Regulation of iron metabolism: translational effects mediated by iron, heme, and cytokines.

Recent advances in the knowledge of iron metabolism underscore its complex relationship to overall cell metabolism. One of the key components of the iron uptake and storage pathway is ferritin, a protein that sequesters iron in a nontoxic form. Ferritin synthesis is translationally regulated by iron. Molecules such as nitric oxide and cytokines also affect transcriptional and/or posttranscriptional ferritin synthesis. Conversely, iron-containing molecules affect expression of mitochondrial aconitase, erythroid aminolevulinic acid synthase, and nitric oxide synthase. This observation indicates a complex linkage between iron metabolism and a variety of other important cell activities. The finding that the cytoplasmic iron-responsive protein (IRP) has two forms also raises intriguing questions about the relationship between the cytoplasmic aconitase and translational regulation of mRNAs such as ferritin. At least one of the IRPs can be phosphorylated. These recent discoveries open exciting new avenues for research that should lead to a better understanding of cellular iron metabolism.