Superfund Research Program

Detection of Cr-DNA Adducts in Human Cells

Project Leader: Max Costa
Grant Number: P42ES010344
Funding Period: 2000 - 2006

Project-Specific Links

Final Progress Reports

Year:   2005 

Nickel (Ni) ions are very potent at inhibiting the prolyl hydroxylases that modify HIF-1α and target its degradation by VHL mediated ubiquitination. This causes HIF-1α, which normally has a half-life of about 5 minutes to be highly stabilized for at least 3 days following the removal of extracellular Ni ions. When HIF-1α was stabilized by Fe chelation, its levels rapidly disappeared within one or two hours after the Fe chelator was removed from the media. Continued inhibition of HIF-1α  prolyl hydroxylation in the oxygen-dependent domain as assessed by VHL binding assays was observed for at least 3 days after removal of extracellular Ni ions. In fact, when Ni ions were added directly to recombinant prolyl hydroxylase (1-3), an IC-50 inhibitory concentration in the high nM or low μM range was observed. These inhibitory levels were the lowest effects ever reported of Ni ions on any enzyme. HIF-dependent prolyl hydroxylases requires Fe, oxygen, oxogluterate and ascorbic acid, and project researchers believe that Ni ions are very effective inhibitors because they can bind to the Fe site on the enzyme. In fact, Ni ions have about 3 orders of magnitude higher binding affinity for the Fe in prolyl hydroxylase. The stabilization of HIF-1α results in the activation of HIF downstream genes. The reserachers are currently investigating whether these effects of Ni ions on HIF-1α can also be observed in vivo using mice exposed to Ni ions via their drinking water. Some preliminary measurements indicate that HIF-1α is in fact stabilized in the liver of mice exposed to Ni ions in their drinking water. They are currently conducting further work in this area.