Phosphorylation of EWS and EWS-Fli1 in response to DNA damage

In Ewing's sarcomas, chromosomal translocations cause the N-terminal domain of the Ewing's sarcoma protein (EWS) to fuse with the DNA-binding domains of the Ets family of transcription factors. Here we show that EWS and EWS-Fli1, the fusion most frequently found in Ewing's sarcomas, become phosphorylated at Thr79 in response to either mitogens or DNA damaging agents. The much weaker mitogen-induced phosphorylation of EWS is catalysed by the MAP kinases ERK1 and ERK2, while the much stronger phosphorylation of EWS induced by the DNA alkylating agent methyl methanesulphonate (MMS) can be catalysed by JNK and at least one other protein kinase distinct from ERK1/ERK2. In contrast, the phosphorylation of EWS-Fli1 induced by MMS was largely mediated by p38α/p38β MAPKs. MMS induced a much stronger phosphorylation of EWS-Fli1 than EWS in heterodimers comprising both proteins.