Cobalt Inhibits the Interaction between Hypoxia-inducible Factor-α and von Hippel-Lindau Protein by Direct Binding to Hypoxia-inducible Factor-α

The hypoxia-inducible factor (HIF) activates the expression of genes that contain a hypoxia response element. The α-subunits of the HIF transcription factors are degraded by proteasomal pathways during normoxia but are stabilized under hypoxic conditions. The von Hippel-Lindau protein (pVHL) mediates the ubiquitination and rapid degradation of HIF-α (including HIF-1α and HIF-2α). Post-translational hydroxylation of a proline residue in the oxygen-dependent degradation (ODD) domain of HIF-α is required for the interaction between HIF and VHL. It has previously been established that cobalt mimics hypoxia and causes accumulation of HIF-1α and HIF-2α. However, little is known about the mechanism by which this occurs. In an earlier study, we demonstrated that cobalt binds directly to the ODD domain of HIF-2α. Here we provide the first evidence that cobalt inhibits pVHL binding to HIF-α even when HIF-α is hydroxylated. Deletion of 17 amino acids within the ODD domain of HIF-2α that are required for pVHL binding prevented the binding of cobalt and stabilized HIF-2α during normoxia. These findings show that cobalt mimics hypoxia, at least in part, by occupying the VHL-binding domain of HIF-α and thereby preventing the degradation of HIF-α.