Fig. 4

YB-1 inhibition weakened CDK4/6i resistance. A. PARP1 and p-YB-1 were decreased when treated with abemaciclib and LJI308 in three breast cancer cell lines. B. MTT assay was used to assess the cytotoxic killing effect of combined therapy with abemaciclib and LJI308 in four cell lines. C–D. The YB-1 plasmid was transfected into MCF7 cells, and the inhibitory effect of abemaciclib in the YB-1 group was slower than that in the control group. E–F. MCF7AR cells were treated with abemaciclib and LJI308, and the combined inhibitory effect was confirmed by the crystal violet staining assay. G. We selected abemaciclib-treated MCF7 cells from six time points during the AR screening process. Elevated PARP1 and p-YB-1 levels were observed almost as simultaneously as MCF7 cells gradually gained resistance to abemaciclib. H. The cell cycle assay showed that G1 phase increased remarkably when treated with combined therapy of abemaciclib and olaparib. I–J. The cell apoptosis induced by the combined therapy of abemaciclib and LJI308 was assessed by flow cytometry, and the result analysis statistics are shown. K–L. The PARP1 and p-YB-1 proteins were detected by antibody when abemaciclib treatment was performed by immunofluorescence assay. The merged image shows their colocalization in the nucleus. Red represents PARP1, green represents p-YB-1 and blue represents DAPI. M–N. The lower fluorescence intensity represents attenuated DNA replication, and DNA replication stagnation was induced by the combined treatment of abemaciclib and LJI308 for the EDU assay. The results presented have been repeated in 3 biological replicates. Data, means ± SEMs, *, P < 0.05, **, P < 0.01, ***, P < 0.001