BACKGROUND: Ewing sarcoma is a paradigm of solid tumour -bearing chromosomal translocations resulting in fusion proteins that act as deregulated transcription factors. Ewing sarcoma translocations fuse the EWS gene with an ETS transcription factor, mainly FLI1. Most of the EWS -FLI1 target genes still remain unknown and many have been identified in heterologous model systems. METHODS: We have developed a stable RNA interference model knocking down EWS -FLI1 in the Ewing sarcoma cell line TC71. Gene expression analyses were performed to study the effect of RNA interference on the genetic signature of EWS -FLI1 and to identify genes that could contribute to tumourigenesis. RESULTS: EWS -FLI1 inhibition induced apoptosis, reduced cell migratory and tumourigenic capacities, and caused reduction in tumour growth. IGF-1 was downregulated and the IGF-1/IGF-1R signalling pathway was impaired. PBK/TOPK (T-LAK cell-originated protein kinase) expression was decreased because of EWS -FLI1 inhibition. We showed that TOPK is a new target gene of EWS -FLI1. TOPK inhibition prompted a decrease in the proliferation rate and a dramatic change in the cell's ability to grow in coalescence. CONCLUSION: This is the first report of TOPK activity in Ewing sarcoma and suggests a significant role of this MAPKK-like protein kinase in the Ewing sarcoma biology.

Bone and soft tissue sarcomas are an infrequent and heterogeneous group of mesenchymal tumors including more than a hundred different entities attending to histologic patterns. Research into the molecular aspects of sarcomas has increased greatly in the last few years. This enormous amount of knowledge has allowed, for instance, to refine the classification of sarcomas, improve the diagnosis, and increase the number of therapeutical targets available, most of them under preclinical evaluation. However, other important key issues, such as sarcomagenesis and the cell of origin of sarcomas, remain unresolved. From a molecular point of view, these neoplasias are grouped into 2 main types: (a) sarcomas showing relatively simple karyotypes and translocations, which originate gene fusions (eg, EWS-FLI1 in Ewing sarcoma) or point mutations (eg, c-kit in the gastrointestinal tumors) and (b) sarcomas showing unspecific gene alterations, very complex karyotypes, and no translocations. The discovery of the early mechanisms involved in the genesis of sarcomas, the more relevant signaling pathways, and the development of genetically engineered mouse models could also provide a new individualized therapeutic strategy against these tumors. This review describes the clinical application of some of the molecular alterations found in sarcomas, some advances in the field of sarcomagenesis, and the development of animal models.