Fig. 1: Elevated RSK3 is responsible for BETi resistance.

a Western blotting was performed to detect the protein levels of RSK3 in MDA-MB-231 and BT549 cells treated with DMSO or JQ1 (1 μM) for 0, 12 and 24 h. b The vector controls and RSK3-overexpressing BLBC cell clones were treated with DMSO or JQ1 (1 μM) for 48 h, and luminescent cell viability assays were performed to measure the killing effects. Statistical data (mean ± SD) are shown (***P < 0.001, one-way ANOVA). c Tumoursphere formation in RSK3-overexpressing BLBC cells and their vector controls was observed with or without JQ1 (1 μM) treatment. Statistical data of tumoursphere numbers are shown (*P < 0.05, **P < 0.01; one-way ANOVA). d Measurement of apoptosis in RSK3-overexpressing MDA-MB-231 cells and vector control with or without JQ1 (1 μM) treatment by Annexin V-FITC flow cytometry assay. Statistical data (mean ± SD) are shown based on three independent experiments. A representative experiment is shown (**P < 0.01, one-way ANOVA). e RPS6KA2-knockdown clones and shRNA control BLBC cells were treated with JQ1 (1 μM) for 48 h, the killing effects were detected by luminescent cell viability assay (**P < 0.01, ***P < 0.001; one-way ANOVA). f Annexin V-FITC flow cytometry assay was used to measure the synergistic pro-apoptotic effects of JQ1 on the silencing of RPS6KA2. Statistical data of three independent experiments are shown. A representative experiment is shown (**P < 0.01, one-way ANOVA). g Tumoursphere was counted in RPS6KA2-knockdown BLBC cells and their shRNA controls in the absence or presence of JQ1 (1 μM) treatment. Statistical data (mean ± SD) were shown (**P < 0.01, one-way ANOVA). h–i BALB/c nude mice were injected with RPS6KA2-knockdown or shRNA control MDA-MB-231 cells (n = 7), following treatment with vehicle control or JQ1 (35 mg/kg). After 25 days, tumours were weighed and images were taken. h Growth curves of xenograft tumours are shown (*P < 0.05, ***P < 0.001); i Photographs of tumours are shown. Source data are provided as a Source Data file.