Retinoic acid activates human inducible nitric oxide synthase gene through binding of RARα/RXRα heterodimer to a novel retinoic acid response element in the promoter

Human inducible nitric oxide synthase (hiNOS) catalyzes nitric oxide (NO) which has a significant effect on tumor suppression and cancer therapy. Here we revealed the detailed molecular mechanism involved in the regulation of hiNOS expression induced by retinoic acid (RA). We showed that RARα/RXRα heterodimer was important in hiNOS promoter activation, hiNOS protein expression, and NO production. Serial deletion and site-directed mutation analysis revealed two half-sites of retinoic acid response element (RARE) spaced by 5 bp located at −172 to −156 in the hiNOS promoter. EMSA and ChIP assays demonstrated that RARα/RXRα directly bound to this RARE of hiNOS promoter. Our results suggested the identification of a novel RARE in the hiNOS promoter and the roles of the nuclear receptors (RARα/RXRα) in the induction of hiNOS by RA.