Sensitization to proteasome inhibitors after introducing CDK5 shRNAs in OPM1 cells. OPM1 cells were infected with control virus and 5 different CDK5 shRNA-expressing viruses. At day 2 and day 3 after infection, expression of GFP was detected by FACScan analysis and expression of CDK5 was assayed by Western blot (A-B). MTT assay was set for each shRNA-infected cell sample at day 3 after transfection. Three proteasome inhibitors were added at the indicated concentration. Cell viability was measured at day 3 after exposure, and the dose-responsive curve was made for each control and CDK5 shRNA-infected cells (C).