Differential roles of SS18-SSX fusion gene and insulin-like growth factor-1 receptor in synovial sarcoma cell growth.

Recently we demonstrated that the synovial sarcoma specific fusion gene SS18-SSX is crucial for cyclin D1 expression and is linked to cell proliferation. In this report we explore the role of SS18-SSX and IGF-1R for their potential functions in cellular proliferation and survival in cultured synovial sarcoma cells. We found that targeting of SS18-SSX mRNA by antisense oligonucleotide treatment drastically and rapidly decreased cell proliferation but caused only a slight increase of apoptosis. The synovial sarcoma cells were confirmed to express IGF-1R, and treatment with an IGF-1R inhibitor resulted in substantially reduced cell viability by inducing apoptosis in these cells. Conversely, inhibition of the IGF-1R resulted only in a slight to moderate decrease in DNA synthesis. In conclusion, SS18-SSX and IGF-1R seem to play important but different roles in maintaining malignant growth of synovial sarcoma cells. Whereas SS18-SSX maintains cyclin D1 and cell proliferation, IGF-1R protects from apoptosis.

A novel case of synovial sarcoma of the kidney: impact of SS18/SSX analysis of renal hemangiopericytoma-like tumors.

We report a new case of synovial sarcoma of the kidney. The patient underwent nephrectomy because of a large tumor in the right kidney. The histologic diagnosis was hemangiopericytoma. Less than 1 year after primary surgery the patient was reoperated due to massive local recurrence. Histology now revealed a poorly differentiated tumor tissue with hemangiopericytoma-like features. Immunostainings showed immunoreactivity to cytokeratin, epithelial membrane antigen, and vimentin. The tumor was negative to CD34 and factor VIII. The tumor cell proliferation, assessed by Ki-67, was high. RT-PCR analysis and sequence analysis demonstrated the presence of SS18/SSX2 fusion gene. Review of the histologic specimens from the original tumors confirmed hemangiopericytoma-like morphology. The new diagnosis was poorly differentiated synovial sarcoma. At the time of reoperation, lung metastases were detected radiologically, reflecting a very aggressive phenotype. To our knowledge, this is the third case of poorly differentiated synovial sarcoma of the kidney. Common for all these three cases is the hemangiopericytoma-like histology and a very aggressive clinical behavior. These circumstances accentuate the impact of SS18/SSX analysis in diagnosis of renal hemangiopericytoma-like tumors.

Gene expression profile by blocking the SYT-SSX fusion gene in synovial sarcoma cells. Identification of XRCC4 as a putative SYT-SSX target gene.

Increasing evidence suggests that the SYT-SSX fusion gene plays an important role in synovial sarcoma development and progression. However, very little is known about the downstream targets of SYT-SSX. In this study, we used antisense oligonucleotides to block the expression of the SYT-SSX fusion gene in synovial sarcoma cells. By comparing SYT-SSX inhibited cells with noninhibited cells, the gene expression profile was analysed using cDNA microarray and established by real-time PCR. Herewith, using a filter containing 1176 cancer-relevant genes, we found that the DNA repair gene XRCC4 and the DNA mismatch repair gene MSH2 were downregulated, whereas the gene encoding for the serine/threonine protein kinase PRK (also known as CNK), and the macrophage inhibitory cytokine MICI (also known as PLAB) were upregulated after the inhibition of SYT-SSX. In comparison, expression of the XRCC4 gene was undergoing the strongest alteration. Consistently, the protein expression of XRCC4 was found to be decreased after SYT-SSX inhibition, whereas there were no detectable changes for the other gene products. Our study provides some clues to elucidate the signaling pathways of the SYT-SSX fusion gene, as well as it demonstrates a valuable model system for search for other SYT-SSX targets.

A novel type of SYT/SSX fusion: methodological and biological implications.

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.