Biochemical and cytogenetical characterization of Chinese hamster ovary X-ray-sensitive mutant cells xrs 5 and xrs 6. V. The correlation of DNA strand breaks and base damage to chromosomal aberrations and sister-chromatid exchanges induced by X-irradiation.
The X-ray-sensitive Chinese hamster ovary (CHO) mutant cell lines xrs 5 and xrs 6 were used to study the relation between X-ray-induced DNA lesions and biological effects. The frequencies of chromosomal aberrations and sister-chromatid exchanges (SCE) were determined in wild-type CHO-K1 as well as mutants xrs 5 and xrs 6 cells following X-irradiation under aerobic and anaerobic conditions. Furthermore, we used a newly developed immunochemical method (based on the binding of a monoclonal antibody to single-stranded DNA) to assay DNA single-strand breaks (SSBs) induced by gamma-rays in these CHO cells, after a repair time of up to 4 h. For all cell lines tested the frequency of X-ray-induced chromosomal aberrations was strongly increased after irradiation in air compared with hypoxic conditions. When compared to the wild-type line, the xrs mutants known to have a defect in repair of DNA double-strand breaks (DSBs) exhibited a markedly enhanced sensitivity to aerobic irradiation, and a high OER (oxygen enhancement ratio) of 2.8-3.5, compared with 1.8-2 in CHO-K1 cells. The induction of SCE by X-rays was relatively little affected in CHO-K1 irradiated in air compared with hypoxic conditions (OER = 0.8), and in xrs 5 (OER = 0.7). A dose-dependent increase in the frequency of SCEs was obtained in xrs 6 cells treated with X-rays in air, and a further increase by a factor of 2 was evident under hypoxic conditions (OER = 0.4). With the immunochemical assay of SSB following gamma-irradiation, no difference was found between wild-type and mutant strains in the number of SSBs induced. The observed rate of rejoining of SSBs was also the same for all cell lines studied.
Darroudi
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Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden, The Netherlands.
Natarajan
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AT
van der Schans
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GP
van Loon
A A
AA
D000818:Animals; D000911:Antibodies, Monoclonal; D002460:Cell Line; D002869:Chromosome Aberrations; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000276:immunology / Q000378:metabolism / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004797:Enzyme-Linked Immunosorbent Assay; D005720:Gamma Rays; D006863:Hydrogen-Ion Concentration; D007158:Immunologic Techniques; D051379:Mice; D009154:Mutation; D010100:Oxygen; D011836:Radiation Tolerance; D012854:Sister Chromatid Exchange; D014965:X-Rays
D000911:Antibodies, Monoclonal; D004277:DNA, Single-Stranded; D004247:DNA; D010100:Oxygen