EZH2 is required for survival of BRCA1-deficient but not BRCA1-proficient tumors cells. (a) Ezh2 mRNA expression measured by quantitative RT-PCR in BRCA1-deficient cells (in red, K 14cre; B rca 1F/F; p 53F/F(KB1P)) and in BRCA1-proficient cells (in blue, K 14cre;Brca1w.t/w.t; p 53F/F(KP)) after treatment with siRNAs against Ezh2 or 5 μM 3-deazaneplanocin A (DZNep; shown as fold induction relative to Hprt). (b) EZH2 levels analysed by western blot after KB1P and KP cells were treated with siRNAs targeting Ezh2 or non-targeting siRNAs (siNTC) and 5 μM DZNep or vehicle (dimethyl sulfoxide (DMSO)) for the indicated period. (c) Phase-contrast images of BRCA1-deficient and BRCA1-proficient cells treated for 48 hours with control (ctrl) siRNAs, siRNAs against Ezh2 or 5 μM DZNep (original magnification 10×). (d) Growth curves of KB1P (depicted in red) and KP cell lines (depicted in blue) treated with control (ctrl) siRNAs, siRNAs against Ezh2 or 5 μM DZNep. Data measured by Cell Titer Blue and represented as the mean ± standard error of the mean (three independent experiments). The depicted cell lines are representative for all three KB1P and KP cell lines.