CDK2 is particularly degraded by the proteasome during AML cellular differentiation. (A) Effect of ATRA, TPA, DMSO, and Dasa on the cellular differentiation of NB4 and U937 cells, as assessed by CD11b expression. NB4 and U937 cells were treated with 0.1 or 1 µM ATRA for 72 hours, 10 ng/mL TPA for 24 hours, 1% DMSO for 120 hours, and 5 or 10 µM Dasa for 72 hours, respectively. (B-D) Protein expression levels of different CDK (CDK1, CDK2, CDK4, and CDK6) in NB4 and U937 cells after treatments, as evaluated by western blotting. (B) Both cells were treated as indicated in panel A. (C) NB4 and U937 cells were treated with 0.1 or 1 µM ATRA for the indicated times in the presence of vehicle or 1 μM MG132 for the final 8 hours of incubation. (D) Both cells were treated with 10 ng/mL TPA for 24 hours in the presence of vehicle or 1 μM MG132 for the final 8 hours of incubation. (E) Western blotting of STAT1, PU.1, and CDK2 in primary patient blasts (Leu-1-4) treated with 10 µM ATRA for 7 days. (F) Western blotting of RUNX2 and CDK2 in human osteosarcoma U2OS cells incubated with 5 µM ATRA for the indicated times. *P < .05; ***P < .001 vs control. Data are shown as mean ± standard deviation (SD), n = 3. Other data are representative of at least 3 individual experiments and 1 representative image is shown. Con, control; DMSO, dimethyl sulfoxide.