Effects of 14-3-3ζ on viability and colony formation of tamoxifen-resistant (TamR) MCF-7 cells. (a) Sensitivity to tamoxifen measured as a function of cell viability in response to increasing concentrations of ligand for 96 hours. Vehicle-treated control cells were set at 100%. (b) Cell viability monitored over time in TamR cells with siCtrl or si14-3-3ζ and treatment with tamoxifen (Tam) for the days indicated. (c) Colony formation of TamR Ctrl siRNA or 14-3-3ζ siRNA cells in soft agar after 15 days in the presence of vehicle, Tam (1 μM), raloxifene (1 μM), fulvestrant (ICI 182,780) (1 μM) and Tam plus ICI (10 nM and 1 μM). Colonies were stained, counted, and photographed.