EWS-FLI1 inhibits TNFα-induced NFκB-dependent transcription in Ewing sarcoma cells

Ewing sarcoma is primarily caused by a t(11;22) chromosomal translocation encoding the EWS-FLI1 fusion protein. To exert its oncogenic function, EWS-FLI1 acts as an aberrant transcription factor, broadly altering the gene expression profile of tumor cells. Nuclear factor-kappaB (NFκB) is a tightly regulated transcription factor controlling cell survival, proliferation and differentiation, as well as tumorigenesis. NFκB activity is very low in unstimulated Ewing sarcoma cells, but can be induced in response to tumor necrosis factor (TNF). We wondered whether NFκB activity could be modulated by EWS-FLI1 in Ewing sarcoma. Using a knockdown approach in Ewing sarcoma cells, we demonstrated that EWS-FLI1 has no influence on NFκB basal activity, but impairs TNF-induced NFκB-driven transcription, at least in part through inhibition of NFκB binding to DNA. We detected an in vivo physical interaction between the fusion protein and NFκB p65, which could mediate these effects. Our findings suggest that, besides directly controlling the activity of its primary target promoters, EWS-FLI1 can also indirectly influence gene expression in tumor cells by modulating the activity of key transcription factors such as NFκB.

Research highlights
► EWS-FLI1 interferes with TNF-induced activation of NFκB in Ewing sarcoma cells.
► EWS-FLI1 knockdown in Ewing sarcoma cells increases TNF-induced NFκB binding to DNA.
► EWS-FLI1 reduces TNF-stimulated NFκB-dependent transcriptional activation.
► Constitutive NFκB activity is not affected by EWS-FLI1.
► EWS-FLI1 physically interacts with NFκB p65 in vivo.