Heme controls ferroportin1 (FPN1) transcription involving Bach1, Nrf2 and a MARE/ARE sequence motif at position -7007 of the FPN1 promoter.
BACKGROUND
Macrophages of the reticuloendothelial system play a key role in recycling iron from hemoglobin of senescent or damaged erythrocytes. Heme oxygenase 1 degrades the heme moiety and releases inorganic iron that is stored in ferritin or exported to the plasma via the iron export protein ferroportin. In the plasma, iron binds to transferrin and is made available for de novo red cell synthesis. The aim of this study was to gain insight into the regulatory mechanisms that control the transcriptional response of iron export protein ferroportin to hemoglobin in macrophages.


METHODS
Iron export protein ferroportin mRNA expression was analyzed in RAW264.7 mouse macrophages in response to hemoglobin, heme, ferric ammonium citrate or protoporphyrin treatment or to siRNA mediated knockdown or overexpression of Btb And Cnc Homology 1 or nuclear accumulation of Nuclear Factor Erythroid 2-like. Iron export protein ferroportin promoter activity was analyzed using reporter constructs that contain specific truncations of the iron export protein ferroportin promoter or mutations in a newly identified MARE/ARE element.


RESULTS
We show that iron export protein ferroportin is transcriptionally co-regulated with heme oxygenase 1 by heme, a degradation product of hemoglobin. The protoporphyrin ring of heme is sufficient to increase iron export protein ferroportin transcriptional activity while the iron released from the heme moiety controls iron export protein ferroportin translation involving the IRE in the 5'untranslated region. Transcription of iron export protein ferroportin is inhibited by Btb and Cnc Homology 1 and activated by Nuclear Factor Erythroid 2-like involving a MARE/ARE element located at position -7007/-7016 of the iron export protein ferroportin promoter.


CONCLUSIONS
This finding suggests that heme controls a macrophage iron recycling regulon involving Btb and Cnc Homology 1 and Nuclear Factor Erythroid 2-like to assure the coordinated degradation of heme by heme oxygenase 1, iron storage and detoxification by ferritin, and iron export by iron export protein ferroportin.
Marro
Samuele
S
Department of Pediatric Oncology, University of Heidelberg, Im Neuenheimer Feld 153, 69120 Heidelberg, Germany.
Chiabrando
Deborah
D
Messana
Erika
E
Stolte
Jens
J
Turco
Emilia
E
Tolosano
Emanuela
E
Muckenthaler
Martina U
MU
D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D005290:Ferric Compounds / Q000494:pharmacology; D006418:Heme / Q000494:pharmacology*; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism; D006454:Hemoglobins / Q000494:pharmacology; D007501:Iron / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011524:Protoporphyrins / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D034622:RNA Interference; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects*; D000098742:Ferroportin
C486316:Bach1 protein, mouse; D050976:Basic-Leucine Zipper Transcription Factors; D027682:Cation Transport Proteins; D005290:Ferric Compounds; D006454:Hemoglobins; D051267:NF-E2-Related Factor 2; D011524:Protoporphyrins; D000644:Quaternary Ammonium Compounds; D000098742:Ferroportin; D006418:Heme; D007501:Iron; D051547:Heme Oxygenase-1; C013531:ferric ammonium citrate