Clioquinol, a Cu(II)/Zn(II) chelator, inhibits both ubiquitination and asparagine hydroxylation of hypoxia-inducible factor-1alpha, leading to expression of vascular endothelial growth factor and erythropoietin in normoxic cells.

We found that the Cu(II) and Zn(II)-specific chelator Clioquinol (10-50 microM) increased functional hypoxia-inducible factor 1alpha (HIF-1alpha) protein, leading to increased expression of its target genes, vascular endothelial growth factors and erythropoietin, in SH-SY5Y cells and HepG2 cells. Clioquinol inhibited ubiquitination of HIF-1alpha in a Cu(II)- and Zn(II)-dependent manner. It prevents FIH-1 from hydroxylating the asparagine residue (803) of HIF-1alpha in a Cu(II)- and Zn(II)-independent fashion. Therefore, it leads to the accumulation of HIF-1alpha that is prolyl but not asparaginyl hydroxylated. Consistent with this, co-immunoprecipitation assays showed that Clioquinol-induced HIF-1alpha interacted with cAMP-responsive element-binding protein in normoxic cells, implying that Clioquinol stabilizes the trans-active form of HIF-1alpha. Our results indicate that Clioquinol could be useful as an inducer of HIF-1alpha and its target genes in ischemic diseases.