title: p53-mediated regulation of proliferating cell nuclear antigen expression in cells exposed to ionizing radiation.
abstract: The proliferating cell nuclear antigen (PCNA) is a highly conserved cellular protein that functions both in DNA replication and in DNA repair. Exposure of a rat embryo fibroblast cell line (CREF cells) to gamma radiation induced simultaneous expression of PCNA with the p53 tumor suppressor protein and the cyclin-dependent kinase inhibitor p21(WAF1/Cip1). PCNA mRNA levels transiently increased in serum-starved cells exposed to ionizing radiation, an observation suggesting that the radiation-associated increase in PCNA expression could be dissociated from cell cycle progression. Irradiation of CREF cells activated a transiently expressed PCNA promoter chloramphenicol acetyltransferase construct through p53 binding sequences via a mechanism blocked by a dominant negative mutant p53. Electrophoretic mobility shift assays with nuclear extracts prepared from irradiated CREF cells produced four p53-specific DNA-protein complexes with the PCNA p53 binding site. Addition of monoclonal antibody PAb421 (p53-specific) or AC238 (specific to the transcriptional coactivator p300/CREB binding protein) to the mobility shift assay distinguished different forms of p53 that changed in relative abundance with time after irradiation. These findings suggest a complex cellular response to DNA damage in which p53 transiently activates expression of PCNA for the purpose of limited DNA repair. In a population of nongrowing cells with diminished PCNA levels, this pathway may be crucial to survival following DNA damage.
authors.affiliation: Programs in Molecular and Cellular Biology and Lung Biology, Department of Pathology, Tulane Cancer Center and Tulane/Xavier Center for Bioenvironmental Research, New Orleans, Louisiana 70112, USA.
authors.forename: J
authors.initials: J
authors.lastname: Xu
authors.forename: G F
authors.initials: GF
authors.lastname: Morris
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D005720:Gamma Rays; D005786:Gene Expression Regulation / Q000528:radiation effects; D018809:Proliferating Cell Nuclear Antigen / Q000235:genetics*; D051381:Rats; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D018809:Proliferating Cell Nuclear Antigen; D016159:Tumor Suppressor Protein p53