Fig. 4
Ser675 phosphorylation of β-catenin in the Wnt pathway mediates resistance to olaparib but can be inhibited by palbociclib. a The phosphorylation level of specific sites of β-catenin in cells treated with drugs as indicated for 12 h. The phosphorylation sites marked in green negatively regulate the Wnt pathway, while those marked in red promote nuclear translocation, thereby positively regulating the Wnt pathway. b Western blot (WB) analysis showing the levels of β-catenin, phosphorylated β-catenin (pβ-cateninSer552 and pβ-cateninSer675) and RAD51 (a homologous recombination repair marker) in MDA-MB-436, HCC1937 and SUM149 cells. c CCK-8 analysis of parental HCC1937 cells and cells with acquired resistance to olaparib at different concentrations of olaparib. d Expression difference in Wnt signalling pathway-related proteins and Rad51 between parental HCC1937 and acquired olaparib-resistant cells assessed by WB analysis. e The viability of parental HCC1937 cells, HCC1937 cells with acquired olaparib resistance and CTNNB1 OE HCC1937 cells treated with 20 μM olaparib for 5 days. f Growth curves of HCC1937 and CTNNB1 OE HCC1937 cells with acquired olaparib resistance under the indicated treatments. g WB analysis of β-catenin, pβ-cateninSer675 and c-myc protein levels in CTNNB1 KD HCC1937 cells with or without β-catenin mutant overexpression. h (Left) The viability of the control and HCC1937 cells expressing β-cateninWT, mutant β-cateninS675D or β-cateninS675A under the indicated treatments. (Right) The four cell types under combined treatment for 5 days. Student’s t-test; ***p < 0.001, **p < 0.01, *p < 0.05; ns, not significant. The data are presented as the means ± SEMs. Con: Control; Ola: Olaparib; Palb: Palbociclib