PGE2 derived from stearic acid (SA)-activated macrophages stimulates the cAMP→PKA pathway leading to increased aromatase transcription in preadipocytes. A, THP-1 cells were untreated or treated with control siRNA or siRNA to COX-2. Subsequently, the THP-1 cells were treated with vehicle (Control) or 10 µM SA for 24 hours. The abundance of COX-2 protein in cell lysates (inset) was determined by immunoblotting. β-actin was used as a loading control. Levels of PGE2 in the medium were determined by enzyme immunoassay. B-H, preadipocytes were treated with THP-1 cell-derived CM for 24 hours prior to measurements of cAMP (B), PKA activity (C), relative aromatase expression (D), aromatase activity expressed as femtomoles/µg protein/minute (E), aromatase mRNA derived from promoters I.3 (F) and II (G), and PR protein levels (H). Columns, means (n=6); bars, SD. *, P < 0.05.