Expression of human PrP mildly suppresses TNF-α-mediated death of MCF-7 breast carcinoma cells. (A) PrP expression was assessed by western blotting of three pools of vector-transfected MCF-7 cells (lanes 1–3) and six pools of MCF-7 cells transfected with a human PrP plasmid (lanes 4–9). (B) Pools of MCF-7 cells were treated with 100 ng/ml of recombinant TNF-α for 43 h. Cell viability was determined by the MTT assay. Absorbance values are expressed as a percentage of those in non-treated control samples. Data represent the mean ± SEM from 3 vector-transfected pools and 6 PrP-transfected pools. *p = 0.0042, human PrP vs. vector. (C) Pools of MCF-7 cells were treated with 100 ng/ml of recombinant TNF-α for 43 h. Cell viability was determined by flow cytometry after staining with propidium iodide. 10,000 cells were counted for each condition, and data are expressed as the percentage of cells containing sub-2n DNA. Data are derived from 4 MCF-7(hPrP) pools (mean ± SEM) and one vector control pool.