Figure 3.

Marked increase in C/EBPε mRNA expression by ectopic expression of PML/RARα, but not PLZF/RARα, in U937 cells. U937PR9 or U937B412 cells, stably transfected with zinc-inducible PML/RARα or PLZF/RARα expression vectors, respectively, were cultured either with (+) or without (–) 100 μM ZnSO₄ with or without, ATRA and analyzed for induction of C/EBPε mRNA expression. (a) Time response by ATRA (10^–8 M) in U937PR9 cells. Northern blot analysis was performed using 20 μg of total RNA from U937PR9 cells exposed for various lengths of time to ATRA. (b) Dose response by ATRA in U937PR9 cells. Northern blot analysis was performed using 20 μg of total RNA of U937PR9 cells exposed to various concentrations of ATRA for 24 hours. (c) Dose response by ATRA in U937B412 cells. Northern blot analysis was performed using 30 μg of total RNA of U937B412 cells exposed to various concentrations of ATRA for 3 days. The top panels show the 1.2-kb C/EBPε transcript after hybridizations with full-length C/EBPε, and the bottom panels show the hybridizations with either β-actin or GAPDH probe to confirm equivalent RNA loading.