The interaction between eIF4F and iron response protein with IRE‐mRNA

Abstract

Cellular iron homeostasis is accomplished by the coordinated, regulated expression of iron uptake and storage proteins (e.g. ferritin). The cytoplasmic iron regulatory proteins, IRPs, control cellular iron levels by binding to iron response element (IRE) mRNAs. IRPs act as repressors for IRE-mRNA coding for iron storage proteins and binding is high under low iron conditions. The eukaryotic initiation factor 4F, eIF4F, binds to the 5′UTR of mRNA and enhances 40S interaction with the RNA. Fluorescence anisotropy determined eIF4F/IRP binding to ferritin IRE was competitive (eIF4F/IRE Kd=39.8±5.6nM; IRP/IRE Kd=14.2±0.3nM). The binding of eIF4F to the IRE is strengthened 4 fold by addition of Mn2+ (50μM) and 1.3 fold by addition of Mg2+ (1mM). This trend is opposite to the IRP/IRE binding, which is weakened by adding Fe2+, Mn2+ or Mg2+ at the same conditions. These results suggest metal ions affect 5′UTR IRE translation by (1) releasing the IRP1 repressor and (2) increasing the eIF4F affinity for 5′ UTR IRE-mRNA. This work is supported in whole or in part, by National Institutes of Health Grants DK20251 (D.J.G. and E.C.T.) and National Science Foundation Grant MCB 0814051 (D.J.G.)