Cell-cycle-dependent repair of potentially lethal damage in the XR-1 gamma-ray-sensitive Chinese hamster ovary cell.
Repair of potentially lethal damage (PLD) was investigated in a gamma-ray-sensitive Chinese hamster cell mutant, XR-1, and its parent by comparing survival of plateau-phase cells plated immediately after irradiation with cells plated after a delay. Previous work indicated that XR-1 cells are deficient in repair of double-strand DNA breaks and are gamma-ray sensitive in G1 but have near normal sensitivity and repair capacity in late S phase. At irradiation doses from 0 to 1.0 Gy (100 to 10% survival), the delayed- and immediate-plating survival curves of XR-1 cells were identical; however, at doses greater than 1.0 Gy a significant increase in survival was observed when plating was delayed (PLD repair), approaching a 20-fold increase at 8 Gy. Elimination of S-phase cells by [3H]thymidine suicide dramatically increased gamma-ray sensitivity of plateau-phase XR-1 mutant cells and reduced by 600-fold the number of cells capable of PLD repair after a 6-Gy dose. In contrast, elimination of S-phase cells in plateau-phase parental cells did not alter PLD repair. These results suggest that the majority of PLD repair observed in plateau-phase XR-1 cells occurs in S-phase cells while G1 cells perform little PLD repair. In contrast, G1 cells account for the majority of PLD repair in plateau-phase parental cells. Thus, in the XR-1 mutant, a cell's ability to repair PLD seems to depend upon the stage of the cell cycle at which the irradiation is delivered. A possible explanation for these findings is discussed.
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Wistar Institute of Anatomy and Biology, Philadelphia, Pennsylvania 19104.
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D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D004247:DNA / Q000528:radiation effects; D004260:DNA Repair / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D007399:Interphase; D007700:Kinetics; D009154:Mutation; D011836:Radiation Tolerance
D004247:DNA