Heavy Metal Exposure Influences Double Strand Break DNA Repair Outcomes

Area of Science:

• Environmental Health
• Molecular Biology
• Genetics

Background:

• Heavy metals (cadmium, arsenic, nickel) are carcinogens.
• Mechanisms of heavy metal-induced genetic damage involve DNA double-strand breaks (DSBs) and impaired DNA repair.
• Understanding how metals affect DNA repair pathways is crucial for assessing cancer risk.

Purpose of the Study:

• To evaluate the impact of heavy metal exposure on DNA double-strand break (DSB) repair pathways.
• To determine if heavy metal effects on DSB repair are metal-specific and dose-dependent.
• To investigate the role of specific DNA repair pathways in mediating heavy metal-induced genetic alterations.

Main Methods:

• Utilized two established culture assay systems to study DNA repair.
• Exposed cells to varying doses of nickel chloride (NiCl2), arsenic trioxide, and cadmium.
• Analyzed DNA repair outcomes, including homologous recombination (HR), single-strand annealing (SSA), and non-homologous end joining (NHEJ) variants.
• Performed sequence verification to identify genetic deletions and insertions.

Main Results:

• Heavy metal exposure significantly altered DSB repair outcomes in a metal- and dose-dependent manner.
• Low NiCl2 doses promoted HR and SSA, while higher doses inhibited them.
• Arsenic trioxide exposure favored error-prone alternative non-homologous end joining (alt-NHEJ) and inhibited HR.
• Nickel and cadmium exposure increased Alu-mediated mutagenic recombination, primarily via SSA.
• All tested heavy metals shifted alt-NHEJ repair outcomes, increasing non-templated sequence insertions at DSB sites.

Conclusions:

• Heavy metals reprogram cellular DNA double-strand break repair pathways.
• Altered DNA repair choices by heavy metals lead to specific genetic outcomes, including deletions and insertions.
• These findings highlight a novel mechanism for heavy metal-induced genotoxicity and potential carcinogenicity.