Involvement ofp53 in ionizing-radiation-induced DNA repair

Exposure of mammalian cells to ionizing radiation (IR) evokes physiological responses including cell-cycle arrest, DNA-repair induction, and if severely damaged apoptosis. This dissertation reports the DNA-repair processes induced by IR, and the involvement of the tumor suppressor protein p53 in these processes. Shuttle vector pZ189 containing IR-caused base damage plus single-strand break (ocDNA) or ultraviolet radiation damage (uvDNA), and pZ189 containing a double-strand break (linDNA) were used as probes to measure excision and recombination repair activities, respectively, of unirradiated or {dollar}gamma{dollar}-irradiated human lymphoblasts, expressing wild-type (p53{dollar}sp{lcub}rm wt{rcub}{dollar}) or mutant (p53{dollar}sp{lcub}rm mut{rcub}{dollar}) or no p53 (p53{dollar}sp{lcub}rm null{rcub}{dollar}).; Excision repair fidelity of p53{dollar}sp{lcub}rm wt{rcub}{dollar}, p53{dollar}sp{lcub}rm mut{rcub}{dollar} and p53{dollar}sp{lcub}rm null{rcub}{dollar} cells were similar. However, exposure of lymphoblast hosts to low-dose radiation altered both excision repair in a p53-dependent manner. Irradiation enhanced the fidelity of excision repair in p53{dollar}sp{lcub}rm wt{rcub}{dollar} hosts, but in p53{dollar}sp{lcub}rm mut{rcub}{dollar} or p53{dollar}sp{lcub}rm null{rcub}{dollar} hosts. Irradiation altered recombination repair in time-dependent manner: repair fidelity increased two-fold compared with unirradiated control hosts if plasmid transfection occurred immediately after host irradiation, but decreased two-fold if transfection occurred 2hrs post-host-irradiation. However, unlike its effects on excision repair, IR-modulation of recombination repair fidelity was similar in p53{dollar}sp{lcub}rm wt{rcub}{dollar}, p53{dollar}sp{lcub}rm mut{rcub}{dollar} and p53{dollar}sp{lcub}rm null{rcub}{dollar} cells.; DSB-rejoining capacity differed between irradiated p53{dollar}sp{lcub}rm wt{rcub}{dollar} and p53{dollar}sp{lcub}rm mut{rcub}{dollar} or p53{dollar}sp{lcub}rm null{rcub}{dollar} hosts. Immediately after host irradiation, DSB-rejoining capacity in p53{dollar}sp{lcub}rm wt{rcub}{dollar} hosts was similar to that in unirradiated p53{dollar}sp{lcub}rm wt{rcub}{dollar} hosts, but increased significantly in irradiated p53{dollar}sp{lcub}rm mut{rcub}{dollar} and p53{dollar}sp{lcub}rm null{rcub}{dollar} hosts. These data show that low-dose IR modulates DNA excision- and recombination-repair in mammalian cells and that p53 is required for both these processes.