RETRACTED: Hypoxia-inducible factor 1α (HIF-1α) is a non-heme iron protein - Implications for oxygen sensing (Retracted Article)

The hypoxia-inducible factor 1 complex (HIF-1) is involved in the transcriptional activation of several genes, like erythropoietin and vascular endothelial growth factor, that are responsive to the lack of oxygen. The HIF-1 complex is composed of two b-HLH proteins: HIF-1 beta, that is constitutively expressed, and HIF-1 alpha, that is present only in hypoxic cells. The HIF-1 alpha subunit is continuously synthesized and degraded by the ubiquitin-proteasome under oxic conditions. Hypoxia, transition metals, iron chelators, and several antioxidants stabilize the HIF-1 alpha protein, allowing the formation of the transcriptionally active HIF-1 complex. The mechanisms of oxygen sensing and the pathways leading to HIF-1 alpha stabilization are unclear. Because the involvement of a heme protein oxygen sensor has been postulated, we tested the heme sensor hypothesis by using a luciferase-expressing cell line (B-l), that is highly responsive to hypoxia, Exposure of B-l cells to carbon monoxide and heme synthesis inhibitors failed to show any effect on the hypoxia responsiveness of these cells, suggesting that heme proteins are not involved in hypoxia sensing. Measurement of iron in recombinantly expressed HIF-1 alpha protein revealed that this protein binds iron in vivo. Iron binding was localized to a 129-amino acid peptide between sequences 529 and 658 of the HIF-1 alpha protein. Although the exact structure of the iron center has not been yet defined, a 2:1 metal/protein molar ratio suggests a di-iron center, probably similar to the one found in hemerythrin. This finding is compatible with a model where redox: reaction may occur directly in the iron center of the HIF-1 alpha subunit, affecting its survival in oxic conditions.