses regarding the type of fusion genes have been based on PCR amplification of the fusion transcript, requiring access to good-quality RNA. In order to obtain an alternative tool to diagnose and follow this malignancy, we developed a fluorescence in situ hybridization (FISH) assay that could distinguish between the two most common fusion genes, that is, SS18-SSX1 and SS18-SSX2. The specificity of the selected bacterial artificial chromosome clones used in the detection of these fusion genes, as well as the sensitivity of the analysis in metaphase and interphase cells, was examined in a series of 28 synovial sarcoma samples with known fusion gene status. In all samples, the type of fusion was correctly identified by FISH. Thus, the assay described here should be useful for clarifying unresolved chromosome markers and for identifying fusion gene status in samples from which RNA of sufficient quality for PCR could not be extracted.

Storlazzi CT, Mertens F, Mandahl N, et al.
A novel fusion gene, SS18L1/SSX1, in synovial sarcoma.
Genes Chromosomes Cancer. 2003; 37(2):195-200 [PubMed] Related Publications
Synovial sarcoma is an aggressive soft tissue tumor that is characterized cytogenetically by the t(X;18)(p11;q11) translocation, resulting in fusion between the SS18 gene on chromosome 18 and one of the SSX genes on the X chromosome. The three fusion genes that have been detected thus far, SS18/SSX1, SS18/SSX2, and SS18/SSX4, account for more than 95% of the synovial sarcomas. Because SS18/SSX fusions do not seem to occur in other tumor types, and because synovial sarcomas may sometimes be difficult to distinguish from other spindle cell tumors, molecular genetic analysis has become established as an important diagnostic tool. Upon cytogenetic analysis of a soft-tissue tumor that showed classic synovial sarcoma morphology, we detected two supernumerary marker chromosomes but no rearrangement of chromosomes X or 18. By fluorescence in situ hybridization, the marker chromosomes were shown to contain material from chromosomes X and 20, including the SSX gene cluster on the X chromosome and the SS18L1 gene, which shows strong homology with the SS18 gene, on chromosome 20. Further RT-PCR analysis and sequencing of the amplified products revealed a novel SS18L1/SSX1 fusion transcript in which nucleotide 1216 (exon 10) of SS18L1 was fused in-frame with nucleotide 422 (exon 6) of SSX1. Thus, the existence of genetic heterogeneity has to be taken into account when RT-PCR is used for the diagnosis of synovial sarcoma.

Törnkvist M, Brodin B, Bartolazzi A, Larsson O
A novel type of SYT/SSX fusion: methodological and biological implications.
Mod Pathol. 2002; 15(6):679-85 [PubMed] Related Publications
Synovial sarcoma (SS) is a rare soft-tissue tumor that affects children and young adults. It is characterized by the chromosomal translocation t(X;18)(p11.2;q11.2), which results in the fusion of the SYT gene on chromosome 18 with a SSX gene on chromosome X. In the majority of cases, SYT is fused to exon 5 of SSX1 (64%), SSX2 (36%), or, rarely, SSX4. A novel fusion transcript variant deriving from the fusion of SYT to exon 6 of SSX4 gene (SYT/SSX4v) was found coexpressed in one of the previously reported SYT/SSX4 cases. In the present investigation, we describe a new SS case that was previously shown to be negative for SYT/SSX1 and SYT/SSX2 expression by conventional reverse transcription polymerase chain reaction (RT-PCR) methods. By redesigning and optimizing the RT-PCR protocol, we were able to detect SYT/SSX4v as the sole fusion transcript expressed in this tumor sample. This finding suggests that this novel fusion gene, which involves exon 6 of SSX only, is sufficient to keep the transforming function conferred by the SYT/SSX translocation of SS. In about 3% of morphologically, ultrastructurally, and immunohistochemically defined SS, the SYT/SSX fusion transcript is not detected using conventional RT-PCR. Here we demonstrate that optimization of the RT-PCR method is important for detecting different and unexpected SYT/SSX variants, which otherwise could be overlooked. Using nine cases of SS in which SYT/SSX fusion transcripts were not detected by conventional RT-PCR methods, we demonstrate the presence of SYT/SSX transcripts in two cases using the proposed RT-PCR approach. Applications of optimized RT-PCR can contribute to reduce false-negative SYT/SSX SS cases reported in literature.

