title: Analysis of repair processes by the determination of the induction of cell killing and mutations in two repair-deficient Chinese hamster ovary cell lines.
abstract: Two UV sensitive DNA-repair-deficient mutants of Chinese hamster ovary cells (43-3B and 27-1) have been characterized. The sensitivity of these mutants to a broad spectrum of DNA-damaging agents: UV254nm, 4-nitroquinoline-1-oxide (4NQO), X-rays, bleomycin, ethylnitrosourea (ENU), ethyl methanesulphonate (EMS), methyl methanesulphonate (MMS) and mitomycin C (MMC) has been determined. Both mutants were not sensitive to X-rays and bleomycin. 43-3B was found to be sensitive to 4NQO, MMC and slightly sensitive to alkylating agents. 27-1 was sensitive only to alkylating agents. The results suggest the existence of two repair pathways for UV-induced cytotoxicity: one pathway which is also used for the removal of 4NQO and MMC adducts and a second pathway which is also used for the removal of alkyl adducts. Parallel to the toxicity, the induction of mutations at the HPRT and Na+/K+-ATPase loci was determined. The increased cytotoxicity to UV, MMC and 4NQO in 43-3B cells and the increased cytotoxicity to UV in 27-1 cells correlated with increased mutability. It was observed that the increase in mutation induction at the HPRT locus was higher than that at the Na+/K+-ATPase locus. As only point mutations give rise to viable mutants at the Na+/K+-ATPase locus the lower mutability at this locus suggests that defective excision repair increases the chance for deletions. Despite an increased cytotoxicity to ENU in 27-1 cells the mutation induction by ENU was the same in 27-1 and wild-type cells at both loci, which suggests that the mutations are mainly induced by directly miscoding adducts (e.g. O-6 alkylguanine), which cannot be removed by CHO cells. As EMS and MMS treatment of 27-1 cells caused an increase in mutation induction at the HPRT locus and a decrease at the Na+/K+-ATPase locus it indicates that these agents induce a substantial fraction of other mutagenic lesions, which can be repaired by wild-type cells. This suggests that O-6 alkylation is not the only mutagenic lesion after treatment with alkylating agents.
mesh_terms: D015112:4-Nitroquinoline-1-oxide / Q000494:pharmacology; D000477:Alkylating Agents / Q000494:pharmacology; D000818:Animals; D001761:Bleomycin / Q000494:pharmacology; D002460:Cell Line; D006224:Cricetinae; D004260:DNA Repair; D004351:Drug Resistance; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000528:radiation effects; D006147:Guanine / Q000031:analogs & derivatives; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D016685:Mitomycin; D008937:Mitomycins / Q000494:pharmacology; D009153:Mutagens / Q000494:pharmacology*; D010053:Ovary; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics; D014466:Ultraviolet Rays
chemical_list: D000477:Alkylating Agents; D008937:Mitomycins; D009153:Mutagens; D001761:Bleomycin; D016685:Mitomycin; D015112:4-Nitroquinoline-1-oxide; D006147:Guanine; C008449:O-(6)-methylguanine; D007041:Hypoxanthine Phosphoribosyltransferase; D000254:Sodium-Potassium-Exchanging ATPase