ATF3 overexpression reduces sensitivity to endocrine therapy in MCF7 cells. (a) Cell proliferation of MCF7 empty and ATF3 overexpressing (OE) cells treated for eight days with E2, TAM, or deprived from E2 and measured at indicated time points with nuclei count in fluorescent microscopy. All values are normalized to a seeding control. (b) Cell cycle distribution of MCF7 empty and ATF3 OE cells treated for four days with E2, TAM, or without E2. Plots represent the percentage of cells in the different cell cycle phases determined by BrdU/7AAD staining. Statistics performed on the S phases (white bars) (c) Measurement of apoptosis rate in MCF7 empty and ATF3 OE cells treated for four days with E2, TAM and without E2. Plots represent the percentage of early apoptotic cells determined by Annexin V/PI staining. (d) Representative microscopy images of transwell invasion assay through Matrigel and relative quantification of the number of invading cells. Values are expressed as relative to the unstimulated WT control. Data are represented as mean ± SEM, n = 3. *** p-value < 0.001, ** p-value < 0.01, * p-value < 0.05.