Figure 3. MDM2 knockdown impedes mitosis and significantly decreases the number of estrogen-driven S phase cells.

(A) & (B) T47D cells ((A) inducible shmdm2 clonal and vector pool; (B) constitutive shmdm2 and vector pool) grown in the presence of estrogen in 3D matrigel for 3.5 weeks. The cells were fixed, permeabilized, blocked, stained with phospho-histoneH3 antibody and mounted with DAPI containing mounting media. Images were taken with confocal microscope. Quantitative analysis of phospho-histone H3 positive cells were performed by capturing optical Z-stack sections of masses and dividing the number of positive phospho-histone H3 cells by the total number of masses. (A) The number of masses counted in each group for 2 independent experiments were control vector -shRNA induction (29, 30), control vector +shRNA induction (30, 30), mdm2shRNA -shRNA induction (29, 30) and mdm2shRNA +shRNA induction (30, 30). (B) The number of masses counted in each group for 2 independent experiments were control vector (49, 60) and shmdm2 (48, 60). Average of two independent experiments are shown for each knockdown method. The p-value determined by 2-tailed Student t-test comparing with and without MDM2 knockdown was p-value=0.001 (A) and p-value=0.009 (B). Two independent scorers counted the numbers of masses for each independent experiment. (C) Representative confocal Z-stack image (single slice) showing DAPI, phospho-histone H3 and GFP in estrogen-treated inducible clonal T47D.shmdm2 cells in the presence and absence of 4μg/ml doxycycline. (D) Cell cycle analysis by FACS (Fluorescence Activated Cell Sorting). T47D cells were harvested, fixed and stained with propidium iodide and subjected to cell cycle analysis by FACS. Data are presented as percent of cells in S phase in a total population of 10,000 cells and analyzed by FACS in each group. Average of 4 independent experiments are shown. The p-value was determined by 2-tailed Student t-test and * represents a p-value ≤ 0.05