Effects of DR4 or DR5 knockdown on snake venom toxin induced cell viability inhibition and caspase-3 activation. a, HCT116 cells and HT-29 cells were transfected with non targeting control siRNA or DR4 or DR5 siRNA (100 nM) as described in Methods for 24 h. Then, implemented snake venom toxin was treated (1 μg/ml) for another 24 h. Thereafter, cell viability was measured by direct counting after trypan blue staining. b, Equal amounts of total proteins (50 μg/lane) were subjected to 12% SDS-PAGE. Expression of DR4, DR5, cleaved caspase-3 and β-actin was detected by Western blotting using specific antibodies. β-actin protein was used an internal control. Each band is representative for three experiments. Columns, means of three experiments, with triplicates of each experiment; bars, SD. *, p <0.05, significantly different from non treated control group. #, p <0.01 significantly different from sc siRNA -treated group.