Yang K, Lui WO, Xie Y, et al.
Co-existence of SYT-SSX1 and SYT-SSX2 fusions in synovial sarcomas.
Oncogene. 2002; 21(26):4181-90 [PubMed] Related Publications
The chromosomal translocation t(X;18)(p11.2;q11.2) is tightly linked to the tumorigenesis of synovial sarcoma. Through this translation the SYT gene on chromosome 18 is fused with a testis/cancer antigen gene on the X chromosome, generating either a SYT-SSX1, SYT-SSX2, or less often a SYT-SSX4 fusion gene. It has been anticipated that the individual synovial sarcoma carries only one of these variants, however, in this study we demonstrated that SYT-SSX1 and SYT-SSX2 co-exist in a significant proportion of the cases. From 121 SYT-SSX positive primary tumors, co-expression of SYT-SSX1 and SYT-SSX2 was seen in 12 cases (10%), which were characterized in further detail both at the RNA, DNA and chromosomal level. In all 12 cases the SYT-SSX1 and SYT-SSX2 fusions resulted in identical SYT-SSX fusion transcripts. However, at the genomic level the translocations were different, and most likely occurred between variable intronic sites in the target genes. By interphase FISH analyses of 10 cases SYT-SSX2 translocations were found to be the most abundant in all but one of the cases, in which SYT-SSX1 was predominating. The findings reveal a new heterogenous feature of synovial sarcoma, accounting for approximately 10% of all cases, which may shed light on the molecular genetic mechanisms behind translocations in general, and on the etiology of synovial sarcoma in particular.

Tamborini E, Papini D, Mezzelani A, et al.
c-KIT and c-KIT ligand (SCF) in synovial sarcoma (SS): an mRNA expression analysis in 23 cases.
Br J Cancer. 2001; 85(3):405-11 [PubMed] Free Access to Full Article Related Publications
In a previous immunophenotypic molecular-based analysis it was shown that bcl2 over-expression characterizes the SS gene profile in addition to the non-random translocations. Here we show that the over-expression of an additional potentially antiapoptotic gene, the c-KIT gene, is associated with this tumour. Interestingly, whereas bcl2 over-expression appears to be restricted to the spindle cell tumoral component, c-kit mainly involves the epithelial component of biphasic SS. Twenty-three primary and metastatic samples from 21 patients were analysed by immunophenotyping (23/23), immunoprecipitations and Western blotting (3/23), and RT-PCR (23/23). Ten cases were biphasic and 13 monophasic in sub-type. Twelve, 10 and 1 case carried the SYT-SSX1, SYT-SSX2 and SYT-SSX4 fusion transcript, respectively. Co-presence of both c-Kit and SCF mRNA was observed in almost all cases (20/23), suggesting the occurrence of an autocrine loop. Immunophenotyping, confirmed by biochemical analyses, showed a modulation of c-Kit expression which was faint in the spindle and strong in the epithelial component, respectively. The study was complemented by c-Met/HGF receptor/ligand expression and c-Met protein analysis with results superimposable to those already reported. Since in each tumour, epithelial and spindle cell components harbour the same type of translocation t(X;18) the present findings suggest a shifting of the anti-apoptotic role from BCL2 to c-KIT gene during the transition from the uncommitted spindle to the differentiated epithelial cells.

