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DNA effects in repair-deficient V79 Chinese hamster cells studied with the comet assay
Abstract:
Using the alkaline comet assay (single cell gel electrophoresis), we studied the induction and persistence of DNA damage induced by methyl methanesulfonate (MMS) and neocarzinostatin (NCS) in the repair-deficient Chinese hamster cell lines V-E5 and XR-V15B. Effects in the comet assay were analyzed directly after treatment as well as after a postincubation period in mutagen-free medium to gain insight into the DNA repair capacities of the mutant cell lines in relation to different primary DNA lesions. Both mutagens caused a concentration-related increase in DNA strand breakage in both mutant cell lines and in the normal parental cell lines. Repair of MMS-induced DNA damage during postincubation was similar in normal and mutant cell lines, while diminished repair was seen after NCS treatment in XR-V15B cells. Our data show that XR-V15B cells only repaired about 30% of NCS-induced DNA damage within 1 h, while the parental V79 cell line repaired about 70%. Since this cell line is defective in the repair of DNA double-strand breaks (DSB), the results indicate that NCS-induced DSB significantly contribute to the genotoxic effects seen in the comet assay. However, compared to previously studied induction of gene mutations and chromosome aberrations, detection of NCS-induced DNA effects with the comet assay was less sensitive and increased DNA migration only occurred under strong cytotoxic conditions.
Insights
This study investigated DNA damage and repair in Chinese hamster cells using the comet assay. XR-V15B cells showed impaired repair of neocarzinostatin-induced DNA damage, indicating a role for double-strand breaks in genotoxicity.
Area of Science:
- Molecular Biology
- Genetics
- Toxicology
Background:
- DNA damage and repair mechanisms are crucial for maintaining genomic stability.
- Deficiencies in DNA repair pathways can lead to increased sensitivity to genotoxic agents.
- The alkaline comet assay is a sensitive method for detecting DNA strand breaks and alkali-labile sites.
Purpose of the Study:
- To investigate the induction and persistence of DNA damage induced by methyl methanesulfonate (MMS) and neocarzinostatin (NCS) in repair-deficient Chinese hamster cell lines.
- To assess the DNA repair capacities of V-E5 and XR-V15B cell lines for different primary DNA lesions.
- To elucidate the contribution of DNA double-strand breaks (DSB) to the genotoxic effects of NCS.
Main Methods:
- Utilized the alkaline comet assay (single cell gel electrophoresis) to measure DNA damage.
- Treated Chinese hamster cell lines (V-E5, XR-V15B, and parental V79) with MMS and NCS.
- Analyzed DNA damage directly after treatment and after a postincubation period in mutagen-free medium.
Main Results:
- Both MMS and NCS induced a concentration-dependent increase in DNA strand breakage in all cell lines.
- Repair of MMS-induced DNA damage was similar in normal and mutant cell lines.
- XR-V15B cells exhibited diminished repair of NCS-induced DNA damage (30% repair in 1h) compared to parental V79 cells (70% repair in 1h), suggesting NCS-induced DSB contribute significantly to genotoxicity.
Conclusions:
- The XR-V15B cell line, deficient in DNA double-strand break repair, shows impaired repair of NCS-induced DNA damage.
- NCS-induced DNA double-strand breaks are a significant factor in the genotoxic effects observed.
- The comet assay is less sensitive for detecting NCS-induced DNA effects compared to gene mutations and chromosome aberrations, requiring strong cytotoxic conditions for observable DNA migration.