Copper-dependent and -independent hypoxia-inducible factor-1 regulation of gene expression

Hypoxia-inducible factor-1 (HIF-1) regulates the expression of the vascular endothelial growth factor (VEGF), a process requiring copper (Cu) participation. HIF-1 is also involved in the expression of more than a hundred of genes, but it is unknown how HIF-1 differentially controls the expression of these genes timely and spatially. The present study was undertaken to test the hypothesis that Cu is not required for the expression of all HIF-1-regulated genes, thus exploring mechanistic insights into the differential control of multiple gene expression by one transcription factor. Human umbilical vein endothelial cells (HUVECs) were treated with siRNA targeting HIF-1 alpha to define the essential role of HIF-1 in the regulation of BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3) and insulin-like growth factor 2 (IGF-2) expression. A Cu chelator, tetraethylenepentamine (TEPA), was used to reduce intracellular availability of Cu. In comparison, a zinc chelator, N,N,N',N'-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN), was used to reduce intracellular zinc concentration. The expression of both BNIP3 and IGF-2 was completely suppressed in the HIF-1 alpha deficient cells. The removal of Cu suppressed the expression of BNIP3, but did not affect that of IGF-2. The reduction of intracellular zinc did not cause the same effect. Further screening identified a group of genes whose expression required Cu and the others did not need Cu. The present study thus demonstrates Cu-dependent and -independent HIF-1 regulation of gene expression, indicating a mechanism for differential control of multiple gene expression by one transcription factor.