Panagopoulos I, Mertens F, Isaksson M, et al.
Clinical impact of molecular and cytogenetic findings in synovial sarcoma.
Genes Chromosomes Cancer. 2001; 31(4):362-72 [PubMed] Related Publications
Synovial sarcoma is an aggressive soft-tissue tumor that accounts for up to 10% of soft-tissue sarcomas. Cytogenetically, synovial sarcoma is characterized by the t(X;18)(p11;q11), found in more than 95% of the tumors. This translocation results in rearrangements of the SYT gene in 18q11 and one of the SSX1, SSX2, or SSX4 genes in Xp11, creating a SYT/SSX1, SYT/SSX2, or SYT/SSX4 chimeric gene. It has been shown that patients with SYT/SSX1 fusion genes have a shorter metastasis-free survival than do patients with SYT/SSX2. Previous studies have also suggested that clonal evolution may be associated with disease progression. In the present study, RT-PCR analysis showed that all 64 examined synovial sarcomas from 54 patients had SYT-SSX chimeric genes. SYT/SSX1 was found in 40 tumors from 33 patients, SYT/SSX2 in 23 tumors from 20 patients, and SYT/SSX4 in one case. Two patients had variant SYT/SSX2 transcripts, with 57 bp and 141 bp inserts, respectively, between the known SYT and SSX2 sequences. Patients with tumors with SYT/SSX1 fusions had a higher risk of developing metastases compared to those with SYT/SSX2 fusions (P = 0.01). The reciprocal transcripts SSX1/SYT and SSX2/SYT were detected using nested PCR in 11 of the 40 samples with SYT/SSX1 and 5 of the 23 samples with SYT/SSX2, respectively. Among 20 blood samples, SYT/SSX1 and SYT/SSX2 were detected in one sample each. The t(X;18), or variants thereof, was found cytogenetically in all patients but three. Among 32 primary tumors, the t(X;18) or a variant translocation was the sole anomaly in 10. In contrast, of the seven metastatic lesions that were investigated prior to radiotherapy, only one had a t(X;18) as the sole anomaly; all other tumors displayed complex karyotypes. Cytogenetic complexity in primary tumors was, however, not associated with the development of metastases. Tumors with SYT/SSX2 less often (4/12 vs. 7/15) showed complex karyotypes than did tumors with SYT/SSX1, but the difference was not significant. Combining cytogenetic complexity and transcript data, we found that the subgroup of patients with tumors showing simple karyotypes and SYT/SSX2 fusion had the best clinical outcome (2/8 patients developed metastases), and those with tumors showing complex karyotypes together with SYT/SSX1 fusion the worst (6/7 patients developed metastases). This corresponded to 5-year metastasis-free survival rates of 0.58 and 0.0, respectively (P = 0.02).

Brodin B, Haslam K, Yang K, et al.
Cloning and characterization of spliced fusion transcript variants of synovial sarcoma: SYT/SSX4, SYT/SSX4v, and SYT/SSX2v. Possible regulatory role of the fusion gene product in wild type SYT expression.
Gene. 2001; 268(1-2):173-82 [PubMed] Related Publications
The synovial sarcoma translocation t(X;18)(p11.2; q11.2) results in the fusion of the SYT gene on chromosome 18 to exon 5 of either SSX1 or SSX2 genes on chromosome X. We recently reported that the SSX4 gene is also involved in such a translocation. In the present investigation we cloned and sequenced the full-length cDNA of SYT/SSX1, SYT/SSX2 and SYT/SSX4 from synovial sarcoma tissues. We isolated a novel fusion transcript type variant involving the fusion of SYT with exon 6 of the SSX4 gene (SYT/SSX4v). The SYT/SSX4 and SYT/SSX2 open reading frame also differed from previously reported SYT/SSX sequences by an in-frame addition of 93bp exon located in the junction between exon 7 and 8 of the SYT. This exon is identical to that reported for the murine SYT but has not been previously found in the human transcript. Two SYT transcripts, with and without the 93 bp exon, were co-expressed in mouse NIH3T3 cells, human malignant cells and human testis tissue, but not in human normal fibroblasts. Stable transfection of an SYT/SSX4 expression vector into human and murine cell lines correlated with a down-regulation of SYT transcripts. This was also observed in a synovial sarcoma tumor expressing SYT/SSX4. This suggests that the SYT/SSX fusion gene may regulate SYT expression from the normal allele and as such alter the normal function of SYT.

