Ewing's sarcoma is a highly malignant bone-associated cancer of children and young adults that usually expresses the EWS/FLI fusion protein. EWS/FLI is the key oncoprotein in Ewing's sarcoma, and functions as an aberrant transcription factor. We recently demonstrated that EWS/FLI downregulates many more genes than it upregulates, and that a portion of these are directly regulated by EWS/FLI binding. This suggests that the widely-accepted model of EWS/FLI functioning as a transcriptional activator may be incomplete, and that it may act as a transcriptional repressor in some settings. Furthermore, our work identified a number of dysregulated genes that are required for the oncogenic behavior of Ewing's sarcoma cells, but suggested that additional targets remain to be identified. Finally, we made the unexpected discovery that EWS/FLI upregulates some of its targets by binding to GGAA-containing microsatellites. This was surprising because these microsatellites do not conform to known EWS/FLI binding sites, nor have they been previously implicated in cancer development. Based on our preliminary data, we hypothesize that EWS/FLI functions as a transcriptional activator at some loci, and as a repressor at other loci, that both of these functions are required to dysregulate critical target genes to induce oncogenic transformation, and that polymorphisms that effect transcriptional function at these loci modulate Ewing's sarcoma susceptibility or prognosis. Experiments are now proposed to test this hypothesis. The transcriptional repression domain of EWS/FLI will be defined, and its role in both the transcriptional and oncogenic function of EWS/FLI determined. Identification and analysis of genes directly regulated by EWS/FLI using both experimental and computational approaches will allow for the identification of new key targets that are involved in the development of Ewing's sarcoma. Analysis of microsatellites in patients and populations will help to define the role of these elements in disease phenotypes and susceptibility to Ewing's sarcoma. At the completion of these studies, we will have developed a deeper understanding of the mechanistic basis of Ewing's sarcoma and applied it translationally. This may allow for the development of new prognostic or therapeutic approaches to this disease, and may impact on our understanding of other ETS-associated cancers as well.

Public Health Relevance

Many cancers are associated with abnormal ETS proteins, such as prostate cancer, leukemia, breast cancer, and sarcoma. Ewing's sarcoma, with its abnormal ETS protein EWS/FLI, serves as a paradigm to understand the function of ETS proteins in cancer. Thus, understanding the mechanisms by which EWS/FLI causes Ewing's sarcoma may identify new approaches for treating this very aggressive cancer of children and young adults, and may also allow for an improved understanding and treatments of other ETS-associated cancers as well.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Cancer Molecular Pathobiology Study Section (CAMP)
Program Officer
Mietz, Judy
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Utah
Schools of Medicine
Salt Lake City
United States
Zip Code
Gorthi, Aparna; Romero, July Carolina; Loranc, Eva et al. (2018) EWS-FLI1 increases transcription to cause R-loops and block BRCA1 repair in Ewing sarcoma. Nature 555:387-391
Pishas, Kathleen I; Lessnick, Stephen L (2018) Ewing sarcoma resistance to SP-2509 is not mediated through KDM1A/LSD1 mutation. Oncotarget 9:36413-36429
Pishas, Kathleen I; Drenberg, Christina D; Taslim, Cenny et al. (2018) Therapeutic Targeting of KDM1A/LSD1 in Ewing Sarcoma with SP-2509 Engages the Endoplasmic Reticulum Stress Response. Mol Cancer Ther 17:1902-1916
Johnson, Kirsten M; Mahler, Nathan R; Saund, Ranajeet S et al. (2017) Role for the EWS domain of EWS/FLI in binding GGAA-microsatellites required for Ewing sarcoma anchorage independent growth. Proc Natl Acad Sci U S A 114:9870-9875
Johnson, Kirsten M; Taslim, Cenny; Saund, Ranajeet S et al. (2017) Identification of two types of GGAA-microsatellites and their roles in EWS/FLI binding and gene regulation in Ewing sarcoma. PLoS One 12:e0186275
Theisen, Emily R; Pishas, Kathleen I; Saund, Ranajeet S et al. (2016) Therapeutic opportunities in Ewing sarcoma: EWS-FLI inhibition via LSD1 targeting. Oncotarget 7:17616-30
Lerman, Daniel M; Monument, Michael J; McIlvaine, Elizabeth et al. (2015) Tumoral TP53 and/or CDKN2A alterations are not reliable prognostic biomarkers in patients with localized Ewing sarcoma: a report from the Children's Oncology Group. Pediatr Blood Cancer 62:759-65
Fadul, John; Bell, Russell; Hoffman, Laura M et al. (2015) EWS/FLI utilizes NKX2-2 to repress mesenchymal features of Ewing sarcoma. Genes Cancer 6:129-43
Chaturvedi, Aashi; Hoffman, Laura M; Jensen, Christopher C et al. (2014) Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma. Mol Biol Cell 25:2695-709
Sankar, Savita; Theisen, Emily R; Bearss, Jared et al. (2014) Reversible LSD1 inhibition interferes with global EWS/ETS transcriptional activity and impedes Ewing sarcoma tumor growth. Clin Cancer Res 20:4584-97

Showing the most recent 10 out of 24 publications