title: Epigenetic gene silencing is a novel mechanism involved in delayed manifestation of radiation-induced genomic instability in mammalian cells.
abstract: We examined mechanisms involved in delayed mutagenesis in CHO-LacZeo cells harboring the fusion gene between the bacterial LacZ and the Zeocin-resistance genes. After X irradiation, Zeocin-resistant primary colonies were isolated, and the primary clones were subjected to the secondary colony formation in the absence of Zeocin. We found that the surviving primary clones showed a significantly higher delayed mutation frequency compared with those derived from nonirradiated CHO-LacZeo cells. The mutation spectrum of the LacZ gene was analyzed by the LacZ gene-specific PCR. We found that more than 90% of the spontaneous and direct mutants were PCR-product negative, indicating that deletion of the LacZ gene was a predominant change in these mutants. While deletion of the LacZ gene was also observed in delayed mutants, we found that more than 20% of delayed mutants had a PCR product similar to that of the parental CHO-LacZeo cells. These PCR product-positive mutants spontaneously reverted to LacZ-positive (LacZ(+)) cells, and all of these mutants became LacZ-positive after 5-azacytidine treatment. These results indicate that epigenetic gene silencing, in addition to elevated recombination, is involved in delayed mutagenesis, which is a novel mechanism underlying delayed manifestations of radiation-induced genomic instability.
authors.affiliation: Division of Radiation and Life Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8523, Japan. kzsuzuki@nagasaki-u.ac.jp
authors.forename: Keiji
authors.initials: K
authors.lastname: Suzuki
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yamaji
authors.forename: Shinko
authors.initials: S
authors.lastname: Kobashigawa
authors.forename: Rie
authors.initials: R
authors.lastname: Kawauchi
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Shima
authors.forename: Seiji
authors.initials: S
authors.lastname: Kodama
authors.forename: Masami
authors.initials: M
authors.lastname: Watanabe
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004307:Dose-Response Relationship, Radiation; D044127:Epigenesis, Genetic / Q000235:genetics* / Q000528:radiation effects*; D020868:Gene Silencing / Q000502:physiology / Q000528:radiation effects*; D042822:Genomic Instability / Q000528:radiation effects*; D009154:Mutation / Q000235:genetics* / Q000528:radiation effects*; D011829:Radiation Dosage