Translational regulation via iron-responsive elements by the nitric oxide/NO-synthase pathway.

Nitric oxide (NO) produced from L-arginine by NO synthases (NOS) is a transmitter known to be involved in diverse biological processes, including immunomodulation, neurotransmission and blood vessel dilatation. We describe a novel role of NO as a signaling molecule in post-transcriptional gene regulation. We demonstrate that induction of NOS in macrophage and non-macrophage cell lines activates RNA binding by iron regulatory factor (IRFs), the central trans regulator of mRNAs involved in cellular iron metabolism. NO-induced binding of IRF to iron-responsive elements (IRE) specifically represses the translation of transfected IRE-containing indicator mRNAs as well as the biosynthesis of the cellular iron storage protein ferritin. These findings define a new biological function of NO and identify a regulatory connection between the NO/NOS pathway and cellular iron metabolism.