Figure 1

OPG attenuates TRAIL-induced apoptosis in a TRAIL binding-independent manner. CaOV3 cells (A) and OVCAR3 cells (B) were preincubated for 1 h with OPG (25 ng/ml), washed extensively to remove any OPG, and treated with TRAIL (50 ng/ml) for 48 h. The cells were then washed, seeded at different densities and incubated in fresh medium. Viable colonies were counted after 14 days and data were expressed at fold increase relative to control (untreated) cells. Results are from three independent experiments and express as mean fold increase ± SD. * P < 0.01 compared to control. CaOV3 and OVCAR3 cells (C) and primary tumor cells OVC238A (D) were preincubated for 1 h with OPG (25 ng/ml), washed and incubated with TRAIL (50 ng/ml) for 24 h, and apoptosis was assessed. Apoptosis is expressed as fold increase relative to control (untreated) cells with the mean of triplicates from three independent experiments ± SD. * P < 0.01; ** P < 0.001. (E) Concentration of OPG released in conditioned medium from CaOV3, OVCAR3 and OVC238A cells measured by ELISA.