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Isolation and partial characterization of human cell mutants differing in sensitivity to killing and mutation by
Abstract:
Isogenic variants resistant to alkylating agents have been isolated from the human lymphoblast cell line TK6. The cell lines may be divided into four classes on the basis of resistance to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The sensitive TK6 parental line shows a 37% survival after 45-min exposure to 0.04 microM MNNG; the three classes of more resistant mutants show 37% survival after 45-min exposure to 2 microM (MF lines), 6 microM (MT lines), and greater than or equal to 10 microM (MX line) MNNG. A representative MF line, MF1, is resistant to both killing and mutation by MNNG or N-methyl-N-nitrosourea. An MT clone, MT1, is highly resistant to killing but hypermutable by MNNG. The MT1 line, like the parental TK6, does not remove O6-methylguanine adducts from the DNA. Our data are consistent with the hypothesis that the MT1 line possesses a nonexcision pathway of defense against killing by alkylating agents. Rather than preventing alkylation of DNA or removing alkylated adducts, the MT1 cells appear to be tolerant of the adducts that are not removed from the DNA.
Insights
Researchers developed human cell lines resistant to DNA-damaging alkylating agents. A specific mutant line, MT1, shows resistance to killing but increased mutation rates, suggesting a novel DNA repair pathway.
Area of Science:
- Molecular Biology
- Genetics
- Toxicology
Background:
- Alkylating agents are genotoxic compounds that damage DNA.
- Understanding cellular resistance mechanisms is crucial for cancer therapy and risk assessment.
- Human lymphoblast cell lines are valuable models for studying DNA repair and mutagenesis.
Purpose of the Study:
- To isolate and characterize isogenic human cell lines resistant to alkylating agents.
- To investigate the mechanisms of resistance and mutagenesis in response to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).
- To explore novel DNA repair pathways involved in cellular defense against alkylating agents.
Main Methods:
- Isolation of isogenic variants from the TK6 human lymphoblast cell line.
- Exposure of cell lines to varying concentrations of MNNG to determine survival rates.
- Assessment of mutation frequencies in resistant cell lines.
- Analysis of O6-methylguanine adduct removal in DNA.
Main Results:
- Four classes of MNNG-resistant cell lines were generated, exhibiting differential resistance levels.
- The MF1 line showed resistance to both killing and mutation by MNNG and N-methyl-N-nitrosourea.
- The MT1 line displayed high resistance to killing but was hypermutable by MNNG.
- MT1 cells, similar to parental TK6 cells, did not remove O6-methylguanine adducts from DNA.
Conclusions:
- The MT1 cell line possesses a non-excision DNA repair pathway conferring tolerance to alkylating agent-induced DNA adducts.
- This suggests a cellular defense mechanism that does not involve preventing DNA alkylation or removing adducts.
- The findings provide insights into alternative DNA repair strategies and their implications for mutagenesis.