title: PolyADP-ribose-mediated regulation of p53 complexed with topoisomerase I following ionizing radiation.
abstract: This investigation demonstrates that the p53 and topoisomerase I (topo I) proteins which form a molecular complex in vivo are polyADP ribosylated following 1 Gy of gamma irradiation. Immunoprecipitations using a topo I monoclonal antibody were performed on protein extracts from gamma-irradiated TK6 human lymphoblastoid cells. Western blots on topo I immunoprecipitations probed with a polyADP-ribose polymer antibody demonstrated that several proteins, including p53, are co-immunoprecipitated with topo I. Furthermore, p53 and topo I are ADP ribosylated within 15 min following gamma irradiation. Unlike the other proteins within the complex, p53 is polyADP ribosylated at low levels in non-irradiated cells, and it is also the most heavily polyADP ribosylated following irradiation. Radiation induced polyADP ribosylation persists for at least 48 h following exposure. The DNA damage response does not involve the recruitment of free p53 to complex with topo I; the amount of p53 protein complexed with topo I was found to be independent of radiation exposure. It has recently been reported that p53 acts to catalytically stimulate the activity of topo I in the absence of DNA damage. We hypothesize that the rapid modification of the complex by polyADP ribosylation following radiation is a regulatory response to diminish topo I cleavage in the presence of DNA damage.
authors.affiliation: Environmental Toxicology Program, University of California, 5419 Boyce Hall, Riverside, CA 92521, USA.
authors.forename: H M
authors.initials: HM
authors.lastname: Smith
authors.forename: A J
authors.initials: AJ
authors.lastname: Grosovsky
mesh_terms: D004249:DNA Damage; D004264:DNA Topoisomerases, Type I / Q000378:metabolism / Q000528:radiation effects*; D005720:Gamma Rays; D006801:Humans; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D011233:Precipitin Tests; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D016159:Tumor Suppressor Protein p53; D011065:Poly(ADP-ribose) Polymerases; D004264:DNA Topoisomerases, Type I