Oxidative stress induces activation of a cytosolic protein responsible for control of iron uptake.
A cytosolic protein, named iron-responsive element-binding protein (IRE-BP), is sensitive to cellular iron concentration. At low cytosolic iron level, IRE-BP is activated and binds to stem-loop untranslated regions (IRE regions) of transferrin and ferritin mRNAs, activating and inhibiting their translations, respectively. This concerted mechanism permits a fine control of iron homeostasis in the cell. The activity of IRE-BP can be measured by its binding to IRE regions, using a protein band-shift electrophoretic assay. Damage to cells by oxidative stress is known to be mediated by iron. We observed that IRE-BP is rapidly activated by exposure of V79 Chinese hamster ovary cells to H2O2. However, if cell extracts are exposed to H2O2 IRE-BP activation is not observed. Therefore, the activation is not a direct consequence of the H2O2 attack to IRE-BP. The in vivo IRE-BP-activation by H2O2 is not prevented by hydroxyl radical scavengers or by the iron chelator 1,10-phenanthroline, indicating that Fenton reaction is not involved in the process. In fact, simultaneous exposure of cells to H2O2 and 1,10-phenanthroline produces an even stronger activation than exposure to H2O2 alone. The interpretation of the mechanism of IRE-BP activation by oxidative stress is hampered by the fact that the mechanism of IRE-BP modulation by cytosolic iron has not been established. It has been recently shown that the iron-sulfur cluster in IRE-BP must be completely disassembled in order for activation to occur and that this is triggered by low iron in the cell. It is likely that IRE-BP senses Fe(II) and that its oxidation to Fe(III) by H2O2 or chelation by 1,10-phenanthroline set up a program for increasing iron uptake. The physiological consequences of this activation still has to be assessed.
Martins
E A
EA
Department of Biochemistry, Institute of Chemistry, São Paulo, Brazil.
Robalinho
R L
RL
Meneghini
R
R
D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D005347:Fibroblasts; D016166:Free Radical Scavengers; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007501:Iron / Q000378:metabolism*; D007502:Iron Chelating Agents; D035925:Iron-Regulatory Proteins; D007939:Leukemia L1210; D051379:Mice; D018384:Oxidative Stress / Q000502:physiology*; D010618:Phenanthrolines; D011485:Protein Binding; D016601:RNA-Binding Proteins / Q000378:metabolism*
D016166:Free Radical Scavengers; D007502:Iron Chelating Agents; D035925:Iron-Regulatory Proteins; D010618:Phenanthrolines; D016601:RNA-Binding Proteins; D006861:Hydrogen Peroxide; D007501:Iron; C025205:1,10-phenanthroline