The Ewing’s sarcoma cell lines A673, SK-ES1, and A4573, which carry the EWSR1-FLI1 translocation types I, II, and III, respectively, and the HEK293 cell line from human embryonic kidney infected with AgT from SV40 (293T), were cultured in RPMI 1640 media (Gibco) and supplemented with 10% fetal bovine serum, l-glutamine, and penicillin/streptomycin. Cells were cultured at 37°C with 5% CO2. The A673 and SK-ES1 cell lines harboring shCTRL and shRING1B with seq#1 and seq#2 as well as A673 cell line with doxycycline inducible knockdown of EWSR1-FLI1 were previously described (11 (link), 18 (link)). hpMSCs were isolated following published protocols (21 (link)). Ectopic expression of EWSR1-FLI1 3xFLAG C terminus in HeLa cells was induced with doxycycline (0.5 μg/ml) (34 (link)).
All experiments performed with AZD1152 were incubated 72 hours, with the exception of RNA expression assays that were incubated 24 hours. For IC50 calculations, A673, SK-ES1, A4573, and 293T cell lines were seeded at 2000 cells per well in 96-well culture plates. AZD1152 and PRT4165 (Sigma-Aldrich) was added to complete growth medium; after 72 hours, cells were subjected to the ATPlite assay (PerkinElmer), and measurements were performed using a Tecan plate reader. Inhibitory concentrations were calculated using OriginPro 9.0 software.