The effect of GPI-80 level on cell growth. PC3 cells (closed circle), #22 (closed diamond) and #22ΔGPI-80 (open circle) were cultured in various conditions. The cells (3 × 103 cells/0.5 mL/well) were cultured in a 24-well culture plate (a), or on 0.5% agarose (b), for 10 days. For colony formation assay (c), the cells were cultured for 20 days. The data are representative of more than four independent experiments. The statistical significance (a–c) was calculated using one-way ANOVA with Bonferroni’s post hoc test, compared with each other (*, p < 0.05; **, p < 0.01; ***, p < 0.001; ns, not significant). To check the modulation of redox potential on cell growth (d), the cells (2.5 × 104 cells/mL) were cultured in a 96-well plate for 3 days in the presence of N-acetylcysteine. The data are represented as the mean ± standard error from seven independent experiments. The statistical significance (d) was calculated using two-tailed unpaired Student’s t-test, compared between #22mock and #22ΔGPI-80 cells treated with similar dose of N-acetylcysteine (*, p < 0.05).