Effects of siRNA inhibition of CHOP expression on bortezomib-induced changes in I-45-BTZ-R cell viability. A: I-45-BTZ-R cells were transfected with 100 nM CHOP-specific siRNA or control siRNA. After 48 hours, cells were treated with 200 nM bortezomib for an additional 48 hours, and then CHOP protein expression was determined by Western blot analysis. B: I-45-BTZ-R cells were treated as described above, and then cell viability was determined using the XTT assay. Values are the mean ± SD of three experiments. * p < 0.05 as compared to treatment with bortezomib following transfection with control siRNA.