Effects of silencing CKS1B or SKP2 and overexpressing a nondegradable form of p27^Kip1 on MM cell growth and survival.CKS1B, SKP2, and CDKN1B (p27^Kip1) mRNA expression was evaluated by microarray analysis 5 days after lentiviral infection in (A) JJN3, (B) OCI-MY5, and (C) XG-1 cells expressing a nonspecific scrambled shRNA (SCRAM), CKS1B shRNA, or SKP2 shRNA. All experiments were performed in duplicate, and the results were expressed as the mean ± standard error. Western blot analysis on nuclear fractions of the same aliquots of cells shown in panels A, B, or C confirmed that CKS1B shRNA and SKP2 shRNA efficiently inhibited CKS1B and SKP2 protein expression, respectively, and increased p27^T187A levels in (D) JJN3, (E) OCI-MY5, and (F) XG-1. Cullin 1A (Cul1A) expression was used as control for the specificity of CKS1B and SKP2 action. p27^T187A overexpression was confirmed in all 3 cell lines 5 days after lentiviral infection, compared to the control cells infected with an empty vector (EV). Histone 1 was used as a loading control. Effects of CKS1B or SKP2 shRNA and p27^T187A overexpression on (G,I,K) cell proliferation and (H,J,L) cell viability in (G-H) JJN3, (I-J) OCI-MY5, and (K-L) XG-1. Total number of cells and cell viability were evaluated every day after lentiviral infection by trypan blue exclusion. Error bars represent standard error of the mean for 2 independent experiments.