Important contributions of DR4 to rhTRAIL-induced apoptosis. A: Apoptosis assay in SW948. Cells were pre-incubated with 10 μg/ml antagonistic anti-DR4 (αDR4), anti-DR5 (αDR5) antibodies or IgG1 control for 1 h before 4-5 h rhTRAIL treatment (0.1 μg/ml). Values are mean ± SD of at least three independent experiments. B: rhTRAIL binding to DR4 and DR5 in SW948 cells. Cells were incubated with increasing concentrations of rhTRAIL before detection of accessible cell surface DR4 and DR5. Values are expressed as the mean fluorescence intensity (MFI) and are mean ± SE of at least three independent experiments. C: Apoptosis assay in SW948-TR. CHX (5 μg/ml) was combined or not with the blocking antibodies 1 h before TRAIL treatment as described in (A).