The SLC11A3 gene, encoding for a main iron export protein, is controlled posttranscriptionally by iron

Abstract

Ferroportinl (FP1), the product of the SLC11A3 gone, is the main iron export protein in mammals and its mutation leads to the autosomal form of hemochromatosis (Montosi et al., J Clin Invest 108: 619-623, 2001). Aim: to find out whether and how SLC11A3 gene expression is controlled by iron. We generated luciferase (LUC) reporter gone containing a 2.7 Kb SLC11A promoter region, transfected HepG2 and CACO2 cell lines by lipofection, in the presence of iron or the iron chelator deferoxamine (DFO). Iron led to a 2-3 fold increase and DFO a 50-70% decrease of LUC activity in both cells types in five experiments performed in triplicate, with no change in LUC mRNA. The Iron Regulatory Protein (IRP) activity (RNA-gel shift analysis) was down-regulated by iron and up-regulated by DFO, as expected. After deletion of the 5' promoter region iron and DFO were still able to modulate LUC activity. Using a LUC construct harboring a mutated Iron Responsive Elements (IRE) present at the 5' mRNA UTR of FP1 (deltaIRE-LUC), no change of LUC activity was detected upon iron manipulation. In vitro, wild-type and not deltaIRE-LUC was able to bind recombinant IRP. We demonstrate that SLC11A3 gone is controlled by intracellular iron prosttranscriptionally, through the cytoplasmic IRP system. We propose that during iron starvation IRP activation, by binding the FP1 5' UTR IRE, leads to translational block ofFP1 mRNAs, as occurs with ferritin 5' UTR IRE. This leads to decreased iron egress. The opposite holds true during iron overload.