Tamborini E, Agus V, Mezzelani A, et al.
Identification of a novel spliced variant of the SYT gene expressed in normal tissues and in synovial sarcoma.
Br J Cancer. 2001; 84(8):1087-94 [PubMed] Free Access to Full Article Related Publications
Synovial sarcoma (SS) is cytogenetically characterized by the translocation t(X;18)(p11.2-q11.2) generating a fusion between the SYT gene on chromosome 18 and one member of the SSX family gene (SSX1; SSX2; SSX4) on chromosome X. Here, we report for the first time that 2 forms of SYT mRNA are present in both normal tissues and SSs. By amplifying the full-length SYT cDNA of two SSs, we detected 2 bands, here designated N-SYT and I-SYT. The latter, previously undescribed, contains an in-frame insertion of 93 bp. Its sequencing revealed a 100% homology with the mouse SYT gene. These two SYT forms were present, although in different amounts, in all human normal tissues examined, including kidney, stomach, lung, colon, liver and synovia. Coexistence of N-SYT and I-SYT (both fused with SSX) was detected in a series of 59 SSs (35 monophasic and 24 biphasic) and in a SS cell line. A preliminary analysis of the differential expression levels of N-SYT and I-SYT in SSs revealed that the latter was consistently overexpressed, suggesting a role in SS pathogenesis.

Mancuso T, Mezzelani A, Riva C, et al.
Analysis of SYT-SSX fusion transcripts and bcl-2 expression and phosphorylation status in synovial sarcoma.
Lab Invest. 2000; 80(6):805-13 [PubMed] Related Publications
Synovial sarcomas (SS) are characterized by a chromosomal translocation t(X;18)(p11.2;q11.2) which usually fuses the SYT gene from chromosome 18 to SSX1 or SSX2 genes on chromosome X. Also, a variant SYT-SSX4 fusion gene has recently been shown in a single SS case. In addition to these cytogenetic changes, bcl-2 expression, as assessed by immunohistochemistry, has been reported to be an almost general constitutive alteration of SS. In the present work, we analyze a series of 36 SS surgical samples (from 34 patients) by RT-PCR for the presence of the SYT-SSX1 or the SYT-SSX2 fusion transcript. The analysis was extended to SYT-SSX4 on SYT-SSX1-negative and SYT-SSX2-negative cases only. Our results showed a significant correlation between the SYT-SSX2 fusion and the monophasic SS histologic subtype. SYT-SSX1 fusion transcripts were present in both monophasic and biphasic tumors. The SYT-SSX4 fusion type was detected in a single monophasic SS. In the same series of SS cases, we also confirmed and extended the previously reported constitutive expression of bcl-2 protein, by using both immunohistochemical and western blot analysis. Moreover, we demonstrated that the BCL-2 gene is not rearranged or amplified at genomic level, indicating that the high levels of bcl-2 expression observed in SS might result from transcriptional activation of the gene and/or protein stabilization. Finally, we show that bcl-2 is not phosphorylated in tumors from patients who had been preoperatively treated with radio/chemotherapy, in tumors from untreated patients, or in an SS cell line (CME-1) after in vitro treatment with cytotoxic concentrations of DNA-damaging agents or taxanes. These data indicate that SS cells are unable to activate an apoptosis pathway involving bcl-2 phosphorylation/inactivation and may provide a possible explanation for the limited effectiveness of conventional pharmacological treatments of this tumor type.

