The MCF-7 cell line used originated from the American Type Culture Collection and was acquired through CRUK cell bank (London, UK). MCF-7EpiR cells and mouse embryo fibroblasts (MEFs) have previously been described 8 (link), 9 (link). Cells were cultured in DMEM (Sigma-Aldrich, Poole, UK) supplemented with 10% (v/v) FCS and 2 mM glutamine at 37°C. Epirubicin Hydrochloride [2 mg/ml (3.4 mM) in 0.9% Sodium chloride, Medac, Germany] was obtained from Imperial College Healthcare (UK, London). The pcDNA3-Flag-OTUB1 and -OTUB1(C91S) plasmids used in this study have previously been described 17 (link). The eGFP-FOXM1 and pcDNA3-FOXM1 expression plasmids have also been described 10 (link). For ubiquitination studies, cells were treated with 10 μM MG132 (M7449; Sigma-Aldrich) for 6 h before collection for analysis. Cells were transfected using FuGENE 6 transfection reagent (Promega, Southampton, UK) and XtremeGENE HP reagent (Roche Diagnostics, Welwyn Garden City, UK) as recommended by the manufacturers.