Depletion of NPM1 by siRNA significantly enhances sensitivity of Mt NPM1 expressing AML cells to Ara-C and ATRA. (A,B) OCI-AML3 cells were transfected with control or NPM1 siRNA for 24 hours, followed by treatment with 0.5-5μM Ara-C or 0.25-2μM of ATRA for an additional 48 hours. Cells were stained with annexin V and propidium iodide and the percentages of apoptotic cells were determined by flow cytometry. Columns represent the mean of 3 independent experiments. Bars represent the SEM.