ATRA induces Stat1 mRNA and protein expression and transcriptional activation of an interferon-responsive promoter in U-937 cells.

(A) Cells were induced for 72 hours by TPA (0.16 μmol/L), VitD₃ (0.1 μmol/L), ATRA (1 μmol/L), or IFN-γ (100 U/mL). Stat1 and GAPDH mRNA levels were determined by Northern blot. (B, C) Cells were induced by ATRA and collected at the indicated times, and protein extracts were prepared and analyzed by Western blot using α-Stat1 antibodies. (D) U-937 cells stably transfected with a GBP promoter-driven luciferase reporter plasmid were stimulated with ATRA or VitD₃. Cells were collected at the indicated times, and extracts were prepared, and luciferase activity was measured. The graph shows fold induction over untreated cells for RLU values correlated to protein concentration. Data are presented as mean ± SD (n = 3).