Skytting B
Synovial sarcoma. A Scandinavian Sarcoma Group project.
Acta Orthop Scand Suppl. 2000; 291:1-28 [PubMed] Related Publications
UNLABELLED: Synovial sarcoma accounts for 5-10% of all soft tissue sarcomas. More than 90% are found in the extremities or trunk wall. Characteristic for synovial sarcoma is the translocation t(X;18) (p11.2;q11.2). Cloning of the breakpoints of this translocation revealed fusion of two novel genes, SYT and SSX. The SYT gene, located on chromosome 18, is fused with one of three closely related genes; SSX1, SSX2 or SSX4 located on the X chromosome. The long term survival rates have continuously improved and have at best been reported to around 50%. However, since almost no population based studies on synovial sarcoma have been reported, these improvements may be due to differences in patient selection due to a changes in referral practice. This project was based on a consecutive series of synovial sarcoma patients from the Scandinavian Sarcoma Group Register acquired during a 9-year period. Only surgically treated patients without metastases at diagnosis were included in the prognostic analyses. The tumors were defined clinically, histopathologically, molecular and cytogenetically and these features were related to clinical course.
EPIDEMIOLOGY: 34 of 104 patients developed metastases. The overall 5 and 7 years survival rates were 0.76 (95% CI 0.66-0.83) and 0.69 (0.58-0.78), respectively. Large tumor size and amputation were significantly associated with impaired metastasis free survival. In addition, patients with local recurrence had a higher risk for metastases following the local event.
HISTOLOGY: All were high grade lesions, 74 Grade III and 30 IV. Kaplan-Meier estimates of metastasis-free survival at 5 years were 83% (95% CI 72-92%) for patients with Grade III tumors versus 31% (95% CI 13-51%) for Grade IV. Histologic grading conveyed more prognostic information than any single histologic factor. Immunostaining with anti-Ki-67 antibodies (MIB1) and p53 based on formalin-fixed paraffin-embedded material from 86 patients revealed that MIB-1 > or = 10% was associated with poorer metastasis-free survival but p53 was not.
GENETICS: Type of fusion transcripts (SYT-SSX1 or SYT-SSX2) and Ki-67 were assessed in fresh frozen tissue from 33 patients. The 5-year metastasis-free survival for patients with SYT-SSX1 was 42% versus 89% for those with SYT-SSX2. The hazard ratio for metastasis associated with the SYT-SSX1 fusion transcripts was 7 (95% CI 1.5-36, log-rank p = 0.004). There was a significant association between SYT-SSX1 and high tumor proliferation rate. Comparative Genomic Hybridization revealed DNA sequence copy number changes in 35 of 69 tumor specimens. The frequency of aberrations/tumor were higher in monophasic tumors than in biphasic. Gains of chromosome 8 were associated with large tumors (> 5 cm). There was no obvious association between secondary aberrations and clinical outcome.
CONCLUSIONS: Large tumor size, local recurrence, histologic Grade IV, MIB1 index > or = 10 and possibly SYT-SSX1 fusion transcript were associated with impaired clinical outcome.

dos Santos NR, Torensma R, de Vries TJ, et al.
Heterogeneous expression of the SSX cancer/testis antigens in human melanoma lesions and cell lines.
Cancer Res. 2000; 60(6):1654-62 [PubMed] Related Publications
The SSX genes, located on the X chromosome, encode a family of highly homologous nuclear proteins. The SSX1 and SSX2 genes were initially identified as fusion partners of the SYT gene in t(X;18)-positive synovial sarcomas. Recently, however, it was found that these two genes, as well as the highly homologous SSX4 and SSX5 genes, are aberrantly expressed in different types of cancers, including melanomas. Because normal SSX expression has been detected only in the testis and, at very low levels, the thyroid, these proteins are considered as new members of the still growing family of cancer/testis antigens. These antigens are presently considered as targets for the development of cancer immunotherapy protocols. In the present study, we developed a monoclonal antibody found to recognize SSX2, SSX3, and SSX4 proteins expressed in formaldehyde-fixed and paraffin-embedded tissues. This antibody was used to investigate SSX expression in normal testis and thyroid, benign melanocytic lesions, melanoma lesions, and melanoma cell lines. SSX nuclear expression in the testis was found to be restricted to spermatogenic cells, mainly spermatogonia. Of 18 melanoma cell lines analyzed, 9 showed SSX RNA and protein expression, although heterogeneously and at variable levels. Treatment of an SSX-negative cell line with 5-aza-2'-deoxycytidine, a demethylating agent, led to SSX RNA and protein expression, indicating a role for methylation in transcription regulation. Thirty-four of 101 primary and metastatic melanoma cases and 2 of 24 common nevocellular and atypical nevus cases showed SSX nuclear staining. Again, SSX expression was heterogeneous, ranging from widespread to scarce. Our findings stress the importance of assessing the a priori SSX expression status of melanoma cases that may be selected for immunotherapeutic trials.

Scanlan MJ, Altorki NK, Gure AO, et al.
Expression of cancer-testis antigens in lung cancer: definition of bromodomain testis-specific gene (BRDT) as a new CT gene, CT9.
Cancer Lett. 2000; 150(2):155-64 [PubMed] Related Publications
In an effort to define new cancer-testis (CT) genes, we investigated whether BRDT, a testis-restricted member of the RING3 family of transcriptional regulators, is also expressed in cancer. Standard RT-PCR expression analysis detected BRDT transcripts in 12 of 47 cases of non-small cell lung cancer and single cases of both squamous cell carcinoma of the head and neck (1/12) and esophagus (1/12) but not in melanoma or in cancers of the colon, breast, kidney and bladder. Typing of 33 non-small cell lung cancers for coexpression of a panel of CT antigens revealed a high incidence (60%) of MAGE-3 mRNA expression, followed by MAGE-1 (36%), CT7/MAGE-C1 (30%), CT10 (30%), SSX4 (23%), BRDT (21%), NY-ESO-1 (21%) and HOM-MEL-40/SSX2 (15%). The coexpression pattern of these antigens provides a foundation for developing a polyvalent lung cancer vaccine.

