Iron Regulatory Protein-1 Protects against Mitoferrin-1-deficient Porphyria

• Published in: The Journal of biological chemistry 2014-03, Vol.289 (11), p.7835-7843
• Main Authors: Chung, Jacky, Anderson, Sheila A., Gwynn, Babette, Deck, Kathryn M., Chen, Michael J., Langer, Nathaniel B., Shaw, George C., Huston, Nicholas C., Boyer, Leah F., Datta, Sumon, Paradkar, Prasad N., Li, Liangtao, Wei, Zong, Lambert, Amy J., Sahr, Kenneth, Wittig, Johannes G., Chen, Wen, Lu, Wange, Galy, Bruno, Schlaeger, Thorsten M., Hentze, Matthias W., Ward, Diane M., Kaplan, Jerry, Eisenstein, Richard S., Peters, Luanne L., Paw, Barry H.
• Format: Article
• Language: English
• Subjects: 5-Aminolevulinate Synthetase - metabolism; Animals; Blastocyst - cytology; Cell Biology; Cell Differentiation; Cell Line, Tumor; Erythropoeisis; Fe-S Cluster Biogenesis; Female; Gene Expression Regulation; Genotype; HEK293 Cells; Heme; Heme - chemistry; Humans; Iron; Iron - chemistry; Iron Regulatory Protein 1 - metabolism; Iron-sulfur Protein; Iron-Sulfur Proteins - metabolism; Male; Membrane Transport Proteins - metabolism; Mice; Mice, Inbred C57BL; Mitochondrial Solute Carrier; Mitochondrial Transport; Porphyrias - metabolism; Protein Biosynthesis; Protoporphyrin; Protoporphyrins - metabolism; Zebrafish
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.547778

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 MFRN1 (mitoferrin-1, 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. Background: Heme and [Fe-S] cluster assembly are tightly regulated processes that require mitochondrial iron. Results: Loss of mitochondrial iron activates the [Fe-S]-dependent RNA-binding activity of IRP1 that inhibits protoporphyrin biosynthesis. Conclusion: IRP1 forms a critical feedback mechanism, preventing protoporphyrin accumulation under limiting mitochondrial iron conditions. Significance: This study provides evidence linking heme biogenesis to that of [Fe-S] clusters synthesis.