Stable expression of PrP weakly suppresses death of immortalized Prn-p0/0hippocampal neurons after serum deprivation. (A) Two untransfected lines of Prn-p0/0HpL cells (3–2 and 3–4) were subjected to 72 hours of serum deprivation. Cell viability was determined by MTT assay. Absorbance values are expressed as a percentage of those in non-treated control samples at each timepoint. Data are from one representative experiment. (B) Immunofluorescence analysis of mouse PrP expression in two PrP-expressing lines of HpL3-4 cells (4-1 and 4-2), and one vector-transfected line. PrP was detected by staining with the PrP antibody (green). Cells were counterstained with giantin, a marker for the Golgi apparatus (red). PrP expression was detectable on the cell surface and in the Golgi apparatus. Bar = 50 μm. (C) HpL3-4 cell lines were subjected to 96 hours of serum deprivation, after which cell viability was determined by flow cytometry after propidium iodide staining. 10,000 cells were counted for each condition. Data are expressed as the percentage of cells containing sub-2n DNA content, and represent the mean ± SEM from three independent experiments. *p < 0.01, PrP vs. vector. Relative PrP expression for each cell line is indicated below each set of bars by the number of "+" symbols.