title: Antigenotoxic effects of p53 on spontaneous and ultraviolet light B--induced deletions in the epidermis of gpt delta transgenic mice.
abstract: Tumor development in the skin may be a multistep process where multiple genetic alterations occur successively. The p53 gene is involved in genome stability and thus is referred to as "the guardian of the genome." To better understand the antigenotoxic effects of p53 in ultraviolet light B (UVB)-induced mutagenesis, mutations were measured in the epidermis of UVB-irradiated p53(+/+) and p53(-/-) gpt delta mice. In the mouse model, point mutations and deletions are separately identified by the gpt and Spi(-) assays, respectively. The mice were exposed to UVB at single doses of 0.5, 1.0, or 2.0 kJ/m(2) . The mutant frequencies (MFs) were determined 4 weeks after the irradiation. All doses of UVB irradiation enhanced gpt MFs by about 10 times than that of unirradiated mice. There were no significant differences in gpt MFs and the mutation spectra between p53(+/+) and p53(-/-) mice. The predominant mutations induced by UVB irradiation were G:C to A:T transitions at dipyrimidines. In contrast, in unirradiated p53(-/-) mice, the frequencies of Spi(-) large deletions of more than 1 kb and complex-type deletions with rearrangements were significantly higher than those of the Spi(-) large deletions in p53(+/+) counterparts. The specific Spi(-) mutation frequency of more than 1 kb deletions and complex types increased in a dose-dependent manner in the p53(+/+) mice. However, no increase of such large deletions was observed in irradiated p53(-/-) mice. These results suggest that the antigenotoxic effects of p53 may be specific to deletions and complex-type mutations induced by double-strand breaks in DNA.
authors.affiliation: Division of Genetics and Mutagenesis, National Institute of Health Sciences, Tokyo, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Masumura
authors.forename: Yasuteru
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: Megumi
authors.initials: M
authors.lastname: Ikeda
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Asami
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Tsukamoto
authors.forename: Hironobu
authors.initials: H
authors.lastname: Ikehata
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kuroiwa
authors.forename: Takashi
authors.initials: T
authors.lastname: Umemura
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Nishikawa
authors.forename: Masae
authors.initials: M
authors.lastname: Tatematsu
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ono
authors.forename: Takehiko
authors.initials: T
authors.lastname: Nohmi
mesh_terms: D000818:Animals; D001483:Base Sequence / Q000528:radiation effects*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010430:Pentosyltransferases / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D012867:Skin / Q000378:metabolism / Q000528:radiation effects*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D029968:Escherichia coli Proteins; D016159:Tumor Suppressor Protein p53; D010430:Pentosyltransferases; C071962:Gpt protein, E coli