(A–F) ATR knockdown, ATR inhibition with VX970, or SUN2 knockdown reduces β-catenin nuclear localization in MDA-MB-231 cells, as determined by nuclear-cytoplasmic fractionation and immunoblotting. Quantification was performed using 1-way ANOVA or Student’s t test (n = 3). (G–J) SUN2 knockdown or ATR inhibition reduces the association of α-catenin with β-catenin and KASH2. Protein interactions were assessed by α-catenin immunoprecipitation followed by immunoblotting. Data were analyzed by 2-way ANOVA (n = 3). (K and L) SUN2 knockdown decreases β-catenin recruitment to the ZEB1 and SNAIL1 promoter regions, as determined by ChIP-qPCR. Statistical significance was assessed using 1-way ANOVA (n = 3). (M) ATR knockdown reduces the expression level of ZEB1 and Snail1. MDA-MB-231 cells infected with lentivirus encoding control or shATR were harvested, and the mRNA levels of ZEB1 and Snail were detected by RT-qPCR (n = 3). Statistical analysis was performed using 1-way ANOVA. (N) SUN2 knockdown reduces the expression level of ZEB1 and Snail1. MDA-MB-231 cells infected with lentivirus encoding control or shSUN2 were harvested, and the mRNA level of ZEB1 and Snail was detected using RT-qPCR (n = 3). Statistical analysis was performed using 1-way ANOVA. (O and P) MDA-MB-231 cells infected with lentiviruses encoding control, shSUN2, shATR, or both shSUN2 and shATR were harvested for RNA extraction, and the expression of ZEB1 and Snail was subsequently assessed. Statistical analysis was performed using 1-way ANOVA. (Q) ATR expression level is positively correlated with ZEB1 and Snail1. The data were extracted from the TCGA database. All statistical data represent biological replicates, and results are expressed as mean ± SD. Western blot and co-IP experiments were independently repeated at least 3 times with similar results.