The cell lines, MEG-01 (non-DS AMKL), K562 (chronic myeloid leukemia; erythroblastic leukemia), Kasumi-1 (t(8;21)-positive acute myeloid leukemia) and HL60 (acute promyelocytic leukemia), were purchased from ATCC (Manassas, VA). The CMY and CMK cell lines (DS-AMKL) were kindly provided by Dr. Shai Izraeli (Tel Aviv University). The cell lines were grown in RPMI-1640 medium supplemented with 10% fetal bovine serum and 4mM L-glutamine. For differentiation experiments, AMKL cell lines (MEG-01, CMY and CMK) were treated either with DMSO (control) or with 5 nM phorbol 12-myristate 13-acetate (PMA; Sigma Aldrich, St. Louis, MO) and incubated for 4 and 8 days to evaluate SON expression during megakaryocytic differentiation. Day 0 samples were used as a control for each treatment group. For knockdown experiments, cells were nucleofected with Amaxa Nucleofector II for siRNA transfection and incubated for 2 to 5 days depending on the purpose of experiments. The SON siRNA sequence used for nucleofection is GCAUUUGGCCCAUCUGAGAtt (Silencer Select siRNA custom synthesis product by Life Technologies/ThermoFisher, Waltham, MA) which was verified for its effectiveness and specificity in previous studies [21 (link), 28 (link)]. RUNX1 siRNA (siRNA ID s229352) and negative control siRNA (UAACGACGCGACGACGUAAtt; custom synthesis product) was purchased from ThermoFisher Scientific.