The role of the iron responsive element in the control of ferroportin1/IREG1/MTP1 gene expression

Background/Aims: MTP1/Ferroportin1/IREG1, the product of the SLC40A1 gene, is a main iron export protein in mammals. However, the way this gene is regulated by iron is still unclear. The aim of this study was to investigate the functional role of genomic SLC40A1 elements in response to iron. Methods: Vectors containing either similar to 2.6 kb 5' flanking region or deletion constructs, including one devoid of an iron responsive element (SLC40A1-DeltaIRE-Luc), were analyzed by luciferase reporter gene in transfected HepG2, CaCO2 and U937 cells. Expression of iron genes and activity of the iron regulatory protein were also studied. Results: Iron increased and desferrioxamine decreased luciferase activity in all the cell types using both the full-length construct and the promoter deletion constructs, in the absence of changes in SLC40A1 or luciferase mRNA levels. To test the role of the SLC40A1 5' untranslated region, we first demonstrated that wild type and not SLC40A1-DeltaIRE-Luc could bind iron regulatory protein. Then, in cells transfected with SLC40A1-DIRE-Luc, we found that, in spite of iron regulatory protein activation, the response to iron manipulation was lost. Conclusions: We demonstrate that the iron responsive element in the SLC40A1 gene is functional and that it controls gene expression through the cytoplasmic iron regulatory protein system. (C) 2003 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.