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Nickel(II) interferes with the incision step in nucleotide excision repair in mammalian cells
A Hartwig1, L H Mullenders, R Schlepegrell
1Department of Biology and Chemistry, University of Bremen, Germany.
Abstract:
Nickel compounds are carcinogenic to humans and experimental animals. However, the mechanisms leading to tumor formation are still not understood since the mutagenic potential is rather weak. In contrast, nickel(II) enhances the cytotoxicity and genotoxicity in combination with several other DNA-damaging agents. To elucidate possible interactions with DNA repair processes, the effect of nickel(II) on the nucleotide excision repair pathway has been investigated after UV irradiation in HeLa cells. Nickel(II) blocks the removal of cyclobutane pyrimidine dimers as determined by T4 endonuclease V-sensitive sites. When the alkaline unwinding technique was applied, significantly less transient DNA strand breaks after UV irradiation were detected in the presence of nickel(II) compared to UV alone, suggesting an inhibition of the incision step of nucleotide excision repair. Once incisions are made, the ligation of repair patches is delayed as well in nickel-treated cells, as observed by the alkaline unwinding and nucleoid sedimentation techniques. This inhibition of DNA repair is partly reversible by the addition of magnesium(II), indicating that the competition between Ni2+ and Mg2+ may provide an important mechanism for the disturbance of DNA-protein interactions involved in the repair process. Since the repair inhibition is observed at noncytotoxic concentrations of nickel(II), it may well be relevant for its carcinogenic action.
Insights
Nickel(II) inhibits DNA repair pathways crucial for removing DNA damage, potentially explaining its carcinogenic effects. This nickel-induced repair inhibition is partially reversible by magnesium(II).
Area of Science:
- Environmental Health
- Molecular Biology
- Toxicology
Background:
- Nickel compounds are carcinogenic, but the mechanisms remain unclear due to weak mutagenic potential.
- Nickel(II) amplifies the cytotoxicity and genotoxicity of other DNA-damaging agents.
Purpose of the Study:
- To investigate the impact of nickel(II) on the nucleotide excision repair (NER) pathway after UV irradiation.
- To elucidate the role of nickel(II) in DNA repair inhibition and its connection to carcinogenicity.
Main Methods:
- HeLa cells were exposed to UV irradiation in the presence and absence of nickel(II).
- DNA repair inhibition was assessed by measuring cyclobutane pyrimidine dimer removal (using T4 endonuclease V).
- DNA strand breaks and ligation were analyzed using alkaline unwinding and nucleoid sedimentation techniques.
Main Results:
- Nickel(II) blocked the removal of cyclobutane pyrimidine dimers, indicating interference with NER.
- Nickel(II) reduced transient DNA strand breaks post-UV, suggesting inhibition of the incision step in NER.
- The ligation of DNA repair patches was delayed in nickel(II)-treated cells.
- Magnesium(II) partially reversed the DNA repair inhibition, pointing to Ni2+/Mg2+ competition.
Conclusions:
- Nickel(II) significantly inhibits key steps in the nucleotide excision repair pathway at non-cytotoxic concentrations.
- This inhibition of DNA repair by nickel(II) may be a critical factor in its carcinogenic action.
- Competition between nickel(II) and magnesium(II) ions likely disrupts DNA-protein interactions essential for DNA repair.