[Show abstract][Hide abstract]ABSTRACT: Synovial sarcoma is a rare malignant soft tissue tumor affecting mainly adolescents and young adults. The hallmark of synovial sarcoma is the presence of a reciprocal balanced t(X;18) translocation, leading to the fusion of the SS18 gene to either the SSX1, SSX2 or rarely the SSX4 gene, resulting in a chimeric transcriptional modifier. Therapeutic outcome of synovial sarcomas is primarily determined by the efficiency of surgery as a high tendency for local relapse is documented. Standardized chemo- and radiotherapy are further therapeutic options, however, specific targeted therapies are currently not available. Recently, several expression profiling studies in mesenchymal malignancies revealed gene expression signatures indicating WNT signaling activation in synovial sarcomas. This study was performed to examine the functional relevance of WNT signaling in synovial sarcomas and to evaluate if interference with the WNT signaling pathway might represent an option in the development of novel and highly selective drugs in the treatment of synovial sarcoma. To assess the prevalence of WNT signaling activation in a set of 30 synovial sarcoma tumor samples, nuclear staining of beta-catenin was analyzed immunohistochemically. Nuclear beta-catenin signals were observed in a significant subset of these tumors, indicating activation of the WNT signaling pathway. In order to evaluate whether WNT activation is molecularly dependent on the SS18/SSX fusion proteins, tetracycline-inducible systems overexpressing the SS18/SSX fusion proteins were established in T-Rex293 cells. In luciferase reporter assays employing the TOP-/FOPflash system, expression of SS18/SSX proteins effectively activated TCF/beta-catenin mediated transcriptional activity, which was associated with nuclear recruitment of beta-catenin. Five human synovial sarcoma cell lines were subsequently treated with small molecular inhibitors of WNT signalling. In MTT assays, a significant dose-dependent inhibition of cellular growth was observed, which was accompanied by decreased expression of the WNT downstream targets c-Myc and Cyclin D1. In flow cytometric analyses, the growth effects exerted by the inhibitors were shown to be due to a reduction of cellular proliferation combined with an increase of apoptosis. In summary, our data emphasize the pivotal role of WNT signaling in synovial sarcoma and indicate its functional dependence on the characteristic SS18/SSX translocations. Furthermore, our study demonstrates that targeting the WNT signaling pathway provides a specific, molecularly founded therapeutic strategy in the treatment of synovial sarcoma. Additional functional studies in vitro and in vivo are required to further understand the role of WNT signaling and its therapeutic applicability in synovial sarcomas.
[Show abstract][Hide abstract]ABSTRACT: Synovial sarcomas account for 5-10% of all malignant soft tissue tumors. They have been shown to express different membranous growth factor receptors, many of them signaling via intracellular kinase cascades. In our study, the functional role of PI3K/AKT signals in synovial sarcoma is analyzed with regard to tumor biology and therapeutic applicability. Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT, its targets p-(Ser9)-GSK-3β and p-(Ser2448)-mTOR and the cell cycle regulators Cyclin D1 and p27(KIP1) were performed in 36 synovial sarcomas. The PIK3CA gene was screened for mutations. In vitro, four synovial sarcoma cell lines were treated with the PI3K inhibitor LY294002. Phosphorylation of AKT, GSK-3β and mTOR was assessed, and cellular proliferation and apoptosis were analyzed to functionally characterize the effects of PI3K inhibition. Finally, coincubations of LY294002 with cytotoxic drugs were performed. Most tumors showed significant expression levels of p-AKT, p-GSK-3β and p-mTOR, indicating activation of the PI3K/AKT signaling cascade in synovial sarcomas; Cyclin D1 and p27(KIP1) were differentially expressed. Mutations in the PIK3CA gene could be excluded. In vitro, PI3K inhibition diminished synovial sarcoma cell growth accompanied by reduced phosphorylation of AKT, GSK-3β and mTOR. Mechanistically, PI3K pathway inhibition lead to enhanced apoptosis and decreased cellular proliferation linked to reduced Cyclin D1 and increased p27(KIP1) levels. Simultaneous treatment of synovial sarcoma cell lines with LY294002 and cytotoxic drugs resulted in additive effects. In summary, PI3K signaling plays an essential role in growth control of synovial sarcomas and might be successfully targeted in multimodal therapeutic strategies.
Full-text Article · Oct 2011 · International Journal of Cancer
[Show abstract][Hide abstract]ABSTRACT: Epigenetic changes including histone methylation, histone acetylation, and DNA methylation are thought to play important roles in the onset and progression of cancer in numerous tumor types. Recent evidence shows that dysregulated epigenetic modifications are as significant as genetic mutations and can act as oncogenic driver lesions causing autonomous growth of cancer cells. Here, we investigated the role of lysine-specific demethylase 1 in mesenchymal tumors. Lysine-specific demethylase 1 is the first discovered histone lysine demethylase and can demethylate both H3K4me2/1 and H3K9me2/1. By analyzing a total of 468 tumors, we describe for the first time high lysine-specific demethylase 1 expression in several highly malignant sarcomas, including synovial sarcomas, rhabdomyosarcomas, desmoplastic small round cell tumors and malignant peripheral nerve sheath tumors. Among the intermediate tumors only solitary fibrous tumors were found to be highly lysine-specific demethylase 1 positive, whereas lysine-specific demethylase 1 expression was low or absent in benign tumors. Lysine-specific demethylase 1 inhibition with small molecule inhibitors resulted in growth inhibition of synovial sarcoma cells in vitro and an increase in global H3K4me2 methylation. Sarcomas continue to remain a clinical challenge and therefore the identification of both diagnostic markers and novel drug targets for the development of new therapeutic options are needed. Our results suggest that dysregulation of lysine-specific demethylase 1 is associated with highly malignant sarcomas proposing them as molecular tumor markers as well as targets for the treatment of these tumor types.