Topo I activity in PC3-derived prostaspheres. PC3-derived spheres were collected and dissociated enzymatically to single cells. (A) Adherent PC3 and prostasphere-derived cells were stained for CD133 stem cell marker and analyzed by immunostaining. Results represent 3 different prostasphere cultures. PC3-derived prostaspheres were isolated and nuclear extracts were made. Equal quantities of total nuclear proteins (25 ng) were added to a topo I-specific reaction mixture and reaction products were analyzed by agarose gel electrophoresis. (B) Representative result of topo I DNA-relaxation activity. (C) Quantification analysis of topo I activity. Results represent means ± SE of 3 experiments. Statistical significance was determined by the student’s t-test analysis: **p < 0.01, compared to the adherent control.