Biochemical and cytogenetical characterization of Chinese hamster ovary X-ray-sensitive mutant cells xrs 5 and xrs 6. VI. The correlation between UV-induced DNA lesions and chromosomal aberrations, and their modulations with inhibitors of DNA repair synthesis.
The role of UV-induced DNA lesions and their repair in the formation of chromosomal aberrations in the xrs mutant cell lines xrs 5 and xrs 6 and their wild-type counterpart, CHO-K1 cells, were studied. The extent of induction of DNA single-strand breaks (SSBs) and DNA double-strand breaks (DSBs) due to UV irradiation in the presence or absence of 1-beta-D-arabinofuranosylcytosine (ara-C) and hydroxyurea (HU) was determined using the alkaline and neutral elution methods. Results of these experiments were compared with the frequencies of induced chromosomal aberrations in UV-irradiated G1 cells treated under similar conditions. Xrs 6 cells showed a defect in their ability to perform the incision step of nucleotide repair after UV irradiation. Accumulation of breaks 2 h after UV irradiation in xrs 6 cells in the presence of HU and ara-C remained at the level of incision breaks estimated after 20 min, which was about 35% of that found in wild-type CHO-K1 cells. In UV-irradiated CHO-K1 and xrs 5 cells, more incision breaks were present after 2 h compared with 20 min post-treatment with ara-C, a further increase was evident when HU was added to the combined treatment. The level of incision breaks induced under these conditions in xrs 5 was about 80% of that observed in CHO-K1 cells. UV irradiation itself did not induce any detectable DNA strand breaks. Accumulation of SSBs in UV-irradiated cells post-treated with ara-C and HU coincides with the increase in the frequency of chromosomal aberrations. These data suggest that accumulated SSBs when converted to DSBs in G1 give rise to chromosome-type aberrations, whereas strand breaks persisting until S-phase result in chromatid-type aberrations. Xrs 6 appeared to be the first ionizing-radiation-sensitive mutant with a partial defect in the incision step of DNA repair of UV-induced damage.
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
D000818:Animals; D002460:Cell Line; D002869:Chromosome Aberrations; D006224:Cricetinae; D003412:Cricetulus; D003561:Cytarabine / Q000494:pharmacology; D004247:DNA / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects*; D004277:DNA, Single-Stranded / Q000528:radiation effects; D006918:Hydroxyurea / Q000494:pharmacology; D009154:Mutation; D011836:Radiation Tolerance; D014466:Ultraviolet Rays; D014965:X-Rays
D004277:DNA, Single-Stranded; D003561:Cytarabine; D004247:DNA; D006918:Hydroxyurea