We focus on iron sensing and molecular regulation of iron homeostasis in vertebrates by regulatory proteins (IRP).
IRP are cytosolic iron-regulated RNA binding proteins that bind to iron responsive elements (IRE) in the untranslated regions of at least 10 mRNA thereby controlling mRNA fate. We work primarily on IRP1, a bifunctional protein acting as either a high affinity IRE RNA binding protein or, in the iron loaded form, as the cytosolic isoform of the Fe-S cluster enzyme aconitase. Our work demonstrated that IRP1 is regulated by PKC-dependent phosphorylation.
Using biochemical, molecular and genetic approaches and mammalian cells we defined the sites of phosphorylation and mechanisms through which phosphorylation affected IRP1 function including programmed novel changes in stability of the Fe-S cluster controlling the RNA binding function that alters the sensitivity of regulation by oxygen and nitric oxide.
We collaborated on and developed genetic approaches in yeast to define how phosphorylation affected the dual functions of IRP1. Our RNA studies established the secondary structure of IRE and defined mechanisms underlying a translational regulatory hierarchy. As an outgrowth of this work we recently demonstratedthat IRP1 and IRP2 have unique and separable roles in iron metabolism including demonstrating that dysregulation of HIF2α mRNA translation in IRP1 deficient mice causes profound disturbances in erythropoiesis. HIF2α regulates many aspects of the adaptive response to hypoxia and iron deficiency through its ability to activate or repress a wide-array of genes. From our perspective this most notably includes the cytokine erythropoietin, iron transporters required for the assimilation of dietary iron and the iron regulatory protein hepcidin. Our current work focuses on these and other components of the IRP1-HIF2α regulatory axis.