Effect of ATRA on LPS-induced AP-1– and NF-κB–dependent transcription in THP-1 cells. THP-1 cells were transfected with p(AP-1)₄LUC or p(κB)₄LUC (6 μg) using DEAE-dextran. After 46 hours, cells were divided into four equal portions and incubated with or without LPS (10 μg/mL) for 5 hours in the presence or absence of a 30-minute pretreatment with ATRA (1 × 10⁻⁵ mol/L). AP-1–mediated transcription (A) and c-Rel/p65–mediated transcription (B) are shown. Luciferase activity (light units) expressed by p(AP-1)₄LUC and p(κB)₄LUC was used to determine fold inductions (mean ± SE) in three independent experiments.