EWSR1 and Ewing sarcoma: In line with the doxycycline-inducible EWS/FLI1 KD model, shRNA-mediated KD of FLI1 did not lead to consistent changes in SIX1 mRNA in either the A673 (Fig. 7a, b) or EWS-502 (Fig. 7c, d) systems, but did lead to marked reduction in SIX1 protein levels (Fig. 7e, f), demonstrating that EWS/FLI1 is a strong regulator of SIX1 protein expression in ES.