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Involvement of p53 in X-ray induced intrachromosomal recombination in mice
J Aubrecht1, M B Secretan, A J Bishop
1Department of Cancer Cell Biology, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 2115, USA.
Abstract:
The tumor suppressor gene Trp53 (also known as p53) is the most frequently mutated gene in human cancers. p53 is induced in response to DNA damage and effects a G(1) cell cycle arrest. It is believed that p53 plays a key role in maintaining genomic integrity following exposure to DNA-damaging agents. We determined the frequency of spontaneous and DNA damage-induced homologous intrachromosomal recombination in p53-deficient mouse embryos. Homologous intrachromosomal recombination events resulting in deletions at the pink eyed unstable (p(un)) locus result in reversion to the p gene. Reversions occurring in embryonic premelanocytes give rise to black spots on the gray fur of the offspring. Pregnant C57BL/6J p(un)/p(un) p53(+/-) mice were exposed to X-rays (1 Gy) or administered benzo¿apyrene (B¿aP; 30 or 150 mg/kg i.p.) 10 days after conception. Frequencies of spontaneous p(un) reversions in p53(-/-) and p53(+/-) animals were not significantly different compared with their wild-type littermates. X-ray treatment increased the recombination frequency in wild-type and p53(+/-), but surprisingly not in p53(-/-) offspring. In contrast, B¿aP treatment caused a dose-dependent increase in p(un) reversion frequencies in all three genotypes. Western blot analysis of embryos indicated that p53 protein levels increased approximately 3-fold following X-ray treatment, while B¿aP had no effect on p53 expression. These results are in agreement with the proposal that p53 is involved in the DNA damage response following X-ray exposure and suggest that X-ray-induced double-strand breaks are processed differently in p53(-/-) animals.
Insights
The tumor suppressor Trp53 (p53) is crucial for DNA repair. This study found p53-deficient mice showed increased recombination after benzo(a)pyrene exposure but not X-rays, suggesting different DNA damage processing.
Area of Science:
- Genetics
- Molecular Biology
- Cancer Research
Background:
- The Trp53 (p53) tumor suppressor gene is frequently mutated in human cancers.
- p53 responds to DNA damage by inducing cell cycle arrest and is believed to maintain genomic integrity.
- Homologous intrachromosomal recombination is a key mechanism for DNA repair.
Purpose of the Study:
- To investigate the role of p53 in DNA damage-induced homologous intrachromosomal recombination.
- To determine if p53 deficiency affects spontaneous or induced recombination frequencies.
- To compare the effects of X-rays and benzo(a)pyrene on recombination in p53-deficient mice.
Main Methods:
- Utilized p53-deficient (p53(-/-), p53(+/-)) and wild-type mouse embryos carrying the pink eyed unstable (p(un)) locus.
- Exposed pregnant mice to X-rays or benzo(a)pyrene (B(a)P) during embryonic development.
- Quantified spontaneous and induced p(un) reversion frequencies, indicative of recombination events.
- Analyzed p53 protein levels via Western blot.
Main Results:
- Spontaneous p(un) reversion frequencies were similar across all p53 genotypes.
- X-ray treatment increased recombination in wild-type and p53(+/-) but not p53(-/-) embryos.
- Benzo(a)pyrene (B(a)P) treatment caused a dose-dependent increase in recombination in all genotypes.
- X-ray exposure elevated p53 protein levels, while B(a)P did not affect p53 expression.
Conclusions:
- p53 plays a role in the DNA damage response to X-ray-induced double-strand breaks.
- X-ray-induced double-strand breaks appear to be processed differently in p53-deficient cells.
- The response to benzo(a)pyrene-induced DNA damage and recombination is independent of p53 status.