Figure 6

MDR1 expression is aberrant in APE1 acetylation site mutant expressing MM cells. (A) At 2 hours after melphalan treatment, APE1 was enriched by pulldown and blotted with anti-lysine acetylation antibody. (B) The Western blot showed expression levels of MDR1 in RPMI-8226/LR5, U266/LR6 and their parental cell lines RPMI-8226 and U266. The representative blots showed that melphalan resistant cells have higher expression levels of MDR1. (C) MDR1 protein expression was detected by Western blot at 48 hours after APE1 siRNA or pcDNA-APE1 was transfected into RPMI-8226 cells. MDR1 expression was downregulated after knockdown of APE1 in RPMI-8226 cells, and MDR1 was upregulated after overexpression of APE1. In addition, APE1 ^WT or APE1 ^K6R/K7R was transfected 24 hours after APE1 shRNA infection. 48 hours later, MDR1 levels were detected by Western blot. (D) MDR1 siRNA was applied to the pcDNA-APE1 transfected RPMI-8226 cells at 48 hours post 15 μM melphalan treatment, and cell viability was measured by a CCK-8 kit. The results were from three independent experiments.