PMSB5 as a possible mediator to enhance bortezomib sensitivity after CDK5 silencing. (A) Viability assay was performed with a validated PMSB5 siRNA and 2 CDK5 siRNAs transfected-KMS11 cells in the presence of various doses of bortezomib. (B) Immunoblotting analysis confirmed that PMSB5 protein level decreased substantially at 72 hours after transfection of KMS11 cells with different CDK5 siRNA species. (C) At 24 hours after transfection, only CDK5 expression was down-regulated. (D) Overexpression of an siRNA-resistant CDK5 mutant in KMS11 cells impaired cdk5 siRNA-induced bortezomib sensitization. KMS11 cells were infected with the lentiviruses expressing either wild-type or mutated CDK5. After confirming expression of exogenous CDK5, both infected cells were subsequently transfected with NT and CDK5_4 siRNA. At 24 hours after transfection, cells were treated with various doses of bortezomib, and cell viability was assessed after 72 hours of treatment. The data at each point represent the mean values of 6 wells (mean ± SD). (E) Western blot analysis of CDK5 and PSMB5 expression in KMS11 cells that overexpress wild-type CDK5 and mutant CDK5 at day 3 after introduction of control oligos (NT) and CDK5_4 siRNA.