HL-60 cells were treated with 1μM ATRA for the indicated times and the percent of differentiated cells was determined by measuring CD11b expression (A) and of apoptotic cells using Annexin V (B). HL-60 cells were treated with 1μM ATRA for the indicated times and the levels of Mcl-1, Bcl-2, cleaved caspase-9,-8,-3, PARP and β-actin were determined using specific antibodies with Western blot (C). HL-60 cells transfected with Mcl-1 siRNA or control siRNA were treated with 1μM ATRA for 2 days. The protein levels of PARP, Mcl-1, Bcl-2 and β-actin were determined using specific antibodies with Western blot (D) and the percent of apoptotic cells was determined using FACS of cells stained with Annexin V-FITC (E).