Effect of STI571 and ATRA on the degradation of PML-RARα, RARα, and RXR as well as proteasome activity in NB4 cells.
NB4 (A and B), or HL-60 and U937 (C) cells were seeded at an initial concentration of 2 × 105/mL and treated for 3 days (B and C) with the indicated compounds and for the indicated amount of time. (A and D) Western blot analysis (50 μg protein/lane) was performed with specific antibodies against PML-RARα, RARα, RXRα, and β-actin. On the right side of panel A, the position of the molecular weight standard is indicated. (D) Proteasome-dependent proteolytic activity was measured with a specific fluorogenic peptide substrate. Results are the mean ± SD of 3 separate culture dishes. The results are representative of at least 3 independent experiments. ■, control; ▨, STI571; ░, ATRA; ▪, STI571 plus ATRA; **, significantly lower than the corresponding group treated with ATRA alone (P < .01 according to the Student ttest); °°, significantly lower than the corresponding control group (P < .01 according to the Student t test).
