Fig. 2. rBM increases ER protein levels in a clonal mammary epithelial cell line. (A) Morphological changes in Scp2 cells. Cells grown on plastic formed a flattened monolayer (a), whereas cells grown on top of rBM aggregated and formed acinus-like structures (b). Bar, 100 µm. They progressively become rounded when cultured in the presence of increasing concentrations of rBM (c-e). Bar, 100 µm. (B) In Scp2 cells grown as indicated in A for 3 days, ER protein levels were determined by western blot (a, representative gel) quantified by densitometry and expressed relative to the values measured on plastic (a, bar graph). In Scp2 cells grown for the indicated hours after the addition of serum-free medium containing lactogenic hormones in the presence (grey bars) or absence (black bars) of 2% rBM (b), ER protein levels were determined by western blot and expressed relative to the values measured on plastic 2 hours after the addition of the new medium. n=5; *P<0.05. (C) Immunofluorescence of ER in Scp2 cells grown for 2 days on plastic (a,b) or in the presence of 2% rBM (c,d). Note that not all the cells (DAPI staining of DNA; blue) stained for ER (green), and that the staining for ER was predominantly nuclear. Bar, 20 µm. The table (e) shows mean ± s.e.m. corresponding to percentages of ER-positive cells and to ER expression levels quantified in single cells grown on plastic or in the presence of rBM. Intensity of fluorescence was expressed as arbitrary units (A.U.). At least 100 cells were analyzed for each culture condition. The proportion of ER-positive cells was higher in the presence of rBM.