Abstract
Iron regulatory protein 1 (IRP1) is a cytosolic bifunctional [4Fe-4S] protein which exhibits aconitase activity or binds iron responsive elements (IREs) in untranslated regions of specific mRNA encoding proteins involved in cellular iron metabolism. Superoxide radical (O2.-) converts IRP1 from a [4Fe-4S] aconitase to a [3Fe-4S] „null” form possessing neither aconitase nor trans-regulatory activity. Genetic ablation of superoxide dismutase 1 (SOD1), an antioxidant enzyme that acts to reduce O2.- concentration, revealed a new O2.--dependent regulation of IRP1 leading to the reduction of IRP1 protein level and in consequence to the diminution of IRP1 enzymatic and IRE-binding activities. Here, we attempted to establish whether developmental changes in SOD1 activity occurring in the mouse liver, impact IRP1 expression. We show no correlation between hepatic SOD1 activity and IRP1 protein level neither in pre- nor postnatal period probably because the magnitude of developmental fluctuations in SOD1 activity is relatively small. The comparison of SOD1 activity in regards to IRP1 protein level in the liver of threeSOD1 genotypes (Sod1+/+, Sod1+/- and Sod1-/-) demonstrates that only drastic SOD1 deficiency leads to the reduction of IRP1 protein level. Importantly, we found that in the liver of fetuses lacking SOD1, IRP1 is not down-regulated. To investigate O2.--dependent regulation of IRP1 in a cellular model, we exposed murine RAW 264.7 and bone marrow-derived macrophages to paraquat, widely used as a redox cycler to stimulate O2.-production in cells. We showed that IRP1 protein level as well as aconitase and IRE-binding activities are strongly reduced in macrophages treated with paraquat. The analysis of the expression of IRP1-target genes revealed the increase in L-ferritin protein level resulting from the enhanced transcriptional regulation of the LFt gene and diminished translational repression of L-ferritin mRNA by IRP1. We propose that O2.--dependent up-regulation of this cellular protectant in paraquat-treated macrophages may counterbalance iron-related toxic effects of O2.-.
Highlights
Cellular iron homeostasis has to complete two major biological tasks: (i) ensure the availability of iron for fundamental metabolic processes; (ii) minimize the ability of the metal to catalyze the formation of highly toxic hydroxyl radical through the Fenton reaction
Using wild-type fetuses and mice we aimed to test the hypothesis that Iron regulatory protein 1 (IRP1) protein level in the liver during mouse development is associated with changes in superoxide dismutase 1 (SOD1) activity
Our results clearly show that developmental changes in SOD1 activity do not influence IRP1 level in the liver (Fig 1A)
Summary
Cellular iron homeostasis has to complete two major biological tasks: (i) ensure the availability of iron for fundamental metabolic processes; (ii) minimize the ability of the metal to catalyze the formation of highly toxic hydroxyl radical through the Fenton reaction. These processes are largely controlled by the post-transcriptional IRP/IRE regulatory system. Iron regulatory proteins (IRP1 and IRP2) are cytoplasmic proteins that play a critical role in this regulation by interacting with mRNA hairpin structures called iron responsive elements (IREs). Resulting decrease in intracellular IRP1 protein level leads to the reduction of its enzymatic and trans-regulatory activity [12,13,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
