Knockdown of NPM1 enhances ATRA- induced differentiation of AML cells. (A) OCI-AML3 and HL-60 cells were transfected with control or NPM1-siRNA for 24 hours. After this, cells were treated with 0.25μM ATRA and incubated for an additional 72 hours. Differentiation was evaluated by staining the cells with Alexa 488-conjugated–anti-CD11b antibody followed by flow cytometry. Columns represent the mean of 3 independent experiments. Bars represent the SEM. (B) OCI-AML3 cells were transfected with control or NPM1 siRNA for 24 hours. Then, cells were treated with 0.25μM ATRA for an additional 72 hours. At the end of treatment, immunoblot analyses were performed for NPM1, Mt-NPM1, p53, p21, and C/EBPα on the total cell lysates. The expression levels of β-actin in the lysates served as the loading control.