title: Defective p53 engagement after the induction of DNA damage in cells deficient in topoisomerase 3beta.
abstract: The type IA topoisomerases have been implicated in the repair of dsDNA breaks by homologous recombination and in the resolution of stalled or damaged DNA replication forks; thus, these proteins play important roles in the maintenance of genomic stability. We studied the functions of one of the two mammalian type IA enzymes, Top3beta, using murine embryonic fibroblasts (MEFs) derived from top3beta(-/-) embryos. top3beta(-/-) MEFs proliferated more slowly than TOP3beta(+/+) control MEFs, demonstrated increased sensitivity to DNA-damaging agents such as ionizing and UV radiation, and had increased DNA double-strand breaks as manifested by increased gamma-H2-AX phosphorylation. However, incomplete enforcement of the G(1)-S cell cycle checkpoint was observed in top3beta(-/-) MEFs. Notably, ataxia-telangiectasia, mutated (ATM)/ATM and Rad3-related (ATR)-dependent substrate phosphorylation after UV-B and ionizing radiation was impaired in top3beta(-/-) versus TOP3beta(+/+) control MEFs, and impaired up-regulation of total and Ser-18-phosphorylated p53 was observed in top3beta(-/-) cells. Taken together, these results suggest an unanticipated role for Top3beta beyond DNA repair in the activation of cellular responses to DNA damage.
authors: Section of Infectious Diseases, Departments of Internal Medicine and Immunobiology, Yale University School of Medicine, New Haven, CT 06520.
authors: Subhasis
authors: S
authors: Mohanty
authors: Terrence
authors: T
authors: Town
authors: Tomohito
authors: T
authors: Yagi
authors: Christina
authors: C
authors: Scheidig
authors: Kelvin Y
authors: KY
authors: Kwan
authors: Heather G
authors: HG
authors: Allore
authors: Richard A
authors: RA
authors: Flavell
authors: Albert C
authors: AC
authors: Shaw
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009153:Mutagens / Q000494:pharmacology; D010766:Phosphorylation; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D004264:DNA Topoisomerases, Type I; D006657:Histones; D009153:Mutagens; D016159:Tumor Suppressor Protein p53; C475961:gamma-H2AX protein, mouse