PPP6R3 and breast cancer: The effect of silencing of each of CHKA, SAPS3 and LRP5, was assessed using validated siRNA SMARTpools, on ER-driven proliferation in a panel of ER-positive breast cancer cell lines that harbored amplification of CHKA, LRP5 and SAPS3 (that is, SUM44 and MDA-MB134-VI) or normal copy number at 11q13-q14 (that is, T47D and MCF7), as defined by copy number analysis (Additional file 4: Figure S3A).