Cobalt inhibits
prolyl hydroxylases, leading to the accumulation of
hypoxia-inducible factor-1α (HIF-1α) and a concomitant increase in the transcriptional activity of HIF-1. Therefore,
cobalt has been under development as a drug for activating HIF-1 under some disease conditions. However, it has been shown that ischemic conditions resulted in the loss of
copper, and the activation of HIF-1 would not occur unless
copper was supplemented. The present study was undertaken to test the hypothesis that
copper is also required for the
cobalt activation of HIF-1 transcriptional activity. Human umbilical vein endothelial cells subjected to treatment with
cobalt chloride (
CoCl(2)) at concentrations above 25 μM for 2 h resulted in an accumulation of HIF-1α, which was determined by Western blot analysis, and an increase in the expression of
vascular endothelial growth factor (
VEGF), which was determined by real-time reverse transcription-polymerase chain reaction analysis for
mRNA levels and
enzyme-linked
immunosorbent assay analysis for
protein levels. The
copper chelator tetraethylenepentamine at 25 μM did not significantly affect the accumulation of HIF-1α but blocked increases in
VEGF mRNA and
protein levels, an effect that could be reversed by the addition of 25 μM
copper sulfate (CuSO(4)). In addition, gene silencing of the
copper chaperone for
Cu,Zn-superoxide dismutase blocked
VEGF expression with little effect on
cobalt-induced HIF-1α accumulation. The present study thus demonstrates that
copper was required for
cobalt-activated transcriptional activity of HIF-1, although
copper did not affect
cobalt-induced accumulation of HIF-1α in the cells.