Fig. 3

YB-1 inhibition decreased the PARP1 level and mediated CDK4/6i sensitivity. A. p-YB-1 was elevated in MCF7-AR cells compared with parental MCF7 cells, and the protein levels of p-YB-1 and PARP1 were positively correlated. B-C. The expression of p-YB-1 and PARP1 showed the same trend in seven breast cancer cell lines, and p-YB-1/PARP1 was positively correlated with the Abemaciclib IC₅₀. D. Comparative analysis suggested that the YB-1 mRNA level was positively correlated with the CDK4/6i IC₅₀. E. PARP1 was markedly reduced when cells were treated with the YB-1 inhibitor LJI308, which can decrease the level of p-YB-1. F–H. The PARP1 protein level decreased when YB-1 was silenced. I. YB-1 silencing increased CDK4/6i sensitivity, and the inhibitory effect was confirmed by YB-1 silencing. J–K. YB-1 overexpression enhanced CDK4/6i resistance in MCF7AR cells according to the MTT assay. L. p-YB-1 and PARP1 were positively correlated and upregulated consistently in the three cell lines treated with abemaciclib. M–N. The fluorescence levels of p-H2AX and p-YB-1 were increased simultaneously in MCF7 cells treated with abemaciclib and reached their maximum when treated with abemaciclib at 10 μM. Orange represents p-H2AX, green represents p-YB-1 and blue represents DAPI. O. Three sequence primers for the promoter region of PARP1 were used for the ChIP assay, and the data demonstrated that YB-1 binds to the P2 primer in the promoter region of PARP1. The IgG antibody was used as a negative control. The results presented have been repeated in 3 biological replicates. Data, means ± SEMs, *, P < 0.05, **, P < 0.01, ***, P < 0.001