Retinoic acid inhibits NurRE-directed POMC transcription. AtT-20 cells were transfected with AP-1-LUC (a), NurRE-LUC (b), NBRE-LUC (c), CRE-LUC (d), GRE-LUC (e), POMC-LUC (f), or POMC-mut-NurRE-LUC (g) or cotransfected with POMC-LUC and COUP-TFI expression vector or control vector (h), and treated with 10 nM retinoic acid (RA), 100 nM CRH, 100 nM dexamethasone (Dex), or 5 μM forskolin (Forsk) or their combinations, as indicated. After a 6-hour treatment, luciferase activity was measured and normalized as described in Methods. Values indicate the mean ± SE of luciferase-to-β-galactosidase ratio of one representative experiment out of three, each of them with triplicates of each treatment. *P < 0.01 compared with the corresponding basal values, **P < 0.01 compared with CRH or forskolin stimulation, determined by ANOVA in combination with the Scheffé test. Similar results were obtained after a 24-hour treatment with retinoic acid.