Iron Regulatory Protein-1 Protects Against Mitoferrin1-deficient Porphyria [Metabolism]

February 7th, 2014 by Chung, J., Anderson, S. A., Gwynn, B., Deck, K. M., Chen, M. J., Langer, N. B., Shaw, G. C., Huston, N. C., Boyer, L. F., Datta, S., Paradkar, P. N., Li, L., Wei, Z., Lambert, A. J., Sahr, K., Wittig, J. G., Chen, W., Lu, W., Galy, B., Schlaeger, T.

Mitochondrial iron is essential for the biosynthesis of heme and iron-sulfur ([Fe-S]) clusters in mammalian cells. In developing erythrocytes, iron is imported into the mitochondria by mitoferrin1 (MFRN1, SLC25A37). Although loss of MFRN1 in zebrafish and mice leads to profound anemia, mutant animals showed no overt signs of porphyria, suggesting that mitochondrial iron deficiency does not result in an accumulation of protoporphyrins. Here, we developed a gene-trap model to provide in vitro and in vivo evidence that iron regulatory protein-1 (IRP1) inhibits protoporphyrin accumulation. Mfrn1+/gt;Irp1-/- erythroid cells exhibit a significant increase in protoporphyrin levels. IRP1 attenuates protoporphyrin biosynthesis by binding to the 5′-iron response element (IRE) of alas2 mRNA, inhibiting its translation. Ectopic expression of alas2 harboring a mutant IRE, preventing IRP1 binding, in Mfrn1gt/gt cells mimics Irp1-deficiency. Together, our data support a model whereby impaired mitochondrial [Fe-S] cluster biogenesis in Mfrn1gt/gt cells results in elevated IRP1 RNA-binding that attenuates ALAS2 mRNA translation and protoporphyrin accumulation.