Lasota J, Jasinski M, Debiec-Rychter M, et al.
Detection of the SYT-SSX fusion transcripts in formaldehyde-fixed, paraffin-embedded tissue: a reverse transcription polymerase chain reaction amplification assay useful in the diagnosis of synovial sarcoma.
Mod Pathol. 1998; 11(7):626-33 [PubMed] Related Publications
Identification of the t(X;18)(p11.2;q11.2) translocation and detection of the resulting SYT-SSX1 or SYT-SSX2 fusion transcripts are useful diagnostic markers for synovial sarcoma. In this study, we developed a polymerase chain reaction (PCR) assay to amplify SYT-SSX fusion transcripts. The primer sequences were designed to generate small PCR products and to amplify sequences of all known SSX genes as fusion partners for the SYT gene. RNA was obtained from formaldehyde-fixed and paraffin-embedded tissues of 22 immunohistochemically characterized synovial sarcomas, 6 of them cytogenetically confirmed as t(X;18) positive. The SYT-SSX fusion transcripts were detected in 21 of the 22 analyzed cases. The type of the fusion was identified by the specific restriction enzyme digestion pattern as SYT-SSX1 in 13 cases and SYT-SSX2 in 7 cases; in 1 case, the type could not be assigned. None of the cases showed involvement of the SSX3, SSX4, or SSX5 genes, the other members of the SSX gene family. In seven cases, the SYT-SSX1 or SYT-SSX2 fusion transcripts were demonstrated in frozen tissue using a different PCR assay. The PCR products were confirmed as SYT-SSX sequences by sequencing in five randomly selected cases. Fifteen other sarcomas and related tumors were negative for SYT-SSX fusion transcripts. The PCR assay used in this study performs well in formaldehyde-fixed and paraffin-embedded tissue, and it shows a high specificity. This assay can be used as an adjunct test for diagnostically difficult cases or in retrospective studies to refine the diagnosis of synovial sarcoma in archival material.

Gure AO, Türeci O, Sahin U, et al.
SSX: a multigene family with several members transcribed in normal testis and human cancer.
Int J Cancer. 1997; 72(6):965-71 [PubMed] Related Publications
Analysis of t(X;18) translocation in synovial sarcoma had previously led to the definition of the SSX2 gene, the fusion partner on chromosome X. Subsequent screening of testicular cDNA libraries identified 2 highly homologous genes, SSX1 and SSX3. Among these 3 genes, SSX2 has been found to be identical to HOM-MEL-40, which codes for an immunogenic tumor antigen expressed in various human cancers. SSX2 thus belongs to the family of cancer/testis (CT) antigens, i.e., immunogenic protein antigens with characteristic mRNA expression in normal testis and in cancer. To define additional CT antigens, we have immuno-screened a testicular cDNA expression library with an allogeneic serum from a melanoma patient, and both SSX2 and SSX3 were isolated. Further studies using testicular cDNA and SSX probes defined 2 new members of this gene family, SSX4 and SSX5, while a shorter cDNA variant of SSX4 was also identified. All 5 members of the SSX family shared strong sequence homology, with nucleotide homology ranging from 88 to 95% and amino acid homology ranging from 77 to 91%. Genomic cloning of a prototype SSX gene (SSX2) showed that its coding region is encoded by 6 exons, and the shortened form of SSX4 cDNA represents an alternatively spliced product lacking the 5th exon. Analysis of SSX mRNA expression by gene-specific RT-PCR confirmed that all 5 SSX genes are expressed in testis. In addition, analysis of a panel of 12 melanoma cell lines showed strong mRNA expression of either SSX1 (3/12), SSX2 (3/12), SSX4 (1/12), or SSX5 (1/12), indicating variable activation of the genes in malignant cells.

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